Methods to avoid low Power Factor

Some of the methods to improve power factor are:

1.     Induction motors have maximum power factor when they are fully loaded and power factor starts falling down when the motor loading is reduced and becomes worst during no load. Hence, it is important not to have motors too big for a specified job than  its required ratings. If however if the induction motor whose stator is delta connected is to run on less than half load for considerable time, it is adviced to connect the stator in star. This will not allow the drop in power factor to much extent. This is due to the fact that application of reduced voltage per phase gives rise to the reduced magnitude of the rotating magnetic field and hence less magnetising current and higher or better power factor.

2.     Reduction in the air gap of the induction machine is done as much as possible to enhance the power factor. This can be achieved by the use of ball or roller bearings in the place of sleeve bearings. A similar improvement in the transformer can also be achieved by employment of inter leaved instead of butt jointed cores. Grain oriented high permeability cores of the transformers will also reduce the magnitude of the magnetising current.

3.     Use of over excited synchronous motors in the place of induction motors.

4.     High speed Induction motors will always have better power factor compared to low speed induction motors. This is due to the fact that for a given power torque developed by the induction motor becomes less as the speed of the motor increases. Torque developed also depends on the square of the magnitude of the rotating flux. Therefore reduced torque relates to reduced magnitude of the rotating flux. Further, the number of poles of high speed induction motors are less. Therefore high speed motors requires less amount of magnetizing current. Also these motors being smaller in frame size are also more economical both from the point of view of initial cost and running cost.