Study On The Discharge Characteristics And The Operation Of The Dirty Insulator String

The pollution flashover is the regional accident which has great harm to the power supply reliability and is regarded as the top archenemy to the power system. It is of paramount importance to prevent pollution flashover accidents and ensure the safe operation of the power grid. Insulation flashover, as a result of the pollution, is the second leading cause in contribution to power grid accident, only next to the lightning, but the loss brought by it is as ten times as that by the lightning.There have been many researches on the characteristics of DC/AC pollution flashover of insulator at home and abroad, however the comprehensive analysis of the factors such as withstand voltage, flashover performance and leakage current, as well as the comprehensive evaluation of insulation status of the lines, are still scarce. Under the comprehensive summarization of former domestic and foreign researches, the withstand performance and flashover characteristics of glass insulators (FC-100/146), porcelain insulators (XP-70) and composite insulators (FXBW—220/110—2150) of 220kV lines are tested in the phytotron in The State Key Laboratory of Power Transmission Equipment & System Security and New Technology and the leakage current are analyzed. Based on different impacts of ESDD, NSDD and the uneven distribution of pollution on the withstand and flashover characteristics of insulators, it can be concluded from the testing result and theoretical analysis that: the withstand and flashover voltage of insulators decrease along with the increase of ESDD, NSDD; The withstand and flashover voltage of insulators rise along with the increase of unevenness of the distribution of the pollution and reach a minimum when the distribution is even, while it has a great possibility for the flashover taking place on the wet insulators; The relationship between the max virtual value and ESDD shows a exponential function; The same goes with the impact of NSDD but these two rules are essentially different. According to these relationship, the security region in which the mean virtual value of withstand and leakage currents are both less than 40mA. According to the security region and the practical status of pollution, the cleaning period of insulator and the transition to condition based cleaning can be decided to improve the reliability of transmission lines.