Improvements in Insulated Electric Conductors.
Year: 1892

page_text: Date of Application, 29th Mar., 1892-Accepted, 30th Apr., 1892
COMPLETE SPECIFICATION.
Improvements in Insulated Electric Conductors.
A communication 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.1.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 insulating layer, or dielectric, in direct contact with the conductor, or in con-
tact 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 this invention consists in the means employed to attain this
object, and in the construction and adaptation of the parts; and consists, primarily,
in interposing, between the insulating layer or dielectric and the conductor, air
spaces preferably made continuous, together with certain intermediate and supple-
mentary aids to insulation, 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 this invention, showing the
successive layers of material cut away so as to display the different coverings
of the conductor in their relative positions.
Figure 2 is a similar view of the conductor, provided with the intermediate
covering or separating device.
Figure 3 is a similar view of the conductor provided with a different form of
said device.
Figure 4 is a central transverse section on the plane of the line y-y in Figure 1.
Figure 5 is a similar section on the plane of the line x-x in Figure 3.
In all the views, the parts are shown in relative positions only, and not in
necessarily relative sizes.
In the drawings
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 is the intermediate covering or separating device, placed between
the conductor W and the insulating layer, or dielectric, 1. Its purposes are (1) to
prevent the insulating layer from coming into direct contact with the conductor;
(2) to provide air spaces between them; (3) to support the insulating layer and
keep it substantially concentric with the conductor; and (4) to furnish compara-
tively 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 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

page_text: under these conditions, the degree of flexibility required will be greater and suffi-
cient to prevent buckling or rupture. By the term "ordinary conditions" are
meaut such conditions as insulated conductors of the class herein described would
be subjected to naturally by an intelligent and skilled workman; 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.
When the intermediate covering C is made in the form illustrated in Figures 1, 2
and 4, it is provided with the raised portions or corrugations e, the outer edges of
which are substantially equidistant from the axis of the conductor and from each
other and which serve to support the insulating layer or dielectric I, and keep it
away from those portions of the covering c¹ which are directly in contact with
the conductor W, forming, between the dielectric and the covering C, air spaces A
which, in the form illustrated in these figures, are substantially parallel to the axis
of the conductor. In this form, under some conditions, the device may be provided
with means for preventing the corrugations from being flattened against the con-
ductor when subjected to external pressure. I is the insulating layer or dielectric,
surrounding the intermediate covering C and which touches only the outer portions
thereof, and it is made sufficiently stiff to prevent its collapsing under usual
conditions and touching the surface c¹ which forms the inner wall of the air
passage A. L is a waterproof protecting covering, usually made of lead, and
applied over the dielectric in the usual manner, and F represents a further covering
or layer composed of fibrous material saturated with a waterproof compound and
outside the covering L when its use is deemed desirable.
In Figures 3 and 5, a second form of this intermediate covering or separating
device is illustrated. In these figures; W is the conductor, C¹ is the covering
which is provided with bosses or projections c³, which have the same functions as
the corrugations in the device first described. This covering is made of strips of
insulating material previously prepared and wound around the conductor. The
dielectric I is placed around the covering in the manner hereinafter stated, forming
the air spaces A³. The general nature of this invention will be readily understood
from the above description, and it is now proposed to describe the best means
known to my correspondent of carrying out the same and to specify the materials
which should preferably be employed therein, and the methods of constructing and
putting together the several parts.
The intermediate covering, or its equivalent, which may be called the "separating
device"
on account of its obvious functions, is made preferably of some fibrous
material, such as paper, which can be made to possess insulating properties by
saturating it with an insulating varnish or paint, such as a good Japan dryer,
containing a large quantity of shellac, and which can be formed while hot into the
desired shape and will retain its position when cold, or under ordinary conditions.
If the material employed be not of itself sufficiently rigid to resist the usual
condition of external pressure, it may be reinforced as above suggested. The same
end may be effected by thickening the covering at certain points, or by adding
external longitudinal strips thereto, by cement or otherwise, before it is applied to
the conductor. 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 into
contact with the conductor.
The second form of the separating device C¹ may be made of any suitable
material possessing insulating properties, for instance, of vulcanised soft rubber,
and is treated with suitable cements to cause it to adhere to the surface of the
conductor. It is obvious that the bosses or projections are to be made sufficiently
close together to support the dielectric. However formed or of what material this
device is made, if made of separate pieces afterward united, their edges should be
closely cemented, and the points of contact between it and the dielectric should

page_text: be as few in number as possible. Other equivalents of the intermediate 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 in detail may be made
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 insulating material
suitable for use in this connection. Under some conditions of use, the dielectric
may be separately formed into tubes and the conductor, already provided with the
separating 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 L, which is usually made of lead, is applied upon the dielectric I, 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
paraffine 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 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 the
moisture or gaseous vapours, and serves at the same time to seal up any minute
holes which may exist in the lead sheath.
The ends of the insulated conductor should always be sealed with waterproof
tape, during the process of manufacture whenever practicable, and, when finished,
should always be sealed by this or other suitable means; otherwise, the insulation
resistance of the conductor is liable to rapidly diminish, owing to the effect of
moisture and vapours, which may enter the air spaces, attacking the insulating
materials.
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.
The invention can be applied to concentric cables, if special care is 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.
But 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.
It is not requisite that the air passages between the separating device and the
dielectric should be continuous or communicating in order to obtain this object, but
a great advantage is found in making them so, because a current of warm dry air
may be passed through the air spaces of the insulated conductor, even after
it is placed in position, to remove any moisture which may get inside of the air
passages.
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 of a conducting wire and a corrugated covering of insulating
material surrounding said wire.
2. In combination, an electric conductor, an exterior insulating layer I, and an

page_text: intermediate corrugated covering C, whereby air spaces are formed between the
conductor and the exterior layer, substantially as shown and described.
3. The combination with an electric conductor W, and an exterior insulating
layer I, of means placed intermediate, the same composed of insulating material
closely adhering to the conductor and having portions thereof permanently
projecting from its exterior surface and in close contact with the interior surface of
the exterior layer, whereby air surfaces are formed between the conductor' and the
exterior layer.
4. The combination, with an electric conductor and an exterior insulating layer,
of an intermediate corrugated covering, the folds of which form, with the exterior
layer, the walls of continuous air passages, as set forth.
5. The combination, with an electric conductor and' an exterior insulating layer,
of the intermediate covering composed of more or less flexible material possessing
insulating properties and closely adhering to the surface of the conductor and
provided with raised portions c, the outer surfaces of which are substantially
equidistant from the axis of the conductor and which serve as a support for said
exterior insulating layer and form therewith the continuous air passages A.
6. The combination, with the electric conductor and its surrounding insulating
layer, of the intermediate covering provided with bosses or projections, substantially
as described.
7. The combination, with the electric conductor and the insulating layer, of the
intermediate covering wound around the conductor and provided with bosses or
.projections, as described.
8. An insulated electric conductor comprising the conductor W and the insulating
layer 1, the corrugated' covering C intermediate the conductor and the insu
lating layer I, and the protecting covering or sheath L, substantially as shown
and described.
9. An insulated electric conductor comprising the conductor W and the insulating
layer I, the corrugated covering C between the conductor and the layer I, the
protecting layer or sheath L next to the layer I and the outer waterproof
covering F, substantially as shown and described!
Dated this 28th day of March 1892.
WM. P. THOMPSON & Co.,
Agents for the Applicant.