Transformers are represented in EMTDC through one of two fundamental methods: The classical approach and the unified magnetic equivalent circuit (UMEC) approach.
The classical approach should be used to model windings placed on the same transformer leg. That is, each phase is a separate, single-phase transformer with no interaction between phases. The UMEC method takes inter-phase interactions into account: Thus, 3-phase, 3-limb and 3-phase, 5-limb transformer configurations can be accurately modeled.
Representation of core non-linearities is fundamentally different in each model type. Core saturation in the classical model is controlled through the use of a compensating current source injection across selected winding terminals. The UMEC approach uses a fully interpolated, piecewise linear f-I curve to represent saturation.