Hybrid HVAC/HVDC systems are a solution for the integration of large scale of renewables energies placed at long distance of the AC power system. However, when disturbances occur in the HVDC system, new behaviors are present in the power system. This paper studies the impact on AC systems when DC faults occur, evaluating short circuit and transient stability performance. As test system, the benchmark system of two areas and four generators is modified by including an HVDC network. This HVDC grid connects distant renewable energy sources to the main AC system. In this system, the evaluation of the short-circuit levels is conducted, as well as the response of the AC system to DC system's faults under two different protection schemes of the HVDC grid.