Improvements in Alternating Current Arc Lamps.
Year: 1895

page_text: Date of Application, 30th July, 1895-Accerted, 15th Feb., 1896
COMPLETE SPECIFICATION.
Improvements in Alternating Current Arc Lamps.
I, JAMES DEVONSHIRE, Secretary to The British Thomson-Houston, Limited,
of 38, Parliament Street, Westminster, in the County of Middlesex, (a communica-
tion to me from abroad from Charles E. Harthan, of Lyun, in the County of
Essex, State of Massachusetts, 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:-
My invention relates to electric are lamps and has for its object to provide a
lamp in which some of the difficulties attendant upon alternating current lamps as
generally constructed may be obviated and their efficiency increased.
In the operation of alternating current arc lamps upon constant potential
circuits, it is necessary to use a comparatively fine and soft quality of carbon, in
order that the arc may start easily and may also be maintained during the normal
running of the lamp. A hard carbon will not ordinarily give sufficient gas or
vaporized carbon in the arc to maintain it with certainty.
It has therefore now
become the custom to use so-called "cored" carbons, that is, carbons having an
inner core composed of a material softer and more easily volatilized than the other
part of the electrode. The use of such carbons in alternating arc lamps, on a
constant potential circuit leads, however, to the following difficulty: When the
lamp is started into operation with a new carbon, the soft inner core extending
to the tip of the electrode is quickly volatilized and produces a large amount of
hot and highly conducting carbon vapour, thus largely reducing the resistance of
the arc.
In lamps which are regulated solely by the action of the series coil, the
core is drawn up to lengthen the are; but notwithstanding this the resistance on
starting a lamp not provided with the improvements of this invention is still so low
even when the series magnet has lifted the core, that an abnormally heavy current
flows and a so-called "flaming" are is produced. When, therefore, a number of
such lamps are turned on simultaneously, the heavy demand for current overloads
the dynamo, and the lamps may be unable to start normally at all.
The same condition of overload may be brought about in case the lamps have
been burning for a while or until the softer interior carbon has been burned back
from the point of the electrode. The carbons are then cold, when the lamps are
brought into operation, and there is not enough hot conducting vapour to maintain
the arc formed when the series coil attracts its core. When the arc is thus
extinguished the carbons fall together, and this action is repeated very rapidly
giving rise to an annoying flickering or vibration which continues until the carbon
points have been sufficiently heated to reduce the resistance of the arc; but this
vibration operates the feeding mechanism of the lamp, and in consequence when
the arc staits it is much too short even in the extreme attracted position of the
core. The resistance being thus cut down, the same condition of overload is
produced at the station. It is not sufficient to overcome this difficulty to give the
solenoid core an exceptional traverse, because the lifting of the upper carbon and
its release occurring only at the extreme position of the core, a long traverse acts
to diminish the sensitiveness of the feed and therefore considerable current variation
occurs before the regulation of the arc length.
The present invention aims to obviate these objections, and enables me to start
lamps under all conditions with either their normal current or with current less

page_text: than the normal, which gradually rises to the normal current. This is precisely
the opposite of what takes place in commercial alternating lamps at the present
time, upon which this invention is founded, wherein the lamp starts at an abnormally
heavy current and gradually comes down to a normal. To illustrate specifically, a
thirteen ampere, thirty volt lamp may be started, if constructed in accordance with
my present improvements, with as small a current as six or eight amperes,
gradually running up to its full current of thirteen amperes, and upon a slight
decrease of the current, feeding the carbons together; without these improvements,
the current at starting may easily run up to twenty-two amperes, an increase of
over fifty per cent. Where a circuit has a number of lamps in operation and these
are required to be started simultaneously, this leads to the difficulties already
pointed out.
My invention overcomes these difficulties and attains the ends just described by
applying to the solenoid core a spring operating to assist the core in its rise and so
arranged that when the core is at its lowest or unattracted position, the spring is
least effective, and gradually becomes increasingly effective as the core is attracted
into the coil and, consequently, as the attractive force in the coil becomes less
and less.
I have called this action of the spring "progressive," aud where that word
occurs in this Specification, it is intended to have the significance just pointed out.
The lifting power of the series magnet, while sufficient throughout a certain
range, is not, without the spring, easily made sufficient through such a range as is
required to separate the carbons at the start, when the core is down to the end of
the carbon and the resistance of the arc, therefore, is abnormally low. The spring
acting under an increasing leverage serves two purposes. It tends in any position
in which the core may be to assist the uplifting power of the core, and in the
higher positions of the core has an effect which increases this lifting power, and
thereby gives the core the power to lift even though its magnetic effect may have
fallen off.
The addition of an assisting spring of uniform pull throughout its entire range of
movement will render possible a less number of ampere turns in the series coil, by
decreasing the work it has to do, but it does not change the length of traverse.
The introduction of the assisting spring, the power of which increases as much as,
or more rapidly than, the pull upon the solenoid core decreases, not only
accomplishes the same purpose, but also increases the possible length of traverse,
notwithstanding the fact that the pull on the core due to the magnet alone becomes
less and less as the core rises. The lamp herein described is thus able to diaw a
very long are, if it be necessary to do this in order to cut down the current, but its
normal regulation is accomplished with a very small change in the current
strength. In lamps containing this invention, furthermore, it is not necessary to
employ a resistance in the lamp circuit as has heretofore been necessary with
constant potential alternating arc lamps, and thereby a very considerable gain in
efficiency is secured. With the assisting spring present, the arc is drawn to an
al normal length and thus prevents the extraordinary flow of current when the
lamp is starting up with new carbons, due to the large amount of conducting
vapour, as already explained. The difficulty heretofore has been that the pull of
the solenoid upon its core has not been powerful enough throughout its entire range
of movement. It is amply sufficient in the lower position of the core, but too weak
in its upper position.
The accompanying drawings show embodiments of the invention.
Therein Fig. 1 is a side elevatiou, partly broken away and partly diagrammatic,
of my improved lamp;
Figs. 2, 3, and 3* are details ;
Figs. 4, 5 and 6 are modifications.
The construction of the lamp outside of the particular improvements herein
detailed and forming no part of my present invention is described in my previous
Lotions Patent No 12388 of 11th Jul 1905
V Hies and 24 is the vibrating

page_text: frame supporting or carrying the wheelwork, it is pivotted at P to the main
supporting frame B of the apparatus, and is rotatable about this pivot, being
carried in one direction by the weight of the parts and in the other by the
attraction of the solenoid C and the assisting spring Z which is connected at its
forward end to the frame V through the plate F and the pin and slot
connection I, S, illustrated to the right hand of Fig. 2. The shape of the plate F
is best seen in Figs. 2, 3 and 34, where my improvement is shown removed from
the other parts of the lamp. The said plate F is pivotted on knife edges at P' on
supports H, H, and is bent down at a right angle and provided with a slot S
engaging a pin I upon the gear-supporting pivotted frame V to which the core K
is connected. The support H is a fixed brass plate fastened at P, p, to the main
supporting frame B of the apparatus, and H₁ is a bent supporting arm thereof.
One end of the spring Z is attached in any convenient way to the outer end of the
plate F at a point O, and its other end as shown in Figs. 2, 3 and 34 is connected
to a screwed rod a' passing through fixed abutment a and provided with adjusting
nut a³. The plate F may be turned to the position shown in dotted lines
at F, Fig. 2, and may then be slipped out or in through the slots shown at its
bearings.
When the solenoid core K is in its lowest or unattracted position, the spring Z
is least effective in lifting the weight of the moving parts, because it occupies the
position of the lower dotted line d, Fig. 2, and is pulling nearly in line with the
pivot P, or on a centre, as commonly said; but as the core K is attracted, and
the power of the coil in lifting the weight of the moving parts decreases, the
spring Z gradually takes the position shown in full lines, and becomes therefore
increasingly effective. The strength of the spring Z is made such, and its point of
attachment to the frame so arranged as to make the assisting force just the amount
desired. That adjustment is of course made which tends to bring about and
maintain the normal resistance of the arc, or value of current. By thus decreasing
the effective lifting power of the solenoid core in its lowest position and supplying
an assisting force as it is attracted, it is possible to start the arc with much less
than the normal current, as already pointed out, the current gradually rising until
it attains the normal; or, if so desired, by proper adjustment the lamp will start
with very nearly its normal current and regulate itself to maintain it.
Referring now to Figs. 4, 5 and 6, I show how my invention may be modified by
various attachments of the spring Z and yet secure the same results of operation.
In Fig. 4 the spring exerts an increasing force as it approaches the position of the
dotted line, being carried by a bell-crank lever G, and attached at h to the frame
of the lamp and at the other end by its adjusting arrangements a, a', a³, to the
arm A of the bell-crank G. It will be seen that the lift of the core K tends to
throw the spring away from the centre h against which it pulls, thus assisting the
core in its rise, as already pointed out.
In Fig. 5, one end of the spring Z is attached to any stationary point, for
instance, at h on the stationary arm X, and the other end is attached to the lever Q
to which the solenoid core is elastically connected, for example as by a spring k, as
in the Letters Patent No. 13388 of A.D. 1895 herein before referred to. In this
case the spring Z is brought to the position of the dotted line Z', and, as will be
readily understood, becomes increasingly effective.
In Fig. 6, both ends of the spring Z are attached to moving parts, one end
going to the end of the lever L. the other to the end of the lever L. The lever L
is pivotted at P³ and the lever L' at P, and they have a slotted connection at L*.
When the core K is attracted into the solenoid coil, the free ends of both
levers L, L' move down and the spring Z is given an increasing leverage, becoming
more and more effective, it being understood that the effect of the increasing
leverage is so arranged as to more than counterbalance any decrease in the power
of the spring due to its contraction.
In Figs. 4 and 5 I have indicated the springs Z' assisting to support or balance
the weight of the solenoid core K and so forth, as in my application already

page_text: referred to; these form no part of the present invention, being merely auxiliary in
their action, so far as my present improvement is concerned. In the arrangement
shown in Fig. 1, they may be dispensed with, and the spring Z made to serve
alone, if desired.
So far as I am aware, it is new to apply a spring progressively assisting the
action of the actuating magnet in an arc lamp; and the claims now to be made
are to be construed broadly in this respect.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The method of operating an arc lamp, which consists in progressively assisting
the action of the magnet core, substantially as described.
2. The method of operating an arc lamp, which consists in mechanically assisting
the action of the magnet core or armature and in graduating such assistance so that
its amount is a minimum at one end of the traverse of the core, and a maximum at
the other end of the traverse of the core, substantially as set out and described
herein.
3. In an arc lamp, a coil, a core actuated by the coil, feeding mechanism for the
lamp operated or controlled by the core, and a spring arranged to progressively
assist the action of the core, substantially as described.
4. In an are lamp, a coil, a core actuated thereby, feeding and arc-striking
mechanism operated or controlled by the core, and a spring arranged to
progressively assist the motion of the core, substantially as described.
5. In an alternating current are lamp, the combination of the carbons and
feeding mechanism with a magnet receiving alternating currents whose core
controls the feeding mechanism, and a spring arranged to progressively assist the
movement of the core as set forth.
6. In an electric arc lamp, a series coil, a core actuated thereby, gearing for the
lamp controlled by the core of the coil, a spring attached at one end to
the stationary part of the lamp and at the other by suitable connections to the
core, the spring being so arranged as to assist the lift of the core to a minimum
amount at one end of the traverse, and a maximum amount when the core is in its
extreme attracted position, substantially as described.
7. In an electric arc lamp, a series coil, a core therefor, gearing carried in a
frame pivoted in the lamp, one end of the frame being attached to the core,
a spring attached to a stationary part of the frame, and a plate forming with the
part of the frame to which the spring is attached a toggle mechanism, the spring
being attached at its other end to the plate; whereby the lift of the core tends to
bring the spring into a position where its pull will assist the core more and more as
the core rises, substantially as set out herein.
8. In an electric arc lamp, a coil, a core actuated thereby, mechanism operating
the lamp actuated by the coil, a spring arranged to assist the coil, as herein set
out, the spring being attached at one end to a stationary part of the lamp and at
its other to a lever connected to the core, and adapted by the motion of the core to
bring the spring into a position of greater activity in assisting its action, substan-
tially as described.
Dated this 30th day of July 1895