A New Technique For Induction Motor Soft-starting

The start of high power rating motor will generate high current surge,which will endanger the safty of the motor and drop the system voltage.Some device are used to reduce the voltage applied the terminal of the motor at starting,such as the â–³/Y starter,autotransformer.In the last few decades, thyristorized soft starters are being incresingly used to replace conventional reduced voltage starters,which are reliable,sample and cheape. The present soft starter has limited applications where the starting torque requirement of the load is not high and the torque of the load is a function of the speed,such as with fans or pumps.The problem occurs due to the quadratic relationship between voltage and electro-magnetic torque.A small drop of voltage produces the considerable reduce of the electro-magnetic torque.The motor with high load may fail to start. Because of the inverse proportion relationship between the electro-magnetic torque and the ac power supply frequency,we can reduce the supply frequency to increase the starting torque.Converters can do it but be used to start induction motor unusually,which are complicated and expensive. The strategy the paper proposed can reduce the supply frequency and increase the starting torque without changing the conventional circuit. We will explain the theory applied the proposed strategy with mathematic langue to attest its feasibility.Then the simulation will be made,whose result will be compared with conventional soft starter.We will see the proposed strategy can increase the starting torque with falling voltage efficaciously.The system applied new trategy will be introduced.The result of system running will be accord with the theory. At end of the paper,we will discuss another applications of the new soft-starter.