Title of Invention

OIL FILTRATION UNIT FOR A TAP SELECTOR SWITCH

Abstract

An oil filtration unit for a tap selector switch comprises a pressure vessel (1), which is connectible into a switch oil circuit of the tap selector switch and which comprises a cylinder (2) with a base and with a removable lid (3) sealingly mounted on an encircling flange (4) at the upper end of the cylinder (2). A removable oil filter insert (18) is arranged in the vessel (1) to filter oil in the oil circuit. For mounting the insert (18), the cylinder flange (4) has a radially inwardly projecting flange portion (17) and the insert (18) has a collar (14) seated on the flange portion so as to suspend the insert (18) in the cylinder (1). The collar (24) can be resilient so as to slightly deform when the lid (3) is fitted. The lid (3) and the filter insert (18) can thus be fitted to and removed from the cylinder (2) of the pressure vessel (1) separately from each other.

Full Text

An oil filter installation for a tap selector swiftly and a filter insert for the installation are described in Maschinenfabrik Relnhausen publication "Oil Filter Installation Type 51 -Operating Instruction", print mark BA 18/03de-1196/1000. This oil filter installation comprises, inter alia, a pump unit, which comprises a pump motor, a conveying pump and a pressure vessel. The pressure vessel is constructed as a steel cylinder with a lid and a base and receives the filter insert in its interior. In the case of tap selector switches with mechanical switching contacts which operate under more difficult conditions, such as at particularly high switching frequency or with frequent overload, or which are subject to a constant current operation, the switch oil in the interior of the tap selector switch is strongly contaminated in a relatively short time by the effects of the unavoidable switching arcs. To counteract this, it is recommended to undertake a periodic filtering of the switch oil, which is possible with the described oil filter installation without interruption of the transformer operation. Such an oil filter installation can be provided with filter inserts functioning in different ways. On the one hand, paper filter inserts can be used to clean the oil of solid components, whereby the number of the inspections which are otherwise required at short intervals in the case of high switching frequency, together with an oil change necessary at the same time, can be reduced. On the other hand, combination filter inserts can be used particularly when, apart from filtering out contaminating solid components from the oil, an additional reduction in water content is needed. This will be required in many cases when the tap selector switch is used in countries with tropical or subtropical climate, extremely high air humidity or the like. Both kinds of filter inserts are mounted in the same manner in the pressure vessel of the pump unit. The pressure vessel has a removable lid which has, at its inward side, a threaded bolt which projects centrally into the interior of the pressure vessel when the lid is fastened down. The filter insert in turn has a central continuous opening which extends in longitudinal direction and into which the threaded bolt of the lid is inserted during assembly. At the other side of the filter insert, from which the end of the threaded bolt projects, a locking counter-member and a fastening nut is fitted to the projecting end of the bolt to secure the filter insert to the lid. This known arrangement, i.e. manner of mounting the filter insert, has, however, various disadvantages. Firstly, for a change of the filter, the lid of the pressure vessel together with the filter insert has to be detached and lifted out of the pressure vessel . The entire assembly then has to be placed separately on a disassembly surface. Only then is the fastening nut accessible, able to be loosened and then removed together with the counter-member, after which the filter insert can be drawn off the threaded bolt of the lid. This requires considerable physical exertion, since the filter insert is then saturated by switch oil and has a not appreciable weight. Moreover, the task is often made more difficult due to restricted space conditions. Overall, the handling is unsatisfactory. On the other hand, it is unavoidable that, during this common removal of the components of lid and filter insert from the pressure vessel, excess oil drips out of the insert and contaminates the surroundings as well as the service engineer carrying out the operations. It is therefore the object of the invention to provide an oil filtration unit in which a filter insert can be mounted in simple and secure manner and yet readily removed when required. According to the present invention there is provided an oil filtration unit for a tap selector switch having an oil circuit for switch oil for switching contacts of the tap selector switch, the unit comprising a pressure vessel connectable into the oil circuit and comprising an upright cylinder with a base and with a removable lid sealingly mounted on an encircling flange provided at the upper end of the cylinder, and a removable oil filter insert arranged in the pressure vessel to filter oil in the oil circuit, characterized in that, the cylinder flange has an inwardly projecting flange portion extending annularly into the interior of the cylinder and the filter insert has a collar seated on the flange portion to suspend the filter insert of the cylinder. Preferably, the collar is substantially stair-shaped in cross-section. For preference, the flange portion of the cylinder flange is substantially step-shaped in cross- section and the lid has a portion of substantially corresponding step-shaped cross-section. In a preferred embodiment, at least one controlling, checking or measuring device is mounted on the cylinder flange at a mounting point thereof and the lid is recessed in the region of the mounting point to permit removal of the lid without detaching the device or devices. The filter insert itself preferably comprises a substantially cylindrical wall which encloses filter means and which is closed at its lower end by a base and closed at its upper end apart from a central opening, the collar being arranged at an upper region of the wall to extend outwardly therefrom and to bear on the cylinder flange at least in wide regions of the circumference of the filter insert. The collar can be disposed in a substantially horizontal plane and for preference is resilient and so bears against the flange portion as to be resiliently deformed. To assist handling, the filter insert can be provided at its upper end with resilient lifting elements which project upwardly from the insert when the lid is removed from the flange of the cylinder of the vessel and which are pressed down by the lid when mounted on the cylinder flange. A particular advantage of the oil filtration unit embodying the invention is that the pressure vessel lid and the filter insert, which were previously firmly connected together, are divided into two separate components which remain separate even in the assembled state. The cylinder of the pressure vessel thus has at its upper region the flange portion at which the filter insert can be suspended by its collar. The filter insert is thus no longer fastened to the lid of the cylinder and lowered into this cylinder on placing of the lid on the cylinder, but rather the filter insert supports itself by the collar resting on the flange portion. This support is independent of whether the lid is fitted or not. A substantially simplified assembly and disassembly thereby results. The lid can initially be removed separately and put down and thereafter the filter insert can be removed and reinserted separately. If the collar of the filter insert is resilient, when the lid is secured in place the collar is pressed against the flange portion of the cylinder flange and deforms in the elastic range, i.e. it bears tightly against the contour of the flange portion. If this flange portion has a stair-shaped cross-section, an automatic centring of the filter insert takes place during securing of the lid. The collar of the filter insert can be so dimensioned with respect to the material used and the geometric shape that the mentioned deformation is confined to the elastic range so that the filter insert is readily reusable, i.e. it can be removed and reinserted several times. Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic sectional elevation of part of an oil filtration unit, which embodies the invention, for a tap selector switch; Fig. 2 is the detail "A" of Fig. 1, to enlarged scale; Fig. 3 is a schematic sectional elevation of the upper part of a first form of filter insert usable in the unit of Fig. 1; Fig. 4 is a schematic sectional elevation of the upper part of a second form of filter insert usable in the unit of Fig. 1; Fig. 5 is a schematic plan view of the filter insert of Fig. 2. Referring now to the drawings, there is shown in Fig. 1 the upper part of a pressure vessel 1 of an oil filter installation in an oil filtration unit for a tap selector switch. The switch makes use of oil filtered by the installation. The lower part of the pressure vessel 1 accommodates a pump motor and a conveying pump; these, and further components of the oil filter installation which are disposed externally of the pressure vessel, are not illustrated. The actual pressure vessel 1 consists of a steel cylinder 2 with a base (not shown) and a lid 3. At the upper part of the cylinder 2 there is provided an encircling flange 4 which is welded to the cylinder and has a plurality of threaded bores In radial arrangement. The lid 3 is fastened to the flange 4 and thus to the cylinder 2 by screws 5, which correspond with the threaded bores. The lid 3 carries a pipe elbow 6, which can be connected to a return run of a switch oil circuit of the tap selector switch. A flange 7 of the pipe elbow 6 is tightly secured to the lid 3 by screws 8 with the interposition of seals. The pipe elbow 6 communicates with the interior of the pressure vessel 1, more precisely with the interior of a filter insert to be located in the vessel, via a bore 10 in the lid 3. A pressure relief or bleed screw 9 is disposed in the upper region of the pipe elbow 6. Further coupling and connecting means are omitted for reasons of clarity. At one point of its circumference, the flange 4 has a bore 11, which communicates with the interior of the pressure vessel 1, more precisely with a region which, when the filter insert is inserted, is situated externally of this insert. Mounted above this bore is a connecting block 12 which provides a connection to a manometer 13 mounted thereon and to a pressure switch 14. The flange 4 also has an annular encircling groove 15 with an inserted seal which, during securing of the lid 3 by means of the screws 5, produces a tight seal between the lid and the flange. The lid 3 is provided at its inner side with a further annularly encircling groove 16 receiving an Inserted seal, the function of which is explained below. In its inner region, the flange 4 has a receiving flange portion 17, which extends annularly in step-like manner into the interior of the cylinder 2. The cylinder 2 contains a filter insert 18, which comprises an outer cylindrical, preferably metallic, wall 19, which encloses filter material 20, and an inner wall. In the illustrated example, a simple paper filter is provided, but other filter elements, including composite filter inserts and/or inserts with zeolite filling, are possible. The filter insert has a base 22 with a dosable opening 21. The upper end 23 of the filter insert 18 is closed by cover, which has a central opening for the flow of oil from the interior of the filter insert to the pipe elbow 6. Near the top of the wall 19, the filter insert 18 has an annular encircling resilient collar 24, which is part of the cover and which extends substantially horizontally outwards in such a manner that, in the inserted state of the filter insert 18, the insert rests by this collar 24 on the flange portion 17. The filter insert 18 is initially inserted from above into the aperture surrounded by the flange 4 and thereby into the cylinder 2. After full insertion, the collar 24 of the filter insert 18 rests annularly on the flange portion 17. Subsequently, the lid is fitted and screw-connected by means of the screws 5 to the flange 4 and thereby the cylinder 2. On tightening of the screws, the lid 3 is moved downwardly by a small amount and thereby also the filter insert 18. The receiving collar 24 deforms elastically and adapts itself at least partially to the step-like contour of the flange portion 17. The seal, which is inserted in the annular groove 15 in the flange 4, seals this flange relative the lid 3 and thereby also seals off the free volume in the cylinder 2 externally of the filter insert 18. The further seal, which is inserted in the groove 16 at the inward side of the lid 3, seals the collar 24 relative to the lid 3. The filter insert 18 is thereby hermetically sealed. The switch oil to be filtered is forced, by the pump in the pressure vessel 1, from outside through the circumferential surface of the filter insert 18 into the interior of the wall 19 and in that case flows through the filter material 20. The cleaned switch oil subsequently passes through the bore 10 in the lid 3 and the pipe elbow 6 back to the tap selector switch. Fig. 2 shows the detail "A" of Fig. 1 to an enlarged scale. It is clearly recognisable in that case how the collar 24 in the mounted state bears tightly against the contour of the flange portion 17. The collar 24 can to particular advantage consist of steel having a thickness of about 0.8 millimetres and be of deep-drawing quality, for example St 1203. The elastic deformation of the collar 24 in the case of this material should not exceed about 2 millimetres. This is achievable by suitable dimensioning of the lid 3, flange portion 17 and collar 24 relative to each other. In Fig. 3, the upper part of a first form of filter insert 18 is illustrated by itself. By appropriate dimensioning of the spacing "a" of the collar 24 from the upper end 23 of the filter insert 18, it can be determined, in conjunction with appropriate dimensioning of the mentioned other components, how far the upper end 23 projects upwardly. The lid 3 rests on this upper end 23 and, when the lid 3 is secured by tightening of the screws 5, the inward surface of the lid 3 urges the entire filter insert 18 downwardly by a certain amount, which causes elastic deformation of the collar 24 in dependence substantially on the selected spacing "a". In Fig. 3 it can be seen that the collar 24 in the unloaded state extends approximately horizontally. After removal of the filter insert 18, the collar assumes this position again, since the deformation has, as already mentioned, taken place only in the elastic range. The filter insert 18 is thus mountable and demountable repeatedly. In a particularly advantageous modification, the receiving flange 17 is formed in step shape and corresponds with an appropriate step in the lid 3, as illustrated in Figs. 1 and 2. This has the advantage that, on the loosening of the lid 3, an additional volume is freed, which receives the oil flowing back out of the pipe elbow 6 and thus prevents overflowing and resultant contamination. Moreover, it is advantageous to provide the lid 3 with screws 5 around only part of the circumference and to recess the region of the lid 3 adjacent to the connecting block 12, manometer 13 and pressure switch 14 or other checking elements arranged at the flange 4. As a result, the lid 3 can be detached, removed and refitted without having to detach these components. A second form of the filter insert is shown in Figs. 4 and 5. In this case, the upper region of the filter insert is formed with an annular groove 25, which is bounded by an inner flank 26. Lifting-out handles 28 and 29 are fastened to the base 27 of the groove 25. The handles 28 and 29 are formed in such a manner of resilient material that, in the relieved state, they project upwardly by the amount "b". It is thereby possible to get hold of the entire filter insert 18 in simple manner and lift it out of the cylinder 2, particularly without coming into contact with the switch oil. In the mounted state of the filter insert 18, the resilient handles 28 and 29 are urged into the groove 25 by the then tightly fitting lid 3, so that they no longer protrude out of the upper region of the filter insert 18. For this purpose, it is necessary for the depth "c" of the annular groove 25 to be selected to be suitably greater than the thickness of the handles 28 and 29. On opening of the lid 3, the handles 28 and 29, due to their resilient construction, move out of the upper region of the insert 13 and thereby above the height of the level of the switch oil and are easy to grip. In Figs. 4 and 5, there are shown two lifting-out handles 28 and 29, which consist of spring wire and at their ends have eyelets fastened to the base 27 by means of screws 30. It is in that case evident from Fig. 5 that the handles 28 and 29 - shown in the raised state as in Fig. 4 - are shaped so that, seen from above, they have a shape concentric with the groove 25 and in the compressed state disappear without mutual obstruction completely into the groove 25. WE CLAIM: 1. An oil filtration unit for a tap selector switch having an oil circuit for switch oil for switching contacts of the tap selector switch, the unit comprising a pressure vessel connectable into the oil circuit and comprising an upright cylinder with a base and with a removable lid sealingly mounted on an encircling flange provided at the upper end of the cylinder, and a removable oil filter insert arranged in the pressure vessel to filter oil in the oil circuit, characterized in that, the cylinder flange has an inwardly projecting flange portion extending annularly into the interior of the cylinder and the filter insert has a collar seated on the flange portion to suspend the filter insert of the cylinder. 2. The unit according to claim 1, wherein the collar is substantially stair-shaped in cross section, 3. The unit according to claim 1 or claim2, wherein the flange portion of the cylinder flange is substantially step-shaped in cross-section and the lid has a portion of substantially corresponding step-shaped cross-section. 4. The unit according any one of the preceding claims, wherein at least one controlling, checking or measuring device is mounted on the cylinder flange at a mounting point thereof and the lid is recessed in the region of the mounting point to permit removal of the lid without detaching the device or devices. 5. The unit according to any one of the preceding claims, wherein the filter insert comprises a substantially cylindrical wall which encloses filter means and which is closed at its lower end by a base and closed at its upper end apart fi-om a central opening, the collar being arranged at an upper region of the wall to extend outwardly therefi-om and to bear on the cylinder flange at least in wide regions of the circumference of the filter insert. 6. The unit according to any one of the preceding claims, wherein the collar is disposed in a substantially horizontal plane. 7. The unit according to any one of the preceding claims, wherein the collar is resilient and so bears against the flange portion as to be resiliently deformed. 8. The unit according to any one of the preceding claims, wherein the filter insert is provided at its upper end with resilient lifting elements which project upwardly fi-om the insert when the lid is removed fi-om the flange of the cylinder of the vessel and which are pressed down by the lid when mounted on a cylinder flange.

Documents:

1185-mas-1999 abstract-duplicate.pdf

1185-mas-1999 abstract.pdf

1185-mas-1999 claims-duplicate.pdf

1185-mas-1999 claims.pdf

1185-mas-1999 correspondence-others.pdf

1185-mas-1999 correspondence-po.pdf

1185-mas-1999 description(complete)-duplicate.pdf

1185-mas-1999 description(complete).pdf

1185-mas-1999 drawings-duplicate.pdf

1185-mas-1999 drawings.pdf

1185-mas-1999 form-1.pdf

1185-mas-1999 form-19.pdf

1185-mas-1999 form-26.pdf

1185-mas-1999 form-3.pdf

1185-mas-1999 form-5.pdf

1185-mas-1999 petition.pdf