MET-Apr-2021

Q1. With reference to squirrel cage, induction, electric motors: A. Describe the construction of such a motor. B. Sketch the torque against speed curve of such a motor; C. Describe a method employed by a retrofitted device used to improve the part load performance of an induction motor.

Q2. Sketch and describe an arrangement for automatic connection of emergency batteries upon loss of main power. Include in your answer: A. Means of obtaining D.C. charging supply from a.c. mains; B. A method of maintaining charge on lead acid batteries; C. The arrangement to check that a battery operates a loss of main power D. The length of time for which emergency batteries of passenger and cargo ships must provide power.

Q3. A) Describe the circuit breaker for an a.c. generator using a sketch to show how arcing is Controlled. (B)Explain the sequence of events that might occur if the breaker opens on a short circuit and state the check you would require following such event; (C) Give a safe procedure to follow should a main circuit breaker fail to open under fault Condition.

Q4. 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.

Q5. (a) With reference / to the insulation testing of marine electrical plant: i. State the reason for insulation testing: ii. State the precautions to be observed when testing intrinsically safe equipment type Ex.1. (b). Describe the overhaul of a D.C. motor which has been subject to excessively damp condition or flooding with seawater.

Q6. 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. A total load of 8000 kW at 0.8 power factor is supplied by two alternators in parallel. One alternator supplies 6000 kW at 0.9 power factor. Find the KVA rating of the other alternator and the power factor.

 

Q7. A. Explain the preference for a 60 Hz system. Describe the dangers of running a 50 Hz system from a 60 Hz supply. B. A ring-main, 900m long, is supplied at a point A at a p.d. of 220V. At a point 

B, 240m from A, a load of 45A is drawn from the main, and at a point C, 580m from A, measured in the some direction, a load of 78A is taken from the main. If the resistance of the main (lead and return) is 0.25 ohm per kilometre, calculate the current which will flow in each direction round the main from the supply point A and the potential difference across the main, at the load where it is lowest.

Q8. A. Describe the no-load saturation characteristic of a d.c. generator.

B. A 4-pole machine running at 1500 r.p.m. has an armature with 80 slots and 6 conductors per pole.
The flux per pole is 6 x 106 lines. Determine the terminal e.m.f. of d.c. generator if the coils are lap connected. If the current per conductor is 100 A, determine the electrical power.
 

Q9. A. Explain how the efficiency and regulation of a transformer can be assessed by open circuit and short circuit tests?

B. A 25 kVA signal phase transformer 2200:200V has a primary and secondary resistance of 1Ω and 0.01 Ω respectively. Find the equivalent secondary resistance and full load efficiency at 0.8pf lagging, if the iron losses of the transformer are 80% of the full load copper losses.

 

Q10. 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.