DieselShip's Online Content Library

Q1. With reference to an emergency source of electrical power in cargo ships:

a) Describe a typical power source (6)

b) Give a typical list of essential services, which must be supplied simultaneously. (5)

c) Explain how the emergency installation can be periodically tested. (5)

Q2. a) Sketch a reverse current trip. (8)

b) Explain briefly how the reverse current trip operates. (4)

c) Explain why there is a time delay incorporated before the reverse current trip operates. (4)

Q3. a) Briefly discuss the conditions that needs to be satisfied for synchronizing (8)

b) Explain, working of a synchroscope with the help of a sketch. (8)

Q4. a) Sketch and describe a star-delta starter for starting an induction motor (10)

b) Three similar coils, each having a resistance of 10 ohms and an inductance of 0.02 H are connected in

i) Star

ii) Delta to a 3-phase, 50-Hz supply with 500V

Calculate the total power absorbed and the line current in each case. (6)

Q5. A 4-pole lap wound DC shunt generator has an open e.m.f of 250V when the flux per pole is 0.08 Wb and the speed is 10 rev/sec. The speed of the generator is reduced to 10 per cent and the flux per pole is increased by 5% when the generator supplies a load of 100A. Determine the terminal voltage, if the armature resistance is 0.06 ohms and the new total field circuit resistance is 200 ohm. (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

Q7. a) Name the three main types of A.C. motor and explain the use to which they are put in marine engineering. (6)

b) A four-pole motor is fed at 440V and takes an armature of 50 A. The resistance of the armature circuit is 0.28 ohm. The armature winding is wave connected with 888 conductors and the useful flux per pole is 0.023 Wb. Calculate the speed. (10)

Q8. a) List the parts of an alternator fitted with temperature alarms. (6)

b) Explain why heaters are fitted to an Alternator. (6)

c) Explain the function of an automatic voltage regulator. (4)

Q9. a) What is meant by the term ‘back e.m.f.’ as applied to an electric motor? (6)

b) A 40 kW,220V shunt motor has a full-load efficiency of 90 per cent, an armature resistance of 0.075 ohms and a shunt motor-field resistance of 55 ohms. When ‘at starting’, the starter handle is moved onto the first stud, it is desired to limit the current, through the armature to 1.5 times the value which it has when the motor is on full load. What must be the total value of the starting resistance? If, on overload, the speed falls to 90 per cent of its normal full-load value. What would be the armature current? Neglect the effect of armature reaction. (10)