In dc machines ___

Electrical Engineering MCQ Electrical Machines MCQ
1

In dc machines,

  1. reactance voltage is proportional to armature current
  2. reactance voltage is proportional to core length
  3. reactance voltage is due to self-flux of the coil undergoing commutation
  4. armature-cross flux is neutralized by interpolar flux
  5. interpolar mmf is more than armature mmf in the interpolar zone From these, the correct answer is

A. 1, 2, 3, 4
B. 1, 2, 5
C. 2, 3, 4
D. 1, 3, 5

Show Answer

Answer: B

Share your understanding of this question with the correct explanation.

2

The correct answer is B. The following statements are correct:

  1. Reactance voltage is proportional to armature current.
  2. Reactance voltage is proportional to core length.
  3. Interpolar mmf is more than armature mmf in the interpolar zone.

Explanation:

  1. Reactance voltage is proportional to armature current: The reactance voltage in a DC machine is caused by the inductive reactance of the armature winding. This reactance voltage is directly proportional to the armature current flowing through the winding.
  2. Reactance voltage is proportional to core length: The reactance voltage is also influenced by the length of the magnetic core in the machine. A longer core length results in a higher reactance voltage.
  3. Interpolar mmf is more than armature mmf in the interpolar zone: In a DC machine, the interpole (or commutating pole) is designed to neutralize the armature reaction and aid in commutation. To achieve this, the interpolar mmf (magneto-motive force) is intentionally made greater than the armature mmf in the interpolar zone. This ensures effective commutation and reduces sparking at the brushes.

Therefore, the correct answer is B, as statements 1, 2, and 5 are correct.