Improvements in or connected with Electric Conductors.
Year: 1891

page_text: Date of Application, 5th May, 1891-Accepted, 6th June, 1891
COMPLETE DIEULTIVATION.
Improvements in or connected with Electric Conductors.
A communication from abroad by JAMES B. WILLIAMS, M.D., of Oakland, in the
State of California, United States of America, Physician.
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 and 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:-
This invention relates to insulated electric conductors, and its novelty consists in
the means employed to keep the conductor substantially concentric with the
dielectric by which it is insulated when the said dielectric is softened by the action
of heat.
Insulated electric conductors of the class herein referred to consist of a central
metallic conductor, which may be solid, stranded or tubular, and which is sub-
stantially circular in cross-section surrounded by a dielectric which is usually
protected by a metallic sheath, or a waterproof protecting covering composed of
other suitable materials.
The dielectrics employed may be divided into two classes, vulcanized and unvul-
canized. The former contain indiarubber or gutta percha necessarily, while the
latter may or may not contain them. The former are not readily softened by heat
while the latter are. The dielectrics whether vulcanized or not, may, upon another
principle of classification, be divided into those which are simple, or composed of a
homogeneous composition, and those which are compound, or formed of layers of
different materials, for instance, having an inner layer of one kind of material and
an outer layer of another kind.
Dielectrics which are simple and unvulcanized should, in use, be protected by a
waterproof protecting covering which is usually composed of lead; but, if vulcanized,
they do not generally need such protection unless the electric conductors which
they are employed to insulate are placed underground, or in situations where they
are apt to be exposed to the action of moisture, gases, etcetera, and the same is true
of those compound dielectrics the outer layer of which is composed of a vulcanized
composition.
Under the usual conditions of use to which insulated electric conductors are sub-
jected, it will occur at times, either through outside influences, or by the passage of
currents of unusual strength through the conductor, that the dielectrics will become
heated and softened and thus gradually offer less resistance to the weight of the
conductors, which gradually sinks down until it comes into sufficiently close contact
with the exterior surface of the dielectric so as to destroy its value. This is
especially apt to occur when insulated electric conductors of great length are
employed which rest against hard substances such as pipes in the ground and the
like.
This phenomenon has rendered impracticable the use, as dielectrics, of many
materials possessing good insulating properties, especially those which are readily
softened by heat, except by the employment of large quantities of fibrous material
mingled therewith and surrounding the conductor. This invention has for its
object the overcoming of this difficulty by keeping the conductor in position and
substantially concentric with its dielectric under conditions when the material of
the dielectric itself will become soft.
This purpose is accomplished by placing, around the conductor, and imbedded in

page_text: the dielectric, a structure, which is termed a "centering device," composed of suit-
able fibrous material saturated with a suitable insulating material, which applied
thereto by means of heat, or in solution in a suitable solvent, and the kind of
insulating material used depends, in each instance, upon the dielectric employed.
Thus, if the dielectric is composed of unvulcanized material readily liquefied by
heat, the insulating material should be of such a nature that it will require a
higher temperature to soften it than that required to soften the materials com-
posing the dielectric; and if the dielectric is composed wholly, or in part, of vul-
canized material, the insulating material must be of such a nature that it will not
be injuriously affected by sulphur during the process of vulcanization.
In all cases, the centering device, of whatever kind, should be prepared for.use
before it is imbedded in the dielectric by thoroughly saturating the fibrous
material used in its formation, when the same is dry, with the insulating material
used, preferably by means of a suitable solvent so that the interstices of the fibrous
material will be completely filled with the solid particles of the insulating
material.
In the drawings, in which the same letters refer to the same parts in all of the
figures:-
Figure 1 is a longitudinal central section of an insulated electric conductor
provided with the centering device.
Figure 2 is a transverse section of the same.
Figures 3 and 4 are perspective views of conductors provided with different
forms of the centering device; together with their several coverings and with
parts cut away to show the layers of material in their relative positions.
Figure 5 is a transverse section of an insulated conductor provided with a
protecting layer formed of insulating material and placed outside of the dielectric,
and
Figure 6 is a similar view showing the conductor surrounded by a compound
dielectric.
The parts are shown in relative positions, but rot in necessarily relative sizes.
W is the central metallic conductor surrounded by its_dielectric D, which is in
turn surrounded by a waterproof protecting covering L, usually made of lead.
C is the centering device consisting of a structure of fibrous material saturated
with an insulating material and placed around the conductor W, and imbedded in
the dielectric D in the manner shown. P is a protecting layer surrounding the
dielectric and placed inside of the protecting covering L, and is preferably made
of fibrous material saturated with a suitable insulating material, for instance,
rubber tape. C¹ is the centering device made in the form of an
"open" braid.
D' is a compound dielectric consisting of an inner layer u, of unvulcanised
material and an outer layer of vulcanised material. When the centering device
is in the form of a spiral, its pitch will depend, in each instance, upon the
thickness and kind of material used as a dielectric, the size of the conductor and
the conditions under which it is to be used, for instance, if the insulated conductor
is to be kept straight or nearly so and is to be used in comparatively cool
situations, the pitch of the spiral should be steeper than when it is to be frequently
bent or used in situations where the insulated conductor is liable to be exposed to
the effects of heat. An intelligent and skilled workman can readily determine the
proper distances apart of the turns of the spiral in each instance, and no fixed
rules therefor can be given. The cord should be wound smoothly and evenly, and
its outer surfaces should be substantially equidistant from the axis of the
conductor. If the thickness of the dielectric is such, or if, for any other reason, a
single cord is not large enough, three cords may be employed, two being wound
side by side and the third on top of them.
The method of applying the centering device depends in each case upon the
kind of centering device used, and the kind and quality of the dielectric in which
it is imbedded; and methods by which the centering device, in its simplest form,
that is, that of a spiral composed of a single cord of fibrous material such as

page_text: cotton, saturated with a suitable insulating material, can be applied, will be
specified:
-
1. When the dielectric is simple and composed of material readily liquefied by
heat, for instance, a composition formed of rosin, asphalt and linseed oil, combined
by means of heat, the cord is first wound spirally around the conductor and secured
thereto whenever necessary by means of a suitable cement whenever the insulating
material with which the cord is saturated does not itself cause the cord to adhere
to the conductor. In the majority of cases, the cord should be kept warm enough
to make it plastic while it is being wound around the conductor. The dielectric
is then applied by passing the conductor, around which the centering device has
been wrapped, through a suitable vessel containing the material of which the
dielectric is composed in a melted state. A lead sheath can then be applied upon
the dielectric by means of a suitable lead press.
2. When the dielectric is simple and vulcanisable, the centering device may be
applied to the conductor in the manner above stated, and the material of which
the dielectric is composed, in a strip of suitable dimensions and warm enough to be
plastic, is then applied upon the conductor and centering device by means of
suitable rolls, which not only cause the centering device to become imbedded in
the dielectric, but, in addition, make the latter round, even and smooth. In some
cases, the dielectric may be first applied to the conductor and the cord forced into
it, while both are rendered plastic by heat, by means of suitable apparatus, and, if
the centering device is not thus completely imbedded in the dielectric, a strip of
the material of which the dielectric is composed is applied upon the exposed
portions of the centering device and the inner layer of the dielectric by means of
suitable rolls.
3. When the dielectric is compound, the centering device is placed in position
in its inner layer in the manner above stated, and its outer layer, which, in every
case, is relatively thin, is applied upon the inner layer and the exposed portions of
the centering device, if the latter is not completely imbedded in the inner layer by
means of suitable rolls.
When the centering device is not formed of a single cord, the best method of
applying it is to first cement the device to the conductor, and then apply the
dielectric rendered plastic or liquid by heat, as the case may be, by means of
suitable apparatus. But each case will depend upon the kind of device used, and
the method of applying it must be determined by the intelligence and skill of the
workman. After the centering device and dielectric have been applied to the
conductor, the dielectric, if vulcanisable, is vulcanised under pressure in the usual
manner. In the majority of cases, it is desirable to protect the dielectric during
vulcanisation from the action of moisture by a sheath of tin, which is afterwards
removed. After vulcanisation, if any spaces should be found to exist in the
dielectric, they should be filled with paraffin or other suitable material. In some
cases, the outer layer of a compound dielectric can be formed of suitable material
which has been vulcanised in sheets and then cut into strips which are wound
spirally upon the inner layer containing the centering device, the spirals being
cemented together, and to the inner layer with any suitable cement.
centering device and dielectric have been placed in position and are ready for
may, under some circumstances, be desirable or even necessary to surround
the dielectric with a protecting layer P, formed of insulating material, to act
mainly as a support, and which is composed of different ingredients than those of
the dielectric, for instance, one or more layers of paper, saturated with paraffin,
and which will always remain interposed between the dielectric and the external
waterproof covering, as illustrated in Figures 4 and 5 herein. The insulated
conductor, whether provided or not with this protecting layer, should always,
when the dielectric is unvulcanised and usually when it is vulcanised, be provided
with an external waterproof protecting covering, usually made of lead.
use,
After the
The principle upon which the operation of the centering device depends will now
be readily understood. When the material composing the dielectric becomes heated

page_text: and softened from any cause, and thus offers less resistance to the weight of the
conductor, the insulating material, with which the centering device is preferably
saturated, is not softened, and the conductor is kept in place and prevented from
sinking through the dielectric and coming in contact with the exterior waterproof
covering. While insulated electric conductors, provided with vulcanised dielectrics,
have been in common use for many years, heretofore there has been no means
known to the inventor whereby the conductors could be kept in the centers of their
surrounding dielectrics when heated sufficiently to soften the latter, and the value
of a centering device in this connection will be at once apparent to anyone familiar
with the conditions under which such insulated electric conductors are used. My
correspondent is well aware that this difficulty has been overcome in the case of
insulated conductors provided with unvulcanised dielectrics and protected by a lead
sheath by first wrapping the conductor with one or more layers of fibrous material,
like ordinary cotton yarn, and then saturating the yarn with the dielectric liquefied
by heat. In most cases, the insulation resistance of the dielectric so used is much
higher than that of the fibrous material saturated with it, but, on account of the
comparatively large quantity of fibrous material usually present in this class of
insulating coverings, the efficiency of such coverings is not as high as it would be
if the insulating material were in much greater proportion than the fibrous material.
It is evident therefore that any device, which will allow the proportion of insulating
material to be greatly increased and the proportion of fibrous material at the same
time to be much diminished in any particular covering, must necessarily cause the
efficiency of such covering to be raised. Furthermore, if such dielectrics are
readily softened by heat and the centering devices herein specified are formed of
fibrous material unsaturated with an insulating material not readily softened by
heat, for instance, a spiral formed of ordinary cotton yarn or of tightly twisted
cord, the unsaturated fibrous material will absorb the material of the dielectric
during the process of manufacture and any temperature which will soften the
material of the dielectric will necessarily soften that absorbed by the fibrous
material, and consequently the conductor will become eccentric with the outer
waterproof protecting covering by reason of its own weight, and the feeble support
of such a centering device under the conditions named, except where a tightly
twisted rope is used, when it will keep the conductor concentric with the outer cover,
but cause leakage, unless the insulation resistance of such a spiral is greater than that
of the dielectric, which ought not to be so in practice; but if the fibrous material
be first saturated with an insulating material not readily softened by heat it will
absorb but a very small quantity of the dielectric during the process of manufacture
and the centering device will remain firm and hard and keep the conductor sub-
stantially concentric with its outer covering when the dielectric is quite soft and in
some cases entirely melted.
When vulcanised dielectrics are employed, the necessity for saturating the
fibrous material of the centering device with an insulating material having a
relatively higher melting point, is not so great, and good results might be obtained
in some cases by the employment of dry fibrous material if tightly twisted, but
when unvulcanised dielectrics, which are readily softened by heat, are employed,
the necessity for using an insulating material, which requires a higher temperature
to soften it than that required to soften the material composing the dielectric, is
apparent.
It is evident that wide modifications in detail may be made in the invention,
especially in the form and materials used for the centering device without departing
from its essential features. The device may be made in the form of an 'open braid
or almost any practical structure having raised portions, and any of the well known
fibrous materials and insulating materials suitable for the accomplishment of this
purpose may be used; but however, the device is formed or of whatever materials,
its outer surfaces should be substantially equidistant from the axis of the conductor
and the insulating material with which it is saturated must be of such a nature that
it will require a higher temperature to soften it than that required to soften the

page_text: material of an unvulcanised dielectric when the latter is used and in the case of a
vulcanised dielectric will not be injuriously affected by sulphur during the process
of vulcanisation.
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. In an insulated electric conductor, the combination with the conductor and its
surrounding dielectric, of a centering device composed of fibrous material saturated
with a suitable insulating material not so readily softened by heat as the material
of the dielectric.
2. In an insulated electric conductor, the combination with, the conductor
provided with a dielectric wholly or partly composed of vulcanised material, of a
centering device composed of fibrous material saturated with a suitable insulating
material not injuriously affected by sulphur during the process of vulcanisation.
3. The combination, with an electric conductor provided with a compound
dielectric, the inner layer of which is composed of unvulcanised material and the
outer layer of vulcanised material, of a centering device consisting of fibrous
material also surrounding the conductor and imbedded in the dielectric and
saturated with a suitable insulating material not so readily softened by heat as the
material composing the dielectric and not injuriously affected by sulphur during the
process of vulcanisation.
4. The combination, with an insulated electric conductor provided with a
surrounding dielectric protected by one or more layers of suitable material, of a
centering device consisting of a structure of fibrous material, for example spirally
wound cord or open braid, also surrounding the conductor and imbedded in the
dielectric and saturated with a suitable insulating material, not so readily softened
by heat as the materials composing the dielectric and not injuriously affected by
sulphur.
5. The combination, with an electric conductor, provided with a surrounding
dielectric and a centering device imbedded within the same suitable to its conditions
of use, and a layer of fibrous material surrounding the dielectric and saturated with
a suitable protecting insulating material.
Dated this 4th day of May 1901
WM. P. THOMPSON & Co.,
Agents for the Applicant.