The Diseases Of Electrical Machinery 1904
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ELECTRICAL MACHINERY. 7
Such motors with variable speed must always
be specially calculated and designed with regard to
sparking, so that they can withstand the weakening
of the field. The author has published—in the
Elektrotechnischen Anzeiger 1902, in the Handbuchder
Elektrotechnik, vol. ix. part 2, and in other places—
some artides on the speed regulation of continuous-
current motors. We may here draw attention to the
connection of motors (in three wire systems) to cir-
cuits that work at 110 volts and 220 volts, and also
to the use of motors with two windings and two com-
mutators, which may be connected as desired either
in series or in parallel. Both methods allow of 100
per cent, variation in speed.
Booster.—In this respect the working of boosters,
such as are used with accumulator batteries, is very
unsatisfactory. Boosters are built to generate about
50 volts in order to be able, in series with an ordi-
nary 110 or 220 volt generator, to charge a battery
of 60 cells. When commencing charging, when the
battery is half discharged, the booster should not
generate more than 20 volts. The charging is there-
fore commenced with a total pressure of 130 volts.
One may consider how very difficult it is to build a
dynamo which with constant speed will stand a regu-
lation of the voltage to less than 50 per cent, of its
normal value, while generating the full load current
all the time. These machines, therefore, must be
specially calculated with the greatest care in respect