Remanence detection and low-frequency degaussing for power transformers based on modified J-A model

Inrush currents are high magnitude currents generated typically during energization of a transformer, being a large transient caused by saturation of the magnetic core of the transformer. The magnitudes of the inrush currents can be initially several times the rated load current which will cause error actions of the relay protection equipment [1]. When a transformer is put into operation at the optimal angle, the residual flux becomes the main factor leading to inrush currents. Measuring methods on residual flux before often had to saturate transformers during the detection and were complex and not accurate enough [2]. Besides, in past AC-degaussing methods, high-power supplies were used but hard to carry [3].