
Economic Use of Power 287
in Figure11.8. 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 negative power is converted into the electrical power and fed back to the lines,
that is, the machine now works as the generator. On the left-hand side of zero speed,
at negative speed (i.e., running backward), the motor torque is still positive, again
giving negative mechanical pow