A MICROPROCESSOR-CONTROLLED VARIABLE IMPEDANCE ADAPTIVE FAULT CURRENT LIMITER

The growth of electric power consumption has resulted in a corresponding increase in the fault current. In some cases, power utilities are faced with fault current levels which can exceed the rated capacity of the installed equipment. One method, to correct the problem, is to use a fault current limiter. The limiter must limit the peak current to a level below that of the momentary capabilities of the system components and limit the subsequent current peaks to a level which allows correct relay operation within the interrupting capabilities of the circuit breakers. This work describes the design and modelling of a microprocessor controlled variable impedance fault current limiter. The limiter consists of an LC series circuit tuned to be of minimum impedance at the supply frequency. A thyristor controlled reactor is shunt connected across the capacitor. By varying the firing angle of a thyristor pair, the impedance of the limiter is varied to allow the necessary current limitation, so that, the system is protected and all circuit breaker relays can operate. The fault current limiter is successfully modelled using a digital computer and validated in the laboratory with a prototype test setup. © 1990 IEEE