Current NEMA designation identifying AC induction motor frames.
(NEMA has dimension tables which offer standard frame measurements.)
Replaced the previous standard “U” frame in 1965.
A small generator normally used as a rotational speed-sensing
device. Tachometers are typically attached
to the output shaft of DC or AC variable-speed motors requiring close speed
regulation. The tachometer feeds its
signal to a control which adjusts its output to the DC or AC motor accordingly
(called “closed loop feedback” control).
Has direct effect on motor life when considering life expectancy. The following application considerations that affect a motor’s operating temperature should be taken into account:
1. Bearings
2. Lubricants
3. Duty Cycle
4. Radial Loading
5. Axial Loading
6. Mounting
7. Enclosure
8. Ambient Temperature
9.
Ventilation
As a general rule, each 10oC increase in total temperature
over the maximum permissible to the motor’s insulation system, reduces its life
by half. Bearing or gear lubricant life
is reduced by half for every 25oF (approximately 14oC)
increase in temperature. Heat eventually
causes deterioration of most lubricants and seals leading to leakage and increased
friction.
Some of the electrical energy losses inherent in motors are converted to heat causing some of the motor parts to heat up when the motor is running. The heated parts are at a higher temperature than the air surrounding them, which causes a rise above room (ambient) temperature.
It is important to match the proper motor and insulation system
(NEMA temp. codes) to the expected ambient temperature. If a motor has been built with greater than
1.0 service factor, then it can operate at a temperature somewhat higher than
the motor’s rated operating temperature. In
all cases, the actual insulation thermal capability usually is higher than the
motor’s operating temperature to allow for any excessive heat areas. This is called hot spot allowance. Each temperature code has an associated temperature
rise which when added to the ambient and hot spot should not exceed the temperature
handling of the insulation system.
Tests conducted to determine the temperature rise of certain
parts of a motor above the ambient temperature, when operating under specific
conditions.
ROUTINE
A routine test is a basic test done in the factory to the requirements
of NEMA MG1, paragraph 12.51 ad IEEE-112-1978. It includes the following measurements: no
load current/watts; winding resistance; and high potential test.
COMPLETE
A complete test is a test which meets the requirements of IEEE-112-1978.
It includes the test conducted in a Routine Test as well as a full-load
heat run; no-load current and watts determination of torque; efficiencies at
125, 100, 75, 50 and 25 percent of full load; power factor at 125, 100, 75,
50 and 25 percent of full load.
WITNESS
A witness test is a test performed with a customer representative
present.
NOISE
A test performed to verify the motor sound level, conducted
in accordance with IEEE-85. The tests
are performed under no-load conditions in sound room.
An inherent overheating protective device which is responsive
to motor temperature and when properly applied to a motor, protects the motor
against dangerous overheating due to overload or failure to start.
This protection is available with either manual or automatic reset.
A semiconductor used to measure temperature that can be attached
to an alarm or meter to detect motor overheating.
THERMOCOUPLE – THERMAL DETECTION DEVICE
A temperature-detecting device made of two dissimilar metals,
which generates a voltage as a function of temperature. Thermocouples can be attached to a meter or
alarm to detect overheating of motor windings or bearings.
Units applied directly to the motor’s windings which senses
winding temperature and may automatically break the circuit in an overheating
situation.
Turning force delivered by a motor or gearmotor shaft, usually expressed in
Lbs. Ft =
HP x 5250 = full load torque ¸ RPM
A motor enclosure, which prevents free exchange of air between
the inside and the outside of the enclosure but is not airtight. Different methods of cooling can be used with
this enclosure.
TOTALLY – ENCLOSED AIR – TO – AIR COOLED MACHINE
A totally enclosed machine cooled by circulating internal air
through a heat exchanger which in turn, is cooled by circulating external air.
Provided with an air-to-air heat exchanger for cooling ventilating air
and fan or fans integral with rotor shaft or separate, for circulating external
air.
Provides for exterior cooling by means of a fan(s) integral
with the machine, but external to the enclosed parts.
TOTALLY – ENCLOSED PIPE VENTILATED MACHINE
A totally-enclosed machine except for openings arranged so
inlet and outlet ducts or pipes may be connected to them for the admission and
discharge of ventilating air. Air may
be circulated by means integral with the machine or by means external to and
not part of the machine. In latter case,
these machines shall be known as separately-forced-ventilated machines.
A totally-enclosed machine cooled by circulating air which
in turn, is cooled by circulating water. Provided
with water-cooled heat exchanger for cooling ventilating air and fan or fans,
integral with rotor shaft or separate, for circulating ventilating air.
A device which converts electrical power (alternating current)
to electrical power of a different voltage. In this device, both primary and secondary windings are usually
stationary and are would on a common magnetic core.
Special bearings used to handle higher than normal axial forces
exerted on the shaft of the motors, as is the case with some fan or pump blade
mountings.
A motor in which heat is dissipated by air-to-air heat exchange.