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In an alternator, if the load power factor changes from lagging to leading, the armature reaction effect shifts from:

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  1. demagnetising to magnetising
  2. magnetising to cross-magnetising
  3. cross-magnetising to demagnetising
  4. demagnetising to cross-magnetising

Answer (Detailed Solution Below)

Option 1 : demagnetising to magnetising
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Armature Reaction in Alternator

In an alternator, armature reaction refers to the effect of the armature current on the magnetic field of the machine. This interaction results in a distortion of the magnetic field, leading to changes in the terminal voltage

Nature of armature reaction on alternator:

qImage6817553f6444521feb0d3403

Power factor

Nature

Unity

Cross-magnetizing

Zero PF lagging

Purely demagnetizing

Zero PF leading

Purely magnetizing

0.8 lagging

Partially cross-magnetizing and partially demagnetizing

0.8 leading

Partially cross-magnetizing and partially magnetizing

 

From the above table, if the load power factor changes from lagging to leading, the armature reaction effect shifts from demagnetising to magnetising.

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More Alternator and Synchronous Motors Questions

Q1.Which statements about voltage drop in an alternator are correct? I. The voltage drop due to armature resistance (IaRa) is in phase with the armature current (Ia). II. At unity power factor, the voltage drop IaRa directly subtracts from the generated EMF (E). III. For a leading power factor load, IaRa contributes to an increase in terminal voltage (V). IV. Armature resistance has no effect on voltage regulation.
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Q1.If a 6-pole induction motor operates on a 60 Hz supply, its synchronous speed is _____________.
Q2.How are the segments of the commutator insulated from each other?
Q3.Which statements about voltage drop in an alternator are correct? I. The voltage drop due to armature resistance (IaRa) is in phase with the armature current (Ia). II. At unity power factor, the voltage drop IaRa directly subtracts from the generated EMF (E). III. For a leading power factor load, IaRa contributes to an increase in terminal voltage (V). IV. Armature resistance has no effect on voltage regulation.
Q4.What does the flux created by the load current in the primary winding, which links only with the primary winding, represent?
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