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

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

3. IEEE Std 693 - 1997 Electrical Equipment for Sub Stations
Based on IEEE
Very major revision
Basically a new standard
Three Qualification Levels
Low, Moderate & High
User determines Qualification Levels
IEEE is basically a completely new standard
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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
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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
Purpose of this slide is to outline the presentation
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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
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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
This all done by purchaser of equipment - we react to his specification
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9. General Requirements for Bushings
Bushings as components of larger equipment
Annex D of IEEE Transformers
Requirements depend on system voltage
Bushings not specifically addressed in the standard except as part of a larger piece of equipment, ie, transformer
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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
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.
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11. 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
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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
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
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13. Transformer Tank Amplification Factor = 2
2.0 g
Transformer Tank Amplification Factor = 2
1.0 g
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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
Two methods of shake table testing are allowed.
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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
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.
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16. 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
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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
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
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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
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
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19. 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.
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20. 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
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21. 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
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22. Bushing Qualification @ Moderate Level by Direct Testing
Same except this is Moderate Level
1 g
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23. Shake Table Test Set-up
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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
The ABB Alamo story on bushing qualification
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25. ABB Bushing Qualification Summary
High - Static Pull Test
Bushings 25 kV through 138 kV
High - Shake Table
Bushings 161 kV through 196 kV
full test of seismically worse bushing in family
Moderate - Shake Table
Bushings 362 kV
This is our actual performance
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26. 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.
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27. ABB
Components USA
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