Note: Descriptions are shown in the official language in which they were submitted.
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36 CA 3519
MODIFIED ROUND ROLL CAPACITOR
Bàckground of the Invention
In Canadian application S.N. 379,085, filed
June 5, 1981 - Grahame, there is described a number of
fluid blends for certain capacitors defined as those
capacitors having electrodes comprising paper strips
which are metallized on both sides with a dielectric strip
positioned between the electrodes. These capacitors,
referred to as metallized paper capacitors were predominately
manufactured in a round roll, round casing form because
certain parameters such as winding tension, space
factor and roll integrity were deemed critical, and
optimally obtainable only in the geometry of a round
roll. Because of the criticality of the structure,
great emphasis was placed on the kind of fluid to be
used for impregnation because the characteristics of the
fluid were required to be specifically correlated with
the round structure.
In the noted Canadian application, it was
discovered that such a capacitor could be greatly improved
by the use of certain fluid blends of esters and hydrocarbons.
Evidently the use of single chemical compounds and
particularly blends of hydrocarbons and esters preserved
the total optimum characteristics of the round roll
25~ construction while at the same time improving performance.
The prior art flattened or oval capacitor roll
construction detracted from the integral rigid geometric
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round roll. The flattening process introduced wide
variances in winding tensions and space factor and a
general relaxation of stresses in the flattened areas.
Fluid impregnants in these capacitors could not perform
well because of the nonuniformity of the space factor,
and limited swelling of the resin dielectric by the fluid
left nonunifoxmly filled spaces in some parts of the roll.
However, the flattened or oval roll construction is
desirable for many reasons including its space saving
considerations and its ability to thermally expand and
contract more favorably.
Summary of the Invention
It has been discovered that a modified round roll
capacitor can be manufactured which will duplicate the
desirable physical characteristics of the flattened or
oval shape while at the same time retaining all the
electrical and fluid impregnation characteristics of the
round roll construction. Moreover, the new modified round
roll permits the use, not only of a wider variation of
impregnants without sacrifice of electrical characteristics,
but also the use of more advantageo~s impregnants which
are less limited by the criteria of the former round roll
construction.
Brief Description of the Drawings
This invention will be best described in connection
with the following description and the~drawings in which
FIG. 1 is an illustration of a preferred embodiment of a
modified round capacitor roll of this invention.
FIG. 2 is a cross-sectional view of spaced metaIlized
paper strips and an intermediate synthetic resin strip
which are wound into the roll of FIG~ 1.
FIG. 3 is a cross-sectional illustration of the
capacitor roll of FIG. 1.
FIG. 4 is an illustration of the capacitor roll of
FIG. 1 before its modification.
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FIG. 5 is an illustration of a complete modified
round roll capacitor of this invention.
Description of Preferred Embodime~nts
Referring now to FIG. 1, the exemplary capacitor roll
section 10 comprises a core member 11 on which is a tightly
wound series of synthetic resin strips 12 and metallized
paper electrodes~13. The roll section 10 is wound with
the electrodes i-n ofset relationship to each other so
that the metallized edges 14 of one electrode are exposed
at one end 15 of the roll section and the exposed edges 16
of the other metallized electrode are exposed at the other
end 17 of the roll section. A suitable metal such as
aluminum or zinc is sprayed at each end of the roll section
to form coatings 18, and electrode leads 19 and 20 are
joined to coatings 18.
As illustrated more clearly in FIG. 2 the metallized
paper ele,ctrodes 13 comprise a thin, high density paper
strip 21 on which is a layer or coating 22 of aluminum.
A number of materials may be employed for paper 13
including woven and nonwoven polymeric materials or other
porous and wicking materials which will permit the ingress
of dielectric fluids therein and therealong. However,
in the practice of this invention, ~apacitor tissue is
preferred which is about 1.0 density. Such tissue is
commercially available as Kraft capacitor tissue.
The paper strips 21 are coated with a metal layer 22
on both sides thereof, a combination referred to as
doubly metallized paper. Prefer~bly the metal is aluminum
or zinc which are vacuum deposited on the paper by
well-known vacuum deposition to provide a uniform high
purity metal layer. Such layers are measured in terms of
" their ohms resistance per square unit of area of electrode
foil and a range for the present invention is from about
4.0 to about 7.0 ohms per square unit of area.
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36-CA-351
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The synthetic resin strips 12 may be single or
multiple strips of one or more of the more common
dielectric resins such as the polyolefins, polycarbonates
and polyamines, etc., and homopolymers and copolymers
thereof. However, a resin comprising electrical capacitor
grade polypropylene is a preferred resin strip for this
invention. Capacitor grade polypropylene film is a higher
purity, smoother polypropylene film of enhanced dielectric
characterlstics.
The particular shape of the modified round roll of
- this invention is more clearly illustrated in FIG. 3.
Referring now to FIG. 3, there is shown a relatively
thick roll section having relatively large opposed
flat sides 23 and 24 and transversely thereof a pair of
smaller sides 25 and 26. In a typical capacitor roll, the
inner turns of the roll closPr to the core structure 27
show a more flattened or straight sided configuration.
As the number of turns increase the sides 25 and 26 became
more arcuate. Alternately described, the roll 10 comprises
a pair of inwardly facing arcuate sides 25 and 26 joined
by opposing flat sides 23 and 24. The final shape of the
core structure 27 is the same, i.e., the cross sectional
geometries of the roll section and the core structure are
near identical, as shown in FIG. 3. The shape and
structure described is predetermined and fixed by the
shape of the core structure 27 and the method of manufacture
of the roll 10. For example, the composite as illustrated
i~ FIG. 2 is wound in roll form on a thic~ deformable core
or tube 29 (FIG. 4) on a high-speed automatic winding
machine. In this process the core 2g remains a part of
the capacitor roll as illustra-ted in FIG. 4 in a round
roll design. Such a hard wound roll on a rigid core member
is also described in U. S. Patent 3,987,348, Flanagan.
Ordinarily an oval roll capacitor such as described
in U. S. Patent 4,117,579, Shaw, is wound directly on a
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machine arbor, removed from the arbor and flattened, no
core member being necessary or desirable. Once a roll
is flattened the inner turns of the roll are in a relaxed
state and tend to wrinkle, thus deleteriously affecting
space factor between turns. ~lso the tension in the roll
ends decrease to change the space factor. These items
tend to worsen during the life of the capacitor. Prior
oval roll-capacitors, other than the double metallized
paper capacitors were nctcritical in this respect.
However, the double-metallized paper construction capacitor
requires careful electrode and dielectric alignment and
maintenance of uniform space factor throughout the roll.
The uniform space ~actor reIates to looseness and tightness
of the roll, the original winding tension, and the final
rigid structure. These factors are not found in prior
oval rolls.
In the present invention a capacitor roll is made up
with all the criteria of a round roll design such as the
round roll 28 of FIG. 4. Roll 28 includes a rigid central
core tube 29, which is of a predetermined compressibility.
The roll 2~ is then simply flattened to a modified round
roll design which returns the essential characteristics
of the round roll design.
The modified round roll 10 of this invention includes
the most important concept of central integrity. Central
integrity is defined by having the roll include a
predeterminedly compressible, flattened or deformable core
structure 27 within the finished roll. The space taken
up by this flattened central integrity core structure 27
restricts or limits the flattening process so that the
roll is more of a modified round roll than the usual
flattened oval. Furthermore, the core structure 27 was
less deformable than the capacitor roll so that it provides
a continuing resistance to the flattening process and
continuing support to the roll to maintain tension and
central integrity to the structure.
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The core structure 27 was, in one example originally
a spiral wound paper tube of approximately 0.080 lnch wall
thickness and extending over the length of the roll 28.
This tube is illustrated as core 29 of FIG. 4. The paper
tube 29 serves as a mandrel or core member on which the
roll 28 is wound on a winding machine. When the winding
operation is finished, the roll 28 and core member 29 are
removed from the machine as a unit placed in a press and
flattened to the coniguration shown in FIGS. 1 and 3 where
the tube 29 becomes a precisely flattened core structure 27.
The core structure 27 need not be paper but can be
made of any fibrous, plastic or other material which will
easily deform to the illustrated position and be compatible
with t~e capacitor environment. The final thickness of
the core structure 27 or wall thickness of core 29 are
easily determined by empirical relationships depending on
the final design size of the roll across the major flats
and the number of turns in the roll. Ordinarily, with a
wound Kraft paper tube where the paper is typically about
0.003 inch to 0.026 inch to about 0.030 inch to 0.1~0 inch.
Space factor of the roll is more preserved, particularly
in the inner turns and across the major flats. Moreover,
the core structure 27 becomes a variable compressible fluid
filled structure to preserve the roll integrity. All of
the space in the central part of the roll is essentially
- filled by the core structure 27 and there is no unfilled
space. The core structure 27 is a solid core and the
total roll is a solid structure.
In the flattening process, the complete inner
periphery of the roll is supported because the core 29
is less compressible than the xoll. More importantly,
as the core 29 is being flattened, it exerts a powerful
lateral force in the roll serving to maintain the winding
tension in the roll end windings. At the end of thè
flattening process, the compressed core 26 comprises an
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36-CA-3519
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easily impregnable structure which lends continuing central
integrity to the roll. Se~uential pressing of the roll
indicates that the core structure continually adjusts to
the changing volume without any buckling, probably because
of its greater wall thickness.
The capacitor roll 10 is assembled as described, and
inserted within a preformed casing 30 of FIG. 5. In FIG. 5
casing 30 includes a pair of terminals 31 and 32 to which
leads 19 and 20 of FIG. 4 are attached. ~lso the casing 30
is filled with a suitable impregnating fluid 31 such as
those disclosed and described in the noted copending
Grahame invéntion. A typical practice of this invention
is as follows.
Example 1
A number of capacitors were made up following the
construction of FIGS. 1-5 of this specification. The
capacitors were rated 12 mfd, 530 VAC. Double metallized
paper thickness was 0.36 mil. The dielectric strips were
polypropylene o 0.394 mil thickness. The core tube was
spiral wound paper and had a wall thickness of 0.100 inch.
The capacitors were wound very tightly on the core tube,
removed from the winding machine and placed in a hydraulic
press to be flattened to the configuration of FIG. 3.
Thereafter, the capacitor rolls were sealed in a casing
and impregnated with a blend of 40% phenyl xylyl ethane
and 60~ di 2-ethyl hexyl phthalate ester. Typical
electrical tests revealed a capacitance of 12.23 mfd and
a percent power factor of 0.018.
While this invention has been disclosed with respect
to particular embodiments thereof, numerous modifications
may be made by those skilled in the art without departing
from its true spirit and scope. Therefore, it is intended
that the appended claims cover all such modifications and
variations which come within the true spirit and scope
of the present invention.
