Stu Nishenko, Khalid Mosalam, Shakhzod Takhirov, and Eric Fujisaki SEISMIC SEISMIC PERFORMANCE OF PERFORMANCE OF INSULATORS IN INSULATORS IN ELECTRIC ELECTRIC SUBSTATIONS SUBSTATIONS
Dec 23, 2015
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
2
+ + +
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
3
Insulators in Substation EquipmentInsulators in Substation Equipment
Circuit breaker bushings, interrupter housings, and support columns
4
Interrupter
Bushings
Insulators in Substation EquipmentInsulators in Substation Equipment
Transformer bushings,Surge arresters
5
Surge arrester
Bushing
Insulators in Substation EquipmentInsulators in Substation Equipment
Instrument transformers6
Insulators in Substation EquipmentInsulators in Substation Equipment
Bus supports
7
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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