A method is introduced for testing insulators under icing conditions. The method is based on and developed from those described in the standard of IEC60-1, IEC 60507 and IEEE Task Force on Insulator Icing Test Methods, which give instructions to test insulators under pollution. Then, the paper explores the effects of various factors, including ice thickness, pollution severity on the surface of insulators before ice accretion, atmospheric pressure, and shed profiles, on the flashover performance of short samples of two different types of silicone rubber (SIR) composite long rod insulators intended for ultra high voltage (UHV) ac transmission lines. The experiments were carried out in the multi-function artificial climate chamber in the High Voltage and Insulation Technological Laboratory of Chongqing University, China. The experimental results reveal the regularity of the effects of ice thickness, pollution severity and atmospheric pressure on the average flashover voltage of two types of composite insulators. Those can provide reference for the outdoor insulation design for UHV ac transmission lines.Index Terms -UHV, Composite insulator, silicone rubber, icing flashover, low air pressure, outdoor insulation.

Transmission-line icing presents a serious threat to the safe operation of power systems. Therefore, the icing condition of overhead transmission lines must be accurately calculated for online monitoring and prewarning systems. Based on the icing data obtained at Xuefeng Mountain Natural Icing Stations (XMNIS), the cross-sectional shape of glaze icing on conductors was studied, and the correction coefficient of the actual nonuniform ice was proposed to provide an accurate and convenient method for field icing measurement. In addition, by analyzing the characteristics of the tension and tilt of the insulator string at the iced tangent tower, a new mechanical calculation model considering the ice and wind loads was established. One-month field observations and experiments were conducted in XMNIS, and it is shown that the calculation results have good agreement with experiment results, which suggests that the model can be used for ice thickness calculation and online monitoring on transmission lines.Index Terms-Angle, correction coefficient of ice shape, icing thickness, mechanical calculation model, overhead transmission line.

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Ice melting with dc is one of the key technologies to prevent the Chinese power grid from ice storms. Especially after the severe ice storm in the southern part of China in early 2008, dc ice-melting technology has drawn more attention than ever before. However, there are few satisfactory methods to select correct parameters so the ice-melting project rarely achieves desired effects in some cases when applied in Hunan, Guizhou, and other provinces in China. Therefore, it is of great significance to develop a method to estimate parameters which is applicable in the practical situation for dc ice melting. To handle this, the factors, such as wind velocity, ambient temperature, current density and ice-layer thickness were analyzed and then a dc ice-melting model is put forward in this paper. Both the results of simulations and experiments show that the ice-melting process can be divided into three stages composed of temperature rising, ice melting, and ice shedding, among which the ice melting is the key stage consuming most of the ice-melting time. In this stage, an elliptic airgap is formed and widened gradually with an influence on the ice-melting time and the temperature of the conductor. The experiments in the artificial climate chamber demonstrate that the results of the presented model are consistent with those of the experiments generally, so it can be employed to estimate the parameters of ice melting in practical engineering as reference.

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Based on the artificial pollution tests, the effects of pollution and high altitude on the flashover performance of short samples of five kinds of UHV/EHV dc composite long rod insulators are analyzed. The exponent characterizing the influence of salt deposit density on the flashover voltage is related with the profile and the material of the insulator shed. The values of the samples' exponents vary between 0.24 and 0.30, which are smaller than those of porcelain or glass cap-and-pin insulators, namely, the influence of the pollution on the composite long rod insulators is less, relatively. Thus, the composite insulators have certain advantages in severe pollution regions. The best ratio of the leakage distance to the arcing distance is about 3.35. The exponent characterizing the influence of air pressure on the flashover voltage is related with the profile and the material of the insulator shed and the pollution severity, the values of the samples' exponents vary between 0.6 and 0.8, which are larger than those of porcelain or glass cap-and-pin insulators. Therefore, the dc composite insulator used in high altitude regions should have enough arcing distance. Based on the test results, if insulator sample Type E is selected for the ±800 kV UHV dc transmission lines, the basic arcing distance should be no less than 8.16 m and the basic leakage distance no less than 30.2 m.

Abstract:In this study, icing flashover performance tests of typical DC porcelain, glass, and composite insulators are systematically carried out in a multifunction artificial climate chamber. The DC icing flashover voltages of seven typical insulators under various conditions of icing thickness, pollution severity before icing, string length, and atmospheric pressure are obtained. The relationships between icing thickness, salt deposit density as well as atmospheric pressure and the 50% icing flashover voltage are analyzed, and the formulas are obtained by regression method. In addition, the DC icing flashover voltage correction method of typical porcelain, glass, and composite insulator in the coexisting condition of high altitude, contamination, and icing is proposed.