Electrical Machines
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. interpolarmmf is more than armature mmf in the interpolar zone From these, the correct answer is

 1, 2, 3, 4
 1, 2, 5
 2, 3, 4
 1, 3, 5

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Electrical Machines
In a DC shunt generator working on load, the brushes are moved forward in the direction of rotation, as a result of this, commutation will

  improve and terminal voltage will rise .
 improve but terminal voltage will fall.
  worsen and terminal voltage will rise.
  worsen and terminal voltage will fall

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Electrical Machines
Consider the following statements about commutating poles which are fitted on most large dc Shunt motors: 1. The commutating poles are placed in the geometric neutral plane and their number is usually Equal to the number of main poles 2. The winding on the commutating poles is connected in series with the shunt-field winding on the main poles 3. The polarity of the commutating pole must be that of the next pole further ahead 4. The commutating poles neutralize the reactance voltage produced in the coil undergoing Commutation. Of these statements,

 1, 2 and 3 are correct
 1, 2 and 4 are correct
 1 and 4 are correct
 2, 3 and 4 are correct

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