Determination of Equivalent Capacitors in a Double-break Vacuum Circuit Breaker Based on an Impulse-voltage Method

The stray parameters of a double-break vacuum circuit breaker (VCB) have a significant influence on the voltage distribution of the two breaks. The stray parameters are equivalent to two main equivalent capacitors. The two main equivalent capacitors are the equivalent break capacitor (C1) and the equivalent capacitor between the middle point of the two breaks and earth (C2). The objective of this paper is to determine the capacitance of C1 and C2 based on an impulse-voltage method. A 40.5 kV double-break VCB was studied in the experiment. An 8.5 kV pulse was applied on the double-break VCB. The voltage curves on each break were measured by two high voltage probes. A simulation circuit was set up. The parameters were tuned in the simulation circuit to match the simulated output curve with the measured output curve. The capacitance of C1 and C2 were obtained. For the test VCB, C1 was determined as 16 pF and C2 was determined as 27 pF. C1 was agreed with a measurement by a precise LCR instrument. The impulse-voltage method needed only a few shots to determine approximate C1 and C2 without using precise and expensive instruments.