The Research On The Three-Phase To Four-Phase Impedance Matching Balance Transformer

This thesis concerns on the key technologies of four-phase power transmission and transformation along with'a new three-phase to four-phase impedance matching balance transformer'. The application characteristics of the novel transformer in the fields of four-phase power transmission and transformation, also four-phase rectification and traction power supply have been explored. The research is significant in theory, which has wide application prospect.In China, the main power supply region is far apart from the main load region, it is unavoidable that divert the electricity from the western region to the east . It is expected that the capacity of diversion the electricity from the western region to the east will up to 140000MW till 2020. Compared with three-phase transmission, the four-phase transmission can greatly increase the density of electricity transmission and decrease the transmission corridor cost. Also it can reduce the electromagnetic pollution of the transmission line. It has important significance for our stability of country's power grid to pay more attentions to the four-phase transmission, and put it into practice in proper occasion.According to'long-term develop layout of railway', China will build or upgrade electrical-railway about 30000km till 2020. Develop the new three-phase to four-phase impedance match balance transformer is very important to the stability of the traction power supply.This thesis studied principle of the balance transformer, then compared the wiring and operation characteristics of Scott-Teaser transformer, Le Blanc transformer, Wood Bridge transformer, three-phase to two-phase impedance match balance transformer, four-phase four-core transformers and Y N/ balance transformer. The study has formed a whole theory system of balance transformer, which is the reference of the novel balance transformer research.The theory and wiring topology of a novel three-phase to four-phase impedance match balance transformer has been put forwards. The various relations of three-phase side and four-phase side have been analyzed, such as impedance match relation, ampere-turn balance relation, power balance relation and the conversion relation of current and voltage. The author concerns more on the deduction of the identification of equivalent impedance between the windings.The mathematic model of the novel three-phase to four-phase impedance match balance transformer has been established, and the characteristic of transformer in both balance status and asymmetry status have been analyzed according to the established model. Also the bus admittance matrix of the transformer in phase coordinate has been determined, which formed a foundation of the theory of three-phase to four-phase impedance match balance transformer.This thesis deduced three constraint relations in interior winding of the novel transformer, whose variable are short-circuit impedance between windings. And then the equivalent circuit of four-phase side has been settled as the theory and calculating foundation.Based on the principle of three-phase to four-phase impedance match balance transformer and the constraint relation of impedance, the parameter design and calculation of 100kVA model machine has been done. The critical technology of the design is how to realize the constraint relation of impedance by the structure layout of the windings, and apply the Finite Element Optimization Method to verify the correctness of the design. Base on the design parameters, the simulink model of the novel transformer have been established.The short-circuit currents in short fault status have been calculated, according to the established transformer mathematic model and verified the results by the simulink model, which is a basic reference of the novel transformer fault protection. This thesis has studied the application characteristic of the novel transformer in the field of four-phase transmission, urban light railway and four-phase rectifying. The compatibility of the novel transformer in three-phase transmission system has been discussed.The wiring layout of the novel transformer that apply to the electrical-railway AT power supply system has been proposed. The simulation of the application of novel transformer in AT power system has been performed, which demonstrated great advantages in negative sequence current suppression and cost reduction.This thesis proposed the concept of four-phase rectifying for the first time. The wiring layout of the novel transformer applying to four-phase rectifying has been presented, which extended a new access of harmonic suppression; The relations of output voltage, current and power factor with the trigger angle have been deduced; The simulation model of four-phase rectifying has been established, and the simulation results are consistent with theory calculation results, which verified the correctness of the theory analyses. Meanwhile, the harmonic of four-phase rectifying system has been calculated, and both theory and simulation revealed that the DC side of the four-phase rectification circuit exist harmonic only in multiples of four, which raised the lowest order of system harmonic. Given the same output voltage, the cost of insulation equipment and maintenance in four-phase rectifying largely reduced compared with three-phase rectifying. The lower thermal losses and better power stability are the merits of four-phase rectifying, and it is definitely worth to be further studied.