MATLAB-Simulink S-Function for modeling a digital MHO distance relay

A new model for Mho relay algorithm in MATLAB based on Fast Fourier Transform Algorithm (FFT) has presented in this paper. The proposed MHO algorithm evaluated by using MATLAB to models a power system and simulates many fault conditions on a selected transmission line such as different fault locations, resistances with various fault angles. The proposed model has been tested under different conditions for single line to ground (SLG) fault, double line fault (LL), double line to ground fault (LLG) and three phase fault. All types of faults were applied at different locations to test the proposed model. A Mho R- jX plain has been created inside the proposed model to show the trajectory of measured apparent impedance by the relay. The results show that the relay operates correctly under different locations for each fault type.