MET-Jul-2021 (2)

Q1. A. Describe with the aid of a simple sketch the arrangement of the three-phase winding of an alternator showing the neutral point; 

B. Explain why for most ships the neutral point is insulated; 

C. Explain why in some installations the neutral point is Earthed.

Q2. (a) Sketch power circuit diagram for a star/delta starter and label it. (b) Narrate the sequence of operation of the circuit sketched in Q2(a). (c) Mention any two advantages of star/delta starter over the direct online starter. (d) State any two limitations of the star/delta starting.

Q3. With reference to U.M.S. operations:

A. State with reasons the essential requirements for unattended machinery spaces;
B. As a second Engineer, describe how you would respond to the irretrievable failure of the Machinery space fire alarm system whilst the ship is on the voyage.

Q4. Explain why it is necessary to have reverse power protection for alternators intended for Operation. 

A. Sketch a reverse power trip; 

B. Explain briefly the principle on which the operation of this power trip is based and How tripping is activated.

Q5. With reference to alkaline batteries used onboard ships.

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.

Q6. 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. Discuss different methods of speed control of a d.c. series motor by adjusting field ampere-turns. 

B. A 230 V, d.c. shunt motor runs at 1000 r.p.m and takes 5 amperes. The armature resistance of the motor is 0.025Ω and shunt field resistance is 230 Ω Calculate the drop in speed when the motor is loaded and takes the line current of 41 amperes. Neglect armature reaction. 

 

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 a 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 a three-phase current has been introduced.

 

Q9. A. Briefly describe the maintenance routines carried out for emergency batteries onboard.

B. A power of 36 W is to be dissipated in a register connected across the terminals of a battery, having emf of 20V and internal resistance of 1Ω.

Find:

(i) What value of resistance will satisfy this condition.
(ii) The terminal voltage of the battery for each of the resistances and

(iii) The total power expenditure in each case.

 

Q7. 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;
ii. The speed of the rotor when the slip is 4 per cent;
iii. The motor frequency when the speed of the rotor is 600 r.p.m