Analytical model of iron losses in power transformers

The authors have improved a circuit model of transformers by defining a conductance whose losses will be close to the iron losses under any circumstance. Connecting a constant conductance G_cs in parallel with the main magnetizing inductance is very popular in the literature; however, it is acceptable only if the flux amplitude and frequency are reasonably constant during the time of operation, and if the value can be properly adjusted. Here, they replace G_cs with a nonlinear dynamic conductance G_cd, whose losses are a function of flux amplitude. This conductance is based on the concept of dynamical hysteresis. Its definition is such that it is determined by the same test results used for G_cs. Knowing the values of losses given by the manufacturer of the sheets, and the measured values of iron losses of a transformer, one can then analytically express the building factor as a function of the maximum flux density. The authors have applied the method to a three-leg 10-kVA transformer. It allows one to identify the cases when iron losses may be ignored, when they may be represented by a constant conductance, and when they must be represented by a nonlinear conductance.