Models of Ferroresonant Transformers

A ferroresonant transformer is analyzed based on the equivalent magnetic circuit and then using magnetic-field equations. It is shown that the Fourier analysis provides a quick and reliable method for the prediction of output voltage and current at resistive or reactive loads. The finite-element model with the voltage-driven coils is used to verify and correct the predicted fundamental and high harmonics as well as losses in the transformer. The direct solution of the nonlinear differential equations for the coupled electrical and magnetic circuits is also considered as an alternative way to analyze the resonance. However, this approach requires applying the appropriate initial conditions that are estimated from Fourier analysis. The voltage waveforms predicted from the calculation models are in good agreement with the oscilloscope screenshots.