Analysis of Live Working Safety on 500kV AC Transmission Line with Defective Composite Insulators

The conductive defects in the transmission line insulators decrease the insulation length and the minimum approach distance and threaten the safety of the live working on the transmission line. In this paper, the maximum conductive defect length parameters for the live working safety on the 500kV AC transmission line with I-type composite insulators were given by the impulse discharge experiments of the defective composite insulators and the the calculations of the live working risk rates. Since the electric field distribution of the insulator changes with the length and the position of the defects, the models of 500 kV transmission line composite insulators with the conductive defects were built and the electric field distribution characteristic parameters were calculated. The experiments and the calculation results showed that when the conductivity defect was at the high voltage end of the insulator, the maximum defect length was 0.7 m for the live working safety and the maximum electric field of the insulator was 6151kV/m, and the maximum length of the defect was 0.9 m and the electric field of the defect was 446kV/m when the conductive defect was in the middle of the insulator. Before the live working on transmission line with composite insulators, the on site measurement of the insulator electric field distribution should be carried out, the length and position of the defects in the insulator could be determine and the safety of live working could also be evaluated.