29 + Interview Questions in Armature Windings in Dc Machines Page 1 InterviewSolution

1.	Wave winding machines are used in ______ currents applications.(a) High(b) Moderate(c) Low(d) Can be used anywhereThis question was addressed to me in an online interview.Asked question is from Wave Winding in portion Armature Windings of DC Machines
Answer» Correct choice is (c) Low Explanation: Lap winding machine has the advantage of large number of parallel paths and lower CONDUCTOR current and is THEREFORE USED in low voltage and HIGH current applications. WAVE winding has fixed number of parallel paths so, wave wounded machine is used in low currents application.

Discussion

2.	What is the relation between conductor current and armature current in wave winding?(a) Ic = Ia(b) Ic = 2Ia(c) Ic = 4Ia(d) Ic = Ia/2This question was addressed to me by my school teacher while I was bunking the class.This is a very interesting question from Wave Winding in chapter Armature Windings of DC Machines
Answer» The CORRECT option is (d) IC = Ia/2 The BEST explanation: the number of parallel paths in the in a wave winding is equal to 2. So, armature current will GET divided equally into total number of conductors/paths. CONDUCTOR current in a wave wounded machine is half of the Ia.

Discussion

3.	What is the spacing between the brushes for a wave winding when a machine is 6-pole DC armature with 16 slots having 2-coil sides per slot and single-turn coils.(a) 4 segments(b) 8 segments(c) 16 segments(d) 12 segmentsI have been asked this question in an online quiz.I'm obligated to ask this question of Wave Winding topic in section Armature Windings of DC Machines
Answer» Right answer is (b) 8 SEGMENTS The BEST explanation: Only 2 brushes are required in this case as the number of POLES in WAVE winding is equal to 2. So, spacing between the brushes is equal to total number of segments i.e. total slots divided by 2. Spacing between brushes = C/A = 16/2 = 8 segments.

Discussion

4.	Number of parallel paths in wave winding are ______(a) Equal to P(b) Equal to P/2(c) 2(d) Depends on other parametersThis question was posed to me by my school teacher while I was bunking the class.Query is from Wave Winding in division Armature Windings of DC Machines
Answer» Right choice is (C) 2 Easy EXPLANATION: In wave winding all coils are divided into 2 groups- all coils carrying clockwise current are series connected and so are all coils with counter-clockwise current- and these 2 groups are in parallel because the winding is closed. THUS, a wave winding has 2 parallel paths irrespective of number of poles.

Discussion

5.	What is the relation between number of parallel paths(A) and number of poles(P)?(a) A = P(b) A < P(c) A > P(d) No relation existsThe question was posed to me in an online interview.Asked question is from Lap Winding topic in division Armature Windings of DC Machines
Answer» The correct OPTION is (a) A = P To explain: Complex winding can be divided into different parallel PATHS lying under different pole PAIRS. It is, THEREFORE, concluded that the NUMBER if parallel paths is equal to the number of poles. In wave winding number of parallel paths is equal to 2.

Discussion

6.	What is the symmetry requirement of lap winding?(a) 2C/P= 0(b) 2C/P= integer(c) 2C/P= non-integer(d) Can’t express mathematicallyI got this question in my homework.I would like to ask this question from Lap Winding in division Armature Windings of DC Machines
Answer» RIGHT answer is (b) 2C/P= integer The best explanation: To avoid no-load CIRCULATING CURRENTS and certain consequential commutation problems, all the parallel paths must be identical so as to have the same number of coil-sides. Symmetry THUS requires ratio of 2C/P is equal to the integer. Also, US/P equal to integer REPRESENTS the same.

Discussion

7.	What is the value of Yf for a lap winding with a 4-pole, 12-slot armature with two coil sides/slot? (Assume single-turns coils – progressive winding)(a) 3(b) 5(c) 7(d) 9I have been asked this question during an online interview.My question is taken from Lap Winding topic in portion Armature Windings of DC Machines
Answer» The correct choice is (b) 5 Explanation: Coil span is defined as a ratio of NUMBER of slots in the armature winding which are also equal to the number of commutator segments to the number of poles. Here, Slots in the armature winding= 12, Number of poles= 4. YCS= 12/4= 3. Yb = 2YCS +1= 7 Yf =Yb – 2= 7-2= 5.

Discussion

8.	What is the value of Yb for a lap winding with a 4-pole, 12-slot armature with two coil sides/slot. Assume single-turns coils.(a) 3(b) 5(c) 7(d) 9I had been asked this question at a job interview.I want to ask this question from Lap Winding topic in portion Armature Windings of DC Machines
Answer» Correct answer is (c) 7 Easy EXPLANATION: COIL span is defined as a ratio of number of slots in the armature winding which are ALSO equal to the number of COMMUTATOR segments to the number of poles. Here, Slots in the armature winding= 12, Number of poles= 4. YCS= 12/4= 3. Yb = 2YCS +1= 7.

Discussion

9.	What is the condition of retrogressive winding?(a) Yb > Yf(b) Yb < Yf(c) Yb = Yf(d) No condition in bterms of Yb and YfThe question was posed to me in semester exam.The doubt is from Lap Winding topic in chapter Armature Windings of DC Machines
Answer» Right answer is (b) YB < Yf The BEST I can explain: The coil side displacement of the front-end connection is CALLED the front-pitch. The coil side displacement of the back-end connection is called the back-pitch. The direction in which the winding progresses DEPENDS UPON which is more, Yb or Yf. For retrogressive winding Yb < Yf .

Discussion

10.	Resultant pitch in the lap winding is__________(a) Depends on Yb value(b) Depends on Yf value(c) Depends on Yb and Yf value(d) Always equal to 2I had been asked this question in homework.Query is from Lap Winding in division Armature Windings of DC Machines
Answer» The correct OPTION is (d) Always equal to 2 Explanation: In a lap winding the “finish” of one coil is connected to “start” of the ADJOINING coil. The coil side displacement of the front-end connection is called the front-pitch. The coil side displacement of the back-end connection is called the back-pitch. Resultant-pitch is equal to difference between Yb and Yf which is equal to 2, IRRESPECTIVE of Yb and Yf value.

Discussion

11.	When coil sides are pole pitch apart, the DC armature winding is called as ___________(a) Multiplex(b) Fractional-pitch(c) Full-pitch(d) Pole-pitchThis question was addressed to me in an internship interview.The origin of the question is Armature Winding and Commutator in division Armature Windings of DC Machines
Answer» Correct choice is (c) Full-PITCH To explain: Pole pitch is called as center to center distance between two adjacent poles. When measured in electrical degrees ONE pole ITCH is equal to 1800. Coil span is simply a peripheral distance between two sides of a coil. If the coil span is equal to the pole pitch, then the armature winding is said to be full pitched coil.

Discussion

12.	For a 2-pole DC machine with coil span equal to 6, what are the number of commutator segments?(a) 3(b) 12(c) 4(d) 8This question was posed to me during an internship interview.My question comes from Armature Winding and Commutator topic in portion Armature Windings of DC Machines
Answer» The correct answer is (B) 12 Explanation: Coil span is defined as a ratio of NUMBER of SLOTS in the armature winding which are ALSO equal to the number of commutator segments to the number of poles. Here, Number of poles= 2, Slots in the armature winding= S= P* YCS. Here, YCS= 6, P=2. Thus S=12. C=S=Number of commutator segments.

Discussion

13.	What is the nature of the coils when YCS value is non-integral?(a) Long-pitched(b) Medium-pitched(c) Short-pitched(d) Can’t be determined by YCS valueThis question was addressed to me in a national level competition.My query is from Armature Winding and Commutator topic in division Armature Windings of DC Machines
Answer» Correct answer is (c) Short-pitched To explain I would say: Coil-side VOLTAGES AROUND the coil are additive most of the time (except when coil-sides lie NEAR the magnetic neutral region). Thus YCS= Nearest lower INTEGER, which MEANS that for non-integral S/P, the coils are short-pitched.

Discussion

14.	As the armature rotates, the number of coils in series tapped by the brush pairs_________(a) Remains same(b) Increases(c) Decreases(d) Depends on rotor speed and direction of torqueThis question was addressed to me in exam.This is a very interesting question from Armature Winding and Commutator in division Armature Windings of DC Machines
Answer» The correct choice is (a) Remains same The explanation is: Brushes are located ELECTRICALLY in magnetically neutral region. Adjoining brush pairs are at constant DC voltage and the NUMBER of coils tapped by brush pairs ALSO remain constant. Their disposition RELATIVE to the POLES is the same.

Discussion

15.	What is the effect of armature coils at points where brushes are located?(a) Induces positive emf(b) Induces negative emf(c) Induces zero emf(d) Depends on the speed of rotorI had been asked this question in my homework.I want to ask this question from Armature Winding and Commutator topic in division Armature Windings of DC Machines
Answer» The correct answer is (c) Induces zero EMF Easy EXPLANATION: BRUSHES are at magnetically neutral region hence, INDUCED emf DUE to armature coils at brushes will be equal to zero. As in the magnetically neutral region change in flux will be equal to the zero, emf will not be induced (Faraday’s law).

Discussion

16.	What is the difference of DC voltages in the adjoining Brushes?(a) Depends on the Shaft speed(b) Zero(c) Non-zero(d) Depends on the various other parametersThis question was posed to me during an online exam.I'd like to ask this question from Armature Winding and Commutator in division Armature Windings of DC Machines
Answer» Right answer is (b) Zero For EXPLANATION: Brushes are located electrically in the magnetically NEUTRAL region. Due to their location adjoining brushes are at constant DC voltage and the coil in series between the CONSTITUTE one parallel PATH.

Discussion

17.	In a DC machine, how coil-side emf varies towards the outer side of poles?(a) Decreases(b) Remains same(c) Increases(d) First increases the decreasesThe question was asked by my college director while I was bunking the class.My doubt stems from Armature Winding and Commutator in portion Armature Windings of DC Machines
Answer» The correct ANSWER is (a) Decreases Best explanation: Coil side current pattern is the same as the emf pattern. Only difference is that while the coil-side emf reduces towards the outer side of poles, the current remains the same in all the coil-sides EXCEPT for ALTERATIONS from pole to pole, while the coil side current reverses, the current EXCHANGED with external circuit must be unidirectional.

Discussion

18.	Armature winding is mounted on a __________(a) Stator(b) Rotor(c) Can be mounted anywhere on stator or rotor(d) Not requiredI have been asked this question in exam.My doubt stems from Armature Winding and Commutator in division Armature Windings of DC Machines
Answer» The correct option is (b) Rotor Best EXPLANATION: A DC MACHINE is a heteropolar structure with STATIONARY poles and the rotating armature. FIELD coil is mounted on stator. In an AC machine armature winding is located at rotor while field coil is located at stator. An ‘armature’ is a moving part as it a ‘rotor’.

Discussion

19.	What will be the value of “Yf + Yb” for a wave winding?(a) Equal to Yc(b) Half of the Yc value(c) Double of the Yc value(d) Four times Yc valueI got this question in an online quiz.My doubt is from Wave Winding in portion Armature Windings of DC Machines
Answer» The correct option is (C) DOUBLE of the Yc value Best explanation: In the wave winding, as the NUMBER of coil-sides is double the number of segments, the TOP coil-side of the second coil will be numbered as (1+2Yc). After numbering other coil sides, 1 + 2Yc – Yf = 1+ YB So Yf + Yb = 2Yc.

Discussion

20.	Current flowing through the armature conductors Ic is related to total current Ia by_______(a) Ic = A Ia(b) Ic = Ia/A(c) Ic = A^2 Ia(d) Ic = A/IaI got this question during an interview.Question is from Lap Winding topic in portion Armature Windings of DC Machines
Answer» The correct option is (b) Ic = IA/A The BEST I can explain: Two positive and two NEGATIVE BRUSHES are RESPECTIVELY connected in parallel for feeding the external circuit. As per the ring diagram Ia splits into the number of poles equally. Poles = Parallel paths. Thus, Ic = Ia /A.

Discussion

21.	Commutator performs rectification so that output of the machine is unidirectional.(a) True(b) FalseThis question was addressed to me in an online quiz.Question is from Armature Winding and Commutator topic in division Armature Windings of DC Machines
Answer» Correct option is (a) True For EXPLANATION I would say: Since it is a DC machine the generated output must be DC. Any electrical machine works on induced emf concept which is AC in nature. Commutator and brush ASSEMBLY of the DC machine performs the mechanical RECTIFICATION process so; induced AC is converted into DC(Unidirectional).

Discussion

22.	For a wave wounded machine number of brushes for small, large machines respectively is _________________(a) 2, 2(b) 4, 2(c) 2, P(d) Both values depend on the given conditionsThis question was posed to me during an interview for a job.The above asked question is from Wave Winding in portion Armature Windings of DC Machines
Answer» Correct choice is (c) 2, P The best explanation: For a small wave wounded machine number of PARALLEL PATHS are 2, thus 2 brushes are USED. For a large machine total number of brushes is EQUAL to the total number of poles. The spacing between adjacent brushes is C/P commutator segments.

Discussion

23.	Equalizer rings are needed in the wave winding.(a) True(b) FalseThe question was posed to me in final exam.I want to ask this question from Wave Winding topic in chapter Armature Windings of DC Machines
Answer» The correct answer is (b) False To explain: The armature coil FORMS 2 parallel paths under the influence of all pole-pairs so that the effect of the MAGNETIC circuit asymmetry is equally present in both the parallel paths resulting in equal parallel-path voltages. Thus, equalizer rings are not needed in WAVE winding.

Discussion

24.	For a conductor current equal to 4mA, Current carried by a particular brush in a 2-pole machine will be _____(a) 16mA(b) 8mA(c) 2mA(d) 10mAThis question was posed to me in an international level competition.My question comes from Wave Winding in portion Armature Windings of DC Machines
Answer» The CORRECT answer is (b) 8mA To explain I would say: Conductor current in a wave wounded machine is half of the Ia. So, Ia= 8mA. All positive and all negative BRUSHES are respectively connected in PARALLEL to feed the external CIRCUIT. Thus, IBRUSH = Ia /(P/2). Solving we get Brush current = 8mA.

Discussion

25.	Equalizer rings are needed in lap winding.(a) False(b) TrueThis question was addressed to me in an international level competition.This key question is from Lap Winding topic in portion Armature Windings of DC Machines
Answer» Right answer is (b) True The explanation is: Each parallel PATH in lap winding is under the influence of one PAIR of poles, so if a machine consists of multiple pairs of poles then dissimilarities occurs, DUE to which unequal voltages may be induced in the paths and a circulating current may flow. In wave winding each path is under the influence of all poles, so voltages are induced in each path CAUSING no such dissimilarities like lap winding. EQUALIZERS in lap windings are used to remove this dissimilarity, they’re not needed in wave winding.

Discussion

26.	Coil span for 4-pole, 12-slot armature winding is_______(a) 24(b) 48(c) 8(d) 3I have been asked this question in an internship interview.Asked question is from Armature Winding and Commutator topic in chapter Armature Windings of DC Machines
Answer» The correct ANSWER is (d) 3 The best explanation: Coil SPAN is DEFINED as a ratio of number of slots in the armature winding which are also equal to the number of COMMUTATOR segments to the number of poles. Here, Slots in the armature winding= 12, Number of poles= 4. YCS= 12/4= 3.

Discussion

27.	For a wave winding when a machine is 6-pole DC armature with 16 slots having 2-coil sides per slot and single-turn coil, Yf value is ____(a) 5(b) 3(c) 2(d) 7The question was posed to me in a job interview.My question is based upon Wave Winding in chapter Armature Windings of DC Machines
Answer» Right option is (a) 5 For explanation: Ycs = 16/6 = 2 SLOTS (NEAREST lower integral value) Yb= 2*2+1 = 5 Yc= 2(16-1)/6 = 5 segments Yf = 2Yc – Yb = 5.

Discussion

28.	Value of commutator pitch in lap winding is_____(a) +2(b) +1 or -1(c) -2(d) Different for different parametersI got this question during an online interview.This intriguing question comes from Lap Winding topic in chapter Armature Windings of DC Machines
Answer» The correct choice is (b) +1 or -1 Explanation: Two ends of coil are connected ACROSS the adjacent commutator segments. Depending on the type of winding that is, RETROGRESSIVE or PROGRESSIVE, we have two values for commutator pitch. For progressive winding, commutator pitch = +1. For retrogressive winding, commutator pitch = -1.

Discussion

29.	For a progressive wave winding Yc = ______(a) 2C/P(b) 2(C+1)/P(c) 2(C-1)/P(d) 2C/(P+1)I got this question in an interview for internship.My question is from Wave Winding topic in chapter Armature Windings of DC Machines
Answer» CORRECT choice is (b) 2(C+1)/P Easy EXPLANATION: Starting at segment 1 and after going through P/2 coils or Yc (P/2) SEGMENTS, the winding should end in segment 2 for PROGRESSIVE winding or segment (C) for retrogressive winding. That is mathematically, Yc (P/2) = (C+1) Yc = 2(C+1)/P

Discussion

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Wave winding machines are used in ______ currents applications.(a) High(b) Moderate(c) Low(d) Can be used anywhereThis question was addressed to me in an online interview.Asked question is from Wave Winding in portion Armature Windings of DC Machines

Number of parallel paths in wave winding are ______(a) Equal to P(b) Equal to P/2(c) 2(d) Depends on other parametersThis question was posed to me by my school teacher while I was bunking the class.Query is from Wave Winding in division Armature Windings of DC Machines

What is the relation between number of parallel paths(A) and number of poles(P)?(a) A = P(b) A < P(c) A > P(d) No relation existsThe question was posed to me in an online interview.Asked question is from Lap Winding topic in division Armature Windings of DC Machines

What is the symmetry requirement of lap winding?(a) 2C/P= 0(b) 2C/P= integer(c) 2C/P= non-integer(d) Can’t express mathematicallyI got this question in my homework.I would like to ask this question from Lap Winding in division Armature Windings of DC Machines

What is the value of Yb for a lap winding with a 4-pole, 12-slot armature with two coil sides/slot. Assume single-turns coils.(a) 3(b) 5(c) 7(d) 9I had been asked this question at a job interview.I want to ask this question from Lap Winding topic in portion Armature Windings of DC Machines

What is the condition of retrogressive winding?(a) Yb > Yf(b) Yb < Yf(c) Yb = Yf(d) No condition in bterms of Yb and YfThe question was posed to me in semester exam.The doubt is from Lap Winding topic in chapter Armature Windings of DC Machines

Resultant pitch in the lap winding is__________(a) Depends on Yb value(b) Depends on Yf value(c) Depends on Yb and Yf value(d) Always equal to 2I had been asked this question in homework.Query is from Lap Winding in division Armature Windings of DC Machines

For a 2-pole DC machine with coil span equal to 6, what are the number of commutator segments?(a) 3(b) 12(c) 4(d) 8This question was posed to me during an internship interview.My question comes from Armature Winding and Commutator topic in portion Armature Windings of DC Machines

Armature winding is mounted on a __________(a) Stator(b) Rotor(c) Can be mounted anywhere on stator or rotor(d) Not requiredI have been asked this question in exam.My doubt stems from Armature Winding and Commutator in division Armature Windings of DC Machines

What will be the value of “Yf + Yb” for a wave winding?(a) Equal to Yc(b) Half of the Yc value(c) Double of the Yc value(d) Four times Yc valueI got this question in an online quiz.My doubt is from Wave Winding in portion Armature Windings of DC Machines

Current flowing through the armature conductors Ic is related to total current Ia by_______(a) Ic = A Ia(b) Ic = Ia/A(c) Ic = A^2 Ia(d) Ic = A/IaI got this question during an interview.Question is from Lap Winding topic in portion Armature Windings of DC Machines

Commutator performs rectification so that output of the machine is unidirectional.(a) True(b) FalseThis question was addressed to me in an online quiz.Question is from Armature Winding and Commutator topic in division Armature Windings of DC Machines

Equalizer rings are needed in the wave winding.(a) True(b) FalseThe question was posed to me in final exam.I want to ask this question from Wave Winding topic in chapter Armature Windings of DC Machines

For a conductor current equal to 4mA, Current carried by a particular brush in a 2-pole machine will be _____(a) 16mA(b) 8mA(c) 2mA(d) 10mAThis question was posed to me in an international level competition.My question comes from Wave Winding in portion Armature Windings of DC Machines

Equalizer rings are needed in lap winding.(a) False(b) TrueThis question was addressed to me in an international level competition.This key question is from Lap Winding topic in portion Armature Windings of DC Machines

Coil span for 4-pole, 12-slot armature winding is_______(a) 24(b) 48(c) 8(d) 3I have been asked this question in an internship interview.Asked question is from Armature Winding and Commutator topic in chapter Armature Windings of DC Machines

For a wave winding when a machine is 6-pole DC armature with 16 slots having 2-coil sides per slot and single-turn coil, Yf value is ____(a) 5(b) 3(c) 2(d) 7The question was posed to me in a job interview.My question is based upon Wave Winding in chapter Armature Windings of DC Machines

Value of commutator pitch in lap winding is_____(a) +2(b) +1 or -1(c) -2(d) Different for different parametersI got this question during an online interview.This intriguing question comes from Lap Winding topic in chapter Armature Windings of DC Machines

For a progressive wave winding Yc = ______(a) 2C/P(b) 2(C+1)/P(c) 2(C-1)/P(d) 2C/(P+1)I got this question in an interview for internship.My question is from Wave Winding topic in chapter Armature Windings of DC Machines