www.examrace.com

1.

1.1

1.2

1.3

SECTION- A

In each of sub question (1.1 to 1.25) four alternatives A, B, C and D are provided of which one is correct. Indicate in your book, at the space provided, the correct answer by writing the alphabet corresponding to the answer.

A si nu said al source of val tage v and fi'equ en cy f is connected to a seri e~ it v ari able resistance, R and a fixed reactance, X. The I ocus of the o e current-phasor, I, as R is varied fi'om 0 to oo is: 0 (a) a semicircle with a diameter of~. r ~ (b) a straight line with a slop of ; ~ (c) an ellipse w1th ~as maJor ax1s. 0 + (d) a c1rcle ofrad1us ; and ongm at (o, ~). CJ A c1rcu1t With a resistor, inductor and 4a~enes IS resonant of t0 Hz. If all the component values are now~o e~new resonant frequency 1s: (a) 2t

0 (b) still (c) to (d) to

4 2

In the circuit shown i i~is desired to have a constant direct current i(t) L

through the ideal i lliii~~F~~L;. ne nature of the voltage source v(t) must be: (a) constant v~ i(t) (b) linearly in 1 oltage (c) :;_~~~p ~ v(t) (d) ~~a~ increasing voltage

L~"'~'" ~a~ "' Lho tr '"'m '""" ""' '"'"" m "'LA " ' " (b) ~11 Transm1ss1on hne P (c) o z. = 300n (d) 0, 5 Zo = Sugar .mpedance

Load 300n

www.examrace.com

1.5 The laws of electrom agnatic induction (Faraday's and Lenz's law) are summarized in the foil owing equation:

1.6

1.7

1.8

1.9

(a) e = iR

(c) d'fl e=--dt

di (b) e =L-dt

(d) None of the above

A synchronous generator connected to an mfi n1 te bus 1s overex c1te~. o der g only the react1ve power, from the pomt of v1ew of the system, th d 1 acts as

(a) a capaCitOr (b) an Inductor r ~ (c) a res1stor (d) None of the a~

A 3 phase squ1rrel cage mduct1on motor has a full O dioctency of 0.8 and a maximum efficiency of 0.9. It IS operated at as~ applying a reduced val tage. The effi c1en cy of the motor at th 1 s oper ng nt 1 s: (a) less than 0.4 ~ r than 0.6 (c) 1n the range of0.8 0.1 .t "'I.U n e of the above The effiaency of a 100 KVA trar.~s r ~98 at full as well as at half load. For th 1 s transformer at fi.J II I oad the er

None of the above

(a) harmonr>._< (c) (d) 1311> harmonic

1.10 Series ca, cl t1 ~en sat1 on 1n EH V tr ansm 1 ss1 on II n es 1 s used to (a)~e e e ~e loading (b he stability of the system c) e the voltage profile (d) improve the protection of the line

(a) low cost of HVDC terminals (b) no harmonic problems (c) minimum line power losses (d) simple protection

www.examrace.com

1.12 The output of a linear time invariant control system is c(t) for a certain input r(t). If r(t) is modified by passing it through a block whose transfer function is e- and then app I ied to the system, the modified output of the system wou I d be

(a) __:_{1_ 1+ e'

(c) c(t-1)u(t-1)

1.13 None of the pales of a lin ear control system bounded input, the output of this system (a) is always bounded (c) always tends to zero

1.14 The phase I ead com pensat1on 1s used to

1.15

(a) (b) (c) (d)

0

(b) 2

0

(b)

(d)

is:

(c) 5 (d) -1

_,] 0 1 0 ~ . The sum of the eigen values of them atrix A is: 0 0 3 -1 0 0

(a) 10 (b) -10 (c) 24 (d) 22

Ax= b. the

1.18 A d .c. val tm eter has a sen si tivi ty of 100 0 D./val t. When it measures half fu II seale in 10 ov range, the current through the val tm eter is

www.examrace.com

1.19. A moving coil galvanometer ism ade into a d.c. ammeter by connecting (a) a I ow resistance across the meter (b) a high resistance in series with the meter (c) a pure inductance across the meter (d) a capacitor in series with the meter

1.20. The open collector outputs of two 2-inputs NAND gates are conn common pull up resistor. If the input to the gates are P, Q and R, t5s tive , the output is equal to -- --(a) P.QRS. (b) PQ+RS (c) P.Q+RS ,..)~ .S

1. 21. In standard TTL gates, the totem pole output stage is prim ari I ~to (a) increase the noise margin of the gate ~ .. + (b) decrease the output switching delay "-/ (c) facilitate a wired OR logic connection CJ (d) increase the output impedance of the~ .....

1. 2 2. One of the app li cations of current m i rr4,s ~ V (a) output current limiting ~ (b) obtaining a very high curre n (c) current fee db ad< (d) temperature stabiliz~

1.23. The uncontrolled e~~w1tch employed in power electronic converters is: (a) thyristor ~ .. r (b) bipolar junction transistor (c) diode '(..1 (d) MOSFET

1.24. The M~\s~ch 1n 1ts on-state may be considered equ1valent to: ~~ (b) Inductor (c) capaator (d) battery

1. ~~ ,~ om m utat1on c1rcu1t em played to turn off an SCR, satisfactory turn-off 1s ~ ~a1ned when

(a) circuit turn-off time < device turn-off time (b) circuit turn-off time > device turn-off time (c) circuit time constant > device turn-off time (d) circuit time constant < device turn-off time

www.examrace.com

2. Questions 2.1 to 2 .2 0 are accompanied by four answers of which one is correct. Indicate the correct answer, in the space provided in the answer book, by writing the alphabet A, B, Cor D. For each of questions 2.21 to 2 .25, three items are given on the left side and more than three on the right. For each item on the left, match a sui tab I e answer from the items on the right (e.g.A-Q, B-S, C-T). Write your answer in the space provided in the answer b oak.

2.1 Viewed fi'om the terminals A, B the following circuit shown in Fig. reduced to an equivalent circuit of a single voltage source in seri e ,...

www.examrace.com

2. 6. A 50 Hz transformer having equal hysteresis and eddy OJ rrent I asses at rated excitation is opera ted at 45 Hz at 90% of its rated val tag e. Com pared to rated operating point, the core I asses under this con di ti on:

2.7.

2.8.

2.9.

(a) reduce by 10% (b) reduce by 19% (c) reduce by 14.5% (d) remain unchanged

The armature of a single phase alternator is completely wound with T s~irn coils distributed uniformly. The induced voltage in each turn is 2V (rm s he f of the whole winding is ~ (a) 2T volt (b) 1.11 T volt (c) 1.414 T volt (do . volt

A 2 40 V d .c. shunt motor with an armature resistance of I";, ~ s a full I oad current of 40 A. Find the ratio of the stalling torque to the ful~rque when a resistance of Hl. is connected in series with the arm at + (a) 4 (c) 6

2.10. A power station consists of t > syn~onou s generators A and B of ratings 25 0 MVA and 500 MVA with in 1. .u. and 1 p.u ., respectively on their own base

2.11.

MVA ratings. The . merti a constant for the system on 10 0 MVA common base is: (a) 2.6 (c) 1.625 (d) 9.0

For the netwo/":t.., n in Fig.2 .11, the zero sequence reactance's in indicated. The ~~uence driving point reactance of the node 3 is: p .u. are

G .,. X.,o=O.l

(b) 0.30

x .. =o.os i U h x.o=O~ " I .,.

(c) 0.10 (d) 0.20

www.examrace.com

2.12. The Laplace transform of (t2 -2t) u(t-1)is:

(a) 2 -s 2 -s -e --e 53 52

(b) 2 -2s 2 -s -e --e 53 52

(d) None of the above

2.13. For block diagram shown in Fig.2 .13 ~~:lis given by Hz

+ R(s)

2.14.

2.15.

5 2

(c) 0 1 0 3

(d) 1 0 1 2

5 2

0 1 3

0

1 0 1 2

2 2.16. The value of J ( ~) dx computed using Simpson's rule with a step size of h = 0.25

I is: (a) 0.69430 (b) 0.69385 (c) 0.69325 (d) 0.69415

www.examrace.com

2.17. Fig. 2.17 shows the input attenuator of d c probe .------,

a multi meter. The meter reads fu II seale .,.M~_._, -.11N--'H~----ep with 12 V at M, with the range switch at L ______ ] position 'q'. What is the required 2Mn 6Ma val tage at M to obtain fu 11-scal e deft ection with the range switch at position ~s'?

(a) 1 v (c) 120 V

(b) 150 v (d) 147 v

2.18. Fig. 2.18 shows the el ectrostati '4-'"'--l the accel er ati ng voltage, the to:

dVA

12Mn

20kn

Electron Trajectory \ (a) LL,; ;f

(b) L~~o ~ ~e~b~e=am~~~-+--------+--

q

v

ange

d + (o)~ _...Deflection plate df---~ 0

Fluorescent screen

~ -2 When the firing angIe tx of a single phase, fully controlled rectifier feeding constant d. c. current into a I oad is 3 0, the di spl acem ent power factor of the rectifier is:

(a) 1 (b) 0.5 1 (c) J3 (d) J3 2

www.examrace.com

2.20. A 3-phsae, fully controlled, converter is feeding power into a d.c. load at a constant OJ rrent of 15 0 A. The rm s OJ rrent through each th yri star of the converter is:

(a) 50A

2.21.

2.22.

2.23. Circuit (a)

(b) 100A

Measurement (A) Transients (B) Frequency

150./2 (c) ..fj (d) 150 J3

Instrument used . ~ (P) Signal generator 0~' ( Q) Spectrum analyzer (C) Harmonic content (R) Digital storage osco (S) Pulse counter

Test r ~ M: chine (A) No load and blocked rotor. ~ransformer (B) Sump ner's test ( Q) Induction machine

(S) DC machine

~flj (P) High-pass filter

(Q) Amplifier

>--'--ev .

www.examrace.com

2.24.

2.25.

(c) (R) Com par a tor

(S)

Logic 0 (rfllf u;ct1on (A) X+ Y (B) XV (C) X Y t')...Gcarr~

"'V(s)NOR

foil owm g ch aracten st1 cs ag a1n th val es:

v..,~''"" Values (P) 0.7 V (Q) 0.2 v ~~ X ~sat (R)6V

(S) 50 V

rce or a long time. At t = 0, the switch is thrown to 24 V. termine iL (o) and Vc (o)

Write the differential equation governing v c(t) fort> 0 (c) Compute the steady state value ofVc(t).

t=O

24V i, L R,

iRz

R, CT i, l

Vc:(t)

1

Match its

www.examrace.com

4. A 50 hp, 6 pole, 50 Hz slip-ring induction motor runs at 960 rpm on full load with a rotor current of 40 A. allowing 3 00 w for the cop per I ass in the short d rcui tin g gear and 120 0 W for mechanical I asses, find the resistance R 2 per phase of the 3 phase rotor winding.

5. Each conductor of a 3 3 K v, 3-ph ase system is suspended by a string of similar in suI ars. The ratio of shunt capacitance to mutual capacitance Cal cui ate the val tag e across each insulator, and the string efficiency.

6. Find the value of S at the end of the execution of the foil owing pro~ (given in FORTRAN CODE as well as C code). CJ'\,J

FORTRAN CODE C Function MOD (A,B) Returns the value C (A modulo B) ~ .. +

S=O '(.) DO 1 1 = 1,100 IF (MOD) (1, 7). EQ.O) G 0 TO 1 IF (MOD) (1,10). EQ.7) GO TO 1 s = s +1

1 CONTINUE c co

1f (!(1% 7)) go ~ C ~ ~~=+11~)~jFp; Skip: '++ ;""(J } .

put of logical 1 only for the input combination (A = 1; B = C = D = 0). It is that the foil owing com bi nations of input are forbidden:

ABCD = 1010, 1011, 1100, 1101, 1110, 1111 Evaluate the I ogi cal ex pression for the output and realize the same with two input NAND gates. Assume that com pi em ents of in puts are not available.

www.examrace.com

8.

9.

10.

11.

12.

SECTION- B (50 Marks)

Answer any TEN questions from this section. All questions carry equal marks.

A circuit con si sting of a single resi star R and an inductor L in series is drive 25 V rm s, 50 Hz sinusoidal voltage source. A capacitor is to be placed in with the source to improve the power factor. Given that the aver .D:--.. ... d1 ss1 pated 1n the R 1 s 100 W and that the react1ve power delivered to t 1 Var, what value of C will y1eld a 0.9 p.f. laggmg as seen by the sou~

Determine the Impedance seen by the source V5 = 24LO'In tGe~hown 1n Flg.9.

zn -jln -jzn

v,

An infinite number of charges, X = 4, X = 8, X = 16 and SO 0, due to these system of~g

An electron moves~n e lane with a speed of 106 m/s. Its velocity vector makes an angle of -axis. A m agnatic field of magnitude 10-2 T exists along. the v-an : a Jte the m agnatic force exerted on the electron and its d1rect1on. '(./!'

ge'lV a tor delivers 60 K w at 2 40 v and 3 60 rpm . The armature and ces are 0. 0 15 0. and 6 on respectively. Cal cui ate the speed of the ng as a shunt motor and taking 60 KW input at 240 V. Allow 1 volt

r contact drop.

www.examrace.com

14. For the given network in Fig.14, obtain the bus admittance matrix (Ysus) using the data given:

15.

Lines between nodes 1- 2

1- 3

2-3

Shunt reactor at node 1- 2

Impedance p. u. Half of 11 ne ~ Ji.~dm 1 ttance 0.0 + J0.05 J1.25 CJ"' 0.0 + J0.02 J0.50

0.0 + J0.02 ~ ...... Impedance 4 "'v O.O+J2. ~

In a power system, the fuel in hour of pi ants 1 and 2 are given as Ft = 0.20 P12+ 30 P~ F2= 0.25 P22+~0 -c,;r

Thelimitsofg0 . 20 s Pt s 40 s P2s 2

MW, n " g Transmission losses.

Rs per hour Rs per hour

Fin~dhe no~c operating schedule of generation, if the load demand is 130

16. tern tor is connected to an infinite bus as shown in Fig.16. It delivers 1.0 rrent at 0. 8 p f I ag gi ng at V = 1. 0 p .u. The reactance Xd of the altern a tor is

p .u. Determine the active power output and the steady state power I i mit.

excitation corresponding to operation at stabi I i ty I im it.

%

~ V=l.OLO

www.examrace.com

17. The state-space representation of a system is given by:

[XI]= [-5 1] [XI] x2 -6 0 x2 Find the Lap I ace transform of the state transition matrix. Find also the vali!IM:Ii x1 at t = 1 if x1 (o) = 1 and x2 (o) = o.

18.

20 dB/dec

log., .,,

19.

. Find the transformation matrix using the householder's method

www.examrace.com

21. A symmetrical 40 0 v, 3 -phase sup pi y is connected to the network shown in Fig.21. the phase sequence is RYB. Find the reading on the wattmeter. R1 = 300.;X1 =500. and X 2 = 400..

R

B

y 22.

23.

For V0 = d estimate the input resistance of the circuit.

Va

www.examrace.com

24. Show that the cirruit given in Fig .24 will work as an oscillator at f = - 1-, if 27rRC

25. (a)

(b) (c)

Rz

+ >--.,._--eVa .. c

R c

(l) = CJ

Construct the truth table for the~~ In F1g.2s. Q1, Q:a and Q3 are outputs and the clock pulses are ~~~nused J, K mputs are assumed to be at I og 1c 1. All f11 p-fl ops a~ power ON. Sketch the output wavefor Qt. 2, and Q3 .

c R

arm?

(a) Write down the d i fferen ti al equation governing the speed t>O.

(b) Evaluate the time taken for the speed to reach 100 0 rpm .

www.examrace.com

27. A d. c. motor driven from a fully contrail ed 3 phase converter shown in Fig. 2 7, draws a d. c. current of 100 A with n egl i gi bl e ripple. (a) Sketch the a.c. line current iA for one cycle (b) D eterm in e the 3 rd and s11> harm ani c component of the line current as a

percentage of fun dam ental current.

3 phase input

i. A _ _.,. _ _.

B ------l---e c------l--~--~

lOOA