A Review of Electric Utility’s Experiences with Polymeric Insulators

A Review of Electric Utility’s Experiences with Polymeric Insulators Khaled Y. Al-Soufi Ibrahim O. Habiballah KFUPM, Saudi Arabia December, 2004

Outline • Introduction • International Survey • County’s service Experience • Laboratory Test Methods • Conclusion

Introduction • Gulf Council Countries (GCC) are extended along the coast of the Arabian Gulf and through vast desert areas • These areas are affected by severe weather conditions which are characterized by high temperature, large daily and seasonal temperature variations and high humidity levels through the summer months

Introduction • The severity and diversity of these weather conditions affect the performance of the electrical network hardware, such as the insulators

Introduction • Various kind of polymers, such as silicone rubber, EPDM (Ethylene Propylene Dine Monomer), EVA (Ethylene Vinyl acetate Copolymer) and PTFE (Poly Tetrafluoro Ethylene) were used for outdoor insulation in different applications including transmission/ distribution insulators, post type insulators and hollow core types for apparatus

Introduction • A serious problem with polymeric insulators, however, is their sensitivity to atmospheric and electrical stresses in outdoor applications which can lead to the aging phenomena of the polymeric insulator and may lead to reduction in the useful life of the insulators

Introduction • Selection of a polymeric insulator for a given site must be based on careful analysis and testing • The main objective of this paper is to present a thorough literature review and investigations of local and international electric utility’s experiences with polymeric insulators

Introduction • The paper will also present the major procedure needed to assess the performance of such insulators in the GCC area

International Survey • Through the last three decades huge amount of data collected about polymeric insulator performance and utility service experiences • CIGRE, EPRI, Japanese manufacturer and research centers conducted international surveys about utilities service experience with polymeric insulators

International Survey • The CIGRE working group dealing with polymeric insulators distributed questionnaire in 1987, with various questions on experience with polymeric insulators to many electricity companies all over the world

International Survey • The major outcome regarding the use of polymeric insulators: To combat vandalism, easy transportation and installation, anti-contamination capabilities, high strength-to-weight ratio and for aesthetic appearance

International Survey • CIGRE made another survey in 2000 • This survey indicated the findings of the previous Cigre survey and nominated silicone rubber material as the most widely used for polymeric insulators in Africa, Asia, Australia, Canada, Europe, South America and Middle East

International Survey • EPRI of the USA has distributed questionnaire to the utilities in the USA in 1989 • The survey indicated that the polymeric post insulators were used more frequently at the 115 kV and 138 kV levels, whereas polymeric suspension insulators are most prevalent at 230 kV

International Survey • Reasons cited by utilities for this early survey gave high percentage to combating vandalism, and then other reasons follow as experimenting and light weight.

International Survey • EPRI made another recent survey “Polymer Insulator Survey” in 2002 • The results of the survey indicated that the failure rate for all manufacturers that provided sales information was 1 in every 65,500 units sold

International Survey • Japan started a “Research and Evaluation Program on Non-ceramic insulators in October 1997, to evaluate the fundamental performance of polymeric insulators and investigate their use status in Europe, North America, Australia

International Survey • Reason for use: High percentage goes to easy installation, lightweight, vandalism, contamination performance, easy maintenance, Cost, Strength, and Radio noise • About 80% of the responses indicated the interest in future utilization

County’s service Experience • SEC-ERB, Saudi Arabia, adopted polymeric insulator, on trial basis, in three different lines of 230 kV • The first line started on 1995 and was affected by desert pollution • The second line started on 1996 and was affected by semi-coastal pollution • The third line started on 1996 and affected by coastal and industrial pollution

County’s service Experience • The polymeric insulators presented excellent performance through the period of data collection (1995 – 2001 • These lines behaved well without flashovers and didn’t need washing through the whole trial evaluation period

County’s service Experience • Samples of these insulators were subjected later to mechanical, electrical laboratory testing and material evaluation • The electrical and mechanical results proved the superior performance of these silicone rubber polymeric insulators

County’s service Experience • There were signs of minor degradation but without effect on the overall performance of these insulators • SEC-ERB considered the performance of the polymeric insulator satisfactory and cost effective as it helps to decrease the maintenance requirements

County’s service Experience • Tunisian electrical company (STEG) erected more that 18 test stations distributed in representative area of the country to collect data about insulator performance • After five years in service, STEG confirmed the satisfactory performance of the polymeric insulators on medium and high voltage lines

County’s service Experience • Ageing aspects were noticed on the polymeric insulators after 18 to 24 months of services, which include discoloring and erosion • Silicone rubber sheds maintain hydrophobicity features for longer time than EPR or EPDM rubbers

County’s service Experience • Some of the units showed water–tightness defects for the first generation insulators. Newer versions were working fine • The alternate shed insulators (shed’s slope < 18o) more suitable for desert and coastal areas

County’s service Experience • Powerlink Company is the operator of the transmission grid in the north-eastern Australian State • They are using polymeric insulators since 20 years ago

The main problem cause a worry for them is the bird attacks which eat part of the insulator and render it useless County’s service Experience

Laboratory Test Methods • Most of the laboratory tests tried to check the aging mechanism of the insulator housing • The IEC 1109 defined extensive evaluation program for all parts of the polymeric insulator

Laboratory Test Methods • The aging process and evaluation of the shed material are addressed through lengthy testing technique of 1000 hours and 5000 hours in a salt fog chamber • The insulator should be subjected to electrical and weather parameters stress, as UV, humidity, heat, and rain in systematic manner for the defined period

Laboratory Test Methods • This accelerated aging test is trying to simulate the effect of the harsh environment combined with electrical arcing stress • The rotating wheel test is intended to evaluate the shed material and the interfacing between sheds, rod and end fittings

Laboratory Test Methods • The inclined plane test is intended to evaluate the resistance of the material against tracking and erosion under HV stress • Field inspection provides clear reference picture to simplify in-service inspection for the utilities

Laboratory Test Methods • ESDD and NSDD measurements. include timely measurement for the level of contamination on the insulator surface • Contact angle measurement: provides quick evaluation for the hydrophobicity conditions of the insulator surface

Conclusion • Polymeric insulators have proved itself in many locations through the worlds as very good insulator against contamination • Silicone rubber insulating material is considered through laboratory evaluation and field experience as the most suitable for HV application in harsh environment

Conclusion • The construction of the polymeric insulator, type of shed material, end fitting, fiber glass rod and manufacturing process are decisive factors in the overall insulator performance • The GCC weather conditions are very harsh and require careful selection for the polymeric insulator

Conclusion • There is clear need to adopt short and long term evaluation methods for the polymeric insulator in cooperation with researching universities and testing laboratories

A Review of Electric Utility’s Experiences with Polymeric Insulators