Current transformer saturation detectors for busbar differential protection

Busbar differential relays may operate incorrectly due to current transformer (CT) saturation. In this paper two different techniques are suggested to detect CT saturation. The first proposed algorithm is based on the fact that the wave shape of the CT secondary current is changed significantly at the instant of the saturation. Based on this feature, an algorithm which uses second derivative of CT output current is developed. The second proposed method utilizes the zero crossing principle. It compares the predicted and measured zero crossing of the current signal. The proposed method is able to detect even small CT saturation events. A real 400 kV busbar is simulated using PSCAD/EMTDC for evaluating performance of the proposed algorithms. Obtained results demonstrate the precise operation of the both proposed algorithms in different conditions.