Impedance Matching Balance Transformer Protection Research

Railway transportation is the main way of our country's carrying trade. As important electric equipment, Railway traction transformer carries weight on steady operation of the electrified railway. The Impedance-Matching Balance Transformer (IMBT), adapting to the developing requirements of electric railway in our country, is a kind of new traction transformer, which have many merits, such as restraining the affection of negative current to electric power system, high using rate of capability and so on. IMBT has been one of the main connections of railway traction transformer. So it is very useful to research the structure and protective relaying of IMBT, in order to enhance the speed of the construction and development of the electric railway and manufacture protective relaying devices with better quality and function.According to the configuration and electromagnetic relationship of IMBT we analyze the basic nature, the running principle and the data selection of electrified railway impedance-matching balance traction transformer, and describe the equivalent circuit, which can convert three-phase voltage into perpendicular two-phase voltage. This thesis also gives transformation relationships between current and voltage respectively, and a variable range of impedance-matched factor, analyses the fault state of IMBT, and then gives the formula to calculate short circuit current.The problems that affect the conventional transformer differential protection are summarized, some normal ways are also introduced in this paper. Based on the detailed analysis of the traditional element of balance transformer differential protection principles and the compare of the sensibility of the differential criteria using fault component current and operational current, a new differential protective criteria using both the fault components current and phase current is given. This thesis also gives a magnetizing inrush current criteria based the even harmonic content. Some problems of balance transformer differential protection are solved in a certain extent.A model representing power supply system of electrical railway traction is designed in PSCAD/EMTDC. Various simulations are carried out on the model under different conditions including normal operation, faults and magnetizing inrush current. The characteristic of waveforms and harmonic content are analyzed in detail under these conditions. This thesis also confirms the differential protection criteria using both the fault component current and operational current in EMTDC.Some other protections are summarized and protection logical diagrams are also presented based on the balance transformer differential protection. These make all of the protections as a whole and afford some theoretical basis for the latter part of the hardware design.