What are the different types of interpoles in DC electric machines?

In DC electric machines, interpoles, also called commutating poles, play a crucial role in reducing sparking at the commutator. They are placed between the main poles and have several key types based on their construction and the specific function they perform:

1. Compensating Windings: Although not a type of interpole by the strict definition, compensating windings serve a closely related purpose. They are placed in slots on the faces of the main poles and carry current in the opposite direction to the armature. This helps to neutralize the armature’s magnetic effect in the vicinity of the main poles and improve commutation, but they are not considered interpoles since they don’t have their independent pole structures.

2. Interpoles or Commutating Poles: Strictly speaking, these are the actual interpoles in DC machines. They are specially designed electromagnets placed symmetrically between the main poles. Their primary function is to improve the commutation process by ensuring that the short-circuited coils (undergoing commutation) are subject to a magnetic field that aids in their rapid commutation. The key characteristic of interpoles is that their polarity is the same as that of the next main pole in the direction of rotation.

There’s a little misunderstanding in categorizing compensating windings under interpoles, as they serve similar but distinctly different purposes in the context of DC machines. The main type of interpole is thus the one