The Commutation ability is one of the important operating characteristics of the carbon brush. Hitherto, there are many methods, for example black band method, search coil method, null point method, pulse height analyzer method and NEMA method.
In this paper, one method of commutation ability test is proposed, using only one brush on the simplified equivalent circuit of d. c. machine, while NEMA method uses two brushes. The shape and size of the non sparking region built by L (self inductance of the commutating coil) and I (brush current) is the measure of commutation ability. The generation of arc is detected by the voltage drop between the commutator and brush trailing side. This test could be recommended owing to its simple and rapid process.