Q2. Briefly explain the principle of operation of Variable Frequency Drives (VFD). Discuss the
advantages and disadvantages of VFDs onboard merchant vessels? (16)
Q4. (a) Explain the principle of a Transformer? Discuss the various types of transformers used onboard? (8)
(b) In a container ship, a 3-ph, delta/delta connected 6600/440 V, 60 Hz transformer is feeding AMP supply from shore to 440 Volt switchboard. Transformer primary current takes a line current of 100 amp, when secondary load of 0.8 lagging p.f. is connected. Determine each coil-current and KW output of transformer. (8)
Q5. A circuit has a resistance of 3Ω and an inductance of 0.01H. The voltage across its ends is 60V and the frequency is 50Hz. Calculate
a) The impedance (6)
b) The power factor (5)
c) The power absorbed. (5)
Q4. With respect to Alternators onboard:
a) Briefly explain true power, Apparent power and power factor? (8)
b) The alternator is rated for 750 KVA at 0.85 PF, what is the maximum load (Kilo Watt) that can be put on it? Would you be overloading the alternator if the kilowatt reading were now 620 KW and the power factor 0.80? (8)
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