Seismic Blue 1.1 (1)

Seismic Considerations &

Seismic Considerations &

Power Bushings

Power Bushings

Using IEEE Standards

Using IEEE Standards

 ABB

IEEE 693 - 1997

IEEE 693 - 1997

IEEE Recommended Practice for IEEE Recommended Practice for Seismic Design of Substations

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

European Standards

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

IEEE 693-1997



Performance Levels



Selection of performance Level

Requirements for bushings



Test Methods



Qualification of bushings < 161 kV

Qualification of bushings

 161 kV

Performance Levels



Low = 0.1 g,



Moderate = 0.5 g,

High = 1.0 g,

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

General Requirements for Bushings

 Bushings as components of larger equipment  Annex D of IEEE 693 - Transformers

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

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 

Bushing Seismic Considerations



Bushing is not at ground level



Bushing acceleration is amplified by

transformer structure



Bushing acceleration =

2x ground acceleration

Transformer tank:

Transformer Tank

Amplification Factor = 2

Shake Table Testing of Bushings



Method 1

 Test at 1/2 level and

 Calculate to demonstrate a 2x safety factor



Method 2

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

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

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

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

Shake Table Testing of Bushings

Using Full Test Method

 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

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)

2 g

Bushing Qualification @

Bushing Qualification @

Shake Table

Test Set-up

 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

 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

 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)

 ABB