AN ANALYSIS OF THE EFFECT OF FAULT IMPEDANCE ON THE OPERATION OF DISTANCE RELAYS

Abstract

The exact solution of the equations for the behaviour of transmission lines leads to terms involving hyperbolic functions of the quantity (ZY)fr. It is customary to call this argument the complex or hyperbolic angle of the line. In the analysis of relay operations, it has, however, been usual to assume linear variation of the line constants, without taking note of the hyperbolic angle of the line. In this paper the hyperbolic relation for transmission lines has been used to discuss the effect of fault impedance on the impedance seen by distance relays and on their operation. The effect of different types of variation in the fault impedance on the relay operation is also discussed. The final relations developed are applied to the case of a 235 miles long transmission line and the effect on relay operation indicated.