electric motor

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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.

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).

electric motor

[i¦lek·trik ′mōd·ər]
(electricity)
References in periodicals archive ?
Use of Innovative Technologies in the North American Small Alternating Current Motors Market to Overcome Competition from Asian Products
The US Department of Energy estimates that alternating current motors consume more than 65% of the electricity produced today.
These electronic devices, now installed in more than 200 locations here and abroad, reduce the amount of electricity required to run alternating current motors by 15 to 35 percent, substantially cutting energy costs for the user.
OTC: PREF), based in Ann Arbor, have proved capable, in more than a hundred installations here and abroad, of reducing the electricity needed to drive alternating current motors from 15 to as much as 40 percent without affecting their operation, according to Stephen Shulman, president and chief executive officer.
These energy savings are significant, says Stephen Shulman, president of Power Efficiency, because the 2 billion alternating current motors country-wide consume 60 percent of all electricity generated in the United States -- far more than lights.
The device, based partly on technology licensed from NASA, is a motor controller for alternating current motors which reduces the electricity needed to run them from 15 to as much as 40 percent.
When fitted on alternating current motors, the "Performance Controllers" save from 15 to 40 percent of the electricity formerly required for operation, plus reducing wear and extending the life of the motors, Shulman said.
When applied to alternating current motors, these devices have shown reductions in energy required for operation as high as 40 percent.
Power Efficiency Corporation (OTC:PREF) announced today that it has received and filled an order for use in the automotive industry for its proprietary "Performance Controller," which can reduce the electric energy required to run alternating current motors by 15 to 40 percent.
The company's "Performance Controllers" reduce the electric energy required by alternating current motors from 15 to 40 percent, providing substantial savings for their operators.

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