Polymer Insulator Survey 2002: Utility Field
Experience and In-Service Failures
Product ID 1007752
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Polymer Insulator Update 2002: Utility Field
Experience and In-Service Failures
Product ID 1007752
Technical Update, March 2003
EPRI Project Manager
A. Phillips
EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA
800.313.3774 • 650.855.2121 • askepri@epri.com • www.epri.com
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CITATIONS
This document was prepared by
EPRI
3412 Hillview Ave.
Palo Alto, CA 94303
Principal Investigator
A. Phillips
This document describes research sponsored by EPRI.
The publication is a corporate document that should be cited in the literature in the following
manner:
Polymer Insulator Survey 2002: Utility Field Experience and In-Service Failures, EPRI, Palo
Alto, CA, 2003.1007752.
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ABSTRACT
Polymer insulators, also known as composite or non-ceramic insulators (NCI), are proliferating
on transmission systems due to their ease of handling, resistance to vandalism, and relatively low
cost. Polymer insulators are a relatively new technology with certain advantages and
disadvantages. Long-term field experience remains limited, and the number and type of failures
that have occurred are not well defined. To help fill information gaps, EPRI conducted a survey
of electric utility field experience with polymer insulators.
Survey results provide the industry with essential information for making better decisions
regarding the selection, application, and maintenance of polymer insulators—and ultimately
extend polymer insulator life expectancy and avoid outages from premature failures.
Additionally, survey results pertaining to insulator failures will be added to the NCI Failure
Database that EPRI started in 1997. This database contains detailed information about individual
insulator failures and contains photographs of the individual failures where possible.
This Technical Update describes the survey and presents its findings, which include utility field
experiences with polymer insulators, data on in-service failures, and an analysis of the failure
database. The update also presents an overview of EPRI's polymer insulator research.
Together with other deliverables from EPRI's comprehensive polymer insulator research effort,
the survey results and failure database will help member utilities to increase transmission service
reliability and reduce operations and maintenance costs through the correct selection and
application of this technology.
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CONTENTS
1 INTRODUCTION AND DESCRIPTION OF SURVEY............................1-1
2 SURVEY RESPONSES .........................................................................1-1
3 FAILURES OF POLYMER INSULATORS IN SERVICE.......................3-1
4 ANALYSIS OF THE POLYMER INSULATOR FAILURE DATABASE.4-1
5 EPRI RESEARCH IN POLYMER INSULATORS ..................................5-1
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1
INTRODUCTION AND DESCRIPTION OF SURVEY
Introduction
Although the use of polymer insulators—also called composite or non-ceramic insulators
(NCI)—has become more widespread, the extent to which they are used remains largely
unknown. Service experience and the number of failures that have occurred are also not well
defined. To address this issue EPRI performed a survey of electric utility experience with
polymer insulators in October and November 2001.
Survey results will provide the industry with valuable information to support better decision
making regarding the selection, application and maintenance of polymer insulators.
Additionally, results pertaining to insulator failures will be added to EPRI's NCI Failure
Database that EPRI started in 1997. This database not only contains detailed information about
individual insulator failures, it also contains photographs taken of the individual failures where
possible. This database is unique in that it is not a static snapshot of the current situation with
regards to failures, but is rather a living database with detailed information about individual
failures that is added to as failures occur.
Survey Description
The survey was performed by email and telephone. The survey consisted of two components:
1. A questionnaire regarding the utilities' previous and current usage of polymer insulators as
well as application information. The questionnaire addressed:
•
Reasons for using polymer insulators
•
Configurations
•
Voltage levels
•
Manufacturers
•
Inspection, removal and laboratory testing
•
Corona (grading) rings
2. Detailed information about individual failures that utilities may have experienced. Utilities
often submitted images of the failures. The failure information obtained was added to the
EPRI NCI Failure Database.
Identifying the correct individual to complete the questionnaire often required a number of phone
calls and emails. It is possible that within a single utility that more than one person was qualified
to complete the questionnaire, and that the answers supplied by different individuals may differ.
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The answered obtained are therefore “to the best knowledge” of the individual identified in each
utility.
The answers to certain questions were also often approximations, e.g., number of polymers
installed. When interpreting the results this should be taken into account.
The survey was limited overhead transmission line insulators, i.e., 69 kV and above.
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2 SURVEY RESPONSES
Utilities Surveyed, Removal From Service, and Failures
Approximately 140 utilities were contacted to participate in the survey, and 70 utilities provided
results. All the utilities contacted were based in the United States and Canada except for one
utility based in Southern Africa.
Of the 70 utilities that completed the survey, 65 utilities used polymer insulators on their
transmission systems and five did not. The level of usage of polymer insulators varied from
application on test lines to widespread usage.
Of the 65 utilities that had applied polymer insulators on their system, six no longer install them.
Another four utilities stated that in the future they plan to only apply polymer insulators on a
limited basis in special situations, such as in high-vandalism areas.
We were unable to obtain information on the total number of units in-service from the utilities
surveyed. Record keeping appears to be poor and information is difficult and labor-intensive to
obtain. Most of the numbers obtained from utilities were "best guesses."
Of the 65 utilities using polymer insulators, 60 were able to identify the year in which they
started applying them. Figure 2-1 graphically represents the results. The average year that the
respondents started using polymer insulators was 1985.
8
7
Results from 60
Utiltit
No. of Utilities
6
5
4
3
2
1
2001
1999
1997
1995
1993
1991
1989
1987
1985
1983
1981
1979
1977
1975
1973
0
Figure 2-1: The number of utilities that started applying polymer insulators in a specific year
A number of utilities remarked that the year they specified for using polymer insulators was
when they installed a “test line.” They did not actually begin widespread use of polymers until a
later date.
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Thirty-six of the 65 utilities had removed polymer insulators from service due to concerns of
their continuing reliable operation. Twenty-six utilities were confident that they had not
removed any units due to concerns and three utilities did not know whether they had removed
units from service. Approximately 7000 polymer insulators had been removed from service due
to concerns of reliability. The age of the units removed was undefined.
Of the 65 utilities that applied polymer insulators, 36 (55%) had experienced failures and 29
(45%) had not. A more detailed analysis of failures may be made and published in a separate
publication.
Reasons for Using Polymer Insulators
Utilities cited a wide range of reasons for using polymer insulators rather than traditional ceramic
insulators. The 65 utilities provided 150 reasons for using polymer insulators, and many utilities
cited more than one reason. Figure 2-2 provides a breakdown of the responses.
Other
4%
Delivery
3%
Performance
3%
Lack of porcelain
manufacturers
3%
Mechanical
Strength
3%
Lightweight
42%
Less Maintenance
4%
Resistance to
contamination
7%
Gun
shot/vandalism
13%
Cost
18%
Figure 2-2: Reasons for applying polymer insulators (out of 150 reasons provided by the
respondents)
The main reason given for using polymer insulators is that they are lightweight and hence easy to
handle. Cost and resistance to vandalism (gunshot damage) were also cited as important reasons
for selecting polymer insulators. The category labeled “Other” in Figure 2-2 includes “variable
end fitting types,” “to gain experience,” “industry trend,” “environmentally compatible” and
“safety.” Each of these represented less than 2% of the total responses and hence they were
grouped under “Other”.
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Configurations
Figure 2-3 shows in what configurations the 65 utilities utilized the polymer insulators. It can be
seen that most common configurations in which polymer insulators are applied are suspension
and post insulators.
60
86%
85%
50
65 out of 70 utilites use
polymer insulators
40
30
42%
28%
20
10
0
Suspension
Dead End
Post
Braced Post
Figure 2-3: Number of utilities that utilize polymer insulators in different configurations
An important finding is that only 28% of the utilities surveyed utilize polymer insulators in deadend configurations compared to 86% that apply polymer insulators in suspension configurations.
The reason for this was not asked in this survey but it maybe surmised that dead-end insulators
are considered higher risk.
Voltage Levels
Figure 2-4 shows how many utilities apply polymer insulators at each voltage level. Also shown
is the number of utilities that have transmission lines at each of the voltage levels.
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70
110%
Count of Utilitites with Voltage Level
60
89%
Number of Utilities
50
71%
100%
% use of Polymer Insulators
90%
86%
70%
69%
63%
40
50%
50%
30
30%
25%
20
10%
10
0
Perecentage Use of Polymer Insulators
Count of Utilities Using Polymer Insulators @ Voltage Level
-10%
69
115-138
161
220-230 275-360 400-500
765
400-500
DC
Voltage Levels (kV)
Figure 2-4: Number of utilities that apply polymer insulators at each voltage level as well as the
number of utilities that have transmission lines at each voltage level. The line indicates the results
as a percentage
It can be seen from Figure 2-4 that for AC transmission the largest percentage of utilities apply
polymer insulators at the 115–138 kV level with the 220-230 kV level next. The percentage of
utilities applying polymers reduces as the voltage increases. When considering the results at 69
kV, it should be noted that since only transmission companies were surveyed.
It should also be kept in mind that Figure 2-4 only indicates the number of utilities that use
polymers at specific voltage levels. Figure 2-4 provides no indication as to the number of units
applied.
Number of Units in Service and Service Experience
Each of the major manufacturers that supply the North American Market were contacted and the following
information requested:
1. Number of unit sold in North America - 69kV and above - both suspension and post.
2. Number of insulator years in-service in North America (calculated by multiplying the number of
insulators sold in any year by the age today).
Results were obtained from the following manufacturers: Ohio Brass, NGK, Reliable, Sediver and K-line.
No results were obtained for any other manufacturers.
It was reported that the total number of suspension and post units including and above 69kV sold to the
North American market was 3,938,000 units. The total number of service years indicated was 25,163,000
(the service years indicated is based on the date of sale, not on the date of installation).
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Based on the above results it maybe calculated that the average age of the polymer insulators sold is 6.4
years (for the manufacturers that provided information). For individual manufacturers the average values
vary between 2.8 and 8.7 years. It should be noted that these are average values.
These results are considered to be best estimates and may include some inaccuracies. Although all of
the major manufacturers continuing to service the market are represented, no information was obtained
about a major design that is longer marketed.
Manufacturers
Figure 2-5 shows how many utilities have applied polymer insulators from each of the main
manufacturers.
50
45
71%
66%
40
55%
No. of Utilities
35
45%
30
25
20
15
17%
10
8%
5
2%
3%
H
Other
0
A
B
C
D
E
F
Manufacturer
Figure 2-5: Number of utilities that have applied polymer insulators from the main manufacturers.
The data labels indicate a percentage of the total number of utilities that apply polymer insulators.
It should be noted that Figure 2-5 does not indicate how many units have been applied from each
manufacturer, and hence provides no market share information.
Inspection, Removal, and Laboratory Testing
Of the 65 utilities that applied polymer insulators, 52 reported that they inspected their polymer
insulators while in service and 13 did not. This result may be misleading, as it appears that most
respondents were referring to generic inspections rather than specific polymer insulator
inspections. Figure 2-6 shows the types of inspections that are utilized and how many utilities
use these techniques.
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45
60%
40
35
45%
30
25
20
15
12%
10
5
3%
2%
0
Bucket Truck
Climbing
Heli flyby
Heli hover
Walking
Figure 2-6: Number of utilities that use different inspection techniques
As can be seen from Figure 2-6, walking and fast flyby inspections are the most common. The
EPRI report, Assessment and Inspection Methods (TR-104449-V2) published in 1995, showed
that walking inspections are more effective than fast flyby inspections while climbing
inspections were found to be the most effective. It should be noted that EPRI research has also
shown that training inspectors to identify defective polymer is also essential for effective
inspections. A number of EPRI tools are available to aid in training of staff. These include
Guide to Visual Inspection of NCI (1000098) and an educational video, Storing, Transporting
and Installing Polymer Insulators (1006467). These products can be ordered from
www.epri.com.
The EPRI base-funded Overhead Transmission Assessment and Inspection Methods Project is
also developing educational tools to address training issues. Anyone interested in the research
effort should contact Andrew Phillips, aphillip@epri.com.
Inspection
Technique
Bucket Truck
Climbing
Fast Flyby
Hovering
Walking
No. of Utilities
using
technique
2
8
29
1
39
No. of Utilities
that indicated
schedule
1
3
12
1
20
Range of
Inspection
Schedule
12 months
48-60 months
6-12 months
As needed
6-60 months
Average
Inspection
Schedule
12 months
56 months
7.8 months
As needed
19.6 months
Table 2-1: Comparison of inspection schedule for different techniques. Since not all of the
utilities surveyed answered the questions, the number that provided schedule information is
indicated.
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It can be seen from Table 2-1 that although fast flyby inspections are less effective than walking
inspections for identifying defective units, they are conducted on a more regular basis.
Twelve of the utilities that perform inspections utilized inspection tools to inspect the polymer
insulators and other components on the transmission line. Figure 2-7 shows the range of
inspection tools utilized by the individual utilities and the number of utilities that use these tools.
Only one utility utilizes more than one type of inspection tool.
7
Number of Utiltites
6
5
4
3
2
1
0
Binoculars
Daytime Corona
Camera
IR
Nightscope
Stabilized
Binoculars
Figure 2-7: Inspection tools used by utilities surveyed
Figure 2-7 shows that most utilities that inspect their polymer insulators do not use inspection
tools, i.e., only 12 out of 52 used inspection tools. The most common inspection tools used are
infrared cameras and binoculars (both stabilized and non-stabilized). All of the inspecting
utilities did visual inspections and it is surmised that, although not indicated by the responses,
most inspectors had access to binoculars for the visual inspections.
The EPRI base-funded Enhanced Non-Ceramic (Polymer) Insulator research project is currently
researching and developing new inspection tools to identify high-risk polymer insulators inservice. Anyone interested in the research effort should contact Andrew Phillips,
aphillip@epri.com.
Only 35% of the 65 utilities applying polymer insulators performed laboratory testing on units.
It was unclear whether this testing was on new or in-service units.
Corona (Grading) Rings
The results of the corona ring section of the survey maybe summarized as follows:
•
Above 200 kV, all utilities, apart from one at 345 kV, use corona rings.
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•
At 161 kV, five out of nine utilities do not use corona rings.
•
At 115/138 kV, two utilities use corona rings
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3 FAILURES OF POLYMER INSULATORS IN
SERVICE
In 1997 EPRI started a database recording failures of transmission polymer insulators in the
field. Information, and images where possible, are obtained on each individual failure and stored
in an electronic database, which maybe queried at a later date. Information on failures as far back
at the 1970s was obtained.
Information is obtained from the relevant utility using a questionnaire containing a range of
standard questions. Often the utility is unable to answer all of the questions in the questionnaire.
This is often the case when utilities provide information on failures that did not occur recently.
Description of Failures
For purposes of the database a failure was defined as either of two conditions:
•
The insulator was unable to insulate the line from ground
•
The insulator lost its mechanical strength.
Precluded from this survey are two types of failures:
•
Flashover due to external contamination, e.g., due to marine pollution
•
Failure due to extreme mishandling, e.g., the unit is broken during installation
The main failure modes of polymer insulators are described below. This material is not intended
to be comprehensive. Rather, it is intended to be a brief overview of the main types of failure
modes. More detailed descriptions of failure modes are presented in the EPRI report Application
Guide for Transmission Line NCI (TR-111566).
Brittle Fracture (Stress Corrosion Cracking of Fiberglass Rod)
Brittle fracture failures are a mechanical failure of the fiberglass rod, i.e., a complete separation
as shown in Figure 3-1.
Features of a brittle fracture are:
•
One or more smooth, clean planar surfaces, mainly perpendicular to the axis of the fiberglass
rod giving the appearance of the rob being cut.
•
Several planar fracture planes separated by axial delaminations.
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•
Residual mechanical fracture surfaces, i.e., broomstick.
Broomstick
Axial
Delamination
Planar Fracture
Planes
Figure 3-1: Photograph of a brittle fracture. Note the several separate flat transverse fracture
planes and the “broomstick.”
Brittle fractures are caused by chemical attack of the fiberglass rod [correct?] when nonsiliceous ions are leached from the fibers and the surrounding thermoset resin matrix is
hydrolyzed. This chemical attack together with the mechanical load results in a transverse crack.
The crack will continue to develop until the remaining cross section of the rod can no longer
support the applied load and total separation occurs. Brittle fractures are more accurately called
stress corrosion cracking.
Flashunder (Tracking in or along fiberglass rod and the resulting flashover)
Flashunder is an electrical failure mode. This failure mode occurs when moisture comes in
contact with the fiberglass rod and tracks up the rod, or the interface between the rod and rubber.
When the moisture—and by-products of discharge activity due to the moisture—extend a critical
distance along the insulator, the insulator can no longer withstand the applied voltage and a
flashunder occurs.
Features of a flashunder include:
•
Tracking through the rod or along the rod-rubber interface
•
Puncture holes and splits along length of insulator due to internal discharge activity and the
power arc during failure.
Figure 3-2 shows images of a flashunder and the associated features.
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Tracking through rod or
along rod / rubber
Splits and puncture
Two halves of a dissected polymer insulator that
has failed due to a flashunder.
External photograph of the live end of an insulator
that has failed due to a flashunder.
Figure 3-2: Two photographs showing a flashunder and the associated features
In a number of cases after a flashunder occurs and the line is reenergized, the insulator may
provide sufficient insulation to prevent an immediate outage. This is due to the resulting power
arc drying out the insulator and improving the insulation ability of the unit. However, with time
or renewed wetting the unit may result in further outages until the progressive damage renders
the insulator useless.
Destruction of rod by discharge activity
Destruction of the rod by discharge activity is a mechanical failure mode. Moisture and other
contaminants penetrate the weather-shed system and come in contact with the rod resulting in
internal discharge activity. These discharges destroy the rod until the unit is unable to hold the
applied load and the rod separates.
Dissection of failed unit.
End fitting of failed unit.
Figure 3-3: Photographs of unit that failed due to destruction of the rod by discharge activity
Mechanical Failure due to End Fitting Pullout or Mechanical Failure of the Rod
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These are mechanical failure modes. In these cases either the rod mechanically fails when the rod
separates from the end fitting or the rod it self mechanically fails. These failures may occur due
to errors in the manufacturing process, e.g., overheating of the fiberglass rod, decomposition of
the epoxy in an epoxy cone type end fitting, etc. Care has been taken not to include failures of
this type that are the result of mishandling or overloading. Figure 3-4 shows an example of a
unit that has failed due the rod pulling out of the end fitting due to decomposition of the epoxy
cone.
Dissected end fitting of failed unit.
Rod from failed unit.
Figure 3-4: Photographs of unit that failed due to decomposition of the epoxy cone
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4 ANALYSIS OF POLYMER INSULATOR FAILURE
DATABASE
As of September 2002 EPRI has collected 161 failures from 48 different utilities. With four
exceptions, all of the failures were collected from North American utilities. Of the 161 failures,
130 occurred in North America.
Although the database contains a comprehensive number of failures in North America, no
attempt was made to collect information on a significant number of failures internationally due to
the logistics involved. A review of a recent paper, IEEE Task Force Report: Brittle Fracture in
NCI, PE-504PRD (02-2002) indicates that there are an additional 46 international brittle fracture
failures that are not included in the EPRI failure database. The Task Force report only reported
brittle fracture failures and hence the total number of failures worldwide may be larger. The total
number of failures worldwide therefore exceeds 200.
It should also be kept in mind that not all of the failures that have occurred are recorded in the
EPRI failure database. EPRI is continuing to obtain failure information to increase the accuracy
of the database and results.
Failure Rates
Of the 130 failures reported in North America, 60 related to the manufacturers that provided information
on the number of units sold. Based on this information the average failure rate for all the manufacturers
that provided sales information was 1 in every 65,500 units sold. Apart from one manufacturer that has
experienced no failures, the individual manufacturer failure rates varied from 1 in every 65,000 to 1 in
every 31,000 units sold.
Utilizing the average failure rate data indicated above maybe misleading as 70 of the failures in the
database (not accounted for in the above analysis) were for a design no longer in service and for which
no sales information was available. If sales data for this design could be obtained and the 70 failures
could be taken into account the average failure rate for installed units would be higher.
Year, Age and Installation Date of Failed Units
Figure 4-1 shows the years in which the failures recorded in the database occurred.
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25
No. of Failures
20
15
10
5
19
79
19
80
19
81
19
82
19
83
19
84
19
85
19
87
19
88
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
n/
a
0
Year
Figure 4-1: Graph showing the years in which the failures were reported to have occurred. (N/A =
the year of the failure was undefined.)
It is expected that the percentage of failure captured by the database increased after 1997 as
failures were actively sought.
Figure 4-2 shows the age of the units that failed calculated from the date of installation and date
of failure. The age of 48 of the failures could not be determined, mostly due to incomplete utility
records regarding installation date.
14
12
No. of Failures
10
8
6
4
2
0
0 1
2
3 4
5 6
7 8
9 10 11 12 13 14 15 16 17 18 20 29
Age in Years
Figure 4-2: Age of failures in years
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As can be seen a large number of failures occur within two years of installation. This could be
seen as weeding out the bad actors or units that initial defects.
20
18
16
No. of Failures
14
12
10
8
6
4
2
19
70
19
79
19
80
19
81
19
83
19
84
19
85
19
86
19
87
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
0
Year of Installation
Figure 4-3: Year of manufacture of failed units
Accurate values for the year of installation were only available for 70% of the failures. Although
approximate dates are available for a large portion of the remaining 30%, the data are not
represented in Figure 4-3.
Failure Modes and Reasons for Failures
The modes of failure of the collected data are shown in Figure 4-4.
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100
90
Total No. of Brittle Fractures = 136
with IEEE TF Worldwide Data
No. of Failures
80
70
60
50
Worldwide
North America
40
30
20
10
0
Brittle
Fracture
Flashunder
Mechanical
Failure
Rod
destroyed by
discharge
activity
N/A
Failure Mode
Figure 4-4: Graph indicating the number of insulators that failed from each type of failure mode. (N/A
indicates that the failure mode could not be confirmed or that the failure is still under investigation.) Note
that the worldwide number of failures recorded is low. If the worldwide data from the IEEE TF report were
included, the total number of brittle fractures would be 136.
As can be seen from Figure 4-4, the main failure mode is brittle fracture followed by flashunder.
The column labeled N/A indicates that the failure mode could not confirmed by the utility or that
the failure is still under investigation. In most cases the failure modes were determined by
EPRI, third party, and manufacturer investigations.
Figure 4-5 shows the reason for failure for the recorded failures. N/A indicates that conclusive
information regarding the reason for failure could not be obtained or the failure investigation is
still underway.
100
90
No. of Failures
80
70
60
50
40
30
20
10
0
Rod overheated
during molding
Manufacturer
Defect
Water ingress
thru polymer
weather shed
system
N/A
Water ingress
thru end fitting
seal
Reason for Failure
Figure 4-5: Reason for failure
It can be seen from Figure 4-5 that main reason for failure is water ingress through the end fitting
seal. Care should be taken in attributing all of these failures to manufacturer defects alone. In
fact a significant portion maybe attributed to mishandling. A common reason for failure due to
mishandling is over torquing of the unit during installation, which in turn damages the end fitting
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seal. It is often difficult at time of failure to determine whether a unit was mishandled during
installation. In actual fact only seven of the utilities that provided information noted that the
units were mishandled. Even in cases where the manufacturer's report on the failure indicated
mishandling, the corresponding utility did not necessarily indicate or agree that mishandling was
involved
Description of Units that Failed
The voltage level, weather shed material type, insulator type, manufacturer and grading ring are
all parameters one can consider when evaluating the failures recorded.
60
No. of Failures
50
40
30
20
10
0
69-90kV
115-161kV
230-275kV
345-400kV
500kV
765kV
Voltage Level
Figure 4-6: Number of failures as a function of voltage level
It can be seen from Figure 4-6 that failures occur across all the voltage ranges. Care should be
taken when interpreting the results shown. It should be kept in mind that at the lower voltages the
likelihood of the failure being reported, both internal to the utility and to EPRI, is lower. The
number of miles that exist at each voltage level and the number of polymer insulators applied at
these voltage levels also need to be taken into account.
1%
EP
SIR
N/A
37%
62%
Figure 4-7: Split of failures between different rubber types. Note: SIR/EP alloy base insulators
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have been included with EP insulators. N/A indicates that the utility that submitted the data was
not sure of the rubber material type.
90
80
70
No. of Failures
60
50
40
30
20
10
0
Suspension
Dead End
Post
Braced Post
Other
Unknown
Figure 4-8: Configuration of the failures. Note: Other refers to configurations not covered by the
standard terminology often due to lack of standardization in nomenclature. Unknown usually
occurred when the failure happened a considerable amount of time prior to the questionnaire
being completed, or incomplete field reports were submitted.
The largest number of failures reported occurred on suspension units. It should be noted that the
population of suspension units is far larger than dead-end units, hence the failure rate for deadend units is probably higher than that for suspension units.
80
Rod destroyed by discharge
activity
N/A
70
Mechanical Failure
No. of Failures
60
Flashunder
50
Flashover
40
Brittle Fracture
30
20
10
0
A
C
D
E
F
H
N/A
Manufacturer
Figure 4-9: The number of failures sustained by different manufacturers subcategorized by failure
mode
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As can be seen from Figure 4-9, the lion's share of the failures recorded in the database have
been sustained by one manufacturer. When interpreting these results the total number of units
installed by each manufacturer should be taken into account. Some of the manufacturers shown
have a very small portion of the total market in the area surveyed.
Of the 105 failed polymer insulators that were applied at voltage levels equal to and greater than
230 kV, 65% had corona rings installed, 32% did not have grading rings installed and
information was not available 5% of the units.
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5 EPRI RESEARCH IN POLYMER INSULATORS
Polymer insulators are a relatively new technology. As the industry gains experience and
confidence in applying polymer insulators, the number of units being applied will increase. In
order to address unknowns associated with polymer insulators, EPRI has undertaken a multiyear
research effort to address a range of important issues, including:
•
Selection of Polymer Insulators
•
Application
•
Inspection
•
Live Working
•
Fundamental Research
Past Deliverables
Over the past decade EPRI has produced numerous deliverables that are available to EPRI
members. These include:
Application Guide for Transmission Line NCI (TR-111566), November 1998 - This report will
aid utility engineers involved with designing, procuring, installing, handling, inspecting, and live
working with NCI. The report also provides information on the makeup of NCI, test methods,
standards, failure modes, assessment procedures, and how to apply NCI in contaminated
environments.
Electric Field Modeling of NCI and Grading Ring Design and Application (TR-113977),
December 1999 - This report aids utility engineers in the application of grading rings on NCI to
grade the surrounding electric field to prevent premature NCI aging and unwanted audio noise
and radio interference. The application of grading rings is discussed in detail and methods of
evaluating grading ring designs are given. The report also discusses methods of modeling NCI
using both FEM and BEM methods and discusses approximations that may be made. A section
on understanding grading ring design is presented as well as examples of E-field magnitudes that
have been determined for NCI applied between 115 kV and 500 kV.
Initial Investigation into the Effect of Elevated Conductor Temperature on the Operation of
NCI (1000033), April 2000 - This report describes an initial investigation into the effect of
elevated conductor temperatures on the operation of NCI. The testing determined the
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temperatures that an NCI end fitting would be subjected to if an NCI were applied with minimal
hardware and the conductor temperature reached 200°C. The results are compared against
previous testing and manufacturers' recommendations.
Guide to the Visual Inspection of NCI (1000098), June 2000 - This guide provides a catalog of
photographs that illustrate various conditions and factors that commonly affect NCI in the field,
along with their possible causes, a risk-assessment rating, and suggested actions for utility
personnel. The guide is designed to aid utility field crews in assessing the condition of NCI in
service, identifying specific problems, and deciding on a course of action. We believe it will
also facilitate a discussion of the findings and results between utility crews, engineers, managers,
and researchers. The report maybe obtained by downloading a PDF file from EPRIweb or in
black and white from the EPRI Distribution Center. High-quality color copies of this report have
been printed and are available from (413) 499-5701.
500 kV Non-Ceramic Insulator Aging Chamber: Final Report (1000719), December 2000 This report describes the 500 kV aging test in which more than 20 NCI from five different
manufacturers were evaluated for more than six years in an accelerated environment. The
stresses to which the insulators were subjected as well as the condition of the insulators during
and after the test are described. This report is intended to aid utilities in selecting NCI and
comparing different designs.
Storing, Transporting and Installing Polymer Insulators, (1006353), September 2001 - This
educational video helps utilities educate transmission line workers and warehouse staff on
correct handling procedures for polymer insulators.
Storing, Transporting and Installing Polymer Insulators: Viewing Guide for Educational
Video (1006467), November 2001 - A viewing guide that personnel who have watched the
video may take away with them as a set of notes. The viewing guide is pictorial and is based on
the educational video described above.
Identifying Defects in Polymer Insulators that are Detrimental to Live Working (1001747),
July 2002 - The lack of appropriate tools and techniques to live working in and around polymer
insulators has been cited as the single largest reason why transmission asset owners are reluctant
to embrace this technology. This technical progress report covers a background study that
outlines the concerns and then surveyed what is presently being researched both with EPRI and
elsewhere. The report provides a springboard for future research activities to develop tools
capable of assessing the integrity of polymer insulators before and during live working.
Ongoing Research
The EPRI Overhead Transmission Program is undertaking a comprehensive research effort to
address the range of issues associated with polymer insulators. Tasks that are currently under
way include:
230 kV Aging Test - An accelerated aging test was initiated in January 2001 at EPRI's field
testing laboratory in Lenox, MA, to compare the long-term performance of 35 polymer insulators
from five manufacturers in four different configurations (i.e., V-string, I-string, dead-end post,
and braced post). The results of these aging tests will aid utilities in the selection of the proper
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polymer insulators; the condition assessment of polymer insulators already in-service; and the
selection of most effective grading ring designs. It is expected that this test will run until the end
of 2003 and the results will be published in 2004. The aging test is described in detail in a
technical brief, New 230 kV Aging Chamber to Test Transmission/Substation Components
(1001463), which may be ordered from www.epri.com.
End Fitting Assessment - The design of six different end-fitting seals has been evaluated using
an accelerated aging test. The aging test included mechanical, environmental and electrical
stresses. The mechanical performance on the attachment of the fiberglass rod onto the end fitting
under combined static load, torquing and aeolian vibration. The test results of this investigation
will be published at the end of 2002.
Development of Corona Ring Inspection and Installation Guide - A field guide is being
developed to assist utility personnel in the installation and inspection of corona rings. The guide
covers the installation procedure for five different manufacturers in pictorial form. A pictorial
inspection guide for units already in-service is also included. The inspection guide provides
criteria on what action to take if a specific type of condition is observed.
Development of In-Service Inspection Tools - As the population of in-service polymer
insulators increases and ages, inspection will only increase in importance. EPRI is researching
and developing new inspection tools to identify high-risk polymer insulators in-service. Anyone
interested in the research effort should contact Andrew Phillips, aphillip@epri.com.
Live Working With Polymer Insulators - An essential requirement for ensuring worker safety
when working with polymer insulators is to confirm their electrical and mechanical integrity for
the duration of the work. EPRI is reviewing existing integrity evaluation techniques that have
been developed based on long-term aging results. The relation to short-term integrity will be
investigated. EPRI will also develop effective inspection techniques and tools to address live
working issues, as well as specific techniques for live working with polymer insulators.
Polymer Insulator Failure Database - EPRI will continue to maintain the failure database to
provide utilities with valuable information for making decisions about applying polymer
insulators or removing existing units from service.
A concurrent Tailored collaboration Project entitled “Collaborative NCI Project” is also
underway. This project utilizes in-house utility research that was previously not available to all
the EPRI members. In-house research on a specific topic from a number of sources is combined
with EPRI research to provide a broader perspective. In many cases the information from
research reports is distilled into a guide that can be more easily used by engineering staff. The
following deliverables have already been produced and provided to the participants:
•
Effect of Elevated Conductor Temperature on Polymer Insulators and the Effect of High
Temperatures on Post Insulators.
•
Storing, Transporting and Installing Polymer Insulators: A Practical Guide
•
The Effect of Elevated Temperatures on Polymer Insulators: A Materials Perspective
•
E-field Magnitudes on Polymer Insulators – 115 to 765 kV (being finalized)
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•
Guide to the Maintenance of Insulators in a Contaminated Environment (being finalized)
A workshop on the above topics is also proposed. Additional deliverables are also under
discussion.
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About EPRI
EPRI creates science and technology
solutions for the global energy and energy
services industry. U.S. electric utilities
established the Electric Power Research
Institute in 1973 as a nonprofit research
consortium for the benefit of utility members,
their customers, and society. Now known
simply as EPRI, the company provides a wide
range of innovative products and services to
more than 1000 energy-related organizations
in 40 countries. EPRI’s multidisciplinary team
of scientists and engineers draws on a
worldwide network of technical and business
expertise to help solve today’s toughest
energy and environmental problems.
EPRI. Electrify the World
© 2002 Electric Power Research Institute (EPRI), Inc. All
rights reserved. Electric Power Research Institute and EPRI
are registered service marks of the Electric Power Research
Institute, Inc. EPRI. ELECTRIFY THE WORLD is a service
mark of the Electric Power Research Institute, Inc.
1007752
Printed on recycled paper in the United States
of America
EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA
800.313.3774 • 650.855.2121 • askepri@epri.com • www.epri.com
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