Breakdown of 15 kV Insulators Under Bipolar Oscillating Impulse Voltage

Lightning overvoltages depend on several parameters and may deviate significantly from the standard lightning impulse waveshape. Voltages induced on overhead power distribution lines by nearby strokes may often exhibit bipolar characteristic. This paper investigates the behavior of a typical 15 kV pin-type porcelain insulator subjected to a bipolar impulse, representative of a lightning-induced voltage. It is shown that a simple modification on the method proposed by Savadamuthu et al. to estimate the insulation strength of small (a few mm) insulation systems subjected to bipolar oscillating voltages leads to promising results in terms of predicting the occurrence of flashovers on the 15 kV insulator.