US1752281A - Insulator-bushing joint - Google Patents

Description

March 25, 1930. A. o. AUSTIN 1,752,281

INSULATOR BUSHING JOINT Filed Aug. 11, 1924 2 Sheets-Sheet 1 /VVE/VTOR I w ATTORNEVS x fl BYW.

March 25, 1930.

A. o. AUSTIN l,752,281

INSULATOR BUSHING JOINT Filed Aug. 11, 1924 2 Sheets-Sheet 2 /NVENTOR BY a?. dwa::

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A TTORNEY Patented Mar. 25, 1930 UNITED STATES PATENT OFFICE AETHUE O. AUSTIN, OF NEAR BABBEBTON, OHIO, ASSIGNOB., BY MESNE ASSIGNMENTS, '1'0 THE OEIO BRASS COMPANY, OF MANSFIELD, OHIO, A COBPORATION OF NEW JERSEY INSULATOR-BUSHING JOINT Application filed August 11, 1924. Serial No. ?31,501.

This invention relates to insulator bushings for electrical. conductors and especially to joints between the parts of the dielectrc members and has for its object the provision of improved insulator bushing in which the dielectric parts will be united y a tight jont which will not be afiected by temperature changes or other Operating conditions.

The invention is exemplified in the combination and arrangement of parts shown in the accompanying drawings and described in the following specification and it is more particularly pointed out in the appended clams.

In the drawings- Fig. 1 is an elevation with parts n section showing one embodiment of the present invention.

Fig. 2 is a fragmentary enlarged section showing the joint between the outer shell members of the bushing. p

Fig. 3 is a view similar to Fig. 2 showing a slightly different form of the invention.

Fig. 4 is a view similar to Figs. 2 and 3 illustrating another modification. p

Fig. 5 is a view similar to Fig. 1 showing a different' species of the invention.

In bushings used for very high voltages it is exceedingly difficult to make the bushings in a single piece of suflicient size to withstand the voltage. In order to insure 'greater reliabilit and lower the cost it is desirable to make t e bushings up in a number of parts and so combine them that they will function as a whole. One of the more feasi ble means is to provide outer shells of the desired contour and depend upon inner members or battles to withtsand the electrical Stress. In order to make the electrical discharge take the path determined by the outer i contour, the intervening space, within the outer shell, is filled with an insulating oil or compound. Since the presence of the insulating compound is essential to prevent flashover of the much shorter path, within the.

shell, it is necessar to retain the insulating compound by avoi ing leaks. As the dielectric members usually have a much smaller.

coeificient of expansion than `the other members, made of metal, it is exceedingly diflicult to maintain a tight joint between the dielectric member and the metal members in order owing to the relatively large diameter involved.

In the form of the invention shown in Fig. 1, the bushing is composed'of an'upper dielectric member 10 having weather sheds or fianges- 11. The dielectric member 10 is attached to the metal flange 12 by cement 13 or other holding material 'such as lead or fusible metal. The lower or complementary, dielectric member 14: is attached to a metallic -flange 15 by suitable holding material 16 as in the case of member 10. 'The two com lementary shells are provided with bolts 1 or other suitable-means for clamping the two parts together with an 'intervening gasket 18. As long as the asket 18 will form a tight joint between t e * dielectric members 10 and 14 there will be no leakage of oil or compound at the center joint and practically the only function of the flange pieces 12 and 1 5 is to maintain the pressure on the gasket 18 between the two dielectric pieces 10 and 14 to prevent leakage from the inside. The construction is a decided im rovement and has advantage over" the one w ere the dielectric member is clamped on the flan e with an intervening gasket as will be seen y the fol lowin analysis. i

Bus ings used either as entrance bushings or on oil circuit breakers are subject to fluotuation in temperature. As the temperature rises the 'metal flanges' have a linear expension and tend to draw away from the dielecmember which may cause damage, particularly where the diameters are large. With a Construction as shown, the expansion of the metallic members will atfect the dielectric member but little, particularly if there is resiliency in the joint 13 or in a portion of the gripping members 12 and 15 to compensate for the unequal thermal expansion and contraction of the porcelainshell members and the metal holding members. This resiliency may be obtained by the use of resilient sanded joints covered in Patent No. l,284z,975, granted November 19, 1918.

In the arrangement shown it will be seen that it is possible to clamp or tighten the di electric members directly upon each other, the essential being that the joint is not made between a dielectric member and a metallic sleeve or flange. The gasket 18 may be of any suitable material such as cork, fibre, asbestos or a metallic ring similar to those composed of thin Copper and asbestos. here the edges of the porcelain are ground they may be clamped directly together altho it is usually preferable to use a slight cushion or gasket. here they are clampcd directly together it is usually advisable to use paint, varnish or glue which will take care of any unevenness and prevent leakage of oil or compound. The use of gaskets is generally preferable, however, as the two part s can be readily removed in case of damage to a part whereas this would be exceedingly diflicult if the parts were clamped together with an insulating paint or glue.

l Vhere the resilient joint is used and the pressure is unequal on the two sides of the flanges, there may be a tendency to leak thru the joints 16 and 13, particularly if these joints are of open Construction. This condition is likely to exist where the bushings are used in pressure apparatus or in the case of conservator type transformers in which the transformer housing is filled with liquid under pressure supplied from an elevated reservoir or those using `pressure regulated traps. Where conditions are favorabie, this can be taken care of by coating one side of the gasket. If the gasket is impervious it will prevent this leak. If, however, the gasket is of a poro'us nature, there may he a leak thru the same. In some cases this may be revented by paint or coating the gasket wit a va'rnish, glue or other material. In some cases, however, this may not be sufllciently effective owing to the danger of pin holes.

To avoid this difliculty, the arrangement shown in Fig. 3 is very effective. In Fig. 3 a thin metallic dam 19 is preferably inserted in the gasket 18 which, in this case, is made in two parts. This dam may be of metal or suitable impervious material such as a varnished sheet of paper or fibre. In general, however, if the metal is thin, the friction is suflicient to cause the metal dam to niove with the gasket so it will not tend to destroy the joint. This member may be in the form of a flat ring or may be corrugated or waved to provide resiliency and better grip and more surface between the gasket on either side. It is evident that where a slight protection only is desired, that the dam 19 may have gasket material on one side only. ln general, however, it is preferable to place gasket material on each side as the path of leakage is double thru the gasket material, making leakage practically impossible even under severe conditions such as high temperatures and pressures.

Where the dam 19 is wholly or partlymetallic, it may be used for a further advantage which is shown in F ig.' 5. In Fig. 5 the metallic dam 23 has a projecting portion 20 which is turned upward and makes electrical contact with a spring member 21 attached to an internal metallic shield 22. The dam 23 makes electrical contact with the flange 15 thru the bolt 17. With this arrangement the screen shield 22 is at the same potential as the holding members 12 and 15. This tends to prevent charging current starting along the surface of the dielectric members and to prevent flashover of the bushag. Where greater metallic contact is desired between the flange and dam 23, the outer end of the dam 23 is turned down over the lower half of the gasket 18 so as to make direct contact with the holding member or flange 15. The center rod 24 may form the center electrode or conductor which it is desired to insulate from the flange 15.

It is not necessary to cement or attach the holding members 12 and 15 permanently to 'the dielectric shells as a removable or clamping fiange may be used as shown at 25 in Fig. 4. In general, this flange may be made in two parts and if fairly heavy, it is desirable to place a gasket 26 between the fiange and the dielectric member. The dielectric member may be beveled outwardly as shown in the drawin to retain the flange 25. If the portion ad acent to the dielectric member is not too heavy or of suitable material it may have uniform thickness and be compressed so it will engage the bevel on the dielectric bushing or if a gasket space is sufficient, the ring may be passed over the enlargement at the edge of the dielectric member and the spacer dropped into place. Where the portion of the dielectric member at the joint is larger than the rest of the bushing, the holding fiange or rin may be dropped down over and need not %e split.

In order to provide means for filling the casing the dielectric member 10 may have a triangular notch in its lower edge and the flange 12 may be similarly notched to receive a block 27 havin an opening therethrough in the outer end o which a plug 28 is thread ed to close the openin suitable packing or gaskets are interpose between the block 27 and the adjacent edges of the dielectric members to form a tight joint. The baflle member 29 is shown as Secured to the shell member 14 by a cement or other suitable joint 30 which also carries an electrostatic screen 31. Other baflles 32 may be cemented or otherwise suitably Secured to the central eonduc` tor 32.

It will be evident that the gasket may be used between the dielectric member only. It is also, evident that the edge of the dielectric members and the flanges need not be in the same plane. Where the dielectric member projects beyond the holding flange, reater pressure wll be obtained on the gas et between the dialetric members than between the metal flanges. If the dielectric members are set back from the face of the holding flange the pressure may be controlled or reduced.

I claim:

1. An insulator bushing comprising a pair of shell members having edges arranged to register With each other, means for clamping said shell members together to form a closed chamber, said means comprising a separately formed flange Secured to one of said shell members adjacent the edge thereof but displaced outwardly from said edge in a position to leave said edge exposed, an imperforate dam held between the edges of said shell members and completely spanning the joint between said flange and its shell member to prevent leakage through said joint and a gasket between said edges.

2. An insulator bushing comprising a pair of shell members having edges thereof arranged to register 'with each other, means for clamping said shell members together to form a closed casing, said means conprising a flange secured to the outer surface of one of said shell members adjacent the end thereof but displaced outwardly from said edge in position to leave said edge exposed, a packing of yielding material interposed between said edges, and a layer of impervious material completely spanning the joint between said flange and its shell member.

3. An insulator bushing comprising a pair of dielectric shell members having registering edges, means for clamping said shell members together to form a closed casing, and a thin metal sheet interposed between said edges, said metal sheet having a different coeflicient of expansion 'for temperature changes from that of said shell members, the clamping force between said shell members being sufficient to constrain said sheet to expand and contract radially in unison with said Shell members for temperature changes.

4. An insulator bushing comprising a pair of porcelain shell members having registering edges, means for clamping said shell mem- I bers together to form a closed casing, a pair of gaskets interposed between the adjacent edges of said shell members, and a thin metal dam interposed between said gaskets, the pressure onsaid shell members being suflicient to constrain the packing formed by said gaskets and dam to expand and contract radially .in unison with said shell members for temperature changes.

5. A bushig insulator comprising a pair of dielectric shell members, having registering open ends, flanges Secured to said shell members respectively and connected together to hold said shell members in registration to form a closed housing, a gasket interposed between the registering ends of said shell members, a metallic dam bridging the space hetween each flange and its shell member and extending into the inte'ior of said housing, the outer portion of said dam being electricaly connected with said fianges, a conductor extending through said housing, a tubular dielectric baflle disposed within said housing and surrounding said conductor, a conductor shield surrounding said baflle and electrically connected with said dam, the opposite edges of said shield being rolled to form heads, and dielectric flanges on said bafile overlying the edges of said shield and forming pockets for said heads.

(i. In combination, a pair of dielectric shell members having open sides facing each other with the surrounding edges in confronting relation, langes formed of material having a different coeflicient of eXpansion for temperature changes from that of the material of said shell members, said flanges being Secured respectively to said shell members adjacent said edges, means connecting said flanges for pressing said shell members toward each other to maintain a tight joint between said edges, said joint being adapted to contract and expand in its entirety in unison with said shell members for temperature changes to avoid relative movement of the parts of said joint, and a compensating connection between said flanges and said shell members to permit relative movement thereof due to unequal thermal expansion and contraction.

7. In combination, a pair of dielectric shell members having o en sides facing each other with the surroun ing edges in confronting relation, metal supports Secured to said shell members respectively, and having compesating connection therewith to permit relative movement of said supports and their respective shell members due to unequal thermal expansion and contraction, and means for connecting said supports together to draw said shell members toward each other and maintain a tight joint between said confronting edges, said joint being thermally ex` pansible and contractable in 'its entirety in unison With said shell members to avoid reiative movement of the parts of said joint for temperature changes.

llO

8. A bushing insulator comprising a pair of dielectric shell members having open sides facing each other and having their edges, surrounding said sides, in confrontin relation, to form a housing, a separately ormed clamping ring surrounding the rim portion of each of said shell members and disposed entirely outside of the outer pe'iphery of said housing, means for connecting said clamping rings to press said confronting edges together, the material of each of said shell members being extended inwardly substantially as far, at the confronting edge of said member, as it is throughout the portion thereof in radiai registration With its clamping ring, so that the confronting edges of said shell members will be in direct alignnient in the direction of the axis of said housing With the material immediately within said clamping rings.

In test-imony whereof I have si name to this specification on this it August, A. D. 1924.

ARTHUR O. AUSTIN.

ed my day of

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