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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.

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.

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 from IEC 60129, IEC 60507, and IEEE Std.-4-1995 on standard techniques for high-voltage testing.

The influence of the physical aspect of ice accumulation and of water conductivity on the withstand voltage of high-voltage (HV) insulators was determined. Two cap-and-pin insulators and one column type insulator were subjected to flashover testing in a climate room. Artificial ice was accumulated from supercooled droplets at an air temperature of -12/spl deg/C. The electrical conductivity of the spray water between 5 and 150 /spl mu/S/cm was adjusted by adding sodium chloride to de-ionized water. The results obtained indicated that, under experimental conditions, the highest probability of flashover resulted from uniform ice accretion. The withstand voltage of the insulators decreased as the conductivity of the spray water increased. In addition, a series of outdoor camera observations made it possible to compare the aspects of ice accretion during actual freezing rain to those obtained in the laboratory. >

This is a position paper prepared by the IEEE Task Force on Insulator Icing Test Methods. 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 from IEC 60129, IEC 60507, and IEEE Standard 4-1995 on standard techniques for high-voltage testing.