Buy 3 Phase Induction Motor

A 3-phase induction motor consists of a stator and a rotor. The stator carries a 3-phase stator winding while the rotor carries a short-circuited winding called rotor winding. The stator winding is supplied from a 3-phase supply. The rotor winding drives its voltage and power from the stator winding through electromagnetic induction and hence the name.

Variable frequency drives (VFDs) control the speed of AC induction motors and often save energy, especially while running applications like pumps and fans. When sized correctly, VFDs can also be used for phase conversion if you need to run a three-phase motor but are limited to single-phase supply.

For example, to maintain a set PSI or flow rate on a pumping system, a VFD can be used to automatically accelerate or decelerate the pump to meet the immediate demands of the system. Or on Hammer Mills and large cone crushers, like those found in a Metso HP4, the VFD can be used to increase torque when a load surge requires more output from the motor for a short amount of time.

For small shops or home use, keep in mind that VFDs are the number one power polluters on the planet. They pollute power quality even more when used as a phase converter. Talk to your sales engineer to see if using a line reactor is the right option for you.

Variable torque drives are for simple centrifugal equipment like fans and pumps. These drives allow the motor to apply only the torque necessary to run the application at slower speeds. Centrifugal applications rarely exceed the rated current, so variable torque drives only need a one-minute overload current capacity of 120%.

Newer inverter-rated motors use wire designed to handle the high voltages that drives can create. You also can help protect your motors with grounding rings, isolated bearings and special cooling features like a separate fan.

We carry a complete line of MDI inverter-grade motors as well as Aegis shaft grounding rings should you need to upgrade your existing motor to be better prepared to handle the stresses of running off of a VFD.

An induction motor or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.[1] An induction motor can therefore be made without electrical connections to the rotor.[a] An induction motor's rotor can be either wound type or squirrel-cage type.

Three-phase squirrel-cage induction motors are widely used as industrial drives because they are self-starting, reliable, and economical. Single-phase induction motors are used extensively for smaller loads, such as garbage disposals and stationary power tools. Although traditionally only used for one-speed service, single- and three-phase induction motors are increasingly being installed in variable-speed applications using variable-frequency drives (VFD). VFDs offer especially important energy savings opportunities for existing and prospective induction motors in applications like fans, pumps and compressors that have a variable load.

In 1824, the French physicist François Arago formulated the existence of rotating magnetic fields, termed Arago's rotations. By manually turning switches on and off, Walter Baily demonstrated this in 1879, effectively the first primitive induction motor.[2][3][4][5][6][7][8]

The first AC commutator-free polyphase induction motors were independently invented by Galileo Ferraris and Nikola Tesla, a working motor model having been demonstrated by the former in 1885 and by the latter in 1887. Tesla applied for US patents in October and November 1887 and was granted some of these patents in May 1888. In April 1888, the Royal Academy of Science of Turin published Ferraris's research on his AC polyphase motor detailing the foundations of motor operation.[5][11] In May 1888 Tesla presented the technical paper A New System for Alternating Current Motors and Transformers to the American Institute of Electrical Engineers (AIEE)[12][13][14][15][16] describing three four-stator-pole motor types: one having a four-pole rotor forming a non-self-starting reluctance motor, another with a wound rotor forming a self-starting induction motor, and the third a true synchronous motor with a separately excited DC supply to the rotor winding.

George Westinghouse, who was developing an alternating current power system at that time, licensed Tesla's patents in 1888 and purchased a US patent option on Ferraris' induction motor concept.[17] Tesla was also employed for one year as a consultant. Westinghouse employee C. F. Scott was assigned to assist Tesla and later took over development of the induction motor at Westinghouse.[12][18][19][20] Steadfast in his promotion of three-phase development, Mikhail Dolivo-Dobrovolsky invented the cage-rotor induction motor in 1889 and the three-limb transformer in 1890.[21][22] Furthermore, he claimed that Tesla's motor was not practical because of two-phase pulsations, which prompted him to persist in his three-phase work.[23] Although Westinghouse achieved its first practical induction motor in 1892 and developed a line of polyphase 60 hertz induction motors in 1893, these early Westinghouse motors were two-phase motors with wound rotors until B. G. Lamme developed a rotating bar winding rotor.[12]

The General Electric Company (GE) began developing three-phase induction motors in 1891.[12] By 1896, General Electric and Westinghouse signed a cross-licensing agreement for the bar-winding-rotor design, later called the squirrel-cage rotor.[12] Arthur E. Kennelly was the first to bring out the full significance of complex numbers (using j to represent the square root of minus one) to designate the 90º rotation operator in analysis of AC problems.[24] GE's Charles Proteus Steinmetz greatly developed application of AC complex quantities including an analysis model now commonly known as the induction motor Steinmetz equivalent circuit.[12][25][26][27]

Induction motor improvements flowing from these inventions and innovations were such that a 100-horsepower induction motor currently has the same mounting dimensions as a 7.5-horsepower motor in 1897.[12]

In both induction and synchronous motors, the AC power supplied to the motor's stator creates a magnetic field that rotates in synchronism with the AC oscillations. Whereas a synchronous motor's rotor turns at the same rate as the stator field, an induction motor's rotor rotates at a somewhat slower speed than the stator field. The induction motor stator's magnetic field is therefore changing or rotating relative to the rotor. This induces an opposing current in the rotor, in effect the motor's secondary winding.[28] The rotating magnetic flux induces currents in the rotor windings,[29] in a manner similar to currents induced in a transformer's secondary winding(s).

The induced currents in the rotor windings in turn create magnetic fields in the rotor that react against the stator field. The direction of the rotor magnetic field opposes the change in current through the rotor windings, following Lenz's Law. The cause of induced current in the rotor windings is the rotating stator magnetic field, so to oppose the change in rotor-winding currents the rotor turns in the direction of the stator magnetic field. The rotor accelerates until the magnitude of induced rotor current and torque balances the load on the rotor. Since rotation at synchronous speed does not induce rotor current, an induction motor always operates slightly slower than synchronous speed. The difference, or \"slip,\" between actual and synchronous speed varies from about 0.5% to 5.0% for standard Design B torque curve induction motors.[30] The induction motor's essential character is that torque is created solely by induction instead of the rotor being separately excited as in synchronous or DC machines or being self-magnetized as in permanent magnet motors.[28]

For rotor currents to be induced, the speed of the physical rotor must be lower than that of the stator's rotating magnetic field ( n s {\\displaystyle n_{s}} ); otherwise the magnetic field would not be moving relative to the rotor conductors and no currents would be induced. As the speed of the rotor drops below synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the windings and creating more torque. The ratio between the rotation rate of the magnetic field induced in the rotor and the rotation rate of the stator's rotating field is called \"slip\". Under load, the speed drops and the slip increases enough to create sufficient torque to turn the load. For this reason, induction motors are sometimes referred to as \"asynchronous motors\".[31]

The number of magnetic poles, p {\\displaystyle p} , is equal to the number of coil groups per phase. To determine the number of coil groups per phase in a 3-phase motor, count the number of coils, divide by the number of phases, which is 3. The coils may span several slots in the stator core, making it tedious to count them. For a 3-phase motor, if you count a total of 12 coil groups, it has 4 magnetic poles. For a 12-pole 3-phase machine, there will be 36 coils. The number of magnetic poles in the rotor is equal to the number of magnetic poles in the stator.

where n s {\\displaystyle n_{s}} is stator electrical speed, n r {\\displaystyle n_{r}} is rotor mechanical speed.[34][35] Slip, which varies from zero at synchronous speed and 1 when the rotor is stalled, determines the motor's torque. Since the short-circuited rotor windings have small resistance, even a small slip induces a large current in the rotor and produces significant torque.[36] At full rated load, slip varies from more than 5% for small or special purpose motors to less than 1% for large motors.[37] These speed variations can cause load-sharing problems when differently sized motors are mechanically connected.[37] Various methods are available to reduce slip, VFDs often offering the best solution.[37] 59ce067264

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