A new method for overcurrent relay (O/C) using neural network and fuzzy logic

For coordination of O/C relays, it is necessary to model the relay characteristics and calculate the time dial setting (TDS) of the relays. The O/C relays´ characteristics are normally modeled by a polynomial using a curve fitting technique. A new method for calculating the TDS and t (operating time of O/C relays) based on a neural network and fuzzy logic is used. In this method, fuzzy logic uses the same information as the neural network. Also the variation of t with the TDS is not assumed linear, therefore t is calculated with a high accuracy. In addition, in the method used for determination of the TDS, we do not need to use numerical analysis and mathematical equations, so the calculation speed as well as the accuracy is increased.