DieselShip's Online Content Library

Q9. (a) List the causes for impairment of stability of a vessel. (6)

(b) A box-shaped vessel floats upright on an even keel as shown in fresh water of density 1000 kg per cubic meter, and the center of buoyancy is 0.50 m above the keel. Find the height of the center of buoyancy above the keel when the vessel is floating in salt water of density 1025 kg per cubic meter. (10)

Q5. (a) On what factors does the capacitance of a parallel-plate capacitor depend? (6)

(b) A tuned circuit consisting of a coil having an inductance of 200µH and a resistance of 20Ω in parallel with a variable capacitor is connected in series with a resistor of 8000Ω across a 60 V supply having a frequency of 1 MHz. Calculate: (10)

(a) The value of C to give resonance.

(b) The dynamic impedance and the Q factor of the tuned circuit.

(c) The current in each branch

Q6. a) Which of the following three motors has the poorest speed regulation: shunt motor, series Motor or cumulative compound motor? Explain. (6)
b) An 18.65 KW,4-pole,50HZ, 3 phase induction motor has friction and windage losses of 2.5 percent of the output. The full load slip is 4% compute for full load
(i) the rotor Cu loss
(ii) the rotor input
(iii) the shaft torque
(iv) the gross electromagnetic torque. (10)

Q5. A) Explain how the efficiency and regulation of a transformer can be assessed by open circuit and short circuit tests? (6)
b) A tuned circuit consisting of a coil having an inductance of 200 mH and a resistance of 20 Ω in parallel with a variable capacitor is connected in series with a resistor of 8000 Ω across a 60V supply having a frequency of 1 MHz Calculate:
a) The value of C to give resonance.
b) The dynamic impedance and the Q factor of the tuned circuit.
c) The current in each branch. (10)

Q6. A total load of 8000 kW at 0.8 power factor is supplied by two alternators in parallel. One alternator supplies 6000kW at 0.9 power factor. Find the kVA rating of the other alternator and the power factor. (16)

Q7. a) D.C. motors are used where very high torque and/or precise speed control is required. How does the control of magnetic field flux and armature current relate to the starting characteristics of a D.C. motor in such applications? (6)

b) A 220 V, D.C. shunt motor has an armature resistance of 0.5 ohm and an armature current of 40 A on full load. Determine the reduction in flux necessary for a 50 per cent reduction in speed. The torque for both conditions can be assumed to remain constant. (10)

Q8. A. Sketch an arrangement showing the principal of proportional plus integral (P+I) control loop.

B. Compare the series and parallel resonance circuits. Find the frequency at which the following circuit resonates.

Q7. A. Which of the following three motors has the poorest speed regulation: shunt motor, series Motor or cumulative compound motor? Explain.

B. A 440V shunt motor takes an armature current of 30A at 700 rev/min. The armature resistance is 0.7ohm. If the flux is suddenly reduced by 20 per cent, to what value will the armature current rise momentarily? Assuming unchanged resisting torque to motion, what will be the new steady values of speed and armature current? Sketch graphs showing armature current and speed as functions of time during the transition from initial to final, steady-state conditions.

Q6. A. Describe the effect of the following loads on power factor: -

(i) Induction motors; (ii) Transformers; (iii) Partly loaded motors; (iv) Cage type motors.

B. In a 50-Kav, star-connected, 440-V, 3-phase, 50-Hz alternator, the effective armature resistance is 0.25 ohm per phase. The synchronous reactance is 3.2 ohm per phase and leakage reactance is 0.5 ohm phase. Determine at rated load and unity power factor:

(a) Internal e.m.f Ea (b) no-load e.m.f E0 (c) percentage regulation on full-load (d) value of synchronous reactance which replaces armature reaction.

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.

Q6. A. What is Prismatic Co-efficient (C_P). Derive the formula C_P = C_b/C_m , where  C_b= Co-efficient of fineness and C_m = midship section area co-efficient.

B. The length of a ship is 18 times the draught. while the breadth is 2.1 times the draught. At the load water plane, the water plane area co-efficient is 0.83 and the difference between the TPC in sea water and the TPC in fresh water is 0.7. Determine the length of the ship and the TPC in fresh water.

Q10. (a). Explain the various efficiencies associated with propeller and shafting arrangement.

(b) A propeller 6m diameter has a pitch ratio of 0.9, BAR 0.48 and, when turning at 110 rev/min, has a real slip of 25% and wake faction 0.30. If the propeller delivers a thrust of 300 KN and the propeller efficiency is 0.65. Calculate:

i. Blade area;

ii Ship speed;

iii. Thrust power;

iv Shaft power

v. Torque.