Application of test results to the calculation of short-circuit levels in large industrial systems with concentrated induction-motor loads

The paper reviews the problems associated with determining the duty of circuit breakers in industrial power systems, and considers particularly the contribution made by induction motors. Original test results are presented and compared with calculated induction-motor fault contributions. A simple empirical method for calculation is proposed, and results of a survey of constants for 415V and 3.3kV motors are given. Current switchgear specifications are considered in relation to their application to industrial systems, to show those points which require special attention.