| At present at rural power grid especially at those which are located at power grid and far from the transformer substation, the fluctuation range of voltage is wide and beyond the national allowable value. This situation brings power equipment and people’s lives serious damage and seriously restricts the development of rural economy. Under the electric system reactive power is sufficient condition, installing on-load automatic voltage regulating device is one of the most effective methods to stable system voltage.This paper studies one kind non-contact on-load automatic voltage regulating technology based on positive and negative voltage regulating. This kind technology uses power electronic component as tap changer which is inserted into distribution transformer and uses microcontroller technology. After power on, the system monitors the secondary side voltage of transformer, decides the tap changer’s position where it should be and makes regulating windings and main winding in series positive and negative. And then it changes the secondary side voltage of distribution transformer to realize on-load automatic voltage regulating function.This project uses solid state relay as executive mechanism of on-load automatic voltage regulating tap changer and designs three on-load voltage regulating schemes. Direct-connected scheme has the disadvantage of insufficient withstand voltage of SSR. Yet chained connected scheme is proposed. In chained connected scheme SSR which put in circuit are overabundance, and then harmonic generates while changing over. Therefore choose positive and negative voltage regulating scheme as main circuit wiring scheme of on-load tap changer. Compare with direct-connected scheme, positive and negative voltage regulating scheme can double voltage regulating range with the same regulating winding and maximum withstand voltage of the component. Compare with chained connected scheme, positive and negative voltage regulating scheme can reduce the number of the tandem working SSR and improve functional reliability and can reduce harmonic pollution of the transformer. In positive and negative voltage regulating scheme, it changes two SSR working condition at every phase while changing over which makes control structure and control flow simple.According positive and negative voltage regulating scheme, this project chooses40A/660V zero passage SSR as executive mechanism of tap changer. Insert RC buffered guard circuit at the two ends of SSR alternating side. Meanwhile determine interim resistance value of interim circuit and design the SSR working flow while changing over. According positive and negative voltage regulating scheme and SSR working flow, this paper designs hardware circuit and software structure of microcontroller system. To ensure distribution transformer can work after power on, this paper designs startup organization which used antiparallel SCR.Through theory analysis and laboratory experimental result, use positive and negative voltage regulating technology, when power grid voltage fluctuate from87.3%to113.3%rated voltage, can make output voltage fluctuate97%to103%rated voltage. The voltage rate of change descends20%. When power grid voltage fluctuates from85.5%to114.3%rated voltage, it can make output voltage fluctuate95%to104%rated voltage. The voltage rate of change descends19.8%. Positive and negative voltage regulating technology realizes the function of distribution transformer non-contact on-load automatic voltage regulating and achieves stabilizing power grid voltage aim. In the voltage regulating process the output voltage waveform is good and there is no impulse current and harmonic component generated. Positive and negative voltage regulating technology has the advantages of wide voltage regulating range, stabilized working performance and feasible frequently regulating. Therefore Positive and negative voltage regulating technology is suitable for rural power grid especially those wide range of fluctuation of voltage rural area... |
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