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Pollution flashover has been a serious threat to the operation safety for the power system. Online monitoring is one most important way for the operation and maintenance of power system. The leakage current on insulator surface is a comprehensive reflection of the insulator surface contamination, environmental conditions and other affecting factors. The purpose of outdoor insulation state on-line monitoring could be achieved by measuring and monitoring the leakage current on insulator surface. This paper showed that close relationship existed between leakage current in both low humidity and saturated moisture conditions. A negative exponential relationship exists between pollution flashover voltage and a new parameter I* which could reflect the insulator shape and the maximum leakage current under saturated humidity. The flashover voltage under saturated humidity could be predicted through current obtained under low humidity conditions. A contamination pre-warning system was constructed in accordance using this mathematical model combined with some hardware system. Pilot systems were established in some typical polluted area in Jiangsu Province. The results showed that the system could achieve online monitoring purposes. , and 1993, respectively. He has worked at Tsinghua University since 1993. His major research fields are high voltage insulation and electrical discharge, flashover mechanism on contaminated insulators, and application of pulsed electric fields.

The uneven distribution of voltage along the composite insulator strings harmed their electrical and mechanical properties heavily, which threatened the safety of power system. Inserting metal electrodes in the silicone rubber sheds of composite insulator helps increase their self-capacitance, thereby ameliorating the voltage distribution along the string. In this paper, a new structure of weather sheds with metal electrodes inserted has been designed. Tests on composite insulators with different metal electrodes setup were conducted to examine their voltage distribution performance. Corona inception voltage of the mentioned composite insulators was obtained by a remote monitoring system as a criterion of the voltage distribution performance. Simulation model of the insulators were set up and calculation of their voltage and electric field distribution were carried out by finite element method (FEM). The calculation result was in good compliance with the experiment result. The applied voltage at the live end of composite insulator decreased by 4% when inserting electrodes in the weather sheds, which was verified by both experiment and simulation results.