Q1. a) Write a short note on the principle of operation of induction motors (8)
b) What is slip for an induction motor? (4)
c) If a 6-pole motor is supplied at 60Hz and runs with a slip of 5%. What is the actual rotor speed? (4)
Q1.a) Explain three methods of overcurrent protection for electrical circuit. (8)
b) Explain with aid of diagram, the meaning of the term inverse current time characteristic (8)
Q3. With reference to batteries onboard:
a) Distinguish between ‘Lead acid cell’ and ‘Alkaline cell’ (6)
b) Describe how a battery of alkaline cells may be tested for its usefulness, after a long storage and if found deficient, how it can be remedied? (6)
c) Explain how the ambient temperature is taken into account when determining the condition of the battery (4)
Q2. With Respect to Insulated and Earthed Neutral Systems used on board:
a) Discuss the Advantages and Disadvantages of both Insulated and Earthed Systems used on board. (8)
b) Discuss the consequences of earth fault in an earthed distribution system. (4)
c) What would be the Ohmic value of the NER to limit the earth fault to the full load rating of a 2 MW, 0.8 pf, 3.3KV, 3Phase A.C. generator? (4)
Q5. a) Describe the different type of losses occurring in the Power Transformers. (4)
b) A single-phase power transformer supplied a load of 20 KVA at a P.F of 0.81 (lagging). The iron loss of the transformer is 200 W and the copper loss at this load is 180 W. Calculate
(i) The efficiency
(ii) If the load is now changed to 30 KVA at a p.f of 0.91 (lagging). Calculate the new efficiency
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