Line protector having arrester and fail-safe circuit bypassing the arrester

Abstract

A line protector has an arrester through which overvoltages on the line of short duration are grounded. The arrester may be of the type having an arc gap sealed within a gas tube. For an overvoltage of longer duration, a pellet is melted causing a spring to close a circuit bypassing the gas tube and provide a direct metallic path from the line to ground. A secondary arc gap between opposed conductors separated by an insulating sleeve has an arc-over voltage that is greater than the normal arc-over voltage of the first-mentioned arc gap and provides a path to ground for short duration overvoltage conditions in the event of failure of the arrester. Excessive current across the secondary arc gap may melt the insulator sleeve and engage the opposed conductors for grounding purposes.

The invention is claimed as follows: 
     
       1. A line protector comprising means forming a circuit that comprises in series a fusible solder pellet, spaced electrodes forming an arc gap, first conductor means for connection to a line to be protected, and second conductor means for connection to ground such that an overvoltage surge of short duration at said line will pass current through said series circuit for discharge to ground; said arc gap being sealed in a cold cathode gas tube of which said electrodes form a part; means including said solder pellet normally preventing said first and second conductor means being in contact, and spring means for bringing said first and second conductor means into contact exteriorly of said tube to bypass said arc gap upon melting of said solder pellet due to an overvoltage surge of longer duration across said series circuit and thereby provide a direct metallic path from said line to ground.Iadd., said gas tube having a central axis, means forming a secondary arc gap between said first and second conductor means comprising members that are radially outwardly of said axis, and a perforated insulating member between said members and in close contact with each. .Iaddend. 
     
     
       2. A line protector according to claim 1, .[.further including means forming a secondary arc gap between said first and second conductor means exteriorly of said tube.]. said secondary arc gap being less .Iadd.in width .Iaddend.than the arc gap .Iadd.width .Iaddend.in said tube and having an arc-over voltage that is greater than the arc-over voltage of the arc gap in said tube. 
     
     
       3. A line protector according to claim 1 in which one of said conductor means includes a cup, said solder pellet and said tube are in said cup, .Iadd.said insulating member is .Iaddend.an insulating sleeve .Iadd.that .Iaddend.surrounds said cup, and the other conductor means surrounds said insulating sleeve. 
     
     
       4. A line protector according to claim 3 in which said insulating sleeve is perforated .[.to provide an air gap between said sleeve and said other conductor means.]. .Iadd.in a number of places. .Iaddend. 
     
     
       5. A line protector according to claim 4 in which said other conductor means includes a shunt member that surrounds said insulating sleeve and a cap that surrounds and engages said shunt member. 
     
     
       6. A line protector according to claim 5 in which said other conductor means further includes a disc within said shunt, said spring means is in said cap and imposes pressure on said shunt and disc, said disc engaging said cup upon melting of said solder pellet. 
     
     
       7. A line protector comprising means forming a circuit that comprises in series a surge arrester .Iadd.of the cold cathode gas tube type having coaxial electrodes, .Iaddend.first conductor means for connection to a line to be protected, and second conductor means for connection to ground such that an overvoltage surge of short duration at the line will pass current through said series circuit for discharge to ground; fusible means normally preventing said first and second conductor means from being in contact, spring means for bringing said first and second conductor means into contact exteriorly of said surge arrester upon melting of said fusible means due to an overvoltage surge of longer duration across said series circuit to provide a direct metallic path from said line to ground bypassing said arrester, and means forming an arc gap between said first and second conductor means for providing a discharge path to ground in the event of failure of said surge arrester .Iadd.due to leakage of gas therefrom, said last-named means comprising a perforated insulating member defining said arc gap between portions of said first and second conductor means that are radially outwardly of the electrode axis. .Iaddend. 
     
     
       8. A line protector comprising a cap, a metallic shunt member within the cap and being slidable relative thereto, a tubular insulating sleeve within the shunt member, a metallic disc member within the shunt member, a metallic cup within the sleeve and being slidable relative thereto, said sleeve being perforated to provide an air gap between the cup and the shunt member, a meltable pellet within the cup, a cold cathode surge arrester tube within the cup and having spaced electrodes respectively in electrical contact with the solder pellet and the disc, said electrodes providing a sealed arc gap within the tube that is greater .Iadd.in width .Iaddend.than .Iadd.the width of .Iaddend.said air gap, the environment within said tube being such that the arc-over voltage is less than the arc-over voltage at said air gap, and a spring within said cap for moving an assembly comprising said shunt, said disc, said arrester, and said sleeve upon melting of said pellet to cause said disc to engage said cup. 
     
     
       9. A line protector comprising first conductive means that includes a tubular cap and structure slidably telescoped within the cap coaxial therewith, second conductive means coaxial with said cap, a surge arrester having opposed conductor elements, said first and second conductive means being respectively connected to said conductor elements to provide a current path through said arrester from one conductive means to the other conductive means upon an overvoltage surge of short duration across said surge arrester, spring means in said cap urging said slidable structure toward said second conductive means, and a fusible element preventing engagement of said movable structure with said second conductive means except on melting of said fusible element due to an overvoltage surge of longer duration across said arrester, the engagement of said movable structure and said second conductive means forming a metallic current path bypassing said arrester.Iadd., and an insulating sleeve interposed between and spacing said first and second conductive means, said sleeve having at least one perforation constituting an air gap between said first and second conductive means. .Iaddend. 
     
     
       10. A line protector according to claim 9 in which said second conductive means comprises a cup, said arrester and said fusible element being in said cup, and said fusible element is disposed between said arrester and the base of said cup. 
     
     
       11. A line protector according to claim 9 in which said conductor elements form an arc gap .Iadd.radially outwardly of the surge arrester. .Iaddend. 
     
     
       12. A line protector according to claim 9 in which said fusible element is a current-carrying pellet in conductive connection with one of the conductor elements of the arrester. .Iadd. 13. A line protector comprising means forming a circuit that comprises in series a fusible solder pellet, spaced electrodes forming an arc gap, first conductor means for connection to a line to be protected, and second conductor means for connection to ground such that an overvoltage surge of short duration at said line will pass current through said series circuit for discharge to ground; said arc gap being sealed in a cold cathode gas tube of which said electrodes form a part; means including said solder pellet normally preventing said first and second conductor means being in contact, and spring means for bringing said first and second conductor means into contact exteriorly of said tube to bypass said arc gap upon melting of said solder pellet due to an overvoltage surge of longer duration across said series circuit and thereby provide a direct metallic path from said line to ground, and in which one of said conductor means includes a cup, said solder pellet and said tube are in said cup, an insulating sleeve surrounds said cup, and the other conductor means surrounds said insulating sleeve. .Iaddend..Iadd. 14. A line protector according to claim 13 in which said insulating sleeve is perforated to provide an air gap between said sleeve and said other conductor means. .Iaddend..Iadd. 15. A line protector according to claim 14 in which said other conductor means includes a shunt member that surrounds said insulating sleeve and a cap that surrounds and engages said shunt member. .Iaddend..Iadd. 16. A line protector according to claim 15 in which said other conductor means further includes a disc within said shunt, said spring means is in said cap and imposes pressure on said shunt and disc, said disc engaging said cup upon melting of said solder pellet. .Iaddend.