JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II NETWORK THEORY Previous Question Paper (April - 2018 - R13)

B.Tech | II | II | R13 | April - 2018

Answer PaperPaper Code: 114ACMaximum Marks: 75Time: 3 Hours

Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.

Part A

125 marks

What is a phase sequence and what is its importance in 3-phase AC circuits?

2 marks

Answer

Phase sequence is the order in which the three-phase voltages reach their maximum positive value. In a standard positive sequence (a-b-c), phase b lags phase a by 120°, and phase c lags phase b by 120°. It is crucial for determining the direction of rotation of three-phase induction motors and for the correct connection of transformers and power systems.

What are the differences between balanced and unbalanced 3-phase systems?

3 marks

Answer

In a balanced system, the voltages and currents are equal in magnitude and displaced by exactly 120° from each other, resulting in zero neutral current. In an unbalanced system, the magnitudes or phase displacements are unequal, leading to a non-zero neutral current and requiring complex analysis using symmetrical components.

What is an initial condition?

2 marks

Answer

Under what conditions, response of RLC series circuit for step input is: i) under damped ii) over damped. Draw typical responses.

3 marks

Answer

What is difference between driving point function and transfer function?

2 marks

Answer

Define poles and zeros of a network function. Draw pole-zero plot for the network function N(s) = (s+10)/(s^2+10s).

3 marks

Answer

What are 2-port parameters? How are these parameters helpful in describing a 2-port network?

2 marks

Answer

Give expressions for symmetry and reciprocity of Z and Y parameters.

3 marks

Answer

Give expressions for trigonometric and exponential form of Fourier series.

2 marks

Answer

What is the need of filter in electrical network? What are its characteristics?

3 marks

Answer

Part B

210 marks

With a neat circuit and phasor diagram explain the three phase power measurement by two wattmeter method and also derive the expression for Power Factor.

5 marks

Answer

A 3-phase delta connected load has Zab = 100 ohms, Zbc = -j100 ohms and Zca = (70.7 -j70.7) ohms is connected to a balanced 3 phase 400V supply. Determine the line currents Ia, Ib and Ic. Assume the phase sequence abc.

5 marks

Answer

310 marks

For a star connected three phase system, derive relationship between (i) phase voltages and line voltages (ii) phase currents and line currents.

5 marks

Answer

A 3-phase, three-wire, 208 V, ABC systems supplies a delta-connected load of Zab=5∠0, Zbc=4∠30, Zca=6∠-15. Find the line currents and total power consumed in the system.

5 marks

Answer

410 marks

A source voltage of 50 V is applied across a series RL circuit with R=8 ohms and L=5 H at t = 0. Using Laplace Transform method, determine the circuit current i(t) for all t >= 0. Assume zero initial conditions.

5 marks

Answer

A series R-L circuit has R=20 ohms and L=8 H. The circuit is connected across a DC voltage source of 120 V at t=0. Calculate the time at which voltage drops across R and L are same.

5 marks

Answer

510 marks

An R-L-C series circuit with R=2 ohms, L=2 H, C=2 F, are excited by an AC voltage of v(t)=20 sin 2t. Find the current in the network for t>0. Assume at t=0- the network was unenergized.

5 marks

Answer

For a source free RLC series circuit, the initial voltage across C is 10V and initial current through L is zero. If L = 20 mH, C=0.5 µF and R=100 ohm. Evaluate current in the circuit for all t >= 0.

5 marks

Answer

610 marks

Determine driving point impedance Z(s) of a network comprising 5 mH inductor connected in series with a parallel combination of a 5 ohm resistor and 100 µF capacitor. State all critical frequencies of Z(s).

5 marks

Answer

Consider circuit shown in Figure 1. The input to circuit is voltage of voltage source, vi(t). The output is voltage across 8 ohm resistor, vo(t). The network function that represents this circuit is H(jω) = Vo(jω)/Vi(jω) = 30 / (jω + 0.66). Determine value of inductance, L.

5 marks

Answer

710 marks

Discuss necessary conditions for driving point and transfer functions.

5 marks

Answer

The transform voltage V(s) of a network is given by V(s) = 3 / [(s+2)(s^2+2s+2)]. Plot pole-zero diagram in s-plane and obtain time domain response v(t).

5 marks

Answer

810 marks

Derive impedance parameters in terms of transmission parameters.

5 marks

Answer

Find ABCD parameters of the network shown in figure 2.

5 marks

Answer

910 marks

Two 2-port networks A and B are connected in parallel. Each of these networks has their own y-parameters. Show that resultant y-parameters of the combined parallel network is sum of y-parameters of the individual networks A and B.

5 marks

Answer

Determine Z-parameters for network shown in Figure 3.

5 marks

Answer

1010 marks

Discuss about time scaling, duality and time shifting properties of Fourier transform.

5 marks

Answer

Design a constant-K low pass filter with cut-off frequency of 1 kHz and design impedance is 600 ohms.

5 marks

Answer

Determine voltage across 3H inductor and 4Ω resistor respectively, by the Fourier transform method, if circuit shown in Figure 4, is excited by a current source iS(t) = 50 cos(5t) A. Show that result so obtained is steady state response of the circuit.

10 marks

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II NETWORK THEORY Previous Question Paper (April - 2018 - R13)

Part A

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Part B

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