DieselShip's Online Content Library

Q1. a) What is feedback control? Explain open loop and close loop systems with reference to shipboard applications? (8)

b) What is P, PI and PID control. Make a neat comparison among all these methods of controlling with examples. (8)

Q2. Briefly describe following with respect to protective relaying:

a) Principle of working and characteristics of induction type relays. (6)

b) Static and digital relays. (5)

c) Protection of alternators, motors, transformer and busbar. (5)

Q3. A. Explain how the efficiency and regulation of a transformer can be assessed by open circuit and short circuit tests? (10)

B. What is meant by equivalent resistance? (6)

Q4. With reference to a 3 speed A.C. cage motor driven cargo winch:

A. Sketch a circuit diagram for a pole change motor. (8)

B. Describe how speed changes and braking are achieved. (8)

Q5. With respect to High Voltage Electric system:

a) What are reasons for using high voltage on board ship? Enumerate the advantages and disadvantages of using HV systems onboard ship? (6)

b) There are mainly four types of high voltage testing methods applied on high voltage equipment and these are i) Sustained low frequency tests ii) Constant DC/AC test iii) High frequency test and iv) Surge or impulse test. Briefly explain how these tests are conducted. (10)

Q6. a) Describe International protection rating and types of insulation. (6)

(b) A total load of 8000 kW at 0.8 power factor is supplied by two alternators in parallel. One alternator supplies 6000 kW at 0.9 power factor. Find the kVA rating of the other alternator and the power factor. (10)

A) Electric motors contain a stationary member as well as a rotating member. For each of the following machines, identify in which part of the motor three field winding and the armature winding are located: three phase induction motor, three phase synchronous motor, d.c. motor. (6)

B) A 220 V, d.c. shunt motor has an armature resistance of 0.5 ohm and an armature current of 40 A on full load. Determine the reduction in flux necessary for a 50 per cent reduction in speed. The torque for both conditions can be assumed to remain constant. (10)

Q8. 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)

Q9 a) Explain the preference for a 60 Hz system. Describe the dangers of running a 50 Hz system from a 60 Hz supply. (6)

b). A ring-main, 900m long, is supplied at a point A at a p.d. of 220V. At a point B, 240m from A, a load of 45A is drawn from the main, and at a point C, 580m from A, measured in same direction, a load of 78A is taken from the main. If the resistance of the main (lead and return) is 0.25 ohm per kilometre, calculate the current which will flow in each direction round the main from the supply point A and the potential difference across the main, at the load where it is lowest. (10)

Q10. a) (i) What is direct-connected alternator? (3)

(ii) How is a direct-connected exciter arranged in an alternator? (3)

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)