Silicone rubber insulators for polluted environments part 1: enhanced artificial pollution tests

The development of polymeric materials for outdoor insulation has been much aided by existing standard laboratory tests such as inclined-plane procedures. The position is less satisfactory in respect of the optimization of insulator profiles and the choice of the minimum unified specific creepage distance (USCD) for a given site pollution severity (SPS). Standard tests currently under revision are stated to be 'not directly applicable to polymeric insulators'. Such tests are, therefore, urgently needed to discriminate the pollution performance of silicone-rubber insulators of different housing materials and profiles, to quantify the inverse relationship of pollution severity and flashover voltage and to assess the influence of wetting rate. A suitable test strategy would also avoid housing damage from excessive flashovers. A new test procedure is presented here to achieve these objectives. This is not confined to flashover voltage measurements. A high-resolution data acquisition system is used to monitor and store the waveforms of the applied test voltage and leakage current throughout tests on 11kV silicone-rubber insulators. This enhancement provides a further basis for the quantitative comparison of insulators in artificial pollution testing, because the results corroborate the inverse relationship between flashover voltage and pre-flashover leakage current. Part 2 demonstrates the pollution performance of 11kV silicone-rubber insulators when surface texturing is used to increase USCD values.