HIGH-SPEED RESISTANCE MEASUREMENT OF CLOSING SWITCHES USING A TRANSMISSION-LINE DISCHARGE TECHNIQUE

Time-dependent resistance of a high voltage. high current, closing switch was measured via the discharge of a low impedance transmission line. With this technique, only the current waveform of the switch, the initial open circuit voltage, and the transmission-line characteristics need to be known to determine the switch resistance waveform. Under certain conditions a simple lossless transmission-line formula is sufficient for the calculation of the switch resistance waveform. However, if the transmission-line losses cannot be neglected a correction can be readily implemented through numerical signal processing. The bandwidth of this technique is limited to the bandwidth of the switch current record only. This is particularly useful in the measurement of the resistance of high voltage, high current switches where inductive pick-up noise in the switch voltage waveform is large and where high voltage probes of sufficiently high bandwidth are not readily available. In this article, both simulated and experimental examples are given, together with the method of calculation of switch resistance which takes into account practical transmission line losses. It was found that best results are obtained if the magnitude of the switch resistance is higher than or of a similar order as the characteristic impedance of the transmission line.