JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II ELECTRICAL TECHNOLOGY Previous Question Paper (November/December - 2017 - 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 and may have a, b, c as sub questions.
Part A
What is critical field resistance and critical speed of a d.c generator?
Answer
Critical field resistance is the maximum resistance of the shunt field circuit beyond which the d.c. generator fails to excite. Critical speed is the minimum speed below which the generator fails to build up its voltage on open circuit.
Write the expressions for core losses and remedial measures to reduce them in a dc machine.
Answer
Core losses (iron losses) consist of hysteresis loss (Wh = η Bmax1.6 f V) and eddy current loss (We = Ke Bmax2 f2 t2). Remedial measures include using silicon steel for the core to reduce hysteresis loss and using thin, insulated laminations to reduce eddy current loss.
What is the principle of operation of single phase transformer?
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Derive the condition for maximum efficiency of a 1-phase transformer.
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Define slip.
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Define crawling and cogging.
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Write the EMF equation of Alternator.
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Define Distribution and Coil span factors.
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What is the difference between Moving Coil and Moving iron Instruments?
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What are the applications of stepper motor?
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Unit I
Derive emf equation of dc generator.
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Explain Magnetization and load characteristics of DC generators.
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Discuss the various methods of speed control of a D.C motor.
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Unit II
Derive an emf equation of a single phase transformer.
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Explain about hysteresis and eddy current losses occur in a transformer.
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A 10kVA, 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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Unit III
Explain Principle of operation of three-phase induction motors.
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Distinguish the difference between squirrel cage and slip ring induction motor.
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Explain different starting methods of 3-phase induction motor.
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Unit IV
Draw the phasor diagram of the synchronous generator on load. Explain the meaning synchronous reactance.
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Explain constructional features of alternator.
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Explain the Principle of operation of alternator.
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Write short notes on SC,OC tests on alternator.
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Unit V
Explain the construction and operation of an a.c. tachometer.
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How the shaded pole motor works explain in detail?
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Explain construction and working of moving coil instruments.
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What are the applications of synchro?
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