DieselShip's Online Content Library

Q1. (a) With reference to single phasing applied to A.C. motors: (8)

(i) Explain the meaning of single phasing

(ii) Describe its effect

(iii) State the most common cause of single phasing.

(b) Sketch a simple diagram of a direct online starter, showing in detail the overload and single-phase protection trip. (8)

Q2. If the motor terminal markings are unknown how would you identify the start, run and common terminal connections. (16)

Q3. (a) Sketch and describe the working of a Lead-Acid battery. (12)

(b) What routine maintenance is carried out on these batteries? (4)

Q4. With the aid of a circuit diagram, explain how a Galvanometer can be used as an Ammeter. (16)

Q5. With the aid of a simple circuit diagram, explain the electrical distribution system for essential loads on board a cargo ship. (16)

Q6. (a) Explain Kirchhoff’s current law (6)
(b) In the given circuit, find the current value 12 (10)

Q7. (a) Compare constant current method and constant voltage method of charging batteries. (6)
(b) 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 (10)

Q8. (a) Define work, Power and Efficiency (6)
(b) A shunt motor has an armature resistance of 0.2 ohms and with an armature current of 120 amperes runs at 750 r.p.m. off a 400-volt supply. Calculate the speed and armature current of the motor if the flux per pole is reduced to 75 per cent of its initial value, the total torque remaining unaltered. (10)

Q9. (a) Explain what is meant by phase difference between voltage and current values. (6)
(b) An inductance coil has a resistance of 19.5Ω and when connected to a 220V, 50Hz supply, the current passing is 10A. Find the inductance of the coil. (10)