124 + Interview Questions in Transformers in Electrical Machines Page 2 InterviewSolution

51.	Two single phase transformers A and B are operating in parallel having same impedance. But the x/r ratio of them are not equal. Then total kVA output of the output will be ___________(a) less than sum of kVA of A and B(b) more than sum of kVA of A and B(c) equal to sum of kVA of A and B(d) any of the mentionedThe question was asked in an interview.This intriguing question comes from Parallel Operation of Single Phase Transformers topic in division Transformers of Electrical Machines
Answer» The correct choice is (a) less than sum of kVA of A and B For EXPLANATION I WOULD say: As the leakage REACTANCES are not same for both the transformers, then IA < I2 and Ib < I/2. So the kVA will ALSO be less than sum of individual A and B.

Discussion

52.	A 2000/1000/500 three winding transformer is to be used as auto transformer with supply of 3000 V. Two loads of 1050 kVA at 3500V and other one at 180 kVA at 1000V. The total kVA supplied will be?(a) 1230 kVA(b) 1440 kVA(c) 1680 kVA(d) 1150 kVAThe question was posed to me in final exam.Asked question is from Parallel Operation of Single Phase Transformers in chapter Transformers of Electrical Machines
Answer» RIGHT option is (a) 1230 KVA The best EXPLANATION: Total kVA = 1050+180 = 1230 kVA.

Discussion

53.	Which if the conditions is must be fulfilled for satisfactory parallel operation of transformers?(a) Same voltage ratio(b) Leakage impedances should be inversely proportional to kVA of the transformer(c) Same pu impedance(d) Correct polarityThis question was addressed to me in an interview for job.My question is taken from Parallel Operation of Single Phase Transformers in section Transformers of Electrical Machines
Answer» CORRECT OPTION is (d) Correct polarity Easiest EXPLANATION: out of all, polarity must be correct for the CONNECTED transformers.

Discussion

54.	Transformer operating in parallel will share a common load in the best possible manner if ____________(a) leakage impedances are proportional to their kVA rating(b) pu leakage impedances are equal(c) leakage impedances are equal(d) any of the mentionedThe question was asked in unit test.My question comes from Parallel Operation of Single Phase Transformers in division Transformers of Electrical Machines
Answer» Right CHOICE is (b) pu leakage IMPEDANCES are equal Best EXPLANATION: For same pu leakage IMPEDANCE, parallel operation of transformers become feasible.

Discussion

55.	The efficiency of a transformer can be calculated accurately from ___________(a) Open circuit test, Short circuit test(b) Open circuit test, Short circuit test, Sumpner’s test(c) Sumpner’s test(d) load testThe question was asked by my college director while I was bunking the class.I'm obligated to ask this question of Transformer Losses and Efficiency topic in chapter Transformers of Electrical Machines
Answer» Right ANSWER is (a) Open circuit test, Short circuit test The best I can explain: OC and SC tests together can help to ESTIMATE the most CORRECT value of the EFFICIENCY for the given transformer.

Discussion

56.	From the above graph of the core losses per cycle is, the eddy losses per phase for a transformer at a operating frequency of 40 Hz is?(a) 15 W(b) 20W(c) 35W(d) 32WThe question was asked at a job interview.This intriguing question originated from Transformer Losses and Efficiency in division Transformers of Electrical Machines
Answer» The correct choice is (a) 15 W The EXPLANATION: PE = k2f^2; USING the slope of the LINE, (k2)50 = 0.8 – 0.5 = 0.3 (k2) = 0.006 Pe = 50500.006 = 15 W.

Discussion

57.	From the above graph of the core losses per cycle is, the hysteresis losses per phase for a transformer at a operating frequency of 40 Hz is?(a) 20W(b) 30W(c) 80W(d) 32WI had been asked this question during an internship interview.My question is based upon Transformer Losses and Efficiency topic in chapter Transformers of Electrical Machines
Answer» CORRECT OPTION is (a) 20W Easiest EXPLANATION: Ph = K1f = 0.540 = 20W.

Discussion

58.	The full load voltage drop in a 1-phase transformer is 2% and 4% respectively due to resistance and leakage reactance. Then the voltage drop is zero at __________(a) 0.45 lagging(b) 0.45 leading(c) 0.9 lagging(d) 0.9 leadingThis question was addressed to me during an interview for a job.My question is from Transformer Losses and Efficiency topic in chapter Transformers of Electrical Machines
Answer» The correct answer is (C) 0.9 lagging Easiest EXPLANATION: Z = 4.47; cosθ = PERCENTAGE x/percentage z = 4/4.47 = 0.89.

Discussion

59.	The full load voltage drop in a 1-phase transformer is 2% and 4% respectively due to resistance and leakage reactance. Then the voltage drop is maximum at __________(a) 0.45 lagging(b) 0.45 leading(c) 0.9 lagging(d) 0.9 leadingI got this question in class test.The above asked question is from Transformer Losses and Efficiency in portion Transformers of Electrical Machines
Answer» The CORRECT CHOICE is (a) 0.45 lagging To elaborate: Z = 4.47; cosθ = percentage r/percentage z = 2/(4.47) = 0.45.

Discussion

60.	The load current at which maximum efficiency occurs is independent of the load power factor.(a) True(b) FalseI had been asked this question in an interview.Origin of the question is Transformer Losses and Efficiency topic in chapter Transformers of Electrical Machines
Answer» Correct answer is (b) False Explanation: Because Core LOSSES and the EFFECTIVE resistance of the SECONDARY are ALMOST UNAFFECTED by load p.f.

Discussion

61.	The efficiency of a 20 KVA, 2000/200 V, single phase transformer at unity pf is 98%. The given total losses at full load is 200 W. The pu resistance is?(a) 0.01(b) 0.1(c) 1.0(d) 0.0196The question was posed to me in class test.My question is from Transformer Losses and Efficiency in portion Transformers of Electrical Machines
Answer» The CORRECT CHOICE is (a) 0.01 Best explanation: PU resistance = OHMIC losses/KVA = 200/20000 = 0.01 pu.

Discussion

62.	The efficiency of a 20 KVA, 2000/200 V, single phase transformer at unity pf is 98%. The total losses at this condition is?(a) 408W(b) 4.08kW(c) 204W(d) 2.04kWI had been asked this question during an interview for a job.The origin of the question is Transformer Losses and Efficiency topic in chapter Transformers of Electrical Machines
Answer» CORRECT option is (a) 408W For explanation: EFFICIENCY = 1-(losses/input) = 1-(losses/output+losses) 0.98 = 1-(Losses/20000+losses) Losses = 408 W.

Discussion

63.	It is possible to attain maximum efficiency in a transformer when the ______(a) core losses are equal to rated full load copper losses(b) core losses are more than rated full load copper losses(c) core losses and full load copper losses are constant(d) copper loss also becomes constantI have been asked this question in examination.This interesting question is from Transformer Losses and Efficiency topic in section Transformers of Electrical Machines
Answer» RIGHT OPTION is (a) core losses are equal to rated full load COPPER losses Easy EXPLANATION: Maximum efficiency is ACHIEVED at the condition when fixed core losses and copper losses at rated condition are equal.

Discussion

64.	Mutual flux ______ at the lagging loading and it _____ at the leading power factor.(a) decreases, increases(b) increases, increases(c) decreases, decreases(d) increases, decreasesI have been asked this question by my school principal while I was bunking the class.Query is from Transformer Losses and Efficiency in division Transformers of Electrical Machines
Answer» The CORRECT choice is (a) DECREASES, INCREASES Explanation: The MUTUAL FLUX falls when the transformer is working at lagging p.f. and it increases at leading p.f.

Discussion

65.	Which of the following mentioned losses occur in a transformer?(a) Hysteresis losses; Eddy current losses; Dielectric losses; Stray load losses(b) Hysteresis losses; Eddy current losses;(c) Dielectric losses; Stray load losses(d) Hysteresis losses; Eddy current losses; Stray load lossesI have been asked this question during an interview.My doubt is from Transformer Losses and Efficiency in portion Transformers of Electrical Machines
Answer» Correct answer is (a) HYSTERESIS losses; Eddy CURRENT losses; Dielectric losses; Stray load losses The best EXPLANATION: Hysteresis losses-DUE to magnetic material; Eddy current losses-on the core area; Dielectric losses- due to insulation material; Stray load losses- due to leakage through the parts of the transformer.

Discussion

66.	If the pu impedance of a single phase transformer is 0.01+j0.05, then its regulation at p.f. of 0.8 leading will be?(a) 3.8%(b) 2.2%(c) -3.8%(d) -2.2%I have been asked this question by my college director while I was bunking the class.This intriguing question originated from Voltage Regulation of Transformer in section Transformers of Electrical Machines
Answer» The correct option is (d) -2.2% Easiest EXPLANATION: V.R. = (r(pu)cosθ-x(pu)sinθ)100 % = (0.010.8 – 0.050.6)100 = -2.2%.

Discussion

67.	If the pu impedance of a single phase transformer is 0.01+j0.05, then its regulation at p.f. of 0.8 lagging will be?(a) 3.8%(b) 2.2%(c) -3.8%(d) -2.2%The question was posed to me during an interview for a job.The question is from Voltage Regulation of Transformer in portion Transformers of Electrical Machines
Answer» The correct CHOICE is (a) 3.8% EXPLANATION: V.R. = (r(PU)cosθ+x(pu)sinθ)100 % = (0.010.8 + 0.050.6)100 = 3.8%.

Discussion

68.	A 200/400 V single phase transformer has leakage impedance z= r+jx. Then we can expect magnitude of load pf of ____ at zero voltage regulation.(a) cosθ = x/z(b) cosθ = r/z(c) cosθ = x/r(d) cosθ = r/xThis question was posed to me in final exam.My query is from Voltage Regulation of Transformer in chapter Transformers of Electrical Machines
Answer» The CORRECT CHOICE is (a) cosθ = x/z The best I can EXPLAIN: Cosθ = x/z for the TRANSFORMER at zero V.R.

Discussion

69.	A 200/400 V single phase transformer has leakage impedance z= r+jx. Then we can expect zero voltage regulation at power factor of ___________(a) x/r leading(b) x/r lagging(c) r/x leading(d) r/x laggingThis question was posed to me in an online interview.This interesting question is from Voltage Regulation of Transformer topic in portion Transformers of Electrical Machines
Answer» RIGHT OPTION is (a) x/r LEADING The best I can EXPLAIN: ZVR OCCURS at the leading pf of load at x/r.

Discussion

70.	While estimating voltage regulation of a transformer, keeping ___________(a) primary voltage constant(b) secondary voltage constant(c) voltage changes constant at primary(d) all of the mentionedI have been asked this question in quiz.Asked question is from Voltage Regulation of Transformer in section Transformers of Electrical Machines
Answer» The correct OPTION is (a) PRIMARY voltage CONSTANT Easiest EXPLANATION: V.R. is calculated keeping the primary constant because then the core flux will change and the change of SECONDARY voltage cannot be fixed.

Discussion

71.	If the per unit leakage impedance for the primary of a transformer is ‘x’ on the given rated base value. If the voltage and volt-amperes are doubled, then the changed per unit impedance will be ___________(a) 0.5x(b) 2x(c) 4x(d) xThis question was posed to me in an interview for job.This question is from Voltage Regulation of Transformer in division Transformers of Electrical Machines
Answer» RIGHT answer is (a) 0.5x To explain I would SAY: pu(NEW base) = (x)(MVA(new)/MVA(old))(KV(old)/kV(new))^2 = x2(1/4) = 0.5x.

Discussion

72.	While conducting testing on the single phase transformer, one of the student tries to measure the resistance by putting an ammeter across one terminal of primary and other to secondary, the reading obtained will be ___________(a) infinite(b) zero(c) finite(d) negative finiteThe question was posed to me in a national level competition.I need to ask this question from Voltage Regulation of Transformer topic in section Transformers of Electrical Machines
Answer» Correct answer is (a) infinite The EXPLANATION: As the primary and secondary are PHYSICALLY ISOLATED, the impedance will be infinite for not electrically connected CIRCUIT.

Discussion

73.	While conducting open circuit test and short circuit test on a transformer, status of low-voltage and high-voltage windings will be such that in ____________(a) OC test – h.v. open, SC test-l.v. short-circuited(b) OC test – l.v. open, SC test-h.v. short-circuited(c) OC test – l.v. open, SC test-l.v. short-circuited(d) OC test – h.v. open, SC test-h.v. short-circuitedThe question was posed to me during a job interview.My doubt stems from Voltage Regulation of Transformer topic in chapter Transformers of Electrical Machines
Answer» The correct CHOICE is (a) OC test – h.v. OPEN, SC test-l.v. short-circuited The explanation is: In CONDUCTING short CIRCUIT test, l.v. winding is short circuited. In OC test h.v. is open circuited.

Discussion

74.	A 10 kVA, 400/200 V, 1-phase transformer with 2% resistance and 2% leakage reactance. It draws steady short circuit current at which angle?(a) 45°(b) 75°(c) 135°(d) 0°I got this question in an interview.Query is from Voltage Regulation of Transformer topic in portion Transformers of Electrical Machines
Answer» RIGHT ANSWER is (a) 45° To explain: The power FACTOR ANGLE will be ATAN(x/r) = 45°.

Discussion

75.	Transformers with high leakage impedance is used in ___________(a) arc welding(b) power distribution(c) power generating terminals(d) none of the mentionedThe question was asked in an international level competition.My doubt is from Open Circuit and Short Circuit Test in section Transformers of Electrical Machines
Answer» Correct answer is (a) ARC WELDING To EXPLAIN I would say: The feature of the high IMPEDANCE is extracted in the arc welding APPLICATIONS.

Discussion

76.	A single phase transformer of 2200/220 V having rated l.v. current of 150 A has to undergo open circuit test on h.v side. The instruments used are voltmeter of 200V and ammeter of 1A. Then the results ___________(a) will be wrong(b) will be accurate(c) of ammeter will burn(d) none of the mentionedI have been asked this question in examination.I would like to ask this question from Open Circuit and Short Circuit Test in chapter Transformers of Electrical Machines
Answer» CORRECT choice is (C) of ammeter will BURN Explanation: The current in the h.v. winding will be around 10 A but the ammeter is of 1 A RATING. So, it will burn off.

Discussion

77.	A single phase transformer of 2000/200 V having rated l.v. current of 100 A has to undergo short circuit test on l.v. side. Which of the below instruments range should be used?(a) 200V,10A(b) 20V, 10A(c) 300V,100A(d) 200V,50AThe question was posed to me in final exam.This question is from Open Circuit and Short Circuit Test in chapter Transformers of Electrical Machines
Answer» Right answer is (a) 200V,10A The EXPLANATION: Short circuit TEST is CONDUCTED on h.v. side, so the measuring instruments will be on the l.v. side. Rated current on the h.v. will be 10A and voltage will be AROUND 5-12% to account for WINDING losses.

Discussion

78.	A single phase transformer of 2200/220 V having rated l.v. current of 150 A has to undergo open circuit test on h.v. side. Which of the below instruments range should be used?(a) 6A, 200V(b) 150A, 22V(c) 60A, 220V(d) 6A, 20VThis question was addressed to me during a job interview.This interesting question is from Open Circuit and Short Circuit Test in portion Transformers of Electrical Machines
Answer» Correct CHOICE is (a) 6A, 200V Easy explanation: Open circuit test is CONDUCTED on l.v. SIDE, so the measuring instruments will be on the h.v. side. So the CURRENT in the h.v. side will be around 3-6% of the rated.

Discussion

79.	Which of the below estimations require results of both open circuit test and short circuit test?(a) Efficiency(b) Equivalent impedance of one side of the winding(c) Voltage regulation for exact circuit(d) All of the mentionedI have been asked this question during an interview for a job.My question comes from Open Circuit and Short Circuit Test in division Transformers of Electrical Machines
Answer» The correct choice is (a) Efficiency The EXPLANATION: All the ESTIMATIONS ASKED will NEED results of both the tests.

Discussion

80.	To conduct the short circuit test, test is conducted on the ___________(a) l.v. side(b) h.v. side(c) primary(d) secondaryI got this question in examination.My doubt is from Open Circuit and Short Circuit Test topic in section Transformers of Electrical Machines
Answer» CORRECT CHOICE is (b) h.v. side To explain: To circulate the rated CURRENT in the winding, we should opt for LOWER value of the current so that winding will not damage.

Discussion

81.	To conduct the open circuit test, test is conducted on the _____________(a) l.v. side(b) h.v. side(c) primary(d) secondaryThis question was addressed to me during a job interview.I'd like to ask this question from Open Circuit and Short Circuit Test topic in division Transformers of Electrical Machines
Answer» Correct option is (a) l.v. SIDE To explain I would say: OC TEST is performed on the l.v. side of the transformer because the l.v. winding will have lower STRESS on the insulation and no damage will OCCUR.

Discussion

82.	Power required during the open circuit and short circuit test is?(a) losses incurring in the transformer(b) executing the power requirements by measuring instruments(c) power for the core losses only(d) all of the mentionedThe question was asked during an interview.I'd like to ask this question from Open Circuit and Short Circuit Test topic in division Transformers of Electrical Machines
Answer» RIGHT option is (a) LOSSES incurring in the transformer Best EXPLANATION: The POWER measured while conducting the tests is the winding losses and the core losses.

Discussion

83.	In a transformer ______ decreases with increase of the leakage flux.(a) secondary terminal voltage(b) secondary induced voltage(c) primary induced voltage(d) all of the mentionedI have been asked this question by my college professor while I was bunking the class.This interesting question is from Equivalent Circuit of Transformer in section Transformers of Electrical Machines
Answer» Correct ANSWER is (a) secondary terminal VOLTAGE Easiest explanation: The LEAKAGE is modelled as the reactance which incurrs as a loss to the terminal voltage not the INDUCED voltage.

Discussion

84.	The flux involved in the emf equation of a transformer has __________(a) rms value(b) average value(c) total value(d) maximum valueI got this question in my homework.The question is from Equivalent Circuit of Transformer in portion Transformers of Electrical Machines
Answer» Correct option is (d) maximum value For EXPLANATION: The flux is ALWAYS taken at its peak in the practical calculation CASES.

Discussion

85.	If the frequency at the primary supply is varied gradually, then the secondary terminal voltage will __________(a) not change(b) vary directly(c) will vary oppositely(d) will vary inverse of frequencyI had been asked this question during an interview for a job.The origin of the question is Equivalent Circuit of Transformer topic in division Transformers of Electrical Machines
Answer» Right ANSWER is (a) not change For explanation: The CHANGES in the frequency is not reflected DUE to the flux density variation correspondingly.

Discussion

86.	There are two identical transformers A and B such that flux density applied to B is doubled. Then magnetizing current of B is?(a) larger than A(b) double of A(c) half of A(d) same as that of A.I had been asked this question in an interview for job.This intriguing question originated from Equivalent Circuit of Transformer topic in section Transformers of Electrical Machines
Answer» Right OPTION is (a) larger than A Best explanation: When we DOUBLE the FLUX density, as per the magnetization curve of the CORE, the magnetizing current is MUCH larger than double of the machine A.

Discussion

87.	For a single phase transformer operating at normal operating conditions has useful flux of 1 Wb. If the machine is loaded at 0.8 p.f., then its mutual flux __________(a) may decrease to 0.98 Wb(b) remains constant(c) may increase 1.02 Wb(d) may decrease to 0.8 WbI have been asked this question by my school principal while I was bunking the class.The question is from Equivalent Circuit of Transformer in section Transformers of Electrical Machines
Answer» The CORRECT answer is (a) may decrease to 0.98 Wb The EXPLANATION: The mutual FLUX will decrease by a very small amount.

Discussion

88.	If a transformer is fed from a dc rather than a 1-phase ac supply, then the transformer will __________(a) burn its windings(b) operate normal(c) will not operate(d) will give very small leakage fluxThe question was posed to me in a national level competition.I'm obligated to ask this question of Equivalent Circuit of Transformer topic in portion Transformers of Electrical Machines
Answer» Right choice is (a) BURN its windings To elaborate: Dc is nothing but AC at ZERO FREQUENCY. So the reactance will be zero and the current will be limited solely by the small resistance of the winding which will produce very high amount of current to flow through the windings, so burning them up.

Discussion

89.	A single phase transformer has emf per turn having 2310/220 V, 50Hz transformer as 13 V. Then the estimated primary turns will be?(a) 189 turns(b) 179 turns(c) 176 turns(d) 190 turnsThe question was asked by my school principal while I was bunking the class.Asked question is from Equivalent Circuit of Transformer topic in portion Transformers of Electrical Machines
Answer» Right ANSWER is (a) 189 turns Explanation: N2 = Total secondary voltage/Emf per TURN = 220/13 = 16.92 = 17(approx) For N2 = 17, N1 = 178.5. But it is not an integer, so this approximation is wrong. If N2 = 18, N1=189 turns.

Discussion

90.	A single phase transformer has emf per turn having 2310/220 V, 50Hz transformer as 13 V. The core area is(in square cm)?(a) 393(b) 277.8(c) 358.92(d) 450.03The question was asked in examination.I'm obligated to ask this question of Equivalent Circuit of Transformer in division Transformers of Electrical Machines
Answer» Correct choice is (a) 393 Easiest explanation: Emf per TURN = 1.44fflux DENSITY * AreaN2 Area = 220/(181.44501.4) = 393 sq.cm.

Discussion

91.	In a transformer if the frequency of the supply is varied then the magnetizing current in the core also varies.(a) True(b) FalseThis question was posed to me during an online interview.This interesting question is from Equivalent Circuit of Transformer in section Transformers of Electrical Machines
Answer» Right CHOICE is (b) False Easy explanation: The magnetizing CURRENT does not depend on the frequency of the supply fed to it.

Discussion

92.	CRGO Laminations in a transformer are used to minimize __________(a) eddy current loss(b) hysteresis loss(c) both eddy current and hysteresis loss(d) ohmic lossThis question was addressed to me in homework.My question comes from Equivalent Circuit of Transformer in portion Transformers of Electrical Machines
Answer» RIGHT choice is (c) both eddy current and hysteresis loss For explanation: CRGO STEEL is rolled grain type DOMAINS which not only help for faster reversals but also the REDUCTION of eddy current losses.

Discussion

93.	A 400/200V transformer has total resistance of 0.04 p.u on its L.V side. This resistance when referred to H.V side would be?(a) 0.04(b) 0.02(c) 0.01(d) 0.08This question was posed to me in an online quiz.This intriguing question originated from Transformer Phasor Diagram in portion Transformers of Electrical Machines
Answer» CORRECT answer is (a) 0.04 To ELABORATE: The PER unit value does not change from the winding SIDE of a TRANSFORMER.

Discussion

94.	Energising the transformer primary from a triangular wave flux makes the output voltage as __________(a) square wave shifted by 90°(b) a sine wave(c) a triangular wave(d) a square waveI have been asked this question during an online interview.I'd like to ask this question from Transformer Phasor Diagram in division Transformers of Electrical Machines
Answer» The correct choice is (d) a square wave Best explanation: E = -N*dϕ/dt. Differentiation of TRIANGULAR wave results in square wave.

Discussion

95.	Energizing thetransformer primary from a triangular wave voltage source makes the output voltage as __________(a) zero(b) a sine wave(c) a triangular wave(d) a pulsed waveI had been asked this question during an interview.The doubt is from Transformer Phasor Diagram topic in portion Transformers of Electrical Machines
Answer» The CORRECT option is (c) a triangular wave For EXPLANATION I would say: Output will follow the shape of INPUT wave. As the primary input is triangular in shape, its SECONDARY will ALSO be same.

Discussion

96.	In case of a power transformer, the no load current in terms of rated correct is?(a) 10-20%(b) 2-6%(c) 15-20%(d) 30-50%This question was addressed to me during an interview.This interesting question is from Transformer Phasor Diagram in section Transformers of Electrical Machines
Answer» The CORRECT answer is (b) 2-6% The best explanation: The air gap is very less in the transformer, so the MAGNETIZING CURRENT NEEDED is around 2-6% only.

Discussion

97.	In a single phase transformer,the no-load current lags the applied voltage by __________(a) 90°(b) about 75°(c) 0(d) about 110°I have been asked this question in class test.Asked question is from Transformer Phasor Diagram topic in portion Transformers of Electrical Machines
Answer» CORRECT CHOICE is (b) about 75° For explanation: CHECK the phasor DIAGRAM.

Discussion

98.	We laminate transformer core to reduce ___________(a) eddy current loss(b) hysteresis loss(c) both eddy current and hysteresis loss(d) ohmic lossI got this question in an internship interview.The doubt is from Transformer Phasor Diagram topic in section Transformers of Electrical Machines
Answer» The CORRECT ANSWER is (a) eddy current loss Best explanation: Laminations PROVIDE larger area so that the current PATH increases and current reduces.

Discussion

99.	Considering a transformer at no load is excited at rated voltage. A small recognizable gap is made in the yoke of the limbs. With this altercation, the transformer core flux ___________(a) will decrease and magnetizing current will increase(b) will remain constant and magnetizing current will increase(c) as well as magnetizing current will increase(d) as well as magnetizing current both will decreaseI have been asked this question in homework.This interesting question is from Transformer Phasor Diagram in chapter Transformers of Electrical Machines
Answer» Right CHOICE is (b) will remain constant and magnetizing current will increase To EXPLAIN I would say: The reluctance of the path increases here after making the cut. so the magnetizing current will increase but the core FLUX will be same as it depends on the APPLIED voltage not the reluctance.

Discussion

100.	In an oil filled transformer, the application of oil is for ___________(a) cooling(b) insulation(c) both cooling and insulation(d) preventing the accumulation of dustThis question was addressed to me in an internship interview.My question is from Transformer Phasor Diagram in chapter Transformers of Electrical Machines
Answer» CORRECT answer is (c) both cooling and INSULATION To ELABORATE: Oil can be USED not only for cooling but also for insulation from the metallic parts.

Discussion

Explore topic-wise InterviewSolutions in .

The load current at which maximum efficiency occurs is independent of the load power factor.(a) True(b) FalseI had been asked this question in an interview.Origin of the question is Transformer Losses and Efficiency topic in chapter Transformers of Electrical Machines

To conduct the short circuit test, test is conducted on the ___________(a) l.v. side(b) h.v. side(c) primary(d) secondaryI got this question in examination.My doubt is from Open Circuit and Short Circuit Test topic in section Transformers of Electrical Machines

The flux involved in the emf equation of a transformer has __________(a) rms value(b) average value(c) total value(d) maximum valueI got this question in my homework.The question is from Equivalent Circuit of Transformer in portion Transformers of Electrical Machines

In a transformer if the frequency of the supply is varied then the magnetizing current in the core also varies.(a) True(b) FalseThis question was posed to me during an online interview.This interesting question is from Equivalent Circuit of Transformer in section Transformers of Electrical Machines

In case of a power transformer, the no load current in terms of rated correct is?(a) 10-20%(b) 2-6%(c) 15-20%(d) 30-50%This question was addressed to me during an interview.This interesting question is from Transformer Phasor Diagram in section Transformers of Electrical Machines

In a single phase transformer,the no-load current lags the applied voltage by __________(a) 90°(b) about 75°(c) 0(d) about 110°I have been asked this question in class test.Asked question is from Transformer Phasor Diagram topic in portion Transformers of Electrical Machines

We laminate transformer core to reduce ___________(a) eddy current loss(b) hysteresis loss(c) both eddy current and hysteresis loss(d) ohmic lossI got this question in an internship interview.The doubt is from Transformer Phasor Diagram topic in section Transformers of Electrical Machines