Dynamic Capacitance Measurement of SF6 Circuit Breaker During Opening Operation

In order to mine the state information of SF₆ circuit breakers (CBs) interruption chamber and evaluate the contacts state, a method of measuring and calculating the dynamic capacitance between contacts in CBs opening process was proposed. The test CB is connected in series with a high frequency AC power supply, and the voltage and current of the circuit breaker are measured during the opening process. The fundamental frequency components of the voltage and current are extracted by the short-time Fourier transform, and the dynamic capacitance curve as a function of time is calculated. The results show that due to the variation of capacitance, there are a large number of harmonics with frequencies close to the fundamental frequency in terminal voltage and current. During the first two cycles after contacts separation, the capacitance drops sharply to 33.25 pF, then with the increase of the contact distance, the capacitance decreases much more slowly and tends to be constant, and the capacitance is 20.70pF after the completion of the opening.