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The simple split-phase (induction-start-induction-run) motor has a small-gage start winding with fewer turns than the main winding to create more resistance and put the start winding’s field at a different electrical angle than that of the main - causing the motor to rotate until it reaches 75% of rated speed. They’re also classified by how they are started, as these motors alone develop no starting torque, but require external means for initial actuation. Single-phase AC motors power myriad low-horsepower commercial and industrial applications where three-phase power is impractical they’re not efficient, but can last a lifetime. This causes the rotor to follow the field generated by the stator, to rotate the output shaft.ĪC induction motor capabilities for force, torque, and speed: AC induction motors are either single-phase or poly-phase. Current is induced in the rotorâs conducting bars, and associated magnetic fields interact with those of the stator. This allows the induction of rotor current to flow, and production of torque to drive attached load while overcoming internal losses. In practice, an AC induction motor is an asynchronous motor (in which the rotor lags field speed) so its rotor must spin more slowly than the field, or slip. Synchronous speed is the fastest theoretical speed a motor can possibly spin - when the rotor spins at the same speed as the motor’s internal rotating magnetic field. As mentioned, the rotor turns when the moving magnetic field induces current in the shorted conductors, and the rate at which it rotates is the motor’s synchronous speed - determined by power-supply frequency and the number of stator poles. The rotor also has laminations radial slots around the laminations contain the bars. The AC inductor rotor assembly resembles a cage consisting of aluminum or copper conducting bars connected by short-circuiting end rings - hence the nickname squirrel cage for induction motors. The windings that accept the external power supply are run through the slots. This exploded view of a Leeson Electric AC induction motor shows the stator windings, rotor (in red), support bearings, cooling fan (in white) and other elements.Īn induction motor’s stator consists of a stack of thin, highly permeable steel laminations with slots the laminations are either secured in a steel or cast-iron frame that provides a mechanical support. These AC induction motors are quite common - the workhorse of industry. The rotor current’s effect on the air gap flux causes torque.ĪC induction motors are built by manufacturers according to established National Electrical Manufacturers Association (NEMA) standards in myriad fractional and integral horsepower ratings and associated frame sizes.
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Illustrated here are magnet-induced flux and current-induced flux, upon which all electric motor operation is based.Īs the rotor’s induced current and magnetism cause it to follow the field generated by the stator, rotary motion is output.īecause an AC induction motor increases the flux enclosed by its stationary coils, it is a transformer with a rotating secondary (rotor). Conducting bars in the rotor interact with the stator’s magnetic fields current is induced in those bars, which in turn generate magnetic fields that are attracted to those of the stator. The stationary outer stator is connected to an external electrical power source this is fed to the rotor’s poles in a rotating progression that causes revolutions of the magnetic field within the motor. In all its iterations, the induction motor induces magnetism that is leveraged to output rotary motion. 1st of 3 technologies: AC induction motors here we outline the capabilities of driven AC induction motors, permanent-magnet motors, and servomotors - the three major technologies with partially overlapping functionalities for larger, higher-end applications requiring precisely metered torque, speed, or positioning. This file type includes high resolution graphics and schematics when applicable.Įngineers today are tasked with applying myriad motor technologies because most rotary motion is ultimately powered by electric motors.