Search

In selecting adequate insulators for substations at distribution and transmission voltage levels, special measures may be needed in locations exposed to freezing conditions. This first part of the paper describes the environmental and insulator parameters that influence the risk of flashover on station insulators exposed to freezing conditions. Index Terms--Climate, contamination, flashover, fog, high voltage, ice, insulator coordination, snow, station insulators.

In locations exposed to freezing conditions over the station service life, additional measures for selecting adequate station insulators at distribution and transmission voltage levels should be taken. This second part of the paper describes the selection process and mitigation options, based on the environmental parameters, as discussed in Part I. These include insulator size, shape, surface material, surface quality, electric field improvement, and orientation. Index Terms--Climate, contamination, flashover, fog, high voltage, ice, insulator coordination, snow, station insulators.

Test methods for evaluating flashover voltage of ceramic and nonceramic insulators under ice, snow, and cold-fog conditions are recommended. The paper describes the procedure to be followed at various stages of an evaluation test including preparation of the test object, insulator precontamination, ice, snow, and cold-fog deposits as well as voltage applications and flashover voltage evaluation. Some relevant parameters for ice accretion, flashover voltage evaluation, artificial pollution, and power source requirements are taken tram IEC 60129, IEC 60507, and IEEE Std.-4-1995 on standard techniques for high-voltage testing. Index Terms--Contamination, flashover, fog, high voltage transmission, ice, insulator, snow, statistical interpretation, test methods.

This paper presents the results of round robin tests performed to evaluate the electrical performance of Room Temperature Vulcanizing (RTV) silicone rubber coatings used for improving the contamination performance of outdoor ceramic insulators. The tests, performed in six different laboratories, included several salt-fog chambers and a tracking wheel. Most test facilities were equipped with an on-line data acquisition system for measurement of leakage current activity. Four generic formulations of RTV silicone rubber coatings applied on ceramic rods were evaluated. The results indicate a general consensus in the ranking of the coatings' leakage current suppression capability, despite the variation in the experimental conditions employed. This suggests that guidelines for a laboratory test for evaluating the RTV coating material's electrical performance under contaminated conditions could be developed. Key Words: RTV coatings, accelerated aging, erosion, leakage current, water repellency.

The results and analysis of surface resistance measurements performed on nonceramic insulators (NCI) are presented in this paper. The goal of this study was to determine if the surface resistance measurement procedure can be formalized to ensure repeatable and reproducible results. The NCIs evaluated had housing materials made from one type of silicone rubber and one type of ethylene propylene diene terpolymers (EPDM) rubber. A porcelain post insulator was used as a reference. The Task Force concluded that it is possible to establish a standard for surface resistance measurement in the laboratory. Such a standard is valuable since surface resistance provides: 1) an indication of aging on NCI housing material and 2) a more sensitive indicator of true contamination severity on insulators than provided by conventional ESDD (equivalent salt deposit density) measurements. As a first step in this direction, guidelines for measurement have been provided in this paper. Suggestions for future work needed for standardization are also included in the paper. Index Terms--Aging, contamination, hydrophobicity, nonceramic/composite insulators, surface resistance.