| With the continuous development of the power grid construction level,the stability and reliability of the power grid are constantly strengthened.But in the field of low voltage distribution network,the network equipment and the failure rate has been high,especially in the lOkV distribution network,often appear because of the voltage transformer(PT)saturation caused by ferroresonance overvoltage caused by a serious threat to the safe and stable operation of power distribution network.Although a lot of researches have been carried out by scholars at home and abroad,the mechanism of ferromagnetic resonance has been explored,and many suppression measures have been summarized from engineering.However,because of the large system diversity and complex external influence factors,the suppression measures are not universally applicable,and the application effect is not good.Therefore,it is very necessary to study the ferromagnetic resonance law of neutral point ungrounded system,as well as the influence of external excitation factors and harmonic elimination measures on ferromagnetic resonance,and further provide guidance for the selection of harmonic elimination measures.In this paper,the lOkV power supply system of a typical 110kV substation in Heze,Shandong province is selected as the research object.The parameters of PT and transformer in the system are determined through theoretical deduction and test,and then the simulation model of substation is built.Through the electromagnetic transient simulation software(EMTP)to calculate the model changes at the ferromagnetic resonance operation modes,different system of PT air bus switching,single-phase grounding fault of grounding resistance and the impact of external factors with the further exploration in the system adopt trend of ferroresonance elimination after application of different harmonic.By contrast,the quantitative simulation,summarizes the effect of different harmonic elimination measures and scope.The results show that under different operation modes due to different Xco/Xm values,the results of different magnetic resonance;in the three-phase ofclosing PT bus with air closing(single phase delay)will appear ferroresonance,while the air line does not appear ferroresonance;on Ferroresonance intensity of single-phase grounding fault is stimulated by disappear than that with PT air bus switch,and intermittent arc grounding may cause serious ferroresonance.The grounding resistance of single-phase grounding fault has little influence on ferromagnetic resonance,but the difference of the failure time will lead to the change of ferromagnetic resonance.Through the research on the resonant suppression measures are found:in the PT high voltage side of the neutral point of installing nonlinear resistor or harmonic elimination device can effectively suppress ferroresonance caused by single-phase grounding,but eliminator heat capacity needs to be meet the requirements of the system;the 4PT method can inhibit ferroresonance,but is in the closed triangle will large circulation,and we should pay attention to the saturation problem of zero sequence PT.Increasing the power to ground capacitance can effectively suppress the ferroresonance excited by the PT air bus switching,but the increase of the ground capacitance will lead to the increase of PT over current.The opening in the PT two side of the triangle with resistance or can effectively inhibit the single-phase grounding fault and fault disappearance of ferromagnetic resonance caused by harmonic elimination device,but can not effectively solve the current phenomenon of frequency resonance,but also need to grasp the investment opportunity,the best in the grounding fault disappears,avoid circulation. |
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