Introduction: The design of the first two trial units incorporates a non linear high temperature superconducting ceramic in series with a circuit breaker for the clamping and clearance of fault energy. When the material is operated at below its critical temperature it loses all electrical resistance, thereby allowing load current to flow with negligible losses. In the event of a fault, the increased current density or the loss of cooling medium (liquid nitrogen) causes the temperature of the superconducting material to rise and it reverts to a normal resistive state.

Being a solid state device, the resistive Superconducting Fault Current Limiter (SFCL) has been proven to operate in a few milliseconds, after which the impedance remains high until the fault is cleared by conventional means (protection operated circuit breakers, fuses, etc.). The resistive SFCLs operation is sufficiently fast to ensure that the first peak of the fault current is limited. The subsequent limited current can be set to suit a specific application.

The third trial unit design employs a pre saturated core reactor design. A superconducting winding carries a DC current that drives the core into saturation under normal operation. The AC current is unimpeded under normal operation: however, in the event of a fault, the magnetic field opposes the DC field with sufficient magnitude to drive the core out of saturation, thus effectively inserting an inductance into the AC circuit, reducing the peak fault current to approximately 40% of its prospective value.

Objectives: This project aims to design, develop and trial three 11kV SFCL devices on three GB networks.