This paper proposes a wye-delta soft start method of the three-phase induction motors and its control device based on SCR switches. Comparing with traditional wye-delta start, this method can suppress inrush current effectively both in the initial stage with wye connection and the transforming stage from wye to delta. With the sequence trigger control strategy of SCRs, the smooth transition of the magnetic flux and lower inrush current can be realized. Furthermore, this paper also discusses the best transforming point from wye to delta connection on the basis of comparison of start current wave at various slip of motor. And the method is verified by the simulation on a 2.2kW induction motor.
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