Fuzzy-logic algorithm for detection of intermittent earth faults

Abstract

In the case of faults which are especially ‘difficult’ to detect, the effectiveness of the operation of protections can be improved using fuzzy logic. It refers mainly to the intermittent earth faults. The intermittent faults in the MV distribution grids are often unnoticed by the conventional earth fault protections and, consequently, are not eliminated. In such faults, the periodically non-stationary measuring signals are generated. By smoothing the waveform, for example by averaging it within an appropriate interval, the criterion value falls below the start-up value and the fault discrimination using traditional binary logic (true/false – fault/ lack of fault) is not ensured. The fuzzy logic fits here better. In the work, the protection with fuzzy decision system is proposed.