Detection of High Impedance Faults by Distance Relays Using Prony Method

Transmission lines are usually suspended from steel towers and provided with one or more earth wires. Therefore the earth fault resistance during flash over on the isolators is only few ohm. In the case of rare arc faults, at mid-span, or during flash over to trees, very high impedance faults may result. Depending on the setting of the zones in R-direction, a maximum of some tens of ohms can be detected. Larger resistances are outside the reach of the distance protection, and must be detected by a separate earth fault protection. Distance relays must operate whenever a fault occurs. Therefore, detecting high impedance faults is an important issue since the relay should be able to differentiate the fault condition and load condition. This paper presents a new method for detecting a high impedance fault, based on extracting components of the current waveform using the Prony method. The merit of the method is demonstrated by simulating different high impedance fault conditions using the MATLAB/SIMULINK.