A method for the evaluation of the behavior of a 15 kV insulator under bipolar oscillating impulse voltages. (July 2019) - Silva, Alexandre Rigotti
Highlights: Clarification that bipolar lightning surges in distribution networks are not rare; Test results regarding the behavior of distribution insulators under bipolar lightning impulses; The Savadamuthu et al. method is unsuitable for application to MV insulation systems; New method for the analysis of the behavior of MV insulators under bipolar impulses. Abstract: Lightning overvoltages are affected by many parameters and may differ substantially from the standard lightning impulse waveshape. Voltages induced on overhead power distribution lines by lightning flashes terminating on a point in their vicinity not rarely exhibit bipolar characteristic. In this paper the behavior of a typical 15 kV pin-type porcelain insulator subjected to bipolar oscillating impulses representative of lightning-induced voltages is investigated. It is shown that the method proposed by Savadamuthu et al. to estimate the insulation strength of small insulation systems subjected to bipolar oscillating voltages is not able to predict any of the flashovers observed on the insulator. However, a simple but effective modification of the method to estimate the three basic parameters of the model results in a better criterion to evaluate whether a semi-cycle contributes to the flashover process and leads to a significant improvement in the rate of success of the procedure in predicting the occurrence of flashovers.