GB2191259A

GB2191259A - Sealed electrical apparatus

Info

Publication number: GB2191259A
Application number: GB08710652A
Authority: GB
Inventors: Minoru Nakahata; Masami Kii; Nobuyuki Orito; Masashi Uenushi; Seiichi Miyamoto; Hideki Miyatake
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1986-05-06
Filing date: 1987-05-06
Publication date: 1987-12-09
Anticipated expiration: 2007-05-06
Also published as: KR870011723A; KR900008870B1; GB2191259B; GB8710652D0; DE3715105A1

Description

GB2191259A SPECIFICATION a hermetically-sealed vessel of a conventional

sealed electrical apparatus.

Sealed electrical apparatus It is yet another object of the present inven tion to provide a sealed electrical apparatus BACKGROUND OF THE INVENTION 70 having a hermetically-sealed vessel which can

This invention relates to a sealed electrical be more easily and cheaply manufactured than apparatus of the type comprising a hermeti- a hermetically-sealed vessel of a conventional cally-sealed vessel which contains a switch or sealed electrical apparatus.

other electrical device in an atmosphere of a A sealed electrical apparatus in accordance dielectric gas. More specifically, it relates to a 75 with the present invention has a hermetically sealed electrical apparatus having a hermeti- sealed vessel which is filled with a dielectric cally-sealed vessel with a light-weight, easily- gas and houses an electrical device such as a manufactured cover. switch. The vessel has at least one opening A conventional sealed electrical apparatus formed therein, and the opening is covered comprises a box-shaped vessel which houses 80 with a cover having a two- layer structure. The an electrical device for power transmission cover comprises an inner casing and an outer and distribution such as a switch. The vessel casing, each of which is formed from a metal is typically made of steel plates which are sheet. The inner casing has a plurality of in welded together with airtight welds to form a dentations of a uniform depth formed therein box. A dielectric gas, such as sulfur hexafluo- 85 by plastic working, and the undersurfaces of ride, is sealed within the vessel and surrounds the indentations are welded to the inner sur the electrical device. Openings for bushings face of the outer casing. The outer casing and other connectors are formed in the plates may be a flat sheet, or it may have indenta by machining. tions formed therein by plastic working which When an internal short or a ground fault 90 abut against and are secured to the indenta- occurs in the electrical device, a pressure of tions of the inner casing by welding. The inner at least several atmospheres may develop casing seals the dielectric gas within the ves within the vessel, and therefore the steel sel, and the inner and outer casings together plates which constitute the vessel must be give the cover the necessary strength. The able to resist this internal pressure. Further- 95 cover is secured to the body of the vessel more, the plates must be able to resist defor- with bolts. An airtight seal between the cover mations due to stresses which develop at the and the body of the vessel is provided by a time of welding. For this reason, the plates packing material which is disposed there are inevitably be thick and therefore heavy, between.

with the result that the entire vessel is heavy 100 In a preferred embodiment, the hermetically and cumbersome. The assembly and tran- sealed vessel is a T-shaped vessel having two sporting of the vessel therefore requires the cylindrical portions which intersect at right use of heavy equipment. In addition, an allow- angles and form the body of the vessel. The ance must be added to the dimensions of the three outer ends of the cylindrical portions are plates to compensate for welding deformaopen and are covered by corresponding tions, and this increases the cost and weight covers having the above- described structure.

of the steel plates. The vessel is preferably formed from a pluralFurthermore, it requires a high degree of ity of sections which are joined to one welding skill and careful quality control to pro- another by welding. The seams between adja- duce welds which are completely airtight so 110 cent sections of the vessel are straight lines as to obtain an airtight vessel, and therefore which extend parallel to the longitudinal axis the manufacturing costs of a conventional of one of the cylindrical portions of the ves sealed electrical apparatus are high. sel. Each of the sections has a rim formed In addition, a box-shaped vessel is weak along the edges thereof which adjoin the other with respect to internal pressure and can eas- 115 sections, and adjoining sections are joined to ily deform. Therefore, the walls of the vessel one another by welding their rims together.

must be reinforced, the structure of the vessel is complicated, and its manufacture is difficult. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a side elevation of a first em SUMMARY OF THE INVENTION 120 bodiment of a sealed electrical apparatus in

It is an object of the present invention to accordance with the present invention.

provide a sealed electrical apparatus having a Figure 2 is a plan view of the embodiment hermetically-sealed vessel which requires a of Fig. 1.

lesser amount of airtight welding to manufac- Figure 3 is a schematic view of the embodi ture than a hermeticaily-sealed vessel of a 125 ment of Fig. 1, showing the connection be conventional sealed electrical apparatus. tween an internal electrical device and an ex It is another object of the present invention ternal electrical device.

to provide a sealed electrical apparatus having Figure 4 is a crosssectional view of Portion a hermetically-sealed vessel which is lighter]V of Fig. 3, showing the structure of one of and yet has a strength comparable to that of 130 the three covers of the vessel.

2 GB2191259A 2 Figure 5 and Figure 6 are perspective views ing or other plastic working method. The in illustrating one form of the vessel of Fig. 1. dentations 11 a have a uniform depth. The in Figure 7 and Figure 8 are perspective view dentations 11 a serve as a means of strength illustrating another form of the vessel of Fig. ening the inner casing 11 and of connecting 1. 70 the inner casing 11 to the outer casing 12. A Figure 9 is a perspective view of yet channel 11 b is formed around the entire outer another form of the vessel of Fig. 1. periphery of the inner casing 11, also by plas Figure 10 is a horizontal cross-sectional tic working. The channel 1 '1 b fits around a rim view of a cover of a second embodiment of 2c which extends around the periphery of the the present invention. 75 open end of the vessel body 2. The outer In the drawings, the same reference numer- surface of the channel 11 b is flush with the als indicate the same or corresponding parts. outer surface of the indentations 1 la. The outer casing 12 is a flat, metal sheet whose DESCRIPTION OF THE PREFERRED EMBODI- innner surface is secured to the undersurfaces

MENTS 80 of the indentations 1 '1 a of the inner casing 11 Hereinbelow, a number of preferred embodi- by welding. The outer casing 12 is also ments of a sealed electrical apparatus in ac- welded to the outer surface of the channel cordance with the present invention will be 1 '1 b along the entire outer periphery thereof.

described while referring to the accompanying The cover 5 is secured to the body 2 of the drawings. Figs. 1 through 4 of which illustrate 85 vessel 1 by a plurality of bolts 14 which pass a first embodiment. This embodiment com- through holes formed in the outer casing 12 prises a T-shaped, hermeticallysealed vessel and screw into corresponding supports 2d 1 having two cylindrical portions 2a and 2b which are secured to the outer surface of the which intersect at right angles and form the vessel body 2. A packing 13 is disposed in body 2 of the vessel 1. A conventional dielec- 90 side the channel 11 b of the inner casing 11, tric gas such as sulfur hexafluoride is sealed and when the cover 5 is bolted to the vessel within the vessel 1. The vessel body 2 has an body 2, the packing 13 is compressed be opening at each of three ends of the cylindri- tween the channel 11 b and the rim 2c of the cai portions 2a and 2b, and the three open- vessel body 2, thereby guaranteeing an air- ings are sealed by a first cover 3, a second 95 tight seal between the vessel body 2 and the cover 4, and a third cover 5, respectively. The cover 5.

first cover 3 serves as a control panel for Because of the two-layered structure of the operating an internal electrical device 7 such cover 5, the ratio of the stiffness to the as a switch which is housed within the vessel transverse cross-sectional area of the cover 5 1. Although not shown in Figs. 1 and 2, the 100 is much greater than that of a cover made of first cover 3 supports an external electrical a solid steel plate. Accordingly, by suitably device 8 which is connected to the internal selecting the thickness of the inner and outer electrical device 7 by an operating shaft 9 casings and the distance therebetween, the which enables the internal electrical device 7 cover 5 can be far lighter and yet have a to be operated from outside the vessel 1. The 105 comparable or superior strength to a conven- portion of the operating shaft 9 which passes tional cover. Furthermore, as the dielectric gas through the first cover 3 is supported by a is sealed within the vessel 1 by the packing sealed bearing 10 which is mounted on the 13 which is compressed between the inner first cover 3. The first cover 3 also has unil- casing 11 and the rim 2c, it is not necessary lustrated taps bolted thereon for the external 110 to weld the cover 5 to the vessel body 2, electrical device 8. The second cover 4 serves and the welds between the inner casing 11 as a bushing installation surface and has a and the outer casing 12 do not need to be plurality of bushings 6 mounted thereon. The airtight, so a vessel having covers with this bushings 6 connect the internal electrical de- structure can be more easily manufactured vice 7 to a power supply and a load. The 115 than a conventional vessel. In addition, be third cover 5 serves as a maintenance inspec- cause the cover 5 is formed from thin sheets, tion cover which can be opened to enable the installation portions for the installation of internal electrical device 7 to be maintenanced. bushings and other members can be easily The openings at the ends of cylindrical portion formed by punching or burring instead of by 2a are large enough to enable the internal 120 expensive machining, which must be per electrical device 7 to be inserted and removed formed on a cover made of a steel plate.

from the vessel body 2. The embodiment of Fig. 1 provides the fur Each of the three covers 3-5 has a two- ther advantage over a conventional sealed layer structure like that shown in Fig. 4, which electrical apparatus that it has a circular is a cross-sectional view of Portion IV of the 125 transverse cross section instead of being box third cover 5 of Fig. 3. Each cover is formed shaped, making it better suited to withstand from an inner casing 11 and an outer casing the pressure of the dielectric gas within the 12. The inner casing 11 is made from a disk- vessel 1. Stresses generated in the walls of shaped metal sheet and has a plurality of inthe vessel 1 by gas pressure are uniformly dentations 1 la formed therein by deep draw- 130 distributed around the circumference thereof, 3 GB2191259A 3 and the vessel walls can be thinner than for a the upper section 19 has longitudinally-extend conventional box-shaped vessel, and it is not ing rims 19a which abut against and are necessary to reinforce the vessel walls. welded to the longitudinally- extending rims As shown in Figs. 5 and 6, the body 2 of 18a of the lower sections 18a. Circumferenti the vessel 1 can be formed by welding two 70 ally-extending rims 18b and 19b are formed cylinders 15 and 16 together. However, this on the ends of the upper and lower sections method is disadvantageous in that it requires 18 and 19, respectively, 'and these combine the cutting of a hole in the center of the up- to form rims 2c on which covers can be in per cylinder 15 and cutting the upper end of stalled in the manner described previously. A the branching cylinder 16 so as to conform to 75 vessel body 2 having this construction pro the shape of the upper cylinder 15, both of vides the same advantages as the vessel body which are complicated processes on account 2 of Fig. 8.

of the curved shapes. Furthermore, welding Fig. 10 illustrates the structure of a second the two cylinders together along the curved cover 20 of a second embodiment of a sealed upper surface of the branching cylinder 16 is 80 electrical apparatus in accordance with the extremely difficult, and there is a great possi- present invention. As in the first embodiment, bility of welding strains and welding defects the second cover 20, which is used as a developing. bushing installation surface, has a two-layer Therefore, the vessel body 2 is preferably structure and is formed from an inner casing formed from a plurality of sections which can 85 21 and an outer casing 22. In contrast with be fitted together into the shape of two inter- the first embodiment, both the inner casing 21 secting cylinders and connected by welding and the outer casing 22 are made from metal along straight lines, such as shown in Figs. 7 sheets having indentations 21a and 22a, re and 8. These figures illustrate an example of a spectively, formed therein by deep drawing or vessel body 2 which is formed from two iden- 90 other suitable press forming method. The in- tical, T-shaped sections 17. Each section 17 dentations 21 a in the inner casing 21 have a has straight, longitudinally-extending rims 17a uniform depth. The inner casing 21 has a cir formed along its length and circumferentially- cular shape, and a channel 21c which fits extending rims 17b which extend around the around the rim 2c of the vessel body 2 is cirumference of the ends of the sections 17. 95 formed around the entire periphery of the in The sections 17 and the rims thereof can be ner casing 21. The outer surface of the chan easily manufactured by plastic working such nel 21c is welded along its entire outer peri as press working. The two sections 17 are phery to the inner surface of the outer casing combined with one another as shown in Fig. 22. The indentations 22a in the outer casing 8 with the longitudinal ly-extending rims 17a 100 22 also have a uniform depth and are formed abutting, and the rims 17a are then secured in locations which correspond to the locations to one another by airtight welds to form a Tof the indentations 21a in the inner casing 21 shaped vessel body 2. When the two sec- so that the undersurface of each indentation tions 17 are joined together, the circumferen- 21 a in the inner casing 21 will abut against tailly-extending rims 17b combine to form the 105 the undersurface of one of the indentations rims 2c of the vessel body 2, to which covers 22a in the outer casing 22. The abutting sur like that shown in Fig. 4 are secured in the faces of the indentations 21a and 22a are above-described manner. secured to one another by welding.

With a vessel body 2 having this construc- The inner casing 21 and the outer casing tion, there is no need to perform the compfi- 110 22 have bushing installation holes 21b and cated machining which is necessary when 22b, respectively, formed therein in corre manufacturing a vessel body 2 from two cylin- sponding locations where there are no inden ders, as shown in Fig. 5. Furthermore, as the tations. The bushing installation holes are two sections 17 are joined together by simple formed in the casings by burring. The diam- welds along straight lines, the vessel body 2 115 ters of the bushing installation holes are cho is cheaper and easier to manufacture, there is sen so that the sides of the bushing installa less possibility of welding deformations and tion holes 21b of the inner casing 21 will welding defects, and the dimensional accuracy overlap the sides of the bushing installation of the vessel can be increased. Furthermore, holes 22b of the outer casing 22. The over- the longitudinally-extending rims 17a increase 120 lapping portions of the bushing installation the rigidity of the vessel body 2. holes are secured to one another by airtight Fig. 9 illustrates another example of a ves- welding. Bushings 6 are inserted into the sel body which is formed from three sections bushing installation holes and secured to the consisting of two identical lower sections 18 outer casing 22 by bolts 25 which pass and an upper section 19, all of which are 125 through holes formed in the bushings 6 and formed by press working. The upper and the outer casing 22 and screw into nuts 26 lower sections fit together to form a T-shaped which are welded to the inner surface of the vessel body. The two lower sections 18 have outer casing 22. To prevent the dielectric gas long itudina lly-extend ing rims 18a which abut which is sealed within the vessel 1 from leak- against and are welded to one another, and 130 ing out through the bushing installation holes, 4 GB2191259A 4 0-rings 24 are provided around the bushings 2. A sealed electrical apparatus as claimed

Claims

6 between the bushings 6 and the outer cas- in Claim 1, wherein said outer

casing is flat ing 22. A packing 13 is disposed in the chan- metal sheet whose inner surface is welded to nel 21 c of the inner casing 21 and the cover the undersurface of said indentations of said 20 is secured to the supports 2d of the ves- 70 inner casing.

sel body 2 by bolts 14 in the same manner 3. A sealed electrical apparatus as claimed as in the first embodiment. The other two in Claim 1, wherein said outer casing is a covers of the vessel 1 can have the same metal sheet having indentations of a uniform structure as the cover 20 of Fig. 10, or a depth formed therein, the undersurface of structure like the cover 5 illustrated in Fig. 4. 75 each of the indentations in said outer casing The structure of this embodiment is otherwise abutting against and being welded to the un identical to that of the embodiment of Fig. 1. dersurface of one of the indentations in said A cover having the structure illustrated in inner casing.

Fig. 10 has the same advantages as the cover 4. A sealed electrical apparatus as claimed of Fig. 4. It is lightweight yet strong, and the 80 in Claim 2, wherein said indentations in said only portions which require airtight welding inner casing are formed by press forming.

are the overlapping portions of the bushing 5. A sealed electrical apparatus as claimed installation holes. Furthermore, because the in- in Claim 4, wherein said press forming is deep ner and outer casings are made from thin drawing.

sheets, holes for the installation of the bush- 85 6. A sealed electrical apparatus as claimed ings can be formed therein easly and inexpen- in Claim 3, wherein said indentations in said sively by burring. inner casing and said outer casing are formed Since the bushing installation holes 21b and by press forming.

22b are formed in portions of the inner and 7. A sealed electrical apparatus as claimed outer casings between indentations, similar 90 in Claim 6, wherein said press forming is deep bushing installation holes can be formed in a drawing.

cover having the structure illustrated in Fig. 4, 8. A sealed electrical apparatus as claimed and bushings 6 can be mounted thereon in in Claim 1, further comprising a packing which the same manner. is disposed between the inner surface of said In the above-described embodiments, the 95 inner casing and said vessel body along the sealed vessel 1 has the shape of a T with periphery of said opening.

three openings formed therein, but there is no 9. A sealed electrical apparatus as claimed restriction on the shape of the vessel or the in Claim 8, wherein said vessel body has a number of openings formed therein. For rim formed thereon which extends around the example, instead of being circular, the 100 periphery of said opening, and said inner cas transverse cross-sectional shape of the vessel ing has a channel formed therein around the body 2 may be elliptical. Furthermore, in Fig. periphery thereof which fits over said rim, said 1, the first through third covers are used as a packing being disposed inside said channel control panel, a bushing installation surface, and being compressed between said channel and a maintenance inspection cover, respec- 105 and said rim when said cover is bolted to said tively, but the uses of the covers can be intervessel body.

changed with no change in the effects of the 10. A sealed electrical apparatus as present invention. claimed in Claim 1, wherein said vessel body comprises a first and a second cylindrical por CLAIMS 110 tion which intersect one another at right 1. A sealed electrical apparatus comprising: angles in the shape of a T, said second cylin a sealed vessel comprising a vessel body drical portion branching from said first cylindri having one or more openings formed therein cal portion, said vessel body having openings and one or more covers, each of which at the opposite ends of said first cylindrical covers one of said openings in said vessel 115 portion and at the end of said second cylindri body, each of said covers comprising an inner cal portion which is not connected with said casing and an outer casing each of which is first cylindrical portion, each of said three formed from a metal sheet, said inner casing openings being covered by one of said having a plurality of indentations of a uniform covers.

depth formed therein, the undersurfaces of 120 11. A sealed electrical apparatus as said indentations being secured to the inner claimed in Claim 10, wherein one of said surface of said outer casing, said cover being covers is a control panel, another of said bolted to said vessel body; covers is a bushing installation surface, and an electrical device which is housed inside the third of said covers is a maintentance in- said vessel body; 125 spection cover.

a dielectric gas which is sealed inside said 12. A sealed electrical apparatus as vessel and surrounds said electrical appartus; claimed in Claim 10, wherein said vessel body and comprises a plurality of sections which are means for operating said electrical device joined by airtight welding, each of the seams from the outside of said vessel. 130 between adjacent sections being a straight line GB2191259A 5 which is parallel to the longitudinal axis of one of said cylindrical portions, each of said sections having rims formed along the edges thereof which border the adjacent section, the rims of adjacent sections being welded to one another by airtight welding.

13. A sealed electrical apparatus as claimed in Claim 12, wherein said vessel body comprises two identical sections.

14. A sealed electrical apparatus as claimed in Claim 12, wherein said vessel body comprises three sections.

15. A sealed electrical apparatus as claimed in Claim 12, wherein said sections are formed by press working.

16. A sealed electrical apparatus as claimed in Claim 1, further comprising a bushing which is mounted on said cover and electrically connected to said electrical device.

17. A sealed electrical apparatus as claimed in Claim 16, wherein:

a bushing installation hole is formed in said inner casing and said outer casing by burring in a portion where there are no indentations, the sides of the bushing installation hole in said inner casing and the sides of the bushing installation hole in said outer casing extending towards one another and overlapping and being secured to one another in the overlapping portion by airtight welding; and said bushing is inserted into said bushing installation hole and is secured to said outer casing.

18. A cover for sealing an opening in a vessel housing an electrical device, wherein the cover comprises an inner casing and an outer casing each of which is formed from a sheet material, the inner casing having a plurality of indentations of a uniform depth formed therein the under surfaces of said indentations being secured to the inner surface of the outer casing, and the cover is provided with means for attaching the cover to the vessel.

19. An electrical apparatus substantially as hereinbefire described with reference to Figs. 1 to 4, 5 and 6, 7 and 8, 9 or 10 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd, Dd 8991685, 1987. Published at The Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies may be obtained.