Power Protection and Conditioning
2/50 Voltage Wave
Voltage surge with a virtual front
time of 1.2 ms and a time to
half-value of 50 ms delivered
across an open circuit.
8/20 Current Wave
Current surge with a virtual front
time of 8 ms and a time to halfvalue of 20 ms delivered into a
short circuit.
AC (Alternating Current)
Current that reverses direction
in response to voltage that is
changing polarity.
AC Power Interface
The electrical points where an
SPD is electrically connected to
the AC power system.
Active Tracking® Filter
A Surge Suppressor/Electrical
Noise lter device, that
suppresses both transient and
Low voltage electrical noise
found on the AC line.
Active Tracking® Filter Plus:
A device that both divert
or clamp high amplitude
transients, and attenuate lowenergy, high frequency noise.
Air-Cooled
A product cooled by the natural
circulation of air.
Ambient Noise Level
The sound level of the area
measured in decibels.
Ambient Temperature
The temperature of the air
surrounding a product.
Ampacity
The current-carrying capacity
of an electrical conductor or
device.
Ampere
The practical unit of electric
current.
Attenuation
Decrease in signal voltage or
power.
Autotransformer
A transformer in which part
of one winding is common to
both the primary and secondary
circuits associated with that
winding.
Banked
Two or more transformers
connected together to increase
kVA.
Basic Impulse Level (BIL)
A measure of the ability of the
insulation system to withstand
very high voltage surges. For
example, a 600-volt class
transformer has a 10 kV BIL
rating.
Battery Run Time
The amount of time (in minutes)
a battery system can support
a load.
Blackout
Slang term for the total loss of
electrical power for more than
one minute.
Breakdown Voltage
The maximum AC or DC
voltage which may be applied
from input to output and/or
chassis of a power supply.
See Hi-Pot.
Brownout
Slang term for an extended
voltage reduction (more than a
few cycles) of more than 10%.
Bypass
A mechanical or electronic
switch to provide an alternate
path for the line current.
CBEMA
An acronym for Computer
and Business Equipment
Manufacturers Association.
Replaced by the Information
Technology Industry Council
(ITIC).
CE Mark
(Conformité Européenne) A marking that shows the
product meets the fundamental
safety, health, environmental
and consumer protection
requirements of the European
Community.
Chassis
The metal framework or case
in which an electrical circuit or
system is constructed.
Combination Wave
Also called combination
surge. A surge delivered by
a generator which has the
inherent capability of applying a
1.2/50 ms voltage wave across
an open circuit and delivering
an 8/20 ms current wave into
a short circuit. The exact wave
that is delivered is determined
by the generator's ctive
impedance.
Common-Mode Noise
Noise that occurs between the
current carrying conductors and
ground.
Compensated Transformer
A transformer with a turn’s ratio
which provides a higher rated
voltage at no-load and rated
voltage at rated load. Normally
used on units rated 2 kVA or
smaller.
Constant Current Power Supply
A power supply that regulates
its output current for changes in
line, load, ambient temperature,
and time.
Constant Voltage Power Supply
A power supply that regulates
its output voltages for
changes in line, load, ambient
temperature and time.
Constant Voltage Transformer
(CVT)
A power conditioner that
provides a stable and regulated
sinewave output voltage.
Continuous Duty
The service requirement
that demands operation at a
constant load for an indenite
period of time.
Control Transformer
Usually referred to as an
Industrial Control transformer.
Designed for good voltage
regulation characteristics when
low power factor and /or large
inrush currents are drawn
(5 to 15 times normal).
Conductor Losses
Losses in the transformer
winding that are incidental to
the carrying of the load. These
losses include those due to
resistance as well as to stray
and eddy currents.
Core
The steel that carries the
magnetic ux in a transformer.
Core Loss
Losses caused by a
magnetization of the core.
Crest Factor
The ratio of the peak value
and RMS value of a voltage or
current waveform.
Cross-Regulation
In a multiple output power
supply, the percent voltage
change at one output caused
by the load change on another
output.
12
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Power Protection and Conditioning
Crowbar
An overvoltage protection
circuit which rapidly places a
low resistance shunt across the
power supply output terminals
if a predetermined voltage is
exceeded.
CSA
Canadian Standard Association
Current Limiting
See Output Current Limiting.
DC
(Direct Current) Current that
ows in only one direction.
Decibel (db)
A unit used to express the
magnitude of a change in
signal or sound level, either an
increase or decrease.
Delta Connection
A method used for connecting
the three windings of a threephase transformer (or three
single-phase transformers). The
windings are connected
in series, the three-phase
supply being taken from or
supplied to the junctions.
Delta-Wye
The method of connection for
both primary and secondary
windings of a three-phase
transformer bank.
Derating
The specied reduction in an
operating parameter to improve
reliability.
Differential Mode Noise
Noise that occurs between the
current carrying conductors.
DIN Rail
A standard rail (typically 35
mm wide) that mounts to
the chassis and allows other
electrical components to be
installed and replaced easily.
Distribution Transformer
Any transformer rated between
3 and 500 kVA and a primary
voltage of 601 volts or less.
Double Conversion UPS
See On-line UPS
Double Wound Transformer
A transformer with double
wound coils on both the
primary and secondary.
Drift
The change in output voltage of
a power supply over a specied
period of time, following a
warm-up period, with all other
operating parameters such
as line, load, and ambient
temperature held constant.
Drive Isolation Transformer
A transformer designed to
withstand the additional heat
and mechanical stress caused
by DC drives.
Dry Type Transformer
A transformer cooled by a
medium other than a liquid,
usually through the circulation
of air.
Dual Wound Coils
Two part windings that can be
connected in series or parallel
to adjust the voltage or current.
Dynamic Load Regulation
The ratio of change in output
voltage to change in load
current.
Eddy Currents
Additional currents caused by a
magnetic eld.
Efficiency
A measure of energy loss in a
circuit.
Electronic Tap Changing
Regulator
An electronic switching system
used to adjust for changes
in line voltage to maintain
the output voltage within
acceptable levels.
Electrostatic Shield
A grounded conductor placed
between the primary and
secondary winding to greatly
reduce or eliminate line-toline or line-to-ground noise.
Often referred to as a “Faraday
shield”.
EMC
(Electromagnetic Compatibility)
A directive necessary to get
the CE Mark, which shows the
electrical device will not create
high levels of EMI and will not
fail due to normal levels of EMI.
EMI
See Noise/Electrical Noise.
Encapsulated
A method of sealing a
device with epoxy to resist
environmental effects.
ESR
Equivalent Series Resistance.
The amount of resistance in
series with an ideal capacitor
which exactly duplicates the
performance of a real capacitor.
Excitation Current
The steady rate current
that keeps the transformer
energized after the inrush
has dissipated, with all other
windings open- circuited. Also
called “magnetizing” or “no-load
current.”
Faraday Shield
See Electrostatic Shield.
FCAN and FCBN Taps
Acronyms for Full Capacity
Above Normal and Full
Capacity Below Normal.
Ferroresonance
A method of producing a
constant voltage by use of a
special saturated transformer.
Invented and patented by
Joseph Sola in 1938.
Ferroresonant Power Supply
A stabilized power supply
(CVDC) driven by a constant
voltage transformer.
Filter
A device that reduces
unwanted electrical noise.
FL
Full-load
Flyback Converter
A power supply switching
circuit which normally uses a
single transistor. During the rst
half of the switching period the
transistor is on and energy is
stored in a transformer primary;
during the second half period
this energy is transferred to the
transformer secondary and the
load.
Foldback Current Limiting
A power supply output
protection circuit whereby the
output current decreases with
increasing overload, reaching a
minimum at short circuit.
Force Air Cooled
A means of accelerating
heat dissipation to lower the
temperature rise of an electrical
device.
Forward Converter
A power supply switching
circuit in which energy is
transferred to the transformer
secondary when the switching
transistor is on. In this circuit
minimal energy is stored in the
transformer.
Frequency (Hertz)
Cycles per second.
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13
Power Protection and Conditioning
Full Bridge Rectifier
A power switching circuit
in which four diodes are
connected in a bridge
conguration.
Ground Loop
The condition of having two or
more ground references in a
common system.
Half Bridge Rectifier
A power switching circuit similar
to the full bridge converter
except that only two diodes are
used.
Harmonics Distortion
The distortion of the AC
waveform due to the addition
of sinewaves of different
frequencies being added to the
AC voltage.
Hi-Pot Test
High Potential Test. A test to
determine if the breakdown
voltage of a transformer or
power supply exceeds the
minimum requirement.
Holdup Time
The length of time a power
supply’s output voltage remains
within specications following
the loss of input power.
Impulse
A high amplitude, short
duration spike (milliseconds)
superimposed on the normal
voltage or current.
Input Line Filter
A low-pass or band-reject lter
at the input of a power supply
which reduces line noise fed
to the supply. This lter may
be external to the device.
Input Voltage Range
The high and low input voltage
limits within which a device
meets its specications.
Inrush Current
The peak instantaneous input
current drawn by a device at
turn-on.
Inrush Current Limiting
A circuit which limits the inrush
current during turn-on of a
device.
Inverter
A power converter that changes
DC input power into AC output
power.
Isolation Transformer
A transformer in which the input
winding and the output winding
are not electrically connected.
Isolation
The electrical separation
between input and output of a
circuit.
Isolation Voltage
The rated AC or DC voltage
which may be continuously
applied from input to output
and/or chassis of a device.
See Hi-Pot.
kVA Rating
A measurement of apparent
power. 1 kVA = 1000 VA.
KW Rating (kilowatts)
A measurement of real power
delivered to a load 1 KW =
1000 VA x Power Factor
Leakage Current
The AC or DC current owing
from input to output and/or
chassis of an isolated device at
a specied voltage.
Line Regulation
The change in output voltage
due to a variation in input
voltage.
Linear Power Supply
A power supply that uses a
control device, like a transistor,
in series (or parallel) with the
load. The control device adjusts
the effective resistance to give a
constant voltage output.
Linear Regulator
See Linear Power Supply.
Load Regulation
The change in output voltage
due to a variation in load.
Local Sensing
Using the power supply output
voltage terminals as the sense
points to provide feedback to
the voltage regulator.
Low Voltage Transients
High frequency noise
LVD
Acronym for Low Voltage
Directive. A European
Community directive which
shows the device is not a shock
or re hazard.
Maximum Continuous Operating
Voltage (MCOV)
The maximum designated
rootmean-square (rms) value
of the power frequency voltage
that may be continuously
applied to the mode of
protection of an SPD.
Modes of Protection
Electrical paths where the SPD
offers defense against transient
overvoltages. Examples include
Line to Neutral (L-N), Line to
Ground (L-G), Line to Line (L-L)
and Neutral to Ground (N-G).
MOV
Acronym for Metal-OxideVaristor. A voltage sensitive
device used to limit overvoltage
conditions on AC power and
data lines.
MTBF
Acronym for Mean Time
Between Failure. The statistical
failure rate of a device.
Noise/Electrical Noise
Also called electromagnetic
interference, or EMI. Unwanted
electrical signals that produce
undesirable effects and
otherwise disrupt the control
system circuits.
Nominal Value
The stated or objective value for
a quantity.
Normal Mode Noise
See Differential Mode Noise.
Off-Line UPS
A UPS where the inverter is
normally off until there is a
power failure. Also known as a
Standby UPS.
On-Line UPS
A UPS where the inverter is
always powering the load. AC is
converted to DC to charge the
battery then DC is converted to
AC to power the load. On-Line
UPS are often referred to as a
“Double Conversion UPS”.
Output Current Limiting
An output protection feature
which limits the output current
to a predetermined value in
order to prevent damage to
the device under overload
conditions.
Output Voltage
The nominal value of the
voltage at the output terminals
of a device.
Overload Protection
See Output Current Limiting.
14
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Power Protection and Conditioning
Overshoot
A transient change in output
voltage, in excess of specied
output accuracy limits, which
can occur when a power supply
is turned on or off, or when
there is a step change in line or
load.
OVP
Acronym for Overvoltage
Protection. A power supply
feature which shuts down the
supply, or crowbars or clamps
the output, when its voltage
exceeds a preset level.
Parallel Operation
The connection of the outputs
of two or more identical devices
to obtain a higher output power.
PARD
Acronym for Periodic and
Random Deviation. A term used
for the sum of all ripple and
noise components measured
over a specied band width and
stated in either peak-to-peak or
RMS values.
PE
Acronym for Protective
Earthing. The incoming earthing
conductor provided by the
utility.
PI Filter
A commonly used lter at the
input of a switching supply or
DC/DC converter to reduce
reected ripple current. The
lter usually consists of two
parallel capacitors separated
by a series inductance and is
generally built into the supply.
Post Regulator
A linear regulator used on the
output of a switching power
supply to improve line and load
regulation and reduce output
ripple voltage.
Power Boost™
Describes the advanced
overload capability of the SDN
and SDP power supplies to
power high inrush loads without
oversizing.
Power Factor
The ratio of true power Watts)
to apparent power (VA).
Power Fail Detection
A power supply option which
monitors the input voltage
and provides an isolated logic
output signal when there is loss
of line voltage.
Pre-regulation
The regulation at the front-end
of a power supply, generally by
a type of switching regulator,
this is followed by output
regulation, either by a linear or
switching type regulator.
PWM Inverter
Acronym for Pulse Width
Modulation. An efcient method
of creating sinewave power.
Push-Pull Converter
A power switching circuit
which uses a center-tapped
transformer and two power
switches which are driven on
and off alternately. This circuit
does not provide regulation by
itself.
Rated Output Current
The continuous load current
that a device was designed to
provide.
Rectification
The conversion of alternating
current to direct current.
Redundancy
The addition of extra devices to
provide a backup in the event
of the loss of one of those
devices.
Remote Sensing
The ability for a power supply to
sample the load voltage located
a distance away, and adjust for
the resulting voltage drop.
Return
The name for the common
terminal of the output of a
power supply; it carries the
return current for the outputs.
Reverse Voltage Protection
A feature which protects a
power supply against a reverse
voltage applied at the input or
output terminals.
Ripple
A small AC voltage on the DC
output of a power supply that
remains after ltering.
Ripple and Noise Pertibations
Small AC voltage on the output
of a DC power supply at a
specied bandwidth. This is
the result of feed through of the
rectied line frequency, internal
switching transients and other
random noise.
Sag
A temporary drop in the RMS
voltage, which may last from
one cycle to a few seconds.
Short-Circuit Protection
A feature which protects the
device from a short-circuit
so that the device will not be
damaged.
SNMP
Acronym for Simple Network
Management Protocol. A
standard for LAN management
messaging and control of
network devices and their
functions.
Soft Start
A feature which limits the
start-up switching currents of
a switching supply and causes
the output voltage to rise
gradually to its nal value.
SPD
Surge Protective Device.
Divert or clamp high amplitude
transients.
Standby UPS
See Off-Line UPS.
Static UPS
See On-Line UPS.
Step-Up/Step-Down
Transformers
A transformer that either
increases or decreases the
input voltage.
Swell
A temporary increase in the
RMS voltage, which may last
from a half cycle to a few
seconds.
Switching Frequency
The rate at which the voltage is
switched in a DC-DC converter
or switching power supply.
Switching Regulator
A high efciency circuit used to
regulate output voltages.
Switchmode Power Supplies
(SMPS)
A power supply that uses a
switching regulator.
Temperature Coefficient
The average percent change
in output voltage per degree
Centigrade change in ambient
temperature over a specied
temperature range.
Temperature Range, Operating
The ambient temperature range
within which a device may be
safely operated and meets its
specications.
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15
Power Protection and Conditioning
Temperature Range, Storage
The ambient temperature range
within which a device may be
safely stored, non-operating,
with no degradation in its
subsequent operation.
Thermal Protection
An internal safeguard circuit
that shuts down the unit in
the event of excess internal
temperatures.
THD
Acronym for Total Harmonic
Distortion. The ratio of the
harmonic content to the
fundamental frequency
expressed as a percent of the
fundamental.
Transfer Time
The amount of time a device
takes to switch from one mode
of operation to another.
Transformer
An electrical device that
changes AC voltage from one
level to another.
Transformer Turns Ratio
The ratio of primary turns to
secondary turns.
Transient
A high amplitude, short
duration (milliseconds) spike
superimposed on the normal
voltage or current. Sometimes
called a spike or a surge.
Transient Recovery Time
The time required for the
output voltage of a device to
settle within specied output
accuracy limits following a step
change in output load current
or a step change in input
voltage.
Transverse Mode Noise
See Differential Mode Noise.
TVSS
Transient Voltage Surge
Suppressor. Also known as
SPD
UL
Acronym for Underwriters
Laboratories tested.
UL Recognized
Designation given to
components that when used
properly in an end product are
deemed to be safe.
UL Listed
Designation given to products
ready for end use.
Undervoltage
See Brownout.
UPS
Acronym for Uninterruptible
Power Supply. A device which
supplies power to the critical
load when the existing AC line
voltage is not within normal
operating values, or fails
completely.
VA
Acronym for Voltamp. A
measure of power. 1000 VA =
1 kVA.
VFD
Variable Frequency Drive.
Voltage Balance
The difference in magnitude,
in percent, between the two
output voltages of a dual
output power supply where the
voltages have equal nominal
values with opposite polarities.
Warm-Up Drift
The initial change in output
voltages of a device from
turn-on until it reaches thermal
equilibrium.
Warm-Up Time
The time required, after initial
turn-on, for a device to meet its
performance specications.
16
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© January 2017
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