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.
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.
