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

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References in periodicals archive ?
GE explained that a standard AC induction motor can be designed to run efficiently at high speed, but should the application demand operation at slow speeds, as is the case with appliances and HVAC equipment, energy efficiency suffers.
This ST7MC starter-kit presents and takes full advantage of the leading features of the ST7MC product family to control sensor and sensorless BLDC and induction motors from 12V to 400V, with various control topologies.
induction motor is operating under variable load or is under loaded.
manufacturer of energy-saving devices using a patented technology for alternating current induction motors, announced the installation of its energy-saving controllers at the Fashion Institute of Technology of the State University of New York (FIT/SUNY).
Power Efficiency Corporation designs and manufactures controllers that reduce the amount of energy used by alternating current induction motors.
Until quite recently, micro-controllers have been used extensively in vector control of induction motors.
The C-BCT research program is sponsored by the Army Research Laboratory and is tasked to develop, demonstrate and deploy applications of copper-based alloys to make significantly lighter, more efficient AC induction motors for use in defense and industrial systems.
GE is one of the pioneers that use both high power induction motors and PWM for marine use.
Induction motors are designed to operate at the knee point of the magnetization characteristic to make full use of the magnetic material.
By optimizing motor flux levels over the entire operating speed range, WEG variable frequency drives help WEG induction motors run cooler - and longer
3] Casadei, D, Profumo, F, Serra, G and Tani, A;" FOC DTC: Tox Viable Schemes for induction Motors Ttorque Control", IEEE Trans.