The saturation of current transformer results in the decrease of reliability and rapidity of transformer differential protection. The waveform similarity is used to extract the phase information of the current on both sides of the transformer

especially when the current transformer is saturated. A transformer differential protection criterion against current transformer saturation based on waveform similarity is proposed to identify various faults including saturation of current transformer. The results of simulation and dynamic simulation tests show that the criterion can make correct judgments when identifying faults inside and outside the transformer

especially when the current transformer is saturated. In the case of noise interference

the fault can be identified effectively only by simple processing.