Improvements relating to Electric-conductors.
Year: 1893

page_text: Date of Application, 26th May, 1893
Complete Specification Left, 26th Feb., 1894-Accepted, 28th Apr.,
1894
PROVISIONAL SPECIFICATION.
Improvements relating to Electric-conductors.
I, WILLIAM LEIGH DUDGEON, of 112, Fenchurch Street, in the City of
London, Engineer, do hereby declare the nature of this invention (a communication
to me by La Société Anonyme John Cockerill, of Seraing, Belgium, Engineers) to
be as follows:-
This invention relates to electric conductors for use in mines and other places
containing explosive gases where it is of great importance to guard against
sparking.
Sparks can, generally speaking, only be caused by complete or partial breakage
of the cables, for it is always possible to eo place commutators or incandescent
lamps as to prevent all possibility of communication between them and the explosive
medium.
According to this invention the electric conducting cables are divided into
sections joined together by means of couplings so constructed as to allow of the
disconnection or rupture of the small or secondary wire of the cable long before
the joint of the cable properly so called becomes broken. In the circuit of the
secondary wire and at the commencement of the conducting line to be protected
are placed in series two disconnecting electro-magnets and also a shunt, each
electro-magnet liberating its armature when the current no longer passes through
it, and the shunt interrupting the secondary circuit when its magnetism increases.
A fusible wire is interposed in the secondary wire in order to serve as a protection
against any abnormal current. The secondary wire can be put to earth in such a
manner that the earthing shall be made to indicate any leakage before the same
becomes dangerous.
The coupling is advantageously formed double, that is to say, with an interior
coupling which serves to connect the secondary wire, and an exterior coupling
which connects the cable properly so-called. The coupling is enclosed in an india-
rubber tube of suitable resistance, the ends of which are firmly bound to the
cable.
If a sufficient strain be applied to the cable to cause the coupling to give way,
the first part to become uncoupled will be the small internal or secondary wire as a
stretching of a few millimetres will be sufficient to part the two ends of the
internal coupling. If the strain causes a further stretching the two parts of the
coupling will completely separate from each other, but only after some time as
the outer coupling has a much greater length of contact than the inner one.
construction of the couplings can of course be varied according to the requirements
of each particular case, but the principle must always remain the same, that is the
secondary wire must always uncouple before the cable properly so-called.
Dated the 24th day of May 1893.
The
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.

page_text: CODILELE DI MUITICATION.
Improvements relating to Electric-conductors.
I, WILLIAM LEIGH DUDGEON, of 112, Fenchurch Street, in the City of
London, Engineer, do hereby declare the nature of this invention (a communication
to me by La Société Anonyme John Cockerill, of Seraing, Belgium, Engineers)
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 electric conductors for use in mines and other places
containing explosive gases where it is of great importance to guard against
sparking.
Sparks can, generally speaking, only be caused by complete or partial breakage
of the cables, for it is always possible to so place commutators or incandescent
lamps as to prevent all possibility of communication between them and the explosive
medium.
According to this invention the electric conducting cables are divided into
sections joined together by means of couplings so constructed as to allow of the
disconnection or rupture of the small or secondary wire of the cable long before
the joint of the conducting wires of the cable becomes broken. In the circuit of
the secondary wire and at the commencement of the conducting line to be protected
are placed in series two disconnecting electro-magnets and also a shunt, each
electro-magnet liberating its armature when the current no longer passes through
it, and the shunt interrupting the secondary circuit when its magnetism increases.
A fusible wire is interposed in the secondary wire in order to serve as a protection
against any abnormal current. The secondary wire can be put to earth in such a
manner that the earthing shall be made to indicate any leakage before the same
becomes dangerous.
The coupling is advantageously formed double, that is to say, with an interior
coupling which serves to connect the secondary wire, and an exterior coupling
which connects the conducting wires. The coupling is enclosed in an india-rubber
tube of suitable resistance, the ends of which are firmly bound to the cable.
To enable my invention to be fully understood I will describe the same by
reference to the accompanying drawing, in which
1
Figure 1 is a section of a cable such as I employ; and,
Figure 2 is a section of the coupling drawn to an enlarged scale:
Figures 3 and 4 are similar views of the two parts of the coupling separated:
Figure 5 is a diagram illustrating the arrangement of the circuits, the couplings
and the electro-magnets:
Figures 6 and 7 are diagrams illustrating the operation of my invention under
certain conditions hereinafter specified.
The cable comprises a series of conducting wires a, a and a single wire b
(hereinafter referred to as the secondary wire) the said wires being insulated and
enclosed in insulating and protecting material and finally surrounded by wires c in
the usual manner.
As hereinbefore stated the cable is made in sections and these sections are
advantageously connected by couplings such as d (Figure 2).
Each of these couplings has two parts e and shewn detached respectively in
Figures 3 and 4. The part e is in the form of a tube connected to the conducting
wires a, a and has within it at one end a socket 9 connected to the secondary
wire b but insulated from the said tube. The part of the coupling is also in the
form of a tube connected to the conducting wires a, a and adapted to fit into the
tube e, and the secondary wire is connected to a rod insulated from but projecting
beyond the end of the surrounding tube so that when the two parts of the coupling
are placed together, as shewn in Figure 2, the end of the rod h will enter the
socket g.

page_text: The coupling thus described is enclosed in an air-tight casing or envelope such
as an india-rubber tube i the ends of which are tightly bound to the cable. This
casing or envelope allows of regulating the resistance which the cable should offer
to strains and also acts as an insulator.
If a cable provided with a coupling constructed as hereinbefore described is
subjected to any undue strain the two parts e, f of the coupling will slip relatively
with one another, the first effect of which slipping will be to disconnect the rod /
from the socket g to break the circuit of the secondary wire without disturbing the
connection between the two tubes connected to the main conducting wires.
j, k are two electro-magnets which are arranged with their armatures j', in the
circuit of the main conducting wires a, a so that when the said armatures are not
attracted by their magnets the circuit through such conducting wires will be broken.
The said magnets are placed in such positions as to include between them that part
of a cable the sparking caused by the breakage of which might produce serious
results. The diagram, Figure 5, shews the magnets placed at the points of junction
of branch cables with main cables, the said branch cables being flow and return
cables each composed of three sections, the thick lines indicating the conducting
wires a and the thin lines the secondary wires b.
The circuits of the electro-magnets are as follows:-A branch from the wires a
of the positive cable passes through the electro-magnet j, then through a small
shunt (the purpose of which is hereinafter described) and thence to the secondary
wire of the negative cable. At its end most remote from the magnets the negative
cable has its secondary wire connected with the end of the secondary.wire of the
positive cable, which wire is connected to the electro-magnet which is also
connected to the conducting wires a, a of the negative cable.
At the end of the line of conductors the secondary wire is connected by a small
coupling m which contains a fusible wire » and the secondary wire is shewn
I would here
connected with the earth at o for purposes hereinafter described.
observe that the secondary wire of the two cables transmits currents of contrary
polarity.
If now the armatures j¹, k¹ of the electro-magnets are pressed to close the circuit
the current from the main cables will immediately pass through them, the current
also flowing to the magnet j, thence through the secondary wire of the cable, and
thence through the magnet k to the main conductor a, whereby the said magnets are
energized thus attracting the armatures and keeping the main circuit closed to.
supply currents to lamps or other apparatus in the circuit.
Suppose now that an accidental strain be exerted on the cable tending to break it,
the section on which this strain is exerted will immediately uncouple and as the
secondary wire will be the first uncoupled the current will be interrupted in the
circuit of the electro-magnet before the coupling itself has become entirely discon-
nected. As soon as the circuit of the electro-magnets is interrupted the armatures
nove to break the main circuit of the two cables so that if the two parts of
the coupling become completely detached no spark can be produced at the instant
of breakage as no current exists. It the accident has not rendered the coupling
unserviceable it will suffice to reunite the coupling and repair the india-rubber
envelope; the current must be re-established by hand, which is done by pressing
the two armatures of the electro-magnets.
It is obvious that a cable may be damaged in other ways than by longitudinal
strains; it might for instance be crushed or even cut and sparks be produced
thereby.
I will describe by reference to Figure 6 how crushing will shut off the current.
The crushing of the cable or other similar accident will naturally have the effect
of causing contact between the secondary wire b and the wires a, the result of
which is that the whole of the current will pass through the secondary wire and
short circuit the portion of the cable beyond the fault. Suppose this short circuiting
to take place at p (Figure 6) for instance, the current after flowing through the
wires a of the positive cable as far as the fault will return through the secondary

page_text: wire to the magnet and thence flow to the wires a of the negative cable, the
result of which is that the magnet, will receive no current. The armature of the
electro-magnet; will therefore be released and the current interrupted. If the short
circuiting had taken place on the negative cable the result would have been naturally
the same but in this case the electro-magnet k would have severed the current.
Suppose short circuiting to take place on both cables simultaneously (although
this is highly improbable) the cable is still protected. It will be understood by
reference to Figure 7 that each of the electro-magnets j, k traversed by a current
of about double the power of that by which they are ordinarily energized will,
instead of releasing their armatures retain them with greater force. To obviate
this the small shunt 7 (Figure 5) is provided. Under normal conditions this small
shunt retains the secondary circuit closed. When, however, the magnetism of its
coil is increased it attracts its armature and interrupts the current in the secondary
wire whereby the magnets, & are deprived of current and so release their armatures
to break the main circuit. The secondary wire is protected by the fusible wire n,
hereinbefore referred to, against currents of abnormal strength.
In order to indicate any leakage from the cable before such leakage becomes
dangerous, the secondary wire is put to earth as shewn at o, Figure 5, and the two
electro-magnets j, being in series on a shunt cicunt are placed under the same
conditions as the well known earth indicators; if therefore a leak were to take
place in the cable, the corresponding electro-magnet would disconnect its armature
and the current would be stopped.
It may
be well to add that the two electro-magnets j, k and the small shunt / are
placed in a hermetically closed metal box so that all communication between the
magnets and the air in the place to be protected is entirely prevented.
It is to be understood that I do not confine myself to the construction of the
couplings as hereinbefore described, as such may be varied according to the
requirements of each particular case, but the principle must remain the same, that
IS, the secondary wire must always uncouple before the cable properly so-called. Or,
instead of using a coupling, the ends of each section might be bound together by
means of wire wound spirally like a spring, the secondary wire being on the
contrary continuous and of smaller diameter at the junction. Under any strain
to which the cable may be put the secondary wire will then break whilst the
conducting wires would simply stretch.
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 :-
1. An electric conducting cable of the kind shewn in Figure 1 made in sections
jointed by means of couplings of suitable construction so as to allow of the disjunction
of the small or secondary wire of the cable before the conducting wires become
uncoupled, substantially as described.
2. The arrangement in the circuit of the secondary wire and at the point where
the conducting line enters an area to be protected, of two disconnecting electro-
magnets and a shunt, each electro-magnet liberating its armature when the current
no longer passes through it, and the shunt interrupting the secondary circuit when
its magnetism increases, substantially as described.
3. The combination with an electric cable having a secondary wire and electro-
magnets and a shunt in circuit as bereinbefore described of a fusible wire and an
earth connection substantially as, and for the purposes, described.
Dated this 26th day of February 1894
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.