DieselShip's Online Content Library

Q10. A. Describe how protection against short circuit is provided in a 3 phase induction motor circuit.
b) An eight – pole alternator running at a speed of 720rev/min supplies current to synchronous and induction motors with forty – eight poles. Calculate the frequency and speed of rotation of the motors if thr induction motor runs with 2 percent slip.

Q8. A. (i) What is direct-connected alternator? (3)

(ii)  How is a direct-connected exciter arranged in an alternator? (3)

B. A twelve-pole, three-phase, delta-connected alternator runs at 600 rev/min and supplies a balanced star-connected load. Each phase of the load is a coil of resistance 35 ohm and inductive reactance 25 ohm. The line terminal voltage of the alternator is 440V. Determine (a) frequency of supply, (b) current in each coil, (c) current in each phase of the alternator, (d) total power supplied to the load. (10)

Q9. A three-phase transformer has 560 turns on the primary and 42 turns on the secondary. the primary winding are connected to the line voltage of 6.6KV. Calculate the secondary line voltage when the transformer is connected a) Star-Detta b) Detta-Star

Q6. (a) Define TPC. Explain why TPC for a given draught will vary with the density of the water in which the ship floats (6)
(b) The pitch angle, measured at a distance of 2m from the centre of the boss, was found to be 21.5  Calculate the pitch of the propeller (10)

Q6. A vessel of 10000 t displacement burns 25 t of fuel per day when her speed is 12 Knots. Calculate the probable consumption of fuel over a voyage of 3000 nautical miles at a speed of 11 knots with a displacement of 11000 t. (16)

Q9. a) Explain what is meant by synchronous or resonant vibration (6)

b) A ship's speed is increased by 20% above normal for 8 hours, reduced by 10% below normal for 10 hours and for the remaining 6 hours of the day the speed is normal. Calculate the percentage variation in fuel consumption in that day from normal. (10)

Q8. Find the length of manganese wire required to make a 15.7 Ω resistor, if the diameter is 0.315 mm and the resistivity is 407 μΩ mm (16)

Q6. a) Describe a simple single-phase transformer. (6)

b) A 15 KVA, 440 / 110- volt, 50 Hz cycle/sec, single-phase transformer has primary and secondary resistance of 0.12 ohm and 0.0077 ohm respectively. The iron loss of the transformer is 0.16 kW. Calculate the efficiency of the transformer (10)

i) On full load unity power factor

ii) on 80 per cent full load at a power factor of 0.9 lagging

Q6. (a) Describe the basic principles of a self-excited generator (6)

(b) The armature resistance of a 200 V, shunt motor is 0.4 ohms and the no-load armature current is 2A. When fully loaded and taking an armature current of 50 A, the speed is 1200 rev/min. Find the no-load speed and state the assumption made in the calculation (10)

Q7. (a) What is meant by statical stability? What are the factors that influence stability? (6)

(b) A box barge 25 m long and 4 m wide floats in fresh water at a draught of 1.2 m and has an empty mid length compartment 5 m long. The bottom of the barge is lined with teak (rd 0.805) 120 mm thick. After grounding all the teak is torn off and the centre compartment laid open to the sea. Calculate the final draught. (10)

Q6. (a) The capacitor-start induction run motor has a much higher starting torque than the resistance split-phase motor. Explain (6)

(b) An eight-pole armature is wound with 480 conductors. The magnetic flux and the speed are such that the average e.m.f. generated in each conductor is 2.2 V, and each conductor is capable of carrying a full load current of 100 A. Calculate the terminal voltage on no load, the output current on full load and the total power generated on full load when the armature is:

(i) Lap connected

(ii) Wave connected (10)

Q6. a) Which of the following three motors has the poorest speed regulation: shunt motor, series Motor or cumulative compound motor? Explain. (6)
b) An 18.65 KW,4-pole,50HZ, 3 phase induction motor has friction and windage losses of 2.5 percent of the output. The full load slip is 4% compute for full load
(i) the rotor Cu loss
(ii) the rotor input
(iii) the shaft torque
(iv) the gross electromagnetic torque. (10)