The UMEC (Unified Magnetic Equivalent Circuit) transformer model is based primarily on core geometry. Unlike the classical transformer model, magnetic coupling between windings of different phases, and coupling between windings of the same phase are taken into account. There are a few UMEC transformer models available in the master library (MLIB\PSYS_V2) which are _rtds_1P2W_UMEC, _rtds_1P3W_UMEC, _rtds_1P4W_UMEC, _rtds_3P2W_UMEC and _rtds_3P3W_UMEC.
The UMEC transformer model is based on the magnetic circuits, so it needs the physical core structure parameters in the computation process. Normalized core parameters are used in the model so that requirements of physical data are minimized. Only 4 core aspect ratios are needed. If a three limb core is selected in the CONFIGURATION menu, two ratios are needed, the ratio of core yoke length (Ly) to the core winding−limb length (Lw), and the ratio of core yoke area (Ay) to the core winding−limb area (Aw). If the 5 limb core is selected, two additional parameters are required, the ratio of core yoke length (Ly) to the core outer −limb length (Lo) and the ratio of core yoke area (Ay) to the core outer−limb area (Ao). The core structures of 3 and 5 limb transformer as shown in the following figures.