Many switches are used in HVDC converter stations. On the AC side of the converters, breakers, load break switches, disconnect and earthing (grounding) switches are used in much the same way as for conventional AC substations. On the DC side of the converters, the role of the switches is similar, that is to disconnect and earth parts of the system to facilitate maintenance and repair. The switches disconnecting parts of the system, are normally foreseen with blocking systems to prevent unwanted reconnection and are interlocked with earthing devices to prevent inadvertent energization of the grounded parts of the system. A second main reason for introducing these switches particularly in HVDC systems is the possibility to reconfigure the system after a fault or during maintenance. HVDC systems are important elements in high voltage grids which should be in operation as much as possible. In general, these systems incorporate a lot of redundancy and the possibility to operate in reduced modes such as at lower voltage or with reduced current. Several bypass switches are incorporated in the design to facilitate the transition from one state to the other state. It is expected that the introduction of meshed or radial HVDC grid will increase the use of switches even more. HVDC Circuit breakers, described in Chap. 51, “HVDC Circuit Breakers,” will play an important role in this respect but also synchronisation for connecting elements will increase.