34 + Interview Questions in Synchronous Machine Stability in Electrical Machines Page 1 InterviewSolution

1.	When an alternator is loaded suddenly the torque produced in damper is?(a) Induction motor(b) Induction generator(c) Synchronous motor(d) Synchronous generatorI got this question in an international level competition.Enquiry is from Hunting and Damper Windings topic in chapter Synchronous Machine Stability of Electrical Machines
Answer» The CORRECT OPTION is (a) Induction motor Explanation: Sudden loading will reduce the SPEED of the MACHINE and so there will be small SLIP induced in the machine, making it operate as induction motor.

Discussion

2.	When the rotor speed becomes greater than synchronous speed, which type of torque is produced in damper winding?(a) Induction generator(b) Synchronous generator(c) Reluctance motor(d) Induction motorI have been asked this question during an online interview.My query is from Hunting and Damper Windings in division Synchronous Machine Stability of Electrical Machines
Answer» Correct ANSWER is (a) INDUCTION generator The best I can explain: The slip will become NEGATIVE and it will operate in GENERATING mode.

Discussion

3.	At synchronous speed, relative speed between rotating air-gap flux and damper is?(a) zero(b) Ns(c) lesser than Ns(d) more than zeroI have been asked this question in a national level competition.I'm obligated to ask this question of Hunting and Damper Windings in portion Synchronous Machine Stability of Electrical Machines
Answer» RIGHT OPTION is (a) ZERO Easiest EXPLANATION: It is zero.

Discussion

4.	Damper winding should have ___________(a) high resistance(b) low starting torque(c) low resistance(d) low reactanceI got this question in an interview for internship.This is a very interesting question from Hunting and Damper Windings in chapter Synchronous Machine Stability of Electrical Machines
Answer» RIGHT choice is (c) low RESISTANCE For explanation I would SAY: For desired hunting, the DAMPER winding should have low resistance.

Discussion

5.	Turbo generators do not use damper winding due to ___________(a) solid steel rotor core(b) laminated armature(c) soft iron core(d) small current flow in pole shoesThis question was addressed to me in a job interview.This is a very interesting question from Hunting and Damper Windings in division Synchronous Machine Stability of Electrical Machines
Answer» Right answer is (a) solid STEEL rotor core To EXPLAIN: Because eddy CURRENT in the q-axis produce the same effect as the DAMPER in salient pole MACHINE.

Discussion

6.	The damper winding are placed in ___________(a) pole shoes(b) series with armature(c) series with field(d) rotor slotsI had been asked this question during an online interview.My question comes from Hunting and Damper Windings topic in division Synchronous Machine Stability of Electrical Machines
Answer» Correct choice is (a) POLE SHOES The EXPLANATION: The DAMPER WINDING are placed in pole shoes.

Discussion

7.	Damper windings are made of ___________(a) copper(b) iron(c) silicon(d) cast ironI have been asked this question at a job interview.My enquiry is from Hunting and Damper Windings topic in portion Synchronous Machine Stability of Electrical Machines
Answer» Correct option is (a) copper To EXPLAIN I WOULD say: They are made of copper as the CURRENT also FLOWS through them.

Discussion

8.	Using a _____ can be used to limit hunting.(a) Flywheel(b) DC Exciter(c) Large load(d) Any of the mentionedThis question was posed to me in homework.The doubt is from Hunting and Damper Windings topic in portion Synchronous Machine Stability of Electrical Machines
Answer» Correct answer is (d) Any of the MENTIONED For explanation I would SAY: Any METHOD mentioned will DIMINISH the TRANSIENTS in the machine.

Discussion

9.	Employment of damper winding will reduce hunting.(a) True(b) FalseThis question was addressed to me in an interview for job.Origin of the question is Hunting and Damper Windings topic in division Synchronous Machine Stability of Electrical Machines
Answer» RIGHT CHOICE is (a) True Explanation: Damper WINDING are MECHANICAL windings which also REDUCE the hunting.

Discussion

10.	What are the probable causes of hunting?(a) sudden change in load(b) fault in supply(c) sudden change in field current(d) all of the mentionedI had been asked this question in an interview for job.Asked question is from Hunting and Damper Windings in chapter Synchronous Machine Stability of Electrical Machines
Answer» Correct answer is (d) all of the mentioned The best explanation: Changing the load SUDDENLY, excitation or the faults will cause TRANSIENTS in the MACHINE.

Discussion

11.	Effects of hunting are/is ___________(a) mechanical stress(b) surge in current(c) rise in temperature(d) all of the mentionedI have been asked this question in semester exam.The doubt is from Hunting and Damper Windings in chapter Synchronous Machine Stability of Electrical Machines
Answer» Correct CHOICE is (d) all of the MENTIONED For explanation: HUNTING CAUSES all the mentioned effects on the synchronous machine.

Discussion

12.	The satisfactory operation of the synchronous machine means ___________(a) mechanical speed of rotor is equal to stator field speed(b) mechanical speed is zero(c) stator field is stationary(d) none of the mentionedThe question was posed to me in a national level competition.Origin of the question is Hunting and Damper Windings topic in chapter Synchronous Machine Stability of Electrical Machines
Answer» Right option is (a) MECHANICAL SPEED of rotor is equal to stator field speed For EXPLANATION: The relative speed should be ZERO between the rotor and the stator field.

Discussion

13.	The relative speed between rotor and stator field is zero. This means ___________(a) mechanical speed of rotor is equal to stator field speed(b) mechanical speed is zero(c) stator field is stationary(d) none of the mentionedThis question was addressed to me in homework.Enquiry is from Hunting and Damper Windings topic in portion Synchronous Machine Stability of Electrical Machines
Answer» Right choice is (a) MECHANICAL speed of ROTOR is equal to STATOR field speed Easy EXPLANATION: The relative speed is between the rotor and the stator field.

Discussion

14.	Which one of the following is the base reason to place field on rotor in the alternator?(a) Small power in field circuit(b) Insulation of high voltage is made easy on stator than on rotor(c) Huge power in stator(d) Large current in the statorThis question was addressed to me in unit test.I want to ask this question from Synchronous Machine Stability topic in portion Synchronous Machine Stability of Electrical Machines
Answer» Correct answer is (b) Insulation of HIGH voltage is made easy on STATOR than on rotor To explain I would say: Providing insulation BECOMES easier as the stator will be stationary.

Discussion

15.	If it is planned to bring an incoming alternator to the operating alternator in parallel, then which of the criteria can be ignored?(a) Prime mover speed(b) Voltage magnitude(c) Frequency(d) Phase sequence of the alternatorI have been asked this question by my college professor while I was bunking the class.My question is based upon Synchronous Machine Stability topic in chapter Synchronous Machine Stability of Electrical Machines
Answer» Correct OPTION is (a) PRIME MOVER speed To explain: To operate under synchronising conditions, there must be same voltage, FREQUENCY and phase sequence for the machines in the PARALLEL.

Discussion

16.	The supply voltage to an induction motor is decreased by 10%. By what percentage, approximately, will the maximum torque decrease?(a) 5%(b) 10%(c) 20%(d) 40%The question was asked by my school teacher while I was bunking the class.Query is from Synchronous Machine Stability in division Synchronous Machine Stability of Electrical Machines
Answer» Right ANSWER is (C) 20% To elaborate: TORQUE is proportional to V^2. Torque will change by TWICE percentage of the change in voltage i.e. 20%.

Discussion

17.	In a salient pole synchronous machine the air gap is least under the middle of the pole shoe and increases outwards.(a) True(b) FalseThe question was asked in semester exam.The query is from Synchronous Machine Stability topic in section Synchronous Machine Stability of Electrical Machines
Answer» CORRECT answer is (a) True Easy explanation: AIR GAP for a salient POLE structure is minimum at mid of a GIVEN pole.

Discussion

18.	Series capacitors will improve the ___________(a) SSSL(b) Transient stability(c) Hunting(d) StiffnessI have been asked this question in a job interview.I'm obligated to ask this question of Synchronous Machine Stability topic in division Synchronous Machine Stability of Electrical Machines
Answer»

Discussion

19.	Transient stability limit is less important than SSSL.(a) True(b) FalseThe question was posed to me in an interview.My doubt stems from Synchronous Machine Stability in portion Synchronous Machine Stability of Electrical Machines
Answer» Right OPTION is (b) False The best I can explain: Transient stability is more of concern due to the reason that the MACHINE may loose synchronism due to SUDDEN DISTURBANCES.

Discussion

20.	If the load angle is increased till 135°, the consequence will be ___________(a) loss of synchronism(b) no alternation of synchronism(c) increase in stability limit(d) reduction in stability limitThis question was posed to me in an interview for internship.The origin of the question is Synchronous Machine Stability topic in portion Synchronous Machine Stability of Electrical Machines
Answer» CORRECT OPTION is (a) loss of synchronism The best EXPLANATION: Because load ANGLE is more than 90°.

Discussion

21.	Which motor can conveniently operate at lagging as well as leading power factor?(a) Synchronous motor(b) Slip ring induction motor(c) Squirrel cage induction motor(d) Stepper motorI had been asked this question in examination.I would like to ask this question from Synchronizing Power and Synchronizing Torque in section Synchronous Machine Stability of Electrical Machines
Answer» Right CHOICE is (a) Synchronous MOTOR The explanation: Its the synchronous motor which can favourably operate both at leading and lagging POWER factor.

Discussion

22.	Steady state stability limit is defined as maximum power flow possible through a particular point without loss of stability when the ___________(a) power is increased gradually(b) power is increased suddenly(c) power is reduced gradually(d) power is reduces suddenlyThe question was posed to me at a job interview.This key question is from Synchronous Machine Stability in section Synchronous Machine Stability of Electrical Machines
Answer» RIGHT CHOICE is (a) POWER is increased gradually To explain I would say: Steady state analysis involves study of STABILITY at gradual changes in the machine.

Discussion

23.	Variation in the dc excitation of a synchronous motor causes variation in ___________(a) armature current and power factor(b) power factor(c) armature current(d) speedThe question was posed to me in semester exam.Question is from Synchronizing Power and Synchronizing Torque in division Synchronous Machine Stability of Electrical Machines
Answer» The correct OPTION is (a) armature current and POWER factor The EXPLANATION: Armature current and power factor both will vary by varying the dc excitation.

Discussion

24.	In a synchronous motor the back emf peak set up in the stator depends on ___________(a) rotor excitation(b) supply voltage(c) rotor speed(d) load on the motorThis question was addressed to me during an interview.The origin of the question is Synchronizing Power and Synchronizing Torque in portion Synchronous Machine Stability of Electrical Machines
Answer» RIGHT CHOICE is (a) ROTOR EXCITATION Explanation: It will DEPEND on the excitation.

Discussion

25.	The operation of a synchronous motor operating on constant excitation across infinite bus will not be stable if power angle δ?(a) exceeds internal angle θ(b) is less than θ(c) is more than θ/2(d) is less than θ/2The question was asked during an online exam.Enquiry is from Synchronizing Power and Synchronizing Torque in section Synchronous Machine Stability of Electrical Machines
Answer» Correct choice is (a) exceeds internal angle θ To EXPLAIN I would SAY: Power angle should not exceed θ, to OPERATE under NORMAL conditions.

Discussion

26.	Electromagnetic torque is present in rotating machines when ____________(a) both stator and rotor windings carry current(b) rotor windings carry current(c) stator windings carry current(d) any of the mentionedThe question was posed to me in an interview.This question is from Synchronizing Power and Synchronizing Torque in chapter Synchronous Machine Stability of Electrical Machines
Answer»

Discussion

27.	For a 4-pole 3 phase, 400V alternator has synchronizing power of 300 units. Then the synchronizing power per mechanical degree is?(a) 300(b) 1200(c) 900(d) 600This question was posed to me in semester exam.Enquiry is from Synchronizing Power and Synchronizing Torque topic in chapter Synchronous Machine Stability of Electrical Machines
Answer» Right option is (a) 300 For EXPLANATION: P(sy, MECH) = POLES* P(sy,ELE)/2 P(sy,ele) = 300 units.

Discussion

28.	Which of the following is/are used in synchronous machines to maintain mechanical stability?(a) Damper winding(b) Interpole winding(c) Compensating winding(d) Equalizer ringsI had been asked this question in an online quiz.My question comes from Synchronizing Power and Synchronizing Torque topic in section Synchronous Machine Stability of Electrical Machines
Answer» Right choice is (a) DAMPER winding To explain I WOULD say: Damper WINDINGS are the dummy windings which HELP to stablize the machine during TRANSIENT instability.

Discussion

29.	Synchronizing power is __________(a) transient in nature(b) steady state in nature(c) pulsating at small frequencies(d) constant for a machineThe question was asked during an interview.This question is from Synchronizing Power and Synchronizing Torque topic in portion Synchronous Machine Stability of Electrical Machines
Answer» CORRECT choice is (a) transient in nature The best EXPLANATION: It is transient in nature and determines stability while DISTURBANCES.

Discussion

30.	Which of the following makes synchronizing power to come to play in the machine?(a) Disturbance in power mover(b) Disturbance in field current(c) Disturbance in load(d) All of the mentionedThis question was posed to me in an online quiz.This key question is from Synchronizing Power and Synchronizing Torque in chapter Synchronous Machine Stability of Electrical Machines
Answer» CORRECT CHOICE is (a) Disturbance in POWER mover The explanation: Any disturbance will lead to transients to ARISE and so the synchronizing power.

Discussion

31.	As load angle is increased, degree of stability __________(a) reduces(b) increases(c) remains same(d) no change in stabilityI had been asked this question in quiz.Question is from Synchronizing Power and Synchronizing Torque in chapter Synchronous Machine Stability of Electrical Machines
Answer» RIGHT ANSWER is (a) reduces The EXPLANATION is: Synchronizing power = EV*cosδ/X.

Discussion

32.	An over excited synchronous machine is more stable than under excited.(a) True(b) FalseI got this question in an interview.My enquiry is from Synchronizing Power and Synchronizing Torque in section Synchronous Machine Stability of Electrical Machines
Answer» Correct OPTION is (a) True To EXPLAIN I WOULD say: Synchronizing power is directly proportional to the EXCITATION.

Discussion

33.	Large stiffness coefficient represents ____________(a) motor speed remains practically constant(b) large fluctuations due to mechanical load(c) motor speed is variable to changes(d) no such significance with speedI had been asked this question in final exam.This question is from Synchronizing Power and Synchronizing Torque in division Synchronous Machine Stability of Electrical Machines
Answer» RIGHT answer is (a) motor speed remains practically constant Best explanation: LARGE stiffness REPRESENTS the TIGHT COUPLING in the machine and more stability.

Discussion

34.	The coupling angle or load angle of a synchronous motor is defined as the space angle between __________(a) rotor and stator poles of opposite polarity(b) rotor and stator poles of same polarity(c) rotor and stator teeth(d) rotor and resultant magnetic fieldThis question was posed to me in an interview for internship.My question is based upon Synchronizing Power and Synchronizing Torque topic in section Synchronous Machine Stability of Electrical Machines
Answer»

Discussion

Explore topic-wise InterviewSolutions in .

Damper winding should have ___________(a) high resistance(b) low starting torque(c) low resistance(d) low reactanceI got this question in an interview for internship.This is a very interesting question from Hunting and Damper Windings in chapter Synchronous Machine Stability of Electrical Machines

The damper winding are placed in ___________(a) pole shoes(b) series with armature(c) series with field(d) rotor slotsI had been asked this question during an online interview.My question comes from Hunting and Damper Windings topic in division Synchronous Machine Stability of Electrical Machines

Damper windings are made of ___________(a) copper(b) iron(c) silicon(d) cast ironI have been asked this question at a job interview.My enquiry is from Hunting and Damper Windings topic in portion Synchronous Machine Stability of Electrical Machines

Using a _____ can be used to limit hunting.(a) Flywheel(b) DC Exciter(c) Large load(d) Any of the mentionedThis question was posed to me in homework.The doubt is from Hunting and Damper Windings topic in portion Synchronous Machine Stability of Electrical Machines

Employment of damper winding will reduce hunting.(a) True(b) FalseThis question was addressed to me in an interview for job.Origin of the question is Hunting and Damper Windings topic in division Synchronous Machine Stability of Electrical Machines

Effects of hunting are/is ___________(a) mechanical stress(b) surge in current(c) rise in temperature(d) all of the mentionedI have been asked this question in semester exam.The doubt is from Hunting and Damper Windings in chapter Synchronous Machine Stability of Electrical Machines

In a salient pole synchronous machine the air gap is least under the middle of the pole shoe and increases outwards.(a) True(b) FalseThe question was asked in semester exam.The query is from Synchronous Machine Stability topic in section Synchronous Machine Stability of Electrical Machines

Series capacitors will improve the ___________(a) SSSL(b) Transient stability(c) Hunting(d) StiffnessI have been asked this question in a job interview.I'm obligated to ask this question of Synchronous Machine Stability topic in division Synchronous Machine Stability of Electrical Machines

Transient stability limit is less important than SSSL.(a) True(b) FalseThe question was posed to me in an interview.My doubt stems from Synchronous Machine Stability in portion Synchronous Machine Stability of Electrical Machines

As load angle is increased, degree of stability __________(a) reduces(b) increases(c) remains same(d) no change in stabilityI had been asked this question in quiz.Question is from Synchronizing Power and Synchronizing Torque in chapter Synchronous Machine Stability of Electrical Machines

An over excited synchronous machine is more stable than under excited.(a) True(b) FalseI got this question in an interview.My enquiry is from Synchronizing Power and Synchronizing Torque in section Synchronous Machine Stability of Electrical Machines