Multiterminal Operation of HVDC Converter Stations

In the present stage of HVDC transmission technique, future applications may be outlined for which a multiterminal operation of HVDC converter stations would appear necessary or desirable. Simple problems, such as tapping of an HVDC transmission, can be solved by means of the known control and protection methods of the two-terminal operation. An unrestricted multiterminal operation, however, involves a number of additional requirements that relate to the control and protection equipment. For instance, it demands balancing of the reference values of all converter stations, which can be realized with a central electronic equipment. But it is also possible to indicate control methods for multiterminal operation that do not call for central reference value balancing and special communication facilities between the different stations. A problem of particular importance in multiterminal operation is the dc circuit breaker. The functions to be assumed by such an HVDC breaker may be derived from its interaction with the electronic control and protection equipment.