JNTU
JNTU B.Tech II ELECTRICAL SYSTEMS Previous Question Paper (May/June - 2019 - 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. Each question carries 10 marks and may have a, b, c as sub questions.
Part A
What is the difference between Independent and Dependent Sources?
Answer
An independent source provides a specified voltage or current that is completely independent of any other circuit variables. A dependent source provides a voltage or current whose value is controlled or determined by another voltage or current existing elsewhere in the circuit.
States the maximum power transfer theorem.
Answer
The Maximum Power Transfer Theorem states that for a given DC network with an internal resistance, the maximum power is transferred from the source to the load when the load resistance is exactly equal to the Thevenin equivalent resistance of the network as viewed from the load terminals.
What is a ‘j’ operator? State its significance.
Answer
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What are the advantages of poly phase system?
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What are the difference between shell and core type transformer?
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Define the Electromotive force and Reluctance.
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Define the Armature Torque and shaft Torque.
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What are the methods of compensating armature reaction?
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What are the factors to be consider for controlling the speed of DC motors?
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Why single phase induction motor is not self staring.
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Part B
State and explain Kirchoff’s Laws.
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Determine the current in the battery, the current in each branch and the p.d across AB in the network shown in figure 1.
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State and explain the superposition theorem.
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Find RAB across A and B terminals of the figure 2.
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A voltage of (100+ j60) volts drives a current of (4-j5) Amp through a series R-L-C Circuit. Determine:
- The complex expression for impedance
- Power consumed
- Power factor
- Draw the phasor diagram.
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A step voltage is applied across R-L circuit by closing the switch at t=0. Derive an expression for current flowing through the circuit when t > 0. Use Laplace transform method.
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What is a transformer? How does it transfer electrical energy from one circuit to another?
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A single phase transformer with a ratio of 440/110V takes on no load current of 4A at 0.3 p.f lagging. If the secondary supplies a current of 60A at 0.85 p.f lagging, estimate the current taken by primary.
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Why the transformer is rated in kVA but not in kW.
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A 30 kVA, 200/120V, 50 Hz transformer has a high voltage winding resistance of 0.1 ohm and a leakage reactance of 0.22 ohm. The low voltage winding resistance is 0.035 ohm and the leakage reactance is 0.012 ohm. Find the equivalent winding resistance, reactance and impedance referred to the low voltage side.
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Explain the construction features of a DC machine with the help of neat sketches.
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Derive an expression for e.m.f generated in a d.c generator.
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Explain the basic Principle of DC Motor.
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A 220V motor has an armature circuit resistance of 0.5Ω. If the full load armature current is 35A and the no load armature current is 6A. Find the change in back e.m.f from no-load to full-load.
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Explain the Measurement of three phase power using two wattmeter method.
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What are the methods used for power factor improvement?
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Explain the working of 3-ϕ Induction motor.
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A 3-phase induction motor is wound for 4 poles and is supplied from 50 Hz systems. Calculate (i) the synchronous speed, (ii) the speed of the motor when slip is 4% and (iii) the rotor current frequency when the motor runs at 600 r.p.m.
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