DieselShip's Online Content Library

Q7. A resistor of ohm value 3 ohms is connected in series with a coil of inductance 0.1 H and resistance 1 ohm. If 100 V at a frequency of 50 Hz is applied to the circuit find the current flowing.

Q8. (a) Explain various powers and efficiencies in the Propulsion plant of a ship (6)
(b) A vessel with a displacement of 12250 t burns 290 t of fuel while travelling at a speed of 15 knots on a voyage of 2850 nautical miles. On a voyage of 1800 nautical miles at a speed of 13 knots and a displacement of 14200 t, estimate the quantity of fuel that will be burnt. (10)

Q7.  The pitch of a propeller is measured by means of a batten and cord. The horizontal ordinate is found to be 40 cm while the vertical ordinate 1.15 m at a distance of 2.6 m from the centre of the boss. calculate the pitch of the propeller and the blade width at that point. (16)

Q6. A. What are the characteristics of PN junction diode? Point out its specifications. Also point out the significance of dynamic and static resistances. (6)

B. A 72 KVA transformer supplies a heating and lighting load of 12 KW at unity power factor and a motor load of 70 kVA at 0.766 (lagging) power factor: Calculate the minimum rating of the power-factor improvement capacitors which must be connected in the circuit the ensure that the transformer does not become overloaded. (10)

Q7. a) Describe the principle of variable-capacitance transducer. (6)

b) A coil of resistance 10 ohms and inductance 100mH is connected in series with two parallel capacitors each of value 100 mF across a 250 V, 50Hz supply. determine (10)

i) The circuit current

ii) The total power factor

iii) The power taken from the supply.

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)

Q9. (a) Describe the effect of running an induction motor on reduced voltage (6)

(b) A 90V D.C. generator is used to charge a battery of 40 cells in series, each cell having an average e.m.f. of 1.9 V and an internal resistance of 0.0025 Ω. If the total resistance of the connecting cells is 1Ω, calculate the value of the charging current (10)

Q7. (a) What is Freeboard of a Ship? Why oil tankers have less freeboard? (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 5m long. The bottom of the barge is lined with teak (rd 0.805) 120mm 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. Explain distribution factor and pitch factor for alternator windings.

B. A 3phase, 4pole 24 slot alternator has its armature coils short pitched by one slot. Find the distribution factor and pitch factor.

Q8. A. What is meant by “Resonance” in RLC circuits? Compare the series and parallel resonance circuits.

B. Find the frequency at which the following circuit resonates.

Q7. Two 10 MVA 3 phase Alternator operate in parallel to supply at 0.8 power factor with lagging load of 15 MVA. If the output of one Alternator is 8 MVA at 0.9 lagging. A. Calculate the output of second Alternator. B. Calculate the value of Power factor of second Alternator.

Q9. Sketch a graph of starting current, and torque against the speed of rotation for a single cage motor.  B. A 230V motor, which normally develops 10Kw at 1000 rev/min with an efficiency of 85%, is to be used as a generator. The armature resistance is 0.15Ohm and the shunt field resistance is 220Ohm. If it is driven at 1080 rev/min and the field current is adjusted to 1.1A by means of the shunt regulator what output in Kw could be expected as a generator, if the armature copper loss was kept down to that when running as a motor.