Overload protection tube
AssigneeInternational Standard Electric Corporation
InventorsYves Dominique Le Cain, Ali Nagati, Bruno A. F. Pellet
Life of this patent
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Abstract
A reliable overload protection tube utilizes a meltable sealing material to mount an electrode within a metallic enclosure. The interelectrode gap between the tube electrodes is adjusted to determine the desired tube breakdown voltage. Voltage in excess of breakdown ionizes the tube and conducts the overload current safely to ground. The sealing material upon excess overload current becomes heated and melted allowing the electrodes to move into a short circuit contact to ground.
Claims7
An overload protection discharge tube comprising an enclosure, an opening in the enclosure, a first electrode extending through said opening and having a first discharge surface inside said enclosure, a plug between said first electrode and said enclosure to hermetically seal said opening onto said first electrode, a second electrode having a second discharge surface inside said enclosure facing said first discharge surface and being separated from said first discharge surface by a discharge gap, and a gas atmosphere filling said enclosure at a pressure lower than atmospheric pressure, wherein said plug is comprised of a material which will soften at a temperature lower than the softening temperatures of the other portions of said discharge tube to enable the atmospheric pressure to drive said first electrode until said first discharge surface comes in contact with said second discharge surface, when said discharge tube is overheated due to abnormal operating conditions.
A process for manufacturing an overload-protection discharge tube including an enclosure, an opening in the enclosure, a first electrode extending through said opening and having a first discharge surface inside said enclosure, a plug between said first electrode and said enclosure to hermetically seal said opening onto said first electrode, a second electrode having a second discharge surface inside said enclosure facing said first discharge surface and being separated from said first discharge surface by a discharge gap, and a gas atmosphere filling said enclosure at a pressure lower than atmospheric pressure, wherein said plug is comprised of a vitreous material which will soften at a temperature lower than the softening temperatures of the other portions of said discharge tube to enable the atmospheric pressure to drive said first electrode until said first discharge surface comes in contact with said second discharge surface, when said discharge tube is overheated due to abnormal operating conditions, comprising the steps of:
- providing a metallic enclosure having at least one discharge electrode;
- providing a plug made from a vitreous material having a discharge electrode through its center;
- pumping and filling the tube with a controlled atmosphere;
- positioning the vitreous plug relative to the enclosure to provide a predetermined interelectrode gap resulting in a corresponding tube breakdown voltage;
- and
- sealing the tube by bonding the vitreous plug with the metallic enclosure.
Dependencies are inferred from the claim text.