38/404/CDV ® Project number Numéro de projet
Submitted for parallel voting in CENELEC
COMMITTEE DRAFT FOR VOTE (CDV) PROJET DE COMITÉ POUR VOTE (CDV) IEC 61869-2 Ed. 1.0 Secretariat / Secrétariat
IEC/TC or SC: 38 CEI/CE ou SC: Date of circulation Date de diffusion
Italy Closing date for voting (Voting mandatory for P-members) Date de clôture du vote (Vote obligatoire pour les membres (P))
2010-10-22
Soumis au vote parallèle au CENELEC Also of interest to the following committees Intéresse également les comités suivants
TC13, TC85, TC95, TC99
2011-03-25 Supersedes document Remplace le document
38/357A/CD – 38/361B/CC
Proposed horizontal standard Norme horizontale suggérée Other TC/SCs are requested to indicate their interest, if any, in this CDV to the TC/SC secretary Les autres CE/SC sont requis d’indiquer leur intérêt, si nécessaire, dans ce CDV à l’intention du secrétaire du CE/SC Functions concerned Fonctions concernées Safety Sécurité
EMC CEM
Environment Environnement
Quality assurance Assurance qualité
CE DOCUMENT EST TOUJOURS À L'ÉTUDE ET SUSCEPTIBLE D E MODIFICATION. IL NE PEUT SERVIR DE RÉFÉRENCE.
THIS DOCUMENT IS STILL UNDER STUDY AND SUBJECT TO CHANGE. IT SHOULD NOT BE USED FOR REFERENCE PURPOSES.
LES RÉCIPIENDAIRES DU PRÉSENT DOCUMENT SONT INVITÉS À PRÉSENTER, AVEC LEURS OBSERVA TIONS, LA NOTIFICATION DES DROITS DE PROPRIÉTÉ DONT ILS AURAIENT ÉVENTUELLEMENT CONNAISSANCE ET À FOURNIR UNE DOCUMENTATION EXPLICATIVE.
RECIPIENTS OF THIS DOCUMENT ARE INVITED TO SUBMIT, WITH THEIR COMMENTS, NOTIFICATION OF ANY RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE AND TO PROVIDE SUPPORTING DOCUMENTATION.
CEI 61869 Ed. 1: TRANSFORMATEURS Title : IEC 61869 Ed. 1: DE MESURE - Partie 2: Transformateurs de TRANSFORMERS Part courant Transformers Titre :
Note d'introduction
ATTENTION VOTE PARALLÈLE CEI – CENELEC L’attention des Comités nationaux de la CEI, membres du CENELEC, est attirée sur le fait que ce projet de comité pour vote (CDV) de Norme internationale est soumis au vote parallèle. Les membres du CENELEC sont invités à voter via le système de vote en ligne du CENELEC.
INSTRUMENT 2: Current
Introductory note
ATTENTION IEC – CENELEC PARALLEL VOTING The attention of IEC National Committees, members of CENELEC, is drawn to the fact that this Committee Draft for Vote (CDV) for an International Standard is submitted for parallel voting. The CENELEC members are invited to vote through the CENELEC online voting system.
Copyright © 2010 International Electrotechnical Commission, IEC. IEC. All rights reserved. It is permitted to download this electronic file, to make a copy and to print out the content for the sole purpose of preparing National Committee positions. You may not copy or "mirror" the file or printed version of the document, or any part of it, for any other purpose without permission in writing from IEC.
® Registered trademark of the International Electrotechnical Commission
FORM CDV (IEC) 2009-01-09
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INSTRUMENT TRANSFORMERS Part 2: Current Transformers Transformers
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CONTENTS
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FOREWORD............................................ FOREWORD.......................... .................................... .................................... .................................... .................................... .................. - 10 -
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52
INTRODUCTION.............................................................. INTRODUCTION............................................ .................................... .................................... .............................. ............ - 11 1 Scope............................... Scope................................................ ................................... ................................... .................................. .................................. .................... ... - 13 2 Normative references ................................ .................................................. ................................... .................................. ............................. ............ - 13 3 Definitions ................................... ..................................................... ................................... ................................... .................................... ......................... ....... - 13 3.1 3. 1 General definitions ................................. .................................................. ................................... ................................... ....................... ...... - 13 3.1.1 Instrument transformer ................................. .................................................. .................................. ....................... ...... - 13 3.1.2 Enclosure .................................... ..................................................... ................................... .................................... ...................... .... - 13 3.1.3 Primary terminals ................................... .................................................... ................................... ............................. ........... - 13 3.1.4 Secondary terminals .................................. ................................................... ................................... .......................... ........ - 13 3.1.5 Secondary circuit ................................. .................................................. .................................. ................................ ............... - 13 3.1.6 Section .................................. ................................................... ................................... ................................... ............................ ........... - 13 3.1.200 Current transformer ................................... .................................................... ................................... .......................... ........ - 13 3.1.201 Measuring current transformer ................................. .................................................. ............................. ............ - 13 3.1.202 Protective current transformer ................................ ................................................. .............................. ............. - 13 3.1.203 Class PR protective current transformer ................................ ............................................... ............... - 14 3.1.204 Class PX PX protective current transformer ............................... ............................................... ................ - 14 3.1.205 Class TPX protecti protective ve curren currentt transfor transformer mer for tran transie sient nt perform performance ance ......... ... - 14 3.1.206 Class TPY protectiv protective e current current transf transforme ormerr for transi transient ent perfor performance mance ......... ... - 14 3.1.207 Class TPZ protectiv protective e current current tran transfor sformer mer for for transie transient nt perfor performance mance ......... ... - 14 3.1.208 Multi-ratio current transformer ................................. ................................................... ............................. ........... - 14 3.2 3. 2 Definitions related to dielectric ratings ................................ ................................................. .............................. ............. - 15 3.2.1 Highest voltage for system (Usys) ................................. ................................................... ........................ ...... - 15 3.2.2 Highest voltage for equipment (Um ( Um)...................... )....................................... ................................ ............... - 15 3.2.3 Rated insulation level .................................. ................................................... .................................. ........................ ....... - 15 3.2.4 Isolated neutral system............................................... system................................................................ .......................... ......... - 15 3.2.5 Resonant earthed system (a system earthed through an arcsuppression coil) ................................. .................................................. .................................. ................................ ............... - 15 3.2.6 Earth fault factor .................................. ................................................... .................................. ................................ ............... - 15 3.2.7 Earthed neutral system ................................... ..................................................... .................................... .................... .. - 15 3.2.8 Solidly earthed neutral system............................................... system.............................................................. ............... - 15 3.2.9 Impedance earthed neutral system ............................... ............................................... ........................ ........ - 15 3.2.10 Exposed installation .................................. ................................................... .................................. .......................... ......... - 15 3.2.11 Non-exposed installation installation ................................. .................................................. .................................. .................... ... - 15 3.3 3. 3 Definitions related to current ratings .................................... ..................................................... ............................. ............ - 15 3.3.200 Rated primary current (I ( I pr ..................................................... ................................ .............. - 15 pr ) ................................... 3.3.201 Rated secondary current (I (I sr ................................................... ............................. ............ - 15 sr ) .................................. 3.3.202 Rated short-time thermal current (I ( I th ................................................... .................. - 15 th ) ................................. 3.3.203 Rated dynamic current (I ( I dyn )................................................................ ................. - 15 dy n)............................................... 3.3.204 Rated continuous thermal current (I ( I cth ................................................ ............... - 15 ct h) ................................. 3.3.205 Exciting current (I ( I e) e ) ................................... .................................................... ................................... .......................... ........ - 15 3.4 3. 4 Definitions related to accuracy ................................... ..................................................... .................................... .................... .. - 16 3.4.1 Actua Act uall tran tr ansf sfor orma matition on rati ra tio o (k) (k ).................................. ................................................... ............................. ............ - 16 3.4.2 Rated transformation ratio (k ) ..................................................... .......................... ......... - 16 r r .................................... 3.4.3 Ratio error ( error ( ε ..................................................... ................................... .................................. ................. - 16 ε ) ...................................
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53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77
3.4.4 Phase displacement ( ∆φ ) .................................. .................................................... ................................... ................. - 16 3.4.5 Acc urac ur acyy clas c lasss ... ... ... ... ... ... ... ... ..... ... ..... ... ... ... ... ... ... ..... ... ..... ... ... ... ... ... ... ..... ... ..... ... ... ... . - 16 3.4.6 Burden ................................. ................................................... .................................... ................................... ............................ ........... - 16 3.4.7 Rated burden.................................................. burden.................................................................... .................................... .................... .. - 16 3.4.8 Rated output (S ( S ) ..................................................... ................................... ............................. ........... - 16 r .................................... 3.4.200 Rated resistive burden (R ( R b ) .................................. .................................................... ................................ .............. - 16 3.4.201Secondary 3.4.201 Secondary winding resistance (R (R ct ................................................... ..................... ... - 16 ct ) ................................. 3.4.202 Composite error ( ε c c )..................................... )....................................................... .................................... ....................... ..... - 16 3.4.203 Rated instrument limit primary current (I ( I PL ........................................... ......... - 17 PL ) .................................. 3.4.204 Instrument security factor (FS ( FS)) ................................... .................................................... .......................... ......... - 17 3.4.205 Secondary limiting e.m.f for e.m.f for measuring current transformers................. - 17 3.4.206 Rated accuracy limit primary current (I ( I alf .............. ......... ......... ......... ......... ......... ......... ....... ... - 17 alf ) .......... 3.4.207 Acc 3.4.207 Acc uracy ura cy lim it fact fa ctor or ( ALF AL F ) ................................... ..................................................... ................................ .............. - 17 3.4.208 Secondary Secondary limiting e.m.f. e.m.f. for protective current current transformers ......... .............. ....... .. - 17 3.4.209 Saturation flux ( Ψ s ) ................................... .................................................... ................................... .......................... ........ - 17 3.4.210 Remanent flux ( Ψ r r ) .................................... ..................................................... ................................... .......................... ........ - 17 3.4.211 Remanence factor (K ( K r ) ................................... ..................................................... .................................... .................... .. - 18 3.4.212 Rated secondary loop time constant (T ( T s ) .................................. .............................................. ............ - 18 3.4.213 Excitation characteristic ................................ ................................................. ................................. ....................... ....... - 18 3.4.214 Rated knee point e.m.f. (E ( E k ) ................................. ................................................... ................................ .............. - 18 3.4.215 Rated turns ratio ................................. ................................................... .................................... ................................ .............. - 18 3.4.216 Turns ratio error ( ε t ) .................................. ................................................... ................................... .......................... ........ - 18 3.4.217 Dimensioning factor (K ( K x ) ................................... ..................................................... ................................... ................. - 18 3.4.218 Rated primary short-circuit current (Ipsc)............................................... )..................................................... ...... - 18 3.4.219 Instantaneous error current (iε) ................................. ................................................... ................................ .............. - 19 -
78
ˆ ) ................................. 3.4.220 Peak value of total error ( ε ................................................... ................................... ................. - 19 -
79
ˆac ) ......... 3.4.221 Peak value of alternating error component ( ε ............. ......... ......... ......... ......... ......... ......... .... - 19 -
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101
3.4.222 Specif Specified ied duty cycle cycle (C-0 (C-0 and and / or or C-0-CC-0-C-0) 0) ........ ......... ......... ......... .......... ... - 19 3.4.223 Specified primary time constant (TP) ................................. ................................................... ........................ ...... - 20 3.4.224 Fault Fault durati duration on (t’, (t’, t’’)............... ......... ......... .......... ......... ......... ......... ......... . - 20 3.4.225 Specified time to accuracy limit (t’al , t’’al) ................................. ................................................... .................. - 20 3.4.226 Fault repetition time (tfr ) .................................. .................................................... .................................... ....................... ..... - 20 3.4.227 Secondary loop resistance (Rs) ................................... .................................................... ............................. ............ - 20 3.4.228 Rated symmetrical short-circuit current factor (Kssc) ......... .............. ......... ......... ......... ......... ......... .... - 21 3.4.229 Rated transient dimensioning factor (Ktd) ................................. ................................................... .................. - 21 3.4.230 Low leakage reactance current transformer ................................ .......................................... .......... - 21 3.4.231 High leakage leakage reactance current transformer .................................. ......................................... ....... - 22 3.4.232 Rated equivalent limiting secondary voltage (Ual)....................................... )......................................... - 22 ....... - 22 3.4.233Peak 3.4.233 Peak value of the exciting secondary current at U al )l ........................ al (Î al a )................. 3.4.234 Factor of construction F c ................................. ................................................... .................................... .................... .. - 22 Definitions related to other ratings.................................................. ratings.................................................................... .................. - 23 3.5.1 Rated frequency (f R ................................................... ................................... .......................... ........ - 23 R ) .................................. 3.5.2 Mechanical load (F) (F ) ................................... .................................................... ................................... .......................... ........ - 23 3.5.3 Internal arc fault protection instrument transformer .............................. .............................. - 23 Definitions related to gas insulation .................................. ................................................... ................................ ............... - 23 3.6.1 Pressure relief device ................................ ................................................. .................................. .......................... ......... - 23 3.6.2 Gas-insulated Gas-insulated metal-enclosed metal-enclosed instrument instrument transformer .......... .............. ......... .......... ....... .. - 23 3.6.3 Closed pressure system ................................. .................................................. ................................... ..................... ... - 23 3.6.4 Rated filling pressure.................................................. pressure.................................................................... .......................... ........ - 23 -
3.5 3. 5
3.6 3. 6
61869-2 ed. 1 © IEC 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150
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3.6.5 Minimum functional pressure ................................... .................................................... ............................. ............ - 23 3.6.6 Design pressure of the enclosure ................................. .................................................. ........................ ....... - 23 3.6.7 Design temperature of the enclosure ................................. .................................................. ................... .. - 23 3.6.8 Abs olut ol ute e leak le akag age e r ate at e ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ..... ... ..... ... ... ... ... ... ... .... ... . - 23 3.6.9 Relative leakage rate (F re )l ................................. .................................... ................................... ................. - 23 re )............... 3.7 3. 7 Index of abbreviations .................................. ................................................... .................................. .................................. ................... - 23 Normal and special service conditions ................................. .................................................. .................................. ..................... .... - 25 4.1 4. 1 General .................................. ................................................... ................................... .................................... ................................... ..................... .... - 25 4.2 4. 2 Normal service conditions .................................. ................................................... .................................. ............................. ............ - 25 4.2.1 Ambi Am bien entt air ai r temp te mper erat atur ure e ... ... ... ... ... ... ... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... ... ... ... ..... ... ..... ... .. - 25 4.2.2 Altit Alt itud ude e ... ... ... ... ... ... ... ... ... ... ... ..... ... ..... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ..... ... ..... ... ... ... - 25 4.2.3 Vibrations or earth tremors ................................ ................................................. .................................. ................... - 25 4.2.4 Other service service conditions for indoor indoor instrument transformers transformers ........ ............. ......... .... - 25 4.2.5 Other service service conditions for outdoor outdoor instrument transformers transformers .......... ............... ..... - 25 4.3 4. 3 Special service conditions .................................. ................................................... ................................... ............................. ........... - 25 4.3.1 General ................................. ................................................... ................................... ................................... ............................ .......... - 25 4.3.2 Altit Alt itud ude e ... ... ... ... ... ... ... ... ... ... ... ..... ... ..... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ..... ... ..... ... ... ... - 25 4.3.3 Ambi Am bien entt temp te mper erat atur ure e ... ... ... ... ... ... ..... ... ..... ... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... ... ... ... ..... ... ..... ... .. - 25 4.3.4 Vibrations or earth tremors ................................ ................................................. .................................. ................... - 25 4.3.5 Earthquakes .................................. .................................................... ................................... ................................... .................... .. - 25 4.4 4. 4 System earthing ................................... .................................................... ................................... .................................... ......................... ....... - 25 Ratings.............................................. Ratings............................ .................................... ................................... ................................... .................................... .................... - 25 5.1 5. 1 General .................................. ................................................... ................................... .................................... ................................... ..................... .... - 25 5.2 5. 2 Highest voltage for equipment ................................. ................................................... .................................... ....................... ..... - 25 5.3 5. 3 Rated insulation levels ................................. .................................................. .................................. ................................. .................. .. - 25 5.3.1 General ................................. ................................................... ................................... ................................... ............................ .......... - 25 5.3.2 Rated primary terminal terminal insulation level ................................. ................................................. ................ - 25 5.3.3 Other requirements for primary terminals insulation.............................. insulation.............................. - 26 5.3.4 Between-section insulation requirements............................................ requirements.............................................. .. - 26 5.3.5 Insulation requirements for secondary terminals .................................. .................................... - 26 5.3.200 Inter-turn insulation requirements .................................. .................................................. ....................... ....... - 26 5.4 5. 4 Rated frequency .................................. .................................................... .................................... ................................... ......................... ........ - 26 5.5 5. 5 Rated output .................................. ................................................... ................................... .................................... ............................... ............. - 26 5.6 5. 6 Rated accuracy class ................................... ..................................................... ................................... .................................. ................. - 26 5.6.200 Measuring current transformers .................................. ................................................... .......................... ......... - 26 5.6.201 Protective current transformers.............................................. transformers............................................................. ............... - 28 5.200 Standard values of rated primary current .................................. ................................................... ........................ ....... - 32 5.200.1 Single ratio transformers ................................ .................................................. ................................... .................... ... - 32 5.200.2 Multi-ratio transformers ................................... .................................................... .................................. .................... ... - 33 5.201 Standard values of rated secondary currents................................................ currents.................................................... .... - 33 5.202 Rated continuous thermal current .................................. ................................................... .................................. ................... - 33 5.203 Short-time current ratings .................................. .................................................... ................................... ............................. ............ - 33 5.203.1 Rated short-time thermal current (I ( I th ................................................... .................. - 33 th ) ................................. 5.203.2 Rated dynamic current (I ( I dyn )................................................................ ................. - 33 dy n)............................................... Design and construction .................................. .................................................... ................................... .................................. ....................... ...... - 34 6.1 6. 1 Requirements for liquids used in equipment ............................... ................................................ ...................... ..... - 34 6.1.1 General ................................. ................................................... ................................... ................................... ............................ .......... - 34 6.1.2 Liquid quality ................................. ................................................... ................................... .................................. .................... ... - 34 6.1.3 Liquid level device .................................. ................................................... .................................. ............................. ............ - 34 -
61869-2 ed. 1 © IEC 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201
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6.1.4 Liquid tightness ................................... ..................................................... ................................... ............................... .............. - 34 6.2 6. 2 Requirements for gases used in equipment ................................ ................................................. ...................... ..... - 34 6.2.1 General ................................. ................................................... ................................... ................................... ............................ .......... - 34 6.2.2 Gas quality ................................. ................................................... .................................... ................................... ...................... ..... - 34 6.2.3 Gas monitoring device ................................. ................................................... ................................... ....................... ...... - 34 6.2.4 Gas tightness ................................... ..................................................... ................................... .................................. ................. - 34 6.2.5 Pressure relief device ................................ ................................................. .................................. .......................... ......... - 34 6.3 6. 3 Requirements for solid materials used in equipment .................................. ......................................... ....... - 34 6.4 6. 4 Requirements for temperature rise of parts and components ............................ ............................ - 34 6.4.1 General ................................. ................................................... ................................... ................................... ............................ .......... - 34 6.4.2 Influence of altitude on temperature-rise........................................... temperature-rise............................................... .... - 35 6.5 6. 5 Requirements for earthing of equipment ................................ ................................................. ........................... .......... - 35 6.5.1 General ................................. ................................................... ................................... ................................... ............................ .......... - 35 6.5.2 Earthing of the enclosure ................................... .................................................... .................................. ................... - 35 6.5.3 Electrical continuity ................................ ................................................. .................................. ............................. ............ - 35 6.6 6. 6 Requirements for the external insulation.............................................. insulation........................................................... ............. - 35 6.6.1 Pollution .................................. .................................................... .................................... ................................... ......................... ........ - 35 6.6.2 Altit Alt itud ude e ... ... ... ... ... ... ... ... ... ... ... ..... ... ..... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ..... ... ..... ... ... ... - 35 6.7 6. 7 Mechanical requirements ................................. .................................................. .................................. ................................ ............... - 35 6.8 6. 8 Multiple chopped impulse on primary terminals ................................ ................................................ ................ - 35 6.9 6. 9 Internal arc fault protection requirements ................................. .................................................. ........................ ....... - 35 6.10 Degrees of protection by enclosures............................................ enclosures............................................................. ..................... .... - 35 6.10.1 General ................................. ................................................... ................................... ................................... ............................ .......... - 35 6.10.2 Protection of persons against access to hazardous parts and protection of the equipment against ingress of solid foreign objects ...... - 35 6.10.3 Protection against ingress of water.......................................... water....................................................... ............. - 35 6.10.4 Indoor instrument transformers ................................ ................................................. ............................. ............ - 35 6.10.5 Outdoor instrument transformers ................................ ................................................. .......................... ......... - 35 6.10.6 Protection of equipment against mechanical impact under normal service conditions ................................... .................................................... ................................... ............................. ........... - 35 6.11 Electromagnetic Compatibility (EMC) .................................. ................................................... ............................. ............ - 35 6.11.1 General ................................. ................................................... ................................... ................................... ............................ .......... - 35 6.11.2 Requirement for Radio Interference Voltage (RIV) ................................ ................................ - 35 6.11.3 Requirements for immunity ................................ .................................................. ................................... ................. - 35 6.11.4 Requirement for transmitted overvoltages.................................. overvoltages............................................. ........... - 35 6.12 Corrosion ................................. ................................................... ................................... ................................... .................................... .................... - 35 6.13 Markings ................................... .................................................... .................................. .................................. ................................... .................... .. - 35 6.13.200 Terminal markings – General rules.................................... rules......................................... ..... - 35 6.13.201 Rating plate markings ................................. .................................................. ........................... .......... - 36 6.13.202 Marking of the rating plate of a measuring current transformer ................................. ................................................... .................................... ................................... ...................... ..... - 37 6.13.203 Marking of the rating plate of a class P protective current transformer ................................. ................................................... .................................... ................................... ...................... ..... - 37 6.13.204 Marking of the rating plate of class PR protective current transformers .................................. .................................................... .................................... ................................... ................... .. - 37 6.13.205 Marking of the rating plate of class PX protective current transformers .................................. .................................................... .................................... ................................... ................... .. - 38 6.13.206 Marking of the rating plate of current transformers for transient performance .................................. .................................................... ................................... ....................... ...... - 38 6.14 Fire hazard .................................. .................................................... ................................... ................................... .................................. ................ - 39 Tests ................................... ..................................................... ................................... ................................... ................................... ................................. ................ - 39 -
61869-2 ed. 1 © IEC 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249
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General .................................. ................................................... ................................... .................................... ................................... ..................... .... - 39 7.1.1 Classification of tests .................................. .................................................... .................................... ....................... ..... - 39 7.1.2 List of tests .................................. .................................................... ................................... ................................... ...................... .... - 39 7.1.3 Sequence of tests ................................... .................................................... .................................. ............................. ............ - 40 7.2 7. 2 Type tests ................................... ..................................................... .................................... ................................... ................................. ................ - 40 7.2.1 General ................................. ................................................... ................................... ................................... ............................ .......... - 40 7.2.2 Temperature-rise test ................................... .................................................... .................................. ....................... ...... - 40 7.2.3 Impulse voltage withstand test on primary terminals ............................. ............................. - 42 7.2.4 Wet test for outdoor type transformers............................................ transformers.................................................. ...... - 43 7.2.5 Electromagnetic Compatibility (EMC) tests ................................. ........................................... .......... - 43 7.2.6 Test for accuracy ................................. ................................................... ................................... ............................... .............. - 43 7.2.7 Verification of the degree of protection by enclosures........................... enclosures........................... - 47 7.2.8 Enclosure tightness test at ambient temperature ................................ .................................. .. - 47 7.2.9 Pressure test for the enclosure ................................ ................................................. ............................. ............ - 47 7.2.200 Short-time current test ................................. ................................................... ................................... ....................... ...... - 47 7.3 7. 3 Routine tests .................................. .................................................... ................................... ................................... ............................... ............. - 48 7.3.1 Power-frequen Power-frequency cy voltage withstand withstand tests on primary terminals ......... ............. .... - 48 7.3.2 Partial discharge measurement .................................. .................................................. .......................... .......... - 48 7.3.3 Power-frequency voltage withstand withstand tests between sections .................. .................. - 48 7.3.4 Power-frequency voltage withstand withstand tests on secondary terminals ......... - 48 7.3.5 Test for accuracy ................................. ................................................... ................................... ............................... .............. - 48 7.3.6 Verification of markings .................................. ................................................... .................................. ..................... .... - 50 7.3.7 Enclosure tightness test at ambient temperature ................................ .................................. .. - 50 7.3.7.1 Closed pressure systems for gas ................................. ........................................... .......... - 50 7.3.7.2 Liquid systems ................................. ................................................... .................................... .................... .. - 50 7.3.8 Pressure test for the enclosure ................................ ................................................. ............................. ............ - 50 7.3.200 Inter-turn overvoltage test............................................. test.............................................................. ........................ ....... - 50 7.4 7. 4 Special tests ................................... .................................................... .................................. .................................. ............................... .............. - 51 7.4.1 Chopped Chopped impulse voltage withstand withstand test on primary terminals terminals .......... .............. .... - 51 7.4.2 Multiple chopped impulse test on primary terminals .............................. .............................. - 51 7.4.3 Measurement of capacitance and dielectric dissipation factor ............... - 51 7.4.4 Transmitted overvoltage test ................................... .................................................... ............................. ............ - 52 7.4.5 Mechanical tests................................................ tests................................................................. .................................. ................... - 52 7.4.6 Internal arc fault test ................................. ................................................... ................................... .......................... ......... - 52 7.4.7 Enclosure tightness tests at low and high temperatures........................ temperatures........................ - 52 7.4.8 Gas Dew point test ................................... ..................................................... .................................... .......................... ........ - 52 7.4.9 Corrosion test ................................... ..................................................... ................................... .................................. ................. - 52 7.4.10 Fire hazard test ................................... ..................................................... ................................... ............................... .............. - 52 7.5 7. 5 Sample tests .................................. .................................................... ................................... ................................... ............................... ............. - 52 8 Rules for transport, storage, erection, operation and maintenance ............................ ............................ - 52 9 Safety........................................ Safety......................................................... ................................... .................................... ................................... ........................... .......... - 52 10 Influence of products on the natural environment ................................. ................................................... ..................... ... - 52 Ann ex 2A Protective current transformers classes P, PR, PX (Normative) ...................... ...................... - 53 2A.1 Vector diagram .................................. ................................................... .................................. ................................... ............................. ........... - 53 2A.2 Turns correction ................................... ..................................................... ................................... ................................... ......................... ....... - 53 2A.3 The error triangle ................................... ..................................................... .................................... ................................... ...................... ..... - 53 2A.4 Composite error ................................... ..................................................... ................................... ................................... ......................... ....... - 54 2A.5 Direct test for composite error ................................ ................................................ ................................. .......................... ......... - 55 -
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2A.6 2A.7
Alter Alt erna natitive ve meth me thod od for fo r the th e dire di rect ct meas me asur urem emen entt of com posi po site te err or ... ..... ... ..... ..... ..... ... ... - 56 Use of composite error ................................. .................................................. .................................. .................................. ................... - 56 -
252 253 254 255 256 257 258 259 260 261 262 263 264 265
Ann ex 2B Prot Pr otec ectitive ve curr cu rren entt trans tr ansfo form rmers ers class cl ass es for fo r tran tr ansi sien entt perf pe rfor orma manc nce e (Normative) ................................. ................................................... .................................... ................................... ................................... ......................... ....... - 58 2B.1 Basic theoretical equations for transient dimensioning............................... dimensioning...................................... ....... - 58 2B.1.1 Short-circuit ................................... .................................................... ................................... ................................... .................... ... - 58 2B.1.2 Transient factor ................................ ................................................. .................................. .................................. ................... - 59 2B.1.3 Duty cycles ................................. ................................................... ................................... ................................... ....................... ..... - 64 2B.2 Determination of the magnetizing characteristic of protective current transformers for transient performance ................................ .................................................. ................................... .................... ... - 65 2B.2.1 General ................................. ................................................... ................................... ................................... ............................ .......... - 65 2B.2.2 A.C. A. C. meth me thod od ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .. - 65 2B.2.3 D.C. method .................................. ................................................... ................................... .................................... .................... .. - 66 2B.2.4 Capacitor discharge method ................................... ..................................................... .............................. ............ - 68 2B.3 Determination of the error at limiting conditions of protective current transformers for transient performance ................................ .................................................. ................................... .................... ... - 69 -
266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283
2B.3.1 Direct test ................................. ................................................... .................................... ................................... ........................ ....... - 69 2B.3.2 Indirect test ................................... ..................................................... .................................... ................................... ................... .. - 70 2B.4 Alter Alt erna natitive ve meas me asur urem emen entt of the th e s tead te adyy sta s tate te rati ra tio o erro er rorr ... ... ..... ... ..... ... ... ..... ... ..... ... ..... ... ..... ... ... - 7 2 Ann ex 2C Tech Te chni niqu que e used us ed in temp te mper erat atur ure e rise ri se test te st of oil-i oi l-imm mm ersed er sed tran tr ansf sfor orme mers rs to determine the thermal constant by an experimental estimation (informative).............. - 74 Ann ex 2D Dete De term rmin inat ation ion of the th e t urns ur ns rati ra tio o erro er rorr (inf (i nform orm ative) ati ve) ... ... ... ... ... ... ... ..... ... ..... ... ... ... ..... ... ..... ... - 7 6 -
284
Figure 2 A.6 ................................... ..................................................... .................................... .................................... .................................... ............................. ........... - 56 -
285 286 287 288
Fig. 2B.1: Short-circuit current with highest peak ( γ = 90°) and lower asymmetry ( γ = 1 40°) ................................... ..................................................... .................................... ................................... ................................... ............................... ............... .. - 58 Fig. 2B.2: Magnetic-flux for the two cases in Fig. 2B.1............................................ 2B.1..................................................... ......... - 59 Fig. 2B.3: Relevant time ranges for calculation of transient factor ................................ .................................... .... - 59 -
289
Fig. 2B.4 Determination of K tf for fo r δ = 3° (T s=61 ms) and f=50 Hz .......... ............... ......... ......... .......... ......... ........ .... - 60 -
290
Fig. 2B.5 Determination of K tf for fo r δ = 1.5° (T s =122 ms) and f=50 Hz...................... Hz................................ .......... - 61 -
291
Fig. 2B.6 Determination of K tf for fo r δ = 0.1° (T s = 1.8 s) and f=50 Hz ......... ............. ......... .......... ......... ......... ....... .. - 61 -
292
Fig. 2B.7 Determination of K tf for fo r δ = 3° (T s =50 ms) and f=60 Hz ......... .............. ......... ......... ......... ......... ......... .... - 61 -
293
Fig. 2B.8 Determination of K tf for fo r δ = 1.5° (T s =100 ms) and f=60 Hz...................... Hz................................ .......... - 62 -
294
Fig. 2B.9 Determination of K tf for fo r δ = 0.1° (T s = 1.5 s) and f=60 Hz ......... ............. ......... .......... ......... ......... ....... .. - 62 -
295
Fig. 2B.10 Determination of K tf for fo r δ = 3° (T s =182 ms) and f=16.7 Hz............................. Hz............................... - 62 -
FIGURES Figure 201 - Duty cycles ................................. ................................................... ................................... ................................... ............................. ........... - 19 Figure 202 - Primary time constant T p ................................... .................................................... ................................... .......................... ........ - 20 Figure 203 - Relevant peaks of magnetic flux for determination of Ktd ............................ ............................ - 21 Figure 2 A.1 ................................... ..................................................... .................................... .................................... .................................... ............................. ........... - 53 Figure 2 A.2 ................................... ..................................................... .................................... .................................... .................................... ............................. ........... - 54 Figure 2 A.3 ................................... ..................................................... .................................... .................................... .................................... ............................. ........... - 54 Figure 2 A.4 ................................... ..................................................... .................................... .................................... .................................... ............................. ........... - 55 Figure 2 A.5 ................................... ..................................................... .................................... .................................... .................................... ............................. ........... - 55 -
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Fig. 2B.11 Determination of K tf for fo r δ = 1.5° (T s=365 ms) and f=16.7 Hz........................... - 63 -
297 298 299 300 301 302
Fig. 2B.12 Determination of K tf for fo r δ = 0.1° (T s= 5.5 s) and f=16.7 Hz ......... .............. .......... ......... ......... ....... .. - 63 Fig. 2B.13: Basic circuit .................................... ...................................................... .................................... .................................... ........................... ......... - 65 Fig. 2B.14: Determination Determination of remanence factor by hysteresis loop .............................. ................................... ..... - 66 Fig. 2B.15: Circuit for d.c. method............................................ method.............................................................. ..................................... ...................... ... - 67 Fig. 2B.16: Typical records .................................... ...................................................... ..................................... ..................................... ..................... ... - 67 Fig. 2B.17: Circuit for capacitor discharge method ................................. .................................................. .......................... ......... - 68 -
303 304 305
Fig. 2B.19: Measurement of error currents .................................. ................................................... .................................. .................... ... - 70 Fig. 2B.20 Simplified equivalent circuit of the current transformer ................................... ..................................... - 72 Figure C200.1 - Graphical extrapolation to ultimate temperature rise ............................... ............................... - 75 -
306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323
TABLES Table 20 1 – Limits of current error and phase displacement for measuring current transformers (classes from 0.1 to 1).............................................. 1)................................................................ ................................... ................. - 27 Table 20 2 – Limits of current error and phase displacement for measuring current transformers for special application ................................... .................................................... ................................... ............................. ........... - 28 Table 20 3 – Limits of current error for measuring current transformers (classes 3 and 5) - 28 Table 20 4 – Definitions of protective classes ................................. .................................................. ................................. ................ - 28 Table 205 – Limits of error for protective current transformers class P and PR ................ ................ - 29 Table 206 – Error limits for TPX, TPY and TPZ current transformers................................ transformers................................ - 31 Table 207 – Specification Method for TPX, TPY and TPZ current transformers ................ ................ - 32 Table 208 – Markings of of terminals .................................. ................................................... .................................. ................................ ............... - 36 Table 209 – List of tests....................................... tests........................................................ .................................. ................................... .......................... ........ - 39 Table 210 – Gas type and pressure during type, type, routine and special tests ....................... ....................... - 40 Table 211 – Additional type tests for protective current transformers for transient performance ................................. .................................................. .................................. ................................... ................................... ............................... .............. - 44 -
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INTERNATIONAL ELECTROTECHNICAL COMMISSION
325 326 327 328 329 330 331 332
____________
333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365
38/404/CDV
INSTRUMENT TRANSFORMERS Part 2: Current Transformers Transformers FOREWORD 1) The International Electrotechnical Electrotechnical Commission Commission (IEC) is a worldwide organization organization for standardization comprising comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in t he electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and nongovernmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the t wo organizations. 2) The formal decisions decisions or agreements of IEC on technical technical matters express, as as nearly as possible, possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees. 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with an IEC Publication. 6) All users should ensure that they have the the latest edition of this publication. publication. 7) No liability shall be attached to IEC or its directors, employees, employees, servants or agents including including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications. 8) Attention is drawn to the Normative references references cited in this publication. publication. Use of the referenced publications publications is essential for the correct application of this publication. 9) Attention is drawn to the possibility possibility that some of the elements of this IEC Publication may be the subject subject of patent rights. IEC shall not be held responsible for identifying any or a ll such patent rights.
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INTRODUCTION
367 368
This International Standard IEC 61869-2 has been prepared by subcommittee 38: Instrument transformers.
369 370 371
TC 38 decided to restructure the whole set of stand-alone Standards in the IEC 60044-X series and transform it into a new set of standards composed of General Requirements documents and Specific Requirements documents.
372 373
This Standard is the first issue of Specific Requirements for current transformers and shall be read together with IEC 61869-1 General Requirements for Instrument Transformers
374 375
This Standard covers all specific requirements formerly found in the 60044-1 and 60044-6 standard. Additionally, it introduces some technical innovations:
376 377 378 379 380 381 382 383 384
• • • • • • •
requirements for gas-insulated instrument transformers additional special tests requirements for internal arc fault protection requirements for degrees of protection by enclosure requirements for resistance to corrosion requirements for safety and environmental concerns
standardization and adaptation of the requirements of current transformers for transient performance The text of this standard is based on the following documents: FDIS
Report on voting
38/XX/FDIS
38/XX/RVD
385 386 387
Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table.
388
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
389 390
This standard is Part 2 of IEC 61869, published under the general title Instrument transformers. transformers.
391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408
This part 2 is to be read in conjunction with, and is based on, IEC 61869-1: “General Requirements” - first edition (2007)- however the reader is encouraged to use its most recent edition. This Part 2 follows the structure of IEC 61869-1 and supplements or modifies its corresponding clauses. When a particular subclause of Part 1 is not mentioned in this Part 2, that subclause applies. When this standard states “addition”, “modification” or “replacement”, the relevant text in Part 1 is to be adapted accordingly. For additional clauses, subclauses, figures, tables, annexes or note, the following numbering system is used: – c laus la uses es,, subc su bcla laus uses es,, tabl ta bles es and an d f igure igu ress that th at are ar e num bere be red d s tart ta rtin ing g from fr om 201 20 1 are ar e addit ad dit ion al to those in Part 1; – addi ad ditio tio nal na l anne an nexes xes are ar e lett le tter ered ed 2A, 2B, 2B , etc. et c. An over ov ervie vie w of the th e pla nned nn ed set se t of stan st andar dar ds at the th e date da te of pub lic atio at ion n of this thi s docu do cume ment nt is given below:
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61869-2 ed. 1 © IEC PRODUCT FAMILY STANDARDS
61869-1
61869-6
GENERAL REQUIREMENTS FOR INSTRUMENT TRANSFORMERS
ADD ITI ONA L GENERAL REQUIREMENT FOR ELECTRONIC INSTRUMENT TRANSFORMERS AND LOW POWER STAND ALO NE SENSORS
38/404/CDV
PRODUCT PRODUCTS STANDARD
OLD STANDARD
61869-2
ADD ITI ONA L REQ UIREM UI REM ENTS EN TS FOR CURRENT TRANSFORMERS TRANSFORMERS
60044-1
61869-3
ADD ITI ONA L REQ UIREM UI REM ENTS EN TS FOR INDUCTIVE VOLTAGE TRANSFORMERS
60044-2
61869-4
ADD ITI ONA L REQ UIREM UI REM ENTS EN TS FOR COMBINED TRANSFORMERS
60044-3
61869-5
ADD ITI ONA L REQ UIREM UI REM ENTS EN TS FOR 60044-5 CAPACITIVE VOLTAGE TRANSFORMERS
61869-7
ADD ITI ONA L REQ UIREM UI REM ENTS EN TS FOR ELECTRONIC VOLTAGE TRANSFORMERS
60044-7
61869-8
ADD ITI ONA L REQ UIREM UI REM ENTS EN TS FOR ELECTRONIC CURRENT TRANSFORMERS
60044-8
61869-9
DIGITAL INTERFACE FOR INSTRUMENT TRANSFORMERS
61869-10
ADD ITI ONA L REQ UIREM UI REM ENTS EN TS FOR LOW POWER STAND-ALONE CURRENT SENSORS
61869-11
ADD ITI ONA L REQ UIREM UI REM ENTS EN TS FOR LOW POWER STAND ALONE VOLTAGE SENSOR
61869-12
ADD ITI ONA L REQ UIREM UI REM ENTS EN TS FOR COMBINED ELECTRONIC INSTRUMENT TRANSFORMER TRANSFORMER OR COMBINED STAND ALO NE SEN SOR S
61869-13
STAND ALONE MERGING UNIT
60044-7
409
The updated list of standards issued by IEC TC38 is available at the website: www.iec.ch
410 411
The committee has decided that the contents of this publication will remain unchanged until 2011-12. At this date, the publication will be
412 413 414 415
• • • •
416 417
Add itio it iona nalllly, y, an appl ap plic icat ation ion guid gu ide e (IEC (I EC 6186 61 869. 9... ..)) for fo r prot pr otec ectition on curr cu rren entt tran tr ansf sfor orme mers rs is unde un der r preparation, to give information about
418 419 420 421
• • •
reconfirmed, withdrawn, replaced by a revised edition, or amended.
theoretical background of the calculations for current transformers for transient performance the choose of of the the specific protection classes depending on the application the relations between the different class types
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INSTRUMENT TRANSFORMERS
422 423 424 425 426
Part 2: Current Transformers Transformers
427
1
Scope
428 429 430
This International Standard is applicable to newly manufactured magnetic current transformers for use with electrical measuring instruments or/and electrical protective devices having rated frequencies from 15 Hz to 100 Hz
431
2
432 433 434 435 436 437 438
The following referenced documents are essential for the application of this document. For dated refer referen ence ces, s, only only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
Normative references
IEC 61869-1: General Requirements for Instrument Transformers, including the references mentioned in Clause 2 of IEC 61869-1
439
3
Definitions
440
This clause of IEC 61869-1 is applicable with the addition of specific definitions
441
3.1
442
3.1.1 Instrument transformer
443
3.1.2 Enclosure
444
3.1.3 Primary terminals
445
3.1.4 Secondary terminals
446
3.1.5 Secondary circuit
447
3.1.6 Section
448
3.1.200 Current transformer
449 450 451
An ins trum tr umen entt tran tr ansf sfor orme merr in which whi ch the th e seco se cond ndar aryy curr cu rren ent, t, in norm no rmal al cond co nditi ition onss of use, us e, is subsu bstantially proportional to the primary current and differs in phase from it by an angle which is approximately zero for an appropriate direc tion of the connections. [IEV 321-02-01]
452
3.1.201 Measuring current transformer
453 454
A curr cu rren entt trans tr ansfo form rmer er inte in tend nded ed to supp su pply ly an info in form rm ation ati on sign si gnal al to meas me asur urin ing g inst in stru rume ment ntss and an d meters. (IEV321-02-18)
455
3.1.202 Protective current transformer
456 457
A curr cu rren entt trans tr ansfo form rmer er inten int ende ded d to tran tr ansm smitit an info in form rmat atio ion n sign si gnal al to prot pr otec ectitive ve and an d cont co ntro roll devices (IEV321-02-19)
General definitions
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3.1.203 Class PR protective current transformer
459 460 461
A curr cu rren entt trans tr ansfo form rmer er with wit h lim ited it ed rema re mane nenc nce e fact fa ctor or for fo r whic wh ich, h, in some so me case ca ses, s, a valu va lue e of the th e secondary loop time constant and/or a limiting value of the winding resistance may also be specified
462
3.1.204 Class PX protective current transformer
463 464 465 466
A tran tr ansf sform orm er of low lo w leak le akage age reac re acta tanc nce e for fo r which whi ch know kn owle ledg dge e of the th e tran tr ansf sfor orme merr seco se cond ndar aryy excitation characteristic, secondary winding resistance, secondary burden resistance and turns ratio is sufficient to assess its performance in relation to the protective relay system with which it is to be used.
467
3.1.205 3.1 .205 Cla Class ss TPX protective protective curren currentt trans transforme formerr for for transient transient performance performance
468 469 470 471
ˆ ) during specified transient duty cycle. Accuracy limit defined by peak value of total error ( ε No limit for remanent flux.
472
3.1.206 3.1 .206 Cla Class ss TPY protective protective curren currentt trans transforme formerr for for transient transient performance performance
473 474 475 476
ˆ ) during specified transient duty cycle. Acc urac ur acyy lim l imitit defi de fine ned d by peak pe ak valu va lue e of tota to tall erro er ror r ( ε The remanent flux is limited.
477
3.1.207 3.1 .207 Cla Class ss TPZ protective protective curren currentt transf transformer ormer for transient transient performance performance
478 479
ˆac ) during specified transient Accuracy limit defined by peak value of alternating error com ponent (ε duty cycle.
480
-
Specified secondary phase displacement at Ipr
481
-
No requirement concerning instantaneous error current iε
482 483
-
Remanent flux to be practically negligible
484
3.1.208 Multi-ratio current transformer
485 486
Current transformer on which more ratios are obtained by connecting the primary winding sections in series or parallel or by means of taps on the secondary winding
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487
3.2 Definitions related to dielectric dielectric ratings
488
3.2.1 Highest voltage for system (U sys) sys)
489
3.2.2 Highest voltage for equipment (Um )
490
3.2.3 Rated insulation level
491
3.2.4 Isolated neutral system
492 493
3.2.5 Resonant earthed earthed system system (a system earthed through through an arc-suppression coil)
494
3.2.6 Earth fault factor
495
3.2.7 Earthed neutral system
496
3.2.8 Solidly earthed neutral system
497
3.2.9 Impedance earthed neutral system
498
3.2.10 Exposed installation
499
3.2.11 Non-exposed installation
500
3.3
501
3.3.200
502
The value of the primary current on which the performance of the transformer is based
503
[IEV 321-01-11 modified]
504
3.3.201
505
The value of the secondary current on which the performance of the transformer is based
506
[IEV 321-01-15 modified]
507
3.3.202
508 509
The r.m.s. value of the primary current which a transformer will withstand for one second without suffering harmful effects, the secondary winding being short-circuited
510
3.3.203
511 512 513
The peak value of the primary current which a transformer will withstand, without being damaged electrically or mechanically by the resulting electromagnetic forces, the secondary winding being short-circuited
514
3.3.204
515 516 517
The value of the current which can be permitted to flow continuously in the primary winding, the secondary winding being connected to the rated burden, without the temperature rise exceeding the values specified.
518 519 520
Note: If a current transformer is equipped with cores h aving different ratios (e.g. 1200/5 and 4000/1), I cth ct h shall be stated as an uniform absolute value, applicable for all cores (e.g. “Icth ct h 1440 A”)
521
3.3.205
522 523 524
The r.m.s. value of the current taken by the secondary winding of a current transformer, when a sinusoidal voltage of rated frequency is applied to the secondary terminals, the primary and any other windings being open-circuited
Definitions related to current ratings Rated primary current ( I pr pr )
Rated secondary current ( I sr sr )
Rated short-time thermal current ( I th th )
Rated dynamic current (I dyn dyn )
Rated continuous thermal current (I cth cth )
Exciting current (I e) e)
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525
3.4 Definitions related to accuracy
526
3.4.1 Actual transformation ratio (k)
527
3.4.2 Rated transformation ratio (k ) r r
528
3.4.3 Ratio error ( ε ε )
529 530
Clause § 3.4.3 of IEC 61869-1 is applicable with the addition of the following: The Th e ratio error (current error) expressed in per cent is given by the formula:
531
ε =
(k r I s − I p ) I p
⋅ 100%
532
where
533
k r r is the rated transformation ratio;
534
I p
is the actual primary current;
535
I s
is the actual secondary current when I p is flowing, under the conditions of measurement
536 537
3.4.4 Phase displacement ( ∆φ )
538
3.4.5 Accuracy class
539
3.4.6 Burden
540
3.4.7 Rated burden
541
3.4.8 Rated output (S r r )
542
3.4.200
543
Rated value of the secondary connected resistive burden in ohms
544
3.4.201
545 546
Secondary winding d.c. resistance in ohms corrected to 75 ºC or such other temperature as may be specified.
547
NOTE: The actual winding resistance Rct will be ≤ a possibly defined upper limit.
548
3.4.202
549
Under steady-state conditions, the r.m.s. value of the difference between:
550 551 552 553
a) the instantaneous values of the primary current, and b) the instantaneous values of the actual secondary current multiplied by the rated transformation ratio, the positive signs of the primary and secondary currents corresponding to the convention for terminal markings.
554 555
The composite error ε c is generally expressed as a percentage of the r.m.s. values of the primary current according to the formula:
Rated resistive burden ( R b) Secondary winding resistance ( R ct ct )
Composite error * ( ε c c )
556 557 558 559
ε c
=
100 I p
1
T
( k i T ∫
r s
0
where k r r is the rated transformation ratio; I p is the r.m.s. value of the primary current; ————————— * See annexe 2A.
− i p ) 2 d t
61869-2 ed. 1 © IEC
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560
i p
is the instantaneous value of the primary current;
561
i s
is the instantaneous value of the secondary current;
562
T is the duration of one cycle.
38/404/CDV
Rated instrument limit primary current ( I PL PL )
563
3.4.203
564 565 566
The value of the minimum primary current at which the composite error of the measuring current transformer is equal to or greater than 10 %, the secondary burden being equal to the rated burden
567 568
NOTE The composite error error should be greater than 10 %, in order order to protect the apparatus supplied supplied by the instrument transformer against the high currents produced in the event of system fault.
569
3.4.204
570
The ratio of rated instrument limit primary current to the rated primary current
571 572 573
NOTE 1 Attention should be paid paid to the fact that the actual instrument instrument security factor is affected affected by the burden. As bur den de n val ue is sig nif ica ntly nt ly lowe lo werr th an rate ra ted d one , large la rge r cur rent re nt val ues will wil l be pro duc ed on the sec ondar on dar y side si de in case of short circuit current.
574 575 576
NOTE 2 In the event of system fault currents flowing through the primary winding winding of a current transformer, the safety of the apparatus supplied by the transformer is greatest when the value of the rated instrument security factor (FS) is small.
577
3.4.205
578 579
The product of the instrument securit y factor FS, the rated secondary current and the vectorial sum of the rated burden and the impedance of the secondary winding
580 581 582
NOTE 1 The method by which the secondary limiting e.m.f. is calculated calculated will give a higher value than the real one. It was chosen in order to apply the same test method as in 7.3.5.201 and 7.2.6.201 for protective current transformers.
583
Other methods may be used by agreement between manufacturer and purchaser.
584 585
NOTE 2 For calculating the secondary limiting e.m.f., the secondary winding resistance should be corrected to a temperature of 75 °C.
586
3.4.206
587 588
The value of primary current up to which the transformer will comply with the requirements for composite error
589
3.4.207
590
The ratio of the rated accuracy limit primary current to the rated primary current
591
3.4.208
592 593
The product of the accuracy limit factor, the rated secondary current and the vectorial sum of the rated burden and the impedance of the secondary winding
594
3.4.209
595 596 597
That peak value of the flux which would exist in a core in the transition from the non-saturated to the fully saturated condition and deemed to be that point on the transient Ψ -i -i e characteristic for the core concerned at which a 10 % increase in Ψ causes i e to be increased by 50 %
Instrument security factor ( FS )
Secondary limiting e.m.f for e.m.f for measuring current transformers
Rated accuracy limit primary current (I alf alf )
Accuracy limit factor ( ALF ALF )
Secondary limiting e.m.f. for protective current transformers
Saturation flux ( s)
598 599
3.4.210
Remanent flux ( r )
600 601
That value of flux which would remain in the core 3 min after the interruption of an exciting current of sufficient magnitude to induce the saturation flux ( Ψ s )
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602
3.4.211
Remanence factor ( K r )
603
The ratio K r = Ψ r / r / Ψ s , expressed as a percentage (%)
604
3.4.212
605 606 607
Value of the time constant of the secondary loop of the current transformer obtained from the sum of the magnetizing and the leakage inductance (L ( Ls ) and the secondary loop resistance ( R s)
608
T s = L s / R s
Rated secondary loop time constant (T s)
609
3.4.213
Excitation characteristic
610 611 612 613 614
A grap gr aphic hical al or tabu ta bula larr pres pr esen enta tatio tio n of the th e relat re lat ion ship sh ip betw be twee een n the th e r.m .s. .s . valu va lue e of the th e exci ex cititing ng current and a sinusoidal r.m.s. e.m.f. applied to the secondary terminals of a current transformer, the primary and other windings being open-circuited, over a range of values sufficient to define the characteristics from low levels of excitation up to1.1 the rated knee point e.m.f.
615
3.4.214
616 617 618
That minimum sinusoidal e.m.f. (r.m.s.) at rated power frequency when applied to the secondary terminals of the transformer, all other terminals being open-circuited, which when increased by 10 % causes the r.m.s. exciting current to increase by no more than 50 %
619
NOTE: The actual actual knee point e.m.f. will be ≥ the rated knee point e.m.f.
Rated knee point e.m.f. (E k )
620 621
3.4.215
622
The required ratio of the number of primary turns to the number of secondary turns
623 624
EXAMPLE 1 EXAMPLE 2
1/600 (one primary primary turn with six hundred secondary turns) 2/600 (two primary turn with six hundred secondary turns).
625
3.4.216
Turns ratio error ( t )
626
The difference between the rated and actual turns ratios, expressed as a percentage
627
Rated turns ratio
ε t =
(actual turns ratio − rated turns ratio) rated turns ratio
× 100%
628
3.4.217
Dimensioning factor (K x )
629 630 631
A fact fa ctor or assi as sign gned ed by the th e purc pu rcha hase serr to indic in dicat ate e the th e mult mu ltip iple le of rate ra ted d seco se cond ndar aryy curr cu rren entt (I sn sn ) occurring under power system fault conditions, inclusive of safety factors, up to which the transformer is required to meet performance requirements.
632 633
3. 3.4.2 4.218 18
634 635 636
The r.m.s. value of primary symmetrical short-circuit current on which the rated accuracy performance of the current transformer is based. (While ith concerns the thermal limit, Ipsc is related to the accuracy limit.)
637
NOTE: Usually, I ps c will be smaller than i th .
638
Rated primary short-circuit current (Ipsc)
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639
3. 3.4.2 4.219 19
Instantaneous error current (i )
640 641 642 643 644 645 646 647 648
Difference between the instantaneous values of the secondary current (is) multiplied by (k r ), and the primary current (ip):
ε
i ε = k r ⋅ i s - i p When both alternating current components (isac , ipac) and direct current components (isdc , ipdc) are present, the constituent components (iεac , iεdc) are separately identified as follows:
i ε = i ε ac + i ε dc = (k r ⋅ i sac - i pac ) + (k r ⋅ i sdc - i pdc )
649 650
Peak value of total error ( ε ˆ )
651
3. 3.4.2 4.220 20
652 653 654 655
Maximum value (î ε) of instantaneous error current (see 3.4.219) for the specified duty cycle, expressed as a percentage of the peak value of the rated primary short-circuit current: iˆε
ˆ= ε
656
2 ⋅ I psc
⋅ 100%
657
Peak value of alternating error component ( ε ˆac )
658
3. 3.4.2 4.221 21
659 660 661
Maximum value iˆε ac of the alternating current component (see 3.4.219), expressed as a percentage of the peak value of the rated primary short-circuit current
ˆac ε
662
=
iˆε ac
2 ⋅ I psc
⋅ 100%
663 664
3. 3.4.2 4.222 22
665 666 667
Duty cycle in which during each specified energization, the primary energizing current is assumed to have a DC offset.
668 669 670 671 672 673
C-O
Specified duty cycle (C-0 and / or C-0-C-0)
C-O-C-O
Figure 201 - Duty cycles
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674
3. 3.4.2 4.223 23
675 676 677 678
That specified value of the time constant of the d.c. component of the primary short circuit current on which the performance of the current transformer is based.
679 680 681
Specified primary time constant (TP)
Figure 202 - Primary time constant T p
682 683
3.4.224 3.4 .224
Fault duration duration (t’, t’’)
684 685 686 687 688
t’: duration of first fault t’’: duration of second fault (if any) See figure 201
689
3. 3.4.2 4.225 25
690 691 692 693 694
Time during which the specified accuracy is maintained. t’al is used for the first energization, t’’al for the second energization (if any). See figure 201 NOTE - This time will usually be defined by the critical measuring time of the associated protection scheme. For determination of the magnetic core flux, it is necessary to consider the total fault duration.
695
3.4.226 3.4 .226
696 697
Time interval between interruption and re-application of the primary short-circuit current during a circuit breaker auto-reclosing duty cycle in case of a non-successful fault clearance. See figure 201
698
3. 3.4.2 4.227 27
699 700
Total resistance of the secondary circuit
701
Specified time to accuracy limit (t’al , t’’al)
Fault repetition repetition time (tfr )
Secondary loop resistance (Rs)
R s = R b + R ct
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702 703
3. 3.4.2 4.228 28
Rated symmetrical short-circuit current factor (Kssc)
704
K ssc =
705
The ratio:
706
3. 3.4.2 4.229 29
707 708 709 710 711 712 713 714 715 716 717 718
The ratio Ψa / Ψ s , where
I psc I pr
Rated transient dimensioning factor (Ktd)
pea k value val ue of the total magneti magneticc flux of the asymmetri asymmetrical cal primary primary current current within within the relevant relevant Ψa is the peak time interval1 at rated burden. is the peak valu e of the steady state a.c. a.c. flux of the the appropriate appropriate symmetrical symmetrical primary primary current current at rated burden. See figure figure 203. Ψ s
Note 1: The worst case inception angle of the asymmetric primary short circuit current which leads to the highest possible peak of the magnetic flux shall be considered. See annex B.1. The possibility for reduction of the asymmetry by restricting the current inception angle will be discussed in the application guide.
719 720
Figure 203 - Relevant peaks of magnetic flux for determination of Ktd
721 722
3.4.230
Low leakage reactance current transformer
723 724 725 726
Current transformer for which a knowledge of the secondary excitation characteristic and secondary winding resistance is sufficient for an assessment of its transient performance for any combination of primary current and burden.
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727
3.4.231
High leakage reactance current transformer
728 729 730
Current transformer which does not satisfy the requirements of 3.4.230, and for which an additional allowance is made by the manufacturer to take account of influencing effects which result in additional leakage flux.
731 732
3. 3.4.2 4.232 32
Rated equivalent limiting secondary voltage (Ual)
733 734
That r.m.s. value of the equivalent secondary circuit voltage at rated frequency necessary to satisfy the specified duty cycle:
735
U al = K ssc ⋅ K td ⋅ ( Rct + Rb ) ⋅ I sr
736
3.4.233
Peak value of the exciting secondary current at U al al (Î al a ) l
739
3.4.234
Factor of construction Fc
740 741 742 743
The factor of construction F c reflects the possible differences in measuring results at limiting conditions between direct test and indirect test methods. F c is based on magnetic flux measurements:
737 738
744 745 746 747 748 749 750 751 752 753 754 755
F c
=
Ψind Ψdir
where
Ψdir is the magnetic flux corresponding to error limiting conditions, measured in a direct test. The corresponding instantaneous error current Iε d shall also be determined.
Ψind is the magnetic flux measured in an indirect test, determined for the above mentioned magnetizing current Iε d . The measuring procedure is given in annex B.3.3.4
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3.5 Definitions related to other other ratings
757
3.5.1 Rated frequency (f R R )
758
3.5.2 Mechanical load (F) (F )
759
3.5.3 Internal arc fault protection instrument transformer
760
3.6 Definitions related to gas insulation
761
3.6.1 Pressure relief device
762
3.6.2 Gas-insulated metal-enclosed instrument transformer
763
3.6.3 Closed pressure system
764
3.6.4 Rated filling pressure
765
3.6.5 Minimum functional pressure
766
3.6.6 Design pressure of the enclosure
767
3.6.7 Design temperature of the enclosure
768
3.6.8 Absolute leakage rate
769
3.6.9 Relative leakage rate (F re re ) l
770
3.7 Index of abbreviations
771 IT
Instrument Transformer
CT
Current Transformer
U sys sys
Highest voltage for system
U m
Highest voltage for equipment
I pr
Rated primary current
I sr
Rated secondary current
I th
Rated short-time thermal current
I dy n
Rated dynamic current
I ct h
Rated continuous thermal current
I e
Exciting current
k
Actua Act uall tra t ransf nsf orm atio at ion n rati ra tio o
k r r
Rated transformation ratio
ε
Ratio error
∆φ
Phase displacement
S r r
Rated output
38/404/CDV
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61869-2 ed. 1 © IEC R b
Rated resistive burden
R ct
Secondary winding resistance
εc
Composite error
I PL
Rated instrument limit primary current
FS
Instrument security factor
I al f
Rated accuracy limit primary current
ALF
Acc urac ur acyy lim l imitit fact fa ctor or
Ψ s
Saturation flux
Ψ r r
Remanent flux
K r
Remanence factor
T s
Rated secondary loop time constant
E k
Rated knee point e.m.f.
ε t
Turns ratio error
K x
Dimensioning factor
f R
Rated frequency
F
Mechanical load
F re re l
Relative leakage rate
Î al
Peak value of the exciting secondary current at Ual
I psc
Rated primary short-circuit current
iε
Instantaneous error current
K ss c
Rated symmetrical short-circuit current factor
K td td
Rated transient dimensioning factor
t’
Duration of first fault
t’’ t’ ’
Duration of second fault
t’ al
Permissible time to accuracy limit in the first fault
t’’ t’ ’al
Permissible time to accuracy limit in the second fault
t fr
Fault repetition time
T p
Specified primary time constant
U al al
Rated equivalent limiting secondary voltage
38/404/CDV
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61869-2 ed. 1 © IEC
ˆ ε
Peak value of total error
ˆac ε
Peak value of alternating error component
38/404/CDV
772 773 774 775
4 Normal and special service conditions
776
4.1 General
777
4.2 Normal service conditions
778
4.2.1 Ambient air temperature
779
4.2.2 Altitude
780
4.2.3 Vibrations or earth tremors
781
4.2.4 Other service conditions for indoor instrument instrument transformers
782
4.2.5 Other service conditions for outdoor instrument transformers
783
4.3 Special service conditions
784
4.3.1 General
785
4.3.2 Altitude
786
4.3.2.1 Influence of altitude on external insulation insulation
787
4.3.2.2 Influence of altitude on temperature-rise
788
4.3.3 Ambient temperature
789
4.3.4 Vibrations or earth tremors
790
4.3.5 Earthquakes
791
4.4 System System earthing
792
5 Ratings
793
5.1 General
794
5.2 Highest voltage for equipment
795
5.3 Rated in sulation levels
796
5.3.1 General
797
5.3.2 Rated primary terminal insulation level
798 799 800
Clause 5.3.2 of IEC 61869-1 is applicable with the addition of the following: For a current transformer without primary winding and without primary insulation of its own, the value U m = 0,72 kV is assumed.
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801
5.3.3 Other requirements for primary terminals insulation
802
5.3.3.1 Partial discharges
803
5.3.3.2 Chopped lightning impulse
804
5.3.3.3 Capacitance and dielectric dissipation factor
805
5.3.4 Between-section insulation requirements
806
5.3.5 Insulation requirements for secondary terminals
807
Clause 5.3.5 of IEC 61869-1 is applicable with the addition of the following:
808 809 810
The secondary winding insulation of class PX current transformers having a rated knee point e.m.f. E k ≥ 2 kV shall be capable of withstanding a rated po wer frequency withstand voltage of 5 kV r.m.s. for 60 s.
811
5.3.200 Inter-turn insulation requirements
812
The rated withstand voltage for inter-turn insulation shall be 4,5 kV peak.
813 814 815
For class PX transformers having a rated knee point e.m.f. of greater than 450 V, the rated withstand voltage for the inter-turn insulation shall be a peak voltage of 10 times the r.m.s. value of the specified knee point e.m.f., or 10 kV peak, whichever is the lower.
816
NOTE 1 Due to the test test procedure, the wave shape may be highly distorted. distorted.
817
5.4 Rated frequency
818
5.5 Rated output
819
The standard values of rated output up to 30 VA are:
820
2,5 – 5,0 – 10 – 15 and 30 VA.
821
Values above 30 VA may be selected to suit the application.
822 823 824 825
NOTE For a given transformer, provided provided one of the values of rated output is standard standard and associated with a standard accuracy class, the declaration of other rated outputs, which may be non-standard values, but associated with other standard accuracy classes, is not precluded.
826
5.6 Rated a ccuracy class
827
5.6.200
Measuring current transformers
828
5.6.200.1
Accuracy class designation for measuring current transformers
829 830
For measuring current transformers, the accuracy class is designated by the highest permissible percentage current error at rated current prescribed for the accuracy class concerned.
831
5.6.200.2
832
The standard accuracy classes for measuring current transformers are:
833
Standard accuracy classes
0,1 - 0,2 – 0,2S –0,5 - 0,5S – 1 – 3 – 5
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834 835 836
5.6.200.3 Limits of current error and phase displacement for measuring current transformers
837 838 839
For classes 0.1 – 0.2 – 0.5 and 1, the current error and phase displacement at rated frequency shall not exceed the values given in Table 201 when the secondary burden is any value from 25 % to 100 % of the rated burden.
840 841 842
For classes 0.2 S and 0.5 S the current error and phase displacement at the rated frequency shall not exceed the values given in Table 202 when the secondary burden is any value from 25 % and 100 % of the rated burden.
843 844 845
For class 3 and class 5, the current error at rated frequency shall not exceed the values given in Table 203 when the secondary burden is any value from 50 % to 100 % of the rated burden.
846 847 848
The secondary rated burden used for test purposes shall have a power-factor of 0,8 lagging except that when the burden is less than 5 VA VA,, a power-factor of 1,0 shall be used. In no case shall the test burden be less than 1 VA.
849 850 851 852
For current transformers having a rated burden not exceeding 15 VA, an extended range of burden can be specified. The current error and phase displacement shall not exceed the values given in tables 200.1 and 200.2, when the secondary burden is any value from 1 VA to 100 % of the rated burden. In this case the power factor shall be 1.0
853 854
NOTE 1 For current transformers with with a rated secondary current of of 1A, a range limit lower lower than 1 VA may be agreed.
855 856
NOTE 2 At the moment, there is not sufficient experience about the possibility to perform the accuracy measurements at lower current values (test equipment and uncertainty of the obtained results).
857 858 859
NOTE 3 In general the prescribed limits limits of current error and phase displacement displacement are valid for any given position position of an external conductor spaced at a distance in air not less than that required for insulation in air at the highest voltage for equipment (U ( U m).
860 861
Special conditions of application, including lower ranges of operation voltages associated with high current values, should be a matter of separate agreement between manufacturer and purchaser.
862 863
For multi-ratio transformers with tappings on the secondary winding, the accuracy requirements refer to the highest transformation ratio, unless otherwise specified.
864 865
When the requirements refer to highest transformation ratio, the manufacturer shall give information about the accuracy class and the rated burden for the other tappings.
866 867 868
Table 201 – Limits of current error and phase displacement for measuring current transformers (classes from 0.1 to 1) Accuracy class
Percentage current (ratio) error at percentage of rated current shown below
Phase displacement at percentage of rated current shown below Minutes
0.1 0.2 0.5 1
869
Centiradians
5
20
100
120
5
20
100
120
5
20
100
120
0,4 0,75 1,5 3,0
0,2 0,35 0,75 1,5
0,1 0,2 0,5 1,0
0,1 0,2 0,5 1,0
15 30 90 180
8 15 45 90
5 10 30 60
5 10 30 60
0,45 0,9 2,7 5,4
0,24 0,45 1,35 2,7
0,15 0,3 0,9 1,8
0,15 0,3 0,9 1,8
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Table 202 – Limits of current error and phase displacement for measuring current transformers for special application
870 871 Accuracy class
Percentage current (ratio) error at percentage of rated current shown below
Phase displacement at percentage of rated current shown below Minutes
1 0.2 S 0.5 S
5
0,75 0,35 1,5 0,75
872 873 874 875 876 877
Centiradians
20
100
120
1
5
20
100
120
1
5
20
100
120
0,2 0, 2 0,5 0, 5
0,2 0,5
0,2 0,5
30 90
15 45
10 30
10 30
10 30
0,9 2,7
0,45 1,35
0,3 0, 3 0,9 0, 9
0,3 0,9
0,3 0,9
Table 203 – Limits of current error for measuring current transformers (classes 3 and 5) Class
Percentage current (ratio) error at percentage of rated current shown below 50
120
3
3
3
5
5
5
878 879 880
Limits of phase displacement are not specified for class 3 and class 5.
881
5.6.200.4
882 883
Current transformers of accuracy classes 0.1 to 1 may be marked as having an extended current rating provided they comply with the following two requirements:
884 885
a) the rated continuous thermal current shall be the rated extended primary current expressed as a percentage of the rated primary current;
886 887
b)
888
5.6.201
889 890 891 892 893 894 895
Extended current ratings
the limits of current error and phase displacement prescribed for 120 % of rated primary current in Table 201 shall be retained up to the rated extended primary current.
Protective current transformers
Three different approaches are designated to define protective current transformers. In practice, each of the three definitions may result in the same physical realization. For relations between the class definitions, refer to the application guide. Table 204 – Definitions of protective classes
Designation
Limit for remanent flux
P
no
PR
yes
PX
no
1
1
Explanation Defining a current transformer to meet the requirements of a short circuit current under symmetrical steady state condition, (eventually overdimensioning it in order to make it suitable for asymmetrical short circuit current) Defining a current transformer by requiring its magnetizing characteristic.
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61869-2 ed. 1 © IEC 1
TPX TP X
no
TPY TP Y
yes
TPZ TP Z
yes
38/404/CDV
Defining a current transformer to meet the requirements of an asymmetrical short circuit current
896 897
Note 1: Although there is no limit of remanent flux, air gaps are allowed, e.g. in split core current transformers.
898 899
5.6.201.1
Class P protective transformers
900
5.6.201.1.1
Standard accuracy limit factors
901
The standard accuracy limit factors are:
902
5 – 10 – 15 – 20 – 30
903
5.6.201.1.2
Accuracy class designation
904 905 906
For protective current transformers, the accuracy class is designed by the highest permissible percentage composite error at the rated accuracy limit primary current prescribed for the accuracy class concerned, followed by the letter “P” (meaning protection).
907
5.6.201.1.3
908
The standard accuracy classes for protective current transformers are:
Standard accuracy classes
909
5P and 10P
910
5.6.201.1.4
Limits of errors for protective current transformers
911 912
At rate ra ted d freq fr eque uenc ncyy and an d wit h rate ra ted d burd bu rden en conn co nnec ecte ted, d, the th e cur rent re nt error er ror , phas ph ase e disp di spla lace ceme ment nt and composite error shall not exceed the values given in Table 205. 205 .
913 914 915
For testing purposes when determining current error and phase displacement, the burden shall have a power-factor of 0,8 inductive except that, where the burden is less than 5 VA, a power-factor of 1,0 is permissible.
916 917
For the determination of composite error, the burden shall have a power-factor of between 0,8 inductive and unity at the discretion of the manufacturer.
918 919
Table 205 – Limits of error for protective current transformers class P and PR Accuracy class
920 921
Current error at rated primary current %
Phase displacement at rated primary current
minutes
centiradians
Composite error at rated accuracy limit primary current %
5P
±1
± 60
± 1,8
5
10P
±3
–
–
10
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61869-2 ed. 1 © IEC 922
5.6.201.2
Class PR protective current transformers
923
5.6.201.2.1
Standard accuracy limit factors
924
The standard accuracy limit factors are:
925
38/404/CDV
5 – 10 – 15 – 20 – 30
926
5.6.201.2.2
Accuracy class designation
927 928 929
The accuracy class is designated by the highest permissible percentage composite error at the rated accuracy limit primary current prescribed for the accuracy class concerned, followed by the letters "PR" (indicating protection low remanence).
930
5.6.201.2.3
931
The standard accuracy classes for low remanence protective current transformers are:
Standard accuracy classes
932
5 PR and 10 PR
933
5.6.201.2.4
Limits of error for class PR PR protective protective current transformers
934 935
At rate ra ted d freq fr eque uenc ncyy and an d wit h rate ra ted d burd bu rden en conn co nnec ecte ted, d, the th e cur rent re nt error er ror , phas ph ase e disp di spla lace ceme ment nt and composite error shall not exceed the values given in Table 205. 205 .
936 937 938
For testing purposes when determining current error and phase displacement, the burden shall have a power-factor of 0,8 inductive except that, where the burden is less than 5 VA, a power-factor of 1,0 is permissible.
939 940
For the determination of composite error, the burden shall have a power-factor of between 0,8 inductive and unity at the discretion of the manufacturer.
941
5.6.201.2.5
942
The remanence factor (K (K r r ) shall not exceed 10 %.
943
NOTE Insertion of one or more air air gaps in the core may be a method method for limiting the remanence remanence factor.
944
5.6.201.2.6
945
If required, the value shall be specified by the purchaser.
946
5.6.201.2.7
947
If required, the maximum value shall be agreed between manufacturer and purchaser.
948
5.6.201.3
949
The performance of class PX current transformers shall be specified in terms of the following:
950 951
a) rated primary current (I pr ); b) rated secondary current (I sr );
952 953 954 955 956
c) rated turns ratio. The turns ratio error shall not exceed ±0,25 %; d) rated knee point e.m.f. (E k ); e) maximum exciting current (I e) at the rated knee point e.m.f. and/or at a stated percentage thereof; f) maximum value of secondary winding resistance (R ct );
Remanence factor ( K r r )
Secondary loop time constant (T s )
Secondary winding resistance ( R ct ct )
Class PX protective current transformers
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61869-2 ed. 1 © IEC 957 958
g) rated resistive burden (R b ); h) dimensioning factor (K x ).
959
NOTE The rated knee point e.m.f. is generally generally determined determined as follows:
38/404/CDV
E k = K x ⋅ (R ct + R b ) × I sr
960 961 962
5.6.201.4
Protective current transformers for transient performance
963
5.6.201.4.1
Standard values of rated resistive burden (R b)
964 965 966 967 968 969 970 971
Standard values of rated resistive burden in ohms for class TPX, TPY and TPZ current transformers are: 0.5 – 1 – 2 – 5 Ohm The preferred values are underlined. The values are based on a rated secondary current of 1A. For current transformers having a rated secondary current other than 1 A, the above values shall be adjusted in inverse ratio to the square of the current.
972 973
5.6.201.4.2
Error limits for TPX, TPY and TPZ current transformers
974 975 976 977
found.6. The errors shall not exceed the values given in Error! Reference source not found.6.
Table 206 – Error limits for TPX, TPY and TPZ current transformers
978 Class
At rated primary current
At accuracy limit condition
Phase displacement(2)
Ratio error [%] %
Min
Centirad
TPX TP X
1. 0 ±1.0
± 60
1. 8 ± 1.8
ˆ = 10 % ε
TPY TP Y
1. 0 ±1.0
± 60
1. 8 ± 1.8
ˆ = 10 % ε
TPZ TP Z
±1.0
180 ± 18
5.3 ± 0.6 0. 6
ˆac ε
= 10 %
NOTE 1 – all error limits shall be observed at Rct, which is defined at 75°C. NOTE 2 - The absolute value of the phase displacement may in some cases be of less importance than achieving minimal deviation from the average value of a given production series. NOTE NOT E 3 - Since the total permissible error limit is 10 %, the transient transient dimensioning factor shall shall be considered conjunctively with the secondary circuit time constant:
ˆ= ε
979
K td ω ⋅ T s
⋅ 100%
(3)
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980
5.6.201.4.3
Limits for remanence factor ( K r r )
981 982
TPX: no limit TPY: K r ≤ 10%
983 984 985
TPZ: K r ≤ 10% (given by the design. In practice, K r << 10%) Therefore, the remanent flux can be neglected.
986
5.6.201.4.4
987 988 989 990 991 992 993 994 995 996
The two specification methods are illustrated in Table 207. In some cases, the definition of one specific duty cycle cannot describe all protection requirements. Therefore, the alternative definition offers the possibility to specify “overall requirements”, which cover the requirements of different duty cycles.
Specification Methods
The specifications shall not be mixed, otherwise the current transformer may be overdetermined.
Table 207 – Specification Method for TPX, TPY and TPZ current transformers
997 Standard specification
Alternative specification
CT class designation (TPX, TPY, or TPZ)
CT class designation (TPX, TPY, or TPZ)
Ratio to which the specification applies
Ratio to which the specification applies
1
Rated symmetrical short-circuit current factor Kss c
1
Rated symmetrical short-circuit current factor Kss c
Duty cycle, consisting of for C-O cycle:
t’al
Rated transient dimensioning factor Ktd
for C-O-C-O cycle:
t’al , t’, tfr , t’’al
Rated secondary loop time constant T S
2
Rated primary time constant T p Rated resistive burden R b
Rated resistive burden R b
998 999 1000 1001 1002
Note 1: If not specified, for multi-ratio transformers with tappings on the secondary winding, the accuracy requirements refer to the highest transformation ratio. It has to be considered, that usually the given accuracy requirements can be fulfilled for one ratio only.
1003
Note 2: for TPY cores only
1004
5.200 Standard values of rated primary current
1005
5.200.1 Single ratio transformers
1006
The standard values of rated primary currents are:
1007
10 – 12,5 – 15 – 20 – 25 – 30 – 40 – 50 – 60 – 75 A,
1008
and their decimal multiples or fractions.
1009
The preferred values are those underlined.
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1010
5.200.2 Multi-ratio transformers
1011
The standard values given in 5.200.1 refer to the lowest values of rated primary current.
1012
5.201 Standard values of rated secondary secondary currents
1013
The standard values of rated secondary currents are 1 A, 2 A and 5 A
1014 1015
For protective current transformers for transient performance, the standard value of the rated secondary current is 1 A.
1016
5.202 Rated continuous thermal current current
1017
The standard value of rated continuous thermal current is the rated primary current.
1018 1019
When a rated continuous thermal current greater than rated primary current is specified, the preferred values are 120 %, 150 % and 200 % of rated primary current.
1020
5.203 Short-time current ratings
1021
All Al l c urr ent en t tran tr ansf sfor orme mers rs shal sh alll com ply pl y wit w ith h the th e f ollo ol lowin win g r equi eq uire reme ment ntss
1022
5.203.1
1023
A r ated at ed short sh ort -tim -t ime e t herm he rmal al curr cu rren entt (I ( I th th ) shall be assigned to the transformer (see 3.4.202).
1024
5.203.2
1025 1026 1027
The value of the rated dynamic current (I (I dyn dyn ) shall normally be 2.5 times the rated short-time thermal current (I ( I th th ) and it shall be indicated on the rating plate when it is different from this value (see 3.3.203).
1028 1029
Rated short-time thermal current ( I th th )
Rated dynamic current (I dyn dyn )
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6 Design and construction
1031
6.1 Requirements for liquids used in equipment
1032
6.1.1 General
1033
6.1.2 Liquid quality
1034
6.1.3 Liquid level device
1035
6.1.4 Liquid tightness
1036
6.2 Requirements for gases used used in equipment
1037
6.2.1 General
1038
6.2.2 Gas quality
1039
6.2.3 Gas monitoring device
1040
6.2.4 Gas tightness
1041
6.2.4.1 General
1042
6.2.4.2 Closed pressure pressure systems systems for gas
1043
6.2.5 Pressure relief device
1044
6.3 Requirements for solid materials used in equipment equipment
1045
6.4 Requirements for temperature temperature rise of parts and components
1046
6.4.1 General
1047
Clause 6.4.1 of IEC 61869-1 is applicable with the addition of the following:
1048 1049 1050 1051
The temperature rise of a current transformer when carrying a primary current equal to the rated continuous thermal current, with a unity power-factor burden corresponding to the rated output, shall not exceed the appropriate value given in table 5 of IEC61869-1. IEC61869-1 . These values are based on the service conditions given in clause 4
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6.4.2 6.4 .2 Influence Influen ce of altitude altitu de on temperature-rise temperat ure-rise
1053
6.5 Requirements for earthing of equipment
1054
6.5.1 General
1055
6.5.2 Earthing of the enclosure
1056
6.5.3 Electrical continuity
1057
6.6 Requirements for th e external insulation
1058
6.6.1 Pollution
1059
6.6.2 Altitude
1060
6.7 Mechanical requirements
1061
6.8 Multiple chopped imp ulse on primar y terminals
1062
6.9 Internal arc fault protection requirements
1063
6.10
1064
6.10.1 General
1065 1066
6.10.2 Protection Protection of persons agai nst access to ha zardous parts and protection of the equipment against ingress of solid foreign objects
1067
6.10.3 Protection against ingress of water
1068
6.10.4 Indoor instrument transformers
1069
6.10.5 Outdoor instrument transformers
1070 1071
6.10.6 Protection Protection of equipment against mechanical impact under normal service conditions
1072
6.11
1073
6.11.1 General
1074
6.11.2 Requirement for Radio Interference Voltage (RIV)
1075
6.11.3 Requirements for immunity
1076
6.11.4 Requirement for transmitted overvoltages
1077
6.12
Corrosion
1078
6.13
Markings
1079
6.13.200 Terminal markings – General rules
1080
In addition to clause 6.13 of IEC 61869-1 the terminal markings shall identify
1081 1082 1083 1084
a) b) c) d)
Degrees of protection by enclosures
Electromagnetic Compatibility (EMC)
the primary and secondary windings; the winding sections, if any; the relative polarities of windings and winding sections; the intermediate intermediate tapings, if any.
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6.13.200.1
Method of marking
1086 1087
The marking shall consist of letters followed, or preceded where necessary, by numbers. The letters shall be in block capitals.
1088
6.13.200.2
1089 1090
The markings of current transformer terminals shall be as indicated in the following Table 208.
1091
Table 208 – Markings of terminals
Markings to be used
P1
P2
P1
P2
Primary terminals
Secondary terminals S1
S1
S2
Figure 1 – Single ratio transformer.
C1
S2
S3
Figure 2 – Transformer with an intermediate tapping on secondary winding.
C2
P2
P1
P1 Primary terminals
P2
1S1 Secondary terminals S1
S
S2
Figure 3 – Transformer with primary winding in 2 sections intended for connections either in series or in parallel.
1 1
1S2
2S1
2S2
S 12
S 21
S 22
Figure 4 – Transformer with 2 secondary windings; each with its own magnetic core. (Two alternative markings for the secondary terminals.)
1092
6.13.200.3
Indication of relative polarities
1093
All Al l the th e term te rmin inals als mark ma rked ed P1, S1 and an d C1 shal sh alll h ave the th e same sa me polar po lar ity it y at a t the th e same sa me inst in stan ant. t.
1094
6.13.201 Rating plate markings
1095 1096
In addition to previous paragraphs, all current transformers shall carry at least the following markings:
1097
a) the rated primary and secondary current, i.e.:
1098
k r = I pr / Isr (e.g. 100/5 A)
1099 1100 1101 1102 1103 1104
b) the rated output and the corresponding accuracy class, together with additional information specified in the later parts of these recommendations (see 6.13.202 and/or 6.13.203, 6.13.204 and 6.13.205); In addition, the following information shall be marked: c) the rated short-time thermal current (I th th ) and the rated dynamic current if it differs from 2,5 times the rated short-time thermal current (e.g. 13 kA or 13/40 kA);
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1105 1106
d) on transformers with two two or more secondary windings, the use use of each winding and its corresponding terminals
1107
e) the rated continuous thermal current
1108
Examples:
1109
For single core current transformer with secondary taps: I cth ct h = 120 %
1110
For multiple core current transformer (300/5 A and 4000/1 A): I cth ct h = 360 A
1111
For current transformer with primary reconnection (4x300/1 A): I cth ct h = 4x360 A
1112
6.13.202 Marking of the rating plate of a measuring current current transformer transformer
1113 1114
The accuracy class and instrument security factor shall be indicated following the indication of corresponding rated output (e.g. 15 VA class 0.5 FS 10).
1115 1116
Current transformers having an extended current rating (see 5.6.200.4) shall have this rating indicated immediately following the class designation (e.g. 15 VA class 0.5 ext. 150 %).
1117 1118 1119
For current transformers having a rated burden not exceeding 15 VA and an extended burden down to 1 VA, this rating shall be indicated immediately before the burden indication (for example, 1..10 VA class 0,2).
1120 1121 1122
NOTE The rating plate may contain information information concerning several combinations of ratios, output and accuracy class that the transformer can satisfy (for example, 15 VA class 0,5 – 30 VA class 1) and in this case non-standard values of output may be used (for example, 15 VA class 1..7 VA class 0,5 in accordance with note to 5.5).
1123
6.13.203 Marking of the rating plate of a class P protective current transformer transformer
1124 1125 1126
The rating plate shall carry the appropriate information in accordance with 6.13.201. 6.13.201. The Th e rated accuracy limit factor shall be indicated following the corresponding output and accuracy class (e.g. 30 VA class 5P 10). 1
1127
6.13.204 Marking of the rating rating plate of class PR protective current transformers transformers
1128 1129 1130
The rating plate shall carry the appropriate information in accordance with 6.13.201. 6.13.201. The Th e rated accuracy limit factor shall be indicated following the corresponding output and accuracy class (e.g. 10 VA class 5PR 30). 1
1131
6.13.204.1
1132 1133
a) secondary loop time constant (T s ) b) maximum value of of secondary winding resistance (R (R ct )
1134 1135
NOTE 1 A current transformer satisfying satisfying the requirements of several combinations combinations of output and accuracy class class and accuracy limit factor may be marked according to all of them.
1136 1137
Example: (30 VA class 1) (15 VA class 1, ext. 150 %)
Additional marking (when required)
(30 VA class 5PR 10) (15 VA class 5PR 20)
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6.13.205 Marking of the rating rating plate of class PX protective current transformers transformers
1140
6.13.205.1
1141
Refer to 6.13.201. The rated turns ratio is given by Ipr and an d I sr. sr .
1142
6.13.205.2
Principal marking
Additional marking
1143 1144 1145
a) maximum exciting current (I e ) at the rated knee point e.m.f. and/or at the stated percentage thereof; b) maximum value of secondary winding winding resistance (R ct )
1146 1147 1148 1149 1150 1151 1152
c) rated knee point e.m.f. (E k k );
1153
or dimensioning factor (K (K x ) rated resistive burden (R ( R b).
6.13.205.3
Examples:
1154 1155 1156 1157 1158 1159 1160
Ek=200V Ie<=0.2A Rct<=2.0Ω or Ie<=0.2A Rct<=2.0 Ω Kx=8 Rb=3.0 Ω
1161 1162
6.13.206 Marking of the rating plate of current current transformers transformers for transient transient performance
1163
6.13.206.1
1164
Refer to 6.13.201
1165
6.13.206.2
1166 1167
Add ition iti onal ally, ly, the th e clas cl asss mark ma rkin ing g c onsi on sist stss of the th e foll fo llow owing ing 2 eleme ele ment nts: s:
1168 1169 1170 1171 1172
Principal marking
Additional marking
a) Definition part (compulsory) contains the essential information which is necessary to determine whether the current transformer fulfils given requirements (consisting of duty cycle and T p) Examples with K ssc . =20, Ktd =12.5: Rb 5
TPX 20*12.5 Rct 2.8
Rb 5
TPY 20*12.5 Rct 2.8
Rb 5
TPZ 20*12.5 Rct 2.8
1173 1174 1175
b) Complementary part (optional)
Ts 250 ms
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The complementary part represents one of many possible cycles, leading to the same value of Ktd . The determination of K td is explained in annex B.1. Examples: Marking:
Meaning:
Cycle 100ms, Tp 100 ms
t’al =100ms Tp=100ms
Cycle (40-100)-300-40ms, Tp 100ms
t’ al =40ms, t’=100ms, t fr =300ms, t’’ al =40ms, Tp =100ms
1179 1180 1181
If actual values of Rct have to be mentioned on the rating plate, this value shall fulfill the following condition:
( Rct * 0.8) ≤ R ≤ Rct
1182 1183 1184 1185
where R is the measured value.
1186
6.14
1187
7 Tests
1188
7.1 General
1189
7.1.1 Classification of tests
1190
7.1.2 List of tests
1191
The list of tests is given in Table 209.
Fire hazard
1192
Table 209 – List of tests T e s t s Type tests
Sub c l a us e 7.2
Temperature-rise test
7.2.2
Impulse voltage test on primary terminals
7.2.3
Wet test for outdoor type transformers
7.2.4
Electromagnetic Compatibility tests
7.2.5
Test for accuracy
7.2.6
Verification of the degree of protection by enclosures
7.2.7
Enclosure tightness test at ambient temperature
7.2.8
Pressure test for the enclosure
7.2.9
Short-time current test
7.2.200 Routine tests
7.3
Power-frequency voltage withstand tests on primary terminals
7.3.1
Partial discharge measurement
7.3.2
Power-frequency voltage withstand tests between sections
7.3.3
Power-frequency voltage withstand tests on secondary terminals
7.3.4
Test for accuracy
7.3.5
Verification of markings
7.3.6
Enclosure tightness test at ambient temperature
7.3.7
Pressure test for the enclosure
7.3.8
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38/404/CDV 7.3.200
Special tests
7.4
Chopped impulse voltage withstand test on primary terminals
7.4.1
Multiple chopped impulse test on primary terminals
7.4.2
Measurement of capacitance and dielectric dissipation factor
7.4.3
Transmitted overvoltage test
7.4.4
Mechanical tests
7.4.5
Internal arc fault test
7.4.6
Enclosure tightness test at low and high temperatures
7.4.7
Gas dew point test
7.4.8
Corrosion test
7.4.9
Fire hazard test
7.4.10 Sample tests
7.5
1193 1194 1195 1196 1197
For testing of gas-insulated instrument transformers, the type and pressure of the gas shall be according to Table 210
1198 1199
Table 210 – Gas type and pressure during type, routine and special tests Test
Gas type
Pressure
Same fluid as in service
Minimum functional pressure
Same fluid as in service
Rated filling pressure
n/a
Reduced pressure
Dielectric, RIV Acc ura cy Temperature rise Internal arc Short-circuit Mechanical Tightness Gas dew point Transmitted overvoltages
a For gas-insulated instrument transformers installed installed on GIS, the wet test and RIV test are not applicable.
1200 1201 1202
7.1.3 Sequence of tests
1203
7.2 Type Type tests
1204
7.2.1 General
1205
7.2.1.1 Information for for identification of specimen
1206
7.2.1.2 Information to be included in type-test type-test reports
1207
7.2.2 Temperature-rise test
1208
7.2.2.200
1209 1210
For current transformers in three phase gas-insulated metal enclosed switchgear, all three phases have to be tested in the same time.
General
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1211 1212 1213 1214
The current transformer shall be mounted in a manner representative of the mounting in service and the secondary windings shall be loaded with the designated burdens. However, because the position of the current transformer in each switchgear can be different, it is left to the manufacturer’s choice how to arrange the test set up.
1215
7.2.2.201
1216 1217 1218
The sensors to measure the ambient temperature shall be distributed around the current transformer, at an appropriate distance according to the current transformer ratings and at about half-height of the transformer, protected from direct heat radiation.
1219 1220 1221
To minimise the effects of variation of cooling-air temperature, particularly during the last test period, appropriate means should be used for the temperature sensors such as heat sinks of time constant approximately equal to that of the transformer.
1222
The average readings of two sensors shall be used for the test.
1223
7.2.2.202
1224
The test can be stopped when the following conditions are met:
Cooling-air temperature
Duration of the test
1225 1226
-
the test duration duration is at least least equal to three times the current transformer thermal time time constant
1227 1228 1229
-
the rate of temperature rise of the windings and of the top-oil immersed current transformer does not exceed 1 K per hour, during three consecutive temperature rise readings.
1230 1231
The manufacturer shall estimate the thermal time constant by one of the following methods:
1232
-
1233 1234
confirmed during the temperature rise test -
1235 1236
1239
during the test, from the temperature rise curve(s) or temperature decrease curve(s) recorded during the course of the test and calculated according to Annex C
-
1237 1238
before the test, based on the results of previous tests on a similar design and shall be
during the test, as the point of intersection intersection between the tangent to the temperature rise curve originating at 0 and the maximum estimated temperature rise
-
during the test, as the time elapsed until 63 % of maximum estimated temperature rise.
1240
7.2.2.203
Temperatures and temperature rises
1241 1242 1243
The purpose of the test is to determine the average temperature rise of the windings and, for oil-immersed transformers the temperature rise of the top oil, in steady state conditions when the specified losses are injected in the current transformer.
1244 1245 1246
The average temperature of the windings shall, when practicable, be determined by the resistance variation method, but for windings of very low resistance thermometers, thermocouple or other appropriate temperature sensors may be employed.
1247 1248 1249
Thermometers or thermocouples shall measure the temperature rise of parts other than windings. The top oil temperature shall be measured by sensors applied to the top of metallic head directly in contact with the oil.
1250 1251
The temperature rises shall be determined by the difference in respect to the ambient temperature measured as indicated in 7.2.2.201
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1252
7.2.2.204
Test modalities for current transformers having U m <525 kV
1253 1254
The test shall be performed applying to the primary winding the rated continuous thermal current with the secondary(s) closed on the rated burden.
1255 1256
7.2.2.205 Test modalities for oil-immersed current transformers having U m 525 kV
1257
The test shall be performed applying simultaneously to the current transformer:
1258 1259
•
the rated continuous thermal current to the primary winding with the secondary winding(s) closed on the rated burden;
1260 1261
•
the highest voltage of the equipment divided by √ 3 between the primary winding and earth at which also a terminal of the secondary winding(s) shall b e connected.
1262 1263 1264
Note - The test current can be also applied to one or more secondary windings with the primary and the nonsupplied secondary windings short-circuited.
1265
7.2.3 Impulse voltage withstand test test on primary primary terminals
1266 1267 1268
The test voltage shall be applied between the terminals of the primary winding (connected together) and earth. The frame, case (if any), and core (if intended to be earthed) and all terminals of the secondary winding(s) shall be connect ed to earth.
1269
7.2.3.1 General
1270
Clause 7.2.3.1 of IEC 61869-1 is applicable with the addition of the following:
1271 1272
For three-phase current transformers for gas insulated substation, each phase shall be tested, one by one. During the test on each phase, the other phases will be earthed.
1273 1274
For the acceptance criteria of gas-insulated metal enclosed transformers, refer to IEC 62271203 clause 6.2.4.
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1275
7.2.3.2 Lightning impulse voltage test test on primary primary terminals
1276
7.2.3.2.1 Instrument transformers having U m < 300 kV
1277
7.2.3.2.2 Instrument transformers having U m
1278
7.2.3.3 Switching impulse voltage test
1279
7.2.3.3.1 General
1280
7.2.4 Wet test for outdoor type transformers
1281
7.2.5 Electromagnetic Compatibility (EMC) tests
1282
7.2.5.1 RIV test
1283
7.2.5.2 Immunity test
1284
7.2.5.3 Not applicable
1285
7.2.6 Test for accuracy
1286
7.2.6.200
1287 1288 1289
Type tests to prove compliance with 5.6.200.3 shall, in the case of transformers of classes 0.1 to 1, be made at each value of current given in Table 201 at 25 % and at 100 % of rated burden (subject to 1 VA minimum).
1290 1291
Transformers having extended current ratings greater than 120 % shall be tested at the rated extended primary current instead of at 120 % of rated current.
1292 1293
Transformers of class 3 and class 5 shall be tested for compliance with the two values of current given in Table 203 at 50 % and at 100 % of rated burden.
1294 1295
7.2.6.201 Test for current error and phase displacement of protective current transformers
1296 1297
Tests shall be made at rated primary current to prove compliance with 5.6.201.1.4 in respect of current error and phase displacement.
1298
7.2.6.202
1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315
a) Compliance with the limits of composite composite error given in Table 204 shall be demonstrated by a direct test in which a substantially sinusoidal current equal to the rated accuracy limit primary current is passed through the primary winding with the secondary winding connected to a burden of magnitude equal to the rated burden but having, at the discretion of the manufacturer, a power-factor between 0,8 inductive and unity (see annexes A.4, A.5, A. 5, A.6, A. 6, A.7 A. 7 ). The test may be carried out on a transformer similar to the one being supplied, except that reduced insulation may be used, provided that the same geometrical arrangement is retained.
300 kV
Test for accuracy of measuring current transformers
Test for composite error
NOTE Where very high primary currents and single bar-primary bar-primary winding current current transformers are concerned, concerned, the distance between the return primary conductor and the current transformer should be taken into account from the point of view of reproducing service conditions. conditions.
b) For current transformers having substantially continuous ring cores, cores, uniformly distributed secondary winding(s) or uniformly distributed portions of tapped winding(s) and having either a centrally located primary conductor(s) or a uniformly distributed primary winding, the direct test may be replaced by the following indirect test, provided that the effect of the return primary conductor(s) is negligible.
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1316 1317 1318 1319 1320 1321 1322 1323
With the primary winding open-circuited, the secondary winding is energized at rated frequency by a substantially sinusoidal voltage having an r.m.s. value equal to the secondary limiting e.m.f. The resulting exciting current, expressed as a percentage of the rated secondary current multiplied by the accuracy limit factor, shall not exceed the limit of composite error given in table 204.
1324 1325
NOTE 2 In determining the composite composite error by the indirect indirect method, a possible difference difference between turns ratio and rated transformation ratio need not be taken into account.
NOTE 1 In calculating the secondary secondary limiting e.m.f., e.m.f., the secondary winding impedance should be assumed assumed to be equal to the secondary winding resistance measured at room temperature and corrected to 75 °C.
1326
7.2.6.203
Proof of low leakage reactance type
1327 1328
Current transformers shall, in addition to the requirements of clause 7.2, be tested as prescribed below.
1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340
In order to establish proof of low leakage reactance design, it shall be shown by a drawing that the current transformer has a substantially continuous ring core, with air gaps uniformly distributed, if any, uniformly distributed secondary winding, a primary conductor symmetrical with respect to rotation and the influences of conductors of the adjacent phase outside of the current transformer housing and of the neighbouring phases are negligible. If compliance with the requirements of low leakage reactance design cannot be established to the mutual satisfaction of the manufacturer and purchaser by reference to drawings, then the composite error shall be determined for the complete secondary winding using either of the direct methods of test given in annexes A.5 or A.6, at a secondary current of K x ⋅ I sn sn and with a secondary burden R b. Proof of low leakage reactance design shall be considered to have been established if the value of composite error from the direct method of test is less than 1,1 times that deduced from the secondary excitation characteristic.
1341 1342 1343
NOTE The value of primary current current required to perform direct composite error error tests on certain transformer types types may be beyond the capability of facilities normally provided by manufacturers. Tests at lower levels of primary current may be agreed between the m anufacturer and purchaser.
1344 1345
7.2.6.204
1346 1347
To prove compliance of the current transformer with the requirements of this standard, the following additional tests shall be performed.
1348 1349 1350
Table 211 – Additional type tests for protective current transformers for transient performance
Additional type tests for protective current transformers for transient performance
Test
Protection class
Reference
TPX
TPY
TPZ
Determination of the secondary winding resistance R ct
X
X
X
Determination of the steady state ratio error and phase displacement
X
Determination of the secondary loop time constant T constant T s
7.2.6.204.1 X
X 7.2.6.204.2
X 7.2.6.204.3
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X 7.2.6.204.4 X
X
X
7.2.6.204.5
1351 1352 1353
Determination of the secondary winding resistance R ct
1354
7.2.6.204.1
1355 1356 1357
The secondary winding resistance shall be measured and corrected to 75 ºC.
1358 1359
7.2.6.204.2 Determination of the steady state ratio error and phase displacement
1360 1361 1362 1363 1364 1365 1366 1367
The Th e ratio error and the phase displacement shall be measured at rated current. The results shall correspond to a secondary winding temperature of 75 °C. Therefore the actual value of the secondary winding temperature shall be measured, and the difference to its value corrected to 75°C shall be determined. The error measurement shall be made with the burden R b increased by the above mentioned difference of winding resistance.
1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382
Alter Alt erna natitivel vel y, for fo r TPY TP Y and an d TPZ core co ress the th e phas ph ase e dis plac pl acem emen entt at 75°C 75 °C ( ∆ϕ 75 ) may be determined by measuring at ambient temperature ( ∆ϕ amb ) and calculating as follows:
∆ϕ 75 = ∆ϕ amb
Rct + Rb Rct amb + Rb
where Rct amb is the winding resistance at the ambient temperature. The ratio error is not affected by this resistance correction. For type and routine testing, a direct test method (using a primary current source and a reference current transformer) has to be applied. For low leakage reactance CT’s, an indirect test method is given in annex B.4. It may be applied for on-site measurements and for monitoring purposes.
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1383 1384 1385
7.2.6.204.3
Determination of the secondary time constant T s
1386 1387 1388 1389 1390
The secondary loop time constant (Ts) shall be determined and shall not differ from the value on the rating plate by more than ±30 % for class TPY and ±10 % for class TPZ current transformers. In general, Ts shall be determined according to the following equation:
T S =
1391 1392 1393 1394
If ∆ϕ is expressed in minutes, the following approximate formula may be applied: T S [ s ] =
1395 1396 1397 1398 1399 1400 1401
3438 ∆ϕ [min] ⋅ ω
Since this method may cause difficulties for high ratio transformers and small phase angles due to uncertainty of the measurement of low phase displacement, an alternative method may be used in these cases by calculation of T S using the value of L m (see clause - 46 -)
1402
1403
1 ω * tan(∆ϕ )
T S
7.2.6.204.4
=
Lm
( Rct + Rb )
Determination of the magnetic characteristic
1404 1405 1406 1407 1408 1409 1410 1411
The magnetising inductance Lm shall be determined by one of the methods described in annex B.2.
1412 1413
The remanence factor (K ) r r shall be determined to prove compliance with clause 5.6.201.4.3. For test methods, refer to annex B.2.
1414 1415 1416 1417
Note: This type test shall be performed for each specific realization of current transformer. Usually, it is made for each production series.
1418
7.2.6.204.5
1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433
The purpose of the type test is to prove the compliance with the requirements at limiting conditions. For test methods refer to annex B.3.
a) magnetising inductance L m
b) remanence factor (K r r )
Determination of the error at limiting conditions
The direct test may be replaced by an indirect test, if at least one of the following two conditions is fulfilled: a) The current transformer is of the low leakage reactance type (see 7.2.6.203) b) A type test report of a current transformer is available, having - substantially the same construction and - similar rated primary short-circuit current. The test can be performed on a full scale model of the active part of the current transformer assembly inclusive of all metal housings but without insulation.
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If compliance between direct and indirect test is given, a type test shall be declared as relevant for similar designs (dimensions, electrical requirements). If Fc is greater than 1.1, it shall be considered in the dimensioning of the core.
1440
7.2.7 Verification of of the degree of protection by enclosures enclosures
1441
7.2.7.1 Verification of the IP coding
1442
7.2.7.2 Mechanical impact test
1443
7.2.8 Enclosure tightness test at ambient ambient temperature
1444
7.2.8.1
1445
7.2.9 Pressure test for the enclosure
1446
7.2.200 Short-time current test
1447 1448 1449
This test shall be made with the secondary winding(s) short-circuited, and at a current I for a time t , so that (I ( I 2t ) is not less than (I ( I 2th ) * 1s and provided t has a value between 0,5 s and 5 s.
1450 1451 1452
The dynamic test shall be made with the secondary winding(s) short-circuited, and with a primary current the peak value of which is not less than the rated dynamic current (I ( I dyn dyn ) for at least one peak.
1453 1454
The dynamic test may be combined with the thermal test above, provided the first major peak current of that test is not less than the rated dynamic current (I ( I dyn dyn ).
1455 1456
The transformer shall be deemed to have passed these tests if, after cooling to ambient temperature (between 10 °C and 40 °C), it satisfies the following requirements:
1457 1458 1459 1460 1461 1462 1463
a) it is not visibly visibly damaged; b) its errors after demagnetization do not differ from those recorded before the tests by more than half the limits of error appropriate to its accuracy class; c) it withstands the dielectric tests specified in 7.3.1, 7.3.2, 7.3.3 and 7.3.4, but with the test voltages or currents reduced to 90 % of those given; d) on examination, the insulation next to the surface of the conductor does not show significant deterioration (e.g. carbonization).
1464 1465
The examination d) is not required if the current density in the primary winding, corresponding to the rated short-time thermal current (I (I thth ), does not exceed:
1466 1467 1468 1469
–
1470 1471 1472 1473 1474
–
Closed pressure systems for gas
180 18 0 A/ mm 2 where the winding is of copper of conductivity not less than 97 % of the value given in IEC 60028. 120 12 0 A/ mm 2 where the winding is of aluminium of conductivity not less than 97 % of the value given in IEC 60121.
NOTE Experience has shown shown that in service the requirements for thermal thermal rating are generally fulfilled fulfilled in the case of class A insulation, provided that the current density in the primary winding, corresponding to the rated short-time thermal current, does not exceed the above-mentioned values.
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7.3 Routine tests
1476
7.3.1 Power-frequency voltage withstand tests tests on primary terminals
1477
Clause 7.3.1 of IEC 61689-1 is applicable with the addition of the following:
1478 1479 1480
The test voltage shall be applied between the short-circuited primary winding and earth. The short-circuited secondary winding(s), the frame, case (if any) and core (if there is a special earth terminal) shall be connected to earth.
1481
7.3.2 Partial discharge measurement
1482
7.3.2.1 Test circuit and instrumentation
1483
7.3.2.2 Partial discharge discharge test procedure procedure
1484
7.3.3 Power-frequency voltage withstand tests tests between sections
1485
7.3.4 Power-frequency voltage withstand tests tests on secondary terminals
1486
Test shall be performed to demonstrate compliance with 5.3.5
1487
7.3.5 Test for accuracy
1488
7.3.5.200
1489 1490 1491 1492
The routine test for accuracy is in principle the same as the type test in 7.2.6.200, but routine tests at a reduced number of currents and/or burdens are permissible provided it has been shown by type tests on a similar transformer that such a reduced number of tests are sufficient to prove compliance with 5.6.200.3
1493
7.3.5.201
1494
A t est es t may ma y b e perf pe rfor orme med d using us ing the th e follo fo llo win g indir in direc ectt t est: es t:
1495 1496 1497
–
1498 1499 1500
The resulting exciting current (I ( I e), expressed as a percentage of the rated secondary current ( I sr factor FS shall be equal to or exceed the rated value sr ) multiplied by the instrument security factor FS of the composite error of 10 %:
1501
I e ⋅100 % ≥ 10% I sr ⋅ FS
1502 1503 1504
If this result of measurement should be called into question, a controlling measurement shall be performed with the direct test (see annexes A.5, A.6), the result of which is then mandatory.
1505 1506 1507 1508 1509
NOTE The great advantage of the the indirect test is that that high currents are not necessary necessary (for instance 30 000 A at at a primary rated current 3000 A and an instrument security factor 10) and also no burdens which must be constructed for 50 A. The effect of the return primary conductors is not physically effective at the indirect test. Under service conditions the effect can only enlarge the composite error, which is desirable for the safety of the apparatus supplied by the measuring transformer.
1510 1511
7.3.5.202
1512 1513
Tests shall be made at rated primary current to prove compliance with 5.6.201.1.4 in respect of current error and phase displacement.
Tests for accuracy of measuring current transformers
Instrument security factor ( FS )
wit h the th e prim pr imar aryy win ding di ng open op en-c -circ irc uite ui ted, d, the th e seco se cond ndar aryy wind wi nding ing is ener en ergi gized zed at rate ra ted d frequency by a substantially sinusoidal voltage having an r.m.s. value equal to the secondary limiting e.m.f.
Tests for current error and phase displacement of class P protective current transformers
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1514
7.3.5.203
Test for composite error
1515 1516
For all transformers qualifying under item b) of 7.2.6.202, the routine test is the same as the type test.
1517 1518 1519 1520 1521
For other transformers, the indirect test of measuring the exciting current may be used, but a correction factor shall be applied to the results, the factor being obtained from a comparison between the results of direct and indirect tests applied to a transformer of the same type as the one under consideration (see note 2), the accuracy limit factor and the conditions of loading being the same.
1522
In such cases, certificates of test should be held available by the manufacturer.
1523 1524 1525
NOTE 1 The correction factor is equal equal to the ratio of the composite error obtained by the direct method and the exciting current expressed as a percentage of the rated secondary current multiplied by the accuracy limit factor, as determined by the indirect method specified in item a) of 7.2.6.201
1526 1527
NOTE 2 The expression “transformer of the same type” type” implies that the ampere ampere turns are the same irrespective irrespective of ratio, and that the geometrical arrangements, magnetic materials and the secondary windings are identical.
1528 1529
7.3.5.204
1530 1531
Class PR current transformers shall, in addition to the requirements of clause 7.3.5.202 and 7.3.5.203, be subjected to the routine tests prescribed below.
1532
7.3.5.204.1
1533 1534
The remanence factor (K ) r r shall be determined to prove compliance with clause 5.6.201.2.5. For test methods, refer to annex B.2.
1535
7.3.5.204.2
1536 1537
The secondary loop time constant (T (T s) shall be determined. It shall not differ from the specified value by more than ±30 %. For determination methods, refer to 7.2.6.204.3
1538
7.3.5.204.3
1539 1540 1541 1542 1543 1544 1545
The secondary winding resistance shall be measured and an appropriate correction applied if the measurement is made at a temperature which differs from 75°C or such other temperature as may have been specified. The value so adjusted is the rated value for R for R ct . NOTE For determination determination of secondary loop loop resistance (Rs (Rs = R ct + R b), R b is the rated resistive burden which, in the case of class PR current transformers, is taken as being equal to the resistive part of the burden used in accordance with 5.6.201.1.4 for the determination of current error and p hase displacement.
1546
7.3.5.205
1547
Class PX current transformers shall be tested as prescribed below.
1548
7.3.5.205.1
1549 1550 1551
A sinu si nuso soid idal al e.m. e. m.f. f. of rate ra ted d freq fr eque uenc ncyy equa eq uall to the th e rate ra ted d knee kn ee-p -poin oin t e.m. e. m.f. f. shal sh alll be appl ap plie ied d to the complete secondary winding, all other windings being open-circuited and the exciting current measured.
1552 1553 1554 1555
The e.m.f. shall then be increased b y 10 % and the exciting current shall not increase b y more than 50 %. The exciting voltage shall be measured with an instrument which has a response proportional to the average value, but calibrated in r.m.s. The exciting current shall be performed using an r.m.s measuring instrument having a minimum crest factor of at least 3.
Test for current error and phase displacement of class PR protective current transformers
Determination of remanence factor ( K r r )
Determination of secondary loop time constant (T s)
Determination of secondary winding resistance (R ct )
Tests for class PX protective current transformers
Rated knee point e.m.f. (E k k ) and maximum exciting c urrent (I e )
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Other measurement methods may not deliver the correct results because of the nonsinusoidal nature of the measured signal
1558 1559 1560 1561
The excitation characteristic shall be plotted at least up to the rated knee point e.m.f. The exciting current (I (I e ) at the rated knee-point e.m.f. and at any stated percentage, shall not exceed the rated value. The number of measurement points shall be agreed between the manufacturer and the purchaser.
1562
7.3.5.205.2
1563 1564
The resistance of the complete secondary winding shall be measured. The value obtained when corrected to 75 °C shall not exceed the specified value.
1565
7.3.5.205.3
1566 1567
The turns ratio shall be determined in accordance with Annex D. The turn’s ratio error shall not exceed the value given in c).
1568 1569
NOTE A simplified test test involving measurement measurement of the ratio error with zero connected burden burden may be substituted by agreement between the manufacturer and purchaser.
1570 1571
7.3.5.206
Additional routine tests for protective current transformers for transient performance
1572
7.3.5.206.1
Determination of the secondary winding resistance R ct
1573
This test is identical with the type test described in 7.2.6.204.1
1574 1575
7.3.5.206.2 Determination of the steady state ratio error and phase displacement
1576
This test is identical with the type test described in 7.2.6.204.2
1577
7.3.5.206.3
1578
This test is identical with the type test described in 7.2.6.204.3
1579
7.3.5.206.4
1580 1581
The routine test shall be made as an indirect test according to 7.2.6.204.5
1582
7.3.6 Verification of markings
1583
7.3.7 Enclosure tightness test at ambient ambient temperature
1584
7.3.7.1 Closed pressure pressure systems systems for gas
1585
7.3.7.2 Liquid systems
1586
7.3.8 Pressure test for the enclosure
1587
7.3.200 Inter-turn overvoltage test
1588
Tests shall be performed to demonstrate compliance with 5.3.200.
1589
The inter-turn overvoltage test shall be performed in accordance with one of the following procedures.
1590
If not otherwise agreed, the choice of the procedure is left to the manufacturer.
Secondary winding resistance ( R ct ct )
Turns ratio error ( t )
Determination of the secondary time constant Ts
Determination of the error at limiting conditions
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1591 1592 1593 1594 1595
Procedure A: with the secondary windings open-circuited (or connected to a high impedance device which reads peak voltage), a substantially sinusoidal current at a frequency between 40 Hz and 60 Hz (in accordance with IEC 60060-1) and of r.m.s. value equal to the rated primary current (or rated extended primary current (see 5.6.200.4) when applicable) shall be applied for 60 s to the primary winding.
1596 1597
The applied current shall be limited if the test voltage of 4,5 kV peak is obtained before reaching the rated current (or extended rated current).
1598 1599 1600 1601
Procedure B: with the primary winding open-circuited, the prescribed test voltage (at some suitable frequency) shall be applied for 60 s to the terminals of each secondary full winding, providing that the r.m.s. value of the secondary current does not exceed the rated secondary current (or rated extended current).
1602
The value of the test frequency shall be not greater than 400 Hz.
1603 1604 1605
At this th is freq fr eque uenc ncy, y, if the th e volt vo ltag age e val ue achi ac hiev eved ed at the th e rate ra ted d sec onda on dary ry curr cu rren entt (or (o r rate ra ted d extended current) is lower than 4,5 k V peak, the obtained voltage is to be regarded as the test voltage.
1606 1607
When the frequency exceeds twice the rated frequency, the duration of the test may be reduced from 60 s as below: duration of test ( s) = 60 ⋅
1608
twice the rated frequency test frequency
1609
with a minimum of 15 s.
1610 1611 1612 1613
NOTE The inter-turn overvoltage overvoltage test is not a test test carried out to verify the suitability of a current transformer to operate with the secondary winding open-circuited. Current transformers should not be operated with the secondary winding open-circuited because of the potentially dangerous overvoltages and overheating which can occur.
1614 1615 1616
7.4 Special tests
1617
7.4.1 Chopped impulse impulse voltage withstand test on primary primary terminals terminals
1618
7.4.2 Multiple chopped chopped impulse test on primary primary terminals terminals
1619
7.4.3 Measurement of capacitance and dielectric dissipation dissipation factor
1620
Clause 7.4.3 of IEC 61869-1 is applicable but with the addition of the following:
1621 1622 1623 1624 1625 1626
The test voltage shall be applied between the short-circuited primary winding terminals and earth. Generally the short-circuited secondary winding(s), any screen, and the insulated metal casing shall be connected to the measuring bridge. If the current transformer has a special device (terminal) suitable for this measurement, the other low-voltage terminals shall be short-circuited and connected together with the metal casing to the earth or the screen of the measuring bridge.
1627
NOTE In some cases, cases, it is necessary necessary to connect the earth to other points of the bridge.
1628 1629
The test shall be performed with the current transformer at ambient temperature, the value of which shall be recorded.
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1630
7.4.4 Transmitted overvoltage test
1631
7.4.5 Mechanical tests
1632
7.4.6 Internal arc fault test
1633
Clause 7.4.6 of IEC 61869-1 is applicable with the addition of the following note:
1634 1635 1636
NOTE: For top core oil-immersed current transformers, the area in which failure in service incept in many cases is located in the upper part of the main insulation. For hair pin oil-immersed current transformers this area is generally located in the bottom part of the m ain insulation.
1637
7.4.7 Enclosure tightness tests tests at low and high temperatures
1638
7.4.8 Gas Dew point test
1639
7.4.9 Corrosion test
1640
7.4.9.1 Test procedure
1641
7.4.9.2 Criteria to pass the test test
1642
7.4.10 Fire hazard test
1643
7.5 Sample tests
1644
8 Rules for transport, storage, erection, operation and maintenance
1645
9 Safety
1646
10 Influence of products on the natural environment
1647 1648 1649 1650
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Annex A Protective current transformers classes P, PR, PX (Normative)
1651 1652 1653
A.1
1654 1655 1656 1657
If consideration is given to a current transformer which is assumed to contain only linear electric and magnetic components in itself and in its burden, then, under the further assumption of sinusoidal primary current, all the currents, voltages and fluxes will be sinusoidal, and the performance can be illustrated by a vector diagram such as figure 2A.1. l m l a l e
1658
Vector diagram
1659
E s
1660
l s
l” p
∆φ
1661 l e
1662
Φ
O 1663
Figure 2A.1
1664 1665 1666 1667 1668 1669 1670
In figure 2A.1, I s represents the secondary current. It flows through the impedance of the secondary winding and the burden which determines the magnitude and direction of the necessary induced voltage E s and of the flux Φ which is perpendicular to the voltage vector. This flux is maintained by the exciting current I e, having a magnetizing component I m parallel to the flux Φ , and a loss (or active) component I a parallel to the voltage. The vector sum of the secondary current I s and the exciting current I e is the vector I ″ ″ p representing the primary current divided by the turns ratio (number of secondary turns to number of primary turns).
1671 1672 1673 1674
Thus, for a current transformer with turns ratio equal to the rated transformation ratio, the difference in the lengths of the vectors I s and an d I ″ ″ p , related to the length of I ″ ″ p , is the current error according to the definition of 3.4.3, and the angular difference ∆φ is the phase displacement according to 3.4.4.
1675
A.2
1676 1677 1678 1679 1680 1681 1682 1683 1684
When the turns ratio is different from (usually less than) the rated transformation ratio, the current transformer is said to have turns correction. Thus, in evaluating the performance, it is ″ p , the primary current divided by the turns ratio, and I ′ ′ p , necessary to distinguish between I ″ the primary current divided by the rated transformation ratio. Absence of turns correction ″ p . If turns correction is present, I ′ ′ p is different from I ″ ″ p , and since I ″ ″ p is used in means I ′ ′ p = I ″ the vector diagram and I ′ ′ p is used for the determination of the current error, it will be seen that turns correction has an influence on the current error (and may be used deliberately for ″ p have the same direction, so turns correction that purpose). However, the vectors I ′ ′ p and an d I ″ has no influence on phase displacement.
1685 1686
It will also be apparent that the influence of turns correction on composite error is less than its influence on current error.
1687
A.3
1688 1689 1690
In figure 2A.2, the upper part of figure 2A.1 is re-drawn to a larger scale and under the further assumption that the phase displacement is so small that for practical purposes the two ″ p can be considered to be parallel. Assuming again that there is no turns vectors I s and an d I ″
Turns correction
The error triangle
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correction, it will be seen by projecting I e to I p that with a good approximation the in-phase ″ p and component ( ∆I ) of I e can be used instead of the arithmetic difference between I ″ an d I s to obtain the current error and, similarly, the quadrature component (∆ I q ) of I e can be used to express the phase displacement.
1695
l m
1696
l e
l a 1697
∆l
∆l q
1698
l s
l” p
1699 1700
Figure 2A.2
1701 1702
″ p is It will further be seen that under the given assumptions the exciting current I e divided by I ″ equal to the composite error according to 3.4.202.
1703 1704 1705
Thus, for a current transformer without turns correction and under conditions where a vector representation is justifiable, the current error, phase displacement and composite error form a right-angled triangle.
1706 1707 1708 1709 1710
In this triangle, the hypotenuse representing the composite error is dependent on the magnitude of the total burden impedance consisting of burden and secondary winding, while the division between current error and phase displacement depends on the power factors of the total burden impedance and of the exciting current. Zero phase displacement will result when these two power factors are equal, i.e. when I s and an d I e are in phase.
1711
A.4
1712 1713 1714 1715
The most important application, however, of the concept of composite error is under conditions where a vector representation cannot be justified because non-linear conditions introduce higher harmonics in the exciting current and in the secondary current (see figure 2A.3).
Composite error
1716 1717 1718 1719 1720 1721 1722
Figure 2A.3
1723 1724
It is for this reason that the composite error is defined as in 3.4.202 and not in the far simpler way as the vector sum of current error and phase displacement as shown in figure 2A.2.
1725 1726
Thus, in the general case, the composite error also represents the deviations from the ideal current transformer that are caused by the presence in the secondary winding of higher
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1727 1728
harmonics which do not exist in the primary. (The primary current is always considered sinusoidal for the purposes of this standard.)
1729
A.5
1730 1731 1732 1733 1734 1735 1736 1737
Figure 2A.4 shows a current transformer having a turns ratio of 1/1. It is connected to a source of primary (sinusoidal) current, a secondary burden Z B with linear characteristics and to an ammeter in such a manner that both the primary and secondary currents pass through the ammeter but in opposite directions. In this manner, the resultant current through the ammeter will be equal to the exciting current under the prevailing conditions of sinusoidal primary current, and the r.m.s. value of that current related to the r.m.s. value of the primary current is the composite error according to 3.4.202, the relation being expressed as a percentage.
Direct test for composite error
P
S
P
S
1738 1739 1740
ZB
∼ A
1741 1742
Figure 2A.4
1743 1744
Figure 2A.4 therefore represents the basic circuit for the direct measurement of composite error.
1745 1746 1747 1748 1749 1750
Figure 2A.5 represents the basic circuit for the direct measurement of composite error for current transformers having rated transformation ratios differing from unity. It shows two current transformers of the same rated transformation ratio. The current transformer marked N is assumed to have negligible composite error under the prevailing conditions (minimum burden), while the current transformer under test and marked X is connected to its rated burden. N
P
1751 S
P
P
S
S
X
P S
1752 1753
ZB A1
A2
1754 1755
Figure 2A.5
1756 1757 1758 1759 1760
They are both fed from the same source of primary sinusoidal current, and an ammeter is connected to measure the difference between the two secondary currents. Under these conditions, the r.m.s. value of the current in the ammeter A 2 related to the r.m.s. value of the current in ammeter A 1 is the composite error of transformer X, the relation being expressed as a percentage.
1761 1762 1763 1764
With this method, it is necessary that the composite error of transformer N is truly negligible under the conditions of use. It is not sufficient that transformer N has a known composite error since, because of the highly complicated nature of composite error (distorted waveform), any composite error of the reference transformer N cannot be used to correct the test results.
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A.6
1766 1767
Alter Alt erna natitive ve mean me anss may ma y be used us ed for fo r the th e meas me asure ure ment me nt of comp co mpos ositite e erro er rorr and an d one on e meth me thod od is shown in figure 2A.6.
1768
Alternative method for the direct measurement of composite error
N
P S
1769
P
P
S
S
X
P S
Z’ B
1770
S A1
1771
A2
ZB
N’ S
1772
P
P
1773
Figure 2A.6
1774 1775 1776 1777 1778 1779
Whilst the method shown in figure 2A.5 requires a “special” reference transformer N of the same rated transformation ratio as the transformer X and having negligible composite error at the accuracy limit primary current, the method shown in figure 2A.6, enables standard reference current transformers N and N′ to be used at or about their rated primary currents. It is still essential, however, for these reference transformers to have negligible composite errors but the requirement is easier to satisfy.
1780 1781 1782 1783 1784 1785 1786 1787 1788
In figure 2A.6 X is the transformer under test, N is a standard reference transformer with a rated primary current of the same order of magnitude as the rated accuracy limit primary current of transformer X (the current at which the test is to be made), and N ′ is a standard reference transformer having a rated primary current of the order of magnitude of the secondary current corresponding to the rated accuracy limit primary current of transformer X. It should be noted that the transformer N ′ constitutes a part of the burden Z B of transformer X and must therefore be taken into account in determining the value of the burden Z ′ ′ B . A1 and an d A2 are two ammeters and care must be taken that A2 measures the difference between the secondary currents of transformers N and N ′ .
1789 1790
If the rated transformation ratio of transformer N is k r r , of transformer X is k rx rx and of transformer N′ is k ′ ′ r , the ratio k r r must equal the product of k of k ′ ′ r and an d k rx rx :
1791
i.e. k r r = k ′ ′ r × k rx rx
1792 1793 1794
Under these conditions, the r.m.s. value of the current in ammeter A 2, related to the current in ammeter A2 , is the composite error of transformer X, the relation being expressed as a percentage.
1795 1796 1797 1798
NOTE When using the methods methods shown in figures 2A.5 and 2A.6, care should be taken to use use a low impedance impedance instrument for A2 since the voltage across this ammeter (divided by the ratio of transformer N ′ in the case of figure 2A.6) constitutes part of the burden voltage of transformer X and tends to reduce the burden on this transformer. Similarly, this ammeter voltage increases the burden o n transformer N.
1799
A.7
1800 1801
The numeric value of the composite error will never be less than the vector sum of the current error and the phase displacement (the latter being expressed in centiradians).
1802 1803
Consequently, the composite error always indicates the highest possible value of current error or phase displacement.
1804 1805
The current error is of particular interest in the operation of overcurrent relays, and the phase displacement in the operation of phase sensitive relays (e.g. directional relays).
Use of composite error
61869-2 ed. 1 © IEC
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1806 1807
In the case of differential relays, it is the combination of the composite errors of the current transformers involved which must be considered.
1808 1809 1810
An addit ad ditio iona nall adva ad vant ntag age e of a lim itatio ita tio n of comp co mpos osite ite erro er rorr is the th e res ulti ul ting ng limit lim itat ation ion of the th e harmonic content of the secondary current which is necessary for the correct operation of certain types of relays.
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Annex B Protective current transformers classes for transient performance (Normative)
1811 1812 1813 1814
B.1
Basic theoretical equations for transient dimensioning
1815
B.1.1
1816
The general expression for the instantaneous value of a short-circuit current may be written: ⎡ −t / T p cos(γ − ϕ ) − cos(ω t + γ − ϕ )⎤ i (t ) = 2 I psc e (1) (1 )
Short-circuit
⎢⎣
1817
where Initial ac short-circuit current at accuracy limit of current transformer I psc = K ssc I pn
I psc
T p
=
L p
Primary time constant
R p
γ ϕ =
Switching or fault inception angle arctan
X p R p
1818
⎥⎦
= arctan (ω T p )
Phase angle of system short-circuit impedance
when the equivalent voltage source in the short-circuit with R p and an d X p is
= −U max cos(ω t + γ ) (2) (2 ) For simplification purpose the fault inception angle and system impedance angle can be summed up to one single angle which makes the problem easier to understand from the mathematical point of view. θ = γ − ϕ (3) (3 ) ⎡ −t / T p cos(θ ) − cos(ω t + θ )⎤ i (t ) = 2 I psc e (4) (4 ) u (t )
1819 1820 1821
⎢⎣
⎥⎦
1822 1823 1824 1825 1826
The angles θ and an d γ describe the same problem of variable fault inception angle and therefore can be used alternating where suitable but according to their definition. Fig. 2B.1 shows two typical primary short-circuit currents. The first one occurs with a fault inception angle of γ = 90° which leads to the highest peak current and the highest magnetic peak flux (Fig. 2B.1) whereas the second one occurs with γ = 140° which leads to a lower
1827 1828
asymmetry. Cases like the latter one is important for short t al when the current and magnetic flux are higher than in the case for highest peak current.
1829 1830 1831
Fig. 2B.1: Short-circuit current with highest peak ( = 90°) and lower asymmetry ( = 140°)
1832
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1833 1834
Fig. 2B.2: Magnetic-flux for the two cases in Fig. 2B.1
1835 1836
A poss po ssibl ibl y redu re duce ced d rang ra nge e of fault fa ult ince in cept ptio ion n angl an gle e γ m ≥ 90° can be used to define a reduced
1837 1838 1839
asymmetry which may lead to a reduced factor K td in some special cases. Such calculation is shown in the application guide to this standard.
1840
B.1.2
1841 1842 1843
The Th e transient dimensioning factor K td is the final parameter for the core dimensioning and is given on the rating plate. It can be calculated from different functions of the transient factor K as given in the equations below and showed in Fig. 2B.3. tf
1844 1845
The transient factor K tf given in this section is derived from the differential equation of the
1846 1847 1848 1849 1850
equivalent circuit with a constant inductivity of the current transformer core, with an ohmic burden and without consideration of remanence . The exact solution of the differential equation is given in the application guide whereas the formulas given in this annex are given either as curve diagrams or as simplified formulas. K and the magnetic flux depend likewise on time and in the end of the accuracy limit time tf
1851 1852 1853 1854 1855
required by the protection system. By calculating with the linear inductivity the solution is only valid up to the first saturation of the current transformer.
Transient factor
t al
1856 1857 1858
Fig. 2B.3: Relevant time ranges for calculation of transient factor
1859 1860 1861 1862
In some cases the protection system may require a t al which is not constant and depends on different parameters of the short-circuit current. Therefore the transient dimensioning factor K can also be tested and given by the manufacturer of the protection system. td
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A gene ge nera rall over ov ervie view w with wi th a flow fl ow char ch artt and an d with wi th exam ex ampl ples es is give gi ven n in the th e appl ap plic icat atio ion n guid gu ide e to this standard. The typical curve of the transient factor (Fig. 2B.3) consists of three ranges defined by three functions of K tf : Range 1:
0 ≤ t al < t tf ,max :
The first range begins at zero time and ends when the curve of K tf ,ψ touches its ψ max envelope curve of peaks K tfp at the time t tf ,max
=
π + ϕ
(5) (5 )
ω
1875
Within this time range K tf ,ψ considers the worst case switching angle θ (t al ) which leads ψ max
1876
to the highest flux at the accuracy limit time t al . Figures 2B.4 … 12 show the curves for
1877
different t al and secondary time constants T s versus the primary time constant T p for given configurations of secondary time constant and frequency.
1878 1879 1880
Fig. 2B.4 Determination of K tf for fo r = 3° (T s=61 =6 1 ms) and f=50 Hz
61869-2 ed. 1 © IEC
Fig. 2B.5 Determination of K tf for fo r = 1.5° (T s=122 ms) and f=50 Hz
Fig. 2B.6 Determination of K tf for fo r = 0.1° (T s = 1.8 s) and f=50 Hz
Fig. 2B.7 Determination of K tf for fo r = 3° (T s =50 =5 0 ms) and f=60 Hz
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Fig. 2B.8 Determination of K tf for fo r = 1.5° (T s=100 ms) and f=60 Hz
Fig. 2B.9 Determination of K tf for fo r = 0.1° (T s = 1.5 s) and f=60 Hz
Fig. 2B.10 Determination of K tf for fo r = 3° (T s =182 ms) and f=16.7 Hz
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Fig. 2B.11 Determination of K tf for fo r = 1.5° (T s=365 ms) and f=16.7 Hz Ktf,
ψmax
= 0.1° (Ts = 5.5 s) , f = 16.7 Hz
6
tal 42 ms 39 ms 36 ms 33 ms
5
4
30 ms 27 ms
3
24 ms 21 ms
2
18 ms 15 ms 12 ms 9 ms 6 ms
1
Fig. 2B.12 Determination of K tf for fo r = 0.1° (T s= 5.5 s) and f=16.7 Hz
0
0 10 20 30 40 50 60 70 80 90 100 11 1 10 12 120 13 1 30 14 140 15 1 50 16 1 60 17 170 18 1 80 19 190 20 2 00
Tp [ms]
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≤ t al < t tfp ,max
1881
Range 2:
1882
The second time range continues with the envelope curve K tfp for fo r γ = 90° which leads to the
1883
highest peak flux, therefore θ = 90° − ϕ . K tfp
1884 1885 1886
t tf , max
ω T s T p
=
T p
− T s
cos(θ )⎛ ⎜e
−t / T p
⎝
t ,max tfp
1890 1891 1892 1893
−t / T s ⎞
⎟ + sin(θ )e ⎠
−t / T s
+1
(6) (6 )
up to the curve maximum at the time T p
1887 1888 1889
−e
=
Range 3:
T p T s T p
− T s
t tfp ,max
ln
T s
cos(θ ) +
− T p sin(θ ) 2 ω T
T s
(7) (7 )
s
cos(θ )
≤ t al
The third time range continues with the constant maximum K tfp , max given in eqn. (8) for higher accuracy limit times. T p ⎤ T s −T p
K tfp,max
⎡ T p ⎢ T p + T ⎛ ⎞ ⎢ T s s = ⎜⎜ ω T p cos(θ ) + sin(θ ) ⎟⎟ ⋅ T s ⎝ ⎠ ⎢⎢ ⎢⎣
1898
B.1.3
Duty cycles
1899 1900 1901 1902 1903 1904 1905
The transient dimensioning for autoreclosure duty cycles has to be done separately for each cycle according to the equations given above.
cos(θ ) +
− T p sin(θ ) ⎥ 2 ω T
T s
s
cos(θ )
⎥ ⎥ ⎥ ⎥⎦
+1
(8) (8 )
1894 1895 1896 1897
1906 1907 1908 1909
Gapped cores For gapped cores the magnetic flux and therefore the transient factor declines exponentially with secondary time constant T s (which changes with the actual operational burden) during the open time. − t / T " (9) (9 ) K td ,(C −O −C ) = K td (t ' ) ⋅ e fr s + K td (t al ) Nongapped Cores For nongapped cores remanence is possible and there is no significant flux declination in the worst case. " K td ,(C −O −C ) = K td (t ' ) + K td (t al ) (10)
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1910 1911 1912 1913
B.2
Determination of the magnetizing characteristic of protective current transformers for transient performance
1914 1915 1916 1917
B.2.1
General
1918 1919 1920 1921 1922 1923 1924
Measuring the core magnetization characteristic implies establishing the relationship between the core secondary linking flux and magnetizing current. If an arbitrary voltage u(t) is applied to the secondary terminals (see figure 2B.13), the core flux ψ (t) linked through the secondary winding at time t is related to this voltage through the equation: t
ψ (t ) =
1925
∫ (u(t ) − R
ct
⋅ im (t ))dt
(11)
0
1926 1927 1928
The methods described in the following clauses take advantage of this relationship. im
Rct
u(t)
1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945
Fig. 2B.13: Basic circuit
For TPX current transformers it is necessary to demagnetize the core before each test, because of the high remanence factor. For TPY current transformers the remanent flux is often so low that it can be neglected. Demagnetization requires additional m eans by which the core can be subjected to slowly decreasing hysteresis loops starting from saturation. A direct current source will normally be provided when the d.c. test method has to be used. The a.c. method or d.c. method may be applied. While the a.c. measuring method is easier to apply, it may lead to high voltages, and to too high remanence flux values due to additional eddy currents.
1946
B.2.2
A.C. method
1947 1948 1949 1950
A subst su bstan antitial ally ly sinu si nuso soid idal al a.c. a. c. volt vo ltag age e u(t) u( t) is appl ap plie ied d to the th e seco se cond ndar aryy term te rmina ina ls. ls . The Th e test te st may ma y be performed at reduced frequency f’ to avoid unacceptable voltage stressing of the winding and secondary terminals.
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61869-2 ed. 1 © IEC 1951 1952 1953 1954 1955 1956 1957 1958
The knee point shall be determined according to 7.3.5.205.1. The magnetising inductance L m shall be determined by measuring the secondary inductance between 20% and 90% of knee point e.m.f. E k as follows (i 20 and i90 are peak values of the magnetizing current values at the appropriate percentages of E k):
1959 1960 1961 1962 1963 1964 1965 1966 1967
Lm
=
0.7 E k (i90 − i20 ) * 2π f '
(12)
In determining the remanence factor K r by the a.c. test method, it is necessary to integrate the exciting voltage according to equation (11). The integrated voltage with the corresponding current i m will display a hysteresis loop, showing the saturation flux ψ s. The flux value at zero crossing of current is deemed to represent the remanent flux ψ r . The remanence factor K r is then calculated according to 3.4.211 as K r =
1968 1969 1970 1971 1972 1973
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ψ r ψ s
(13)
At lower frequencies, effects of undue eddy current losses in the core and capacitive curren ts between the winding layers will be less likely to cause false readings.
1974 1975
Fig. 2B.14: Determination of remanence factor by hysteresis loop
1976 1977 1978 1979
B.2.3
1980 1981 1982 1983
The d.c. saturation method uses a d.c. voltage u(t) of such duration that saturation flux is reached. The flux measurement is derived according to equation (11), where u(t) is the voltage across the terminals.
1984
D.C. method
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Fig. 2B.15: Circuit for d.c. method
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
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The applied voltage source shall be suitable to reach saturation. The discharge resistor R d shall be connected, as otherwise the core inductance may cause very high overvoltages when switch S is opened and the inductive current interrupted. Some time after the switch S has been closed, the exciting current im will be deemed to have reached its maximum value (I m ) at which the core flux would remain constant. The rising values of the magnetizing current and of the flux shall be recorded up to the time at which the values become constant, then the switch S will be opened. Typical test records of the flux ψ(t) and of the magnetizing current i m(t) are shown in figure 2B.16.
im ψ
From oscillograph
From X-Y recorder ψ
im ψ
2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027
im
t
2002 2003
Fig. 2B.16: Typical records The magnetizing inductance (Lm ) may be deduced according the following equation: Lm
=
0.7ψ s i90 − i20
(14)
where i90 and i20 are magnetizing current values at the appropriate percentages of ψ s . At the th e open op enin ing g of swit sw itch ch S, a decr de crea easi sing ng magn ma gnet etiza iza tion ti on curr cu rren entt flows fl ows thro th roug ugh h the th e seco se cond ndar aryy winding and the discharging resistor Rd . The corresponding flux value decreases, but may not fall to zero at zero current. When a suitable exciting current i m has been chosen to achieve the saturation flux ψ s, the remaining flux value at the zero current shall be deemed to be the remanent flux ψ r . For TPY current transformers the remanence factor K r is determined ψ (15) K r = r ψ s For a TPY current transformer whose core has not been demagnetized before, the remanence factor (K r ) may be determined by an additional test in which the secondary terminals have been interchanged. In this case, the remanence factor Kr may be calculated as above, but assuming for ψ the halved value of the remanent flux measured in the second test.
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2028 2029 2030 2031 2032 2033 2034 2035 2036 2037
2038 2039 2040 2041 2042 2043 2044 2045 2046
B.2.4
Capacitor discharge method
The capacitor discharge method uses the charge of a capacitor for energizing the current transformer core from the secondary. The capacitor is charged with a voltage sufficiently high to produce saturation flux.
Fig. 2B.17: Circuit for capacitor discharge method
The derivation of the magnetizing inductance (Lm ) and of the remanence factor Kr is identical with the method given B2.3 (d.c. method).
K r =
ψ r ψs
2047 2048 2049 2050
Fig. 2B.18: Typical records for capacitor discharge method
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2051 2052 2053 2054 2055
B.3
2056
B.3.1
2057 2058 2059 2060 2061
The instantaneous error current can be measured in different ways. In all cases, the errors of the measuring system shall not exceed 10 % of the error limit corresponding to the class of the tested CT during the whole of the duty cycle.
2062
B.3.2
2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089
Class TPX current transformers should be demagnetized before the direct test because of the high remanence factor. It may be necessary to demagnetize class TPY current transformers if the remanence factor Kr is not negligible.
2090 2091 2092 2093 2094 2095 2096 2097 2098 2099 2100 2101
Determination of the error at limiting conditions of protective current transformers for transient performance
General
Direct test
Two direct tests are performed at rated frequency and with rated secondary burden: a) The rated primary short-circuit current at rated frequency is applied without any offset. The a.c. component of the total error is measured and shall be in accordance with the theoretical value 1/ ωT s. b) The rated primary short-circuit current at rated frequency is applied with the required offset. For specified values of primary time constant up to 80 ms, the test is performed in the specified accuracy limiting condition (specified duty cycle). The primary time constant shall not deviate by more than 10 % from the specified value. For specified values of primary time constant above 80 ms, the tests can be performed in equivalent accuracy limiting conditions (by modifiing duty cycle and/or burden), subjected to agreement between user and manufacturer. During the energization period, the first peak of the primary current shall be not less than the value corresponding to the specified conditions. The secondary linked flux shall be recorded. The error in flux measurement shall not exceed 5 %.
Ψ (t ) =
Rct + Rb Rb
t
⋅ ∫ Rb ⋅ i s dt 0
For class TPX and TPY current transformers, the instantaneous error current i ε ε is measured ˆ shall be determined according to 3.4.602. Its value shall as iε = i s ⋅ k r − i p . The error value ε not exceed the limit given in table 1. For class TPZ current transformer, the a.c. component of the error current is measured as one ˆac shall be determined half of the peak-to-peak value (see figure 2B.19). The error value ε according to 3.4.603. Its value shall not exceed the limit given in table 206. Note: It is possible that the class definition does not contain a duty cycle.
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In this case, for test purposes, a duty cycle leading to the given K td value shall be agreed between user and manufacturer.
iε
a
=
ˆi εdc
b
For TPY : ˆi ε
2107 2108 2109
=
c
=
2 ˆi εac
For TPZ : ˆi e
=
ˆi εac
c
=
ˆi εac
+
ˆi εdc
b =
2
Fig. 2B.19: Measurement of error currents
2110 2111 2112 2113
B.3.3
Indirect test
2114 2115 2116 2117 2118 2119 2120
B.3.3.1
For TPX and TPY current transformers, the peak value of the exciting secondary current (Î alal) shall not exceed the value given below: I al ≤
)
2121 2122 2123 2124 2125
2135 2136
2 ⋅ I sn ⋅ K ssc ⋅
ˆ [%] ε 100 %
For TPZ current transformers, the a.c. peak value of the exciting secondary current (Î alal) shall not exceed the value given below: I al ≤
)
2126 2127 2128 2129 2130 2131 2132 2133 2134
Limits of exciting secondary current (Î alal )
⎛ K td − 1
2 ⋅ I sn ⋅ K ssc ⋅ ⎜⎜
⎝
ω T S
+
ˆac [%] ⎞ ε
⎟
100 % ⎠⎟
NOTE - For TPZ current transformers the accuracy is specified only for the a.c. component while, in the determination of the permissible value of Ial during indirect tests, it is necessary to take into account also the d.c. component of the exciting current. In the above equation, the d.c. component is represented by (Ktd – – 1) and the permissible error in the a.c. component by 0.1 .
B.3.3.2
A.C. method
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The a.c. method shall be applied according to annex B.2.2 The voltage shall be increased up to U al . The appropriate excitation current Î alal shall not exceed the limit given in annex B.3.3.1
2141 2142
The magnetic flux at accuracy limiting condition is given by
2 ⋅ U al
Ψal =
2143
ω
2144 2145 2146
B.3.3.3
2147 2148 2149 2150 2151
The d.c. method shall be applied according to annex B.2.3.
2152 2153 2154
D.C. method and capacitor discharge method
The magnetic flux
Ψ (t ) and the exciting current im (t) shall be recorded.
At a magn ma gnet etic ic flux fl ux at acc urac ur acyy lim l imititing ing cond co ndititio ion n
2156 2157 2158 2159 2160 2161 2162 2163 2164 2165 2166 2167 2168 2169 2170 2171 2172 2173 2174
2 ⋅ K td ⋅ K ssc ⋅ I sn ⋅ ( Rb + Rct )
Ψal =
2155
ω
the appropriate value of the exciting current Î alal shall be determined. This value shall not exceed the limit given in B.3.3.1.
B.3.3.4
Determination of Fc
Acc ord ing in g to the th e def initi ini tion on of Fc , the flux values at error limiting condition in direct and indirect test have to be determined for the same value of magnetizing current. In the first step, the magnetic flux ψ di r shall be determined in the direct test as the peak value of the relevant flux within the duty cycle. The appropriate error current Iε d shall also be measured. The magnetic flux ψ ind is determined in a indirect test as the flux corresponding to a magnetizing current equal to I εd F c may now be calculated as
F c
=
Ψind Ψdir
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2175 2176 2177 2178 2179 2180 2181 2182 2183 2184 2185 2186 2187 2188 2189 2190 2191 2192 2193 2194
B.4
Alternative measurement of the steady state ratio error
For low leakage reactance current transformers, the following indirect test will lead to results which are very close to the results obtained in the direct test. Nevertheless, routine tests for steady state ratio error determination shall always be performed as a direct test, as this method gives the highest evidence of the “low leakage reactance property” of a core, including magnetic “homogenousness” of the iron core. On the other hand, the alternative method is suitable for on-site measurements, and for monitoring purposes. In this case, it shall be noted that this method never considers the influence of current flow in the neighbourhood of the current transformer.
For the determination of the ratio error the following simplified equivalent circuit diagram is used:
Ip*N p /N s= I s+ I e
E0
2195 2196
Fig. 2B.20 Simplified equivalent circuit of the current transformer
2197 2198 2199 2200 2201 2202 2203 2204
A subs su bsta tant ntia iallllyy sin s inuso uso idal id al volt vo ltag age e is appl ap plie ied d to the th e seco se conda nda ry term te rmin inals als S1 – S2 of the CT. The test voltage across the terminals Us Test and the current I s Test are measured. The injected voltage should generate an e.m.f. across the main inductivity with the same amplitude than during operation with a certain current and the actual burden. The e.m.f. can be calculated from the test results by subtracting the voltage drop across the winding resistance RCT from the test voltage U s Test across the S1 – S2 terminals. This subtraction has to be done in the complex plane. The measured current I s Test is equal the error current I e.
2205
The ratio error can be expressed as:
2206 I s − I p
2207
Ratio error = I p
2208 2209
I sn I pn
I sn
=
I s I pn I p I sn
−1
[1] [1 ]
I pn
With: I p N p N s
= I e + I s ⇒ I p =
( I e + I s ) N s N p
[2] [2 ]
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the ratio error can be expressed as:
2211
Ratio error =
I s N p I pn
( I e + I s ) N s I sn
−1
38/404/CDV
[3] [3 ]
2212 2213 2214 2215
To determine the ratio error for a certain secondary current I s the following test procedure is proposed:
2216 2217
•
2218
Calculation of the secondary voltage across S 1 – S 2: U s
= I s ( Rb + jX b )
2219
•
Measurement of the secondary winding resistance R (value at the actual temperature)
2220
•
Calculation of the corresponding e.m.f. ******** R, not Rct E 0 = I s Rct + U s
2221 2222
•
Injection of
2223
U s Test = E 0 + I s Test Rct
2224
into the secondary terminals S 1 – S2
( with I s Test = I s )
2225
•
Measurement of the voltage U p Test across P 1 - P2
2226
•
Calculation of the turns ratio N p
2227 2228 2229 2230
N s
•
=
U p Test E 0
Calculation of the corresponding Ip I P =
( I s + I s Test ) N s N p
2231 2232 2233
The ratio error can be calculated as:
2234
Ratio error =
2235 2236 2237 2238
I s N p I pn
( I
N s I sn s Test + I s )
−1
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Annex C Technique used in temperature rise test of oil-immersed transformers transformers to determine the thermal constant by an experimental estimation (informative)
2239 2240 2241 2242 2243 2244
List of symbols:
2245
θ θ( t )
Temperature in °C
2247 2248
θa
External cooling medium temperature (ambient air or water) assumed to be constant
2249
∆θ
2250
2254
θu , ∆θ u ε ( t ) T o h θ1, θ2 , θ3
Oil temperature rise above θ a Ultimate values in steady state
2255 2256
In principle, the test should continue until the steady-state temperature rise (of the oil) is ascertained.
2246
2251 2252 2253
Oil temperature, varying with time (this may be top oil, or average oil)
Remaining deviation from steady-state value θ u Time constant for exponential variation of bulk oil temperature rise Time interval between readings Three successive temperature readings with time interval h between them.
2257
θu = θa + ∆θ u
(1 )
2258
θ ( t ) = θ a + ∆θ u (1 - e - t/To )
(2)
2259
The remaining deviation from steady state is then:
2260 2261
ε ( t ) = θ u - θ( t ) = ∆ θu x e- t/To It is considered that:
(3 )
2262
-
the ambient temperature is kept as constant as possible
2263 2264
-
the oil temperature θ(t) will approach an ultimate value θu along an exponential function with a time constant of To.
2265
-
The equation 2 is a good approximation of the temperature curve (see fig.2B.1)
2266 2267 2268
Given three successive readings ∆θ 1, ∆θ 2 and an d ∆θ 3 , if the exponential relation of equation (2), is a good approximation of the temperature curve, then the increments will have the following relation:
2269
∆θ 2 − ∆θ1 h/T =e o ∆θ 3 − ∆θ 2
2270
T o = ln
2271
2272
h ∆θ 2 − ∆θ1
(4) (4 )
∆θ 3 − ∆θ 2
The readings also permit a prediction of the final temperature rise:
∆θ u =
(∆θ 2 )2 − ∆θ1∆θ 3 2 ∆θ 2 − ∆θ1 − ∆θ 3
(5) (5 )
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38/404/CDV
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Successive estimates are to be made and they should converge. In order to avoid large random numerical errors the time interval h should be approximately T o and an d ∆ θ 3/ ∆ θ u should be not less than 0,95.
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A more mo re accu ac cura rate te valu va lue e of stea st eadydy- rate ra te temp te mper erat atur ure e rise ri se is obta ob tain ined ed by a leas le astt squa sq uare re meth me thod od of extrapolation of all measured points above approximately 60 % of ∆θ u ( ∆ θ u estimated by the three point method).
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A dif fere fe rent nt num erica er ica l f ormu or mulat lat ion io n is:
2280
∆θ u = ∆θ 2 +
(∆θ 2 − ∆θ1 ) − (∆θ 3 − ∆θ 2 ) ∆θ − ∆θ1 ln 2 ∆θ 3 − ∆θ 2
(6) (6 )
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Figure 2C.1 - Graphical extrapolation to ultimate temperature rise
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Annex D Determination of the turns ratio error (informative)
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38/404/CDV
The actual transformation ratio is affected by errors from three sources:
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a) the difference between the turns ratio and the rated transformation ratio
2289
b) the core excitation current (I e )
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c) the currents which flow in the stray capacitances associated with the windings.
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In most cases, it is reasonable to assume that for a given secondary winding induced e.m.f. (E s ), the error currents due to stray capacitances and core magnetization will maintain a constant value irrespective of the value of the primary energizing current. E s can theoretically be maintained at a constant value for a range of energizing currents, provided that the secondary loop impedance can be appropriately adjusted. For current transformers designed to be of the low leakage reactance type, the secondary leakage reactance can be ignored and only the secondary winding resistance has to be considered. Thus, for any two currents l's and I"s the basic equation defining the test requirement is given by I 'S ( R
+ R'b ) = E S = I ' 'S ( R + R' 'b )
where R is the actual resistance of the secondary winding. Ass uming um ing that th at the th e meas me asur ured ed ratio ra tio erro er rors rs are ar e ε ’c and an d ε ’’ c , the turns ratio error is denoted as ε t , and the combined magnetization and stray currents are given by Ix. The respective error currents will be given by: K I ' K I ' ' (ε 'C −ε t ) ⋅ n s = I X = (ε ' 'C −ε t ) ⋅ n s
100
whence:
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-
ε t =
ε 'C ⋅ I 'S −ε ' 'C ⋅ I ' 'S I 'S − I ' ' S
If I’S = 2I’’ S, the turns ratio error is given by 2 ε ’ c – ε’’ c . A test te st at rate ra ted d curr cu rren entt wit h minim mi nim um seco se cond ndar aryy conn co nnec ecte ted d bur den, de n, foll fo llowe owed d by a test te st at half ha lf rated current and suitable increase in secondary loop resistance, will usually give satisfactory results.
