|
 What
Is Power Factor Correction(PFC)?
Power Factor Correction, in
detail (or, more than you probably need to know about
PFC):
The Power Factor (PF) of an electrical
installation is the ratio between the amount of power that is
actually used (aka Real Power, where k = kilowatts, or a unit of
1000 watts, expressed as kW) and the amount of power that is
actually supplied (aka Apparent Power or kVA). It is a measure of
how efficiently the installation uses electrical energy. Reactive
Power (kVAR) is shown at right angles to real power because it is
out of phase and does no useful work. A Power Factor of 0.75 means
the installation is using only 75% of the power being supplied to
it. The relationship
between real power, reactive power and apparent power can be
expressed by representing the quantities as vectors (see diagram
below). Real power is represented as a horizontal vector and
reactive power is represented as a vertical vector. The apparent
power vector is the hypotenuse of a right triangle formed by
connecting the real and reactive power vectors. This representation
is often called the power triangle. Using the Pythagorean
Theorem, the
relationship among real, reactive and apparent power is:
(apparent
power)2 = (real power)2 + (reactive
power)2
Reactive Power
(VAR) can be interpreted as wattless or wasted power and it
represents an extra burden on your Utility’s supply system (the cost
of which they pass on to you).
Real and reactive powers can also be calculated directly
from the apparent power, when the current and voltage are both
sinusoids with a known phase angle between them:
- (real power) = (apparent power) *
cos(theta)
- (reactive power) = (apparent power) *
sin(theta)
The ratio of real power to apparent power is called power factor
and is a number always between zero and one.
General Mathematics in Electric
Power:
In circuits
Electric power, like mechanical power, is represented by the
letter P in electrical equations. The term wattage is
used colloquially to mean "electric power in watts."
In direct current resistive circuits, instantaneous electrical
power is calculated using Joule's Law, which is named after the
British physicist James Joule, who first showed that heat and
mechanical energy were interchangeable.
-
where
- P is the power (watt or W)
- V is the potential
difference (volt or V)
- I is the current (ampere or
A)
For example:
- .
Joule's law can be combined with Ohm's law to produce two more
equations:
- where R is the
resistance (Ohm or Ω).
For example:
-
and
-
In alternating current circuits, energy storage elements such as
inductance and capacitance may result in periodic reversals of the
direction of energy flow. The portion of power flow that, averaged
over a complete cycle of the AC waveform, results in net transfer of
energy in one direction is known as real power (also referred to as
active power). That portion of power flow due to stored energy, that
returns to the source in each cycle, is known as reactive power.
The relationship between real power, reactive power and apparent
power can be expressed by representing the quantities as vectors.
Real power is represented as a horizontal vector and reactive power
is represented as a vertical vector (as in the first diagram above).
The apparent power vector is the hypotenuse of a right triangle
formed by connecting the real and reactive power vectors.
In space
Electrical power flows wherever electric and magnetic fields
exist in the same place. The simplest example of this is in
electrical circuits, as the preceding section showed. In the general
case, however, the simple equation P =
IV must be replaced by a more complex
calculation, the integral of the vector cross-product of the
electrical and magnetic fields over a specified area, thus:
-
The result is a scalar since it is the surface integral of
the Poynting vector.
HOW IS POWER FACTOR
CORRECTED?
Generally, by capacitors placed on the line in key places. Find
out more, RETURN TO
POWER OPTIMIZATION PAGE
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