In TEFC motors, interior heat losses are dissipated indirectly through enclosure fins, mostly by forced air convection. An induction motor can therefore be made without electrical connections to the rotor. Single-phase induction motors are used extensively for smaller loads, such as household appliances like fans. By manually turning switches on and off, Walter Baily demonstrated this in 1879, effectively the first single phase induction motor winding design pdf induction motor.
1885 and by the latter in 1887. October and November 1887 and was granted some of these patents in May 1888. Ferraris’s research on his AC polyphase motor detailing the foundations of motor operation. DC supply to rotor winding. Tesla’s patents in 1888 and purchased a US patent option on Ferraris’ induction motor concept.
Tesla was also employed for one year as a consultant. Tesla and later took over development of the induction motor at Westinghouse. 1889 and the three-limb transformer in 1890. 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. By 1896, General Electric and Westinghouse signed a cross-licensing agreement for the bar-winding-rotor design, later called the squirrel-cage rotor. 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 induction motor’s rotor, in effect the motor’s secondary winding, when the latter is short-circuited or closed through an external impedance. The induced currents in the rotor windings in turn create magnetic fields in the rotor that react against the stator field. 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 will start to rotate in the direction of the rotating stator magnetic field. The rotor accelerates until the magnitude of induced rotor current and torque balances the applied mechanical load on the rotation of the rotor. Since rotation at synchronous speed would result in no induced rotor current, an induction motor always operates slightly slower than synchronous speed.