Resumen cei 61869.pdf

38/404/CDV COMMITTEE DRAFT FOR VOTE (CDV) PROJET DE COMITÉ POUR VOTE (CDV) IEC 61869-2 Ed. 1.0

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Submitted for parallel voting in CENELEC Soumis au vote parallèle au CENELEC

Secretariat / Secrétariat

IEC/TC or SC: 38 CEI/CE ou SC: Date of circulation Date de diffusion

Italy Closing date for voting (V oting mandatory for P-members) Date de clôture du vote (Vote obligatoire pour les membres (P))

2010-10-22

2011-03-25

Also of interest to the following committees Intéresse également les comités suivants

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TC13, TC85, TC95, TC99

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

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Titre :

CEI 61869 Ed. 1: TRANSFORMATEURS DE MESURE - Partie 2: Transformateurs de courant

IEC 61869 Ed. 1: TRANSFORMERS Part Transformers

Note d'introduction

Introductory note

AT TEN TION TIO N VOTE VOTE PARALL ÈLE 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.

Title

:

INSTRUMENT 2: Current

AT TEN TION TIO N IEC – CENELEC PARALLEL VOTING 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.

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® Registered trademark of the International Electrotechnical Commission

FORM CDV (IEC) 2009-01-09

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IEC 61869-2

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INSTRUMENT TRANSFORMERS Part 2: Current 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 ( ε ..................................................... ................................... .................................. ................. - 16 ε ) ...................................

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3.4.4 Phase displacement ( ∆φ ) ..................................................................... - 16 3.4.5 Acc uracy class ..................................................................................... - 16 3.4.6 Burden ................................................................................................. - 16 3.4.7 Rated burden........................................................................................ - 16 3.4.8 Rated output (S ) r .................................................................................. - 16 3.4.200 Rated resistive burden (R b ) .................................................................. - 16 3.4.201Secondary winding resistance (R ct ) ...................................................... - 16 3.4.202 Composite error ( ε c ).............................................................................. - 16 3.4.203 Rated instrument limit primary current (I PL ) ........................................... - 17 3.4.204 Instrument security factor (FS) ............................................................. - 17 3.4.205 Secondary limiting e.m.f for measuring current transformers................. - 17 3.4.206 Rated accuracy limit primary current (I alf ) ............................................ - 17 3.4.207 Acc uracy lim it factor ( ALF ) ................................................................... - 17 3.4.208 Secondary limiting e.m.f. for protective current transformers ................ - 17 3.4.209 Saturation flux ( Ψ s ) .............................................................................. - 17 3.4.210 Remanent flux ( Ψ r ) ............................................................................... - 17 3.4.211 Remanence factor (K r ) ......................................................................... - 18 3.4.212 Rated secondary loop time constant (T s ) .............................................. - 18 3.4.213 Excitation characteristic ........................................................................ - 18 3.4.214 Rated knee point e.m.f. (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 x ) ...................................................................... - 18 3.4.218 Rated primary short-circuit current (Ipsc)..................................................... - 18 3.4.219 Instantaneous error current (iε) ................................................................. - 19 -

78

ˆ ) .................................................................... - 19 3.4.220 Peak value of total error ( ε

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âc ) ........................................ - 19 3.4.221 Peak value of alternating error component ( ε

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 Specified duty cycle (C-0 and / or C-0-C-0) ........ ......... ......... ......... .......... ... - 19 3.4.223 Specified primary time constant (T P) ......................................................... - 20 3.4.224 Fault duration (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 reactance current transformer ......................................... - 22 3.4.232 Rated equivalent limiting secondary voltage (Ual)........................................ - 22 - 22 3.4.233Peak value of the exciting secondary current at U al (Î a )........................ l 3.4.234 Factor of construction F c ....................................................................... - 22 Definitions related to other ratings.................................................................... - 23 3.5.1 Rated frequency (f R ) ............................................................................. - 23 3.5.2 Mechanical load (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 metal-enclosed instrument transformer .......................... - 23 3.6.3 Closed pressure system ....................................................................... - 23 3.6.4 Rated filling pressure............................................................................ - 23 -

3.5

3.6

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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 Absolute leakage r ate ........................................................................... - 23 3.6.9 Relative leakage rate (F re ).................................................................... - 23 l 3.7 Index of abbreviations ...................................................................................... - 23 Normal and special service conditions ....................................................................... - 25 4.1 General ............................................................................................................ - 25 4.2 Normal service conditions ................................................................................ - 25 4.2.1 Ambient air temperature ....................................................................... - 25 4.2.2 Altitude ................................................................................................. - 25 4.2.3 Vibrations or earth tremors ................................................................... - 25 4.2.4 Other service conditions for indoor instrument transformers ................. - 25 4.2.5 Other service conditions for outdoor instrument transformers ............... - 25 4.3 Special service conditions ................................................................................ - 25 4.3.1 General ................................................................................................ - 25 4.3.2 Altitude ................................................................................................. - 25 4.3.3 Ambient temperature ............................................................................ - 25 4.3.4 Vibrations or earth tremors ................................................................... - 25 4.3.5 Earthquakes ......................................................................................... - 25 4.4 System earthing ............................................................................................... - 25 Ratings...................................................................................................................... - 25 5.1 General ............................................................................................................ - 25 5.2 Highest voltage for equipment .......................................................................... - 25 5.3 Rated insulation levels ..................................................................................... - 25 5.3.1 General ................................................................................................ - 25 5.3.2 Rated primary terminal insulation level ................................................. - 25 5.3.3 Other requirements for primary terminals insulation.............................. - 26 5.3.4 Between-section insulation requirements.............................................. - 26 5.3.5 Insulation requirements for secondary terminals ................................... - 26 5.3.200 Inter-turn insulation requirements ......................................................... - 26 5.4 Rated frequency ............................................................................................... - 26 5.5 Rated output .................................................................................................... - 26 5.6 Rated accuracy class ....................................................................................... - 26 5.6.200 Measuring current transformers ............................................................ - 26 5.6.201 Protective current 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.................................................... - 33 5.202 Rated continuous thermal current ..................................................................... - 33 5.203 Short-time current ratings ................................................................................. - 33 5.203.1 Rated short-time thermal current (I th ) ................................................... - 33 5.203.2 Rated dynamic current (I dyn)................................................................ - 33 Design and construction ............................................................................................ - 34 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 -

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6.1.4 Liquid tightness .................................................................................... - 34 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 Requirements for solid materials used in equipment ......................................... - 34 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............................................... - 35 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 Requirements for the external insulation........................................................... - 35 6.6.1 Pollution ............................................................................................... - 35 6.6.2 Altitude ................................................................................................. - 35 6.7 Mechanical requirements .................................................................................. - 35 6.8 Multiple chopped impulse on primary terminals ................................................ - 35 6.9 Internal arc fault protection requirements ......................................................... - 35 6.10 Degrees of protection by 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....................................................... - 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............................................. - 35 6.12 Corrosion ......................................................................................................... - 35 6.13 Markings .......................................................................................................... - 35 6.13.200 Terminal markings – General 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 -

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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 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.................................................. - 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........................... - 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 Routine tests .................................................................................................... - 48 7.3.1 Power-frequency voltage withstand tests on primary terminals ............. - 48 7.3.2 Partial discharge measurement ............................................................ - 48 7.3.3 Power-frequency voltage withstand tests between sections .................. - 48 7.3.4 Power-frequency voltage 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..................................................................... - 50 7.4 Special tests .................................................................................................... - 51 7.4.1 Chopped impulse voltage withstand test on primary 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................................................................................... - 52 7.4.6 Internal arc fault test ............................................................................. - 52 7.4.7 Enclosure tightness tests at low and high 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 Sample tests .................................................................................................... - 52 8 Rules for transport, storage, erection, operation and maintenance ............................ - 52 9 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

Alternative method for the direct measurement of com posite 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 Protective current transformers class es for transient performance (Normative) ............................................................................................................... - 58 2B.1 Basic theoretical equations for transient 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. method ......................................................................................... - 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 Alternative measurement of the s teady state ratio error .................................... - 7 2 Ann ex 2C Technique used in temperature rise test of oil-imm ersed transformers to determine the thermal constant by an experimental estimation (informative).............. - 74 Ann ex 2D Determination of the t urns ratio error (inform ative) ........................................... - 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 = 140°) ......................................................................................................................... - 58 Fig. 2B.2: Magnetic-flux for the two cases in Fig. 2B.1..................................................... - 59 Fig. 2B.3: Relevant time ranges for calculation of transient factor .................................... - 59 -

289

Fig. 2B.4 Determination of K tf for δ = 3° (T s =61 ms) and f=50 Hz ..................................... - 60 -

290

Fig. 2B.5 Determination of K tf for δ = 1.5° (T s =122 ms) and f=50 Hz................................ - 61 -

291

Fig. 2B.6 Determination of K tf for δ = 0.1° (T s = 1.8 s) and f=50 Hz .................................. - 61 -

292

Fig. 2B.7 Determination of K tf for δ = 3° (T s =50 ms) and f=60 Hz .................................... - 61 -

293

Fig. 2B.8 Determination of K tf for δ = 1.5° (T s =100 ms) and f=60 Hz................................ - 62 -

294

Fig. 2B.9 Determination of K tf for δ = 0.1° (T s = 1.5 s) and f=60 Hz .................................. - 62 -

295

Fig. 2B.10 Determination of K tf for δ = 3° (T s =182 ms) and f=16.7 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 δ = 1.5° (T s =365 ms) and f=16.7 Hz........................... - 63 -

297 298 299 300 301 302

Fig. Fig. Fig. Fig. Fig. Fig.

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 -

2B.12 Determination of K tf for δ = 0.1° (T s = 5.5 s) and f=16.7 Hz .............................. - 63 2B.13: Basic circuit ................................................................................................... - 65 2B.14: Determination of remanence factor by hysteresis loop ................................... - 66 2B.15: Circuit for d.c. method.................................................................................... - 67 2B.16: Typical records .............................................................................................. - 67 2B.17: Circuit for capacitor discharge method ........................................................... - 68 -

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)................................................................................. - 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................................ - 31 Table 207 – Specification Method for TPX, TPY and TPZ current transformers ................ - 32 Table 208 – Markings of terminals ................................................................................... - 36 Table 209 – List of tests................................................................................................... - 39 Table 210 – Gas type and pressure during type, routine and special tests ....................... - 40 Table 211 – Additional type tests for protective current transformers for transient performance .................................................................................................................... - 44 -

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INSTRUMENT TRANSFORMERS Part 2: Current Transformers FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization 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 or agreements of IEC on technical matters express, as nearly as 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 latest edition of this publication. 7) No liability shall be attached to IEC or its directors, employees, servants or agents 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 cited in this publication. Use of the referenced publications is essential for the correct application of this publication. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent rights. IEC shall not be held responsible for identifying any or a ll such patent rights.

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366

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.

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 lauses, subclauses, tables and f igures that are num bered s tarting from 201 are addit ion al to those in Part 1; – additio nal annexes are lettered 2A, 2B, etc. An overvie w of the pla nned set of standar ds at the date of pub lic ation of this document 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 ENTS FOR CURRENT TRANSFORMERS

60044-1

61869-3

ADD ITI ONA L REQ UIREM ENTS FOR INDUCTIVE VOLTAGE TRANSFORMERS

60044-2

61869-4

ADD ITI ONA L REQ UIREM ENTS FOR COMBINED TRANSFORMERS

60044-3

61869-5

ADD ITI ONA L REQ UIREM ENTS FOR 60044-5 CAPACITIVE VOLTAGE TRANSFORMERS

61869-7

ADD ITI ONA L REQ UIREM ENTS FOR ELECTRONIC VOLTAGE TRANSFORMERS

60044-7

61869-8

ADD ITI ONA L REQ UIREM ENTS FOR ELECTRONIC CURRENT TRANSFORMERS

60044-8

61869-9

DIGITAL INTERFACE FOR INSTRUMENT TRANSFORMERS

61869-10

ADD ITI ONA L REQ UIREM ENTS FOR LOW POWER STAND-ALONE CURRENT SENSORS

61869-11

ADD ITI ONA L REQ UIREM ENTS FOR LOW POWER STAND ALONE VOLTAGE SENSOR

61869-12

ADD ITI ONA L REQ UIREM ENTS FOR COMBINED ELECTRONIC INSTRUMENT 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 itionally, an application guide (IEC 61869...) for protection current transformers is under 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 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

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 references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

439

3

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 trument transformer in which the secondary current, in normal conditions of use, is substantially 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 current transformer intended to supply an inform ation signal to measuring instruments and meters. (IEV321-02-18)

455

3.1.202 Protective current transformer

456 457

A current transformer intended to transmit an information signal to protective and control devices (IEV321-02-19)

Normative references

IEC 61869-1: General Requirements for Instrument Transformers, including the references mentioned in Clause 2 of IEC 61869-1

Definitions

General definitions

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458

3.1.203 Class PR protective current transformer

459 460 461

A current transformer with lim ited remanence factor for which, in some cases, a value of the 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 transform er of low leakage reactance for which knowledge of the transformer secondary 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 Class TPX protective current transformer for transient 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 Class TPY protective current transformer for transient performance

473 474 475 476

ˆ ) during specified transient duty cycle. Acc uracy limit defined by peak value of total error ( ε The remanent flux is limited.

477

3.1.207 Class TPZ protective current transformer for transient performance

478 479

âc ) 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 ratings

488

3.2.1 Highest voltage for system (U 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 system (a system earthed 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 shall be stated as an uniform absolute value, applicable for all cores (e.g. “Icth 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 )

Rated secondary current ( I sr )

Rated short-time thermal current ( I th )

Rated dynamic current ( I dyn )

Rated continuous thermal current ( I cth )

Exciting current ( I 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

528

3.4.3 Ratio error ( ε )

529 530

Clause § 3.4.3 of IEC 61869-1 is applicable with the addition of the following: The 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

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 )

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 R ct 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 )

Composite error * ( ε c )

556 557 558 559

ε c

=

100 I p

1

T

( k i T ∫

r s

0

where k 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

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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.

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 should be greater than 10 %, in order to protect the apparatus 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 to the fact that the actual instrument security factor is affected by the burden. As bur den val ue is sig nif ica ntly lower th an rated one , large r cur rent val ues will be pro duc ed on the sec ondar y side in case of short circuit current.

574 575 576

NOTE 2 In the event of system fault currents flowing through the primary 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 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 e characteristic for the core concerned at which a 10 % increase in Ψ causes i e to be increased by 50 %

Rated instrument limit primary current ( I PL )

Instrument security factor ( FS )

Secondary limiting e.m.f for measuring current transformers

Rated accuracy limit primary current ( I alf )

Accuracy limit factor ( 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 / 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 ( 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 graphical or tabular presentatio n of the relat ion ship between the r.m .s. value of the exciting 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 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 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%

Dimensioning factor ( K x )

628

3.4.217

629 630 631

A factor assigned by the purchaser to indicate the multiple of rated secondary current (I sn ) occurring under power system fault conditions, inclusive of safety factors, up to which the transformer is required to meet performance requirements.

632 633

3.4.218

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 (I psc)

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639

3.4.219

Instantaneous error current (i )

640 641 642 643 644 645 646 647 648

Difference between the instantaneous values of the secondary current (i s) multiplied by (kr ), 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

3.4.220

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 âc )

658

3.4.221

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

âc ε

662

=

iˆε ac

2 ⋅ I psc

⋅ 100%

663 664

3.4.222

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

3.4.223

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 (T P)

Figure 202 - Primary time constant T p

682 683

3.4.224

684 685 686 687 688

t’: duration of first fault t’’: duration of second fault (if any)

689

3.4.225

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

695

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

3.4.227

699 700

Total resistance of the secondary circuit

701

Fault duration (t’, t’’)

See figure 201

Specified time to accuracy limit (t’ al , t’’al)

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.

Fault repetition time (t fr )

Secondary loop resistance (R s)

R s = R b + R ct

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702 703

3.4.228

Rated symmetrical short-circuit current factor (K ssc)

704

K ssc =

705

The ratio:

706

3.4.229

707 708 709 710 711 712 713 714 715 716 717 718

The ratio Ψ a / Ψ s , where

I psc I pr

Rated transient dimensioning factor (K td)

Ψa is the peak value of the total magnetic flux of the asymmetrical primary current within the relevant time interval1 at rated burden. Ψ s is

the peak valu e of the steady state a.c. flux of the appropriate symmetrical primary current at rated burden. See figure 203. 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

3.4.232

Rated equivalent limiting secondary voltage (U al)

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 (Î a ) l

739

3.4.234

Factor of construction F c

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 I ε 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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61869-2 ed. 1 © IEC 756

3.5 Definitions related to other ratings

757

3.5.1 Rated frequency (f R )

758

3.5.2 Mechanical load (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 )l

770

3.7 Index of abbreviations

771 IT

Instrument Transformer

CT

Current Transformer

U 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

Actual transf orm ation ratio

k r

Rated transformation ratio

ε

Ratio error

∆φ

Phase displacement

S r

Rated output

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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 uracy limit factor

Ψ s

Saturation flux

Ψ 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 l

Relative leakage rate

Î al

Peak value of the exciting secondary current at U al

I psc

Rated primary short-circuit current

iε

Instantaneous error current

K ss c

Rated symmetrical short-circuit current factor

K td

Rated transient dimensioning factor

t’

Duration of first fault

t’’

Duration of second fault

t’ al

Permissible time to accuracy limit in the first fault

t’’al

Permissible time to accuracy limit in the second fault

t fr

Fault repetition time

T p

Specified primary time constant

U 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

âc 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 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

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 earthing

792

5 Ratings

793

5.1 General

794

5.2 Highest voltage for equipment

795

5.3 Rated insulation 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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38/404/CDV

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 procedure, the wave shape may be highly 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 one of the values of rated output is 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 accuracy 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, 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 a rated secondary current of 1A, a range limit 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 of current error and phase displacement are valid for any given 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 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 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 0,5

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 0,9

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

no

TPY

yes

TPZ

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:


909

5P and 10P

910

5.6.201.1.4

Limits of errors for protective current transformers

911 912

At rated frequency and wit h rated burden connected, the cur rent error , phase displacement and composite error shall not exceed the values given in Table 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:


932

5 PR and 10 PR

933

5.6.201.2.4

Limits of error for class PR protective current transformers

934 935

At rated frequency and wit h rated burden connected, the cur rent error , phase displacement and composite error shall not exceed the values given in Table 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 r ) shall not exceed 10 %.

943

NOTE Insertion of one or more air gaps in the core may be a method for limiting the 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 )

Secondary loop time constant (T s )

Secondary winding resistance ( R 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 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

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

±1.0

± 60

± 1.8

ˆ = 10 % ε

TPY

±1.0

± 60

± 1.8

ˆ = 10 % ε

TPZ

±1.0

180 ± 18

5.3 ± 0.6

âc 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 3 - Since the total permissible error limit is 10 %, the transient dimensioning factor shall be considered conjunctively with the secondary circuit time constant:

ˆ= ε

979

K td ω ⋅ T s

⋅ 100%

(3)

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38/404/CDV

980

5.6.201.4.3

Limits for remanence factor ( K 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 TS

2

Rated primary time constant T p Rated resistive burden R b

Rated resistive burden Rb

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.

61869-2 ed. 1 © IEC

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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 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

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 c urr ent transformers shall com ply with the f ollowin g r equirements

1022

5.203.1

1023

A rated short -time t hermal current (I 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 dyn ) shall normally be 2.5 times the rated short-time thermal current (I 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 )

Rated dynamic current ( I dyn)

61869-2 ed. 1 © IEC

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1030

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 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 systems for gas

1043

6.2.5 Pressure relief device

1044

6.3 Requirements for solid materials used in equipment

1045

6.4 Requirements for temperature rise of parts and components

1046

6.4.1 General

1047


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. These values are based on the service conditions given in clause 4

61869-2 ed. 1 © IEC

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38/404/CDV

1052

6.4.2 Influence of altitude on temperature-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 impulse on primary terminals

1062

6.9 Internal arc faul t protection requirements

1063

6.10

1064

6.10.1 General

1065 1066

6.10.2 Protection of persons against access to hazardous parts and protection of the equipment against ingress of solid foreign objects

1067

6.10.3 Protection against ingress of w ater

1068

6.10.4 Indoor instrument transformers

1069

6.10.5 Outdoor instrument transformers

1070 1071

6.10.6 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 tapings, if any.

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1085

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 the terminals marked P1, S1 and C1 shall h ave the same polar ity at the same instant.

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 = Ipr / 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 ) 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);

61869-2 ed. 1 © IEC

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38/404/CDV

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: taps: I 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). 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 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 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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61869-2 ed. 1 © IEC

38/404/CDV

1138 1139

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 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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61869-2 ed. 1 © IEC 1176 1177 1178

38/404/CDV

The complementary part represents one of many possible cycles, leading to the same value of K td . 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 on GIS, the wet test and RIV test are not applicable.

1200 1201 1202

7.1.3 Sequence of tests

1203

7.2 Type tests

1204

7.2.1 General

1205

7.2.1.1 Information for identification of specimen

1206

7.2.1.2 Information to be included in 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 is at least equal to three times the current transformer thermal 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 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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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 on 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 on 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 300 kV

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 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.6, 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.

Test for accuracy of measuring current transformers

Test for composite error

NOTE Where very high primary currents and single bar-primary winding current transformers are 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.

b) For current transformers having substantially continuous ring 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 error by the indirect method, a possible difference between turns ratio and rated transformation ratio need not be taken into account.

NOTE 1 In calculating the secondary limiting e.m.f., the secondary winding impedance should be 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 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 required to perform direct composite error tests on certain transformer 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 s

7.2.6.204.1 X

X 7.2.6.204.2

X 7.2.6.204.3

- 45 -

61869-2 ed. 1 © IEC Determination of the magnetic characteristic Determination of the Error at limiting conditions

38/404/CDV

X 7.2.6.204.4 X

X

X

7.2.6.204.5

1351 1352 1353


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 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

Alternativel y, for TPY and TPZ cores the phase dis placement at 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

∆ is expressed in minutes, the following approximate formula may be applied: T S [ s ] =

1395 1396 1397 1398 1399 1400 1401

1404 1405 1406 1407 1408 1409 1410 1411

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

a) magnetising inductance L m The magnetising inductance Lm shall be determined by one of the methods described in annex B.2. b) remanence factor (K r )

1412 1413

The remanence factor (K ) 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.

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.

61869-2 ed. 1 © IEC 1434 1435 1436 1437 1438 1439

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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 the degree of protection by 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 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 2t ) is not less than (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 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 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 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 th ), does not exceed:

1466 1467 1468 1469

–

1470 1471 1472 1473 1474

–

Closed pressure systems for gas

180 A/ mm 2 where the winding is of copper of conductivity not less than 97 % of the value given in IEC 60028. 120 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 that in service the requirements for thermal rating are generally 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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1475

7.3 Routine tests

1476

7.3.1 Power-frequency voltage withstand tests on primary terminals

1477


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 test procedure

1484

7.3.3 Power-frequency voltage withstand tests between sections

1485

7.3.4 Power-frequency voltage withstand 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 may b e performed using the follo win g indirect t est:

1495 1496 1497

–

1498 1499 1500

The resulting exciting current (I e), expressed as a percentage of the rated secondary current (I sr ) multiplied by the instrument security factor FS shall be equal to or exceed the rated value 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 indirect test is that high currents are not necessary (for instance 30 000 A 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 primary win ding open-circ uited, 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.

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 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” implies that the ampere turns are the same 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 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 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 ct .

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 sinusoidal e.m.f. of rated frequency equal to the rated knee-poin t e.m.f. shall be applied 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 )

Determination of secondary loop time constant ( T s)

Determination of secondary winding resistance ( R ct )

NOTE For determination of secondary loop resistance (Rs = Rct + Rb), Rb 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.

Tests for class PX protective current transformers

Rated knee point e.m.f. ( E k ) and maximum exciting current ( I e )

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1556 1557

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 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 involving measurement of the ratio error with zero connected 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


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


1577

7.3.5.206.3

1578


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 temperature

1584

7.3.7.1 Closed pressure 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 )

Turns ratio error ( t )

Determination of the secondary time constant T s

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 frequency, if the voltage val ue achieved at the rated sec ondary current (or rated 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) =

1608

60 ⋅

twice the rated frequency test frequency

1609

with a minimum of 15 s.

1610 1611 1612 1613

NOTE The inter-turn overvoltage test is not a 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 voltage withstand test on primary terminals

1618

7.4.2 Multiple chopped impulse test on primary terminals

1619

7.4.3 Measurement of capacitance and dielectric 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, it is 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 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

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 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 necessary to distinguish between I ″ p , the primary current divided by the turns ratio, and I ′ p , the primary current divided by the rated transformation ratio. Absence of turns correction means I ′ p = I ″ p . If turns correction is present, I ′ p is different from I ″ p , and since I ″ p is used in 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 that purpose). However, the vectors I ′ p and I ″ p have the same direction, so turns correction 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 vectors I s and I ″ p can be considered to be parallel. Assuming again that there is no turns

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 component (∆I ) of I e can be used instead of the arithmetic difference between I ″ p and 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

It will further be seen that under the given assumptions the exciting current I e divided by I ″ p is 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 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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1765

A.6

1766 1767

Alternative means may be used for the measure ment of composite error and one method 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 A2 are two ammeters and care must be taken that A 2 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 , of transformer X is k rx and of transformer N′ is k ′ r , the ratio k r must equal the product of k ′ r and k rx :

1791

i.e. k r = k ′ r × k 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 shown in figures 2A.5 and 2A.6, care should be taken to use a low 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

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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 additional advantage of a lim itatio n of composite error is the res ulting limitation of the 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)

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 =

1818

⎥⎦

Switching or fault inception angle arctan

X p R p

= arctan (ω T p )

Phase angle of system short-circuit impedance

when the equivalent voltage source in the short-circuit with R p and X p is

= −U max cos(ω t + γ ) (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) ⎡ −t / T p cos(θ ) − cos(ω t + θ )⎤ i (t ) = 2 I psc e (4) u (t )

1819 1820 1821

⎢⎣

⎥⎦

1822 1823 1824 1825 1826

The angles θ and 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 possibl y reduced range of fault inception angle 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 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

t required al

Transient factor

by the protection system. By calculating with the linear inductivity the solution is only valid up to the first saturation of the current transformer.

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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61869-2 ed. 1 © IEC 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874

A general overview with a flow chart and with examples is given in the application guide 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 max touches its envelope curve of peaks K tfp at the time t tf ,max

1875 1876 1877 1878 1879 1880

38/404/CDV

=

π + ϕ

(5)

ω

Within this time range K tf ,ψ max considers the worst case switching angle θ (t al ) which leads to the highest flux at the accuracy limit time t al . Figures 2B.4 … 12 show the curves for 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.

Fig. 2B.4 Determination of K tf for = 3° (T s=61 ms) and f=50 Hz

61869-2 ed. 1 © IEC

Fig. 2B.5 Determination of K tf for = 1.5° (T s=122 ms) and f=50 Hz

Fig. 2B.6 Determination of K tf for = 0.1° (T s = 1.8 s) and f=50 Hz

Fig. 2B.7 Determination of K tf for = 3° (T s =50 ms) and f=60 Hz

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Fig. 2B.8 Determination of K tf for = 1.5° (T s=100 ms) and f=60 Hz

Fig. 2B.9 Determination of K tf for = 0.1° (T s = 1.5 s) and f=60 Hz

Fig. 2B.10 Determination of K tf for = 3° (T s =182 ms) and f=16.7 Hz

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Fig. 2B.11 Determination of K tf for = 1.5° (T s=365 ms) and f=16.7 Hz Ktf,

ψmax

6

= 0.1° (Ts = 5.5 s) , f = 16.7 Hz

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 = 0.1° (T s= 5.5 s) and f=16.7 Hz

0

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

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 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 tfp ,max

1890 1891 1892 1893

−t / T s ⎞

⎟ + sin(θ )e ⎠

−t / T s

+1

(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)

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)

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) 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 substantially sinusoidal a.c. voltage u(t) is applied to the secondary termina ls. The test may 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

38/404/CDV

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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61869-2 ed. 1 © IEC 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

38/404/CDV

Fig. 2B.15: Circuit for d.c. method 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 i m 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

=

0.7 i90

s

− i20

(14)

where i90 and i 20 are magnetizing current values at the appropriate percentages of ψ s . At the opening of switch S, a decreasing magnetiza tion current flows through the secondary winding and the discharging resistor R d . 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 K r =

r

ψ s

(15)

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 K r 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 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 âc 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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38/404/CDV

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

=

î εdc

b

For TPY : î ε

2107 2108 2109

=

c

=

2 î εac

For TPZ : î e

=

î εac

c

=

î εac

+

î 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 al) 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 al) shall not exceed the value given below: I al ≤

)

2126 2127 2128 2129 2130 2131 2132 2133 2134

Limits of exciting secondary current (Î al )

⎛ K − 1 ε ˆ [%] ⎞ ⎟⎟ 2 ⋅ I sn ⋅ K ssc ⋅ ⎜⎜ td + ac ω T 100 % ⎝ S ⎠

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 al 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 magnetic flux at acc uracy limiting condition

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 al shall be determined. This value shall not exceed the limit given in B.3.3.1.

B.3.3.4

Determination of F c

Acc ord ing to the def inition 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 substantially sinuso idal voltage is applied to the seconda ry terminals S1 – S2 of the CT. The test voltage across the terminals U s 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 R CT from the test voltage U s Test across the S 1 – 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]

I pn

With: I p N p N s

= I e + I s ⇒ I p =

( I e + I s ) N s N p

[2]

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61869-2 ed. 1 © IEC 2210

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]

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 S1 – 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 Is Test = Is )

2225

•

Measurement of the voltage Up 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 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

Oil temperature rise above θ a Ultimate values in steady state

2254

∆θ θu , ∆θ u ε(t ) T o h θ1, θ2 , θ3

2255 2256

In principle, the test should continue until the steady-state temperature rise (of the oil) is ascertained.

2246

2250 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 ∆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)

∆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)

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2273 2274 2275

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 ∆ θ 3/ ∆ θ u should be not less than 0,95.

2276 2277 2278

A more accurate value of steady- rate temperature rise is obtained by a least square method of extrapolation of all measured points above approximately 60 % of ∆θ u ( ∆ θ u estimated by the three point method).

2279

A dif ferent num erica l f ormulat ion is:

2280

∆θ u = ∆θ 2 +

(∆θ 2 − ∆θ1 ) − (∆θ 3 − ∆θ 2 ) ∆θ − ∆θ1 ln 2 ∆θ 3 − ∆θ 2

(6)

2281

2282 2283

Figure 2C.1 - Graphical extrapolation to ultimate temperature rise

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