Study On Microprocessor Based Resonance Elimination Device In Distribution Network

In the neutral point ungrounded distribution network, ferroresonance occursfrequently which is caused by the nonlinear excitation characteristics of the voltagetransformer (PT), it affect the safe operation of the system seriously. Installingmicroprocessor based resonance elimination device is commonly used measures atpresent. Microprocessor based resonance elimination device operating costs and easymaintenance, further a system simply install a this device only. However, the device isdifficult to recognize the fundamental frequency resonant with the single-phase earth.This paper studies the issue, the main work and conclusions are as follows:At first, this paper introduced the research on identification PT ferroresonancefrom single-phase and summarized deficiencies of existing methods.The paper builded a simulation model of PT ferroresonance on ATP–EMTP andstudied fault characteristics of ferroresonance, found that zero-sequence voltagedistortion when ferroresonance occurs. Besides, it simulated harmonic eliminationmeasures of put damping resistor in PT openings triangular, found the resistance issmaller, the effect of harmonic elimination is better within the allowable range.It can find the differences between base frequency resonance and single-phaseearth by analyzing zero sequence voltage of them. The paper proposed that it candistinguish ferroresonance and single-phase earth by comparing the zero-sequencevoltage to the standard sine wave. So the sine fitting algorithm is presented. First,sampled data of zero-sequence voltage is fitted to sine function of50Hz, it can get thatthe zero sequence voltage is power frequency or not by analyzing the amplitude ofwhich. Second, to the case of that zero-sequence voltage is power frequency, thefundamental frequency resonance can be correctly identified from single-phase earthfault by calculating waveform distortion level due to zero-sequence voltage is distortedif fundamental frequency resonance occurred.Taking into account the measurement accuracy of the actual PT fully, as itverifyed the sine fitting algorithm by simulation data by mathematical rounding errorsinstead of measurement error of actual PT, the results show that the sine fittingalgorithm can overcome the influence of the PT measurement error to discriminatesingle-phase groude and ferromagnetic resonance effectively.Finally, it develop microprocessor based resonance elimination device combining of FFT algorithms and sine fitting algorithms. The paper introduced the overallarchitecture of the hardware system, what is more, described the design principles andspecific implementations of each functional module; it designed the device softwaresystems using modularization, especially introduce the main program module andbring forward specific flow chart; and tested Microprocessor based resonanceelimination device by experiment, the test results show that the device can identifyfault type and acted raliablity.