electric motor

Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to electric motor: Electric generator

motor, electric,

machine that converts electrical energy into mechanical energy. When an electric current is passed through a wire loop that is in a magnetic field, the loop will rotate and the rotating motion is transmitted to a shaft, providing useful mechanical work. The traditional electric motor consists of a conducting loop that is mounted on a rotatable shaft. Current fed in by carbon blocks, called brushes, enters the loop through two slip rings. The magnetic field around the loop, supplied by an iron core field magnet, causes the loop to turn when current is flowing through it. In an alternating current (AC) motor, the current flowing in the loop is synchronized to reverse direction at the moment when the plane of the loop is perpendicular to the magnetic field and there is no magnetic force exerted on the loop. Because the momentum of the loop carries it around until the current is again supplied, continuous motion results. In alternating current induction motors the current passing through the loop does not come from an external source but is induced as the loop passes through the magnetic field. In a direct current (DC) motor, a device known as a split ring commutator switches the direction of the current each half rotation to maintain the same direction of motion of the shaft. In any motor the stationary parts constitute the stator, and the assembly carrying the loops is called the rotor, or armature. As it is easy to control the speed of direct-current motors by varying the field or armature voltage, these are used where speed control is necessary. The speed of AC induction motors is set roughly by the motor construction and the frequency of the current; a mechanical transmission must therefore be used to change speed. In addition, each different design fits only one application. However, AC induction motors are cheaper and simpler than DC motors. To obtain greater flexibility, the rotor circuit can be connected to various external control circuits. Most home appliances with small motors have a universal motor that runs on either DC or AC. Where the expense is warranted, the speed of AC motors is controlled by employing special equipment that varies the power-line frequency, which in the United States is 60 hertz (Hz), or 60 cycles per second. Brushless DC motors are constructed in a reverse fashion from the traditional form. The rotor contains a permanent magnet and the stator has the conducting coil of wire. By the elimination of brushes, these motors offer reduced maintainance, no spark hazard, and better speed control. They are widely used in computer disk drives, tape recorders, CD drives, and other electronic devices. Synchronous motors turn at a speed exactly proportional to the frequency. The very largest motors are synchronous motors with DC passing through the rotor.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Electric Motor


a machine that converts electrical energy into mechanical energy. The electric motor is a basic type of motor used in industry, transportation, homes, and elsewhere. Electric motors can be classified by the kind of current used for their drive. The DC motors have the advantage of an economical and smooth regulation of their rotational speed (rpm). The AC motors include synchronous and asynchronous electric motors. In a synchronous motor the rotational speed (rpm) is rigidly dependent on the frequency of the feeder current. In an asynchronous motor the rotational speed decreases as the load increases. A third type of alternating current motor is the commutator motor, which permits a smooth regulation of rotational speed within wide limits.

The asynchronous motor is the most widely used; it is simple to manufacture and is reliable in operation (particularly the squirrel-cage motors). Their main disadvantages are a considerable consumption of reactive power and the lack of a smooth (gradual) speed regulation. In many high-power electric drives, synchronous electric motors are being used. DC motors are utilized if speed regulation is of paramount importance; the more expensive and less reliable AC commutator motors are very occasionally used in these cases. The power rating of electric motors ranges from a fraction of a watt to dozens of megawatts. Electric motors have various forms of frame construction: open frame, in which the rotating and current-carrying parts are protected against accidental touching and foreign objects; protected frame (including drop-proof and spray-proof designs); closed frame (dust-proof and moisture-proof); hermetic frame; and explosion-proof frame (in case of an explosion of gases inside the motor, any flame is confined to the interior of the motor housing).

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

electric motor

[i¦lek·trik ′mōd·ər]
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The global electric motor market size was valued at $96,967.9 million in 2017, and is projected to reach $136,496.1 million by 2025, growing at a CAGR of 4.5% from 2018 to 2025.
The source explained that factories would have an opportunity to improve the efficiency of the used engines and that the energy consumption of electric motors would be reviewed through a consultative team in cooperation with Lawrence Berkeley National Laboratory.
Rupert Jeffries of Collingwood Rigby, asset managers for the Estate, said: "TEC Electric Motors is a big local success story, having reported year-on-year growth since its inception in 2006."
The general approach to overcome these issues is to substantially increase the dielectric strength value of the magnet wire used in the electric motor windings.
Pakdemirli also noted that at the first stage, tractors with electric motors will be used in Turkey, and after that, their export to neighboring countries is expected.
Electric motors company YASA revealed on Monday the a long-term joint innovation agreement with an undisclosed automotive OEM.
Police and hospital sources said that a 17-year-old girl identified as Farzana Bibi was washing clothes after switching on electric motor pump at her house in Makhdoom Pur area of Uch Sharif.
In order to overcome these problems, an electric driven AMT was proposed in [12] for a parallel plug-in hybrid electric vehicle (PHEV) such that the engine and traction electric motor were positioned on the same shaft with an automatic clutch and an electric motor was integrated to the AMT for shifting purpose.
The petrol engine drives the front wheels while the electric motor drives the back.
In 2014, AC motors accounted for the majority of revenue share of 80.0% in the overall electric motors market and commonly used in most of the electric motor driven systems.
Electric motor refurbishment and repair services market is also witnessing growth as electric motors are being extensively employed for various applications in diverse sectors such as oil & gas, petrochemical & refining, commercial and power plants.