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.