DieselShip's Online Content Library

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

(b) The 1/2 ordinates of a waterplane 120 m long are as follows: (10)

Section AP 1/2 1 1½ 2 3 4 5 6 7 8 8½ 9 9½ FP

½ ord 1.2 3.5 5.3 6.8 8.0 8.3 8.5 8.5 8.5 8.4 8.2 7.9 6.2 3.5 0 m

Calculate:

(a) Waterplane area

(b) Distance of centroid from midships.

Q5. With reference to three phase induction motors:

a) Explain the phenomenon of crawling and cogging in these motors (6)

b) A three-phase induction motor is wound for four poles and is supplied from a 50 Hz System calculate:

a) The synchronous speed

b) The speed of rotor when the slip is 4 per cent.

c) The rotor frequency when the speed of the rotor is 600 r/min. (10)

Q6. A) What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature resistance. (6)

b) A three-phase induction motor is wound for four poles and is supplied from a 50 HZ system.

Calculate:

(i) The synchronous speed

(ii) The speed of the rotor when the slip is 4 percent

(iii) The rotor frequency when the speed of the rotor is 600 r/min. (10)

Q5. A 400V, 4-pole, 50 Hz, 3-phase, 10 hp, star connected induction motor has a no load slip of 1% and full load slip of 4%, find the following:

(i) Syn speed

(ii) No -load speed

(iii) Full load speed

(iv) Frequency of rotor current at full load

(v) Full – load torque (16)

Q6. a) Describe the working of a single-phase full wave rectifier with a resistive load. Draw the load voltage and current waveforms. (8)

b) Diode half wave rectifier supply a resistive load of 100Ω from a 100 V ac r.m.s voltage source. The diode is a resistance of 5Ω during conduction state. Calculate

i) The DC output voltage

ii) DC average load current (8)

Q9. A. Explain the potential hazards if liquid-cooled transformers are used.

B. What are the losses in transformers? Mention the various factors which affect these losses. In a 25 KVA, 3300/233 V, single phase transformer, the iron and full-load Cu. Losses are respectively 350 and 400 watts. Calculate the efficiency at half-full load, 0.8 power factor

Q6. A. Describe the normal criteria used for setting thermal protection relays and its advantage compared to magnetic types.

B. The low-voltage release of an a.c. motor-starter consists of a solenoid into which an iron plunger is drawn against a spring. The resistance of the solenoid is 35 ohm. When connected to a 220 V, 50 Hz, a.c. supply the current taken is at first 2A, and when the plunger is drawn into the “full-in” position the current falls to 0.7 A. Calculate the inductance of the solenoid for both positions of the plunger, and the maximum value of flux-linkages in weber-turns for the “full-in” position of the plunger.

Q3. What would be value of Neutral Earthing Resister in a high voltage ship of three phase alternators to limit the earth fault current to the full load of rating of a 4 MW having 0.8 power factor generating 6600 volts?

Q7. A. What is leakage flux as it applies to the iron-core transformer? How is it taken into account in the analysis of the transformer? (6)

B. The following results were obtained on a 50 KVA transformer: open circuit test-primary voltage, 3300 V; secondary voltage, 415 V; primary power, 430 W. Short circuit test-primary voltage, 124 V; primary current, 15.3 A; primary power, 525 W; secondary current, full load value. Calculate:

(i) The efficiencies at full load and at half load for 0.7 power factor

(ii) The Voltage regulations for power factor 0.7 (i) Lagging, (ii) Leading

(iii) The secondary terminal voltages corresponding to (i) and (ii). (10)

Q10. a) (i) What is direct-connected alternator? (3)

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

b) Find the synchronous impedance and reactance of an alternator in which a given field current produces an armature current of 200 A on short circuit and a generated e.m.f. of 50V on open- circuit. The armature resistance is 0.1 ohm. To what induced voltage must the alternator be excited if it is to deliver a load of 100A at a p.f of 0.8 lagging, with a terminal voltage of 200V. (10)

Q8. A. Define longitudinal centre of gravity (LCG) and longitudinal centre of buoyancy (LCB).

B. A ship 120m long floats has draughts of 5.50m forward and 5.80m aft; MCT1 cm 80 tonne m, TPC 13, LCF 2.5m forward of midships. Calculate the new draughts when a mass of 110 tonne is added 24m aft of midships.

Q10.A. Describe briefly the significance of the factor of subdivision.

B. A ship of 8000 tonne displacement floats upright in seawater. KG = 7.6m and GM = 0.5m. A tank, KG is 0.6m above the keel and 3.5m from the centreline, contains 100 tonne of water ballast. Neglecting the free surface effect, calculate the angle which the ship will heel, when the ballast water is pumped out.