Overview about research project Energy handling capability

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1 Cigré WG A3.25 meeting San Diego October 16, 2012 Max Tuczek, Volker Hinrichsen, TU Darmstadt Note: all information beginning from slide 21 are provisional results in the frame of Cigré WG A3.25 work, subject to possible corrections and extensions and not yet published. They shall, therefore, be used for personal or internal information only and not be further distributed. Care should be taken when conclusions shall be drawn. TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

2 Contents Single impulse energy handling capability (A3.17) Energy handling capability for double impulse stresses Repeated AC energy impacts Repeated AC versus 90/200 µs energy impacts Thermal stability of complete arresters and related simulation Max1's project Max2's project TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

3 Several thousand samples from seven manufacturers worldwide Most extensive energy handling research program on MO resistors so far MO resistors, Size 1 Diameter (55 65) mm Typical for a Class 3 station arrester Height (35 45) mm MO resistors, Size 2 Diameter (37.45) mm Typical for a Class 1/10-kA arrester Height (35 45) mm Different aspect ratios different failure mechanisms TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

4 Test current impulse shapes standard currents as per IEC Long duration current impulse 1 ms 2 ms 4 ms Lightning discharge current 90/200 µs High current impulse 4/10 µs: 65 ka 200 ka... plus non-standard stress: Alternating current 50 Hz î 10 A î 100 A î 300 A TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

5 Flowchart of the Test Procedure initial measurement energy test with impulse OK mechanical lyfailed No exit measurement failed Yes New approach! initial measurement U ch1 at I ch = 0.12 ma/cm² (after 5 s) P ct1 at 0.8 x U ch1 (after 1 min) U res1 at I = I N U ch... "characteristic" voltage; indicates changes of the U-I-characteristic in the continuous operating range; may be U ref exit measurement U ch2 at I ch = 0.12 ma/cm² (after 5 s) P ct2 at 0.8 x U ch1 (after 1 min) U res2 at I = I N U res3 at I = 1.5 ka/cm² TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

Failure modes important for manufacturers The different

(puncture, cracking, flashover, change of

material and to design and optimize it with regard to

6 Failure modes important for manufacturers The different physical failure modes under single impulse stress (puncture, cracking, flashover, change of U-I-characteristics) are usually not of interest to the end-user. But they do allow the manufacturers to assess their material and to design and optimize it with regard to particular aspects of energy handling capability. TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

7 exit measurement!!! 95% U U 105% U ch1 ch2 ch1 Yes mechanically failed during residual voltage tests No Yes!!! No 95% U U 105% U res1 res2 res1 Yes OK No failed TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

8 mean failure energy in Overview about research project Preliminary Results 50% Failure Energy Size 1 (diameter 60 mm, height 40 mm) Manufacturers S, T, U, V, X, Z s AC 100 ms peak current density in A/cm² Note: "rated" energies usually specified in the range TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16, S T U V X Z 4 ms 250 µs Failed by puncture and flashover of the coating system!

9 W "Bath tub curve"? Switching duty 4ms 100 ms 10 s t No minimum of energy handling capability for switching surges There may be a minimum at > 10 s difficult to investigate (nonadiabatic) TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

Failure mechanisms: % 100 80 60 40 20 0 S CR BR FO ÜB PU DU MF Uch Uref Ures

10 Failure mechanisms: % S CR BR FO ÜB PU DU MF Uch Uref Ures 4 ms 2 ms 1 ms 90/200 µs CR FO PU MF Uch... Ures... Cracking Flashover Puncture Mechanical failure during exit measurement Change of "characteristic" voltage Change of residual voltage % U CR BR FO ÜB PU DU MF Uch Uref Ures 4 ms 2 ms 1 ms 90/200 µs Impulse shapes: 4/10 µs 90/200 µs 1 ms 2 ms 4 ms TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

Failure mechanisms: % 100 80 60 40 20 0 X CR BR FO ÜB DU PU MF Uch Uref Ures

11 Failure mechanisms: % X CR BR FO ÜB DU PU MF Uch Uref Ures 4 ms 2 ms 1 ms 90/200 µs CR FO PU MF Uch... Ures... Cracking Flashover Puncture Mechanical failure during exit measurement Change of "characteristic" voltage Change of residual voltage Impulse shapes: 4/10 µs 90/200 µs 1 ms 2 ms 4 ms TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

12 Comparison: with and without complex failure criterion TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

13 Mean failure energy in Size 2 (diameter 40 mm, height 40 mm) Manufacturers S, U, V, W, Y ms 1 ms 90/200 µs 4/10 µs Amplitude of current density in A/cm² S U V W X Y Failed by change of U ch! TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

14 Failure mechanisms: % S CR BR FO ÜB PU DU MF Uch Uref Ures 4 ms 1 ms 4/10 µs CR FO PU MF Uch... Ures... Cracking Flashover Puncture Mechanical failure during exit measurement Change of "characteristic" voltage Change of residual voltage % U 20 0 CR BR FO PU ÜB DU MF Uch Ures MF Uref Ures 1 ms 4/10 µs 4 ms % V CR BR FO ÜB DU PU MF Uref Uch Ures 4 ms 1 ms 4/10 µs Impulse shapes: 4/10 µs 90/200 µs 1 ms 2 ms 4 ms % CR BR FO ÜB PU DU MF Uref Uch Ures W 4 ms 1 ms 4/10 µs TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

15 Failure mechanisms: CR FO PU MF Uch... Ures... Cracking Flashover Puncture Mechanical failure during exit measurement Change of "characteristic" voltage Change of residual voltage % Y CR BR FO ÜB DU PU MF Uref Uch Ures 2 ms 4/10 µs Impulse shapes: 4/10 µs 90/200 µs 1 ms 2 ms 4 ms TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

16 Preliminary Results 50% Failure Energy Change of Characteristic Voltage for Size 2 change of char. voltage in % ka î in A S U V W Y -40 TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

Mean value of current density amplitude in A/cm² 10000 1000 100 10 1 Different

.24 mm Cigré varistors: diam. 60 mm, height 40..45 mm 0.

17 Mean value of current density amplitude in A/cm² Different failure criteria 0.1 Ringler's varistors: diam mm, height: mm Cigré varistors: diam. 60 mm, height mm Time in ms S T U V X Z [Rin 1997] TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

18 Mean failure energy in Overview about research project Compared with former investigations (Ringler et al., 1997 see orange curve), an increase of (10 20)% in energy handling capability can be observed. These are the good news for the user! S T U V X Z [Ringler 1997] 200 a.c Amplitude of current density in A/cm² 4 ms 1 ms TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16, /200 µs Different failure criterion But 90/200 µs impulses give impulse energy values lower than expected (influence of coating system!) Different failure mechanism for 90/200 µs

19 Problem for Energy Specification: Outliers Energie in Versuchsnummer TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

20 Preliminary Results 50% Failure Energy Conclusions so far Compared with former investigations (Ringler 1997), energy handling capability has increased by %. 50% failure energy is times higher than actually specified "rated" energies; no figures can be derived for extremely low failure probabilities (<< 1%). The linear "log (current) vs. log (time to failure)" (Ringler) dependence could be verified, except for the new 90/200 µs impulse, where puncture and flashover of the coating may become the limiting factor potential for improvement; important for line arrester applications. Varistors for station and distribution application were directly compared only minor differences by different aspect ratios. "Mechanical failure" and "visible damage" are not sufficient failure criteria; changes of U-I-characteristics have to be considered as well. TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

21 Energy handling capability for double impulse stresses up to mechanical failure LD current impulses 3 mechanical failure of MOV 2 U in kv I in ka t in ms TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

22 Energy handling capability for double impulse stresses up to mechanical failure double impulse stresses single impulse stresses 2 x 1.85 ms, d = 80 ms 2 x 1.85 ms, d = 3 s 40 MOV 1 make size 2 1 x 2 ms 1 x 4 ms TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

23 Energy handling capability for double impulse stresses up to mechanical failure double impulse single impulse impulse length/ Time interval 1.85 ms/ 3 s 1.85 ms/ 80 ms 2 ms 4 ms (sum) mean failure energy in p.u. Coefficient of variation 1,04 1,02 1,02 1,0 0,09 0,12 0,10 0,07 No difference in energy handling capability! TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

24 initial measurement n times Repeated stresses energy pre-stress energy impact with AC cool down to ambient temperature exit measurement application of energy TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

25 Repeated stresses initial measurement 1,4 n times 1,2 energy pre-stress cool down to ambient temperature exit measurement failure energy in p.u. 1 0,8 0,6 0,4 0,2 No change in energy handling capability by ac pre-stresses! application of energy number of previous impacts TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

26 Repeated stresses initial measurement energy pre-stress cool down to ambient temperature exit measurement n times application of energy mean change of U ch in % number of previous impacts TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

27 initial measurement n times energy pre-stress cool down to ambient temperature energy impact with AC vs. energy impact with 90/200 µs exit measurement application of energy TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

28 Energy impact with AC vs. 90/200 µs Energy impact *) max. 20 impulses or max. 20 times 4 cycles Sample No. (each box = one sample; 20 samples per kind of stress 90/200 µs Impulse *) 4 cycles AC *) #1 TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

29 Energy impact with AC vs. 90/200 µs Energy impact *) max. 20 impulses or max. 20 times 4 cycles Sample No. (each box = one sample; 20 samples per kind of stress 90/200 µs Impulse *) 4 cycles AC *) #2 TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

30 Energy impact with AC vs. 90/200 µs Energy impact *) max. 20 impulses or max. 20 times 4 cycles Sample No. (each box = one sample; 20 samples per kind of stress 90/200 µs Impulse *) 4 cycles AC *) #3. and so on TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

31 Energy impact with AC vs. 90/200 µs Energy impact x Varistor failure at impulse no. x 90/200 µs Impulse 4 cycles AC TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

32 Energy impact with AC vs. 90/200 µs Energy impact x Varistor failure at impulse no. x 90/200 µs Impulse 4 cycles AC TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

33 failure energy in p.u. *) Application of energy (AC up to mechanical failure) after 20 pre-stresses *) 1 p.u. = mean AC failure energy 0.00 Pre-stress: TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

34 Energy impact with AC vs. 90/200 µs Summary/ Conclusions: for 400 at 90/200 µs many mechanical failures of MOV, but only after a high number (usually > 10) of stresses for 300 and 400 at AC many mechanical failures just at the first impulse for 400 at AC high failure rate at high number of stresses for 90/200 µs remarkable reduction of energy handling capability; distinct decrease with increasing magnitude of pre-stress impulses; remaining max. failure energy = 10% of the mean AC failure energy!! for AC virtually no impact on energy handling capability by pre-stresses for 200 at AC those samples failed at very low energy levels, which probably would have had failed at higher magnitude of pre-stresses Routine tests at AC considered more sensitive than LD impulse testing TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

35 Energy handling capability of used MOV (from grid) TUD High-Voltage Lab Cigré WG A3.25 meeting Paris France, August 28,

36 MO resistor TUD High-Voltage Lab Cigré WG A3.25 meeting 36/??

37 Energy handling capability of used MOV (from grid) Main failure mechanism: Change of characteristic voltage TUD High-Voltage Lab Cigré WG A3.25 meeting Paris France, August 28,

38 Thermal stability limit of complete EHV/UHV arresters TUD High-Voltage Lab Cigré WG A3.25 meeting Paris France, August 28,

39 TUD High-Voltage Lab Cigré WG A3.25 meeting Paris France, August 28,

40 energy impact U c U c TUD High-Voltage Lab Cigré WG A3.25 meeting Paris France, August 28,

41 t ambient 16 C TUD High-Voltage Lab Cigré WG A3.25 meeting Paris France, August 28,

42 Arithmetic mean temperature, above ambient temperature / K thermal equival. arrester with grading arrester without grading 213,6 215,8 215,0 220,8 212,5 223,5 t ambient 16 C TUD High-Voltage Lab Cigré WG A3.25 meeting Paris France, August 28,

43 Thermal stationary temperature at diff. ambient temperatures 250 t ambient : height / cm C 30 C 40 C 40 C* *with grading ring temperature (above ambient temperature) / K TUD High-Voltage Lab Cigré WG A3.25 meeting Paris France, August 28,

Thermal stability limit at different ambient temperatures 250 22 C stable 22 C instable 200 30 C stable 30 C instable 40 C stable 40 C instable height

44 Thermal stability limit at different ambient temperatures C stable 22 C instable C stable 30 C instable 40 C stable 40 C instable height / cm absolute temperature / C TUD High-Voltage Lab Cigré WG A3.25 meeting Paris France, August 28,

45 Conclusions so far. Findings suggest that the importance of field grading may have been overestimated in the past. Evidently, perfect grading is not essential to achieve. The manufacturer has mainly to determine the permissible operating temperatures in the upper part of the arrester, which is primarily a matter of material. A higher average overtemperature under continuous operation stress (U = Uc) will also reduce the thermal energy handling capability of the arrester, because the average temperature of an ungraded arrester will be higher than that of perfectly graded one (see slide 43). TUD High-Voltage Lab Cigré WG A3.25 meeting Paris France, August 28,

46 Follow-up work in progress 1. Reproduction of the experimentally found thermal behavior by a coupled thermal and non-linear resistive/capacitive FEM simulation 2. Application and validation of the simulation model to simulate thermal stability under real conditions (temperature rise adiabatically and in zero time) Temperature Time Experiment Simulation 3. Simulation: "Playing" with the external grading system for optimization purposes TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

47 TUD High-Voltage Lab Cigré WG A3.25 meeting San Diego, October 16,

Surge arrester POLIM-H.. ND

DATA SHEET Surge arrester POLIM-H.. ND Technical data Classification according to EN 50526-1 and IEC 62848-1 Nominal discharge current I n (8/20 µs) 10 ka peak Class DC-B High current impulse I hc (4/10