Electrical Machines Questions and Answers – Constructional Features of Rotating Electrical Machines-2

«
»

This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Constructional Features of Rotating Electrical Machines-2”.

1. Which type of slots are used in the construction of large size and small size induction motors respectively?
a) open slots and semiclosed slots
b) semiclosed slots and open slots
c) open slots and open slots
d) semiclosed slots and semiclosed slots
View Answer

Answer: a
Explanation: Large size motors use open slots, so that already prepared and properly insulated coils can be inserted in open slots. Small size induction motors use semiclosed slots, so as to reduce the effective gap length between stator and rotor.
advertisement

2. In which of the following applications, wound rotor type of induction motor is used?
a) where the driven load requires speed control
b) where high starting torque is required
c) when external resistance is to be inserted
d) any of the mentioned
View Answer

Answer: d
Explanation: Only in wound rotor type of induction motor, external resistance can be inserted in series with the rotor winding, for speed and starting torque control.

3. For an induction motor, Which of the following statements are correct?

(i) squirrel cage type is simpler and more economical in construction
(ii) wound rotor type requires less maintenance
(iii) squirrel cage type is more rugged and requires less maintenance
(iv) no external resistance can be inserted in the rotor circuit of squirrel cage induction motor
(v) no external resistance can be inserted in the rotor circuit of a wound rotor induction motor 
Note: Join free Sanfoundry classes at Telegram or Youtube
advertisement
advertisement

a) (ii), (v), (iii)
b) (ii), (iii), (v)
c) (i), (iii), (iv)
d) (i), (ii), (iv)
View Answer

Answer: c
Explanation: The squirrel cage type is simpler and more economical in construction, requires less maintenance than wound rotor type, since the former doesn’t require slip rings and carbon brushes.

4. What are the advantages of providing the field winding on rotor and armature winding on the stator?
a) more economical
b) more efficient
c) efficient cooling
d) all of the mentioned
View Answer

Answer: d
Explanation: If the armature winding is on the stator, only two slip rings are required which implies less losses, more efficiency and more economy. Also, stationary armature winding can be cooled more efficiently.
Take Electrical Machines Practice Tests - Chapterwise!
Start the Test Now: Chapter 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
advertisement

5. The stator frame and end covers in synchronous and induction machines are designed to ___________
a) carry the magnetic flux
b) to serve as a mechanical support
c) to provide cooling or to carry induced EMF
d) any of the mentioned
View Answer

Answer: b
Explanation: The stator frame and end covers serve merely as a mechanical support to the stator core, and are not designed to carry the magnetic flux.

6. What is the advantage of connecting two coils in parallel?
a) reduce the amount of copper required
b) increase the current per parallel path to double the value
c) increase the voltage capacity
d) all of the mentioned
View Answer

Answer: b
Explanation: The parallel connection of two coils will increase the current per parallel path to double the value.
advertisement

7. In a synchronous machine, salient pole construction has been found to suit best for ___________
a) low speed prime movers
b) high speed prime movers
c) medium speed prime movers
d) any of the mentioned
View Answer

Answer: a
Explanation: For accommodating large number of poles, the rotor diameter must be comparatively increased, and from mechanical considerations, salient pole construction has been found to suit best for low speed prime movers.

8. What is the equation for frequency of generated EMF?
a) f = PN/120 Hz
b) f = 120/PN Hz
c) f = P/120 Hz
d) f = N/120 Hz
View Answer

Answer: a
Explanation: f = PN/120 Hz in India and many other countries, alternators feeding the power system generates at a frequency of 50 Hz.
advertisement

9. How many poles should the alternators driven by the oil engines and hydraulic turbine prime movers must have, for better operation?
a) fewer number of poles
b) larger number of poles
c) medium number of poles
d) any of the mentioned
View Answer

Answer: b
Explanation: Oil engines and hydraulic turbines operate best at relatively low speeds, therefore, the alternators driven by these prime movers must have relatively large number of poles, as f ∝ 1/N.

10. Large synchronous machines are constructed with armature winding on the stator because stationary armature winding. Which of the following statements are correct?

(i) can be insulated satisfactorily for higher voltages
(ii) can be cooled more efficiently
(iii) would lead to reduced slip ring losses
(iv) would have no slot harmonics
(v) would have reduced armature reactance

a) (i), (ii), (iii), (iv)
b) (i), (ii), (iii), (v)
c) (i), (ii), (iii), (iv), (v)
d) (i), (ii), (iv), (v)
View Answer

Answer: b
Explanation: If the armature winding is on the stator, only two slip rings are required, which implies less losses, more efficiency and more economy. Also, stationary armature windings can be cooled more efficiently.

Sanfoundry Global Education & Learning Series – Electrical Machines.

To practice all areas of Electrical Machines, 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.