Aging of Live Working Tools and Equipment

Part 1: Project Overview

1013891

ELECTRIC POWER RESEARCH INSTITUTE 3420 Hillview Avenue, Palo Alto, California 94304-1338 PO Box 10412, Palo Alto, California 94303-0813 USA

800.313.3774 650.855.2121 askepri@epri.com www.epri.com

Aging of Live Working Tools and Equipment

Part 1: Project Overview

1013891

Technical Update, September 2007

EPRI Project Manager

G. Gela

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

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ORGANIZATION(S) THAT PREPARED THIS DOCUMENT

EPRI

This is an EPRI Technical Update report. A Technical Update report is intended as an informal report of continuing research, a meeting, or a topical study. It is not a final EPRI technical report.

NOTE

For further information about EPRI, call the EPRI Customer Assistance Center at 800.313.3774 or e-mail askepri@epri.com.

Electric Power Research Institute, EPRI, and TOGETHERSHAPING THE FUTURE OF ELECTRICITY are registered service marks of the Electric Power Research Institute, Inc.

Copyright 2007 Electric Power Research Institute, Inc. All rights reserved.

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CITATIONS This document was prepared by

EPRI-Lenox 115 East New Lenox Road Lenox, MA 01240

Principal Investigators G. Gela D. Childs

This document describes research sponsored by the Electric Power Research Institute (EPRI).

This publication is a corporate document that should be cited in the literature in the following manner:

Aging of Live Working Tools and Equipment: Part 1: Project Overview. EPRI, Palo Alto, CA: 2007. 1013891

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PRODUCT DESCRIPTION Live working tools and equipment are often exposed to harsh conditions during use that cause aging or deterioration of their inherent integrity. So far, there has been a lack of detailed knowledge of aging mechanisms and rates as well as the end-of-life criteria of live working tools and equipment. For this reason, the Electric Power Research Institute (EPRI) launched a pilot project to study the issue. This report summarizes the relevant work performed in 2007 and outlines planned future work.

Results and Findings Trunnions. Recently, a utility reported a failure of a trunnion while in service. The failure was attributed to wear or aging of trunnion threads during years of use and the resulting mechanical fatigue. Fortunately, a secondary stop nut prevented dropping of the conductor supported by the strain stick and the aged trunnion. Although such incidents are rare in the industry, any field failure must be investigated in detail to determine the cause of the problem and to derive lessons learned that help avoid future recurrences.

In 2007, several trunnions were removed from the field, provided to the EPRI-Lenox, Massachusetts laboratory, and mechanically tested under linearly increasing loading conditions (that is, no shock load). No threads were ripped out during the tests, and the reported incident could not be reproduced with linearly increasing load.

Conductive suits. EPRI research in the 1980s and 1990s investigated the design, performance, and function of conductive suitsparticularly the effect of laundering of suits on their shielding properties. The research discovered evidence of significant deterioration as a result of laundering. The EPRI report TR-104640 was reviewed, and sections related to the aging of suits are summarized in the current report.

Live working rope. In view of 1) significant changes in the performance requirements of rope used for live working purposes and 2) the resulting market unavailability of live working rope, EPRI recently launched a significant project to assess service performance requirements and test procedures for live working rope. The results of this research are contained in EPRI reports 1013603 and 1013897 (the latter is being developed) and appear to support the International Electrotechnical Commission (IEC) approach to performance requirements and testing of rope.

One section of EPRI report 1013897 is dedicated to rope damage and another to decisions regarding repair and/or retirement. Excerpts from these sections are also summarized in the current report.

Challenges and Objectives Little is known about the aging and deterioration of live working tools and equipment. Few quantitative guidelines are available for determining the end-of-life of a tool or piece of equipmentthat is, the point at which the tool and equipment should be retired from serviceor for removing tools and equipment for re-evaluation.

The objective of this effort is to explore in depth the aging of live working tools and equipment that results from field use and to develop end-of-life or replacement criteria.

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Applications, Value, and Use Quantitative information on the aging of live working tools and equipment will allow utilities to improve inspection and repair methods as well as schedules. Definitive end-of-life criteria will allow utilities to plan the replacement and removal from service of live working tools and equipment.

EPRI Perspective The lack of detailed knowledge of aging mechanisms and rates and of the end-of-life criteria of live working tools and equipment often prevents utilities from optimizing inspection intervals and repair strategies of tools and equipment. Further, it does not facilitate proper asset management and replacement of aging or failing tools and equipment.

It is recommended that these issues be explored in depthboth in terms of a detailed analysis of available (though admittedly limited) literature data and through appropriate testing. Industry experience should also be collected and documented, especially regarding service histories of tools and equipment and in terms of any reported incidents that are attributable to the aging of live working tools and equipment. Research of these issues is planned for 20082009.

Approach This report summarizes the work performed in 2007 and outlines planned future work. In 2007, several trunnions were removed from the field, provided to the EPRI-Lenox laboratory, and tested following a field failure. A previously published report on conductive suits was reviewed, and findings on the aging of suits were extracted. The report on live working rope (under preparation) was reviewed with the goal of extracting information on the aging and deterioration of live working ropes.

Keywords Live working Live line maintenance Live line tools Live line equipment Transmission lines

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ABSTRACT Live working tools and equipment are often exposed to harsh conditions during use that cause aging or deterioration of their inherent integrity. However, little is known about the rate of aging or deterioration. Few quantitative guidelines are available for determining the end-of-life of a tool or equipment, i.e., the point at which the tool and equipment should be retired from service, or for removing tools and equipment for re-evaluation.

The lack of detailed knowledge of aging mechanisms and rates, and of the end-of-life criteria of live working tools and equipment often prevents utilities from optimizing inspection intervals and repair strategies of tools and equipment, and does not facilitate proper asset management and replacement of aging or failing tools and equipment. In 2007, EPRI launch a pilot project to study these issues.

This report summarizes the work performed in 2007 and outlines planned future work.

In 2007, several trunnions were removed from field, provided to the EPRI-Lenox laboratory and tested mechanically under linearly increasing loading conditions (no shock load). No threads were ripped out in the tests and the reported incident could not be reproduced with linearly increasing load.

A previously published EPRI report TR-104640 on conductive suits was reviewed and findings regarding aging of suits were extracted. The research discovered evidence of significant deterioration due to laundering.

In view of significant changes in the performance requirements of rope used for live working purposes, and the resulting market unavailability of live working rope, EPRI recently launched a significant project to assess service performance requirements and test procedures for live working rope. The results of this research are contained in EPRI reports 1013603 and 1013897 and they appear to support the IEC approach to performance requirements and testing of rope. A section of EPRI report 1013897 is dedicated to rope damage and another section to decisions regarding repair and/or retirement. Excerpts from these sections are summarized.

It is recommended to explore the issue in depth both in terms of a detailed literature search and through appropriate testing. Industry experience should also be collected and documented, especially regarding service histories of tools and equipment and in terms of any reported incidents that are attributable to aging of live working tools and equipment. Research of these issues is planned for the years 2008 and 2009.

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ACKNOWLEDGEMENTS

EPRI acknowledges the contributions of the following utilities that provided test data and test samples for this project:

Georgia Power PSEG Western Area Power Administration

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CONTENTS

1 AGING AND END-OF-LIFE CRITERIA..................................................................................1-1 Insulating Tools ....................................................................................................................1-1 Trunnions .............................................................................................................................1-2 Conductive Clothing.............................................................................................................1-2 Live Working Rope...............................................................................................................1-2 Need for Research...............................................................................................................1-2

2 TESTS ON STRAIN STICK TRUNNIONS .............................................................................2-1 Recent Reported Trunnion Failure.......................................................................................2-1 Tension Tests on Used Trunnions .......................................................................................2-3

The MTS Test Equipment ..............................................................................................2-4 The Test Setup...............................................................................................................2-4 Test Procedure...............................................................................................................2-4 Test Results ...................................................................................................................2-5

3 AGING OF CONDUCTIVE CLOTHING..................................................................................3-1 Background..........................................................................................................................3-1 Replacement or End-of-Life Criteria.....................................................................................3-2

4 LIVE WORKING ROPE ..........................................................................................................4-1 Background..........................................................................................................................4-1 Types and Effects of Damage..............................................................................................4-1

Excessive Tension/Shock Loading ................................................................................4-1 Cyclic Tension Wear ......................................................................................................4-1 External Abrasion...........................................................................................................4-3 Pulled Strands and Yarns ..............................................................................................4-3 Flex Fatigue Pulleys, Rollers, Chocks, Fairleads, Blocks ...........................................4-4 Sunlight Degradation......................................................................................................4-5 Dirt and Grit ....................................................................................................................4-5

Disposition of Live Working Rope ........................................................................................4-6 Repairing the Rope ........................................................................................................4-6 Retiring the Rope ...........................................................................................................4-6

5 CONCLUSIONS AND PLANNED FUTURE WORK ..............................................................5-1 Trunnions .............................................................................................................................5-1 Conductive Suits ..................................................................................................................5-1 Live Working Rope...............................................................................................................5-1 Future Research Plans ........................................................................................................5-1

6 REFERENCES .......................................................................................................................6-1

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1 AGING AND END-OF-LIFE CRITERIA Live working tools and equipment are often exposed to harsh conditions during use that cause aging or deterioration of their inherent integrity. However, little is known about the rate of aging or deterioration. Few quantitative guidelines are available for determining the end of life of a tool or equipment, i.e., the point at which the tool and equipment should be retired from service, or for removing tools and equipment for re-evaluation.

Insulating Tools

For example, IEEE Std 516-2003 Clause 4.5.1.1 contains the following qualitative recommendations for re-testing of insulating tools [1]:

4.5.1.1 When to perform shop or laboratory testing Insulating tools should be shop maintained and tested at an interval dependent on their exposure, manner of use, care they receive, individual company policy, and as field inspection dictates. Wood tools should be checked more frequently during periods of high humidity or after exposure to moisture.

The following field observations, if present, should warrant the removal of tools from service and their return to the laboratory or shop for repair and electrical testing:

a) A tingling or fuzzy sensation when the tool is in contact with energized conductor or hardware.

b) Failure to pass the electric test or the moisture-meter test (see 4.4.4 and 4.4.5).

c) Deep cuts, scratches, nicks, gouges, dents, or delamination in the stick surface.

d) A mechanically overstressed tool showing such evidence as damaged, bent, worn, or cracked components.

e) A loss or deterioration of the glossy surface.

f) A pole inadvertently cleaned with a soap cleaner (see 4.4.3).

g) Improper storage or improper exposure to weather.

h) An electrically overstressed tool showing evidence of electrical tracking, burn marks, or blisters caused from heat.

Clause 4.5.3 of IEEE Std 516-2003 contains the following recommendation for an end-of-life criterion of insulating tools [1]:

h) If the current continues to rise after full voltage is reached, the test should be discontinued, the pole should be cleaned or refinished, and the pole should be

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retested. If the condition is not corrected, the pole should be removed from service.

Trunnions

Recently, a utility reported a failure of a trunnion while in service. The failure was attributed to wear or aging of trunnion threads during years of use and the resulting mechanical fatigue. Fortunately, a secondary stop nut prevented dropping of the conductor supported by the strain stick and the aged trunnion. While such incidents are rare in the industry, any field failure must be investigated in detail to determine the cause of the problem and to derive lessons learned that help avoid future recurrences.

Conductive Clothing

Clause 5.4.5 of IEEE Std 516-2003 recognizes deterioration or aging of conductive clothing and contains general qualitative criteria regarding repair and re-testing [1]:

5.4.5 Conductive clothing

All conductive clothing should be inspected visually before and after use to check for rips, brown or burnt marks, punctures, or any damage that can prevent complete shielding. A defect in the conductive clothing or its bonding apparatus should be a reason for removing it from service, instituting immediate repairs, if possible, and testing.

Particular care should be given to removing any dirt or gravel that may be embedded in conductive shoes.

EPRI research in 1980s and 1990s investigated the effect of laundering of conductive suits on their shielding properties [2] and discovered evidence of significant deterioration.

Live Working Rope

In view of significant changes in the performance requirements of rope used for live working purposes, and the resulting market unavailability of live working rope, EPRI recently launched a significant project to assess service performance requirements and test procedures for live working rope. The results of this research are contained in EPRI reports 1013603 and 1013897 and they appear to support the IEC approach to performance requirements and testing of rope.

A section of EPRI report 1013897 is dedicated to rope damage and another section to decisions regarding repair and/or retirement. Excerpts from these sections are included below.

Need for Research

The lack of detailed knowledge of aging mechanisms and rates, and of the end-of-life criteria of live working tools and equipment prompted EPRI to launch a pilot project to study the issue.

This report summarizes the work performed in 2007 and outlines planned future work.

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2 TESTS ON STRAIN STICK TRUNNIONS A strain stick is installed between a conductor and a support point on a structure when removing the insulator string. The stain stick normally includes a long threaded jack screw and a brass nut, known as the trunnion. After the strain stick is installed, the trunnion is turned with a wrench to bring the conductor closer to the insulator support point, thus relieving the tension in the insulator string. The insulator string is then detached and removed, and the train stick, together with the jack screw and the trunnion, supports the conductor. Figures 2-1 and 2-2 show an example of the installed strain sticks before and after removal of the suspension I-insulator string, respectively.

Figure 2-1 Strain sticks and the insulator string before insulator removal

Figure 2-2 Strain sticks after removal of the insulator string

Recent Reported Trunnion Failure

Field report indicates that a trunnion threads were stripped completely from a trunnion used to release tension on a 500 kV dead-end insulators before the insulator was removed. An auxiliary nut close to the trunnion was used as a backup, and the nut and the insulators string absorbed the shock load.

While such incidents are rare in the industry, any field failure must be investigated in detail to determine the cause of the problem and to derive lessons learned that help avoid future recurrences.

The trunnion, shown in Figure 2-3, was inspected prior to use and tested with the trunnion gauge of the type shown in Figure 2-4. The trunnion passed the test. The test consists of trying to screw in the gauge into the trunnion, as shown in Figure 2-5. The threads on the gauge are wider than those in the trunnion (and on the jack screw). If the trunnion threads are damaged (worn out), the gauge can usually be screwed in. If the threads are not damaged, the gauge cannot be

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screwed in, as shown in Figure 2-5. Figure 2-6 shows a comparison of the gauge thread and the jack screw thread.

Figure 2-3 Failed trunnion (model E401-2068)

Figure 2-4 Example of a trunnion thread gauge (AB Chance T401-2265)

Figure 2-5 Use of the trunnion thread gauge on trunnion E401-2066

Figure 2-6 Comparison of threads on a trunnion thread gauge and on a jack screw

No service history is available on the failed trunnion, however, it is thought to be of an older design since the threaded neck is relatively short. Commercially available trunnions, such as AB Chance E401-066 or E401-2068 have longer necks.

Figures 2-7 and 2-8 show (from two angles) a comparison of the threads inside the trunnion in question. Figure 2-9 shows the damaged thread that pulled out of the trunnion, and Figure 2-10 shows the jack screw with damaged thread.

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Figure 2-7 Comparison of the damaged threads inside the failed trunnion, and undamaged threads in a healthy trunnion. Note also that the healthy trunnion has a longer neck.

Figure 2-8 Another view of the damaged threads inside the failed trunnion, and undamaged threads in a healthy trunnion. The difference in neck lengths of the failed and the healthy trunnions is clearly visible

Figure 2-9 Thread coil that pulled out of the failed trunnion

Figure 2-10 View of the damaged threads on the jack screw that supported the failed trunnion

Tension Tests on Used Trunnions

In view of the failure described above, EPRI received used trunnions from two utilities, and also located some trunnions that were available at the Lenox laboratory. No service history is available on the trunnions, however, it is reasonable to expect that trunnions provided by utilities experienced greater use that those available at the Lenox laboratory.

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All trunnions were tested using the gauge prior to tension tests. Only linearly increasing loading (no shock load) tests were performed in the MTS machine available at the laboratory. Only trunnion models E401-2066 (see Figure 2-5 for an example) were tested.

The MTS Test Equipment

The MTS machine used for tests consists of:

MTS servo model 760C261A, Manifold model 293.11 A-01 (computer controlled hydraulic test apparatus used to apply the tension loads)

MTS Test Star II integrated data acquisition system and test controller (test software used to monitor load, temperature and linear displacement)

MTS load cell rated for 100 kips Test Ware SX software The MTS machine is calibrated with accordance with NIST requirements and specifications. The accuracy of the MTS machine is 1% of the full-scale value.

The Test Setup

The trunnions were placed on (screwed onto) a jack screws and mounted in the test bed, see Figure 2-11. Two steel plates, one on each side of the trunnion were used to engage on the trunnion pins, as shown in Figure 2-12.

Figure 2-11 Top view of the jack screw with the trunnion mounted in the test bed

Figure 2-12 Top view of the attachments to the trunnion pins

Test Procedure

The test procedure was as follows:

1. Install the trunnion on the jack screw. 2. Install the sample in the MTS machine. 3. Pull to 27,000 lbs.

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4. Remove the sample from the MTS machine. 5. Remove the trunnion from the jack screw. 6. Test the trunnion thread with the gauge. 7. Re-install the trunnion on the jack screw. 8. Pull to failure. 9. Note failure mode (stripped thread, thread pulled out, etc.)

The tension force was increased at a rate of about 200 lbs per second.

Test Results

In all tests to 27,000 lbs, the trunnions withstood the test without apparent damage to the threads, but suffered bending of the pins that also results in deformation of the strength fins (triangular wedged between the pin and the trunnion body), see Figure 2-13. Also, all trunnions suffered binding of the internal bearings so that the nut could no longer rotate inside the trunnion body.

Figure 2-14 shows an example of the MTS test record for a test to 27,000 lbs.

When the trunnions were subjected to tests to failure (i.e., beyond 27,000 lbs with a prospective maximum force setting of 50,000 lbs), the threads did not rip out, however, the jack screw broke and could not be un-screwed from the trunnion. Figures 2-15 and 2-16 show the side view and the bottom view of a trunnion with a section of the broken jack screw that could not be removed. Only two trunnions were tested beyond 27,000 lbs due to shortage of jack screws. In both tests, the jack screw failed at about 33,000 lbs, see Figure 2-17. Also, after the second failure test, the jack screw could not be screwed into a good (untested) trunnion, suggesting that that the jack screw itself was stretched somewhat. Figure 2-18 shows a comparison of the jack threads with the trunnion gauge. This point should be investigated further.

In one test, the trunnion was inadvertently installed backwards on the jack screw. This resulted in the tension force during test to be applied essentially against the retaining C-spring in the trunnion, rather than against it body. In this case, failure of the C-spring occurred at 11,000 lbs. Since in this test the steel plates holding the trunnion in the setup (see Figure 2-12) acted against the fins on the trunnion, the fins exhibited significant damage, see Figure 2-19.

It should be noted that all tests involved only linearly increasing loading conditions (no shock load) that was increased at a rate of about 200 lbs per second. Dynamic (shock) load tests should be performed in the future to represent more accurately the situation in which threads were ripped out of the trunnion in the reported incident. It should also be noted that a similar incident occurred several decades ago and prompted the development of the trunnion thread gauge. The effectiveness of the gauge in detecting deterioration of threads should also be investigated.

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Figure 2-13 Figure showing the bending of trunnion pins and deformation of strength fins after a test to 27,000 lbs.

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Figure 2-14 Typical force-time graph for a test to 27,000 lbs on a trunnion

Figure 2-15 Side view of the trunnion and broken jack screw

Figure 2-16 Bottom view of the trunnion and broken jack screw

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Figure 2-17 Typical force-time graph for a test to failure, in which the jack screw failed (broke) at 33,000 lbs

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Figure 2-18 Comparison of jack screw thread with the gauge thread after the second failure of the jack screw

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Figure 2-19 Damage to strength fins resulting from a test in which the trunnion was installed backwards

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3 AGING OF CONDUCTIVE CLOTHING

Background

Conductive clothing, or suit, is typically worn by workers performing live work on transmission lines at voltages between 115 kV and 800 kV. The clothing may consists of a jacket, pants, socks and gloves, or a complete suit with socks and gloves attached. The jacket portion usually includes a hood and a face mask. A tether attached at the waist is used to bond the suit to grounded or energized parts.

The conductive suit is intended to provide the wearer with shielding from the electric field, and to prevent currents from flowing in the wearers body. Conductive suits have been used since early 1960s and have evolved over the years both in functionality and durability. Modern suits may also designed to provide shielding from high-frequency fields such as those near PCS (Personal Communications System) antennas, and may also have FR (Flame Retardant) properties.

To perform its intended functions of shielding and protecting from flow of currents in the workers body, a conductive suit must meet certain electrical and mechanical criteria [3, 4]. It must provide complete coverage of the wearers body, i.e., it must form a complete and continuous layer over the entire body (no holes, rips, etc.). The electrical resistance of the suit in service must be small so that potential differences among various parts, developed as result of currents induced in the suit, does not exceed values that would cause discomfort for the wearer. The suit resistance must also be small compared to the effective resistance of the wearers body (even when the worker is perspiring in a hot environment), so that the suit, rather than the wearers body is the preferred path for the induced currents. The suit fabric must be constructed with sufficient density of conductive elements (threads of fibers) to provide continuous current paths and to form an effective barrier against penetration of spark discharges through the fabric into the wearers body.

During its life cycle, the suit is subjected to hard wear and undergoes many launderings or drycleanings. It can sustain damage such as tears, burns, loosening of components (fasteners, bonding lead connections, etc.) and impregnation with substances adverse to its function (oil. grease, solvents, corrosive liquids, abrasives). The following kinds of damage can occur:

Conductive Material Corrosion: In some older suits that relied on silver-plating or silver deposit, or suits using copper conductors, the conductive material is quite prone to corrosion or erosion due to corrosive liquids, corrosive atmospheres or perspiration. This reduces the amount of conductive material, and hence the suits conductivity, finally leading to complete failure to provide an adequate current path or adequate shielding. Corrosion of the conductive fiber surfaces will also increase interstrand resistance leading to increased overall resistance if the material relies on fiber-to-fiber contact.

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Fiber Breakage: Conductive fibers may fatigue due to repeated flexing or they may be broken by externally applied forces, leading to a progressive or local increase in suit resistance.

Loosening of Weave: The weave loosens leading to reduction of contact pressure, or complete loss of contact, between conductive elements both within the weave and in the yarn itself. Suit resistance will increase, and excessive loosening might reduce the screening properties of the fabric and possibly permit contact spark penetration through the fabric.

Fastener Damage: Conductive fasteners (press-studs, bonding straps) may lose contact with conductive elements of the cloth due to fatigue from wear or breakage from excessive force.

Stitching Damage: Stitching loosens or fails leading to increase in resistance between parts. Fabric Shrinkage: Shrinking of the base fibers and stitching thread, with none occurring in

the conductive fibers, leading to distortions in the yarn, weave and stitching. This could either increase the resistance due to disruption of fibers or decrease resistance due to tightening of the weave.

Tearing: Tears or holes in the material will disrupt continuity, result in local loss of shielding and could allow contact sparks to penetrate the material.

Impregnation of Fabric: The fabric becomes impregnated with non-conductive material which coats the conductive fibers that rely on contact to provide continuity. Contact resistance is thereby increased or contact is interrupted leading to increased suit resistance.

Laundering of conductive suits is responsible for much of the suit deterioration with use, which can be tracked with relative ease as a function of the increase of suit resistance with washing occurrences. Tests at several utilities point to noticeable deteriorating influence of laundering on the conductivity of suits with fabric containing stainless steel fibers.

For example, Figure 3-1 shows the resistances (in ) of two suits measured by a utility after each of 20 successive washings. Figure 3-2 shows the average of 21 suit resistance measurements (in k) for each of 8 washings. One utility dry-cleaned the suits only to avoid increase in suit resistance by laundering.

Replacement or End-of-Life Criteria

Use and, in particular, laundering of the suit greatly influences its performance, i.e., comfort to the wearer. While specific resistance, screening efficiency and shielding efficiency tests can be performed [3, 4] to monitor the deterioration of a suit, it is difficult to predict when a suit will become uncomfortable to the wearer. Many variables are involved, including the system voltage, the particular configuration of the worksite, the size, location and posture of the worker, the method of bonding of the suit to the energized conductor or grounded structure, the method of suit-to-body bonding, the value of the suit-to-body contact resistance, the behavior of the suit material in the strong electric field, the age and condition of the suit, etc.

It is essentially up to the wearer to monitor the comfort level and to decide when a suit should be re-tested and/or removed from service.

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Figure 3-2 Change in suit resistance with number of washing operations

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4 LIVE WORKING ROPE

Background

In view of significant changes in the performance requirements of rope used for live working purposes [5], and the resulting market unavailability of live working rope, EPRI recently launched a significant project to assess service performance requirements and test procedures for live working rope. The results of this research are contained in EPRI reports 1013603 and 1013897 [6, 7], and they appear to support the IEC approach [8] to performance requirements and testing of rope.

A section of EPRI report 1013897 is dedicated to rope damage and another section to decisions regarding repair and/or retirement. Excerpts from these sections are included below.

Types and Effects of Damage

Knowing the causes and appearance of damage is essential to a good rope inspection and essential for determining retirement criteria. Cuts, abrasion, and sunlight exposure on smaller ropes, due to their reduced bulk, suffer a proportionately greater loss of strength than larger ropes. Extra attention is recommended when inspecting small diameter ropes.

Excessive Tension/Shock Loading

Overloading or shock loading a rope above the working load limit can cause significant loss of strength and/or durability. However, the damage may not be detectable by visual or tactile inspection. The usage history of a rope is the best method to determine if excessive tension or shock loading has occurred. Overloading and shock loading are difficult to define and the inspector must take a conservative approach when reviewing the history of the rope. Repeated overloading will result in similar damage as that caused by cyclic. Shock loading may cause internal melting of fiber.

Cyclic Tension Wear

Ropes that are cycled for long periods of time within a normal working load range will gradually lose strength. This loss of strength is accelerated if the rope is unloaded to a slack condition or near zero tension between load cycles. The subsequent damage is commonly referred to as fatigue. Although there are various mechanisms for the breakdown of synthetic fibers under cyclic tension, the most common is fiber to fiber abrasion. Figure 4-1 shows an undamaged rope (upper rope) and an example where long term loading and unloading has caused a breakdown of yarns in the outer braid of a double braided rope (lower rope).

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Figure 4-1 Example of an undamaged rope (upper rope) and rope damage due to cyclic tension (lover rope)

Braided ropes develop many broken filaments at the crossover points of strands in the braid due to fiber-on-fiber abrasion. Occasionally, the broken ends of yarns may appear as if cut square (a magnifying glass may be necessary to see this). These broken filaments give the rope a fuzzy appearance on the outside and over the entire length that was under load; this can be so extreme as to obscure the underlying braid structure. Figures 4-2 shows an extreme example of a braided rope with excessive damage from frequent loading and unloading.

Figure 4-2 Fiber abrasion from cyclic tensioning alone

For braided ropes, broken filaments within the rope can also mat, entangle and/or leave a powdery residue. Extreme internal filament breakage will make the rope very hard, lose flexibility and be noticeably larger in diameter (with a subsequent reduction in length); it may be

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so hard that it is impossible to pry the rope open to examine the interior structure. Melted fiber and fusion may be observed in the core rope or between core and cover. Figure 4-3 shows an example of rope damage that resulted in exposing the inside of the structure.

Figure 4-3 Damage that resulted in exposing the inside of the structure

External Abrasion

Most external abrasion is localized. Gouges and strips along one side of the rope are common; these display cut fibers and are often accompanied by fusion. Damage sufficient to degrade the rope is usually obvious. External abrasion can be distinguished from cyclic fatigue since the interior of the rope will not have damage and the damage is rarely uniform as seen in Figure 4-4.

Figure 4-4 Extensive external abrasion

Pulled Strands and Yarns

Strands and rope yarns can be snagged and pulled out of the rope structure, see Figure 4-5. The level of damage is a function of the percentage of the rope cross section that has been lost.

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Figure 4-5 Pulled strand in new double braid rope

Flex Fatigue Pulleys, Rollers, Chocks, Fairleads, Blocks

Constant bending of any type of rope causes internal and external fiber abrasion. This is frequently caused by running on pulleys. But, other types of flexing such as frequent bending over a small radius surface, can also cause fatigue damage. Flexing over fixed surfaces is often accompanied by surface wear, especially if sliding action is also present. Wear will appear on the surface of the contact area. The fibers will become matted on the surface and/or glazed from heat build-up, especially with ropes using polypropylene fibers. Broken filaments and fusion will be found inside the rope over the bending zone but not elsewhere in the rope, see Figure 4-6.

Figure 4-6 External & internal damage running over pulley

Broken filaments

Strands are fused

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Sunlight Degradation

Ultra-violet (UV) radiation from direct sunlight will cause brittle and weak outer rope yarns. UV degradation is difficult to inspect visually unless the outer filaments are broken. Flex the rope or pick at a few outer filaments, to see if they break. Discoloration may be observed in some cases, as shown in Figure 4-7.

Figure 4-7 UV (sunlight) degradation of polypropylene rope

Dirt and Grit

Dirt and grit cause internal fiber abrasion in ropes that are in regular use. Oil and grease deposits, of themselves, do not damage most rope materials. However, they trap dirt and grit and may make the rope difficult or unpleasant to handle. Most ropes can be forced open for internal inspection. A magnifying glass may be helpful for identification of fine particles, as shown in Figure 4-8.

Figure 4-8 Dirt and grit (revealed by low level magnification)

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Disposition of Live Working Rope

It is expected that a rope will be left in normal service if no significant damage is identified. However, when a rope is considered to be damaged, in accordance with the inspection and evaluation criteria, a decision must be made to repair or retire the rope based on the results of the inspection. Downgrading should not be allowed due to the difficulty of estimating residual strength and the danger associated with identification.

Repairing the Rope

If the rope shows local damage but otherwise appears in good condition, it may be possible to remove the damaged sections and resplice the rope. After completion of new eye splices or end-to-end splices, the rope should pre-tensioned or load-cycled to 1.5 times of the WLL (Working Load Limit) to set the splice, if possible. Splicing should be done by a qualified person.

Washing with water or mild detergent may be appropriate to clean the rope. Strong detergent solutions or solvents must be avoided as they can remove fiber finishes (lubricants) which can be essential for abrasion and fatigue resistance.

Caution: Splicing of a heavily used rope may be impossible, or very difficult. In such cases, there often is a significant strength loss in the splice; consultation with a qualified person may be appropriate.

Retiring the Rope

Rope must be retired if it is damaged and cannot otherwise be repaired or a use cannot be found for it in a downgraded condition.

Retired ropes must be disposed of in accordance with any applicable regulations and rendered unsuitable for future use.

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5 CONCLUSIONS AND PLANNED FUTURE WORK This pilot project on aging mechanisms and rates, and end-of-life criteria of live working tools and equipment has identified a significant lack of available information for most live working tools and equipment.

Trunnions

Recently, a utility reported a failure of a trunnion while in service. The failure was attributed to wear or aging of trunnion threads during years of use and the resulting mechanical fatigue. Fortunately, a secondary stop nut prevented dropping of the conductor supported by the strain stick and the aged trunnion. While such incidents are rare in the industry, any field failure must be investigated in detail to determine the cause of the problem and to derive lessons learned that help avoid future recurrences.

In 2007, several trunnions were removed from field, provided to the EPRI-Lenox laboratory and tested mechanically under linearly increasing loading conditions (no shock load). No threads were ripped out in the tests and the reported incident could not be reproduced with linearly increasing load.

Conductive Suits

EPRI research in 1980s and 1990s investigated the design, performance and function of conductive suits, and especially of effect of laundering of suits on their shielding properties. The research discovered evidence of significant deterioration due to laundering. The EPRI report TR-104640 was reviewed and sections related to aging of suits are summarized. Further research of deterioration of new suit materials is needed.

Live Working Rope

In view of significant changes in the performance requirements of rope used for live working purposes, and the resulting market unavailability of live working rope, EPRI recently launched a significant project to assess service performance requirements and test procedures for live working rope. The results of this research are contained in EPRI reports 1013603 and 1013897 and they appear to support the IEC approach to performance requirements and testing of rope.

A section of EPRI report 1013897 is dedicated to rope damage and another section to decisions regarding repair and/or retirement. Excerpts from these sections are summarized.

Future Research Plans

It is recommended to explore the issue of aging mechanisms and rates, and end-of-life criteria of live working tools and equipment in depth both in terms of a detailed analysis of available

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(though admittedly limited) literature data, and through appropriate testing. Industry experience should also be collected and documented, especially regarding service histories of tools and equipment and in terms of any reported incidents that are attributable to aging of live working tools and equipment. Research of these issues is planned for the years 2008 and 2009.

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6 REFERENCES

1. IEEE Std 516-2003, IEEE Guide for Maintenance Methods on Energized Power Lines 2. Electrical Performance of Conductive Suits, Final Report, EPRI, Palo Alto, 1995, TR-

104640 3. IEEE Std 1067-2005, IEEE Guide for In-Service Use, Care, Maintenance, and Testing

of Conductive Clothing for Use on Voltages up to 765 kV ac and 750 kV dc 4. IEC Publication 60895 Ed 2., Live working conductive clothing for use at nominal

voltage up to 800 kv AC and 600 kv DC, 2002 5. ASTM F1701, Standard Specifications for Unused Polypropylene Rope with Special

Electrical Properties 6. Investigate Use of and Requirements for Live Working Rope. EPRI, Palo Alto, CA: 2006.

1013603 7. Performance and Use of Rope in Live Working. EPRI, Palo Alto, CA: 2006. 1013897 8. IEC Publication 62192, Ed. 1: Live working - Insulating ropes, in preparation.

Electric Power Research Institute 3420 Hillview Avenue, Palo Alto, California 94304-1338 PO Box 10412, Palo Alto, California 94303-0813 USA

800.313.3774 650.855.2121 askepri@epri.com www.epri.com

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The Electric Power Research Institute (EPRI)

The Electric Power Research Institute (EPRI), with major locations in Palo Alto, California; Charlotte, North Carolina; and Knoxville, Tennessee, was established in 1973 as an independent, nonprofit center for public interest energy and environmental research. EPRI brings together members, participants, the Institute's scientists and engineers, and other leading experts to work collaboratively on solutions to the challenges of electric power. These solutions span nearly every area of electricity generation, delivery, and use, including health, safety, and environment. EPRI's members represent over 90% of the electricity generated in the United States. International participation represents nearly 15% of EPRI's total research, development, and demonstration program.

TogetherShaping the Future of Electricity

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Printed on recycled paper in the United States of America 1013891

1 AGING AND END-OF-LIFE CRITERIAInsulating ToolsTrunnionsConductive ClothingLive Working RopeNeed for Research2 TESTS ON STRAIN STICK TRUNNIONSRecent Reported Trunnion FailureTension Tests on Used TrunnionsThe MTS Test EquipmentThe Test SetupTest ProcedureTest Results3 AGING OF CONDUCTIVE CLOTHINGBackgroundReplacement or End-of-Life Criteria4 LIVE WORKING ROPEBackgroundTypes and Effects of DamageExcessive Tension/Shock LoadingCyclic Tension WearExternal AbrasionPulled Strands and YarnsFlex Fatigue Pulleys, Rollers, Chocks, Fairleads, BlocksSunlight DegradationDirt and GritDisposition of Live Working RopeRepairing the RopeRetiring the Rope5 CONCLUSIONS AND PLANNED FUTURE WORKTrunnionsConductive SuitsLive Working RopeFuture Research Plans6 REFERENCES