The commutation is the exchange of energy between rotor and stator and versa in the change of a blade of the commutator, roller chain where the coils are connected in series. During this switching the coil is temporarily short circuited by the brushes, which helps to release stored energy, before the current flows in the opposite direction. It is necessary to induce an electromotive force that cancels the resultant of the switching process, obtained through the switching poles and besides canceling the switching, these poles weaken the stator flux.
In large machines this phenomenon is abolished through compensating windings that generate a flow with the same intensity and opposite direction of the reaction flow. In motors, the switch serves to reverse the direction of the electric current making the electromagnet poles also reverse, so the rotor will remain spinning.
Since this current inversion is not immediate, an electromotive force is induced, which causes a short-circuit current to circulate in the collector, the turns, and the brushes. Then, the interruption of this current gives rise to the appearance of sparks in the contacts of the brushes with the collector, which can affect the collector and must therefore be eliminated.