Improving On Auxiliary System Of 8G Locomotive

The electrified railway network is powered by single-phase supply. The three-phase motors in auxiliary system of the 8G type locomotive are operated by single-phase to three-phase with a starting capacitor. This leads to high starting current, low torque and many motors broken. Soft starter is widely used in the starting of three-phase asynchronous motor because of its small starting current and economy of energy sources.Basing on present status analysis of asynchronous motorr starting technique, a new low cost method of soft starting is proposed, which achieves not only single-phase to three-phase converting but also lower starting current. In this paper, a new method of reducing power supply frequency in discrete steps is proposed to guarantee higher starting torque and smaller starting current at the starting time. Discrete variable frequency method can obtain low frequency through controlling the triggering time of thyristors.After taking further research on how to realize frequency-control, the paper give the minimum triggering angle, choose frequency steps, frequence switching time and decide the time of plunging into the capacitor. This paper sets up the system model by using MATLAB/SIMULINK, makes simulation for this system and compares simulating result with direct capacitor start way. It proves that this method can obtain high starting torque at the starting time.In this paper, based on theoretical analysis and simulation technique, experiment which used TMS320LF 2047A DSP as micro-computer is completed. The result approves that the soft starter can start motor smoothly with smaller starting current and higher startup torque at low frequence.However,at 50 Hz because of the capacitor the three-phase power is not symmetry any more and the torque is reduced. Further study indicate that this method can obtain enough torque for fanner load in 8G locomotive. When the motor connected to fanner is started it can work as a phase-split motor which can suply three-phase power for the motor connected to compressor.