Electrical Machines
Minimum allowable resistivity of power transformer insulating oil is generally taken as

 3 X 1012 Ω - cm at 27°C and 0.3 X 1012
 2 X 1012 Ω - cm at 27°C and 0.2 X 1012
 4 X 1012 Ω - cm at 27°C and 0.4 X 1012
  1 X 1012 Ω - cm at 27°C and 0.1 X 1012

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Electrical Machines
The following statements relate to compensating winding (CW) and interpole winding (IW) of a dc machine : 1. CW neutralizes the armature reaction under a pole pitch 2. IW is connected in series with armature circuit 3. IW produces mmf in the commutating zone only 4. CWmmf is directed along the brush axis 5. Mmf produced by IW is equal to armature mmf From these, the correct statements are

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

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Electrical Machines
In a loaded DC generator, if the brushes are given a shift from the interpolar axis in the direction of rotation, then the commutation will

 deteriorate with rise in terminal voltage.
 improve with fall of terminal voltage.
 improve with rise in terminal voltage.
 deteriorate with fall of terminal voltage.

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