Reducing the Fault-Transient Magnitudes n Multiterminal HVdc Grids by Sequential Tripping of Hybrid Circuit Breaker Modules

A sequential switching strategy for hybrid dc circuit breaker (CB) is proposed to improve transients during dc fault interruption in multiterminal high voltage direct current (HVdc) grids. Compared to the conventionally tripped dc CB, the proposed switching strategy, which sequentially trips the breaking modules within the CB, reduces the peak fault current and overvoltage as well as fault clearance time. These metrics are analytically computed through a time-domain calculation approach considering the traveling wave phenomena in dc transmission systems. By rescheduling the tripping sequence and optimal rating and number of individual modules of the CB, the energy distributed among the modules is well balanced. Finally, an analytic evaluation of the proposed sequential tripping is performed and, subsequently, the best practice and the optimal design process are provided. Performance of the sequential switching strategy as well as the optimal design process are verified through simulation studies in the PSCAD/EMTdc software environment.