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 inverter motors requiring close speed regulation. The tachometer feeds its signal to a control that adjusts its output to the DC motor or AC inverter motors accordingly (called “closed-loop feedback” control).
Has a 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
3. Duty Cycle
4. Radial Loading
5. Axial Loading
8. Ambient Temperature
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.
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 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 a 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.
Tests conducted to determine the temperature rise of certain parts of a motor above the ambient temperature when operating under specific conditions.
A variety of tests are conducted to ensure motor performance, efficiency, and manufacturing integrity:
COMPLETE A complete test is a test that 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.
A test performed to verify the motor sound level, conducted in accordance with IEEE-85. The tests are performed under no-load conditions in the sound room.
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.
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 that 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.
Units applied directly to the motor’s windings which senses winding temperature and may automatically break the circuit in an overheating situation.
The 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 the 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
It 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 the 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.
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.
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.
A motor in which heat is dissipated by air-to-air heat exchange.