JNTU
JNTU B.Tech II ELECTRICAL TECHNOLOGY Previous Question Paper (April/May - 2018 - R16)
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.
Part A
Give the function of commutator in a DC generator.
Answer
The commutator acts as a mechanical rectifier. It converts the alternating current (AC) induced in the armature conductors into unidirectional direct current (DC) in the external circuit.
What is an equalizer bar? How is it used?
Answer
An equalizer bar is a low-resistance copper conductor used to connect points of equal potential on the armature windings of DC generators operating in parallel. It is used to prevent circulating currents between machines due to small differences in induced EMF, thereby ensuring stable parallel operation and preventing unequal load sharing.
Why transformer rating in VA?
Answer
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Draw the phasor diagram of 1-ϕ transformer on no-load.
Answer
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Define slip speed of 3-ϕ I.M.
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Write the merits and demerits of slip-ring induction motor.
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What is synchronous impedance?
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Explain coil span factor.
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What is use of Damping torque?
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Compare spring control torque method with gravity control method.
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Part B
Explain the principle of operation of DC generator.
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A 6-pole, Lap wound armature has 840 conductors and flux per pole of 0.018 Wb. Calculate the emf generated when the machine is running at 600 rpm.
Answer
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Derive the torque equation of a DC motor.
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A 200V DC shunt motor takes a total current of 100 A and runs at 750 rpm. The resistance of the armature winding and shunt field winding is 0.1 ohms and 40 ohms respectively. Find the total copper losses.
Answer
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Derive the induced e.m.f equation of transformer.
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A 1,000/200 V transformer takes 0.3 A at p.f of 0.2 on open circuit. Find the magnetizing, and iron loss component of no-load primary current.
Answer
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What do you understand by efficiency of a transformer? Derive the condition for maximum efficiency.
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A single phase transformer working at unity power factor has an efficiency of 80 % at both one half load and at the full load of 600 W. Determine the efficiency at 70 % of full load.
Answer
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Explain working principle of 3-phase induction motor.
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A 3-phase, 6-pole, 50 Hz induction motor develops 4 kW including friction and windage losses at 950 rpm. If the stator loss is 250 W. Find the slip of the induction motor.
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Derive the expression for Torque-Slip characteristics of a 3-phase Induction Motor.
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The power input to the rotor of a 400V, 50Hz, 6 pole, 3-phase induction motor is 75 KW. The rotor electromotive force is observed to make 100 complete alterations per minute. Calculate (i) slip (ii) rotor speed.
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Derive EMF Equation of alternator.
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Discuss how regulation of an alternator can be determined by synchronous impedance method.
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Derive the relation between speed, frequency and number of poles in an alternator.
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Give the constructional details of both salient pole and cylindrical rotor synchronous machines.
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Explain the construction and operation of Capacitor start-run motor.
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What are the applications of synchro?
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Explain the construction and operation with a neat diagram Permanent Magnet Moving Coil instruments.
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