Improvements in Electric Arc Lamps.
Year: 1897

page_text: Date of Application, 24th Aug., 1897-Accepted, 2nd Oct., 1897
Improvements in Electric Arc Lamps.
I, THOMAS SPENCER, residing at 2219 Green Street, in the City and County of
Philadelphia, and State of Pennsylvania, United States of America, Electrical
Engineer, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by
the following statement:-
It has hitherto been impossible to produce a commercially successful enclosed
arc light by means of an alternating electric current passed between opposed solid
carbon-electrodes.
An arc so maintained, frequently breaks or goes out in consonance with minute
variations of the electro motive force of the arc. The light thus produced is,
therefore commercially valueless by reason of its lack of uniformity.
It is true that a commercial alternating arc light may be produced by the use
of cored carbon electrodes. It is, however, impracticable to enclose such an arc,
for the reason that an opaque film of impurities from the core is rapidly deposited
upon the inner surface of the transparent enclosure of said arc and its effective
luminosity thereby at once diminished.
It is the object of my present invention to automatically regulate the alternating
current supplied to an enclosed are between solid carbon electrodes, from instant
to instant, in exact accordance with the fluctuation of electro motive force at said
arc, and thus counterbalance the latter, with the resulting production, at said
arc, of a light that is steady, or without apparent fluctuations in luminosity.
To this end my invention broadly speaking, consists in providing in electric
circuit with each individual arc, a choking coil capable of automatic variation as
to its magnetic field and consequent variation in its self-induction,-together with
means whereby the space between the solid carbon electrodes of the arc may be
varied; said variations being occasioned by and being corrective of, variations
from the normal condition or relation of the supply of current to the individual
arc with which said coil co-operates.
The variations of electro motive force resulting from the physical approach or
recession of the solid carbon-electrodes do not interfere with the corrective effect
of the variations in current supply occasioned by the aforesaid variations in the
magnetic field and self-induction of the choking coil, but, upon the contrary, both
means of regulation are inter-dependent and supplemental of each other.
By the term "choking-coil" herein employed, is meant a coiled electric con-
ductor, which, in addition to the mere ohmic resistance and self-induction
inherent in all conductors of electricity, but contingent upon the character, dis-
position, etc., of the particular conductor of which said coil is composite, is
provided with material of high magnetic permeability inserted within the field of
force of said coil, the static co-efficient of self-induction of said coil being
augmented by the work done in its magnetic field.
I am aware that coils of the foregoing general character have hitherto been
used in the distribution of alternating currents of electricity, and I, therefore, do
not claim broadly upon the use of such coils, but only the use of choking coils of
the peculiar character, and in the manner and relation herein definitely specified.
"

page_text: In the drawing, Figure 1 is a diagram of my invention applied to an arc
lamp, comprising enclosed solid carbon electrodes.
Figure 2 is a primary form of my invention' shown in Figure 1, the means for
automatically effecting the relative movement of the solid carbon electrodes being
omitted.
In Figure 1, A is an electric generator, and a, a, the conductors connecting said
generator with a lamp structure B.
C; C¹, are 'the carbon electrodes, and D the transparent' globe, or case, enclosing
them.
In circuit with the electrodes C, C, is a choking coil E, comprising the hollow
coiled conductor e, surrounded by material e of high magnetic permeability, pre-
ferably soft iron, built up in laminations, or comprising closed circuits of wire.
Within the hollow of the coil E, is a core F, also preferably of soft iron.
The core F is adapted for reciprocation within the coil E, and is suitably con-
nected with the electrode C, so that the latter partakes of the reciprocatory
movement of the core F.
The device illustrated in Figure 1 is so proportioned that, under normal con-
ditions, the parts stand in the position indicated in said figure."
!
"
An increase of electro motive force at the arc, between said electrodes C, C¹,
results in diminishing the total current passing through the entire device.. The
core F, being only maintained at its normal height by the magnetic effect of a
normal current, the diminution of current causes the core to descend, and thereby
restores the electrical equilibrium of the device, in a two-fold manner: First, the
change in the magnetic field of the coil by reason of the descent of its magnetic
core F, decreases the self induction of said coil, thus giving passage to a larger
current than the normal current; Second, the electro motive force at the arc is
reduced by the physical approach of the electrode C to the electrode C¹.
If the electro motive force at the arc between the solid carbon electrodes C C¹,
is decreased below the normal, the reverse of the above described action takes
place, the core F, being then. raised by the increase of current through the entire
device.
The variation in the magnetic field of the coil E, thus produced, increases the
self induction of the coil, and the choking action of the coil E, thus augmented,
reduces the supply of current.
This regulating action is of course supplemented by the simultaneous increase in
the arc space between the electrodes C and C¹, which augments the normal electro
motive force of the arc.
During the operation of the lamp the core F is almost constantly in motion.
I have omitted from the drawing the details of the ordinary lamp structure,
but have indicated in dotted lines in Figure 1, at G, a hinged clutch connective
of said core F and the electrode C.
This clutch engages the electrode C by means of an aperture in it through which
the electrode is passed. The clutch G, moreover, maintains the electrode C in
fixed relation with the core F while the aperture in said clutch is inclined with
relation to said core.
When, however, in the downward movement of the core and electrode, the clutch
is swung toward the core by contact with the fixed stop g, the electrode C is
released and dropped a short distance through said clutch before being again
gripped.
The feeding action of the carbon electrode described in the foregoing paragraph
may be effected by means of any suitable mechanism, but the form of said
mechanism is not of the essence of the invention.
In Figure 2, I have shown, a primary form of my invention, which differs from
the device of Figure 1 in that the means for regulating the lamp by the physical
approach and recession of the solid carbon electrodes is omitted, the regulation
of the lamp being entirely effected by means of the choking coil E, which operates
in the manner described in relation to Figure 1.

page_text: The core F may be provided with an auxiliary balance spring, opposed to the
sucking action of the coil E, or, as indicated in Figure 2, said core F may be
provided with a supplemental weight f.
I am aware that attempts have been made to maintain a constant luminosity
in an alternating current arc by means of an automatically variable ohmic resistance
in electric circuit with said arc.
It is well known, however, that such regulation of a lamp operated by an
alternating electric current, is of small value, in that it requires such a period of
time for each regulating action of the device as to be visibly manifest in the
fluctuation of luminosity of the arc. I have found that the regulation of a similar
arc by means of a choking coil of the peculiar character and operation herein set
forth, is accomplished with such rapidity as to eliminate said fluctuations in the
luminosity of the arc..
According to the commonly accepted theory, choking coils occasion a lag in
the place of the alternating electro motive force, presented at their terminals, and
thus limit the passage of the alternating current through them. The restricting
or choking effect of such a coil upon the electric current differs from the effect of
a coil having mere ohmic resistance, in that, within limits determined by the
proportions of the choking coil, a greater alteration in the voltage of a current
passing through said coil results from a given alteration in the current, than if
said current met with the mere ohmic resistance.
It is therefore possible, by the use of choking coils having automatically variable
self induction, to more rapidly correct the abnormal variations of electro motive
force, which arise in an alternating arc lamp, than if an automatically variable
ohmic resistance were provided.
By the use of the herein described system of regulation, with a current the
maximum voltage of which is 100, I find it possible to maintain an enclosed alter-
nating are of constant luminosity, between ordinary one-half inch solid carbon
electrodes. The average current at said are being eighty volts and six amperes.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what I
clain is:
In combination, in an enclosed arc lamp adapted to be operated by an alternating
current, opposed solid carbon electrodes, an enclosure for the proximal ends of
said electrodes, a choking coil in electric circuit with said electrodes, an auto-
matically movable core for said choking coil, and means connective of said core
and one of said electrodes, whereby a reciprocatory movement of said core may be
imparted to said electrode,-substantially as set forth.
Dated this 17th day of July, A.D. 189;.
Witnesses:
FREDERIC NORMAN DIXON.
THOMAS KEYS LANCASTER.
THOMAS SPENCER.