In this paper, the generator circuit breaker (GenCB) is simulated using ATP- EMTP software package. Four main stages of the breaker’s operating processes are considered, namely; the closed contacts stage, the arc burning stage, the arc extinguishing stage and the opened contacts stage. Therefore, not only the dynamic conductance during current zero are considered but also the effects of arc voltage on the arcing times are included. The simulation is tested in a representative network and the results are compared with IEEE Generator Circuit Breaker standards. A new mitigation technique is introduced to reduce the transient recovery voltage and the rate of rise of re-striking voltage during switching period. The results show that the new technique reduces both the TRV and RRRV effectively with respect to previous ones.