57 questions from the UPSC 2018 examination.
57 questions
A generator is connected to an infinite bus as shown in the figure. Derive the expressions for real power and reactive power supplied by the generator to the infinite bus : [Diagram showing a generator E angle delta connected through jX to an infinite bus at |V| angle 0]
For the system shown in the figure, S_D1 and S_D2 are complex power demands at bus-1 and bus-2 respectively. If |V_2| = 1 p.u., compute VAR rating of the capacitor (Q_G2) connected at bus-2 in MVAR : [Diagram showing SG1 at bus 1 with V_1 = 1 angle 0 p.u., line impedance X = j0.5 p.u. connected to bus 2 with Q_G2, S_D1 = (1+j0) p.u. and S_D2 = (1+j0) p.u.]
For the open-loop transfer function G(s)H(s) = K / (s(s+4)(s+5)), determine the following : (i) Point of intersection of asymptotes with real axis (ii) Point of intersection of root locus with imaginary axis and the value of K at this point
Design a PCM system that multiplexes three signals m1, m2 and m3 having bandwidths 5 kHz, 10 kHz and 5 kHz respectively. Each signal is sampled at its Nyquist rate and quantized to 256 levels. (i) Sketch the block diagram of the system. (ii) What is the maximum bit duration that can be used? (iii) What is the channel bandwidth required to pass the PCM signal? (iv) What is the commutator speed in revolutions per second?
For the op-amp circuit shown in Figure 1(d), determine the gain A_v = v_o / v_i. Assume that all resistors are equal. Figure 1(d)
(i) A travelling \bar{E} field in the free space of amplitude 100 V/m strikes a perfect dielectric as shown in Figure 7(a)(i). Determine the value of E_t. Figure 7(a)(i) (ii) A uniform plane wave in air partially reflects from the surface of a material whose properties are unknown. Measurements of the electric field in front of the interface region yield a 1.5 m spacing between maxima, with the first maximum occurring 0.75 m from the interface. A standing wave ratio of 5 is measured. Determine the intrinsic impedance \eta_w of the unknown material.
A 3-phase, 11 kV transmission line delivers a load of 2395 kVA at 0.8 p.f. (lag) over a distance of 25 km. The transmission line has an impedance per phase of (3.25 + j7.55) ohms. Determine the sending-end voltage and sending-end power factor.
Consider a unity feedback control system whose forward path transfer function is given by G(s) = 9 / (s(s+1)). Determine- (i) percentage overshoot resulting from application of unit step input; (ii) steady-state error resulting from application of unit step and unit ramp input.
Write about the selection of various circuit breakers for different ranges of system voltage. Mention the type of circuit breaker to be recommended by the utilities for a particular range of voltage. Discuss the difficulty in the development of high voltage DC (HVDC) circuit breaker. Describe its construction and principle of operation.
Using Thevenin's theorem, find the current through the 40 \Omega resistor connected between terminals a and b in Figure 5(e). Figure 5(e)
Find i_o(t) in the circuit shown in Figure 6(b) using Fourier transform method when i_s(t) = 10 sin 2t Amp. Figure 6(b)
Draw output voltage and current waveforms and determine r.m.s. output voltage of a three-phase half-wave rectifier supplied by three-phase balanced a.c. supply. Also determine the form factor. If the supply voltage of the above converter is 220 V (r.m.s.) at 50 Hz and the load is of 1 kW at 200 V, purely resistive, determine power consumed by the load with given supply voltage.
Consider the block diagram of a system shown below : [Diagram showing E(s) -> [K / s(Ts+1)] -> theta(s)] Write the differential equation relating theta to e and hence write the state model of the system choosing state variables as theta(t) and theta_dot(t). Sketch Bode plot of a lead compensator.
A squirrel cage induction motor has a starting current of six times the full load current, at a slip of 0.04. Calculate the line current and starting torque in p.u. (per unit) of full load values for the following starting methods: (i) Direct switching (ii) Star-Delta starting
The characteristic equation of a system is given by s^4 + 3s^3 + 10s^2 + 20s + 100 = 0. By Routh-Hurwitz criterion, determine the number of poles of the system with positive real parts.
A 400 volts D.C. shunt motor draws 30 amperes while supplying the rated load at a speed of 120 rad/sec. The armature resistance is 1.0 ohm and the field winding resistance is 250 ohms. Determine the external resistance that must be inserted in series with armature circuit so that, the armature current should not exceed 150% of its rated value, when the motor is plugged. Find the braking torque, at the instant of plugging.
Design a synchronous counter using D flip flop that counts in the following sequence : 6, 3, 5, 0, 2, 6, 3, 5, 0, 2, 6, ... Draw the circuit.
Derive the expression of total average power in three-phase balanced circuit.
An SSB transmitter transmits with 10 kW power. This transmitter is to be replaced by a standard amplitude modulated signal with same total power content. Determine the carrier power and each sideband power, when the percentage modulation is 80%.
An energy meter is designed to have 80 revolutions of the disc per unit of energy consumed. Calculate the number of revolutions made by the disc when measuring the energy consumed by the load carrying 30 A at 230 V and 0.6 power factor. Find the percentage error if the meter actually makes 330 revolutions. Also specify whether the meter runs slower or faster.
A D.C. generator has an armature e.m.f. of 100 volts, when the useful flux per pole is 20 mWb and the speed is 800 r.p.m. Calculate the generated e.m.f. (i) with the same flux and a speed of 1000 r.p.m. (ii) with flux per pole of 24 mWb and a speed of 900 r.p.m.
An 11 kV, 100 MVA alternator is provided with differential protection. The percentage of winding to be protected against phase-to-ground fault is 85%. The relay is set to operate when there is 20% out of balance current. Determine the value of the resistance to be placed in the neutral-to-ground connection.
(i) Derive the Maxwell's equation for time varying magnetic field based on Ampere's circuital law. (ii) A parallel plate capacitor with plate area of 5 cm^2 and plate separation of 3 mm has a voltage of 50 sin 10^3 t V applied to its plates. Calculate the displacement current assuming \epsilon = 2 \epsilon_0.
Write the step-by-step procedure to obtain source code by using Shannon-Fano algorithm. Obtain the source code for a source that generates messages with the following probabilities : m_1 p_1 = 1/4, m_2 p_2 = 1/4, m_3 p_3 = 1/8, m_4 p_4 = 1/8, m_5 p_5 = 1/16, m_6 p_6 = 1/16, m_7 p_7 = 1/16, m_8 p_8 = 1/16. Also calculate the efficiency of the code.
A wattmeter reads 5 kW when its current coil is connected in red phase and its voltage coil is connected between neutral and red phase of a symmetrical three-phase star-connected system supplying a balanced three-phase inductive load of 25 A at 440 V. What will be the reading of the wattmeter if the connection of the current coil remains unchanged and voltage coil is connected between blue and yellow phase? Hence determine the total reactive power in the circuit.
Find the Laplace transform of the periodic function f(t) shown in Figure 1(b). Figure 1(b)
Convert a D flip flop to function as an S-R flip flop. Draw the circuit.
Which method is used to eliminate the effect of stray capacitances in a four-arm AC bridge? Describe with circuit diagram.
In the circuit shown in Figure 3(c), find the voltage v_o across the 8 \Omega resistor. Figure 3(c)
The magnetizing and loss component of exciting current of a current transformer rated 1000/5 A, are 15 A and 9 A respectively. The phase angle between secondary winding induced voltage and current is 40 degree. Determine the phase angle error of the transformer.
The integrator circuit shown in Figure 4(c) is to be used to generate a triangular waveform from a 500 Hz square wave connected to its input. Suppose that the square wave alternates between \pm 12 V. (i) Find the minimum slew rate required for the amplifier. (ii) Find the maximum output voltage the amplifier can generate. Figure 4(c)
Draw the schematic diagram for interfacing an 8-bit analog to digital converter to 8085 microprocessor using 8255 PPI.
Determine the feedback fraction and the operating frequency for the oscillator circuit shown in Figure 6(c). Figure 6(c)
Explain five addressing modes of 8085 microprocessor.
A three-phase generator rated 11 kV, 20 MVA has a solidly grounded neutral. Its positive, negative and zero sequence reactances are 60%, 25% and 15% respectively. Calculate the value of the reactance that should be placed in generator neutral such that the current for single line-to-ground fault does not exceed the rated current.
Explain how the spectra of amplitude-modulated signal are displayed on a spectrum analyzer.
For the circuit shown in Figure 8(a), v(t) = 311.12 sin 377t volts : (i) Find the values of \bar{I}_1, \bar{I}_2, \bar{I}_3, \bar{I}_4 \text{ and } \bar{I}_5. (ii) Also compute \bar{V}_{bc} \text{ and } \bar{V}_{cd}. (iii) Compute the power supplied by the source. (iv) Find the line power factor. Figure 8(a)
A three-phase power system consists of a synchronous machine connected through a lossless transmission line to an infinite bus. A fault occurs on the transmission line. The maximum power transfer of this system when no fault is 5 p.u. and the power transfer is 2.5 p.u. The power angle curves during the fault and post-fault conditions have peak values of 2 p.u. and 4 p.u. respectively. Determine the permissible increase in the angular displacement between the voltages at the two ends of the system beyond which the circuit breakers could not clear the fault in time for the system to remain in synchronism.
What do you mean by maskable interrupts? Which interrupt cannot be masked? Write an assembly language program to enable RST 6.5 interrupt.
Write an 8085 microprocessor assembly language program to turn ON an LED connected to bit 4 of the 8155 I/O port B. Use address of port B as 22(16).
Calculate the output voltage v_o in terms of the input voltages v_{i1}, v_{i2}, v_{i3} \text{ and } v_{i4} \text{ for the circuit shown in Figure } 8(\text{b}). Figure 8(b)
A buck converter (D.C.-D.C. converter) has LC filter in the output to reduce ripple in output voltage. For continuous conduction mode, draw the waveforms of output voltage, inductor current and capacitor current. If the converter is switched at frequency 'f', prove that minimum values of 'L' and 'C' for \Delta I_L ripple in inductor current and \Delta V_0 ripple in output voltages are given by C = \frac{(1 - D)}{8 L (\Delta V_0 / V_0) f^2} \text{ and } L = \frac{V_0 (1 - D)}{(\Delta I_L) f} Assume any data missing. D is duty cycle of switch and V_0 is the average output voltage.
(i) Draw thyristor gate characteristics and state its application in design of gate drive circuit. (ii) A thyristor has a maximum average gate power dissipation limit of 0.4 watts. It is triggered with pulsed gate current of frequency 20 kHz at a duty ratio of 0.5. If the gate cathode voltage drop is 1 volt, find permissible peak gate current magnitude.
For the open-loop transfer function G(s)H(s) = 1 / ((s+p_1)(s+p_2)) ; p_1, p_2 > 0 sketch Nyquist plot. Comment on the stability of the closed-loop system.
A signal having probability density function f(x) = { ke^(-|x|); -4 < x < 4 ; 0; elsewhere } is quantized with four quantization levels. (i) Determine the value of k. (ii) Determine step size s. (iii) Determine the four quantization levels.
The antenna current of a transmitter is 11.5 amperes, when it is modulated to a depth of 45% by an audio wave. The current increases to 12.5 amperes on account of simultaneous modulation by another audio sine wave. Find the modulation index of the second audio wave.
(i) A low loss transmission line has characteristic impedance Z_0 = 70 \Omega and is terminated by another impedance of 115 - j80 \Omega. The wavelength on the line is 2.5 m. Find: I. SWR (Standing Wave Ratio) II. Maximum and minimum line impedance, Z_{1max} and Z_{1min} (ii) If the input impedances of a short and open circuited transmission line of length 1.5 m are Z_{SC} = -j78 \Omega and Z_{OC} = j90 \Omega respectively, determine the characteristic impedance Z_0 and propagation constant \gamma of the line.
Two substations are connected by two lines in parallel with negligible impedance, but each containing a tap-changing transformer of reactance 0.18 p.u. on the basis of its rating of 200 MVA. Find the net absorption of reactive power in MVAr when the transformer taps are set to (1:1.1) and (1:0.9) respectively. Assume per unit voltages to be equal at two ends of the substation.
Differentiate between the following pairs of instructions : (i) LDA addr and STA addr (ii) LDAX rp and SHLD addr (iii) LDAX rp and STAX rp (iv) RLC and RAL (v) PCHL and SPHL
A full bridge or H-bridge inverter has a switching sequence which results in a square wave output voltage. Let the switching frequency be 50 Hz and inverter is supplying a RL load having R = 10 \Omega and L = 30 mH. Determine: (i) An expression for load current (ii) The power absorbed by load (iii) The average current in the D.C. source (iv) The area in output voltage waveform where antiparallel diodes across switches conduct (Assume Input D.C. voltage = 100 V)
A single tone FM is represented by the voltage equation as v(t) = 12 \cos(6 \times 10^8 t + 5 \sin 1250 t). Determine : (i) Carrier frequency (ii) Modulation frequency (iii) Maximum deviation (iv) Bandwidth (v) Power dissipated in a 10 \Omega resistance
A 220 volts, 1500 r.p.m., 50 A separately excited D.C. motor is fed from a three-phase fully controlled rectifier. The rectifier is supplied with a balanced three-phase source with phase voltage of 230 volts (r.m.s.) at 50 Hz. Motor is holding an overhauling load at 1200 r.p.m. at full load torque. Determine the firing angle of converter if armature resistance is assumed to be 0.2 \Omega.
A convolutional encoder is shown below : [Diagram showing convolutional encoder with input U, shift registers, and outputs V1, V2] (i) Write down all the generator sequences and corresponding generator polynomial. (ii) Determine the output sequence V, if the input sequence is U = (1 0 0 1 1).
Convert the following logic equation to NAND logic and draw the circuit using NAND gates: Z = (A + B) C + A (B + C)
The maximum efficiency of a 50 KVA transformer is 97.4% and occurs at 90% of full load, at unity power factor. Calculate the efficiency at (i) Full load at 0.8 power factor (p.f.) (ii) Half the full load at 0.9 power factor (p.f.)
Draw the block diagram of a DPSK communication system. The data stream to be transmitted by means of DPSK is d(t) = 0010011001110. Determine the DPSK bit stream. Sketch BPSK waveform if the transmitted data stream is 101000 and carrier frequency is f_c.
For the system, whose open-loop transfer function is G(s)H(s) = K / ((s+2)^2 (s+3)), determine K which satisfies the following specifications : (i) Position error constant K_p >= 2 (ii) Gain margin >= 3