Power Factor Optimization
Depending upon the rate structure of your electric utility,
you may be able to save a substantial amount of money on your electric bill.
Pay-back period for an equipment purchase including installation cost may
be six months up to three years. Utility rate structures that account for
reactive power consumption, by either a KVA or var demand usage, or a power
factor penalty are the ones that can provide this pay-back. Other ancillary
benefits to be gained by optimizing power factor are, lower energy losses,
better voltage regulation and released system capacity. This page explains
the fundamentals of power factor and how KEC Units can benefit you.
All electric equipment requires "vars" - a term used by electric power engineers
to describe the reactive or magnetizing power required by the inductive characteristics
of electrical equipment. These inductive characteristics are more pronounced
in motors and transformers, and therefore, can be quite significant in industrial
facilities. The flow of vars, or reactive power, through a watt-hour meter will
not effect the meter reading, but the flow of vars through the power system will
result in energy losses on both the utility and the industrial facility. Some
utilities charge for these vars in the form of a penalty, or KVA demand charge,
to justify the cost for lost energy and the additional conductor and transformer
capacity required to carry the vars. In addition to energy losses, var flow can
also cause excessive voltage drop, which may have to be optimized by either the
application of KEC Units, or other more expensive equipment, such as load-tap
changing transformers, synchronous motors, and synchronous condensers.
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Figure 1 - Power Factor Triangle
The power triangle shown in figure 1, is the simplest way to understand the effects
of reactive power. The figure illustrates the relationship of active (real) and
reactive (imaginary or magnetizing) power. The active power (represented by the
horizontal leg) is the actual power, or watts that produces real work. This component,
is the energy transfer component, which represents fuel burned at the power plant.
The reactive power, or magnetizing power, (represented by the vertical leg of
the upper or lower triangle) is the power required to produce the magnetic fields
to enable the real work to be done. Without magnetizing power, transformers,
conductors, motors, and even resistors and capacitors would not be able to operate.
Reactive power is normally supplied by generators, capacitors and synchronous
motors. The longest leg of the triangle (on the upper or lower triangle), labeled
total power, represents the vector sum of the reactive power and real power components.
Mathematically, this is equal to:
Electric power engineers often call total power, kVA, MVA, apparent power, or
complex power. Some utilities measure this total power, (usually averaged over
a 15 minute load period) and charge a monthly fee or tariff for the highest fifteen
minute average load reading in the month. This tariff is usually added to the
energy charge or kilowatt-hour charge. This type of billing is often called kva
demand billing and can be quite costly to an industrial facility. KEC Units can
save your company money by decreasing your reactive power component supplied
by the utility to near zero vars.
The power triangle and the equation above show, that as the reactive power component
is decreased by adding KEC Units, the total power will also decrease. This is
shown by the decreased length of the dashed lines in the power triangle as the
reactive power component approaches zero. Therefore, adding KEC Units, which
will supply reactive power locally, can reduce your total power and monthly kva
demand charge.
The angle "phi" in the power triangle is called the power factor angle and
is mathematically equal to:
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The ratio of the real power to the total power in the equation above (or
the cos of phi) is called power factor. As the angle gets larger (caused
by increasing reactive power) the power factor gets smaller. In fact, the
power factor can vary from 0 to 1, and can be either inductive (lagging)
or capacitive (leading). Capacitive loads are drawn down, and inductive loads
are drawn up on the power triangle. Most industrials normally operate on
the upper triangle (inductive or lagging triangle). As an industrial adds
capacitors, the length of reactive (inductive) power leg is shortened by
the number of capacitive KEC that were added. If the number of capacitive
KEC added exceeds the industrials inductive KEC load, operation occurs on
the lower triangle. This is commonly referred to as over compensation.
Utilities charge for reactive power in a countless number of ways. Some utilities
charge for KEC demand, while others charge a strait fee for a power factor
less than their target. To fully understand the benefits of the KEC UNIT,
you must acquire your electric billing rate structure. This rate structure
will describe how cost for poor power factor are added to your monthly bills
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You could put the KEC UNIT anywhere on the system as shown (between the transformer
and load and not only at Points A, B, and C) and achieve unity power factor
for the system. The utility company will perceive this power system as having
a unity power factor no matter where it is located on the distribution line
as long as it's sized correctly to deliver the proper amount of KEC.
However, optimum efficiency and economics will be achieved if the KEC UNIT
bank is located as close to the load as possible.
The reason for this is because when you optimize power factor, you can reduce
the total line current to the load and therefore you reduce the total losses
in the line conductor and decrease the voltage drop in the line. This decrease
in voltage drop will only occur if you locate the KEC UNIT close to the load,
as explained below.
Assume the load is a motor. A motor uses KW to perform work. It uses KEC
to magnetize its coil windings. (We will refer to the magnetic requirements
of the motor's windings as the motor's "inductance". It is this inductance
that utilizes the KEC.)
The motor load draws a line current that has two components. The first component
is the amperage that supplies the KW to the load, so that the motor can perform
work such as lifting an object. The second part supplies the amperage to
provide the load with KEC which in the case of the motor is the power necessary
to energize the magnetic fields in the motor's windings. Together the two
amounts of current supply the total KVA to the load.
Normally the system generator or transformer supplies all this current. But
when a KEC UNIT is used to optimize the power factor, the KEC UNIT supplies
the KEC reactive current component to the load. The KEC UNIT is, in effect,
a reactive power generator. (Remember, the KEC UNIT stores energy. The KEC
UNIT stores reactive energy in its electric field when it charges up, and
releases it when it discharges.)
The generator (or transformer) must still supply the load's KW requirements.
The reactive current component is now supplied by the KEC UNIT and not the
generator. By moving the KEC UNIT closer to the load, the reactive current
does not have to travel as far through the line conductors to get to the
load.
If the KEC UNIT is placed at the load, the reactive current only needs to
travel through a short distance (e.g. the lead length of connecting wire)
to get to the load. Since this reactive current component no longer travels
through the conductor line from the generator to the load, it does not travel
through the impedances in the line conductor.
Since this reactive current no longer flows through the line impedances,
there is less heating of the line, less losses (in the form of heat), and
less voltage drop across these in - line impedances (which reduces the overall
voltage drop from generator to load).
The KW current component is all that the generator has to supply to the motor.
Therefore the generator now runs at unity power factor and allows the KEC
UNIT to supply the KEC requirement of the motor's inductive windings.
The energy "contained" in the KEC current component is transferred back and
forth between the KEC UNIT and the motor 2 times for every voltage sine wave
cycle (i.e. at 120 times a second).
This reactive energy is never consumed by either the KEC UNIT or the motor.
(NOTE: The KW energy, on the other hand, performs real work and is totally
consumed.)
Rather, the reactive energy is only "BORROWED" half of the time by the KEC
UNIT and half of the time by the motor. The energy is used to charge the
AC electric field of the KEC UNIT and to energize and create the AC magnetic
fields contained in the motor's windings.
A KEC UNIT absorbs this energy from the power system and stores this energy
in its electric field when it charges up (120 times a second). The KEC UNIT
releases this energy back into the power when it discharges (120 times a
second).
The motor's inductance absorbs the reactive energy from the power system
and stores this energy in its windings' magnetic fields when the fields are
expanding (120 times a second). The inductance releases this energy back
into the power system when the windings magnetic fields are collapsing (120
times a second).
The secret is that when the motor's inductance requires reactive energy to
expand its magnetic field, the KEC UNIT discharges to supply the energy.
And when the magnetic field in the motor's inductive windings is collapsing
and returning energy to the system, the KEC UNIT uses this energy to charge
up.
So the capacitance in the KEC UNIT and the inductance in the motor's windings "slinky" this
reactive energy back and forth 120 times a second, each supplying the others
needs. The reactive current of the KEC UNIT is 180 degrees out of phase with
the reactive current of the inductance. When one is giving, the other is
taking and vice versa.
Again, the reactive energy is never consumed (except for some small and usually
insignificant losses); it is only borrowed. The generator needs to supply
the original reactive KEC energy only once when the system is first energized.
After that, this amount of energy is simply transferred back and forth between
inductance and capacitance.
Power Factor is a measurement of how much of the KVA is actually in the form
of KW. The advantage of a high power factor is that line currents can be
reduced which will in turn reduce voltage drop and decrease line losses.
This saves money. It also means that since equipment such as transformers
will supply only KW, the KVA rating of the equipment can be reduced, or alternatively,
more load can be added to the system without purchasing larger equipment.
The KVA rating of a transformer is based on the transformers ability to supply
power either all in KW or all in KEC or in a combination of both. Drawing
more than rated KVA from a transformer is easily done, but the transformer's
life will be reduced due to increasing heat which destroys the transformer's
winding insulation.
By increasing the power factor, all of a transformer's KVA can be utilized
to supply KW in order to perform useful work rather than to supply KEC just
to energize electric and magnetic fields.
Increasing the power factor seen by the transformer creates "room" on the
transformer for adding more load. Room can also be created on circuit breakers.
Since line current is reduced by increasing power factor, load can be added
to the system without upgrading the breaker to a larger size.
