Study On On-load Automatic Tap-changer Based On Thyristor

Since power transformer has invented, its working principle and basic function is not changed. But along with the development and strength of electric power system, its scale expands day by day, and the power network structure and run mode are complex day by day, which cause the electric power system voltage stable question become more and more prominent. In view of this kind of question, electric power department has taken some measures, for example using off-circuit tap-changing and mechanical on-load tap-changer. The most deficiency of off-circuit tap-changing is no electric charges switch. The widespread applied mechanical on-load tap-changer produces electric arc in tap switching, movement speed is slow, voltage regulating response time is long, and failure rate is high. Therefore voltage regulating time is unable to be controlled accurately. In view of mechanical on-load tap-changer's insufficiency, this paper proposed on-load automatic voltage regulating tap-changer based on power electronic technology and single chip microcomputer technology.This design can realize real-time monitor to power network voltage fluctuation, and may realize function of automatically steady distribution transformer output voltage simultaneously. This control system uses single chip microcomputer AT89C52 as core. According to monitored voltage value compares with the hypothesis datum value, the single chip microcomputer sends out trigger pip for power electronic device via trigger circuit to realize the tap-changer automatic switch, and then realize the goal of transformer two side voltage basic stable, and gets up the function of on-load automatic voltage regulation.Directed towards lower withstand voltage value of con-contact on-load tap-changer based on solid state relay, this paper proposes the thyristor of higher withstand voltage value takes as design scheme of on-load tap-changer.The scheme takes two counter-parallel thyristors as ac switch on transformer tap.Work state of the tap is desided by control unit using single chip microcomputer AT89C52 as core.Simultaneously the rated tap is connected current-limiting resistance for limiting circulation.When the tap shifts,the current-limiting resistance is connected with shifting circuit and acted as limiting circulation.According to definitenesss of operating mechanism proposal, this paper has carried on thyristor choice work, has designed correspondingly cross-zero triggering circuit based on MOC3061 and can inhibit the overvoltage's effective measure——resistance capacitance buffercircuit. At the same time it carried on the design of on-load automatic voltage regulating tap-changer control system software and hardware. In view of work feature of thyristor counter-parallel, the item designed overvoltage detecting circuit and corresponding interrupt service subroutine. According to the acquisition data that from gathering unit, it designed tap-changer transfer subroutine and thyristor triggering subroutine. The paper compared three kinds startup mechanism proposal and adopted contactor as the startup mechanism finally,which has solved insufficiency triode AC switch withstand voltage and gets rid of the battery power supply startup mechanism shortcoming that is unable to startup after the transformer had stopped running for a long time, and it ensures the on-load tap-changer can put into operation at any time.Theoretical analysis and experimental result indicates that on-load automatic voltage regulating tap-changer has meet the demand of 10kV power network work, it can achieve on-load automatic voltage regulating quickly and steadily, its withstand voltage value is higher, and it suits for low pressure power user power supply. It has broad development prospect.