Electricity: electrical systems and devices – Electrostatic capacitors – With protection or compensating means
Reexamination Certificate
2000-01-05
2001-11-06
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
With protection or compensating means
C361S314000, C361S301500
Reexamination Certificate
active
06313978
ABSTRACT:
FIELD OF INVENTION
The invention herein relates to a capacitor having a capacitive element in a housing and insulating fluid surrounding the capacitive element, a pressure responsive interrupter means, and a volume of compressible air confined within the housing which facilitates operation of the pressure responsive interrupter means.
BACKGROUND OF INVENTION
Capacitors of the type typically used in motor run applications have a housing and a capacitive element of wound polymer film within the housing. The housing is at least partially filled with an insulating fluid. The capacitive element is connected to terminals on the exterior of the housing, and a pressure responsive interrupter system is associated with the terminals and conductors connecting the capacitive element with the terminals. If the capacitive element fails, it may do so in a sudden and violent manner, producing heat and out-gassing such that high internal pressures are developed within the housing. The pressure responsive interrupter system is designed to break the connection between the capacitive element and the terminals in response to the high internal pressure, thereby removing the capacitive element from a circuit and stopping the high heat and over-pressure condition within the housing before the housing ruptures.
The housings have often been constructed of metal, with the terminals and pressure responsive interrupter system on a metal cover of the metal housing. It had always been assumed that metal enclosures were necessary for strength, due to the high internal pressures that are developed within the housings during a fault or run-away defective condition, and due to the force required to lift or bend the metal cover to insure disconnection of the capacitor terminals from the internal capacitive element. However, in recent years capacitors with plastic housings have appeared on the market, including pressure responsive interrupter systems that operate by bending or lifting a plastic cover. Typical capacitors with plastic enclosures are shown in U.S. Pat. Nos. 5,019,934, 5,148,347 and U.S. Pat. No. 5,381,301.
In order to insure that the pressure responsive interrupter systems of plastic housing capacitors perform consistently and reliably, it was found necessary to underfill the housings with insulating fluid, leaving a substantial amount of air within the capacitor housing. The additional air is believed to act as a cushion during the violent, uncontrolled reaction that takes place when sudden failure of the capacitor is induced by the rigorous standards of UL testing, and similar reaction can take place when the capacitor fails under real-world situations. When the capacitor housing is entirely or nearly filled with insulating fluid, the plastic housing tends to rupture, but when the housing is partially filled with insulating fluid, the plastic housing is able to maintain integrity while the pressure responsive interrupter system operates in its intended manner.
However, one of the major drawbacks of leaving air space in this type of capacitor is that the capacitive element may not be totally immersed in the insulating fluid. This is especially true if the capacitor is mounted in a horizontal position or in an inverted position, and inverted mountings are becoming increasingly popular. When the insulating fluid does not fully cover the capacitor element, at least a portion the end spray area of the capacitive element is exposed to the air and possible development of corona, leading to capacitor degradation. Additionally, the capacitive element tends to generate heat during use, and the heat is best dissipated through the surrounding insulating fluid. When areas of the capacitive element are not covered by fluid, they develop excessive heat which has a deleterious effect on long term capacitor performance. Typically, there is a reduction in capacitance value to below acceptable limits, an increase in dissipation factor which indicates internal arcing, and eventual separation of end spray material. This excessive capacitive loss and increase in dissipation factor will usually result in a runaway failure mode, with the sudden and violent reaction requiring successful operation of the pressure responsive interrupter system.
Nevertheless, a capacitor with a plastic housing has certain advantages over a capacitor with a metal housing. These advantages include lower costs, and the insulating properties of a plastic housing compared to the conductive properties of a metal housing. Overcoming the drawbacks of the prior capacitors with plastic housings would therefore be an advance in the art.
SUMMARY OF THE INVENTION
It is a principal object of the invention herein to provide an improved, fluid-filled capacitor.
It is also an object of the invention herein to provide a fluid-filled capacitor with a plastic housing.
It is an additional object of the invention to provide a fluid-filled capacitor in which the capacitive element is substantially fully immersed in fluid.
It is another object of the invention to provide a fluid-filled capacitor in which the pressure responsive interrupter system operates reliably before rupture of the housing.
In carrying out the invention, there is provided a capacitor with a housing having a case and a cover, the cover having terminals thereon for connecting the capacitor in the electrical circuit. A capacitive element is received in the housing and connected with the terminals. A pressure responsive interrupter means is associated with the capacitive element, cover and terminals for breaking the connection between the capacitive element and the terminals upon a high pressure condition in the housing. Air chamber defining means confines a compressible volume of air within the housing, and an insulating fluid is provided within the housing substantially surrounding the capacitive element. The air in the air chamber defining means is compressed upon a high pressure condition within the housing caused by failure of the capacitive element, which cushions the high pressure condition prior to operation of the pressure responsive interrupter means.
According to further aspects of the invention, the housing is fabricated of plastic. Also, a plastic cover of the housing bends outwardly to break the connection between at least one terminal and the capacitive element within the housing.
According to additional aspects of the invention, the air chamber defining means includes a piston slidingly and sealingly engaged with the side wall of the housing to confine a volume of air, and the piston may be displaced to compress the volume of air. Further, the piston may be positioned adjacent a bottom end of the housing, opposite the cover. The piston may include a center shaft for centering and elevating the capacitive element within the housing, creating space for insulating fluid adjacent one end of the capacitive element.
According to further aspects of the invention, the volume of air in the air chamber defining means, prior to compression of the air therein, occupies about 15% to about 40% of the volume of the housing, and desirably about 25-30% of the volume. This aspect of the invention is advantageously carried out in a cylindrical housing of approximately 4 inches in length and 2 inches in diameter, having a piston defining an air chamber approximately ⅜ inch to 1½ inches in length, and preferably about ¾ inch in length.
According to other aspects of the invention, the air chamber defining means is flexible film positioned within the housing and defining one or more air pockets.
In further carrying out the invention, operation of the pressure responsive interrupter means is facilitated by confining a compressible volume of air in the housing. Further, the compressible volume of air displaces the fluid so that the capacitive element is substantially immersed in the fluid.
Other and more specific objects and features of the invention will in part be recognized by those skilled in the art and will in part appear in the following description of the preferred embodiments
Stockman Richard W.
Stockman Robert M.
Zacherl Dean T.
American Radionic Co., Inc.
Reichard Dean A.
Thomas Eric W.
Ware Fressola Van der Sluys & Adolphson LLP
LandOfFree
Fluid-filled capacitor with pressure interrupter means and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fluid-filled capacitor with pressure interrupter means and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fluid-filled capacitor with pressure interrupter means and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2592853