Seismic Considerations & Power Bushings ABB Components USA Seismic Considerations & Power Bushings Using IEEE Standards

IEEE Recommended Practice for Seismic Design of Substations ABB Alamo has used and will use this standard to qualify bushings

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 IEEE 693-1997 is basically a completely new standard djr 2/00

European Standards IEC Technical Report 1463

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

IEEE 693-1997 Performance Levels Selection of performance Level Requirements for bushings Test Methods Qualification of bushings < 161 kV Qualification of bushings  161 kV Purpose of this slide is to outline the presentation djr 2/00

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

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 This all done by purchaser of equipment - we react to his specification djr 2/00

General Requirements for Bushings Bushings as components of larger equipment Annex D of IEEE 693 - Transformers Requirements depend on system voltage Bushings not specifically addressed in the standard except as part of a larger piece of equipment, ie, transformer djr 2/00

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 The Low level addresses such things as equipment foundations and basic site preparation in non earthquake prone areas. Does not require any testing. Very large equipment cannot be tested due to shake table limitations so standard provides for calculations. djr 2/00

Qualification of Bushings 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 The feeling is that earthquake worthiness of small bushings can be adequately demonstrated by cantilever test. Large bushings require shake table testing Pass = no damage & no leaking djr 2/00

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 This is important. The bushing (according to IEEE 693) must withstand horizontal acceleration that is twice the specified ground acceleration for the transformer. This because the transformer structure amplifies the acceleration at the bushing flange. Note that the IEC requirement is only 1.5 times the ground acceleration djr 2/00

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

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 Two methods of shake table testing are allowed. djr 2/00

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 The 1/2 test method works well for structures that behave linearly and are predictable. For example, a steel structure - results at one level can be calculated upward to a higher level with good accuracy. Not true a complex composite structure like a bushing. This is the reason that we prefer the full test method for our bushings. djr 2/00

Shake Table Testing of Bushings Using 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

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 Slide shows that the 1/2 test method applies 1/2 the required ground acceleration to the shake table. This is ok when equipment sits on the ground. Not ok for equipment mounted on top of another sturcture djr 2/00

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 Bushings must account for the amplification effect of the transformer structure. IEEE 693 defines the amplification at 2 x Since this test is at 1/2 value, the shake table must be set up for twice the 1/2 value which is then, the full value, ie, 1/2 x 2 = 1 djr 2/00

Shake Table Testing of Bushings Using 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 Here again, bushing must be tested at twice the ground acceleration. Since this is a Full Test, the shake table is set up at 2x the specified ground acceleration. djr 2/00

Shake Table Testing of Bushings Using 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

Bushing Qualification @ High Level by Direct Testing This is test set up for qualification of a bushing on the shake table at the High Level. High Level = 1.0 g ground acceleration Bushing acceleration is 2 x = 2.0 g This slide also demonstrates creative use of PowerPoint 2 g djr 2/00

Bushing Qualification @ Moderate Level by Direct Testing Same except this is Moderate Level 1 g djr 2/00

Shake Table Test Set-up djr 2/00

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 The ABB Alamo story on bushing qualification djr 2/00

ABB Bushing 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 This is our actual performance djr 2/00

ABB Bushing 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 The 500 kV bushing “failed” at 0.5 g at the flange (0.25 ground acceleration) The failure was very minor, ie, slight oil seepage during the shaking but no continuous leak once the shaking stopped. The same bushing was tested a second time to see if the leaking became any worse with repeated tests. It did not - the leak (really a seep) was no worse during the second test. This indicates that some “relatively” minor design changes would get the bushing to pass at 0.5 g at the flange (0.25 g on the ground). It would take a more dramatic redesign to get to the Moderate Level of 0.5 g on the ground which means 1.0 g at the flange. djr 2/00

ABB Components USA djr 2/00