Xingliang Jiang

Flashover Performance of Pre-contaminated and Ice-covered Composite Insulators to be Used in 1000 kV UHV AC Transmission Lines

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.

Comparison of DC Pollution Flashover Performances of Various Types of Porcelain, Glass, and Composite Insulators

Based on the artificial pollution tests, the flashover performance of various types of DC porcelain and glass suspension insulators as well as composite long-rod insulators were analyzed and compared. The test results show that there is a nearly linear relation between the pollution flashover voltage and the disc-type insulator string length. The flashover voltage gradients of the insulators are affected by their materials and shed shapes. The antipollution performances of glass insulators are superior to those of porcelain insulators with the same profile. The flashover voltage gradients of composite insulators are higher than those of porcelain or glass ones. The exponent characterizing the influence of salt deposit density on the pollution flashover voltage is dependent on the profile and the material of insulators, and the values of the composite insulators exponents are smaller than those of porcelain or glass insulators, namely, the influence of the pollution on the composite insulators is relatively less. The effectiveness of leakage distances of porcelain or glass insulators is less than 0.9 while that of composite insulators is higher than 0.9.

Study on Pollution Flashover Performance of Short Samples of Composite Insulators Intended for /spl plusmn/800 kV UHV DC

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 plusmn800 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.

Study on AC Artificial-Contaminated Flashover Performance of Various Types of Insulators

Artificial pollution tests have been carried out to study AC flashover performances of various types of porcelain, glass, and polymeric insulators in this paper. The experimental results show that the polluted flashover voltage Uf is affected by equivalent salt deposit density rhoESDD and nonsoluble deposit density rhoNSDD, the influences of which are independent of each other. Based on the analyses of the flashover voltages, the correction formulas of the flashover voltages Uf of various insulators at various rhoESDD and rhoNSDD levels are pointed out. The experimental results also show that there is a distinct difference among the flashover voltages of various types of polluted insulators. At the same pollution degree, the antipollution performance of the fog-type glass insulator is better than those of the outer-rib porcelain insulators. In terms of the effectiveness of creepage distance of insulators, the antipollution performance of polymeric insulators is superior to those of porcelain and glass insulators.

Investigation of flashover voltage and non-uniform pollution correction coefficient of short samples of composite insulator intended for ±800kV UHVDC

Differences in the amount of pollution on the top and bottom surfaces of an insulator have a great influence on the DC pollution flashover voltage. Up to now, many investigations have been carried out on non-uniform pollution flashover performance of porcelain and glass insulators, but very few on composite insulators. In this paper the influence of non-uniform pollution distribution on DC composite insulators on their flashover performance was analyzed, and a correction formula for the non-uniform pollution flashover voltage was proposed, based on artificial pollution tests carried out on short samples of a composite insulator intended for ±800 kV UHVDC. The test results showed that, when the ratio (T/B) of the salt deposit density (SDD) on the top surface to that on the bottom surface is between 1/1 and 1/10, the value of the characteristic exponent a indicating the effect of SDD on the flashover voltage ranges from 0.22 to 0.255. The value of a is nearly independent of T/B. However, the flashover voltage U50 decreases with the increase in T/B. The correction formula indicating the influence of non-uniform pollution distribution on the flashover voltage could be expressed as K=1 - b×log(T/B). For the tested composite insulators, the factor b was 0.141 to 0.156, which is smaller than that of porcelain or glass insulator. That is to say, the influence of T/B on the flashover voltage of the composite insulator is weaker than those on the porcelain and glass insulators.

Effects of shed configuration on AC flashover performance of ice-covered composite long-rod insulators

The flashover tests of artificially ice-covered composite long-rod insulators, including four types with a nominal voltage of 110 kV, four types of 220 kV and four types of 500 kV, were carried out in the multi-function artificial climate chamber. The result indicates that, firstly, icing flashover performance of the improved composite insulators for icing regions is not always superior to that of the standard composite insulators when icing is light. Meanwhile, Eh (flashover voltage gradient of dry arcing distance) first increases and then decreases with the increase of CF (creepage factor, namely the ratio of creepage to dry arcing distance). Secondly, when icing is moderate, the icing flashover performance is influenced by such main factors as shed diameter, shed spacing and the configuration of sheds with different diameters. In this situation, Eh of the improved composite insulators is higher than that of the standard composite insulators, and ice-covered composite insulator with three or four different shed diameters has better flashover performance than that with two different shed diameters. Thirdly, when icing is heavy, compared with the moderate icing condition, the difference of Eh between the improved composite insulators and the standard composite insulators diminishes. Finally, when icing is moderate or heavy, there is no obvious regular relation between CF and Eh.

DC flashover performance and effect of sheds configuration on polluted and ice–covered composite insulators at low atmospheric pressure

How to choose external insulation under high altitude, pollution and icing conditions for UHVDC transmission project is a complicated problem. To provide technical reference to this engineering roadblock, the dc icing flashover performance of seven types of pre-polluted short samples of composite insulators at low air pressure simulated by the multifunction artificial climate chamber was researched in this paper. The influences of ice thickness, pollution and air pressure on icing flashover performance were analyzed. The correct formula of dc icing flashover gradient of seven types of pre-polluted specimens at high altitude was presented. The influence of the sheds configuration parameters on the flashover gradient was discussed. And the selection of sheds configuration was suggested.

Equivalence of Influence of Pollution Simulating Methods on DC Flashover Stress of Ice-Covered Insulators

The solid-layer method (SLM) and the icing-water- conductivity method (IWCM) are widely used in the insulator icing tests, but little research has been dedicated to the equivalence of these two methods. Based on the research on dc flashover performance of ice-covered insulators in the artificial climate chamber, this paper studied the equivalent relation between SLM and IWCM according to the equivalent principle of the flashover stress of ice-covered insulators. The results show that the influence of these two methods on flashover stress of iced insulator is equivalent, and this equivalence is determined by the configuration of insulator as well as the icing degree, but the icing flashover stress of the same type of insulators which are on the same pollution level simulated by the two different methods is consistent.

Effect of hydrophobicity coating on insulator icing and DC flashover performance of iced insulators

How to decrease the ice on insulators and increase the flashover voltage of iced insulator are hot topics of power system in the world. Many tests have been carried out to investigate whether the permanent room temperature vulcanized (PRTV) coating can change the electrical characteristics of iced insulators both in laboratory and field. Firstly, the test to investigate the icing and electrical characteristic of dc insulator with PRTV coating was carried out. Moreover, comparison has been made between artificial polluted insulator and field polluted insulators. Results indicate that the PRTV coating can not decrease the ice accretion on insulators. Instead, it results in accumulating more ice at the beginning of icing regime, but the influence of PRTV coating will not be remarkable to accumulate ice when there is heavy ice on insulators. . In addition, the PRTV coating can decrease the flashover voltage by 10%. It is also revealed that the flashover voltage for the artificial polluted insulators is lower than that of the field polluted insulators due to the non-uniform of the natural pollution.

Evaluating the safety condition of porcelain insulators by the time and frequency characteristics of LC based on artificial pollution tests

Leakage current (LC) measurement is one of the effective methods for analysis of polluted insulators. But the traditional evaluation methods do not combine well the time-domain with frequency-domain characteristics of LC. In order to evaluate the safety condition of polluted insulators more effectively, an artificial neutral network (ANN) based method was developed in this paper. Firstly, a large number of artificial pollution tests for IEC standard suspension insulators were investigated under different relative humidity (RH) and salt deposit density (SDD). Then, based on the experimental data, the characteristics of LC were analyzed in both time-domain and frequency-domain. The results showed that the peak values of the LC (Ih ) has no relation with SDD when the RH is low ,but when the RH is high, the Ih increases with the increase of SDD; the phase difference (¿) between LC and applied voltage decreases with the increase of RH, the LC becomes inductive when strong local arc occurs; the total harmonic distortion (THD) of LC increases slowly with the increase of RH when the pollution is light, but decreases firstly, then increases with the increase of RH when the pollution is middle or heavy level, the value reaches to minimum when the RH is about 80%. Consequently, Ih, ¿ and THD were proposed as characteristic parameters to evaluate the safety condition of polluted insulators. Finally, an ANN with fuzzy output was developed to evaluate the safety condition of polluted insulators. The input parameters of the ANN were Ih, ¿ and THD, while the output parameters were fuzzified into four fuzzy subsets, the capability of ANN was validated by 8 pairs of testing samples, and the effects of SDD and RH on the performance of insulators were discussed.