Research and development of a full-bridge cascaded hybrid HVDC Breaker for VSC-HVDC applications

This paper proposes and demonstrates a novel full-bridge cascaded hybrid HVDC breaker to meet the application requirement of voltage source convert (VSC) based high voltage directcurrent (HVDC) system. The world first five-Terminal Zhoushan HVDC project constructed by State Grid Corporation of China (SGCC) adopts the topology of half-bridge submodules and has been put into operation since 2014. However, due to the absence of a HVDC circuit breaker, this five-Terminal system is susceptible to dc-side faults, which cause high fault current and rapid voltage collapse that propagates throughout the network and forces the whole system out of operation within a short time. To clear the DC fault, it depends on using of the slow-Action AC circuit breaker interruption in a long time for the system recovery. This compromises the operation reliability and economical efficiency to the project. This paper gives a detailed description of the proposed hybrid HVDC breaker, including its full-bridge cascadedtopology designs, operation principles and test results. The paper also presents a prototype development of the main components, such as the semiconductor switches and the ultra-fast disconnector (UFD) as well as the power-supply unit, in terms of the reliability and compact modular design. Various tests are implemented to verify the overall performances of the hybrid HVDC breaker prototype. The testing results show that the full-bridge cascaded hybrid HVDC breaker fulfills the application requirement of VSC-HVDC system and is planned to be installed at the five-Terminal Zhoushan project. The rated values for the hybrid HVDC breaker presented in the paper are as follows: Rated voltage: 200kV Maximum breaking current:15kA Breaking time (excluding fault clearance time): <3ms Transient interruption voltage (TIV): >300kV Power loss: <0.01%.