Calculation of time constant of direct test and analysis of its influence on short circuit breaking test

Based on the expression of short-circuit current, according to the existing test data, three kinds of calculation methods of DC component of short circuit current decay time constant are derived. Analyzing the applicable conditions of different methods, and from the DC component, arcing time, final current half wave parameter, recovery voltage and TRV parameter, the influence of different DC component time constant on direct current short-circuit current interruption performance in direct test is analyzed, and the standard time constant parameter is quantified. The results show that the greater the time constant of the system is, the greater the percentage of the DC component is, and the slower the attenuation is, the longer the arc window is, the greater the energy of the arc is, when the current is zero, the di/dt and TRV are reduced. Taking a pilot test data as an example,a simulation model is built to simulate the 12 kV/40 kA short-circuit fault. The simulation results verify the validity and correctness of the time constant analysis scheme for short-circuit interruption, which provides a good theoretical reference for direct short-circuit test.