Abstract
A surge arrester for the power supply of low-voltage systems, having a housing, two electrodes which are situated axially opposite one another, an arc combustion chamber formed in the interior of the housing, and a trigger aid. A spark gap is formed between the two electrodes so that an arc is produced when the spark gap between the two electrodes is triggered, the axial distance between end faces of the two electrodes being so large that the arc voltage is greater than the expected line voltage. Conversion of energy within the surge arrester is reduced by the arc combustion chamber having an inner region and at least one expansion region into which the arc can propagate after triggering. The inner region is arranged between the two electrodes and is delimited axially by the end faces of the electrodes and is delimited longitudinally by the at least one expansion region.
Claims
1-13. (canceled)
14. A surge arrester for power supplies of low-voltage systems, comprising: a housing, two electrodes which are situated axially opposite one another, an arc combustion chamber formed within the housing, and a trigger aid, wherein a spark gap is formed between the electrodes so that an arc is produced when the spark gap between the two electrodes is triggered, wherein an axial distance a between end faces of the electrodes is so large that the arc voltage U.sub.L is greater than an expected line voltage U.sub.N, wherein the arc combustion chamber has an inner region and at least one expansion region into which the arc can propagate after triggering, wherein the inner region is arranged between the two electrodes and is axially delimited by the end faces of the electrodes, and wherein the at least one expansion region adjoins a longitudinal side of the inner region, and at least two side walls of the expansion region are at least partially composed of insulating material.
15. The surge arrester according to claim 14, wherein the at least one expansion region comprises two expansion regions, each of which adjoins a respective one of opposite longitudinal sides of the inner region, and wherein the two expansion regions have essentially the same dimensions, so that the inner region is essentially centrally arranged in the arc combustion chamber.
16. The surge arrester according to claim 14, wherein said at least one expansion region adjoins a longitudinal side of the inner region, and wherein a longitudinal side of the inner region that is situated opposite the expansion region is closed.
17. The surge arrester according to claim 14, wherein the expansion region has a height which is greater than the height of the inner region.
18. The surge arrester according to claim 14, wherein the expansion region has a length which is greater than the length of the inner region, whereby a longitudinal side of at least one of the electrodes adjoins the expansion region.
19. The surge arrester according to claim 14, wherein the expansion region, in cross section, expands from the inner region outwards.
20. The surge arrester according to claim 14, wherein the side walls of the expansion region are configured in a manner such that the expansion region has an area in which a distance between the side walls is reduced relative to other areas of the expansion region.
21. The surge arrester according to claim 20, wherein the area in which the distance between the side walls is reduced extends essentially perpendicularly relative to a connecting line between the two electrodes and over a entire height of the expansion region, whereby a line-shaped or ribbon-shaped region is formed centrally between the end faces of the two electrodes.
22. The surge arrester according to claim 14, wherein the side walls of the expansion region are formed at least partially spherically so that the expansion region has a concave cross section in at least certain areas.
23. The surge arrester according to claim 14, wherein at least one opening is formed in at least one of the side walls of the expansion region, through which opening hot, ionized gas can flow out of the arc combustion chamber.
24. The surge arrester according to claim 14, wherein insulating material is a hard gassing insulation material.
25. The surge arrester according to claim 14, wherein the trigger aid has a resistive area and a short insulation area, the resistive area being connected on one side to one of the electrodes and on another side to the insulation area.
26. The surge arrester according to claim 14, wherein the side walls of the expansion region and the inner region of the arc combustion chamber, except in a region of the trigger aid, are composed of the insulating material.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIGS. 1a & 1b are simplified perspective plan and sectional views of a surge arrester,
[0036] FIG. 2 is a longitudinal section through a surge arrester,
[0037] FIG. 3 is a cross-sectional view taken at a right angle to the view of FIG. 2,
[0038] FIGS. 4a-4e show five different embodiments of the arc combustion chamber of a surge arrester,
[0039] FIGS. 5a & 5b are simplified depictions of a further embodiment of a surge arrester, in a longitudinal section and from above,
[0040] FIG. 6 is a simplified longitudinal sectional view of a further embodiment of a surge arrester, and
[0041] FIG. 7 is a simplified longitudinal sectional view of an alternative embodiment of the surge arrester according to FIG. 6.
DETAILED DESCRIPTION OF THE INVENTION
[0042] FIG. 1 shows a simplified depiction of a surge arrester 1 according to the inventiononce in a perspective depiction diagonally from above (FIG. 1a) and once in a perspective depiction diagonally from the sideof a surge arrester 1 cut open lengthwise (FIG. 1b). The surge arrester 1 has a housing 2 with two electrodes 3, 4 which are situated axially opposite one another, and an arc combustion chamber 5 which is formed in the interior of the housing 2. The simplified depiction of the surge arrester according to FIG. 1 shows thereby only one part of the housing 2, whereby in particular the housing part that closes off the housing 2 at the top is omitted, so that a view into the arc combustion chamber 5 formed in the interior of the housing 2 is possible. In addition to the housing 2 (shown only schematically in the figures), the surge arrester 1 may additionally have an outer housing as well, which housing is composed of, for example, steel, by which means a high pressure resistance can be ensured.
[0043] A spark gap is formed between the two electrodes 3, 4, so that an arc 6, indicated in the FIGS. 2 to 7, is created when the spark gap between the two electrodes 3, 4 is triggered. In order to prevent the occurrence of a system follow current or to extinguish a flowing system follow current as quickly as possible, the axial distance a between the end faces 3a, 4a of the two electrodes 3, 4 which are situated opposite to one another, is selected to be so large that the arc voltage U.sub.L is greater than the expected line voltage U.sub.N. The distance a between the end faces 3a, 4a of the two electrodes 3, 4 can thereby amount to between 5 mm and 20 mm.
[0044] As the simplified depictions of the surge arrester 1 according to the invention show, the arc combustion chamber 5 has an inner region 7 and at least one expansion region 8 into which a pending arc 6 can propagate after triggering. In the embodiment examples of the surge arrester 1 shown in FIGS. 1 to 4, only one expansion region 8 is formed in the arc chamber 5 in each case, while in the embodiment examples according to FIGS. 5 to 7 the arc combustion chamber 5 has two expansion regions 8, 8, which adjoin two longitudinal sides of the inner region 7 that are situated opposite one another.
[0045] As is, for example, visible in FIG. 1b, the inner region 7 of the arc combustion chamber 5, which is arranged between the two electrodes 3, 4 and is axially delimited by their end faces 3a, 4a, turns into the substantially larger expansion region 8that is, the inner region 7 is connected to the expansion region 8 along its entire longitudinal side and not just via a narrow channel. Altogether, the arc combustion chamber 5 has, as a result, a substantially larger volume than the surge arresters known from the state of the art, in which the arc combustion chamber is normally cylindrical, whereby the diameter of the arc combustion chamber normally corresponds to the dimensions of the end faces of the electrodes.
[0046] In the surge arrester 1 according to the invention, at least the two side walls 9, 10 of the expansion region 8 are at least partially composed of insulating material 11. Preferably, the side walls as well as the end faces of the expansion region 8 are wholly composed of insulating material, so that the arc combustion chamber 5 is completely surrounded by insulating material.
[0047] FIG. 2 schematically shows that, in a surge arrester 1 according the invention, the arc 6 can propagate varyingly far into the expansion region 8 of the arc combustion chamber 5, depending on the instantaneous current strength of the surge current to be discharged. The greater the amplitude of the surge current, the further the arc 6 will normally propagate into the expansion region 8 of the arc combustion chamber 5. This is possible because the arc combustion chamber 5 is not limited to the inner region 7 between the two electrodes 3, 4 but rather has in the expansion region 8 an additional large region which extends perpendicularly to the connecting line between the two electrodes 3, 4, by which means a relatively high-volume gap or insulation room for the arc 6 is made available. As a result, it is possible for the arc 6 to always propagate inside of the arc combustion chamber 5 such that it takes on a form that is energetically most favorable, so that the arc voltage during a rise in the amplitude of the surge current does not increase or only increases relatively little. By this means, a linearization of the arc voltage during the discharge process is achieved, so that the conversion of energy inside of the arc combustion chamber 5 is also as low as possible.
[0048] As FIGS. 2 and 3 also especially show, the expansion region 8 has a height H which is substantially greater than the height h of the inner region 7 of the arc combustion chamber 5. Additionally, the expansion region 8 has, according to FIGS. 1 and 2, a length L which is greater than the length l of the inner region 7, whereby the length l of the inner region corresponds to the distance a between the end faces 3a, 4a of the two electrodes 3, 4. The two electrodes 3, 4 consequently protrude with not only their end faces 3a, 4a, but also a corresponding length into the arc combustion chamber 5, so that the two electrodes 3, 4 adjoin with their longitudinal sidesthe upper side, in the figuresthe expansion region 8. This makes it possible for the bottoms of the arc 6as shown in FIG. 2.to wander outward on the longitudinal side of the two electrodes 3, 4 after triggering.
[0049] FIGS. 4a to 4d depicts different variants of the arc combustion chamber 5 in cross section. These differ from each other in the configuration of the expansion region 8 or the formation of the side walls 9, 10 of the expansion region 8. In each of the variants according to FIGS. 4a to 4d, the expansion region 8 has, in each case, a larger width in the upper region than in the lower region. The enlargement of the expansion region 8 can thereby be linear (FIG. 4a), so that the expansion region 8 has a somewhat V-shaped cross section. Additionally, an arched (FIGS. 4b and 4c) or a step-shaped (FIG. 4d) progression of the side walls 9, 10 is possible. The two embodiment examples according to FIGS. 4b and 4c differentiate themselves in that the expansion region 8 in the embodiment example according to FIG. 4b has, somewhat above the inner region 7, a region 12, in which the distance between the side walls 9, 10 of the expansion region 8 is reduced, while the expansion region 8 in the embodiment example according to FIG. 4c broadens continually from the inner region 7 up to its upper edge.
[0050] FIG. 4e shows an embodiment example in which the expansion region 8 diminishes in cross section from the inner region 7 toward its upper end. Because the expansion region 8 has a longer length L than the inner region 7 in this embodiment example as well, a configuration of this sort of the expansion region 8 or of the arc combustion chamber 5 also makes possible a widening of the arc 6 during a rise in the surge current to be discharged. The shorter distance between the side walls 9, 10, realized in the upper part of the expansion region 8, leads, in this area, to a stronger cooling of an arc 6, which counteracts a further widening of the arc 6. As a result, excessive extension of an arc 6 (which is connected with an increase in the arc voltage) is prevented.
[0051] In the end, the different geometric configurations of the arc combustion chamber 5, shown in the figures, all make it possible for an arc 6 to propagate into the expansion region 8 in such a way that it takes on its energetically most favorable form, so that the arc voltage remains approximately constant, even during a rise in the amplitude of the surge current to be discharged. By appropriately dimensioning the arc combustion chamber 5, especially by means of a respective choice of the axial distance a between the end faces 3a, 4a of the two electrodes 3, 4, it can be ensured that the arc voltage U.sub.L is always somewhat above the expected line voltage U.sub.N.
[0052] In the embodiment example according to FIGS. 5a & 5b, the region 12, in which the distance between the side walls 9, 10 of the expansion region 8 is reduced, extends perpendicularly to the connecting line between the two electrodes 3, 4 and over the entire height of the two expansion regions 8, 8 or the arc combustion chamber 5. The line- or ribbon-shaped region 12, which constitutes a bottleneck for the arc 6, is thereby formed centrally between the end faces 3a, 4a of the two electrodes 3, 4. The shorter distance between an arc 6 and the two side walls 9, 10 in the region 12that is, inside of the bottleneckcauses the side walls 9, 10 in the region 12 to emit more gas than in the adjoining expansion region 8, in which the arc 6 is further from the side walls 9, 10. This leads to two gas streams 13indicated in FIG. 5a with arrowsdirected oppositely to one another out of the bottleneck 12 into the adjoining expansion region 8. The two gas streams 13 lead, after the discharge process of the surge current, to a strengthened and quicker deionization of the region 12, so that the danger of a renewed triggering of the spark gap in the case of pending line voltage is reduced.
[0053] In the two embodiment variations of the surge arrester 1 or the arc combustion chamber 5 according to the FIGS. 6 and 7, the arc combustion chamber 5 has two expansion regions 8, 8, which adjoin two longitudinal sides of the inner region 7 which are situated opposite to one another. The two electrodes 3, 4 are thereby arranged centrally in the arc combustion chamber 5, so that the two expansion regions 8, 8 have the same dimensions and are symmetrically arranged with regard to the inner region 7.
[0054] To specifically manipulate the stream of the hot, ionized gas inside of the arc combustion chamber 5 and to enable a specific flow of the plasma out of the arc combustion chamber 5, openings 14 are formed in the side walls 9, 10 of the inner region 7 as well as the expansion regions 8, 8 in the embodiment variation according to FIG. 7, through which openings hot, ionized gas can flow out of the arc combustion chamber 5. Furthermore, the pressure inside of the arc combustion chamber 5 can be specifically reduced or set by means of the formation of the openings 14. Moreover, additional cooling effects can be achieved by means of the formation of the openings 14 and the gas streams created thereby.
[0055] Because, in the surge arrester 1 according to the invention, the distance a between the end faces 3a, 4a of the two electrodes 3, 4 is selected to be so large that the arc voltage U.sub.L is greater than the expected line voltage U.sub.N, a trigger aid is provided in the region of the arc combustion chamber 5, by means of which the desired response voltage of the surge arrester 1 can be adjusted. In the embodiment example shown in FIG. 1, the trigger aid comprises a resistive area 15 and a short insulation area 16, whereby the resistive area 15 is connected on the one side to the one electrode 4 and on the other side to the insulation region 16. In addition, however, other types of known (known per se from the state of the art) trigger aids can be employed which lead to a triggering of the surge arrester 1 at the desired response voltage.
