Seismic Blue 1.1 (1)

 ABB Components

USA

Seismic Considerations & Power Bushings

Using IEEE Standards

 ABB

Components USA

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

 ABB

Components USA

IEEE Std 693 - 1997 

Electrical Equipment for Sub Stations



Based on IEEE 693-1984





Very major revision



Basically a new standard

Three Qualification Levels 



 ABB

Low, Moderate & High

User determines Qualification Levels

Components USA

European Standards

IEC Technical Report 1463

 ABB

Components USA

IEC Technical Report 1463 

Covers seismic qualification of power  bushings



Based on static coefficient calculations

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Based on cantilever withstand of bushing

  Not

 ABB

widely accepted in North America

Components USA

IEEE 693-1997

 ABB

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Performance Levels

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Selection of performance Level

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Requirements for bushings

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Test Methods

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Qualification of bushings < 161 kV

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Qualification of bushings  161 kV

Components USA

Performance Levels (ground acceleration)

 ABB

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Low = 0.1 g, horizontal acceleration peak

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Moderate = 0.5 g, horizontal acceleration peak

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High = 1.0 g, horizontal acceleration peak

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Vertical acceleration = 0.8 x horizontal

Components USA

Selection of Performance Level

 ABB

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By User of equipment

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Expected ground acceleration by earthquake hazard method or …

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… by seismic exposure maps and site conditions

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Select Performance Level to match the expected ground acceleration

Components USA

General Requirements for Bushings

 ABB

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Bushings as components of larger equipment

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Annex D of IEEE 693 - Transformers

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Requirements depend on system voltage

Components USA

Testing for Seismic Performance Levels 

Low: 0.1g, horizontal 

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Moderate: 0.5 g, horizontal 

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Testing required (when practical with equipment size)

High: 1.0 g, horizontal 

 ABB

Equipment testing not required

Testing required (when practical with equipment size)

Components USA

Qualification of Bushings Less than 161 kV

161 kV and Higher



Static Pull Test

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Shake Table test

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Force = 2 x weight

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Time history method

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Applied horizontally

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Test by design family

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at top of bushing

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

Duration = 2 seconds

Test most seismically vulnerable family member 

Pass = no damage & no leaking  ABB

Components USA

Bushing Seismic Considerations 

Bushing is not at ground level

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Bushing acceleration is amplified by transformer structure

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Bushing acceleration = 2x ground acceleration

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Transformer tank:  

 ABB

 Amplification factor = 2, or Super Elevation factor  (IEC) = 1.5

Components USA

2.0 g

Transformer Tank Amplification Factor = 2 1.0 g  ABB

Components USA

Shake Table Testing of Bushings 

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Method 1 

Test at 1/2 level and

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Calculate to demonstrate a 2x safety factor

Method 2 

 ABB

Test at full level

Components USA

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

 ABB

Components USA

Shake Table Testing of Bushings Using 1/2 Level Test Method

 ABB

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For large equipment where not practical to test at full level.

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Must demonstrate by calculation that equipment can withstand forces 2 times as great as test values

Components USA

Example of 1/2 Test Method (Power Transformer)

 ABB

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Purpose of test: demonstrate that transformer is qualified for the High Performance Level where ground acceleration = 1.0 g

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Shake Table set-up at 1/2 value = 0.5 g

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Use calculations to show that the test results at 0.5 g can be extended to 1.0 g

Components USA

Example of 1/2 Test Method (Transformer Bushings) 

 ABB

Purpose of test: 

demonstrate qualification at High Performance Level



ground acceleration = 1.0 g

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Bushing acceleration is 2 times ground acceleration because of tank effect

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Bushing must withstand 2 x 1.0 g = 2.0 g

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Shake Table set-up at 1/2 value = 1.0 g

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Use calculations to show that the test results at 1.0 g can be extended to 2.0 g

Components USA

Shake Table Testing of Bushings Using Full Test Method 



 ABB

(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

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Bushing must withstand 2 x 1.0 g = 2.0 g

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Shake Table set-up at full value = 2.0 g

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Bushing directly qualified by Test

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Calculations not required

Components USA

Shake Table Testing of Bushings Using Full Test Method 

Moderate Level (0.5 g) 



Bushing tested at 1.0 g

High Level (1.0 g) 

 ABB

(Full Performance Level Test)

Bushing tested at 2.0 g

Components USA

Bushing Qualification @ High Level by Direct Testing

2g  ABB

Components USA

Bushing Qualification @ Moderate Level by Direct Testing

1g  ABB

Components USA

Shake Table Test Set-up

 ABB

Components USA

 ABB



Qualify bushings based on IEEE 693-1997

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Actual shake table test used for higher voltage bushings

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 ABB

 Components USA

ABB full line of ANSI/IEEE bushings has  been tested and qualified according to IEEE 693-1997

Components USA

 ABB

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Qualified @ High - Static Pull Test 

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Bushing Qualification Summary

Bushings 25 kV through 138 kV

Qualified @ High - Shake Table 

Bushings 161 kV through 196 kV 



Qualified @ Moderate - Shake Table 

Bushings 362 kV 

 ABB

full test of seismically worse bushing in family

full test of seismically worse bushing in family

Components USA

 ABB



Bushing Qualification Summary

500 kV bushing   

not qualified at moderate  passed 0.45 g at flange equivalent to 0.22 g, ground acceleration 



 ABB

(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

Components USA

 ABB Components USA

 ABB

Components USA