Discussion on standard waveform in the lightning impulse voltage test

The lightning-impulse voltage test of electrical equipment is specified in IEC 60060-1 "Highvoltage test techniques", whereby the standard waveform has a front time and a time to halfvalue of 1.2/50 μs. These values have been unchanged from IEC Ed. 1 in 1962 through to Ed. 3 in 2010, and further study is also ongoing with 1.2/50 μs as a starting point in the currently active WG "Adaptation of TC 42 standards to UHV test requirements". The present paper initially reviewed how studies had been conducted to establish the lightning-impulse test in the U.S.A. and investigated the flow of how the study results linked to IEC Ed. 1 together with the standards in Europe. Eventually, it seems that, in terms of the flow from the U.S.A., the current numerical values of 1.2/50 μs were most probably derived from the lightning surge observation results at the Wallenpaupack-Siegfried 220-kV system of the Pennsylvania Power & Light Company in 1929 and so forth. Subsequently, major characteristics of recent lightning surge observation results were analyzed from the perspective of current actual electrical facilities and equipment. Consequently, points common to the data of 1929 in terms of the average values and the breadth of the distribution emerged in the crest value - front time and crest value - time to half-value plots. At the same time, differences due to the individual conditions of the individual measurement positions were also recognized. The detailed analysis and study of the standard waveform of the lightning-impulse test based on the analysis results are considered issues to be addressed.

I. Introduction

The test standards used to check the dielectric strength of electrical equipment are specified in IEC 60060–1 “High-voltage test techniques Part 1” [1] governed by IEC TC42 “High-voltage and high-current test techniques”. In these standards, the standard lightning-impulse voltage is defined as follows: “The standard lightning-impulse voltage is a smooth full lightning-impulse voltage having a front time of and a time to half-value of “ (Hereinafter in the present paper, T1: Front time and T2: Time to half-value are expressed as uniformly, according to the current means of description, including cases where other methods of description were historically used in the U.S.A.). The latest IEC is that revised and published in 2010 mainly for electrical equipment of 800 kV or less, including the introduction of a waveform conversion method using the test voltage function (K-factor function) and the clarification of standard values, such as the overshoot rate [2], [3]. Currently, studies are ongoing in the WG 19 “Adaptation of TC 42 standards to UHV test requirements” to establish standards for UHV-class electrical equipment [4], [5].