Improvements in Insulated Electric Conductors.
Year: 1891

page_text: te of Application, 19th May, 1891-Accepted, 4th July, 1891
COMPLETE SPECIFICATION.
Improvements in Insulated Electric Conductors.
A communication from abroad by JAMES B. WILLIAMS, M.D., of Oakland, in the
County of Alameda and State of California, United States of America.
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E. of the Agency for
Foreign Patent Solicitors, 6 Lord Street, Liverpool and 6 Bank Street,
Manchester, both in the County of Lancaster, & 323 High Holborn, in the County.
of Middlesex, Civil 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 :-
The object of this invention is to produce an insulated electric conductor which
shall have a higher insulation resistance and a lower electrostatic capacity than
insulated conductors made in the manner now usually employed, that is, by placing
the dielectric in direct contact with the conductor, or in contact with a layer of
fibrous material closely wrapped around the conductor, the size of the conductor,
the thickness of the dielectric and the kind of material used, and the conditions of
use being the same in both cases. The novelty of the invention consists primarily
in interposing isolated or non-communicating air spaces between the dielectric and
the conductor, by means of what may be called a "separating" device, whereby the
efficiency of the insulation is materially increased.
In the drawings, in which the same letters refer to the same parts in all of the
figures:
Figure 1 is a perspective view of a chosen form of the invention showing the
conductor surrounded by the separating device in the form of a cylindrical
covering provided with embossed annular projections and ready for the application
of the dielectric :-
Figure 2 is a longitudinal section of the same after the dielectric and its exterior
covering. have been applied and showing the hollow spaces under the raised portions
of the separating device (when it is not made solid originally) filled with suitable
reinforcing material;
Figure 3 is a similar view of the same showing the separating device made solid
and an intermediate covering placed between the separating device and the
dielectric, and
Figure 4 is a similar view of the conductor provided with the separating device
in the form of rings.
In these:-
W represents the central metallic conductor. It is shown in cylindrical form,
and it may be single, stranded, or tubular, but it should be substantially circular in
cross section. C represents the intermediate covering or separating device placed
around the conductor W and between it and the insulating layer or dielectric 1.
Its purposes are:-
1. To prevent the insulating layer from coming in direct contact with the
conductor,
2. To form non-communicating or isolated air space between the dielectric and
the conductor,
3. To support the insulating layer and keep it substantially concentric with the
conductor, and
4. To furnish comparatively few paths by which the electric current can escape
from the conductor..
This covering or separating device may consist of any suitable material, possessing
insulating properties, and which remains elastic and more or less flexible under
ordinary conditions of manufacture and use. By. the terms elastic and more
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is
or less flexible" is meant that, if the insulated conductor is to be kept comparatively
straight during its manufacture, placing and use, the materials need to be elastic
only and possess only a very slight degree of flexibility; but if it is to be bent
under these conditions, the degree of flexibility required will be greater and
sufficient to prevent buckling or rupture. By the terin ordinary conditions
meant such conditions as insulated conductors of the class herein described would
naturally be subjected to by an intelligent and skilled workmau; for instance, that
the insulated electric conductor during the manufacture, placing and use thereof,
should be kept as straight as possible, and that, if bent or coiled, the curves should
be large.
I' is the insulating layer, or dielectric, surrounding the separating device C and
which touches only the outer portions thereof. It is made sufficiently stiff to
prevent its collapsing under usual conditions. L is a waterproof protecting
covering, and applied over the dielectric in the usual manner, and usually made of
lead, and F is a further covering composed of fibrous material saturated with a
waterproof compound and placed outside of the covering L, when its use is deemed
desirable.
The separating device C shown in the drawings consists of a cylinder e provided
with embossed annular projections c which, when the device is placed in position, are
each continuous and form a structure consisting of connecting rings substantially
paraliel with each other and at right angles to the axis of the conductor in which
they have a common centre and the outermost surfaces of which are substantially
equidistant therefrom and form with the dielectric isolated air spaces A. In
Figure 4 of the drawings is illustrated a modification of this form of the device in
which is omitted the portion of the cylindrical shell shown in the other figures
and the device is made of independent rings R suitably prepared and placed on the
conductor at intervals.
In Figure 2 is shown the means employed for reinforcing and strengthening the
raised portions of the separating device when there are hollows underneath them so
that they may be better adapted to resist external pressure, and which consists in
filling these hollows with some plastic material which becomes hard in course of
time. In using such a filling, care must be taken that it does not destroy, or
seriously impair, the primary functions of the separating device. In cases where
the dielectric used is composed of soft materials, a cylindrical air tight shell, or
support is used, illustrated in Figure 3 and placed between the separating device
and the dielectric to serve as a support for the latter.
It is obvious that the separating device may be made of widely different materials,
and the particular kind employed in each instance is largely a matter of selection
for the skilled workman. It is made preferably of some thick fibrous material such
as paper which can be made to possess insulating properties by saturating it with
an insulating varnish such as good Japan dryer containing a large quantity of
shellac, and which can be formed, while hot, into the desired shape and which will
retain its shape when cold or under ordinary conditions. If the material employed
be not itself sufficiently rigid to resist the usual conditions of external pressure, it
may be reinforced as above suggested. The same end may be effected by
thickening the covering or by adding and securing external strips thereto by cement
or otherwise. But however it is formed,.it should be made, wherever it touches the
exterior surface of the conductor, to closely adhere thereto by a cement suitable to
the conditions of its manufacture and use, for instance, shellac dissolved in alcohol,
and should so support the insulating layer, or dielectric, that it will not come in
contact with the conductor.
If it be made of separate pieces afterwards united, their edges should be closely
cemented and the points of contact between it and the dielectric should be as few
in number as possible. By making the air spaces, A, non-communicating, the
admission of moisture or other objectionable matter is, in its deleterious effects,
confined to.a. minimum, because such matter is confined to a limited space and
cannot materially affect the conductor as a whole. Equivalents of the intermediate

page_text: covering or separating device will readily occur to the minds of persons skilled in
the art, and it is obvious that, in this respect, wide modifications may be made in
detail without departing from the essential features of the invention.
The insulating layer, or dielectric I, consists either of a single layer, or of two or
more single layers united to form one general layer, composed of any well known
insulating material suitable for use in this connection. Under some conditions of
use, the dielectric may be separately formed in tubes, and the conductor, already
provided with the centering device, placed within the same.
Under many conditions of use, it is desirable that the insulated conductor should
be further protected; and, to effect this purpose, a waterproof protecting covering,
which is usually made of lead, is applied over the dielectric, and, when this material
is employed, it may be placed in position in the usual manner, by a lead press, and,
if the material of the dielectric is such that it is apt to be injured by the heat of
the press, a thin layer of paper, saturated with good paraffin wax and carefully
applied to the outside of the dielectric, will be found to afford efficient protection.
In any case, the dielectric should be kept as cool as possible in its passage through
the press and the lead sheath should be chilled thereafter at once.
If desired, a layer F of suitable material may be formed outside of the covering L,
as a further protection. It is preferably put on in the form of a tape or braid and
is saturated with a good waterproof paint, one containing a large quantity of elastic,
flexible, bituminous matter, for instance. The purpose of this layer is to protect
the layer immediately underneath it from the action of moisture or gaseous vapours,
and serves at the same time, to seal up any minute holes which may exist in the
lead sheath.
It is evident that the invention is not applicable to conductors of small size on
account of the difficulty of properly forming and placing the intermediate covering
or separating device and the surrounding dielectric in position. The limit of size
will depend upon the materials used, the method chosen for forming the device and
the conditions of its subsequent use.
But
The invention can be applied to concentric cables, if special care be taken in
selecting the materials which are used in the manufacture of the different layers and
in the manner in which these different layers are formed on the conductors.
the feasibility of so doing depends upon the circumstances of each case and can
scarcely be predetermined. The principle upon which the efficiency of the
invention depends is that comparatively few paths are furnished by which the
electric current can escape from the conductor, and any deleterious or objectionable
matter admitted between the conductor and the dielectric is confined to a limited
space.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me
by my foreign correspondent, I declare that what I claim is :-
1. The combination, with an electric conductor and its surrounding dielectric, of
intermediate means secured to the surface of the conductor and consisting of a
structure of fibrous material saturated with an insulating material, whereby non-
communicating air spaces are formed between the conductor and the dielectric.
2. The combination, with an electric conductor and its surrounding dielectric
provided with an intermediate structure consisting of insulating material whereby
non-communicating air spaces are formed between the conductor and the dielectric,
of a covering also composed of insulating material placed intermediate the said
structure and the dielectric and adapted to support the latter.
3. The combination, with an electric conductor and its surrounding dielectric, of
rings composed of more or less flexible material possessing insulating properties,
secured at intervals on the conductor and having a common centre in its axis and
the outer surfaces of which are in contact with the interior surface of the dielectric,
whereby isolated air-spaces are formed between the conductor and the dielectric.
4. The combination, with an electric conductor and its surrounding dielectric

page_text: provided with a separating device having raised portions whereby non-com-
municating air-spaces are formed between the conductor and its dielectric, of
means such as a filling of suitable material whereby the raised portions of said
separating device are reinforced on their under side and are prevented from being
flattened by external pressure.
Dotad this 1941 dan of Man. 1001
WM. P. THOMPSON & Co.,
Agents for the Applicant.