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Q1. Direct on line starting for large induction motors such as those for bow thruster units, may not be viable.

A. State the reasons for this. (4)

B. Sketch a starting system that may be used for such motors. (8)

C. Describe the starting method sketched in B. (4)

Q2. a) Sketch a basic circuit showing a D.C, winch motor driven by a Ward Leonard circuit powered by a single speed squirrel cage motor. (8)

b) Explain how reversal of the winch motor is achieved using the Ward Leonard system. (4)

c ) State advantage and disadvantage of the Ward Leonard drive system. (4)

Q3. a) Draw a circuit diagram of a transistor connected as a common emitter amplifier including Bias resistors, coupling and decoupling capacitors. (10)

b) Explain the operation of the circuit components (6)

Q4. A. Describe a brush less alternator with A.C. exciter static A.V.R.. (8)

B. State the output voltage characteristics for this type of machine. (8)

Q5. a) Explain the purpose of a rectifier and the effect of over current and of overvoltage on rectifiers. (6)

b) Three equal resistors are connected to a three-phase system, if one resistor is removed find the reduction in load if they are connected in (a) Star, (b) Delta. (10)

Q6. A. What are the characteristics of PN junction diode? Point out its specifications. Also point out the significance of dynamic and static resistances. (6)

B. Draw the circuit of Half-wave rectifier and its output waveform. A diode whose internal resistance is 20 Ω is to supply power to 1000 Ω load from 110 V (RMS) source. Calculate

(i) Peak load current, (ii) DC load current, (iii) AC load current. (10)

Q7. a) Describe the no-load saturation characteristic of a D.C. generator. (6)

b) Find the synchronous impedance and reactance of an alternator in which a given field current produces an armature current of 200 A on short-circuit and a generated e.m.f. of 50V on open- circuit. The armature resistance is 0.1 ohm. To what induced voltage must the alternator be excited if it is to deliver a load of 100A at a p.f. of 0.8 lagging, with a terminal voltage of 200V. (10)

Q8. A. What is a commutator? Discuss its rectifying action in detail.

B. Calculate the e.m.f. generated by a 4-pole, wave wound armature having 40 slots with 18 conductors per slot when driven at 1000 r.p.m. The flux per pole is 0.015 wb.

Q9. a) Show how the power that is transferred across the air gap of the three-phase induction motor is represented. Explain the terms. What portion of this is useful power? (6)

b) A 440 V load of 400 kW at 0.8 (lagging) power factor is jointly supplied by two alternators A and B. The kW load on A is 150 kW and the KVAr load on B is 150 KVAr (lagging). Determine the kW load on B, the KVAr load on A, the power factor of operation on each machine and the current loading of each machine. (10)

Q10. A. Why is a synchronous motor not self-starting? What are the various ways in which it can be started? (6)

B. A 500V, single phase synchronous motor gives a net output mechanical power of 7.46kW and operates at 0.9 power factor lagging. Its effective resistance is 0.8 Ω. If the iron and friction losses are 500 w and excitation losses are 800w, calculate the armature current and the commercial efficiency. (10)