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.