Function of Compensating winding
The compensating winding are used in DC machines to neutralize the cross magnetizing effect of armature reaction.
These are generally used only large machines which are subjected to large fluctuations due to
their size and cost.
their size and cost.
Need of Compensating Winding
The cross magnetizing effect changes with load current and it results in shifting of the magnetic flux. The machines which are subjected to large changes in load will experience the sudden changes in shifting of the flux. This will result in a statically induced emf in the armature of the DC machine. This statically induced emf in armature may strike an arc between the commutator segments and it may result in complete short circuiting of armature due to the flash-over over the whole commutator.
Compensating Winding in the DC Machines
The compensating winding are placed in stator in the slots of poles shoes of the field winding. These winding are connected in series with armature in such a way that the current direction in the compensating winding at a certain pole flow opposite to that of armature conductor under that pole.
Number of compensating winding Required
To effectively neutralize the cross-magnetizing effect, the mmf generated by the compensation winding must counterbalance the mmf of the armature.
Hence,
ZcIa=ZaIa/A
⇒Zc=Za/A
Where Zc is the number of compensating conductors per pole
Za is the number of armature conductors per pole
Ia is the total armature current ⇒Ia/A is armature current per conductor
A is the number of parallel paths of armature which
= 2 for wave winding
= P (number of poles) for lap winding
= 2 for wave winding
= P (number of poles) for lap winding
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