DC flashover performance of an inclined insulator string under heavy icing conditions

In this study, the DC flashover performance of an inclined insulator string of four insulator units fully bridged with ice was investigated. Moreover, a DC arc model to predict the critical flashover voltage for the inclined insulator string was elaborated. For the laboratory experiments, glaze ice was deposited artificially in a uniquely designed cold room at CIGELE laboratories using a pneumatic spray nozzle system. This type of ice is known as the most dangerous one as it is associated to the highest probability of flashover of an ice-covered insulator. The conductivity of applied water was adjusted to 60 and 100 μS/cm by adding sodium chloride (NaCl) to deionized water feeding the nozzles. The flashover performance of test insulator string was measured under a melting regime, as prescribed in IEEE Std. 1783. This procedure simulates conditions generally observed for insulator flashovers on natural sites. Based on the experimental results obtained, it was found that the maximum withstand voltage of an inclined insulator string at a swing angle of 30° is about 20-40% higher than that of the same insulator string in a vertical position under the same experimental conditions. Moreover, there was good concordance between the experimental results and the ones calculated from the model developed in this study.