Impact of rain on insulator performance

There is the concern, supported by some field experience, that the standardized wet test methods may not be sufficient to cater for heavy rain conditions. The purpose of this report is to analyse the state of the art about the performance of insulators under rain conditions, including heavy rain, in terms of service and laboratory experience. The analysis is implemented by new ad hoc tests. On the basis of the analysis the relevance of the problem is assessed in relation to the various environmental conditions, arriving at the conclusion that additional heavy rain tests may be necessary to verify the insulator performance under AC and DC at service voltages, but only for environments characterized by very heavy rain conditions in terms of rain intensity and water conductivity.