Note: Descriptions are shown in the official language in which they were submitted.
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This invention rela-tes to liquid dielectric impregnated
capacitors.
Typically, the outer can of such a capacitor has a fill
hole through which dielectric liquid is added after the capacitor
element has been mounted in the can. The fill hole must then be
sealed. In Dubilier United States Patent No. 3,258,666 the fill
hole is sealed with solder. Thomas United States Patent No.
1,497,415 shows a molded oil filled condenser with a threaded plug
in a fill hole. In Rayno United States Patent No. 3,389,311 the
dielectric liquid is added through the electrode lead openings in
the can, without a separate fill hole.
SUMMARY OF THE INVENTION
The invention provides a highly effective, reliable,
long-lasting fill hole seal, which can be inexpensively and auto-
matically installed. The disadvantages of a solder seal (e.g.,
contamination of the capacitor by soldering fluxes, and latent
defects such as bubbles caused by overheating during the soldering
process) are avoided. The seal is applicable to cans of a variety
of metals, even including aluminum. In the case of pitch potted,
halogenated hydrocarbon dielectric capacitors, contamination of the
dielectric by the pitch during operating is minimized.
In general the invention features a capacitor of the type
having a liquid dielectric impregnated capacitor element mounted in
a metal can, electrical terminals passing through openings into the
can, and a fill hole through a wall of the can for addition there-
through of liquid impregnant, that improvement comprising a sleeve-
like, integral extension of the wall surrounding the fill hole and
coaxial therewith, the extension being of circular cross-section,
and a solid, resilient plug inserted in the hole and extending
coaxially therewith, the unstressed outside diameter of the plug
being larger than the corrésponding inside diameter oE the
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extension whereby the plug when inserted in the hole is in
compression, one end of the plug extending ou-twardly of the wall
a distance sufficien-t so that downward manual pressure on -the plug
will cause it to bend slightly and thus resist being pushed down
through the extension, -the other end of the plug extending into
the can beyond the extension to provide a reexpanded portion which
resists upward withdrawal of the plug.
In preferred embodiments a silicone plug extends 0.031"
- 0.005" outwardly beyond the outer surface of the wall; the
unstressed outside diameter of the plug is sufficiently larger
than the corresponding inside diameter of the extension to cause
compression of the plug by at least 15~; the extension has a flared
portion in the plane of the wall, and a cylindrical portion
extending inwardly from the wall; the cross-sectional area of the
plug is less thant 0.~2 square inch; and the plug extends across the
plane of a paper insulating strip extending along the undersurface ~
of the wall, and the strip is cut away adjacent the plug so that ~ -
the plug is free-standing and contacts only the extension.
Other advantages and features of the invention will be
20 apparent from the description and drawings herein of a preferred ;~
embodiment thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of a capacitor embodying
the invention;
Fig. 2 is a front elevation, partially broken away, of ~ -
the capacitor of Fig. l;
Fig. 3 is a sectional view taken along 303 of Fig. 2;
Fig. 4 is a fragmentary sectional view taken along 4-4
of Fig. 3; and
Fig. 5 is a fragmentary, semi-schematic sectional view ~ -
showing installation of a plug in a fill hole.
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DESCRIPTION OF ~ E PREFERRED EMsoDIMENT
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Referring to the drawings, capacitor 10 has an outer
aluminum can 12 con-taining a conventional capacitor element 14
having alternate dielectric and electrically conductive layers, and
a halogenated hydrocarbon dielectric liquid. Leads 16 connect the
capacitor conductors to terminals 18 rr~oun-ted in cover 20 of the can
and sealed thereto by silicone bushings 22. Paper insulating
strip 24, supported by the terminals, extends along the under-
surface of cover 20 just below the bushings.
Collar 30, integral with can cover 20, extends down from
the cover to define a hole 32 through which the capacitor is filled
with the liquid dielectric. The collar is flared at 34 in the
plane of the cover and otherwise has a smooth surfaced cylindrical
wall 36 which extends 0.038" below the cover.
Resilient, cylindrical, silicone plug 38 serves as a
seal for fill hole 32, and has an outside diameter (0.125" in the
example shown) sufficiently larger than the inside diameter of
collar portions 36 (0.100" in the example shown) to cause compres-
sion of the plug by at least 15% (preferably 20~
To ensure the integrity of the fill hole seal, plug 38
has a portion 40 extending sufficiently below collar 30 to prevent,
by reexpansion of that plug portion, upward withdrawal of the plug,
and a portion 42 extending above the plane of cover 20 sufficiently
so that downward finger pressure on the plug causes portion 42 to
bend slightly and thus resist being pushed down through the collar.
However, plug portion 42 should be short enough to prevent the plug
from being damaged by manipulation. In the example, shown portion
42 extends 0.031" t 0.005" above the outer surface of cover 20, a
critical dimension. Further, plug portion 40 should be short
30 enough to avoid contact with the capacitor element and thus the
application of potentially seal-wéakening stresses to the plug.
To further avoid such stresses, insulating strip 24 is cut away at
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44 around the plug, which thus contacts only collar 30.
Capacitor 10 is assembled by plaeing element 14 in the
can, attaching the cover, and adding -the liquid dielectric through
hole 32. Silicone rod 46, compressed in quide 50 to slightly less
than the inside diameter of collar 30, is forced into the fill
hole while being held in place by pressure pads 52. The guide is
then withdrawn to allow eutters 54 to engage the rod, severing the
silicone to leave plug 38.
The very small cross-sectional area of plug 38 (preferably
always less than 0.02 square inch) minimizes any contamination of
the dieleetrie liquid by the piteh potting typieally used for
; ballast eapacitors and typically drawn into sueh eapaeitors by
solution in the halogenated hydrocarbon upon temperature fluctuation
during operation.
Other embodiments (e.g., the use of non-setting, resilient :
material other than silicone for plug 38; or the use of a metal
other than aluminum for can 12, ete.) are within the following :
claims. ~ ~
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