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

A dynamic model that computes the flashover voltages of polluted insulators energized with DC voltage is presented. The salient feature of this model is that it takes into account the configuration of the insulator profile at every instant, which plays an important role in the flashover process of the DC polluted insulators. A number of practical insulator geometries have been studied, and the validity of the model is verified by comparing the computed results with the experimental results of previous researchers. >

Dynamic arc modeling of pollution flashover of insulators under DC voltage

The number of single-phase faults in the transmission networks in wintertime increases substantially during cold atmosphere precipitation and after ice accretions followed by a rise in air temperature above 0/spl deg/C. >

Flashover problems caused by ice build up on 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 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

A field observation of ice accretion on Hydro-Quebec HV insulators was carried out, as well as a laboratory investigation of the AC flashover performance of various types of insulators covered with artificial ice. The field observations made it possible to identify the type and physical aspect of naturally occurring ice accretions produced during freezing rain precipitation. The laboratory investigation was conducted in a 4.8/spl times/2.8 m/spl times/3.8 m climate room using a HV transformer of 120 kV, 240 kVA with a short-circuit impedance of 5%. A method based on the standard IEC 507 method was developed for measuring the maximum withstand voltage (V/sub WS/) of ice-covered insulators. Various factors were investigated, including the effects on the insulator V/sub WS/ of such particulars as type, thickness, and uniformity of the ice, as well as the arcing distance of the insulators and the conductivity of freezing water. The effects of uniform ice, 2 cm thick, on 5 IEEE insulator units was thus considered to be equivalent to the effect of an ESDD of about 0.13 mg/cm/sup 2/ on the same insulators. >

AC flashover performance of insulators covered with artificial ice

This paper describes the results of investigation made into the performance of insulators covered with snow or ice. The AC and DC withstand voltages of snow-covered insulators were characterized by the conductivity of water melted from the snow. The AC withstand voltage of ice-coated insulators was characterized by the length of icicles and conductivity of the water melted from the ice. And the switching impulse flashover voltage of snow-covered insulator strings was almost proportional to gap length between the arcing horns or the insulator strings. Flashover voltage of a 75% snow-covered insulator string, which means the worst case, was 40 ?65% of the positive wet flashover voltage of the clean insulator string.

Performance of Insulators Covered With Snow or Ice

This paper describes the results of investigation into the performance of suspension type insulators for HVDC transmission line under polluted condition. Shed profile plays a big role in determining DC withstand voltage value. The withstand voltage value for DC is lower than that for AC rms, and the higher the deposit density is, the smaller becomes the atio of the DC value to the AC.

Performance of Insulators for Direct Current Transmisson Line Under Polluted Condition

This report presents results of investigation into the pollution performance of disc insulators with M& E ratings of 66,000-, 90,000- and 120,900-lbs. intended to be used for UHV systems compared with others. Fog type disc insulators have a withstand voltage 140 to 160% of the corresponding standard disc insulators. Withstand voltage is proportional to string length up to 500 kv (860 kv phase-to-phase). An insulator with larger diameter has a lower withstand voltage per leakage distance if pollutant deposit density is the same, and collects less pollutant deposit in a naturally polluted atmosphere.

Performance of Heavy Duty UHV Disc Insulators Under Polluted Condition

As an effective measure to prevent pollution flashover troubles in substations, fixed-type hot-line insulator washing has been widely used. The fundamental study on electrical performances of polluted insulators under washing and the performance of a fixed- type washing system are described. It also discusses the necessity of insulation coordination for pollution.

Hot-Line Washing of Substation Insulators

This paper describes the power frequency withstand voltage test results of contaminated bushing shells for UHV transmission systems up to 15 m under fog condition. Described first are the facilities for testing such tall bushing shells of a large diameter. The test results show a linearity in relationship between effective length and withstand voltage both by the fog withstand method and the equivalent fog method. Assessment of 20 different shed shapes is made. The relation between average diameter and withstand voltage can be expressed in a quadratic curve.

Tetsuo Fujimura

Papers

Performance of Insulators Covered With Snow or Ice

Performance of Insulators for Direct Current Transmisson Line Under Polluted Condition

Performance of Heavy Duty UHV Disc Insulators Under Polluted Condition

Hot-Line Washing of Substation Insulators

Flashover Voltage Characteristics of Contaminated Bushing Shells for UHV Transmission Systems