07-09-2016, 09:52 AM
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What is Power Factor?
To understand power factor, we’ll first start with the definition of some basic terms:
KW is Working Power (also called Actual Power or Active Power or Real Power).
It is the power that actually powers the equipment and performs useful
work.
KVAR is Reactive Power.
It is the power that magnetic equipment (transformer, motor and relay)
needs to produce the magnetizing flux.
KVA is Apparent Power.
It is the “vectorial summation” of KVAR and KW.
Let’s look at a simple analogy in order to better understand these terms….
Let’s say you are at the ballpark and it is a really hot day. You order up a
mug of your favorite brewsky. The thirst-quenching portion of your beer
is represented by KW (Figure 1).
Unfortunately, life isn’t perfect. Along with your ale comes a little bit of
foam. (And let’s face it…that foam just doesn’t quench your thirst.) This
foam is represented by KVAR.
The total contents of your mug, KVA, is this summation of KW (the beer)
and KVAR (the foam).
What Causes Low Power Factor?
Since power factor is defined as the ratio of KW to KVA, we see that low power
factor results when KW is small in relation to KVA. Remembering our beer mug
analogy, this would occur when KVAR (foam, or Mac’s shoulder height) is large.
What causes a large KVAR in a system? The answer is…inductive loads.
Inductive loads (which are sources of Reactive Power) include:
" Transformers
" Induction motors
" Induction generators (wind mill generators)
" High intensity discharge (HID) lighting
These inductive loads constitute a major portion of the power consumed in
industrial complexes.
Reactive power (KVAR) required by inductive loads increases the amount of
apparent power (KVA) in your distribution system (Figure 4). This increase in reactive
and apparent power results in a larger angle " (measured between KW and KVA). Recall
that, as " increases, cosine " (or power factor) decreases.
Why Should I Improve My Power Factor?
You want to improve your power factor for several different reasons. Some of the
benefits of improving your power factor include:
1) Lower utility fees by:
a. Reducing peak KW billing demand
Recall that inductive loads, which require reactive power, caused
your low power factor. This increase in required reactive power
(KVAR) causes an increase in required apparent power (KVA),
which is what the utility is supplying.
So, a facility’s low power factor causes the utility to have to
increase its generation and transmission capacity in order to handle
this extra demand.
By raising your power factor, you use less KVAR. This results in
less KW, which equates to a dollar savings from the utility.
b. Eliminating the power factor penalty
Utilities usually charge customers an additional fee when their
power factor is less than 0.95. (In fact, some utilities are not
obligated to deliver electricity to their customer at any time the
customer’s power factor falls below 0.85.) Thus, you can avoid
this additional fee by increasing your power factor.
2) Increased system capacity and reduced system losses in your electrical
system
By adding capacitors (KVAR generators) to the system, the power
factor is improved and the KW capacity of the system is increased.
For example, a 1,000 KVA transformer with an 80% power factor
provides 800 KW (600 KVAR) of power to the main bus.
1000 KVA = (800 KW)2 + ( ? KVAR)2
KVAR = 600