Experiment_18_The_Wound-Rotor_Induction_Motor – Part III

Experiment_18_The_Wound-Rotor_Induction_Motor – Part III

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18 1 Experiment 18 The Wound-Rotor Induction Motor – Part III OBJECTIVE To observe the characteristics of the wound-rotor induction motor at no-load and full-load. To observe speed control using an external variable resistance. DISCUSSION The three ends of the three-phase rotor windings are brought out to three slip rings mounted on the rotor shaft. The brushes bearing on the slip rings play an important role in realizing maximum advantage from the wound-rotor motor. By connecting the brushes through rheostats, it becomes possible to develop a higher starting torque than is possible with a squirrel-cage motor. On starting, the full resistance of the rheostats is maintained in the rotor circuit, thus providing the very maximum starting torque. As the motor approaches normal operating speed, the rheostat resistance is gradually reduced until it is out of the circuit entirely at full speed. Although the starting torque of the wound-rotor motor is higher, it is not as efficient as the squirrel cage motor at full speed, because the resistance of the rotor windings is always more than that of a squirrel cage motor. A special feature of the wound-rotor motor is its variable speed capability. By varying the rheostat resistance, it is possible to vary the percentage of slip and thus, vary the motor speed. In such cases, below full speed operation means the motor is running at reduced efficiency and mechanical output power. In addition, because of a high rotor resistance, the motor is made more susceptible to variation in speed as the load changes. EQUIPMENT REQUIRED
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This note was uploaded on 02/11/2012 for the course EEE 360 taught by Professor Gorur during the Spring '08 term at ASU.

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Experiment_18_The_Wound-Rotor_Induction_Motor – Part III

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