Research On Influence Factors And Elimination Methods Of Ferroresonance Overvoltage In Power Distribution Network

Ferroresonance overvoltage fault occurs frequently in the distribution network where the neutral point is not effectively grounded.Regional chain failure can be caused and the safe and stable operation of the power grid is seriously affected.In recent years,a large number of cables were put into operation.Meanwhile,the transformation of network structure and load types becomes more and more complex which can easily lead to ferroresonance overvoltage fault.Therefore,it is significant to study the influential factors of ferroresonance overvoltage and research on the resonant type identification method and the suppression measures by theoretical analysis and electromagnetic transient simulation in order to maintain the safe and stable operation of the power grid.Based on the analysis of the ferroresonance overvoltage principle and corresponding methods,an equivalent circuit model of ferroresonance is established by combining the equivalent model of power system network and the relationship between voltage and current characteristics of voltage transformers is deduced.Aiming at a certain 110 kV substation in the site,the electromagnetic transient simulation model of ferroresonance overvoltage is established and the fault characteristics of ferroresonance overvoltage in substation are analyzed through parameters calculation and model selection of typical electric equipment.The simulation results are in agreement with the volt-ampere characteristics theoretical derivation results.The time-domain transient process of ferroresonance overvoltage is studied by inductive-capacitive parallel circuit model.The relation equation between the flux of the voltage transformer and the network parameters is deduced and the resonant operating point of the actual line parameters is calculated.The main influential factors of magnetic resonance overvoltage are analyzed theoretically.Based on the simulation model of ferroresonance overvoltage in 110 kV substation,the influences of distribution network parameters,voltage transformer magnetization characteristics and excitation mode on the characteristics of ferroresonance overvoltage(amplitude,resonant frequency and fault duration)are analyzed.The results show that the line parameter,voltage transformer parameter and the excitation conditions all affect the amplitude,frequency and fault duration of the ferroresonance overvoltage to a certain extent.Aiming at the fault type identification of ferroresonance overvoltage,wavelet transform is used to analyze the time-frequency characteristics of voltage transformer opening triangular voltage waveform.The resonant frequency is determined according to the waveform energy under different scales and the fault moment is identified through singular point analysis.Resonance identification method is proposed based on the comparison between the real-time magnetic flux calculation and the system resonance operation point and is verified by electromagnetic transient simulation.Different resonance suppression strategies are simulated by the 110 kV substation simulation model.The results show that the neutral point non-linear resistance of the voltage transformer effectively suppresses the ferroresonance and ensure the normal measurement accuracy of the voltage transformer at the same time.