The maloperation and refuse operation of transformer differential protection often occur in recent years. The field data show that the fault of differential protection often occurs in the situation which is more complex than the typical no-load energizing of transformer. It is necessary to study the action of transformer differential protection in the complex electromagnetic transient environment. Aiming at those problems

the mechanism and characteristics of inrush current in the case of remanence

DC bias and CT saturation of transformer are studied

the causes of malo-peration and refuse operation of differential protection in the above cases are analyzed

the factors leading tomaloperation and refuse operation of transformer are summarized

and the corresponding measures to improve the correct operation rate of differential protection in complex electromagnetic transient are put forward in order to guarantee the safe operation of power system.