Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Reexamination Certificate
2002-08-06
2004-09-07
Toatley, Jr., Gregory J. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
Reexamination Certificate
active
06788519
ABSTRACT:
DESCRIPTION
The invention relates to a spark-gap arrangement encapsulated in a pressure-proof housing, for the purpose of diverting harmful disturbances due to overvoltage, comprising at least two electrodes disposed substantially opposite one another in a housing that is conductive or provided with a conductive coating, between which a discharge space is formed and which are insulated from the housing, according to the precharacterizing clause of claim
1
.
Encapsulated lightning guards with no blow-out function but with surface-gap discharge have been known in the state of the art for years and are marketed, e.g., under the protected trade names DEHNbloc or DEHNgap by the firm of DEHN+SÖHNE Gmbh+Co. KG. Lightning guards on a spark-gap basis for use in low-voltage power-supply systems accordingly include an electrode configuration disposed within a pressure-proof, insulated housing. The pressure-proof housing itself is formed by a metal jacket. By varying the configuration of the electrodes, various response-voltage values can be achieved. The customary dynamic value of the response voltage in known spark-gap lightning guards is about 4 kV. In these solutions according to the state of the art, the response voltage is predetermined by the distance between the electrodes or can be adjusted.
Particularly in applications involving the protection of electronic devices in the area of information technology and data processing, however, it is desirable for the response voltages to be lower, in the region of ca. 1.5 kV. The small electrode separations required, however, cannot be achieved without additional provisions and/or technological complications.
In guards of the blow-out type, which are unencapsulated, it is possible to lower the response voltage by providing an additional trigger electrode. This trigger electrode, in combination with an electrical triggering device comprising a triggering transformer, causes ignition of a subsidiary spark gap with the result that ignition of the main spark gap is initiated immediately thereafter.
The construction of a spark gap with trigger electrode along with associated triggering device will now be explained in detail with reference to FIG.
1
. After the gas diverter (GDT) shown there has been ignited, a pulse transformer TR generates an ignition voltage such that it ignites the subsidiary spark gap F
1
and, immediately thereafter, the main spark gap F
2
.
The response of the subsidiary spark gap F
1
is thus initiated by ignition of the gas diverter. The response voltage of gas-filled overvoltage diverters can be varied over quite a wide range and is unproblematic for voltages below 1 kV. The quasi-external subsidiary ignition is amplified by the pulse transformer TR to a voltage level that can reliably ignite the above-mentioned subsidiary spark gap F
1
.
Hence with a known arrangement according to
FIG. 1
it is possible to ignite the spark gap with small input voltages, and thus to achieve the desired protection at low voltage levels, e.g. 1.5 or 2 kV.
In order to apply this proposed method to spark gaps in a pressure-proof encapsulation, it would be necessary to solve the structural problem of inserting a high-voltage trigger electrode through the capsule wall in a pressure-tight manner and making electrical contact with said electrode.
However, this can be achieved only with considerable effort during manufacture and hence is associated with higher costs.
It is thus the objective of the invention to disclose a spark-gap arrangement encapsulated in a pressure-proof manner that comprises at least two electrodes disposed substantially opposite one another in a housing that is conductive or has a conductive coating and forming between them a discharge space, such that the arrangement makes possible a low response voltage in the range of ≦2 kV with no need to employ trigger electrodes known per se, which must extend externally or be electrically connected outside the capsule.
The objective of the invention is achieved with an object having the characteristics given in claim
1
, while the subordinate claims present at least useful embodiments and further developments.
Accordingly, the basic idea underlying the invention is that the metallic housing or metal jacket of the pressure-proof encapsulation of the spark-gap arrangement is used indirectly as trigger electrode, so that a triggering and hence a reduced response voltage can be achieved with no additional elaborate meaures. Preferably the electrodes of the spark-gap arrangement are so shaped as to form a cavity that is quasi closed off toward the interior, such that parts of the outer surfaces of the electrodes are situated in the immediate vicinity of the metal jacket of the housing or a metal coating, being separated therefrom by a relatively thin insulating layer. By this means the outer surface of the jacket or a metallic coating applied thereto can be used as trigger electrode.
The embodiment in which the electrodes form a cavity offers a substantial advantage in that the arc that is generated is surrounded entirely by electrode material, which resists burning away, so that the stress imposed on all the other structural parts by the arc can be considerably reduced. As a result, in combination with the electrode arrangement, even very large pulse currents can be reliably controlled in an extremely small space.
In the case in which high-energy ignition pulses between the electrodes are needed to trigger the main spark gap, and there is a risk of damage to the metal jacket of the housing, in the interior of the housing there is provided a coating of materials resistant to burning away, such as tungsten-copper. Triggering elements provided within the housing that are in electrical contact therewith can extend for different distances into the discharge space or arcing chamber and can also subdivide these spaces into geometrically separated regions, which has positive effects with respect to optimizing an ability to extinguish secondary currents, because in this special configuration of the triggering elements it is possible to generate partial arcs arranged in series.
In another embodiment the trigger electrodes provided in the interior of the housing can consist of a conductive plastic, such as polymethylene oxide (POM). The advantage derived here is that the tendency of the trigger electrode to burn away is similar to that of the insulating material present in the arcing chamber. Because of the release of conductive particles from the plastic that results from the action of the arc, the ignition energy that causes flash-over across the spark gap can be further reduced, so that with relatively little ignition energy large flash distances can be achieved.
If a plastic is chosen that gives off gas, in addition the ability of the spark-gap arrangement to extinguish secondary currents can be further improved.
When the material used for the trigger electrode is a relatively high-resistance, conductive plastic, the bulk resistance of the plastic material can be used to optimize the triggering circuit. As a result, an external protective resistor such as is required in the state of the art is no longer needed, and there is no danger that partial currents will flow over the externally provided wiring. That is, the bulk resistance of the plastic prevents an undesired fraction of the secondary current from flowing through an external pulse transformer.
Hence in accordance with the invention it becomes possible to apply a triggering voltage by way of the conductive housing in order to form a subsidiary spark gap in the discharge space, such that by way of the spark generated in the subsidiary gap within the housing the actual main spark gap between the electrodes can be ignited with little energy.
Preferably the insulation disposed between the discharge space and the housing is interrupted to form an opening in the region of the subsidiary spark gap.
Within this opening in the insulation can be disposed an insulating electrode spacer, adjusted to the shape of the housing and pr
Hierl Stefan
Koenig Raimund
Krauss Bernhard
Waffler Michael
Zahlmann Peter
Benenson Boris
Dehn + Soehne GmbH + Co.KG
Toatley , Jr. Gregory J.
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