Improved Means for Enabling Electric Arc Lamps to be Used Advantageously in Parallel Circuit with One Another or
Year: 1884

page_text: Improved Means for Enabling Electric Arc Lamps to be Used
Advantageously in Parallel Circuit with One Another or
JAMES EDWARD HENRY GORDON of 28 Collingham Place Kensington in the
County of Middlesex Electrical Engineer. do hereby declare the nature of my
Invention for "IMPROVED MEANS FOR ENABLING ELECTRIC ARO LAMPS TO BE
USED ADVANTAGEOUSLY IN PARALLEL CIRCUIT WITH ONE ANOTHER OR WITH
INCANDESCENT LAMPS" to be as follows:-
This Invention has for its object to provide improved means for enabling electric
are lamps to be used advantageously in parallel circuit with one another or with
incandescent lamps when they are fed with an alternating current.
For this purpose I interpose in each of the parallel branch circuits in which an
arc lamp is placed an inductive resistance coil whose true resistance is small and
which will allow without much waste a considerable current to pass through it
and through the lamp-but which has a large co efficient of self induction so that
if the resistance of the lamp be cut out as when the carbons of the lamp touch or
approach too close together the amount of current which can then pass will rapidly
reach a maximum of but moderate strength in excess of that previously required
for the lamp
Such an inductive resistance coil can be formed of an insulated conductor which
is of sufficient size not to in itself interpose much resistance to the passage of the
current and which is wound in adjacent coils around a core of soft iron. By
making the core of sufficient size and a suitable shape the resistance coil can be
adjusted so as to allow of the amount of current required for the lamp being passed
through it with but little loss but so as not to allow of the passage of a much
greater strength of current.
I am aware that when are lamps have been used in parallel circuit a non
inductive resistance of fine wire has in some cases been interposed in each of the
branch circuits. The advantage derived from the use of such resistances is
however but small I am also aware that in some electric arc lamps the current
passing to the carbons of the lamp has been passed through a solenoid coil which
has been used to control the distance apart of the carbons and that such solenoid
coil with its moveable iron core would to some extent act as an inductive resistance
CD 011

page_text: coil if the lamp were worked with an alternating current but the action of such
coils would be quite inadequate to effect my object whereas by the use of a
separate and independent inductive resistance coil of adequate dimensions I am
enabled very effectually to control the passage of the current to the lamp. For
example with an inductive coil which I have used and whose true resistance was
8 of an ohm and using an alternating current of 86 volts. E. M. F. the current
passed through the resistance and the lamp was 16 amperes-On short circuiting
the lamp the current only rose to 19 amperes whereas with a non inductive
resistance of 3 ohm it would have risen to 286 amperes.
The inductive resistance may be placed at the point where the branch to the arc
lamp leaves the main-in which case it acts instead of a fusible cut off in
preventing undue heating of the branch wires if a short circuit should take place.
This is an advantage as it is well known that fusible cut offs cannot conveniently
be used with arc lamps :-

page_text: I, JAMES EDWARD HENRY GORDON of 28 Collingham Place Kensington in the
County of Middlesex Electrical Engineer do hereby declare the nature of my
Invention for "IMPROVED MEANS FOR ENABLING ELECTRIC ARC LAMPS TO BE
USED ADVANTAGEOUSLY IN PARALLEL CIRCUIT WITH ONE ANOTHER OR WITH
INCANDESCENT LAMPS" and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement :-
This Invention has for its object to provide improved means for enabling electric
are lamps to be used advantageously in parallel circuit with one another or with
incandescent lamps, when they are fed with an alternately current.
For this purpose I interpose in each of the parallel branch circuits in which an
arc lamp is placed an inductive resistance coil whose true resistance is small and
which will allow without much waste a considerable current to pass through it and
through the lamp-but which has a large co-efficient of self induction so that if
the resistance of the lamp be cut out as when the carbons of the lamp touch or
approach too close together the amount of current which can then pass will
rapidly reach a maximum of but moderate strength in excess of that previously
required for the lamp.
Such an inductive resistance coil can be formed of an insulated conductor which
is of sufficient size not to in itself interpose much resistance to the passage of the.
current and which is wound in adjacent coils around a core of soft iron. By
making the core of sufficient size and a suitable shape the resistance coil can be
adjusted so as to allow of the amount of current required for the lamp being
passed through it with but little loss but so as not to allow of the passage of a
much greater strength of current.
I am aware that when are lamps have been used in parallel circuit a non
inductive resistance of fine wire has in some cases been interposed in each of the
branch circuits. The advantage derived from the use of such resistances is
however but small. I am also aware that in some electric are lamps the current
passing to the carbons of the lamps has been passed through a solenoid coil which
has been used to control the distance apart of the carbons and that such solenoid
coil with its moveable iron core would to some extent act as an inductive
resistance coil if the lamp were worked with alternating current but the action of
such coils would be quite inadequate to effect my object whereas by the use of a
separate and independent inductive resistance coil of adequate dimensions I am
enabled very effectually to control the passage of the current to the lamp. For
example with an inductive coil which I have used and whose true resistance was
3 of an ohm and using an alternating current of 86 volts. E. M. F. the current
passed through the resistance and the lamp was 16 amperes. On short circuiting
the lamp the current only rose to 19 amperes whereas with a non-inductive
resistance of 3 ohm it would have risen to 286 amperes.
The inductive resistance may be placed at the point where the branch to the
are lamp leaves the main in which case it acts instead of a fusible cut off in
preventing undue heating of the branch wires if a short circuit should take place.―
This is an advantage as it is well known that fusible cut offs cannot conveniently
be used with arc lamps.
In carrying out my Invention any coil of wire of sufficient size with an iron core
may be used as the inductive resistance subject only to the condition that the wire
is wound in a continuous spiral or spirals like the wire of an electro magnet and
not doubled back upon itself like the wire of an ordinary resistance coil.

page_text: Coils without iron cores if large enough will work in a certain degree but not
nearly so well as with iron cores as without an iron core much more wire is
required and therefore the proportion of the true to the inductive resistance is
greatly increased.
In case the wires for several lamps branch from one point care must be taken
not to put the inductive resistances close together. They should be 6 or 8 inches
apart at least. If close their mutual induction causes the lamps to flicker.
The shape of the coil should be such that for a given quantity of wire, that is
for a given true resistance the inductive resistance should be as great as possible
that is so that with the desired inductive resistance the quantity of wire and the
true resistance should be as small as possible.
Professor Clerk Maxwell has shown (see Maxwell's Electricity 2nd Ed. vol. II.
8,706 p. 316) that "the coil of maximum self induction." is a circular coil with the
wire wound in a channel of square section the mean diameter of the coil i.e. the
diameter at the centre of the wire channel being 3.7 times the side of the wire
channel.
I therefore preferably make my inductive resistances in the proportion and of
the form shown in the annexed Drawing although it is not absolutely essential
that they should be so formed.-The cast iron core a forms the bobbin on which
the coils of insulated wire b are wound. The core is hollow in the centre and is
slit to stop the circulation of currents in the iron. One of the flanges is made
with lugs extending from it to enable the coil to be fixed to a wall.
The inner sides of the square channel may be covered with a layer c of asbestos
to protect the wire from the heat generated in the iron. An inductive resistance
such as shown in the Drawing is of a size suitable for being used with arc lamps
fed with a current of a strength say from 15 to 20 amperes with 100 volts. on the
main.
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 claim is :-
First. The improved means herein before described for enabling electric aro
lamps to be used advantageously in parallel circuit with each other or with
incandescent lamps when fed by the alternating current consisting in inserting in
each branch going from the main to an arc lamp "an inductive resistance"
consisting of a coil of wire with an iron core so proportioned that the true
resistance is small and that the inductive resistance is small as long as the current
is of the moderate strength required for the arc lamp but in which the apparant
resistance will owing to self induction enormously increase if owing to the short
circuiting of the lamp or any other cause the current tries to increase above a
valve a little exceeding its proper amount.
Second. The use of such inductive resistances in branches leading to arc lamps
as a protection against over heating of the wires and instead of the fusible cut outs
more commonly used for that purpose.