Identifying Inrush Current for Large-Scale Wind Parks Transformers Based on Difference Function of Differential Current

Traditional second harmonic restraint method used in large-scale wind parks (WPs) transformers of may lead to incorrect action of relay protection. Regarding the above issues, a method for identifying inrush current of WP transformer based on difference function of differential current is proposed. First, currents on both sides of transformer are collected and differential current is used to construct a first-order difference function and a second-order difference function. In order to eliminate influence of attenuated direct current component, a criterion is formed by taking the second-order difference function as abscissa and the first-order difference function as ordinate. The principle is that on the plane composed of differential current signal and its difference function, the distance between any two adjacent points does not change much when inrush current does not occur, but changes significantly when inrush current occurs. According to the feature, identification criteria of inrush current is constructed. A system model is established by electromagnetic transient tool and results show that the proposed method can accurately and sensitively identify internal faults and inrush current, regardless of fault locations and fault types.