Answer Posted / suresh
The power factor of an AC electric power system is defined
as the ratio of the real power flowing to the load to the
apparent power  , and is a number between 0 and 1
(frequently expressed as a percentage, e.g. 0.5 pf = 50%
pf). Real power is the capacity of the circuit for
performing work in a particular time. Apparent power is the
product of the current and voltage of the circuit. Due to
energy stored in the load and returned to the source, or due
to a non-linear load that distorts the wave shape of the
current drawn from the source, the apparent power can be
greater than the real power.
In an electric power system, a load with low power factor
draws more current than a load with a high power factor, for
the same amount of useful power transferred. The higher
currents increase the energy lost in the distribution
system, and require larger wires and other equipment.
Because of the costs of larger equipment and wasted energy,
electrical utilities will usually charge a higher cost to
industrial or commercial customers where there is a low
Linear loads with low power factor (such as induction
motors) can be corrected with a passive network of
capacitors or inductors. Non-linear loads, such as
rectifiers, distort the current drawn from the system. In
such cases, active power factor correction is used to
counteract the distortion and raise power factor. The
devices for correction of power factor may be at a central
substation, or spread out over a distribution system, or
built into power-consuming equipment.
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