| Alternator |
A
synchronous machine used to convert mechanical power into
alternating current electric power. |
| 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. |
| Base
Line |
A
vibration reading taken when a machine is in good operating
condition that is used as a reference for monitoring and analysis. |
| 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. |
| 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. |
| Constant Horsepower
Motor |
A term used to describe a
multispeed 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. |
| Constant
Torque Motor |
A
multispeed motor for which the rated horsepower varies in direct
ratio to the synchronous speeds. The output torque is essentially
the same at all speeds. |
DELTA
Connection |
A three-phase winding
connection in which the phases are connected in series to form a
closed circuit. |
| Design |
NEMA
design letters A, B, C, D, and E define certain starting and running
characteristics of polyphase 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. |
| 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 can not, reach an equilibrium temperature
have a short-time or intermittent-duty rating. Short-time ratings
are usually one hour or less for motors. |
| 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. |
| Foot-Pound |
The amount of work, in the
English system, required to raise a one pound weight a distance of
one foot. |
| Frequency |
The
number of cycles in a time period (usually one second). Alternating
current frequency is expressed in cycles per second, termed Hertz
(Hz). |
| Full-Load Current |
The current required for
any electrical machine to produce its rated output or perform its
rated function. |
| Full-Load
Speed |
The
speed at which any rotating machine produces its rated output. |
| Full-Load Torque |
The torque required to
produce rated power at full-load speed. |
| Harmonic |
A
multiple of the fundamental electrical frequency. Harmonics are
present whenever the electrical power waveforms (voltage and
current) are not pure sine waves. |
| Hertz (Hz) |
The preferred terminology
for cycles per second (frequency). |
| 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. |
| IEC |
International
Electrotechnical Commission. |
| IEEE |
Institute
of Electrical and Electronics Engineers. |
| 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. |
| Insulation
Class |
A letter
or number that designates the temperature rating of an insulation
material or system with respect to thermal endurance. |
| Kilowatt |
A unit of electrical
power. Also, the output rating of motors manufactured and used off
the North American continent. |
| Locked-Rotor
Current |
Steady-state
current taken from the line with the rotor of a motor at standstill
and at rated voltage and frequency. |
| 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. |
| Megohmmeter |
An
instrument for measuring insulation resistance. |
| Motor |
A rotating machine that
converts electrical power (either alternating current or direct
current) into mechanical power. |
| NEC |
National
Electrical Code. |
| NEMA |
National Electrical
Manufacturers Association. |
| 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. |
| Part-Winding Starting |
A part-winding start
polyphase 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). |
| Poles |
The
magnetic poles set up inside an electric machine by the placement
and connection of the windings. |
| 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. |
| Power
Factor |
The
ratio of watts to volt-amperes of an ac electric circuit. |
| Rated Temperature Rise |
The permissible rise in
temperature above ambient for an electric machine operating under
load. |
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. |
| Rotor |
The rotating element of
any motor or generator. |
| 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. |
| 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. |
| Starting
Torque |
The
torque produced by a motor at rest when power is applied. For an ac
machine, this is the locked-rotor torque. |
| Stator |
The stationary part of a
rotating electric machine. Commonly used to describe the stationary
part of an ac machine that contains the power windings. |
| Synchronous
Speed |
| The
speed of the rotating machine element of an ac motor that
matches the speed of the rotating magnetic field created by
the armature winding. |
|
Synchronous
speed =
|
(Frequency x
120)
(Number of Poles) |
|
| 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. |
| 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). |
| Trending |
Analysis of the change in
measured data over at least three data measurement intervals. |
| Variable-Torque
Motor |
A
multispeed motor in which the rated horsepower varies as the square
of the synchronous speeds. |
| 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. |
| WYE-DELTA
Starting |
Wye-delta
is a connection which is used to reduce the inrush current and
torque of a polyphase 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. |
1724 Tomich Court