InterviewSolution
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InterviewSolution
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. |
A synchronous machine is operating at constant load and at unity power factor. If its excitation is increased, then it operates as ___________(a) generator at lagging p.f(b) motor at lagging p.f(c) absorber of reactive power(d) generator at leading p.fThis question was posed to me in homework.I want to ask this question from Starting of Synchronous Motors topic in section Synchronous Motors of Electrical Machines |
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Answer» The correct option is (a) GENERATOR at LAGGING p.f |
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| 2. |
Power factor of a synchronous motor varies when the ___________(a) applied voltage is varied(b) load is changed(c) supply frequency and field excitation is changed(d) all of the mentionedThis question was addressed to me by my college professor while I was bunking the class.Enquiry is from Starting of Synchronous Motors in section Synchronous Motors of Electrical Machines |
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Answer» Correct choice is (a) applied voltage is varied |
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| 3. |
A synchronous machine is operating at constant load and at unity power factor. If its excitation is increased and then it operates as ___________(a) motor at leading p.f(b) motor at lagging p.f(c) absorber of reactive power(d) generator at leading p.fThis question was posed to me in exam.My question comes from Starting of Synchronous Motors in chapter Synchronous Motors of Electrical Machines |
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Answer» CORRECT ANSWER is (a) motor at leading p.f The best I can explain: It will OPERATE at leading p.f. if it was inmotoring mode. |
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| 4. |
The reactive power output of a synchronous generator is limited by ___________(a) armature current and field current(b) field current and load angle(c) load angle and prime mover input(d) armature current and prime mover inputThe question was posed to me during an interview.My doubt is from Starting of Synchronous Motors topic in chapter Synchronous Motors of Electrical Machines |
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Answer» RIGHT OPTION is (a) armature current and field current To ELABORATE: Q=f(IA,If). |
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| 5. |
A 3-phase, 400V, synchronous motor is providing load at 0.8 p.f. lagging. If the field current of the motor is continuously increased, then the _____________(a) power factor increases and then decreases(b) power factor is not affected(c) power factor decreases upto a certain value of field current and then increases(d) power facor increases simplyI got this question in an interview for job.This intriguing question originated from Starting of Synchronous Motors in section Synchronous Motors of Electrical Machines |
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Answer» Right answer is (a) power FACTOR increases and then decreases |
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| 6. |
In a 3-phase cylindrical-rotor alternator, synchronous reactance is sum of mutual and leakage reactance.(a) True(b) FalseThe question was posed to me during an online interview.This intriguing question originated from Starting of Synchronous Motors topic in division Synchronous Motors of Electrical Machines |
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Answer» Correct OPTION is (b) False |
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| 7. |
A synchronous machine with its field winding on stator and polyphase armature winding on rotor. At steady state, which of the following is not true for its air gap field?(a) stationary w.r.t. stator(b) rotating at double the speed Ns w.r.t. rotor(c) rotating in direction opposite to rotor(d) rotating at Ns w.r.t. rotorThis question was posed to me during a job interview.This question is from Starting of Synchronous Motors topic in portion Synchronous Motors of Electrical Machines |
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Answer» CORRECT choice is (d) ROTATING at Ns w.r.t. rotor To EXPLAIN I WOULD say: The air gap will not be at synchronous SPEED w.r.t. rotor. |
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| 8. |
These days alternators are designed to have larger air gaps for __________(a) stable parallel operation(b) higher stability limit(c) sinusoidal mmf distribution(d) all of the mentionedThe question was posed to me during an interview for a job.The question is from Starting of Synchronous Motors in section Synchronous Motors of Electrical Machines |
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Answer» Right choice is (a) stable PARALLEL operation |
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| 9. |
Rating of the dc motor to be used in the starting of SM, should be higher than the synchronous motor.(a) True(b) FalseI got this question in quiz.My question is from Starting of Synchronous Motors topic in division Synchronous Motors of Electrical Machines |
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Answer» The CORRECT option is (b) False |
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| 10. |
Auxiliary method of starting is not possib1e due to the fact that ____________(a) it can not be started under load(b) it can be only started under load(c) it is less efficient(d) all of the mentionedI have been asked this question during an online exam.I would like to ask this question from Starting of Synchronous Motors topic in section Synchronous Motors of Electrical Machines |
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Answer» The correct choice is (a) it can not be started under load |
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| 11. |
Synchronous motors are ___________(a) not self starting(b) self starting(c) single excited(d) none of the mentionedThe question was posed to me in final exam.My enquiry is from Starting of Synchronous Motors in portion Synchronous Motors of Electrical Machines |
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Answer» CORRECT answer is (a) not self starting To EXPLAIN: The average torque developed in the synchronous MOTOR is ZERO. |
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| 12. |
Synchronous compensators are ________(a) over excited synchronous motor with no mechanical load(b) over excited synchronous motor with mechanical load(c) under excited synchronous motor with no mechanical load(d) normally excited synchronous motor with no mechanical loadThis question was addressed to me at a job interview.My question is taken from Power Factor Correction by Synchronous Motors in section Synchronous Motors of Electrical Machines |
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Answer» The correct ANSWER is (a) over excited synchronous motor with no mechanical LOAD |
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| 13. |
For a power system having induction motor loads, an overexcited synchronous motor is also attached. The induction motor will now operate at ________(a) lagging(b) leading(c) reduced power factor(d) increased power factorThis question was posed to me in a job interview.My question is taken from Power Factor Correction by Synchronous Motors topic in chapter Synchronous Motors of Electrical Machines |
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Answer» Right option is (a) lagging |
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| 14. |
For a power system having induction motor loads, an overexcited synchronous motor is also attached. Then the over all power factor?(a) improves(b) degrades(c) becomes upf(d) remains sameI had been asked this question by my college professor while I was bunking the class.Origin of the question is Power Factor Correction by Synchronous Motors topic in portion Synchronous Motors of Electrical Machines |
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Answer» Right answer is (a) IMPROVES |
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| 15. |
When the excitation voltage is increased from 1 to 1.3 pu of a 3-phase synchronous motor. Then load angle for the constant power operation ________(a) must be decreased(b) can also be increased(c) increased(d) decreasedI have been asked this question by my college professor while I was bunking the class.I'm obligated to ask this question of Power Factor Correction by Synchronous Motors topic in section Synchronous Motors of Electrical Machines |
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Answer» The correct ANSWER is (a) must be decreased |
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| 16. |
The inverted V plots is plotted between ________(a) power factor vs field current for constant shaft load(b) field current vs power factor for variable shaft load(c) armature current vs field current(d) terminal voltage vs power factorI have been asked this question in an internship interview.This intriguing question originated from Power Factor Correction by Synchronous Motors in portion Synchronous Motors of Electrical Machines |
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Answer» Right OPTION is (a) power factor vs field CURRENT for CONSTANT shaft load |
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| 17. |
When a constant power output is desired to maintain ________(a) Ef*sinδ and Ia*cosθ are to be maintained constant(b) Ef*sinδ is be maintained constant(c) Ia*cosθ is to be maintained constant(d) Ef*sinδ and Ia*sinθ are to be maintained constantThe question was posed to me in exam.This intriguing question originated from Power Factor Correction by Synchronous Motors topic in portion Synchronous Motors of Electrical Machines |
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Answer» The correct option is (a) Ef*sinδ and Ia*cosθ are to be maintained constant |
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| 18. |
The excess flux in synchronous motor is neutralized by ________(a) armature winding by drawing demagnetizing component of the current from ac supply(b) armature winding by drawing magnetizing component of the current from ac supply(c) fieldwinding by drawing demagnetizing component of the current from dc supply(d) field winding by drawing magnetizing component of the current from dc supplyThis question was addressed to me in an interview for job.Enquiry is from Power Factor Correction by Synchronous Motors topic in division Synchronous Motors of Electrical Machines |
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Answer» Right option is (a) ARMATURE winding by drawing demagnetizing component of the current from ac supply |
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| 19. |
We can increase the torque of a reluctance synchronous motor if we __________(a) Increase reluctance of the magnetic circuit along the direct axis(b) Decrease the reluctance of the magnetic circuit along the quadrature axis(c) Increase the ratio of the quadrature axis reluctance to direct axis reluctance(d) Decrease the ratio of quadrature axis reluctance to direct axis reluctanceI have been asked this question in unit test.Question is from Synchronous Motor Phasor Diagram in chapter Synchronous Motors of Electrical Machines |
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Answer» Correct choice is (c) Increase the RATIO of the quadrature AXIS RELUCTANCE to direct axis reluctance |
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| 20. |
Switched reluctance motors are basically __________(a) salient pole synchronous motor but without excitation winding(b) stepper motor with salient poles(c) synchronous motor with salient poles on stator and rotor(d) stepper motor with closed loop control and with rotor position sensorI got this question in homework.My question is based upon Synchronous Motor Phasor Diagram in chapter Synchronous Motors of Electrical Machines |
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Answer» Right CHOICE is (d) stepper MOTOR with closed loop control and with rotor POSITION sensor |
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| 21. |
The operating point for an over excited alternator working near zpf lagging power factor gives ‘A’ as the operating point. Then if the same machine is working as an over excited synchronous motor will give same operating point at __________(a) zpf leading(b) zpf lagging(c) upf(d) there will never be the same operating point for the machine as motor as well as generatorThis question was addressed to me in an international level competition.I need to ask this question from Synchronous Motor Phasor Diagram topic in division Synchronous Motors of Electrical Machines |
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Answer» RIGHT answer is (a) zpf LEADING Best explanation: Yes, by MAKING it from lag to leading POWER factor, a synchronous machine can have same operating POINT for the alternator as well as synchronous motor. |
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| 22. |
In the figure below, the point ‘F’ corresponds to _______ which can be obtained by ________(a) field current required to circulate short circuit current, SCC(b) field current required to circulate full load current, SCC(c) mmf required to cancel the hysteresis losses, SCC(d) mmf required to compensate the leakage reactances, SCCI have been asked this question in an international level competition.My query is from Synchronous Motor Phasor Diagram in chapter Synchronous Motors of Electrical Machines |
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Answer» The CORRECT answer is (a) field current REQUIRED to CIRCULATE SHORT circuit current, SCC |
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| 23. |
From the figure shown below for the OCC and SCC of a three phase alternator, the point ‘L’ corresponds to _______ and the point ‘A’ can be obtained by _____ the alternator.(a) terminal voltage, over exciting(b) excitation voltage, over exciting(c) terminal voltage, under exciting(d) excitation voltage, under excitingThis question was addressed to me in semester exam.Asked question is from Synchronous Motor Phasor Diagram in section Synchronous Motors of Electrical Machines |
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| 24. |
The zero power factor of an alternator can be obtained by _________ at rated Ia.(a) over exciting(b) conducting short circuit of secondary terminals(c) under excitation(d) running as reluctance motorThe question was posed to me in an online quiz.The doubt is from Synchronous Motor Phasor Diagram in portion Synchronous Motors of Electrical Machines |
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Answer» The CORRECT option is (a) over exciting |
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| 25. |
Synchronous motor delivers lagging power at __________(a) leading pf(b) lagging pf(c) zero pf(d) unity pfThis question was addressed to me by my school teacher while I was bunking the class.This question is from Synchronous Motor Phasor Diagram in portion Synchronous Motors of Electrical Machines |
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Answer» RIGHT answer is (a) LEADING pf The EXPLANATION is: As Q < 0 for SYNCHRONOUS motor at leading pf. |
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| 26. |
The voltage equation of synchronous motor is?(a) Ef = Vt + Ia*(ra+jXa)(b) Ef = Vt – Ia*(ra+jXa)(c) Ef = Vt + Ia*(ra-jXa)(d) Ef = Vt – Ia*(ra-jXa)I have been asked this question in an internship interview.I want to ask this question from Synchronous Motor Phasor Diagram topic in section Synchronous Motors of Electrical Machines |
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Answer» The CORRECT OPTION is (a) Ef = Vt + Ia*(ra+jXa) |
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