Research On On-load Automatic Tap-changer Based On Power Electronic Technology

Voltage is an important index of quality of power supply. Recent years, the request of all levelsconsumers to the quality of voltage rise continuously. Therefore, in order to assure thedependability of electric power system supplying and customers' consume, electric powerdepartment has taken a series of measures to improve the voltage quality. Under the condition ofsystem reactive adequatly, adding on-load voltage regulating device is valid one of the mosteffective method in stabilize system voltage.This paper studies a on-load tap-changer which has the function of real-time monitor voltagefluctuation and stabilizes the output voltage automatically. It based on power electroniccomponents, applied single chip microcomputer control technology. After the action of startupmechanism, control system electrify and monitoring secondary side voltage of transformer whichdecompressed by isolation transformer. Then it export correspond command according to themonitoring voltage and carry through automatic switching of tap-changer. It can achieve on-loadautomatic voltage regulating.Through analysising and comparing for main circuit project of on-load tap-changer, beingrelative to the design which main circuit project of the on-load tap-changer adopting soild staterelay, though the agent structure of main circuit project which based on IGBT is concise, controlprocess is acutance, its corresponding protection circuit and snubber circuit are too huge,meanwhile the economical efficiency descends seriously. So the design of main circuit projectadoptes solid state relay as operating mechanism of on-load tap-changer finally.The problem of on-load tap-changer startup is one of the most important aspects in theitem. So this item adopts the technology combining independent startup mechanism based onTRIAC and photoelectric coupler, the device can eliminate the disadvantage that accumulator cellstartup scheme can't startup after the transformer and power net had stopped run for a long time. Itensures the on-load tap-changer can put into operation in any time and operate safely.The key question of whether the device can apply in dirtributiong transformer is that the powerelectronic components can not be damaged under the over-voltage of power system and powerfrequency withstand voltage. This paper enhances the withstand voltage level and workingpefrformance of the on-load tap-changer by hang floating ground and other technologies, satisfyingthe engineer requests completely. The thoery analysis, simulation run in laboratory results prove that the on-load tap-changerwhich based on above techniques has meet the demand of the same voltage class power net, it canachieve on-load automatic voltage regulating quickly and steadily. When power net voltagefluctuating range is±10%, the range of output voltage fluctuate can not more than±5% of ratingvlotage, the fluctuate range of voltage reduce more than 5%. At the same time, it doesn't generateharmonic pollution and be harmless to electric network environment.The designed distribution transformer which employs on-load automatic voltage regulatingtap-changer has run for half year in rural electricity system, it provers safty, reliable, good result instabilize voltage automatically.