PICA 2001 Preview

This letter reviews the general model of transformers with off-nominal turns ratios used in power systems steady-state studies. The conventional model of the load tap change transformer (LTC) is shown in terms of the analytical expressions that represent this device. A general model incorporating the effects of the transformers with off-nominal turns ratios with the phase shifting transformers is presented. The differences between the alternative models, in which the admittance is represented either on the tap side or on the opposite tap side of the transformer, are explained. It is also shown that, if the admittance is represented on the tap side, its value must be suitably adjusted. An example illustrates the differences in terms of numerical results from these models.