Electric Motor Control
10th Edition
ISBN: 9781305177611
Author: Herman
Publisher: Cengage
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Question
Chapter 25, Problem 1SQ
To determine
What are the five commonly used starting methods for the motors.
Expert Solution & Answer
Explanation of Solution
Generally, the polyphase induction motor is a self-starting motor. The commonly used starting methods for a polyphase squirrel cage induction motor are as follows:
- 1. Full-voltage starting:
An automatic starting or hand-operated switch is connected to the motor directly across the line.
- 2. Primary-resistance starting:
A resistance unit is connected in series with a stator to reduce the starting current.
- 3. Autotransformer or compensator starting:
Low voltage starting is applied by performing an automatic or manual switching between the taps of an autotransformer.
- 4. Impedance starting:
A reactor is connected in series with a motor to reduce the starting voltage.
- 5. Star-delta starting:
To get the reduced starting voltage, a stator is connected in star connection for starting and delta connection for running condition.
Conclusion:
Thus, the commonly used starting methods for a polyphase squirrel cage induction motor are listed.
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with steps."
Find Laplace transform and the corresponding ROC for
x(t) = e−3sin(2t) u(t)dt
Three similar coils, connected in star, take a total
power of 1.5 kW, at a power factor of 0.2, from a
three-phase, 400 V, 50 Hz supply. Calculate: (a) the
resistance and inductance of each coil; (b) the line
currents if one of the coils is short-circuited.
(a) Three 20 µF capacitors are star-connected across
a 400 V, 50 Hz, three-phase, three-wire supply.
Calculate the current in each line. (b) If one of the
capacitors is short-circuited, calculate the line cur
rents. (c) If one of the capacitors is open-circuited,
calculate: the line currents and the p.d. across each
of the other two capacitors.
ANS:
1.525 A; 2.64 A, 2.64 A, 4.57 A; 1.32 A, 1.32 A, 0;
210 V
Chapter 25 Solutions
Electric Motor Control
Ch. 25 - Prob. 1SQCh. 25 - When can full-voltage starting be used?Ch. 25 - Name the simplest, most rugged, and most reliable...Ch. 25 - Define the term slip.Ch. 25 - When the voltage is reduced to start a motor, what...Ch. 25 - Why is it more advisable to start some machines at...Ch. 25 - Prob. 7SQCh. 25 - Prob. 8SQCh. 25 - Prob. 9SQCh. 25 - Prob. 10SQ
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