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Q6. A) Explain the effect of making incorrect phase and starter connections. (6)
b) A 440V shunt motor takes an armature current of 30A at 700 rev/min. The armature resistance is 0.7 Ohm. If the flux is suddenly reduced 20 percent, 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. (10)

Q6. a) Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse.

b) A 440 V shunt motor takes an armature current of 30 A at 700 rev/min. The armature resistance is 0.7 ohm. If the flux is suddenly reduced 20 per cent, to what value will the armature current rise momentarily? Assuming unchanged 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.   (10)

Q6. Two 220 V d.c. generators each having linear external characteristics, operated in parallel. One machine has a terminal voltage of 270 V on no load and 220V at a load current of 35 A, while the other has a voltage of 280 V at no load and 220V at 50 A. Calculate the output current of each machine and the bus bar voltage when the total load is 60 A. what is the kW output of each machine under this condition. (16)

Q7. (a) What do you understand by ‘coffin plate’?

(b) A ship displacing 10000 tonne and travelling at 16 knots has a fuel consumption of 41 tonne per day. Calculate the consumption per day if the displacement is increased to 13750 tonne and the speed is increased to 17 knots. Within this speed range, fuel consumption per day varies as (speed)^3/8 (10)

Q4. a) Explain the significance of the root mean square value of an alternating current or

voltage wave form; Define the form factor of such a wave form. (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 to ensure that the transformer does not become overloaded (10)

Q5. a) Show how the power that is transferred across the air gap of the three-phase induction motor is represented. Explain the terms. What portion of this is useful power? (6)
b) A 440V shunt motor takes an armature current of 30A at 700 rev/min. The armature resistance is 0.7 Ohm. If the flux is suddenly reduced 20 percent, 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. (10)

Q6. (a) What are the factors which determine the synchronous speed of a motor? (6)
(b) A three-phase induction motor is wound for four poles and is supplied from a 50 Hz System, Calculate:
(i) The synchronous speed
(ii) The speed of the rotor when the slip is 4 percent
(iii) The rotor frequency when the speed of the rotor is 600 r/min. (10)

Q4. (a) Describe how protection against short circuit is provided. (6)
(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. (10)