DieselShip's Online Content Library

Q1. (a) Sketch a circuit diagram for an automatic voltage regulator illustrating how the A.V.R. utilizes a silicon-controlled rectifier to control the excitation system for an alternator. (10)

(b) Describe how the A.V.R. monitors output and controls the excitation system. (6)

Q2. Overcurrent protection relays are built into main alternator breakers to safeguard the individual alternators and the distribution system against certain faults.

(a) Sketch a typical relay. (8)

(b) Describe the operation of the relay sketched in (a) (8)

Q3. (a) Sketch and describe a power (watt) meter for an A.C. switchboard. (8)

(b) State why type of load governs power factor and give examples of power factor for a resistance load and for normal marine operation. (8)

Q2. Explain clearly why, in D.C. installation, a compound-wound electric generator is usually adopted for ship lighting purposes. Compare it's performance with that of shunt and series wound machines. What attention does such a machine require when working and what care is necessary for its maintenance in a satisfactory condition? (16)

Q1. With reference to an emergency source of electrical power in cargo ships:

a) Describe a typical power source (6)

b) Give a typical list of essential services, which must be supplied simultaneously. (5)

c) Explain how the emergency installation can be periodically tested. (5)

Q6. (a) What are the different types of DC motors? (6)

(b) A 10 H.P. 230 V shunt motor takes an armature current of 6A from 230 V mains at no load runs at 1200 r.p.m. The armature resistance is 0.25Ω. Determine speed and electromagnetic torque when the armature takes 36 amps with the same flux. (10)

Q7. An amplifier has an open-circuit voltage gain of 1000, an input resistance of 2000 Ω and an output resistance of 1.0 Ω. Determine the input signal voltage required to produce an output signal current of 0.5A in a 4.0Ω resistor connected across the output terminals. If the amplifier is then used with negative series voltage feedback so that one tenth of the output signal is fed back to the input, determine the input signal voltage to supply the same output signal current. (16)

Q8. (a) Explain how fluorescent tubes power factor is improved. (6)

(b) A fluorescent lamp taking 80W at 0.7 power factor lagging from a 230V, 50-Hz supply is to be connected to unity power factor. Determine the value of the correcting approach required. (10)

Q9. (a) Explain about non-linear resistors with some examples and illustration on how they differ from linear resistor. (6)

(b) A half-wave rectifier is used to supply 50V d.c. to a resistive load of 800Ω. The diode has a resistance of 25 Ω. Calculate a.c. voltage required. (10)