1993 Volume 113 Issue 11 Pages 1291-1300
Pole-changing is a simple method for changing the speed of a cage induction motor. However, excessive currents and torques appear during deceleration of the motor by pole-changing. These characteristics are unfavorable for shafts and couplings of the motor system. And further, these cause the sudden voltage drop of the supply. From user's viewpoint, it is desirable to control these currents and torques as low as possible.
In order to decelerate the speed by pole-changing, first, the supply is removed from the delta connected high speed terminals. Next, the supply is connected to low speed terminals, and finally, the winding is changed to the parallel _??_ connection. From the simulation results, the authors discuss the effects of the supply removal period, impressed voltage phase and the period between the supply impression and the changing to the parallel _??_ on the motor. This discussion gives the conclusion that the transient current and torque can not sufficiently controlled even when the above conditions are appropriately selected.
In order to reduce these transient current and torque sufficiently, this paper proposes a method in which external resistors are inserted in series with the three-phase primary winding. From the simulation results, it is found that the inserted resistance of 1.55 times the locked rotor impedance of the induction motor, can sufficiently reduce the excessive transients.