An Impedance Measurement of a Small-Capacitance Circuit using Transient Responses for Lightning Surge Analysis

A method to measure a small capacitance with its loss resistance using a set of transient current waveforms is proposed in this paper. The parameters are obtained from the time constants in the time domain. The method has high resistance to extraneous noise, because a time-to-frequency transformation, which is sensitive to noise, is not required. The transient current waveforms are obtained by a voltage or current source, a current transformer, and a waveform recorder. The measured capacitance by the proposed method is not affected by the capacitance of the voltage probe, because it is obtained without any voltage information. The sheath surge impedance of the current injection cable, which is indispensable for the transient measurement, is corrected. The application of the method has the advantage in that it allows the modeling of a fast transient of a power apparatus, comparing it with the steady-state measurement using an impedance measuring instrument. The proposed method is applied to create an equivalent circuit between electrodes implanted into a piece of wood, and its reliability is confirmed by comparison between the measured and calculated results. Stray capacitances of a miniature circuit breaker are also measured, and the results show that the proposed method is applicable to equipment in power systems. (c) 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.