Honolulu star-bulletin. [volume] (Honolulu [Oahu, Hawaii]) 1912-2010, 1917-04-14
CONDITIONS GOVERNING GENERATOR OUTPUT
"s" ARE DISCUSSED BY EXPERTS ON ELECTRICITY
(ey Special Permission from Motor
49, Ape)

the aTmature, the manner in which
these wires are inteFconnected, which
determine the number OF different cir.
cults through the armature wind
ing; the number OF magnetic lines,
called the magnetic flux, entering or
leaving the armature at the different
poles; the number OF magnetic poles
forming the magnetic circuit. and the
speed at which the arrnature is revolv-
ing In the magnetic field.
After the genera or is costructed the
number OF wires on the surface OF the
armature and the number OF different
circuits through the armature are all
fixed, while the speed and number OF
magnetic lines, or magnetic flux, to
the pole may either or both be chang
ed .. ~
The speed of the generator. Of
course depends upon the speed Of the
device driving II and the manner in
which the generator is connected in
this device. The armature of the
generator may be mounted on the
shaft Of the driving device or II may
be geared or connected to the shaft by
a clutch or chain. In some cases the
construction OF the driving cluch is
such that the armature Of the generator
never exceeds predetermined speed
regardless Of the extent to which
the speed OF the driving device in.
creases.
The magnetic flux per pole depends
upon the form of the magnetic cir.
cults; II the kind OF material compos
ing the magnetic circuit remains
constant then the electrical pressu e
generated in the armature winding will
vary directly as the speed of the arma-
ture. starting at nothing for no speed
and increasing directly as the speed
increases. The relation Of the electri-
cal pressure generated to the speed is
shown graphically In Fig. /, In which /
speed and the number of ampere turns |
acting on each magnetic pole.
Changing Magnetic FIux
The number OF ampere turns, mag I
-netizlng effect. OF q coll IL equal to the !
IDoduct Of the number Of turns In the !
coil and the current In these turns.
After machine is once constructed
the form Of the magnetic circuit, the
Kind OF material composing the mag
netic circuit and the number Of turns
in the different wfndings about thei
fields are ell fixed and constant in
value. The only way, then-neglect.
ing armature reaction, which will be
explain later-that the magnetic fIux !,
entering or leaving the armature at
the different poles may be changed
is by varying in value Of the current
in the field windings.
Assuming for convenience that the
lux to q pole Is measured
along the horizontal and pressure
along the vertical. II the magnetic
flux to a pole be changed, say decreas-
ed, then there will be a correspond
ing decrease in the pressure general.
ed for the different speeds as indicat-
ed by the dotted curve.
II the speed Of the machine be main.
tanned constant and the magnetic flux
per pole be increased, there will be an
increase in the electrical pressure in
the armature winding. as shown gra-
phically I'm Fig. 2, In which magnetic
flux is measured along the horizontal
and pressure along the vertical II the
speed of the machine be changed, say
then there will be CORE
spending decrease IN the pressure gen.
Grated, for the different values Of mag
netic flux per pole, as indicated by the
pressure.
The magnetic flux per pole does not
have definite relation to the current
in the field winding surrounding the,
pole, due to the fact that the perme-
ability of the iron forming the mag.
netic circuit Is not constant but de-
pends upon the degree to which IL is
You can think of the
OF the iron as being its
property to conduct magnetic flux as
to the ability Of air to con-
duct magnetic flux, which for conven-
fence is assured TO have q permeabil-
Ity of one. The relation between the
flux per role and the current
in the field winding is shown In Fig.
). 1t will be seen from an inspection
Of this curve that the magnetic flux at
first increases very rapidly, due to an
Increase in the value OF the field cur Il. /.
rent, but after the flux has reached a
value represented by the point A in the
curve the increase due TO an increase
IN field current IL decidedly less. When
The magnetic flux has reached the ,
value represented by the point A the
magnetic circuit is said TO be saturat-
ed, and above this point there is very
little increase In flux, even though
there be a large Increase in the field
current.
SeIf-Exeited shuut Generator
The connections of the selfexcited
;hunt generator, that is one supplying
It's own fled current, have been given.
When the armature starts TO rotate
here is one electrical pressure gener-
ated in its winding, due to the residual
magnetic flux in the magnetic circuit.
which produces current in the field
winding, and this current increases
he magnetic flux per pole. AS re-
suit Of both the speed and magnetic /,
lux increasing the generator pressure
increases more rapidly than If the ,
speed alone we're 70 increase. After
the magnetic slux has reached GER
tain value, however. the magnetic cir. {
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