ABSTRACT
Circuit models are often used when a transformer is part of a larger circuit such as a utility network. This chapter considers the transformers that are operating at steady-state power frequencies, generally 50 or 60 hertz. In developing a circuit model of the core, three-phase cores and transformers can be analyzed as three separate single-phase units. The chapter focuses on a two-winding transformer having a primary and secondary winding. The primary winding is attached to the input power source, while the secondary winding feeds a load. The chapter explores how the parameters of the circuit model can be extracted from test data and can be used to obtain the core power factor, that is, the fraction of the core power that is dissipated as loss. Transformer impedances, along with other quantities such as voltages and currents, are often expressed in the per-unit (pu) system, that is, as a ratio with respect to the transformer's nominal or rated phase quantities.
