DieselShip's Online Content Library

Q5. a) List the factors that determine the starting torque of the three-phase induction motor. How does this torque generally compare with the value of the rated torque? (6)
b) The low-voltage release of an a.c. motor-starter consists of a solenoid into which an iron plunger is drawn against a spring. The resistance of the solenoid is 35 ohm. When connected to a 220 V, 50 Hz, a.c. supply the current taken is at first 2 A, and when the plunger is drawn into the “full-in” position the current falls to 0.7 A. Calculate the inductance of the solenoid for both positions of the plunger, and the maximum value of flux-linkages in weber-turns for the “full-in” position of the plunger. (10)

Q9. A. List the factors that determine the maximum developed torque of the induction motor. (6)

B. The primary and secondary windings of a 500 KVA transformer have resistance of 0.42 Ω and 0.0019 Ω respectively. The primary and secondary voltages are 11000 V and 415 V respectively and the core loss is 2.9 kW, assuming the power factor of the load to be 0.8. Calculate the efficiency on (i) Full load (ii) Half load. (10)

Q4.a) Explain what is meant by the terms wave form, frequency, and average value. (6)

b) A moving coil ammeter, a thermal ammeter and a rectifier are connected in series with a resistor across 110 V sinusoidal a.c. supply. The circuit has a resistance of 50Ω to current in one direction and, due to the rectifier, an infinite resistance to current in the reverse direction. Calculate

(i) The reading on the ammeters

(ii) The form and peak factors of the current wave (10)

Q5. a) Explain the applications of PN junction diode (6)

b) In a full wave rectifier without filter, the load resistance is 4 k Ω. Each diode has a forward resistance of 0.8 k Ω. If the peak voltage applied to each diode is 120 V at 50Hz, calculate:

(i) The average value of current.

(ii) Efficiency and

(iii) Regulation at a load current of 10mA (10)

Q7. (a) What is Freeboard of a Ship? Why oil tankers have less freeboard? (6)

(b) A ship’s length at the waterline is 180 meters, with a maximum beam of 30 meters and a draft of 9 meters. If the ship’s volume of displacement is 38,880 cubic meters, calculate its block coefficient. (10)

Q6. A. What are the characteristics of PN junction diode? Point out its specifications. Also point out the significance of dynamic and static resistances.

B. Draw the circuit of Half-wave rectifier and its output waveform. A diode whose internal resistance is 20 is to supply power to 1000 load from 110 V (RMS) source. Calculate

(i) peak load current, (ii) DC load current, (iii) AC load current.

Q7. With reference to adjoining circuit calculate following. (a) Current in each branch of circuit. (b) Total current.

Q7. A. Describe how protection against short circuit is provided in a 3 phase induction motor circuit.

B. Explain how rotating magnetic field is produced in three phase winding with three phase supply. A 4-pole, 3-phase induction motor operates from a supply whose frequency is 50 Hz. Calculate

(i) Speed at which the magnetic field of the stator is rotating,

(ii) speed of the rotor when the slip is 0.04,

(iii) the frequency of the rotor current when the slip is 0.03.

Q10. A. How does change to frequency affect the operation of the transformer? What makes this ratio different from the ratio of transformer? B. A 550 KVA, 50 Hz single phase transformer has 1875 and 75 turns in the primary and secondary windings respectively. If the secondary voltage is 220 V, calculate (i)Primary voltage; (ii)Primary and secondary currents; iii. Maximum value of flux.

Q8. The armature and filed resistances of a 220 V shunt motor are 0.25 ohm and 110 ohm respectively and when running on load, the motor takes 6 A. Calculate the losses attributable to iron, friction and windage and assuming this value to remain constant on loads, determine the efficiency when the current supplied is 62 A.

Q9. (a) Define longitudinal centre of gravity (LCG) and longitudinal centre of buoyancy (LCB). (6)

(b) The immersed cross-sectional areas of a ship 120m long, commencing from aft are 2, 40, 79, 100, 103, 104, 104, 103, 97, 58 and 0 m². Calculate:

(i) Displacement

(ii) Longitudinal position of the centre of buoyancy. (10)

Q9. A) Describe the effect of cavitations on the propeller blades. (6)

B) A propeller 4.6m diameter has a pitch of 4.3m and boss diameter of 0.75 m. The real slip is 28% at 95 rev/min. Calculate the speed of advance, thrust and thrust power.  (10)