Improvements in Safety Devices for Electrical Circuits.
Year: 1898

page_text: Date of Application, 9th June, 1898
Complete Specification Left. 31st Aug.. 1898-Accepted. 5th Nov., 1898
PROVISIONAL SPECIFICATION.
Improvements in Safety Devices for Electrical Circuits.
LOUIS JOHN STFRLE, Electrical Engineer, of 14, Clarendon Road, Holland
Park, London, W., in the County of Middlesex, do hereby declare the nature of
this invention to be as follows:-
When high tension currents of electricity are reduced, by means of trans-
formers, into low tension currents, there exists some danger of the high tension
current passing to the low tension circuit, should a fault exist in the system.
In such a case it is necessary that connection should be automatically made
between the low tension system and earth to enable the high tension current
to pass directly to earth. This is effected by this invention in the following
manner One pole of the low tension system is electrically connected to a piece
of metal (preferably of carbon on account of its non-fusing properties, and in the
form of a cylinder, or other shape oftering a convex surface) When I use a
cylinder I may use a tube or cover of insulating material in which an aperture 18
made round a portion of its periphery To the insulating tube or cover is fixed a
thin sheet some insulating material (preferably mica) of a predetermined thick-
ness in which perforations or slits are made allowing portions of the metal
cylinder at the back to be exposed at the place where the aperture exists in the
outer tube.
The sheet of thin insulating substance might also consist of suitable thickness
if some insulating varnish applied to the metallic piece, scraped away in places to
lay the metal bare
This thin insulation acts as a separation between the stretched metallic wire
or strip connected to earth and the metallic surface behind it, the aperture in the
outer insulating cap, acting as a guide for the wire or stamp The latter I prefer
to make in the form of a stirrup fixed at both ends to a metal piece for securing
to a pillar or terminal connected to earth The stirrup of wire will lie in the
aperture in the outer tube and will bear evenly and tightly over the slits or per-
forations in the thin sheet of insulating substance, or the connections may be
reversed, the stretched wire in this case being connected to one part of the
secondary circuit to be protected
If then, a fault exists in the system, and the high tension current passes to the
low tension circuit, a spark will be set up between the metallic surface and the
stretched wire, the latter will be fused and the act of so doing will release some
contrivance which will make substantial metallic connection between the secondary
low tension circuit and earth By thus employing a thin sheet of insulating
material of an accurately predetermined thickness for determining the distance
between the metallic piece and the wire or thin atrip, a great difficulty is avoided
of having to acourately readjust such distance between the two parts every time
the apparatus is set for action, in order to ensure that the spaiking shall take
place at a comparatively low tension, from 300 to 400 volts, the sparking gap
required for such a tension being only a few thousandths part of an inch.
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page_text: The apparatus may be arranged in a variety of ways for carrying out the said
invention.
The above arrangement can also be employed for arresting an electric current
of high potential, such as is induced in quickly breaking a circuit of high self
or mutual induction, the electromotive force in such a case being sometimes so
high as to break down insulation in the coils or in conductors and instruments
connected to the circuit For this purpose the metallic cylinder would be con-
nected to one terminal of the one circuit and the stretched wire to the other
terminal When the voltage has risen to a certain value sufficient to set up a
spark between the metallic surface and the stretched wire, the latter will be
fused and in the act of so doing will release a contrivance which will short-circuit
the terminals of the circuit to be protected and thus arrest any further rise of
potential.
The above device can obviously be applied for protecting life, or the circuit
itself, on which an undue rise of potential may take place.
DAL T
1000
Improvements in Safety Devices for Electrical Oircuits.
I, LOUIS JOHN STEELE, Electrical Engineer, residing at 14, Clarendon Road,
Holland Park, London, 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 :-
This invention relates to safety devices to be used in connection with electrical
circuits, and is an amplification of the invention described in the specifications of
Letters Patent No. 25344 of 1894 which were granted to me and one Walter Claude
Johnson jointly. In the cited patent a safety device is set forth which consists
of a conducting plate connected to the circuit to be protected, a fuse wire or strip
stretched over the said plate between a holding device and a terminal connected
with earth, and an insulating strip having a number of holes in it and which is
adapted to intervene between the stretched wire or strip and the said conducting
plate so as to distance the said wire and the plate's contact surface. In this
device the fuse wire or strip when "not blown" constitutes the element for holding
the catch which retains the contact piece, for putting the carcuit to earth, in an
off" position against the energy of a spring which operates the said contact
piece, and the conducting plate is carried by a means wholly independent of the
other parts of the safety device for keeping it, with the insulating layer between,
in tight contact with the said fuse wire; the primary means relied upon for
this last mentioned being a spring
56
The improvements according to this invention are such as to dispense with the
independent means for carrying and keeping the conducting plate and insulating
strip in contact with the wire, and also to considerably improve the working of
the safety device and render it more positive and reliable in being brought into
action; it being understood that the sparking range between the fuse wire or
strip and the conducting plate has to be accurately determined by the thickness of
the insulating strip or layer, hence the necessity of the said insulating strip
and contact plate being kept constant and stretched against the fuse wire.
26
According to this invention the conducting piece in the circuit to be protected
is carried either by the catch which retains the contact maker in an off" position
or by the contact maker itself, the first named for choice, and the fuse wire or
strip, which is connected to the circuit to be protected, 18 adapted to pass around

page_text: or loop itself onto the conducting piece, and constitute the means for retaining
the contact maker in an "off" position until the fuse wire has "blown" the said
fuse wie being tensioned and stretched around the said conducting piece and kept
in that state by a main spring or other means which operates the contact maker
when released
The improvements according to this invention are shown in the accompanying
sheet of drawings as applied to an earthing device for transformers and such like,
and will be hereinafter particularly described in connection therewith, but the
same is equally applicable to any device which may be arranged to intervene
between any primary and secondary circuit, and capable of being connected up
so that any abnormal current in the secondary circuit shall be passed back to the
primary circuit instead of to earth In the said sheet of drawing an earthing
device fitted with the improvements is shown in plan in Fig 1, parts thereof being
in section Fig. 2 is a vertical section through Fig 1 on the bioken line I, and
shows clearly the dispositions of the primary parts which hold the contact maker
in its "off" position and release it, whilst Figs 3, 4, 5, 6, and 7 show separately
the parts which are assembled in Fig 2
In the said figs, is the contact maker which is adapted to intervene between
a terminal connected to the cucuit to be protected and a terminal connected
with earth This contact maker is fitted with a strong spring m, whose tendency
18 to constitute it into an ordinary fly switch, and it, and also the terminals ca, c³,
are mounted and carried upon a non-conducting canier part a which forms the
base of the earthing device
The contact maker is held in an «
off" position
(as shown in Fig 1) so as to tension its operating spring m by the fuse wire g,
which is connected to the circuit to be protected. certain parts which will be
hereinafter fully described, a catch plate, 4, jointed to the carrier base a, and a
peg upon the contact maker c, intervening between the said wire and the
contact maker.
The fuse wire g 18 carried by a conducting plate q³, clamped onto a bracket, g',
connected electrically with the terminal, and is made in the form of a loop or
stirrup-bow shape, so as to indirectly fit around a conducting piece d (preferably
of carbon on account of its non-fusing properties) or zinc oi, a similar metal on
account of its non-arcing properties) which is carried upon a post, d³, standing
up from a plate, d³, integral with the catch, c, which engages the pog of the
contact maker This conducting piece d is shown in the drawings in the form of
a cylinder although it may be of a coned shape and is enclosed on covered by an
insulating cap, f, which has a part circumferential slit or cut-away part within
it; the said cap fitting over the conducting ovlinder and being carried by the
post,, so as to be removably fixed thereto The looped fuse wire g 18 adapted to
le within the slit or cut-away part, in the insulating cap, so that it may
surround the carbon cylinder d, but the said wire is not in actual contact with the
surface of the said cylinder at any point, as the part of the cylinder it surrounds
is sheathed with a thin layer of insulating material, e, having within it a numbei
of perforations or holes The looped fuse wne q fits over the insulating laver e,
(which is preferably of mica) and holds the said layer tightly to the periphery
of the carbon conducting piece, the tension put upon the sand wire through the
spring m, which operates the contact maker c, serving to accomplish this. The
surface of the conducting piece may be covered with a partly conducting sub-
stance such as tissue paper over which plumbago has been subbed to carry the
current better to the fuse wire or strip
A slot o' 18 formed in the plate y³ as an easy means for engaging the said plate
with the bracket ³, and also as a slight adjustment so as to keep the catch well
up to the peg of the contact maker, so that it shall communicate to the wire
the power of the spring The position of the plate 18 secured by the screw up
nut g, it being one of the features of this invention that a fuse wire) after having
been "blown can be easily replaced so as to again release the earth circuit and
pass the current again into the low tension circuit for use.
"

page_text: To set the earthing device (as shown in Fig 1) the contact maker is first made
to engage the catch, c, through its peg 5, the spring m being further put into tension
thereby. The catch is then, as it were, locked, so as to engage the peg, by
the looped fuse wire g holding the plate carrying the carbon cylinder, and
which is integial with it, in check by exerting a pulling in tendency upon it,
which always brings the nose of the catch in the path of the contact maker's peg
so long as the voltage in the low tension circuit is of a certain value, so that the
contact maker will be held in an "off" position and against a moving force by the
Baid fuse wire, but immediately a leakage occurs and an abnormal current passes
into the low tension circuit, a sparking will take place between the fuse wire and
the carbon cylinder at one of the points opposite the holes or piercings in the
insulating layer, and this will cause the said fuse we to be severed. This sever-
ing of the fuse wire frees the catch and releases the contact maker, which
immediately closes the earth encuit with the low tension one
The conducting piece d need not be a cylinder, it may be a segment only of a
cylinder, or it may take any other form which provides a convex surface so that
a looped fuse wire may bind itself evenly over its insulated surface, and instead
of the spring m of the contact maker being solely relied upon for keeping constant
the fuse wire to the surface of the insulating layer, a secondary spring may be
used in combination with the plate or the catch, whose tendency is to free
the catch from the contact maker
The insulating layer e 18 of an accurate predetermined thickness so as to adjust
the sparking distance between the fuse wire g and the conducting piece d, and it
will be obvious how necessary it 18 to keep the fuse wire constant against the
surface of the insulating layer when a sparking is deaned at a voltage from three
to four hundred, and the dimensions of the sparking gap is only a few thousandth
parts of an inch
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is:-
First In combination in a safety device for electrical circuits, a fly switch or
contact maker adapted when on to put a cucuit to be protected to earth or
to safety, a conducting piece having a semi-cucular on convex or coned surface
preferably covered with a fibrous part-conducting matraial and which is carried
either upon the said contact piece or a part adapted to engage it, and which said
conducting piece is connected to earth, a looped fuse wire or stip which is con-
nected to the circuit to be protected and which is adapted to be stretched indirectly
over the circular or convex surface of the conducting piece and to exert a pull
thereon so as to hold the contact piece in an "off" position and retain it until the
fuse wie is "blown" by an abnormal current, and a pierced insulating layer
which is adapted to interpose between the curved surface of the conducting
piece and that part of the fuse wire which surrounds it, substantially as described.
Second In combination in a safety device for electrical cucuits, a fly switch
or contact maker adapted when to put a protected circuit to earth or safety,
a catch such as arranged to engage the said fly switch and which may or may
not be fitted with an additional spring, a conducting piece d having a semi-circular
of convex or coned surface and which is carried by the said catch and connected
to earth, a looped fuse wire or strip g which is connected to the cucuit to be
protected and which is adapted to be stretched indirectly over the conducting piece
and to exert a pull thereon so as to hold the catch in engagement with the contact
piece until the blowing of the fuse wire, and a pierced insulating laver e which is
adapted to interpose between the curved surface of the conducting piece and that
part of the fuse wire which surrounds it, substantially as described and set forth.
Third In combination in a safety device for electrical circuits; a fly switch
or contact maker e adapted to connect the terminals c, c³, and being fitted with a
spring m, a catch which engages a part of the said contact maker, a conducting
"4
onl

page_text: cylinder or cone d attached to a part integral with the said catch, and which is
connected to the earth terminal ³, a pierced insulating layer adapted to surround
the said conducting cylinder or a part of it, a looped fuse wire g which is connected
to the terminal of the protected circuit and which 18 adapted to be stretched
from a bracket g³ over the pierced insulating layer surrounding the cylinder and
to exert a pull thereon so as to hold the catch in engagement with the contact
piece until the fuse wire "blows," and an insulating cap f having a cut-away
part within it, and which 18 adapted to fit over the conducting cylinder and
the insulating layer and to enclose them and protect them from damage, sub-
stantially as described and set forth in the sheet of drawings.
Fourth The particular construction arrangement and combination of the parts
forming the improved safety device as described and set forth with reference to
the figs. of the drawings
W P. THOMPSON & Co.,
11, Burlington Chambers, New Street, Birmingham,
Also of Laverpool, London, and Manchester,
Patent Agents for the Applicant.