Stu Nishenko, Khalid Mosalam, Shakhzod Takhirov, and Eric FujisakiSEISMIC PERFORMANCE OF INSULATORS IN ELECTRIC SUBSTATIONS

Porcelain Insulators*+++

Insulators in Electric SubstationsUsed in almost every substation equipmentApparatus, e.g., bushings, circuit breaker interrupter housings, surge arresters, instrument transformersPosts, e.g., bus supports, capacitor racks, air core reactors, disconnect switchesPorcelainTraditional material of choice; long history of useBrittle and massiveoften a weak link during earthquakes*

Insulators in Substation EquipmentCircuit breaker bushings, interrupter housings, and support columns*InterrupterBushings

Insulators in Substation EquipmentTransformer bushings,Surge arresters*Surge arresterBushing

Insulators in Substation EquipmentInstrument transformers*

Insulators in Substation EquipmentBus supports*

Insulators in Substation EquipmentAir disconnect switches*Post insulator

Insulators in Substation EquipmentCircuit switchers*Post insulator

Insulators in Substation EquipmentCapacitor racks/ platforms*Post insulator

Insulators in Substation EquipmentAir core reactors*Post insulator

Insulators in Substation EquipmentCable terminations*

Typical mechanical propertiesElastic Modulus: 10,000 14,000 ksiModulus of Rupture: 7 16 ksi, COV = 0.06 - 0.15Unit weight: 140 170 lb/ft3Physical configurationLoad carrying cores: 3 8 diaLengths depend on insulation level required: 14 at 12kV service 152 at 500kV serviceSheds used to increase surface length and prevent flashover eventCharacteristics of Porcelain Post Insulators*

Porcelain Post InsulatorsShedsDuctile iron end fitting with Portland cement grout in jointLoad-carrying porcelain core*

Load Rating of Post InsulatorsRated for cantilever load capacity (fixed-base, load at tip)Also rated for tension, compression, torsionQuasi-static, monotonic load testsAssign load rating as dependable breaking strengthTypically rating = Mean 2, or -3Sometimes rated according to ANSI Technical Reference Standard*

Governed by IEEE 693 Std.Qualified by test or analysis as part of the equipmentDesigned for elastic behaviorAllowable Strength = 50% of dependable capacity at 0.5g Required Response SpectrumOften the controlling element in an equipment qualificationSeismic Design of Substation Insulators*

Insulator Damage During EarthquakesCircuit breaker support columns*

Insulator Damage During EarthquakesTransformer bushings*

Insulator Damage During EarthquakesSurge arresters*

Insulator Damage During EarthquakesInstrument transformers*

Insulator Damage During EarthquakesBus supports (posts)*

Insulator Damage During EarthquakesAir disconnect switches (posts)*

Insulator Damage During EarthquakesCircuit switchers (posts)*

Insulator Damage During EarthquakesCapacitor racks (posts)*

Better understanding of effects of cyclic loadingSimple, reliable damage detection techniques for post-shake test inspection/ assessmentImproved insulator analysis modelsBetter understanding of failure mechanismsMethods for seismic qualification testing with varied support characteristicsIndustry Needs*

Porcelain Post Insulator Studies at PEERPost insulator cyclic load testingDevelopment of finite element analysis modelsHybrid simulation of disconnect switch on support*

Post Insulator Cyclic Load TestingObtained static break test data from insulator manufacturerTested 6 posts of 2 different cross sections Tested with cyclic load reversals, increasing magnitudeUsed hammer blows at intermediate points, to attempt to detect damage*

Cyclic Load Test Sequence*

Post Insulator Cyclic Load TestingTwo types of failures observed

Cross-section #1: Cyclic Test Mean Breaking Strength = 0.84*Static Test MeanCross-section #2: Cyclic Test Mean Breaking Strength = 1.21*Static Test MeanHammer blows unable to detect damage*

Post Insulator F.E. Model Development*

Post Insulator F.E. Model DevelopmentFurther development in progressParametric studies and comparisons with test dataFrequencyForce/ displacement *

Qualification of Equipment With Varied SupportsVaried supports may be used by different utilities for same equipmentRepeated tests are costlyTest of equipment on full-scale support is generally requiredLead time is long*

Hybrid Simulation of Disconnect Switch on SupportJaw PostBraced frame support structure*

Concept for Hybrid Simulation of Disconnect Switch on SupportComputational SubstructureInsulatorEarthquake motionSupport structureresponse or from Physical Substructure (switch jaw end with blade open)shake table test*

Hybrid Simulation of Disconnect Switch on SupportForce feedbackDisplacement command*

AcknowledgementsCo-AuthorsStu Nishenko, Sr. Seismologist, PG&EKhalid Mosalam, Professor of Civil and Environmental Engineering, UC BerkeleyShakhzod Takhirov, Sr. Development Engineer, UC BerkeleyBonneville Power AdministrationCalifornia Energy CommissionPacific Gas and Electric Company*