Evaluation procedures for lightning impulse parameters in case of waveforms with oscillations and/or an overshoot

Definitions of standards IEC 60 and IEEE Std 4 are insufficient for the evaluation of lightning impulse parameters of waveforms with oscillations and/or overshoot. This has brought about different interpretations in the estimation of these parameters, especially when using digital recorders. Large discrepancies have resulted from the different interpretations. The working group 33.03 of CIGRE has collected various opinions about this problem. These are presented, analysed and discussed in this paper. Different ways of determining mean curves of impulses with oscillations and/or overshoot are proposed. In addition, different alternatives for the definitions of overshoot amplitude and duration are suggested for impulses with overshoot. The problems and alternative solutions are discussed in the light of analyzing three impulses of the IEC Test Data Generator. This illustrates clearly the need to change the above mentioned standards. Simple, easily applicable, reproducible and technically justified definitions are required in order to take advantage of the accuracy and facilities of digital recorders in impulse measurements. This paper offers the basis for further discussion on the subject before WG 33.03 of CIGRE makes its final proposal. Further studies with practical test impulses are still needed.