6278d1346421803 old question papers ongc graduate trainee ongc electrical electronics questions...

8/12/2019 6278d1346421803 Old Question Papers Ongc Graduate Trainee Ongc Electrical Electronics Questions Answers

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Paper Type : Question-Paper

Test Date : 05 Aug 2012

Test Location : Electronics and electrical -2012

TYPICAL QUESTIONS & ANSWERS OBJECTIVE TYPE QUESTIONS

Q.1 The two windings of a transformer is(A) conductively linked.(B) inductively linked.(C) not linked at all.(D) electrically linked.Ans B

Q.! A salient "ole synchronous motor is running at no load. #ts field current is switched off.vThemotor will(A) come to sto".(B) continue to run at synchronous s"eed.

(C) continue to run at a s"eed slightly more than the synchronous s"eed.(D) continue to run at a s"eed slightly less than the synchronous s"eed.Ans B

Q.$ The d.c. series motor should always %e started with load %ecause(A) at no load& it will rotate at dangerously high s"eed.(B) it will fail to start.(C) it will not develo" high starting tor'ue.(D) all are true.Ans A

Q. The fre'uency of the rotor current in a $ "hase * +,& "ole induction motor at fullvload s"eedis a%out(A) * +,.(B) !* +,.(C) ! +,.(D) -ero.Ans C

Q. #n a ste""er motor the angular dis"lacement(A) can %e "recisely controlled.(B) it cannot %e readily interfaced with micro com"uter %ased controller.(C) the angular dis"lacement cannot %e "recisely controlled.(D) it cannot %e used for "ositioning of work ta%les and tools in C machines.Ans A

Q./ The "ower factor of a s'uirrel cage induction motor is(A) low at light load only.(B) low at heavy load only.(C) low at light and heavy load %oth.


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(D) low at rated load only.Ans A

Q.0 The generation voltage is usually(A) %etween 11 2 and $$ 2.

(B) %etween 1$! 2 and ** 2.(C) %etween ** 2 and 0** 2.(D) one of the a%ove.Ans A

Q.3 4hen a synchronous motor is running at synchronous s"eed& the dam"er winding "roduces(A) dam"ing tor'ue.(B) eddy current tor'ue.(C) tor'ue aiding the develo"ed tor'ue.(D) no tor'ue.Ans D

Q.5 #f a transformer "rimary is energised from a s'uare wave voltage source& its out"ut voltage will%e(A) A s'uare wave.(B) A sine wave.(C) A triangular wave.(D) A "ulse wave.Ans A

Q.5 #f a transformer "rimary is energised from a s'uare wave voltage source& its out"ut voltage will%e(A) A s'uare wave.(B) A sine wave.(C) A triangular wave.(D) A "ulse wave.Ans A

Q.1* #n a d.c. series motor the electromagnetic tor'ue develo"ed is "ro"ortional to(A) #a .(B) 1 !6a(C)#6a1Ans B

Q.11 #n a $ 7 "hase induction motor running at sli" 8s9 the mechanical "ower develo"ed in terms ofair ga" "ower :g is(A) (s ;1 ) :g .(B) :g6(1; s)(C) (1; s ) :g .(D) s < :g .Ans C


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Q.1! #n a $ 7 "hase induction motor the ma=imum tor'ue(A) is "ro"ortional to rotor resistance r! .(B) does not de"end on r! .(C) is "ro"ortional to root of r! .

(D) is "ro"ortional to r!6!Ans B

Q.1$ #n a d.c. machine& the armature mmf is(A) stationary w.r.t. armature.(B) rotating w.r.t. field.(C) stationary w.r.t. field.(D) rotating w.r.t. %rushes.Ans C

Q.1 #n a transformer the voltage regulation will %e ,ero when it o"erates at

(A) unity ".f.(B) leading ".f.(C) lagging ".f.D) ,ero ".f. leading.Ans B

Q.1 The ma=imum "ower in cylindrical and salient "ole machines is o%tained res"ectively at loadangles ofAns 5* degree>5* degree

Q.1/ The "rimary winding of a !!*6/ 2& * +, transformer is energised from 11* 2& /* +, su""ly.The secondary out"ut voltage will %e(A) $./ 2.(B) !. 2.(C) $.* 2.(D) /.* 2.Ans C

Q.10 The emf induced in the "rimary of a transformer(A) is in "hase with the flu=.(B) lags %ehind the flu= %y 5* degree.(C) leads the flu= %y 5* degree.(D) is in "hase o""osition to that of flu=.Ans C

Q.13 The relative s"eed %etween the magnetic fields of stator and rotor under steady stateo"eration is ,ero for a(A) dc machine.(B) $ "hase induction machine.(C) synchronous machine.


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(D) single "hase induction machine.Ans all o"tions are correct

Q.15 The current from the stator of an alternator is taken out to the e=ternal load circuit through(A) sli" rings.

(B) commutator segments.(C) solid connections.(D) car%on %rushes.Ans C

Q.!* A motor which can conveniently %e o"erated at lagging as well as leading "ower factors is the(A) s'uirrel cage induction motor.(B) wound rotor induction motor.(C) synchronous motor.(D) DC shunt motor.Ans C

Q.!1 A hysteresis motor(A) is not a self;starting motor.(B) is a constant s"eed motor.(C) needs dc e=citation.(D) can not %e run in reverse s"eed.Ans B

Q.!! The most suita%le servomotor for low "ower a""lications is(A) a dc series motor.(B) a dc shunt motor.(C) an ac two;"hase induction motor.(D) an ac series motor.Ans B

Q.!$ The si,e of a conductor used in "ower ca%les de"ends on the(A) o"erating voltage.(B) "ower factor.(C) current to %e carried.(D) ty"e of insulation used.Ans C

Q.! ?ut of the following methods of heating the one which is inde"endent of su""ly fre'uency is(A) electric arc heating(B) induction heating(C) electric resistance heating(D) dielectric heatingAns C

Q.! A two;winding single "hase transformer has a voltage regulation of .@ at full;loadand unity


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"ower;factor. At full;load and *.3* "ower;factor lagging load the voltageregulation will %e(A) .@.(B) less than .@.(C) more than .@.

(D) .@ or more than [email protected] C

@ 2r cos 2= sin 2r".f cos 1 E **E k2A k4 F k2A *o reactive "ower com"onent:ercentage regulation (@) 2r cos G 2= sin 4hen cos *.3 lagging@ 2r cos 2= sin 2r (*.3) 2= (*./)

@ (*.3)2r (*./) 2= at ".f *.3 laggingand @ 2r at unity ".f

Q.!/ #n a dc shunt motor the terminal voltage is halved while the tor'ue is ke"t constant. Theresulting a""ro=imate variation in s"eed HwH and armature current H #a H will %e(A) Both w and #a are dou%led.(B) w is constant and #a is dou%led.(C) w is dou%led while #a is halved.(D) w is constant %ut #a is halved.Ans B

2 7 #a or I%T #a & #aE T #a

Q.!0 A %alanced three;"hase& * +, voltage is a""lied to a $ "hase& "ole& inductionmotor. 4henthe motor is delivering rated out"ut& the sli" is found to %e *.*. Thes"eed of the rotor m.m.f. relative to the rotor structure is(A) 1** r.".m.(B) 1! r.".m.(C) ! r.".m.(D) 0 r.".m.Ans D

J 1!*f 6: 1!* = * 6 1**r"m J ( 1;s) 1** (1;*.*) 1!Erelative s"eed 1** 7 1! 0 r"m

Q.!3 An alternator is delivering rated current at rated voltage and *.3 "ower;factor laggingcase. #f it


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is re'uired to deliver rated current at rated voltage and *.3 "ower;factorleading& the re'uired e=citation will %e(A) less.(B) more.(C) more or less.

(D) the same.Ans B?ver e=citation gives leading "ower factor and under e=citation gives lagging ".f .

Q.!5 A ceiling fan uses(A) s"lit;"hase motor.(B) ca"acitor start and ca"acitor run motor.(C) universal motor.(D) ca"acitor start motor.Ans DTo give starting tor'ue and to maintain s"eed.

Q.$* A ste""er motor is(A) a dc motor.(B) a single;"hase ac motor.(C) a multi;"hase motor.(D) a two "hase motor.Ans DJte""er motor works on 1;"hase;? or !;"hase 7? modes of o"eration

Q.$1 The 8sheath9 is used in ca%le to(A) "rovide strength to the ca%le.(B) "rovide "ro"er insulation.(C) "revent the moisture from entering the ca%le.(D) avoid chances of rust on strands.Ans A

The sheath in underground ca%le is "rovided to give mechanical strength.Q.$! The drive motor used in a mi=er;grinder is a(A) dc motor.(B) induction motor.(C) synchronous motor.(D) universal motor.Ans DThe universal motor is suita%le for AC F DC %oth su""ly systems.

Q.$$ A 1 ste";u" transformer has 1!*2 across the "rimary and /** ohms resistanceacross the secondary. Assuming 1**@ efficiency& the "rimary current e'uals(A) *.! Am".(B) Am"s.(C) 1* Am"s.(D) !* Am"s.


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Ans A#1 21 61 1!*6/** *.! (h 1**@& losses are ,ero E21 2 #11)

Q.$ A dc shunt generator has a s"eed of 3** r"m when delivering !* A to the load at theterminalvoltage of !!*2. #f the same machine is run as a motor it takes a line

current of !*A from !!*2 su""ly. The s"eed of the machine as a motor will %e(A) 3** r"m.(B) more than 3** r"m.(C) less than 3** r"m.(D) %oth higher or lower than 3** r"m.Ans C

g Ig (/*A 6 ",) Ig 2 #a a K in generatorm I% (/*A 6 ",) I% 2 ; #a a K in motorIg L I % for same terminal voltageTherefore& g L m

Q.$ A * +,& $;"hase induction motor has a full load s"eed of 1* r.".m. The num%er of"oles ofthe motor are(A) .(B) /.(C) 1!.(D) 3.Ans A s (1;J) J 7J = J1* s (1;J)s 1* 6 (1;J)s (1!* f6 ") 1!* = *6" /*** "s will %e closer to i.e 1*4hen :! K s $*** r"m & not close to 4hen : K s 1** r"m & it is closer to Therefore : for 1*

Q. $/ #n a $;"hase synchronous motor(A) the s"eed of stator MM is always more than that of rotor MM.(B) the s"eed of stator MM is always less than that of rotor MM.(C) the s"eed of stator MM is synchronous s"eed while that of rotor MM is ,ero.(D) rotor and stator MM are stationary with res"ect to each other.Ans D

Because& Motor is magnetically locked into "osition with stator& the rotor "oles areengaged withstator "oles and %oth run synchronously in same direction Therefore&rotor F stator mmf are stationary w.r.t each other.Q.$0 #n a ca"acitor start single;"hase induction motor& the ca"acitor is connected(A) in series with main winding.


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(B) in series with au=iliary winding.(C) in series with %oth the windings.(D) in "arallel with au=iliary winding.Ans BTo make single "hase motor self start. 4e s"lit the "hases at 5* degree. +ence& motor%ehaves

like a two "hase motor.

Q.$3 A synchro has(A) a $;"hase winding on rotor and a single;"hase winding on stator.(B) a $;"hase winding on stator and a commutator winding on rotor.(C) a $;"hase winding on stator and a single;"hase winding on rotor.(D) a single;"hase winding on stator and a commutator winding on rotor.Ans CJynchros The %asic synchro unit called a synchro transmitter. #t9s constructionsimilar to that of aThree "hase alternator.

Q.$5 As the voltage of transmission increases& the volume of conductor(A) increases.(B) does not change.(C) decreases.(D) increases "ro"ortionately.Ans CDecreases due to skin effect.

Q.* The si,e of the feeder is determined "rimarily %y(A) the current it is re'uired to carry.(B) the "ercent variation of voltage in the feeder.(C) the voltage across the feeder.(D) the distance of transmission.Ans AJi,e of conductor de"ends u"on amount of current flow.

Q. 1 The %oundary of the "rotective ,one is determined %y the(A) Nocation of CT(B) sensitivity of relay used(C) Nocation of :T(D) one of theseAns BThe %oundary of the "rotective ,one is determined %y the sensitivity of relay used. #fthe relay ismore sensitive& the "rotective ,one will %e increased.

Q.! #n a three "hase transformer& if the "rimary side is connected in star and secondaryside isconnected in delta& what is the angle difference %etween "hase voltage in thetwo cases.(A) delta side lags %y ;$*O.(B) star side lags %y ;$*O.


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(C) delta side leads %y $*O.(D) star side leads %y ;$*O.Ans C

This is vector grou" and has $*O dis"lacement. Therefore& delta side leads %y $*O.

Q.$ To achieve low :T error& the %urden value should %e PPPPPPPPPPPP.(A) low(B) high(C) medium(D) none of the a%oveAns A #n a :otential transformer& %urden should %e in "ermissi%le range to maintainerrorlessmeasurement.

Q. Jli" of the induction machine is *.*! and the stator su""ly fre'uency is * +,.4hat will %ethe fre'uency of the rotor induced emf(A) 1* +,.

(B) * +,.(C) 1 +,.(D) !** +,.

Ans CRiven s *.*! K f * +,Therefore& fre'uency of rotor induced emf s f *.*! = * 1.* +,

Q. A "ole la" wound dc shunt motor rotates at the s"eed of 1** r"m& has a flu= of *.m4%and the total num%er of conductors are 1***. 4hat is the value of emf(A) 1** 2olts.(B) *.1 2olts.(C) 1 2olts.(D) 1* 2olts.Ans D

Riven 1** r"m& *. m4%& - 1***& : & F A Therefore& I% :- 6 /* A 1** = *. = = 1*** = 1*;$ 6 /* = /*6/ 1* volts

Q./ The synchronous reactance of the synchronous machine is PPPPPPPPPPPPPP.(A) atio %etween o"en circuit voltage and short circuit current at constant field current(B) atio %etween short circuit voltage and o"en circuit current at constant field current(C) atio %etween o"en circuit voltage and short circuit current at different field current(D) atio %etween short circuit voltage and o"en circuit current at different field currentAns. AThe Jynchronous reactance of a synchronous machine is a total steady state reactance&"resented to a""lied voltage& when rotor is running synchronously without e=citation.


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Therefore & SJ If 6 #J Imf of ?C for same #f 6 short circuit current

Q.0 A $ stack ste""er motor with 1! num%ers of rotor teeth has a ste" angle ofPPPPPPPPPPPP.(A) 1!O

(B) 3O(C) !O(D) 1*OAns. DRiven m $& r 1!Jte" angle $/* 6 m = r $/* 6$ = 1! 1*O

Q.3 #n case of a universal motor& tor'ue "ulsation is minimi,ed %y PPPPPPPPP.(A) load inertia(B) rotor inertia(C) %oth rotor and load inertia

(D) none of the a%oveAns C

#n a universal motor& tor'ue "ulsation is minimi,ed %y rotor and load inertia.Q.5 ?il;filled ca%le has a working stress of PPPPPPPPPP k26mm(A) 1*(B) 1!(C) 1$(D) 1Ans DThis is defined %y dielectric strength of mineral oil i.e. 1 k26mm.

Q.* #nverse definite minimum time lag relay is also called PPPPPPPPPPP(A) "ilot relay.(B) differential relay.(C) over current relay.(D) directional overcurrent relay.Ans B#nverse definite minimum time lag relay characteristic is inverse %ut minimum time isfi=ed. The o"erating time is inversely "ro"ortional to the magnitude of actuating'uantity.

Q.1 J"ecific heat of nickel 7chrome is PPPPPPPPPPPPP(A) *.11!(B) *.1*/.(C) *.1*3.(D) *.11*.Ans one of theseJ"ecific heat of ickel;Chrome is * 6kgOC to * 6kgOC


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Q.! The "olarity test is not necessary for the single;"hase transformer shown in ig. 1

so as to correctly determine PPPPPPPPPPPPPof the transformer.figure(A) shunt %ranch "arameters.(B) transformation ratio.(C) series "arameters.(D) any of the a%ove characteristics.Ans D:olarity test is re'uired for "arallel o"eration of transformers to know the direction ofcurrent flow in secondary circuit w.r.t "rimary circuit.

Q.$ The short;circuit ratio of a ty"ical synchronous machine is o%tained from the ?CCand JCCcurves of ig.! as
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As shown in JCC curve the ratio of two field currentsQ. The s"eed;tor'ue characteristics of a DC series motor are a""ro=imately similar tothose of the PPPPPPPPPmotor.(A) universal

(B) synchronous(C) DC shunt(D) two;"haseAns AUniversal motor has same characteristics as DC series motor and also known as an a.cseries motor.

Q. The rotor fre'uency for a $ "hase 1*** :M / "ole induction motor with a sli" of*.* isPPPPPPPP+,(A) 3(B)

(C) /(D) !Ans DRiven 1*** r"m K : /K s *.*Kand f :6 1!* 1*** /61!* * +,otor fre'uency frs f *.* * !.* +,

Q./ The tor'ue;s"eed characteristics of an a.c. o"erated universal motor has aPPPPPPcharacteristic and itPPPPPP %e started under no;load condition.(A) inverse& can(B) nearly inverse& can(C) inverse& cannot(D) nearly inverse& cannotAns C#f tor'ue is ,ero then s"eed may e=ceed u" to infinite& that is dangerous for machineand machine can %e damaged. 16 T

Q.0 #n the heating "rocess of the PPPPPPPPty"e a sim"le method of tem"erature control is"ossi%le %y means of a s"ecial alloy which loses its magnetic "ro"erties at a "articularhigh tem"erature and regains them when cooled to a tem"erature %elow this value.(A) #ndirect induction over(B) core ty"e induction furnace(C) coreless induction furnace(D) high fre'uency eddy currentAns DMagnetic "ro"erty of alloy changes with change of the tem"erature and


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+eat is "roduced due to eddy current i! and i f!

Q.3 #n order to reduce the harmful effects of harmonics on the A.C. side of a high voltageD.C. transmission system PPPPPPare "rovided.(A) synchronous condensers

(B) shunt ca"acitors(C) shunt filters(D) static com"ensatorsAns CSc 16cQ.5 An a.c. tachometer is Vust a PPPPPPPPwith one "hase e=cited from the carrierfre'uency.(A) two;"hase A.C. servomotor(B) two;"hase induction motor(C) A.C. o"erated universal motor(D) hy%rid ste""er motor.

Ans DThis is a s"ecial "ur"ose machine whose stator coil can %e energi,ed %y electronicallyswitched current.

Q./* The tor'ue& in a PPPPPPPPPPPPPis "ro"ortional to the s'uare of the armature current(A) DC shunt motor(B) ste""er motor(C) !;"hase servomotor(D) DC series motorAns DTa .#a and #a K therefore Ta #a!

Q./1 The synchronous s"eed for a $ "hase /;"ole induction motor is 1!** r"m. #f thenum%er of "oles is now reduced to with the fre'uency remaining constant& the rotors"eed with a sli" of @ will %e PPPPPPPPP.(A) 1/5* r"m(B) 10* r"m(C) 1** r"m(D) 101* r"mAns DRiven s1 1!** & :1 /&:! & s *.*&re'uency f s :61!* 1!* /61!* /* +,rotor fre'uency f6 s.f *.* /* $.* +,ow& s! 1!* /* 6 13** and s 7 1!* f 6 :!Therefore& s; 1!* f 6 :! 13**;1!* *.* /*6 13**;5* 101*

Q./! The eddy current loss in an a;c electric motor is 1** watts at * +,. #ts loss at 1**


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+, will %e(A) ! watts(B) 5 watts(C) 1** watts(D) ** watts

Ans DIddy current losses f!ew loss (!f)!ew loss f!E times

Q./$ The ma=imum "ower for a given e=citation in a synchronous motor is develo"edwhen the "ower angle is e'ual to(A) *o(B) o(C) /*o

(D) 5*oAns A: 2# cos:ma= 2#E **

Q. / A commutator in a d.c. machine(A) educes "ower loss in armature.(B) educes "ower loss in field circuit.(C) Converts the induced a.c armature voltage into direct voltage.(D) #s not necessary.Ans CAs name suggests& it commutes ac into dc.

Q./ The s"eed of a d.c. shunt motor at no;load is(A) to 1*@(B) 1 to !*@(C) ! to $*@ (D) $ to *@higher than its s"eed at rated load.Ans ATa #a && constant&ET #a I% 6 or I% initially I% less & so s"eed is less.

Q.// The efficiency of a transformer is mainly de"endent on(A) core losses.(B) co""er losses.(C) stray losses.


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(D) dielectric losses.Ans ACore loss has "rominent value over other losses

Q./0 4hen two transformers are o"erating in "arallel& they will share the load as under

(A) "ro"ortional to their im"edances.(B) inversely "ro"ortional to their im"edances.(C) *@ ; *@(D) !@;0@Ans A+igh rating transformer has higher im"edance.k2A rating #m"edance of transformer

Q./3 #f the voltage is reduced to half& the tor'ue develo"ed %y an induction motor will %ereduced to(A)1of original tor'ue.

(B)!1of original tor'ue.(C)31of original tor'ue.(D)1/1of original tor'ue.Ans BTg 2 or Tg :m (rotor gross out"ut)

Q./5 A $;"hase& ** votts& * +,& 1** 4& "ole s'uirrel cage induction motor with arated sli" of !@ will have a rotor s"eed of(A) 1** r"m(B) 10* r"m(C) 1$* r"m(D) 10* r"mAns B J (1;J) and J 1!* f 6 "1!* = * 6 1** r"mE 1** (1;*.*!) 10* r"mQ.0* #f the "hase angle of the voltage coil of a directional relay is o* & the ma=imumtor'ue angle of the relay is

Ans CTor'ue :ower:ower 2oltageTherefore& #t has same angle as 829 has

Q.01 The voltage at the two ends of a transmission line are 1$! 2 and its reactance is* ohm. The Ca"acity of the line is(A) $./ M4(B) !10.3 M4(C) !1. M4(D) ** M4


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Ans ANine ca"acity is determined %y "ower of line: (2!6) or (2!6-) when cos 1

Q.0! A !!*6* 2& * +,& 2A& single "hase transformer o"erates on !!*2& *+,

su""ly with secondary winding o"en circuited. Then(A) Both eddy current and hysteresis losses decreases.(B) Both eddy current and hysteresis losses increases.(C) Iddy current loss remains the same %ut hysteresis loss increases.(D) Iddy current loss increases %ut hysteresis loss remains the same.Ans A4h khfBm1./ and 4e kef!Bm!.kTherefore& hysteresis and eddy current losses will %e decreased when fre'uencydecreases.

Q.0$ A synchronous motor is o"erating on no;load at unity "ower factor. #f the fieldcurrent is increased& "ower factor will %ecome(A) Neading F current will decrease(B) Nagging F current will increase.(C) Nagging F current will decrease.(D) Neading F current will increase.Ans A#nitially synchronous motor is o"erating at no load and unity "ower factor. 4henfield current increases& the e=citation will increase. Therefore& ".f will %e leading andcurrent will %e # Cos > #

Q.0 A d.c. shunt motor runs at no load s"eed of 11* r.".m. At full load& armature reactionweakens the main flu= %y @ whereas the armature circuit voltage dro"s %y 1*@. Themotor full load s"eed in r.".m. is(A) 1*3*(B) 1!*$(C) 1***(D) 1!**Ans A! 6 1 I%! 6I%1 = 1 6 ! K ! *.51 K I%! *.5I%1E ! 611* *.5 = 16*.5! 1*3*

Q.0 The introduction of inter"oles in %etween the main "ole im"roves the "erformance ofd.c.machines& %ecause(A) The inter"ole "roduces additional flu= to augment the develo"ed tor'ue.(B) The flu= waveform is im"roved with reduction in harmonics.(C) The ine'uality of air flu= on the to" and %ottom halves of armature isremoved.(D) A counter e.m.f. is induced in the coil undergoing commutation.


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Ans DCounter e.m.f is "roduced& it neutrali,es the reactive emf.

Q.0/ The rotor "ower out"ut of a $;"hase induction motor is 1 4 and corres"onding sli"is @.The rotor co""er loss will %e

(A) /** 4.(B) /! 4(C) /* 4(D) 0** 4

Ans Botor co""er losses rotor in"ut; rotor out"utand out"ut (1;s) in"utE #n"ut out"ut6(1;s) 1*** 61;*.* 1/!E loss 1/! ;1** /! wattQ.00 The direction of rotation of hysteresis motor is reversed %y

(A) Jhift shaded "ole with res"ect to main "ole(B) eversing su""ly lead(C) Iither A or B(D) either A nor BAns AThis motor used single "hase& *+, su""ly and stator has two windings. These areconnectedcontinuously from starting to running.

Q.03 A 1.3Oste"& ;"hase ste""er motor has a total of * teeth on 3 "ole of stator. Thenum%er ofrotor teeth for their rotor will %e(A) *(B) *(C) 1**(D) 3*Ans BJte" angle 89 J 7 r 6 J r = $/**E 1;3 ;* r6* r = $/**r *

Q.05 Now head "lants generally use(A) :elton Tur%ines(B) rancis Tur%ine(C) :elton or rancis Tur%ine(D) a"lan Tur%inesAns A#n the hysterisis motor& the direction of rotation can %e reversed %y shifting theshaded "ole regionwith res"ect to main "ole. But not %y changing su""ly lead%ecause it has ac su""ly.

Q.3* The charging reactance of * m length of line is 1**. The charging reactance for1**m


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length of line will %e(A) 1**(B) $***(C) 0*(D) /**

Ans BCharacteristic reactance "er km 1**6* $* ohmsE Characteristic reactance "er 1**km $* = 1** $*** ohms

Q.31 Ilectric ovens using heating elements of PPPPPPPPPPPPPPP can "roduce tem"eratureu"to$***OC.(A) ickel(B) Rra"hite(C) Chromium(D) #ronAns C

Chromium has high melting "oint.

Q.3! #n DC generators& armature reaction is "roduced actually %y(A) #ts field current.(B) Armature conductors.(C) ield "ole winding.(D) Noad current in armature.Ans DBecause load current in armature gives rise to armature mmf which react withmain field mmf.

Q.3$ Two transformers o"erating in "arallel will share the load de"ending u"on their(A) ating.(B) Neakage reactance.(C) Ifficiency.(D) :er;unit im"edance.Ans ATransformers having higher k2A rating will share more load.

Q.3 As com"ared to shunt and com"ound DC motors& the series DC motor will have thehighesttor'ue %ecause of its com"aratively PPPPPPPPPPPP at the start.(A) Nower armature resistance.(B) Jtronger series field.(C) ewer series turns.(D) Narger armature current.Ans DT #a(%efore saturation) #aT #a


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!Q.3 A **k4& $;"hase& *2& *+, induction motor has a s"eed of 5* r.".m. on fullload.Themachine has / "oles. The sli" of the machine will %e PPPPPPPPPPPPPPP.(A) *.*/(B) *.1*

(C) *.*(D) *.*

Ans D s (1;J)5* 1!* = * (1;J)6/J *.*

Q.3/ eduction in the ca"acitance of a ca"acitor;start motor& results in reduced(A) oise.(B) J"eed.

(C) Jtarting tor'ue.(D) Armature reaction.Ans Ceduction in the ca"acitance reduces starting voltage& which results in reducedstarting tor'ue.

Q.30 egenerative %raking(A) Can %e used for sto""ing a motor.(B) Cannot %e easily a""lied to DC series motors.(C) Can %e easily a""lied to DC shunt motors(D) Cannot %e used when motor load has overhauling characteristics.Ans BBecause reversal of #a would also mean reversal of field and hence of I%

Q.33 At "resent level of technology& which of the following method of generating electric "owerfrom sea is most advantageous(A) Tidal "ower.(B) ?cean thermal energy conversion(C) ?cean currents.(D) 4ave "ower.Ans AAt "resent level of technology& tidal "ower for generating electric "ower from seais mostadvantageous %ecause of constant availa%ility of tidal "ower.

Q.35 #f the field circuits of an unloaded salient "ole synchronous motor gets suddenlyo"encircuited& then(A) The motor sto"s.(B) #t continues to run at the same s"eed.(C) #ts runs at the slower s"eed.(D) #t runs at a very high s"eed.Ans B


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The motor continues to run at the same s"eed %ecause synchronous motor s"eeddoes not de"endu"on load& a f.

Q.5* Ilectric resistance seam welding uses PPPPPPPPPP electrodes.

(A) :ointed(B) Disc.(C) lat(D) DomedAns BDisc ty"e electrodes are used for electric resistance seam welding.

Q.51 or N2 a""lications (%elow 1 k2)& PPPPPPPPPPPPPP ca%les are used.(A) :a"er insulated.(B) :lastic.(C) Jingle core ca%les.

(D) ?il filled.Ans Cor low voltage a""lications single core ca%les are suita%le.

Q.5! o load current in a transformer(A) lags the a""lied voltage %y 5*O(B) lags the a""lied voltage %y somewhat less than 5*O(C) leads the a""lied voltage %y 5*O(D) leads the a""lied voltage %y somewhat less than 5*OAns BThe "rimary in"ut current under no load conditions has to su""ly (i) iron losses inthe core i.ehysteresis loss and eddy current loss (ii) a very small amount of Cu lossin the "rimary (there %eing no Cu loss in secondary as it is o"en)

Q.5$ A transformer o"erates most efficiently at $6th full load. #ts iron (:#) and co""erloss (:Cu)are related as(A) 1/ 5 # Cu : :(B) $ # Cu : :(C) $ # Cu : :(D) 5 1/ # Cu : :Ans D#f :Cu is the Cu loss at full load& its value at 0@ of full load is:Cu =(*.0)! 561/ :CuAt ma=imum efficiency& it e'uals the iron loss :# which remains constant throughout. +ence ma=. efficiency at

:# 561/ :Cu?r :# 6 :Cu 561/

Q.5 #n a salient "ole synchronous machine (usual sym%ols are used)(A) =' L =d


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(B) =' =d(C) =' > =d(D) =' *Ans CJince reluctance on the ' a=is is higher& owing to the larger air ga"&

hence =' > =d

Q.5 The armature of a dc machine is laminated to reduce(A) Iddy current loss(B) +ysteresis loss(C) co""er losses(D) friction and windage lossesAns AThinner the laminations& greater is the resistance offered to the induced e.m.f.smaller the currentand hence lesser the #! loss in the core.

Q.5/ The resistance re"resenting mechanical out"ut in the e'uivalent circuit of aninduction motoras seen from the stator isMechanical :ower develo"ed %y the rotor (:m) or gross "owerdevelo"ed %y rotor(:g) rotor in"ut 7rotor Cu losses ($#6! !6 6 J) ;($#6! !6 ) $#6! !6 (16 J ;1)

Q.50 A single "hase +ysteresis motor(A) can run at synchronous s"eed only(B) can run at su% synchronous s"eed only(C) can run at synchronous and su"er synchronous s"eed(D) can run at synchronous and su% synchronous s"eedAns AThe rotor revolves synchronously %ecause the rotor "oles magnetically lock u" with the revolvingstator "oles of o""osite "olarity

Q. 53 The tem"erature of resistance furnaces can %e controlled %y changing the(A) a""lied voltage(B) num%er of heating elements(C) circuit configuration(D) All of the a%oveAns DTem"erature of resistance furnaces can %e controlled %y changing either a""liedvoltage or %ynum%er of heating elements or %y circuit configuration.

Q.55 The line tra" unit em"loyed in carrier current relaying


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(A) offers high im"edance to * +, "ower fre'uency signal(B) offers high im"edance to carrier fre'uency signal(C) offers low im"edance to carrier fre'uency signal(D) Both (A) F (C)Ans B

The line tra" unit em"loyed in carrier current relaying offers high im"edance tocarrier fre'uencysignal.Because carrier fre'uency range is $ km 7 ** k+,SN ! f l4here f increases SN will also increases

Q.1** or a line voltage 2 and regulation of a transmission line (A) W 2(B)2 W 1(C) ! W 2(D) ! 2 W 1

Ans B 162egulation (2* 7 2N ) 6 2* & if 2N is high the (2* 7 2N ) will %e low.Therefore 16

6278d1346421803 old question papers ongc graduate trainee ongc electrical electronics questions...

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