Research On The Technology Of Contactless On-load Automatic Voltage Regulating Based On Optical Trigger

The voltage of power grid was happened to fluctuate and different loads also made difference of the voltage of power grid which was not conducive to operation for electrical equipment. The voltage regulating of transformer was the most direct and effective means of regulating when the reactive power was enough. A contactless on-load voltage regulating prototype was developed in the project “contactless on-load automatic voltage regulating distribution transformer” which this topic was in. The parallel thyristor as tap-changer and the single chip microcomputer as the control core were applied. The prototype was applied to a 50 k VA distribution transformer. The regulating reliability problems were solved after experiments over and over again. However, it was found that there would be a large voltage on the thyristor module and the control system if a phase of the high side of the transformer was happened to link to ground. The transformer and the photoelectric coupler used could not stand such high voltage for now.It was of great value that optical trigger technology which had good insulation effect was applied to the trigger issue of thyristor trigger circuit. The study of contactless on-load automatic voltage regulation technology based on optical triggered was to implement the reliable electrical isolation between high voltage side and the low voltage side of the transformer with optical trigger technology. The single chip microcomputer STC89C52 RC was used to send signals, which made it the core of the control system. After comparing the phase voltage collected and processed on the low side with the setting voltage, the control signal was sent out from STC89C52 RC to trigger circuit on the high side by optical fiber to make the tap-changer switch, which finally achieve the goal of on-load automatic voltage regulation and make the voltage of transformer stable.Four main circuit schemes were designed with the parallel thyristor of high pressure value as tap-changer in this paper. The complete power electronic main circuit design was chosen after comparison. The design adopted optical fiber to trigger the thyristor and optical trigger the bidirectional thyristor to starting mechanism which not only solved the insulation problem between the high and low voltage of the transformer, but also overcome the inherent disadvantages of mechanical contact. According to actual needs, the parameter of the thyristor model was determined and the RC buffer protection circuit was designed after the analysis of the degree of each phase voltage offset neutral on the high side when unbalance operation. Optical fiber adopted matching HFBR-1521 transmitters and HFBR-2521 receiver.The parallel thyristor optical trigger circuit and the starting circuit based on optical trigger were designed in which control signal transmission through optical fiber with high isolation effect. The key point of trigger circuit and startup circuit was the high voltage power supply. This design used AC voltage of tap-changer to get the required DC power supply by regulating, rectifying and filtering. Parameters of electrical devices were designed according to the operation principle and Experiment was made to validate the results.The hardware system and software system of the control unit were improved on the basis of the original control unit to match the optical trigger control signal. The tap-changer conversion subroutine was modified because that the starting circuit and the trigger circuit acted to the contrary under the condition of giving light signal to make the and bidirectional thyristor correctly act to complete the start with the regulating process. The optical trigger the parallel thyristor experiment, the optical trigger starting mechanism experiment and the overall regulating experiment were made in the simulation test in the laboratory. The experimental results showed that the contactless on-load voltage regulating transformer based on optical trigger could realize the function of basic regulating and solve the electrical isolation problem between the high side and the low side of the transformer. And it was of great significance to promote the whole power electrical on-load voltage regulating transformers.