The accurate leakage inductance value of the transformer primary and secondary side leakage inductance is the key to the theoretical and simulation analysis of the transformer inrush current transient characteristics. First, the transformer differential equation is deduced, and two calculation expressions for solving leakage inductance under system balance and unbalance are obtained. Aiming at the scenario where the circular current of the delta winding cannot be measured, a parameter acquisition method based on current coupling characteristics in unsaturated zone is proposed. This method takes advantage of the mutual coupling between the circular current of the delta winding and the non-saturated phase current of the primary side. First judge the unsaturated phase, and then use the opposite of the unsaturated phase current instead of the circulating current to solve the quasi-leakage inductance under the two expressions. The quasi-leakage inductance values in the unsaturated zone are almost equal, and the average value in this zone is used as the calculated value. Simulation data and field record data verify the effectiveness of the method.

leakage inductance,current coupling,unsaturated zone,circulating current