Phase jump correction factor applied to the differential equation algorithm by an adaptive scheme

The measured impedance of distance protections is affected by an error because of the combined effects of fault resistance and prefault load. This study proposes the implementation of an adaptive scheme which applies a correction factor based on the phase jump of the current waveform once fault occurs to improve the apparent impedance estimated by relays based on differential equation algorithms (DEA). The relation between current phase jump, prefault power conditions and fault resistance has been deduced with an experimental curve that relates the error introduced into the estimated apparent impedance with the registered phase jump. Through this experimental curve a correction factor has been obtained as an exponential function of the phase jump that, applied to the apparent impedance measured by the relay, allows mitigation of the adverse effect of prefault power. The proposed adaptive scheme improves significantly the accuracy of the estimated fault location without delaying the response time of the DEA algorithm. The application of this scheme does not require communication links with the remote end of line and is extended to all types of fault.