stu nishenko, khalid mosalam, shakhzod takhirov, and eric fujisaki seismic performance of insulators...

Stu Nishenko, Khalid Mosalam, Shakhzod Takhirov, and Eric Fujisaki

SEISMIC PERFORMANCE SEISMIC PERFORMANCE OF INSULATORS IN OF INSULATORS IN ELECTRIC SUBSTATIONSELECTRIC SUBSTATIONS

Porcelain InsulatorsPorcelain Insulators

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+ + +

Insulators in Electric SubstationsInsulators in Electric Substations

Used in almost every substation equipment

Apparatus, e.g., bushings, circuit breaker interrupter housings, surge arresters, instrument transformers

Posts, e.g., bus supports, capacitor racks, air core reactors, disconnect switches

Porcelain—Traditional material of choice; long history of use

Brittle and massive—often a weak link during earthquakes

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Insulators in Substation EquipmentInsulators in Substation Equipment

Circuit breaker bushings, interrupter housings, and support columns

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Interrupter

Bushings

Insulators in Substation EquipmentInsulators in Substation Equipment

Transformer bushings,Surge arresters

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Surge arrester

Bushing

Insulators in Substation EquipmentInsulators in Substation Equipment

Instrument transformers6

Insulators in Substation EquipmentInsulators in Substation Equipment

Bus supports

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Insulators in Substation EquipmentInsulators in Substation Equipment

Air disconnect switches

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Post insulator

Insulators in Substation EquipmentInsulators in Substation Equipment

Circuit switchers9

Post insulator

Insulators in Substation EquipmentInsulators in Substation Equipment

Capacitor racks/ platforms10

Post insulator

Insulators in Substation EquipmentInsulators in Substation Equipment

Air core reactors

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Post insulator

Insulators in Substation EquipmentInsulators in Substation Equipment

Cable terminations12

Typical mechanical properties Elastic Modulus: 10,000 – 14,000 ksi Modulus of Rupture: 7 – 16 ksi, COV = 0.06 -

0.15 Unit weight: 140 – 170 lb/ft3

Physical configuration Load carrying cores: 3” – 8” dia Lengths depend on insulation level required:

14” at 12kV service – 152” at 500kV service Sheds used to increase surface length and

prevent flashover event

Characteristics of Porcelain Post InsulatorsCharacteristics of Porcelain Post Insulators

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Porcelain Post InsulatorsPorcelain Post Insulators

Sheds

Ductile iron end fitting with Portland cement

grout in joint

Load-carrying porcelain core

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Load Rating of Post InsulatorsLoad Rating of Post Insulators

Rated for cantilever load capacity (fixed-base, load at tip)

Also rated for tension, compression, torsion

Quasi-static, monotonic load tests Assign load rating as dependable

breaking strength Typically rating = Mean – 2σ, or -3σ Sometimes rated according to ANSI

Technical Reference Standard

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Governed by IEEE 693 Std. Qualified by test or analysis as part of

the equipment Designed for elastic behavior Allowable Strength = 50% of

dependable capacity at 0.5g Required Response Spectrum

Often the controlling element in an equipment qualification

Seismic Design of Substation InsulatorsSeismic Design of Substation Insulators

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Insulator Damage During EarthquakesInsulator Damage During Earthquakes

Circuit breaker support columns

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Insulator Damage During EarthquakesInsulator Damage During Earthquakes

Transformer bushings18

Insulator Damage During EarthquakesInsulator Damage During Earthquakes

Surge arresters19

Insulator Damage During EarthquakesInsulator Damage During Earthquakes

Instrument transformers

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Insulator Damage During EarthquakesInsulator Damage During Earthquakes

Bus supports (posts)21

Insulator Damage During EarthquakesInsulator Damage During Earthquakes

Air disconnect switches (posts)22

Insulator Damage During EarthquakesInsulator Damage During Earthquakes

Circuit switchers (posts)23

Insulator Damage During EarthquakesInsulator Damage During Earthquakes

Capacitor racks (posts)24

Better understanding of effects of cyclic loading

Simple, reliable damage detection techniques for post-shake test inspection/ assessment

Improved insulator analysis models Better understanding of failure

mechanisms Methods for seismic qualification

testing with varied support characteristics

Industry NeedsIndustry Needs

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Porcelain Post Insulator StudPorcelain Post Insulator Studies at PEERies at PEER

Post insulator cyclic load testing Development of finite element analysis

models Hybrid simulation of disconnect switch on

support

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Post InsulatorPost Insulator Cyclic Load Testing Cyclic Load Testing

Obtained static break test data from insulator manufacturer

Tested 6 posts of 2 different cross sections Tested with cyclic load reversals, increasing

magnitude Used hammer blows at intermediate

points, to attempt to detect damage

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Cyclic Load Test SequenceCyclic Load Test Sequence

Load StepNumber of

Cycles

0.59*Mean Static 6

0.66*Mean Static 6

0.72*Mean Static 6

0.78*Mean Static 6

0.86*Mean Static 6

0.93*Mean Static 6

1.00*Mean Static 6

Monotonic to failure 128

Post InsulatorPost Insulator Cyclic Load Testing Cyclic Load Testing Two types of failures observed

Cross-section #1: Cyclic Test Mean Breaking Strength = 0.84*Static Test Mean

Cross-section #2: Cyclic Test Mean Breaking Strength = 1.21*Static Test Mean

Hammer blows unable to detect damage

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Post InsulatorPost Insulator F.E. Model Development F.E. Model Development

Name Method Modeling details Caps Sheds Grout Separation,Fracture

M1 HandCalcs.

Beam: lower porcelain section extends to top No No No No

M2 SAP2000 Beam: lower porcelain section extends to top No No No No

M3 SAP2000 Beam elements with variable cross section Iron No No No

M4 DIANA Solid elements with variable cross section Iron No No No

M5 DIANA Solid elements with variable cross section Iron Yes No No

M6 DIANA Solid elements with variable cross section Actual Yes Yes No

M7 DIANA Solid elements with variable cross section Actual Yes Yes Yes

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Post InsulatorPost Insulator F.E. Model Development F.E. Model Development

Further development in progress Parametric studies and comparisons

with test data Frequency Force/ displacement

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Qualification of Equipment With Qualification of Equipment With VVaried Supportsaried Supports

Varied supports may be used by different utilities for same equipment

Repeated tests are costly Test of equipment on full-scale support is

generally required Lead time is long

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Hybrid Simulation ofHybrid Simulation of Disconnect Switch Disconnect Switch on Supporton Support

Jaw Post

Braced frame support structure

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Concept for Hybrid Simulation of Concept for Hybrid Simulation of Disconnect Switch on SupportDisconnect Switch on Support

Computational Substructure

0 10 20 30 40 50 60 70-1.2-0.6

00.61.2

X acc.

(g)

19.489619.489719.489819.4899 19.49 19.490119.490219.490319.4904

0.8

1

1.2

Y acc.

(g)

0 10 20 30 40 50 60 70-1.2-0.6

00.61.2

Time (sec)

Z acc.

(g)

0 10 20 30 40 50 60 70-10

-5

0

5

10

Dis

pla

cem

ent (in)

550 kV Switch Test

0 10 20 30 40 50 60 70-100

-50

0

50

100

Velo

city

(in

/sec)

0 10 20 30 40 50 60 70-4

-2

0

2

4

Time (sec)

Accele

ratio

n (

in/s

ec2)

Insulator

Earthquake motion

Support structureresponse or from

Physical Substructure (switch jaw end with blade open)

shake table test

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Insulator

Calculated support structure response applied to movable platform

Physical Substructure(assumed 1D)

Movable platform

Fixed tracks

DynamicActuator &Load Cell

Earthquake motion

Computational Substructure

Dynamic DOF i

Force feedback

0 10 20 30 40 50 60 70-1.2-0.6

00.61.2

X acc.

(g)

19.489619.489719.489819.4899 19.49 19.490119.490219.490319.4904

0.8

1

1.2

Y acc.

(g)

0 10 20 30 40 50 60 70-1.2-0.6

00.61.2

Time (sec)

Z acc.

(g)

0 10 20 30 40 50 60 70-10

-5

0

5

10

Dis

pla

cem

ent (in)

550 kV Switch Test

0 10 20 30 40 50 60 70-100

-50

0

50

100

Velo

city

(in

/sec)

0 10 20 30 40 50 60 70-4

-2

0

2

4

Time (sec)

Accele

ratio

n (

in/s

ec2)

Displacement command

Hybrid Simulation of Disconnect Switch Hybrid Simulation of Disconnect Switch on Supporton Support

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AcknowledgementsAcknowledgements

Co-Authors Stu Nishenko, Sr. Seismologist, PG&E Khalid Mosalam, Professor of Civil and

Environmental Engineering, UC Berkeley Shakhzod Takhirov, Sr. Development

Engineer, UC Berkeley Bonneville Power Administration California Energy Commission Pacific Gas and Electric Company

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