Leakage current analysis and electric field calculation in salt fog ageing test on polymer insulation material

This paper describes the results of experiments made to examine the electrical insulating characteristics of polymer materials in a salt fog ageing test. In this study, the factors that affect the insulation deterioration from water droplets were analyzed by means of electric field calculation and some experiments. It is demonstrated that water droplets on the polymer surface locally enhance the electric field and may cause partial discharge. From the results of ageing test, when polymer loses its hydrophobicity with ageing time, water drops will elongate, coalesce, and extend with ellipsoidal shape in the direction of electric field, which results in peak value and higher harmonic component in the change curve of the maximum horizontal E-Field at the triple junction increasing remarkably. Simultaneously, increase tendency of the third harmonic wave component with time elapsing can be observed in leakage current waveform, which is in agreement with the results of electric field calculation.