124 + Interview Questions in Transformers in Electrical Machines Page 3 InterviewSolution

101.	In an ideal transformer, the impedance can be transformed from one side to the other ___________(a) in direct proportion to square of turns-ratio(b) in direct proportion to turns-ratio(c) in inverse proportion to square turns-ratio(d) in inverse proportion to turns-ratioThe question was posed to me during an interview.I'd like to ask this question from Transformer Phasor Diagram in division Transformers of Electrical Machines
Answer» Right ANSWER is (a) in DIRECT PROPORTION to square of turns-ratio Best explanation: Impedance is TRANSFORMED in square of the turns-ratio.

Discussion

102.	A transformer has sometimes more than two ratings depending upon the use of ___________(a) the cooling application(b) type of windings(c) type of core(d) type of insulation to be givenI had been asked this question in an interview for job.I want to ask this question from Transformer Phasor Diagram in division Transformers of Electrical Machines
Answer» The correct answer is (a) the COOLING application The explanation is: YES, withdifferent TYPES of the cooling methods, the losses can be varied and so the current and the voltages.

Discussion

103.	Transformer action requires a ___________(a) constant magnetic flux(b) increasing magnetic flux(c) alternating magnetic flux(d) alternating electric fluxI got this question during a job interview.Question is taken from Transformer Phasor Diagram in division Transformers of Electrical Machines
Answer» Correct answer is (c) alternating magnetic FLUX The best I can explain: As PER the FARADAY’s laws, the emf will be induced when flux is TIME varying as in transformer, there is no moving PART.

Discussion

104.	The non linear magnetization curve of a practical transformer will introduce _____________(a) heating(b) higher order harmonics(c) magnetostriction(d) all of the mentionedI have been asked this question in an international level competition.Question is from Transformer Phasor Diagram topic in section Transformers of Electrical Machines
Answer» Right answer is (d) all of the mentioned Easy EXPLANATION: If the magnetization is non linear in nature then it will cause a saturation in the CORE and harmonics will be INTRODUCED to cause humming SOUNDS.

Discussion

105.	If a transformer is fed from a 220V and dc supply 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 fluxI got this question in exam.The doubt is from Transformer Phasor Diagram topic in chapter Transformers of Electrical Machines
Answer» Correct answer is (a) burn its windings Easiest explanation: Dc is nothing but ac at zero frequency. So the REACTANCE offered will be zero at dc and the CURRENT will be limited only 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

106.	The output voltage seen at the CRO connected at the secondary terminals is square wave. Then the flux density used for energizing the primary is?(a) triangular(b) sinusoidal(c) saw tooth wave(d) square waveThe question was posed to me by my school teacher while I was bunking the class.This intriguing question originated from Transformer Phasor Diagram topic in division Transformers of Electrical Machines
Answer» Right OPTION is (a) TRIANGULAR For EXPLANATION: E = -N*dϕ/dt. Integration of square wave will be triangular in nature.

Discussion

107.	Consider a 2-winding transformer as below. If the switch is open then the emf induced across the secondary having transformation ratio of 2 is?(a) zero(b) V1(c) V1/2(d) 2*V1This question was posed to me in a national level competition.I would like to ask this question from Ideal Two Winding Transformer in portion Transformers of Electrical Machines
Answer» The CORRECT choice is (d) 2V1 To EXPLAIN I would say: V2/V1 = 2 S, V2 = 2V1.

Discussion

108.	Consider a 2-winding transformer as below. If the switch is open then the emf induced across the load ‘Zl’ having transformation ratio of 2 is?(a) zero(b) V1(c) V1/2(d) 2*V1I have been asked this question in homework.I need to ask this question from Ideal Two Winding Transformer in division Transformers of Electrical Machines
Answer» The correct CHOICE is (a) ZERO The best explanation: As the secondary SWITCH is kept open, the voltage across load will be zero.

Discussion

109.	Consider a 2-winding transformer as below. If the switch is kept open then the emf induced across the secondary having transformation ratio of ‘2’ is?(a) zero(b) 2E1(c) E/2(d) E1The question was asked by my school principal while I was bunking the class.I'd like to ask this question from Ideal Two Winding Transformer in chapter Transformers of Electrical Machines
Answer» The correct choice is (a) zero To EXPLAIN I WOULD say: The induced emf lags the flux by 90DEGREES.

Discussion

110.	The voltage induced at the end of primary terminals of a two winding transformer consisting of N turns is?(a) -Ndϕ/dt(b) Ndϕ/dt(c) -dϕ/dt(d) -N*dt/dϕThis question was posed to me in an interview for internship.Asked question is from Ideal Two Winding Transformer topic in chapter Transformers of Electrical Machines
Answer» CORRECT CHOICE is (a) -N*dϕ/dt The EXPLANATION: Emf is INDUCED based on the electromagnetic induction principle for N turns WINDING.

Discussion

111.	The shell type transformers have, LV and HV windings are arranged such that _________(a) Half LV near the core and half HV outside LV on each limb(b) LV one one limb and HV on the other(c) Half LV outside the core and half HV inside LV on each limb(d) LV and HV windings are sandwichedI had been asked this question in a job interview.My question is from Transformer Construction topic in section Transformers of Electrical Machines
Answer» Right option is (d) LV and HV WINDINGS are SANDWICHED Explanation: Shell type windng has MIX of LV and HV WINDING sandwiched over each other.

Discussion

112.	Core type transformers have, LV and HV windings are arranged such that _________(a) Half LV near the core and half HV outside LV on each limb(b) LV one one limb and HV on the other(c) Half LV outside the core and half HV inside LV on each limb(d) LV and HV windings are sandwichedI have been asked this question during an internship interview.Question is from Transformer Construction in section Transformers of Electrical Machines
Answer» RIGHT CHOICE is (a) Half LV near the CORE and half HV OUTSIDE LV on each limb The explanation is: Core windng has first of all both the windings on the same limb and HV is placed outside to have TAPPINGS to the transformer.

Discussion

113.	A coupling magnetic field inside a rotating machine or static machine like transformers must involve with _________(a) mechanical parts(b) electrical parts(c) both electrical and mechanical(d) either of the electrical or mechanical partsThis question was addressed to me during an internship interview.Query is from Transformer Construction in chapter Transformers of Electrical Machines
Answer» The correct answer is (a) MECHANICAL parts The BEST I can explain: The COUPLING field should INTERACT with both the electrical as WELL as mechanical parts in order to achieve electromechanical energy conversion.

Discussion

114.	Stepping of the core is implemented in the core to _________(a) reduce conductor material and copper losses(b) reduce core loss(c) to provide mechanical strength(d) to reduce magnetizing currentI have been asked this question during a job interview.My query is from Transformer Construction in section Transformers of Electrical Machines
Answer» RIGHT choice is (a) REDUCE conductor MATERIAL and copper losses The BEST I can explain: Stepping of the core is DONE so that the copper material reduces.

Discussion

115.	Transformers do not require any type of cooling as it well ventilated.(a) True(b) FalseThis question was posed to me during an internship interview.The query is from Transformer Construction in section Transformers of Electrical Machines
Answer» Correct option is (B) False Explanation: It is wrong to say that transformers do not need any cooling. It does need various TYPES of cooling like oil cooling, AIR COOLED etc.

Discussion

116.	Consider two transformers X and Y having identical ratings, but have flux densities of 1.5T and 2T respectively. The weight of the transformer B per KVA will be _________(a) more than that of A(b) lesser than that of A(c) equal to that of A(d) can not be said from the given dataThe question was posed to me in an online interview.My question comes from Transformer Construction in division Transformers of Electrical Machines
Answer» Right OPTION is (b) lesser than that of A The BEST I can EXPLAIN: Flux DENSITY = flux/Area. Hence A has more area than B and so weight of B will be LESS than that of A.

Discussion

117.	Consider two transformers X and Y having exact ratings, but have flux densities of 1.5T and 2T respectively. The weight of the transformer A per KVA will be _________(a) more than that of B(b) lesser than that of B(c) equal to that of B(d) can not be said from the given dataI have been asked this question in a national level competition.The question is from Transformer Construction in portion Transformers of Electrical Machines
Answer» Right option is (a) more than that of B The BEST EXPLANATION: Flux density = flux/AREA. Hence A has more area than B and so weight of A will be more than that of B.

Discussion

118.	It is advised that staggering of the butt joints _________(a) reduces reluctance of the path(b) increases air gap(c) increases mechanical strength(d) all of the mentionedThe question was posed to me in my homework.The doubt is from Transformer Construction topic in portion Transformers of Electrical Machines
Answer» Right choice is (c) increases mechanical STRENGTH The best explanation: STAGGERING is done for the steel butt joints of the transformer to gain more mechanical strength as the CONTINUOUS air gap reduces the same.

Discussion

119.	The leakage flux is the flux in side the transformer which?(a) links either of the windings(b) links both of the windings(c) yoke of the core(d) windows of the coreThe question was posed to me in unit test.The query is from Transformer Construction topic in section Transformers of Electrical Machines
Answer» Correct ANSWER is (a) links either of the WINDINGS Best explanation: Leakage FLUX is meant to to be LOSS as it does not link TWO windings.

Discussion

120.	Which is the most widely used material in the core of the transformer?(a) cold rolled grain oriented sheet steel(b) cold rolled grain steel(c) soft iron(d) steelThe question was asked in an interview for job.This intriguing question originated from Transformer Construction in chapter Transformers of Electrical Machines
Answer» CORRECT OPTION is (a) cold rolled GRAIN oriented sheet steel The BEST I can explain: CRGO has magnetization in the rolling direction and low core losses and very high permeability than present MATERIALS.

Discussion

121.	It was needed that to isolate dc noise coming from the transmitted signal, to attain the same which machine can be used without suffering significant loss?(a) transformer(b) dc machine(c) induction machine(d) stepper motorThe question was asked in an interview for internship.This is a very interesting question from Transformer Construction in portion Transformers of Electrical Machines
Answer» Correct OPTION is (a) TRANSFORMER The best I can EXPLAIN: We should use transformer to achive the isolation of DC.

Discussion

122.	A transformer has comparitively much higher efficiency than a similar induction machine due to _________(a) small air gaps(b) no moving parts(c) strong coupling(d) all of the mentionedThe question was asked during an interview for a job.This interesting question is from Transformer Construction topic in portion Transformers of Electrical Machines
Answer» Correct answer is (d) all of the mentioned For explanation I WOULD say: TRANSFORMER does not has any moving components so losses are anyway REDUCED and also the coupling is very STRONG between two sides.

Discussion

123.	We can employ transformers for a power range of _________(a) lower and higer values(b) lower values(c) higher values(d) medium valuesThis question was posed to me during an interview.My doubt stems from Transformer Construction in chapter Transformers of Electrical Machines
Answer» Correct option is (a) lower and higer values The best explanation: A TRANSFORMER can be put in use UPTO a varying range of the power and it is USUALLY AVAILABLE in READILY in market.

Discussion

124.	The primary and secondary of a transformer are ________ coupled but _______ connected.(a) magnetically, not electrically(b) electrically, not magnetically(c) magnetically, also magnetically(d) electrically, also electricallyThis question was addressed to me in exam.Asked question is from Transformer Construction topic in chapter Transformers of Electrical Machines
Answer» The correct CHOICE is (a) magnetically, not electrically Easiest EXPLANATION: Transformer is the MACHINE which has physical spacing and has MAGNETIC circuit to exchange the VOLTAGE.

Discussion

Explore topic-wise InterviewSolutions in .

Transformer action requires a ___________(a) constant magnetic flux(b) increasing magnetic flux(c) alternating magnetic flux(d) alternating electric fluxI got this question during a job interview.Question is taken from Transformer Phasor Diagram in division Transformers of Electrical Machines

Transformers do not require any type of cooling as it well ventilated.(a) True(b) FalseThis question was posed to me during an internship interview.The query is from Transformer Construction in section Transformers of Electrical Machines

We can employ transformers for a power range of _________(a) lower and higer values(b) lower values(c) higher values(d) medium valuesThis question was posed to me during an interview.My doubt stems from Transformer Construction in chapter Transformers of Electrical Machines