Study on the frequency spectrum of leakage current for the pollution layer dampness of porcelain post insulator in the pollution test

The frequency spectrum of leakage currents of 24 k V~220 kV porcelain post insulators in artificial pollution tests are intensive studied in this paper. The leakage currents had been taken sample by the frequency of 4000 Hz in the case for preventing against frequency spectrum shifting and getting more characteristics of partial discharge. The waveform of leakage currents within the time domain of 2 s were reconstructed by FFT. It was found that the position and value of spectrum hump could change if the arrangement of high voltage line or the surface crack of flange by contacted. There are three parts before the pollution flashover, absorption moisture of pollution layer, stable state and oscillation state. There is new characteristic of frequency spectrum called intermediate state and is different with the others and Φ THD is 0.6 the amplitude of which is lower than 1 mA. The fundamental component is main part of leakage current which could get the highest level and the THD could get lowest level as the pollution flashover. The THD and amplitude increased in orders of magnitude in pollution test of 220 kV porcelain post insulator. The variation ranges of THD are different in each pollution level. The characteristics of intermediate´s electrical load had been analyzed preliminarily which could widen the range of frequency spectrum in this article. The temperature of samples and water vapor could decrease the latent heat of water in the pollution layer and influence the results of pollution test.