Evaluation of parameters of lightning impulse voltages from transformer tests using the new k-factor approach

Present procedures for evaluating full and chopped lightning impulse voltages in accordance with IEC 60060-1:1989 [1] are only an approximation of the physical behavior of the insulation and do not always give reproducible results for impulse waveforms with superimposed oscillation and overshoot. The results of a recent study have provided technical basis for developing new procedures with improved accuracy. This paper evaluates a number of procedures being considered by the relevant CIGRE, IEC and IEEE working groups. In particular, practical waveforms recorded during testing power transformers are evaluated in this study. The evaluation of these waveforms is useful and important because they cover a wide range of practical impulse shapes, overshoot amplitude and frequencies. In addition, the results of the new procedures are compared with those of the procedure specified in IEC 60060-1:1989.