Identification Method of Current Transformer’s Tail Current Based on Waveform Characteristics

After the circuit breaker trips, the secondary side of the current transformer (CT) will produce a tail current, which is affected by factors such as the initial amplitude of the tail current and the time constant of the CT secondary side. The tail current may cause malfunction of the failure protection. At present, the identification method of waveform zero-crossing detection is often used to distinguish fault current and tail current, but in some cases, the method will also be invalid, and need a longer identification time. In order to reduce the speed and improve the reliability of tail current recognition, this paper, based on waveform characteristics, proposes an identification method of current transformer’s tail current. The generation mechanism of tail current is analyzed, and an identification method of tail current based on decrement-concavity characteristics is proposed for the difference of waveform between tail current and fault current in time domain. The reliability of the proposed method is verified by the simulation of PSCAD.