Electrical Engineering UPSC PYQ 2014

Find the values of E and I in the circuit shown in Fig. 1.

For a position control system as shown in the figure below, determine the range of compensator gain K and the location of zero in left half for which the system is stable.

Develop the expression for the slew rate of Op-Amp.

A single-phase fully controlled bridge converter supplies an inductive load. Assuming that the output current is virtually constant and is equal to 20 A, determine the following performance measures, if the supply voltage is 230 V and the firing angle is maintained at 30^\circ : (i) Average output voltage (ii) Supply r.m.s. current (iii) Supply fundamental r.m.s. current (iv) Fundamental power factor (v) Supply power factor (vi) Supply harmonic factor (vii) Voltage ripple factor (viii) Reactive power input

Find the Laplace transform of the signal x(t) = e^{-3t}u(t) + e^{-2t}u(t) and find ROC.

Convert the logical equation Y = (A + \bar{B})(B + \bar{C}\bar{A}) into product-of-sums (POS) form and design circuits using (1) OR and AND gates and (2) NOR gates.

In a 220 kV, 50 c/s power system, the reactance and capacitance upto the circuit breaker are 8 ohms and 0.025 uF respectively. A resistance of 600 ohms is connected across the circuit breaker contacts. Determine the following : (i) Natural frequency of oscillation (ii) Damped frequency of oscillation (iii) Value of Critical Resistance which will give no transient oscillations (iv) The value of resistance which when connected across circuit breaker contacts will give damped frequency of oscillation of one-fourth of the natural frequency of oscillation.

Write the various interrupts available in the microprocessor 8085 in the order of decreasing priority.

A system is modelled in state-space form as X-dot = [ [0 1 0], [0 0 1], [-1 -7 -5] ] X + [ [0], [0], [1] ] u, y = [3 4 0] X. Draw the signal flow graph and obtain the transfer function.

A three-phase balanced delta-connected load gives wattmeter readings of 1050 W and 550 W, when the two-wattmeter method is applied. Calculate the impedance in each arm of the load. Given, line voltage = 200 V.

Derive Helmholtz equation in terms of magnetic field.

Specify multiplexed and non-multiplexed bus lines in 8085 microprocessor.

Explain hardware single stepping used in 8085 microprocessor.

For a 2-bus system shown below, derive expressions for Real Power and Reactive Power at receiving end and sending end.

Describe the various addressing modes in the microprocessor 8085. Give suitable examples for each addressing mode.

A channel with bit rate, Rb = 36 kbps is available for P.C.M. voice transmission. Find the appropriate values of binary digits N, the number of quantization levels (M) and the sampling rate (fs), assuming fm = 3.2 kHz.

Explain the importance of adding impedance in the neutral path of an alternator.

A d.c. shunt motor takes a current of 80 A on a 480 V supply and runs at 960 r.p.m. The armature resistance is 0.25 ohm and the field resistance is 120 ohms. A chopper is used to control the speed of the motor in the range of 400 - 750 r.p.m. having constant torque. The on-period of the chopper is 3 ms. The field is supplied directly from 480 V supply. Determine the range of frequencies of the chopper.

Derive the expression for maximum signal to quantization noise ratio for sinusoidal message input when waveform coding is done by D.M. under no-slope overload condition.

Derive an expression for the Bandwidth of P.C.M. system.

A three-phase, four-pole, 50 Hz induction motor has a chopper-controlled resistance in the rotor circuit for speed control. Load torque is \omega^2. When the thyristor is ON, the torque is 30 N-m at a slip of average 0.03. If \frac{T_{ON}}{T_{OFF}} = 1, compute the average torque and speed. The motor develops a torque of 80 percent of ON torque when the thyristor is OFF. The speed variation ranges down to 1200 r.p.m. from synchronous speed. Determine the ratio \frac{T_{ON}}{T_{OFF}} to give an average torque of 25 N-m.

A random variable has an exponential probability function given by f(x) = ae^{-b|x|}, where a and b are constants. Find (i) the relationship between a and b, and (ii) the distribution function of x.

Explain the method of frequency demodulation using PLL.

A single-phase converter feeds an R-L load having a resistance of 10 ohms in series with an inductance of 20 mH. The converter operates such that the d.c. voltage across the load is 250 V. The thyristor used in the converter has holding current of 300 mA and a delay time of 5 \mu s. Determine the pulse width of gate current.

Using symmetrical component theory for analysing an unbalanced fault, show that under certain circumstances, it is possible that the fault current for a S-L-G fault can exceed the fault current for a 3-phase fault in the same system.

Design a circuit that gives the input-output relationship shown in Fig. 4.

A plant has open-loop transfer function G(s) = 2 / (s (1 + 0.1s) (1 + 0.5s)). Determine the complete stability information of the unity feedback closed loop system by sketching Nyquist path and Nyquist plot.

Find 2's complement of the following numbers : (1) 10010010 (2) 11011000

Determine the inverse z-transform of X(z) = \frac{1}{1 - 1.5 z^{-1} + 0.5 z^{-2}} \text{ for } \text{ROC } |z| > 1

An open-loop configuration of Op-Amp 741C changes its output from +14 V to -14 V each time its input crosses zero volt. If 741C has a typical slew rate of 0.5 V/\mu s, calculate the time between the zero crossings and the maximum frequency at which the output will be distorted.

An approximate Bode plot of magnitude for a system was obtained and is shown below. Identify the system in terms of minimum phase transfer function.

LVDT with bellow is used for measuring the pressure. Draw the circuit diagram of LVDT-bellow system.

Discuss the effect of excitation on armature current for a synchronous motor and compare the performance of 3\phi synchronous motor with 3\phi induction motor.

An IDMT Relay has a current setting of 150% and has a time multiple setting of 0.5. The relay is connected in a circuit through a C.T. having a ratio of 500 : 5 amps. Calculate the time of operation of the relay if the circuit carries a fault current of 6,000 A. Use the table given below :

Describe the voltage-commutated chopper controlling the speed of a d.c. series motor with relevant schematic diagram and associated voltage and current waveforms as a function of time.

Starting from Maxwell's equations \vec{\nabla} \times \vec{E} = - \frac{\partial \vec{B}}{\partial t} \text{ and } \vec{\nabla} \times \vec{H} = \vec{J} + \frac{\partial \vec{D}}{\partial t}, show that \vec{\nabla} \cdot \vec{B} = 0 \text{ and } \vec{\nabla} \cdot \vec{D} = p.

Determine whether the following signal is periodic or aperiodic. Find the fundamental period, if it is periodic : x(n) = \sin \left(\frac{3\pi}{7}n + \frac{\pi}{4}\right) + \cos \frac{\pi}{3}n

Explain what is meant by Bewley-Lattice diagram. What is the use of this diagram?

Define state controllability of a system. Apply the controllability test to determine the controllability of a system modelled by the state-space model as X-dot = [ [-2 -2 0], [0 0 1], [0 -3 -4] ] X + [ [1 0], [0 1], [1 1] ] u1 u2, y = [1 1 0] X.

Explain the function of Schottky diode connected between the collector and base of transistors of TTL gate.

What is the effect of introducing derivative control action on the response of a system? A system has open-loop transfer function given by G(s) = 10 / ((s + 1)(s + 4)). Evaluate the parameters of a PD controller with this system with unity feedback so that the closed loop system has poles located at -3 +- j4. Indicate the nature of closed loop time response to unit step input change.

Draw the approximate time response of an underdamped second order system subjected to unit step input disturbance in desired value for the following cases of complex conjugate poles : (i) with constant real part (ii) with constant imaginary part (iii) with constant damping ratio. In each case consider at least 2 sets of values and mention the most important feature of the response.

A delta-connected balanced three-phase load is supplied from a three-phase, 400 V supply. The line current is 20 A and power taken by the load is 10000 W. Find (i) impedance in each branch and (ii) the line current, power factor and power consumed if the same load is connected in star.

The parity check matrix H-bar of a linear (7, 4) block code is given by H-bar = [ [1 0 1 1 1 0 0], [1 1 0 1 0 1 0], [0 1 1 1 0 1 1] ]. Determine the coded word for the data 0101.

A sinusoidal signal is transmitted using P.C.M. The output signal to quantization noise is required to be 55.8 dB. Find the minimum number of quantization levels. Derive the equation used.

Prove that the torque produced in a shunt motor is proportional to armature current I_a and in case of series motor, it is proportional to I_a^2.

Explain : (i) Direct addressing (ii) Register indirect addressing (iii) Immediate addressing (iv) Register addressing.

The two random variables X and Y are independent and identically distributed each with a Gaussian density function with mean equal to zero and variance equal to \sigma^2. If these two random variables denote the coordinates of a point in the plane, find the probability density function of the magnitude and the phase of that in polar coordinates.

Show how unit protection principle can be employed in balanced voltage system.

The z-parameters of a two-port network are z_{11} = 20 \Omega, z_{22} = 30 \Omega, z_{12} = z_{21} = 10 \Omega. Find y and ABCD parameters of the network.

Obtain the Norton's equivalent circuit at the terminals A and B for the network shown in Fig. 3.

A 550 V, 55 kVA, single-phase alternator has effective resistance of 0.2 \Omega. A field current of 10 A produces an armature current of 200 A on short circuit and an e.m.f. of 450 V on open circuit. Calculate (i) the synchronous reactance and (ii) the full-load regulation with power factor 0.8 lagging.

(i) Draw the equivalent of a medium length transmission line using pi-model. (ii) Assume that the receiving end is supplying a lagging power factor load. Draw the Phasor diagram showing all voltages and currents. (iii) Derive the A, B, C and D constants of this line in terms of line parameters Z and Y.

Describe all-day efficiency of a transformer.

Draw the typical characteristics of an IDMT Relay and explain how to use these curves.

Describe with a block diagram the Ramp type analog-to-digital conversion. Also draw the block diagram of Ramp type digital voltmeter.

The net power flowing out of a given volume \nu is equal to the time rate of decrease in the energy stored within \nu minus the conduction losses. Derive equations to explain.

An analog transducer with a 0 - 10 V input is able to distinguish a change of 1 mV in its signal. Calculate (i) its resolution (ii) the minimum number of bits of ADC so that the digital output has almost the same resolution as transducer. Also calculate the (iii) quantization interval and (iv) number of decision levels.

The sensitivity of LVDT-bellow system is 40 V per mm. The bellows are deflected by 0.15 mm by a pressure of 1.0 x 10^6 N per m^2. Determine the pressure when the output voltage of LVDT is 3.9 V.

A comparator and limiter circuit is shown in Fig. 2. Develop transfer characteristics V_O vs. V_I and explain.

Why the output voltage of an Op-Amp does not respond immediately to the fast-changing input?

Determine whether the following system is linear, time invariant, stable or dynamic : y(n) = 5 x(2n)

Explain the function of piezoelectric crystal as transducer. Specify its use in (i) Kitchen lighter (ii) Ultrasound diagnostic equipments (iii) Industrial cleaning machines.