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Q5. With reference to alkaline batteries used on board ship.

A. Describe the operation of a battery cell and state the material used;

B. Describe how the cells are mounted to form a battery;

C. State the advantages and disadvantages compared with lead-acid batteries.

Q2. A. State the necessary conditions required prior to the synchronizing of electrical alternators.

B. Describe the type of cumulative damage that may be caused when alternators are incorrectly synchronized;

C. Explain how the damage referred to in (b) can be avoided / reduced.

D. For two alternators operating in parallel state the consequences of:

(i) Reduced torque from the prime mover of one machine.

(ii)Reduced excitation on one machine.

Q2. With reference to U.M.S. operations:

A. State with reasons the essential requirements for unattended machinery spaces;

B. As second Engineer, describe how you would respond to the irretrievable failure of the Machinery space fire alarm system whilst the ship is on voyage.

Q3. Compare methods of obtaining speed regulation of three-phase induction motor generally used in tankers by means of:

A. Rotor resistance; B. Cascade system; C. Pole-changing.

Give examples where each system may be employed with advantage.

Q1. A. Sketch a main engine shaft driven generator arrangement with an electronic system for frequency correction.  B. Describe the operation of the generator arrangement sketched in (A).

Q6. 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 the ensure that the transformer does not become overloaded.

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.

Q8. A. What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature resistance.

B. A three- phase induction motor is wound for four poles and is supplied from a 50 Hz system. Calculate.

i. The synchronous speed; (4)

ii. The speed of the rotor when the slip is 4 per cent; (3)

iii. The rotor frequency when the speed of the rotor is 600 r/min. (2)

Q8. A. What are the factors which determine the synchronous speed of a motor?

B. Three conductors fitted side by side in the stator of a salient-pole alternator. Each generates maximum voltage of 200V (sinusoidal). The angle subtended at the centre of the stator between adjacent conductors is 20 electrical degrees. If the three conductors are connected in series, find

(i) the r.m.s. value of the effective voltage and

(ii) the ‘breadth factor’. Using the theory that is the basis of this problem, give one reason why three-phase current has been introduced.

Q10. A. Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse.

B. A coil having a resistance of 10 Ohm, and an inductance of 0.15 H is connected in series with a capacitor across a 100V, 50Hz supply. If the current and the voltage are in phase what will be the value of the current in the circuit and the voltage drop across the coil?