Development of a new derivative-based algorithm to detect current transformer saturation

Derivative-based approaches have been used both in the literature and in the industry to identify fault current distortions caused by current transformer (CT) saturation. This study presents a new simple, but efficient, derivative-based technique to detect CT saturation. First a difference function for the samples on the two sides of the current local extremum is defined. Based on the values of this difference function for various current samples, a variance function is defined. By comparing this variance function with a pair of pre-set thresholds, CT saturation can be determined. This technique is not affected by CT parameters such as CT burden, core remanence or magnetisation curve. The independence of this method from the fault current characteristics, such as decaying DC time constant, noise and so on, is investigated. Numerous simulations were carried out using PSCAD/EMTDC program. The performance of this algorithm for simulated fault currents together with a set of experimental results verify the accurate operation of the proposed method for different conditions including mild and fast CT saturations.