Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04Q—SELECTING
  • H04Q1/00—Details of selecting apparatus or arrangements
  • H04Q1/02—Constructional details
  • H04Q1/028—Subscriber network interface devices
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
  • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
  • H01C7/12—Overvoltage protection resistors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
  • H01R13/00—Details of coupling devices of the kinds covered by groups H01R12/70 or H01R24/00 - H01R33/00
  • H01R13/46—Bases; Cases
  • H01R13/52—Dustproof, splashproof, drip-proof, waterproof, or flameproof cases
  • H01R13/5216—Dustproof, splashproof, drip-proof, waterproof, or flameproof cases characterised by the sealing material, e.g. gels or resins
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
  • H01R4/00—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation
  • H01R4/24—Connections using contact members penetrating or cutting insulation or cable strands
  • H01R4/2416—Connections using contact members penetrating or cutting insulation or cable strands the contact members having insulation-cutting edges, e.g. of tuning fork type
  • H01R4/242—Connections using contact members penetrating or cutting insulation or cable strands the contact members having insulation-cutting edges, e.g. of tuning fork type the contact members being plates having a single slot
  • H01R4/2425—Flat plates, e.g. multi-layered flat plates
  • H01R4/2429—Flat plates, e.g. multi-layered flat plates mounted in an insulating base
  • H01R4/2433—Flat plates, e.g. multi-layered flat plates mounted in an insulating base one part of the base being movable to push the cable into the slot
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T1/00—Details of spark gaps
  • H01T1/14—Means structurally associated with spark gap for protecting it against overload or for disconnecting it in case of failure
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M3/00—Automatic or semi-automatic exchanges
  • H04M3/18—Automatic or semi-automatic exchanges with means for reducing interference or noise; with means for reducing effects due to line faults with means for protecting lines
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04Q—SELECTING
  • H04Q1/00—Details of selecting apparatus or arrangements
  • H04Q1/02—Constructional details
  • H04Q1/035—Cooling of active equipments, e.g. air ducts

Definitions

• the present invention relates to the telecommunications industry, and more particularly to backup devices for gas tube protectors.
• Gas tube protectors are used to protect telecommunications equipment from electrical interference or damage resulting from high voltage lightning pulses.
• a gas contained in the tubes ionizes at high voltages to divert such pulses to ground.
• the tubes also maintain a limited sustained ionization in the presence of a continuing high current overload, such as from an accidental power line crossover.
• prevailing industry practice is to require so- called "vent-safe” and "fail-safe” mechanisms along with the basic gas tube protector itself.
• vent-safe now commonly refers to backup over-voltage protection if the gas "vents” or is lost to the atmosphere.
• the term “fail-safe” now commonly refers to thermal overload protection, although the term taken literally cloaks this connotation.
• Fail-safe protection is now commonly afforded by a fusible metallic or plastic material that, when heated due to the energy from the current overload, yields to a biased shorting member to provide a permanent current shunt around the gas tube. Vent-safe protection is usually provided by an air-gap in the external structure of the device.
• the air-gap is carefully dimensioned to require a firing potential considerably above the normal firing potential of the gas tube itself, so that a properly functioning gas tube will prevent the air-gap from firing. This is important since an over-voltage pulse usually fires harmlessly through a properly functioning gas tube, but may damage the air-gap (which is intended only as a safety backup).
• Such air-gaps are typically designed to fire at about twice the design firing voltage of the gas gap.
• An example of such a device may be found, for example, in U.S. Patent No. 4,212,047 (Napiorkowski, issued July 8, 1980).
• vent-safe device that can readily and inexpensively be utilized in place of existing air-gap vent-safe mechanisms, and which will be reliably environmentally stable over extended periods of unattended service life.
• the vent-safe device should also be functionally compatible with the latest environmental sealing and encapsulation technologies, such as gel encapsulation, to support advances in these technologies and to provide improved environmental isolation of the entire gas tube assembly.
• the present invention meets the above needs and purposes with a new and improved vent-safe mechanism for gas tube protectors, in which the air-gap has been replaced with a layer of solid material having particular non-linear electrical resistive characteristics.
• a solid, carbon black filled polycarbonate based extrusion grade compound is used.
• the film has a thickness from about 0.001 inches to about 0.010 inches or more, and preferably from 0.002 inches to 0.005 inches.
• the film is non-conductive, having an insulation resistance greater than 10 9 ohms when placed between two electrodes, regardless of geometry.
• the breakdown voltage (v B ) of the film is greater than 600 and less than 1000 volts, and can be controlled to a narrow band (e.g., 800 ⁇ v B ⁇ 850 volts, or roughly twice the design breakdown voltage of the gas tube), if desired. (Once a discharge has fired through the film, subsequent breakdown voltages tend to be lower.)
• the initial breakdown voltage proves to be largely independent of contact with encapsulating materials (e.g., silicone gel). Because the film is a thin (1 to 5 mil) insulating plastic, it can be readily substituted for the fusible insulating plastic films in existing designs, such as described in the '047 patent (above).
• the invention significantly improves and simplifies manufacturing tolerances and procedures by eliminating the need to form precise holes and precisely position them in the gas tube vent-safe structure.
• the preferred plastic material has a high heat deflection temperature (ASTM D648), so that it avoids possible deformation during thermal exposure in manufacturing, and exhibits less creep under compression and during temperature cycling.
• a major feature of the present invention has to do with the discharge mechanism itself.
• Filled polymer films have been used in other technical areas for discharging static electricity (e.g., such as used for discharging static electricity in small personal computers). See, for example, U.S. Patents Nos. 4,977,357 (Shrier, issued December 11, 1990) and 5,068,634 (Shrier, issued November 26, 1991).
• U.S. Patents Nos. 4,977,357 Shrier, issued December 11, 1990
• 5,068,634 Shrier, issued November 26, 1991.
• a major distinction, and an important new feature of the present invention is the realization and expectation that the present device will perform in a manner which will be destructive to itself.
• the present invention can handle and discharge high voltage pulses having significant energy, such as caused by lightning pulses.
• prior art devices in other technical applications have not been considered capable of handling such impulses. This has important implications.
• the actual discharge mechanism is a plasma which the high energy of the electrical pulse forms through the plastic film, once the plastic film begins to conduct. This plasma results in a nearly direct short to ground, which is required for effective protection in telecommunications protector devices, and closely mimics the performance of a normal gas tube.
• This sudden plasma-induced increase in conductivity (or reduction in resistance) provides a voltage foldback effect to an extent not seen in non-destructive static load situations, where similar films have been used in other technologies, as mentioned.
• the vent-safe gap (and preferably the entire gas tube device) is encapsulated in an environmentally sealing gel.
• a telecommunications terminal showing such a gas tube (but without the present vent-safe mechanism) encapsulated in a gel, is disclosed, for example, in U.S. Patent Application Serial Number 776,501 (Baum, et al., filed October 11, 1991), assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference for all purposes.
• the gel encapsulant advantageously protects the vent-safe mechanism from environmental contaminants, excludes oxygen from the region of the plasma discharge, and acts as a heat sink. This gel encapsulated plasma discharge substantially reduces the degradation of surrounding materials, prevents combustion, and draws thermal energy away from local hot spots.
• Fig. 1 is a schematic illustration showing a typical 3-element gas discharge tube incorporated into a one pair telecommunications line;
• Fig. 2 is a cross-sectional view of a gas tube such as used in the Fig. 1 circuit;
• FIG. 3 shows a prior art gas tube equipped with an air-gap type vent-safe device
• Fig. 4 illustrates the behavior of an air-gap vent-safe device such as shown in Fig. 3, the effects of water and oil on the breakdown voltage of the air-gap being indicated thereon
• Fig. 5 is an exploded somewhat figurative illustration of a vent- safe device according to the present invention associated with a gas tube protector
• Fig. 6 is a slightly exploded end view of the assembly shown in Fig. 5;
• Fig. 7 is a detail of the ground electrode/film retainer shown in Figs. 5 and 6;
• Fig. 8 is a cross-sectional view similar to Fig. 2 showing the vent- safe device of Figs. 5 and 6 assembled onto the gas tube;
• Fig. 9 shows another embodiment of the invention in which the vent-safe device is separate from and electrically connected to the gas tube;
• Fig. 10 illustrates another embodiment of the present invention in which the gas tube and vent-safe device of Figs. 5-8 is encapsulated in a gel;
• Figs. 11-13 depict the IV-curves for different thicknesses of non ⁇ linear resistive films of the type used in the present invention
• Fig. 14 shows the IV-curve for a gas tube vent-safe device constructed according to Figs. 5-8 and used as a replacement for the air- gap of a commercially available three-element gas tube vent-safe device;
• Fig. 15 shows the IV-curve for a more conductive film
• Fig. 16 depicts an IV-curve for an extruded commercially available film
• Figs. 17-19 depict the electrical impulse breakdown behavior of the Fig. 16 film as a function of current loading.
• Fig. 1 schematically illustrates a typical telecommunications circuit 10 incorporating a gas tube 12 in a telecommunications line 15.
• the gas tube protector 12 has end terminals 16 and 17 (Fig. 2) for connection to the tip and ring sides of the telecommunications circuit, and a center ground terminal 18.
• the main body of the gas tube protector 12 is a ceramic shell 19 (Fig. 2).
• the interior of the tube 12 contains an ionizable gas 20 which ionizes to form a discharge plasma at a predetermined design potential, such as 350-450 volts, as indicated in Fig. 4.
• Fig. 3 shows a typical prior art air-gap gas tube vent-safe device
• the end terminals 26 and 27 on device 25 also function as the electrodes for the air-gap vent-safe operation.
• Each of the end terminals/electrodes 26, 27 has a non-conductive film 28 perforated by holes 29 which separate the electrodes 26, 27 from a ground electrode 30 which is connected to the center ground terminal 31 of the gas tube 12.
• such air-gap vent-safe mechanisms are well known.
• Fig. 4 illustrates the typical breakdown voltage v B for a gas tube (usually around 350-450 volts), and the corresponding breakdown voltage for the air-gap vent-safe system 25.
• a gas tube usually around 350-450 volts
• Fig. 4 pointing respectively left and right
• water which invades the holes 29 will reduce the breakdown voltage of the air-gap vent-safe device; oil will increase it.
• the deleterious effects of environmental pollution, humidity, insect infestation, etc. can cause the air-gap vent-safe device 25 to start firing at voltages comparable to those of the gas tube. This is effectively a system failure.
• efforts by the present inventors to seal the holes 29 from environmental effects by gel encapsulation for example, have inevitably resulted in oil bleeding from the gel into the holes 29. This adversely raises the breakdown voltage beyond the specification design limit.
• the gas tube vent-safe device 40 illustrated in Figs. 5-8 overcomes these prior art limitations.
• the insulating film 45 is solid, not perforated. Thus, it is essentially immune to environmental contamination.
• it can readily be encapsulated, such as in a gel 50 (Fig. 10), without changing the design breakdown voltage of the device.
• Encapsulant 50 is selected of a material which is chemically inert to the film 45. For example, when the film is a polycarbonate, a silicone gel would be appropriate.
• the end terminals 16 and 17 of the gas tube 12 also function as electrodes for the vent-safe device 40.
• a ground electrode 55 connected to the ground terminal 18 on the gas tube 12.
• Further improvement of vent-safe performance is realized by judicious geometric design of the supporting ground electrode/film retainer 55 (Fig. 7) to produce controlled uniformity in the electric field which is developed throughout the film material 45 between the ground electrode 55 and the opposing gas tube electrode 16,17 before and during breakdown. If no special attention were paid to this aspect, the possibility of high variance in v B exists.
• the preferred embodiment of the present invention incorporates such geometric design (in addition to the film material) in order to further improve performance.
• the ends of the ground electrode 55 are partially rolled away at 58 from the opposing gas tube electrode.
• This carries the sharp edge discontinuities of the ground electrode 55 away from the curved surface of the gas tube electrode, thus reducing localized field enhancement in the vicinity of the edges and producing smooth curved electrode surfaces at the minimum separation distance of the opposing electrodes. It also renders the part both simple to manufacture, without extreme tolerance constraints, and affords controlled, repeatable field uniformity for improved performance.
• Device 40 may also be provided with electrodes which are distinct from the terminals 16 and 17 and are electrically connected thereto, such distinct electrodes also being located on the side of the non-linear resistive film 45 opposite the grotmd electrode.
• Fig. 9 illustrates such an alternative gas tube vent-safe device 60 having electrodes 61 and 62 for connection, respectively, to the gas tube end terminals 16 and 17, and a ground electrode 63 for connection to the gas tube ground terminal 18. Electrodes 61 and 62, in a fashion similar to device 40, are separated from ground electrode 63 by a film 65 (the same as film 45).
• Fig. 10 illustrates a gas tube vent-safe device 40 encapsulated in an environmentally sealing gel 50.
• the gel encapsulant 50 not only protects the device 40 from environmental contaminants, but it also excludes oxygen from the region of the plasma discharge and conducts heat away therefrom (acting as a heat sink). This substantially reduces the degradation of surrounding materials, prevents combustion, and attenuates local hot spots.
• Such gels are preferably selected from materials which are chemically inert to the film material 45. Proper selection of the gel material may also promote gradual, partial "healing" of the film 45 in the damaged region of a plasma discharge as the oil filler in the gel migrates to that region of the film.
• the non-linear resistive films 45 and 65 are selected of a material which is substantially non-conductive when the electrical potential between the electrodes is less than the desired breakdown voltage v B .
• the film is thus non-conductive in that state, having an insulation resistance greater than 10 9 ohms.
• the breakdown voltage v B is greater than 600 and less than 1000 volts, and particularly in the vicinity of 800-850 volts.
• Suitable non-linear resistive materials are prepared from a composition which comprises a polymer and, dispersed in that polymer, a particulate conductive filler.
• the resistive material has a resistivity of at least 1 x 10 6 ohm-cm, preferably at least 1 x 10 7 ohm-cm, especially at least 1 x 10 8 ohm-cm.
• the type of polymer used is dependent on the desired physical properties of the resistive material in use, the type of particulate conductive filler, the anticipated use conditions, as well as other factors such as ease of manufacture, maximum exposure temperature, and chemical resistance. Either thermoplastic or thermosetting polymers may be used.
• Polymers which are particularly useful are those which can be formed, for example by extrusion, calendaring, casting, or compression molding, into relatively thin films, e.g., 0.001 to 0.010 inch (0.025 mm to 0.25 mm), and preferably 0.002 to 0.005 inch (0.05 mm to 0.13 mm).
• Particularly suitable polymers include polycarbonates.
• a particulate conductive filler i.e., a material which has a resistivity of less than 10" 1 ohm-cm, preferably less than 10 -2 ohm-cm, particularly less than 10" 3 ohm-cm.
• a particulate filler which may be used are carbon black, graphite, metals, metal oxides, or any of these materials coated onto at least part of an insulating particle such as a glass or ceramic particle.
• a single type of particulate filler may be used or the resistive material may comprise a mixture of two or more different fillers or two or more different sizes or types of the same filler.
• particulate conductive particles which are suitable for use in the invention have an average particle size, i.e. the size of the primary particle, of less than 1 ⁇ m, preferably less than 0.5 ⁇ m, particularly less than 0.1 ⁇ m, e.g. 0.01 to 0.09 ⁇ m.
• the majority of the particles of the particulate filler i.e. at least 50%, preferably at least 60%, particularly at least 70%, especially at least 80%, have an average particle size of 0.01 to 0.09 ⁇ m, preferably 0.02 to 0.08 ⁇ m, particularly 0.03 to 0.07 ⁇ m. If the particles are fused or otherwise associated in the form of an aggregate, e.g.
• the aggregate size be less than 5 ⁇ m, preferably less than 3 ⁇ m, particularly less than 2 ⁇ m, e.g. less than 1 ⁇ m.
• the amount of particulate conductive filler in the resistive material is 5 to 70% by weight of the total composition, preferably 10 to 50% by weight, particularly 15 to 45% by weight, especially 20 to 40% by weight.
• the particulate conductive filler is carbon black, the amount is often 20 to 40% by weight of the total composition, particularly 25 to 35% by weight, especially 30 to 35% by weight.
• Stat-Kon DX7 a carbon black filled polycarbonate based extrusion grade compound with volume resistivity between 10E7 and 10E12 ohm-cm. Films were obtained at a 10 mil thickness and measured 10E7 ohms in insulation resistance at 250 vdc using the film thickness as electrode separation. In fact, any location of the two electrodes on the film always gave the same insulation reading. Thinner films were obtained by compressing the 10 mil film on a hot press down to 2.5 to 4.0 mil. Insulation resistance went up to above 10E12 ohms when measured as above.
• Figs. 11, 12, and 13 depict the IV-curves for Stat-Kon DX7 films of different thicknesses.
• the interesting and very useful features of a Stat- Kon DX7 type material are that the breakdown voltage levels remain relatively independent (as compared to an air-gap) from the film thickness, the insulation resistance remains at a high level, and for thin films around 3 mil, the trigger current is in the micro amp range.
• Fig. 14 shows the IV-curve of a 2.5 mil pressed Stat-Kon DX7 film as replacement for the air-gap of a commercially available three-element gas tube vent-safe device.
• Fig. 11 depict the IV-curves for Stat-Kon DX7 films of different thicknesses.
• the interesting and very useful features of a Stat- Kon DX7 type material are that the breakdown voltage levels remain relatively independent (as compared to an air-gap) from the film thickness, the insulation resistance remains at a high level, and for thin films around 3 mil, the trigger current is in the micro amp
• Material analysis of a single sample from the trial extrusion indicated that the material comprised 30 to 35% by weight carbon black with a particle size of 0.030 to 0.060 nm, 65 to 70% by weight bisphenol-A-polycarbonate, and 1 to 3% by weight filler.
• the present invention provides numerous advantages. Principally, it provides an environmentally stable apparatus for a telecommunications gas tube protector. By eliminating the conventional air-gap, and especially when encapsulating (such as in a gel), the breakdown voltage v B remains reliably stable over very extended periods of time. Once the gas tube fails and the present invention fires in its place, this will, of course, damage the film 45 in the region of the discharge. The inability of such non ⁇ linear resistive films to repeatably conduct such high currents without damage has heretofore been seen as an insurmountable barrier.
• non-linear resistive materials having electrical characteristics similar to the filled polycarbonate films used in the preferred embodiment may be found suitable.
• These can include non- gaseous, but not necessarily solid, materials such as, for example, suitable gels having the desired electrical properties.
• the present invention can be used with two element gas tubes, thus requiring only two electrodes on the vent-safe device itself.

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• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Physics & Mathematics (AREA)
• Computer Networks & Wireless Communication (AREA)
• Electromagnetism (AREA)
• Chemical & Material Sciences (AREA)
• Dispersion Chemistry (AREA)
• Signal Processing (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)
• Emergency Protection Circuit Devices (AREA)
• Buffer Packaging (AREA)
• Elimination Of Static Electricity (AREA)
• Gas-Filled Discharge Tubes (AREA)

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• 1992
  • 1992-08-18 TW TW081106532A patent/TW211079B/zh active
• 1993
  • 1993-06-29 WO PCT/US1993/006218 patent/WO1994000856A1/en not_active Application Discontinuation
  • 1993-06-29 JP JP6502652A patent/JPH07508396A/ja active Pending
  • 1993-06-29 BR BR9306635A patent/BR9306635A/pt not_active Application Discontinuation
  • 1993-06-29 EP EP93916868A patent/EP0649563A4/en not_active Withdrawn
  • 1993-06-29 MX MX9303919A patent/MX9303919A/es not_active IP Right Cessation
  • 1993-06-29 CA CA002139329A patent/CA2139329A1/en not_active Abandoned
  • 1993-06-30 CN CN93109541A patent/CN1085691A/zh active Pending
• 1994
  • 1994-12-29 KR KR1019940704804A patent/KR950702330A/ko not_active Application Discontinuation

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