DieselShip's Online Content Library

Q8. a) What is a Zener diode? (6)

b) Find the generated e.m.f./conductor of a 6-pole d.c. generator having a magnetic flux/pole of 64m Wb and a speed of 1000 rev/min. If there are 468 conductors, connected in six parallel circuits, calculate the total generated e.m.f. of the machine. Find also the total power developed by the armature when the current in each conductor is 50 A. (10)

Q5. A circuit has a resistance of 3Ω and an inductance of 0.01H. The voltage across its ends is 60V and the frequency is 50Hz. Calculate

a) The impedance (6)

b) The power factor (5)

c) The power absorbed. (5)

Q5. A) Explain three methods of overcurrent protection for electric circuit (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,

(i) the impedance (4)

(ii) the power factor (3)

(iii) the power absorbed. (3)

Q9. (a) What are the water pressure loads on the ship's hull. (6)

(b) The water plane area of a ship at 8.4 m draught is 1670 m². The area of successive water planes at 1.40 m intervals below this are 1600, 1540, 1420, 1270, 1080 and 690 m² respectively. Calculate the displacement in fresh water at 8.4 m draught and the draught at which the ship would lie in sea water with the same displacement. (10)

Q6. (a). Explain the significance of the root- mean- square value of an alternating current or voltage waveform; Define the form factor of such a wave form.

(b). A total load of 8000 kW at 0.8 power factor is supplied by two alternators in parallel. One alternator supplies 6000 kW at 0.9 power factor. Find the kVA rating of the other alternator and the power factor.

Q7. With reference to A.C Distribution system:

A. Define power factor and explain the effects of low power factor.

B. 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.

Q10. A. List the factors that determine the starting torque of the three-phase induction motor. How does this torque generally compare with the value of the rated torque? 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.

Q10. A. The capacitor-start induction run motor has a much higher starting torque than the resistance split-phase motor, Explain.

B. An eight-pole armature is wound with 480 conductors. The magnetic flux and each conductor is capable of carrying a full load current of 100A. 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 1. Lap connected 2. Wave- Connected.

Q7. A. Derive an expression for the e.m.f induced in an a.c. generator. B. A 3000 KVA, 6 pole alternators runs at 1000 r.p.m in parallel with other machines on 3300 V bus-bars. The synchronous reactance is 25%. Calculate the synchronizing power for one mechanical degree of displacement and the corresponding synchronizing torque.

Q8. A ship 160m long and 8700 tonne displacement floats at a waterline with

While floating at this waterline, the ship develops a list of 10° due to instability. Calculate the negative metacentric height when the vessel is upright in this condition

Q7. A. Describe stability requirement for dry-docking. B. A ship of 8000 tonne displacement, 110m long, floats in sea water of 1.024t/m3 at draughts of 6m forward and 6.3 m aft. The TPC is 16, LCB 0.6 m aft of midships, LCF 3m aft of midships and MCT1cm 65 tonne m, the vessel now moves into fresh water of 1.000t/m3. Calculate the distance a mass of 50 tonne must be moved to bring the vessel to an even keel and determine the final draught.

Q7. A ship of length 120 m displaces 11750 tonne when floating in sea water of density 1025 kg/m3. The center of gravity is 2m above the center of buoyancy and the waterplane is defined by the following equidistant half-ordinates given in Table Q1:

Calculate EACH of the following:

(a) The area of the waterplane;

(b) The position of the centroid of the waterplane from midships;

(c) The second moment of area of the waterplane about a transverse axis through the centroid;

(d) The moment to change trim one centimeter (MCT1cm).