Improvements in or relating to the Manufacture and Insulation of Electric Cables.
Year: 1894

page_text: Date of Application, 18th Sept., 1894
Complete Specification Left, 9th July, 1895-Accepted, 10th Aug., 1895
PROVISIONAL SPECIFICATION.
Improvements in or relating to the Manufacture and Insulation of
Electric Cables.
I, GEORGE HINDE NISBETT of Ashfield Huyton in the County of Lancaster,
Electrical Engineer, do hereby declare the nature of this invention to be as
follows:-
My invention relates to certain improvements in the construction and methods of
manufacture of electrical cables, whereby in those cables having a fibrous or other
insulating material, protected by a lead or other waterproof sheathing, the moisture
is extracted more thoroughly and quickly and the impregnation (if any) of the
fibre is carried out in such a way as to preclude the possibility of moisture being
taken up by the insulation after being dried. At the same time increased flexibility
of the insulation is secured and also a method of testing the lead or other sheathing
under pressure for the detection of any faults that may be present.
With these objects I proceed as follows:-
I take one or more strips of paper or other insulating material of suitable width
and wind it or them together spirally upon the conductor to be insulated, in such a
manner that a space is left between the sides of adjacent turns so forming a spiral
groove in the insulation from end to end of the conductor. I then take another or
some more strips of insulating material and wind it or them in the same manner
upon the strip or strips already in place, taking care however that the space between
the strips does not coincide in the two layers so as to leave the conductor bare in
any part. Any number of layers may be laid on in this way depending upon the
thickness of insulation required and upon the thickness and number of insulating
strip or strips applied at each operation. In some cases it may be desirable to have
the grooves or channels longitudinal these can be made by using longitudinal
covering strips lapping nearly round, by the insertion of porous tubes among the
conductors, or placing the conductors loose or zig-zagged in tubes.
When the layer
or layers of insulating material have reached the desired thickness a lead or other
waterproof sheathing is applied over the insulation. I then have one or more
spiral grooves or tunnels running through the insulation from end to end of the
cable which will allow of the cable being bent to sharp angles without' any damage
to the insulating material.
The grooves or tunnels may also be made by interposing between each layer or
every few layers of insulating material a number of strands of jute or hemp yarn or
other insulating material, and arranging them in such a way that a small space is
left between adjacent strands. I then cover the conductor so insulated with a
waterproof sheathing by any of the methods commonly in use. I thus have two or
more tunnels or grooves in the insulating material running from end to end of the
cable.
One end of the lead or other sheathing is then sealed up, and the other end is
attached to any suitable apparatus, preferably a pump, by means of which a more
or less perfect vacuum may be maintained in the tunnels or grooves already formed;
by which means the moisture is taken from the insulating material in the form of
vapour and so passes out through the pump or other device. The vacuum may be
applied to the cable for a longer or shorter period, as may be required, and during
its application the cable may be raised to any suitable temperature, or it may remain
at the ordinary temperature of the atmosphere.

page_text: The insulating material may also be dried by drawing dry and preferably hot air
through the tunnels provided as described above by means of a pump or other
device.
The insulation having been sufficiently dried as described, by means of suitable
cocks or valves, the vacuum or hot air is turned off and a quantity of heated oil or
other fluid insulating material is forced into the tunnels by means of a pump or
other arrangement, and the pressure of this fluid inside the cable is raised above
that of the atmosphere. Should there then be any small defect in the lead or other
sheathing, it will at once become evident by reason of the leakage of fluid therefrom.
The end of the cable formerly stopped is then unsealed and the fluid insulator is
allowed to flow out slightly at that end, thus making sure that all the tunnels are
completely filled with fluid from end to end of the cable. The whole cable is then
cooled down to make the insulating compound set solid or semi-solid (it being of a
suitable nature). The cable being thus far completed can be finished off externally
in any of the ordinary ways.
The method described above for the drying of the insulation after the cable has
been sheathed may be applied to any cables that have a space or tunnel or grooves
running the whole or part of the length of either the conductor or conductors, the
insulating material or the lead or other sheathing, or in those in which the sheathing
is put on to the insulation in such a way as to leave a space between the two. For
instance, it can be readily applied to the drying of the insulating material of those
telephone cables in which an air space is left between the conductor and the
insulation in order to obtain a low electrostatic capacity of the conductor.
Dated this 15th day of September 1894.
WM. P. THOMPSON & Co.,
Of 6 Lord Street, Liverpool, Patent Agents for the Applicant.
Improvements in or relating to the Manufacture and Insulation of
Electric Cables.
I, GEORGE HINDE NISBETT of Ashfield, Huyton in the County of Lancaster,
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 certain improvements in the construction and methods of
manufacture of electrical cables, whereby in those cables having a fibrous or other
insulating material, protected by a lead or other waterproof sheathing, the moisture
is extracted more thoroughly and quickly and the impregnation (if any) of the
fibre is carried out in such a way as to preclude the possibility of moisture being
taken up by the insulation after being dried. At the same time increased
flexibility of the insulation is secured and also a method of testing the lead or
other sheathing under pressure for the detection of any faults that may be
present.
For the better understanding of the invention I have appended the accompanying
drawings of a cable, in which,
and
Figure 1 shows the various parts laid bare successively down to the conductor,
Figure 2 is a transverse section.
In the construction of this and similar cables, I proceed as follows:-
I take one or more strips of paper B or other insulating material of suitable
width and wind it or them together spirally upon the conductor E to be insulated,
in such a manner that a space is left between the sides of adjacent turns so forming
a spiral groove in the insulation from end to end of the conductor. I then take
another or some more strips of insulating material C and wind it or them in the

page_text: :
same manner upon the strip or strips already in place, taking care however that.
the space between the strips does not coincide in the two layers so as to leave the
conductor bare in any part. Any number of layers may be laid on in this way
(three, B and C and D are shown) depending upon the thickness of insulation
required and upon the thickness and number of insulating strips applied at each
operation. In some cases it may be desirable to have the grooves or channels
longitudinal these can be made by using longitudinal covering strips lapping
nearly round or by making suitable spaces among or along the conductors, or by
placing the conductors loose or zig-zagged in tubes. When the layer or layers of
insulating material have reached the desired thickness a lead or other waterproof
sheathing is applied over the insulation. I then have one or more grooves or
tunnels running through the insulation from end to end of the cable which will
allow of the cable being bent to sharp angles without any damage to the insulating
material.
The grooves or tunnels may also be made by interposing between each layer or
every few layers of insulating material a number of strands of jute or hemp yarn.
or other insulating material, and arranging them in such a way that a small space.
is left between adjacent strands. I then cover the conductor so insulated with a
waterproof sheathing by any of the methods commonly in use. I thus have two or
more tunnels or grooves in the insulating material running from end to end of the
cable.
One end of the lead or other sheathing is then sealed up, and the other
end is attached to any suitable apparatus, preferably a pump, by means of which
a more or less perfect vacuum may be maintained in the tunnels or grooves
already formed; by which means the moisture is taken from the insulating material
in the form of vapour and so passes out through the pump or other device. The
vacuum may be applied to the cable for a longer or shorter period, as may be
required, and during its application the cable may be raised to any suitable
temperature, or it may remain at the ordinary temperature of the atmosphere.
The insulating material may also be dried by drawing dry and preferably hot
air through the tunnels provided as described above by means of a pump or other
device.
The insulation having been sufficiently dried as described, by means of suitable
cocks or valves, the vacuum or hot air is turned off and a quantity of heated oil or
other fluid insulating material is forced into the tunnels by means of a pump or
other arrangement, and the pressure of this fluid inside the cable is raised above
that of the atmosphere. Should there then be any small defect in the lead or
other sheathing, it will at once become evident by reason of the leakage of fluid
therefrom. The end of the cable formerly stopped is then unsealed and the fluid
insulator is allowed to flow out slightly at that end, thus making sure that all the
tunnels are completely filled with fluid from end to end of the cable. The whole
cable is then cooled down to make the insulating compound set solid or semi-solid
(it being of a suitable nature). The cable being thus far completed can be finished
off externally in any of the ordinary ways.
The method described above for the drying of the insulation after the cable has
been sheathed may be applied to any cables that have a space or tunnel or grooves
running the whole or part of the length of either the conductor or conductors, the
insulating material or the lead or other sheathing, or in those in which the sheathing
is put on to the insulation in such a way as to leave a space between the two.
instance, it can be readily applied to the drying of the insulating material of those
telephone cables in which an air space is left between the conductor and the
insulation in order to obtain a low electrostatic capacity of the conductor.
For
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. The improvement in the manufacture of electric cables, which consists in the

page_text: arrangement of the fibrous, porous or hygroscopic insulation with one, two or more
tunnels therein substantially as described in combination with a waterproof coating,
whereby the insulation can be thoroughly dried (and permeated with oil or other
insulating fluid through the tunnels and then hermetically sealed.
2. The process of drying the fibrous or porous insulation of a cable, which
consists in forming the cable with one or more tunnels running through or alongside
the insulation from end to end and forming more or less of a vacuum in such
tunnels or inducing or forcing a current of a drying fluid through the same
substantially as described.
3. The improvement in or relating to the insulation of an electric cable which
consists in forming it with one or more tunnels through its entire length, extracting
the moisture through the tunnel or tunnels, then filling the latter with oil or other
fluid insulated medium and sealing.
4. The method of testing an electric cable which consists in forming it with a
waterproof armour with a tunnel inside that armour and forcing in oil or other
suitable fluid at above atmospheric pressure substantially as described.
5. The arrangement and construction of electric cables substantially as described
and illustrated in the accompanying drawings.
Dated this 8th day of July 1895.
WM. P. THOMPSON & Co.,
Of Liverpool, Manchester, Birmingham, and London, Patent Agents.