Comprehensive evaluation of the K-factor values in the lightning impulse voltage test techniques for UHV-class electric power equipment

In the 2010 revision of IEC-60060-1 "High-voltage test techniques", the conversion of waveforms using the test voltage function (K-factor) was introduced as one of the major revisions. At present, in IEC TC42 "High-voltage and high-current test techniques," a study is conducted on the standards for the lightning impulse voltage test at WG 19 "Adaptation of TC 42 standards to UHV test requirements." The present paper comprehensively evaluates the experimental results of the K-factor values using the largest possible model assuming UHV-class electric power equipment, as well as the past experimental results of the K-factor values. Initially, these experimental results were evaluated from a view point of insulation properties to clarify the characteristics of the Kfactor values. The adaptation itself of the K-factor evaluation method to also cover UHVclass equipment is considered significant. However, for high-voltage class equipment, since the formative time lag of breakdown is longer due to the long insulation length, resulting in a longer breakdown time, the K-factor values are considered lower than the existing K-factor function. Subsequently, the experimental results of the K-factor values were comprehensively evaluated and compared with the existing K-factor function. The K-factor function may possibly have to be reviewed for UHV-class electric power equipment to take lower values than the existing K-factor function.