The ability to adjust the power factor of one or more loads in a power system can
significantly affect the efficiency of the power system: the lower the PF, the greater
the losses in the power lines. Since most loads in a typical power system are
induction motors, having one or more over-excided synchronous motors (leading
loads) in the system is useful for the following reasons:
1.A leading load supplies some reactive power to lagging loads in the system.
Since this reactive power does not travel along the transmission line, transmission
line current is reduced reducing power losses.
2.Since the transmission line carries less current, the line can be smaller for a
given power flow reducing system cost.
3.The over-excited mode of synchronous motor increases the motor’s maximum
torque.
Usage of synchronous motors or other equipment increasing the overall system’s
PF is called power-factor correction. Since a synchronous motor can provide PF
correction, many loads that can accept constant speed are driven by over-excited
synchronous motors.