Ing. José Correa Guarniz Capitulo de Ingeniería Eléctrica Presidente CDL CDL - CIP CIP PRESENTACIÓN CIP
Selec Selecci ción ón de Par Parar array rayos os Lindher Rojas Tovar ABB - Power Grids Grids High Voltag Voltagee
Agenda
Step by step selection
Step by step selection IEC60099-5 1. Determine application/type of equipment to be protected 2. Match the electrical characteristics 3. Determine the energy requirements 4. Calculate protection levels 5. Check protection margins 6. Consider environmental factors
Step 1 Application Type of equipment being protected – – – – – – – – – – – –
Transformers Transformer neutrals Transmission lines Cables Cable sheaths Rotating machines Switchgear Capacitor banks Reactors GIS Series Capacitors HVDC
Step 2 Match the electrical characteristics
Electrical selection complete
Step 2a Determine Uc Uc is determined from actual service voltage across the arrester, Uca – For phase-ground arresters in 3-phase system: Uca = Us/√3 so any Uc ≥ Us/√3 may be considered equal after consideration of possible voltage fluctuations • Recommended (IEC 60099-5): Uc ≥ 1.05 x Us/√3 – A larger than necessary U c may or may not be beneficial, and must be verified in the various type tests. –
Common choice guide Uc for the arrester need not be higher than the minimum of Ur x 0.8 or in any case 1.1 x U s/ 3 (for Us ≥ 123kV) where: 0.8 is the “design factor” for ZnO arresters and 1.1 covers prolonged undue voltage fluctuations
Step 2b Determine TOV strength Calculate TOV strength (Tr)
– •
–
–
NOTE! Every arrester type has its own specific TOV curve
Refer manufacturer’s curves •
TOV = k x Us/ √3 = k x Uca
•
where k = overvoltage fault factor Ur > TOV/Tr where Tr = arrester TOV withstand strength
Always consider TOV at earth-fault • ke < 1.4 Effectively earthed • ke = 1.73 Non-effectively earthed Consider all other known TOV (amplitude and duration) where: • Ure > TOVe/Tre • Ur1 > TOV1/Tr1, Ur2 > TOV2/Tr2, etc.
Step 2c Select Ur Minimum Ur0 = Uca/0.8 = (Us/√3) / 0.8 – Select rated voltage Ur • Ur = Highest of Ur0, Ure, Ur1, Ur2, etc –
•
Ur > TOV/Tr > (k x Us/√3) /Tr
Select next highest standard rating from manufacturer’s
catalog Common choice guide as preliminary selection criteria To be cautious when specifics are not known (includes combined effects of earthfault and some l oad rejection)
k Duration
Effectively earthed Us < 123kV Us > 123 kV 1.55 1.5 1s 1s
Non-effectively earthed 1.73 10 s or 1 h
Calculation example Ur and Uc Selection Example: Arresters fo r 66 kV System Case 1
1 2 3 4 5
Nominal system voltage Un Max. system voltage Us Arrester location System earthing System fault clearance time
kV kV
Case 2
Case 3
66 66 72,5 72,5 Phase-ground connection Direct Indirect 1s 10 s
66 72,5 Indirect 2 hr
What arrester Ur and Uc woul d yo u select? 6 Assume arrester type already chosen. 7 Avail able arrester rated vol tages: 54, 60, 66, 72, 84, 90, 96 kV 8 From arrester's TOV curves for gi ven times and co nsidering fu ll d uty TOV strength Tr p.u 1,16 1,1 0,96
Calculation example Ur and Uc Selecti on Exampl e: Arresters f or 66 kV System Case 1
1 2 3 4 5
Nominal system voltage Un Max. system voltage Us Arrester location System earthing System fault clearance time
Max. cont. voltage Min. rated voltage
kV kV
Uca kV Ur0 kV
Nearest standard rating Ur0 kV
66 72.5 Direct 1s
72,5/√3 Uca=Us/√3 41.86 Uca/0,8 Ur0=Uca/0.8 52.32 54
Calculation example Ur and Uc Max. cont. voltage
Uca
kV
Duri ng earth-faul t, TOVe
TOVe kV
From TOV curves for gi ven times TOV strength Tre Min. rated voltage, TOV/Tr Ure i.e nearest standard Ure
and p.u kV kV
Hence, ch osen
kV kV
(Uc = 0,8*Ur fo r Us< 123kV)
Ur Uc
Case 1
Case 2
Case 3
41.86
41.86
41.86
1,55*Uca TOVe=kexUca 64.88 72.42 con sidering f ull duty 1.16 1.1 55.93 Ure>TOVe/Tre 60 66 60 48
66 53
1,73*Uca 72.42 0.96 75.43 84 84 67
Calculation example Ur and Uc Selecti on Exampl e: Arresters for 66 kV System Case 1
1 2 3 4 5
No mi nal syst em vo lt ag e Un Max. system voltage Us Arrester location System earthing System fault clearance time
kV kV
Case 2
Case 3
66 66 72,5 72,5 Phase-ground connection Direct Indirect 1s 10 s
66 72,5 Indirect 2 hr
What arrester Ur and Uc woul d yo u select? 6 Assume arrester type already cho sen. 7 Avail able arrester rated volt ages: 54, 60, 66, 72, 84, 90, 96 kV 8 From arrester's TOV curves for gi ven times and consi dering ful l duty TOV strength Tr p.u 1,16 1,1 0,96
Calculation example Ur and Uc Selecti on Exampl e: Arresters fo r 66 kV System Case 1
1 2 3 4 5
No mi nal syst em vo lt ag e Un Max. system voltage Us Arrester location System earthing System fault clearance time
Max. cont. voltage Min. rated voltage
kV kV
Uca kV Ur0 kV
Nearest standard rating Ur0 kV
Case 2
Case 3
66 66 72,5 72,5 Phase-ground connection Direct Indirect 1s 10 s
66 72,5
Indirect 2 hr
72,5/√3
72,5/√3
72,5/√3
41,86 Uca/0,8 52,32 54
41,86 Uca/0,8 52,32 54
41,86 Uca/0,8 52,32 54
Calculation example Ur and Uc
Max. cont. voltage
Uca kV
During earth-fault, TOV
Ue
Case 1
Case 2
Case 3
41.86
41.86
41.86
1,55*Uca 1,73*Uca 64.88 72.42 From TOV curves for gi ven times and con sidering f ull duty TOV strength Tr p.u 1.16 1.1 Min. rated voltage, TOV/Tr Ure kV 55.93 65.83 i.e nearest standard Ure kV 60 66 Hence, chosen
Ur Uc
kV
kV kV
60 48
66 53
1,73*Uca 72.42 0.96 75.43 84 84 67
Step 3 Determine energy requirements –
–
For new installations, a proper transient system study will give an indication of the required arrester classification according to IEC 60099-4, Ed 3.0 For replacement in existing networks, and/or where a system study has not been made, the following common choice guides are proposed
Repetitive Charge Transfer rating, Qrs –
–
Check the line discharge class of the existing surge arresters used in the network If the performance of the old arresters has been satisfactory, then select an arrester with a charge capability at least 10% above the IEC example (L.3) to ensure the discharge capability of the new arresters would not be too low compared with the old ones because of the different test procedures
Step 3 Determine energy requirements Rated Thermal Energy, Wth –
–
Check the line discharge class of the existing surge arresters used in the network If the performance of the old arresters has been satisfactory, then select an arrester with a corresponding thermal energy rating (rounded to the nearest classification value) based on the total energy absorbed in two impulses in the switching surge operating duty test cycle from IEC 60099-4 Ed 2.2, cl 8.5.5
For example, generically for ABB HVAC arresters:
Step 4 Determine Protection levels –
For chosen arrester obtain the residual voltages at different impulses and co-ordinating currents Common choice guide Co-ordinating currents Upl (LIPL), 8/20 µs impulse – 10 kA for Us < 362 kV – 20 kA for Us > 362 kV Ups (SIPL), 30/60 µs impulse – 0.5 kA for Us < 170 kV – 1.0 kA for Us < 300 kV – 2.0 kA for Us > 362 kV
NOTE! Every arrester type has its own specific protection characteristic curves
Step 5 Check protective margins –
Check if protective margins are sufficient for all types of impulses
Withstand level • LIWV = Lightning impulse withstand voltage • SIWV = Switching impulse withstand voltage – Protection level • Upl = Lightning protection level • Ups = Switching protection level –
–
Margins in the order of 15 – 20 % (including distance effects) are generally recommended to consider aged non selfrestoring insulation • Distance effect for fast impulses reduce margins considerably and must be accounted for • Higher margins are recommended if system details are not fully analysed
ABB Surge Arresters
Standard insulation levels
Standard insulation levels (LIWL) for equipment are specified in IEC 60071-1
Step 5 Example of protection margins A 420 kV transformer with arresters fitted has the followi ng parameters System Arresters LIPL 897 kVp LIWL 1425 kV
SIWL 1050 kV
SIPL
728 kVp
What are the protective margins to the transformer’s insulation levels?
a) excluding distance effect
11 m Overhead Line
9m
Step 5 Example of protection margins
a) Excluding distance effect = ((1425/897) –1) x 100 – Margin to LIWL = ((1050/728) – 1) x 100 – Margin to SIWL
= 58% = 44%
Step 6 Consider other environmental conditions Arrester housing insulation withstand (requirements as per IEC 60099-4 up to 1000 masl) The correction factor Ka is based on the dependence of the atmospheric pressure on the altitude. where H is the altitude above sea level (in metres) and the value of m is Lightning m = 1,0 Switching < 800kV m = 1,0 > 800 kV m according to fig 9 IEC 60071-2 Common choice guide
IEC design altitude: 1000 m
LIWV > 1,3 * Upl from 1,15 * e 1000/8150 which reflects a 15% co-ordination factor to take into account discharge currents higher than nominal and the statistical nature of the withstand voltage of the insulation, and a 13% margin to account for variation in air pressure from sea level up to normal service altitudes not exceeding 1 000 m and discharge currents higher than nominal. SIWV > 1,25 x Ups from 1,1 * e m(1000/8150) which reflects a 10% co-ordination factor to take into account discharge currents higher than normal and the statistical nature of the withstand voltage of the insulation, and a 13% margin to account for variation in air pressure from sea level up to normal s ervice altitudes not exceeding 1 000 m PFWV > 1,06 x Ups (as peak value) factor of 1,06 takes into account a safety margin of 1,1 for higher switching impulse currents, an altitude correction factor of 1,13 for 1000 m altitude, and a test conversion factor of 0,6× √2 acc. Table 2 of IEC 60071-2:1996.
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