The Research On The Operational Characteristics Of A New Rectifier Transformer In DC Power Supply System

A plenty of harmonic and reactive power are produced during the conversion ofAC/DC electrical energy in some industries with high energy consumption. Under thebackground of energy conservation and pollution reduction as our nationaldevelopment strategies and increasingly stringent limitation of harmonic by utilitycompanies, energy convention has become an urgent problem in such industries. Inthese AC power supply system, the rectifier transformer is used to transfer theelectrical power from the grid side to the valve side, and the filters are used tocompensate the reactive power and suppress the harmonic. Generally, the filters are setat the grid side and has no effect with the rectifier transformer. Because the filters arealways placed at the grid side of the transformer, they don’t have any influence on thetransformer. With or without filters, the operational parameters of the transformer arenot changed, a large amount of harmonics and reactive power are entirely through therectifier transformer from valve side to grid side which lead to unfavorable effect andincrease the burden on rectifier transformer.Unlike the conventional rectifier transformers, the new rectifier transformer withits filters is a special kind of transformer whose grid side windings are connected topower grid, the valve side windings are connected to the rectifiers, and the filteringwindings are connected to the filters. it can not only enhance the operationalcharacteristics but also suppress the harmonic and compensate reactive power in thetransformer. In this paper these characteristics are systematically studied, and thetheoretical results are compared with the simulation and experiment. The achievedresults are useful for theoretical analysis, design and manufacture, and operation of thenew rectifier transformer. The fundamental research and the related innovativeachievement can be summarized as follows:The paper elaborates the principle of harmonic flux suppression of the newrectifier transformer with filters，and the winding scheme, the equivalent circuit andthe basic relationships between voltages and currents are introduced. And then, theshort circuit impedance in single phase is calculated, furthermore the simulation modelfor the new converter transformer is established according to the real parameters.The relationships between grid side current and valve side current of theconventional and new rectifier transformers are built respectively. On this basis,detailed derivations of relationships between the grid side and load harmonic currents are respectively implemented to analyze the harmonic suppression effect. And then,both relationships between grid side current and load current are respectively built tostudy the characteristics of the reactive compensation and analyze the correspondingoperational parameters in the fundamental situation. Moreover, both relationshipsbetween the valve side and the grid side voltage are respectively deduced to study theeffect of the filters on the valve side voltage. Theoretical analysis shows that the newrectifier transformer with its corresponding filters could effectively suppress theharmonic currents, reduce the grid side current and apparent power, and enhance thegrid side power factor and the load side voltage.The new rectifier transformer with filters is studied as a linear two-port networkwithout independent source. On this foundation, one matrix model for the fundamentalfrequency is deduced to study the reactive compensation characteristics and interiorrelationship between voltage and current of the transformer, and then, the other matrixmodel for the tuned frequency is deduced to study the harmonic suppressioncharacteristics. Moreover, the operational characteristics of the new rectifiertransformer are analyzed according to the both matrices, and simulations of variousoperational situations are implemented to verify the theoretical analysis. The analyticalresults show that the matrix deducing can fully replace traditional mathematicaldeducing and it is easier, more quickly and correctly to study the operationalcharacteristics of the transformer.Some standards and specification for harmonic suppression are introduced. Andtwo key design parameters corresponding to the harmonic flux suppression are studiedto deeply reveal the validity of the design methods of both relative minimum offiltering winding equivalent impedance and optimal tuning of filtering branch. Thecalculation of the grid side harmonic currents of both the conventional and newrectifier transformer is implemented respectively to study if they can satisfy thenational standard. And then, some parameters such as the harmonic loss factor forwinding eddy currents, the harmonic loss factor for other stray currents and k factorare analyzed to study respectively the influences of the harmonic on various windingsof both the conventional and new rectifier transformer. Based on this, the harmonicloss of the new rectifier transformer is studied. The research results show that the newsystem can not only restrict the harmonic current to invade into the grid side but alsoreduce the temperature rise and the transformer capability reduction ratio of thetransformer to a certain extent.For studying the engineering application of the new rectifier transformers with filters in the Industrial rectifying system, the paper states the application backgroundsof both new6-pulse industrial rectifier system and new12-pulse industrial rectifiersystem. And then the electric wiring scheme, the configuration and the main designparameters and their related full-tuned branches of both transformers are introducedrespectively. After that, some engineering tests in both harmonic and fundamentalfrequencies are implemented in both systems. The results verify the well operationalcharacteristic of the new rectifier transformer with filtersCombined with the existing problem of the practice DC power supply system, thisthesis studies the operational characteristics of the new rectifier transformer, revealsits operational regulation in both harmonic and fundamental situation, by mathematicsdeducing，it studies the working mechanism of harmonic suppression and reactivecompensation in the transformer, reveals that the new system can limit the harmonicpollution to the grid and the transformer by analyzing the important standard andtechnical index. The successful application of the new rectifier transformer with filtersin the DC power supply system can provide theoretical and technological foundationfor its further application in electrical railway and HVDC and so on.