Study on the leakage current and the boundary condition of dry band on pollution layer of porcelain post insulator

Abstract

By building a leakage current monitor platform for 24~110 kV porcelain post insulators in artificial pollution tests, we studied the characteristics of the boundary conditions of dry band in pollution layer on the basis of the data of frequency spectrum of leakage current, temperature and humidity of fog room. The offset frequency and spectrum leakage can be dealt with by sampling frequency of 4000 Hz. The total harmonic distortion (THD) is 0.1733~0.3345 before the first dry band appearance if the initial condition is close (the relative humidity is 55%~62%). Under this condition, the fundamental component is measured when the ESDD are (0.06~0.15) mg/cm2 and NSDD is 1.0 mg/cm2 and the absolute humidity (it is equal to the rate of water exchange between pollution layer and air)is also measured when the ESDD are 0.1 mg/cm2 and NSDD is (0.5~1.5) mg/cm2. The results are proportional to variables of pollution layer and the trend curves are fitted. Water in the pollution layer is related with the leakage current though measuring the frequency spectrum of pollution layer that has been found in the tests. The increase of water in pollution layer and leakage current is mutually reinforced before dry band appearance. The THD is closely related with the water of pollution layer. So the THD will rise and the waveform of frequency spectrum is in wave packet when the dry appearance and water of pollution layer decrease.