Explore topic-wise InterviewSolutions in .

This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.

1.

Consider a dc machine having its armature wound in lap fashion having 12 coils and each resistance 0.1 ohms. If it is measured resistance between two adjacent commutator segments, the result will be _________(a) 0.092 ohms(b) 1.1 ohms(c) 1.8 ohms(d) 0.92 ohmsThis question was addressed to me during an online interview.My query is from Armature Windings in section Armature Windings of Electrical Machines

Answer»

Right choice is (a) 0.092 ohms

Explanation: There are 11 resistance which are in PARALLEL to ONE resistance. So taking the EQUIVALENT resistance of 11 series connected resistance and the one SINGLE resistance of the commutator segment.

R(eq) = 0.1||1.1 = 0.0917.
Discussion
2.

A 6-pole lap wound DC generator has a developed power of P watts and brush voltage of E volts. Three adjacent brushes of the machine had been found worn out and got open circuited. If the machine is operated with the remaining brushes, voltage and power that could be obtained from the machine are _________(a) E, P(b) E, 2P/3(c) E/P, 2P/3(d) E, P/3I had been asked this question in an international level competition.Enquiry is from Armature Windings topic in portion Armature Windings of Electrical Machines

Answer» CORRECT answer is (a) E, P

Explanation: Taking Kirchoff’s law into study here, the voltage ACROSS the winding will remain same.

But the current will REDUCE in the overall winding as the resistance has INCREASED, so POWER will decrease by 1/3.
Discussion
3.

While doing regular checks on the dc machine with the lap connected winding, it is reported to have ammeter fluctuations, this can be due to _________(a) different air gaps under poles(b) variable reluctances in the core(c) irregular design deformations(d) all of the mentionedI have been asked this question in an online quiz.The question is from Armature Windings in portion Armature Windings of Electrical Machines

Answer»

The CORRECT answer is (d) all of the mentioned

The explanation: In a LAP WINDING configuration, if the machine as air gap variations due to the DESIGN aspects, it will give circulating current in the WINDINGS.
Discussion
4.

For a given dc machine it is advised to use the dummy windings for a stable operation. But if it has be replaced as it unused component in the machine, then we must _________(a) S/P/2 should not be an integer(b) S/P/2 should be integer(c) S/P should be integer(d) S/P should not be an integerThe question was posed to me during an interview for a job.Origin of the question is Armature Windings in chapter Armature Windings of Electrical Machines

Answer»

The CORRECT CHOICE is (a) S/P/2 should not be an integer

Best explanation: If SLOTS per pole pair is not integer than all the winding will be COMPLETED without adding any dummy coil.
Discussion
5.

For an electrical machine with C number of coils and P poles, the distance between the coils connected by an equalizer ring is?(a) C/P(b) C/2(c) 2C/P(d) C/2PThis question was addressed to me in quiz.My question comes from Armature Windings topic in division Armature Windings of Electrical Machines

Answer»

Correct answer is (c) 2C/P

To ELABORATE: Backward pitch for an equalizer RING = number of coils/pole PAIRS = C/P/2 = 2C/P.
Discussion
6.

With a P-pole DC machine with armature current Ia, the current per brush arm for a lap connected windings is?(a) Ia/P(b) Ia/2P(c) 2Ia/P(d) Ia/4PI have been asked this question during an interview.My enquiry is from Armature Windings in chapter Armature Windings of Electrical Machines

Answer»
Discussion
7.

In AC machines we should prefer double layer winding over single layer windings because _________(a) it requires identical coils(b) it is economical to use(c) it offers lower leakage reactance(d) all of the mentionedI had been asked this question in an international level competition.The question is from Armature Windings in portion Armature Windings of Electrical Machines

Answer»

The correct option is (a) it REQUIRES identical coils

For explanation: DOUBLE layer winding enables more usage of the SPACE and lesser air gaps so the leakage flux ALSO reduces and efficiency improves.
Discussion
8.

We can employ dummy coils in a DC machine to _________(a) compensate reactance voltage(b) reduce armature reaction(c) provide mechanical balance to the armature(d) improve the waveforms generated inside the commutatorI have been asked this question in a national level competition.My doubt stems from Armature Windings in portion Armature Windings of Electrical Machines

Answer»

Correct option is (a) COMPENSATE reactance voltage

Explanation: Dummy coils are placed inside so that to provide mechanical support to dc machine and they do not TAKE PART in the emf DEVELOPMENT.
Discussion
9.

Commutator segments in a DC shunt machine is equal to the number of _________(a) coil sides(b) turns(c) coils(d) slotsThis question was posed to me during an interview.I need to ask this question from Armature Windings topic in chapter Armature Windings of Electrical Machines

Answer» RIGHT option is (a) coil sides

The BEST EXPLANATION: Commutator segments are PLACED as per the coil sides in the MACHINE.
Discussion
10.

A 200V dc machine has 4 poles and 40 coils, having simplex lap winding. The number of commutator segments which required in the given machine will be?(a) 40(b) 20(c) 80(d) 26This question was addressed to me in semester exam.This intriguing question comes from Armature Windings topic in section Armature Windings of Electrical Machines

Answer»

The CORRECT OPTION is (a) 40

The explanation is: It is a simplex winding and so one SEGMENT of COMMUTATOR will be NEEDED for each coil.
Discussion
11.

The commutator pitch for a simplex lap winding is equal to _________(a) 1 and -1(b) 1(c) -1(d) 2 to -2This question was posed to me during a job interview.I need to ask this question from Armature Windings topic in portion Armature Windings of Electrical Machines

Answer» CORRECT ANSWER is (a) 1 and -1

The EXPLANATION: It is EITHER 1 or -1.
Discussion
12.

The simplex lap winding has the range of winding pitch of _________(a) (-2,2)(b) (-1,1)(c) more than 2(d) less than 1This question was posed to me by my school teacher while I was bunking the class.My query is from Armature Windings topic in division Armature Windings of Electrical Machines

Answer»

The correct OPTION is (a) (-2,2)

Best explanation: For a progressive winding, FORWARD pitch – backward pitch = winding pitch

yb = COIL sides/P +or-1 (m)

Here m is such that to make yb an odd integer.
Discussion
13.

Which of the following machines can be used to place open slot winding?(a) ac machine(b) ac commutator machine, ac machine(c) dc machines(d) all of the mentionedThe question was posed to me in an online interview.I'm obligated to ask this question of Armature Windings in section Armature Windings of Electrical Machines

Answer» RIGHT ANSWER is (a) AC machine

To elaborate: Only ac MACHINES are used for open TYPE of winding inside the machine.
Discussion
14.

Concentrated winding differ from distributed winding with the concern of _________(a) identical magnetic axis(b) two magnetic axis(c) no magnetic axis(d) physical spacingThis question was posed to me in quiz.I'm obligated to ask this question of Armature Windings topic in division Armature Windings of Electrical Machines

Answer»

The correct answer is (a) IDENTICAL magnetic AXIS

To explain I WOULD say: Concentrated winding have all turns on ONE magnetic axis.
Discussion
15.

We can place closed windings in _________(a) ac commutator machine(b) stepper motor(c) ac machine(d) dc machineThis question was posed to me in unit test.Asked question is from Armature Windings topic in division Armature Windings of Electrical Machines

Answer»

The correct ANSWER is (a) AC commutator machine

To EXPLAIN: Closed windings are placed only in commutator as it does not need any RECONNECTIONS LATER.
Discussion
16.

DC machines have ________ windings and synchronous machines use ______ windings.(a) closed,open(b) open, closed(c) open, open(d) closed, closedThe question was asked in semester exam.I'd like to ask this question from Armature Windings topic in division Armature Windings of Electrical Machines

Answer»

Right ANSWER is (a) closed,open

To explain I WOULD say: All the commutator machines use closed winding as it has nothing to DEAL with REACTANCE. In ac machines, the winding can be converted

to star to delta and vice versa.
Discussion