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

Porcelain Insulators  

Insulators 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 3

Insulators in Substation Equipment Circuit breaker bushings, interrupter housings, and support columns 4 Interrupter Bushings

Insulators in Substation Equipment Transformer bushings, Surge arresters 5 Surge arrester Bushing

Insulators in Substation Equipment Instrument transformers 6

Insulators in Substation Equipment Bus supports 7

Insulators in Substation Equipment Air disconnect switches 8 Post insulator

Insulators in Substation Equipment Circuit switchers 9 Post insulator

Insulators in Substation Equipment Capacitor racks/ platforms 10 Post insulator

Insulators in Substation Equipment Air core reactors 11 Post insulator

Insulators in Substation Equipment Cable terminations 12

 Typical mechanical properties  Elastic Modulus: 10,000 – 14,000 ksi  Modulus of Rupture: 7 – 16 ksi, COV =  Unit weight: 140 – 170 lb/ft 3  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 Insulators 13

Porcelain Post Insulators Sheds Ductile iron end fitting with Portland cement grout in joint Load-carrying porcelain core 14

Load 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 15

 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 Insulators 16

Insulator Damage During Earthquakes Circuit breaker support columns 17

Insulator Damage During Earthquakes Transformer bushings 18

Insulator Damage During Earthquakes Surge arresters 19

Insulator Damage During Earthquakes Instrument transformers 20

Insulator Damage During Earthquakes Bus supports (posts) 21

Insulator Damage During Earthquakes Air disconnect switches (posts) 22

Insulator Damage During Earthquakes Circuit switchers (posts) 23

Insulator 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 Needs 25

Porcelain Post Insulator Studies at PEER  Post insulator cyclic load testing  Development of finite element analysis models  Hybrid simulation of disconnect switch on support 26

Post Insulator 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 27

Cyclic Load Test Sequence Load Step Number of Cycles 0.59*Mean Static6 0.66*Mean Static6 0.72*Mean Static6 0.78*Mean Static6 0.86*Mean Static6 0.93*Mean Static6 1.00*Mean Static6 Monotonic to failure1 28

Post Insulator 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 29

Post Insulator F.E. Model Development NameMethodModeling detailsCapsShedsGrout Separation, Fracture M1 Hand Calcs. Beam: lower porcelain section extends to top No M2SAP2000 Beam: lower porcelain section extends to top No M3SAP2000 Beam elements with variable cross section IronNo M4DIANA Solid elements with variable cross section IronNo M5DIANA Solid elements with variable cross section IronYesNo M6DIANA Solid elements with variable cross section ActualYes No M7DIANA Solid elements with variable cross section ActualYes 30

Post Insulator F.E. Model Development  Further development in progress  Parametric studies and comparisons with test data  Frequency  Force/ displacement 31

Qualification of Equipment With Varied 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 32

Hybrid Simulation of Disconnect Switch on Support Jaw Post Braced frame support structure 33

Concept for Hybrid Simulation of Disconnect Switch on Support Computational Substructure Insulator Earthquake motion Support structure response or from Physical Substructure (switch jaw end with blade open) shake table test 34

Insulator Calculated support structure response applied to movable platform Physical Substructure (assumed 1D) Movable platform Fixed tracks Dynamic Actuator & Load Cell Earthquake motion Computational Substructure Dynamic DOF i Force feedbac k Displacement command Hybrid Simulation of Disconnect Switch on Support 35

Acknowledgements  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 36