Reduction of inductance and current rating of the coil and enhancement of fault current limiting capability of a rectifier type superconducting fault current limiter

A rectifier type superconducting fault current limiter is mainly composed of a rectifier using diodes and/or thyristors, and a superconducting coil. It has advantages in the following aspects. It can control the fault current level by controlling the coil current. AC losses can be reduced because the current through the superconducting coil is rectified DC current. But the longer the fault current limiting time is, the larger the superconducting coil current becomes and the fault current level increases due to the increase of the coil current. This paper shows how to reduce the inductance and current rating of the coil and how to increase the fault current limiting capability. The idea is to put a resistor in series with the superconducting coil for absorbing the incoming energy into the coil and turn on and off the switching device connected in parallel with the resistor in order to control the coil current in a pre-set region. Simulation results assuming the fault current limiter as an inter-connecting device between a generator of IPP (independent power producers) and utility grids, and some experimental results with a laboratory model will be shown.