Although the fundamental phasor analysis described above provides a conceptual approach to understand the ferroresonance phenomenon, the accuracy of the approach is limited due to the fact that the approach is based on the fundamen-tal-frequency phasors and ignores the harmonic contents of the voltage and current waveforms.
Such harmonics are of significant magnitudes under ferroresonance conditions and cannot be
ignored. Furthermore, this method can only be used for the investigation of fundamental mode of ferroresonance which is only one of the known ferroresonance modes. Due to the aforementioned drawbacks, more elaborate analytical methods
have been proposed which are discussed in the next sections.