Study on the Application of a Flux-Coupling-Type Superconducting Fault Current Limiter for Decreasing HVdc Commutation Failure

Commutation failure is a serious malfunction in high-voltage direct current (HVdc) converters and is mainly caused by ac side faults, where the change of dc current during fault conditions should be given adequate attention. Employing superconducting fault current limiters (SFCLs) for an HVdc system can suppress its dc fault current´s amplitude and maintain a small rate of the dc current change, which is helpful to inhibit the commutation voltage reduction. Accordingly, introducing SFCLs may act as one possible solution to decreasing HVdc commutation failure. In this paper, a flux-coupling-type SFCL is adopted to play this role. The SFCL´s topology structure and working principle are presented first, and then its influence mechanism to HVdc commutation failure is systematically investigated. Further, considering several different fault conditions, the transient performance of a 500-kV HVdc system equipped with the SFCLs is evaluated in MATLAB. From the results, installing the SFCLs can effectively decrease the duration of the commutation failure and facilitate the fault recovery process, and sometimes a possible successive commutation failure is avoided, as a result of improving the power transmission characteristics. Finally, in view of ac loss and equipment selection, the application feasibility of the SFCL for a high-voltage/large-scale system is preliminarily discussed, and some valuable conclusions are obtained.