Glossary of Power Terms

Glossary of Power Terms
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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 multiplied 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 accurate measurement.
Billing consumption — total amount of
energy consumed during a predetermined period (usually 28 to 33 days).
Consumption (active energy) — actual
electrical energy used measured in kilowatthours (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
service nonlinear loads.
Displacement power factor — the difference between apparent power and
true power when only the phase relationship of voltage and current at the fundamental are taken into account.
Distortion factor (%DF) — Total harmonic Distortion referenced to the total
RMS signal (THD-R).
Distortion power factor — the difference 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 force
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 harmonic current.
Peak demand (maximum RMS power)
— the highest average load during a
specified time interval (kW).
Phase — 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 (voltamperes). Expressed in decimal form,
e.g., .98.
Ratchet demand — determining the
billing demand based upon a pre-established peak average demand (usually at
75%, 80%, or 100% of the pre-established 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 connector 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.
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 harmonic 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 transformer derating established by CBEMA
for phase-to-neutral loads.
Watt — the measure of real power. It is
the power expended when one ampere of
direct current flows through a resistance
of one ohm.
True RMS — capabiltity to accurately
measure the value of AC voltage and
current having a nonsinusoidal waveform as well as sinusoidal waveforms.
Wye connection — a connection of
three components made in such a manner that one end of each component is
connected; generally used to connect
devices to a three-phase power system.
Unbalanced load — an AC power
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.
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