Power Factor is
like your Your Mother-In-Law:
Back when I was an engineering student, one of the most difficult concepts for
me to understand in electrical theory was Reactive Power. I mean, come on......it uses
energy, but produces no work.....It can cause your generator’s insulation to
deteriorate, but it produces no heat. To this day I distinctly remember two of the
brightest engineering minds I know arguing over the fact that it even really existed at
all! One of them insisted it was all just a communist plot!
Well.....it was the height of the cold war ya know....
Anyway, the point is that it is far from an intuitive idea.
Okay, it goes something like this.
What we call "Electricity" is actually made up of three parts. Real Power (Kw,
Mw), Apparent Power (Kva), and Reactive Power (Kvar). These 3 parts form the "Power
Triangle"
Real Power (Kw) is the part of the triangle which results in real work done, in the form
of heat energy. This is the power that drives the world.
Apparent Power is that portion of the power triangle that we actually measure.
And then....there is Reactive Power....which serves no real function at all, kinda like a
Mother in Law. We’ll get back to that in a minute.
The phase angle between Real Power and Apparent Power in the power triangle is identified
as the angle "q" which is the Greek letter "THETA". The size, in
degrees, of that angle determines the size of the Reactive Power leg of the triangle. The
cosine of that angle is called Power factor or pf and the value of the pf is inversely
proportional to the amount of reactive power you are generating. What this means is that
the smaller the angle q, the less Reactive Power you are making and the greater your Power
Factor is.
As you can see from the diagram above, a decrease in the phase angle q causes a decrease
in Reactive Power but causes NO CHANGE in Real Power (work). Therefore, less energy is
expended for the same amount of real work done by the system. This means that reactive
power is simply a drain on your resources with no added benefits...... much like your
visiting mother in law is a drain on your wallet, patience, life span etc. The less you
see of her, the more energy you have! If she was completely gone..... you would be in
heaven....at one with the universe...you would be at Unity!.
Unity is when Apparent Power and Real Power are on the same plane, with NO Reactive Power
at all. That means a phase angle q of ZERO, the cosine of which (pf = cosine q) is 1.0 or
Unity.
Running at a unity power factor means that all of your electrical energy is going towards
real work and none is being wasted by Reactive Power. On either side of Unity are
Capacitive (leading) pf and Inductive (lagging) pf. That is for another lesson though. For
now, it is only important to know that most of the world runs at a lagging power factor
because most of the electrical loads in the world are "inductive". Washing
machines, compressors, pumps, motors etc, are all inductive loads. If the electrical
loading of the world was made up of nothing but heaters and lights, we would be at unity.
Why? Because incandescent lights and heaters are "resistive" loads. Resistive
loads have a pf of 1.0. Inductive loads, like a motor, run at lagging pf of around 0.8.
What all that means is that on a world wide scale, pf is a set value in the lagging
direction and cannot be changed.
"Well, thanks a lot" you say. "Here you are telling me to run at a unity
pf, and now I find out it’s impossible". No... it’s not. I said "on a
world wide scale" pf is fixed. At your cogen or power generation facility though, you
have control over your power factor. This means that unless you have a utility restriction
against running at unity, you can do so and let the utility suck up all the
"Vars". Be aware that many utilities impose this restriction so that they are
not forced to have to carry YOUR reactive load.
By manipulating your power factor controls, you will reduce the amount of reactive loading
your system is forced to make. You can actually see this at work if you experiment, but
ask your supervisor first! I can see it now...."But Professor overdrive said I
could!" With approval, move your power factor alternately towards and then away from
1.0 and watch your reactive load rise then fall. You can also watch your generator field
amps decrease, due to the fact that less energy is being used in the generator field
coils. This means that you have more room to the limits of your switchgear and buswork. It
also means less heating of your generator windings and therefor less damage to insulation.
It is important to note here that increasing power factor PAST unity in the capacitive or
"leading" direction can be dangerous. I point this out because following the
logic described above, if a pf of 1.0 is good, a pf of 0.8 Leading (Capacitive) must be
better, right? No. This can cause instabilities in your voltage regulator that could
potentially cause equipment damage, under certain conditions, so just stick to 1.0.
In conclusion, remember that the greater your power factor (up to 1.0) the less reactive
loading you will have (mother in law), and the closer to unity (nirvana) you will be and
therefore the more efficient (happy) you will be!
