Fuzzy Logic Based Overcurrent Protection for Mv Networks

In the paper a novel approach to overcurrent protection stabilisation based on Fuzzy Logic technique is presented. The scheme is intended for MV overhead lines for which the autoreclosure function is applied to enhance reliability of supply in case of intermediate (vanishing) faults. Protection stabilisation is required for the feeders supplying a part of network with numerous loaded MV/LV transformers that may face inrush conditions after reenergising the line. Traditional harmonic restraint approach as for single transformer may not be effective for line overcurrent protection because of different current spectrum as measured at the MV busbars. The new FL protection developed takes both current and voltage signals for further processing and final decision is issued as a result of aggregation of partial decision support coefficients. Application of signal fuzzification and fuzzy settings enables obtaining a relay with increased sensitivity, reliability and much faster than commonly available solutions. The developed fuzzy protection scheme has been tested with EMTP signals and compared with other standard protection approaches.