DieselShip's Online Content Library

Q2. Briefly explain the principle of operation of Variable Frequency Drives (VFD). Discuss the

advantages and disadvantages of VFDs onboard merchant vessels? (16)

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)

Q5. A shunt generator has an induced emf of 254 V. When the generator is loaded, the terminal voltage is 240 V, Neglecting armature reaction, find the load current if the armature resistance is 0.04 ohm and the field circuit resistance is 24 ohms. (16)

Q6. A 100 KVA, 2400/240 V, 50 Hz, 1-phase transformer has no- load current of 0.64 A and a core loss of 700 W, when its high voltage side is energized at rated voltage and frequency . calculate the two components of no-load current. If this transformer supplies a load current of 40 amp at 0.8 lagging power factor at its low voltage side, determine the primary current and its power factor. Ignore leakage impedance drop. (16)

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)

Q1. With Respect to PLC’s used onboard ships:

a) Draw and explain the block diagram of a PLC. (8)

b) Name the onboard ship equipment where PLC’s are used. (4)

c) What are the advantages of PLC controllers over other type of controllers? (4)

Q5. A 400V, 4-pole, 50 Hz, 3-phase, 10 hp, star connected induction motor has a no load slip of 1% and full load slip of 4%, find the following:

(i) Syn speed

(ii) No -load speed

(iii) Full load speed

(iv) Frequency of rotor current at full load

(v) Full – load torque (16)

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)