Analysis of leakage current of long string insulators of high-altitude artificial contamination test

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To study the change rules of leakage current of long string insulators under high altitude condition, and using the current to characterize the insulators' running state and pollution level can be highly useful to prevent flashovers from happening. In this paper, waveforms the leakage current of long string insulators under high altitude condition are measured by artificial pollution tests and the amplitude-frequency characteristics of the leakage current are analyzed. The results show that with the increase of leakage current amplitude, the third harmonic content decreases, the current waveform became more sinusoidal, the phase difference between current and voltage reduces. Through the analysis of maximum leakage current of insulator strings in different salt deposit density (SDD), a linear relationship is found between the maximum leakage current and SDD, thus the insulator pollution level can be characterized with leakage current peak value. Through the analysis of leakage peak currents under different altitudes, it is found that the effects of altitude on the leakage current is the same with the influence of altitude on U50, leakage current peak becomes smaller with the increase of altitude, therefore the leakage current of different altitudes can be corrected by an index n which stands for the effect level of altitude drops on the flashover voltage.