US3513437A - Arc gas expansion chamber for high voltage termination bushings - Google Patents

Description

May 19, 1970 w. A. MCMORRIS ARC GAS EXPANSION CHAMBER FOR HIGH VOLTAGE TERMINATION BUSHINGS Filed Jan. 8, 1968 2 Sheets-Sheet 1 A w y 9W 5 3 k United States Patent US. Cl. 339-111 3 Claims ABSTRACT OF THE DISCLOSURE The application discloses an electrical termination bushing for hermetically sealed high voltage devices such transformers having an internal sealed chamber or external sealed metallic pressure chamber attached thereto for receiving and cooling arc gases generated during load making or load breaking and for limiting gas pressures to a magnitude which will not damage the bushing. One embodiment comprises an annular metallic chamber threaded to an inner end extension of a bushing contact structure and a bushing well formed around the chamber, contact, and an included bushing insert carrying the contact, or a sealed chamber formed in a bushing. A second embodiment contemplates the attachment of a sealed metallic cup to the inner end of a modified conventional bushing by a hollow stud directly connected to the contact structure of the bushing and projecting through the inner end of the bushing casing into the transformer.

BACKGROUND OF THE INVENTION This invention relates to termination bushings and, more particularly to improvements in high voltage termination bushings adapted for use in hermetically sealed devices such as transformers.

As is well known to those skilled in the high voltage termination art, the electrical arcing caused by load-make and load-break operations is a long standing problem which has been approached in several ways. One of the most common solutions utilized in existing high voltage terminations comprises the placement of a gas generating solid material in follower relationship with the contacts so that, when an arc is created, it will react with the solid material to liberate arc extenguishing gases. This scheme has worked well to limit the arcing; but, the proper treatment and handling of the generated gases has now presented a new problem in that the resulting extreme pressures are capable of severely damaging the bushing or ejecting the terminator contact which may ultimately result in personal injury, power failures and expensive maintenance. Even in the absence of a supplied arc extinguishing gas, an ambient gas subjected to high arc current under fault conditions can cause bushing rupture.

In meeting this pressure problem, many existing terminations are designed with a tubular core in which contact is made and through which the arc gases are ducted. When utilized in connection with a hermetically sealed device such as a transformer, the core is extended through the inner end of the bushing and fitted with a one way valve to vent the gases into the transformer. This method is considered undesirable in that the vented gases violate the hermetical seal and contaminate the dielectric liquid placed within the transformer.

As is well understood, these transformers and like electrical apparatus are sealed to prevent the entry of oxygen or moisture which would be harmful to the operation of the electrical apparatus. The pressure within this type of apparatus normally varies up and down as its temeprature changes with varying load, so that at any particular time it may be above or below the outside pressure. Under these ice circumstances there is a possibility that the valve could admit gas into the sealed apparatus when its internal pressure was low. Not only would the oxygen and moisture in such admitted gas be harmful to the electrical apparatus, but it would also shift the range of the internal pressure excursions, which could result in peak pressure exceeding that for which the apparatus was designed. Further, the gases which are discharged into the electrical apparatus during arcing of the contacts carry soot and droplets of molten metal and other contaminants into the electrical apparatus which are detrimental to its operation.

Accordingly, it is one object of this invention to provide an improved high voltage termination bushing for use in transformers or the like which bushing will withstand the pressures generated by are gases while simultaneously maintaining the hermetical seal of the transformer.

A further object of this invention is to provide an inexpensive pressure expansion chamber adapted for use with existing conventional high votlage termination bushings to limit are gas pressures to acceptable magnitudes while preserving the hermetical seal of an electrical device within which the bushing is mounted.

SUMMARY OF THE INVENTION In carrying out this invention, an improved high voltage termination bushing is provided, having an elongated casing with a hollow core. A first electrical contact is positioned within the core and means for receiving and holding a second electrical contact are formed at one end of the casing. A sealed chamber is provided having a connection with the first contact and positioned adjacent the other end of the casing in gas pressure communication with the electrical connection area. Means are provided for hermetically sealing the overall bushing casing to an electrical device.

BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes with claims which particularly point out and distinctly claim the invention which is sought to be protected, the preferred embodiments are disclosed in the following descriptions in connection with the accompanying drawings in which:

FIG. 1 is an exploded sectional elevation view of an improved high voltage bushing showing an internal gas pressure expansion chamber according to one form of this invention, together with a conventional bayonet type terminator;

FIG. 2 is an enlarged sectional view of one form of an internally installed pressure chamber taken along its axis according to the embodiment of the invention shown in FIG. 1;

FIG. 3 is a partial sectional elevation view of an improved high voltage bushing according to this invention showing another form of internal pressure chamber;

FIG. 4 is a sectional elevation view of one type of existing bushing which shows the external attachment of a gas pressure expansion chamber according to another form of this invention; and

FIG. 5 is an enlarged sectional elevation view of the externally mounted chamber taken along its axis.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, in which like numerals are used to indicate like parts throughout the various views thereof, this invention in one embodiment, is shown in FIG. 1 as an improved high voltage bushing 10 with an internally installed gas pressure expansion chamber 12. The bushing 10 is of the kind used in hermetically sealed electrical apparatus, such as a transformer, and includes a composite, substantially cylindrical housing, comprising an outer bushing well 14 and an inner bushing insert 16.

The bushing well 14 may be molded to a metal plate or wall member for hermetically sealing to a transformer in the manner more fully described and claimed in application Ser. No. 470,068, filed July 7, 1965 for Plastic Bushing for Electrical Apparatus and Method of Making, in the names of F. S. Nichols, G. F. Lipsey and G. C. Nonken, and assigned to the same assignee as this invention, now Pat. No. 3,388,212.

The bushing well 14 is constructed of an insulating material, such as a molded epoxy resin and is formed with a large hollow core. The core extends from the top of the housing well 14 to a wall 18 formed at the bottom in which is formed an aperture 20 which is concentric with the core but of lesser diameter.

The cylindrical gas pressure expansion chamber 12 is inserted into the lower end of the hollow core of the bushing well 14. The chamber 12 is preferably constructed of a good heat conducting metal such as copper. As is best shown in FIG. 2, chamber 12 is provided with a threaded hole 22 in the upper horizontal wall 24 and a threaded bore hole 26 in the bottom horizontal wall 28 which bore hole 26 is of the same size and in line with the threaded hole 22 of the upper wall 24. The bottom wall 28 is formed with a downward projecting cylindrical protrusion 30 which fits through the aperture 20 formed in the bushing well wall 18 and is sealed thereto so as to provide a hermetical seal about the bottom of the bushing. A contact 32 for connecting internal transformer leads is formed on the outer bottom surface of the protrusion 30.

A tubular metal female contact 34 which is threaded at the lower end 36 passes through the hollow core of the bushing well 14 and threadedly engages chamber 12 at threaded hole 22 and bore hole 26. Gas ports 38 are provided in the threaded wall portion 36 of contact 34 to provide a means for pressure communication between the interior of contact 34 and the chamber 12. With the contact 34 properly positioned within chamber 12, the chamber 12 constitutes an annular gas expansion chamber which completely surrounds the threaded portion of the contact 34.

A sleeve 40 of gas generating material of the same inside and outside diameters as the contact 34 fits within the core of the bushing insert 16 in a position above and in line with tubular contact 34. When properly positioned, the lower end of the bushing insert 1 6 is flush against the upper horizontal wall 24 of the chamber 12. The upper lip 42 of bushing insert 16 is specially formed as the male member of a bayonet connection which male member plugs into a female member 44 carried within a terminator housing 46. A male contact 48 is mounted within the terminator housing 46 which contact 48 is designed to engage contact 34 in proper electrical connection and which housing 46 is adapted to receive the upper end of bushing insert 16 and hold it by the bayonet lock created in the aforementioned manner. Contact 48 is provided with a follower 50 of gas generating insulating material similar to sleeve 40.

The bushing well 14 may be mounted and hermetically sealed to a transformer or other electrical apparatus by means of a metal plate 52 which is molded within the bushing well 14 and Welded to the transformer wall 54, as described in the aforementioned patent application Ser. No. 470,068.

In operation, Whenever a load make or load break is executed and an arc is created, the arc acts upon the gas generating material 40 and 50 to produce high pressure gases which in turn act to extinguish the arc. The gases so generated are then vented down through the core of the tubular contact 34, out through the gas ports 38 and into the chamber 12 as indicated by the arrows in FIG. 1. Within the metal chamber 12, the gases expand and cool so as to dissipate the shock energy caused by the suddenly generated gases which dissipation ultimately prevents power failure and personal or equipment injury.

FIG. 3 shows another form of the invention in which a pressure chamber 12a is formed directly in the bushing 10a. As is shown, the bushing 10a, which is preferably molded of an epoxy resin material, has a gas expansion chamber formed in bushing 10a during molding. A terminal member 30a, preferably of copper, may also be molded into the bushing 10a. Contact member 34a is generally similar to contact 34 of FIG. 1 and is threaded into bore 26a of terminal 30a. Contact 34a is also provided with ports 38a to permit the generated gases to expand into pressure chamber 12a.

In FIG. 3, bushing 10a is shown as a one piece bushing, rather than the two part member shown in FIG. 1. Of course, it will be understood that the upper portion of bushing 10a will be similar to bushing 10, so that it may be connected to any desired type of termination member, for example that shown in FIG. 1. As shown, a metal plate 52a may be molded to the bushing 10a, as described in aforementioned patent application 470,068. Plate 52:: may then be welded to the wall or cover 54a of an electrical apparatus. As in the form of invention shown in FIG. 1, the pressure chamber 12a is attached to one end of the electrical contact 34a so as to allow expansion of any gases generated during making or breaking an electrical connection to contact 34a.

FIG. 4 shows a second embodiment of the invention comprising a modified conventional terminator bushing 10b comprising an outer bushing well 14b and an inner bushing insert 16b. Bushing 1% includes a tubular contact 56 which is provided at its lower end with internal threading 58. A hollow stud 60 which has outside threading at each end 62 and 64 is mated to the internal threading 58 of contact 56 at one end of the stud 60 and positioned within the bushing in such a manner that the other end of stud 60 protrudes out through the bottom of bushing well 14b. A cylindrical metallic gas pressure chamber 12b is provided which is formed with a threaded hole 22b in one of the parallel walls on the axis of the cylinder. The threaded hole 22b mates with the protruding threaded portion 64 of stud 60 and, when the chamber 12b is properly connected to the stud 60, it forms a hermetical seal therewith. A terminal 66 is provided at the lower end of chamber 12b for electrical connection to the internal leads of the electrical apparatus.

In operation, when an arc is created during load-make or load-break activities, the generated gas supplied by the gas generating material 4019 reacting with the arc is vented down through the tubular contact 56 and hollow stud 60 into the sealed pressure chamber 12b. The pressure chamber 12b provides sufficient space to contain the suddenly generated gas and to limit the resulting pressure to a value that will not damage the bushing or eject the terminator. Likewise, the hermetical seal is maintained and the dielectric liquids are not contaminated by the gaseous products. The chamber 12b comprising a metal of high thermal conductivity such as copper, cools the gases and is especially effective in dissipating shock at elevated operating temperatures which may range up to C. It will also be seen that this embodiment of the present invention is adapted for economical installation in existing terminator bushings and requires a minimum of modification to the bushing.

From the above description of the preferred embodiments of this invention it is believed clear that all of the objects and advantages herein before set forth have been attained. However, it should be understood that while there has been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

What is claimed as new and which it is desired to secure by Letters Patent of the United States is:

1. An eiectrical termination bushing having an elongated casing with a hollow core, a first electrical contact within the core, means for receiving a second electrical contact at one end of the casing to engage in electrical connection with said first electrical contact, means for hermetically sealing said casing to an electrical apparatus housing, said first electrical contact being an elongated tube, one end of said tube making said electrical connection with the second electrical contact, threading on the other end of said tube, a gas chamber comprising an annular sealed metallic pressure chamber, a terminal on one end of said gas chamber, the other end of said gas chamber and said threaded end of said tube interconnected to provide gas pressure communication from said electrical connection end of said tube to said gas chamber.

2. An electrical termination bushing as set forth in claim 1 in which said gas chamber is threadedly mounted on said threaded end of said elongated tube and is fitted within the core of said casing.

3. An electrical termination bushing as set forth in claim 1 in which one end of a hollow stud is threaded to said threaded end of said tube and said gas chamber is threaded to the other end of said hollow stud, said gas chamber mounted outside the' core of said casing.

References Cited UNITED STATES PATENTS RICHARD E. MOORE, Primary Examiner US. Cl. X.R.

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