All types of Motor & Generators - AC & DC

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All types of Motor & Generators - AC & DC

By | July 2013
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All types of Motor & Generators - AC & DC, Starters:Induction Motor (3 Phase):The production of a rotating magnetic field (RMF) is essential for the operation of alternating current (a.c.) induction motors. The speed of rotation of an RMF is known as the synchronous speed and this will be governed by the value of the supply frequency and the number of poles wound within each phase winding. Each of the phase windings are 120 electrical degrees apart. Synchronous speed can be calculated using the following equation:-

The synchronous speed is magnetic flux speed within the windings (stator). The two major components of a three phase induction motor are the (Stator) which houses the phase windings and the (Rotor) the rotating part which reacts to the RMF. Energizing the stator winding causes the following to occur:• The RMF travels at synchronous speed. • Stator flux induces an emf into the rotor bars. • Rotor current flows in the rotor bars producing an opposing magnetic flux to the stator. • Rotor flux reacts with the stator flux which in turn causes motor rotation (torque). • Torque is maintained because the rotor runs at a slower speed than the RMF. This is referred to as the slip speed usually around 4%. In other words the stator is dragging the rotor along in a rotational force. The stator core is laminated to reduce eddy current loss. The operation of a three phase motor relies on:• Electromagnetic induction • Force on a current carrying conductor when under the influence of a magnetic field. • The stator which houses three phase windings and produces the RMF. • The rotor which has conductor bars that react to the RMF. Slip: - It is the term used to describe the differential between the synchronous speed (RMF) and the actual rotor speed. The larger the slip the larger the amount of torque developed.

Slip is determined by: nslip = nsyn - nrotor (rpm) Where: nslip = Slip speed nsyn = Synchronous speed nrotor = Rotor speed. The actual rotor speed is...
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