Surge voltage arrester with fail-safe feature
AssigneeReliable Electric Company
InventorBertram W. Baumbach
Life of this patent
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Abstract
A surge voltage arrester utilizes for surge protection a varistor of the zinc oxide type between a line terminal and a ground terminal. The varistor is of a type that has a resistance which decreases as increasing voltage is applied thereacross. With increasing temperature the leakage current through the varistor increases at a given voltage. At a critical temperature and voltage condition, the varistor is subject to a thermal runaway condition which would cause the varistor to fail expelling hot particles. To avoid this failure condition, a fail-safe mechanism is provided which connects the line terminal to the ground terminal by-passing the varistor when there is an overcurrent condition on the line that results in heating of the varistor.
Claims8
A surge voltage arrester for a communications line comprising a line terminal adapted for connection to a line to be protected, a ground terminal, means forming a first electrical circuit between said terminals that is substantially non-conductive for line voltages below a predetermined value but becomes substantially conductive to arrest surge voltages on the line above said predetermined value, said first circuit including circuit component means having a resistance that decreases as increasing voltage is applied thereacross and which heats excessively in an overcurrent condition in the protected line, said component means being further characterized as passing increased current for a given voltage upon increased temperature, a normally-open second electrical circuit coupled between said terminals and including a pair of contactors electrically connected respectively to said terminals, means applying pressure tending to bring said contactors into engagement, and heat-deformable means operable in opposition to said pressure-applying means to maintain said contactors apart, said heat-deformable means deforming sufficiently upon heating of said component means to cause said contactors to engage so that said second circuit closes and provides a direct conductive path between said terminals.
A surge voltage arrester comprising a line terminal adapted for connection to a line to be protected, a ground terminal, means forming a first electrical circuit between said terminals that is substantially non-conductive for line voltages below a predetermined value but becomes substantially conductive to arrest surge voltages on the line above said predetermined value, said first circuit including a varistor that passes increased current for a given voltage upon increased temperature and which is capable of heating to a thermal runaway condition in an overcurrent condition in the protected line, a normally-open second electrical circuit coupled between said terminals and including a pair of contactors electrically connected respectively to said terminals, means applying pressure tending to bring said contactors into engagement, and heat-deformable means operable in opposition to said pressure-applying means to maintain said contactors apart, said heat-deformable means being in thermal conducting relation to said varistor, said heat-deformable means deforming sufficiently upon heating of said varistor in said overcurrent condition to cause said contactors to engage so that said second circuit closes and provides a direct conductive path between said terminals.
A line protector comprising a line terminal and a ground terminal, a first electrical circuit from the line terminal to the ground terminal and having varistor means heatable in the event of an overcurrent condition on the line, a normally open second circuit coupled between said terminals and including heat sink means in thermally conductive relation with said heatable varistor means for producing one or more hot spots in said heat sink means in said overcurrent condition, spring loaded contactor means in said second circuit having multiple fingers tending to close said contactor means and thereby close said normally open second circuit, and means normally preventing said contactor means from closing and being heat deformable at least in the region of a hot spot such that one or more of said fingers closes said second circuit depending upon the hot spot location.
Dependencies are inferred from the claim text.