This paper deals with discontinuous pollution layers deposited on the insulator surface. TWO zones are known to form: a clean (dry) zone and a polluted (wetted) zone. The influence of the length and position of the dry zone on the leakage current and the arc length are investigated. These were made on a plane experimental model under ac voltage. Two configurations were studied: pollution deposited near the HV electrode, and pollution deposited near the ground electrode. This study was made using pollution layers with different conductivities. Based on the experimental results, a theoretical model allowing us to calculaie the gap impedance, the transferred (gap) voltage and the leakage current was established. This model enables to predict the pollution severity based on the sample's equivalent impedance.

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