Q8. The centre of gravity of a ship of 5000 tonne displacement is 6 m above the keel and 1.5 m forward of midships. Calculate the new position of the centre of gravity if 500 tonne of cargo are placed in the t’ween decks 10 m above the keel and 36 m aft of midships. (16)
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)
Q8. a) Describe the means by which the magnetic flux associated with a conductor may be changed (6)
b) Find the generated e.m.f./conductor of a 6-pole d.c. generator having a magnetic flux/pole of 64m Wb and a speed of 1000 rev/min. If there are 468 conductors, connected in six parallel circuits, calculate the total generated e.m.f. of the machine. Find also the total power developed by the armature when the current in each conductor is 50 A. (10)
Q6. a) Explain how excitation of the rotor is produced and supplied. (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-volts 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)
Q7. A 4 pole, lap wound shunt generator delivers 200 A at terminal voltage of 250 V. It has a field and armature resistance of 50 Ω and 0.05 Ω respectively. Determine: (16)
(a) Armature current
(b) Generated e.m.f
(c) Current per armature parallel paths
(d) Power developed
Q9. A vessel about to complete loading in a summer zone is expected to enter a winter zone after steaming from the loading port for 10 days. On passage, fuel consumption is expected to be 30 tonnes per day and water consumption 15 tonnes per day. The ship is at present floating in water of density 1.013 tonnes/m3 at a draft of 9.0m. (16)
Summer load draft: 9.475m FWA: 203mm TPC: 30 tonnes/cm Find
(a) The maximum permissible draft on completion of loading.
(b) The amount of cargo which the vessel can load. (Note: A vessel passing from a summer zone to a winter zone, or from a tropical zone to summer zone, must arrive at the zone boundary at the draft appropriate to that zone).
Q5. a) Which has the greater equivalent resistance; two equal capacitors in series or in parallel? Explain with reasons? (6)
b) A circuit has a resistance of 3Ω inductance of 0.01H. The voltage across its end is 60V and the frequency is 50Hz. Calculate
a) the impedance
b) the power factor
c) the power absorbed. (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.
Q9. A. Explain the working principal of a 3-phase induction motor. What are the various types of rotors? B. An 18.65Kw, 6-pole, 50Hz, 3 phase slip ring induction motor runs at 960 rpm on full load with a rotor current per phase of 35A, allowing 1Kw for mechanical losses, find the resistance per phase of 3-phase rotor winding.
Q7. A. Describe the possible causes and the effect of running a three-phase motor with one phase open circuited. B. A 440V shunt motor tenets 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.
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