An increasing share of renewable energy sources within the power generation infrastructure as well as the aspect of increasing energy trading demand a higher flexibility within the power transmission system infrastructure in Germany and Europe. High voltage direct current (HVDC) transmission systems are one major key technology offering this flexibility and transportinh high shares of renewable energy to distanced load centers. For the timely integration of HVDC corridors within an existing high voltage alternating current (HVAC) grid infrastructure, the utilization of existing transmission corridors implicates economic and ecological advantages. Thus, the parallel routing of high voltage AC and DC circuits becomes a realistic scenario, which has to be coped with. Studies of electromagnetic coupling between these systems already addressed the effect of fundamental frequency coupling. A major open point ist the handling of intersystem faults between both systems.