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

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(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 :

r₁ = 0.128 W, r₂ = 0.0935 W, (x₁ + x₂) = 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 10⁸ m/s.

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)

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^oW, Z_ca = 10 - 0^oW and Z_ca = 10 - 45^oW.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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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.

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

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

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, V₁ =1<0^o, Z₁ = (0.05 +j 0.02) pu and P₂ + jQ₂ = (1.0 + j 0.6)pu. using load flow study iteratively compute V₂ abd P₁ + jQ₁. Also determine the reactive power that must be injected to bus 2 to maintain |V₁| = |V₂| = 1.0 pu.

(b) A discrete memory less source is emitting the symbols X₁, X₂, and X₃ 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/s² + 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 (C₁) whose loss part is represented by a Series redistrict (P₁), RT1 hr: Plantains a 150pf resista11:E (R) 3152, contains a variable capacitor (C) in parallel with a variable non-inductive resistance (R₃) 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,C₄ (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:

g₁ = [1 0 0]
g₂ = [1 0 1]
g₃ = [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 = [K₁ K₂ K₃] 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 10⁶ kg/cm² . what is the stress applied to the steel bar if strain gauge resistance becomes 350.5W ?