Electrical Machines Questions and Answers – Analysis of the Equivalent Circuit

«
»

This set of Electrical Machines Questions and Answers for Experienced people focuses on “Analysis of the Equivalent Circuit”.

1. Below is the torque slip characteristic of the induction machine. What can be inferred from it?
R22 gt R21 can be inferred from the torque slip characteristic of the induction machine
a) R22 > R21
b) R22 < R21
c) R22 = R21
d) R22 = -R21
View Answer

Answer: a
Explanation: As rotor resistance increases, the starting torque will increase but not the maximum torque. But the slip at which the maximum torque occurs will change.
advertisement

2. Choose the most appropriate from the following characteristics of 3 phase induction motor torque-slip characteristics.
a) The characteristics of 3 phase induction motor torque-slip characteristics - option a
b) The characteristics of 3 phase induction motor torque-slip characteristics - option b
c) The characteristics of 3 phase induction motor torque-slip characteristics - option c
d) The characteristics of 3 phase induction motor torque-slip characteristics - option d
View Answer

Answer: a
Explanation: As rotor resistance increases, the starting torque will increase but not the maximum torque. But the slip at which the maximum torque occurs will change.

3. If the reactance of the 3-phase slip ring induction motor is increased then the torque-slip characteristic varies as?
a) Reactance of 3-phase slip ring induction motor is increased for varies - option a
b) Reactance of 3-phase slip ring induction motor is increased for varies - option b
c) Reactance of 3-phase slip ring induction motor is increased for varies - option c
d) Reactance of 3-phase slip ring induction motor is increased for varies - option d
View Answer

Answer: a
Explanation: Torque is inversely proportional to reactance
Note: Join free Sanfoundry classes at Telegram or Youtube
advertisement
advertisement

4. The reactance vs slip is given by?
a) The reactance vs slip graph - option a
b) The reactance vs slip graph - option b
c) The reactance vs slip graph - option c
d) The reactance vs slip graph - option d
View Answer

Answer: a
Explanation: Slip is inversely proportional to the slip.

5. Induction generator is equivalent to _________
a) underexcited alternator
b) dc generator
c) over excited alternator
d) leading over excited alternator
View Answer

Answer: a
Explanation: It is similar to underexcited alternator.
Take Electrical Machines Practice Tests - Chapterwise!
Start the Test Now: Chapter 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
advertisement

6. When an induction generator is connected to an infinite bus, it _________
a) requires no capacitor bank
b) requires star connected capacitor bank
c) requires delta connected capacitor bank
d) requires any capacitor bank
View Answer

Answer: a
Explanation: There is no requirement of the capacitor bank when induction generator is connected to infinite bus.

7. Torque produced by induction generator is negative.
a) True
b) False
View Answer

Answer: a
Explanation: Because the developed torque is produced opposite to the rotating field.
advertisement

8. Slip greater than unity is obtained practically by _________
a) plugging
b) changing phase sequence
c) changing stator leads
d) any of the mentioned
View Answer

Answer: d
Explanation: The direction of the rotating field can be reversed by any one of the methods.

9. Changing the rotor resistance will also affect _________
a) starting torque, speed, current
b) maximum torque, speed, current
c) maximum torque, speed, current, starting torque
d) speed and current
View Answer

Answer: a
Explanation: Rotor resistance does not alter the maximum torque of the induction machine.
advertisement

10. At starting, developed mechanical power is _____ and developed torque is ______
a) zero, not zero
b) zero,zero
c) not zero, zero
d) not zero, maximum
View Answer

Answer: a
Explanation: At start, torque is not zero.
P α (1-s)/s; so it is zero at s = 1.

11. Mechanical power developed in the braking region of the induction motor is _________
a) negative
b) positive
c) zero
d) any of the mentioned
View Answer

Answer: a
Explanation: slip is more than one, so Pm will be negative.

12. Developed torque during plugging is _________
a) negative
b) positive
c) zero
d) any of the mentioned
View Answer

Answer: b
Explanation: Torque will not be negative in braking mode in the induction motor.

13. In the 3-phase induction motor developed torque during plugging is ______ mechanical power developed in the braking region of the induction motor is ______
a) positive, negative
b) negative, positive
c) positive, positive
d) negative, negative
View Answer

Answer: a
Explanation: Tem is positive while Pm will be negative in braking or plugging operation.

14. The power slip characteristic is given as?
a) The power slip characteristic graph - option a
b) The power slip characteristic graph - option b
c) The power slip characteristic graph - option c
d) The power slip characteristic graph - option d
View Answer

Answer: a
Explanation: Mechanical power developed is negative in braking and generating mode and it is zero at starting.

Sanfoundry Global Education & Learning Series – Electrical Machines.

To practice all areas of Electrical Machines for Experienced people, here is complete set of 1000+ Multiple Choice Questions and Answers.

advertisement
advertisement
Subscribe to our Newsletters (Subject-wise). Participate in the Sanfoundry Certification contest to get free Certificate of Merit. Join our social networks below and stay updated with latest contests, videos, internships and jobs!

Youtube | Telegram | LinkedIn | Instagram | Facebook | Twitter | Pinterest
Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

Subscribe to his free Masterclasses at Youtube & technical discussions at Telegram SanfoundryClasses.