Digital Simulation of Distance Relay for Long Transmission Line

This paper presents the design and modeling of Distance relay with the help MATLAB/SIMULINK. A transmission line network has been developed and fault voltages and currents generated due to various symmetrical and unsymmetrical faults have been plotted. The input voltage and current to the transmission line network during fault conditions consist of DC offset values and higher order harmonics. As these are unwanted signals, they need to be filtered out. For proper functioning of the distance relays, the Discrete Fourier Transform (DFT) is used which can easily eliminate these unwanted signals. The response of the proposed distance relay model was plotted on an R-X diagram. The results were obtained for a single line to ground (SLG) fault, double line fault (LLG) and three phase fault (LLLG) at distinct locations of a long transmission line of length 250 kilometers on a power system network.