JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year ELECTRICAL SYSTEMS Previous Question Paper (November/December - 2018 - R13)
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.
Part A
State Norton’s Theorem.
Answer
Norton’s Theorem states that any linear, bilateral, active two-terminal network can be replaced by an equivalent circuit consisting of a current source (Norton current, IN) in parallel with a resistor (Norton resistance, RN).
Find the current flowing through R1, R2, and R3 as shown in figure 1.
Answer
Since the figure is not provided, the currents are determined by applying Kirchhoff's Laws or Nodal Analysis. For a circuit with resistors R1, R2, and R3, the branch currents are calculated using Ohm's Law (I = V/R) after simplifying the circuit network to find the equivalent resistance and total source current.
What are the different types of power available in AC circuits? What are their units?
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Define Resonance. What are its applications?
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Draw the phasor diagram of a transformer with inductive load.
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Define m.m.f and reluctance.
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What is the use of commutator in DC machine?
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Define Armature Reaction. What are its effects?
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Define slip of an induction motor. Write its expression.
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Define power factor. What are the disadvantages of low power factor?
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Part B
State and explain Superposition Theorem with the help of an example.
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Transform the network shown in figure 2 into its Star equivalent.
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State and explain dependent and independent sources.
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Solve the network shown using Thevenin’s Theorem across A and B terminals and draw thevenin’s equivalent circuit shown in figure 3.
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Derive an expression for the current, impedance, average power for a series RC circuit excited by a sinusoidally alternating voltage and also find the power factor of the circuit. Draw the phasor diagram.
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A series circuit consists of a resistance of 4Ω, an inductance of 500mH and a variable capacitance connected across a 100V, 50Hz supply. Calculate:
a) The capacitance required to give series resonance
b) The voltages generated across both the inductor and capacitor.
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A single phase transformer has a turn ratio of 6. The resistance and reactance of primary winding are 0.9Ω and 5Ω respectively and those of the secondary are 0.03Ω and 0.13Ω respectively. If 330 V at 50 Hz is applied to the high voltage winding with the low-voltage winding short circuited. Find the current in the low-voltage winding and its power factor. Neglect magnetizing current.
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Write in detail how the various losses are produced in a transformer. Also explain how these losses can be reduced.
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Derive the equation for the voltage generated in a d.c generator.
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A 2 pole d.c generator has 240 conductors on its armature. It is driven by a prime mover at a constant speed of 800 r.p.m. If the flux per pole is 0.3 wb, calculate the emf generated.
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Explain the principle of operation of a dc motor with neat diagram.
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A 80KW, 250V shunt motor takes 10A when running on no-load. The resistance of the armature and field are 0.5 and 100 respectively. i) Estimate motor efficiency when loaded to carry 120A. ii) Estimate maximum efficiency of motor.
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Explain the working principle of three phase induction motor.
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Explain in detail how power in three phase circuits can be measured using two wattmeters. Using this method determine power factor for three phase balanced load.
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