Influence of Rain on the Discharge Characteristics of Linear Polymeric Insulation

The article presents the results of studies on the effect of artificial rain on the discharge processes along 110-500 kV linear polymeric insulation (LPI) that occur under the influence of standard lightning and switching voltage impulses of positive and negative polarities. The obtained results are analyzed proceeding from solution of the equation of voltage balance across the insulation at the complete flashover occurrence moment. It is shown that for all of the examined insulation designs, the discharge processes in them caused by the effect of positive polarity impulses either do not depend or depend only slightly on the test conditions (in a dry state or under rain conditions). The discharge is formed mainly along a purely air path, due to which rain either does not affect or affects insignificantly the LPI electrical strength. A strong negative effect of rain on the discharge characteristics of linear insulation is manifested only in the case of negative polarity impulses. In this case, a sharp decrease in the 50% insulation breakdown voltages (in the extreme case, down to 30-36%) is accompanied by the appearance of upward moving negative cascade leader flashovers, which extend to more than half of the insulation length. As a result, the insulation electrical strength turns to be noticeably lower than with impulses of positive polarity, which must be taken into account in designing the 110–500 kV LPI.