A variable data-window phaselet transformer differential protection algorithm based on recursive least square theory

With the application of high and extra-high voltage transformer, traditional differential protection algorithm based on half period data window will possess a switching interval of 30 ms or even longer, which could hardly satisfy the quickness of protective relaying. When external fault occurs, inceptive fault transient component, inrush current, CT saturation, and harmonics would amplify the unbalance current, which easily bring about the malfunction of differential protection. This paper proposes an algorithm which based on recursive least square theory, and combine with variable data window phaselet algorithm to improve transformer differential protection. This least square based method is adaptive, and modulate the length of data window dynamically, and is accompanied by the continuous outlet frequency judgment, in order to ensure the correctness in the interferences of inrush current and inner fault. Simulation shows that algorithm is able to boost the reliability and sensitivity of transformer differential protection, and is significantly practicable than traditional methods.