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Field Guide:Visual Inspection of Polymer Insulators
1013283
Effective December 6, 2006, this report has been made publicly available in accordance with Section 734.3(b)(3) and published in accordance with Section 734.7 of the U.S. Export Administration Regulations. As a result of this publication, this report is subject to only copyright protection and does not require any license agreement from EPRI. This notice supersedes the export control restrictions and any proprietary licensed material notices embedded in the document prior to publication.
Field Guide: Visual Inspection of Polymer Insulators
1013283
Technical Update, May 2006
EPRI Project ManagerA. Phillips
ELECTRIC POWER RESEARCH INSTITUTE3420 Hillview Avenue, Palo Alto, California 94304-1395 • PO Box 10412, Palo Alto, California 94303-0813 • USA
800.313.3774 • 650.855.2121 • [email protected] • www.epri.com
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ORGANIZATION(S) THAT PREPARED THIS DOCUMENT:
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Copyright © 2006 Electric Power Research Institute, Inc. All rights reserved.
iii
CITATIONS
This report was prepared byElectric Power Research Institute (EPRI)1300 W.T. Harris Blvd.Charlotte, NC 28262
Principal InvestigatorsA. PhillipsT. Shaw
This report describes research sponsored by EPRI.
The report is a corporate document that should be cited in the literature in the following manner:
Field Guide: Visual Inspection of Polymer Insulators. EPRI, Palo Alto, CA: 2006. 1013283.
CONTENTS
1. Anatomy of a Polymer Insulator . . . . . . . . . . . . . . . .1
2. Definition of Dimensions . . . . . . . . . . . . . . . . . . . . . .5
3. Maintenance Priority Rating . . . . . . . . . . . . . . . . . . .9Maintenance Priority Rating . . . . . . . . . . . . . . . . . . .10
4. Sheds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13Splits and Punctures . . . . . . . . . . . . . . . . . . . . . . . . .14Torn or Damaged . . . . . . . . . . . . . . . . . . . . . . . . . . .16Gunshot Damage . . . . . . . . . . . . . . . . . . . . . . . . . . .18
5. Sheath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21Exposed Rod (Electrical Activity) . . . . . . . . . . . . . . .22Exposed Rod (Mishandling) . . . . . . . . . . . . . . . . . . .24Unclipped Sections . . . . . . . . . . . . . . . . . . . . . . . . . .26Splits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28Gunshot Damage . . . . . . . . . . . . . . . . . . . . . . . . . . .30
6. Sheds and Sheath . . . . . . . . . . . . . . . . . . . . . . . . . . .33Whitening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36Animal Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Undermining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42Alligatoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44Erosions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48Crazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50Fungus or Mold Growth . . . . . . . . . . . . . . . . . . . . . .52Insect Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54Hydrophobicity Loss (SIR) . . . . . . . . . . . . . . . . . . . .56Silicone Grease on Surface . . . . . . . . . . . . . . . . . . .58
v
7. Corona Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61Flashover Damage . . . . . . . . . . . . . . . . . . . . . . . . . .62Incorrect Position . . . . . . . . . . . . . . . . . . . . . . . . . . . .64Loose Ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66Gunshot Damage . . . . . . . . . . . . . . . . . . . . . . . . . . .68
8. End Fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71Flashover Damage . . . . . . . . . . . . . . . . . . . . . . . . . .72Degraded Seal . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76
9. Failure Mode Guide . . . . . . . . . . . . . . . . . . . . . . . . . .79Failure Mode Distribution . . . . . . . . . . . . . . . . . . . . .80Brittle Fracture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82Flashunder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84Destruction of Rod by Discharge Activity . . . . . . . . .86Mechanical Failure: Rod Failure . . . . . . . . . . . . . . . .88Mechanical Failure: End Fitting Pullout . . . . . . . . . . .90
Contact Information . . . . . . . . . . . . . . . . . . . . . . . . . . .93
Anatomy of a Polymer Insulator
ELECTRIC POWERRESEARCH INSTITUTE
Corona Ring (Installed Incorrectly) Corona Ring
Dimension Definition Properties Influenced
Connection Physical location Length of conductors and
hardware in configuration
Dry Arc Power frequency, Distance lightning, and (with no switching surge corona ring) performance
Definition of Dimensions
ELECTRIC POWERRESEARCH INSTITUTE
Dimension Definition Properties Influenced
Dry Arc Power frequency, Distance lightning, and (with corona switching surgering) performance
Leakage Contamination(Creepage flashoverDistance) performance
72.DEFINITION OF DIMENSIONS
Maintenance Priority Rating
ELECTRIC POWERRESEARCH INSTITUTE
Each polymer insulator condition illustrated in this Guide has been assigned a Maintenance Priority Rating which indicates the severity of the problem.
The Maintenance Priority Ranking below is only a recommendation provided by EPRI.
Maintenance Priority Rating
113. MAINTENANCE PRIORITY RATING
MaintenancePriority Rating Definition
A Good or like new. No action required.
B Low degree of damage, wear, decay.Monitor for future damage.
C Moderate degree of damage, wear, decay.Consider replacement.
D High degree of damage, wear, decay.Remove polymer insulator from service.
Maintenance Priority Rating
154. SHEDS
What You See: Splits or punctures in sheds (splits often along mold line).
Possible Cause: Aging and/or poor design or manufacture, mishandling.
Resulting Failure Mode: Exposure of rod � Brittle Fracture, Flashunder, Rod Destruction by Discharge Activity
Rating Observation Action
B Split localized to sheds Monitor for growth ofsplits and possibleprogression to sheath
C Split progressingtowards or close tosheathPuncture through shed
Remove polymer insulator from serviceat next opportunity
Splits and Punctures
C
174. SHEDS
Torn or Damaged
What You See: Torn/damaged sheds – damage does not extend to sheath; rod not exposed.
Possible Cause: Mishandling during shipping, storage, or installation.
Resulting Failure Mode: Tear extends to sheath � Exposure of rod � Brittle fracture, Flashunder,Destruction of rod by discharge activity
C
Rating Observation Action
B Tear is across shed Monitor for growth of splitsand possible progressionto sheath
C Tear has progressed or is progressing to the sheath
Remove polymer insulator from serviceat next opportunity
194. SHEDS
Gunshot Damage
What You See: Sheds punctured/broken by gunshot.
Possible Cause: Gunshot.
Resulting Failure Mode: Discharge activity from lodged bullets � Shed/sheath damage � Exposure of rod �Brittle Fracture, Flashunder, Destruction of rod by discharge activity
B or C
Rating Observation Action
B Damage to sheds only Monitor for growth of splitsand possible progressionto sheath
C Bullets lodged in sheds Monitor for discharge activity, remove polymerinsulator from service atnext opportunity
235. SHEATH
What You See: Severe degradation of rubber and rod is exposed to elements.
Possible Cause: Excessive electrical activity, harsh environment, poor design and/or manufacturing.
Resulting Failure Mode: Exposed rod � Brittle fracture, Flashunder, Destruction of rod by discharge activity
Rating Observation Action
D Exposed rod Remove polymer insulatorfrom service
Exposed Rod (Electrical Activity)
D
255. SHEATH
Exposed Rod (Mishandling)
What You See: Exposed rod and damage to rubber sheath.
Possible Cause: Mishandling during shipping, storage, or installation.
Resulting Failure Mode: Exposed rod � Brittle fracture, Flashunder, Destruction of rod by discharge activity
Rating Observation Action
D Exposed rod Remove polymer insulatorfrom service
D
275. SHEATH
Unclipped Sections
What You See: Rubber sections unclipped from one another or end fitting; rod may be exposed.
Possible Cause: Mishandling during shipping, storage, and installation.
Resulting Failure Mode: Exposed rod � Brittle fracture, Flashunder, Destruction of rod by discharge activity
Rating Observation Action
D Exposed rod- between end fitting and
sheath sections- between sheath sections
Remove polymerinsulator from service
D
295. SHEATH
What You See: Splits along sheath sections.
Possible Cause: Excessive discharge activity and/or weathering of material.
Resulting Failure Mode: Splits extend to rod � Exposure of rod � Brittle fracture, Flashunder, Destruction of rod by discharge activity
SplitsRating Observation Action
C Silicone gel present; rodnot exposed
Monitor for growth of splits,remove at next opportunity
D Exposure of rod Remove polymer insulatorfrom service
C
D
315. SHEATH
What You See: Sheath punctured/damaged by shot. Bullet maybe lodged in rubber.
Possible Cause: Gunshot.
Resulting Failure Mode: Discharge activity � Increased sheath damage � Exposure of rod � Brittle fracture, Flashunder, Destruction of rod by discharge activity
Rating Observation Action
C Sheath damaged – rodNOT exposed
Remove polymer insulator from service at next opportunity
D Exposure of rod or bullets lodged in sheath
Remove polymer insulatorfrom service
Gunshot Damage
C
356. SHEDS AND SHEATH
What You See: Whitening/white powder or film all along sheath surface. More prevalent closer to end fittings and on surfaces facing the sun.
Possible Cause: Exposure of filler compound due to normal weathering.
Resulting Failure Mode: N/A
Rating Observation Action
A White powder or film on surface
No action necessary
Whitening
A
Note: Adjacent sections may have different levels ofwhitening – not an issue.
376. SHEDS AND SHEATH
What You See: Electrically conductive paths along the surface of sheds and/or sheath.
Possible Cause: Leakage currents on highly contaminated polymer insulator surface.Resulting Failure Mode: Tracking � Exposure of rod � Brittle fracture, Flashunder, Destruction of rod by
discharge activityTracking � Flashover
Rating Observation Action
D Conductive path along surface Remove polymer insulator from service
Tracking
*Images Courtesy of EskomResult of Severe Tracking*
D
396. SHEDS AND SHEATH
What You See: Sheds and sheath have been eaten by birds or rodents.
Possible Cause: Birds or Rodents.
Resulting Failure Mode: Damage extends through sheath � Exposure of rod � Brittle fracture, Flashunder, Destruction of rod by discharge activity
Rating Observation Action
A Minor shed damage No action necessaryB Shed damage only Monitor and leave in service
C Sheath damage, rod notexposed
Remove polymer insulator fromservice at next opportunity
D Rod exposed Remove polymer insulator from service
Animal Damage
Image Courtesy of Powerlink
B
416. SHEDS AND SHEATH
What You See: A puncture hole through sheds, usually at the shed/sheath interface.
Possible Cause: Excessive discharge activity.
Resulting Failure Mode: Exposure of rod � Brittle fracture, Flashunder, Destruction of rod by discharge activity
Rating Observation Action
C Sheath damage,rod not exposed
Remove polymer insulator fromservice at next opportunity
D Rod exposed Remove polymer insulatorfrom service
Undermining
C
436. SHEDS AND SHEATH
What You See: Surface Cracks on rubber sheds/sheath greater than 0.1 mm (0.004 in) in depth.
Possible Cause: Harsh environment or poor polymer insulator design/manufacture.
Resulting Failure Mode: Cracks extend through sheath � Exposure of rod � Brittle fracture, Flashunder, Destruction of rod by discharge activity
Rating Observation Action
B Only sheds cracked Monitor for future damageC Sheath and sheds cracked Consider replacement
D Sheath cracked and moisture penetration possible
Remove polymer insulator from service
Cracking
D
456. SHEDS AND SHEATH
What You See: A roughening of the surface resembling the texture of alligator skin. Material is brittleto the touch. The condition is due to loss of filler material.
Possible Cause: Aging of material, harsh environment, or poor design.
Resulting Failure Mode: Excessive material loss � Exposure of rod � Brittle fracture, Flashunder, Destructionof rod by discharge activity
AlligatoringRating Observation Action
A Limited to surface, material is not brittle
No action
B Significant depth Monitor for increased degradation
C Severe embrittlement Consider removal from service
Shed Bottom
A
Shed Bottom
476. SHEDS AND SHEATH
What You See: Loss (erosion) of material on either sheds or sheath, often close to end fittings.
Possible Cause: Excessive discharge activity, leakage currents, harsh environment, poor design and/or manufacture, incorrect application of corona ring.
Resulting Failure Mode: Excessive material loss � Exposure of rod � Brittle fracture, Flashunder, Destruction of rod by discharge activity
Rating Observation Action
B Shallow surface erosion Monitor for progressionof damage
C Deep surface erosion Consider removal from service
D Excessive surface erosion Remove from service
Erosions
B
496. SHEDS AND SHEATH
What You See: Contamination on polymer insulator sheds and/or sheath.
Possible Cause: Pollutants from marine, agricultural, or industrial sources.
Resulting Failure Mode: Excessive contamination and critical wetting conditions � Flashover
Rating Observation Action
A-C Varying levels of contamination
Depends on level andtype of contamination
ContaminationC
516. SHEDS AND SHEATH
What You See: Shallow cracks on shed surface 0.1 mm (0.004 in) or less in depth.
Possible Cause: Weathering.
Resulting Failure Mode: N/A
Rating Observation Action
A Shallow surface fractures None
Crazing
A
536. SHEDS AND SHEATH
What You See: Fungus contamination on polymer insulator sheds and/or sheath.
Possible Cause: Fungal or mold growth.
Resulting Failure Mode: N/A
Rating Observation Action
A-B Fungus or mold accumulation None
Fungus or Mold Growth
A
Note: Current research indicates that fungus or moldgrowth is not an issue in most cases; there may be aconcern in contaminated environments. Continuedresearch is underway, and specific situations mayrequire special actions.
556. SHEDS AND SHEATH
What You See: Insect activity.
Possible Cause: Spiders, caterpillars, or moths make nests, webs, or cocoons on sheath or shed rubber surfaces.
Resulting Failure Mode: Excessive insect activity and critical wetting conditions � Flashover
Rating Observation Action
A Webs, nests, or cocoons present None
B Excessive webs, nests, or cocoons Consider removal or washing
Insect Activity
Sheds and Sheath
ELECTRIC POWERRESEARCH INSTITUTE
Hydrophobicity Loss (SIR) (Silicone Rubber Insulators only)
B A
Total Loss of Hydrophobicity
576. SHEDS AND SHEATH
What You See: Silicone rubber polymer insulator only – Insulator wets out (water does not bead);effect may be localized at live end.
Possible Cause: Aging due to electrical and/or environmental stress.
Resulting Failure Mode: In a contaminated environment, the risk of flashover may increase.
Rating Observation Action
A Localized loss of hydrophobicity None
B Complete loss of hydrophobicity Monitor for damageor contamination
Hydrophobicity Loss (SIR)
Localized Loss of Hydrophobicity
A
596. SHEDS AND SHEATH
What You See: Silicone grease on polymer insulator sheds and/or sheath. Mainly at shed/sheath interface.
Possible Cause: Natural aging of polymer insulator. Happens with certain polymer insulator designs.
Resulting Failure Mode: N/A
Rating Observation Action
A Grease on sheds and/orsheath
Check to see if shedsand/or sheath are split
Silicone Grease on SurfaceA
Corona Rings
ELECTRIC POWERRESEARCH INSTITUTE
Flashover Damage
B
D
Remove from Service
Leave in Service
637. CORONA RINGS
What You See: Corona ring broken/punctured by flashover.
Possible Cause: Flashover due to lightning and/or power arc follow-on currents.
Resulting Failure Mode: Damage to corona ring � Corona activity � Audio noise, Radio Interference
Rating Observation Action
B Damaged but no AN/RI complaints Leave in service
C Damaged with AN/RI complaints Replace at next opportunityand check for other damage
D Serious damage Remove from polymer insulator
Flashover Damage
Leave in Service
B
Corona Rings
ELECTRIC POWERRESEARCH INSTITUTE
Incorrect Position
Correct Position Backwards Installation Correct Position
C
657. CORONA RINGS
What You See: Corona ring installed backwards or in incorrect position.
Possible Cause: Incorrect installation. Check manufacturer’s recommendations.
Resulting Failure Mode: Damaged sheds/sheath � Exposure of rod � Brittle fracture, Flashunder, Destructionof rod by discharge activity
Rating Observation Action
C Corona ring backwards or inincorrect position
Reinstall corona ring correctly;check for degradation of rubber material
Incorrect Position
Incorrect Position
C
Note: Refer to EPRI Guide 1008741, Field Guide: Corona Rings forPolymer Insulators.
677. CORONA RINGS
What You See: Grading ring is loose or not perpendicular to polymer insulator.
Possible Cause: Poor installation or falling ice.
Resulting Failure Mode: Damaged sheds/sheath � Exposure of rod � Brittle fracture, Flashunder, Destruction of rod by discharge activity
Rating Observation Action
C Corona ring is loose Reinstall corona ring correctlyand check for damage toinsulator
Loose RingC
697. CORONA RINGS
What You See: Bullet hole(s) in ring.
Possible Cause: Gunshot.
Resulting Failure Mode: Corona activity � AN/RI
Rating Observation Action
B Damaged but no AN/RIcomplaints
Leave in service
C Damaged with AN/RIcomplaints
Replace at next opportunity and checkfor other damage
Gunshot Damage
B
738. END FITTINGS
What You See: End fitting burned by flashover.
Possible Cause: Lightning and/or power arc follow-on currents.
Resulting Failure Mode: Exposure of rod to moisture � Brittle Fracture, Flashunder, Exposure of Rod to DischargeActivity, possible Mechanical Failure due to end fitting pullout
Rating Observation Action
C End fitting damaged byflashover, rod not exposed
Remove polymer insulatorfrom service at next opportunity
D End fitting damaged byflashover, rod exposed
Remove polymer insulatorfrom service
Flashover DamageD
758. END FITTINGS
What You See: Degraded sealant and rust surrounding end fitting seal.
Possible Cause: Aging, harsh environment, poor design or manufacture, and/or mishandling during installation.
Resulting Failure Mode: End fitting seal failure � Moisture penetration � Brittle fracture, Flashunder,Destruction of rod by discharge activity
Rating Observation Action
C Degraded endfitting seal
Remove polymer insulator fromservice at next opportunity
B Degraded end fitting seal
Monitor for progression ofdamage
Degraded SealC
778. END FITTINGS
What You See: Corrosion (rust) on polymer insulator metal end fittings.
Possible Cause: Harsh environment and/or poor galvanization.
Resulting Failure Mode: End fitting seal failure � Moisture penetration � Brittle fracture, Flashunder, Destruction of rod by discharge activityEnd fitting failure � Mechanical failure
Rating Observation Action
B Corrosion and rust accumulation of end fitting
Monitor for further damage
Corrosion
B
Failure Mode Guide
ELECTRIC POWERRESEARCH INSTITUTE
Failure Mode Distribution: Based on 221 failures recorded in EPRI Failure Database
Although EPRI has endeavored to collect information about as many failures as possible,only a percentage of the failures to date have been recorded. Most failures collected have beenin North America. If you have information about any failures that may not be recorded pleasecontact Dr. Andrew Phillips, [email protected], 704.595.2234.
Failure Mode Distribution
819. FAILURE MODE GUIDE
0.5%
8.1%10.4%
24.9%
51.1%
BrittleFracture
Flashunder MechanicalFailure:
Rod Failure
Destruction of Rod by Discharge
Activity
End Fitting Pullout
Failure Mode
% o
f Fa
ilure
s R
eco
rded
(22
1)
5%
15%
25%
35%
45%
55%
Failure Mode Distribution
Failure Mode Guide
ELECTRIC POWERRESEARCH INSTITUTE
Brittle Fracture
Broomstick
Fracture Planes
Axial Delamination
839. FAILURE MODE GUIDE
Type: Mechanical.Identifying Features: Flat Fracture Plane (single or multiple), Multiple fracture planes maybe separated by axial
delamination. Broomstick.Possible Cause: Moisture coming in contact with fiberglass rod. Moisture penetration occurs either through
end fitting seal or through rubber weathershed system.51% of 221 Failures Collected
Brittle Fracture
Failure Mode Guide
ELECTRIC POWERRESEARCH INSTITUTE
Flashunder
Tracking Through Rod Tracking Through/Along Rod/Rubber Interface
859. FAILURE MODE GUIDE
Flashunder
Type: Electrical.Identifying Features: Tracking through the rod or along the rod/rubber interface. Extends significant length of
insulator. Puncture holes and splits along length of polymer insulator due to power arc and internal discharge activity bursting out.
Possible Cause: Moisture coming in contact with fiberglass rod. Moisture penetration occurs either throughend fitting seal or through rubber weathershed system.
25% of 221 Failures Collected
Tracking Through Rod Splits and Puncture Holes
879. FAILURE MODE GUIDE
Destruction of Rod by Discharge Activity
Type: Mechanical.Identifying Features: Charred / carbonized fiberglass rod. Often frayed ends of fibers exposed.
Possible Cause: Moisture coming in contact with fiberglass rod. Moisture penetration occurs either through end fitting seal or through rubber weathershed system.
8% of 221 Failures Collected
899. FAILURE MODE GUIDE
Mechanical Failure: Rod Failure
Type: Mechanical.Identifying Features: Rod Failure - Broken rod and / or frayed fibers.
Possible Cause: Manufacturing issues (QC) or mishandling during storing, transporting and installing.Usually occurs due to mishandling (See image marked 2).Three cases have been observed due to overheating of the rod during manufacturing and severe overload (See images marked 1).
10% of 221 Failures Collected
1 2
919. FAILURE MODE GUIDE
Mechanical Failure: End Fitting Pullout
Type: Mechanical.Identifying Features: Pullout – rod separated from end fitting. Occurs on both crimped and epoxy cone end fittings.
Possible Cause: Manufacturing issues (QC) or mechanical overstress or degradation of epoxy compound(See images marked 3).
1% of 221 Failures Collected
3 3
Failure Mode Guide
ELECTRIC POWERRESEARCH INSTITUTE
If you experience, or have experienced, any failures of polymer insulators, it would be appreciated if you could informEPRI of these failures. By recording failures in a central repository, industrywide issues and concerns can be identified.By making the industry aware of these concerns, unexpected failures may be avoided in the future. Your assistance inthis regard is appreciated.
If you have any questions about the information provided in this Guide, if you want to communicate findings or actions taken in the field, or if you have suggestions for making the Guide more useful to you, please contact Dr. Andrew J. Phillips at EPRI (see contact information below).
93
Contact Information
Dr. Andrew J. PhillipsTransmission and SubstationsEPRIP.O. Box 217097Charlotte, NC 282219625 Research DriveCharlotte, NC 28262
Cell: 704.953.4030Tel: 704.595.2234
Fax: 704.595.2867E-mail: [email protected]
NOTE: If you find any new conditions that are not identified in this guide, please send us a detailed description, along with any photographs.
Thank you.CONTACT
Other EPRI Visual Field Guides
Corona Rings for Polymer Insulators, 1008741Visual Inspection of Steel Structures, 1012311
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1013283ELECTRIC POWER RESEARCH INSTITUTE
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