Parameter determination for modeling system transients-Part III: Transformers

Transformer modeling for transient simulations has many challenges because of nonlinear and frequency-dependent behavior. Some of the model parameters are relatively easy to obtain from standard factory tests. Other parameters can only be obtained from special tests or by estimation. This paper provides guidelines for the estimation of transformer model parameters for low- and mid-frequency transient simulations. The paper also discusses several transformer models that can be used for transient simulation.

I. Introduction

Several factors make transformer modeling a difficult task: transformer behavior is nonlinear and frequency dependent; many variations on core and coil construction are possible (Figs. 1 and 2); there are many physical attributes whose behavior may need to be correctly represented (core configuration, coil configuration, self- and mutual inductances between coils, leakage fluxes, skin effect, and proximity effect in coils, magnetic core saturation, hysteresis, and eddy current losses in core, capacitive effects). Fig. 1. Three-phase core designs. (a) Triplex core. (b) Three-legged stacked core. (c) Shell core. (d) Five-legged stacked core. (e) Five-legged wound core. Fig. 2. Winding designs. (a) Concentric design. (b) Interleaved design. (c) “Pancake” design.