Transcript Seismic Considerations - Transformer components

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Seismic Considerations &
Power Bushings
Using IEEE Standards
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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
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Three Qualification Levels
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Very major revision
Basically a new standard
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)
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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
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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
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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
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Testing for Seismic Performance Levels
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Low: 0.1g, horizontal
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Moderate: 0.5 g, horizontal
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Equipment testing not required
Testing required (when practical with equipment size)
High: 1.0 g, horizontal
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Testing required (when practical with equipment size)
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Qualification of Bushings
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Less than 161 kV
Static Pull Test
Force = 2 x weight
Applied horizontally
at top of bushing
Duration = 2 seconds
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161 kV and Higher
Shake Table test
Time history method
Test by design family
Test most seismically
vulnerable family
member
Pass = 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:
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Amplification factor = 2, or
Super Elevation factor (IEC) = 1.5
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2.0 g
Transformer Tank
Amplification Factor = 2
1.0 g
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Shake Table Testing of Bushings
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Method 1
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Test at 1/2 level and
Calculate to demonstrate a 2x safety factor
Method 2
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Test at full level
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Shake Table Testing of Bushings
1/2 Test + Calculation Method
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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 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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Example of 1/2 Test Method
(Power Transformer)
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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
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Example of 1/2 Test Method
(Transformer Bushings)
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Purpose of test:
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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 Bushings
Using Full Test Method (Full Performance Level Test)
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Purpose of test:
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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 Bushings
Using Full Test Method (Full Performance Level Test)
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Moderate Level (0.5 g)
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Bushing tested at 1.0 g
High Level (1.0 g)
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Bushing tested at 2.0 g
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Bushing Qualification @
High Level by Direct Testing
2g
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Bushing Qualification @
Moderate Level by Direct Testing
1g
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Shake Table
Test Set-up
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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
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Qualified @ High - Static Pull Test
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Bushings 25 kV through 138 kV
Qualified @ High - Shake Table
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Bushings 161 kV through 196 kV
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full test of seismically worse bushing in family
Qualified @ Moderate - Shake Table
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Bushings 362 kV
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full test of seismically worse bushing in family
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ABB Bushing Qualification Summary
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500 kV bushing
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not qualified at moderate
passed 0.45 g at flange
equivalent to 0.22 g, ground acceleration
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(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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