Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1992-09-15
1994-06-28
Hofsass, Jeffery A.
Communications: electrical
Condition responsive indicating system
Specific condition
340653, 361118, 25022715, 385 13, G08B 2100
Patent
active
053250877
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention relates primarily to surge arresters, but is also applicable to transformers, switches, insulators, and cable terminations and splices.
Surge arresters are connected to electrical power equipment, such as transformers, switchgears and overhead conductors, in order safely to divert to earth any excess current that would otherwise flow through and damage the equipment. Such excess current could arise, for example, from a lightning strike. Surge arresters typically comprise one or more surge arresting elements for example varistors made of a metal oxide such as zinc oxide, and/or silicon carbide material and/or a spark gap, and a plurality of such elements are usually mounted end-to-end in a linear stack, being urged together and into good electrical contact with a pair of end electrodes by one or more conductive springs. The stack of surge arresting elements is encased within an outer insulating housing that provides mechanical strength and that protects the elements electrically and also against adverse environmental conditions. The outer housing may be made of porcelain or of an insulating and substantially non-tracking polymeric material, which may be recoverable, for example by the application of heat thereto. The surge arresting elements may be encased in a reinforced resin to enhance the physical and electrical protective thereof, before the outer housing is positioned thereon. Examples of such surge arresters are disclosed in U.S. Pat. No. 4,812,944, GB-A-2073965, GB-A-2188199, U.S. Pat. No. 4,262,318, U.S. Pat. No. 4,656,555, U.S. Pat. No. 4,495,381, and U.S. Pat. No. 4,335,417.
When surge arresters operate, that is to say when they switch from their normally insulating mode to a conducting mode, the high current that flows therethrough creates large mechanical forces and generates a large quantity of heat, and such an environment is preferably withstood by the mechanical protection applied to the surge arresting elements. In some cases, however, the current flow may not be so severe as to produce externally-visible damage yet the surge arresting elements may still be significantly damaged, that is to say damaged to an extent that would impair subsequent operation of the arrester, with the possibility of the associated equipment then not being properly protected.
Japanese Patent Publication No. 1-136305 discloses a surge arrester in which a single plastics optical fibre is introduced through and exits from a metal cover or electrode at one end of a plurality of surge arresting elements that are mounted within and radially spaced from a porcelain outer insulating housing. Within the housing, the optical fibre is looped in heat-transferable manner around one of the elements located towards said one end of the arrester, which element is said to be characteristic of the plurality of elements. Light incident on the optical fibre is compared with light emergent therefrom, and any difference therebetween is monitored and taken to be indicative of heating of the surge arresting elements. Should such difference exceed a predetermined value, then electrical breakdown of the surge arrester can occur.
It is one object of the present invention to provide an improved surge arrester whose internal integrity can be monitored externally thereof in a convenient manner without the surge arrester having to be dismantled.
In accordance with one aspect of the present invention, there is provided a surge arrester comprising a plurality of surge arresting elements mounted within a protective housing, wherein an optical fibre arrangement is disposed within the housing so as to be in good thermal contact with substantially all of said elements thereby to provide an indication of damage to the surge arresting elements.
Thus, in contrast with JP 1-136305, the present invention requires thermal contact of optical fibres not with a single characteristic surge arresting element, but with substantially all, usually all, of them. This is because the characteristics of these elements, usually metal oxide v
REFERENCES:
patent: 4298794 (1981-11-01), Snizer et al.
patent: 4307607 (1981-12-01), Saaski et al.
patent: 4532499 (1985-07-01), Collin
patent: 4840480 (1989-06-01), Starke et al.
Patent Abstract of Japan vol. 13, No. 386 (E-812) (3734) Aug. 25, 1989, & Jp-A-1 136305 (Mitsubishi Electric Corp.) May 29, 1989 [plus unofficial translation].
Burkard Herbert G.
Hofsass Jeffery A.
Raychem GmbH
Zavell A. Stephen
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