Seismic Considerations & Power Bushings

1. ABBComponents USA Seismic Considerations &Power Bushings Using IEEE Standards

2. IEEE 693 - 1997 IEEE Recommended Practice for Seismic Design of Substations

3. IEEE Std 693 - 1997 • Electrical Equipment for Sub Stations • Based on IEEE 693-1984 • Very major revision • Basically a new standard • Three Qualification Levels • Low, Moderate & High • User determines Qualification Levels djr 2/00

4. European Standards IEC Technical Report 1463

5. IEC Technical Report 1463 • Covers seismic qualification of power bushings • Based on static coefficient calculations • Based on cantilever withstand of bushing • Not widely accepted in North America djr 2/00

6. IEEE 693-1997 • Performance Levels • Selection of performance Level • Requirements for bushings • Test Methods • Qualification of bushings < 161 kV • Qualification of bushings  161 kV djr 2/00

7. Performance Levels (ground acceleration) • Low = 0.1 g, horizontal acceleration peak • Moderate = 0.5 g, horizontal acceleration peak • High = 1.0 g, horizontal acceleration peak • Vertical acceleration = 0.8 x horizontal djr 2/00

8. Selection of Performance Level • By User of equipment • Expected ground acceleration by earthquake hazard method or … • … by seismic exposure maps and site conditions • Select Performance Level to match the expected ground acceleration djr 2/00

9. General Requirements for Bushings • Bushings as components of larger equipment • Annex D of IEEE 693 - Transformers • Requirements depend on system voltage djr 2/00

10. Testing for Seismic Performance Levels • Low: 0.1g, horizontal • Equipment testing not required • Moderate: 0.5 g, horizontal • Testing required (when practical with equipment size) • High: 1.0 g, horizontal • Testing required (when practical with equipment size) djr 2/00

11. Less than 161 kV Static Pull Test Force = 2 x weight Applied horizontally at top of bushing Duration = 2 seconds 161 kV and Higher Shake Table test Time history method Test by design family Test most seismically vulnerable family member Pass = no damage & no leaking Qualification of Bushings djr 2/00

12. Bushing Seismic Considerations • Bushing is not at ground level • Bushing acceleration is amplified by transformer structure • Bushing acceleration = 2x ground acceleration • Transformer tank: • Amplification factor = 2, or • Super Elevation factor (IEC) = 1.5 djr 2/00

13. 2.0 g Transformer Tank Amplification Factor = 2 1.0 g djr 2/00

14. Shake Table Testing of Bushings • Method 1 • Test at 1/2 level and • Calculate to demonstrate a 2x safety factor • Method 2 • Test at full level djr 2/00

15. Shake Table Testing of Bushings 1/2 Test + Calculation Method • Only practical method for some large equipment • Good when structure behaves in linear fashion and is predictable • Not good for bushings because of the non-linearity of the bushing’s mechanical system, ie, gasket + porcelain + spring clamps djr 2/00

16. Shake Table Testing of BushingsUsing 1/2 Level Test Method • For large equipment where not practical to test at full level. • Must demonstrate by calculation that equipment can withstand forces 2 times as great as test values djr 2/00

17. Example of 1/2 Test Method(Power Transformer) • Purpose of test: demonstrate that transformer is qualified for the High Performance Level where ground acceleration = 1.0 g • Shake Table set-up at 1/2 value = 0.5 g • Use calculations to show that the test results at 0.5 g can be extended to 1.0 g djr 2/00

18. Example of 1/2 Test Method(Transformer Bushings) • Purpose of test: • demonstrate qualification at High Performance Level • ground acceleration = 1.0 g • Bushing acceleration is 2 times ground acceleration because of tank effect • Bushing must withstand 2 x 1.0 g = 2.0 g • Shake Table set-up at 1/2 value = 1.0 g • Use calculations to show that the test results at 1.0 g can be extended to 2.0 g djr 2/00

19. Shake Table Testing of BushingsUsing Full Test Method(Full Performance Level Test) • Purpose of test: • demonstrate qualification at High Performance Level • ground acceleration = 1.0 g • Bushing acceleration is 2 times ground acceleration because of tank effect • Bushing must withstand 2 x 1.0 g = 2.0 g • Shake Table set-up at full value = 2.0 g • Bushing directly qualified by Test • Calculations not required djr 2/00

20. Shake Table Testing of BushingsUsing Full Test Method(Full Performance Level Test) • Moderate Level (0.5 g) • Bushing tested at 1.0 g • High Level (1.0 g) • Bushing tested at 2.0 g djr 2/00

21. Bushing Qualification @High Level by Direct Testing 2 g djr 2/00

22. Bushing Qualification @ ModerateLevel by Direct Testing 1 g djr 2/00

23. Shake TableTest Set-up djr 2/00

24. ABB Components USA • Qualify bushings based on IEEE 693-1997 • Actual shake table test used for higher voltage bushings • ABB full line of ANSI/IEEE bushings has been tested and qualified according to IEEE 693-1997 djr 2/00

25. ABBBushing Qualification Summary • Qualified @ High - Static Pull Test • Bushings 25 kV through 138 kV • Qualified @ High - Shake Table • Bushings 161 kV through 196 kV • full test of seismically worse bushing in family • Qualified @ Moderate - Shake Table • Bushings 362 kV • full test of seismically worse bushing in family djr 2/00

26. ABBBushing Qualification Summary • 500 kV bushing • not qualified at moderate • passed 0.45 g at flange • equivalent to 0.22 g, ground acceleration • (with tank amplification factor = 2) • failure mode (@ 0.50 g at flange) • slight leak at flange during shake test • re-sealed after test • no worse after second test djr 2/00

27. ABB Components USA djr 2/00