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AC-Alternating Current Electrical current that
continually reverses direction, with this change in direction being
expressed in Hertz, or cycles per second.
Ampere
Quantitative unit of measurement of
electrical current. Abbreviated as Amp or A.
Capacitor
An electrical component which
stores electrical charges. It consists of two metallic plates
separated by a dielectric (non-conducting) material. When used in
conjunction with other components it can provide a high-frequency
filtering capability.
Clamping Level
This generally is used to describe
the voltage level which causes the surge diversion device to start
to divert surge energy. A related, but more important parameter is
the Suppressed Voltage.
Response Time
The time it takes a surge
protection device to switch from its "off" condition to an "on",
diverting mode. This occurs when a incoming surge voltage exceeds
the clamping threshold level of the MOV or other suppression
component. Organizations such as IEEE, NEMA and Underwriters
laboratories consider response time to be a non-issue since MOV’s,
Avalanche diodes etc (and the surge protectors that use them) have
response times that are 100 to 1000 times faster than any transient
that they are likely to encounter.
Combination Pulse
A high energy test pulse specified
by ANSI C62.41-1991. Also called a "unipolar pulse".
Common
Mode Voltage
A voltage, that appears on the
phase and neutral wires of the power system when compared with the
system ground wire.
Current
Current, expressed in units of
amperes, or simply amps, is the flow of electrons through a
conductor. AC, or alternating current, is a current in which the
flow of electrons reverses periodically. In the United States the
current reversal occurs 60 times a second.
EMI - Electro-Magnetic Interference
Electrically induced noise or
transients.
Energy
Maximum allowable energy (in
joules) for a single impulse on a 10/1000 µs current waveform.
Indicative of the maximum amount of energy that the suppressor can
dissipate. This energy is dependent upon three (3) variables:
Voltage, Current, and Time. Any variation of the three will effect
this figure.
Filter
Consists of a combination of
components that allows only certain frequencies, or a band of
frequencies, to pass.
Frequency
The frequency of alternating
voltage is the number of times per second that it changes polarity
from positive to negative. In the United States, the power line
frequency is 60 Hertz, 60 cycles per second.
Ground
For safety reasons, electrical
systems in the USA have a wire connected to earth ground at the
service entrance. This "ground" wire is run along with the two
current carrying wires.
Headroom
Headroom is the voltage difference
between the peak of the 50/60 Hz power line sine wave voltage and
the ‘Threshold voltage" of the MOV (or other) suppression elements.
A minimum spacing of 15% above the sine wave peak is considered
essential.
Hertz
The unit of frequency, one cycle
per second of alternating current.
Impedance
Similar to electrical resistance,
since it is a measure of the opposition to the flow of electrical
current. Impedance is meaningful only for a changing current and
changes value as the frequency of the applied waveform changes.
Inductance
The property of an electrical
component , which opposes the flow of electric current. An inductor
has the property of impedance, the opposition to the flow of
electric current.
Joule
A joule Is a measure of the energy
contained in an impulse or conversely it is a measure of the
absorption capability of a surge protection device.1 joule = 1 watt
x 1 second.
Let-Through Voltage
The residual transient voltage that
would appear across equipment after an upstream surge protection
device has operated. It is important to remember that the
"let-through" voltage is the sum of the voltage drop across the
surge protector itself plus the voltage drops that appear across the
wiring that connects the protector to the power lines. The protector
clamping voltage is only one part of the let-through voltage and
frequently is of secondary importance to the wiring drop.
Maximum Operating Voltage:
Maximum allowable
continuous sinusoidal voltage (RMS) at 50-60hz. If suppressor is
exposed to a continuous voltage higher than RMS voltage stated in
specification, the suppressor may suffer damage.
Measured Limiting
Voltage:
The maximum magnitude of voltage
that is measured across the terminals of the SPD during the
application of impulses of specified wave shape and amplitude.
MOV-Metal Oxide Varistor
In many respects a nearly ideal
suppression component. In standby mode, the MOV presents a very high
resistance in shunt with the power line – drawing negligible
current. When an incoming transient exceeds a critical voltage
threshold, the MOV switches rapidly to a near "short-circuit"
diverting mode -handling many thousands of transient amperes. When
the transient surge expires, the MOV components reset instantly to
the reset mode-ready to respond to future transients.
Modes of
Protection
Refers to the presence of MOV (or
other) components connected between phases to neutral, phases to
ground, neutral to ground and between phases.
Neutral
One of the wires used in the USA to
distribute power within a building. The neutral wire is generally
bonded to earth ground at a building service entrance, but unlike
the ground wire, the neutral wire also carries load current.
Noise
A signal frequency(s) that may be
riding on top of the power line sine wave. A number of systems use
the power lines to carry signals and data to other locations.
Attempts to filter out the "so called noise" may disrupt the current
or future operation of these systems. It is wiser to provide L/C
filtering immediately in front of sensitive equipment, if it is ever
needed. It seldom is!
Normal
Mode Voltage
Voltage appearing between the phase
wires and neutral of the power system wiring.
Peak
Current –
I peak
A common measure, used by marketing
people, to express the relative peak current handling capability
(8/20us)of a surge suppression device. Frequently, it merely
represents the peak current rating of an MOV multiplied by the
number of MOV’s in parallel. The "true" peak current rating of a
protector requires a careful assessment of the fuse characteristics,
the number of parallel protection circuits, are all of them
monitored etc. Bellcore specifications to protect their Central
Offices, a highly computerized facility, have found and specified
surge current values of 20kA, (8/20 us) waveform, to be
satisfactory.
Phase Angle
The point on the sine wave at which
a transient occurs. IEEE states that transients can occur at any
phase angle. It is important to be able to see suppression device
response to transients at varying phase angles.
Power
Power, in watts, is the product of
voltage (in volts) and current (in amps). Energy in joules is equal
to power (in watts) multiplied by time (in seconds).
Resistance
A property of electrical conductors
or electrical insulators which characterizes their ability to
conduct or resist the flow of electricity.
Ringwave
A low-energy test waveform
specified by ANSI C-62.41-1991.
SPD
Surge Protection Device. Also
referred to as TVSS (Transient Voltage Surge Suppressor).
Suppressed Voltage Rating SVR
Suppressed Voltage Rating is a
rating based on the measured limiting voltage determined during the
transient-surge suppression test. UL 1449 2nd edition
designates the rating of a surge suppressor range from 330 volts up
to 6 kV. SVR ratings are not in themselves indicative of superior
performance, since installation and cabling play a critical role in
overall performance.
Series Type Surge Protector
A form of surge protector which
handles the continuous AC power line current but opposes surge
current flow toward the load. Series type surge protectors must be
rated to handle the continuous 50/60 Hertz current, hence they are
seldom employed at building entry or mid-building locations. See
Shunt Type Surge Protectors.
Service Life
The number of surges of given
magnitude that can be suppressed by the suppressor, a measure of
reliability.
Shunt Mode
Shunt type surge protector which
divert large surge current directly to ground, are not constrained
by the continuous power line currents and thus are employed
effectively on power systems with capabilities exceeding 5000 Amps
(rms).
Sine Wave
The waveform that appears on the AC
power lines. The 50/60 Hertz sine wave is a periodic voltage
waveform that oscillates above and below a zero axis. When displayed
on an oscilloscope it appears as an undulating wave with voltage
appearing on the "y" axis and time on the "x" axis.
Single Phase
The portion of a power source that
represents only a single phase of the three phases that are often
available.
Spike
See surge
Surge
A brief transient wave of voltage,
current or power in an electrical circuit, lasting for less than 1%
of the power wave cycle duration.
Swell
A momentary voltage increase of the
power line voltage, lasting up to several seconds. A swell is not
considered to be a transient over voltage, but the TVSS device must
operate at a level in excess of the peak voltage of the swell
voltage. Otherwise, the surge protector will be attempting to clip
the power line 50/60 Hz waveform and will sustain major damage. This
necessary spacing is called headroom.
TVSS
Transient Voltage Surge Suppressor.
Also called Surge protection Device (SPD).
Transient
An abnormal over voltage of
microsecond duration. Also called a surge or spike.
Voltage Drop
The change in potential between two
points in a circuit caused by a current flow through components
within a circuit.
Voltage Reference
A voltage point from which a
measurement is taken.
Voltage Threshold
The voltage level at which the
connected circuit changes its response.
Watts
The unit of measure of actual
power. Watts are the product of volts times current.
Waveform
The graphic depiction of an
electrical voltage, current or power, typically versus time.
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