Introduction to Electrical Power and Power Electronics

275Economical Use of Power

10.7.1 indUCtion Motor torqUe versUs sPeed CUrve

If the induction motor speed were varied over an extended speed range from syn-

chronous speed backward to twice the synchronous speed forward, the theory we

covered in Chapter 4 will give the motor torque versus speed characteristic shown

in Figure 10.8. It shows that above the synchronous speed, the motor—although

running in the same positive direction—develops negative torque, giving negative

mechanical power, meaning it absorbs the mechanical power at the shaft instead

of delivering. Since the current also becomes negative (owing backward to the

source), this negativ ...