Discharging arcs in commutation motors

Electromagnetic interference (EMI) in electric motors with mechanic commutators consists of two phenomena: commutating electromagnetic interference, just due to the changes in motor magnetic energy, and switching electromagnetic interference due to mechanical performance of the commutators as switches. The first phenomenon does not cause commutator wear, but the second causes both: the excessive EMI especially by voltage spikes and discharging arcs, which additionally could reignite drawn arcs, and further on, causing the severe commutator wear. This reignited drawn arc makes progress from the short one to the longer one, being more severe due to material transfer jagging edges and surfaces of commutator bars and brushes. Preventing the overvoltage spikes, and so far the ignition of the discharging arc results, besides reducing EMI, in avoidance of the drawn arc reignition and minimizing also the commutator wear. The paper gives also a method of determining a quenching capacitance value.