Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Patent
1994-08-30
1996-06-11
Pellinen, A. D.
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
361177, H07H 904
Patent
active
055262198
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a surge arrester arrangement comprising a surge arrester with an elongated insulating casing, in which a number of preferably cylindrical arrester elements of metal oxide varistor material are arranged between two end electrodes, as well as a cut-out device, arranged in series with the arrester, for automatic disconnection of the arrester in the event of arrester failure.
BACKGROUND ART
For a surge arrester placed between phase and ground, an arrester failure in all probability will result in a permanent ground fault. The arrester must then be disconnected or be replaced before the system can be energized again.
For arresters in stations, the relatively short shutdown required for a replacement is acceptable in view of the low risk of an arrester failure. In addition, the risk of operating the system without arrester protection for vital components in the station cannot be taken. Thus, a three-phase surge arrester in a station must be replaced by a new arrester.
The situation is somewhat different for surge arresters placed in the towers of a power line to protect against back flashover caused by lightning, or against switching surges. A failure of such an arrester resulting in a permanent ground fault may entail a lengthy shutdown before the defective arrester has been located and replaced. On the other hand, it is usually acceptable that the arrester is disconnected only. Therefore, if the arrester is provided with a cut-out device which automatically disconnects the arrester in the event of a failure, the operation of the line may continue and any defective arresters be located and replaced at some suitable time.
Surge arresters with cut-out devices are previously known, for example from the U.S. Pat. Nos. 2,305,436 and 4,308,566. However, these prior art cut-out devices have a complicated design, which renders manufacture difficult and increases the risk of malfunction.
The purpose of the present invention is to provide a surge arrester arrangement with a cut-out device which is simple and inexpensive to manufacture and which functions in a reliable manner. This is achieved by a cut-out device with the characteristic features described in claim 1. The cut-out device according to the invention includes a metal oxide block with a larger area than the blocks in the arrester, that is, with a higher relative energy capability. With such a design, the block in the cut-out device can only fail if the arrester connected in series with the device has failed, whereby incorrect tripping of the device is prevented.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be explained in greater detail by describing an embodiment with reference to the accompanying drawing, wherein
FIG. 1 shows in axial section a cut-out device for a surge arrester designed according to the invention, and
FIG. 2 shows a side view of a surge arrester assembly including the cut-out device.
DETAILED DESCRIPTION
In the drawings, FIG. 2 shows a power line 30 which, by means of a suspension insulator chain 31, is suspended from a power line tower, of which only an end portion of the horizontal cross beam 32 of the tower is shown in Figure. At the outer end of the cross beam a surge arrester 33 is arranged. The lower end of the surge arrester is connected to the line 30 via a flexible conductor 34 and a cut-out device 35. The surge arrester .times.may be of the normally occurring design with an elongated insulating casing 36, in which a number of preferably cylindrical ZnO blocks 37 are arranged between two end electrodes 38 and 39.
Referring now to FIG. 1, the central part of the cut-out device 35 consists of a cylindrical ZnO block 1 with larger diameter than the ZnO blocks 37 in the surge arrester with which the cut-out device is intended to be connected in series. The ZnO block 1 is arranged between two electrode plates 2, 3 of metal, making contact with the end surfaces of the block, and is surrounded by a rotationally symmetrical polymer casing 4, which on the lower side of
REFERENCES:
patent: 4547831 (1985-10-01), Hellman et al.
patent: 4710847 (1987-12-01), Kortschinski et al.
Stenstrom Lennart
Thors Bengt
Asea Brown Boveri AB
Medley Sally C.
Pellinen A. D.
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