DieselShip's Online Content Library

Q1. Describe an electric telegraph system and describe its operation. (16)

Q2. (a) (i) Describe with the aid of a sketch the operation of a synchroscope.

ii) State the information obtained from it. (8)

b) Suggest a substitute in the event of synchroscope and stand by light failure. (8)

Q3. Explain the possible consequences if the following electrical current faults are not rectified: - (16)

a) Earth current leakage.

b) Currents induced into the shafting of rotating machinery.

c) Overload currents.

d) Arcing at contact terminals.

e) Short circuit currents.

Q4. In the event of a failure of the main electrical power supply on a ship, an emergency source of power must be available. State the circuits which must be fed from such a source and discuss the reasons governing the selection of such circuits. (16)

Q5. a) State the conditions, which must be satisfied before an a.c. generator can be paralleled with live bus bars. (8)

b) After an a.c. generator has been paralleled explain how the following are achieved for the incoming generator

i) correct kW load sharing. (4)

ii) correct load current when the generator has power factor different to the other generators. (4)

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) Describe the principle of variable-capacitance 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) Describe the means by which the magnetic flux associated with a conductor may be changed (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)