DieselShip's Online Content Library

Q1. (a) Compare methods of obtaining speed regulation of three-phase induction motor generally used in tankers by means of: (16)
i. Rotor resistance.
ii. Cascade system.
iii. Pole-changing.

Give examples where each system may be employed with advantage.

Q2. Tank liquid level sensors are an integral part of ships. Describe with the aid of suitable sketches the working principle of:
(a) Capacitive type level sensor (6)
(b) Ultrasonic level sensor (5)
(c) Float (5)

Q3. With reference to squirrel cage, induction, electric motors:

A. Describe the construction of such a motor. (6)

B. Sketch the torque against speed curve of such a motor. (5)

C. Describe a method employed by a retrofitted device used to improve the part load performance of an induction motor. (5)

Q4. a) Explain the significance of the root mean square value of an alternating current or

voltage wave form; Define the form factor of such a wave form. (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 to ensure that the transformer does not become overloaded (10)

Q5. a) Show how the power that is transferred across the air gap of the three-phase induction motor is represented. Explain the terms. What portion of this is useful power? (6)
b) A 440V shunt motor takes an armature current of 30A at 700 rev/min. The armature resistance is 0.7 Ohm. If the flux is suddenly reduced 20 percent, 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. (10)

Q6. (a) What are the factors which determine the synchronous speed of a motor? (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)

Q7.  With reference to the Maritime Labour Convention (MLC) 2006. Discuss the requirements for seafarers regarding: -
a) Minimum age to work onboard vessels (5)
b) Seafarers Employment agreements (5)
c) Hours of work and hours of rest. (6)

Q7. With reference to entry into enclosed spaces onboard:
a) Define “Enclosed space” and give example of enclosed spaces onboard (6)
b) Describe the checks done for testing the atmosphere inside such enclosed spaces. (5)

c) Explain safety precautions taken prior to entry into enclosed spaces onboard vessel. (5)

Q9. With reference to free fall lifeboat of an ocean-going ships:
a) Periodical maintenance, tests and checks on lifeboat and releasing gear. (6)
b) Secondary means of lowering. (5)
c) Lifeboat Drills. (5)