The left figure is the characteristics on induction motors. It illustrates that the ac induction motor’s efficiency increases in a high-speed range with the reduce of the impedance of the aluminum conductor of the rotor. Oppositely, when designed to have a high impedance, the motor has an increased amount of torque in a low-speed range.
As what has been reflected from the right figure,when the load increases, the speed of low-impedance motors do not reduce a lot. The torque increases and becomes stable.
That is to say, motors’ speed remains though the change happens in the load.
In the right figure, the horizontal axis is the torque value and the vertical axis is the rotating speed.
The relationship between the torque and current is not linear.
Compared with ac induction motor, ac reversible motor has got the similar features as what has been stated above. The only distinction existed between them is that the reversible motor has a higher starting torque for improving the instant reversing characteristics.