DieselShip's Online Content Library

Q6. a) Derive the expression for current and voltage relations between line and phase values in the star and delta cases. Draw vector diagram. (6)

b) A balanced delta connected load is connected to a 415V, 50 Hz Supply. If the per phase impedance of the load is (8+j12) ohm, calculate (i) the phase current of the load. (ii) line current (iii) power consumed by each phase. (10)

Q9. a) Explain the term Angle of loll and state the dangers it poses to a vessel. What action to be taken to correct angle of loll. (6)

B. A forward deep tank 12 m long extends from a longitudinal bulkhead to the ship’s side. The widths of the tank surface measured from the longitudinal bulkhead at regular intervals are 10, 9, 7, 4 and 1 m. Calculate the second moment of area of the tank surface about a longitudinal axis passing through its centroid. (10)

Q8. A ship 96 m long floating at 5 m fwd draft and 6.4 m aft draft. MCTC 180 tm, TPC 16. COF is 2 m abaft of midships. Find the location where a weight of 50 t should be placed so as to keep the aft draft constant. (16)

Q8. a) What is the effect of density of water on draught and TPC? (6)

b) A ship of 15000 t displacement floats at a draught of 7 m in water of RD 1.000. It is required to load the maximum amount of all to give the ship a draught of 7 m in sea water of RD 1.025. If the water plane area is 2150 m², Calculate the mass of oil required. (10)

Q6. a) State Ohm's Law. (3)

b) State the limitations of Ohm's Law. (3)

c) 3 resistors of value 2 Ω, 4 Ω and 8 Ω are connected in series across a supply of 42 V. Find the current taken from supply and voltage drop across each resistor. (10)

Q9. The following are the results of measurements taken at intervals over a half cycle of alternating voltage:

Time (t milliseconds)
0
0.45
0.95
1.5
2.1
2.5
3.1
3.9
4.5
5.0

Voltage (V volts)
0
20
36
40
37.5
33
32
31
20
0
Calculate the R.M.S value, average value and frequency of the wave. (16)

Q7. A 24V emergency battery is to be charged from the 110V ship's mains when the e.m.f. per cell has fallen to a minimum value of 1.8V. The battery consists of 12 cells in series, has a capacity of 100 Ahr at a 10 hr rate and the internal resistance is 0.03Ω/cell. If charging continues until the voltage per cell rises to 2.2V, find the value of the variable resistor needed to control the charging. The charging current can be assumed to be equal to the maximum allowable discharge current (16)

Q8. a) Explain how excitation of the rotor is produced and supplied. (6)

b) A 75-kW, 400-V, 4-pole, 3-phase star connected synchronous motor has a resistance and synchronous reactance per phase of 0.04 Ohm and 0.4 Ohm respectively. Compute for full-load 0.8 p.f. lead the open circuit e.m.f. per phase and mechanical power developed. Assume an efficiency of 92.5%. (10)

Q6. (a) Describe the provisions of additional structural strength to withstand pounding. (6)

(b) A vessel travelling at 17 knots turns with a radius of 450 m when the rudder is put hard over. The centre of gravity is 7 m above the keel, the transverse metacentre 7.45 m above the keel and the centre of buoyancy 4 m above the keel. If the centripetal force is assumed to act at the centre of buoyancy, calculate the angle of heel when turning. The rudder force may be ignored. (10)

Q4. a) Why is it important to maintain high efficiency of operation? And low values of voltages regulation for power transformers? (6)

b) A shunt motor supplied at 230 V runs at 900 rpm. When the armature current is 30 A, the resistance of the armature circuit is 0.4 Ω. Calculate the resistance required in series with the armature circuit to reduce the speed to 500 rpm. Assume that the armature current is 25 Amps. (10)

Q4. (a) Why is a synchronous motor not self-starting? What are the various ways in which it can be started?

(b) Differentiate Ge and Si diode characteristics. The reverse bias saturation current for a P-N junction diode is 1.0 µA at 300 K. Determine its AC resistance at 150 mV Forward bias. (10)

Q6. With reference to Diesel engine driven alternator:

a) Explain the significance of the term “speed droop” during the parallel operation of alternators. Assuming two alternators are running in parallel, outline the frequency vs load characteristics of the alternators while load sharing. (8)

b) Two 3Ø alternators operate in parallel, the rating of A is 1000 kW and B is 800 kW. The droop setting of each generator is 4%, If the load to be shared by both the generators is 1000 kw, calculate the load sharing by generators A and B, if the original frequency at no-load is 62Hz. (8)