Power transformer protection using fuzzy logic based-relaying

Recently, the frequency environment of power system has been made more complicated and the quantity of 2nd frequency component in inrush current of power transformer has been decreased because of the improvement of core steel. Traditional approaches will likely be mal operated in the case of magnetizing inrush with low second harmonic component and internal faults with high second harmonic component. This paper proposes a new relaying algorithm to enhance the fault detection sensitivities of conventional techniques by using a fuzzy logic approach. The proposed fuzzy-based relaying consists of flux-differential current derivative curve, harmonic restraint, and percentage differential characteristic curve. To get the trip or no trip in the output by fuzzy rule base, different values i.e. small, medium and large values (with the standard formulae) from different fault cases are derived. Therefore, there is clear fault discrimination between magnetizing inrush and internal faults. So that power transformer will be protected.