| Due to the special geographical conditions,most of the railway power supply systems adopt 10 kV、35kV neutral ungrounded system,which often occurs faults such as wire breakage and short circuit.At the same time,electromagnetic voltage transformers are widely used in the power supply system in order to monitor and measure the voltage and metering electric energy of the power network.During switching operation or failure of the system,the normal working state of the voltage transformer will be destroyed until the inductance parameters and capacitance parameters reach an unfavorable match,resulting in saturation of the PT excitation and the occurrence of ferromagnetic resonance overvoltage,which seriously affects the reliability of railway power supply system and the safety of railway transportation.At present,there are many kinds of ferromagnetic resonance suppression measures in both theoretical research and engineering practice,but each measure has its limitations and applicable conditions.Therefore,it is necessary to analyze the specific situation,through the comparative analysis of various measures,select the practical inhibition measures.In this paper,the mechanism of ferromagnetic resonance overvoltage,the conditions and the characteristics of frequency division,fundamental frequency and high frequency ferromagnetic resonance overvoltage are analyzed first.Based on the principle analysis,application range analysis and simulation analysis of the neutral point series damping resistance suppression technology,open triangle parallel damping resistance suppression technology and other suppression measures such as 4 PT,neutral point access small resistance or arc suppression coil,the common ferromagnetic resonance influencing factors of railway power supply system,such as external excitation mode,grounding resistance value of single-phase grounding fault point,time of disappearance of single-phase grounding fault,etc.,applicable range of each suppression measure is obtained.Finally,this paper further explains the characteristics of ferromagnetic resonance,judging process,disposal method,preventive measures and so on.By comparing the effect of various suppression measures,the neutral point series damping resistance is suitable for all kinds of fully insulated voltage transformers,which has the advantages of wide application,small volume and low cost,but also has the advantages of limited thermal capacity,limited resonance of the PT and influence measurement accuracy.The grounding measures of neutral point through small resistance or arc suppression coil have the advantages of reducing the probability of arc grounding overvoltage,and at the same time,there are defects such as affecting the reliability of power supply system and detecting the inaccuracy of grounding fault type of system.Through the research of this paper,it is hoped that it can provide useful reference for railway power supply maintenance personnel to deeply understand PT ferromagnetic resonance,fault judgment in actual operation of equipment,selection of PT in engineering practice and selection of harmonic elimination measures. |
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