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SECTION- A

1. This question consists of 25 (TWEN TTY FIVE) su b-qu esti ons. Each sub-question carries 0 N E mark. The answers to these su b-q uesti ons MUST be written on I y in the ap prop ri ate boxes corresponding to the questions in the first page of the answer b oak.

1.1 When the plate area of a parallel pi ate capacitor is increased k in capacitor VOl tag 8 con Stant, th 8 force between th 8 pi ates a (a) increase (b) decreases (c) remains constant

(d) may increase or decrease depending on the metal making s

1.2 direction. The m agnatic field along a line running r I ~ these wires and midway between them

(a) depends u pan I (b) rz:r: (c) depends upon d d~y (d) depends upon the permeability of me ... v een the wires

An electromagnetic field is rad~ate ~ (a) a stationary point charge (b) a capacitor with a DC val tag e

(c) a conductor carrying a DC rre (d) an oscillating dipole

Tho m obili~ of'" •:~'9"'"''"' ;, '"P'~"d io Orm' of (a) cm2 /V-s . / V-s (c) cm2 /V (d)cm2 /s

'"ooh.,~m~"""''""'' MO'"' ;, "''"~"'by fuo •ymb"

,,, ~·" (b) ---1 ~

1.3

1.4

1.5

(d)

1.6 As the temperature is increased, the voltage across a diode carrying a diode carrying a constant current

(a) increases (b) decreases

(c) remains constant

(d) may in crease or decrease d ep ending up on the doping I eve Is in the junction

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1.7

1.8

1.9

1.10

1.11

1.12

A single channel digital storage oscilloscope uses a 10 bit, 10 7 sam pies per second Anal og-to-D i gi tal Converter. For a 10 0 KHz sine wave input, the number of sam pies taken per cycle of the input wi II be

(a) 107 (b) 104 (c) 103 (d) 102

Higher synchronous reactance is preferred in the present day a~ter to because one can have

(c) reduced transient currents

(a) reduced sub-tran si en t currents (b) reduced harm on i c <:5u e

(d) higher voltage regulation with load r ~ A series R -L -c circuit when excited by a 10V sinusoidal val tag~e of v ari able frequency, exhibits resonance at 100 Hz and has a 3~n~idth of 5 Hz. The val tage across the inductor L at resonance is: "-/

(a) 10 V (b) 1o.J2v (c) ~ (d) 200V

The RM S value of a half-wave recti fi ed4m t:l;j; square wave current of 2 A is:

(a) ../2A (b) 1A . ~c) ;A (d) ./3A

arge errors whi I e measuring power in ac si nee the val tage across and the current

(b) current coi I are not in quadrature

zon- zoo v-

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1.14

1.15

1.16

1.17

An overhead I i ne having a surge impedance of 400 n is connected in series with an underground cable having a surge impedance of 1000.. If a surge of so kV travels from the I in e end towards the line-cable junctions, the value of the transmitted val tag e wave at the junction is:

(a) 30 kV (b) 20 kV (c) 80 kV (d) -30 kV

The I oad carrymg capab 111 ty of a I ong AC tr an sm 1 ss1 on I me 1s: ~ (a) always lim 1ted by the conductor s1ze

(b) lim 1 ted by stab 111 ty cons1 der at1 ons 0 (c) reduced at a I ow am b1 ent temperatures

(d) decreased by the use of bundled conductors ofsmgle conG

Corona losses are m1n1m1zed when ~ + (a) conductor s1 ze 1s reduced (b) sm o u ctor 1 s reduced

(C) sharp pOintS are prOVIded In th 8 line hardw ar '! (d) current dens1ty 1n conductors 1s reduce7i.d '-J In a DC transm1ss1on lme ~ (a) 1 t 1 s necessary for the e an rece1 vmg end to be opera ted 1n

synchrom sm .

(b) the effects of i ndu cti ve a e reactances are greater than in an AC transmission line of the sa rat .

(c) there are not effects ~..., cti ve and capacitive reactances

(d) power transfer ~~ited by stability considerations.

1.18 Steady state s~~_:Fwer system is the ability of the power system to (a) maintain g t the rated voltage level

(b)~ain in fr cy exactly at 50 Hz (c) m · t a • inning reserve margin at all times (d) · ynchronism between machines and on external tie lines

1.19. ~actions of a feeder are provided with circuit breakers CB1, CB2, CB3, CB4, ~~d CB6. For a fault F as indicated in Fig.1.19.

CB2 CB3 CB4

(a) CBS must be set to trip after CB1 trips

(b) CBS must be set to trip after CB3 and CB4 trips

(c) CBS must be set to trip after CB2 trip

CBS F

(d) CBS must be set to trip before CB1, CB2, CB3 and CB4 trips

CB6

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1. 2 0. A 4-p ole I ap-wou nd DC genera tor has a d eve I oped power of P watts and val tage of E val ts. Two adjacent brushes of he machine are removed as they are worn out. If the machine operates with the remaining brushes, the developed voltage and power that can be obtai ned from the machine are

(a) E, P E p

(b) -,-2 2

(c) p

E,-4

1. 21. Starting torque can be obtained in the case of a single with i den tical main and auxiliary windings by connecting

(a) a capacitor across the mains

(b) a capacitor in series with the machine

(c) a capacitor in series with the aux iIi ary winding

(d) the main and the auxiliary windings in series

p (d) E, -

2

ph"' '"'"'~ uO

1.22. The windings of a QkVA, v1 volt, three-phaoe,on: ected, core type v2

transformer are reconnected to work U1)j phase transformer. The maximum voltage and the power ratings o h w confi gur ati on are,

(a) 3V1 , 3Q (b) V1 'Q .t., 3V1 , 2Q (d) 2V1 '2Q

3V2 V2 ~~ .fiv2 2V2 3

1. 2 3. Resonant converters are basi ca use, to

(a) generate large peaky~l e (b) reduce the switching losses

(c) eliminate har~~~ (d) convert a squ). ... r · o a sine wave

1.24. A PWM switchi~ft, e is used with a three phase mverter to

(a)~edu the~rmomc d1stort1on w1th modest filtenng

(b) m t ht' load on the DC s1de

(c s he life of the battenes

d) e I ow order harm om cs and mcrease h1 g h order harm om cs

starting torque per ampere of the line current drawn:

(a) Direct line starting

(b) Auto transformer method of starting

(c) Series inductor method of starting

(d) Star-Delta method of starting

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2.

2.1

2.2.

2.3.

2.4.

This question consists of 25 (TWEN TTY FIVE) su b-q uesti ons. Each sub -question carries TWO marks. The answers to these sub -questions MUST be written on I y in the appropriate boxes corresponding to the questions in the first page of the answer b oak.

The col or code of a 1 k n resistance is:

(a) black, brown, red (b) red, brown, brown ~ (c) brown, black, red (d) black, black, red

A rectangular current pulse of duration T and magnitude I ho lace transform

(a) ! (b) (~)exp(-Ts)CJ

(c) (~)exp(Ts) (d) m[ef~)J

A rectan gu I ar val tage pulse of mag n1 tude ~~n T 1 s ap pll ed to a sen es com bmat1 on of res1 stance R and cap ac1tan ¥ v:.. e-rn ax 1m u m val tag e developed

(c) V (d) Vexp(;~)

l~e peak amplitude 1 V and frequency 0.5 Hz is mation of 1 n resistance and 1 F cap ad tance, the

(b) % (d)

X Q

(a)

(b) X= 0, Y = 1

(c) X= 1, y = 0 y

(d) X= 1, Y = 1

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2.6.

2.7.

2.8.

2.9.

2.10.

The logic function f = ( x.y) + ( x.y) is the same as

(a) f=(x+y)(x+:¥)

(b) f = (x+y)+(x+y)

(c) t = (x.y).(x.:Y)

A dB

0 0 dB

6 dB per octive

~-- .~ (d) None of(a), (b) (c).

0~'

The function corresponding to the Bode lot of Fig;: is:

1

r ~ (•) A •Jf /f1 (b) '(J!,'~

1 •

(c) A=(1+jftlf) (d) v f/ For a sm gl e phase overhead I me h avm g ~~~ per conductors of d1 am eter 1 em, spaced 60 em between centers, th:fCIU a 1n m H/km 1s:

(a) 0.05+0.2ln60 ~( 0.2ln60

(c) 0.05+0.21n(60

) (d) 0.21n(60

) 0.5 0.5

'""''' '""'" ':~~"" <wo ""''' '""' '"''" '"'~ m "'·'·' The voltage drop fi'om ~~~ 0 0 25 A +J · n B C

(a) 4.5 v 0 .5 v 230V O+J0.35a (c) 30 V ( 20 V

,--,L--, 30A,

\ 0-81eg '-.:"'---'

in ~~ ! nsum er has a daily load pattern of 2000 kW, 0.8 lag for 12 D{Ll""a:i.~ 1~0 0 k w U PF for 12 hours. The I oad factor is:

(b) 0.75 (c) 0.6 (d) 2.0

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2.12. A 3-phase, 11 kV, 50 Hz, 200 kW load has a power factor of 0.8 lag. A delta connected 3-p hase capacitor is used to imp rove the power factor to unity. The capacitance power phase of the capacitor in microfarads is

(a) 3.948 (b) 1.316 (c) 0.439 (d) 11.844

2.13. A 10 kVA, 400 V/200V single-phase transformers with 10% impedanc~dr a steady short circuit I i ne current of

(a) 50 A (b) 150 A (c) 250 A (d) 350 '

2.14. The percentage resistance and percentage reactance of a 10 kVA0:/ 200 v, 3-phase transformer are 2% and 10% respectively. If the coa~~ in the machine are 1%, the maximum possible percentage effi ci enc of t transformer IS:

(a) 98.32 (b) 97.25 (c) 96.8:r>e +(d) 96.12

2.15. A 400V/100V, 10 kVA two-winding transfor~s~nected as an auto­transformer across a suitable voltage sou~lllo..~ximum rating of such an arrangement caul d be

(a) 50 kVA (b) 15 kVA .t. .,~ .5 kVA (d) 8.75 kVA

2.16. A DC shunt motor is runni~n· 1~~p, when excited with 220 v DC. N egl ecti ng the I asses and satu 1 the peed of the motor when connected to a 17 5 V DC supply is:

(a) 750 RPM (b)~ (c) 1050 RPM (d) 1200 RPM

2.17. A three phase al t~~Yw:u nd with a 6 0 degree phase-spread armature windings and ~~s 0 kVA. If the armature is reconnected utilizing all the coi Is for sin gl p s eration with a phase spread of 180 degrees, the new rating of the m 1n s

(a) 100 (b) 200 kVA (c) 250 kVA (d) 300 kVA

percentage resistance f % percentage reactance of 6% is su ppl yi ng a current of 50 A to a

· · ·ve load. The value of the load voltage is:

...... ~ 194 V (b) 390 V (c) 192 V (d) 196 V

~~For a dual ADC type 3 ~digit DVM, the reference voltage is 100 mV and the first

integration time is set to 3 00 m s. For same in put voltage, the "dei nteg ration" period is 370.2 m s. The DVM will indicate

(a) 123.4 (b) 199.9 (c) 100.0 (d) 1.141

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2. 2 0. When a resi star R is connected to a current source, it consumes a power of 18 w. when the same R is connected to a voltage source having the same magnitude as the current source, the power absorbed by R is 4. 5 W. The mag ni tude of the current source and the value of R are

(a) JiBA and 10. (b) 3A and 20.

(c) 1A and 180. (d) 6A ad 0.5 n

2.21.

th erm ocou pie type, 5 A fu 11-scal e, el ass 1 meter. The meter read1 wo d II e 1n

therange CJ (a) 5A±1% (b) (2+3.J2)A±1

(c) 3A±1.7% (d) 2A±2~~~ +

2.22. Currents I 1,I2 and I 3 meet at a JUnction (no~n~Uit. All currents are

marked as entenng the node. ~11..'-'

If I 1 = -6 sm («~t) mA and I2 = 8 cos ( «~t)~, t will be

(a) 10 cos(«~t+ 36.87)mA 14cos («~t+36.87)mA

(c) -14sm(«~t+36.87)mA _,N (d) -10cos(«~t+36.87)mA

2.23. Two 100~A full-scale PM~~~ employed to construct a 10 V and a 100V

(a) 10 kD./V and 10 V (b) 100 kO./V and 10 kO./V

full scale voltmeter~Th s t will have figures of merit (sensitivities) as

(c) 10 kD./V a~ ... k (d) 10 kD./V and 1 kO./V

2.24. A fixed c paci~eactance -j0.020. is connected in parallel across a series com bi nat1 of .i. fixed inductor of reactance jO. 010. and a v ari able resistance R. As R i 1 f?!!'m zero to infinity, the locus diagram of the admittance of this L-c- ·r be

-ci rei e of diameter j 100 and center at zero.

em i -ci rei e of diameter j 50 and center at zero

trai gh t I in e in eli ned at an angle

(d) a straight line parallel to the x-axis

The voltage phasor of a circuit is 10L15° v and the current phasor is 2L-45° A. The active and the reactive powers in the circuit are:

(a) 10 wand 17.32 VAr (b) 5 wand 8.66 VAr

(c) 20 Wand 60 VAr (d) 20.}2 Wand 10./2 VAr

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SECTION- B

This section consists of TWE N TV questions of FIVE marks each. ANY FIFTEEN out of them have to be answered. If more number of questions are attempted, score off the answers not be evaluated, else, on I y the first fifteen u nscored answers wi II be cons1 dered.

3. Solve the c1rcu1t shown 1n F1g .3 usmg the mesh method of analys1s and~m 1

4.

the mesh currents I 1, I 2 and I3 . Evaluate the power developed 1n the 1 v ge

source. zn zv

0 - +\------;

4n lzJ 6n r~ 12V lOV ~

+ •

5. The ratio error of a i

6.

up f burden at ilcu en . Estimate the iron I ass of the current transformer at this op er ati n g n f the secondary has 19 8 turns and a winding resistance of 0. 02 0.. N egl ea age reactance.

A c~a is tni form I y distributed throughout the val u me of a dielectric sphere of i n d dielectric constant sR. based on Gauss I aw, determine the

ex~s for the electric field E as a function of distance r fi'om the center of ~ ~1 here, within the ranges 0 < r < Rand R s r. Indicate expression(s) for the ~IC point (s) on the sketch.

The logic function F = AC + A8D + ACD is to be realized using an 8 to 1 multiplexer shown in Fig. 7, using A, C and D as control inputs.

(a) Indicate the inputs to be applied at the terminals 0 to 7.

(b) Can the function be realize using a 4 to 1 multiplexer? State YES or N 0 .

... _ ..... _- ·- -'"···-··'· -S: .-:- .... _._ .. _: ..... _- _ .. _ .. _ - -·. _ .. : -·-

0 1

2

3 4

5 6

7 D

8xl MUX F

C A

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9.

10.

in terms of capacitor val tage, Vc and inductor current i1•

For the small s1gnal BJT amplifier shown 1n Flg.9, determine at l~o followmg:

(a) qu1escent collector current, IcQ

0 (b) small Signal VOltage gam, (~:} r ~ (c) max 1m u m p oss1b I e swmg of the coli ector current ~

~.:: " r., '(:) 0 +

lue qJ v1 and the average value V0 •

lOkn

skn

v, lkn lOkn

v.

Va

llOO~F

-;:-

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11. Determine the magnitudes of the symmetrical components ( I•Q•' I •• , I.) of the

currents in a three phase (R VB) three wire system, when a short circuit occurs between R and Y phase wires, the fault current being 100 A.

12.

13.

14.

A 6.6 kV, 50 Hz, single core lead-sheathed cable has the following data~·

Conductor diameter: 1.5 em, length: 4 km

In tern a I diameter of the sheath : 3 em

Resi sti vi ty of in sui ati on : 1.3 x 1012 0.-m 0 Rei ati ve permittivity of i nsu I ati on : 3. 5

Calculate: r ~ (a) the insulation resistance ~

(b) the capacitance and

(c) the max 1m um electn c stress 1n the 1n sui at1 on 0 +

A 66 kV, 3-phase, 50 Hz, 150 km long over::d~ransm1ss1on line 1s open c1 rcu 1 ted at the rece1 vmg end. Each cond u ~~s1 stance of 0. 25 0/k m, an i nd ucti ve reactance of 0. 5 0/k m and a c d m ittance to neutral of 0. 04 x w·• S/km.

(a) Draw the nominal 1t-eq~,ival it and indicate the value of each parameter.

(b) Cal cui ate the receiving en ol t i the sending end voltage is 66 k V.

Determine the require ~in g of the circuit breaker CB for the system shown in fig.14. Consi r";~ as infinite bus. Choose 6 MVA as base.

Transformer: 3-pha , kV, 6 MVA, 0.01 + jO .08 p.u. impedance.

Load: 30 1 kV, 5800 MVA, 0.8 lag, JO .2 p.u. 1m pedance.

<m~~ ~ ::~,:'""1 { ~I----I Load

l Feeder 1 __,

sup ported by a stn ng of 3 susp en s1 on msu lators. The a1 r capac1 tan ce between each cap-pin J u nct1 on and tower 1 s one-fifth of the capac1 tan ce C of each msu lator un 1 t. A guard ring, effective only over the line-end i nsu I a tor unit is fitted so that the val tages on the two units nearest the I in e-end are equal.

(a)

(b)

Cal cui ate the val tage on the I i ne-en d unit.

Cal cui ate the value of capacitance C x required.

[///.Qi'tW//////r.<

c~C's '·

cT~s'

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16. In the circuit shown in Fig .16, the capacitor is i ni tiall y charged to 12 V. find the mathematical expression for the voltage across the capacitor vc after dosing thw

17.

lB.

19.

switch at t = 0.

18n

zn r~ A 3 kW, 400V/200V, Delta/Star, so Hz, three phase, 6-pol~lon motor 1s found to draw a line current of 25 A at a power faet ,.i, when a blocked rotor test is conducted at the rated val tag e. D et m · e (h~ stator and rotor winding resistances in ohms per phase, if theQ loped by the motor under the above con di ti ons is 2 5 N -m .

Two single-phase transformers A and B ha~~ owing parameters:

Transformer A: 400V/200V, percen~e"' ~ce and percentage reactance 3% and 4% resp ecti vel y. .

Transformer B: 5 kVA, 400 · 0 centage resistance and percentage reactance are 4% and 3% res

These two transformers a~n cte in parallel and they share a common load of 12 kW at a power fa or . I agg in g. Determine the active and reactive power delivered by~ra er .

A separately~· d shunt motor is driving a fan load whose torque is proportional t t u e of the speed. When 100 V are applied to the motor, the current ta b the motor is BA, with the speed being 500 rpm. At what applied tage i:ll7 s the speed reach 7 50 rpm and then what is the current drawn e • m ature? Assume the armature circuit resistance to be 10.. Neg ec drop and mechanical I asses.

20~VA, 11 kV, 3-phase star connected alternator 1s synchronized to the bus r d 1 s oper atmg w1 th an 1n du ced EMF of 12 5% of the rated val tag e. If the

current IS SODA, what IS the power factor of operation? The m achme has a synchronous reactance of 5 n and neg llg 1 bl e resistance per ph as e.

2r . A three phase d1ode bndge 1s used to prov1de rectified output from a 400V, 50 Hz, 3-phase supply to a R -L load with 100. resistance and 300 m H inductance. Determine the

(a) DC I eve I of the output voltage (b) R MS value of the diode current,

(c) RMS value of the source current, and /.-1\ A,....,.... -..-.-.nfo n ...,, ... ,... .. .-1 .. -,,"',.... h-.-. ..... t-h.-. ...., -.in~

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22. For the circuit shown in Fig.22, the internal resistance of the ammeters as well as that of the current coi I of the wattmeter are zero, and the val tm eters have a very large figure of merit. A1 is a 6A full scale moving iron type meter. A2 is a

commercial full wave rectifier type meter of full seale SA. V1 is a 50 ov meter of

the peak response type. V2 is a 300V PMMC type meter and w is an

electrodynam om eter type, A1,Az,V1,V2 and W.

230V 50Hz

SA, 2~~~--:~ttmeter. Determme the re~d1n f

.;"" w .... ," /M L '\ A, 0

! \ ' l r I l ,• \ I

\C / ', ··'' ~: ........ _____ ._ .....