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IEEE-PES Task Forces on insulator icing have been active since 1999 in developing icing test methods and recommending insulator selection criteria. Progress towards this goal included methods for obtaining reproducible results and also modeling of important factors. This paper reports on the progress and work accomplished by the PES Task Forces, serving as input data to the joint DEIS/PES task force work initiated recently to expand the technical basis of the existing knowledge. In selecting adequate insulators for substations and lines at distribution and transmission voltage levels, special measures may be needed in locations exposed to freezing conditions. The environmental and insulator parameters that influence the risk of flashover are noted. The selection process and mitigation options, based on these environmental parameters, are then described. The selection criteria include insulator size, shape, surface material, surface quality, electric field improvement, and orientation. Index Terms--Climate, contamination, flashover, fog, high voltage, ice, insulation coordination, snow, line insulators, test methods.

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.

A model for predicting the flashover voltage of ice-covered insulators energized with ac voltage is presented in this paper. The model takes into account the variation of ice surface conductivity as a function of freezing water conductivity. The effects of the length of the arc on its own characteristics, as well as the ac arc reignition condition, were determined in a laboratory investigation using triangular ice samples. The model is applied to a short string of 5 IEEE standard insulator units. There is an excellent concordance between the 50% flashover voltage calculated from the mathematical model and the experimental results.

The electrical performance of outdoor insulation degrades severely during combinations of factors that include surface contamination (C), ice (I), fog (F) and an ambient temperature that rises through 0 [degree] C ([T.sub.0 [degree]]). Failures at operating voltage on 115-kV, 230-kV and 500-kV systems occur with increasing probability under these conditions. A new CF[T.sub.0 [degree]] or 'cold-fog' test method has been developed to reproduce the flashovers at all three voltage levels. Three options are identified for improving CF[T.sub.0 [degree]] performance: use of semi-conductive glazes, substitution of silicone for porcelain and use of silicone coatings on existing porcelain insulators. Keywords: insulator, flashover, high-voltage testing, contamination, icing, fog, temperature

This paper describes observation and analysis of electromagnetic field radiation from lightning strokes to tall structures. Electromagnetic field waveforms and current waveforms of lightning strokes to the CN Tower have been simultaneously measured since 1991. A new calculation model of electromagnetic field radiation is proposed. The proposed model consists of the lightning current propagation and distribution model and the electromagnetic field radiation model. Electromagnetic fields calculated by the proposed model, based on the observed lightning current at the CN Tower, agree well with the observed fields at 2km north of the tower. KEYWORD - Lightning, Electromagnetic field radiation, Lightning to tall structures, EMC, Electromagnetic transient

Accurate estimates of low levels of insulator contamination, in the range of 200 mg/[m.sup.2] (0.02 mg/[cm.sup.2]), can only be obtained if several minor errors in conventional surface contamination measurements are corrected.