This paper proposes to survey a good part of the research work accomplished to date on the atmospheric icing of conductors and insulators in the presence of high voltage, with emphasis laid on the studies carried out at the University of Quebec in Chicoutimi. The review covers laboratory testing and mathematical modelling. The role of several electrical parameters, such as electric field strength and polarity, corona discharge, water droplet charge and ionic wind velocity, on the structure and amount of ice accretion on high–voltage conductors, is discussed. Concerning the icing of insulators, the initiation of electrical discharge on the ice surface, the formation of local arcs along the air gaps and their development to a flashover arc along the insulators are discussed. Basic experiments on the role of several major parameters relating to ice accretion, insulator characteristics and voltage type and polarity, on the maximum withstand voltage of short insulators, are also discussed. Finally, several measures for improving the withstand voltage of insulators are briefly recalled.

Ice accretions on high–voltage conductors and insulators and related phenomena

It has long been realized that the thermal ratings of overhead transmission lines when computed deterministically, are typically conservative, resulting in under-utilization of conductors. A probabilistic method to assess thermal capacity based on risk is presented in this paper. The authors address the potential impacts of thermal overload, the stochastic model of conductor temperature, and the quantitative risk which indicates the average "danger" of an overload. The continuous, short-time and long-time thermal ratings are calculated using the risk of thermal overload. This method can provide technical justification for increased thermal capacity for a transmission line and an evaluation of risk for the given operating conditions.

Increasing thermal rating by risk analysis

Modification of AA-6201 alloy for manufacturing of high conductivity and extra high conductivity wires with property of high tensile stress after artificial aging heat treatment for all-aluminium alloy conductors

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.

Insulator icing test methods and procedures: a position paper prepared by the IEEE task force on insulator icing test methods

Large-scale blackouts typically result from cascading failure in power systems operation. Their mitigation in power system planning calls for the development of methods and algorithms that assess the risk of cascading failure due to relay overtripping, short-circuits induced by overgrown vegetation, voltage sags, line and transformer overloading, transient instabilities, voltage collapse, to cite a few. This paper describes such a method based on composite power system reliability evaluation via sequential Monte Carlo simulation. One of the impediments of the study of these phenomena is the prohibitively large computational burden involved by the simulations. To overcome this difficulty, importance sampling technique utilizing the Weibull distribution is applied to power generator outages. Another method combing importance sampling and antithetic variates together is implemented as well. It is shown that both methods noticeably reduce the number of samples that need to be investigated while maintaining the accuracy at a given level. It is found that the combined method outperforms importance sampling to certain extent. To illustrate the developed techniques, two case studies are conducted and analyzed on the IEEE one-area and three-area reliability test system.

Composite Power System Vulnerability Evaluation to Cascading Failures Using Importance Sampling and Antithetic Variates

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 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 CFT{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 CFT{sub 0{degree}} performance: use of semi-conductive glazes, substitution of silicone for porcelain and use of silicone coatings on existing porcelain insulators.

The Cold Fog Test

An accurate new model for calculating AC resistance of ACSR conductors has been developed and verified for single, two and three layer conductor designs. Current redistribution was found to be far more important in determining the AC/DC resistance ratio than hysteresis losses in the steel core except in single layer conductors. The model suggests ways of reducing the AC resistance and promises to be a useful design tool.

A New Model of AC Resistance in ACSR Conductors

A new sag-tension computer program, STESS has been developed for use in transmission line design and operation The program is based on a conductor model which is more realistic and conceptually simpler than the traditional graphic method

A New Computer Model of ACSR Conductors

This paper describes the development of a mechanical-impedance model of a vibrating single-conductor-damper system and its experimental verification. Measurements are made by the force-velocity method and compared with the corresponding model-generated data. The effects of each of the damper components is demonstrated, and the optimal design of aeolian vibration dampers for an ideal viscous damping medium is established. The optimum locations of dampers are also discussed.

O. Nigol

Papers

The Cold Fog Test

A New Model of AC Resistance in ACSR Conductors

A New Computer Model of ACSR Conductors

Aeolian Vibration Of Single Conductors And Its Control