MET-FEB-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 respect to the High Voltage power systems installation, explain the different types of circuit breaker that are used, comparing them on merits and de-merits. Describe the theory of arc phenomenon and the mechanism fitted to mitigate the arc.

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. With reference to an emergency source of electrical power in cargo ships: -
A. Describe a typical power source.
B. Give a typical list of essential services, which must be supplied simultaneously;
C. Explain how the emergency installation can be periodically tested.

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.

Q6. A. Explain the potential hazards of liquid-cooled transformers are used onboard ships.

B. What are the losses in transformers? Mention the various factors which affect these losses.

In a 25 KVA, 3300/233 V, single phase transformer, the iron and full-load Cu. Losses are respectively 350 and 400 watts.
Calculate the efficiency at half-full load, 0.8 power factor.
 

Q7. A. Describe how protection against short circuit is provided in a 3 phase induction motor circuit.

B. Explain how rotating magnetic field is produced in three phase winding with three phase supply.

A 4-pole, 3-phase induction motor operates from a supply whose frequency is 50 Hz. Calculate
(i) Speed at which the magnetic field of the stator is rotating,
(ii) speed of the rotor when the slip is 0.04,
(iii) the frequency of the rotor current when the slip is 0.03.

 

Q8. A. What is meant by “Resonance” in RLC circuits? Compare the series and parallel resonance circuits.

B. Find the frequency at which the following circuit resonates.

 

Q9. Explain What is meant by, and the significance of, four of the following terms.
I. Voltage Stabilization,
II. Filter choke;
III. Impedance,
IV. Rectification,
V. Grid bias voltage.

Q10. How does the change in rotor-frequency affect the induction motor when the load is changed from no-load to full-load?

B. The total input power to a 500 V, 50Hz, 6-Pole phase induction motor running at 975 rpm is 40kW. The stator losses are 1 kW. Friction and windage losses are 2 kW total. Calculate (i) Slip, (ii) Rotor Cu Loss, (iii) Efficiency