Short-circuit fault current-limiting characteristics of a resistive-type superconducting fault current limiter in DC grids

Resistive-type superconducting fault current limiters (R-SFCLs) can limit short-circuit fault current and help DC circuit breakers (DCCBs) to isolate short-circuit faults in medium voltage and high voltage DC (HVDC) systems. SFCLs are always used with circuit breakers to break short-circuit current in power systems. The interruption characteristics of the DCCBs influence the current-limiting characteristics of the SFCLs. However, there has been a lack of investigation into the current-limiting and interruption characteristics when R-SFCLs are combined with mechanical-type DCCBs (M-DCCBs) based on the self-excited oscillation interruption principle in medium voltage and HVDC systems. The objective of this paper is to obtain the short-circuit fault current-limiting characteristics of a designed R-SFCL combined with an M-DCCB in DC grids. This paper describes the design of a 10 kV DC R-SFCL which was tested in combination with an M-DCCB in a DC circuit in order to obtain the quenched resistance and the required current interruption characteristics. Besides, a modular multilevel converter-based multi-terminal direct current (MMC-MTDC) grid was used to investigate the current-limiting and interrupting characteristics of the R-SFCL and the M-DCCB in a realistic HVDC grid. The experimental results show that in the 10 kV DC circuit the R-SFCL combined with the M-DCCB limited a 10 kA DC to the peak value of 1416 A and then interrupted this limited current successfully. And unlike other methods of DC interruption, this did not create overvoltage after interruption. The highest voltage on the R-SFCL is the system voltage during interruption. This means that the R-SFCL can effectively delay the voltage drop in MMC-MTDC grids, and provide enough time for the M-DCCB to interrupt the limited current. Thus, a combination of R-SFCLs and M-DCCBs might be an effective and reliable method to interrupt short-circuit fault currents in medium voltage and HVDC grids.