Electricity: electrothermally or thermally actuated switches – With separate distinct diverse art-type switching device – Fusible element device with other
Reexamination Certificate
1999-09-01
2001-06-26
Picard, Leo P. (Department: 2835)
Electricity: electrothermally or thermally actuated switches
With separate distinct diverse art-type switching device
Fusible element device with other
C337S002000, C337S405000, C337S406000, C337S006000, C361S103000, C361S106000, C361S104000, C361S124000
Reexamination Certificate
active
06252488
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to metal oxide varistors (MOVs) having thermal protection, and more particularly, to MOVs which contain fusible materials which melt before the MOVs can begin thermal runaway.
2. Description of the Prior Art
In one known prior art device, thermal cut-off fuses are mounted electrically in series with the MOVs and adjacent one face of the MOVs. When the MOV heats up, due to the flow of current through the MOV, it causes a rise in temperature at such face which melts the thermal cut-off fuse which opens the electrical circuit to the MOVs. The thermal cut-off fuse being separated from the MOV surface can be erroneously heated by other nearby components, such as resistors, or erroneously cooled by convection currents in the surrounding housing.
In a further known prior art device, thermal cut-off fuses are located remote from the surface of the MOVs they are to protect and are connected to terminals which engage one face of the MOVs. Based upon the heating the terminals sense, their associated thermal cut-off fuse may be caused to operate. The terminals must have the desired response to heat and the factors of extraneous heating and cooling are also present.
Another device provides protection by utilizing varistors having a relatively low initial conduction voltage and using more of them, in parallel and in conductive relationship with a heat sink, for dissipation of the energy load imposed by multiple lightning strikes, for example.
Still another device uses current limiting fuses between the MOVs and ground. If the current through the fuse is sufficient, the fuse blows and actuates diagnostic circuitry.
SUMMARY OF THE INVENTION
An MOV protection device according to the invention provides a fusible member in intimate contact with the MOV it is to protect and when operated by the heat produced by the MOV opens the electrical path to the MOV. In a first embodiment, a thermal fuse is formed by thermal fuse material on substantially all of one face of the MOV and a lead of the MOV is connected to such thermal fuse. When the MOV temperature reaches the operating temperature of the thermal fuse, it melts and opens the circuit to the MOV. In other embodiments only a portion of one face of an MOV is covered by thermal fuse material and this material is connected to an MOV lead. A further embodiment divides the MOV into two segments and joins them by means of a layer of thermal fuse material. When this layer melts the circuit of the MOV is interrupted.
In all cases the thermal fuse material is in intimate contact with the MOV and is able to directly operate in response to the heating of the MOV. There is little possibility that the thermal fuse material will be influenced by the heat generated by other components or the cooling effects of convection currents in any housing. It is an object of this invention to provide a novel MOV protection device.
It is another object of this invention to provide a novel MOV protection device which protects an MOV against thermal runaway.
It is another object of this invention to minimize the dangers from MOV failures.
It is still another object of this invention to provide a novel MOV protection device which is intimate contact with one face of an MOV.
It is yet another object of this invention to provide a novel MOV protection device which is wired into the circuit with an MOV and upon failure of the protection device opens the circuit of the MOV.
It is still another object of this invention to provide a novel MOV protection device which employs thermal fusible material.
It is yet another object of this invention to minimize the danger of MOV failures.
It is yet another object of this invention to reduce the fire hazard and minimize or eliminate damage to surrounding components and/or nearby personnel caused by MOV burning or explosion when overheated.
It is another object of this invention to provide a novel MOV protection device which employs a thermal fusible material in intimate contact with a MOV and which is in the conductive path to such MOV.
Other objects and features of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principles of the invention, and the best modes which are presently contemplated for carrying them out.
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Campolo Steve
Ziegler William R.
Leviton Manufacturing Co. Inc.
Picard Leo P.
Sutton Paul J.
Vortman Anatoly
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