Sponsored Links
The power factor of an AC electric power system is defined as the ratio of the active (true or real) power to the apparent power
where
Reactive power is required for the magnetization of a motor but doesn't perform any action. The reactive power required by inductive loads increases the amounts of apparent power - measured in kilovolt amps (kVA) - in the distribution system. Increasing of the reactive and apparent power will cause the power factor - PF - to decrease.
It is common to define the Power Factor - PF - as the cosine of the phase angle between voltage and current - or the "cosφ".

The power factor defined by IEEE and IEC is the ratio between the applied active (true) power - and the apparent power, and can in general be expressed as:
PF = P / S (1)
where
PF = power factor
P = active (true or real) power (Watts)
S = apparent power (VA, volts amps)
A low power factor is the result of inductive loads such as transformers and electric motors. Unlike resistive loads creating heat by consuming kilowatts, inductive loads require a current flow to create magnetic fields to produce the desired work.
Power factor is an important measurement in electrical AC systems because
International standards such as IEC 61000-3-2 have been established to control current waveform distortion by introducing limits for the amplitude of current harmonics.
A industrial plant draws 200 A at 400 V and the supply transformer and backup UPS is rated 200 A × 400 V = 80 kVA.
If the power factor - PF - of the loads is only 0.7 - only
80 kVA × 0.7
= 56 kVA
of real power is consumed by the system. If the power factor is
close to 1 the supply system with transformers, cables, switchgear and UPS could be
made considerably smaller.
A low power factor is expensive and inefficient and some utility companies may charge additional fees when the power factor is less than
0.95. A
low power factor
will reduce the electrical system's
distribution capacity by increasing the current flow and causing voltage drops.
The total power required by an inductive device as a motor or similar consists of
The power factor for a three-phase electric motor can be expressed as:
PF = P / [(3)1/2 U I] (2)
where
PF = power factor
P = power applied (W, watts)
U = voltage (V)
I = current (A, amps)
Sponsored Links
Sponsored Links
Engineering ToolBox - SketchUp Edition - enabled for use with the amazing, fun and free Google SketchUp.
© The Engineering ToolBox 2005
9 6 19