Impact of fault resistance on impedance relay: Adaptive Mho directional type scheme development using LabVIEW

Normally, fault resistances come out with errors in the fault calculation algorithm on conventional Mho distance protection scheme which might force the relay to under-reach/over-reach based on the network conditions. With a constrained shape, Mho Directional distance elements can provide more resistive coverage while discriminating between forward and reverse faults. In this work, the recurring effect a fault resistance can have on a Mho Distance protection scheme relay is assessed and analyzed for single line-to-ground(SLG) faults for both protective schemes. Finally, an adaptive correction algorithm is applied to compensate errors introduced in the fault calculation unit using local end data. The design and simulation are performed using LabVIEW and MATLAB/SIMULINK. Magnitudes and angles of three voltages and currents are obtained through Discrete Fourier Transform(DFT). Different scenarios are carried out and validate the effectiveness of the scheme. Moreover, an improved Graphical User Interface(GUI) is developed for easy and convenient interaction between users and the relay model.