Line Distance Protection in Presence of Superconducting Fault Current Limiter

There is an increase in fault current levels seen by utilities due to grid expansion and the addition of new resources. Installation of superconducting fault current limiter (SCFCL) at transmission voltage levels is being explored to reduce the fault levels. The SCFCL limits the fault current by inserting an additional impedance in the network, which may impact the protection system. This paper discusses the impacts of SCFCL on the operation of line distance protection. It is observed that operation of SCFCL may not impact all the distance relays in the substation and near-by substation in the same way, thus a boundary definition method is proposed in this study to identify the affected relays. The definitions of boundary condition based on steady-state fault current values and critical current of the SCFCL are proposed in this study. The impact of SCFCL on the line distance relays which manifest as underreaching of the relays and may also lead to coordination issues and erroneous operation. An implementation method for mitigation which is compatible with existing substation relays is proposed and demonstrated to ensure proper operation of the relays. The proposed mitigation ensures that the system integrity is maintained during faults.