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"T" FRAME
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.
TACHOMETER
A small generator normally used as a rotational speed sensing
device. Tachometers are typically attached to the output shaft of DC or
AC inverter motors requiring close speed regulation. The tachometer feeds
its signal to a control which adjusts its output to the DC motor or AC
inverter motors accordingly (called "closed loop feedback" control).
TEMPERATURE
Has direct bearing on the life of a given motor and when considering
life expectancy, the following application considerations that affect
the motor's operating temperature, should be taken into account
1. Bearing
2. Lubricants
3. Duty Cycle
4. Radial Loading
5. Axial Loading
6. Mounting
7. Enclosure
8. Ambient Temperature
9. Ventilation
As a general rule of thumb each 10ƒC increase in total temperature
over the maximum permissible to the motor insulation system halves its
life. Bearing or gear lubricant life is halved for every 25ƒF (approx.
14ƒC) increase in temperature. Heat eventually causes deterioration of
most lubricants and seals leading to leakage and increased friction.
"T" (TEMPERATURE CODES)
See N.E.C. Temperature
Codes
TEMPERATURE RISE
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 thereby causing a rise above room (ambient) temperature.
It is important to match the proper motor and insulation system (NEMA
temp. codes) to the appropriate ambient temperature. If a motor has been
built with greater than 1.0 service factor then it can run at a temperature
some what 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. (See Insulation
Systems for NEMA standard temperature
codes.) Each temperature code has an associated temperature rise which
when added to the ambient and hot spot should not exceed the temperature
handing of the insulation system.
TEMPERATURE TESTS
Tests conducted to determine the temperature rise of certain
parts of a motor above the ambient temperature, when operating under specific
conditions.
TESTS
A variety of tests are conducted to ensure motor performance,
efficiency, and manufacturing integrity:
COMPLETE
A complete test is a test which meets the requirements of IEEE-112-1978.
It includes the tests conducted in a Routine Test as well as. full-load
heat run; no-load current and watts' determination of torques; 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.
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.
ROUTINE
A routine test is a basic test done in the factory to the requirements
of NEMA MG1, paragraph 12.51 and IEEE-112-1978 and includes the following
measurements: no load current/watts; winding resistance; and high potential
test.
WITNESS
A witness test is a test performed with a customer representative present.
THERMAL PROTECTOR (inherent)
An inherent overheating protective device which is responsive
to motor temperature and which, 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.
THERMISTOR-Thermally Sensitive Resistor
A semiconductor used to measure temperature; 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 generate a voltage as a function of temperature. Thermocouples can
be attached to a meter or alarm to detect overheating of motor windings
or bearings.
THERMOSTAT
Units applied directly to the motor's windings which senses winding
temperature and may automatically break the circuit in an overheating
situation.
TORQUE
Turning force delivered by a motor or gearmotor shaft, usually
expressed in lbs. ft derived by completing H.P. x 5250/RPM = full load
torque.
TOTALLY -ENCLOSED ENCLOSURE
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.
TOTALLY -ENCLOSED FAN-COOLED ENCLOSURE
Provides for exterior cooling by means of a fan(s) integral with
the machine, but external to the enclosed parts.
TOTALLY- ENCLOSED NON-VENTILATED ENCLOSURE:
Has no provisions for external cooling to the enclosing parts.
The motor is cooled by heat radiation from the exterior surfaces to the
surrounding atmosphere.
TOTALLY-ENCLOSED PIPE VENTILATED MACHINE
A totally-enclosed machine except for openings so arranged that
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 a part of the machine.
In latter case, these machines shall be known as separately-forced-ventilated
machines.
TOTALLY-ENCLOSED WATER AIR-COOLED MACHINE
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.
TRANSFORMER
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 wound on a common
magnetic core.
THRUST BEARINGS
Special bearings used to handle higher than normal axial forces
exerted on the shaft of the motor as is the case with some fan or pump
blade mountings.
TUBE COOLED
A motor in which heat is dissipated by air-to-air heat exchange.
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