This study presents a method to analyse the secure and optimal operation of transmission systems consisting of both HVDC (high-voltage direct current) and high-voltage alternating current interconnections under a scenario of high penetration of offshore wind and taking into account the system spinning reserves. Different reliability management strategies are assumed, accounting for a single AC element and/or a single DC element outage and taking into consideration the probability of failure of the different power system components. The cost of operation of the system and the wind energy curtailed over the operating time are determined. This method is applied to a study case, based on the CIGRÉ HVDC Test System. The system behaviour over a complete year is modelled using realistic wind generation and demand based on scaling data from the Belgian power system.