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. With reference to a 3 speed a.c. cage motor driven cargo winch:
a) Sketch a circuit diagram for a pole change motor. (8)
b) Describe how speed change and braking are achieved. (8)
Q3. With reference to preferential tripping in a marine electrical distribution system. a) With the aid of a sketch, describe a typical arrangement to provide three stages of tripping an instantaneous protection against short circuit. (10) b) State why this protection is required. (6)
Q4. a) What are the factors which determine the synchronous speed of a motor? (6) 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. (10)
Q5. 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? (6) 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 2 A, 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. (10)
Q6. A) With the aid of delta and star connection diagrams, state the basic equation from which the delta-star and star- delta conversion equation can be derived. (6) B) Three batteries A, B, and C have their negative terminals connected together. Between the positive terminals of A and B there is a resistor of 0.5 ohm and between B and C there is a resistor of 0.3 ohm Specifications of the three batteries are given below. Battery A 105 V, Internal resistance 0.25 ohm Battery B 100 V, Internal resistance 0.2 ohm Battery C 95 V, Internal resistance 0.25 ohm Determine the current values in the two resistors and the power dissipated by them. (10)
Q7. What is meant by “Control and Management of Ships ballast water and sediments” Why is this term so significant with reference to shipping in recent times. (16)
Q8. a) State the hazards which may be encountered when entering an enclosed space and the precautions that should be taken. (5)
b) Sketch and describe an oxygen analyser which can be used to sample the atmosphere in void or closed spaces. (5)
c) Instruction given to person entering the enclosed space as per the ISM procedures. (6)
Q9. With respect to MARPOL 73/78, Annex-ll, Noxious liquid chemicals are divided into categories.
a) State the number of categories, and what does each category signify. (8)
b) State the requirement of procedures and Arrangements Manual, and what information is available. (8)
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