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(Last update.... 17th
August 2013 ) |
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Power Factor, Power Factor correction, value of capacitors required etc….. |
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Power Factor:
In alternating
current circuits, alternating voltage and alternating current are not always necessarily
in phase with each other. i.e. to say, the current flowing in any circuit
component, which a result of applied voltage, follows the voltage wave form
with a time gap. This time gap could be either ahead of the voltage applied
or it could be behind the voltage applied. In circuit with a lot of
inductance present, the current is behind the voltage applied. In such cases
the current is said to be “lagging”
the voltage, as if it is a bit reluctant to flow. The amount of “lag” depends
on the amount of inductance present. In circuits with a lot of capacitance
present, the voltage follows the current. In such cases the current is said
to be “leading” the voltage. For more detailed
information on the basics click here.
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In case of DC
drives with fully controlled configuration, low speed operation of dc motors
is achieved by firing the thyristors nearer to 180 degrees for getting lower
voltage. Thus, for every sinusoidal cycle of supply, the current starts
flowing late as compared to the voltage.
DC drives, therefore, when
operated at low speeds, cause a very low or “poor” power factor. There is no
way by which this situation could be improved. It is an effect created as a
“by product” of the method used for speed control. Trying to
improve the power factor by putting capacitors near the dc drive is known to
have created problems of blowing of thyristors or fuses for no apparent
reasons. |
Download PDF
version of these pages.
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Speed control not satisfactory
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