|Title of Invention||
|Abstract||The surge arrester has an axially symmetrical active portion (2) arranged between two connection fittings. This active portion contains varistor elements stacked one above the other and also an axially symmetrical connecting element of electrically conductive material arranged in the active portion of the arrester between two successive varistor elements. At least four mounting places, which are uniformly distributed around the axis in the circumferential direction, are formed in the connecting element. Two first of the mounting places support respectively one of two first loops which act with contact force on the connecting element and on the varistor elements abutting the connecting element. Two second of the mounting places support respectively one of two second loops which act with contact force on the connecting element and on the varistor elements located under the connecting element. Such a surge arrester can have large constructional heights and is distinguished in addition by good mechanical and electrical properties.|
SPECIFICATION Surge Arrester
FIELD OF TECHNOLOGY
The starting point of the invention is a surge arrester according to the introductory part of the first patent claim.
STATE OF THE ART
The invention makes reference to a state of the art as given by EP 0 614 198 Bl. A surge arrester described in this state of the art contains two connection fittings and a column of varistor elements, stacked one above the other, between the connection fittings. Electrical contact between the connection fittings and the varistor elements is produced by two or more loops of insulating material, the ends of which are respectively mounted in one of the two connection fittings, and thus also act with a contact force on the varistor elements located therebetween.
For large constructional heights, as are for example required for nominal voltages of more than 70 kV, a surge arrester constructed in such a maimer is in general not used, since then relatively expensive additional measures have to be provided in its manufacture.
A surge arrester is known from EP 0 335 479 Bl with a weather protection housing, two connection fittings brought out of the housing, and an active portion of axially symmetrical construction, located in the interior of the housing, arranged between the connection fittings. The active portion is constructed from several cylindrical modules, which are stacked one above the other in the form of a column. Each module has several cylindrical varistor elements whose ends
abut along the cylinder axis. Electrical contact between the varistor elements is attained by the preponderantly axially-directed thread winding which acts with a pre-stressing force on two metallic end portions which bind the module at the ends. The end portions of adjacent modules are electrically connected together by means of a screw bolt.
The production of such a surge arrester is relatively expensive, since the modules are produced by thread winding in a first step, and in a succeeding second step the modules are then joined together by screwing adjacent end portions of the modules, with the formation of a connecting portion having good electrical conductivity.
BRIEF DESCRIPTION OF THE INVENTION
The invention as set out in the patent claims has as its object to provide a surge arrester of the kind stated at the beginning, which can also be produced with a large constructional height in a simple and cost-efficient manner.
The surge arrester according to the invention is distinguished from the comparable surge arresters according to the state of the art in that it can be made practically with optional constructional height in a simple and economical manner. There is additionally built into the active portion of the surge arrester only, at least one connecting element, which is arranged between two successive varistor elements, and is of electrically conducting material with suitably constructed and arranged mounting places. Loops held on the moimting places are passed in opposite directions and are fixed to mounting places of the connection fittings or of a further connecting element or of two further connecting elements, with the production of contact force. Hence, for its mounting, substantially only one of the prefabricated templates is necessary which have already proved to be effective in the state of the art in the manufacture of surge arresters, and which principally insure axial guiding, and in which the connection fittings, the varistor elements, and also, according to the diameter of the varistor elements and the constructional height, one or more of the connecting elements, are stacked, and are thereafter connected together into the mechanically stable active portion of the surge arrester by the installation of the loops and application of pre-stress.
During the stacking, the mechanical stability of the active portion can be attained by successive bracing of succeeding partial stacks, the pre-stress force being attained by clamping devices integrated mto the fittings and/or the connection elements, or else by spring elements
which are built into the stack formed in the template and which, on installation of the loops, provide the desired contact force and thereby also the required mechanical stability.
An additional clamping device, or additional spring elements, can be saved if the loops are respectively formed by an elastically deformable strip, possibly of glass fibers.
Four loops mounted on the connecting element are sufficient in general for good mechanical stability of the active portion; for example, two of them are arranged diametrally of each other, and are directed in the opposite direction to the other two loops. Increased stability is achieved by the use of six mounting places, arranged offset by about 60 in the circumferential direction and, of which, respectively, three serve to guide the loops in a predetermined first direction and three in the opposite direction. Stability is improved only a little by eight or more mounting places, and this requires, however, an additional production-technical expense. Loops which are directed opposingly on a connection piece can also be arranged without any offset in the circumferential direction and solely offset in the axial direction. If necessary, the connection piece can be formed by two parts which can be connected together so that they can be released or can be mutually separated, and which respectively carry loops which are aligned solely in one direction.
A preferred embodiment example of the invention, and the advantages which can be thereby obtained, are described in further detail hereinafter, with reference to a drawing.
BRIEF DESCRIPTION OF THE DRAWING
In the single drawing, a side view is shown of a surge arrester according to the invention, the axially symmetrical housing of which is shown sectioned.
EMBODIMENTS OF THE INVENTION
The surge arrester shown in the single Figure has a housing 1 of an axially symmetrical form, and a surge arrester active portion 2, of axially symmetrical construction, is arranged in it along the housing axis (not shown). The housing is constructed of an insulating tube 3 provided with screens and made of a weather-resistant material, for example a polymeric material such as a silicone, or a porcelain, and two metallic connection fittings 4 and 5 which are attached to the ends of the tube of insulating material. The connection fittings 4 and 5 respectively have a metal plate (not shown, for clarity) which gas-tightly closes the housing 1, and also a respective cylindrical closure portion 6 or 7, which is arranged with axial symmetry in the interior of the housing 1, and which respectively seals the active portion 2 of the arrester, upward or downward. A bore provided with an internal thread is let into the closure part 6 or 7. A pressure screw 8 or 9, brought outward along the housing axis through the plate of the connection fitting, cooperates with the internal thread. The foot of the pressure screw 8 or 9 is mounted on a metal pressure plate 10 or 11, which is axially displaceable in a recess of the closure portion 6 or 7, of the active portion 2 of the surge arrester.
The active portion of the arrester is constructed as a stack and also contains, besides the two closure portions 6 and 7, cylindrical varistor elements 12 of nonlinear resistance material, which may have a metal oxide basis, such as ZnO in particular, and cylindrically embodied metallic connecting elements 13. There are further provided in the active portion of the arrester 2 further pressin-e plates 10', 11', and also disk-shaped ohmic contact elements 14, which can be arranged between a pressure plate 10,10', 11,1T and an adjacent varistor element 12; between
adjacent varistor elements 12; and between a connecting element 13 and a varistor element 12 or a pressure plate.
Loops of insulating material are denoted by the reference symbol 15; they are preferably formed of a wound, fiber-reinforced strip which is embedded in a polymer matrix and, with the production of contact force, brace two connecting elements 13, or brace the closure portion 6 and the connecting element 13 adjoined to the portion 6 in the active portion 2 of the surge arrester, or brace the closure portion 7 and the connecting element 13 adjoined to the portion 7 in the active portion 2 of the surge arrester. The loops 15 have their ends guided in grooves 16,16' which are formed in the envelope surfaces of the closure portions 6,7 and of the connecting elements 13. The closure portions 6,7 or the connecting elements 13 project beyond the pressure plates 10,10', 11,11' and the varistor elements 12 in the radial direction. The loops 15 mounted in the grooves 16,16' thus have, in a dielectncally favorable manner, a defined distance from the varistor elements 12. An analogous guiding of the loops can be attained if the closure portions 6, 7 and the connecting elements 13 in fact have the same diameter as the varistor elements 12, but now have, instead of the grooves, radially directed projections on which the loops 15 are mounted.
Each of the two connecting elements 13 has six grooves 16,16', which are arranged mutually offset, respectively by about 60°, in the circumferential direction. These grooves all have a semicircular section which is open in the axial direction, and in which an end of one of the loops 15 is mounted. Adjoining the semicircular section are two sections which predominantly pass in the axial direction and in which is held a portion of a respective loop section which runs straight and adjoins the end of the mounted loop. This section runs parallel, and at a
predetermined, dielectrically favorable distance, to the varistor elements which are acted on Avith contact force by the mounted loop.
The sections of the grooves 16 which run straight, run oppositely to the corresponding sections of the grooves 16'. A respective one of three loops is supported in the groove 16' and braces together, with the production of contact force, the connecting element 13 and the closure portion 6 and also the varistor elements arranged between them. The magnitude of the contact force is set during mounting of the surge arrester by turning the pressure screw 8 and by axial displacement of the pressure plate 10 thereby. A respective one of three loops is supported in the groove 16, and braces the two connecting elements 13 and the varistor elements arranged therebetween, with the production of contact force. The contact force is attained here by elastically deformable loops, and if desired can be varied in magnitude by means of a clamping device, with a pressure screw and a clamping plate, which can be built into the connecting element 13. A further, second clamping element can if necessary be built into the connecting element 13, and acts on the section lying thereabove of the active portion 2 of the arrester. The clamping screw 8 and pressure plate 10 can then be dispensed with.
The grooves 16 and 16' follow each other alternately in the circumferential direction of the connecting elements 13. The pre-stress force taken up by the loops is thus uniformly transmitted to the varistor elements 12.
For the production of this surge arrester, there are stacked one above the other in a template, the closure portion 7, the pressure plate 11, the ohmic contact element 14, alternately further ohmic contact elements and varistor elements 12, the pressure plate 11', and the lower connecting element 13. The grooves 16' of the closure portion 7 and grooves 16 of the
connecting element 13 are here set so that they are mutually aligned. Three prefabricated loops 15, which preferably respectively consist of a wound, strip-form prepreg which is hardened after winding, are suspended in the mutually aligned grooves 16,16', and by the rotation of the pressure screws 9, force is exerted on the pressure plate 11 and thus, via the loops 15 which span them, also on all the varistor elements of the active portion of the arrester which are arranged between the parts 7 and 13.
Further varistor elements 12 and ohmic contact elements are now correspondingly stacked on the connecting element 13, and this partial stack is concluded with the further connecting element 13. This partial stack of the active portion of the arrester can be braced with loops which are respectively produced, during the production of the surge arrester, by winding a strip which is acted on by pre-stress force and is laid in the mutually aligned grooves 16 and 16',
In a corresponding manner, the active portion of the arrester can be extended by further partial stacks, and can finally be concluded by the closure portion 6. The active portion can now be placed in the housing 1, which can be closed after filling with a settable insulating medium. Since the loops are applied at a distance from the varistor elements 12 here, the insulating medium encloses the active portion with high reliability, free from gaps and shrink holes. The surge arrester according to the invention thus has, m spite of the optional constructional height, not only good mechanical properties but also good electrical properties.
The housing does not necessarily have to contain insulating material; it can also be metallic. Additional potential-controlling means are then to be provided between the housing wall and the active portion of the arrester, and feedthroughs are to be provided at the ends of the housing.
2 active portion of the arrester
3 insulating tube
4, 5 connection fittings
6,7 closure portions
8,9 pressure screws
10,10', 11,1 r pressure plates
12 varistor elements
13 connecting elements
14 ohmic contact elements
16,16' grooves, mounting places
1. Surge arrester with two current-conducting connection fittings (1,2) spaced apart along an axis, an axially symmetrical active portion (2) arranged between the two connection fittings (1,2) and containing cylindrical varistor elements (12) stacked one above the other, with a housing (1) which receives the active portion and with a mounting having loops (15) and acting on the active portion (1) with contact force, characterized in that the active portion (2) has at least one electrically conductive, axially symmetrical connecting element (13), that the connecting element (13) is arranged between two successive varistor elements (12) in the stack and has at least four mounting places (16,16') which are formed in and/or on the connecting element (13) and are uniformly distributed in the circumferential direction aroxmd the axis, that a respective one of two first loops (15) is supported on two first (16) of the mounting places and acts with a first contact force on the connecting element (13) and a first of the two varistor elements (12), and that a respective one of two second loops (15) is supported on two second (16') of the mounting places and acts with a second contact force on the connectmg element (13) and a second of the two varistor elements (12).
2. Surge arrester according to claim 1, characterized in that the connecting element contains a clamping device which produces the first and/or the second contact force.
Surge arrester according to one of claims 1 or 2, characterized in that each of the
first mounting places (16) is arranged between a respective two of the second
mounting places (16').
Surge arrester according to one of claims 1-3, characterized in that the connecting
portion (13) projects beyond the varistor elements (12) in the radial direction, and
that grooves (16, 16') forming the mounting places are let into the projecting
section of the connecting portion.
Surge arrester according to claim 4, characterized in that the grooves (16, 16')
have a semicircular section which is open in the axial direction and in which one
end of the first or second loop (15) is mounted.
Surge arrester according to claim 5, characterized in that sections adjoin the
semicircular section which are predominantly directed in the axial direction and in
which is mounted respectively a portion of a loop section running in a straight
line, adjoining the end of the loop, and which runs parallel and at a predetermined
distance from the varistor elements (12) on which the loop (15) acts with contact
Surge arrester according to claim 6, characterized in that the sections which run in
a straight line are oppositely aligned in the circumferential direction of successive
Surge arrester according to one of claims 1-7, characterized in that the connecting
portion has six grooves which are mutually offset respectively by about 60 in the
9. Surge arrester, substantially as hereinabove described and illustrated
with reference to the accompanying drawings.
|Indian Patent Application Number||IN/PCT/2000/432/CHE|
|PG Journal Number||50/2007|
|Date of Filing||25-Sep-2000|
|Name of Patentee||M/S. ABB SCHWEIZ AG|
|Applicant Address||Brown Boveri Strasse 6, 5400 Baden|
|PCT International Classification Number||H01C 7/12|
|PCT International Application Number||PCT/CH99/00105|
|PCT International Filing date||1999-03-08|