A New Method on Calculation of Lightning Trip Rate of 35 kV or Under Overhead Distribution Lines in Ungrounded Neutral Point System

In recent methods on calculation of lightning trip rate, it is thought that insulator flashover in one phase could lead to trip. While in ungrounded neutral point system, only insulators flashover in two or three phases could result in trip. A new method on calculation of lightning trip rate of 35kV or under overhead distribution lines with ungrounded neutral point is proposed, consists of direct lightning trip rate and induction lightning trip rate. Couplings of grounded phase on sound phases are considered legitimately. New calculation formulas of arcing rate and induction overvoltage are adopted. Based on different methods, include traditional formulas method, modelling & simulating method with ATP, and new method proposed in this article, lightning trip rate of typical 10kV overhead distribution line is calculated. A comparison between the different calculation values and practical statistics certifies the accuracy of the new method. The research in this article contributes to the absence of an appropriate and accurate method that applies to the calculation of lightning trip rate of overhead distribution lines in ungrounded neutral point system. It also helps to estimate the level of lightning attack accident and provides references to lightning protection in engineering practice.