Research On The Technology Of On-load Automatic Adjustable Capacity Of The Distribution Transformer

The load of rural power grids and some single shift factory fluctuation is large, and difference in peak valley load is big. annual utilization hours is low. so transformer load rate can not be in a reasonable range. It is well known that and the loss of the transformer is related to the rate of load.when transformer no-load condition for a long time, the no-load loss is very big. Therefore, in order to reduce the loss of the transformer, it is of great significance automatically changing the capacity of transformer according to the variation of load. And adjustable capacity transformer has two capacity rely on changing the size of the winding connection. When the load is high, use large capacity; When load is low, using the way to run a small capacity. It is more economical than the "mother-child transformer" which method requires two transformer is. So adjustable capacity transformer has very important practical significance to reduce the loss of the grid which load is large and frequent fluctuations.Firstly, the article introduced and analyzed the capacity adjustment principle and characteristics of adjustable capacity transformer. It mainly introduced and analyzed the principle and pros and cons of series-parallel type and star-triangle type adjustable capacity transformer.And determined the star- triangle type(D- Y) adjustable capacity transformer as the main research object of this article. Then analyzed the principle of energy conservation and loss reduction of adjustable capacity transformer, and further analyzed the comprehensive economy,then proved that compared with the ordinary transformer, adjustable capacity transformer in energy conservation and loss reduction really has a great advantage. The article also discussed the optimization of economic operation of adjustable capacity transformer. And got the the formula of critical tone melting point making use of the method that the loss difference between adjustable capacity and no-adjustable capacity is zero. When the load capacity is less than 55% small capacity of adjustable capacity transformer, convert the capacity of adjustable capacity transformer for small capacity and it can make the operation of transform is always the most economical way.Adjustable capacity switch is one of the most important part of the adjustable capacity transformer. In this paper, it analyzed the characteristics and pros and cons of existing adjustable capacitance switch. Then scheme of on-load automation capacity regulating which composite switch was used as capacity regulating switch was put forward. The composite switch was composed of a electronic switch and a mechanical type of contact switch. It can fully use theadvantages of mechanical switch and power electronic switch, and effectively avoid their respective defects. Then through calculation analysis of the current and voltage of Adjustable capacity switch, proved the technology scheme of composite on-load automatically adjustable capacity switch is feasible. And designed the switching topology diagram of automatic adjustable capacity transformer and arrangement of composite on-load automatic adjustable capacity transformer.In order to make adjustable capacity transformer change capacity with load when when electricity continuously, on-load automatic adjustable capacity controller is necessary. Design scheme of on-load automatic adjustable capacity control system is proposed in this paper. And from two aspects of economic operation and safe operation of on-load automatic adjustable capacity transformer discussed the related of on-load automatic adjustable capacity transformer control strategy. In order to eliminate the influence of load fluctuation and prolong the service life of on-load automatic tuning capacity switch, the control strategy has made the corresponding improvement and perfect. On the premise of meet the demand of power supply, it can make adjustable capacity transformer can automatically adjust the capacity of itself according to the variation of load, and always run under relatively economic operation mode.Lastly, the overvoltage and overcurrent in the process of capacity regulating and its limitation are studied. Meanwhile, the MATLAB/Simulink simulation software was used to simulate the on-load automatic adjustable capacity transformer. The results showed that overvoltage and overcurrent would be generated when the capacity regulating switch was changed. And the overvoltage and overcurrent can be effectively suppressed by the appropriate size of butter resistance at the ends of the switch.