Study Of On-line Insulation Monitoring On 110kV XLPE Cable

XLPE power cable is widely used in grid system for its series of merits. Especially in cities, for the requirement of network structure adjustment and city planning, the mount of cable line increases continuously. At present, there are many XLPE cable lines of 110KV voltage class in service and it is on the swift growth trend. For the power cables in service, it is necessary to carry out on-line insulation monitoring and diagnosis so as to master its insulation condition. The cable lines of 110KV voltage class take an important place in city power grid, so we should pay more attention to it.In this paper, we generally discuss several existed methods about on-line insulation monitoring on cable. Then analyze and compare these methods and figure out their merits and demerits. We also induce their essential: to carry out on-line monitoring is to detect a serial of electric parameters, then base on the correlation of prior data coming from experiment and insulation character of actual cable, we can assess the cable insulation condition.At present, most of the on-line monitoring methods aim at cable line of low voltage level. For those of high voltage level, after the estimate of their insulation parameters we draw the conclusion that those above methods cannot apply to on-line insulation monitoring of 110KV XLPE cable. The paper also points out that partial discharge method and trend management method are the trend of development. Although the validity of partial discharge method is high, its price is relatively higher. So we chose earth line current for trend management. It can achieve certain effect and is economical.As for earth line current method, we designed and finished a set of on-site multi-path earth line current correcting device. This work include the choice of current transformer and the design of amplifier, prior low pass filter, frequency tracing circuit with phase loop, data acquisition based on AT89C55 MCU, keyboard and LCD display module. This paper also discuss in detail about some thoughts in the development process and solution for some actual problems.We also briefly introduce the timing monitor program in upper computer that is used for carrying out trend management and the realization of serial port communication based on RS485 and the establishment of database.We collect the data and save them to database on upper computer. Then we form a time series data and proceed statistic analysis. We longitudinally compare the historical data of certain phase and crossly compare the date phase-to-phase. We combine their results to evaluate the condition of cable insulation.