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)
Q6. With reference to Diesel engine driven alternator:
a) Explain the significance of the term “speed droop” during the parallel operation of alternators. Assuming two alternators are running in parallel, outline the frequency vs load characteristics of the alternators while load sharing. (8)
b) Two 3Ø alternators operate in parallel, the rating of A is 1000 kW and B is 800 kW. The droop setting of each generator is 4%, If the load to be shared by both the generators is 1000 kw, calculate the load sharing by generators A and B, if the original frequency at no-load is 62Hz. (8)
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
Q4. With the aid of suitable line diagrams, sketch and describe a suitable (MGPS) Marine growth protection system installed on vessels to prevent fouling of internal sea water system mention the important precautions, if any while handling the system. (16)
Q5. With reference to three phase induction motors:
a) Explain the phenomenon of crawling and cogging in these motors. (6)
b) The output of an induction motor running at 4% slip is 36.775 kW and the friction and windage losses are 1500W. find the rotor copper loss and motor efficiency if stator losses are 3kW. (10)
Q6. a) Describe the working of a single-phase full wave rectifier with a resistive load. Draw the load voltage and current waveforms. (8)
b) Diode half wave rectifier supply a resistive load of 100Ω from a 100 V ac r.m.s voltage source. The diode is a resistance of 5Ω during conduction state. Calculate
i) The DC output voltage
ii) DC average load current (8)
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