Insulated Electric Conductors.
Year: 1891

page_text: Date of Application, 31st Mar., 1891-Accepted, 2nd May, 1891
DI DOITTUATION.
Insulated Electric Conductors.
I, JAMES DRAPER BISHOP, a subject of the Queen of Great Britain, now
residing at No. 349 West 34th Street, New York City, New York, U.S.A.,
Electrical Engineer, do hereby declare the nature of my invention for INSULATED
ELECTRIC CONDUCTORS, 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. Its object is to insure a
high insulating power, low inductive capacity, cheapness of construction, and
increased lightness and flexibility. An ideal conductor or cable would be one in
which the conductor was maintained throughout the whole length equi-distant from
the protective sheathing by a material offering a maximum electrical resistance and
a minimum inductive capacity. Dry air possesses these qualities to a higher
degree than any other known material, and would be the ideal medium of separation
of the conductor from the enclosing sheath or adjacent conductors, provided the
conductor could be maintained throughout its length with an intervening layer of
stratum of such air between it and its enclosing sheath. The nearer an insulated
conductor approaches this form the greater will be its advantages in a high
resisting power to leakage and a lower inductive capacity, and would also be of
materially decreased weight, of increased flexibility and diminished cost. It is the
object of my invention to surround the conductor as much as is practically possible
with such a protective envelope of dry air and yet maintain it in a fixed relation to
its enclosing sheath. The features of novelty of the invention will be hereinafter
fully described in the Specification and definitely indicated in the appended
claims.
In carrying out my invention I apply an insulating material preferably in strips
spirally around the conductor in such a manner that instead of overlapping on itself
in successive convolutions, as is common in the art, air spaces are established
between the sides of the spiral by giving the thread of the spiral such a pitch that
the edges of the strips cannot overlap but will be separated by a wide space..
These strips may be held up on one another in the same plane to several thick-
nesses so that the thread may be as deep as desired, and thus as great an air space
secured as the design of the cable requires. This result may be accomplished by
giving to the conductor such a rate of feed with reference to the winding machinery
that air spaces of a desired width will be left between the sides of the spiral strip.
When a sufficient thickness of a spirally wound material has been produced the
protective envelope or sheath is applied to the conductor which is then complete.
The insulating material or ribbon which I prefer to use in winding the conductor is
paper, both by reason of its lightness in weight, its cheapness, and its high
insulating power.
In the accompanying drawings which illustrate the invention,
Fig. 1 is a sectional view of a portion of a conductor or cable constructed in
accordance with my invention;
Fig. 2 is a sectional view of a portion of the conductor in which a single spiral
band of insulating material is wound upon the conductor;
Fig. 3 illustrates a method of closing the ends of the conductor so as to prevent
the entrance of moisture to the air spiral; and
J
Fig. 4 illustrates in enlarged view a series of strips piled to the desired thickness
which hold the conductor in fixed relation to its enclosing protective sheath.
A is the conductor, B is a series of superposed strips of insulating material,
preferably paper, wound upon the conductor with a quick pitch so as to leave at
intervals in the length of the conductor wide spaces C C. The sheath D may be

page_text: applied directly to the conductor after being wound with the strip B, as shown in
Fig. 2, or additional spirals of insulating material E F reversely wound may be
applied before the conductor is enclosed in its sheath, as shown in Fig. 1. The
ends of the conductor are finished by completely surrounding them with the
insulating material, as shown at G. This result may be attained by causing the
sides of the strip to come into close contact at the ends of the conductor; or by
applying in any other manner a complete enclosing envelope of the separating and
insulating material at those points.
It will thus be seen that throughout the whole length of the cable or conductor
there exists a spiral air space between it and its enclosing sheath, or several spiral
air spaces when more than one layer of insulating material is applied. The con-
ductor is thus maintained fixedly in its relation to the enclosing sheath and yet the
insulating power of the separating medium is largely increased, and the inductive
capacity largely reduced.
Another special object of my invention is to secure better means of "drying
out." In conductors insulated with porous or fibrous material, such for instance as
strips of felt, linen or paper, the finished insulation, either from constant handling,
dampness of the atmosphere or natural process of manufacture, always holds more
or less moisture which necessitates the "drying out" of the insulated conductor in
heated ovens specially constructed for this purpose.
Such moisture, being a good conductor destroys to a great extent the insulation,
and when such strips are laid on closely and made to overlap, as in the present
state of the art, it is next to impossible to dry out all the moisture because the heat
of the ovens cannot penetrate below the close dense surface.
""
But, by the provision of "air spirals" as indicated above, I expose the insulating
strip to the action of the heat of the "drying oven on all sides of the strip, from
the one next the conductor to the one on the outside and the hot air being thus
allowed free entry all around and through the strips, they are thus more effectually
dried out than is at present possible. Insulation is thereby rendered more effectual
and is secured in much less time than at present required with "solid" as
distinguished from "spiral " strip wound insulation.
And now having particularly described and ascertained the nature of this said
invention, and in what manner the same is to be performed, I declare that what I
claim is :-
1. An electric conductor comprising a conducting core wound with a paper
ribbon, the spiral edges of which are separated by a spiral air space, and enclosed
witbin a protective sheath.
2. An electric conductor comprising a conducting core, an external protective
sheath, and a separating insulating medium wound spirally with intervening air
spaces between its sides, the ends of the conductor being solidly closed to prevent
entrance of moisture to the air spaces.
3. An electric conductor wound with a paper spiral composed of multiple layers
of ribbon, the edges of the spiral being separated by air spaces.
4. An insulated electric conductor constructed in the manner and for the purpose
herein set forth.
S. S. BROMHEAD,
97, Newgate Street, London, E.C., Agent for Applicant.