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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. |
The static excitations mainly comprises of _______(a) brushless excitation system(b) thyrister based excitation system(c) synchronous motor excitation system(d) brushless and thyristor based excitation systemI have been asked this question in class test.My enquiry is from Excitation Systems for Synchronous Machines topic in section Synchronous Machines of Electrical Machines |
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Answer» The CORRECT option is (b) thyrister BASED excitation system |
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| 2. |
The excitation system and speed of alternator has _______(a) linear response(b) exponential response(c) rectangular hyperbola response(d) circular responseThis question was posed to me in homework.This key question is from Excitation Systems for Synchronous Machines in chapter Synchronous Machines of Electrical Machines |
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Answer» The correct OPTION is (a) LINEAR response |
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| 3. |
The zero power characteristics used in the Potier plot can be obtained by loading the alternator using ___________(a) synchronous motor(b) lamp load(c) dc motor(d) induction motorI had been asked this question in an international level competition.My enquiry is from Synchronous Machine Applications topic in section Synchronous Machines of Electrical Machines |
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Answer» Right answer is (a) synchronous motor |
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| 4. |
The power factor of an alternator under short circuit condition will be almost near ____________(a) zero lagging(b) zero leading(c) unity(d) depends on the type of the alternatorThe question was asked in an online interview.Enquiry is from Synchronous Machine Applications in section Synchronous Machines of Electrical Machines |
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| 5. |
In a 3-phase cylindrical rotor alternator the _________(a) field mmf leads air gap flux, air gap flux leads armature flux(b) field mmf leads air gap flux, air gap flux lags armature flux(c) armature mmf leads air gap flux and air gap flux leads field flux(d) armature mmf leads air gap flux and air gap flux lags field fluxThe question was asked in a job interview.I'd like to ask this question from Synchronous Machine Applications in section Synchronous Machines of Electrical Machines |
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Answer» RIGHT option is (a) field mmf leads air gap FLUX, air gap flux leads armature flux To EXPLAIN: Check the PHASOR diagram. |
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| 6. |
Synchronous motor has been preferred for driving the loads requiring high power at low speeds.(a) True(b) FalseThe question was asked in a national level competition.I would like to ask this question from Synchronous Machine Applications topic in section Synchronous Machines of Electrical Machines |
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Answer» Correct CHOICE is (a) True |
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| 7. |
The practical speed ranges for the thermal, nuclear and hydel power plants is (in rpm)?(a) 3000, 3000, 300(b) 3000, 300, 300(c) 1500, 1500, 3000(d) 1000, 500, 3000I have been asked this question during an online exam.Origin of the question is Synchronous Machine Applications in portion Synchronous Machines of Electrical Machines |
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Answer» The correct ANSWER is (a) 3000, 3000, 300 |
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| 8. |
A synchronous machine with its field winding on stator and polyphase armature winding on rotor. At steady state, its air gap field is?(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) all of the mentionedI got this question in quiz.Origin of the question is Synchronous Machine Applications in chapter Synchronous Machines of Electrical Machines |
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Answer» RIGHT CHOICE is (d) all of the mentioned To ELABORATE: All are CORRECT. |
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| 9. |
A synchronous machine with its field winding on rotor and polyphase armature winding on stator. At steady state running condition, its air gap field is?(a) stationary w.r.t. stator(b) rotating at double the Ns w.r.t. rotor(c) rotating at -Ns w.r.t. rotor(d) stationary w.r.t. rotor.The question was asked in my homework.This intriguing question comes from Synchronous Machine Applications in portion Synchronous Machines of Electrical Machines |
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Answer» RIGHT option is (d) stationary w.r.t. rotor. The BEST explanation: As the FIELD is on rotor itself, the sir GAP will be stationary w.r.t. rotor. |
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| 10. |
The condition which allows the torques to be taken care for choosing a synchronous motor is/are?(a) starting torque(b) pull-in torque(c) pull-out torque(d) all of the mentionedI had been asked this question in an interview.I need to ask this question from Synchronous Machine Applications in portion Synchronous Machines of Electrical Machines |
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Answer» Correct ANSWER is (d) all of the mentioned |
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| 11. |
We prefer induction motor over synchronous motor due to ___________(a) no requirement of dc supply(b) starting problems(c) sensitive to environment(d) all of the mentionedThe question was asked in an internship interview.This interesting question is from Synchronous Machine Applications in section Synchronous Machines of Electrical Machines |
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Answer» CORRECT ANSWER is (a) no requirement of dc supply The best I can explain: All the listed FACTORS are disadvantages for USING a synchronous MOTOR. |
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| 12. |
Synchronous compensators are mainly employed for ___________(a) compensating reactive power(b) compensating real power(c) improving power factor(d) compensating field fluxThe question was asked in an internship interview.My doubt is from Synchronous Machine Applications topic in portion Synchronous Machines of Electrical Machines |
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Answer» RIGHT CHOICE is (a) COMPENSATING reactive power The explanation: Synchronous COMPENSATOR is a source for the reactive power. |
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| 13. |
______ alternator is used in thermal stations and ______ alternator is used in hydel plants.(a) Cylindrical-rotor, salient pole(b) Salinet pole, cylindrical-rotor(c) Salient pole, Reluctance(d) Cylindrical-rotor, cylindrical-rotorI had been asked this question in an interview for job.Query is from Synchronous Machine Applications in section Synchronous Machines of Electrical Machines |
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Answer» The correct choice is (a) Cylindrical-rotor, salient pole |
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| 14. |
One of the most prominent component of base loads is ___________(a) synchronous generator(b) induction generator(c) dc series generator(d) all of the mentionedI got this question in final exam.This question is from Synchronous Machine Applications in section Synchronous Machines of Electrical Machines |
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Answer» The CORRECT option is (a) SYNCHRONOUS generator |
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| 15. |
Which of the options given will have no effect on the working of the synchronous motor if ignored?(a) It has comparable reactance(b) It requires dc excitation(c) It can not be started under no load(d) It has tendency to huntThe question was asked during an online exam.My doubt stems from Measurement of Xd and Xq in division Synchronous Machines of Electrical Machines |
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Answer» The correct ANSWER is (a) It has comparable REACTANCE |
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| 16. |
When synchronous motor is running at synchronous speed, the damper winding produces?(a) no torque(b) eddy current torque(c) damping torque(d) torque aiding the developed torqueThe question was asked in an online quiz.This interesting question is from Measurement of Xd and Xq in division Synchronous Machines of Electrical Machines |
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Answer» CORRECT option is (a) no torque To EXPLAIN I WOULD say: As the relative SPEED will be ZERO in the damper winding and the torque too. |
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| 17. |
A stationary alternator is connected to the infinite bus. It should not be connected because ____________(a) it will get short circuited(b) it will operate as induction motor(c) it will reduce bus bar voltage(d) all of the mentionedThis question was posed to me in examination.I need to ask this question from Measurement of Xd and Xq topic in division Synchronous Machines of Electrical Machines |
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Answer» Correct answer is (a) it will GET short circuited |
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| 18. |
Slip test is performed to obtain _____________(a) direct axis reactance and quadrature axis reactance(b) slip(c) positive and negative sequence reactance(d) sub transient reactanceI have been asked this question in an interview for job.This key question is from Measurement of Xd and Xq topic in chapter Synchronous Machines of Electrical Machines |
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Answer» CORRECT CHOICE is (a) direct axis REACTANCE and QUADRATURE axis reactance To explain I would say: Slip test is used to determine the direct axis and quadrature axis reactance. |
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| 19. |
A synchronous motor is operated at a bus voltage of 1.5 pu and drawing 1.0 pu at zpf leading current. Its synchronous reactance is 0.4 pu. What is the excitation emf of the motor?(a) 2.0 pu(b) 1.5 pu(c) 1.0 pu(d) 1.1 puThe question was posed to me in unit test.This intriguing question comes from Measurement of Xd and Xq in chapter Synchronous Machines of Electrical Machines |
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Answer» Right CHOICE is (d) 1.1 pu |
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| 20. |
If the excitation of a 3-phase alternator operating on infinite bus bars is changed, which one of the following will get affected?(a) Active real power of machine(b) Reactive power of machine(c) Terminal voltage of machine(d) Frequency of machineThe question was posed to me during an interview.The above asked question is from Measurement of Xd and Xq in portion Synchronous Machines of Electrical Machines |
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Answer» Correct ANSWER is (B) Reactive power of MACHINE |
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| 21. |
In which one of the following is reluctance power developed?(a) Salient pole alternator(b) Non-salient pole alternator(c) Squirrel cage rotor type induction motor(d) All of the mentionedThis question was posed to me in class test.The doubt is from Measurement of Xd and Xq topic in portion Synchronous Machines of Electrical Machines |
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Answer» RIGHT answer is (a) Salient POLE alternator The EXPLANATION is: Because there is VARIABLE air gap due to SALIENCY of the poles. |
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| 22. |
An alternator with higher value of SCR has ____________(a) better voltage regulation and higher stability limit(b) poor voltage regulation and lower stability limit(c) poor voltage regulation and higher stability limit(d) better voltage regulation and lower stability limitI had been asked this question by my school teacher while I was bunking the class.Asked question is from Measurement of Xd and Xq in section Synchronous Machines of Electrical Machines |
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Answer» Right answer is (a) BETTER voltage regulation and higher STABILITY limit |
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| 23. |
When a 3–phase alternator is suddenly short–circuited at its terminals, the initial value of the short–circuit current is limited by which one of the following?(a) x”d(b) x’d(c) xs(d) Sum of x”d, x’d and xsI got this question in final exam.I'd like to ask this question from Measurement of Xd and Xq topic in portion Synchronous Machines of Electrical Machines |
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Answer» Right choice is (a) x”d |
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| 24. |
If a cylindrical rotor synchronous generator, is connected to the IBB, if the field is made zero, then it behaves as ____________(a) induction generator for a short time(b) induction motor(c) synchronous motor(d) synchronous generatorThe question was posed to me by my college director while I was bunking the class.This question is from Measurement of Xd and Xq topic in portion Synchronous Machines of Electrical Machines |
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Answer» RIGHT option is (b) INDUCTION MOTOR To EXPLAIN I would say: It will ACT as induction motor as there will be difference in the speed. |
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| 25. |
A 3 Phase 400, 100 MVA alternator is connected to infinite bus bar. If the mechanical power input is more than the maximum reluctance power, the reluctance generator will lose synchronizm if ____________(a) field is open circuited(b) field is short-circuited(c) load is removed(d) damper is removedThis question was addressed to me in an online quiz.Question is taken from Measurement of Xd and Xq topic in portion Synchronous Machines of Electrical Machines |
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Answer» Right OPTION is (a) FIELD is open circuited |
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| 26. |
Slip test must be conducted at low armature terminal voltage. This is due to ____________(a) avoiding error due to large slip(b) avoiding error due to small slip(c) avoiding heating(d) all of the mentionedThe question was posed to me in my homework.Enquiry is from Measurement of Xd and Xq in division Synchronous Machines of Electrical Machines |
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| 27. |
The slip test is used to determine ____________(a) Xq(b) Xd(c) Xd and Xq(d) None of the mentionedThe question was asked in an online interview.This question is from Measurement of Xd and Xq topic in chapter Synchronous Machines of Electrical Machines |
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Answer» Correct option is (a) Xq |
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| 28. |
The d-axis reactance is determined by ______________(a) OCC & SCC(b) OCC(c) Slip test(d) SCCI had been asked this question during an interview.My doubt is from Measurement of Xd and Xq topic in portion Synchronous Machines of Electrical Machines |
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Answer» RIGHT answer is (a) OCC & SCC The explanation: Both the OCC as well as short CIRCUIT TEST are used to calculate the d-axis reactance. |
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| 29. |
In a synchronous machine, hunting is predominantly damped by __________(a) mechanical losses in the rotor(b) iron losses in rotor(c) copper losses of stator(d) copper losses of rotorThe question was posed to me in unit test.I need to ask this question from Power Angle Characteristics of Synchronous Machines in division Synchronous Machines of Electrical Machines |
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Answer» CORRECT answer is (d) COPPER LOSSES of rotor To EXPLAIN I would say: The hunting is damped by the copper losses in the rotor. |
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| 30. |
A synchronous machine which is synchronized with an infinite bus. If it is desired to obtain a condition when the machine delivers the real power to the IBB without changing the field excitation, then __________(a) reactive power will be consumed by the machine(b) reactive power will be delivered by the machine(c) no reactive power flow will take place(d) none of the mentionedThis question was posed to me in an internship interview.Question is taken from Power Angle Characteristics of Synchronous Machines in chapter Synchronous Machines of Electrical Machines |
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Answer» The correct CHOICE is (a) REACTIVE power will be consumed by the machine |
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| 31. |
For the effective electromechanical energy conversion in the device, the developed torque depends upon __________(a) stator fieldand torque angle(b) stator field and rotor field(c) stator field and rotor field and the torque angle(d) stator fieldonlyThis question was posed to me in unit test.My question is from Power Angle Characteristics of Synchronous Machines in portion Synchronous Machines of Electrical Machines |
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Answer» RIGHT CHOICE is (C) STATOR field and rotor field and the torque angle Explanation: T α E*V*sinδ. |
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| 32. |
The phasor addition of stator and rotor mmfs in a cylindrical rotor synchronous machine, is possible because __________(a) mmfs are rotating in opposite direction(b) mmfs are rotating in same direction at different speeds(c) mmfs are stationary with respect to each other(d) one mmf is stationary and the other mmf is rotatingI have been asked this question in a job interview.The query is from Power Angle Characteristics of Synchronous Machines in division Synchronous Machines of Electrical Machines |
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Answer» Right answer is (C) MMFS are stationary with respect to each other |
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| 33. |
A synchronous generator is operatingwith a Ef=1.40pu. This machine havingXs of 1.2pu, is delivering a synchronous power of 0.5pu to the bus. If the prime-mover torque is increased by 1%, by how much will the synchronous power P change?(a) 1%(b) 10%(c) -1%(d) 4%The question was posed to me in an online interview.Question is from Power Angle Characteristics of Synchronous Machines topic in division Synchronous Machines of Electrical Machines |
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Answer» The correct choice is (a) 1% |
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| 34. |
A synchronous generator is running over excited with a Ef=1.40pu. This machine, with a synchronous reactance of 1.2pu, is delivering a synchronous power of 0.5pu to the bus. If the prime-mover torque is increased by 1%, by how much will the reactive power, Q change?(a) -0.475 %(b) 0.475%(c) 4.75%(d) -4.75%I got this question at a job interview.I'd like to ask this question from Power Angle Characteristics of Synchronous Machines in chapter Synchronous Machines of Electrical Machines |
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Answer» RIGHT OPTION is (a) -0.475 % For EXPLANATION I WOULD SAY: dQ/dδ = -EVsinδ/X dP/dδ = EVcosδ/X dQ/dP = -tanδ = -tan25.4 = -0.475 dQ = -0.475%. |
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| 35. |
If the synchronous machine is connected to an infinite bus of constant voltage Vt, through a transformed, a transmission line of reactance ‘X’. Then power for a cylindrical machine is?(a) P = (Ef*Vt sinδ)/(Xs + X)(b) P = (Ef*Ef sin2δ)/(Xs + X)(c) P = (Ef*Vt sinδ)/(Xs – X)(d) P = (Vt*Vt sinδ)/(Xs + X)The question was posed to me during a job interview.Question is taken from Power Angle Characteristics of Synchronous Machines in portion Synchronous Machines of Electrical Machines |
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Answer» Right option is (a) P = (Ef*Vt sinδ)/(Xs + X) |
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| 36. |
Maximum power in cylinder rotor alternator occurs at load angle of __________(a) 90 degree(b) 45 degree(c) less than 90 degree(d) 180 degreeThis question was posed to me at a job interview.My question is from Power Angle Characteristics of Synchronous Machines topic in chapter Synchronous Machines of Electrical Machines |
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Answer» The CORRECT choice is (a) 90 degree |
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| 37. |
A cylindrical rotor alternator can also run as reluctance motor.(a) True(b) FalseThis question was posed to me at a job interview.This is a very interesting question from Power Angle Characteristics of Synchronous Machines topic in division Synchronous Machines of Electrical Machines |
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Answer» Right OPTION is (B) False |
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| 38. |
A 3 phase 400V cylindrical rotor is running at 1500rpm. Suddenly the field excitation zero. Then the net reluctance power is?(a) 0(b) sin 2d(c) cos d(d) cos 2dI got this question in class test.I'm obligated to ask this question of Power Angle Characteristics of Synchronous Machines topic in chapter Synchronous Machines of Electrical Machines |
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Answer» The CORRECT ANSWER is (a) 0 |
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| 39. |
A 3 phase 400V salient pole alternator is running at no-load. Suddenly the excitation is removed then the net power in the machine is proportional to _____________(a) sin 2d(b) sin d(c) cos 2d(d) 0This question was posed to me in quiz.I'm obligated to ask this question of Power Angle Characteristics of Synchronous Machines topic in division Synchronous Machines of Electrical Machines |
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Answer» The correct option is (a) sin 2d |
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| 40. |
For a 3 phase 400V alternator having 0.5pu of synchronous reactance and its excitation voltage of 1.2pu and Vt of 1pu. Then the power delivered to the infinite bus is?(a) 2.4pu(b) 4.8pu(c) 1.44pu(d) 1puI had been asked this question in an internship interview.My question comes from Power Angle Characteristics of Synchronous Machines in section Synchronous Machines of Electrical Machines |
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Answer» RIGHT ANSWER is (a) 2.4pu The EXPLANATION is: P = EV/X = 1.2*1/0.5 = 2.4 PU. |
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| 41. |
For a 3 phase 400V alternator supplying a load of 0.8 pf lagging at an armature current of 1.1pu. The power delivered to load is?(a) 0.88pu(b) 0.8pu(c) 0.66pu(d) 1.375puThe question was posed to me in a national level competition.My doubt is from Power Angle Characteristics of Synchronous Machines in portion Synchronous Machines of Electrical Machines |
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Answer» The correct CHOICE is (C) 0.66pu |
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| 42. |
For obtaining maximum current when we conduct the ‘Slip Test’ on a synchronous machine, its armature field will align along __________(a) d-axis(b) q-axis(c) 45° to d-axis(d) 45° to q-axisI had been asked this question in an interview for job.This intriguing question comes from Two Reaction Theory of Salient Pole Machines topic in chapter Synchronous Machines of Electrical Machines |
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Answer» Right answer is (b) q-axis |
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| 43. |
for a synchronous motor, its power factor __________(a) improves with increase in excitation and may even become leading at higher excitations(b) is independent of its excitation(c) decreases with increase in excitation(d) increases with loading for a given excitationThis question was addressed to me in an internship interview.Question is taken from Two Reaction Theory of Salient Pole Machines topic in division Synchronous Machines of Electrical Machines |
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Answer» Right option is (a) improves with increase in EXCITATION and may even BECOME LEADING at higher excitations |
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| 44. |
While finding the parameters for an alternator, its voltage regulation is found to be negative. Then the load connected to it must be __________(a) capacitive nature(b) inductive nature(c) resistive nature(d) can not be judged based on voltage regulationThe question was asked in an interview.This interesting question is from Two Reaction Theory of Salient Pole Machines topic in section Synchronous Machines of Electrical Machines |
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Answer» Correct answer is (a) capacitive nature |
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| 45. |
For a 400 V, 3 phase alternator gives an open circuit voltage of 380V and armature current of 38A at a field current of 20A. Then the synchronous reactance of the machine is?(a) 10 ohm(b) 38/√3(c) 19 ohm(d) 1.9 ohmThe question was asked in homework.I need to ask this question from Two Reaction Theory of Salient Pole Machines topic in portion Synchronous Machines of Electrical Machines |
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Answer» CORRECT choice is (a) 10 ohm Explanation: Z = Vt/Ia at the same FIELD CURRENT = 380/38 = 38 ohms. |
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| 46. |
Mark the correct expression for alternator working at a lagging power factor.(a) tanψ = (IaXq – Vtsinθ)/(Vtcosθ – Ia*ra)(b) tanψ = (IaXq + Vtsinθ)/(Vtcosθ – Ia*ra)(c) tanψ = (IaXq + Vtsinθ)/(Vtcosθ + Ia*ra)(d) tanψ = (IaXq – Vtsecθ)/(Vtcosecθ – Ia*ra)This question was addressed to me at a job interview.Origin of the question is Two Reaction Theory of Salient Pole Machines topic in portion Synchronous Machines of Electrical Machines |
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Answer» Correct answer is (a) tanψ = (IaXq – Vtsinθ)/(Vtcosθ – Ia*ra) |
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| 47. |
A salient pole synchronous generator has following per-unit parameter Xd = 1.2 pu, Xq = 0.8pu, ra = 0.25 ohms. Then the armature current at 0.8 lagging is?(a) 1,-36.9°(b) 1, 36.9°(c) 1, 73°(d) 1, 27°I have been asked this question in final exam.This intriguing question originated from Two Reaction Theory of Salient Pole Machines in chapter Synchronous Machines of Electrical Machines |
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Answer» RIGHT answer is (a) 1,-36.9° For explanation: In PER unit, armature current will be lagging by 36.9°. |
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| 48. |
If the internal power factor angle of synchronous motor is 30 degree. Then the direct-axis component of the armature current will be __________(a) 0.5 pu(b) 0.866 pu(c) 1.73 pu(d) 0The question was asked in a job interview.I'm obligated to ask this question of Two Reaction Theory of Salient Pole Machines topic in section Synchronous Machines of Electrical Machines |
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Answer» RIGHT ANSWER is (a) 0.5 pu Explanation: Id = IA*sinψ = 1*sin30 = 0.5 pu. |
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| 49. |
If the internal pf angle of a synchronous motor is 30 degree. Then the quadrature axis component of the armature is?(a) 0.866 pu(b) 0.5 pu(c) 1.73 pu(d) 0I had been asked this question during an online exam.My query is from Two Reaction Theory of Salient Pole Machines in portion Synchronous Machines of Electrical Machines |
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Answer» CORRECT option is (a) 0.866 pu Easy EXPLANATION: Id = Ia*cosψ = 1*COS(3*0). |
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| 50. |
In salient-pole machines, the armature mmf cannot be accounted for by introducing one equivalent reactance due to __________(a) non-uniform airgap(b) variable resistance(c) non-uniform air gap(d) any of the mentionedI had been asked this question in a job interview.My enquiry is from Two Reaction Theory of Salient Pole Machines in portion Synchronous Machines of Electrical Machines |
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Answer» The correct option is (a) non-uniform airgap |
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