Electric lamp and discharge devices – With gas or vapor – Having electrodes with geometrical relationship
Reexamination Certificate
2000-03-06
2003-05-20
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrodes with geometrical relationship
C313S231110, C313S231210, C313S231410, C361S118000, C361S120000, C361S127000
Reexamination Certificate
active
06566813
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an overvoltage protection device with a first electrode which has a first arcing horn, with a second electrode which has a second arcing horn, with an air-breakdown spark gap which is active between the arcing horns, and with a housing which accommodates the electrodes, the two arcing horns being made and arranged relative to one another such that they diverge from a lower ignition area each to their outer ends, so that the air-breakdown spark gap widens to the outside, proceeding from the ignition area.
2. Description of Related Art
Electrical, but especially electronic measurement, control and switching circuits, mainly also telecommunications means and systems, are sensitive to transient overvoltages, as can occur especially by atmospheric discharges, but also by switching operations and short circuits in power supply grids. This sensitivity has increased to the extent that electronic components, especially transistors and thyristors, are used; mainly integrated circuits which are being increasingly used are greatly endangered by transient overvoltages.
To protect electrical, but especially electronic measurement, control and switching circuits, mainly also telecommunications means and systems, against transient overvoltages, generally, wherever electronic circuits are used, overvoltage protection devices have been developed and used for more than twenty years.
One important component of an overvoltage protection device is at least one spark gap which operates at a certain overvoltage, the operating voltage, and thus, prevents overvoltages which are greater than the operating voltage of the spark gap from occurring in the area protected by this overvoltage protection device.
It was mentioned at the start that the type of overvoltage protection device to which the invention is directed has two electrodes and an air-breakdown spark gap which acts between the electrodes or their arcing horns. In addition to overvoltage protection devices with an air-breakdown spark gap, there are overvoltage protection elements with an air-flashover spark gap in which a creeping discharge occurs upon response. Overvoltage protection devices with an air-breakdown spark gap, as compared to overvoltage protection devices with an air-flashover spark gap, have the advantage of higher current carrying capacity, but the disadvantage of a higher and not especially constant operating voltage. Therefore, various overvoltage protection devices with an air-breakdown spark gap have been proposed which have been improved with reference to the operating voltage. Here, in the area of the arcing horns or the air-breakdown spark gaps which act between the arcing horns, ignition aids have been accomplished in various ways, for example, such that there was at least one ignition aid between the arcing horns which triggers a creeping discharge and which projects partially into the air-breakdown spark gap, the ignition aid being made in the manner of a bridge of plastic.
The overvoltage protection device upon which the present invention is based is known from German Patent DE 44 02 615 C 2 and corresponding U.S. Pat. No. 5,604,400. The known overvoltage protection device has two narrow electrodes which are each made angled and each have an arcing horn and a terminal leg bent away from it. The known overvoltage protection device is characterized in that, based on the electrodes which extend more or less in one plane, it has only a small overall width. Furthermore, the known overvoltage protection device, in any case, when operated for the first time, has a high current carrying capacity and high network follow current extinction capacity. However, problems always arise when an arc jams at one location; this can lead to electrode damage.
Furthermore, German Patent DE 196 04 947 C 1 discloses an overvoltage protection device which is made essentially rotationally symmetrical. The two electrodes are identical and each have arcing horns in the shape of truncated cones, and an ignition bridge for triggering a creeping discharge is located between the two end faces of the arcing horns. This known overvoltage protection device is likewise characterized by high current carrying capacity and a high network follow current extinction capacity. However, the disadvantage is that this known overvoltage protection device has a relative high overall height. Another disadvantage is that, when the spark gap operates, considerable forces act on the extremely sensitive ignition bridge; this can lead to the ignition bridge being damaged.
SUMMARY OF THE INVENTION
A primary object of this invention is, therefore, to devise an overvoltage protection device of the type mentioned above which is characterized by a high current carrying capacity and high network follow current extinction capacity with an overall height which is as small as possible.
The overvoltage protection device as in accordance with the invention, in which the aforementioned object is achieved, first of all, is essentially characterized by the first arcing horn being made in the shape of a truncated cone and the second arcing horn being located concentrically around the first arcing horn. In accordance with the invention, the first electrode with the first arcing horn represents a middle electrode, while the second electrode with the second arcing horn represents an outer electrode. The concentric arrangement of the second arcing horn around the first arcing horn yields a horn spark gap which runs entirely or partially around the center axis of the two electrodes. This yields a peripherally closed spark gap when the second arcing horn is made circular and the surface of the second arcing horn facing the first arcing horn is made in the shape of a truncated funnel.
However, basically, it is also possible to make the second arcing horn such that it has a plurality of arcing horn segments which are spaced apart from one another and arranged concentrically around the first arcing horn. One especially preferred embodiment of the overvoltage protection device according to the invention is provided with a second arcing horn which is made in the shape of a ring segment and the surface of the second arcing horn facing the first arcing horn is made in the shape of a truncated funnel. Preferably, the second arcing horn extends over an angle of roughly 210° to 270°, especially over an angle of roughly 240°. The embodiment of the overvoltage protection device in accordance with the invention in which the second arcing horn is made in the shape of a ring segment is one in which there is a horn spark gap which extends only partially around the center axis of the two electrodes.
In the overvoltage protection device according to the invention, the horn spark gap which runs only partially around the center axis of the electrodes is characterized by a very high current carrying capacity and a, likewise, high network follow current extinction capacity. Furthermore, the concentric arrangement of the second arcing horn around the first arcing horn yields a very low overall height of the overvoltage protection device and a simple structure.
A preferred embodiment of the overvoltage protection device as in accordance with the invention, furthermore, has at least one ignition bridge of electrically insulating material in the ignition area between the two arcing horns. Via the ignition bridge, a creeping discharge is triggered which, once initiated, at a relatively constant, low operating voltage, leads to ignition of the air-breakdown spark gap with a relatively high current carrying capacity. Since, in the overvoltage protection device of the present invention, in contrast to the overvoltage protection device known from German Patent DE 196 04 947 C 1, the spark gap is open in the axial direction instead of the radial direction, the mechanical forces acting on the extremely sensitive ignition bridge are minimized when the spark gap is operated. So that a creeping discharge is possible anywhere on the entirely or parti
Lehmann Eberhard
Scheibe Klaus
Schimanski Joachim
Tews Jörg
Wetter Martin
Nixon & Peabody LLP
Patel Nimeshkumar D.
Phoenix Contact GmbH & Co.
Roy Sikha
Safran David S.
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