--_La Nature._
* * * * *
AN ELECTRICAL GOVERNOR.
We abstract the following from a paper on electric lighting by Prof.
J.A. Fleeming, read before the Iron and Steel Institute, Manchester.
The illustration is from _Engineering_.
[Illustration: ELECTRICAL GOVERNOR.]
One of the questions which most frequently occurs in reference to mill
and factory lighting is whether the factory engines can be used to run
the dynamo. As a broad, general rule, there can be no question that
the best results are obtained by using a separate dynamo engine,
controlled by a good governor, set apart for that purpose. With an
ordinary shunt dynamo, the speed ought not to vary more than 2 or 3
per cent. of its normal value on either side of that value. Hence, if
a dynamo has a normal speed of 1,000, it should certainly not vary
over a greater range than from 970 to 980 to 1,020 to 1,030. In many
cases there may be shafting from which the necessary power can be
taken, and of which the speed is variable only within these limits.
There are several devices by which it has been found possible to
enable a dynamo to maintain a constant electromotive force, even if
the speed of rotation varies over considerable limits.
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