Non-effectively Grounded System Ferroresonance Analysis And Fault Line Selection

Resonant earthed system can also partly become neutral ungrounded system because of improper operations.In the neutral ungrounded system;the frequent ferroresonance over-voltage would seriously affect the operation safety in electric power system.The arc suppression coil can achieve entirety compensating;the series resonance can be aroused by the change of the capacitance current.In addition,after some perturbations and single-phase-to-earth faults disappear,the series resonance can be aroused by arc suppression coil late adjusting.The resonant earthed system is popular in power distribution networks.The problem of fault line selection for singie-phase-to-earth faults in resonant earthed system is one of important topics to the protective relaying.The large numbers of cables are used in power distribution networks at the present time,It make the problem more complexer.Resonance and single-phase-to-earth fault have similar characteristics,the abnormal network voltages and the PT open-delta voltage more than the fifteen percent of phase voltage can be aroused by them,the insulation detection device send out single-phase-to-earth signal,accordingly,the phantom earth fault phenomenon can be genetatedIn this thesis,the problem of fault line selection,ferroresonance over-voltage in resonant earthed system and series resonance are studied.The majority work and achievements in this thesis are as follows:1,The principle of ferroresonance over-voltage is introduced.High frequency,basic frequency and divided frequency ferroresonance over-voltage that is aroused by PT saturation is simulated by MATLAB based on theoretical analysis.The simulation results are proved correct by Peterson experimentation curve.2,The essential reason of PT high voltage fuse breaking is analyzed.The analyse result indicate that the leading reason of PT high voltage fuse breaking is not ferroresonance but is capacitance discharge impact current that emerge after fault recovery.The primary measures to eliminate ferroresonance are introduced.The measures that can eliminate ferroresonance and PT high voltage fuse breaking at the same time are analyzed,simulatd and proved.3,The problem of line selection of single-phase-to-earth fault in the resonant earthed system has not been well settled for a long time.This thesis summarizes the present line selection techniques,analyzes their applicable conditions while expatiating the principle of line selection.Based on this,analyzes the development directions of line selection techniques in future.4,After analyse the transient process of resonant earthed system in detail,a typical radiate resonant earthed system is set up,it is structured by hybrid transmission lines of power cables and overhead lines,then MATLAB is employed for corresponding simulation and the basal data is offered to the resonant earthed system line selection of single-phase-to-earth fault.5,A new method for single-phase grounding fault line selection based on wavelet packets and correlation analysis is proposed,Theoretical analysis and large numbers of simulation results demonstrate that the result of fault line detection using the method is accurate and reliable.6,A method for distinguishing ferroresonance and single-phase-to-earth fault in the neutral ungrounded system or single-phase-to-earth fault and series resonance in resonance earthed system is studied.A integrative over-voltage fault project is presented which integrate fault type distinguishing,automatic tuning of arc suppression coil and fault line selection.Once neutral voltage exceeds 15 percent of rated phase voltage,according to the result of fault type distinguishing,the equipment is capable of automatically taking the corresponding operations.