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

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

ABB Components USA

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