Prevention of Resonant Overvoltage in Substation Transformers due to a Short-Line Lightning Stroke (SLS) by Arresters on Transmission Towers

Abstract

Surge arresters are usually installed in a substation to reduce crest of surge voltage below insulation levels of electric power equipments. Nevertheless, it has been reported that the harmful overvoltage might be induced by local resonance in a transformer winding.
Waveftorms of the surges coming over a substation transformer due to flashover at different transmission towers are calculated by using of digital computer program of the EMTP (model-39). The derived incoming surges are all represented as being oscillatory due to reflections between the flashover arc at the striking point and the transformer. When the lightning striking point is a few km far from the substation, the incoming surge oscillates with some tens of kHz and it might cause a harmful resonant overvoltage in the transformer windings. Thus, this kind of lightning stroke is emphasized in this paper as referred to SLS: short-line lightning stroke. It is pointed out that the lightning arresters installed on the transmission towers is so much effective to prevent an oscillatory incoming surge from occurring.