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Seismic Considerations

Willie Freeman ABB Mount Pleasant, PA IEEE 693 Tutorial May 7, 2009

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IEEE P693/D6, 2008

Recommended Practice for Seismic Designof Substations

a more descriptive title would be:Seismic Qualification of High Voltage

Power Equipment

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Electrical Equipment: Annex C-P

Circuit BreakersTransformer, Liquid Reactor, BushingsDisconnect Switch

Instrument Transformer Air Core Reactor Circuit Switcher Suspended EquipmentBatteries and RacksSurge ArrestersElectronic Devices

Metalclad Switchgear PotheadsCapacitorsGIS Switchgear

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2008 USGS Seismic Hazard Map 2% probability of exceeding in 50 years

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Seismic Qualification Levels

3 2 0erformance

1 6 5igh

0 8 25oderate

0 2 1ow

ResponseAcceleration

gs

GroundAcceleration

gs

IEEE 693Qualification Level

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Response Spectrum(analytical tool)

Plot of response acceleration to an earthquakeground acceleration (input)Theoretical response of SDOF oscillators to input

Applied to dynamic (modal) analysisCalculated theoretical response (not actualresponse)

to shake table input acceleration to determine if test input is sufficient

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Earthquake Response Spectra a t 2 % dam ping

0.1

1

10

0.1 1 10 100

Fr eq ue ncy, Hz

S p e c

t r a

l A c c e

l e r a

t i o n ,

G ' s

.5 G Sine Beat

High Perf ormance

LA 94

SF 89

Kobe 95

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Required Response Spectrum(High RRS, moderate is 50%)

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Static Coefficient Analysis for Breakers 38 kV to 123 kV

Include control cabinets, CTs, stored energysources1.5 x RRS peak x weight of each component intwo principal horizontal direction80% in the vertical directionCombine 3 principal directions by SRSS

Add dead weight and operating loads

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Dynamic Analysis forBreakers 123-145 kV

Finite element modelModal spectrum analysis up to 33 Hz

Account for at least 90 % of massSum (

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Test for Breakers 170 kV and above

Cantilever test of insulatorsResonant frequency search

0.5 g time history test in closed position0.5 g time history test with O-CO operation0.5 g Sine beat test or 1 g time history (new)Repeat resonant frequency searchRepeat cantilever test of composite insulators

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Seismic Qualification of Transformers

Tank, core, coils for 69 kV and above

by static analysis (0.5 g in two horiz. dir.+ 0.4 g vert ) Appendages:

radiators, conservators, 3 x 0.5 g static anal.

control cabinets, 1.5 x 0.5 g static analysis. Apparatus Bushings

Greater than 138 kV by time history test to four

times the RRS (maybe reduced in next fewyears by special test program) 35 to 138 kV by static pull test to 2 x weight

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Test SetupBiaxial or triaxial shake table

Complete breaker or independent pole unit withcontrolsPressurized and controls energized, fullyoperational

Monitor relay and main contacts bounce Accelerometers on major componentsStrain gauges at critical location along load path

Load bolts to anchor breaker Determine: max. stresses, displacements,foundation loads, damping and resonances

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Strain gauges at crit icallocations on bushings,tank and frame

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Comparison of Highest Strain Readings

3.00796265Tank Nozzle/Shell

3.078628Bushing

Cantilever

2.3320789Frame Leg

1.69358212Frame Leg

Ratio1.0 G TimeHistory0.5 G Sine BeatStrain Reading

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Test Response Spectrum (TRS)

Required Response Spectrum(RRS)

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Functional Tests

Pressure reading and leak check before and aftereach runCheck for damage and operational state aftereach runMain contact resistance at beginning and endProduction timing test at beginning and endRepeat production high voltage withstand test atfactory

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Acceptance Criteria

No visible damage to equipment or supportsPorcelain insulator stress < 50% ultimate

Composite insulator stress < 50% SMLStructural design per AISC or Alum. Assoc. manualsMaterials not covered by other codes:

Brittle Materials < 50% of ultimate strength Ductile Materials < 50% of yield strength

Function must be maintained

Sine beat stresses 1.8 x RRS allowablePerformance level (1 g test) - slight bending but no failure

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Documentation

Test PlanCertified ReportSeismic Outline DrawingNameplate stating seismic qualification level

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Good Seismic Design Features:

Avoid stress concentrations in the load path.Reduce weights and moments of equipment.Use composite bushing insulators instead ofporcelain.Use high strength insulation supports in the

interrupter. Avoid bending loads in connections to criticalcomponents such as the tanks or housings.Keep higher stresses in ductile componentsalong the load path and reduce stress in brittleelements to increase damping and improveseismic toughness.

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Good Seismic Designresists shipping stresses