Capacitor with a case seal

An electrical capacitor casing has a fluid filling hole sealed with a self sealing device. The sealing device includes a seat for the seal on the inside of the casing and adjacent of the opening, a resilient gasket, a biasing spring and a retaining housing to form an enclosure for the gasket and spring. A key is used to open the sealing device for drying and filling the case.

BACKGROUND OF THE INVENTION 
A large liquid impregnated electrical capacitor comprises a casing which 
may have a volume of one or more cubic feet and contains a number of 
capacitor roll sections submerged in an impregnant dielectric liquid. 
Ordinarily the impregnant liquid in the sealed capacitor may be introduced 
under a pressure of as much as 10 to 15 pounds per square inch. In order 
to fill the capacitor casing with the liquid impregnant, it has been a 
common practice to fill each casing individually by filling the casing 
through a metal fill tube arrangement which at the termination of the 
filing process is pinched off and sealed by welding or soldering. The 
final capacitor, therefore, includes an appendange or short tube section 
projecting from the casing. Such a projection is undesirable for a number 
of reasons including the fact that it is exposed to mishandling or other 
injurious conditions which could cause leakage of the impregnant from the 
capacitor. At the same time, if the capacitor needs to be repaired in such 
a manner as to require opening of the capacitor, the seal must be broken 
and the filling process again performed through the fill tube. In many 
instances, the pinching and sealing or welding arrangement for the fill 
tube may not be readily available. 
An improved device for filling and sealing a capacitor casing is disclosed 
in U.S. Pat. No. 3,918,474. Supancic, Jr. which includes a fill tube and a 
threaded plug seal device. The seal means has a short sleeve with fill 
holes in its walls and a threaded plug seal therein covering the fill 
holes. The sleeve is permanently mounted in a wall of a casing to project 
into the casing. A fill tube is threaded into the sleeve and initially 
engages the plug seal to move the plug further into the sleeve and away 
from the fill holes while at the same time sealing itself to the casing. 
After filling the casing through the sleeve and fill holes, the fill tube 
is threaded out of the sleeve thus moving the plug seal over the fill 
holes and against a seal in the sleeve before the fill tube itself is 
unsealed from the casing. An advantage of this device is that it provides 
a self-sealing and removable fill tube combination which is adapted for 
reuse. However, a disadvantage is that the plug seal requires special 
machined parts and the opening or closing of the seal is by means of a 
threaded plug seal. 
Quite surprisingly, I have discovered an improved capacitor filling and 
sealing device which is self-sealing and is adapted for reuse, but 
requires no special machining and eliminates the use of a special plug 
seal. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a self-sealing device is 
positioned inside a casing adjacent a wall opening therein. A fill tube is 
inserted into the device to fill the capacitor with a dielectric fluid and 
then, upon retraction of the fill tube, the device automatically forms a 
fluid tight seal with the casing. The sealing device comprises a seat for 
the seal, formed on the inside of the opening, a resilient gasket shaped 
to seal the opening, a biasing spring for urging the gasket into sealing 
relationship with the seal, and a retaining cage or housing mounted to the 
inside of the wall or cover to form an enclosure for the gasket and 
spring, and a guide for aligning the gasket and spring with the seat. 
In order to fill the capacitor casing, a fill tube is inserted in the 
opening. This tube compresses the spring and opens the seal to allow the 
impregnantion of the capacitor unit. The fill tube is thereafter rapidly 
removed from the opening permitting the gasket to reseal the unit. For 
vacuum drying of the capacitor prior to fluid filling a key means is 
employed to keep the seal open to remove moisture.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now to the drawing and in particular to FIG. 1, there is shown a 
power capacitor 10 which is representative of the larger kinds of 
electrical capacitors. Capacitor 10 comprises a casing 12 which may 
embrace a volume of one or more cubic feet. Presently, most casings 12 are 
made of steel and are sealed by welding. At the top of the casing 12 are 
one or more insulated bushings 14 and 16 through which pass electrical 
terminals connecting leads to the capacitor rolls within the casing 12. 
Filling of the casing takes place by means of a fill opening or hole 18 in 
the cover 20 of capacitor assembly. Sealing of the fill hole 18 has been 
accomplished by various prior art methods of sealing capacitor fill 
openings, and include for example, the pinch off tube method as above 
described. The pinch off tube method is eliminated by the capacitor 
filling and sealing device of the present invention which is utilized in 
connection with the fill opening 18 as illustrated. 
Referring now to FIG. 2, the sealing device 22 of the present invention is 
shown in the closed position, and illustrated just above the device 22 is 
a notched key 24 for maintaining the sealing device 22 in the open 
position for vacuum drying as will be hereinafter described. The fill 
opening 18 of the cover 20 is adjacent a retainer cage or housing 26 which 
is suitably joined to cover 20, for example, by riveting as shown by lugs 
or rivets 28 and 29. A unique feature of my invention is that these rivets 
28 and 29 may be formed as an integral part of the cover 20 by means of 
extruding some cover material at sites 30 and 32 to form rivet shanks on 
cover 20. Positioned inside the house 26 is a suitable sealing means such 
as seal gasket 34 which forms a fluid tight seal against the inside or 
seat 36 of the fill opening 18. The seal gasket 34, supported by gasket 
cup washer 38, moves within a predefined portion of the housing 26. 
Between the housing 26 and the gasket cup washer 38, is a biasing spring 
40 that urges the gasket cup washer 38 with the seal gasket 34 set therein 
toward the seat 36 to provide the fluid tight seal. 
In the drying process this seal gasket is held away from the cover 20 by 
means of the notched key 24 inserted in the opening 18. After drying the 
key 24 is removed and the gasket 34 seals the unit until it is ready for 
impregnation. There are small notches on each side of the fill opening 18. 
Matching ears are present on the fill tube (not shown) which is inserted 
and given 1/8 to 1/4 turn. The fill device seals to the cover with an "O" 
ring and after impregnation the fill device is released by a reverse 1/8 
to 1/4 turn. This allows a very quick action of the internal spring loaded 
seal with a minimum of loss impregnant. 
An illustration as shown in FIG. 3 of the sealing device 22 in the open 
position with the key 24 inserted through the fill opening 18 and suitably 
rotated to maintain said position. The base 41 of the key 24 presses down 
on the seal gasket 34 and the gasket cup washer 38 such that the biasing 
spring 40 is compressed. This opens the sealing device 22. By a simple 
rotation the notches on the key 24 disengage from the projections in the 
opening 18 and permit withdrawal of the key 24 which releases the seal 
gasket 34 and permits the seal to close. 
The housing 26 is shown from the bottom view in FIG. 4 and the side view in 
FIG. 5. In one embodiment of this invention the housing 26 has three 
mounting legs 42, 44 and 46 with holes 48, 50 and 52 suitably located 
therein for attaching to the capacitor cover. In FIG. 5 the housing 26 is 
shown with a first channel 54 for guiding the movement of the seal gasket 
34 and the gasket cup washer 38 and a second channel 56 for locating the 
biasing spring 40. 
The novel technique of fastening the housing 26 to an aluminum cover 20 is 
shown in FIG. 2. Welding or brazing this assembly is neither practical nor 
economical. The extruded mounting lugs 28 and 29 are used as rivets and 
allow the mounting of the sealing device 22 to the cover 20 with a single 
operation of a hammer which strikes the three rivets simultaneously. The 
method of extruding or cold flowing of the aluminum into a rivet die, at 
indicated lug sites 30 and 32, assures the leak tightness of the three 
mounting points. 
The sealing device of my invention can be used as a seal for mass 
spectrometer leak testing of the capacitor, or in other suitable 
applications where a device needs to be evacuated and fluid filled from 
the same opening and the opening is required to remain sealed over an 
operating temperature range of between about -40.degree. C. to 150.degree. 
C. Under these conditions a capacitor may have both positive and negative 
pressure therein. 
It will be appreciated that the invention is not limited to the specific 
details shown in the examples and illustrations and that various 
modifications may be made within the ordinary skill in the art without 
departng from the spirt and scope of the invention.