Superconducting Fault Current Limiters for HVDC Systems

High-voltage direct current (HVDC) transmission systems using Voltage-Source Converters (VSC) are widely recognized as offering significant potential for long distance high power delivery, particularly for offshore wind farm connections. One of the barriers for the development of multi-terminal HVDC systems is the lack of technologies which enable direct fault isolation. This paper will investigate DC fault current limiting technology to reduce fault currents to acceptable levels allowing DC circuit breakers to operate quickly and reliably. Superconducting fault current limiters (SFCL) are a promising candidate, satisfying most of the ideal fault current limitation requirements. This paper shows the potential for reducing the fault current to more acceptable levels using SFCLs in VSC-HVDC systems. A summary of the advantages and disadvantages of resistive and inductive SFCLs is also given. An SFCL limits DC fault current very effectively, reducing the fault current the HVDC circuit breaker would have to interrupt. The paper includes a detailed analysis of resistive and inductive SFCLs including aspects of practical design for use in commercial VSC-HVDC systems. Finally, key issues such as cryogenic cooling and superconducting material costs are highlighted.