Power Protection Definitions.
Below is a glossary of terms related to power protection, including UPS, surge
protectors, voltage regulators, and line conditioners. This glossary is not intended to be
a complete list of all terms related to power electronics, but rather a list of terms
relevant to understanding power protection in general.
You can scroll down though the main glossary of terms and definitions, or you can look
through the index immediately below and click on a term to go directly to the definition
of that term. Thanks for stopping by! Let us know of any terms we've overlooked.
AC - Alternating Current
Electrical current that continually reverses direction, with this change in direction
being expressed in hertz, or cycles per second.
Amp or Ampere
Quantitative unit of measurement of electrical current. Abbreviated as A.
APC
A small, little known company that makes UPSs, full company name uncertain.
Blackout
A total loss of electrical power.
Brownout
An low voltage condition over an extended period of time.
Clamping Level
The voltage level above which a surge suppression device diverts energy away from the
load.
Clamping Time
The response time of a surge suppression device in clamping or diverting away from the
load a voltage above the claming level.
Common Mode Noise
Abnormal signals that appear between a current-carrying line and its
associated ground.
Crest Factor
Current
The flow of electricity expressed in amperes. Current refers to the quantity or intensity
of electricity flow, whereas voltage refers to the pressure or force causing the
electrical flow.
DC - Direct Current
Electrical current which flows in one direction.
Dip
A short term voltage decrease. See also "Sag".
EMI - Electro-Magnetic Interference
Electrically induced noise or transients.
Ferroresonant Transformer
A transformer that regulates the output voltage by the principle of ferroresonance: when
an iron-core inductor is part of an LC circuit and it is driven into saturation, causing
its inductive reactance to increase to equal the capacitive reactance of the circuit.
Filter
An electronic device that allows only certain frequencies to pass.
Ground
Ground Fault
An undesirable path that allows current to flow from a line to ground.
Harmonic Distortion
Excessive harmonic (a frequency that is a multiple of the fundamental frequency) content
that distorts the normal sinewave waveform.
Hertz or Hz
The unit of measure of the frequency of alternating current (AC). Also a well-known car
rental agency.
Inverter
The part of a UPS that converts the battery's DC output into AC power.
Isolation
The degree to which a device like a UPS can separate the electrical environment of its
input from its output while still allowing the desired transmission to pass through.
Joules
The amount of energy measured in watt-seconds that a surge suppression device is capable
of directing away from the load in case of a surge or spike.
KVA
Thousand VA
Load
An electrical device connected to a power source is a "load." In reference to a
UPS, the load is the amount of current that is required by the attached electronic
equipment. Rated loaded described in the specifications of the electronic equipment is
often higher than the actual power consumption of the equipment in real world use.
Noise
An undesirable signal that is irregular and is riding on top of the desired signal.
Offline UPS
Overvoltage
An abnormally high voltage, like a surge but lasting for a longer period of time.
Power Factor
The relationship of actual power to apparent power. In reference to a UPS, the
relationship between watts and VA (volt-amperes). It is expressed as watts divided by
volt-amperes (W/VA) and is usually in the range of 0.6-0.71.
PWM - Pulse Width Modulation
Process of varying the width of a train of pulses by tying it to the characteristics of
another signal.
Radio-Frequency Interference
Rectifier/Charger
The part of a UPS that converts the incoming AC utility power to CD power for driving the
inverter and charging the batteries.
Sag
Sealed Lead-Acid Battery
A battery containing a liquid electrolyte that has no opening for water replenishment
Sinewave
A fundamental waveform produced by periodic, regular oscillation that expresses the sine
or cosine of a linear function of time or space or both.
Single Phase
The portion of a power source that represents only a single phase of the three phases that
are available.
Spike
SPS
A term referring to a stand-by or offline type UPS.
Squarewave
Stand-By UPS
Stepwave" Surge
An abnormally high voltage lasting for a short period of time.
Switching Time
The amount of time it takes a stand-by or offline type UPS to switch from utility output
to inverter output after the UPS senses a power interruption. Normally expressed in
milliseconds. See also Transfer Time.
Three Phase
An electrical system with three different voltage lines with sinewave waveforms that are
120 degrees out of phase from one another.
Transfer Time
The amount of time it takes a stand-by or offline type UPS to sense a power interruption
and switch from utility output to inverter output. Normally expressed in milliseconds. See
also Switching Time.
Transformer
A device used to change the voltage of AC power or to isolate a circuit from its power
source.
Transient
An abnormal and irregular electrical event, such as a surge or sag.
Transverse Mode Noise
Noise that is the result of the conversion of common-mode noise to normal-mode noise after
passing through a transformer.
Undervoltage
An abnormal low voltage lasting for a longer period of time than a sag.
UPS - Uninterruptible Power Supply
A general terms used to describe one of several types of battery backup devices, such as
offline or stand-by type, line-interactive type, and online type. Most UPSs also provide
surge protection functionality as well.
VA
See Volt-Ampere
Volt
The quantitative measure describing electrical force or potential.
Volt-Ampere
Volts-amperes. The unit of measure of apparent power that is the traditional unit of
measure for rating UPSs. Compare to watts, which is the unit of measure of actual power.
Voltage Regulator
A device that provides constant or near-constant output voltage even when input voltage
fluctuates.
Watts
The unit of measure of actual power. Compare to volt-amperes (VA), which is the unit of
measure of apparent power.
Waveform
The graphic form of an electrical parameter.
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