The Secret to That Old Black Magic: Mastering the Art of Sparkless Commutation

DC machines have been in operation for more than 100 years. Engineers and technicians understand the dc-motor structure and components since they have experience rebuilding, testing, and making performance adjustments to them. Those that understand commutation, [2], [4] the commutation zone (CZ), and the characteristics of the carbon brush are few in number. Traditionally, the lack of a visible arc has been the defining quality of good commutation; hence, the term "black." The knowledge gap and relatively high-level physical science involved with commutation have led to an art known as "black magic" for achieving the invisible-arc condition [5], [6]. Black magic refers to both the brush coloration and commutation. The purpose of this article is to define the CZ and present the critical components that create it. An explanation of specific brush properties and their contribution to successful commutation is included.