Q2. Diesel electric propulsion is now being chosen as the power plant for an increasingly wide variety of vessels. (16) a) Sketch a simple layout of such an installation. b) Explain the advantages of selecting such a plant.
Q4. (a) Describe how protection against short circuit is provided. (6) (b) Explain how rotating magnetic field is produced in three phase winding with three phase supply. A 4-pole, 3 phase induction motor operates from a supply whose frequency is 50 Hz. Calculate (i) Speed at which the magnetic field of the stator is rotating, (ii) Speed of the rotor when the slip is 0.04, (iii) The frequency of the rotor current when the slip is 0.03. (10)
Q4. A) Explain the potential hazards if liquid-cooled transformers are used. (6) b) What are the losses in transformers? Mention the various factors which affect these losses. In a 25 KVA, 3300/233 V, single phase transformer, the iron and full-load Cu. Losses are respectively 350 and 400 w. Calculate the efficiency at half-full load 0.8 power factor. (10)
Q6. A) Explain the effect of making incorrect phase and starter connections. (6) b) A 440V shunt motor takes an armature current of 30A at 700 rev/min. The armature resistance is 0.7 Ohm. If the flux is suddenly reduced 20 percent, to what value will the armature current rise momentarily? Assuming unchanged resisting torque to motion, What will be the new steady values of speed and armature current? Sketch graphs showing armature current and speed as functions of time during the transition from initial to final, steady-state conditions. (10)
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