Transformer Models Overview

Representation of transformers is a fundamental necessity for the analysis of electromagnetic transients in power systems. There are two primary methods by which transformers are modeled in PSCAD:  The Classical and the Unified Magnetic Equivalent Circuit (UMEC) methods.

 

The classical models are limited to single-phase units, where the different windings are on the same leg of the core.  The UMEC models however, consider the core geometry and also represent inter-phase coupling.

 

Besides this obvious distinction, the primary difference between these two transformer models is how core non-linearity is represented.  In the classical models, the non-linear characteristics are approximated based on the 'knee point', the 'air core reactance' and the magnetizing current at the rated voltage.  The UMEC core characteristics are entered directly in the model as a V-I curve.

 

Unlike the classical transformers, the UMEC models are not equipped with an online tap changer.  There is the ability to include a tap setting on a specific winding, however this setting cannot be changed dynamically during the run.

 

 

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