Numerical and experimental simulation researches on characteristics of ferroresonance based on distributed power grid parameters

In this paper, some models of typical potential transformers (PT) were established by PSCAD/EMTDC considering the non-linear magnetic excitation characteristic. A test system for the experimental research in a 10kV neutral non-grounding distribution power grid was also set up. A series of simulating tests to reproduce ferroresonance initiated by single phase grounding or line breaking fault were carried out. The frequency analysis based on FFT method has been applied on the feature extraction of the voltage and PT current waveforms. The basic characteristics of ferroresonance with frequency, such as the ratio of capacitive reactance and inductive reactance (X
C
/X
L
), the magnitude and waveforms of the overvoltage and PT current, have been studied and summarized. The results of experimental verification indicate that the simulation models are finely closed to the characteristic of real power grid operation. The PT current can reach 5 to 10 p.u. when subharmonic ferroresonance occurs. The deep magnetic saturation of PT will bring the high components of current harmonics.