DieselShip's Online Content Library

Q9. 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 that day from normal.

Q8. (a) Compare Direct current with Alternating current. (6)

(b) A four-pole generator has a flux of 12 mWb/pole. Calculate the value of e.m.f. generated in one of the armature conductors, if the armature is driven at 900 rev/min. (10)

Q9. a) Sketch a schematic arrangement of a three-phase alternator with star connection. (6)

b) A 500V, 3-phase, star-connected alternator supplies a star-connected induction motor which develops 45kW. The efficiency of the motor is 88 percent and the power factor is 0.9 (lagging). The efficiency of the alternator at this load is 80 percent. Determine

a) the line current

b) the power output of the alternator

c) the output power of the prime-mover.  (10)

Q6. a) Explain how excitation of the rotor is produced and supplied. (6)

b) A shunt motor has an armature resistance of 0.2 ohms and with an armature current of 120 amperes runs at 750 r.p.m. off a 400-volts supply. Calculate the speed and armature current of the motor if the flux per pole is reduced to 75 per cent of its initial value, the total torque remaining unaltered. (10)

Q7. A 4 pole, lap wound shunt generator delivers 200 A at terminal voltage of 250 V. It has a field and armature resistance of 50 Ω and 0.05 Ω respectively. Determine: (16)

(a) Armature current

(b) Generated e.m.f

(c) Current per armature parallel paths

(d) Power developed

Q9. A vessel about to complete loading in a summer zone is expected to enter a winter zone after steaming from the loading port for 10 days. On passage, fuel consumption is expected to be 30 tonnes per day and water consumption 15 tonnes per day. The ship is at present floating in water of density 1.013 tonnes/m3 at a draft of 9.0m. (16)

Find:(a) The maximum permissible draft on completion of loading.(b) The amount of cargo which the vessel can load. (Note: A vessel passing from a summer zone to a winter zone, or from a tropical zone to summer zone, must arrive at the zone boundary at the draft appropriate to that zone).

Q5. a) Which has the greater equivalent resistance; two equal capacitors in series or in parallel? Explain with reasons? (6)

b) A circuit has a resistance of 3Ω inductance of 0.01H. The voltage across its end is 60V and the frequency is 50Hz. Calculate

a) the impedance

b) the power factor

c) the power absorbed. (10)

Q5. (a) State briefly. The meaning of the expressions ‘star-connected’ as applied to three -phase a.c. practice. What is the ratio of the maximum line voltage to the maximum phase voltage in each case. (6)
(b) Determine the line current taken by a 440 V, three-phase, star-connected motor having an output of 45 Kw at 0.88 (lagging) power factor and an efficiency of 93 per cent. (10)

Q6. a) What is a silicon-controlled rectifier (SCR)? How is the breakover voltage of the SCR defined?

b) A d.c. motor takes an armature current of 110 A at 480 V. the resistance of the armature circuits is 0.2Ω. The machine has six poles and the armature is lap-connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate

a) The speed:

b) The gross torque developed by the armature. (10)

Q5.a) With the aid of delta and star connection diagrams, state the basic equation from which the delta -star and star- delta conversion equation can be derived (6)

b) A 230/115 V, single phase transformer is supplied with a load of 5A at p.f. 0.86 lagging. The no-load current is 0.2 A at p.f. 0.208 lagging. Calculate the primary current and p.f. (10)

Q8. A. What is a commutator? Discuss its rectifying action in detail.

B. Calculate the e.m.f. generated by a 4-pole, wave wound armature having 40 slots with 18 conductors per slot when driven at 1000 r.p.m. The flux per pole is 0.015 wb.

Q10.  (a). Describe the no-load saturation characteristic of a d.c. generator.

(b). A 4-pole machine running at 1500 r.p.m. has an armature with 80 slots and 6 conductors per pole. The flux per pole is 6 x 106 lines. Determine the terminal e.m.f. of d.c. generator if the coils are lap connected. If the current per conductor is 100 A, determine the electrical power.