Industrial Motor Control
7th Edition
ISBN: 9781133691808
Author: Stephen Herman
Publisher: Cengage Learning
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Question
Chapter 33, Problem 1RQ
To determine
The reason why the contacts often connected in series when controlling small DC motors.
Expert Solution & Answer
Explanation of Solution
To break the motor circuit or to stop the motor the arc formation may occur.
In that case only load contact is required to break the circuit and to stop the motor but in that case current does not fall to zero as like the alternating current. This shows that the arc interruption in case of the DC motor is difficult.
In case the direct current do not fall the zero periodically so the severity of the arc and the risk to the damage is high.
To aid the arc interruption the load contacts in the small DC motor is connected in the series connection. Also, it increases the total air gap between the contacts and in arc quenching.
Thus, the contacts are in series in controlling small DC motor to aid the arc interruption.
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Chapter 33 Solutions
Industrial Motor Control
Ch. 33 - Prob. 1RQCh. 33 - Why is direct current more difficult to interrupt...Ch. 33 - Why are clapper-type contactors generally used to...Ch. 33 - Prob. 4RQCh. 33 - How is the inrush current to large DC motors often...Ch. 33 - Prob. 6RQCh. 33 - How is the FCR connected in relationship to the...Ch. 33 - Prob. 8RQCh. 33 - Prob. 9RQ
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