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The power outage caused by decay-like fracture of composite insulators significantly impacts the power grid. In this paper, a decay-like fractured insulator of 500 kV transmission line is taken as a research object. The detailed observation of core rod and silicone rubber housings, discharge results, temperature rises, and electric field distribution are obtained. (a) The fractured insulator has abnormal heating on the exposed core rod and sheath surface, and the ambient temperature and humidity significantly influence the temperature rise. (b) It is proposed that one of the most obvious characteristics of decay-like insulator is abnormal temperature and temperature rise (such as T > 50°C, ΔT > 30 K). (c) Under the same conditions, temperature rises, electrical discharge, and electrical field strength of decay-like insulator are higher than those of other insulators, and the discharge at the bare core rod is intense. (d) The electric field strength distribution and discharge distribution of decay-like insulator are different from other aging and new insulators. However, the measurement results are significantly affected by test conditions. Therefore, it is difficult to determine whether the composite insulators are decay-like using electric field distribution and UV measurement on site. [ABSTRACT FROM AUTHOR]

The cleaning effect of heavy rain (the rainfall reaches 5 mm every day) on surface contamination of insulators is more effective than dew, fog, mist, and other light rain conditions which can initiate leakage currents and increase the likelihood of flashover. It is well understood that heavy rain can wash away contamination from the surface of high voltage (HV) insulators and thereby reduce the risk of pollution flashover. This study examines the cleaning effect of natural wetting conditions on HV insulators on four 500 kV transmission lines in Hunan Province, China. Historical meteorological data, monthly equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) measurements taken over a period of five years were analyzed to investigate the relationship between rainfall intensity and insulator cleaning. The measured data show that the ESDD/NSDD changes with the seasonal variation, which accumulates in dry season (January–April, about 117–122 days) and is washed off in the wet season (June–October, about 118–127 days). According to the measured data, the ESDD and NSDD on the surface of insulators were affected by the rainfall intensity (in the dry season it is about 1 mm/day and in the wet season it is about 5 mm/day). Based on a comparison of the four study sites, we propose a mathematical model to show the functional relationship between rainfall intensity and insulator self-cleaning capability. The mathematical model’s coefficient of determination (R2) is greater than 0.9 and the effective rate of self-cleaning capability reaches 80%. [ABSTRACT FROM AUTHOR]

Icing poses a serious threat to power transmission in many countries. Various studies on the icing mechanism and icing growth process of transmission lines have been carried out all over the world, whereas there are few reports about the icing growth mechanism and its influencing factors on insulators to date. In this paper, artificial tests of insulator icing were carried out; the influences of temperature, median volumetric diameter (MVD), and wind velocity on the icing accretion process, ice shape, and ice type on the surface of insulators were analyzed systematically; and the icing growth performance of different types of insulators were also analyzed. Test results show that under different icing environments, the icing growth of insulators is always nonlinear; the growth rates of icicles and ice layers increase with the decrease of temperature; with the increase of wind speed, all of the ice thicknesses and the length and diameter of icicles increase significantly; for wet growth, the impact of MVD on icing growth of insulators is not significant; the structure of the insulator has some influence on the icing growth process; and with the increase of length and diameter of icicles, the growth rate of the ice layer on the insulator surface decreases significantly. [ABSTRACT FROM AUTHOR]

DC flashover performance of ice-covered composite insulators with a parallel air gap (CI/PAG) is an important technical consideration when such insulators are used to isolate ground wires for the purpose of DC ice-melting. Tests on tension and suspension types of CI/PAG were thus carried out in the artificial climate chamber to investigate their DC icing flashover performance. The influences of parallel air gap, ice thickness, pollution severity and air pressure on DC negative 50% flashover voltage (U50%) of CI/PAG were investigated. Test results show that the parallel air gap affected both the discharge path and U50%. With increasing ice thickness, U50% declined by up to 52%; this effect was more evident when the breakdown occurred in the air gap. The pollution severity affected U50% only when the flashover happened along insulator surface. With a decrease of atmospheric pressure, U50% decreased. U50% and the ratio of air pressure were in a power function relationship with a positive characteristic exponent which was relevant to the discharge path. [ABSTRACT FROM AUTHOR]

The electrical performance of outdoor insulators decreases under low air pressure conditions. The ac pollution flashover performance of various types of insulators are investigated in the multifunction artificial climate chamber in the State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University. The field investigation of the ac pollution flashover voltage performance are carried out at three different high altitudes including Wangkun station (altitude of 4484 m), Nachitai station (altitude of 3575 m) along the Qingzang railway and Geermu urban (altitude of 2820 m). The test results indicate that the characteristic exponent n describing the influence degree of air pressure on pollution flashover voltage, which has influence on the pollution flashover voltage of insulators, is variable, and the value of n is related to the pollution, insulator type etc. Under ac voltage, n is 0.45-0.85. The composite insulators are superior in external insulation selection in high altitude and heavy polluted areas. The relative error between the field test results and laboratory test results is less than 8 %, so the research results obtained in the laboratory can be applied to engineering design. [ABSTRACT FROM AUTHOR]

The external insulation of electric equipments will be affected by the atmospheric conditions in the high altitude regions. However, a few investigations at the high altitude sites of 3000 m and above have been conducted. This paper reports on the laboratory tests of artificially polluted cap-and-pin porcelain insulators performed at the high altitudes of 2800 m to 4500 m. The test results and analysis show that the pollution flashover voltages in high altitude regions are affected not only by the pollution grades but also by the atmospheric parameters. The exponent characterizing the influence of equivalent salt deposit density is 0.26 to 0.29 and the one characterizing the influence of nonsoluble deposit density is 0.09 to 0.15. The ac pollution flashover voltage Uf will decrease with the decrease of air pressure P and increase with the decrease of ambient temperature t. Uf is a power function of the ration of air pressure P/Po and also is a power function of the ambient temperature coefficient (1 + 0.02(t - 20)). The average exponent characterizing the influence of air pressure is about 0.56 and the exponent characterizing the influence of ambient temperature is about 0.21 for the three types of insulators in the paper. [ABSTRACT FROM AUTHOR]

The newly constructed Qinghai-Tibet Railway connecting Golumd and Lhasa is the highest railway in the world, which is located on the hinterland of Qinghai-Tibet Plateau with the average altitude of above 4000 m. Therefore, the external insulation of electric equipments will be affected by the atmospheric conditions in the high altitude regions. In contrast to many test investigations in the artificial climate chamber, there are few ones at the high altitude sites of 3000 m and above. In the paper, the ac artificial pollution tests of four types of composite insulators are carried out at three high altitude sites of 2820 m, 3575 m and 4484 m along the Qinghai-Tibet Railway. The test results show that the ac pollution flashover voltages in high altitude regions are affected not only by the pollution grades but also by the atmospheric parameters. The pollution flashover voltages will decrease with the increase of air pressure but increase with the decreases of ambient temperature. The exponent characterizing the influence of equivalent salt deposit density is 0.26 to 0.32 and the exponent characterizing the influence of non-soluble deposit density is 0.12 to 0.16, the influence of non-soluble deposit density cannot be neglected. The exponent characterizing the influence of air pressure is 0.507 to 0.587. The exponent characterizing the influence of ambient temperature is about 0.20. Considering the combined influence of the air pressure and ambient temperature, the ac flashover voltage of the polluted composite insulators will decrease by 4.0% to 6.4% for the altitude increased per 1000 m. [ABSTRACT FROM AUTHOR]

This paper explores the influence of air pressure, temperature and humidity on the switching impulse (SI) flashover performance of different types of clean and dry insulators at different high altitude sites of 2820 m to 5050 m along the Qinghai-Tibet Railway, the highest elevation railway in the world. Seven types of insulators are used in the flashover tests: one is a composite insulator, two are glass insulators and four are porcelain insulators. At the test sites, the ambient temperature varies between 6.7 °C to 28.5 °C and the absolute humidity is between 4.11 g/m³ to 9.69 g/m³. The test results show that the 50% switching impulse flashover voltage of different types of insulators at high altitude sites is independent of the materials and sheds of insulators but has a multi-factor non-linear relation with the shortest arc distance, the dry air pressure, the absolute humidity and the ambient temperature. The relative flashover voltage decreased with the ambient temperature is dependent on the voltage polarity, with 0.152% to 0.165% 1°C for negative SI and 0.099% to 0.108% 1°C for positive SI at the ambient temperature of from 6.7 °C to 28.5 °C. The relative flashover voltage increased with the absolute humidity and is dependent on the air pressure. The higher the altitude is, the more the influence is of the absolute humidity on the flashover voltage of insulators. [ABSTRACT FROM AUTHOR]

Based on the artificial pollution tests, the fiashover 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 fiashover 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 fiashover 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 FROM AUTHOR]