A new method to identify CT saturation based on the time difference algorithm

The current transformer (CT) may saturate during internal fault, external fault, exciting inrush current, over-excitation and other phenomena. If CT reaches to the saturation point and the current difference between the two both sides of the transformer is larger than the restrain current, it will result in the mal-operation of the percentage differential protection. As a result, it is vital to identify the CT saturation effectively and block protection reliably when CT saturation occurs. In this paper, on the basis of the traditional time difference method, a new identification method of CT saturation is proposed, which is applied to percentage differential protection. Results from EMTP simulation and Matlab calculation show that this method is able to identify all cases of CT saturation accurately therefore greatly improve the correct action rate of percentage differential protection.