Due to increasing environmental burden and other cost related reasons, the transmission network is undergoing major change globally. One way to utilize transmission corridors more efficiently is to have several three-phase systems in the same tower. This can be multiple AC and DC circuits or AC circuits with different system voltages. The transmission of DC and AC on one tower is a challenging technical territory, particularly in case of intersystem faults. In order to cope with this, new technical solutions are required as well as practical testing of the present protection ideas are needed. This paper presents a PSCAD simulation model in order to investigate the intersystem faults in a hybrid AC/DC line, by utilizing four different cases. These cases have been tested to validate the simulation model and the results are presented. The arising phenomena especially the consequences with respect to the protection systems are discussed.