A fundamental parameter of polluted insulator online monitoring is the leakage current, which has already been shown to be well-related to the pollution discharge of insulators. In this article, in an effort to quantitatively reflect the discharge intensity and the discharge status by the leakage current, we carried out an experimental study on artificial pollution discharge of insulators. A high-speed photographic apparatus was utilized to capture the entire process of local arcs on a porcelain insulator surface, including the arc generation, the arc development, and the flashover, for which the associated leakage current of insulators was synchronously digitized. A comparative analysis of the relation between the two-dimensional discharge image and the leakage current waveform in the process of arc generation and development shows that if the arc area on the insulator surface is relatively small and the leakage current passes through zero, the arc might completely become extinct, whereas this phenomena will not occur if the arc area is larger. In addition, the amplitude of the discharge arc area is found to be roughly proportional to the square of leakage current over the range of leakage current amplitude from 0 to 150 mA. Our results can provide an important guidance for judgment of the discharge status and the discharge intensity on insulator surfaces using the leakage current of insulators.

The leakage current, which is influenced by the operating voltage, the surface contamination, and environmental variables, is one of the most basic online monitoring parameters for the surface contamination status of insulators. However, the impact of temperature and humidity on leakage current have not been expressed concisely nor distinguished according to sunny and rainy weather. In this paper, based on leakage current online monitoring data, the time-domain waveforms of leakage current of an insulator string in Shenzhen, China, were compared with those of the ambient temperature and humidity. Results indicate that the leakage current presents a saddle-shaped curve on days without rain, and that there is a remarkable positive correlation between leakage current and humidity as well as a negative correlation between leakage current and temperature. In a short period (several days) without rain, as long as the relative humidity keeps constant, the leakage current would vary insignificantly, whereas it may vary in a wide range at the same temperature. Moreover, the functional relation mathematical model I = a * e b * RH between the first harmonic component of leakage current and the relative humidity is presented, inferring that the insulator string leakage current depends mainly on the ambient relative humidity in a day without rain. INDEX TERMS Leakage current, ambient temperature, relative humidity, insulator string, on-line monitoring, response mechanism.

Equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) are two basic parameters for the coordination of outdoor insulation and classification of pollution severity. Type XP-70 is usually selected as the test object for classification of pollution distribution in China. In this study, 113 transmission towers representing typical distribution of Shenzhen, China, are selected as observation sites for XP-70 insulators, which have a total of four discs. The ESDD, NSDD and the ratio of NSDD to ESDD for XP-70 insulators with the exposure times of one, two and three years are measured. The following aspects are compared: the difference of natural contamination characteristics of four XP-70 insulators at the same place, the difference of natural contamination characteristics of XP-70 insulators in five different regions (the coastal region, the highway region, the suburb region, the mountain region, and the urban region), and the difference of natural contamination characteristics of XP-70 insulators after years of contamination exposure. The results are as follows: the difference between the ESDD and NSDD of the upper surface of the four discs is significant, whereas that of the lower surface is not. The contamination in the coastal region is the most severe whereas that in the mountain region is the lightest. For the rest three regions, the difference is negligible. The ESDD and NSDD of XP-70 insulators become saturated at different times. We also found that presence of the vulcanized silicone rubber (RTV) coating will significantly increase the ESDD and NSDD of the insulators.