| Shengli Oil Field for the regular occurrence of resonant power grid over-voltage, removal of inductive motor load, etc. will also have a similar over-voltage, Serious voltage transformer burnt.Oscillation in power system circuit, PT is the core inductance components, if there is a large disturbance or operation, PT may be the non-linear core saturation, which with the lines and equipment-to-ground capacitance of the formation of a special single-phase or three-phase resonance circuit, Stimulate continuous, high amplitude of the over-voltage.In the neutral node ungrounded power distribution system, ferroresonance due to the nonlinear excitation inductance of three-phase inductive potential transformer(PT) once happened, has a serious impact on the safety operation of power system.However, the operation parameter is random due to the complexity of system configuration and the variability of operation style. In addition, various prevention measures all have disadvantages, leading inefficacy in certain cases. Therefore, based on the analysis of mechanism and characteristic of ferroresonance of neutral node ungrounded system, it is necessary to discuss more effective preventive methods.This paper models on Shengli oilfield Ninghai substation 35kV power distribution system in Jiaxing. including: connecting nonlinear resistance to the neutral point of three-phase PT high voltage side, connecting single-phase PT to the neutral point of three-phase PT high voltage side, connecting an arc-extinguishing winding to the neutral point of power system, connecting damping resistance or subharmonic ferroresonance eliminator to,the broken delta winding of three-phase PT et al. Then detailed analysis and comparative study on the above prevention measures are presented.Harmonic elimination time in different areas often used in different ways, Power use in the oil field in the Three-Phase Five-PT installation of zero-sequence neutral measures to achieve the PT,High side voltage transformer in the neutral series single-phase voltage transformer. A coil voltage transformer main access into astrocytes, Neutral grounding transformer zero-sequence voltage,Auxiliary voltage transformer secondary main access into a closed triangular coil, The program is equivalent to a neutral point of access to a high-impedance, which resulted in the equivalent three-phase voltage transformer significantly increased, In order to achieve to avoid due to saturation caused by ferroresonance.Substation on the field the second harmonic elimination using a combination of measures to achieve the suppression of resonance,At the same time, over-voltage to lower voltage transformer may be destroyed.onance is effectively eliminated when nonlinear resistance is connected to the neutral point of three-phase PT high voltage side, which not only keep the phase voltages steady but also restrain the inrush currents flowing in the high voltage windings of three-phase PT in the period of earth faults and then at the instant of disappearance. Moreover, zero sequence voltage on the broken deltaWindings operate can reach 100% during earth faults. In this case, the voltage relay can correctly and the system can increase security. Positive temperature coefficient (PTC) thermistor and triple frequency harmonic filter can reduce zerosequence voltage when nonlinear resistance is used to prevent Connecting nonlinear resistance is better than connecting single-phase PT in capability and entirety of ferroresonance elimination. In addition, quantitative research has been done on effective prevention coverage for arc-extinguishing winding. Reasons why the subharmonic ferroresonance eliminator can't prevent ferroresonance effectively are analyzed. Moreover, validity of some other prevention measures is discussed. The results of this paper are proved to be of great use in ferroresonance elimination for electric power department and greatly improving the reliability of power distribution system.
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