Alternator |
A synchronous machine used to convert mechanical power
into alternating current electric power.
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Ambient Temperature |
The temperature of the surrounding cooling medium.
Commonly known as room temperature when the air is the
cooling medium in contact with the equipment.
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Base Line |
A vibration reading taken when a machine is in good
operating condition that is used as a reference for
monitoring and analysis.
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Breakdown Torque |
The maximum torque that an AC motor will develop with
rated voltage applied at rated frequency without an
abrupt drop in speed. Also termed pull-out torque or
maximum torque.
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Code Letter |
A letter which appears on the nameplates of AC motors
to show their locked-rotor kilovolt-amperes per
horsepower at rated voltage and frequency.
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Constant Horsepower Motor |
A term used to describe a multi-speed motor in which
the rated horsepower is the same for all operating
speeds. When applied to a solid state drive unit, it
refers to the ability to deliver constant horsepower
over a predetermined speed range.
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Constant Torque Motor |
A multi-speed motor for which the rated horsepower
varies in direct ratio to the synchronous
speeds. The output torque is essentially the same at
all speeds.
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Delta Connection |
A three-phase winding connection in which the phases are connected in series to
form a closed circuit.
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Design |
NEMA design letters A, B and C define certain starting
and running characteristics of three phase squirrel
cage induction motors. These characteristics include
locked-rotor torque, locked-rotor current, pull-up
torque, breakdown torque, slip at rated load, and the
ability to withstand full-voltage starting.
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Duty |
A continuous or short-time rating of a machine.
Continuous-duty machines reach an equilibrium
temperature within the temperature limits of the
insulation system. Machines which do not, or cannot,
reach an equilibrium temperature have a short-time or
intermittent-duty rating. Short-time ratings are
usually one hour or less for motors.
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Efficiency |
The ratio between useful work performed and the energy
expended in producing it. It is the ratio of output
power divided by the input power.
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Foot-Pound |
The amount of work, in the English system, required to
raise a one pound weight a distance of one foot.
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Frequency |
The number of cycles in a time period (usually one
second). Alternating current frequency is expressed in
cycles per second, termed Hertz (Hz).
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Full-Load Current |
The current required for any electrical machine to
produce its rated output or perform its rated
function.
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Full-Load Speed |
The speed at which any rotating machine produces
its rated output.
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Full-Load Torque |
The torque required to produce rated power at
full-load speed.
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Harmonic |
A multiple of the fundamental electrical frequency.
Harmonics are present whenever the
electrical power waveforms (voltage and current) are
not pure sine waves.
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Hertz (HZ) |
The preferred terminology for cycles per second
(frequency).
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Horsepower |
A unit for measuring the power of motors or the
rate of doing work. One horsepower equals
33,000 foot-pounds of work per minute (550 ft-lbs per
second) or 746 watts.
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IEC
|
International Electrotechnical Commission.
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IEEE |
Institute of Electrical and Electronics Engineers.
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Insulation |
Non-conducting materials separating the
current-carrying parts of an electric machine from
each other or from adjacent conducting material at a
different potential.
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Insulation Class |
A letter or number that designates the temperature
rating of an insulation material or system with
respect to thermal endurance.
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Kilowatt |
A unit of electrical power. Also, the output rating
of motors manufactured and used off the North American
continent.
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Locked-Rotor Current |
Steady-state current taken from the line with the
rotor of a motor at standstill and at rated voltage
and frequency.
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Locked-Rotor Torque |
The minimum torque that a motor will develop at
standstill for all angular positions of the rotor,
with rated voltage applied at rated frequency.
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Megohmmeter |
An instrument for measuring insulation resistance.
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Motor
|
A rotating machine that converts electrical power
(either alternating current or direct current) into
mechanical power.
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NEC |
National Electrical Code.
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NEMA
|
National Electrical Manufacturers Association.
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Newton-Meter
|
Unit of torque, in the metric system, that is a
force of one Newton, applied at a radius of one meter
and in a direction perpendicular to the radius arm.
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Part-Winding
Starting |
A part-winding start three-phase motor is one
arranged for starting by first energizing part of its
primary winding and, subsequently, energizing the
remainder of the primary winding. The leads are
normally numbered 1,2,3 (starting) and 7,8,9
(remaining).
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Poles
|
The magnetic poles set up inside an electric
machine by the placement and connection of the
windings.
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Pound-Foot |
Unit of torque, in the English system, that is a
force of one pound, applied at a radius of one foot,
and in a direction perpendicular to the radius arm.
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Power Factor
|
The ratio of watts to volt-amperes of an AC
electric circuit.
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Rated
Temperature
Rise |
The permissible rise in temperature above ambient
for an electric machine operating under load.
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Resistance
Temperature
Detector (RTD)
|
A device used for temperature sensing consisting of
a wire coil or deposited film of pure metal for which
the change in resistance is a known function of
temperature. The most common type is nickel, with
other types being copper, platinum, and nickel-iron.
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Rotor
|
The rotating element of any motor or generator.
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Service Factor
|
A multiplier which, when applied to rated power,
indicates a permissible power loading that may
be carried under the conditions specified for the
service factor.
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Slip |
The difference between synchronous and operating
speeds, compared to synchronous speed, expressed as a
percentage. Also the difference between synchronous
and operating speeds, expressed in rpm.
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Starting Torque
|
The torque produced by a motor at rest when power
is applied. For an AC machine, this is the
locked-rotor torque.
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Stator
|
The stationary part of a rotating electric machine.
Commonly used to describe the stationary part of an AC
machine that contains the primary windings.
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Synchronous
Speed
|
The speed of the rotating magnetic field created by
the primary winding of a rotating electric machine.
When the speed of the rotating element matches the
speed of the rotating magnetic field, it is said to be
rotating at synchronous speed.
Synchronous speed = Frequency x 120 / Number of poles
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Thermistor |
A resistive device used for temperature sensing
that is composed of metal oxides formed into a bead
and encapsulated in epoxy or glass. A typical
thermistor has a positive temperature coefficient;
that is, resistance increases dramatically and
non-linearly with temperature. Though less common,
there are negative temperature coefficient thermistors.
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Torque |
The rotating force produced by a motor. The units
of torque may be expressed as pound-foot, pound-inch
(English system), or Newton-meter (metric system).
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Trending |
Analysis of the change in measured data over at
least three data measurement intervals.
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Variable
Torque Motor |
A multi-speed motor in which the rated horsepower
varies as the square of the synchronous speeds.
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Wye Connection |
A three-phase winding connection formed by joining
one end of each phase to make a "Y" point. The other
ends of each phase are connected to the line. Also
termed a star connection.
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Wye-Delta Starting |
Wye-delta is a connection which is used to reduce
the inrush current and torque of a three-phase motor.
A wye (star) start, delta run motor is one arranged
for starting by connecting to the line with the
winding initially connected wye (star). The winding is
then reconnected to run in delta after a predetermined
time. The lead numbers for a single run voltage are
normally 1 ,2,3,4,5 and 6.
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