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Q1. A. With respect to measuring instruments, what is the difference between analogue and digital measuring instruments. Explain the working principle of each type. (8)

B. Describe with the aid of simple sketches one analogue and one digital measuring instrument you have used onboard. (8)

Q2. With respect to power transformers explain the following protections: (16)

a. Overload protection.

b. Overcurrent protection for phase faults.

c. Earth Fault protection.

d. Differential protection.

e. Directional protection.

Q3. In A.C. generators, voltage dip occurs in two stages.

A. I. Sketch a voltage-time graph showing the pattern of voltage dip. (6)

II. Referring to this graph, state with reasons the effect on the electrical system of a small power installation when a large load is suddenly switched on. (4)

B. Explain EACH of the following categories of voltage control: (6)

(i) Error operated. (ii) Functional.

Q4. In some circumstances electrical current may be induced into the shafting of rotating machinery.

a) State the problem that may be caused by this current. (6)

b) Explain with aid of sketches, how currents may be avoided or reduced in the following instances:

(i) D.C machines

(ii) Main shafting fitted with a bronze propeller (5X2)

Q5. With reference to preferential tripping in a marine electrical distribution system:

A. State why this facility is required. (4)

B. With the aid of a sketch, describe a typical arrangement to provide three stages of tripping an instantaneous protection against short circuit. (12)

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Q4. With reference to preferential tripping in a marine electrical distribution system:

A. With the aid of a sketch, describe a typical arrangement to provide three stages of tripping an instantaneous protection against short circuit.

B. State why this protection is required.

Q6. A. Explain the significance of the root- mean- square value of an alternating current or voltage waveform. Define the form factor of such a wave form.  (6)

B. A three phase induction motor is wound for four poles and is supplied from a 50 Hz system. Calculate.

i. The synchronous speed.

ii. The speed of the rotor when the slip is 4 per cent.

iii. The rotor frequency when the speed of the rotor is 600 r.p.m. (10)

Q7. A. Differentiate between series and shunt D.C. generators. (6)

B. Three conductors fitted side by side in the stator of a salient-pole alternator. Each generates a maximum voltage of 200V (sinusoidal). The angle subtended at the centre of the stator between adjacent conductors is 20 electrical degrees. If the three conductors are connected in series, find (i) the r.m.s. value of the effective voltage and (ii) the ‘breadth factor’. Using the theory that is the basis of this problem, give one reason why three-phase current has been introduced. (10)

Q8. A. What is a semiconductor? Briefly explain what do you mean by doping?

B. A twelve-pole, three-phase, delta-connected alternator runs at 600 rev/min and supplies a balanced star-connected load. Each phase of the load is a coil of resistance 35 ohm and inductive reactance 25 ohm. The line terminal voltage of the alternator is 440V. Determine (i) frequency of supply (ii) current in each coil (iii) current in each phase of the alternator (iv) total power supplied to the load. (10)

Q8. a) Explain how excitation of the rotor is produced and supplied. (6)

b) A 75-kW, 400-V, 4-pole, 3-phase star connected synchronous motor has a resistance and synchronous reactance per phase of 0.04 Ohm and 0.4 Ohm respectively. Compute for full-load 0.8 p.f. lead the open circuit e.m.f. per phase and mechanical power developed. Assume an efficiency of 92.5%. (10)