Varistor fuse element
The purpose of the invention is to create such a varistor fuse element, which should within a single housing include both a varistor ( 1 ) as well as an electric fuse ( 2 ), wherein said varistor part i.e. a varistor ( 1 ) is intended to protect each electric installation against overvoltage impulses and consequently against current strokes, while the fuse ( 2 ) is capable to transmit the current stroke due to increased voltage and to interrupt each permanently increased electric current, which might occur due to defects on the varistor ( 1 ). Moreover, such varistor fuse should not exceed dimensions of already known and widely used protective means, in particular melting fuses. In accordance with the invention, the fuse ( 2 ) with its round tubular casing ( 20 ) and the varistor, which is also embedded within a round tubular casing ( 10 ), are serial interconnected and arranged coaxially within each other.
1. A varistor fuse element, comprising:
a cylindrical fuse including an electrically insulating fuse body that defines a longitudinal passage, wherein first and second electrically conductive fuse contacts are located on opposite ends of the fuse body, and wherein the longitudinal passage includes an arc extinguishing material;
a cylindrical varistor that is located in the longitudinal passage, that includes a varistor body having a resistance that is dependent on voltage, and that is serially electrically connected to the fuse with an electrically conductive first varistor electrode located on an external surface of the varistor body and electrically connected to the first fuse contact, and an electrically conductive second varistor electrode located on an internal surface of the varistor body such that the first and second varistor electrodes are separated by the varistor body; and
an electrically conductive melting member connecting the second fuse contact and the second varistor electrode in order to connect the first and second fuse contacts, wherein the melting member includes a weak portion having a pre-determined cross-section that is operable to melt and interrupt the connection between the first and second fuse contacts when the fuse is electrically overloaded.
2. The varistor fuse element of claim 1 , wherein the weak portion of the melting member comprises a pre-determined transversal cross-section.
3. The varistor fuse element of claim 2 , wherein a solder electrically connects the melting member to second varistor electrode.
4. The varistor fuse element of claim 3 , wherein the weak portion of the melting member is located adjacent to the solder.
5. The varistor fuse element of 4 , wherein the second varistor electrode is connected to the melting member by the solder until the solder melts.
6. The varistor fuse element of claim 5 , wherein the melting member is pre-tensioned prior to connection to second varistor electrode by the solder such that the melting member is operable to deflect away from the second varistor electrode when the solder melts.
7. The varistor fuse element of claim 3 , wherein the melting temperature of the solder is lower than a melting temperature of the melting member and a melting temperature of the second varistor electrode.
8. The varistor fuse element of claim 3 , wherein the solder includes a resistance that increases in response to increasing temperature.
9. The varistor fuse element of claim 1 , wherein the arc extinguishing material includes silica.
10. A varistor fuse element, comprising:
an electrically insulting cylindrical fuse body having a first end and a second end opposite the first end, wherein the fuse body defines a longitudinal passage extending from the first end to the second end;
a electrically conductive first fuse contact located on the first end of the fuse body;
a electrically conductive second fuse contact located on the second end of the fuse body;
a cylindrical voltage-dependent-resistance varistor body located in the longitudinal passage and including an external surface and an internal surface;
an electrically conductive first varistor electrode located on the external surface of the varistor body and electrically connected to the first fuse contact;
an electrically conductive second varistor electrode located on the internal surface of the varistor body;
an electrically conductive melting member connecting the second fuse contact and the second varistor electrode in order to connect the first fuse contact and the second fuse contact, wherein the melting member includes a portion that is operable to melt and interrupt the connection between the first contact and the second fuse contact when the fuse is electrically overloaded; and
an arc extinguishing material located in the longitudinal passage adjacent the melting member.
11. The varistor fuse element of claim 10 , wherein the weak portion of the melting member comprises a pre-determined transversal cross-section.
12. The varistor fuse element of claim 11 , wherein a solder electrically connects the melting member to second varistor electrode.
13. The varistor fuse element of claim 12 , wherein the weak portion of the melting member is located adjacent to the solder.
14. The varistor fuse element of 13 , wherein the second varistor electrode is connected to the melting member by the solder until the solder melts.
15. The varistor fuse element of claim 14 , wherein the melting member is pre-tensioned prior to connection to second varistor electrode by the solder such that the melting member is operable to deflect away from the second varistor electrode when the solder melts.
16. The varistor fuse element of claim 12 , wherein the melting temperature of the solder is lower than a melting temperature of the melting member and a melting temperature of the second varistor electrode.
17. The varistor fuse element of claim 12 , wherein the solder includes a resistance that increases in response to increasing temperature.
18. The varistor fuse element of claim 11 , wherein the arc extinguishing material includes silica.