The Diseases Of Electrical Machinery 1904
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ELECTRICAL MACHINERY.
9
it is best to excite the field magnets of the booster
either from the main machine, or from the battery
itself.
Commutator Lubrication.—To the numerous
causes of sparking, although there is really no fault
in the armature, belongthe materials so much abhorred
by every dynamo maker which are sold for lubricating
commutators. Whatever they may be called, it is
only in the rarest cases that they are of any use, and
in an exceedingly large number of cases they do con-
siderable damage. One may take it for granted that
the maker has calculated the machine so that it works
sparklessly with the brushes supplied. If however
in spite of this, the machine sparks, the use of some
graphitic compound will not alter the State of affairs.
The undesirable increase in the brush resistance may
cause an otherwise good machine to spark. If one,
however, thinks it necessary to give the collector a
polish, which is in general only possible with carbon
brushes, it should be done with a drop of pure mineral
oil, which must be carefully rubbed over the whole
surface.
[The editor prefers a touch of vaseline, applied on
a bit of clean cotton cloth; cotton waste should not
be used.]
Spare Brushes.—When inserting new brushes, it
is to be very carefully seen that the surface of the new
brushes fits exactly to the surface of the commutator.
It is scarcely to be feared that any one will imitate the