JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II ELECTRICAL SYSTEMS Previous Question Paper (April/May - 2018 - 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.
Main
What is the difference between dependent and independent sources?
Answer
An independent source provides a constant voltage or current regardless of the circuit conditions. A dependent (controlled) source provides a voltage or current whose value depends on the voltage or current elsewhere in the circuit.
State Reciprocity Theorem.
Answer
The Reciprocity Theorem states that in any linear, bilateral, passive network, if a voltage source applied at one pair of terminals produces a current at another pair of terminals, then the same voltage source applied at the second pair will produce the same current at the first pair.
Define power factor and explain its significance.
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A series circuit comprises a coil of resistance 2 Ω and inductance 60 mH, and a 30 μF Capacitor. Determine the Q-factor of the circuit at resonance.
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Define Hysteresis loss and Eddy current loss.
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Draw and explain the phasor diagram of transformer on no load.
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Define armature reaction and explain its effect.
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Explain the classification of Dc generators based on their excitation.
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Draw the circuit diagram of star-delta starter.
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Explain the concept of rotating magnetic field and what is its significance in the operation of three phase induction motor.
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Using mesh analysis, determine the current in 8Ω resistance for the network of Figure 1.
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Explain Star-Delta conversion method.
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State and explain maximum power transfer theorem.
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Using superposition, determine the current through the 4 Ω resistor of Figure 2.
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Three coils each having resistance 3 Ω and inductive reactance 4 Ω are connected (i) in star and (ii) in delta to a 415V, 3-phase supply. Calculate for each connection (1) the line and phase voltages and (2) the phase and line currents.
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A coil of inductance 80mH and negligible resistance is connected in series with a capacitance of 0.25 μF and a resistor of resistance 12.5 Ω across a 100V, variable frequency supply. Determine (i) the resonant frequency, and (ii) the current at resonance. How many times the supply voltage is greater than the voltage across the reactance’s at resonance?
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The power taken by a C–R series circuit, when connected to a 105V, 2.5 kHz supply, is 0.9kW and the current is 15A. Calculate i) the resistance ii) the impedance iii) the power factor and iv) the phase angle between voltage and current.
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A 0.15 μF capacitor and a pure inductance of 0.01H are connected in parallel across a 10V, variable frequency supply. Determine the resonant frequency of the circuit.
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Define Efficiency of transformer? Derive the condition for maximum efficiency of the transformer.
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A 2400V/400V single-phase transformer takes a no-load current of 0.5A and the core loss is 400W. Determine the values of the magnetising and core loss components of the no-load current. Draw the no load phasor diagram for the transformer.
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Following are the test results for the 4KVA, 200/400V, 50Hz, single phase transformer. O.C test : 200V, 0.8A, 70 W S.C test : 17.5V, 9A, 50 W. Calculate the parameters of equivalent circuit of a transformer.
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Derive the equation for the EMF induced in a DC Generator.
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A 4-pole generator has a lap-wound armature with 50 slots with 16 conductors per slot. The useful flux per pole is 30mWb. Determine the speed at which the machine must be driven to generate an e.m.f. of 240V.
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Draw and explain the load characteristics of Series, Shunt and Compound dc motors?
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A 320V shunt motor takes a total current of 80A and runs at 1000 rev/min. If the iron, friction and windage losses amount to 1.5kW, the shunt field resistance is 40 Ω and the armature resistance is 0.2Ω, determine the overall efficiency of the motor.
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Explain about different speed control methods of DC motors.
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Explain the principle of operation of Shaded pole motor.
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Explain the principle of operation of three phase induction motor.
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Explain the two watt meter method of measuring three phase power.
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