# Compensating Windings and Interpoles in DC Generator

### Compensating Winding and Interpoles in DC Generator

In DC compound machine setup by armature current opposes magnetic field flux, this is known as armature reaction. The armature reaction has two effects (i) Demagnetizing effect and (ii) Cross magnetizing effect. Demagnetizing effect weakens the main field flux which in turn decreases the induced e.m.f (as E  Ø)). To overcome this effect a few extra turns/poles are added in series to main field winding. This creates a series field which serves two purposes,

(i) It helps to neutralize the demagnetizing effect of armature reaction.

(ii) If wound for cumulative compounded machine the electrical performance will be improved.

### Compensating Winding

All armature conductors placed under the main poles region produces e.m.f which is at right angle (90°) to the main field e.m.f. This e.m.f causes distortion in main field flux. This is known as cross magnetizing effect. To minimize the cross magnetizing effect compensating winding is used. This compensating winding produces an m.m.f which opposes the m.m.f produced by armature conductors.

This objective. is achieved by connecting compensating winding in series with armature winding. In absence of compensating winding, cross magnetizing effect causes sparking at the commutators and short circuiting the whole armature winding.

Let, Zc = Number of compensating conductors/pole
Za = Number of active armature conductors/pole
Ia = Armature current.
ZcIa= Za (Ia/A)
Where,
Ia/A=Armature current/conductor

Zc= Za/A