The Diseases Of Electrical Machinery
Forfatter: Ernst Schulz
År: 1904
Forlag: E. & F. N. SPON, Ltd.
Sted: London
Sider: 84
UDK: 621.311
Edited with a preface, by Silvanus P. Thompson
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62
THE DISEASES OF
feature which may give rise to faults of insulation as
well as to other faults. Slip-rings can indeed be easily
insulated from one another, and from the shaft. A
fault is, however, more likely to appear there than on
the fixed terminals of the continuous-current machine.
Sparking at the slip-rings may be due to two causes.
It may either be due to a periodically occurring break
in the magnet-winding; or, more usually, it results
from bad material for the brushes or slip-rings, care-
less handling, untruth or dirtiness of the rings.
At any rate, all faults occurring in the exciting
winding of an alternator are easily found. Moreover,
the large number of the poles presents the advantage
that in the case of a breakdown of one pole, one may
without fear cut out one pole, connecting together the
preceding and following poles. Then, by increasing
somewhat the magnetising current, the correct voltage
can be still maintained. This results in an irregularity
in the strength of the various poles, which is however
of no importance, because sparking, such as would
occur with a continuous-current machine under the
same circumstances, is impossible.
Exciter.—The continuous current for the field is
usually supplied by a direct-coupled exciter, which
usually possesses a single shunt winding, but some-
times a series winding ^Iso. With this machine the
same faults may occur that we considered at the be-
ginning, so that it appears useless to add anything
more here.