Electric Motor Control
10th Edition
ISBN: 9781133702818
Author: Herman
Publisher: CENGAGE L
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Question
Chapter 51, Problem 1SQ
To determine
Explain why the three phase braking reduces motor heating when compared with single phase breaking.
Expert Solution & Answer
Explanation of Solution
Discussion:
A DC dynamic brake is a single phase braking used in various induction motors. It requires more current to achieve the braking torque. Therefore, the heat dissipation is more in single phase braking. In a three phase braking, the motor requires less current for the same braking torque, so that the motor heating reduces. Due to the additional winding in a three phase braking motors, the ampere turns are gained.
Conclusion:
Thus, the reason for the reduction of motor heat in three phase braking is explained.
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1- A squirrel cage induction motor is not selected when
(A) initial cost is the main consideration (B) maintenance cost is to be kept low
(C) higher starting torque is the main consideration (D) all above considerations are involved
2- The torque of an induction motor is ..............
(A) directly proportional to slip (B) inversely proportional to slip...
(C) proportional to the square of the slip (D) none of the above
3- Insertion of resistance in the stator of an induction motor.
(A) increases the load torque (B) decreases the starting torque
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tool to slip
10 or of the above
4- Increase in the length of air-gap in the induction motor results in the increasing of its
(A) air-gap flux (B) magnetizing current
(C) speed (D) power factor
5- In cumulatively cascade method for speed controlling, if PA is the number of poles of main motor and
PB is the number of poles of auxiliary motor. Then the speed of the set…
Chapter 51 Solutions
Electric Motor Control
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