Experiment_16_The_Wound-Rotor_Induction_Motor – Part I

Experiment_16_The_Wound-Rotor_Induction_Motor – Part I

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16 1 Experiment 16 The Wound-Rotor Induction Motor – Part I OBJECTIVE To examine the construction of the three-phase wound-rotor induction motor. To understand exciting current, synchronous velocity and slip in a three-phase induction motor. To observe the effect of the rotating field and rotor velocity upon the voltage induced in the rotor. DISCUSSION Electric power companies normally generate and transmit three-phase power. Single-phase power for the individual home is obtained from one phase of the three-phase power lines. Three- phase (poly-phase) motors are commonly used in industry and electric power companies normally supply three-phase power to industrial users. The creation of a rotating stator field using three-phase power is similar to the principle of the split-phase or two-phase (capacitor-run) system. In the three-phase system, a rotating magnetic field is generated in three phases instead of two. When the stator of a three-phase motor is connected to a three-phase power source, currents flow in the three stator windings and a revolving magnetic field is established. These three exciting currents supply the reactive power to establish the rotating magnetic field. They also supply the power consumed by the copper and iron losses in the motor. The velocity of the rotating magnetic field is entirely determined by the frequency of the three- phase power source, and is known as the synchronous velocity. The frequency of electric power systems is accurately maintained by the electric power companies, therefore, the synchronous velocity of the stator field (in r/min) remains constant. (It is, in fact, used to operate electric docks).
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16 2 The wound-rotor consists of a rotor core with the three windings in place of the conducting bars of the squirrel-cage rotor. In this case, currents are induced in the windings just as they would be in shorted turns. However, the advantage of using windings is that the wires can be brought out through slip rings so that resistance, and, therefore, the current through the windings, can be controlled.
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Experiment_16_The_Wound-Rotor_Induction_Motor – Part I

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