Demonstration of a three-dimensional current mapping technique around a superconductor in a prototype of a conventional superconducting fault current limiter*

A Superconducting Fault Current Limiter (SCFCL) is a device that limits large current surges in a power distribution network. Despite its advantages, conventional SCFCL has no mechanism to inhibit the generation of instabilities like hot spots in the superconductor. Such instabilities often damage the superconductor, failing the SCFCL during its operation. Here, we describe the three-dimensional current mapping technique around the superconductor of a prototype superconducting fault current limiter. The SCFCL has an array of Hall sensors distributed around the superconductor inside the SCFCL. Signals from the Hall sensor array are used to generate in real-time three-dimensional maps of local average current distribution at different locations around the superconductor. Our measurement at currents less than the critical current shows a non-uniform current distribution around the superconductor. This is a signature of non-uniform flux pinning across the superconductor. The capability of real-time monitoring and mapping of average local current distribution offers a unique way to detect instabilities around the superconductor in the SCFCL. We propose a design that provides early detection and protection against instabilities developing in the superconductor and offers an added flexibility, namely, allowing for a user-settable fault current threshold. This ability allows fault limiting operation to begin at the initial stages of the fault development. Such flexibility is not offered in conventional SCFCL. Using the above, we also show inherent limitations in the earlier design of metallic shunts placed in direct contact with superconductors.