Digital model for transient studies of a three-phase five-legged transformer

A flux linkage model for a three-phase five-legged transformer is derived for the first time. The effects of mutual and leakage inductances, saturation, eddy current loss, hysteresis and residual fluxes of the nonlinear iron core are included. A straightforward and novel method for determining both the apparent and incremental inductance matrices for a loaded two-winding five-legged transformer is derived. Simulations presented are based on apparent inductance (λ/i) rather than incremental inductance (dλ/di) because this approach was found to be preferable for predicting the behaviour of the laboratory transformer used. Eddy current and hysteresis losses are combined into one core loss term which is accounted for by a voltage-dependence resistance load on the secondary. The model thus yields a completely detailed description of the transformer´s behaviour. A predictor-corrector algorithm written in FORTRAN is used to solve the set of nonlinear differential equations