Study Of The Soft Start System Based On Paralleling Switch Transformer

In the startup process of motor, the starting current is several times, which sometimes has more than 7 times larger than the rated current. At the meantime, the starting torque will increase more than doubled. However, in the modern industry, the high power motor is more and more widely used, especially the application of high voltage and power motor which have a rated voltage as high as 10 k V. As a result, in the direct startup process, the starting current and torque will endanger the safety of the motor. Hence, soft start method is needed for the high power motor starting. Two method which are frequency conversion soft start and thyristor group soft start is commonly used these days and both of them have some limitations.A new technique also called switch transformer can effectively reduce the starting current and starting torque, and improve starting performance, and avoid the instability of the series of the switching devices. In this paper, the paralleling switch transformer technology is discussed based on the problem of motor soft start.Firstly, the principle of switch transformer technology is described, and the characteristics of working process are analyzed. Among which, the mechanism of excitation inrush current and its effect on the motor starting are the focuses of analysis. The transformer capacity calculation principle is obtained as well.Secondly, the principle of high-voltage motor soft start based on switch transformer technology is studied. The co-use of the switch transformer technology is proposed. The mathematical model of soft starting system based on the paralleling switch transformer is established. Based on the simulation analysis, the feasibility of the co-use technology of switching transformer is proved.The paralleling switch transformer module is then designed. The paralleling switch transformer soft starter is a kind of high power AC voltage regulating device which is consisted with several transformer and thyristors. It is mainly applied to the field of high voltage and high power motor soft start. With the application of paralleling switch transformer module, the motor with non-limited large capacity can be smoothly soft started. This technology enables the soft start device to be high performance and high reliability.The experimental prototype of high power motor starter based on paralleling switch transformer technology is designed and fabricated. The relevant experiments is designed and implemented. The experimental results show that, the paralleling switch transformer technology can effectively improve the starting capacity of switch transformer. In the starting process of high power motor, the impacts, which threaten the safety of the system, have been effectively reduced. The system stability and reliability are improved.Finally, MATLAB software is used to develop a simulation program, which is suitable for the simulation and parameter calculation of the motor soft start based on switch transformer technology. The program can obtain the estimation of some electrical parameters in the soft starting process, such as the starting time, the starting current, voltage fluctuation rate and heat flux, etc.