Analysis On The Electrical Characteristics Of The YNvd Traction Transformer

Problems of harmonics, reactive power, negative and neutral sections in electric railway are getting worse as the improvement of railway high-speed and overloading. To meet the demand of traction power supply system's high voltage and high current electricity, to reduce the negative impact of traction power supply system on the power system, the choice of the traction transformer wiring form is very important.Among the balanced transformer at home and abroad, the Scott balanced transformers and balanced impedance transformer have been widely used in our country. The YNvd is a new type of balanced transformer connection. This balanced transformer has their advantages of both Scott and balanced impedance transformers: not only like the balanced impedance transformers, the neutral point of its high-voltage side can be grounded directly, which is suitable for the neutral point operation of China's 110 kV and above high voltage transmission system, and also can lower the costs of insulation . The triangle winding connection of the second side can cause an available road of magnetizing current three harmonic component, which improved the waveform. It also has the characteristics of Scott balanced transformers: there is no electrical connection between the second two phase, and can constitute a AT power supply mode electric railways with high-voltage, high-capacity and long-distance.In allusion to the characteristics of YNvd balanced traction transformer, this thesis researches the electrical characteristics of YNvd transformer by the systematic analysis of multi-winding transformer based on the general transform formula of transformer, as well as transformer winding connection equations, output equations, voltage transfer equation, etc, then simulation analysis of the main characteristics by MATLAB. This thesis discusses and researches the transformer capacity, impedance matching, and the neutral point current of the one side as well, propose the formula of the neutral point current of the one side and the conditions of the load current in secondary side which does not produce current in neutral point. Finally, propose the optimum winding configuration of the inner cores transformer by considering three factors which are capacity, impedance matching and neutral current. All these in-depth study for YNvd balanced transformer have great theoretical and practical value.