[MUSIC PLAYING] - All Right, so just going
to wait a couple of seconds here see if everybody's on. All righty, looks
like everybody's in. So today we're going
to cover something that needs to be addressed. It seems that no one knows
exactly what a var is. So what is a VAR or kVar? Anyone? - Hold on, can I Google it? - Isn't that a value added
reseller or value at risk? - Bar? I go to the bar all the time. Oh wait, you said VAR. - Video assistant referee, duh. - What? - I have no idea. - Hey Alexa, what's a kVAR? - This might answer
your question. According to Fandom, according
to superfriends.fandom.com, Ak-Var is a Kryptonian
who was born on-- - Isn't that the
foam on the beer? - Eric, unmuted yourself please. - Yeah, that's like the wasted
capacity in a transformer. - Now we're getting somewhere. - Wait, isn't that
related to power factor? - I've heard that
explanation many times and I still don't understand it. - VARs are produced
by capacitors, and inductors use VARs. - Oh wait, I found it on Google. It's imaginary power. - Yes. - Power that isn't real? - That really doesn't
make sense to me. - Well Wikipedia says
volt amps reacted, right? - Come on guys, it's the
y-axis on the power triangle. - It's the angle difference
between voltage and current that allows motors to spin. - Very good. That's actually pretty close. - So people think volts
times amps equals watts, but that only works for DC. For AC power systems, volts
times amps equals volt amps, and we also have to consider
real and reactive power. To understand
reactive power we have to understand what a VAR is. - For engineers, electricians,
or anyone dealing with electricity, we ask
them to take a leap of faith to believe, and therefore
understand, electricity, something0 that we can't see. But then we even
go one step further and ask them to believe
in imaginary power, which by definition doesn't exist. Or does it? So for us to understand what
reactive or imaginary power is, we will look at the technical
definition as well as several analogies so
that hopefully, we can all come away with
an understanding of what a VAR really is. - Alternating current, or
AC, is a 60 hertz sine wave that oscillates back and forth. So if you have a regular
incandescent light bulb, the electrons are actually
rubbing back and forth in the wire. The resistance of the
light bulb acts almost like a friction that
heats up the element and causes it to illuminate. If the frequency was lower,
like 2 hertz for example, you would see the
bulb go on and off. But because it is
so fast, the element doesn't have time to cool
down and stop shining. Looking at the graph, we can
see that the voltage and current are in phase for
this resistive load. Because power equals
voltage times current, we can see our power curve. Notice that since the
voltage and current are negative at the same time, it
results in a positive power consumption by the light bulb. Now let's see what a purely
inductive load would look like. Notice how the current lags
the voltage by 90 degrees. Calculating the power yields two
positive and two negative areas in the curve. This right here is why
reactive power is also called imaginary power. The inductor is actually
charging and discharging twice each cycle to yield
no net power consumption. There is still a real
current associated with this imaginary power that
does travel through the wires, but it just oscillates back
and forth through the inductor and yields no work,
just a magnetic field. It is easy to see the 120
hertz power curve here, because there are two complete
power cycles for every one 60 hertz voltage cycle. This concept is the same for
a purely capacitive load, the only difference is that
the current leads the voltage by 90 degrees. The capacitor charges and
discharges twice per cycle, and the reactive power
establishes an electric field between the metal plates. This action, or reaction, is
where the term originates. VAR, or volt amps
reactive, describes how the inductor or
capacitor react to the system by delaying the
current or voltage. Now it is worth noting that
purely inductive or capacitive loads do not exist. This is because
every component has some inherent resistance to it. Real loads are a combination
of resistive, inductive, and capacitive elements. This results in a current that
leads or lags the voltage. The combination
type load results in two large positive humps
and two smaller negative humps. The negative humps
are canceled out by some of the area
of the larger two, and the remainder is
the real power consumed by the load, which in
the case of a motor is released in the form
of mechanical power. Inductive motors cause
the current to lag, and capacitors are used
to force the current back. This is where the terms
leading or lagging power factor come into play. Leading means your system is
more capacitive, and lagging means your system
is more inductive, which is more common. For generators, the
mechanical power input equals the real
electrical power output. The reactive power
required by the generator is only used to excite and
magnetize the inductive field windings. This is where they
get their name, because they produce
a magnetic field. The resultant
magnetic field isn't doing any real work, kind of
like this permanent magnet generator right here. There is a magnet
that, while stationary, isn't doing any work. However, if I spin
the shaft, I'm going to force the
magnetic field to rotate through the armature winding. And this requires
real work because of the electromotive
force, or EMF voltage, induced in those windings. This EMF is physically
resisting my mechanical input because of the electric
power demanded by the load. In my case, it's
just this simple LED, but in the case of
a utility system, the load is a
combination type that requires some reactive power. That reactive power,
although not doing real work, does require real
current, which flows through the armature windings. This is why generators
are rated in volt amps, or apparent power,
which is the rooted sum of the squares of both
real and reactive power. Reactive power current flowing
in the armature windings causes them to overheat,
just like the current of the real power component. Many people just reference
the kilowatt rating, but you have to consider both to
understand the actual capacity of a generator. And keep in mind
that the load is what demands the reactive
power that the generator then supplies. Without a load
there is no current, and you just have
the open circuit voltage multiplied by current of
zero, yielding no power at all. But remember, the armature
windings are inductive, so they play a role
in the overall circuit when a load is connected. - Most of the time when
professors or technical people talk about reactant
power or VARs, they have a hard time
explaining exactly what imaginary power is. To try to make it real
for people to understand, many analogies have been made
to explain the unexplainable. Here are some of our
favorite analogies that might make sense to you. None are perfect,
but maybe visualizing them will help you to
understand or explain to others what a VAR is. Probably the most common analogy
to explain what reactive power is, is the beer analogy. With this one, the
mug size, or capacity, is compared to the kVA rating
of a transformer, which is the transformers capacity. Utilities bill us on
kilowatts, or kilowatt hours, which is real power,
or in the analogy is compared to the beer. The foam takes up space and
essentially wastes capacity of the mug or the transformer. The foam is compared to the
reactive power, or kVAR. So if you remove the foam,
you can fit more beer in the glass, or real power. From a power system
standpoint, adding capacitors compensates for the
motor loads on the system and allows you to add
more real watts or loads to your transformer. The walking analogy explains
real and reactive power in a very simple way. If your goal is to
walk across the room, you can lift your leg a
little and have a long stride. This does the most work, or
moves you forward the most, or you could do a
high knee march, and have a lot of effort without
really moving forward much. Your goal is to move
forward or do work, which is similar to kilowatts. And the upward motion
is required to move, but not helping to move forward,
and this is similar to kVar. The bicycle analogy
is interesting, as it explains power
systems like this. A bicycle with 10
seats has five people with pedals doing the work
and acting like generators, and five of them are just
riders and acting like a load. The generators have
to pull the loads, and as long as the loads
cooperate and sit up straight, the generators can just do real
work, moving the bike forward. This is compared to kilowatts. If the riders or loads
become disruptive and lean, the generators have to lean
the opposite way to compensate. This does no work,
but is required to keep the bike stable. This action is compared to
VARs on the power system. From a business standpoint,
productive or direct employees can build hours directly
against a job, where overhead employees, like
sales or management, are considered non-productive,
or general and overhead. Productive employees
are like the real power, overhead employees are
like the reactive power. Both are needed
to run a company, but only the
productive employees can build labor hours
directly against the job, thereby doing real work. Without the overhead
to manage and create opportunities for
real work to be done, the business would fail. Two other visualizations
include a boat in a channel, and a person pulling
a block on the ground. For both of these examples,
moving the boat or block requires real
work, or kilowatts, and the angle of the rope, or
the hypotenuse of the triangle, is related to kVA. The angle is related to
power factor and ties in the requirement for
reactive power, or VARs. Here at the PSEC, along
with showing real loads and measurements, we often
use many of these analogies to explain react to power. We have also built
the water analogy, which helps to explain some
of these concepts and others. In the water analogy demo,
we use this storage tank as a capacitor and we show this
water wheel as an inductor. The capacitor can be operated in
parallel with the transformer, and shows how you can relieve
the capacity in a transformer. The inductor, or
water wheel, shows how it takes a lot of inrush
current, or inductive kick, to get the motor going. And then once it's
moving, it requires very little real
power, or work, to keep it moving, like a hamster
on a wheel, again, just like a motor, just
enough to overcome friction. For each of us, we have
a favorite analogy, or one of the
technical explanations that makes more
sense than others. For me, to understand
what a VAR is, I personally like the
following explanation using an induction motor. An induction motor
needs a magnetic field to actually spin. So if you have an unloaded
motor and apply voltage, the motor will spin but
it's doing very little work, in fact, just enough
to overcome friction. In order to make the motor
spin, loaded or unloaded, you need a magnetic field. The power required to
create this magnetic field is called reactive power,
imaginary power, or yes, VARs. To maintain this
magnetic field, we really aren't doing any real work. As the motor is loaded
and you're actually doing mechanical work,
like lifting an elevator or moving a conveyor,
you will require some real power, or watts. In fact, the work you
do increases linearly with the real power you put in. But since the magnetic field
is required to spin the motor, loaded or unloaded, the
VARs, or reactive power, increases slightly, but
at a much lower rate per amount of work you put in. The ratio of kilowatts to kVA,
which equals the power factor, reaches the rated power factor
for a motor, which is usually about 0.8 or 0.85 at full load. The power triangle defines
the watts on the x-axis, the VARs on the y-axis,
and the apparent power, or VA on the hypotenuse. You can see how this
power triangle changes from no load at about
0.1 power factor, to 0.8 power factor
at full load. Watts are real power and must
be created by a source of power, like a generator. And to do this, energy in
the form of mechanical power or fuel is used to maintain
conservation of energy. Since magnetic,
or reactive power, requires no energy
to be created, we call it imaginary power. In electrical systems, the
opposite of an inductor is a capacitor. To compensate for inductive
load like a motor, a capacitor it actually
draws current 180 degrees out of phase, and therefore is
said to be a VAR generator and compensates for the
VARs required by the motor. - So now that we have
defined reactive power and looked at several analogies
to explain what a VAR is, let's take a look
at real measurements and see how VARs behave
on power systems. One thing to consider
is that loads take the real and reactive
power that they need. For this case, the load is 71
kilowatts, 73 kilovar, and 101 kVA, with the 0.7 power factor. From a system
standpoint, the addition of capacitors, or VARs, improves
the ratio of real power, or kW, and apparent power, or kVA,
upstream from the capacitor location by reducing the net
reactive power, or kVARs. In this case, we were
adding 15 kVAR at a time until we negate the
73 kVAR of the load. Notice that when we actually
overdo it and overcompensate with capacitors, the kVAR goes
back up, current goes back up, and the power factor
goes down again, but is shown as a
leading power factor. Unfortunately, the
mysterious nature of reactive power and the
fact that VARs are not easily understood has left
the door open for unscrupulous and sometimes unknowing
salespeople to sell capacitors as energy saving devices. They argue that reducing
the volt-amperes level by adding capacitors will reduce
your real power demand, or kW, and your energy usage,
or kilowatt hours. They often confuse people
saying that energy efficiency is the same as the power
factor, but it isn't. Electrical efficiency refers
to power out over the power in. This goes back to our discussion
about the conservation of energy that we
mentioned earlier. The difference in output
and input is kW losses. We did an entire video on
this important subject, because although you can
reduce the reactive power which reduces the current in the
kVA while also improving power factor with
capacitors, you don't save real power as claimed
by these black box companies. Can capacitors save you money? Absolutely, if you have
a power factor penalty, which would only be
the case for some large commercial and industrial
loads, but never for your home. If only everyone understood
the concept of reactive power. So why do you need to
know what a VAR is? To accurately size the
equipment you are using, you have to understand the
difference between watts and volt-amperes for
AC power systems. Professors and teachers gloss
over the concept as if it really isn't that important,
but without understanding VARs or reactive power, you cannot
fully understand the power triangle. Understanding the magnetic
field requirements for motors and how capacitors are used
to supply that field will help you understand reactive
power and VARs. The important thing
you should realize is that reactive power
exists, and loads like motors and capacitors
require actual current even when they were
doing no real work. Hopefully, you now have
a working understanding, and not just an
abstract understanding of reactive power. - To learn more
about reactive power, or if you have a great
analogy that you'd like to share with us to
describe this elusive concept, contact us or your local
Eaton representative to schedule a visit to the
Power Systems Experience Center today.
