MODELING OF ALTITUDE EFFECTS ON AC FLASHOVER OF POLLUTED HIGH-VOLTAGEINSULATORS

The paper introduces a new physical approach to account for the effect of reduced air density on the flashover voltage and critical leakage current of polluted high voltage insulators. The analysis starts by up dating the mathematical model, previously established, of power freque ncy flashover of polluted insulators al normal atmospheric pressure. i t then proceeds to introduce the effect of ambient pressure on the phy sical parameters of the dielectric recovery equation. The effect of re duced pressure on the are boundary radius is investigated. The combine d effect of humidity and reduced air density on the dielectric strengt h at ambient temperature is also accounted for. The above analysis res ults in a new expression for the reignition voltage which includes amb ient pressure effects. The analytical findings are then used to invest igate the effect of reduced air density on the critical leakage curren t and flashover voltage of simple-shaped polluted insulators. The effe ct of more complex profiles is subsequently introduced. The model resu lts are compared with experiments and the agreement established is qui te satisfactory. Finally simple practical altitude correction factors for polluted insulators are proposed.