Electric Motor Control
10th Edition
ISBN: 9781305177611
Author: Herman
Publisher: Cengage
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Question
Chapter 46, Problem 1SQ
To determine
Explain the reason why direct current (DC) controller can be called as a counter emf controller.
Expert Solution & Answer
Answer to Problem 1SQ
DC controller can be called as a counter emf controller because the counter emf of the armature is used for controlling the motor acceleration.
Explanation of Solution
In DC motor, the generated counter electromotive force is proportional to the speed of the motor for constant field. The counter emf can differ from the applied voltage only by armature drop.
DC controller can automatically adjust the starting time intervals, based upon the connected load. If heavy load is connected, it has more inertia to overcome; therefore, long time is required to generate the counter emf. When the DC motor starts, counter emf produced across the armature is very low. As the acceleration of motor increases, the counter emf increases. If the voltage value across the armature reaches a particular value, the starting resistance can be reduced at the correct time by actuating the relay. Therefore, the counter emf is mainly responsible to control the acceleration of motor.
Conclusion:
Thus, the DC controller can be called as a counter emf controller because the counter emf of the armature is used for controlling the motor acceleration.
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Chapter 46 Solutions
Electric Motor Control
Ch. 46 - Prob. 1SQCh. 46 - What physical characteristic distinguishes between...Ch. 46 - Prob. 3SQCh. 46 - What protection is available from excessive...Ch. 46 - How does a field accelerating relay prevent...Ch. 46 - Prob. 6SQCh. 46 - How may more steps of acceleration be added to a...Ch. 46 - Prob. 8SQ
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