This paper presents a simplified equivalent circuit model (ECM) for the post-arc sheath stage in DC vacuum circuit breakers and outlines the method for calculating circuit parameters using the particle-in-cell Monte Carlo collision (PIC-MCC) method. The post-arc sheath is modelled as a parallel combination of a variable resistor and a variable capacitor. Based on a specific DC experimental case

the PIC-MCC simulation provides essential parameters of charged particles and electric field data for calculating equivalent resistance and capacitance. The total current through the circuit components is calculated by applying the transient recovery voltage (TRV)

and the resulting post-arc current (PAC) waveform is compared with experimental results to validate the simplified ECM and the proposed parameter calculation approach. Further simulations study the impact of the initial drift velocity of charged particles on equivalent circuit parameters and PAC traces

showing that higher drift velocities increase capacitance and decrease resistance

leading to higher PAC peaks. The comparison with experimental data indicates that considering the drift velocity contributes to the simulation accuracy.