Research On The Harmonic Resonance Of Substation And Prevention

In recent years, with the increase of nonlinear loads and the use of various power electronic products, massive harmonics are brought in electricity grid, which caused voltage distortion. At the same time, the harmonics may cause parallel and series resonance in partial electricity network. These harmonics will be magnified and resonance overvoltage are produced, which accelerates the aging of electrical equipment insulation , prompts capacitors and reactors damaged, and affects the security of power supply. This thesis researches the principle of resonance in substation, analysis resonance and resonnance elimination based on a practical substation. The difference between resonance and short circuit is also analysed .This provides basis for comprehensive treatment of resonance in substation . The main works are as follows :①The basic principles of transformer substation resonance ,the calculation method of shunt capacitors in series or parallel resonance point and the major damage of resonance are analysed in the thesis. The research status at home and abroad and main measures of prevention and elimination are also mentioned.②This thesis analyses the resonance priciple of shunt capacitors, mainly studies the response of harmonic currents to impedance frequency characteristics and calculation of the resonance range. The resonance harm to capacitors and measures of resonance elimination are also discussed.③This thesis researches on the base of Zunyi substation 110kV power system, and calculates the resonance point when the transformer substation operation in maximum and minimum operation modes. Some elimination measures according to the resonance are put forward, and simulation is used to validate the validity of them. The measures of resonance elimination which change the parameter of capacitor to get rid of resonance range are applied to the practical system, and the validity of the measures are proved.④The theory and phenomena of wire-break resonance due to open phase operation of breaker,single or two phase fusing, line breaking and the one end of breaking line grounding are researched. The empty bus resonance whose resonant wavelengths only stay in the empty bus of substation is also discussed. This thesis calculates the resonance point and put forward the elimination measures according to the resonance .A simulation has validate the validity of the measures.⑤The difference between short circuit and resonance phenomenon is researched. Analysing the cause of virtual earthing which due to the basic frequency resonance and putting forward the discriminating conduct .The difference between empty bus resonance and grounding fault is analysed too. The voltmeter indicates stability when short circuit occurs jitter fast when high frequency ferroresonance occurs and jitter slowly when fraction frequency resonance occurs.