MET-Nov-2020

Q1. Explain the methods used to control the speed of a 3 Phase induction motors. Draw and Explain a Variable Frequency Drive used for optimization of energy efficiency of auxiliary machineries on board vessels.

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. Diesel electric propulsion is now being chosen as the power plant for an increasingly wide variety of vessels.
(a) Sketch a simple layout of such an installation.
(b) Explain the advantages of selecting such a plant.

Q4. A. (i) Discuss the various hazards and problems which are associated with electric cable Insulation in the event of fire.
(ii) Suggest remedies for these problems.
B. State how the spread of fire may be reduced by the method used for installing electric cables.

Q5. A. Describe a brush less alternator with a.c. exciter static A.V.R.; B. State the output voltage characteristics for this type of machine.

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. 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

 

Q8.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 20Ω is to supply power to 1000 Ω load from 110 V (RMS) source. 

Calculate (i) peak load current, (ii) DC load current, (iii) AC load current. 

 

Q9. 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. 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 2A, 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.

 

Q10. 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.