JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year ELECTRICAL TECHNOLOGY Previous Question Paper (May/June - 2019 - 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
Why series motor cannot be started on no-load?
Answer
A DC series motor cannot be started on no-load because at no-load, the armature current is very small, which makes the flux produced by the series field winding extremely low. Since speed is inversely proportional to flux, the motor would attempt to reach a dangerously high, theoretically infinite speed, leading to mechanical destruction of the machine.
What are Faradays laws of Electro Magnetic Induction?
Answer
Faraday's laws of electromagnetic induction are:
- Whenever the magnetic flux linked with a circuit changes, an electromotive force (EMF) is induced in it.
- The magnitude of the induced EMF is directly proportional to the rate of change of magnetic flux linkage.
Draw the equivalent circuit of a transformer.
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What will happen if DC supply is given on the primary of a transformer?
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Why starters are necessary for starting of 3-phase induction motors?
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Define slip and explain significance of slip in three phase induction motor.
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Define the term pitch factor.
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Define synchronous reactance and synchronous impedance of synchronous generator.
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How the direction of rotation is reversed for capacitor start capacitor run motor?
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Write the applications of shaded pole motor.
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Part B
Explain different types of DC generators.
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A Shunt generator delivers 50 KW at 250 V and 400 rpm. The armature and field resistances are 0.02 Ω and 50 Ω respectively. Determine the speed of the machine running as a shunt motor and taking 50 KW input at 250 V. Allow 1V per brush for contact drop.
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Explain different characteristics of DC shunt motor.
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The armature of a 4 – pole Shunt Motor has a lap winding accommodated in 60 slots, each containing 20 conductors. If the useful flux per pole is 23 m Wb, Calculate the Total torque developed when the armature current is 50 A.
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A 50 kVA, 2200 / 220V transformer when tested, given the following results: OC test, measurements on LV side: 405 W, 5 A, 220 V SC test, measurements on HV side: 805 W, 20.2 A, 95 V Draw the circuit model of the transformer referred to the HV and LV sides. Label all the parameters.
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What are the various losses that occur in a transformer? Derive the condition for maximum efficiency of a transformer.
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A 11000/400 V distribution transformer takes a no load primary current of 1 A at a power factor of 0.24 lagging. Find: (i) Core loss current. (ii) Magnetizing current. (iii) Iron loss.
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Explain any one method of starting of an induction motor with neat diagram.
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Explain torque-slip characteristics of three phase induction motor.
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Explain how the rotating magnetic field is developed in a 3-ø induction Motor?
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Calculate the slip speed and rotor frequency of three-phase, 50Hz, 4-pole Induction motor running at 1440rpm.
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Write the differences between salient pole and non salient pole rotor.
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A 600V, 60kVA, 3-phase alternator has an effective resistance of 0.2 ohms. A field current of 10 A produces an armature current of 210A on short-circuit and e.m.f. of 480 V on open circuit. Calculate Full-load regulation with 0.8 p.f. lagging.
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With a neat sketch, explain the EMF method for predetermining the voltage regulation of an alternator.
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Explain the construction, principle of operation and applications of stepper motor.
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Explain the following with reference to the indicating instruments:
a) Deflecting torque
b) Controlling torque
c) Damping torque.
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