JNTU
JNTU B.Tech II ELECTRICAL TECHNOLOGY Previous Question Paper (November/December - 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
What is the function of brushes in a d.c generator?
Answer
The primary function of brushes in a d.c. generator is to collect the current generated in the armature conductors and deliver it to the external circuit. They maintain a sliding electrical contact with the rotating commutator segments, ensuring a continuous path for the current flow from the armature to the load.
Define speed regulation of d.c. motor.
Answer
The speed regulation of a d.c. motor is defined as the change in speed of the motor when the load on its shaft is reduced from rated load to zero, expressed as a percentage of the rated full-load speed.
Where Nnl is the no-load speed and Nfl is the full-load speed. It serves as a measure of the motor's ability to maintain a constant speed under varying load conditions; a lower percentage indicates better speed stability.
What are the various losses present in a transformer?
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Draw equivalent circuit of a short circuit test.
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Define efficiency of IM.
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Give the application of 3-φ I.M.
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What is synchronous reactance?
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What is distribution factor?
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Define Deflecting torque.
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Why PMMC not measure AC quantity.
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Part B
Explain how will you classify DC generators in detail and also explain the types of DC generators.
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A 6-pole wave connected DC generator having 60 slots on its armature with 6 conductors per slot, runs at 750 rpm and generates an open circuit voltage of 230 V. Find the useful flux per pole.
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Explain the losses that occur in a DC machine.
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A 4-pole DC shunt generator with lap connected armature supplies a load of 100 A at 200 V. The armature resistance 0.1 ohms and the shunt field resistance is 80 ohms find the Total armature current.
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Derive from the fundamentals, the E.M.F equation of a single phase transformer.
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Draw a no load phasor diagram and explain it.
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A 15kVA, 1-phase, 50Hz, 500/250V transformer gave following test results: OC test (LV) side: 250V, 3.0A, 200W; SC test (HV) side: 25V, 20A, 300W. Calculate efficiency and regulation at full-load, 0.8 p.f lagging.
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Explain construction and working principle of 3-phase Squirrel cage motor.
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Three phase induction motor is wound for 4 – poles and is supplied from a 230V, 50 Hz supply. Calculate: i) The synchronous speed ii) The speed of the motor when the slip is 2% iii) The rotor frequency.
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Explain different starting methods of 3-Ø Induction motor.
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The frequency of emf in the stator of a 4-pole induction motor is 50Hz, and that of rotor is 1.5Hz. Calculate slip and at what speed will the motor run?
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Explain constructional features of alternator.
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How e.m.f is induced in an 3-phase alternator? Derive the expression for e.m.f?
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Draw the phasor diagram of the synchronous generator on load.
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A 50Hz alternator has a flux of 0.1 Wb/pole, sinusoidally distributed. Calculate the rms value of the emf generated in one turn of the winding, which spans 3/4 of a pole pitch.
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Derive the torque equation of Moving iron instruments.
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Discuss the classification of electrical instruments.
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Explain the construction and operation of stepper motor.
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Explain the construction and operation split phase 1-phase induction motor.
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