Electrical Machines
Breather is provided in a transformer to

 filter the transformer oil.
 provide cold air in transformer.
  absorb moisture of air during breathing.
 absorb moisture from air entering in transformer.

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Electrical Machines
A bipolar dc machine with interpoles has a main-pole flux of ф per pole and an interpole flux of Фᵢ per pole. The yoke of the machine is devide into four quadrants by the main-pole axis and The commutation axis. The flux-distribution in the quadrants will be

 ½ ( ф - фᵢ ) in all the four quadrants
 ½ ( ф + фᵢ ) in two adjacent quadrants and ½ ( ф - фᵢ ) in the remaining two quadrants
 ½ ( ф + фᵢ ) in all the four quadrants
 ½ ( ф + фᵢ ) in two diametrically opposite quadrants and ½ ( ф - фᵢ ) in the remaining two Quadrants

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Electrical Machines
Armature reaction in a DC machine

  makes an angle of 90° with the main pole axis.
 makes an angle with the main pole axis which is load dependent.
 is in direct opposition to the main poles.
 is in the same direction as the main poles.

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