DieselShip's Online Content Library

Q1. (a) With the aid of a circuit diagram explain the working of Bridge rectifier. (8)

(b) Compare the performance of Bridge rectifier with Full wave and Half wave rectifier. (8)

Q2. (a) Explain, with the aid of a sketch, the principle of operation of an earth leakage detection system. (8)

(b) Explain why an insulated neutral system is used extensively on-board ships. (4)

(c) State, with reasons, why a single earth fault on an insulated neutral system should always be cleared as soon as possible (4)

Q3. (a) State FIVE essential electrical services that should be operable under fire conditions. (8) (b) Explain how electric cables for the essential services in part (a) pass through bulkheads whilst maintaining gas tight and watertight integrity. (4)

(c) State the requirements for the cables which supply electrically driven emergency fire pumps. (4)

Q4. (a) Name at least three types of temperature sensing devices for remote indication. (4)

(b) Explain the working of a Thermocouple type temperature sensor. (8)

(c) What are various materials used in a thermocouple? (4)

Q5. (a) What are the hazards associated with batteries? (4)

(b) What safety precautions are to be taken while operating and maintaining the batteries including in battery room. (6)

(c) What are the safety arrangements seen in the Battery room of a ship? (6)

Q6. (a) How does a moving coil ammeter measure large current (6)

(b) A moving coil instrument with a coil resistance of 1.98Ω, produces full scale deflection from a current of 10mA. Determine the value of shunt required to extend the range up to 10A. (10)

Q7. (a) Explain power factor with A.C. Sine wave and phasor diagram. (6)

(b) A circuit has a resistance value of 25Ω and an inductance value of 0.3H. If it is connected to a 230V, 50Hz supply, find the circuit current, the power factor and the power dissipation. (10)

Q8. (a) Compare Direct current with Alternating current. (6)

(b) A four-pole generator has a flux of 12 mWb/pole. Calculate the value of e.m.f. generated in one of the armature conductors, if the armature is driven at 900 rev/min. (10)

Q9. (a) Shunt generators having drooping characteristics are best suited for parallel operation. Discuss (6)

(b) Two 220 V D.C. generators each having linear external characteristics, operated in parallel. One machine has a terminal voltage of 270 V, on no-load and 220 V at a load current of 35 A, while the other has a voltage of 280 V at no-load and 220 V at 50 A. Calculate the output current of each machine and the bus bar voltage when the total load is 60 A. What is the kW output of each machine under this condition. (10)

Q3. With reference to the protection of electric motors explain EACH of the following in relation to fuse back up protection.

a) How a motor fitted with fuse back up protection may exceed its rated temperature without being tripped by the primary protection. (8)

b) The value of current rating at which the over current relay should be set. (8)

Q7. a) State the conditions, which must be satisfied before an A.C generator can be paralleled with live bus-bars. (4)

b) Sketch a lamp-bright configuration for synchronizing lamps. (8)

c) State the advantages and disadvantages of the lamps-bright system over lamps-darks system. (4)

Q3. (a) Sketch, the circuit diagram of an instrument used for measuring electrical insulation resistance. (8)

(b) Describe the circuit diagram sketched in (a), explaining how it operates when measuring electrical insulation resistance. (8)

Q1. a) Explain the working principle of an alkaline battery. (8)

b) Compare the alkaline battery with Lead-Acid battery. (8)

Q4. a) What is the purpose of AVR in an alternator? (6)

b) With the aid of a simple circuit diagram explain the basic working of a brushless alternator. (10)

Q7. In the following circuit, E1 = 13 V, E2 = 19.5 V, R1 = 5 W, R2 = 7 W, R3 = 9 W. Find the current flowing through each resistor. (16)

Q7. A 24V emergency battery is to be charged from the 110V ship's mains when the e.m.f. per cell has fallen to a minimum value of 1.8V. The battery consists of 12 cells in series, has a capacity of 100 Ahr at a 10 hr rate and the internal resistance is 0.03Ω/cell. If charging continues until the voltage per cell rises to 2.2V, find the value of the variable resistor needed to control the charging. The charging current can be assumed to be equal to the maximum allowable discharge current (16)

Q9. A wooden ring having a mean diameter of 200 mm and a cross-sectional area of 400 mm2 is wound uniformly with a coil of 300 turns. If the current passed through the coil is 5 A calculate the value of flux produced in the coil. (16)

Q6. A coil of resistance 10 ohm and inductance 0.1H is connected in series with a capacitor of capacitance 150pF, across a 200 V, 50 Hz supply.

Calculate:

a) the inductive reactance. (3)

b) the capacitive reactance. (3)

c) the circuit impedance. (2)

d) the circuit current. (2)

e) the circuit power factor. (2)

f) the voltage drop across the coil. (2)

g) the voltage drop across the capacitor. (2)