New solutions to decades-old fault current issues
BY JACK McCALL, AMSC
As the demand for electricity has grown, along with the need for increased system reliability, utilities have added generation and built interconnections to more tightly mesh their networks. Both result in higher fault current levels. Electric utilities in Europe have recently begun taking surge protection for the power grid into consideration by employing new fault current limiting solutions that are designed to meet many of the challenges caused by today’s highly interconnected networks and diversified generation sources. As fault levels increase, the ability of stationary equipment to withstand the forces associated with these high fault levels become a concern.
North American electric utilities have long employed a variety of fault current mitigation techniques such as fault current limiting reactors, selective tripping schemes, and so forth. However, each of these schemes has distinct drawbacks. The ideal would be a re-usable, automatic device that did not restrict or impair the operation of the power system during normal operation, but yet could limit fault currents starting with the first cycle peak.
Enter stand-alone superconductor fault current limiters (SFCLs) and superconductor fault current limiting power cables (SFCL cables). Enabled by high-temperature superconductors (HTS), these systems can significantly lower peak currents during faults. This provides utilities with the ability to:
• Greatly reduce the costs of other equipment in their network,
• Defer or eliminate equipment replacement,
• Increase equipment lifetimes,
• Improve grid performance and operation,
• Simplify the integration of renewables, and
• Improve operator safety.
A variety of devices have been designed with HTS elements to act as stand-alone SFCLs. These include resistive fault current limiters (FCLs), shielded core FCLs and saturable core FCLs. In fact, resistive SFCLs have been developed, tested and deployed at both medium and high voltage up to 138 kilovolts (kV).