25 + Interview Questions in Dc Generators in Electrical Machines Page 1 InterviewSolution

1.	The delay of the commutation occurs due base cause of emf induced due to _________(a) self inductance, mutual inductance(b) self inductance(c) mutual inductance(d) leakage inductanceThe question was posed to me during an interview for a job.My doubt stems from Rotating Amplifiers topic in portion DC Generators of Electrical Machines
Answer» RIGHT OPTION is (a) SELF inductance, mutual inductance Easiest explanation: The commutation in dc MACHINES is delayed because of the emf induced in the coils and the mutual interaction of the field with NEIGHBOUR coils.

Discussion

2.	Mark the order for the decreasing order of the voltage regulation for dc generators.(a) DC shunt generator > level compound generator > Differential compound generator(b) DC shunt generator < level compound generator < Differential compound generator(c) Level compound generator > DC shunt generator > Differential compound generator(d) Level compound generator < DC shunt generator < Differential compound generatorI had been asked this question in exam.My doubt stems from Rotating Amplifiers in division DC Generators of Electrical Machines
Answer» Correct answer is (a) DC shunt generator > level compound generator > Differential compound generator The best I can explain: Dc shunt motor is almost constant speed generator and thus its voltage REGULATION is very GOOD than all and differential compound generator has most POOR v.r.

Discussion

3.	Interpoles provide mmf more than armature mmf in a dc machine.(a) True(b) FalseThe question was posed to me during a job interview.Origin of the question is Rotating Amplifiers in portion DC Generators of Electrical Machines
Answer» Right answer is (a) True The explanation: Interpoles NULLIFY ARMATURE cross MAGNETIZING flux and the reactance voltage. So it is more than the armature mmf for a good efficient MACHINE.

Discussion

4.	Amplidynes are best applicable in _________(a) feedback control systems with regulated power supply.(b) power supply(c) speed control of large motors(d) All of the mentionedI got this question by my college director while I was bunking the class.The above asked question is from Rotating Amplifiers topic in chapter DC Generators of Electrical Machines
Answer» The correct OPTION is (a) feedback CONTROL systems with regulated POWER supply. For explanation: Amplidynes find applications in feedback systems with large power HANDLING requirements.

Discussion

5.	In amplidynes, the resultant d-axis flux is _________(a) field flux(b) difference of field flux and main flux(c) sum of field flux and main flux(d) cross magnetizing fluxThis question was addressed to me in examination.My enquiry is from Rotating Amplifiers in section DC Generators of Electrical Machines
Answer» Right OPTION is (a) field flux To explain I would say: The resultant d-AXIS flux lies along the MAIN field poles and are so field flux. The d- axis is COMPLETELY under the control of field winding and is unaffected by DIRECT axis current.

Discussion

6.	An amplidyne, d-axis flux is always neutralized due to _________(a) compensating winding at all possible loads(b) interpoles at all specified loading(c) feedback at all possible loads(d) feedback at fixed loadingThis question was posed to me in unit test.The query is from Rotating Amplifiers in portion DC Generators of Electrical Machines
Answer» Correct answer is (a) COMPENSATING WINDING at all POSSIBLE LOADS For explanation: The d-flux is NEUTRALIZED by compensating winding at all possible loads as the same flux will be produced but in the opposite direction so as to cancel the flux.

Discussion

7.	Metadyne is _________ feedback with respect to main ___________(a) negative, current(b) negative, voltage(c) positive, current(d) positive, voltageThis question was posed to me in final exam.My question is from Rotating Amplifiers in section DC Generators of Electrical Machines
Answer» CORRECT choice is (a) negative, CURRENT To explain I would say: Metadyne is negative feedback with respect to main current FLOWING in the second stage set of motors.

Discussion

8.	In cross field rotating amplifiers, there is _________(a) two stage of flux generators(b) three stage of flux generators(c) four stage of flux generators(d) eight stage of flux generatorsI have been asked this question in an interview for job.My query is from Rotating Amplifiers in section DC Generators of Electrical Machines
Answer» Correct CHOICE is (a) two stage of FLUX generators The best explanation: There are two stages for flux generators in order to have FASTER RESPONSE in the system.

Discussion

9.	The cross field machines have _________(a) two fluxes electrically in quadrature(b) two fluxes mechanically in quadrature(c) one set of brushes per pole(d) all of the mentionedI had been asked this question in semester exam.This interesting question is from Rotating Amplifiers in section DC Generators of Electrical Machines
Answer» CORRECT answer is (a) two fluxes ELECTRICALLY in QUADRATURE The BEST explanation: The cross field MACHINES have two fluxes electrically in quadrature.

Discussion

10.	In rotating amplifiers, armature reaction mmf of the first stage is made to act as field flux for second stage.(a) True(b) FalseThis question was posed to me during an interview.My doubt is from Rotating Amplifiers topic in chapter DC Generators of Electrical Machines
Answer» Right answer is (a) True Easy explanation: Yes, the reaction mmf of the first stage is MADE to ACT as FIELD flux for SECOND stage to have faster TRANSIENT response.

Discussion

11.	The ordinary dc machines are not favourable as amplidynes due to _________(a) sluggish transient response(b) low stability(c) poor gain(d) high steady state errorI got this question in my homework.My enquiry is from Rotating Amplifiers topic in section DC Generators of Electrical Machines
Answer» The correct option is (a) sluggish TRANSIENT response The best I can EXPLAIN: The sluggish transient response of the ORDINARY dc machines MAKES them INAPPROPRIATE to use them in amplidynes.

Discussion

12.	The quantity which make rotating amplifier applicable in large power levels is/are _________(a) high power gain and favourable transient conditions(b) favourable transient conditions(c) high power gain(d) favourable steady state conditionsThis question was addressed to me in final exam.I need to ask this question from Rotating Amplifiers topic in section DC Generators of Electrical Machines
Answer» RIGHT answer is (a) high power gain and FAVOURABLE transient CONDITIONS Best explanation: The rotating AMPLIFIERS have stable transient conditions, which MAKES them favourable to use in high power sectors.

Discussion

13.	The rotating amplifiers are widely used in ____________(a) small amplified outputs(b) large amplified outputs(c) amplified outputs(d) large power gain outputsI have been asked this question in an interview for internship.Question is taken from Rotating Amplifiers topic in chapter DC Generators of Electrical Machines
Answer» Right choice is (b) LARGE amplified OUTPUTS The explanation: The rotating amplifiers are APPLICABLE in feedback systems GIVING large amplified outputs.

Discussion

14.	For a 220-V level compound generator the terminal voltage at the half load is?(a) more than 220-V(b) same as no-load voltage(c) more than no-load voltage(d) lesser than no-load voltageI had been asked this question in an interview.My question is from Operating Characteristics of DC Generators in chapter DC Generators of Electrical Machines
Answer» The CORRECT ANSWER is (b) same as no-load voltage To explain I would say: In a level COMPOUND dc generator the TERMINAL voltage remains same as no load voltage at all the loading.

Discussion

15.	What losses occur in the teeth of dc generator?(a) To reduce hysteresis loss(b) To reduce eddy current loss(c) To reduce eddy current as well as hysteresis losses(d) To achieve high permeabilityI got this question in class test.My doubt stems from Operating Characteristics of DC Generators topic in section DC Generators of Electrical Machines
Answer» Right choice is (c) To REDUCE EDDY current as well as hysteresis LOSSES Explanation: Teeth of the MACHINE has both eddy current losses as well as hysteresis losses.

Discussion

16.	Why is armature of a dc machine made of silicon steel stampings?(a) To reduce hysteresis loss(b) To reduce eddy current loss(c) For the ease with which slots can be created(d) To achieve high permeabilityThe question was asked in examination.Question is from Operating Characteristics of DC Generators topic in section DC Generators of Electrical Machines
Answer» The correct choice is (a) To reduce HYSTERESIS loss The explanation is: The silicon steel has very HIGH permeability and makes the flux past CONSISTENT. THEREBY MAKING lesser losses.

Discussion

17.	The voltage drop in terminal voltage from no-load to full load in a shunt generator can be compenated using _________(a) aiding series field(b) long-shunt, diferential field(c) aiding shunt field(d) any of the measuresThe question was asked in homework.This key question is from Operating Characteristics of DC Generators topic in portion DC Generators of Electrical Machines
Answer» The correct answer is (a) AIDING SERIES field Easy explanation: By aiding the series field the armature reaction drop can be COMPENSATED.

Discussion

18.	Mark the correct order for the external characteristics of compound generators from the below graph.(a) 1: over compound, 2: level compound, 3: under compound, 4: differential compound(b) 1: under compound, 2: level compound, 3: over compound, 4: differential compound(c) 1: differential compound, 2: level compound, 3: under compound, 4: over compound(d) 1: over compound, 2: differential compound, 3: under compound, 4: level compoundThis question was posed to me by my school teacher while I was bunking the class.Asked question is from Operating Characteristics of DC Generators topic in division DC Generators of Electrical Machines
Answer» The correct choice is (a) 1: over COMPOUND, 2: level compound, 3: under compound, 4: differential compound Best explanation: Over compounding provides maximum voltage difference at no load while the differential compunding has LEAST.

Discussion

19.	For a given dc generator, the external characteristic is plotted. Without using further plots, how can we obtain internal characteristic?(a) By adding the IaRa drop to the plot(b) By adding armature reaction(c) By reducing IaRa drop(d) All of the mentionedThe question was asked in semester exam.The above asked question is from Operating Characteristics of DC Generators in section DC Generators of Electrical Machines
Answer» The correct choice is (a) By ADDING the IARA drop to the plot Easiest EXPLANATION: Adding the ARMATURE resistance drop we can obtain the external characteristic for a dc generator.

Discussion

20.	The air gap line represents _________(a) magnetic behaviour of the air gap of the dc machine(b) magnetic behaviour of the air gap of the induction machine(c) magnetic behaviour of the iron core(d) all of the mentionedThe question was posed to me in quiz.My query is from Operating Characteristics of DC Generators topic in chapter DC Generators of Electrical Machines
Answer» CORRECT CHOICE is (a) MAGNETIC behaviour of the air gap of the dc MACHINE To explain I would say: Air gap line in the magnetization curve represents the ideal nature of the machine considering no saturation for the dc machine.

Discussion

21.	The external characteristic is plotted between ____________(a) terminal voltage vs armature current at constant excitation(b) terminal voltage vs field current at constant armature current(c) induced armature emf vs armature current at constant excitation(d) none of the mentionedThe question was posed to me in final exam.This interesting question is from Operating Characteristics of DC Generators topic in portion DC Generators of Electrical Machines
Answer» CORRECT answer is (a) TERMINAL voltage vs armature CURRENT at constant excitation For explanation: The external CHARACTERISTIC is PLOTTED between terminal voltage and armature current at fixed excitation.

Discussion

22.	Armature characteristic is also known as _________(a) regulation characteristic(b) magnetization characteristic(c) external characteristic(d) load characteristicI had been asked this question during an online interview.This is a very interesting question from Operating Characteristics of DC Generators topic in division DC Generators of Electrical Machines
Answer» The correct answer is (a) regulation characteristic Easy explanation: Armature characteristic is ALSO KNOWN as regulation characteristic. It is so called DUE to the FACT that the DIFFERENCE in the terminal voltage helps to determine the voltage deviation.

Discussion

23.	A student forgot to mark the x-y axes in his experiments but he just noted down the cause and the effect for each. How will he conclude about the armature characteristic out of the all plotted graphs?(a) By marking graph for constant terminal voltage(b) By marking graph for constant field current(c) By marking graph for constant armature current(d) By marking graph for constant speedI have been asked this question by my school principal while I was bunking the class.My query is from Operating Characteristics of DC Generators topic in portion DC Generators of Electrical Machines
Answer» The correct ANSWER is (a) By marking GRAPH for constant terminal voltage To elaborate: Armature CHARACTERISTIC is observed at constant terminal voltage for EMF vs armature CURRENT.

Discussion

24.	Choose the most inappropriate out of the following for the no-load characteristics of the dc generator.(a) It is the open circuit characteristic of the machine(b) It is magnetization characteristic of the machine(c) It is conducted on the unloaded machine(d) None of the mentionedI have been asked this question in an international level competition.My question is based upon Operating Characteristics of DC Generators topic in chapter DC Generators of Electrical Machines
Answer» The CORRECT OPTION is (d) None of the mentioned To ELABORATE: All the mentioned NATURE of the characteristics are correct.

Discussion

25.	Which of the following characteristics reveal about the magnetization nature of the machine?(a) No-load characteristics(b) Load characteristics(c) Armature characteristics(d) Both no-load and load characteristicsI got this question in class test.The doubt is from Operating Characteristics of DC Generators in portion DC Generators of Electrical Machines
Answer» Right option is (d) Both no-load and load characteristics For EXPLANATION I would say: Both no-load and load characteristics are required to PREDICT the magnetization of the machine.

Discussion

Explore topic-wise InterviewSolutions in .

Interpoles provide mmf more than armature mmf in a dc machine.(a) True(b) FalseThe question was posed to me during a job interview.Origin of the question is Rotating Amplifiers in portion DC Generators of Electrical Machines

Metadyne is _ feedback with respect to main ___(a) negative, current(b) negative, voltage(c) positive, current(d) positive, voltageThis question was posed to me in final exam.My question is from Rotating Amplifiers in section DC Generators of Electrical Machines

In rotating amplifiers, armature reaction mmf of the first stage is made to act as field flux for second stage.(a) True(b) FalseThis question was posed to me during an interview.My doubt is from Rotating Amplifiers topic in chapter DC Generators of Electrical Machines

The ordinary dc machines are not favourable as amplidynes due to _________(a) sluggish transient response(b) low stability(c) poor gain(d) high steady state errorI got this question in my homework.My enquiry is from Rotating Amplifiers topic in section DC Generators of Electrical Machines

Explore topic-wise InterviewSolutions in .

Interpoles provide mmf more than armature mmf in a dc machine.(a) True(b) FalseThe question was posed to me during a job interview.Origin of the question is Rotating Amplifiers in portion DC Generators of Electrical Machines

Metadyne is _________ feedback with respect to main ___________(a) negative, current(b) negative, voltage(c) positive, current(d) positive, voltageThis question was posed to me in final exam.My question is from Rotating Amplifiers in section DC Generators of Electrical Machines

In rotating amplifiers, armature reaction mmf of the first stage is made to act as field flux for second stage.(a) True(b) FalseThis question was posed to me during an interview.My doubt is from Rotating Amplifiers topic in chapter DC Generators of Electrical Machines

The ordinary dc machines are not favourable as amplidynes due to _________(a) sluggish transient response(b) low stability(c) poor gain(d) high steady state errorI got this question in my homework.My enquiry is from Rotating Amplifiers topic in section DC Generators of Electrical Machines

Metadyne is _ feedback with respect to main ___(a) negative, current(b) negative, voltage(c) positive, current(d) positive, voltageThis question was posed to me in final exam.My question is from Rotating Amplifiers in section DC Generators of Electrical Machines