A2Z Consulting

Leakage flux is a part of the flux produced by a specific winding and linked with this winding only. Inductance associated with this flux is called leakage inductance and each transformer winding has its own leakage inductance. Although leakage inductance is one of the important transformer design parameters, it cannot be easily calculated. Analytical models for transformer leakage inductance calculation are available only for the simplest types of transformer cores and winding types.
The possibility to estimate leakage inductance is even more important in case of multiple winding transformers (used in chained cell topology). Multiple winding transformers are required, for example, for feeding Medium Voltage VFDs based on multi-cell topologies. In these transformers there are several secondary windings coupled with each primary winding. The leakage inductance of secondary windings is unequal due to asymmetric coupling between them and the primary winding. 
During this project, 3D finite element model of 3-phase multiple winding transformer was developed. Using this model, the influence of windings arrangement on the leakage reactance asymmetry was analyzed and design rules for asymmetry reduction were formulated.