JNTU
JNTU B.Tech II NETWORK THEORY Previous Question Paper (May - 2019 - R13)
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.
Part A
Define a three phase electric system and give the common configurations of it.
Answer
A three-phase electric system is a polyphase system consisting of three individual alternating current (AC) circuits, where each circuit operates at the same frequency but is displaced in phase by 120 electrical degrees from the others. This configuration allows for constant power delivery and efficient transmission of electrical energy.
The two common configurations for a three-phase system are:
- Star (Wye) Connection: Where the three phases are connected to a common neutral point.
- Delta Connection: Where the three phases are connected in a closed loop, forming a triangle without a neutral point.
Draw the circuit diagram for measuring reactive power by using a single wattmeter.
Answer
To measure the reactive power (VAR) in a balanced three-phase circuit using a single wattmeter, the pressure coil of the wattmeter is connected across two phases (e.g., phases B and C), while the current coil is connected in series with the third phase (e.g., phase A). This configuration ensures the wattmeter measures the product of the line current (IA) and the line-to-line voltage (VBC) multiplied by the cosine of the phase angle between them.
In a balanced system, the voltage VBC lags the phase voltage VA by 90 degrees. Consequently, the wattmeter reading represents:
Since the total reactive power Q is given by √3 VLIL sin(φ), the actual reactive power is obtained by multiplying the wattmeter reading by √3.
Define transient response or natural response.
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How do you relate and understand the response as over damped, under damped and critically damped?
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Explain the physical interpretation of complex frequency.
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How do you define Driving point impedance and admittance?
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State the application of h-parameters in electronic circuits.
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Derive z-parameters in terms of ABCD parameters.
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Draw the frequency response characteristic of constant K low pass filter.
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State the design parameters of Band pass filter.
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Part B
Derive the relationship between line and phase voltages and currents in a Delta connection.
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A 20 HP induction motor is supplied from a 400 V, 3 phase, 50 Hz power system. The efficiency being 90%, the power factor of operation is 0.8. Obtain i) the active power consumed ii) the apparent power iii) the reactive power and iv) the line current.
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A delta connected load has following impedances ZRY = j10Ω, ZYB = 10Ω, ZBR = - j10Ω. If the load be connected across a three phase 415V supply (balanced), obtain the line currents. Draw the vector diagram.
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Derive the transient response for a series RC circuit with Sinusoidal excitation.
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Find the current in a series R-L circuit having R = 2Ω and L=10 H while a dc voltage of 100 V is applied. What is the value of this current after 5 seconds of Switching On?
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Derive the expression for circuit current of a series RLC circuit excited by DC as input.
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Derive the conditions for symmetry and reciprocity in terms of Y-Parameters.
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Find the y-parameters of the network shown in figure 1.
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Derive the condition for Reciprocity and symmetry in a two port ABCD parameter representation.
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Find the z-parameters of the network shown in figure 2.
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Explain the conditions to be fulfilled for interconnection of two port networks.
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Find voltage and current transformation ratio shown in the figure 3.
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Explain the concept of poles and zeros in a network function. Locate the poles and zeros of a transfer function G(s) = (s+2) / (s^2 + 3s + 4).
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State and explain the properties of transfer functions.
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Compare between Laplace and Fourier transform.
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Find the exponential Fourier series for the following wave form shown in figure 4.
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Obtain the Fourier series for the waveform shown in figure 5.
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Draw the T and ∏-network representation of Band elimination filter.
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