386 / 2022-03-15 18:39:42

Analyze of Transient Current Characteristics of Hybrid DC Circuit Breaker in 500kV VSC-HVDC Grid

VSC-HVDC grid,hybrid DC circuit breaker,transient current,suppression method

Hybrid high voltage DC circuit breaker (DCCB) can quickly break the DC short-circuit current without zero crossing. It is an effective technical means to solve the problem of rapid and selective isolation of DC-side faults in voltage source converter based high voltage direct current (VSC-HVDC) grid which is the important developing direction of power grid in the future. VSC-HVDC grid has the characteristics of low inertia and weak damping., so that the developing speed of DC-side fault current in it is fast and the developing process is complex. The developing speed of fault current in hybrid DCCBs under DC-side fault can reach thousands of AMPS per millisecond. Studying the transient current characteristics of hybrid DCCBs under this case is important to the design and development of DCCBs. At present, the researches on the transient current characteristics under the DC-side fault of VSC-HVDC system do not consider the complex operating logic and cooperating sequence of AC breakers and DCCBs under the real control and protection logic of VSC-HVDC grid after short-circuit faults, and the changes with time of the fault equivalent circuit of VSC-HVDC grid caused by the operations of AC breakers and DCCBs are also not considered. However, under the real control and protection logic, the fault equivalent circuit of VSC-HVDC grid has the nonlinear and time-varying characteristics, which makes the path and rate of change of DCCB transient current complex and time-varying. There is still a lack of research on the DCCB transient current characteristics under the real operating condition of VSC-HVDC grid. Thus, taking the Zhangbei ±500kV VSC-HVDC grid project in China as the background, this paper analyzes the fault equivalent circuits of VSC-HVDC grid and its variation law with time, considering the operating sequence of AC breakers and DCCBs under the real control and protection logic of VSC-HVDC grid after short-circuit faults. Next, the expressions of transient current of DCCBs in each fault developing stage are deduced. The transient current stress evolution characteristics of each branch of DCCB and the influence law of the main circuit parameters of VSC-HVDC grid on them are revealed, which is important and helpful for the device selection and parallel number design of IGBTs in DCCB. On this basis, aiming at the problem that the transient current stress of the main branch of DCCB is severe and there is no effective improvement method, a transient current suppression method based on damping resistance is proposed. The configuration method and switching strategy of damping resistance are proposed, and the DCCB transient current suppression mechanism by using damping resistance is analyzed. Finally, the proposed DCCB transient current expressions, characteristics and suppression method are verified by electromagnetic transient simulation based on PSCAD/EMTDC platform.