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Q3. A. Give a brief outline of the care maintenance that should be given to the stator and rotor of an A.C. generator;

B. Explain what is likely to occur if the driving power of one A.C. generator suddenly fails when two generators are running in parallel. What safety devices are usually provided for such events?

Q1. (a) Sketch power circuit diagram for a star/delta starter and label it.

(b) Narrate the sequence of operation of the circuit sketched in Q1(a).

(c) Mention any two advantages of star/delta starter over direct online starter.

(d) State any two limitations of the star/delta starting.

Q4. 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 installation the neutral point is earthed?

Q4. Differentiate with the aid of simple sketches between two of the following types of electronic circuits.

A. Rectifier circuit (6)

B. Amplifier circuit (5)

C. Oscillator circuit (5)

Q5. With reference to Marine Electrical Circuits:

A. Explain three methods of overcurrent protection for electrical circuit.

B. Explain with aid of diagram, the meaning of the term inverse current time characteristic.

Q6. A. Explain distribution factor and pitch factor for alternator windings.

B. A 3phase, 4pole 24 slot alternator has its armature coils short pitched by one slot. Find the distribution factor and pitch factor.

Q7. A. Describe the no-load saturation characteristic of a d.c. generator.

B. A d.c. motor takes an armature current of 110 A at 480 V. The resistance of the armature circuit is 0.2 . The machine has six poles and the armature is lap-connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate;

(i) The speed;

(ii) The gross torque developed by the armature.

Q8. 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.

B. Two 10 MVA 3 phase Alternator operate in parallel to supply at 0.8 power factor with lagging load of 15 MVA. If the output of one Alternator is 8 MVA at 0.9 lagging.

1. Calculate the output of second Alternator.

2. Calculate the value of Power factor of second Alternator.

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 an 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.

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)