Synchronous Generator(Engineering > Electrical Engineering ) Questions and Answers

Question 1. When two alternators are running in parallel, their RKVA load share is changed by changing their ................ while their kW load share is changed by changing their ..............
  1.    excitation, driving torque
  2.    driving torque, excitation
  3.    excitation, excitation
  4.    driving torque, driving torque
Explanation:-
Answer: Option A. -> excitation, driving torque


excitation, driving torque


Question 2. A three phase alternator has a phase sequence of RYB for its three output voltages. In case the field current is reversed, the phase sequence will become
  1.    RBY
  2.    RYB
  3.    YRB
  4.    none of the above
Explanation:-
Answer: Option B. -> RYB


RYB


Question 3. Two-alternators are running in parallel. If the driving force of both the alternators is changed, this will result in change is
  1.    frequency
  2.    back emf
  3.    generated voltage
  4.    all of the above
Explanation:-
Answer: Option A. -> frequency


frequency


Question 4. In order that two alternators be put in parallel, which of the following factors should be identical for both ?
  1.    Voltage
  2.    Frequency
  3.    Phase sequence
  4.    All of the above
Explanation:-
Answer: Option D. -> All of the above


All of the above


Question 5. In the above figure, the characteristic for unity power factor is represented by the curve maked
  1.    A
  2.    B
  3.    C
  4.    D
Explanation:-
Answer: Option C. -> C


C


Question 6. For 50 Hz system the maximum speed of an alternator can be
  1.    approximately 3600 rpm
  2.    approximately 3000 rpm
  3.    3600 rpm
  4.    3000 rpm
Explanation:-
Answer: Option D. -> 3000 rpm


3000 rpm


Question 7. If the input of the prime mover of an alternator is kept constant but the excitation is changed, then
  1.    the active component of the output is changed
  2.    the reactive component of the output is changed
  3.    power factor of the load remains constant
  4.    power factor of the load changes from lagging to leading
Explanation:-
Answer: Option B. -> the reactive component of the output is changed


the reactive component of the output is changed


Question 8. The driving power from the prime mover driving the alternator is lost but the alternator remains connected to the supply network and the field supply also remains on. The alternator will
  1.    get burnt
  2.    behave as an induction motor but will rotate in the opposite direction
  3.    behave as a synchronous motor and will rotate in the same direction
  4.    behave as a synchronous motor but will rotate in a reverse direction to that corresponding to generator action
Explanation:-
Answer: Option C. -> behave as a synchronous motor and will rotate in the same direction


behave as a synchronous motor and will rotate in the same direction


Question 9. For an alternator when the power factor of the load is unity
  1.    the armature flux will have square waveform
  2.    the armature flux will be demagnetising
  3.    the armature flux will be cross-magnetising
  4.    the armature flux will reduce to zero
Explanation:-
Answer: Option C. -> the armature flux will be cross-magnetising


the armature flux will be cross-magnetising


Question 10. As the speed of an alternator increases
  1.    the frequency increases
  2.    the frequency decreases
  3.    the frequency remains constant but power factor decreases
  4.    none of the above
Explanation:-
Answer: Option A. -> the frequency increases


the frequency increases


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