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ABB Components USA
Seismic Considerations &Power Bushings
Using IEEE Standards
ABB Components USA
ABB Components USA
IEEE 693 - 1997
IEEE Recommended Practice for Seismic Design of Substations
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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
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European Standards
IEC Technical Report 1463
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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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IEEE 693-1997
Performance Levels Selection of performance Level Requirements for bushings Test Methods Qualification of bushings < 161 kV Qualification of bushings 161 kV
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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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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
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General Requirements for Bushings
Bushings as components of larger equipment
Annex D of IEEE 693 - Transformers
Requirements depend on system voltage
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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)
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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
Pass = no damage & no leakingPass = no damage & no leaking
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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
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Transformer Tank Amplification Factor = 2
1.0 g
2.0 g
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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
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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
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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
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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
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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
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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
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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
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2 g
Bushing Qualification @High Level by Direct Testing
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1 g
Bushing Qualification @ Moderate Level by Direct Testing
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Shake TableTest Set-up
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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
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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
full test of seismically worse bushing in family
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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
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ABBComponents USA