Note: Descriptions are shown in the official language in which they were submitted.
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AN INSULATED CONDUCTOR AND PRO OESS
FOR M~KING AN INSULATED ~O~u~lOR
FIELD OF THE lNV~NllON
The present invention relates generally to an
insulated conductor and processes for making an insulated
conductor, and more particularly to processes for making a
high voltage insulated electrical conductor for use in
electrical transformers. Still more particularly, the
invention relates to an insulated conductor and a process
for making an electrical conductor having an insulation
coating disposed thereon of thickness of about 0.00125 to
about 0.00315 inch.
RA~K~ROUND OF THE lNv~NllON
Rectangular conductors with high dielectric
strength insulation, such as polyphenylsulfone, are coated
using thermoplastic extruders equipped with crossheads
tooled to coat rectangular conductors. Typically, the
extruded insulation coating thickness range is about 0.0025
inch (the minimum obtainable) to about 0.0035 inch (easily
obtainable). One of the shortcomings of the extrusion
crosshead is that the coating thickness cannot be controlled
to thin coatings of less than 0.0025 inch. Accordingly, a
goal of the present invention is to provide a process for
making electrical conductors in which the thickness of the
extruded coating can be reduced by about 10~ to about 50~ to
provide a reduced insulation thickness range of about
0.00125 inch to about 0.00315 inch depending on the extruded
starting thickness and the percent reduction utilized. The
process in accordance with the invention provides a coating
of insulative material which can have a prescribed thickness
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less than that produced by the presently available extrusion
process(es).
Sl~MMARY OF T~; lNV~;N-l'lON
An insulated conductor is provided comprising an
electrical conductor and an insulative coating disposed on
the conductor. In accordance with the invention, the
coating has a thickness of about 0. 00125 inch to about
0.00315 inch, and pre:Eerably about 0. 00125 to about 0 .00175
inch.
A process for making an insulated conductor in
accordance with the present invention includes extruding an
insulative material onto a conductor and subsequently roll
reducing the coated conductor so that the insulative
material on the conductor is reduced by about 10~ to about
50~ to a prescribed thickness and the conductor assumes a
prescribed thickness and width. The extruding step
preferably comprising extruding the insulative material to a
thickness of about 0. 0025 inch to about 0. 0035 inch and more
preferably to a thickness of at least about 0. 0025 inch, and
the rolling step preferably comprises rolling the insulative
material to a thickness of about O. 00125 to 0. 00315 inch and
pre:Eerably to a thickness o:E about 0. 00125 to 0 .00175 inch.
In a preferred embodiment o~ the invention, the insulative
material is a thermoplastic polymer, such as
polyphenylsulfone. Furthermore, in preferred embodiments of
the invention, the conductor is generally rectangular in
cross-section. The preferred embodiment of the invention
also includes rolling the conductor to a reduced thickness
and increased surface area, i.e., the rolling step includes
rolling the insulative material to a prescribed thickness
and at the same time rolling the conductor to a reduced
thickness. Thus, both the coating thickness and the shape
of the coated product are altered in the rolling step.
Other features of the invention are disclosed
below.
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BRIEF DESCRIPTION OF ~1~ DRAWINGS
Fig. 1 schematically depicts an extruder and the
process o~ extruding an insulative material onto the sur~ace
o~ a rectangular conductor. The product o~ the extrusion
.~ 5 process is a conductor 10 comprising an electrical conductor
12 and an insulative coating 14.
Fig. 2 schematically depicts the rolling step in
accordance with the present invention, wherein up to ~our
rolls 16a-16d are employed to roll the insulative coating to
a desired thickness, and at same time alter the shape
(thickness or sur~ace area) of the electrical conductor 12.
Fig. 3 illustrates one ~orm o~ trans~ormer; a
trans~ormer 20 comprising a pair of coils 10' (i.e., coils
composed o~ an insulated conductor in accordance with the
present invention) and a core 18.
DET~TT.Rn DESCRIPTION OF ~1~ PREFERRED EMBODIMENTS
The present invention employs developed sizes o~
conductor that can be reduced to the desired dimensions with
the desired thickness o~ insulation. Presently pre~erred
embodiments o~ the invention employ reducing rolls. This
invention, when applied in conjunction with the
thermoplastic extruder, allows rectangular conductors (e.g.,
aluminum or copper) to be produced with the desired
dimensions o~ conductor and insulation thickness. This
invention can be employed to control the insulation
thickness o~ either o~ the two opposing sides o~ the
conductor, or o~ all ~our sides, depending on the roller
con~iguration.
As mentioned, the extrusion o~ thermoplastic
coatings onto rectangular conductors is limited generally to
a minimum thickness o~ 0.0025 inch. This is an inherent
limitation due to the way presently available extruder
crossheads, and their associated die components, apply the
melted polymer to the conductor. This extrusion process is
represented by the block bearing the same name in Fig. 1. A
product o~ this process is a conductor 10 comprising the
electrical conductor 12 and its associated insulative
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coating 14, wherein the coating has a minimum thickness of
0.0025 inch. As indicated above, the extruded insulation
coating thickness can range from about 0.0025 inch (the
minimum obtainable) to about 0.0035 inch (easily
5 obtainable). -
The polymers applicable to high voltage conductors
used in transformers 20 (Fig. 3) must have performance
characteristics that ensure functional life performance for
up to 25 years. These polymers have dielectric strengths
that allow them to be used with coating thicknesses of less
than 0.0025 inch, i.e., in the range of about 0.00125 to
about 0.00315 inch and preferably in the range of about
0.00125 to about 0.00175 inch. The product of the inventive
process disclosed herein is a rectangular conductor 10' (see
Fig. 2) having an insulation of a thickness which meets the
dielectric needs o~ the transformer but does not exceed such
need by an excessive amount. Excessive insulation is costly
from not only a materials cost standpoint but also from a
space factor standpoint, which is a detriment to maintaining
a small core/coil assembly 18, 10' (see Fig. 3). The
core/coil assembly size equates to the cost of the
transformer 20, not only in materials used but also in
electrical losses prevented.
According to the present invention, a set of
reducing rolls is employed to reduce the insulation
thickness. The reducing rolls can be configured in
different ways, such as two flat rolls with parallel axes or
one ~lat roll in combination with a slightly tapered,
grooved roll, or ~our flat rolls (one on each side of the
conductor 12) or four flat rolls as is configured in what is
commonly known as a "Turks" head. These various
con~igurations are represented generally in Fig. 2, which
depicts four flat rolls 16a-16d.
The final size of the conductor product (i.e., the
conductor and insulative coating) with its desired thickness
of insulation is produced by developing a starting size of
conductor with an extrudable thickness o~ insulation that
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when rolled yields a conductor o~ the desired or
predetermined dimensions with the desired or predetermined
thickness o~ insulation.
For the particular trans~ormer application ~or
J 5 which the process/insulated conductor in accordance with the
invention was developed, the conductor typically has a width
no more than about ten times its thickness and the thickness
o~ the insulation is about 0. 00125 to 0. 00175 inch.
However, depending upon required per~ormance
characteristics, ~unctional li~e per~ormance periods,
polymer utilized, dielectric strengths, etc., even lesser
coating thicknesses are possible in accordance with the
process o~ the present invention. For example, coating
thickness less than 0. 00125 inch may be utilized ~or certain
applications, as will be understood to those skilled in the
art, and such reduced coating thicknesses may be obtained by
the inventive process disclosed herein.
The process involves the extrusion o~ a larger
cross-section conductor than the desired ~inal size. This
conductor is then extrusion coated with thermoplastic
insulation. The thickness o~ the coating, ~or example, can
be approximately 0. 0025 inch, which is the minimum thickness
possible by currently available extruders. The coated
conductor is then rolled into a ~inal desired cross-
sectional thickness and width. During the rolling step, the
ratio o~ the conductor sur~ace to the volume o~ the
conductor increases as the conductor cross-section changes
~rom one rectangular shape to a di~erent rectangular shape,
i.e., as the thickness o~ the conductor is reduced. This
means that the insulation thickness is reduced to below the
original 0 .0025 inch, resulting in a more eE~icient
conductor.
Typical dimensions, in inches, o~ a conductor
reduced in a two-way roll are:
- starting base conductor size = 0 1140 thickness
x 0.1620 width.
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- starting coated conductor size = 0.1190
thickness x 0.1670 width.
- rolled bare conductor size = 0.0725 thickness x
0.2090 width.
- rolled coated conductor size = 0.0760 thickness ~-
x 0.2120 width.
In sum, the present invention employs one or more
roll means or apparatus to alter the shape of the coated
conductor to achieve a desired or predetermined thickness of
insulation. The above description of preferred embodiments
is not intended to limit the scope of protection of the
following claims. Thus, for example, except where they are
expressly so limited, the following claims are not limited
to processes employing any particular number, configuration,
or shape o~ roll or means or apparatus.
