Empirical flashover model of EHV post insulators based on ISP parameter in cold environments

The main objective of this contribution is to present an empirical model of ice-covered insulator flashover in accordance with an important flashover index, called icing stress product (ISP). The ISP as the product of the ice mass per centimeter of insulator length and the electrical conductivity of the melted ice accretion is used to establish an empirical model to determine the flashover voltage under icing conditions. To achieve this model, several tests were carried out on post station insulators typically used in Hydro-Quebec 735-kV substations, under DC and AC voltage, to determine the relationship between flashover stress and the ISP. The ISP-based method offers a good tool not only to select insulators for locations exposed to freezing conditions, but also to compare flashover results obtained under different test conditions. Moreover, to study the optimizing method of insulator flashover, the influence of air gaps on the flashover stress of ice-covered post insulators is investigated. The results reveal that the number of air gaps significantly affects the flashover stress. The test results are highly meaningful as they can be used as a reference for ranking several other insulator types and configurations in order to select the appropriate one for cold environments. Moreover, several mitigation options to improve insulator reliability in cold environments are provided.