US2082055A - Bushing insulator - Google Patents

Description

June 1, 1937. R. HIGGINS BUSHING INSULATOR Filed March 27,- 1936 INVENTOR RAL PH H/G G/Ns. BY

Wg, MQ

ATTORNEY Patented .inne 1, IQS? UNITED STATES 7 Claims. (0l. T33-fllt) This invention relates to a bushing insulator such as are used for insulating the conductors leading into housings for electrical apparatus, and particularly toinsulators for high voltage appa- 5 ratus such as transformers and switches. the bushing, the sleeve extending down to the oil 5,

One object of the invention is to provide a level; or a metal sleevefhas been placed about bushing insulator which will decrease the danger the outer surface of the lower bushing member of explosions within the housing on which the extending from the housing cover to the oil level. insulator is mounted. o Such'expedients are effective in short-circuiting Y.

l Anotherl object of the invention is to provide leakage currents over the bushing but are not so 10 improved means for controllingl the electrostatic effective in overcoming charging currents'as they eld about the insulator so as to avoid formation usually do not make perfect contact with the of corona and prevent sparking. entire outer surface of the dielectric member.

A further object of the invention is to provide Furthermore, as heretofore constructed, various l a device of the class named which shall be of expedients for short-circuiting the leakage cur- 15 improved construction and operation. vrents over the bushing above the oil level have Other objects and advantages will appear from been objectionable for the reason that they rethe following description. duce the insulation between the top of the hous- The invention is exemplied by the combination ing and the conductor at the lower end of the and. arrangement of parts shown in the accombushing, thus increasing the danger of ashover 20 panying drawing and described in the following Within the housing. This danger is largely due y specication, and it is more particularly pointed to the tendency for corona to form at the lower out in the appended claims. end of the conductor sleeve and also at the lower In the drawing: end of the bushing where the conductor emerges Fig. l is an elevation partly in section showing from the bushing. The present invention secures -25 one embodiment of the present invention. the advantages of the long ground sleeve and at Fig. 2 is a fragmentary section showing a modithe same time overcomes the diiculties heretohed form oi the invention. fore present when the use oi ground sleeves has Fig. 3 is a fragmentary elevation of the current been attempted. transformer outlet of Fig. 2. in the form of the invention shown in Fig. l, 30 Fig. 4 is a fragmentary section of a portion of the numeral itl designates the upper shell' memthe bushing insulator showing another modiber or cone of abushing insulator and Il the lower cation of one feature of the invention. shell member or dome within the apparatus hous- In housings for electrical apparatus, it is freing. Sleeves l2 and i3 may also be used to proquently the case that-the insulating oil does not vide further insulation about the conductor I4 35 completely ll the space within the housing so and yan outer sleeve or keg l5 may be employed that a portion of the space next the cover is lled outside of the sleeves I2 and It. These insulat- With air or a mixture of gases. In some cases, ing members may all be made of porcelain or particularly ln switch housings, a combustible gas other suitable dielectric material. In practice,

may be generated by arcs below the oil surface it has been found that porcelain has many ad- 40 and this gasy by mixing with the air in the upper vantages in bushing construction over other insupart of the housing, forms an explosive mixture lating materials so far discovered. The cone I0 which, if ignited, may produce a disastrous explois supported by a flange I@ which is bolted to the sion. top Il of the apparatus housing. A metal ground Heretofore where bushing insulators have been sleeve I8 is interposed between the ilange I6 and used having dielectric members extending to the the upper end of the insulating dome II. Suitcover of the housing, lt has sometimes happened able gaskets I9, 20 and 2| are provided to insure that sparking occurs along the dielectric surface, ltight joints between adjacent portions of the which sparking is apt to ignite any explosive mix bushing. The parts of the bushing are held toture which may be within the upper portion of gether by tension on the conductor i4 exerted 50 the housing. This sparking is probably due to by a spring 22 located in an expansion chamber leakage or charging currents over the portion of 23 at the upper end of the bushing, the spring the surface of the lower dielectric member'of the serving to press the bottom of the expansion bushing above the oil and is apt to beiaggravated chamber against a gasket 24 resting on the by deposits of conducting material on the surface cone I 0. The reaction oi the spring is trans- 55 oi the bushing. Such deposits are usually quite irregular and provide gaps over which arcing takes place. 'To avoid this, a conductor sleeve has sometimes been formed on the flange about mitted to the conductor I4 by a ring nut 25. A fitting 26 closes the lower end of the bushing and is threaded onto the conductor I4 and is held tightly against a gasket 21 by the reaction of the spring 22, thus insuring a tight Joint at the lower end of the bushing. A suitable drain plug maybe provided in the tting 25. A collar 28 of molded insulation rests upon the terminal member 25 and supports the system of dielectric sleeves I2 and I3. The keg I5 is secured to the flange I5 by cement 29. The gasket 28 is metallized so as to insure a ground connection between the sleeve I8 and the flange I8. This gasket may be made of cork covered with a thin copper sheet or if an insulating gasket is used, the sleeve I8 may be grounded in any suitable manner.

To avoid the formation of corona at the lower end of the sleeve I8 and the danger of arcing over the dome II from this point, applicant has provided a. flux control member consisting of a metallic coating 38 on the outer surface of the keg I5 which extends below the lower end of the sleeve I8 and within the dome II. This metallic .coating terminates in a` pocket 3I formed by an upwardly and outwardly extend ing flange 32 on the outer face of the keg I 5. The metallized surface 3U is grounded on the flange I5 by any suitable means, such as a jumper 33. The cement 28 also acts as a conductor between the metallized surface 30 and the flange but the Jumper 33 is used to augment the electrical connection provided by the oement. Since the grounded pocket 3| extends closer to the lower terminal of the bushing than does the lower end of the sleeve I8, most of the static lines of force connecting the two oppositely charged conductors will emanate from the flux control pocket 3l through the porcelain surrounding the lower end of the pocket rather than from the lower end of the sleeve I8. This will overcome the tendency for the, formation of corona fromthe lower end of the sleeve and consequent danger of arcing over from this point.

To avoid the formation of corona from the conductor at the lower end of the bushing. the terminal member 28 is provided `with a ring 34 comprising a plate or disc bent to provide a widely rounded lower surface, the outer edge of the plate being bent upwardly and extending into a pocket formed by a flange 35 on the lower end of the dome II. The interior of this pocket is provided with a metallized coating 35 and a metallized gasket 31 consisting of a layer of cork or other suitable resilient material covered by thin sheet metal interposed between .the edge 'of the member forming the ring 34 and the inner surface of the pocket 36. This insures electrical connection between this metallized surface and the ring 34 and at the same time prevents undue pressure between the porcelain and metal at this point. With this arrangement, the greatest concentration of flux will emanate from the surface 35 through the porcelain of the dome AII which will prevent formation of corona or discharge streamers where the flux is most concentrated. The rounded surface of the ring 34 will distribute the flux at the lower portion of the ring so as to prevent concentration and consequent corona at these points. A wrapped control 38 similar to that shown in my prior PatentNo. 1,972,590, granted Sept. 44i, 1934, may be used above the top of the 'flange vI5 to prevent the formation of corona from the upper surface of the flange.

The space between the ground sleeve 'Il and the-dielectric keg I5 may be, in some instances. utilized to considerable advantage for containing the secondary winding of a current transformer, of which the main conductor I4 serves as the primary. An arrangement of this kind is shown in Fig. 2 in which the ground sleeve 35 is provided with a. shoulder 45 which carries 'a ring 4I for supporting the secondary windings 42 of the current transformer. The transformer is provided with a ring core 43. Various taps 44 for the transformer winding may be carried out to terminals 45 supported in an insulating block 45, theterminals extending through the block into an outlet housing 41 provided with suitable contacts for a cable which may be led into the housing through an opening 45.

In the form of the invention shown in Fig. 2, the wrapped control above the flange is replaced by a formed control comprising a pocket having a metallized inner surface 48 enclosed by a flange 58, the surface being provided with a grounded jumper 5I. When the keg 52 carries the flange 5I), the lower end of the keg must be small enough to pass through the ring 53 which supports the keg. In order to permit this, a wrapped control 54 is provided at the lower end of the keg instead of the integrally formed control shown in Fig. 1.

Another form of control for the lower end of the sleeve I8 is shown in Fig. 4 in which the dome 55 is provided with a pocket 55 at its upper end, the inner surface of which is metallized and electrically connected with the ground sleeve I8, the lower end of the pocket extending below the upper outer edge of the dome 55 and the lower edge of the ground sleeve I5. An up wardly extending flange 51 forms a continuation of the pocket wall within the lower end of the sleeve I8 so as to provide an insulated control for the electrostatic lines of force extending inwardly toward the inner conductor I4. In this case the keg 58 may be shorter than the keg I5 in Fig. l and is preferably provided with an upwardly extending outer flange 58 forming a pocket 5I) which provides a supplemental insulated control for the electrostatic eld. The outer surface ofA the lower dome is preferably provided with corrugations 5I for increasing the leakage surface over the dome and decreasing the danger of ilashover on the outside of the lower dome.

I claim:

1. The combination with a housing for electrical apparatus having an opening through the top thereof and having insulating liquid therein, the surface level of which is spaced below the top of said housing, of a bushing insulator comprising a supporting flange mounted on said housing and surrounding said opening, upper and lower dielectric shell members, a conductor insulated from said flange by said members, a ground sleeve electrically connected with said flange and extending downwardly therefrom and adapted Vto bridge the space above the insulating liquid in said housing, said lower shell member being connected with the lower end of said ground sleeve, and a flux control of conducting material electrically connected with said flange and extending below the surface level of the oil in said housing and below the lower end of said ground sleeve, and solid dielectric material disposed about the lower extremity of said flux control.

2. A bushing insulator for use in connection with an electrical apparatus housing comprising a supporting flange having an opening through which a conductor extends, an upper dielectric shell member extending upwardly from said flange for supporting the upper end of said conductor, a ground sleeve extending downwardly from said flange and adapted to bridge the space above the insulating liquid in said apparatus housing, a lower dielectric shell extending downwardly from the lower end of said ground sleeve for insulating the lower end of said conductor from said ground sleeve, said lower dielectric shell member having an outwardly extending flange adjacent its lower end forming a downwardly opening pocket, the upper portion of said pocket being closed by the dielectric material of said shell member, and conducting means disposed within said pocket and electrically connected with said conductor to provide a iiux control for the electrostatic lines of force emanating from the lower end of said conductor where it leaves said lowershell member.

3. A bushing insulator comprising a flange arranged to be mounted on an electrical apparatus housing, a dielectric member extendingupwardly from said flange for supporting a conductor extending through said flange into said housing and for insulating said conductor from said flange, a ground sleeve electrically connected with said flange and extending downwardly therefrom and adapted to bridge the space above -the insulated liquid in said apparatus housing, a dielectric shell extending downwardly from the lower end of said ground sleeve for insulating the lower end of said conductor from said ground sleeve, a iiux control comprising a member of conducting material electrically con-v nected with said ground sleeve and extending below the lower end of said ground sleeve within said shell, solid dielectric material disposed about the lower extremity of said flux control member of conducting material and a second flux control at the lower end of said conductor where it emerges from said dielectric shell, said second flux control comprising a member of conducting material electrically connected with said conductor and extending into a pocket formed in the material of said shell and having its upper portion coveredby the material of said shell.

4. A bushing insulator comprising a supporting flange, a conductor extending through said flange, an upper shell member carried by said flange and supporting the upper end of said conductor, a ground sleeve extending downwardly from said flange and adapted to bridge the space between said flange ami the insulating liquid in an electrical apparatus housing-on` which said flange is mounted, a lower shell member extending downwardly from the lower end of said ground sleeve, a fitting secured to said conductor and supporting said lower shell member, a tubular dielectric member disposed between said conductor and said ground sleeve, a conductor covering for the outer surface of said tubular dielectric member, said conductor covering being electrically connected to said ground sleeve, an upwardly extending flange on the outer surface of said tubular dielectric member forming a pocket closed at its lower extremity, said conductor covering terminating in said pocket to form a flux control to prevent formation of corona at the.

lower extremity of said ground sleeve, a downwardly extending ange on the outer surface of said lower shell member adjacent the lower end thereof forming an upwardly extending pocket closed at its upper extremity, a member of conducting material electrically connected with said conductor and extending into said pocket and forming a flux control for the electrostatic field about said conductor at the lower end of said lower shell member.

5. A bushing insulator comprising a flange, an upper shell member carried by said ange, a conductor extending throughsaid flange and insulated therefrom by said upper shell member, a ground sleeve extending downwardly from said flange, a lower shell member forming a continuation of said ground sleeve and insulating the lowerend of said conductor from said ground sleeve, an insulating keg surrounding said conductor and separating said conductor from said ground sleeve, a covering of conducting material on the outer surface of said keg, said covering being electrically connected with said ground sleeve, a flux control of conducting material electrically connected to said covering, dielectric material-disposed about the lower extremity of said flux control for preventing formation of corona from said flux control, a conductor ring extending outwardly from the lower end of said conductor, saidglower shell member having a pocket therein closed at its upper extremity, the periphery of said ring being disposed in said pocket.'

ground sleeve surrounding said vconductor and extending downwardly from the top of said'hous- 4ing to bridge the space between the top of said housing and the surface level of insulating liquid within said housing, a lower shell member connecting the lower end of said ground sleeve withA said conductor, an insulating keg surrounding said conductor within said ground sleeve, a conductor covering for the outer surface of said keg within said ground sleeve, said conductor covering extending beyond said ground sleeve at both ends of said sleeve and insulated flux controls at both ends of said conductor covering, the flux control at one end of said conductor covering comprising a pocket formed by an integral flange on said keg.

'7. The combination with a conductor, of a bushing insulator for said conductor, said bushing insulator comprising ashell member and a. tubular dielectric member surrounding said conductor and overlapping said shell member, a ground sleeve disposed outside of said tubular dielectric member and forming a continuation of said shell member, said shell member having a'pocket formed therein and located beyond the extremity of said ground sleeve, a conductor lining for said pocket electrically connected with said ground sleeve,l said tubular dielectric member having a flange thereon forming a pocket and a conductor covering for the outer surface of said RALPH HIGGINS.

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