A New Analytical Method for Cross-Country Multi Fault in Double-Circuit Transmission Line & Operation of A Distance Relay

Abstract

To analyze multi faults on a power line, we need to perform many complexed calculations. So, in many cases, we used to do them, using computers, in the actual phase domain. But it is difficult to expose the property and/or the physical meaning of the calculated results, because the computer method is based on many complexed numerical calculations.
This paper represents a new analytical method for short circuit studies, which can deal with crosscountry multi fault in double-circuit transmission line with zero-sequence mutual coupling. This method is based on the well known “two-component network theory” for a balanced three phase double-circuit. Procedure steps are; (1) Represent the network seen from the faulted points, with symmetrical component impedance. (2) Construct the symmetrical equivalent circuits for faults, with imaginary phase shifting transformers. (3) Combine these equivalents with each other, and erase the symmetrical voltages at faulted points, because the phase voltages at faulted points are known. (4) Calculate the currents at the faulted points, by solving the simultaneous linear equations.
We applied this method to an investigation of a distance relay's “ underreach” phenomena in case of cross-country multi fault occured on a double-circuit transmission line. Effects of line constants to this phenomena have been well understood.