Research On Harmonic Elimination Method Of Small Current Grounding Power System

In the small current grounded power system,three-phase five-column electromagnetic voltage transformer is generally installed in the substation bus,and its frequent ferromagnetic resonance threatens the safe and reliable operation of the power grid.The overvoltage may exist for a long time,and this overvoltage may be expressed as a single-phase or multiphase ground voltage rise,or low frequency swing,causing insulation flashover or surge arrester explosion,or produce high value 0 sequence voltage components and cause the phenomenon of illusory grounding and incorrect grounding instructions,or generate overcurrent in a voltage transformer,causing fuse melting wire overheating fault.Therefore,the study of the main causes of PT ferroresonance,the influence factors and the existing control measures of the characteristics of a better prevention and control measures have significant engineering value and practical significance.In this paper,the simulation model of 10 kV and 35 kV distribution system is established by using ATP-EMPT electromagnetic transient simulation software,and the ferromagnetic resonance and low-frequency nonlinear oscillation caused by single-phase grounding fault in the distribution system are simulated.The ferromagnetic resonance of the 10 kV system and the 35 kV system is compared,the influence of PT excitation inductance characteristic,line to ground capacitance,PT primary side equivalent DC resistance and fault elimination time on ferroresonance and low-frequency nonlinear oscillation is discussed,and the influence factors are simulated and analyzed,and the general rules are found.It provides a theoretical basis for studying various restraining measures to prevent ferroresonance.The principle of PT ferromagnetic resonance is introduced and the existing main prevention measures are listed in this paper,among which the most commonly used harmonic elimination measures are the neutral point of PT at one side to add the harmonic eliminator.The principle of preventing PT ferromagnetic resonance is introduced in detail,and the simulation research is carried out.Based on the harmonic elimination effect of the harmonic eliminator,the harmonic elimination effect of the linear resistor is simulated and the variation rule of the linear resistor resistance with the line to ground capacitance is found,which provides a theoretical basis for the application of the linear resistor in practice.