# (Download) UPSC IAS Mains Exam Paper - 2017 : Electrical Engineering

## (Download) UPSC IAS Mains Exam Paper - 2017 : Electrical Engineering

## ELECTRICAL ENGINEERING

(PAPER-I)

**Time Allowed : Three Hours**

**Maximum Marks : 250**

**QUESTION PAPER SPECIFIC INSTRUCTIONS**

**(Please read each of the following instructions carefully
before attempting questions)**

There are **EIGHT** questions divided in two Sections and printed both in
**HINDI** and in **ENGLISH.**

Candidate has to attempt **FIVE** questions in all.

Question Nos. **1 **and** 5** are compulsory and out of the remaining,
**THREE **are to be attempted choosing at least **ONE **question from each
Section.

The number of marks carried by a question/part is indicated against it.

Answers must be written in the medium authorized in the Admission Certificate which must be stated clearly on the cover of this Question-cum-Answer (QCA) Booklet in the space provided. No marks will be given for answers written in a medium other than the authorized one.

Assume suitable data, if considered necessary and indicate the same clearly.

Unless otherwise mentioned, symbols and notations carry their usual standard meanings.

Attempts of questions shall be counted in sequential order. Unless struck off, attempt of a question shall be counted even if attempted partly. Any page or portion of the page left blank in the Question-cum-Answer Booklet must be clearly struck off.

**SECTION-A**

**1. (a) For the circuit shown in Fig. 1(a), find the current through 5 2
resistor by using Thevenin's theorem and verify the same by using superposition
theorem.**

(b) A continuous time signal X(t) is shown in Fig. 1(b). Sketch and label each
of the following signals :

(i) x(t) u(2-t)

(ii) x(t) d(t-7/2)

(c) Show that for a distortionless transmission line, the attenuation
constant a. does not depend on frequency, whereas the
phase constant b depends linearly on it.

(d) For thie circuit given in Fig- 1(d)

(i) draw the input and output waveforms;

(ii) find the average value of the output voltage waveform.

Assume that the diode in the circuit is ideal.

(e) A 15-hp, 220-V, 3-phase, 50 Hz, 6-pole, Y-connected induction Instrar has the following parameters per phase :

r_{1} = 0.128 W, r_{2} = 0.0935
W, (x_{1} + x_{2}) = 0.496
W, r_{e} = 183 W,
xf = 8 W

The rotational losses are equal to the stator core losses (hysteresis and eddy-current). For a slip of 3%, find the line current and power factor.

**2. (a) For the Boolean function**

F (W, X, Y, Z) = [0, 2, 5, 6, 7, 8, 10, 13)

(i) find all the prime implicants;

(ii) give minimal representation;

(iii) find minimal two-level realization using NAND gates only.

(b) (i) What is meant by an infinite transmission line? Also, explain the
term 'electrical length' of a transmission line. In what units is it measured?

(ii) Determine the electrical length of a 20 m long transmission line operating
at 1 MHz, if u = 0.7c on the line. Take c = 3 x 10^{8} m/s.

(c) Discuss the properties of a probability density function. What additional features a normal distribution has?

**3. (a) The following test data were taken on a 30-kVA, 2400/240V, 50-Hz,
single-phase transformer :**

Open-circuit test : V = 2400V, I = 0.3 A, P = 230 W

Short-circuit test : V = 70V, I = 18.8 A, P = 1050 W

Determine the primary voltage, real and reactive power input, and efficiency, when a current of 12.5 A at 240 V is drawn from the low-voltage side by a load of 0.8 p.f. lagging.

(b) A three-phase uncontrolled diode rectifier supplies a constant load current of 10 A and its supply voltage is 400 , V 1ine-to-line. Determine the following performance measures :

(i) Average output voltage

(ii) Supply r.m.s. current

(iii) Supply fundamental r.m.s. Current

(iv) Supply 3rd, 5th, 7th and 9th harmonic r.m.s. current

(v) Supply current displacement factor

(vi) Supply power factor

(vii) AC power (supply power)

(vii) Dc power (load power)

(c) Consider the R-L-C circuit showri in Fig. 3(c), wherein

**4. (a)** Explain and differentiate between the single sideband (SSB)
modulation and double sideband suppressed carrier (DSB-SC) modulation Show the
DSB-SC modulated waveform for any chosen base band signal waveform and spectrum
of the base band and the DSB-SC modulated wave,

(b) Find the Laplace transform of the function ** f(t)** = u (sin 2t).

(c) Find the average voltage at the point V

_{o}, in the circuit given in Fig. 4(c) :

**SECTION - B**

**5. (a) Prove that AB + BC + AC = AB + BC.
**(b) An industrial consumer is operating a 1 kW induction motor at a lagging
power factor of 0.8 and at a source voltage of 200V, r.m.s. In order to reduce
expenditure on power consumption, he wishes to raise the power factor to 0.95
lagging by connecting a circuit element in parallel with the load. Indicate the
type of the circuit element (inductive or capacitive) and find the value if the
operating frequency is 50 Hz.

(c) (i) Explain the operation of Boost converter with voltage and current waveforms across the Boost inductor. Assume continuous conduction.

(ii) Derive its output voltage equation in terms of duty cycle and input voltage.

(d) An amplitude modulated signal, viewed on an oscilloscope, has a crest
voltage of 44 V peak-to-peak. The bottom (or trough) point of the wave measures
6V peak-to-peak. Find the modulation factor, percentage modulation and
peak-to-peak un-modulated carrier voltage.

(e) Obtain z-parameters of a two-port network in terms of its ABCD Parameters.

**6. (a) Find the value of average current flow through the load resistor
for the circuit given in Fig. 6(a).
**(b) Find the value of r.m.s. current drawn from the source.

(b) Determine the transfer function and there from the impulse response of the causal linear time invariant system described by the difference equation

y[n] - 1/4 y[n-1] - 3/8 y[n-2] = -x [n] + 2x [n-1]

(c) (i) Draw the circuit diagram of Wien bridge oscillator using OP-AMP.

(ii) Find the value of R to get a sustained oscillation of 1115 Hz. Assume that
the value of the capacitor is 0.1 uF.

**7. (a) The electric field and magnetic field in free space are given by**

Express these fields in phasor form and determine the constants H_{o},
and bsuch that these fields satisfy Maxwell's
equations. The permeability and permittivity of the free space are 4px
10^{-7} H/m and 8.854 x 10^{-12} F/m. respectively.

(b) Find the state transition diagram and rcalization using J-K flip-flops to
count Mod 7 in the following sequence :

000, 001, 011, 100, 101, 111

(c) A 230-V, 10-hp DC series motor draw a line current of 36 A, when delivering rated power at its rated speed of 1200 r.p.m. The armature circuit resistance is 0.2W and the series field winding resistance is 0.1W. The magnetization curve may be considered linear.

(i) Find the speed of this motor when it draws a line current of 20 A.

(ii) What is the developed torque at the new condition?

**8. (a) **A 400-V, 3-phase balanced source is connected to an unbalanced
D-connected load of impredance Z_{ab} =
10+ 45^{o}W, Z_{ca} = 10 - 0^{o}
W and Z_{ca}
= 10 - 45^{o}W.Determine the
line currents (in phasor form), total active (real) and reactive power.

(b) (i) Draw the circuit diagram of a bandpass filter using OP-AMP. Its
parameters are *f*_{L} = 300 Hz, *f*_{H} = 2 kHz arad
passband gain is 4.

(ii) Calculate thie value of *Q,* Assume that the capacitor value is 0.01
uF.

(c) Differentiate between stationary and non-stationary random processes. Give the properties of the first- and second-order distribution function of stationary random processes.

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## Printed Study Material for IAS Mains General Studies

## ELECTRICAL ENGINEERING

(PAPER-II)

**Time Allowed : Three Hours**

**Maximum Marks : 250**

**QUESTION PAPER SPECIFIC INSTRUCTIONS**

**(Please read each of the following instructions carefully
before attempting questions)**

There are **EIGHT** questions divided in two Sections and printed both in
**HINDI** and in **ENGLISH.**

Candidate has to attempt **FIVE** questions in all.

Question Nos. **1 **and** 5** are compulsory and out of the remaining,
**THREE **are to be attempted choosing at least **ONE **question from each
Section.

The number of marks carried by a question/part is indicated against it.

Answers must be written in the medium authorized in the Admission Certificate which must be stated clearly on the cover of this Question-cum-Answer (QCA) Booklet in the space provided. No marks will be given for answers written in a medium other than the authorized one.

Assume suitable data, if considered necessary and indicate the same clearly.

Unless otherwise mentioned, symbols and notations carry their usual standard meanings.

Attempts of questions shall be counted in sequential order. Unless struck off, attempt of a question shall be counted even if attempted partly. Any page or portion of the page left blank in the Question-cum-Answer Booklet must be clearly struck off.

**SECTION-A**

**1.(a)** For the open-lop transfer function G(s)H(s) = k(s-3)(s-5) /
(s-1)(s+2). find out the break-away and break-in points, if any, for the root
locus. Also specify whether the gain is maximum or minimum al these points.

(b) A delta modulation system is designed to accommodate a band limited analog
signal with maximum frequency of 5000 Hz. The sampling rate is five times the
Nyquist rate. A signal x(t) = sin(200pt) is
applied to this system.

Determine:

(i) the minimum step size required to process the signal without slope
overload distortion and

(ii) maximum signal-to-quantization noise ratio of the system.

(c) (i) Describe the two ways in which the interrupt RST 7.5 in 8085
micro-processor can be disabled.

(ii) Calculate the number of memory chips needed to design 8k-bytes memory for
an 8085 microprocessor. The memory chip size is 1024x1.

(d) (i) Why low resistances are usually constructed as four-terminal
resistances ?

(ii) How can surface resistivity of insulating material he measured using direct
deflection method ?

(e) Explain the principle of percentage biased differential relay with harmonic
restraint.

**2. (a)** For a given unstable open loop system whose transfer function
is G(s)H(s) = s+3 / s(s-1) sketch the Nyquist Contour and Nyquist Plot. Comment
on the stability of the closed-loop system.

(b) What is the difference between cycle stealing DMA and interleaved DMA in
8085 microprocessor ? What is meant by block transfer DMA ?

(c) In a system shown in this above figure, two single phase transformer supply
a 10 KVA resistance load at 200 V. Show that the p.u. load is the same for each
part of the circuit (like part A, B and C) and calculate the voltage at point D.

**3. (a)** In the above figure, V_{1} =1<0^{o}, Z_{1}
= (0.05 +j 0.02) pu and P_{2} + jQ_{2} = (1.0 + j 0.6)pu. using
load flow study iteratively compute V_{2} abd P_{1} + jQ_{1}.
Also determine the reactive power that must be injected to bus 2 to maintain |V_{1}|
= |V_{2}| = 1.0 pu.

(b) A discrete memory less source is emitting the symbols X_{1}, X_{2},
and X_{3} with probabilitics, respectively, 0.2, 0.45 and 0.35.
Construct optimal binary Huffman code for the second extension of the source and
calculate the coding efficiency.

(c) A single phase, 240 V, 20 A, induction type watt-hour meter is working correctly. When tested at half load, rated voltage, and unity power factor, the disc rotates at 32 rpm. Determine the meter constant of the meter. Then, duc to the alteration of the lay adjustment of the meter, the meter reads with 6.7% error at 0.8 p.f. lageing. What is the new phase angle between the supply voltage and the pressure coil flux because of this incorrect lag adjustment?

**4. (a)** Derive an expression for the critical clearing angle for a
power system consisting of a single machine supplying to an infinite bus, for a
sudden load increment.

(b) Consider a unity feedback system having transfer function C(s) / R(s) = a/s^{2}
+ bs + a. Determine the open-loop transfer function and steady state error
coefficients.

(c) A Schering bridge, used to test a specimen, has thc following bridge arms:
arm ab contains the unknown capacitance (C_{1}) whose loss part is
represented by a Series redistrict (P_{1}), RT1 hr: Plantains a 150pf
resista11:E (R) 3152, contains a variable capacitor (C) in parallel with a
variable non-inductive resistance (R_{3}) and am da contains a standard
capacitor (C) of 150 pF. The supply is connected between 4 and c and the
detector is connected between 5 and d. The specimen is tested at a frequency of
50 Hz, it is having a thickness of 6-3 ini and it is tested between Electrode
each having a dimensionn of 0.15 x 0.18m. At balance,C_{4} (0.375uF and
R4 = 423Q. Find the capacitance, dissipation factor and relative permittivity of
the speciman. Given ; Permittivily of free Space = 8.854 x 10^{-12} F/m.

**SECTION - B**

**5. (a) A **20 MVA, 6.6 kV generator, with X_{d} = 10%, X_{a}
= 20% and X_{d} = 100% is connected through a circuit breaker to a
transformer. It is operating on no load when a short circuit occurs between
breaker and transformer.

Find (i) sustained short circuit current througli breaker.

(ii) initial symmetrical rms short circuit current

(b) (i) How long can the INTR pulse stay high in 8085 microprocessor ?

(ii) What is a jump-on-reset circuit in a processor?

(c) How a compensating coil can be utilized in reducing connection errors in
an electrodynamometer type wattmeter ?

(d) An information source is modelled as a bandlimited process with a bandwidth
of 6000 Hz. This process is sampled at a rate higher than the Nyquist rate to
provide a guard band of 6000 H. This process is sampled at a rate higher then
the Nyquist rate to provide a guard band of 2000 Hz. The resulting samples takes
one of the value in the set {-4, -3, -1, 2, 4, 7} with corresponding
probabilities {0.2, 0.1, 0.15, 0.05, 0.3, 0.2}. Determine the rate of the
information of the source.

(e) For y(t) = 0.9t, it is required that the steady slate error should be less than 0.05. Determine the value of gain (K) of proportional controller for the system shown above.

**6. (a) A convolutional code is described by the following generator
sequences:**

g_{1} = [1 0 0]

g_{2} = [1 0 1]

g_{3} = [1 1 1]

(i) Construct the encoder circuit corresponding to this code.

(ii) Draw the state diagram for this code.

(iii) Draw the trellis diagram for a message sequences length of 5 bits.

(iv) Determine the encoded sequence for the message sequence 10111.

(b) The error signal as shown above is given to the controller. the initial controller output is zero. Draw the output of the controller if it is a :

(i) P controller with proportional gain (K_{p}) = 10

(ii) I controller with integral gain (K_{l}) = 2

(c) For a certain lagging power factor load, the sending end and receiving end voltages of a short transmission line of impedance R+jX are cqual. Prove that ratio is v3 for maximum power transmitted over the line under steady state condition.

**7. (a)** A synchronous generator and motor are rated 30,000 kVA, 13.2
kV, and both have subtransient reactanccs of 20%. The line connecting them has a
reactance of 10% on the base of the machine ratings. The motor is drawing 20,000
KW at 0.8 power factor leading and a terminal voltage of 12.8 KV when a
symmetrical three phase fault occurs at the motor terminal. Find the
subtransient currents (i) in the generator, (ii) in the motor and (iii) in the
fault by using the internal voltages of the machines.

(b) (i) In an 8050 microprocessor what is the value of stack pointer after the following program is run ?

MOV - SP, 07FFH

PUSH - B

CALL - Subroutine

POP - B

ADD - B

PUSH - B

HLT

(ii) Suppose that an 8085 microprocessor has received three interrupt requests in the following order: RST 6.5 and RST 5.5. If the three interrupts are nested to what depth does the stack penerate if all registers within the CPU must be saved? Assume that the Stack pointer initially Points to location FFFFH.

(c) Explain in detail different types of frequency instabilities that cause difficulties in spectrum analyzers for display of narrow frequency ranges. A spectrum analyzer is designed using a 10-kHz, 3 dB Glitter and with a noise figure of 23 dB, What is the minimum detectable signal of this spectrum analyzer? What will be the power-level of the third-order intercept point, if this spectrum analyzer possesses a dynamic range of 86 dB ?

**8. (a) **A continuous system has transfer function **C(s)/R(s) =
3/(s-2)(s-3)(s-4). **Find out the state model of the system. Find out the
state feedback gain K = [K_{1} K_{2} K_{3}] such that
the closed loop poles will be at -4, -3, and -2.

(b) Write down expression for the signal set and draw signal space diagram for
coherent quadri-phase shift keying system. For the input binary sequence
11001001, sketch inphase and quadrature components of the modulate quadri-phase
shift keying signal.

(c) (i) Why temperature compensation is needed in strain gauges? A four arm DC
Wheatstone bridge is designed using a single active gauge. How can a dummy gauge
be employed here to achieve temperature compensation ?

(ii) A resistance wire strain gauge with nominal resistance 350 and gauge factor
2 is fastened to a steel bar. The modulus of elasticity of steel is 2.1 x 10^{6}
kg/cm^{2} . what is the stress applied to the steel bar if strain gauge
resistance becomes 350.5W ?