EEA/502

Time:150Minutes

2012

ELECTRICAL ENGINEERING

Paper II

INSTRUCTIONS

Series~

Max.Marks: 150

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EEA/502 ( 3 )

1.

2.

3.

4.

5.

A voltageof sin mt,50 Hz is appliedto a 16.capacitorof 1F. The currentin ampereatt = 1/200s is

(1) 100

(2)

lOOn 112

(3)

100112

(4)

0

Kirchhoff'scurrentandvoltagelawsapplyfor ,7.

(1) resistivecircuitsonly

(2) linearcircuitsonly

(3) nonlinearcircuitsonly

(4) bothlinearandnonlinearcircuits

The starting torque developed in asplit-phase 1-phase induction motor isdirectly related to the phase angle, a,betweenthe two winding currentsby the18.relation

(1) cosa

(2)

sin a

(3)

sin 2a

(4)

tana

In a criticallydampedRLC seriescircuit,the19.time constantof the responseon suddenconstantexcitationis

(1) 1/LC

(2) L/2R

(3) 1/2RC

(4) 2RC

10.The illumination at various points on ahorizontalsurfaceilluminatedby the samesourcevanesas

3(1) cos 8

(2) cos8

(3) 1/r22(4) cos 8

The outer cagewinding in a doublecageinductionmotorhas

(1) lowresistanceandlowinductance

(2) lowresistanceandhighinductance

(3) highresistanceandlowinductance

(4) highresistanceandhighinductance

A 3-phaseslip-ringinductionmotorcanrunat its synchronousspeedwhen

(1) its loadis completelyremoved

(2) its supplyvoltageis increased

(3) externalresistanceis addedin therotorcircuit

(4) emfis injectedin therotorcircuit

A perfectdiffusersurfaceis onethat

(1) diffusesall theinci~entlight

(2) absorbsall theincidentlight

(3) transmitstheincidentlight

(4) scatterslight uniformlyin all directions

Sensitivityofaninstrumentis independentof

(1) amplitudedistortion

(2) frequencyresponse

(3) hysteresisor deadband

(4) All of these,

A shadedpolesingle-phaseinductionmotoralwaysrunsin

(1) clockwisedirection

(2)

anticlockwisedirection

(3)

thedirectionfromtheshadedtounshadedpartof thepoles

(4)

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EEA/502 (4 )

11. Which of the following is absolute116.instrument?

12.

13.

(]J Powerfactormeter

(2) Ammeter

(3) Wattmeter

(4) Tangentgalvanometer

In conversionof 3-phaseto 2-phasesupplywithT-connection,thetransformationratiooftheteaserwill be timesof thatofmaintransformer.

(1) 13

(2)

115

(3)

0,866

(4)

unity

The emf induced in an alternator hasfundamentalcomponentof 1000V andthirdharmoniccomponentof90V. Thevalueofnetemfis

(1) 1004,04V

(2) 1000V

(3) 1030V

(4) 1090V

17.

18.

The voltage regulation of alternatordeliveringequalamountofactiveandleadingreactivepowertotheloadis

(1) zero

(2)

lowpositive

(3)

highpositive

(4)

negative

In a 3-phase,star connectedalternator,afieldcurrentof 5 A gaveopen-circuitvoltageof 415V and short-circuitcurrentof 10A.Thevalueofsynchronousimpedanceis

(1) 2396Q

(2)

415Q

(3)

4792Q

(4)

7188Q

The magnetizingcurrentin a transformerisrichin

(1) 3rd harmonic

(2)

5thharmonic

(3)

7thharmonic

(4)

13thharmonic

14. For high startingtorque,the mostsuitable119.typeof3-phaseinductionmotoris

(1) slipring

(2) squirrelcage

(3) doublecage

(4) deepbarsquirrelcage

Tappingsofa transformerareprovided

(1) at thephaseendof Iv side

(2) at thephaseendofhv side

(3) at theneutralendofhv side

(4) at themiddleofhv side

20.15. When the supply voltageto an induction

motor is reducedby 10%, the maximumtorquewill decreasebyapproximately

(1) 5%

(2) 10%

(3) 20%

(4) 40%

Whichof the followingmethodsis employedforstartinga 3-phasesynchronousmotor?

(1) Star-deltastarter

(2) Damperwinding

(3) Resistancestarterin thestatorcircuit

(4) Damperwindingin conjunctionwith astar-delta starter or anauto-transformerstarter

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21. The efficiency of a properly designed126.synchronousmachineis oftheorderof

(1) 60%

(2) 80%

(3) 92%

(4) 99%

Thesimplestmethodofshiftingloadfromoneshunt generatorto the other running inparallelconsistsin

(1) usingequalizerconnection

(2) adjustingtheirfieldrheostats

(3) adding resistancein their armaturecircuits

(4) Noneof these

22. A synch~onous_motormay fail to pull into127.synchromsmowmgto

The instrumentsaccordingto applicationsmaybeclassifiedas

switchboardandportableinstruments

primaryandsecondaryinstrumentscoilmovingandmoving- iron

instruments

indicatingandrecordinginstruments(4)

(1)

(2)

(3)

(2) lowexcitation

(1) excessiveload

(3) highfriction

(4) Any ofthese

23. In an inductionmotor,skewingof rotorbars128.reduces

(1) eddycurrentsandcopperrequirement

noise,vibrationsandsynchronouscusps

(3) Both(1)and(2)

(4) Noneofthese

If a shuntgeneratordelivers100A at 200V,and the resistanceof the shunt field andarmatureare 100Q and0-01Q respectively,thegeneratedemfwill be(1) 212V

(2) 205V

(3) 210V

(4) 201-02V

The straight line characteristicdrawntangentto the initial portionsof aceandpassingthroughoriginis called

(1) short-circuitcharacteristic

(2) zeropowerfactorcharacteristic

(3) opencircuit characteristicof saturatedmachine

24. In a squirrel cage inductionmotor,high129.startingtorqueis achievedbyusing

(1) highresistancein serieswith therotorcircuit

(2) lowresistanceacrosstherotorcircuit

(3) doublecagerotor

(4) Noneofthese (4) open 'circuit characteristicunsaturatedmachine

of

25. The type of rotor preferredfor alternators130.drivenbysteamturbineis

(1) cylindricalrotor

(2)

slip-ringrotor

(3)

salientpolerotor

(4)

squirrel-cagerotor

At full-loadconditionin a synchronousmotor,the phasor relation between(per phase)terminalvoltageV andinducedemfE is

(1) E leadsV by around50

(2) E leadsV by around25

(3) E lagsV byaround50

(4) E lagsV by around25

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31. InvertedV-curveofa synchronousmotoris 136.

(1) E vs If

(2) V vs IZ

(3) IZvs If

(4) pfvs If

32. A 220 V de machinehas an armatureresistanceof 1 Q. If the full-loadcurrentis20 A, the differencein the inducedvoltagewhenthemachinerunsasa motor,andasa 137.generator,is

If Vth = 10V, Rth = 2 Q andRL = 3 Q, then

currentthroughRL is

(1) 5 A

(2) 3,33A

(3) 2 A

(4) 10A

In demachines,the spacedistributionof airgapflux densitywaveat no-loadis

33.

34.

(1) 20 V

(2) nil

(3) 40 V

(4) 50 V

A Lissajouspatternon an oscilloscopehas5horizontal tangencies and 2 verticaltangencies.The frequencyof the horizontalinput is 1000Hz. What is the frequencyoftheverticalinput?(1) 400Hz

(2) 2,500Hz

(3) 4,000Hz

(4) 5,000HZ

The speedof singlephaseinductionmotorscanbecontrolledby

(1) varyingtheappliedvoltagetotbestatorwinding

(2) varying the numberof poles on thestator

38.

39.

(1) sinusoidal

(2) co-sinusoidal

.(8) flat-topped

(4) rectangular

The flux createdby currentflowingthroughtheprimarywindingofa transformerinducesemfin

(1) primarywindingonly

(2) secondarywindingonly

(3) transformercoreonly

(4) bothprimaryandsecondarywindings

In the givencircuit,the currentflowinginthe2 Q resistoris

(3) either(1)or (2)

(4) Noneofthese

35. Maximumoperatingfrequencyof eRO ISmainlygovernedbyits

(1) verticalamplifier

(2) horizontalamplifier

(3) cathoderay tube

(4) timebasecircuit

+1 3volts2Q

(1) 1A

(2)

15A

(3)

0,8 A

(4)

2A

2Q + 6volts2Q

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EEA/502 ( 7 )

40. The steadystate value of the current in the 145. Synchronousmotorsgenerallyhavegivencircuit is (1) salient pole rotor

16volts+

4Q

4H

(2) smoothcylindrical rotor

(3) either salient pole rotor or smoothcylindrical rotor

(4) None of these

(1)4A146.(2)

2A I

(3)

1A

(4)

None of these

41.

The ratings of a basic meter are 100 mY,1 mA. The voltagerangeof this meteris to beextendedto 1 volt. The value of the seriesresistancerequired to be connectedwith themeteris(1)

400 Q

(2)

900 Q 147.

(3)

100 Q

(4)

1000 Q

42.

A transformerhas hysteresisloss of 30 W, at240 V, 60 Hz. The hysteresisloss at 200 V,50 Hz, will be(1)

28 W

(2)

25 W

(3)

30 W 148.. (4) 36 W43.

In a synchronousmachine, if the field fluxaxis is aheadof the armaturefield axis in thedirectionof rotation,the machineoperatingis(1)

synchronousmotor(2)

synchronousgenerator149.

(3)asynchronousmotor

(4)

asynchronousgenerator

44.

Synchronousgeneratorsare usually drivenby

(1)

steamturbines

(2)

water turbines

(3)

dieselengines

(4)

either steamturbines or water turbinesA capacitorof 1/211: F is connectedin seneswith a 1 Q resistanceto a voltagesource1V,211: Hz. The voltage drop across thecapacitancewould be

(1) 2 V, leading appliedvoltageby 90

(2) 1/.J2 V, lagging appliedvoltageby 45

(3) 1/.J2 V, leading appliedvoltageby 45

(4) .J2 V, lagging appliedvoltageby 90

The differential equationgoverninga certaincircuit is RC(dv/dt) + v = J2 E coswt.Thecorrespondingphasorequationis

(1) (-jwRC + 1)V = E L90

(2) (jw +RC) V = E LO

(3) (jwCR + 1)V =E LO

(4) (jRCw + 1)V =E L90

A seriesgeneratorcan self excite

(1) only if the load current is zero

(2) orily if the load current is not zero

(3) irrespectiveof the value of load current

(4) None of these

Commutatorand brush arrangementin a dcmotoris providedto

(1) 'produceunidirectional torque

(2) reducelosses

(3) produce unidirectional current in thearmature

(4) assist in changing in direction ofrotation of the armature

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EEA/502 (8 )

50. In the two wattmetermethodof measuring156.powerin a balancedthree-phasecircuit,thereadingsoftwowattmetersarein theratioof1 : 2.Thecircuitpowerfactoris

(1) 1/.J2

(2) 1/2

(3) J3/2(4) 1

In a synchronousmotor, squirrel cagewindingis providedformakingmotor

(1) noisefree

selfstarting

(3) cheap

(4) quickstart

51.

52.

Threeimpedancesof ZQ eachareconnectedin delta. Their equivalent starimpedance/phasewill be

(1) Z/J3(2) J3Z(3) Z/3

(4) 3Z

Thefunctionofa shuntin anammeteris to

(1) increasetheinstrumentresistance

(2) bypassthecurrent

(3) reducethe voltage drop across theinstrumentcoil

(4) increasethe current flowing throughtheinstrumentcoil

57.

58.

A shadedpolesingle-phaseinductionmotorcanbeusedfor

(1) wet-grinders

(2) food-mixies

(3) taperecorders

(4) personalcomputersascoolingfan

When a synchronousmotoris started,thefieldwindingis

(1) short-circuited

(2) open-circuited

(3) excitedfroma dcsource

(4) excitedfroma 3-phaseacsource

53. Looptestsin a cablecannotlocatethe

(1) open-circuitfaults 159.(2) short-circuitfaults

(3) earthfault(4) Noneofthese

54. The controllingtorquein gravitycontrolledmeteris proportionalto(1) cose(2) sin8

(3) tan8

(4) e 160.

55. Variationin dc excitationof a synchronousmotorcausesvariationin

(1) speedofmotor

(2) powerfactor(3) armaturecurrent

(4) botharr~aturecurrentandpowerfactor

A meterhasa full scaledeflectionof90at acurrentof 1 A. The responseof themeterissquare-law.Assuming spring control, thecurrentfora deflectionof45will be

(1) 025A

(2) 0,5A

(3) 0,67A

0,707A

A linearsystemwithsystemfunctionR(s)= 1/sis excitedwithunit stepinput.Theoutputfort >0 is givenby

(1) o(t)

(2) 1

t

(4) t2

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61. The essentialconditionfor paralleloperation166. The mostsuitablematerialfor transformeroftwodcgeneratorsis theyhavethesame coreis

(1) kW rating

(2)

terminalvoltage

(3)

operatingspeed

(4)

All of these

62. A dcmotordeliveringconstantpoweroutputinitially operatesat 1500rpm with torquei670deliveredas200Nm.Thetorquedeliveredat1200rpmis

(1) 160Nm

(2)

200Nm

(3)

230Nm

(4)

250Nm

63. The Td vs Ia characteristicof a dc seriesmotoris a

(1) straightlinethroughout

(2) parabolathroughout 168.

(3) straight line from no-loadto certainloadandparabolathereafter

(4) parabolafrom no-loadto certainloadandstraightline thereafter

(1) hotrolledgrainorientedsteel

(2) coldrolledgrainorientedsteel

(3) aluminium

(4) copper

In cascadeoperationoftwoinductionmotors,theratioof mechanicalpowerdevelopedandelectricalpower in the rotor of the main

inductionmotorhavingPI numberof statorpoleswill be

(1) Pi/PZ

(2)

PZ/Pi

(3)

(Pi +Pz)/Pz

(4)

(Pi - Pz)/Pz

The thicknessof statorlaminationsis of theorderof

(1\ 0,5 mm

(2) 1 mm

(3) 0,05mm64. TheLaplaceinverseof siCs+ 2) is givenby

(1) u(t)+ 2e-Ztu(t)

(2) oCt)+2e-Ztu(t)

(3) oCt)- e-Ztu(t)

(4) u(t)-e-Ztu(t)

65. If currentflowing in a lamp dropsby 1percent,thepowerwill bedecreasedby

(1) 2%

(2) 4%

(3) 01%

(4) 1%

(4) Noneofthese

69. In large capacitytransformers,5% of theturnsat the endof hv windingareprovidedwith extra insulation so as to provideprotection

(1) againstcorona

(2)

againstlightning

(3)

duetosurgesoccurringduringswitchingoperation

(4)

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70.

The currentflowingin an inductivecircuit173.consistingof a resistanceandan inductanceIis expressedby i = 1msin wt. The expressionfor theappliedvoltagewill be

(1) v = Vm sin(wt + $)

(2) v = V sin(wt - $)m

In 3-phaseinductionmotors,speedshigherthansynchronousspeedcanbehadby

(1) linevoltagecontrol

(2) rotorslip powercontrol

(3) rotorresistancecontrol

(4) frequencycontrol

(3)

(4)

v = V sin wtm

v = V sin(wt - n/2)m

74. The method of speed control used forincreasingthe speedof a dc shunt motoraboveits ratedspeedis

(1) armatureresistancecontrol

(2) fieldcontrol

71. Varleylooptestsare preferredoverMurraylooptestsbecause

(3) armaturevoltagecontrol

(4) seriesparallelcontrol(1)

(2)

Varleylooptestcanlocateopencircuitfault

Varleylooptestgiveshigheraccuracy

75. If N is thespeed,thenthewindagelossin dcmotoris proportionalto

(3) in Varleylooptestprovisionis madeforthe measurement of total loopresistanceinsteadof obtainingit fromtherelationR = pl/a

(4) Varley loop test can locatethe earthfault

72. For applicationsrequiringspeedratio otherthan2 : 1, the speedcontrolof an inductionmotorcanbeeffectedbyvaryingthenumberof statorpolesemploying

(1) multiplestatorwinding

(2) poleamplitudemodulationtechnique

(3) consequentpole.technique

(4) Any of these

76. If Rt2, Xt2 are the total resistanceandreactanceof the transformerreferredto

secondary,12 is the secondaryload current

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EEA/502 ( 11 )

77. The capacity of three two-winding181.transformersconnectedin Ll - Ll is 100 kVA.If oneoftheunitsgetsdamagedand3-phaseoperation is then performed with twotransformersin opendelta,the new ratingwill be

78.

(1) 50kVA

(2) 5774kVA

(3) 6667kVA 182.(4) 100kVA

In a Scottconnectedtransformer,thenumberof turnsin themainandteasertransformerrespectivelyare

Primaryseriesresistorsareemployedin thestator for startinga 3-phasesquirrelcageinductionmotorto

(1) increasethestartingtorque(2) improvethe pf and efficiencyof the

motor

(3) reducethe voltageappliedacrossthemotorterminals

(4) increasethemotorspeed

In a eRO, the quantityto be measuredISappliedacross

(1) focusingelectrodes(2) cathode

(3) Y-plates

(4) X-plates

80. The startingtorqueof an inductionmotorvariesas

(2) thecross-magnetizingeffectofarmaturemmf

(1) the demagnetizingeffectof armaturemmf

Thepurposeofinterpolesin dcmachinesis tonullify

The resistanceof a wire is 2",.~. If thediameterof the wire is reducedto half,keepingthe samelength,the resistancewillbe

(1) 1~(2) 4 ~

(3) 05Q

(4) 8 Q

In electricdischargelamps,light is producedby

(1) cathoderay emission

ionizationin a gasor vapours(3) heatingeffectof current(4) magneticeffectof current

Whichofthefollowingbulbsoperatesonleastpower?(1) GLS bulb

Torchbulb

(3) Neonbulb

(4) Nightbulb

83.

84.

85.boththecross-magnetizingmmfandthereactancevoltage

thereactancevoltage

(1) T, 13T/2

(2) T/2 +T/2, 13T/2

(3) T/2 +T/2, 2T/13

(4) T/2, 13T/2

(3)

(4)

79.

(1) f

(2) l/f

(3) l/f

(4) f

86. Thegasusedin sodiumvapourlampis(1) argon

(2)

neon(3)

nitrogen(4)

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90. In thecircuitof seriesRL givenin fig.,V is I (3)givenby

94. Two holesare drilled in the discof energymeterontheoppositesidesofthespindle

(1) to increasethedeflectiontorque

(2) to eliminatethecreepingonnoload

(3) forproperventilation

(4) toreducetheweightof thediscforeasyrotation

87. Theveninresistanceis determinedwhenall 191.the

(1) voltagesourcesare short-circuitedandall currentsourcesareopen-circuited

(2) voltagesourcesandcurrentsourcesareleftastheyare

(3) sourcesare replacedby their internalresistances

(4) voltagesourcesare open-circuitedand192.all currentsourcesareshort-circuited

in oe, LV is openand in se, HV isshortedin oe, HV is openand in se, LV isshortedin oe, LV is openand in se, LV isshortedin oe, HV is openand in se, HV ISshorted

(2) Air frictiondamping

Speedof a dc shuntmotorbeyondtheratedspeedcanbeincreasedby

(1) increasingthe resistancein the fieldcircuit

For instrumentswith very weak magneticfield,weuse

(1) Eddycurrentdamping

While performing the open-circuit andshort-circuit tests on a transformer todetermineparameters,the status of lowvoltage(LV) andhigh voltage(HV) windingwill besuchthat

(3) decreasingthe resistancein the fieldcircuit

(4) decreasing the resistance in thearmaturecircuit

(3) Oil frictiondamping

(4) Noneof these

(2) increasing the resistance in thearmaturecircuit

(4)

(1)

93.

VRsint

r-' 1~v )(1) 2 sin t(2) 2 cost(3) sin(t +45)(4) 12 sin(t +45)The speedof a synchronousmotordependsupon

(1) supplyvoltage

(2) supplyfrequency

(3) numberofpoles

(4) both supplyfrequencyand numberofpoles

88. A synchronousmachineconnectedto a powersystem grid bus-bar is operating as agenerator.To makethemachineoperateasamotor,the

(1) directionof rotationis tobereversed

(2) phasesequenceis tobechanged

(3) fieldexcitationis to bedecreased

(4) mechanicalinput is to be lessthanthelossesat theshaft

89.

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95. The purpose of providing compensating199.windingin a dcmotoris to

(1) obtainsatisfactorycommutationduringnormaloperation

(2) reducespeedregulation

(3) prevent commutatorflash-overuponsuddenchangein load

(4) reduceleakagein magneticfield

In a dc shuntmotor,if the terminalvoltageis reducedto half, torque remainingthesame,the

(1) speed will become half and thearmaturecurrentwill alsobecomehalf

(2) speed will become half and thearmaturecurrentremainsthesame

96. The fall in terminalvoltageof a loadeddcshuntgeneratoris mainlydueto

(1) armatureresistancedrpp

(2) demagnetizingeffect of armatureresistance

(3) speedwill becomehalf while armaturecurrentdoubles

(4) speedas well as armaturecurrentwilldouble

(1) zero

97. The voltage regulation of an overcompoundeddcgeneratoronfull-loadis

100. In an alternator,thedistributionfactorkd isgivenby

(na)(1)

kd=sm2

nsin(~)

(2)

nsin(~)

kd = (na)sm2

(na)

(3)

sm2kd=

sin(~)

(4)

kd=sin(~)

(na)

sm2whereen'is thenumberof slotsperpoleand

'a' is the anglein electricaldegreesbetweentheslots.

3Q

2Q

2Q

(1) 5 Q

(2) 2 Q

(3) 4 Q

(4) 6 Q

(3) brushcontactdrop

(4) weakeningeffectof thefieldcurrent

(2) lowpositive

(3) highpositive

(4) negative

98. In thecircuitoffig.below,Req is givenby4Q

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101. The operationof a 3-phasesynchronousmotoroperatingonconstantexcitationacrossinfinitebuswill notbestableif powerangle8

(1) exceedsinternalangle8

(2) is lessthan8

(3) exceeds8/2

(4) is lessthan8/2

106. A synchronousmotor can besynchronouscondenserwhenit is

(1) underloaded

(2)

overloaded

(3)

underexcited

(4)

overexcited

used as

102. The dc motor used for intermittenthightorqueloadsis

(1) dcseriesmotor

(2) dcshuntmotor

(3) differentialcompoundmotor

(4) cumulativecompoundmotor

108. In thegivencircuit,thecurrentisi(t) = 4 sin(500t) A. The appliedvoltageinvoltsis

103. A cumulativedc compoundmotorruns at1500r.p.m.on full load.If its seriesfield isshort-circuited,its speed

(1) becomeszero

(2) remainsunchanged

(3) mcreases

107. If Zd' Xd and Xq are per-phasevaluesofdirect axis synchronousimpedance,directaxis synchronousreactanceand quadrature'axissynchronousreactancerespectively,thenfor a nonsalient-polesynchronousmachine

(1) Xd >Xq

(2)

Xd < Xq

(3)

Xd = Xq

(4)

Xd = Zd

i(t)

104. The followinginstrumentis not a currentoperatedinstrument:

105.

(4) .decreases

(1) electrodynamometerinstrument

(2) electrostaticinstrument

(3) hotwireinstrument

(4) movingcoilinstrument

A synchronousmotoris delivering80%of itsratedoutputandis operatingat UPF. If itsexcitationis increased,then

(1) theoutputdeliveredgetsincreased

(2) its pf becomeslagging

(3) theoutputdeliveredgetsdecreased

(4) its pf becomesleading

rvlV

(1) 40sin(500t)

(2) 56,56sin(500t +45)

(3) 40cos(500t)

(4) 56,56cos(500t +45)

109. Operating torques minstrumentare

(1) deflecting

(2)

controlling

(3)

damping

(4)

All of these

an

IOQ

20mH

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110. In atransformer,theexcitingcurrentwill be1114.in phase quadraturewith the impressedvoltageprovided

(1) only the leakageimpedancedrop ISignored

(2) onlythecorelossis ignored"

(3) both leakageimpedancedrop and thecorelossareignored

(4) onlytheno-loadcopperlossis ignored

A 5 kVA transformerhas a turn-ratioof

(N1/Nz)= 10.The impedanceof theprimarywinding is 3 + j5 ohms while that ofsecondarywindingis 0,5 -+- jO'8 ohms.Theimpedanceof the transformerwhenreferredto theprimarywill be

(1) 3,5+j 5,8ohms

(2) 8'0+j 13ohms

(3) 53,0+j 85o.hms

(4) 3,05+j 508ohms

111. In a 3-phase synchronousmagnitudeof fieldflux

motor, the115. In indicatinginstruments,the springsare

mainlyusedto

(1) remainsconstantat all loads (1)holdthepivotin position

(2)

varieswith load (2)conductthecurrentto thecoils

(3)

varieswith speed (3)controlthemovementofthepointer

(4)

varieswithpowerfactor (4)reducethevibrationsof thepointer

112. A 3-phasesynchronoussupplyforexcitation

(1) continuously

motor needs dc1116. In the circuitof fig. shown,steadystatehasbeen reachedwith the switch open.Theswitchis closedat t = O. The currenti att = 0+is

(2)at thestartinginstantonly

(3)

of statorI

lQ

(4)

NoneoftheseI+/'6VI113. A synchronousmotoroperatingwith normal

excitationadjuststo increasedload due toincreasein(1)

backemf (1)3/2A

(2)

armaturecurrent (2)9/2A

(3)

powerfactor (3)2A

(4)

Noneofthese (4)4A

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117. Thefunctionof a starterin a dcmotoris

(1) tocontrolits speed

(2) to reducethe startingcurrentto safevalues

121. Ward- Leonardmethodof speedcontrolisbasicallya

(1) fieldcontrolmethod

(2) fielddivertermethod

(3) to avoidsparking

(4) to minimize the armature reactioneffect

118. During normal running conditions, thearmaturecurrentdrawnbya dcshuntmotoris givenby

122.

(3) armatureresistancecontrolmethod

(4) voltagecontrolmethod

Two dc series motorsconnectedin seriesdrawcurrentI ampsfromsupplyandrun atspeed N. When the same motors areconnectedin paralleltaking currentI ampsfromthesupply,thespeedofeachmotorwillbe

(1) ViRa(2)

(V - Eb)/Ra

(3)

(V +Eb)/Ra

(4)

(Eb - V)/Ra(1)

(2)

(3)

(4)

N2N

4N

N2

119. In a dcmachine, the laminatedparts arearmatureand

(1) core

(2) yoke

(3) pole

123. The purposeof providingdummycoilsin dcmachinearmatureis to

(1) reduceeddycurrents

(2) increasevoltageinduced

(3) decreasearmatureresistance

(4) provide mechanicalbalance for themotor

(4) poleshoe124. In the circuitof fig. given,vet)for t > 0 is

givenby

T+Iu(t)( )

L~R ~ vet)

1-

(1) IRe-Lt/R

(2)

IR e-RtiL

(3)

IR (1- e-Rt/L)

(4)

IR (1- e-Lt/R\J

(2) shiftingany shadingcoil to the otherhalfof thepole

(3) shiftingtwo shadingcoils to the otherhalf of thepole

(4) shifting all the shadingcoils to theotherhalf of thepole

(1) reversingthesupplyterminals

120. The directionof shadedpole single phaseinductionmotorcanbereversedbyhttp://al

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EEA/502 ( 17)

125. If thebackemfof a dcmotoris doubledand

its speed is also doubled, the torquedevelopedin themachinewill

(1) getdoubled

(2)

become4 times

(3)

gethalved

(4)

remainunaltered

130. For zeroleadingpowerfactor,the effectofarmaturereactionon the main flux in analternatoris

(1) magnetizingonly

(2) demagnetizingonly

(3) cross-magnetizingonly

(4) Noneof these

126. Themostefficientelectricalmachineis the

(1) dcmachine

(2) inductionmotor

(3) synchronousmachine

(4) transformer

127. Oil in a transformeris usedfor

(1) insulation

(2) insulationandcooling

(3) lubriCation

(4) insulation,coolingandlubrication

131. Carbonarclampsarecommonlyusedin

(1) photography

(2) cinemaprojectors

(3) domesticlighting

(4) streetlighting

132. Shadedpoleinductionmotordoesnot havetheadvantageof

(1) highstartingtorque

(2) ruggedconstruction

(3) lowinitial aswell asmaintenancecost

(4) comparativelysmallstartingcurrent

128. Whatpercentof theinputenergyis radiated1133. Which of the followingneedlowestlevelofby filamentlamps? illumination?

(1) 2 to 5 percent

(2) 10 to 15 percent

(3) 25to 30percent

(4) 40to 50percent

129. The no-load current of ainductionmotoris aroundloadcurrent.

(1) Auditoriums

(2) Railwayplatforms

(3) Displays

(4) Fine engravings

single phase1134. Thedistancebetweentwocoilsideswhichare% offull connectedto the samecommutatorsegmentis calledas

(1) 10(1)windingpitch

(2)

20 (2)backpitch

(3)

40 (3)frontpitch

(4)

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135. Brushesin dcmachinesaremadeupof

(1) copper(2)

aluminium

(3)

brass

(4)

carbon

( 18 )

140. 3-phasesynchronousmotorsneed

(1) dcsupplyonly

(2) 3-phaseacsupplyonly

(3) 3-phaseacsupplyaswellasdcsupply

(4) 3-phaseacsupplyaswell as I-phaseacsupply

136. The effectof armaturereactionin a dcmachineoperatingin thesaturationregionis

(1) demagnetizingonly

(2) demagnetizingandcross-magnetizing

(3) cross-magnetizingonly

(4) magnetizingandcross-magnetizing

137. 50 Hz is generatedby a 10 polegeneratorrotatingatanangularvelocityof

141. Thephasesequenceofa 3-phasealternatorisRYB. On reversingthe directionof its fieldcurrent,thephasesequenceis(1. RBY,..d

(2)

RYB

(3)

YRB

(4)

BYR

(1) 31415rad/sec

(2)

6283rad/sec

(3)

50,00rad/sec

(4)

10000rad/sec

138. Whena singlealternatorconnectedtoinfinitebus-barssuppliesa localload,thechangeinexcitationofthemachineresultsin changeof

(1) powerfactor

(2) poweroutput

(3) inputpower

(4) terminalvoltage

139. In a singlephaseinductionmotor

(1) boththe main and auxiliarywindingsareplacedonstator

(2) boththe main and auxiliarywindingsareplacedonrotor

(3) main windingis placedon statorandauxiliarywindingonrotor

(4) auxiliarywinding is placedon statorandmainwindingonrotor

142. Whichof thefollowingstatementsassociatedwitha 3-phaseinductionmotoris true?

(1) The cagerotoris madeofcopper

(2) The rotor is usually connectedto3-phaseacsupply

(3) The statorwindingproducesa rotatingmagneticfield

(4) The rotor laminations should beproperlyinsulatedfromeachother

143. A 3-phaseinductionmotor cannotrun atsynchronousspeed;if it didso

(1) it will draw excessivecurrentcausingdamageto the statorand rotorof themotor

(2) the relativespeedbetweentherotatingflux and rotor will be zeroand so theemfinducedin therotorcircuitandthetorquedevelopedwill bezero

(3) it will developa torquethatmaynotbesufficientto rotatetherotor

(4) air friction will preventthe rotor torotate

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(1) an inductorin series

144. In capacitorstart single-phaseinduction148. The rangeof an electrostaticvoltmetercanmotor,thecurrentin the beextendedby using

(1) startingwindinglagsthevoltage

(2) mainwindingleadsthevoltage

(3) startingwindingleadsthevoltage/

(4) supplylinesleadsthevoltage

145. A 3-phaseinductionmotoris operatingat slips. If the two supplyleadsare interchanged,thenits slipat thatinstantwill be

(1) 2 - s

(2) 2 +s

(3) 1 +s

(4) 1 - s

(2) a resistorin series

(3) a capacitorof capacitancesmallerthanthatof voltmeter,in series

(4) a capacitorof capacitancelargerthanthatofvoltmeter,in series

149. TheRC circuitshownin fig.is fedfromanacsourceof frequencyw radls.Thepowerfactorof thecircuitis

R

146. For precisionwork, the illuminationlevelrequiredis oftheorderof (1)

wC/R

(1)

500- 1000lumens/m2

(2)

200- 2000lumens/m2I(2)

~1+R2C2w2

(3)

50- 100lumens/m2 II~1+R2C2w2(3)(4)

10- 25lumens/m2

(4)RCwl ~1+R2C2w2

C

147. The deflectingtorque of a' moving ironinstrumentis 1150. In a shadedpolemotorthephasesplittingis

achievedbyplacinga shadingcoilat theslotcutaroundthe

(2) .!. 12dL/d8I

(1)largerpartof thepole2 smallerpart of thepole(3)

I dL/d8(3)

boththepartsof thepole

(4)

! I dL/d8 I(4)

Any of these2 http://al

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