Current-limiting reactors

Current-limiting reactors are desirable only insofar as they are strictly reliable protective devices. In this paper general considerations of the factors affecting reliability are outlined, and some of the early weaknesses and the means taken to eliminate them are enumerated. Modern reactors are considered to be reliable and on large systems are considered practically indispensable. The thermal duty of a current-limiting reactor is a consideration affecting the reliability which has been the subject of considerable discussion. Various opinions have been expressed ranging from the idea that a reactor should fail first and open the circuit in the event of short circuit, to the idea that it should have enough thermal capacity to withstand short-circuit currents for long periods of time. A middle ground is suggested in this paper where recognition is given both to the protective function of the reactor and to the practical consideration of dimensions and cost.