Protective-equipment analysis using a digital computer

The paper describes a way of studying the behaviour of power-system protective schemes using step-by-step methods on a digital computer. Initially, a current transformer model is developed, and it is shown that it gives accurate results. The equations governing the performance of a moving-coil relay are then given. A program to determine the behaviour of a restricted earth-fault protective circuit incorporating a high-impedance relay is outlined, and computed results for typical conditions and parameters are given. The effects of parameters such as core permeability are quite evident. It is clear that the methods described could be applied to many schemes to determine their performance and factors such as operating times and stability limits.