Calculation of leakage reactance for HTS transformer windings with magneto-motive force imbalance

In HTS transformer the ampere-turn distribution of the windings is usually made lower density than in the conventional transformer for decreasing the magnetic field. Moreover, in our study the secondary winding, different from the primary which is pancake, is chosen helical for cutting down the circulating current among the branches. So there is a difference of magneto-motive force at the same height of the primary and secondary windings. In this paper, a leakage reactance is calculated on the HTS transformer windings with the different types and “HV—LV—HV ” arrangement on a core limb. An equivalent transformation is proposed about an uneven distributed magneto-motive force, and the effect of some factors on the leakage reactance is analyzed such as the pancake numbers and the gap lengths between two pancakes of the primary. The method is verified valid by the result based on the calculation of leakage magnetic field by finite element method (FEM)