Measurement of inrush current in transformer based on optical current transducer

The accurate measurement of inrush current is a key problem in transformer protection. Traditional electromagnetic current transformer (CT) has nonlinear characteristics of its core. When the transformer generates inrush current, it will be saturated and lead to current distortion, which will lead to transformer differential protection misoperation. Optical current transducer (OCT) is not affected by saturation and can be used to measure and identify inrush current well. This paper analyses the mechanism of inrush current, the reason of CT saturation and the principle of OCT measurement. The simulation and experimental results show that OCT has better measurement quality than traditional CT and superiority to differential protection.