DieselShip's Online Content Library

Q8. Find the length of manganese wire required to make a 15.7 Ω resistor, if the diameter is 0.315 mm and the resistivity is 407 μΩ mm (16)

Q6. a) Describe a simple single-phase transformer. (6)

b) A 15 KVA, 440 / 110- volt, 50 Hz cycle/sec, single-phase transformer has primary and secondary resistance of 0.12 ohm and 0.0077 ohm respectively. The iron loss of the transformer is 0.16 kW. Calculate the efficiency of the transformer (10)

i) On full load unity power factor

ii) on 80 per cent full load at a power factor of 0.9 lagging

Q6. (a) Describe the basic principles of a self-excited generator (6)

(b) The armature resistance of a 200 V, shunt motor is 0.4 ohms and the no-load armature current is 2A. When fully loaded and taking an armature current of 50 A, the speed is 1200 rev/min. Find the no-load speed and state the assumption made in the calculation (10)

Q7. (a) What is meant by statical stability? What are the factors that influence stability? (6)

(b) A box barge 25 m long and 4 m wide floats in fresh water at a draught of 1.2 m and has an empty mid length compartment 5 m long. The bottom of the barge is lined with teak (rd 0.805) 120 mm thick. After grounding all the teak is torn off and the centre compartment laid open to the sea. Calculate the final draught. (10)

Q6. (a) The capacitor-start induction run motor has a much higher starting torque than the resistance split-phase motor. Explain (6)

(b) An eight-pole armature is wound with 480 conductors. The magnetic flux and the speed are such that the average e.m.f. generated in each conductor is 2.2 V, and each conductor is capable of carrying a full load current of 100 A. Calculate the terminal voltage on no load, the output current on full load and the total power generated on full load when the armature is:

(i) Lap connected

(ii) Wave connected (10)

Q4. a) What are the factors which determine the synchronous speed of a motor? (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)

Q6. a) Explain distribution factor and pitch factor for alternator windings. (6)
b) An eight-pole armature is wound with 480 conductors. The magnetic flux and the speed are such that the average e.m.f. generated in each conductor is 2.2 V, and each conductor is capable of carrying a full load current of 100 A. Calculate the terminal voltage on no load, the output current on full load and the total power generated on full load when the armature is
a) lap-connected
b) wave-connected (10)

Q4. a) Describe the possible causes and the effect of running a three-phase motor with one phase open circuit. (6)

b) A heater unit of inductance has a resistance of 6.5 ohms and is intended for use with 100V mains. For 50Hz what voltage would it be suitable when placed in series with an external apparatus, of negligible resistance, having an inductance of 0.01H? If the frequency rises by 5 percent and this voltage remains constant, what would be the resulting change of voltage at the heater terminals? (10)

Q8. A. Sketch an arrangement showing the principal of proportional plus integral (P+I) control loop.

B. Compare the series and parallel resonance circuits. Find the frequency at which the following circuit resonates.

Q7. A. Which of the following three motors has the poorest speed regulation: shunt motor, series Motor or cumulative compound motor? Explain.

B. A 440V shunt motor takes an armature current of 30A at 700 rev/min. The armature resistance is 0.7ohm. If the flux is suddenly reduced by 20 per cent, to what value will the armature current rise momentarily? Assuming unchanged resisting torque to motion, what will be the new steady values of speed and armature current? Sketch graphs showing armature current and speed as functions of time during the transition from initial to final, steady-state conditions.

Q8. An AC Voltage Of 24 V is connected in series with the silicon diode and load resistance 500 Ohm having forward resistance 1O Ohms. Calculate the peak output voltage.

Q6. A. A series circuit having resistance, Inductance and capacitance is to be operated on a constant voltage supply of available frequency. Indicate graphically how changes will take place in the terms, Reactive terms, i.e. Capacitive reactance and inductance reactance; B. A resistance of 130 ? and a capacitor of 30µF are connected in parallel across a 230 Volt, 50Hz supply. Find the current in each component, total current, phase angle and the power consumed.