| In China’s electric power system,110kV or higher voltage grids are designed tobe grounded directly at neutral point.These grids are called solidly earthed neutralsystem.In these grids,from80to90percent faults are phase-to-earthfaults.Therefore,to research if the selections and usage of zero sequence protectionunder different operation modes are the best,and if zero sequence protection can meetthe requirement of "four characters"of protection relay under different operationmodes become important work concerns electric power system’s operation.By analyzing zero sequence voltage when the single-phase ground fault occurredin line of the neutrally directly grounded power network, the system operatingcondition that can protect the installation place of the lowest zero sequence voltage isdeduced in this paper. It provided the theoretical basis to make the zero sequenceprotection play a big role in the spot.On this basis, MATLAB is used in this paper to establish a simple model of atypical bilateral power supply network,considers a variety of fault conditions,a lot ofground fault simulation data can be obtained. Full-wave Fourier algorithm is used inthis paper to write a simulation program which is used to get the zero-sequencecomponents. A simulation analysis is given in this paper, which is about whether thezero-sequence current protection will function well or not when power system worksunder different operating modes, and about the influence of the system operatingmodes to the system zero-sequence protection.This dissertation also analyses the running conditions of zero sequenceprotection in Binhai district grid. |
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