Evaluation on flashover voltage property of snow accreted insulators for overhead transmission lines, part II - flashover characteristics under salt contaminated snowstorm

This paper presents the flashover characteristics of snow-bridged insulators, and the related discharge propagation phenomena in the presence of salt contaminated snowstorms. Two types of flashover tests, a) Snow accretion without voltage application, then apply the voltage after snow accretion, b) Snow accretion during voltage application, were carried out on a 33 kV long rod insulator with the snow conductivity controlled between 180 and 980 μS/cm. Method a simulates the "cold switch-on" situations. In this case, the flashover voltage is found to be inversely proportional to the fifth root of the snow conductivity. Further, the flashover voltage showed a relation to the leakage resistance of snow-bridged insulators. Method b simulates energized situations during a snowstorm. The concept of Method b is equivalent to the “Ice Progressive Stress (IPS)” method described in the IEEE Std. 1783-2009. In this case, partial arc discharges gradually increase owing to the development of snow accretion. Flashovers are mostly induced during the period of snowstorm suspension, because the arc discharge can develop into a flashover without the cooling effect of the blizzard. Melting snow by heating of electric power does affect flashover characteristics. The minimum flashover stress by Method b is lower than that by Method a. However, in particular case of Method b with higher snow conductivity, too much discharge activities prevent snow accretion on the insulator. This leads to snow melting or snow shedding.