Q6. A. What are the characteristics of PN junction diode? Point out its specifications. Also point out the significance of dynamic and static resistances.
B. Draw the circuit of Half-wave rectifier and its output waveform. A diode whose internal resistance is 20 is to supply power to 1000 load from 110 V (RMS) source. Calculate
(i) peak load current, (ii) DC load current, (iii) AC load current.
Q7. With reference to adjoining circuit calculate following. (a) Current in each branch of circuit. (b) Total current.
Q7. A. Describe how protection against short circuit is provided in a 3 phase induction motor circuit.
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.
Q9. A. Explain the working principal of a 3-phase induction motor. What are the various types of rotors? B. An 18.65Kw, 6-pole, 50Hz, 3 phase slip ring induction motor runs at 960 rpm on full load with a rotor current per phase of 35A, allowing 1Kw for mechanical losses, find the resistance per phase of 3-phase rotor winding.
Q7. A. Describe the possible causes and the effect of running a three-phase motor with one phase open circuited. B. A 440V shunt motor tenets an armature current of 30A at 700 rev/min. The armature resistance is 0.7ohm. If the flux is suddenly reduced by 20 per cent, 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.
Q8. A. Define longitudinal centre of gravity (LCG) and longitudinal centre of buoyancy (LCB).
B. The immersed cross-sectional area of a ship 120m long, commencing from aft are 2,40,79,100,103,104,104,103,97, 58 and 0 m2 calculate :
(i) Displacement;
(ii) Longitudinal position of the centre of buoyancy.
Q9. A) Describe the effect of cavitations on the propeller blades. (6)
B) A propeller 4.6m diameter has a pitch of 4.3m and boss diameter of 0.75 m. The real slip is 28% at 95 rev/min. Calculate the speed of advance, thrust and thrust power. (10)
Q8. A ship of 9,900 tonnes displacement has KM=7.3 m and KG=6.4 m she has yet to load two 50 tonne lifts with her own gear and the first lift is to be placed on deck on the inshore side (KG 9 m and center of gravity 6m out from the center line). When the derrick plumbs the quay its head is 15m above the keel an 12m out from the center line.
Calculate the maximum list during operation.
Q7. A Ship of 3,000 tonnes displacement is 100m long has KM=6m, KG=5.5m. The centre of floatation is 2m.aft of amidships. MCTC=40 tonnes-m. Find the maximum trim for the ship to enter a dry dock if the metacentric height at the critical instant before the ship takes the blocks forwarded and aft is to be not less than 0.3m.
Q8. A) Explain how the distribution of masses affects rolling and pitching. (6)
B) A ship turns in a circle of radius 100 metres at a speed of 15 knots. The GM is 2/3 metres and BG is 1 metre. If g = 981 cm/sec2 and 1 knot is equal to 1.8532 Km/hour, find the heel due to turning. (10)
Q9. A. Describe the general precautions to be taken against capsizing. State the recommended criteria for passenger and cargo ships. B. The ½ ordinates of a water plane at 15m intervals, commencing from aft, ar. 1, 7, 10.5, 11, 11, 10.5, 8, 4 and 0m. Calculate: i. TPC; ii. Distance of the centre of flotation from midships; iii. C. Second moment of area of the water plane about a transverse axis through the centre of flotation.
Q7. A. Describe the effect of Cavitation on; The thrust and torque; The propeller blades B.A ship 120m long displaces 10500 tonne and has a wetted surface area of 3000m2. At 15 knots the shaft power is 4100KW, propulsive coefficient 0.6 and 55% of the thrust is available to overcome frictional resistance; calculate the shaft power required for a similar ship 140m long at the corresponding speed. = 0.42 and n = 1.825
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