CA2191737A1 - Telecommunications gas tube apparatus and composition for use therewith - Google Patents
Telecommunications gas tube apparatus and composition for use therewithInfo
- Publication number
- CA2191737A1 CA2191737A1 CA002191737A CA2191737A CA2191737A1 CA 2191737 A1 CA2191737 A1 CA 2191737A1 CA 002191737 A CA002191737 A CA 002191737A CA 2191737 A CA2191737 A CA 2191737A CA 2191737 A1 CA2191737 A1 CA 2191737A1
- Authority
- CA
- Canada
- Prior art keywords
- composition
- gas tube
- gel
- ohm
- linear
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- 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
- H01C7/126—Means for protecting against excessive pressure or for disconnecting in case of failure
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/20—Conductive material dispersed in non-conductive organic material
- H01B1/22—Conductive material dispersed in non-conductive organic material the conductive material comprising metals or alloys
-
- 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
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J17/00—Gas-filled discharge tubes with solid cathode
- H01J17/38—Cold-cathode tubes
- H01J17/40—Cold-cathode tubes with one cathode and one anode, e.g. glow tubes, tuning-indicator glow tubes, voltage-stabiliser tubes, voltage-indicator tubes
-
- 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
Landscapes
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Dispersion Chemistry (AREA)
- Chemical & Material Sciences (AREA)
- Compositions Of Macromolecular Compounds (AREA)
- Organic Insulating Materials (AREA)
- Rigid Pipes And Flexible Pipes (AREA)
- External Artificial Organs (AREA)
- Orthopedics, Nursing, And Contraception (AREA)
- Feeding, Discharge, Calcimining, Fusing, And Gas-Generation Devices (AREA)
Abstract
A telecommunications gas tube apparatus (40) which is suitable for connection to a gas discharge tube (12) and which comprises an electrically non-linear resistive element (45) prepared from an electrically non-linear composition which comprises a polymeric component and a particulate filler. The composition has an initial resistivity i at 25 ~C of at least 109 ohm-cm, and is such that a standard device containing the composition has an initial breakdown voltage VSi, and after the standard device has been exposed to a standard impulse breakdown test, the device has a final breakdown voltage VSf which is from 0.7VSi to 1.3VSi. In addition the composition in the device has a final resistivity f at 25 ~C of at least 109 ohm-cm. Such compositions are useful in providing both vent-safe and fail-safe protection to a gas discharge tube (12).
Description
WO95/33277 '~ 2 ~ ~1737 r~
~ 1 ~Tf'~TI~NC: (:A.C: TTTRP! I~pp}~pl~Tus ~In ~ OblllUN FOR USE ~
s g~R~.R~Nn OF T~ J~VENTIO~
Fi~ld of th~ Tnvent;on 0 This invention relates to gas discharge tube apparatus for tel~ t;~nR equipment and to compositions for use in such apparatus.
Tntrodllction to th~ Tnvention Gas discharge tubes are commonly used to protect teler ;cations e~uipment and circuits from damage in the eveLt of electrical interference or high voltage lightning pulses. Gas tubes used in this way are often oalled gas tube protectors. The tubes contain a gas which ionizes at high voltages to allow electrical pulses to be directed to ground, thus min;m; 7;ng any damage resulting from the pulses. If a ~nt;nn;ng high current overload occurs, e.g. as a result of an ~cr;~nt~l power line crossover, the tubes ~-;nt~;n a limited sustained ionization.
To provide protection in the event of failure from overheating during~sustained over-current conditions, and to assure protection if the ionizable gas vents from the tube, gas tube protectors generally incorporate "fail-safe~ and '~vent-safe" ~h~n;l , respectively. "Fail-safe" refers to thermal damage protection, which is often provided by a fusible metal or plastic material If the material is heated due to the energy from the current overload, it yields to a 3s biased shorting member and provides a pelul~llellL current shunt around the gas tube_ This may occur by melting a thermoplastic film positioned between two electrodes, thus allowing contact between the electrodes and ~hnnt;ng the 2 1 9 1 737 1~ ..,.,.'C-'~
current to ground. "Vent-safe" refers tQ backup overvoltage protection that operates when the gas "vents" or is lost to the atmosphere. Vent-safe protection is often provided by an air-gap that is part of the external structure of the tube.
s The proportions of the air-gap are selected to re~uire a firing potential considerably above, e.g. twice, the normal firing potential of the gas tube itself so that, under normal circumstances, the gas tube will prevent the air-gap from firing. This mln;m;7Pq the chances that the air-gap will be o damaged because although an over-voltage pulse usually fires harmlessly through a properly fllnrt;~n;ng gas tube, it may damage the air-gap which is intended as a safety backup.
To improve the reliability of air-gap vent-safe designs, it is common to enviLl ~ Al ly isolate the air-gap to prevent r~nt~m;nAtion by moigture, air pollution, insects, or other ~ CnVirl ' Al factors. Sealing materials such as encapsulants, potting compounds, conformal coatings, and gels, however, often are of limited utility as they generally cannot restrict all moisture ingress and may themselves penetrate into the air-gap, thus rhAng1ng the voltage discharge levels and/or leading to corrosion. A decrease in the discharge voltage level will eventually lead to electrical shorts at low voltage levels; an increase in the discharge voltage level 2s will defeat the purpose of the air-gap backup.
Some of these problems have been addressed by the r~pl~A~c t of the air-gap by a layer of solid ~t~; Al having particular non-linear electrical resistivity characteristics.
Such an air-gap is described in co-pending, commonly assigned U.S. Patent Application No. 08/Og6,059 ~3ebbaut et al, filed April 10, 1993), the disclosure of which is incorporated herein by reference. Although envil~~ tAlly stable, the solid material is subject to a decrease in breakdown voltage 3s on successive impulses, and, in fact, during normal operation in discharging a high voltage, high energy pulse such as lightning, will be destructive to itself. Furthermore, not all such air gaps provide fail-safe protection.
WO 9S5'33277 - ' 2 1 9 1 7 3 7 r~",, ~ ~
. . .
sn~MARy OF T~ TNVEN~ION
e have now found that if an electrically non-linear s element prepared from an electrically non-linear material ~hich has particular electrical properties when tested for electrical breakdown is used in place of the solid material air-gap described in U.S. Patent Application No. 08/046,059, a gas tube apparatus can be prepared which has both vent-safe 0 and fail-safe propertie~. In addition, because of the nature af the non-linear material and its physical and electrical stability during successive electrical events, the apparatus can be activated repeatedly in typical telecommunication service conditions without failure of the non-linear element.
3ecause the need to replace the element i3 decreased, the r~l; Ah; 1; ty of the telP ;cations system is increased and the cost of r~;nt~n~nre is decreased. In a preferred embodiment, the material comprises a gel which has the ability to conform to the gas tube protector, decreasing the chance of moisture ingress, and providing increased manufacturing tolerances. Furthermore, the gel may be , -t;hle with a gel encapsulant, thus contributing to the envi~ 1 sealing.
In a first aspect, this invention provides a telecom-2s munications gas tube apparatus which comprises (1) a first electrode for electrical crnn~ction to a first t~r~;n~l on a gas discharge tube;
~2) a second electrode for electrical connection to a second t~rm;n~1 on the gas tube; and ~ (3) an electrically non-linear resistive element separating the first and second electrodes, said '3s element comprising an electrically non-linear composition which WosS/33277 2 1 9 1 737 ~ 7 (a) comprises (i) a polymeric component, and (ii~ a particulate filler, (b) has an initial resistivity Pi at 25~C of at s least 109 ohm-cm, and (c) is such that when a standard device rrnt~in~ng the composition has an initial breakdown voltage VSi~ and after the standard device has lo been exposed to a standard impulse breakdown test, the device has a final breakdown voltage Vsf which is from 0.7VSi to 1.3VSi, and the composition in the device has a final resistivity pf at 25~C of at least 109 ohm-cm.
In a second aspect, this invention provides a telecom-munications gas tube apparatus which comprises (1) a first electrode for electrical rnnn~rtion to a first terminal on a gas discharge tube;
~2) a second electrode for electrical rrnn~rt;rn to a second terminal on the gas tube; and 2s (3) an electrically non-linear-resistive element separating the first and second electrodes, said element comprising an electrically non-linear composition which (a) comprises (i) 30 to 95~ by volume of the total composition gel, and (ii) 5 to 70~ by volume of the total composition particulate conductive filler, and 3s (b) has an initial resistivity p~ at 25~C of at least 109 ohm-cm.
W095/33277 , ~ 2 1 9 1 7 3 7 . ~
In a third aspect, this invention provides an assembly which comprises ; (A) a retaining element; and s (B) a telecommunications ga3 tube apparatus of the first aspect of the invention inserted into the rP~;ni element.
0 In a fourth aspect, this invention provide~ an electrically non-linear resistive composition of the type d.isclosed in the first aspect o~ the invention.
RRTR~ D~ 'RTPTI~ N OF T~T~ DRAWING
, , . _ .
Figure 1 is a schematic illustration showing a typical three-element gas discharge tube incorporated into a one pair tel~e ;cations line;
Figure 2 is a cross-sectional view of the gas tube of Figure I;
Figure 3 is an P-~l o~ illustration of a gas tube a;pparatus of the invention;
2s -- ' Figure 4 is a cross-sectional view of a gas tube a]?paratus of the invention which is ~nr~rs~lated in a gel;
Figure 5 is an exploded illustration of an assembly of the invention;
Figure 6 is a cross-sectional view of the assembly of F:igure 5;
' 35 Figure 7 is a schematic illustration showing a standard device for testing the compositions of the invention;
.
W095133277 21 91 737 r~ 7 Figure 8 is a graph of impul~e breakdown in volts as a function of impulse test cycles;
Figures 9 and lo are graphs of impulse breakdown in volts s as a function of the distance between electrodes for compositions of the invention; and Figure 11 is a graph of DC breakdown voltage and impulse breakdown voltage as a function of the distance between electrodes for compositions of the invention.
DET~TTTln DE.~rRTPTI~N OF T~ INVENTION
The gas tube apparatus and the assembly of the invention both comprise an electrically non-linear resistive element which comprises an electrically non-linear composition. In this specification the term "non-linear" means that the composition is substantially electrically nnnrnn~ tive, i.e.
has a resistivity of more than 109 ohm-cm, when an applied voltage is less than the impulse breakdown voltage, but then becomes electrically conductive, i.e. has a resistivity of=
less than 109 ohm-cm, when the applied voltage is equal to or greater than the impulse breakdown voltage. The electrically non-linear composition comprises a polymeric component and a 2s particulate filler. The polymeric ~ Snt may be any ~ ~Liate polymer, e.g. a thermoplastic matçrial such as a polyolefin or a fluoropolymer, a thermosetting material such as an epoxy, an elastomer, a grease, or a gel. The polymeric component is generally present in an amount of 30 to 95~, preferably 35 to 90~, particularly 40 to 85~ by volume of the total composition For many applications it is preferred that the polymeric , Ant comprise a polymeric gel, i.e. a substantially 3s dilute crosslinked solution which exhibits no flow when in the steady-state. The crosslinks, which provide a cnntinnnn~
network structure, may be the result of physical or chemical bonds, crystallites or other junctions, and must remain intact WO95/33277 ,~ 2 ~ 91 737 r~ 7 under the uae conditions of~the gél~ Most gels comprise a fluid-extended polymer in which a fluid, e.g. an oil, fills the interstices of the network. Suitable gels include those compriaing silicone, e.g. a polyorganosiloxane system, ~ polyurethane, polyurea, styrene-butadiene copolymers, styrene--~ isoprene copolymers, styrene-(ethylene/propylene)-styrene (SEPS) block copolymers (available under the t~Pn~mP Septon~
by Kuraray), styrene-(ethylene-propylene/ethylene-butylene)-styrene block copolymers (available under the tradename 0 Septon~ by Ruraray), and/or styrene-(ethylene/butylene)-styrene (SE;3S) block copolymers (available under the tradename Kraton~ by Shell Oil Co.). Suitable P~tPn~r fluids include mineral oil, vegetable oil such as paraffinic oil, Eilicone oil, plasticizer such as trimellitate, or a mixture of these, generally in an amount o~ 30 to 90% by weight of the total weight of the gel. The gel may be a thermosetting gel, e.g.
s:ilicone gel, in which the crosslinks are formed through the u~3e of multifunctional croscl;nk;ng agents, or a thermoplastic gel, in which microphase separation of domains serves as ~lmction points. Di6closures of gels which may be suitable as the polymeric ~ , ~nt in the composition are found in U.S.
Patent Nos. 4,600,261 (Debbaut), 4,690,831 (Uken et al), 4,.716,183 (Gamarra et al), 4,777,063 (Dubrow et al), 4,864,725 (I)ebbaut et al), 4,865,905 (Uken et al), 5,079,300 (Dubrow et 2s al), 5,104,930 (Rinde et al), and 5,149,736 (Gamarra); and in Tn~P~n~t;~n~l Patent Publication Nos. WO86/01634 (Toy et al), WC)88/00603 (Francis et al), WO90/05166 (Sutherland), WC)91/05014 (s~thp~lAn~)/ and W093/23472 (~ammond et al). The di.sclosure of each of these patents and publications is incorporated herein by reference.
It is preferred that the gel have a Voland hardness of 1 to 50 grams, particularly about 5 to 25 grams, especially 6 to 20 grams, have stress relaxation of 1 to 45~, preferably 15 to '3~ 4C~, have tack of 5 to 40 grams, preferably 9 to 35 grams, and . ha.ve an ultimate ~l~ngat;on o~ at least 50~, preferably at leaat 100~, particularly at least 400~, Pcpec;~lly at least 1000~, most especially at least 1500~. The elongation is W095/33277 ' 21 91 737 r~ 7 measured according to ~STM 3217, the disclosure of which is incorporated herein by reference. The Voland hardness, stress r~ t;nn, and tack are measured using a Voland-Stevens Texture Analyzer Model ~FRA having a 1000 gram load cell, a 5 gram trigger, and a 0.25 inch (6.35 mm) ball probe, as described in U.S. Patent No. 5,079,300 (Dubrow et al), the disclosure of which is incorporated herein by reference. To measure the hardness of a gel, a 20 ml glass scintillating vial containing lO grams of gel is placed in the analyzer and lo the stainless steel ball probe is forced into the gel at a speed of 0.20 mm/second to a penetration distance of 4.0 mm.
The Voland hardness value is the force in grams re~uired to force the ball probe at that speed to penetrate or deform the surface of the gel the specified 4.0 mm. The Voland hardness of a particular gel may be directly correlated to the ASTM
D217 cone penetration hardness using the procedure described in U.S. Patent No. 4,852,646 (Dittmer et al), the disclosure of which is incorporated herein by r~f~r~n~.
In addition to the polymeric component, the composition also comprises a particulate filler. The ~iller may be conductive, s~m;cnn~nctive~ nnn~nn~ tive, or a mixture of two or more types of fillers as long as the resulting composition has the appropriate electrical non-linearity. It is generally 2s preferred that the filler be conductive or semiconductive.
Conductive fillers generally have a resistivity of at most lO-3 ohm-cm; semiconductive fillers generally have a resistivity of at most 103 ohm-cm, although their resistivity is a function of any dopant material, as well as temperature and other factors and can be subst~nti~lly higher than 103 ohm-cm.
Suitable fillers include metal powders, e.g. aluminum, nickel, silver, silver-coated nickel, platinum, copper, tantalum, tungsten, gold, and cobalt; metal oxide powders, e.g. iron oxide, doped iron oxide, doped titanium dioxide, and doped 3s zinc oxide; metal carbide powders, e.g. silicon carbide, titanium carbide, and tantalum carbide; metal nitride powders;
metal boride powders; carbon black or graphite; and alloys, e.g. bronze and brass. Particularly preferred as fillers ar~e W09~33277 2 1 ~ 1 7 3 7 ~ g ~luminum, iron oxide (Fe304), iron oxide doped with titanium dioxide, silicon carbide, and 9ilver-coated nickel. If the polymeric component is a gel, it i8 important that the ~elected filler not interfere with the crosslinking of the s gel, i.e. not "poison~ it. The filler iB generally present in an amount of 5 to 70~, preferably 10 to 65~, especially 15 to ~0~ by volume of the total composition.
The volume loading, shape, and size of the filler affect o 1:he non-linear electrical properties of the composition, in part because of the spacing between the particles. Any shape particle may be used, e.g. spherical, flake, fiber, or rod.
17seful compositions can be prepared with particles having an average size of C.OlO to lO0 microns, preferably O.l to 75 rnicrons, particularly 0.5 to 50 microns, especially l to 20 rnicrons. A mixture of different size, shape, and/or type particles may be used. The particles may be magnetic or nonmagnetic.
In addition to the particulate filler, the composition may comprise other conv~n~inn~l additives, including tabilizers, pigments, croRRl;nk;ng agents, catalysts, and i.nhibitors.
2s The compositions of the invention may be prepared by any Eluitable means, e.g. melt-blending, solvent-blending, or i.ntensive mixing, and may be shaped by conventional methods including extrusion, calendaring, casting, and compression molding. If the polymeric component is a gel, the gel may be r~lixed with the filler by stirring and the composition may be poured or cast onto a substrate or into a mold to be cured, often by the addition of heat.
The compositions of the invention have excellent 3s . stability as measured both by resistivity and breakdown voltage. The compositions are electrically insulating and have an initial resistivity Pl at 25~C of at least lO9 ohm-cm, preferably lClO ohm-cm, particularly l0ll ohm-cm, especially W095/33277 ' 21 9 1 737 r~ 7 1012 ohm-cm. ~he initial resistivity value Pi is such that when the composition is formed into a standard device as described below, the initial insulation resistance Ri is at least 109 ohms, preferably at least 101~ ohms, particularly at s least l0ll ohms. An Ri value of at least 109 ohms is preferred when the compositions of the invention are used in tel~ ;cations apparatus. After~bein~ exposed to the standard impulse breakdown test, described below, the final resistivity pf at 25~C is at least 109 ohm-cm, and the ratio of p~ to Pi is at most l x 103, preferably at most 5 x 102, particularly at most 1 x 102, especially at most 5 x 101, most especially at most 1 x 101. The final insulation resistance Rf for a standard device after ~o~,e to the standard impulse breakdown test is at least 109 ohms, preferably at least 10l~ ohms, particularly at least l0ll ohms.
When the composition of the invention is formed into a standard device as described below and exposed to a standard impulse breakdown test, the device has an initial breakdown voltage VSi and a final breakdown voltage Vsf which is from 0.70Vsi to l.30Vsi~ preferably from 0.80VSi to 1.20VSi, particularly from 0.85VSi to 1.15VSi, especially from 0.90VSi to 1.10V~3i. The value of the breakdown voltage is affected~by the volume fraction of~the particulate filler, by the particle 2s size, and by the distance between the particles among other factors. In general, as particle size decreases, the breakdown voltage increases.
Some compositions of the invention will "latch", i.e.
remain in a conductive state with a resistivity of less than 106 ohm-cm, after one voltage discharge. If the latched device is made from a composition comprising a gel, the device can be "reset" into a high resistivity state, i.e. a resistivity of at least 109 ohm-cm, by physical deformation, e.g. flexing, torsion, compression, or tension. The latching behavior is a function of particle size, interparticle spacing, and particle 3hape. In gels, generally small w09~33277 2 T ~ s7 ~ipherical particle~, e.g. 1 to 5;~icrons~, with a Gmall interparticle spacing, e.g. less than 4 microns, will latch.
Under certain electrical conditions, compositions of the s invention, particularly compositions comprising aluminum, will provide fail-safe protection. If exposed to a sufficiently high energy level, e.g. 30A and 1000 volts for a time of 2 seconds to 30 minutes, the particulate filler ca~L fuse together and provide a permanent conductive path between the 0 electrodes, giving a final resistance of less than 10 ohms, e.g. 1 to 10 milliohms. Such behavior is desirable in the event of crossed power lines and results in a permanent short circuit.
The invention is illustrated by the drawing in which Figure 1 is a schematic illustration of a conventional tele~ ;cations circuit 10 which incorporates a gas tube 12 in a tele~ ;cations line. The gas tube 12, which is shown in cross-section in Figure 2, has a first terminal 16 and a second t~rm; n~l 17 for connection to the tip side 13 and the ring side 14, respectively, of the telP ;cations circuit.
In addition, the gas tube 12 has a center ground terLninal 18.
A ceramic shell 19 encloses an ; ~ni 7~hl e gas 20 which ionizes to form a discharge plasma at a given voltage.
2s ~
Figure 3 is an exploded view of a gas tube apparatus 40 oE the invention. In this embodiment, the first terminal 16 and the second t~r~;n~l 17 of the gas tube 12 also function as first and second electrodes, respectively, for the gas tube apparatus 40. (Although not shown, the gas tube may comprise a third terminal which may be connected to a third electrode in the gas tube apparatus. One of the electrodes may be a grounding electrode.) Electrically non-linear resistive element 45 is positioned in contact with first t~rm;n~l 16 and 3~ second terminal 17_ Ground electrode 55 is in physical contact with resistive element 45, and is in electrical contact with ground t~rm;n~l 18 of gas tube 12. In a preferred ~- ti--nt, the non-linear compositiorL comprising wossl33277 2 1 9 1 737 P~"~ c~7 the resistive element haa Gufficient flexibility that it conforms to the shape of gas tube 12.
Figure 4 shows a cross-sectional view of gas tube s apparatue 40 embedded in a gel encapsulant 50. The encapsulant, which may be, e.g. a potting compound, a conformal coating, or a gel, provides enviL~ t~l protection from moisture and other ~nnt~min~nt~. In addition, the encapsulant may exclude oxygen from the plasma discharge, and o act as a heat sink to draw thermal energy away from local hot spots. It is preferred that the resistive element be chemically inert to the encapsulant.
Figure 5 is an exploded view of an assembly 70 of the =
invention and Figure 6 is a cross-sectional view of that assembly. Retaining element 72 i5 designed to contain gas tube 12, resistive element 45, and a ground electrode 55 ' .
Although the resistive element 45 may be laminar as shown, to enhance contact with gas tube 12 the resistive element may be curved or otherwise shaped. Spring leads 76,78 are attached to gas tube 12 and serve to make electrical contact with respective insulation displ~r~ t c~nn~t~rs (not shown).
Gas tube 12 is held in the appropriate position with the resistive element 45 and ground electrode 55 ' by means of 2s retaining element 72, retainer cap 74, and grounding pin 80 which can be inserted into a recess or hole in retainer cap 74. Retainer cap 74 may be ultrasonically welded, glued, or otherwise fused to retaining element 72. To ~-;n~in the proper distance between the gas tube 12 and ground electrode 30 55 ', spacer 56 =protrudes from ground electrode 55 ' . The height of spacer 56 can be eelected to achieve different levels of voltage breakdown. The retaining element 72 may be filled with the encapsulant to surround the contents.
The invention is illustrated by the following examples.
Wog~/33277 p_"~ "
E ~ ~R 1 to 14 ~~ : ~
The ingredients listed in Table I were mixed with a tongue depressor to disperse the particulate filler, degassed s in a vacuum oven for one minute, poured onto a PTFE-coated release sheet and cured. ~ Standard Device, described below, W.18 prepared with an electrode spacirLg of 1 mm. Samples were then subjected to one of three tests, although the Standard Irnpulse 3reakdown Test was extended for several samples from 5 o to 100 cycles. The results, shown in Figures 8 to 11, indicated that the compositions based on silicone gel 1 and thermoplastic gel had excellent stability and reproducibility over 100 cycles based on impulse breakdown and in~ tion resistance. The composition based on silicone gel 2 showed a decrease~in insulation resistance to less than 105 ohms by ~bout 41 cycles. The composition based on a silicone grease skLowed a similar decrease by four cycles (Figure 8). Example 5, based on an epoxy, shattered under the impulse test conditions, but showed a decrease in insulation resistance by 15~ cycles under DC breakdown testing. Figures 9 and 10 show th~e effect of particle size and filler loading on the impulse breakdown voltage for samples which ranged in thickness from 0.25 to 1.0 mm. Figure 11 8hows that for a given particle si~e and loading, the impulse breakdown and the DC breakdown 2s voltage were comparable.
St~n~rd Device A circular sample with a diameter of 11.2 mm (i.e. a surface area of about 1 cm2) and a thickrLess of 1 mm was cut from the cured composition and inserted into the test fixture shown in cross-section in Eigure ~. The test composition sample 90 was positioned between two circular aluminum electrodes 91,92, each with a diameter of about 11.2 mm and a 3s surface in contact with the composition 90 of about 100 mm2.
Polycarbonate sleeve 93 with an inner diameter of slightly more than 11.2 mm waL3 positioned over the assembled electrodes and composition and the assembly was inserted into fixture 94 2 ~ 9 ~ 737 W095/33277 P~
c~nt~;n;ng support elements 95,96 Micrometer 97 was adjusted until the 9pacing between the electrodes 91,92 was 1 mm. (For the Modified Impulse Breakdown Test described below, the micrometer was adjusted to vary the electrode spacing, i.e.
s the sample thickness, from 0.25 to 1_0 mm For gel samples, the sample had an initial thi~knP~R of 1 mm When the micrometer was adjusted to decrease the gample th;~knP~5, excess composition flowed through opening 98 in electrode 94 and between electrodes 91,92 and polycarbonate sleeve 93.) St~n~rd T 1 ge Rr~k~wn Te~t _ _ _ _ A standard device, with dimensions of 1 cm2 x 1 mm was inserted into the test apparatus shown in Figure 7. Prior to testing, the insulation resistance Ri for the device was mea~ured at 25~C with a biasing voltage of 50 volts using a Genrad 1863 Megaohm meter; the initial resistivity Pl was calculated. The device was inserted into a circuit with an impulse generator and for each cycle a high energy impulse with a 10 x 1000 ~8 waveform (i.e. a rise time to maximum voltage of 10 ~s and a hal~-height at lOOQ ~s) and a current of at most lA was applied The peak voltage measured across the device at breakdown, i.e. the voltage at which current begins to flow through the gel, was recorded as the impulse 2s breakdown voltage. For the Standard Impulse Breakdown Test, five cycles were conducted. The final insulation resistance Rf after five cycles for the standard test was measured and the final resistivity pf was calculated.
M~ ied I lse Br~k~wn Test Samples were prepared with electrode spacing varying from 0.25 to 1 mm and were tested following the procedure of the Standard Impulse Breakdown Test.
W09~277 2 1 9 1 737 ~ r~7 1~ 15 ~ ~ .
OC Rr~kdown Test A etandard device was inserted into a circuit and was ubjected to a voltage which increased at a rate of 200 s volts/second (Hipot Model M1000 DC Tester). The DC breakdown - was recorded as the voltage at which 5 ~;ll;c~s of current began to flow through the device.
1 0 ' ~
Al F ll~r Ex~m~l~ Polymer SiZ~ Vol~ I~9~ f Test (~m~ ~ (Q) 1 Silicone gel 1 20 40.0 I1 1012 1012100 2 Thermoplastic gel20 35.1 I1 1012 1012100 3 Silicone grease 20 26.4 I1 1012 <105 4 4 Silicone gel 2 20 40.0 I1 101~ c105 46 Epoxy 20 26.4 D* 101~ c105 15 6 Silicone gel l 1-5 45.6 I2,D
7 Silicone gel 1 1-5 40.0 I2 8 Siiicone gel 1 1-5 35.1 I2 9 Silicone gel 1 1-5 26.4 I2 Silicone gel 1 20 45.6 I2,D
11 Silicone gel 1 20 35.1 I2 12 Silicone gel 1 20 26.4 I2 13 Silicone gel 1 20 19.3 I2 14 Silicone gel 1 20 13.3 I2~*
Notes to Table:
Silicone gel 1 was a mixture of 0.8 parts of a first composition composed of 26~ by weight Nusil~PlyW 7520 CS 170 divinyl terminated polydimethylsiloxane (available from McGhan-Nusil), 73.88~ Carbide L45/50 CS polydimethylsiloxane S; 1; cnn~ fluid diluent (available from Union Carbide), 0.1 Nusil Cat~ 50 catalyst (3 to 4~ plati~um in silicone oil, available from McGhan-Nusil), and 0.02~ T2160 inhibitor (l~3~5~7-tetravinyltetramethylcyclotetr~c;l n~n~, available WO95/33277 '- Ic~ ,5.~'7 16 : ' from Huls) and 1.0 pa~ts of a second composition composed of 26~ by weight Nusil Bly~ 7520 CS 170 polydimethylsiloxane, 73.91~ Carbide B~5/5Q CS silicone fluid diluent, and 0.9 T1915 tetr~ki~' thylsiloxysilane cro~l;nk;ng agent tavailable from ~uls).
Thermoplastic gel c~nt~;r~ 10~ by weight Septon~ 4055 styrene-(ethylene/propylene)-styrene block~copolymer having an ethylene/propylene midblock and a molecular weight of 308,000 (available from Kuraray), 87.5~ Witco~ 380 extender oil (available from Witco), and 1~ Irganox~ B900 antioxidant (available from Ciba-Geigy).
Silicone grease was a mixture of silicon dioxide and 50 cst silicone oil with the SiO2 added until the silicone oil would no longer flow under its own welght.
Silicone gel 2 was SylGard~ Q3-6636 silicone dielectric gel (available from Dow Corning).
Epoxy was A OE~ 18612 5-minute epoxy (available from Ace ~ardware Stores).
Aluminum powder with an average particle size of 20 microns and a sub3tantially spherical shape was product type 26651, available from Aldrich Chemicals.
Aluminum powder with an average particle size of 1 to~ 5 microns (passed 325 mesh) and a substantially spherical shape was product type 11067, available from Johnson Mathey.
2s I1 is the Standard Impulse Breakdown Test.
I2 is the Modified Impulse Breakdown Test.
D is the DC Breakdown Test.
~ 15 to 18 To determine whether compositions of the invention would remain in a c~n~n~t;ng condition after a voltage discharge, standard devices with the compositions shown in Table II were prepared. The initial resistance was measured prior~:to 3s exposing the device to one voltage discharge of the type described in the Standard Impulse Breakdown ~est above. After the discharge the final resistance was measured. A device was deemed to have latched if the final resistance was less than : ~ - ' 21 91 737 W095/33277 1 ll~ ,r~ 7 105 ohms. The approximate spacing between particles was calculated using the formuIa ~ = 4(l-f)r/(3f)~ where A is the mean free path (i.e. the interparticle spacing), f is the volume fraction of particles, and r is the particle radius.
s Whether the composition latched was a function of both the - particle size and loading of the particles. ~The 20 micron a.luminum latched at a higher interparticle spacing, apparently i.n part because not all the particles were completely ~pherical although the particles on average were subst~nt;~lly o spherical.
T~3LE II
Al F ller Tnterp~rticle E8~mpl~ Polymer Siz~ Vol. I~h~ SpSclnc (~m~ m~
Silicone gel 1-5 26.4 No 5.6 16 Silicone gel 1-5 35.1 Yes 3.7 17 Silicone gel 20 35.1 No 24.6 18 Silicone gel 20 45.6 Yes 15.9
~ 1 ~Tf'~TI~NC: (:A.C: TTTRP! I~pp}~pl~Tus ~In ~ OblllUN FOR USE ~
s g~R~.R~Nn OF T~ J~VENTIO~
Fi~ld of th~ Tnvent;on 0 This invention relates to gas discharge tube apparatus for tel~ t;~nR equipment and to compositions for use in such apparatus.
Tntrodllction to th~ Tnvention Gas discharge tubes are commonly used to protect teler ;cations e~uipment and circuits from damage in the eveLt of electrical interference or high voltage lightning pulses. Gas tubes used in this way are often oalled gas tube protectors. The tubes contain a gas which ionizes at high voltages to allow electrical pulses to be directed to ground, thus min;m; 7;ng any damage resulting from the pulses. If a ~nt;nn;ng high current overload occurs, e.g. as a result of an ~cr;~nt~l power line crossover, the tubes ~-;nt~;n a limited sustained ionization.
To provide protection in the event of failure from overheating during~sustained over-current conditions, and to assure protection if the ionizable gas vents from the tube, gas tube protectors generally incorporate "fail-safe~ and '~vent-safe" ~h~n;l , respectively. "Fail-safe" refers to thermal damage protection, which is often provided by a fusible metal or plastic material If the material is heated due to the energy from the current overload, it yields to a 3s biased shorting member and provides a pelul~llellL current shunt around the gas tube_ This may occur by melting a thermoplastic film positioned between two electrodes, thus allowing contact between the electrodes and ~hnnt;ng the 2 1 9 1 737 1~ ..,.,.'C-'~
current to ground. "Vent-safe" refers tQ backup overvoltage protection that operates when the gas "vents" or is lost to the atmosphere. Vent-safe protection is often provided by an air-gap that is part of the external structure of the tube.
s The proportions of the air-gap are selected to re~uire a firing potential considerably above, e.g. twice, the normal firing potential of the gas tube itself so that, under normal circumstances, the gas tube will prevent the air-gap from firing. This mln;m;7Pq the chances that the air-gap will be o damaged because although an over-voltage pulse usually fires harmlessly through a properly fllnrt;~n;ng gas tube, it may damage the air-gap which is intended as a safety backup.
To improve the reliability of air-gap vent-safe designs, it is common to enviLl ~ Al ly isolate the air-gap to prevent r~nt~m;nAtion by moigture, air pollution, insects, or other ~ CnVirl ' Al factors. Sealing materials such as encapsulants, potting compounds, conformal coatings, and gels, however, often are of limited utility as they generally cannot restrict all moisture ingress and may themselves penetrate into the air-gap, thus rhAng1ng the voltage discharge levels and/or leading to corrosion. A decrease in the discharge voltage level will eventually lead to electrical shorts at low voltage levels; an increase in the discharge voltage level 2s will defeat the purpose of the air-gap backup.
Some of these problems have been addressed by the r~pl~A~c t of the air-gap by a layer of solid ~t~; Al having particular non-linear electrical resistivity characteristics.
Such an air-gap is described in co-pending, commonly assigned U.S. Patent Application No. 08/Og6,059 ~3ebbaut et al, filed April 10, 1993), the disclosure of which is incorporated herein by reference. Although envil~~ tAlly stable, the solid material is subject to a decrease in breakdown voltage 3s on successive impulses, and, in fact, during normal operation in discharging a high voltage, high energy pulse such as lightning, will be destructive to itself. Furthermore, not all such air gaps provide fail-safe protection.
WO 9S5'33277 - ' 2 1 9 1 7 3 7 r~",, ~ ~
. . .
sn~MARy OF T~ TNVEN~ION
e have now found that if an electrically non-linear s element prepared from an electrically non-linear material ~hich has particular electrical properties when tested for electrical breakdown is used in place of the solid material air-gap described in U.S. Patent Application No. 08/046,059, a gas tube apparatus can be prepared which has both vent-safe 0 and fail-safe propertie~. In addition, because of the nature af the non-linear material and its physical and electrical stability during successive electrical events, the apparatus can be activated repeatedly in typical telecommunication service conditions without failure of the non-linear element.
3ecause the need to replace the element i3 decreased, the r~l; Ah; 1; ty of the telP ;cations system is increased and the cost of r~;nt~n~nre is decreased. In a preferred embodiment, the material comprises a gel which has the ability to conform to the gas tube protector, decreasing the chance of moisture ingress, and providing increased manufacturing tolerances. Furthermore, the gel may be , -t;hle with a gel encapsulant, thus contributing to the envi~ 1 sealing.
In a first aspect, this invention provides a telecom-2s munications gas tube apparatus which comprises (1) a first electrode for electrical crnn~ction to a first t~r~;n~l on a gas discharge tube;
~2) a second electrode for electrical connection to a second t~rm;n~1 on the gas tube; and ~ (3) an electrically non-linear resistive element separating the first and second electrodes, said '3s element comprising an electrically non-linear composition which WosS/33277 2 1 9 1 737 ~ 7 (a) comprises (i) a polymeric component, and (ii~ a particulate filler, (b) has an initial resistivity Pi at 25~C of at s least 109 ohm-cm, and (c) is such that when a standard device rrnt~in~ng the composition has an initial breakdown voltage VSi~ and after the standard device has lo been exposed to a standard impulse breakdown test, the device has a final breakdown voltage Vsf which is from 0.7VSi to 1.3VSi, and the composition in the device has a final resistivity pf at 25~C of at least 109 ohm-cm.
In a second aspect, this invention provides a telecom-munications gas tube apparatus which comprises (1) a first electrode for electrical rnnn~rtion to a first terminal on a gas discharge tube;
~2) a second electrode for electrical rrnn~rt;rn to a second terminal on the gas tube; and 2s (3) an electrically non-linear-resistive element separating the first and second electrodes, said element comprising an electrically non-linear composition which (a) comprises (i) 30 to 95~ by volume of the total composition gel, and (ii) 5 to 70~ by volume of the total composition particulate conductive filler, and 3s (b) has an initial resistivity p~ at 25~C of at least 109 ohm-cm.
W095/33277 , ~ 2 1 9 1 7 3 7 . ~
In a third aspect, this invention provides an assembly which comprises ; (A) a retaining element; and s (B) a telecommunications ga3 tube apparatus of the first aspect of the invention inserted into the rP~;ni element.
0 In a fourth aspect, this invention provide~ an electrically non-linear resistive composition of the type d.isclosed in the first aspect o~ the invention.
RRTR~ D~ 'RTPTI~ N OF T~T~ DRAWING
, , . _ .
Figure 1 is a schematic illustration showing a typical three-element gas discharge tube incorporated into a one pair tel~e ;cations line;
Figure 2 is a cross-sectional view of the gas tube of Figure I;
Figure 3 is an P-~l o~ illustration of a gas tube a;pparatus of the invention;
2s -- ' Figure 4 is a cross-sectional view of a gas tube a]?paratus of the invention which is ~nr~rs~lated in a gel;
Figure 5 is an exploded illustration of an assembly of the invention;
Figure 6 is a cross-sectional view of the assembly of F:igure 5;
' 35 Figure 7 is a schematic illustration showing a standard device for testing the compositions of the invention;
.
W095133277 21 91 737 r~ 7 Figure 8 is a graph of impul~e breakdown in volts as a function of impulse test cycles;
Figures 9 and lo are graphs of impulse breakdown in volts s as a function of the distance between electrodes for compositions of the invention; and Figure 11 is a graph of DC breakdown voltage and impulse breakdown voltage as a function of the distance between electrodes for compositions of the invention.
DET~TTTln DE.~rRTPTI~N OF T~ INVENTION
The gas tube apparatus and the assembly of the invention both comprise an electrically non-linear resistive element which comprises an electrically non-linear composition. In this specification the term "non-linear" means that the composition is substantially electrically nnnrnn~ tive, i.e.
has a resistivity of more than 109 ohm-cm, when an applied voltage is less than the impulse breakdown voltage, but then becomes electrically conductive, i.e. has a resistivity of=
less than 109 ohm-cm, when the applied voltage is equal to or greater than the impulse breakdown voltage. The electrically non-linear composition comprises a polymeric component and a 2s particulate filler. The polymeric ~ Snt may be any ~ ~Liate polymer, e.g. a thermoplastic matçrial such as a polyolefin or a fluoropolymer, a thermosetting material such as an epoxy, an elastomer, a grease, or a gel. The polymeric component is generally present in an amount of 30 to 95~, preferably 35 to 90~, particularly 40 to 85~ by volume of the total composition For many applications it is preferred that the polymeric , Ant comprise a polymeric gel, i.e. a substantially 3s dilute crosslinked solution which exhibits no flow when in the steady-state. The crosslinks, which provide a cnntinnnn~
network structure, may be the result of physical or chemical bonds, crystallites or other junctions, and must remain intact WO95/33277 ,~ 2 ~ 91 737 r~ 7 under the uae conditions of~the gél~ Most gels comprise a fluid-extended polymer in which a fluid, e.g. an oil, fills the interstices of the network. Suitable gels include those compriaing silicone, e.g. a polyorganosiloxane system, ~ polyurethane, polyurea, styrene-butadiene copolymers, styrene--~ isoprene copolymers, styrene-(ethylene/propylene)-styrene (SEPS) block copolymers (available under the t~Pn~mP Septon~
by Kuraray), styrene-(ethylene-propylene/ethylene-butylene)-styrene block copolymers (available under the tradename 0 Septon~ by Ruraray), and/or styrene-(ethylene/butylene)-styrene (SE;3S) block copolymers (available under the tradename Kraton~ by Shell Oil Co.). Suitable P~tPn~r fluids include mineral oil, vegetable oil such as paraffinic oil, Eilicone oil, plasticizer such as trimellitate, or a mixture of these, generally in an amount o~ 30 to 90% by weight of the total weight of the gel. The gel may be a thermosetting gel, e.g.
s:ilicone gel, in which the crosslinks are formed through the u~3e of multifunctional croscl;nk;ng agents, or a thermoplastic gel, in which microphase separation of domains serves as ~lmction points. Di6closures of gels which may be suitable as the polymeric ~ , ~nt in the composition are found in U.S.
Patent Nos. 4,600,261 (Debbaut), 4,690,831 (Uken et al), 4,.716,183 (Gamarra et al), 4,777,063 (Dubrow et al), 4,864,725 (I)ebbaut et al), 4,865,905 (Uken et al), 5,079,300 (Dubrow et 2s al), 5,104,930 (Rinde et al), and 5,149,736 (Gamarra); and in Tn~P~n~t;~n~l Patent Publication Nos. WO86/01634 (Toy et al), WC)88/00603 (Francis et al), WO90/05166 (Sutherland), WC)91/05014 (s~thp~lAn~)/ and W093/23472 (~ammond et al). The di.sclosure of each of these patents and publications is incorporated herein by reference.
It is preferred that the gel have a Voland hardness of 1 to 50 grams, particularly about 5 to 25 grams, especially 6 to 20 grams, have stress relaxation of 1 to 45~, preferably 15 to '3~ 4C~, have tack of 5 to 40 grams, preferably 9 to 35 grams, and . ha.ve an ultimate ~l~ngat;on o~ at least 50~, preferably at leaat 100~, particularly at least 400~, Pcpec;~lly at least 1000~, most especially at least 1500~. The elongation is W095/33277 ' 21 91 737 r~ 7 measured according to ~STM 3217, the disclosure of which is incorporated herein by reference. The Voland hardness, stress r~ t;nn, and tack are measured using a Voland-Stevens Texture Analyzer Model ~FRA having a 1000 gram load cell, a 5 gram trigger, and a 0.25 inch (6.35 mm) ball probe, as described in U.S. Patent No. 5,079,300 (Dubrow et al), the disclosure of which is incorporated herein by reference. To measure the hardness of a gel, a 20 ml glass scintillating vial containing lO grams of gel is placed in the analyzer and lo the stainless steel ball probe is forced into the gel at a speed of 0.20 mm/second to a penetration distance of 4.0 mm.
The Voland hardness value is the force in grams re~uired to force the ball probe at that speed to penetrate or deform the surface of the gel the specified 4.0 mm. The Voland hardness of a particular gel may be directly correlated to the ASTM
D217 cone penetration hardness using the procedure described in U.S. Patent No. 4,852,646 (Dittmer et al), the disclosure of which is incorporated herein by r~f~r~n~.
In addition to the polymeric component, the composition also comprises a particulate filler. The ~iller may be conductive, s~m;cnn~nctive~ nnn~nn~ tive, or a mixture of two or more types of fillers as long as the resulting composition has the appropriate electrical non-linearity. It is generally 2s preferred that the filler be conductive or semiconductive.
Conductive fillers generally have a resistivity of at most lO-3 ohm-cm; semiconductive fillers generally have a resistivity of at most 103 ohm-cm, although their resistivity is a function of any dopant material, as well as temperature and other factors and can be subst~nti~lly higher than 103 ohm-cm.
Suitable fillers include metal powders, e.g. aluminum, nickel, silver, silver-coated nickel, platinum, copper, tantalum, tungsten, gold, and cobalt; metal oxide powders, e.g. iron oxide, doped iron oxide, doped titanium dioxide, and doped 3s zinc oxide; metal carbide powders, e.g. silicon carbide, titanium carbide, and tantalum carbide; metal nitride powders;
metal boride powders; carbon black or graphite; and alloys, e.g. bronze and brass. Particularly preferred as fillers ar~e W09~33277 2 1 ~ 1 7 3 7 ~ g ~luminum, iron oxide (Fe304), iron oxide doped with titanium dioxide, silicon carbide, and 9ilver-coated nickel. If the polymeric component is a gel, it i8 important that the ~elected filler not interfere with the crosslinking of the s gel, i.e. not "poison~ it. The filler iB generally present in an amount of 5 to 70~, preferably 10 to 65~, especially 15 to ~0~ by volume of the total composition.
The volume loading, shape, and size of the filler affect o 1:he non-linear electrical properties of the composition, in part because of the spacing between the particles. Any shape particle may be used, e.g. spherical, flake, fiber, or rod.
17seful compositions can be prepared with particles having an average size of C.OlO to lO0 microns, preferably O.l to 75 rnicrons, particularly 0.5 to 50 microns, especially l to 20 rnicrons. A mixture of different size, shape, and/or type particles may be used. The particles may be magnetic or nonmagnetic.
In addition to the particulate filler, the composition may comprise other conv~n~inn~l additives, including tabilizers, pigments, croRRl;nk;ng agents, catalysts, and i.nhibitors.
2s The compositions of the invention may be prepared by any Eluitable means, e.g. melt-blending, solvent-blending, or i.ntensive mixing, and may be shaped by conventional methods including extrusion, calendaring, casting, and compression molding. If the polymeric component is a gel, the gel may be r~lixed with the filler by stirring and the composition may be poured or cast onto a substrate or into a mold to be cured, often by the addition of heat.
The compositions of the invention have excellent 3s . stability as measured both by resistivity and breakdown voltage. The compositions are electrically insulating and have an initial resistivity Pl at 25~C of at least lO9 ohm-cm, preferably lClO ohm-cm, particularly l0ll ohm-cm, especially W095/33277 ' 21 9 1 737 r~ 7 1012 ohm-cm. ~he initial resistivity value Pi is such that when the composition is formed into a standard device as described below, the initial insulation resistance Ri is at least 109 ohms, preferably at least 101~ ohms, particularly at s least l0ll ohms. An Ri value of at least 109 ohms is preferred when the compositions of the invention are used in tel~ ;cations apparatus. After~bein~ exposed to the standard impulse breakdown test, described below, the final resistivity pf at 25~C is at least 109 ohm-cm, and the ratio of p~ to Pi is at most l x 103, preferably at most 5 x 102, particularly at most 1 x 102, especially at most 5 x 101, most especially at most 1 x 101. The final insulation resistance Rf for a standard device after ~o~,e to the standard impulse breakdown test is at least 109 ohms, preferably at least 10l~ ohms, particularly at least l0ll ohms.
When the composition of the invention is formed into a standard device as described below and exposed to a standard impulse breakdown test, the device has an initial breakdown voltage VSi and a final breakdown voltage Vsf which is from 0.70Vsi to l.30Vsi~ preferably from 0.80VSi to 1.20VSi, particularly from 0.85VSi to 1.15VSi, especially from 0.90VSi to 1.10V~3i. The value of the breakdown voltage is affected~by the volume fraction of~the particulate filler, by the particle 2s size, and by the distance between the particles among other factors. In general, as particle size decreases, the breakdown voltage increases.
Some compositions of the invention will "latch", i.e.
remain in a conductive state with a resistivity of less than 106 ohm-cm, after one voltage discharge. If the latched device is made from a composition comprising a gel, the device can be "reset" into a high resistivity state, i.e. a resistivity of at least 109 ohm-cm, by physical deformation, e.g. flexing, torsion, compression, or tension. The latching behavior is a function of particle size, interparticle spacing, and particle 3hape. In gels, generally small w09~33277 2 T ~ s7 ~ipherical particle~, e.g. 1 to 5;~icrons~, with a Gmall interparticle spacing, e.g. less than 4 microns, will latch.
Under certain electrical conditions, compositions of the s invention, particularly compositions comprising aluminum, will provide fail-safe protection. If exposed to a sufficiently high energy level, e.g. 30A and 1000 volts for a time of 2 seconds to 30 minutes, the particulate filler ca~L fuse together and provide a permanent conductive path between the 0 electrodes, giving a final resistance of less than 10 ohms, e.g. 1 to 10 milliohms. Such behavior is desirable in the event of crossed power lines and results in a permanent short circuit.
The invention is illustrated by the drawing in which Figure 1 is a schematic illustration of a conventional tele~ ;cations circuit 10 which incorporates a gas tube 12 in a tele~ ;cations line. The gas tube 12, which is shown in cross-section in Figure 2, has a first terminal 16 and a second t~rm; n~l 17 for connection to the tip side 13 and the ring side 14, respectively, of the telP ;cations circuit.
In addition, the gas tube 12 has a center ground terLninal 18.
A ceramic shell 19 encloses an ; ~ni 7~hl e gas 20 which ionizes to form a discharge plasma at a given voltage.
2s ~
Figure 3 is an exploded view of a gas tube apparatus 40 oE the invention. In this embodiment, the first terminal 16 and the second t~r~;n~l 17 of the gas tube 12 also function as first and second electrodes, respectively, for the gas tube apparatus 40. (Although not shown, the gas tube may comprise a third terminal which may be connected to a third electrode in the gas tube apparatus. One of the electrodes may be a grounding electrode.) Electrically non-linear resistive element 45 is positioned in contact with first t~rm;n~l 16 and 3~ second terminal 17_ Ground electrode 55 is in physical contact with resistive element 45, and is in electrical contact with ground t~rm;n~l 18 of gas tube 12. In a preferred ~- ti--nt, the non-linear compositiorL comprising wossl33277 2 1 9 1 737 P~"~ c~7 the resistive element haa Gufficient flexibility that it conforms to the shape of gas tube 12.
Figure 4 shows a cross-sectional view of gas tube s apparatue 40 embedded in a gel encapsulant 50. The encapsulant, which may be, e.g. a potting compound, a conformal coating, or a gel, provides enviL~ t~l protection from moisture and other ~nnt~min~nt~. In addition, the encapsulant may exclude oxygen from the plasma discharge, and o act as a heat sink to draw thermal energy away from local hot spots. It is preferred that the resistive element be chemically inert to the encapsulant.
Figure 5 is an exploded view of an assembly 70 of the =
invention and Figure 6 is a cross-sectional view of that assembly. Retaining element 72 i5 designed to contain gas tube 12, resistive element 45, and a ground electrode 55 ' .
Although the resistive element 45 may be laminar as shown, to enhance contact with gas tube 12 the resistive element may be curved or otherwise shaped. Spring leads 76,78 are attached to gas tube 12 and serve to make electrical contact with respective insulation displ~r~ t c~nn~t~rs (not shown).
Gas tube 12 is held in the appropriate position with the resistive element 45 and ground electrode 55 ' by means of 2s retaining element 72, retainer cap 74, and grounding pin 80 which can be inserted into a recess or hole in retainer cap 74. Retainer cap 74 may be ultrasonically welded, glued, or otherwise fused to retaining element 72. To ~-;n~in the proper distance between the gas tube 12 and ground electrode 30 55 ', spacer 56 =protrudes from ground electrode 55 ' . The height of spacer 56 can be eelected to achieve different levels of voltage breakdown. The retaining element 72 may be filled with the encapsulant to surround the contents.
The invention is illustrated by the following examples.
Wog~/33277 p_"~ "
E ~ ~R 1 to 14 ~~ : ~
The ingredients listed in Table I were mixed with a tongue depressor to disperse the particulate filler, degassed s in a vacuum oven for one minute, poured onto a PTFE-coated release sheet and cured. ~ Standard Device, described below, W.18 prepared with an electrode spacirLg of 1 mm. Samples were then subjected to one of three tests, although the Standard Irnpulse 3reakdown Test was extended for several samples from 5 o to 100 cycles. The results, shown in Figures 8 to 11, indicated that the compositions based on silicone gel 1 and thermoplastic gel had excellent stability and reproducibility over 100 cycles based on impulse breakdown and in~ tion resistance. The composition based on silicone gel 2 showed a decrease~in insulation resistance to less than 105 ohms by ~bout 41 cycles. The composition based on a silicone grease skLowed a similar decrease by four cycles (Figure 8). Example 5, based on an epoxy, shattered under the impulse test conditions, but showed a decrease in insulation resistance by 15~ cycles under DC breakdown testing. Figures 9 and 10 show th~e effect of particle size and filler loading on the impulse breakdown voltage for samples which ranged in thickness from 0.25 to 1.0 mm. Figure 11 8hows that for a given particle si~e and loading, the impulse breakdown and the DC breakdown 2s voltage were comparable.
St~n~rd Device A circular sample with a diameter of 11.2 mm (i.e. a surface area of about 1 cm2) and a thickrLess of 1 mm was cut from the cured composition and inserted into the test fixture shown in cross-section in Eigure ~. The test composition sample 90 was positioned between two circular aluminum electrodes 91,92, each with a diameter of about 11.2 mm and a 3s surface in contact with the composition 90 of about 100 mm2.
Polycarbonate sleeve 93 with an inner diameter of slightly more than 11.2 mm waL3 positioned over the assembled electrodes and composition and the assembly was inserted into fixture 94 2 ~ 9 ~ 737 W095/33277 P~
c~nt~;n;ng support elements 95,96 Micrometer 97 was adjusted until the 9pacing between the electrodes 91,92 was 1 mm. (For the Modified Impulse Breakdown Test described below, the micrometer was adjusted to vary the electrode spacing, i.e.
s the sample thickness, from 0.25 to 1_0 mm For gel samples, the sample had an initial thi~knP~R of 1 mm When the micrometer was adjusted to decrease the gample th;~knP~5, excess composition flowed through opening 98 in electrode 94 and between electrodes 91,92 and polycarbonate sleeve 93.) St~n~rd T 1 ge Rr~k~wn Te~t _ _ _ _ A standard device, with dimensions of 1 cm2 x 1 mm was inserted into the test apparatus shown in Figure 7. Prior to testing, the insulation resistance Ri for the device was mea~ured at 25~C with a biasing voltage of 50 volts using a Genrad 1863 Megaohm meter; the initial resistivity Pl was calculated. The device was inserted into a circuit with an impulse generator and for each cycle a high energy impulse with a 10 x 1000 ~8 waveform (i.e. a rise time to maximum voltage of 10 ~s and a hal~-height at lOOQ ~s) and a current of at most lA was applied The peak voltage measured across the device at breakdown, i.e. the voltage at which current begins to flow through the gel, was recorded as the impulse 2s breakdown voltage. For the Standard Impulse Breakdown Test, five cycles were conducted. The final insulation resistance Rf after five cycles for the standard test was measured and the final resistivity pf was calculated.
M~ ied I lse Br~k~wn Test Samples were prepared with electrode spacing varying from 0.25 to 1 mm and were tested following the procedure of the Standard Impulse Breakdown Test.
W09~277 2 1 9 1 737 ~ r~7 1~ 15 ~ ~ .
OC Rr~kdown Test A etandard device was inserted into a circuit and was ubjected to a voltage which increased at a rate of 200 s volts/second (Hipot Model M1000 DC Tester). The DC breakdown - was recorded as the voltage at which 5 ~;ll;c~s of current began to flow through the device.
1 0 ' ~
Al F ll~r Ex~m~l~ Polymer SiZ~ Vol~ I~9~ f Test (~m~ ~ (Q) 1 Silicone gel 1 20 40.0 I1 1012 1012100 2 Thermoplastic gel20 35.1 I1 1012 1012100 3 Silicone grease 20 26.4 I1 1012 <105 4 4 Silicone gel 2 20 40.0 I1 101~ c105 46 Epoxy 20 26.4 D* 101~ c105 15 6 Silicone gel l 1-5 45.6 I2,D
7 Silicone gel 1 1-5 40.0 I2 8 Siiicone gel 1 1-5 35.1 I2 9 Silicone gel 1 1-5 26.4 I2 Silicone gel 1 20 45.6 I2,D
11 Silicone gel 1 20 35.1 I2 12 Silicone gel 1 20 26.4 I2 13 Silicone gel 1 20 19.3 I2 14 Silicone gel 1 20 13.3 I2~*
Notes to Table:
Silicone gel 1 was a mixture of 0.8 parts of a first composition composed of 26~ by weight Nusil~PlyW 7520 CS 170 divinyl terminated polydimethylsiloxane (available from McGhan-Nusil), 73.88~ Carbide L45/50 CS polydimethylsiloxane S; 1; cnn~ fluid diluent (available from Union Carbide), 0.1 Nusil Cat~ 50 catalyst (3 to 4~ plati~um in silicone oil, available from McGhan-Nusil), and 0.02~ T2160 inhibitor (l~3~5~7-tetravinyltetramethylcyclotetr~c;l n~n~, available WO95/33277 '- Ic~ ,5.~'7 16 : ' from Huls) and 1.0 pa~ts of a second composition composed of 26~ by weight Nusil Bly~ 7520 CS 170 polydimethylsiloxane, 73.91~ Carbide B~5/5Q CS silicone fluid diluent, and 0.9 T1915 tetr~ki~' thylsiloxysilane cro~l;nk;ng agent tavailable from ~uls).
Thermoplastic gel c~nt~;r~ 10~ by weight Septon~ 4055 styrene-(ethylene/propylene)-styrene block~copolymer having an ethylene/propylene midblock and a molecular weight of 308,000 (available from Kuraray), 87.5~ Witco~ 380 extender oil (available from Witco), and 1~ Irganox~ B900 antioxidant (available from Ciba-Geigy).
Silicone grease was a mixture of silicon dioxide and 50 cst silicone oil with the SiO2 added until the silicone oil would no longer flow under its own welght.
Silicone gel 2 was SylGard~ Q3-6636 silicone dielectric gel (available from Dow Corning).
Epoxy was A OE~ 18612 5-minute epoxy (available from Ace ~ardware Stores).
Aluminum powder with an average particle size of 20 microns and a sub3tantially spherical shape was product type 26651, available from Aldrich Chemicals.
Aluminum powder with an average particle size of 1 to~ 5 microns (passed 325 mesh) and a substantially spherical shape was product type 11067, available from Johnson Mathey.
2s I1 is the Standard Impulse Breakdown Test.
I2 is the Modified Impulse Breakdown Test.
D is the DC Breakdown Test.
~ 15 to 18 To determine whether compositions of the invention would remain in a c~n~n~t;ng condition after a voltage discharge, standard devices with the compositions shown in Table II were prepared. The initial resistance was measured prior~:to 3s exposing the device to one voltage discharge of the type described in the Standard Impulse Breakdown ~est above. After the discharge the final resistance was measured. A device was deemed to have latched if the final resistance was less than : ~ - ' 21 91 737 W095/33277 1 ll~ ,r~ 7 105 ohms. The approximate spacing between particles was calculated using the formuIa ~ = 4(l-f)r/(3f)~ where A is the mean free path (i.e. the interparticle spacing), f is the volume fraction of particles, and r is the particle radius.
s Whether the composition latched was a function of both the - particle size and loading of the particles. ~The 20 micron a.luminum latched at a higher interparticle spacing, apparently i.n part because not all the particles were completely ~pherical although the particles on average were subst~nt;~lly o spherical.
T~3LE II
Al F ller Tnterp~rticle E8~mpl~ Polymer Siz~ Vol. I~h~ SpSclnc (~m~ m~
Silicone gel 1-5 26.4 No 5.6 16 Silicone gel 1-5 35.1 Yes 3.7 17 Silicone gel 20 35.1 No 24.6 18 Silicone gel 20 45.6 Yes 15.9
Claims (10)
1. A telecommunications gas tube apparatus which comprises (1) a first electrode for electrical connection to a first terminal on a gas discharge tube;
(2) a second electrode for electrical connection to a second terminal on the gas tube; and (3) an electrically non-linear resistive element separating the first and second electrodes, said element comprising an electrically non-linear composition which (a) comprises (i) a polymeric component, and (ii) a particulate filler, (b) has an initial resistivity pi at 25°C of at least 109 ohm-cm, and (c) is such that when a standard device containing the composition has an initial breakdown voltage VSi, and after the standard device has been exposed to a standard impulse breakdown test, the device has a final breakdown voltage Vsf which is from 0.7VSi to 1.3VSi, and the composition in the device has a final resistivity pf at 25°C of at least 109 ohm-cm
(2) a second electrode for electrical connection to a second terminal on the gas tube; and (3) an electrically non-linear resistive element separating the first and second electrodes, said element comprising an electrically non-linear composition which (a) comprises (i) a polymeric component, and (ii) a particulate filler, (b) has an initial resistivity pi at 25°C of at least 109 ohm-cm, and (c) is such that when a standard device containing the composition has an initial breakdown voltage VSi, and after the standard device has been exposed to a standard impulse breakdown test, the device has a final breakdown voltage Vsf which is from 0.7VSi to 1.3VSi, and the composition in the device has a final resistivity pf at 25°C of at least 109 ohm-cm
2. An apparatus according to claim 1 which further comprises an encapsulant that surrounds the first and second electrodes and the non-linear element.
3. An apparatus according to claim 2 wherein the encapsulant comprises a gel.
4. An apparatus according to claim 1 or 2 wherein VSf is from 0.8vsi to 1.2Vsi.
5. An apparatus according to claim 1 or 2 wherein the ratio of Pi to pf is at most 103.
6. An apparatus according to claim 1 or 2 wherein the polymeric component is a gel.
7. An apparatus according to claim 1 or 2 wherein the particulate filler comprises a conductive filler or a semiconductive filler.
8. A telecommunications gas tube apparatus which comprises (1) a first electrode for electrical connection to a first terminal on a gas discharge tube;
(2) a second electrode for electrical connection to a second terminal on the gas tube; and (3) an electrically non-linear resistive element separating the first and second electrodes, said element comprising an electrically non-linear composition which (a) comprises (i) 30 to 95% by volume of the total composition gel, and (ii) 5 to 70% by volume of the total composition particulate conductive filler, and (b) has an initial resistivity Pi at 25°C of at least 109 ohm-cm.
(2) a second electrode for electrical connection to a second terminal on the gas tube; and (3) an electrically non-linear resistive element separating the first and second electrodes, said element comprising an electrically non-linear composition which (a) comprises (i) 30 to 95% by volume of the total composition gel, and (ii) 5 to 70% by volume of the total composition particulate conductive filler, and (b) has an initial resistivity Pi at 25°C of at least 109 ohm-cm.
9. An assembly which comprises (A) a retaining element; and (B) a telecommunications gas tube apparatus inserted into the retaining element which comprises (1) a gas discharge tube;
(2) a first electrode for electrical connection to a first terminal on the gas tube;
(3) a second electrode for electrical connection to a second terminal on the gas tube; and (4) an electrically non-linear resistive element separating the first and second electrodes, said element comprising an electrically non-linear composition which (a) comprises (i) a polymeric component, and (ii) a particulate filler, (b) has an initial resistivity Pi at 25°C of at least 10 9 ohm-cm, and (c) is such that when a standard device containing the composition has an initial breakdown voltage VSi, and after the standard device has been exposed to a standard impulse breakdown test, the device has a final breakdown voltage VSf which is from 0.7VSi to 1.3VSi, and the composition in the device has a final resistivity pi at 25°C of at least 10 9 ohm-cm.
(2) a first electrode for electrical connection to a first terminal on the gas tube;
(3) a second electrode for electrical connection to a second terminal on the gas tube; and (4) an electrically non-linear resistive element separating the first and second electrodes, said element comprising an electrically non-linear composition which (a) comprises (i) a polymeric component, and (ii) a particulate filler, (b) has an initial resistivity Pi at 25°C of at least 10 9 ohm-cm, and (c) is such that when a standard device containing the composition has an initial breakdown voltage VSi, and after the standard device has been exposed to a standard impulse breakdown test, the device has a final breakdown voltage VSf which is from 0.7VSi to 1.3VSi, and the composition in the device has a final resistivity pi at 25°C of at least 10 9 ohm-cm.
10. An assembly according to claim 9 wherein the retaining element further comprises a gel which encapsulates the gas tube apparatus.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US25187894A | 1994-06-01 | 1994-06-01 | |
| US08/251,878 | 1994-06-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2191737A1 true CA2191737A1 (en) | 1995-12-07 |
Family
ID=22953783
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002191740A Abandoned CA2191740A1 (en) | 1994-06-01 | 1995-05-30 | Telecommunications gas tube apparatus and composition for use therewith |
| CA002191737A Abandoned CA2191737A1 (en) | 1994-06-01 | 1995-05-30 | Telecommunications gas tube apparatus and composition for use therewith |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002191740A Abandoned CA2191740A1 (en) | 1994-06-01 | 1995-05-30 | Telecommunications gas tube apparatus and composition for use therewith |
Country Status (12)
| Country | Link |
|---|---|
| EP (1) | EP0763252A1 (en) |
| JP (1) | JPH10501372A (en) |
| KR (1) | KR970703609A (en) |
| CN (1) | CN1149354A (en) |
| AU (2) | AU2650595A (en) |
| BR (1) | BR9507836A (en) |
| CA (2) | CA2191740A1 (en) |
| CZ (1) | CZ347996A3 (en) |
| FI (1) | FI964764A0 (en) |
| IL (2) | IL113502A0 (en) |
| PL (1) | PL317330A1 (en) |
| WO (2) | WO1995033278A1 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ES2133124B1 (en) * | 1994-05-04 | 2000-04-01 | Cymem S A | IMPROVEMENTS INTRODUCED IN THE PATENT OF INVENTION P-9400938/4, BY: EXTERNAL SHORT CIRCUIT DEVICE FOR PROTECTION MODULES OF TELEPHONE AND SIMILAR EQUIPMENT. |
| IL117529A0 (en) * | 1995-03-22 | 1996-07-23 | Raychem Corp | Button protection device |
| US6251513B1 (en) * | 1997-11-08 | 2001-06-26 | Littlefuse, Inc. | Polymer composites for overvoltage protection |
| SE9704824D0 (en) * | 1997-12-22 | 1997-12-22 | Asea Brown Boveri | Fiber composite articles and method for making such composite articles |
| US7258819B2 (en) | 2001-10-11 | 2007-08-21 | Littelfuse, Inc. | Voltage variable substrate material |
| JP2006012492A (en) * | 2004-06-23 | 2006-01-12 | Shinko Electric Ind Co Ltd | Discharge tube |
| DE102004031325A1 (en) | 2004-06-29 | 2006-01-19 | Bayer Healthcare Ag | Active substance-containing solid shaped articles for external use against parasites on animals |
| PL2287984T3 (en) * | 2009-07-20 | 2012-02-29 | Bettermann Obo Gmbh & Co Kg | Surge absorbers |
| CN105762762B (en) * | 2016-05-13 | 2024-05-03 | 深圳市槟城电子股份有限公司 | Circuit protection device |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1433129A (en) * | 1972-09-01 | 1976-04-22 | Raychem Ltd | Materials having non-linear resistance characteristics |
| US4992333A (en) * | 1988-11-18 | 1991-02-12 | G&H Technology, Inc. | Electrical overstress pulse protection |
| TW211079B (en) * | 1992-06-30 | 1993-08-11 | Raychem Corp | Gas tube vent-safe device |
-
1995
- 1995-04-26 IL IL11350295A patent/IL113502A0/en unknown
- 1995-04-26 IL IL11350395A patent/IL113503A0/en unknown
- 1995-05-30 CN CN95193320A patent/CN1149354A/en active Pending
- 1995-05-30 CZ CZ963479A patent/CZ347996A3/en unknown
- 1995-05-30 WO PCT/US1995/006867 patent/WO1995033278A1/en not_active Application Discontinuation
- 1995-05-30 BR BR9507836A patent/BR9507836A/en not_active Application Discontinuation
- 1995-05-30 WO PCT/US1995/006662 patent/WO1995033277A1/en active Application Filing
- 1995-05-30 PL PL95317330A patent/PL317330A1/en unknown
- 1995-05-30 KR KR1019960706815A patent/KR970703609A/en not_active Application Discontinuation
- 1995-05-30 JP JP8501161A patent/JPH10501372A/en active Pending
- 1995-05-30 AU AU26505/95A patent/AU2650595A/en not_active Abandoned
- 1995-05-30 AU AU26587/95A patent/AU2658795A/en not_active Abandoned
- 1995-05-30 CA CA002191740A patent/CA2191740A1/en not_active Abandoned
- 1995-05-30 CA CA002191737A patent/CA2191737A1/en not_active Abandoned
- 1995-05-30 EP EP95921535A patent/EP0763252A1/en not_active Withdrawn
-
1996
- 1996-11-29 FI FI964764A patent/FI964764A0/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| WO1995033277A1 (en) | 1995-12-07 |
| CN1149354A (en) | 1997-05-07 |
| PL317330A1 (en) | 1997-04-01 |
| CA2191740A1 (en) | 1995-12-07 |
| WO1995033278A1 (en) | 1995-12-07 |
| AU2658795A (en) | 1995-12-21 |
| FI964764A (en) | 1996-11-29 |
| AU2650595A (en) | 1995-12-21 |
| FI964764A0 (en) | 1996-11-29 |
| BR9507836A (en) | 1997-09-01 |
| EP0763252A1 (en) | 1997-03-19 |
| JPH10501372A (en) | 1998-02-03 |
| KR970703609A (en) | 1997-07-03 |
| IL113503A0 (en) | 1995-07-31 |
| IL113502A0 (en) | 1995-07-31 |
| CZ347996A3 (en) | 1997-06-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |