ABSTRACT
This chapter considers three-phase transformers under steady-state balanced conditions. Three-phase power transformers are an extension of the single-phase transformer, where increased number of windings can be connected in different ways. If the three-winding transformer circuit is converted to per unit values having a single power base, and three power voltage bases according to the transformation ratios, the magnetic couplings disappear and a wye-shaped circuit is obtained. In addition, power calculations become independent of single- or three-phase magnitudes being involved. According to the Q–V and P–f regulators available, the steady-state operation conditions of a synchronous generator seen from its output terminals are same as those of an element with specified active power and rms voltage. In balanced steady-state conditions, the induction machine has an analogs behavior to that of a transformer and hence a transformer model can be used to represent this machine. Unlike the magnitude regulating transformer, the phase-angle transformer cannot have an equivalent circuit without coupling or nonreciprocal components.
