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).
Q5. With reference to electronic control systems A. Draw a simple block diagram for temperature control B. Describe each component shown in the diagram in (a).
Q2. Sketch a circuit diagram for an automatic voltage regulator illustrating how the A.V.R. utilizes a Silicon-controlled rectifier to control the excitation system for an alternator.
Describe how the A.V.R. monitors output and controls the excitation system.
Q4. It is proposed to operate a bow thruster’s unit from a 3.3 KV electrical supply outline suitable option for the design of installation under each of the following heading. Protection of main switch board Overload of a bow thrusters motor Cable protection.
Q1. With reference to a three-phase shipboard electrical distribution system: (16)
a) Enumerate the advantages of an insulated neutral system.
b) Enumerate the disadvantages of an insulated neutral system.
c) Describe how the earthed neutral system is Earthed.
d) Compare the use of an insulated neutral system as opposed to the use of an Earthed neutral System with regard to the risk of electric shock from either system.
Q6. A. What are the characteristics of PN junction diode? Point out its specifications. Also point out the significance of dynamic and static resistances.
B. Draw the circuit of Half-wave rectifier and its output waveform. A diode whose internal resistance is 20 is to supply power to 1000 load from 110 V (RMS) source. Calculate
(i) peak load current, (ii) DC load current, (iii) AC load current.
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. 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. 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? B. A twelve-pole, three-phase, delta-connected alternator runs at 600 rev/min and supplies a balanced star-connected load. Each phase of the load is a coil of resistance 35 ohm and inductive reactance 25 ohm. The line terminal voltage of the alternator is 440V. Determine (a) frequency of supply, (b) current in each coil, (c) current in each phase of the alternator, (d) total power supplied to the load.
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