JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year PRINCIPLES OF ELECTRICAL ENGINEERING Previous Question Paper (March - 2022 - R13)
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Main
Obtain an expression for transient current in a RL series circuit excited by D.C. voltage.
Answer
For an RL series circuit with a resistance R and inductance L connected to a DC voltage source V, applying Kirchhoff's Voltage Law (KVL) at t ≥ 0 gives:
This is a first-order linear differential equation. Rearranging the terms:
The solution consists of a complementary function and a particular integral. The steady-state current is I = V/R. The transient solution is of the form i(t) = (V/R) + Ae-(R/L)t. Using the initial condition i(0) = 0, we find A = -V/R. Thus, the expression for transient current is:
Here, L/R is the time constant τ of the circuit, representing the time taken for the current to reach approximately 63.2% of its final value.
In the circuit shown in figure 1, switch S is in position 1 for a long time and brought to position 2 at time t=0. Determine the circuit current.
Answer
When the switch is in position 1 for a long time, the inductor acts as a short circuit in steady state. The initial current through the inductor i(0-) is determined by the source voltage and the resistors in the loop. Since the inductor current cannot change instantaneously, i(0+) = i(0-).
When the switch moves to position 2, the source is disconnected, and the inductor discharges through the remaining resistance Req in the new loop. The current follows the decay equation:
To find the final expression, calculate the initial current i(0+) using the circuit parameters from position 1, determine the equivalent resistance Req seen by the inductor in position 2, and substitute these values into the decay formula.
A series RLC circuit with R = 3 Ω, L = 1H and C = 0.5F, is excited by a unit step voltage. Obtain the expression for I(t) using Laplace Transform method. Assume that the circuit is initially relaxed. Sketch the variation of I(t) and state whether the circuit is over damped, or under damped or critically damped.
Answer
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Define ABCD parameters of a two port network and obtain the relation with Z-parameters. Determine Y-parameters for the bridge- T network shown in figure 2.
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What are the conditions for Reciprocity and symmetry of open circuit impedance parameter?
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Test results for a two port network are:
i) port 2 short circuited: V1 = 50∠0° V, I1 = 2.1∠−30° A, I2 = −1.1∠−20° A.
ii) port 1 short circuited: V2= 50∠0° V, I1 = 3.0∠−15° A, I2 = −1.1∠−20° A.
Find y-parameters.
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Explain in brief units of attenuation and obtain relation between the two units.
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A prototype HPF has cut-off frequency of 10 kHz and design impedance of 600 Ω. Find element values of L and C. Also find attenuation in dB and phase shift in degrees at a frequency of 8 kHz.
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Bring out the draw backs of constant K filters.
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Obtain the necessary equations for a m-derived T-section low pass filter from a proto type constant K-filter.
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Derive the induced e.m.f equation of a D.C. Generator.
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The armature of a 4-pole, lap-wound DC shunt generator has 120 slots with 4 conductors per slot. The flux per pole is 0.05wb. The armature resistance is 0.05 ohm and the shunt field resistance is 50 ohms. Then find the speed of the machine when supplying 45A at terminal voltage of 250V.
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Draw the phasor diagram of Transformer on load assuming the load is a lagging power factor load.
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A single-phase transformer has 500 turns in the primary and 1200 turns in the secondary. The cross-sectional area of the core is 80sq.cm. If the primary winding is connected to a 50 Hz supply at 500V, calculate (i) peak flux-density, and (ii) Voltage induced in the secondary.
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