Electrical Engineering - 2006 Unsolved Paper

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ELECTRICAL ENGINEERING - UNSOLVED PAPER - 2006

SECTION – I

 Single Correct Answer Type
 There are five parts in this question. Four choices are given for each part and one of them is

correct. Indicate you choice of the correct answer for each part in your answer-book by

writing the letter (a), (b), (c) or (d) whichever is appropriate

01 Problem

The following is true

a. A finite signal is always bounded
b. A bounded signal always possesses finite energy
c. A bounded signal is always zero outside the interval [- t0, to] for some to
d. A bounded signal is always finite

02 Problem

x (t) is a real valued function of a real variable with period T. Its trigonometric
Fourier Series expansion contains no terms of frequency ω = 2π (2k)/T; k = 1,
2,.... Also, no sine terms are present. Then x (t) satisfies the equation

a. x (t) = -x (t-T)
b. x (t) = x (T -1) = -x (-t)
c. x (t) = x (T -1) = -x (t - T/2)
d. x (t) = x (t - T) = x (t - T/2)

03 Problem

In the figure the current source is 1 0 A, R = 1 Ω, the impedances are ZC = -
Ω, and Z1= 2jΩ. The Thevenin equivalent looking into the circuit across X-Y is

a. √2 O V, (1 + 2j) Ω
b. 2 45° V, (1 - 2j) Ω
c. 2 450 V, (1 + j) Ω

d. √ 2 450 V, (1 +j) Ω

04 Problem

The three limbed non ideal core shown in the figure has three windings with
nominal inductances L each when measured individually with a single phase AC
source. The inductance of the windings as connected will be

a. very low
b. L/3
c. 3L
d. very high

05 Problem

Which of the following statements holds for the divergence of electric and
magnetic flux densities?

a. Both are zero
b. These are zero for static densities but non zero for time varying densities
c. It is zero for the electric flux density
d. It is zero for the magnetic flux density

06 Problem

In transformers, which of the following statements is valid ?

a. In an open circuit test, copper losses are obtained while in short circuit test,
core losses are obtained
b. In an open circuit test, current is drawn at high power factor
c. In a short circuit test, current is drawn at zero power factor
d. In an open circuit test, current is drawn at low power factor

07 Problem

For a single phase capacitor start induction motor which of the following
statements is valid ?

a. The capacitor is used for power factor improvement
b. The direction of rotation can be changed by reversing the main winding
terminals
c. The direction of rotation cannot be changed
d. The direction of rotation can be changed by interchanging the supply
terminals

08 Problem

In a DC machine, which of the following statements is true ?

a. Compensating winding is used for neutralizing armature reaction while
interpole winding is used for producing residual flux
b. Compensating winding is used for neutralizing armature reaction while
interpole winding is used for improving commutation
c. Compensating winding is used for improving commutation while
interpole winding is used for neutralizing armature reaction
d. Compensating winding is used for improving commutation while
interpole winding is used for producing residual flux

09 Problem

The concept of an electrically short, medium, and long line is primarily based
on the

a. nominal voltage of the line
b. physical length of the line
c. wavelength of the line
d. power transmitted over the line

10 Problem

Keeping in view the cost and overall effectiveness, the following circuit
breaker is best suited for capacitor bank switching

a. vacuum
b. air blast
c. SF6
d. oil

11 Problem

In a biased differential relay, the bias is defined as a ratio of

a. number of turns of restraining and operating coil
b. operating coil current and restraining coil current
c. fault current and operating coil current
d. fault current and restraining coil current

12 Problem

An HVDC link consists of rectifier, inverter transmission line and other
equipments. Which one of the following is true for this link ?

a. The transmission line produces/supplies reactive power
b. The rectifier consumes reactive power and the inverter supplies reactive
power from/to the respective connected AC systems
c. Rectifier supplies reactive power and the inverted consumes reactive
power to/from the respective connected AC systems
d. Both the converters (rectifier and inverter) consume reactive power from
the respective connected AC systems

13 Problem

For a system with the transfer function H(s) = (3(s - 2))/(4s2 - 2s + 1), the matrix
A in the state space form x = Ax + Bu is equal to

1 0 0
a. 0 1 0
1 2 4

0 1 0
b. 0 0 1
1 2 4

0 1 0
c. 3 2 1
1 2 4

1 0 0
d. 0 0 1
1 2 4

14 Problem

A discrete real allpass system has a pole at z = 2 300 : it, therefore

a. also has a pole at (1/2) 30°
b. has a constant phase response over the z- plane: arg |H(z)| = constant
c. is stable only, if it is anticausal
d. has a constant phase response over the unit circle: arg |H(ejΩ)| = constant

15 Problem

The time/div and voltage/div axes of an oscilloscope have been erased. A
student connects a 1 kHz, 5 V p-p square wave calibration pulse to channel 1 of
the scope and observes the screen to be as shown in the upper trace of the
figure. An unknown signal is connected to channel 2 (lower trace) of the scope.
If the time/div and V/div on both channels are the same, the amplitude (p-p)
and period of the unknown signal are respectively

a. 5 V, 1 ms
b. 5V, 2 ms
c. 7.5 V, 2 ms
d. 10V, 1 ms

16 Problem

A sampling wattmeter (that computes power from simultaneously sampled
values of voltage and current) is used to measure the average power of a load.
The peak to peak voltage of the square wave is 10 V and the current is a
triangular wave of 5 A p-p as shown in the figure. The period is 20 ms. The
reading in W will be

a. 0 W
b. 25 W
c. 50 W
d. 100 W

17 Problem

What are the states of the three ideal diodes of the circuit shown in figure ?

a. D1 ON, D2 OFF, D3 OFF
b. D1 OFF, D2 ON, D3 OFF
c. D1 ON, D2 OFF, D3 ON
d. D1 OFF, D2 ON, D3 ON

18 Problem

The speed of a 3-phase, 440 V, 50 Hz induction motor is to be controlled over a
wide range from zero speed to 1.5 time the rated speed using a 3-phase voltage
source inverter. It is desired to keep the flux in the machine constant in the
constant torque region by controlling the terminal voltage as the frequency
changes. The inverter output voltage vs frequency characteristic should be

a. b.

c.

d.

19 Problem

For a given sinusoidal input voltage, the voltage waveform at point P of the
clamper circuit shown in figure will be

a. b.

c. d.

20 Problem

A single-phase half wave uncontrolled converter circuit is shown in figure. A 2 -
winding transformer is used at the input for isolation. Assuming the load current
to be constant and v = Vm sin ωt, the current waveform through diode D2 will be

a. b.

c. d.

21 Problem

x [n] = 0; n < - 1, n > 0, x[- 1 ] = -1, x[0] = 2 is the input and
y [n] = 0; n < - 1, n > 2, y[- 1] = - 1 = y[1], y[0] = 3,
y [2] = -2 is the output of a discrete-time LTI system. The system impulse
response h[n] will be

a. h[n] = 0; n <0, n >2, h[0] = 1, h[1] = h[2] = - 1
b. h[n] = 0; n < -1, n > 1, h[-1] = 1, h[0] = h[1] = 2
c. h[n] = 0; n < 0, n > 3, h[0] = -1, h[1] = 2, h[2] = 1
d. h[n] = 0; n < - 2, n > 1, h[- 2] = h[1] = h[-1] = - h[0] = 3

22 Problem
The expression V = H πR2 (1 - h/H)2 dh for the volume of a cone is equal to
0

R

a. 0 πR2 (1 - h/H)2 dr
R
b. 0
πR2(1 - h/H)2 dh
H
c. 0
2πr H(1 – r/R)2 dh
R
d. 0
2πr H(1 – (r/R))2 dr

23 Problem

The discrete-time signal
x[n] X(z) = z2n
where denotes a transform-pair relationship, is orthogonal to the signal

a. y1[n] Y1(z) =
b. y2[n] Y2(z) = (5n-n)z-(2n+1)
c. y3[n] Y3(z) = 2-|n| z-n
d. y4[n] Y4(z) = 2z-4 + 3z-2+1

Electrical Engineering - 2006 Unsolved Paper

25 Problem

A continuous-time system is described by y(t) = e - | x(t) |, where y (t) is the
output and x (t) is the input y (t) is bounded

a. only when x (t) is bounded
b. only when x (t) is non-negative
c. only for t ≥ 0 if x (t) is bounded for t ≥ 0
d. even when x (t) is not bounded

26 Problem

The running integrator, given by
t
y (t) = x(ť)dť

a. has no finite singularities in its double sided Laplace Transform Y(s)
b. produces a bounded output for every causal bounded input
c. produces a bounded output for every anticausal bounded input
d. has no finite zeroes in its double sided Laplace Transform Y (s)

27 Problem

Two fair dice are rolled and the sum r of the numbers turned up is considered

a. Pr (r > 6) = 1/6
b. Pr (r/3 is an integer) = 5/6
c. Pr (r = 8 | r/4 is an integer) = 5/9
d. Pr (r = 6 | r/5 is an integer) = 1/18

28 Problem

The parameters of the circuit shown in the figure are Rj = 1 MΩ, R0 = 10 Ω, A =
106 V/V. If Vj = 1 μV, then output voltage, input impedance and output
impedance respectively are

a. 1V, ∞, 10Ω
b. 1V, 0, 10Ω
c. 1V, 0, ∞
d. 10V, ∞, 10Ω

29 Problem

In the circuit shown in the figure, the current source I = 1 A, voltage source V =
5V,
R1 = R2 = R3 = 1 W, L1 = L2 = L3 = 1H,
C1 = C2 = 1F.
The currents (in A) through R3 and the voltage source V respectively will be

a. 1, 4
b. 5, 1
c. 5, 2
d. 5, 4

30 Problem

The parameter type and the matrix representation of the relevant two port
parameters that describe the circuit shown are

a. z parameters, 0 0
0 0

1 0
a. h parameters, 0 1

0 0
a. h parameters,
0 0

1 0
a. z parameters, 0 1

31 Problem

Consider the following statements with reference to the equation δp/δt
a. This is a point form of the continuity equation
b. Divergence of current density is equal to the decrease of charge per unit
volume per unit at every point
c. This is Max well's divergence equation
d. This represents the conservation of charge

Select the correct answer.
a. Only 2 and 4 are true
b. 1, 2 and 3 are true
c. 2, 3 and 4 are true
d. 1, 2 and 4 are true

32 Problem

The circuit shown in the figure is energized by a sinusoidal voltage source V1 at a
frequency which causes resonance with a current of I
The phasor diagram which is applicable to this circuit

a. b.

c. d.

33 Problem

An ideal capacitor is charged to a voltage V0 and connected at t = 0 across an
ideal inductor L. (The circuit now consists of a capacitor and inductor alone). If
w let o = 1/√LC, the voltage across the capacitor at time t > 0 is given by

a. V0
b. V0 cos (ω0t)
c. V0 sin (ω0t)
d. V0 e- ω ot cos (ω0t)

34 Problem

A 400 V, 50 Hz, three phase balanced source supplies power to a star
connected load whose rating is 12√3 kVA, 0.8 pf (lag). The rating (in kVAR) of
the delta connected (capacitive) reactive power bank necessary to bring the pf
to unity is

a. 28.78
b. 21.60
c. 16.60
d. 12.47

35 Problem

An energy meter connected to an immersion heater (resistive) operating on an
AC 230 V, 50 Hz, AC single phase source reads 2.3 units (kWh) in 1 hour. The
heater is removed from the supply and now connected to a 400 V peak to peak
square wave source of 150 Hz. The power in kW dissipated by the heater will
be

a. 3.478
b. 1.739
c. 1.540
d. 0.870

36 Problem

A 220 V DC machine supplies 20 A at 200 V as a generator. The armature
resistance is 0.2 ohm. If the machine is now operated as a motor at same
terminal voltage and current but with the flux increased by 10%, then ratio of
motor speed to generator speed is

a. 0.87
b. 0.95
c. 0.96
d. 1.06

37 Problem

A synchronous generator is feeding a zero power factor (lagging) load at rated
current. The armature reaction is

a. magnetizing
b. demagnetizing
c. cross-magnetizing
d. ineffective

38 Problem

Two transformers are to be operated in parallel such that they share load in
proportion to their kVA ratings. The rating of the first transformer is 500 kVA
and its pu leakage impedance is 0.05 pu. If the rating of second transformer is
250 kVA, then its pu leakage impedance is

a. 0.20
b. 0.10
c. 0.05
d. 0.025

39 Problem

The speed of a 4-pole induction motor is controlled by varying the supply
frequency while maintaining the ratio of supply voltage to supply frequency
(V/f) constant. At rated frequency of 50 Hz and rated voltage of 400 V its
speed is 1440 rpm. Find the speed at 30 Hz, if the load torque is constant.

a. 882 rpm
b. 864 rpm
c. 840 rpm
d. 828 rpm

40 Problem

A 3 phase, 4 pole, 400 V, 50 Hz, star connected induction motor has following
circuit parameters
r1 =1.0 Ω, r2' = 0.5 Ω, x1 = x2' = 1.2 Ω, xm = 35 Ω
The starting torque when the motor is started direct-on-line is (use
approximate equivalent circuit model)

a. 63.6 Nm
b. 74.3 Nm
c. 190.8 Nm
d. 222.9 Nm

41 Problem

A 3 phase, 10 kW, 400 V, 4 pole, 50 Hz, star connected induction motor draws
20 A on full load. Its no load and blocked rotor test data are given below :
No Load test: 400W 6A 1002W
Blocked Rotor test : 90V 15A 762W
Neglecting copper loss in no Load test and core loss in Blocked Rotor test,
estimate motor's full load efficiency.

a. 76 %
b. 81%
c. 82.4 %
d. 85%

42 Problem

A 3 phase, 400 V, 5 kW, star connected synchronous motor having an internal
reactance of 10Ω is operating at 50% load, unity pf. Now, the excitation is
increased by 1%. What will be the new load in percent, if the power factor is to
be kept same ? Neglect all losses and consider linear magnetic circuit.

a. 67.9%
b. 56.9%
c. 51%
d. 50%

43 Problem

The A, B, C, D constants of a 220 kV line are:
A = D = 0.94 1°, B = 130 73°, C = 0.001 90°.
If the sending end voltage of the line for a given load delivered at nominal
voltage is 240 kV, then % voltage regulation of the line is

a. 5
b. 9
c. 16
d. 21

44 Problem

A single phase transmission line and a telephone line are both symmetrically
strung one below the other, in horizontal configurations, on a common tower.
The shortest and longest distances between the phase and telephone
conductors are 2.5 m and 3 m respectively. The voltage (volt/km) induced in the
telephone circuit, due to 50 Hz current of 100 amps in the power circuit is

a. 4.81
b. 3.56
c. 2.29
d. 1.27

45 Problem

Three identical star connected resistors of 1.0 pu are connected to an
unbalanced 3 phase supply. The load neutral is isolated. The symmetrical
components of the line voltages in pu are: Vab1 = X θ1, Vab2 = Y θ2. If all the
pu calculations are with the respective base values, the phase to neutral
sequence voltages are

a. Van1 = X (θ1 +30°), Van2 =Y (θ2 - 30°)
b. Van1 =X (θ1 - 30°), Van2 = Y (θ2 + 30°)
c. Van1 = 1/√(3) X (θ1 - 30°), Van2 = 1/√(3) Y (θ2 - 30°)
d. Van1 = 1/√(3) X (θ1- 60°), Van2 = 1/√(3) Y (θ2 - 60°)

46 Problem

A generator is connected through a 20 MVA, 13.8/138 kV step down
transformer, to a transmission line. At the receiving end of the line a load is
supplied through a step down transformer of 10 MVA, 138/69 kV rating. A 0.72
pu load, evaluated on load side transformer ratings as base values, is supplied
from the above system. For system base values of 10 MVA and 69 k V in load
circuit, the value of the load (in per unit) in generator circuit will be

a. 36
b. 1.44
c. 0.72
d. 0.18

47 Problem

The Gauss Seidel load flow method has following disadvantages. Tick the
incorrect statement.

a. Unreliable convergence
b. Slow convergence
c. Choice of slack bus affects convergence
d. A good initial guess for voltages is essential for convergence

48 Problem

The Bode magnitude plot of H(jω) = (104(1 +jω))/((10 + jω)(100 + jω)2) is

a.

b.

c.

d.

49 Problem

A closed-loop system has the characteristic function (s2 - 4) (s + 1) + K (s - 1) = 0.
Its root locus plot against K is

a.

b.

c.

d.

50 Problem

y [n] denotes the output and x [n] denotes the input of a discrete-time system
given by the difference equation y [n] - 0.8 y [n - 1] = x[n] + 1.25 x [n + 1], Its
right-sided impulse response is

a. causal
b. unbounded
c. periodic
d. non-negative

51 Problem

The algebraic equation
F(s) = s5 - 3s4 + 5s3 - 7s2 + 4s + 20 is given. F(s) = 0 has

a. a single complex root with the remaining roots being real
b. one positive real root and four complex roots, all with positive real parts
c. one negative real root, two imaginary roots, and two roots with positive real
parts
d. one positive real root, two imaginary roots, and two roots with negative real
parts

52 Problem

Consider the following Nyquist plots of loop transfer functions overω = 0 to ω

= ∞. Which of these plots represents a stable closed loop system ?

a. (1) only
b. all, except (1)
c. all, except (3)
d. (1) and (2) only

53 Problem

A current of - 8 + 6√(2) (sin ωt + 30°) A is passed through three meters. They are
a centre zero PMMC meter, a true rms meter and a moving iron instrument. The
respective readings (in A) will be

a. 8, 6, 10
b. 8, 6, 8
a. -8, 10, 10
b. -8, 2, 2

54 Problem

A variable w is related to three other variables x, y, z as w = xy/z. The

variables are measured with meters of accuracy ± 0.5 % reading, ± 1% of full

scale value and ± 1.5% reading. The actual readings of the three meters are 80,

20 and 50 with 100 being the full scale value for all three. The maximum

uncertainty in the measurement of w will be

a. ± 0.5 % rdg
b. ± 5.5 % rdg
c. ±6.7% rdg
d. ± 7.0 rdg

55 Problem

A 200/1 Current transformer (CT) is wound with 200 turns on the secondary on
a toroidal core. When it carries a current of 160 A on the primary, the ratio and
phase errors of the CT are found to be -0.5% and 30 minutes respectively. If the
number of secondary turns is reduced by 1 the new ratio error (%) and phase
error (min) will be respectively

a. 0.0, 30
b. -0.5, 35
c. -1.0, 30
d. -1.0, 25

56 Problem

R1 and R4 are the opposite arms of a Wheatstone bridge as are R3 and R2. The
source voltage is applied across R1 and R3. Under balanced conditions which
one of the following is true ?

a. R1 = R3 R4 / R2
b. R1 = R2 R3 / R4
c. R1 = R2 R4 / R3
d. R1 = R2 + R3 + R4

57 Problem

Assuming the diodes D1 and D2 of the circuit shown in figure to be ideal ones, the
transfer characteristics of the circuit will be

a. b.

c. d.

58 Problem

Consider the circuit shown in figure. If the β of the transistor is 30 and ICBO is
20 nA and the input voltage is +5 V, then transistor would be operating in

a. saturation region
b. active region
c. breakdown region
d. cut-off region

59 Problem

A relaxation oscillator is made using OPAMP as shown in figure. The supply
voltages of the OPAMP are ± 12V. The voltage waveform at point P will be

a. b.

c. D.

60 Problem

A TTL NOT gate circuit is shown in figure. Assuming VBE = 0.7 V of both the
transistors, if Vj = 3.0 V, then the states of the two transistors will be

a. Q1 ON and Q2 OFF
b. Q1 reverse ON and Q2 OFF
c. Q1 reverse ON and Q2 ON
d. Q1 OFF ans Q2 reverse ON

61 Problem

A student has made a 3-bit binary down counter and connected to the R-2R
ladder type DAC [Gain = (-1 KΩ/2R)] as shown in figure to generate a staircase
waveform. The output achieved is different as shown in figure. What could be the
possible cause of this error ?

a. The resistance values are incorrect
b. The counter is not working properly
c. The connection from the counter to DAC is not proper
d. The R and 2R resistances are interchanged

62 Problem

A 4 x 1 MUX is used to implement a 3-input Boolean function as shown in
figure. The Boolean function F (A, B, C) implemented is

a. F (A, B, C) = (1, 2, 4, 6)
b. F (A, B, C) = (1, 2, 6)
c. F (A, B, C) = (2, 4, 5, 6)
d. F (A, B, C) = (1, 5, 6)

63 Problem

A software delay subroutine is written as given below:
DELAY: MVI H, 255 D
MVI L, 255 D
LOOP: DCR L
JNZ LOOP
DCR H
JNZ LOOP
How many times DCR L instruction will be executed ?

a. 255
b. 510
c. 65025
d. 65279

64 Problem

In an 8085 A microprocessor based system, it is desired to increment the
contents of memory location whose address is available in (D, E) register pair
and store the result in same location. The sequence of instructions is

a. XCHG INR M
b. XCHG INX H
c. INX D XCHG
d. INR M XCHG

65 Problem

A single-phase inverter is operated in PWM mode generating a single-pulse of
width 2d in the centre of each half cycle as shown in figure. It is found that the
output voltage is free from 5th harmonic for pulse width 144°. What will be
percentage of 3rd harmonic present in the output voltage (V03/V01 max) ?

a. 0.0%
b. 19.6%
c. 31.7%
d. 53.9%

66 Problem

A 3-phase fully controlled bridge converter with free wheeling diode is fed from
400 V, 50 Hz AC source and is operating at a firing angle of 60°. The load current
is assumed constant at 10 A due to high load inductance. The input
displacement factor (IDF) and the input power factor (IPF) of the converter will
be

IDF = 0.867 IPF = 0.828
IDF = 0.867 IPF = 0.552
IDF = 0.5 IPF = 0.478
IDF = 0.5 IPF =0.318

67 Problem

A voltage commutation circuit is shown in figure. If the turn off time of the SCRs
is 50 μ sec and a safety margin of 2 is considered, then what will be the
approximate minimum value of capacitor required for proper commutation?

a. 2.88 μF
b. 1.44 μF
c. 0.91 μF
d. 0.72 μF

68 Problem

A solar cell of 350 V is feeding power to an ac supply of 440 V, 50 Hz through a
3-phase fully controlled bridge converter. A large inductance is connected in the
dc circuit to maintain the dc current at 20 A. If the solar cell resistance is 0.5Ω,
then each thyristor will be reverse biased for a period of

a. 125°
b. 120°
c. 60°
d. 55°

69 Problem

A single-phase bridge converter is used to charge a battery of 200 V having an
internal resistance of 0.2 Ω as shown in figure. The SCRs are triggered by a
constant dc signal. If SCR 2 gets open circuited, then what will be the average
charging current ?

a. 23.8 A
b. 15 A
c. 11.9 A
d. 3.54 A

70 Problem

An SCR having a turn ON time of 5 μsec, latching current of 50 mA and holding
current of 40 mA is triggered by a short duration pulse and is used in the circuit
shown in figure. The minimum pulse width required to turn the SCR ON will be

a. 251 μsec
b. 150 μsec
c. 100 μsec
d. 5 μsec

Directions for question 71 to 73 :

A 4 pole , 50 Hz Synchronous generator has 48 slots in which a double layer
winding is housed Each coil has 10 turns and is short pitched by an angle
to 36 electrical . The fundamental flux per pole is 0.025 wb

71 Problem

The line-to-line induced emf (in volts), for a three phase star connection is
approximately

a. 808
b. 888
c. 1400
d. 1538

72 Problem

The line-to-line induced emf (in volts), for a three phase connection is
approximately

a. 1143
b. 1332
c. 1617
d. 1791

73 Problem

The fifth harmonic component of phase emf (in volts), for a three phase star
connection is

a. 0
b. 269
c. 281
d. 808


A generator feeds power to an infinite bus through a double circuit
transmission line . A3 phase fault occurs at the middle point of the lines.
The infinite bus voltage is 1 pu, the transient internal voltage of the
generator is 1.1 pu and the equivalent of 5 mj /MVA and it was delivering 1.0
pu power prior of the fault with rotor power angle of 30 The system
frequency is 50 Hz.

74 Problem

The initial accelerating power (in pu) will be

a. 1.0
b. 0.6
c. 0.56
d. 0.4

75 Problem

If the initial accelerating power is X pu, the initial acceleration in elect deg/sec2,
and the inertia constant in MJ-sec/elect deg respectively will be

a. 31 .4X, 18
b. 1800X, 0.056
c. X/1800, 0.056
d. X/31.4, 18


P = [-1013] T , q =[-2-5 9] T, r[2-7 12 ]T are three vectors

76 Problem

An orthogonal set of vectors having a span that contains p, q, r is

a. [-6 -3 6]T, [4 -2 3]T
b. [-4 2 4]T, [5 7 -11]T, [8 2-3]T
c. [6 7 -1]T, [-3 12-2]T, [3 9-4]T
d. [4 3 11]T, [1 31 3]T, [5 3 4]T

77 Problem

The following vector is linearly dependent upon the solution to the previous
problem

a. [8 9 3]T
b. [-2 -17 30]T
c. [4 4 5]T
d. [13 2 -3]T

Directions for question 78 to 79

It Is requière to design an anti – aliasing filer for an 8 bit ADC. The fileter Is a first
ordre RC filler with R = 1 and C = F. the ADC Is designed to span a sinusoidal
signal with peak to peak amplitude equal to the full scale range of the ADC.

78 Problem

The transfer function of the filter and its roll off respectively are

a. 1/(1 + RCs), -20 dB/decade
b. (1 + RCs), -40 dB/decade
c. 1/(1 + RCs), -40 dB/decade
d. {RCs/(1 + RCs)}, -20 dB/decade

79 Problem

What is the SNR (in dB) of the ADC ? Also find the frequency (in decades) at the
filter output at which the filter attenuation just exceeds the SNR of the ADC.

a. 50 dB, 2 decades
b. 50 dB, 2.5 decades
c. 60 dB, 2 decades
d. 60 dB, 2.5 decades

80 Problem

The iron loss (Pj) and copper loss (Pc) in kW, under full load operation are

a. Pc = 4.12, Pi = 8.51
b. Pc = 6.59, Pj = 9.21
c. Pc = 8.51, Pj = 4.12
d. Pc = 12.72, Pj =3.07

81 Problem

What is the maximum efficiency (in %) at unity pf load ?

a. 95.1
b. 96.2
c. 96.4
d. 98.1


For a power system the admittance and impedance and impedance
mapedance matrices for the fault studiues are as follows

The pre- fault voltages are 1.0 p. u . At all the buses The system was unloaded
prior to the fault. A soild 3 phase fault takes place at bus 2.

82 Problem

The post fault voltages at buses 1 and 3 in per unit respectively are

a. 0.24, 0.63
b. 0.31, 0.76
c. 0.33, 0.67
d. 0.67, 0.33

83 Problem

The per unit fault feeds from generators connected to buses 1 and 2
respectively are

a. 1.20, 2.51
b. 1.55, 2.61
c. 1.66, 2.50
d. 5.00, 2.50

Directions for question 84 to 85

A voltage commutated chopper operating at 1 kHz is used to control the speed
of dc motor as shown in figure . The load current is assumed to be constant at
10 A

84 Problem

The minimum time in μsec for which the SCR M should be ON is

a. 280
b. 140
c. 70
d. 0

85 Problem

The average output voltage of the chopper will be

a. 70 V
b. 47.5 V
c. 35 V
d. 0 V

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Electrical Engineering - 2006 Unsolved Paper

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