| The electromagnetic potential transformer(PT)is used to detect bus voltage in non-ground neutral system,it often causes ferroresonance overvoltage by the nonlinear excitation characteristics of PT.The mechanism of ferromagnetic resonance overvoltage in distribution network is introduced in detail,including a brief introduction to the neutral grounding mode of the distribution network,the nonlinear characteristic analysis of the core inductor,the physical process analysis of the single-phase ferroresonance and the quantitative analysis of the three phase ferroresonance.From the perspective of the frequency shift overvoltage and harmonic overvoltage,the voltage characteristics of primary side and open side of potential transformer during ferromagnetic resonance are analyzed.The experimental conclusions of Peterson H.A and the range of ferromagnetic resonance parameters are introduced.The identification method of ferromagnetic resonance and other fault characteristics is given when the abnormal voltage of the open delta voltage appears in actual system.The simulation models are built for the system simulation components,including the BCTRAN model of the transformer,the SAT model of the potential transformer,the JMarti model of the LCC overhead line and the MOV Type92 model of the LXQ harmonic eliminator.At the same time,the interpretation of the ATPDraw simulation results are given when the single-phase grounding fault occurs in the neutral point ungrounded system.Through the simulation of ferromagnetic resonance in a simple system,the typical waveforms of ferroresonance with different resonance types are given,the influence of potential transformer with different volt ampere characteristics on ferroresonance and the influence of different single-phase grounding failure disappearance time on Ferroresonance excitation are compared,and the simulation analysis of the ferroresonance excited by the non-synchronous air bus closing are discussed.On the basis of a complete system model,different restraining measures are adopted for the ferroresonance excited by the non-synchronous air bus switching and the single-phase grounding fault.It mainly includes adding small capacitance on system-side busbar to suppress non-synchronous air bus closing resonance.To suppress the ferroresonance excited by single-phase ground fault,the neutral point of the high voltage side of the voltage transformer equipped with a harmonic eliminator,the neutral point of the high voltage side of voltage transformer equipped with anti-vibration PT,voltage transformer opening triangle with damping resistance,and the neutral point of the system side installed with the arc suppression coil are used.A series of conclusions are obtained,which can provide references for the power sector to govern ferroresonance overvoltage. |
