Identification Of Fundamental Frequency Ferroresonance And Single-phase Grounding Fault In Distribution System

Ferromagnetic resonance which triggered by single-phase grounding fault and potential transformer saturation happens frequently in neutral non-grounding power distribution system, the fault characteristics of the two kinds of faults are all shown as the zero sequence voltage rise. It is the most difficult to distinguish fundamental frequency ferroresonance from single-phase grounding,so it may also cause inaccurate judgement by staff, and then cause serious accidents by misoperation of the fault,and make a further expansion of the fault,therefore, it needs accurate identification of single-phase grounding fault and fundamental frequency ferroresonance.This paper analyzes the produce mechanism and fault characteristics of fundamental frequency ferroresonance and single-phase grounding fault in neutral non-grounding system. Using Kirchhoff's law deduce relational expression of zero sequence voltage and zero sequence current that located in the line after failure occurrence, and the distribution of zero sequence current and the changing law of the three-phase voltage in the distribution system after fault are analyzed.After analysis and summary of the fault characteristics of these two types of fault, phase difference of zero sequence component and fluctuation value of zero sequence voltage that are selected on each line after the fault is regarded as criterion of fault feature. Hilbert transform is used to calculate the quantity of phase difference between zero sequence voltage and zero sequence current, and then the result is obtained by comparing the difference of the phase difference. The fluctuation value of zero sequence voltage is used as an auxiliary criterion in order to improve the reliability of fault identification. Adopting fluctuation detection method based on effective value of voltage calculates the fluctuation value of zero sequence voltage after fault, the identification of single-phase grounding fault and fundamental frequency ferroresonance is achieved by comparing with the set threshold.The fault identification method of this paper is proved to have good reliability for the identification of fault types by the simulation of fundamental frequency ferroresonance under different induced modes.