Non-Contact Measurement and Polarity Discrimination-Based Identification Method for Direct Lightning Strokes

Abstract

Direct lightning strokes account for a large proportion of line faults. Lightning faults can be classified into several kinds, and the corresponding protection methods differ. The type of these lightning faults should be identified to establish targeted measures against lightning and improve lightning protection design. In this study, a non-contact multi-physical parameter lightning monitoring system is proposed. The voltage of the insulator string and the lightning grounding current of the transmission tower are chosen as two physical parameters to show the characteristic quantities of different lightning stroke types. These physical parameters are captured using a non-contact overvoltage sensor installed at the cross arm of the tower and several parallel Rogowski coils installed at the tower ground supports. An equivalent electromagnetic transient model of a 110 kV transmission line is developed to identify features of the signals under different lightning strokes. Based on time-domain and wavelet transform modulus maxima (WTMM) analyses, the polarity of insulator voltage, the polarity of tower current, and the mutation polarity of tower current when insulators flashover are extracted as characteristic quantities of polarity discrimination. Six kinds of direct lightning strokes can be identified based on the polarity discrimination method considering the lightning stroke point and the lightning current polarity. The identification method is verified by simulation data and application to an actual example.