76 + Interview Questions in Dc Machines in Electrical Machines Page 1 InterviewSolution

1.	A d.c. generator has been provided tappings on the armature winding at intervals of 120 degrees from the side of commutator. The connection will be __________(a) delta connected alternator(b) star connected alternator(c) star connected induction motor(d) any of the mentionedThe question was posed to me in quiz.My question is based upon DC Machine Applications in portion DC Machines of Electrical Machines
Answer» Correct answer is (a) delta connected alternator For explanation I would SAY: Dc generator if has displaced by 120 DEGREES PHYSICALLY then it will act as Ac machine.

Discussion

2.	A 200 V dc motor has external resistances of Ra and Rf in armature and field circuits respectively. The starting current is reduced when?(a) Ra is maximum and Rf minimum(b) Rf is maximum and Ra minimum(c) Ra is minimum and Rf minimum(d) Ra is maximum and Rf maximumThe question was posed to me in homework.The query is from DC Machine Applications in portion DC Machines of Electrical Machines
Answer» Right choice is (a) RA is MAXIMUM and RF minimum Explanation: When Ra is maximum and Rf minimum then the current to the armature is reduced. And hence the sparkings are reduced while STARTING.

Discussion

3.	Interpoles are used to start the dc motor above the base speed.(a) True(b) FalseI have been asked this question in examination.Asked question is from DC Machine Applications in section DC Machines of Electrical Machines
Answer» The CORRECT answer is (B) False To elaborate: Interpoles do not reduce the flux across the WINDINGS, hence the speed does not RISE above base speed.

Discussion

4.	If a dc shunt motor is stopped by forcing starter handle back to OFF position, then the __________(a) dangerous sparking occurs at last stud(b) dangerous sparking occurs at all stud(c) it stops normally(d) heavy sparkingThe question was posed to me by my college director while I was bunking the class.Question is taken from DC Machine Applications in division DC Machines of Electrical Machines
Answer» The CORRECT choice is (a) dangerous sparking occurs at last STUD To explain I WOULD SAY: The sparking will OCCUR at the last stud not all the studs of the starter.

Discussion

5.	Long back ago, magnetic casette were in use, having permanent magnet dc motors which had?(a) magnets on stator and armature on rotor(b) magnet on rotor and armature on stator(c) electronic commutation(d) all of the mentionedI had been asked this question in a national level competition.This interesting question is from DC Machine Applications in section DC Machines of Electrical Machines
Answer» The CORRECT answer is (a) MAGNETS on STATOR and armature on rotor Easy explanation: PMDC motors have FIELD FIXED on the stator and rotor has coils.

Discussion

6.	Most commercial compound dc generator are normally supplied by manufacturers as ______ compounded machines.(a) over(b) under(c) level(d) none of the mentionedI have been asked this question by my college director while I was bunking the class.My question is based upon DC Machine Applications in chapter DC Machines of Electrical Machines
Answer» Right OPTION is (a) over To explain I would say: Most commercial compound dc GENERATOR are NORMALLY supplied by manufacturers as over compounded.

Discussion

7.	Which of the following are applied with differential compound motor?(a) Hoist(b) Cranes(c) Drilling machines(d) None of the mentionedThis question was addressed to me in a national level competition.This interesting question is from DC Machine Applications topic in chapter DC Machines of Electrical Machines
Answer» The CORRECT CHOICE is (a) Hoist For explanation: PRACTICALLY it is NEVER USED as the speed can rise very high.

Discussion

8.	Most commercial compound dc generator are normally supplied by manufacturers as over compound machines because __________(a) degree of compounding can be adjusted by diverters acrosss series field(b) they have ideally best for HVDC(c) cost effective than shunt(d) zero percent regulationThe question was asked by my college professor while I was bunking the class.The question is from DC Machine Applications topic in section DC Machines of Electrical Machines
Answer» Correct CHOICE is (a) degree of COMPOUNDING can be adjusted by DIVERTERS acrosss series field The best explanation: It is USUALLY over COMPOUNDED so that degree of compounding can be adjusted by diverters across series field.

Discussion

9.	Centrifugal pumps, fans-blowers use __________(a) shunt as well as induction motor(b) only shunt motors(c) only induction motor(d) none of the mentionedI had been asked this question by my college professor while I was bunking the class.My question is taken from DC Machine Applications in chapter DC Machines of Electrical Machines
Answer» Correct choice is (a) shunt as WELL as INDUCTION MOTOR Best explanation: CENTRIFUGAL PUMPS, fans-blowers use shunt as well as induction motor.

Discussion

10.	Hoists, cranes and battery powered vehicles use _________ motors in the locomotive.(a) dc series(b) dc shunt(c) induction(d) reluctanceI had been asked this question in an international level competition.Question is from DC Machine Applications topic in chapter DC Machines of Electrical Machines
Answer» The CORRECT answer is (a) dc series Explanation: Hoists, cranes require large STARTING torque which can be provided by dc series MOTOR.

Discussion

11.	The manufacturer has mentioned a medium starting torque and 15% speed regulation. Which is the most appropriate motor for this requirement?(a) dc shunt motor(b) induction motor(c) differential motor(d) none of the mentionedI got this question during an online exam.I'd like to ask this question from DC Machine Applications in chapter DC Machines of Electrical Machines
Answer» The correct CHOICE is (a) DC SHUNT motor For explanation: The dc shunt motor PROVIDES a MEDIUM values of the torque.

Discussion

12.	There is an application which required pulsating loads, punch presses. The most preferred machines would be __________(a) compound dc machine(b) series dc machine(c) shunt dc machine(d) all of the mentionedThis question was posed to me in exam.This interesting question is from DC Machine Applications topic in division DC Machines of Electrical Machines
Answer» Right answer is (a) compound dc machine The EXPLANATION is: It is compound machine whose flux can VARIED higher as well as lower in order to have variable TORQUES.

Discussion

13.	Separately excited dc generators are used in __________(a) Ward leonard system of speed control(b) Hopkinson’s testing(c) Voltage control(d) None of the mentionedThis question was addressed to me in an interview for job.My question is based upon DC Machine Applications topic in portion DC Machines of Electrical Machines
Answer» Correct answer is (a) WARD LEONARD system of SPEED control The explanation is: Separately excited DC GENERATORS are used in Ward leonard system of speed control.

Discussion

14.	Maximum torque in dc series motor is limited by __________(a) commutation(b) heating(c) field control(d) all of the mentionedI got this question in unit test.Question is from DC Machine Applications topic in section DC Machines of Electrical Machines
Answer» Correct choice is (a) commutation The best EXPLANATION: Commutation is the process which REDUCES the induced emf and so the TORQUE.

Discussion

15.	Inspite of heavy initial investments, dc motors are used due to _____________(a) flexibility and ease of control(b) lower losses(c) improved power factor of the system(d) all of the mentionedThis question was posed to me in an interview for job.This interesting question is from DC Machine Applications in section DC Machines of Electrical Machines
Answer» Correct choice is (a) flexibility and EASE of control Easy explanation: The control of DC machines is very much simplified when compared to other machines. So this MAKES it very USEFUL when compared.

Discussion

16.	Similarity between Hopkinonson’s and field’s test is that _______(a) both need similar mechanically coupled motor(b) both need similar electrically coupled motor(c) regenerative power(d) negligible powerThis question was posed to me in a job interview.Query is from Efficiency and Testing of DC Machines topic in chapter DC Machines of Electrical Machines
Answer» The CORRECT OPTION is (a) both need SIMILAR mechanically coupled motor The explanation is: The machines have to be mechanically coupled TOGETHER.

Discussion

17.	Swineburne’s test is applicable to those machines in which flux is practically _______(a) constant(b) linear(c) non-linear(d) none of the mentionedThe question was asked in an interview.I want to ask this question from Efficiency and Testing of DC Machines in chapter DC Machines of Electrical Machines
Answer» CORRECT option is (a) CONSTANT The explanation: Because the constant losses are KNOWN in advance of the test is CONDUCTED.

Discussion

18.	The efficiency in the swineburne’s test can be found.(a) True(b) FalseThe question was posed to me during an interview for a job.I would like to ask this question from Efficiency and Testing of DC Machines in section DC Machines of Electrical Machines
Answer» The correct answer is (a) True Easiest explanation: Because the CONSTANT LOSSES are KNOWN.

Discussion

19.	Which is the most appropriate relation to find efficiency of the generator?(a) output/(output + losses)(b) (output – losses)/input(c) (output – losses)/(output + losses)(d) any of the mentionedThis question was posed to me during an internship interview.The above asked question is from Efficiency and Testing of DC Machines topic in chapter DC Machines of Electrical Machines
Answer» Correct OPTION is (a) output/(output + losses) The BEST I can EXPLAIN: For a generator the output can be measured and so this expression is USED.

Discussion

20.	In the Hopkinson’s test on two DC machines. Machine A has field current of 1.4A and B has field current of 1.3A. Which machine acts as generator?(a) B(b) A(c) A,B(d) None of the mentionedThis question was addressed to me during an online interview.Enquiry is from Efficiency and Testing of DC Machines topic in division DC Machines of Electrical Machines
Answer» The correct choice is (B) A To ELABORATE: Ea/EB = 1.4/1.3 Ea = 1.077 Eb > Eb So, the machine will act as generator.

Discussion

21.	Hopkinson’s test is also called regenerative test due to ____________(a) energy of one machine is used to drive other(b) feedback(c) losses are least(d) extra motor is usedThis question was posed to me in final exam.Origin of the question is Efficiency and Testing of DC Machines in chapter DC Machines of Electrical Machines
Answer» Correct ANSWER is (a) ENERGY of one machine is used to DRIVE other The explanation is: Regenerative phenomena utilizes the energy of the running machine to tap the dynamically produced energy and use it to CHARGE the battery.

Discussion

22.	In the hopkinson’s test on two DC machines. Machine A has field current of 1.4A and B has field current of 1.3A. Which machine acts as motor?(a) B(b) A(c) A, B(d) None of the mentionedThis question was posed to me by my school teacher while I was bunking the class.I'd like to ask this question from Efficiency and Testing of DC Machines topic in chapter DC Machines of Electrical Machines
Answer» CORRECT answer is (a) B To explain I WOULD SAY: Ea/Eb = 1.4/1.3 Ea = 1.077 Eb > Eb So, the machine will act as motor.

Discussion

23.	If the field current and armature current are reversed, then the __________(a) direction of rotation remains same(b) direction of rotation reverses(c) stops(d) none of the mentionedThis question was posed to me by my college professor while I was bunking the class.This key question is from Efficiency and Testing of DC Machines in division DC Machines of Electrical Machines
Answer» RIGHT choice is (a) direction of rotation remains same To elaborate: When both field CURRENT and armature current are reversed then the direction will not CHANGE.

Discussion

24.	______ test is used for determining the efficiency of a traction motor.(a) Field(b) Retardation(c) Hopkinson(d) Swineburne’sThis question was addressed to me in examination.The query is from Efficiency and Testing of DC Machines topic in chapter DC Machines of Electrical Machines
Answer» The correct option is (a) FIELD For explanation I would SAY: Field TEST is used for FINDING efficiency of a traction MOTOR.

Discussion

25.	Mark the possible causes of overheating of commutator in a DC machine.(a) Overload(b) Restricted ventilation(c) Shorted winding(d) Any of the mentionedI had been asked this question in exam.The query is from Efficiency and Testing of DC Machines in section DC Machines of Electrical Machines
Answer» The correct CHOICE is (a) Overload To ELABORATE: All the FACTORS can CAUSE the OVERHEATING of commutator.

Discussion

26.	The quantities needed to complete retardation test are/is _________(a) dw/dt and moment of inertia(b) dw/dt(c) current(d) any of the mentionedI have been asked this question in my homework.My question is from Efficiency and Testing of DC Machines in portion DC Machines of Electrical Machines
Answer» CORRECT option is (a) dw/dt and moment of inertia For EXPLANATION I WOULD SAY: We need the angular acceleration and the moment of inertia of the machine.

Discussion

27.	Retardation test on DC shunt motor is used for finding _______(a) stray losses(b) copper losses(c) friction losses(d) iron lossesThe question was posed to me in a job interview.My doubt stems from Efficiency and Testing of DC Machines in portion DC Machines of Electrical Machines
Answer» Right OPTION is (a) stray LOSSES Explanation: RETARDATION TEST is used for finding the stray losses.

Discussion

28.	A dc motor is connected in the short-shunt configuration, but the series and the shunt windings get interchanged by mistake and the motor is connected to the rated voltage?(a) neither of the windings get short-circuit(b) series winding gets overloaded(c) shunt winding gets overloaded(d) both of the winding get overloadedThis question was addressed to me during an interview.My doubt stems from Efficiency and Testing of DC Machines topic in division DC Machines of Electrical Machines
Answer» The CORRECT answer is (a) neither of the windings get SHORT-circuit To elaborate: In the short shunt configuration, the winding interchanging does not CHANGE the configuration of the SET up so none of the winding get affected.

Discussion

29.	What is the main concern before doing hopkinson’s test for finding efficiency?(a) needs one motor and one generator is that it(b) ignores iron and stray losses(c) needs one motor(d) requires identical shunt machinesThis question was posed to me by my college professor while I was bunking the class.I want to ask this question from Efficiency and Testing of DC Machines in section DC Machines of Electrical Machines
Answer» Right answer is (d) requires identical shunt machines To explain I WOULD say: It is MUST that both the machines are identical as REQUIRED by the CALCULATIONS.

Discussion

30.	If the magnetic circuit of the dc machine is in the saturation region, the armature reaction __________(a) does not affect flux/pole(b) increases the flux/pole(c) decreases flux/pole(d) affects the flux/pole only when armature current is smallI had been asked this question in class test.This interesting question is from Effect of Brush Shift and Compensation Windings in portion DC Machines of Electrical Machines
Answer» The CORRECT OPTION is (a) does not affect FLUX/pole For explanation: In the saturation REGION the flux will be CONSTANT.

Discussion

31.	The armature reaction is produced mainly by __________(a) load current in armature(b) load current in field(c) all of the mentioned(d) none of the mentionedThe question was asked by my school principal while I was bunking the class.This interesting question is from Effect of Brush Shift and Compensation Windings topic in chapter DC Machines of Electrical Machines
Answer» Correct CHOICE is (a) load current in armature The BEST I can EXPLAIN: The armature reaction is initiated by the loaded conditions of the MACHINE because an unloaded dc machine does not armature flux to get distorted.

Discussion

32.	The compensating winding in dc generator is provided to __________(a) neutralize cross-magnetizing flux(b) neutralize demagnetizing flux(c) neutralize armature mmf(d) maintain magnetizing mmfThis question was addressed to me in quiz.My question is from Effect of Brush Shift and Compensation Windings in chapter DC Machines of Electrical Machines
Answer» Correct ANSWER is (a) NEUTRALIZE CROSS-magnetizing flux Easiest explanation: The COMPENSATING winding functions such that to nullify the cross magnetization effects in the ARMATURE.

Discussion

33.	The commutation process involves basically reversal of current in armature coil as it crosses MNA.(a) True(b) FalseI had been asked this question in an online quiz.This intriguing question originated from Effect of Brush Shift and Compensation Windings topic in portion DC Machines of Electrical Machines
Answer» CORRECT choice is (a) True Best explanation: By reversing the current direction in the MNA the current can be LIMITED in the COILS to avoid sparking.

Discussion

34.	Mark the most incorrect. In dc generator, commutation can be improved by __________(a) using interpoles(b) using carbon brushes(c) shifting brush axis in direction of armature rotation(d) none of the mentionedI had been asked this question during an internship interview.My doubt stems from Effect of Brush Shift and Compensation Windings in chapter DC Machines of Electrical Machines
Answer» Right option is (a) using interpoles The explanation is: All the given measures are USED to eliminate the EFFECT of armature REACTION and hence improves COMMUTATION ALSO.

Discussion

35.	A 400-V, 1000-A, lap wound dc machine has 10 poles, 860 armature conductors. The number of conductors in the pole face to give full compensation if pole face covers 70% of pole span is?(a) 3010(b) 4300(c) 2400(d) 2800The question was posed to me by my college professor while I was bunking the class.This key question is from Effect of Brush Shift and Compensation Windings in section DC Machines of Electrical Machines
Answer» Correct choice is (a) 3010 For EXPLANATION: AT/pole for the COMPENSATING WINDING = 0.7(ZI/2P) = 0.7(860100/2*10) = 3010 AT.

Discussion

36.	Each of the following is valid for interpoles except __________(a) they are connected in parallel with the armature so that they carry part of armature current(b) they are small yoke fixed poles spaced in between main poles(c) their polarity, in case of generator is same as that of main poles ahead(d) they automatically neutralize not only reactance voltage but cross-magnetization alsoI have been asked this question during an online interview.This question is from Effect of Brush Shift and Compensation Windings in chapter DC Machines of Electrical Machines
Answer» Right ANSWER is (a) they are connected in PARALLEL with the armature so that they CARRY part of armature current To explain: All the options are valid for the interpoles EXCEPT a because they are connected in series not in parallel.

Discussion

37.	The number of compensating conductors/pole faces is _______ (where Z is the number of active armature conductors/pole; A is number of parallel paths; Ia is the armature current).(a) Z/AIa(b) 2AIa/Z(c) ZIa/A(d) Z/2A*IaI got this question during a job interview.My question is from Effect of Brush Shift and Compensation Windings in section DC Machines of Electrical Machines
Answer» Correct choice is (a) Z/AIA Explanation: Compensating CONDUCTORS per pole FACE is Z/AIa.

Discussion

38.	The absence of compensating winding lead to __________(a) statically induced emf in armature(b) fluctuations in supply(c) reduction in the flux(d) any of the mentionedI have been asked this question in homework.I'd like to ask this question from Effect of Brush Shift and Compensation Windings in portion DC Machines of Electrical Machines
Answer» RIGHT choice is (a) statically induced emf in ARMATURE To elaborate: The static emf induced inside gets reduced due to the armature reaction in LARGE MACHINES when there is no compensating winding PRESENT.

Discussion

39.	The principle contributors to magneto motive force is/are __________(a) field current and armature current(b) field excitation(c) electromagnetic torque(d) all of the mentionedThe question was posed to me in quiz.My question is taken from Effect of Brush Shift and Compensation Windings in division DC Machines of Electrical Machines
Answer» RIGHT answer is (a) FIELD current and armature current To explain I would say: The interaction between the field excitation and armature supply create the MMF and the interconnected BEHAVIOUR creates the emf.

Discussion

40.	If the critical commutation time is 2 ms but it was observed that the practical commutation took 2.5 ms. This is the case of __________(a) under commutation(b) over commutation(c) critical commutation(d) none of the mentionedThe question was posed to me in quiz.My doubt is from Effect of Brush Shift and Compensation Windings topic in section DC Machines of Electrical Machines
Answer» The CORRECT answer is (a) under COMMUTATION To explain I would say: SINCE the time TAKEN is more than the prescribed time limit for the commutation, it is under commutation.

Discussion

41.	The coil under going commutation lies along _____ while the coil getting short circuited lies along ____ for a practical dc machine.(a) gna, mna(b) mna, gna(c) gna, gna(d) mna, mnaI got this question in semester exam.Query is from Effect of Brush Shift and Compensation Windings topic in chapter DC Machines of Electrical Machines
Answer» Right option is (a) gna, mna To elaborate: In a practical dc machine, the coil undergoing commutation lies ALONG GNA so as the brushes and the coils which actually GET short circuited lies along mna. This LEAD to sparking as a VOLTAGE difference is CREATED at the coils.

Discussion

42.	With no commutating poles used the brushes are given backward lead in the dc motor.(a) True(b) FalseI had been asked this question in my homework.This interesting question is from Effect of Brush Shift and Compensation Windings topic in chapter DC Machines of Electrical Machines
Answer» The correct option is (a) True Best EXPLANATION: The ARMATURE reaction flux at the trailing edge WEAKENS the flux and at the LEADING edge is strengthens the flux in the dc motor.

Discussion

43.	The brushes should be shifted in _______ direction in generator for the satisfactory operation of commutation.(a) forward(b) reverse to rotation(c) all of the mentioned(d) none of the mentionedI got this question in quiz.This intriguing question originated from Effect of Brush Shift and Compensation Windings topic in chapter DC Machines of Electrical Machines
Answer» The CORRECT answer is (a) FORWARD Best explanation: For the generator, the electromagnetic TORQUE PRODUCED is in the opposite DIRECTION and so the induced current. So to eliminate the sparking the brushes should be shifted in the forward direction of rotation.

Discussion

44.	A dc shunt motor is running at 1000 rpm at the rated load torque. If few of the field windings get shot circuited then the __________(a) motor speed will increase and more armature current is drawn(b) motor speed will decrease and more armature current is drawn(c) motor speed will increase and lesser armature current is drawn(d) motor speed will decrease and lesser armature current is drawnThis question was addressed to me in homework.I want to ask this question from MMF and Flux Density Waveforms in DC Machines in portion DC Machines of Electrical Machines
Answer» The correct answer is (a) motor speed will increase and more armature current is drawn For explanation I would SAY: If FIELD WINDING get short circuited, field EXCITATION reduces causing rise in speed and more armature current.

Discussion

45.	The brushes are placed __________(a) along geometrical neutral axis(b) perpendicular to geometrical neutral axis(c) along magnetic neutral axis(d) perpendicular to magnetic neutral axisI had been asked this question during an online interview.The above asked question is from Effect of Brush Shift and Compensation Windings topic in section DC Machines of Electrical Machines
Answer» RIGHT answer is (a) along geometrical neutral axis The explanation: The brushes are placed along geometrical neutral axis so that in ideal conditions commutations take place without sparking. Also PLACING brushes along the magnetic neutral axis requires CONSISTENT variations as load varies which is not desirable.

Discussion

46.	A dc shunt motor is running at 1000 rpm at the rated load torque. If we reverse the supply terminals, then the __________(a) direction of rotation reverses and commutation will be unaffected(b) direction of rotation will be same and commutation will be unaffected(c) direction of ration reverses and commutation will be affected(d) direction of ration will be same and commutation will be affectedThis question was posed to me in unit test.This question is from MMF and Flux Density Waveforms in DC Machines topic in portion DC Machines of Electrical Machines
Answer» Right choice is (B) DIRECTION of rotation will be same and COMMUTATION will be unaffected Best explanation: Reversing the supply in dc MACHINE will not change the direction of rotation and will not affect the commutation too.

Discussion

47.	A dc shunt motor is running at 1000 rpm at the rated load torque. If we reverse the filed winding terminals, then the __________(a) direction of rotation reverses and commutation will be unaffected(b) direction of rotation will be same and commutation will be unaffected(c) direction of ration reverses and commutation will be affected(d) direction of ration will be same and commutation will be affectedI got this question in homework.This interesting question is from MMF and Flux Density Waveforms in DC Machines topic in division DC Machines of Electrical Machines
Answer» Correct choice is (a) direction of ROTATION reverses and commutation will be unaffected Best EXPLANATION: REVERSING the field will CHANGE the direction of rotation but will not AFFECT the commutation.

Discussion

48.	A dc shunt motor is connected to the source through 3-point starter. If the field id kept open and starter handle is moved from off to on position, then __________(a) motor will not start(b) armature will draw large current from source(c) no sparking would occur(d) all of the mentionedThe question was posed to me in homework.This interesting question is from MMF and Flux Density Waveforms in DC Machines in portion DC Machines of Electrical Machines
Answer»

Discussion

49.	A 100KW, 250 V, 400 A, a long shunt compound generator has an armature resistance of 0.025 ohms. There are 1000 shunt fields turns per pole and 3 series field turns per pole. The series field is connected in a such a fashion that positive armature current produces direct-axis MMF which adds to that of the shunt field. Compute the gross MMF at the rated terminal current when shunt field current is 4.7A and speed is 1150 rpm.(a) 5.9AT(b) 3.5AT(c) 4.7AT(d) 1.2ATI had been asked this question in my homework.The above asked question is from MMF and Flux Density Waveforms in DC Machines topic in section DC Machines of Electrical Machines
Answer» Right CHOICE is (a) 5.9AT For explanation I would say: Series field CURRENT = Is = I(l)+I(F) = 400+4.7 = 405 A(APPROX) Main field MMF = I(f)+(Ns/Nf)I(s) = 4.7+(3/1000)405 = 5.9 AT.

Discussion

50.	Compensating winding has an advantage of __________(a) eliminating flux distortion(b) importing speed of response(c) protecting overloading(d) any of the mentionedThis question was addressed to me by my college director while I was bunking the class.I would like to ask this question from MMF and Flux Density Waveforms in DC Machines in section DC Machines of Electrical Machines
Answer» The correct OPTION is (a) eliminating FLUX distortion Explanation: Any of the corrective MEASURES will be APPLICABLE.

Discussion

Explore topic-wise InterviewSolutions in .

Interpoles are used to start the dc motor above the base speed.(a) True(b) FalseI have been asked this question in examination.Asked question is from DC Machine Applications in section DC Machines of Electrical Machines

Hoists, cranes and battery powered vehicles use _________ motors in the locomotive.(a) dc series(b) dc shunt(c) induction(d) reluctanceI had been asked this question in an international level competition.Question is from DC Machine Applications topic in chapter DC Machines of Electrical Machines

Maximum torque in dc series motor is limited by __________(a) commutation(b) heating(c) field control(d) all of the mentionedI got this question in unit test.Question is from DC Machine Applications topic in section DC Machines of Electrical Machines

The efficiency in the swineburne’s test can be found.(a) True(b) FalseThe question was posed to me during an interview for a job.I would like to ask this question from Efficiency and Testing of DC Machines in section DC Machines of Electrical Machines

______ test is used for determining the efficiency of a traction motor.(a) Field(b) Retardation(c) Hopkinson(d) Swineburne’sThis question was addressed to me in examination.The query is from Efficiency and Testing of DC Machines topic in chapter DC Machines of Electrical Machines

Mark the possible causes of overheating of commutator in a DC machine.(a) Overload(b) Restricted ventilation(c) Shorted winding(d) Any of the mentionedI had been asked this question in exam.The query is from Efficiency and Testing of DC Machines in section DC Machines of Electrical Machines

The quantities needed to complete retardation test are/is _________(a) dw/dt and moment of inertia(b) dw/dt(c) current(d) any of the mentionedI have been asked this question in my homework.My question is from Efficiency and Testing of DC Machines in portion DC Machines of Electrical Machines

Retardation test on DC shunt motor is used for finding _______(a) stray losses(b) copper losses(c) friction losses(d) iron lossesThe question was posed to me in a job interview.My doubt stems from Efficiency and Testing of DC Machines in portion DC Machines of Electrical Machines

With no commutating poles used the brushes are given backward lead in the dc motor.(a) True(b) FalseI had been asked this question in my homework.This interesting question is from Effect of Brush Shift and Compensation Windings topic in chapter DC Machines of Electrical Machines