Abstract: Arc interruption of High Voltage Direct Current (HVDC) Circuit Breakers (CBs) is one of the main challenging factors for using HVDC grids. To evaluate the arc interrupting capability in HVDC circuit breakers, black box arc models are used to represent the non-linear arc conductance depending on Cassie and Mayrdynamic arc equations. A real line represents a part of 500 kV electrical connection systems between Egypt and Kingdom Saudi Arabia is simulated to be a faulty load. Cassie breaker in normal operation doesn’t need commutation circuit but in this study, we will investigate the influence of using commutation circuit with Cassie breaker. It is founded that the commutation circuit doesn’t generate resonance but for changing the total impedance of circuit breaker and this leads to decrease both of the arcing voltage and arcing time. Moreover, we will study the effect of using multi-break of Cassie breaker type when using commutation circuit.