Electric Motors Store - Glossary

E - Terms

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EDDY CURRENT
Localized currents induced in an iron core by alternating magnetic flux. These currents translate into losses (heat) and their minimization is an important factor in lamination design.

EFFICIENCY
The efficiency of a motor is the ratio of mechanical output to electrical input. It represents the effectiveness with which the motor converts electrical energy into mechanical energy. NEMA has set up codes which correlate to specific nominal efficiencies. A decrease in losses (the elements keeping the motor from being 100% efficient of 10% constitutes an upward improvement of the motor of one code on the NEMA table. Each nominal efficiency has a corresponding minimum efficiency number.

ELECTRICAL DEGREE
A unit of measurement of time as applied to alternating current. One complete cycle =360 electrical degrees. One cycle in a rotating electric machine is accomplished when the rotating field moves from one pole to the next pole of the same polarity. There are 360 electrical degrees in this time period. Therefore, in a two pole machine there are 360 degrees in one revolution, and the electrical and mechanical degrees are equal. In a machine with more than two poles, the number of electrical degrees per revolution is obtained by multiplying the number of pairs of poles by 360.

ELECTRICAL TIME CONSTANT (for DC Motors)
The ratio of electrical inductance to armature resistance. Electrical time constant in seconds defined as Electrical


where La is the armature circuit inductance in henries and la is the rated full load armature current.

ELECTRICAL UNBALANCE
In a 3 phase supply, where the voltages of the three different phases are not exactly the same. Measured in % of unbalance.

ELECTROMOTIVE FORCE (EMF)
A synonym for voltage, usually restricted to generated voltage.

ENCAPSULATED WINDING
A motor which has its winding structure completely coated with an insulating resin (such as epoxy). This construction type is designed for exposure to more severe atmospheric conditions than the normal varnished winding.

ENCLOSURES
The housing, frame, of the motor of which there are two broad classifications; open and totally closed. There are specific types of each:

MOTOR ENCLOSURES
Reliance Electric offers the industry's widest selection of motor/generator enclosures to meet specific operating needs.

ODG - Open Drip-Proof, Guarded
ODG-FV - Open Drip-Proof, Force Ventilated
ODG-SV - Open Drip-Proof, Separately Ventilated
ODP - Open Drip-Proof
HP - Vertical P-Base, Normal Thrust
LP - Vertical P-base, Medium Thrust, Extended Thrust
Prot. - Protected
TEAO - Totally-Enclosed, Air-Over
TEBC - Totally-Enclosed, Blower-Cooled
TECACA - Totally-Enclosed, Closed Circuit,, Air to Air
TEDC-A/A - Totally-Enclosed, Dual Cooled, Air to Air
TEDC-A/W - Totally-Enclosed, Dual Cooled, Air to Water
TEFC - Totally-Enclosed, Fan-Cooled
TENV - Totally-Enclosed Non-Ventilated
TETC - Totally-Enclosed, Tube Cooled
TEWAC - Totally-Enclosed, Water/Air Cooled
TEXP - Totally-Enclosed, Explosion-Proof
IP-22 - Open Drip-Proof
IP-44 - Totally-Enclosed
IP-54 - Splash Proof
IP-55 - Washdown
WPI - Weather Protected, Type I
WPII - Weather Protected Type II
XE - Premium Efficient
XL - Extra Life
XP - Explosion-Proof
XT - Extra Tough

 

ENDSHIELD
The part of the motor housing which supports the bearing and acts as a protective guard to the electrical and rotating parts inside the motor. This part is frequently called the "end bracket" or "end bell."

EXPLOSION-PROOF ENCLOSURE
A totally enclosed enclosure which is constructed to withstand an explosion of a specified gas, vapor or dust which may occur within it. Should such an explosion occur, the enclosure will prevent the ignition or explosion of the gas or vapor which may surround the motor enclosure. These motors are listed with Underwriter's Laboratories.


EXPLOSION-PROOF-HAZARDOUS LOCATIONS
DIVISION I
- Location in which ignitable concentrations of flammable or combustible material exist and come in contact with the motor.
DIVISION 11 - Locations in which ignitable concentrations of flammable or combustible material exist but are contained within closed systems or containers and normally would not come in contact with the motor.
EXPLOSION-PROOF-U.L. CLASSIFICATIONS CLASS I -Those in which flammable gasses or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures.
Group C - Atmospheres containing ethyl or ether vapors.
Group D - Atmospheres containing gasoline, hexane, benzene, butane, propane, alcohols, acetone, benzol, lacquer solvent vapors, natural gas, etc.
Class 11-Those which are hazardous because of the presence of combustible dust.
Group E - Atmospheres containing metal dust, including aluminum, magnesium, or their commercial alloys.
Group F - Atmospheres containing carbon black, charcoal, coal or coke dust.
Group G - Atmospheres containing flour, starch, grain or combustible plastics or chemical dusts.

 
EXTERNALLY VENTILATED
A motor using an external cooling system. This is required in applications where the motor's own fan will not provide sufficient cooling; this is true for certain duty cycle applications, slow speed motors, also in environments with extreme dirt. Often a duct with an external blower is used to bring clean air into the motor's air-intake.

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