Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

commutator
a cylindrical assembly of copper segments, insulated from each another, that make electrical contact with stationary brushes, to allow current to flow from the rotating armature windings of a DC machine to the external terminals of the machine. It also, enables reversal of current in the armature winding.
See commutation
commutator film
an oxide layer on the commutator surface, indicated by a dark color or a "film," that is required for proper commutator action and full loading of the machine. On a new DC machine commutator, or on a commutator that has just been stoned, there is no "film" on the commutator. It is advisable to refer to the manufacturer's technical manual for the proper procedure to "break in" the commutator and develop the film so the machine can be operated at rated conditions.
DC generator commutator exciter
a source of energy for the field winding of a synchronous machine derived from a direct current generator. The direct current generator may be driven by an external motor, a prime mover, or by the shaft of the synchronous machine.
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