DieselShip's Online Content Library

Q2. a) Explain why it is necessary to have reverse power protection for alternators intended for operation. (6)

b) (i) Sketch a reverse power trip. (5)

(ii) Briefly explain the principle on which the operation of this power trip is based and how tripping is activated. (5)

Q2. List at least two factors that cause deterioration of the frequency response of a transistor amplifier. Explain how each factor affects the performance of the amplifier and the portion of the frequency range where it is effective. (16)

Q3. a) What are the causes of overheating of an induction motor? (4)

b) What preventive measures are provided against damage to an induction motor in installed condition? (3)

c) What is the purpose of “fuse back up protection” provided to an induction motor? (3)

d) How does an induction motor develop torque? (3)

e) What is the condition to be satisfied for achieving maximum running torque in an induction motor? (3)

Q4.a) Explain what is meant by the terms wave form, frequency, and average value. (6)

b) A moving coil ammeter, a thermal ammeter and a rectifier are connected in series with a resistor across 110 V sinusoidal a.c. supply. The circuit has a resistance of 50Ω to current in one direction and, due to the rectifier, an infinite resistance to current in the reverse direction. Calculate

(i) The reading on the ammeters

(ii) The form and peak factors of the current wave (10)

Q5. a) What is leakage flux as it applies to the iron-core transformer? How is it taken into account in the analysis of the transformer? (6)

b) The following results were obtained on a 50 kVA transformer: open circuit test-primary voltage, 3300 V; Second voltage, 415 V: primary power, 430 W. Short circuit test-primary voltage, 124 V: primary current, 15.3 A; primary power, 525 W; secondary current, to be assumed at full load value. Calculate:

(i) The efficiencies at full load and at half load for 0.7 power factor.

(ii) The voltage regulations for power factor 0.7 (i) lagging, (ii) leading

(iii) The secondary terminal voltages corresponding to (i) and (ii) (10)

Q6. a) What is a silicon-controlled rectifier (SCR)? How is the breakover voltage of the SCR defined?

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

a) The speed:

b) The gross torque developed by the armature. (10)

Q8. a) State the hazards which may be encountered when entering an enclosed space and the precautions that should be taken. (5)

b) Sketch and describe an oxygen analyser which can be used to sample the atmosphere in void or closed spaces. (5)

c) Instruction given to person entering the enclosed space as per the ISM procedures. (6)

Q8. With reference to fire smothering agents explain why:

a) Effectiveness of foam is directly related to its degree of effervescence and surface tension. (6)

b) low expansion foam is best suited for use against localized fire, while high expansion foam is most effective in with major conflagrations,

c) In the absence of foam appliances, water jets can be effectively used against oil fires (5)

Q9. With reference to MARPOL Annex I:

a) Draw a 15 ppm oily water separator and explain the principles of operation (8)

b) Periodical maintenance and checks tests required to be done to verify the effectiveness of the above system. (8)