Commutation on direct-current machines

IT is well-known, that in direct-current machines with heavy linear armature load (number of ampere conductors per cm. of armature circumference) the commutation occurs under especially heavy conditions; the reactance voltage in such machines rises to a great value and therefore each in accuracy of the compensation of reactance voltage by means of interpoles produces a great additional current in the armature coils short-circuited by the brushes, which causes sparking at the commutator.