Transformer modelling for distribution system studies. I. Linear modelling basics

A distribution transformer modeling procedure is discussed which represents the distribution transformer with a minimum of input data for network, load, and fault studies, thereby allowing the transformer to be routinely included as part of the distribution network. The models are developed directly from the magnetic circuit of the transformer and described by a Z-parameter model using an ideal transformer matrix T_i, which depends solely on the core structure. Values for T_i are determined for each core structure by analysis of the magnetic fluxes developed in the core. Per-unit models of the distribution transformer are described by a Z -parameter model which includes both the core and copper losses under nominal operating conditions. Y-parameter models are obtained from the Z-parameter models by matrix inversion, and can then be interconnected using the mode-to-branch transformation