DieselShip's Online Content Library

Q1. a) What is the meaning of excitation in an alternator? (6)

b) Explain a brushless alternator with an insight on how the excitation is achieved in these alternators. (10)

Q2. a) What are the differences between synchronous and induction motor? (6)

b) What do you understand by the term ‘slip’? (4)

c) How do you check continuity of a circuit? Explain the process in brief. (6)

Q3. a) Describe an alkaline battery cell, listing the materials used in its manufacture. (6)

b) With reference to alkaline batteries used on ships, state each of the following: (10)

i) Significance of the relative density reading of the electrolyte.

ii) When the electrolyte would normally be renewed.

iii) Reasons why the voltage reading of this type of battery is not necessarily indicative of its condition.

iv) The normal temperature range and safe temperature limit of battery.

v) Effects of high and low temperature.

Q4. Describe with the aid of a diagram the operation of the following components of electrical equipment and explain the purpose of each. (16)

a) Under voltage protection.

b) Miniature circuit breakers.

c) Reverse power tripping.

Q5. With respect to personnel carrying out inspection and maintenance involving entry to boilers and other confined spaces.

a) State the precautions needed for the operation of portable electrical tools and lighting, with respect to safety. (10)

b) Outline the routine checks carried out on the equipments. (6)

Q6. a) Discuss the open circuit and short circuit test performed for transformer. (6)

b) The primary and secondary windings of a 30 KVA, 6000/230V, 1-phase transformer have resistance of 10 Ω and 0.016 Ω respectively. The reactance of the transformer referred to the primary is 34 Ω. Calculate the primary voltage required to circulate full load current when the secondary is short circuited. What is the power factor on the short circuit? (10)

Q7. a) Explain what do you understand by the term ‘transducer’? (6)

b) A coil of resistance 10 ohms and inductance 100mH is connected in series with two parallel capacitors each of value 100 mF across a 250 V, 50Hz supply. determine (10)

i) The circuit current

ii) The total power factor

iii) The power taken from the supply.

Q8. a) What is a Zener diode? (6)

b) Find the generated e.m.f./conductor of a 6-pole d.c. generator having a magnetic flux/pole of 64m Wb and a speed of 1000 rev/min. If there are 468 conductors, connected in six parallel circuits, calculate the total generated e.m.f. of the machine. Find also the total power developed by the armature when the current in each conductor is 50 A. (10)

Q9. a) Sketch a schematic arrangement of a three-phase alternator with star connection. (6)

b) A 500V, 3-phase, star-connected alternator supplies a star-connected induction motor which develops 45kW. The efficiency of the motor is 88 percent and the power factor is 0.9 (lagging). The efficiency of the alternator at this load is 80 percent. Determine

a) the line current

b) the power output of the alternator

c) the output power of the prime-mover.  (10)