Terminology for Electric Machinery

Accelerating Time: The time required for a motor to reach full speed from standstill (zero speed) position.

AC Contactor: An alternating current (ac) contactor is designed for the specific purpose of establishing or interrupting an AC power circuit.

Accelerating Torque: The torque developed from standstill (zero speed) to full speed at nameplate voltage. Sometimes the term "Net Accelerating Torque" is used to mean the excess motor torque capability over the torque for the attached load.

Adjustable Speed: The concept of varying the speed of applications.

Adjustable Speed Drive: A unit comprised of a motor, drive controller and operator’s controls (either manual or automatic). Is also used to refer to the inverter which is a device used to convert standard sine wave power form into a simulated form for varying speed ranges on the driven equipment.

Adjustable Speed Motor: A motor that can be varied in speed over a range, but a motor that is essentially constant speed at any one set speed within that range.

Aerator Motors: A specific duty motor used pump air into a sludge type environment. The large air/liquid interface area provides excellent gas transfer and enables the sludge to be broken down and recycled into the environment.

Air Filter: Filter made from polyurethane (vertical), zinc or stainless steel (horizontal) medium to trap air-borne particles which may clog the operations of a weather protected II (WPII) motor.

Air Gap: The space between the rotating and stationary member in an electric motor.

Air Pressure Differential Switch: For use with air filters on weather protected II (WPII) enclosed motors. This switch will send alarm when a concentration of particles causes a pressure drop in the air flowing through the filter and into the motor. This feature allows the air filter to be used until its maximum capacity is reached.

Allguard Protection: Similar to USEM’s Corro-duty treatment on motors, allguard protects the gearbox from corrosive atmospheres.

Alternating Current: The commonly available electric power supplied by an AC generator and distributed in one, two, and three phase form.

Altitude: The height of the motor in reference to sea level. Standard altitude is 3300 feet, or 1000 meters. Sometimes written as 3300 FASL (feet above sea level).

Ambient Temperature: Ambient Temperature is the temperature of the medium, such as air, water or earth, into which the heat of the equipment is dissipated.

For self-ventilated equipment, the ambient temperature is the average temperature of the air in the immediate neighborhood of the equipment.

For air or gas cooled equipment with forced ventilation, or secondary water cooling, the ambient temperature is taken as that of the in coming air or cooling gas.

For self-ventilated enclosed (including oil immersed) equipment, considered as a complete unit, the ambient temperature is the average temperature of the air outside of the enclosure in the immediate neighborhood of the equipment.

Ampere: The rate of flow of charge in a conductor of one coulomb per second.

Ampere Turn: The magnetomotive force produced by a current of one ampere in a coil of one turn.

Angular Contact Bearing: A specialized thrust bearing used on high-thrust vertical motors. The special angular design reduces friction and wear while supporting the rotating parts.

Angular Velocity: Angular displacement per unit time, measured in degrees/time or radians/time.

Anti-Friction Bearings: A bearing using balls or rollers as the supporting device between hardened races.

Antihunt: Antihunt is the means of reducing or suppressing the oscillation of a system.

Antiplug Protection: The effect of a control function, or a device that operates to prevent application of counter torque, by the motor until the motor speed has been reduced to an acceptable value.

Arctic Duty: Specific duty motors designed to withstand severely cold temperatures and environments. These motors will withstand ambient temperatures to -70° F.

Armature: The laminated iron core with wire wound around it in which electromotive force is produced by magnetic induction in a motor or generator: usually the rotor of a DC motor or the stator of an AC motor.

Armature Control: Abbreviated term for armature voltage control of a DC motor, which describes the usual method of changing the speed of a DC motor by controlling the magnitude of applied armature voltage.

Armature Current: Armature current is the DC current required by a DC motor to product torque and drive a load. The maximum safe, continuous current is stamped on the motor nameplate. This can only be exceeded for initial acceleration, and for short periods of time. Armature current is proportional to the amount of torque being produced, therefore, it rises and falls as the torque demand rises and falls.

Armature Reaction: The current that flows in the armature winding of a D.C. motor tends to produce magnetic flux in addition to that produced by the field current. This effect, which reduces the torque capacity, is called armature reaction and can effect the commutation and the magnitude of the motor’s generated voltage.

Armature Voltage Feedback: Armature voltage can be used as the speed feedback signal to an electronic speed regulator. This voltage is almost directly proportional to motor speed, assuming a constant motor field and ignoring IR drop. Armature voltage feedback is used where the expense of a tachometer generator for speed feedback is not justified and a regulation accuracy of 2-5% is adequate.

Asynchronous Motor: Also called non-synchronous motor, is an AC motor which does not run at synchronous speed. The ordinary induction motor is an asynchronous motor - single or polyphase.

Automotive Duty: Specific duty motors designed to meet the needs of the auto industry which include all cast iron construction, special ambient and temperature rise, and special drains and breathers. (See reference manual for actual automotive duty motor specification.)

Auxiliary Contacts: Auxiliary contacts of a switching device are contacts in addition to the main circuit contacts and operate with the movement of the latter.

Axial Centering Force: The magnetic force on the rotor resulting from its axial displacement from magnetic center.

Axis: A principal direction along which movement of the tool or workpiece occurs. The term "axis" also refers to one of the reference lines of a coordinate system.

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