DieselShip's Online Content Library

Q7. A resistor of ohm value 3 ohms is connected in series with a coil of inductance 0.1 H and resistance 1 ohm. If 100 V at a frequency of 50 Hz is applied to the circuit find the current flowing.

Q8. (a) Explain various powers and efficiencies in the Propulsion plant of a ship (6)
(b) A vessel with a displacement of 12250 t burns 290 t of fuel while travelling at a speed of 15 knots on a voyage of 2850 nautical miles. On a voyage of 1800 nautical miles at a speed of 13 knots and a displacement of 14200 t, estimate the quantity of fuel that will be burnt. (10)

Q7.  The pitch of a propeller is measured by means of a batten and cord. The horizontal ordinate is found to be 40 cm while the vertical ordinate 1.15 m at a distance of 2.6 m from the centre of the boss. calculate the pitch of the propeller and the blade width at that point. (16)

Q6. A. What are the characteristics of PN junction diode? Point out its specifications. Also point out the significance of dynamic and static resistances. (6)

B. A 72 KVA transformer supplies a heating and lighting load of 12 KW at unity power factor and a motor load of 70 kVA at 0.766 (lagging) power factor: Calculate the minimum rating of the power-factor improvement capacitors which must be connected in the circuit the ensure that the transformer does not become overloaded. (10)

Q7. a) Describe the principle of variable-capacitance transducer. (6)

b) A coil of resistance 10 ohms and inductance 100mH is connected in series with two parallel capacitors each of value 100 mF across a 250 V, 50Hz supply. determine (10)

i) The circuit current

ii) The total power factor

iii) The power taken from the supply.

Q9. a) What is meant by the term ‘back e.m.f.’ as applied to an electric motor? (6)

b) A 40 kW,220V shunt motor has a full-load efficiency of 90 per cent, an armature resistance of 0.075 ohms and a shunt motor-field resistance of 55 ohms. When ‘at starting’, the starter handle is moved onto the first stud, it is desired to limit the current, through the armature to 1.5 times the value which it has when the motor is on full load. What must be the total value of the starting resistance? If, on overload, the speed falls to 90 per cent of its normal full-load value. What would be the armature current? Neglect the effect of armature reaction. (10)

Q8. (a) State the relationship between impedance, voltage and current (6)

(b) The filament of a 230V lamp takes a current of 0.261A when working at its normal temperature of 2000° C. The temperature coefficient of the tungsten filament material can be taken as 0.005 ohms/ohms at 0ºC/ºC. Find the approximate current which flows at the instant of switching on the supply to the cold lamp, which can be considered to be at a room temperature of 20° C (10)

Q6. (a) Explain in brief the term 'bulwark" and 'freeing port'. (6)

(b) A ballast tank is 15 m long, 12 m wide and 1.4m deep and is filled with fresh water. Calculate the load on the top and short side, if: (10)

(i) The tank is just completely full

(ii) There is a head of 7m of water above the tank top.

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)