Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Reexamination Certificate
1999-05-18
2001-01-09
Ballato, Josie (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
Reexamination Certificate
active
06172865
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to surge protection for telecommunication devices and is to be used in designing modules having two gas-filled surge arresters arranged in an insulating housing, with each surge arrester having an auxiliary discharge gap and a short-circuit device responding in the event of an overload.
BACKGROUND INFORMATION
In a conventional module of this type (see
FIG. 1
) sold in the U.S. market, both surge arresters, each of which has two electrodes and is surrounded by a metallic sleeve
1
forming the corresponding auxiliary gap, are arranged next to each other in the chambers of an insulating housing
2
. One electrode of each surge arrester is in contact with one plug-in contact part
3
leading outside from housing
2
, while the other electrode is connected to the metallic cover
6
of insulating housing
2
via a low-melting spacer
4
and a helical leaf spring
5
. This cover is used as ground and has a terminal contact leading to the outside. In this conventional module, the auxiliary spark gap of each surge arrester has an air spark gap connected in parallel, which is implemented using a perforated insulating foil (vent-safe characteristic, see U.S. Pat. No. 5,142,434). The surge arrester and the air spark gap are arranged in metallic sleeve
1
. In the conventional module this metallic sleeve
1
and spacer
4
are also arranged in a cup
7
, whose edge is kept at a certain distance x
1
from plug-in contact part
3
. In the event of an overload, spacer
4
melts, and, under the effect of leaf spring
5
, the edge of cup
7
comes into contact with contact part
3
(fail-safe characteristic).
The vent-safe characteristic can be implemented using a metal oxide varistor protected against the effect of moisture instead of an air gap using a moisture-sensitive insulating foil. This metal oxide varistor is designed as a hollow cylinder, provided with metal-plated end faces and placed on the first electrode of the arrester (see, for example, U.S. Pat. No. 5,383,085/German Patent No. 43 31 125 A1). A similar method has also been used in three-electrode arresters (see, for example, U.S. Pat. No. 5,388,023/U.S. Pat. No. 5,633,777), where a cylindrical varistor and a meltable spacer are placed on one of the two end electrodes and secured there using an elastic clip attached to the central electrode and a cap arranged at the end of the elastic clip. The edge of the cap and the respective end electrode, i.e., a contact ring placed on the end electrode, form the two electrodes of a short-circuit device (fail-safe characteristic).
SUMMARY
An object of the present invention is to form the auxiliary gaps using metal oxide varistors and thus to simplify and make cost-effective the design of the module as a whole.
The following measures are provided to achieve this object: The common contact device has a plate whose one side is in direct contact with the second electrode of the two surge arresters. Furthermore, each of the two auxiliary discharge gaps is formed by a varistor provided with two contact surfaces, one contact surface of each of the two varistors being in direct contact with the other side of the plate. Additionally, the plate forms the counter-electrode of the two short-circuit devices and the movable electrode of each short-circuit device has a cap placed on the other contact surface of one varistor with the meltable spacer positioned between them. To make the overall structure of the module complete, each cap is electrically connected to the first electrode of the respective surge arrester via an elastic clip securing the cap.
With such a design of the module, the auxiliary functions “short-circuit” and “overload protection” assigned to the respective surge arrester are arranged constructively separately from the surge arrester and implemented together in a submodule, which is connected to the electrodes of the surge arrester via two simple contact elements. This ensures that the individual components of the module can be assigned to one another by simple assembly steps.
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Boy Juergen
Krost Norbert
Völkner Winfried
Ballato Josie
Deberadinis Robert
Kenyon & Kenyon
Siemens Aktiengesellschaft
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