ŰŰThe Perfect Pour
The term VAR crossed the threshold
from engineering to business jargon
some time ago. While Volt/VAR
management technologies have
been in practice for decades, the
frequency with which the term VAR
now appears suggests that it’s prudent
to revisit the summary explanation
of this unit of measurement.
VAR is the acronym for volt-ampere
reactive, a unit of reactive power in
alternating current (ac) power systems.
Even many non-technical readers are
likely aware that ac electricity reverses
direction many times a second and is
represented by a sinusoidal wave. One
layer of detail lower, current and voltage
are both represented by sinusoidal
waveforms, offset by a half phase (90
degrees) in a purely resistive circuit.
In an ac circuit, current and voltage
are typically out of phase by more
or less than a half phase. When
current lags voltage by more than 90
degrees, the circuit is inductive; when
current leads voltage by more than
90 degrees, the circuit is capacitive.
Generally, power systems suffer from
inductive problems. Transformers,
induction motors, induction generators
(e.g., wind turbines), and high intensity
discharge lighting are causes for a circuit
to be inductive.
Synchronous generators, synchronous
motors, and capacitive loads cause a
circuit to be capacitive in the alternative.
equipped transformers to optimize
voltage in real time without violating
regulations or service agreements.
VAR
VA
W
Figure 1. Summer saison representing real (W), reactive (VAR),
and apparent (VA) power.
Utilities traditionally use capacitor
banks on distribution networks in order
to make circuits less inductive and
maximize useable power. Additionally,
advanced inverters (including those
used with energy storage systems) are
able to supply corrective power
to adjust inductive and capacitive
circuits, which can, in the future,
become an additional ancillary
monetized benefit of such systems.
Volt/VAR optimization programs
control capacitors and tap changer-
Why is this concept important?
The traditional analogy to explain
reactive power and the unit VAR is a
glass of beer (figure 1). Just as within
nearly any ac circuit there is reactive
power (VAR), there is foam in beer.
Unfortunately, only the portion of power
in which voltage and current are in phase
form real power (W for watt) to do useful
work. Real power (W) is the liquid beer
that does real work—quenches your
thirst and provides other side effects.
In total, the apparent power (VA for
volt-ampere) is the sum of the real and
reactive power, or the total glass of beer.
Reducing reactive power is the goal
because both real and reactive powers
need to pass through the generation
and distribution system. Doing so
increases energy efficiency by reducing
total generation needs and reduces peak
demand costs and equipment needs by
transmitting and distributing less total
energy. Utilities strive to maximize
the ratio of real power to reactive
power (perfect power) just as I strive to
maximize the amount of liquid to foam
when I homebrew (perfect pour). ei
Ryan Franks, NEMA Technical Program
Manager (ryan.franks@nema.org),
is a 2014 IEC Young Professional. He
also holds a certification in Brewing
Technology from the Siebel Institute.
A number of voltage-adjustment and reactive power correction technologies, grouped
under the heading of dynamic voltage and VAR control architectures (DVCAs), can help
ensure power delivery that is both reliable at peak loads and continuously efficient. The report forecasts that cumulative
worldwide investment in DVCA technologies is expected to total nearly $17.7 billion from 2014 through 2023.Smart grids
designed with DVCA can be flexible and active throughout the distribution system, with flexible volt/VAR control (VVC)
at primary substations and distribution circuits, active power electronics at the edge of the grid, and VVC embedded in
smart electric vehicle EV chargers and smart photovoltaic (PV) inverters.
What the industry is saying:
Navigant Research
NEMA electroindustry • April 2015 21