RA B. Tech III Year I Semester Examinations, December-2011 NETWORK THEORY (ELECTRICAL AND ELECTRONICS ENGINEERING)

Max. Marks: 75 Answer any five questions All questions carry equal marks ---

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Time: 3 hours

Derive the expression for the power in two wattmeter method for balanced loads. Three star connected impedances Z = 20 450 Ω , Z = 25 600Ω, Z = 15 450Ω, are a b c connected 3 − φ , 400V, 50Hz a.c. supply. Determine the line currents and two wattmeter readings when power is measured by 2 wattmeter method. a, b, c is the phase sequence. [15]

2. a) b)

Explain the steps used to evaluate initial conditions. Discuss the transient analysis of RLC series circuit excited by D.C. voltage. [15]

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In the following circuit shown in Fig-1, switch is closed at time t = 0. a) Obtain the expression for the current i(t).

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Fig-1 b) Discuss the transient analysis of R-C circuit excited by a sinusoidal source. [15] Derive the relationship between Y parameters and h-parameters. Obtain hybrid parameters for the network shown in Fig – 2 [15]

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4. a) b)

Fig-2 1

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c)

Explain the necessary condition for the transfer functions.

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Evaluate short circuit parameter of the following two part network shown in Fig-3

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6.a)

Define the terms driving point immitance and transfer functions. What are poles and zeroes. What is their significance. Draw the pole-zero plot for the following transfer function s 2 + 3s + 2 T ( s) = s ( s 2 + 2s + 2 )( s 2 + 4s + 3)

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5. a) b)

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Fig-3 b) For the following network shown in Fig-4determine h-parameters.

Fig-4 Design a high pass π -network filter, having a cut off frequency of 3250 Hz. The frequency of infinite attenuation may be taken as 2750 Hz. The characteristic impedance is 450 Ω . Explain the analysis of K-Band stop filters. What are the demerits of K-Derived filter? [15]

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7. a)

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b)

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RA The half sinusoidal wave form shown in the following figure - 5 represents the voltage response obtained at output of a half-wave rectifier circuit. Find the Fourier series representation of this wave form.

b) c)

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8. a)

Fig-5 Explain the properties of Fourier transforms. Find the Fourier transform of the function 3e-t cos 4t u(t).

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