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GLOSSARY OF POWER TERMS
Alternating current current that
reverses its direction of flow periodically
(Hz).
Ampere a unit of measure for the rate
of current flow.
Apparent power applied voltage mul-
tiplied by current in an AC circuit. This
value would not take the power factor
into account. Unit is voltamperes (VA).
Balanced load AC power system
using more than two wires, where the
current and voltage are of equal value in
each energized conductor.
Bandwidth the range of frequencies
over which an instrument provides accu-
rate measurement.
Billing consumption total amount of
energy consumed during a predeter-
mined period (usually 28 to 33 days).
Consumption (active energy) actual
electrical energy used measured in kilo-
watthours (kWh) by the watthour meter,
regardless of the power factor.
Crest factor the ratio of the peak
value of a waveform (voltage or current)
to the RMS value.
Current transformer an instrument
accessory which detects current flow
without breaking the circuit under test.
An AC transformer, usually step-down;
typical ratio listing would be 1000:1. This
would indicate 1000A on the primary
and 1A on the secondar y.
Current transformer ratio the ratio of
primary amperes divided by secondary
amperes.
Delta connection a circuit formed by
connecting three electrical devices in
series to form a closed loop; most often
used in three-phase connections.
Demand (active, real, or true power)
the power which is actually consumed by
the load. This measurement takes the
power factor into account.
Demand interval (integration period)
the period of time over which the energy
is averaged. Typical demand intervals are
15, 30, or 60 minutes.
Derating Factor a number defined as
1.414 x average RMS phase current/ peak
phase current. This factor, when applied to
the rated load of a transformer, gives an
indication as to the percent loading that is
reasonable when that transformer must
s e rvice nonlinear loads.
Displacement power factor the dif-
ference between apparent power and
true power when only the phase relation-
ship of voltage and current at the funda-
mental are taken into account.
Distortion factor (%DF) Total har-
monic Distortion referenced to the total
RMS signal (THD-R).
Distortion power factor the differ-
ence between apparent power and true
power at all harmonic frequencies.
Frequency the number of complete
cycles of AC voltage which occurs during
one second (Hz).
Harmonics current or voltages which
have frequencies that are integer
multiples of the fundamental power
frequency; common and sometimes
dangerous in nonlinear loads.
Heating effect temperature increase
in electrical distribution equipment
caused by an increase in RMS current.
Impedance the total opposition to
alternating current flow in an electrical
circuit (Z).
Inductive reactance the force which
acts as a resistance in an inductor to
limit the flow of current. This forc
e
creates a leading power factor in AC
circuits.
Initiator pulses electrical impulses
generated from utility revenue meters.
Each pulse indicates a specific number
of watts consumed. These pulses are
used within energy analyzers to measure
energy consumption and demand.
K factor a number based on the
harmonic content of load current that
determines the maximum safe loading
on a power source.
K-rated transformers a transformer
that is rated or designed to serve as the
source for a predefined capacity of har-
monic current.
Peak demand (maximum RMS power)
the highest average load during a
specified time interval (kW).
P h a s e time relationship between
current and voltage in AC circuits.
Potential transformer an instrument
transformer used to step down high
voltage potentials to lower levels
acceptable for the input of electrical test
instruments.
Power factor the ratio of true power
(watts) to apparent power (voltam-
peres). Expressed in decimal form,
e.g., .98.
Ratchet demand determining the
billing demand based upon a pre-estab-
lished peak average demand (usually at
75%, 80%, or 100% of the pre-estab-
lished peak).
Reactance the opposition to current
flow in an AC circuit introduced through
inductance or capacitance.
Reactive compensation power the
reactive power to be applied to an AC
network for power factor correction;
adding capacitance in order to bring the
voltage and current waveform in phase.
Reactive power (kvar) power which
is actually borrowed from the load and
returned to the power source each cycle;
unused power.
Resolution the smallest unit value
that an instrument can measure.
Resonance when the inductance in
the system and the natural capacitance
of the system, or added capacitors, form
a tuned circuit resonant at one or more
of the harmonic frequencies produced by
nonlinear loads.
RS232 a computer interface connec-
tor used to connect serial devices such
as instruments for information transfer.
Sensitivity the smallest input that will
provide a specified output.
Skin effect phenomenon in which
high harmonic frequencies cause
electrons to flow to the outer sides of a
conductor, reducing its cross-sectional
diameter, and hence its ampacity rating.
GLOSSARY OF POWER TERMS Sliding demand calculating average
demand by averaging the average
demand over several successive time
intervals, advancing one interval at a
time.
THD (%THD, Total Harmonic
Distortion) the contribution of all har-
monic frequency currents or voltages to
the fundamental current or voltage,
expressed as a percentage of the
fundamental.
THDF (Transformer Harmonic Derating
Factor) method of calculating trans-
former derating established by CBEMA
for phase-to-neutral loads.
True RMS capabiltity to accurately
measure the value of AC voltage and
current having a nonsinusoidal wave-
form as well as sinusoidal waveforms.
Unbalanced load an AC p o w e r
system using more than two wires,
where the current is not equal in the
current-carrying wires due to an uneven
loading of the phases.
Watt the measure of real power. It is
the power expended when one ampere of
direct current flows through a resistance
of one ohm.
Wye connection a connection of
three components made in such a man-
ner that one end of each component is
connected; generally used to connect
devices to a three-phase power system.