Q1. Explain with a simple line sketch, a main engine jacket cooling automatic control system capable of maintaining the jacket water temperature within close limits during wide changes in engine load. (16)
Q2. a) What is the function of insulation in an electric conductor? (3)
b) What are the various classes of insulation? (8)
c) What are the desired properties of insulating materials? (5)
Q3.a) How protection is provided for electrical short circuit. (4)
b) Describe the construction and operation of HRC fuses? (8)
c) What are the advantages of HRC fuses. (4)
Q9. (a) Shunt generators having drooping characteristics are best suited for parallel operation. Discuss (6)
(b) Two 220 V D.C. generators each having linear external characteristics, operated in parallel. One machine has a terminal voltage of 270 V, on no-load and 220 V at a load current of 35 A, while the other has a voltage of 280 V at no-load and 220 V at 50 A. Calculate the output current of each machine and the bus bar voltage when the total load is 60 A. What is the kW output of each machine under this condition. (10)
Q5.a) Briefly explain static induction and dynamic induction. (6)
b) A coil of 250 turns is wound uniformly over a wooden ring of mean circumference 500mm and uniform cross-sectional area of 400mm2. If the current passed through the coil is 4A find (a) the magnetizing force (b) the total flux. (10)
Q6. a) Explain how excitation of the rotor is produced and supplied. (6)
b) A shunt motor has an armature resistance of 0.2 ohms and with an armature current of 120 amperes runs at 750 r.p.m. off a 400-volts supply. Calculate the speed and armature current of the motor if the flux per pole is reduced to 75 per cent of its initial value, the total torque remaining unaltered. (10)
Q7. a) State the conditions, which must be satisfied before an A.C generator can be paralleled with live bus-bars. (4)
b) Sketch a lamp-bright configuration for synchronizing lamps. (8)
c) State the advantages and disadvantages of the lamps-bright system over lamps-darks system. (4)
Q8. With reference to a three-phase shipboard electrical distribution system.
a) Enumerate the advantages of an insulated neutral system (4)
b) Enumerate the disadvantages of an insulated neutral system (4)
c) Compare the use of an insulated neutral system as opposed to use of an earthed neutral system with regards to the risk of electric shock from either system. (8)
Q9. a) Differentiate between resistance, induction and impedance in an a.c. circuit. (6)
b) A circuit is made up from resistors of value 2Ω, 4Ω, 5Ω and 10Ω connected in parallel. If the current is 8.6A, find the voltage drop across the arrangement and the current in each resistor. (10)
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