Zero Phase Filtering for Lightning Impulse Evaluation: A K-factor Filter for the Revision of IEC60060-1 and-2

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Description/Abstract

The next revision of the international standard for high voltage measurement techniques, IEC 60060-1, is planned to include a new method for evaluating the parameters associated with lightning impulse voltages. This would be a significant improvement on the loosely defined existing method which is in part reliant on operator judgment and would ensure that a single approach is adopted worldwide to determine peak voltage, front and tail times, realizing standardization in measured parameters across all laboratories. Central to the proposed method is the use of a K-factor to attenuate oscillations and overshoots that can occur with practical generation of impulse voltages for testing on high voltage equipment. It is proposed that a digital filter that matches the K-factor gain characteristic be implemented and used for this purpose. To date causal filter designs have been implemented and assessed. This paper is concerned with the potential application of a non-causal digital filter design to emulate the K-factor. The approach has several advantages; the resulting design is only second order, it can be designed without using optimisation algorithms, it is a zero phase design and it matches the K-factor almost perfectly. Parameter estimation using waveforms from the IEC 61083 -2 Test Data Generator and experimental impulse voltages has been undertaken and obtained results show that the zero phase filter is the ideal digital representation of the proposed K-factor. The effect of evaluating parameters by the proposed method is compared to mean-curve fitting and the challenge of effective front time evaluation is discussed.