How do interpoles reduce sparking in large direct-current commutator motors?

In large direct-current (DC) commutator motors, interpoles are small poles positioned between the main stator poles. These interpoles are equipped with coils that carry the supply current, allowing them to generate a specific voltage in each armature coil as it is being shorted out by the commutator.1

This induced voltage assists in the rapid reversal of current within the armature coil, which is necessary as the coil moves through the commutation process. By facilitating this quick current reversal, interpoles effectively prevent sparking at the commutator, which otherwise occurs when current cannot change direction quickly enough.1