Patent Description:
Frequently, excessive voltage or current is applied across service lines that deliver power to residences and commercial and institutional facilities. Such excess voltage or current spikes (transient overvoltages and surge currents) may result from lightning strikes, for example. The above events may be of particular concern in telecommunications distribution centers, hospitals and other facilities where equipment damage caused by overvoltages and/or current surges and resulting down time may be very costly. <CIT> discloses a known gas discharge tube (GDT) assembly.

According to some embodiments, a gas discharge tube assembly includes a multi-cell gas discharge tube (GDT). The multi-cell GDT includes a housing defining a GDT chamber, a plurality of inner electrodes located in the GDT chamber, a trigger resistor located in the GDT chamber, and a gas contained in the GDT chamber. The inner electrodes are serially disposed in the chamber in spaced apart relation to define a series of cells and spark gaps. The trigger resistor includes an interface surface exposed to at least one of the cells. The trigger resistor is responsive to an electrical surge through the trigger resistor to generate a spark along the interface surface and thereby promote an electrical arc in the at least one cell.

In some embodiments, the multi-cell GDT includes first and second trigger end electrodes, the series of cells and spark gaps extends from the first trigger end electrode to the second trigger end electrode, and the trigger resistor electrically connects the first trigger end electrode to the second trigger end electrode.

In some embodiments, the trigger resistor is exposed to a plurality of the cells and is responsive to an electrical surge through the trigger resistor to generate sparks along the interface surface and thereby promote electrical arcs in the plurality of the cells.

In some embodiments, the multi-cell GDT has a main axis and the inner electrodes and the first and second trigger end electrodes are spaced apart along the main axis, and the trigger resistor is configured as an elongate strip extending along the main axis.

According to some embodiments, the multi-cell GDT includes a plurality of the trigger resistors extending along the main axis and each having an interface surface, and each of the trigger resistors is exposed to a plurality of the cells and is responsive to an electrical surge through the trigger resistor to generate sparks along the interface surface thereof and thereby promote electrical arcs in the plurality of the cells.

In some embodiments, the gas discharge tube assembly includes a trigger device. The trigger device includes a trigger device substrate including an axially extending groove defined therein, and the trigger resistor. The trigger resistor is disposed in the groove such that the interface layer is exposed.

According to some embodiments, the trigger device substrate includes a plurality axially extending, substantially parallel grooves defined therein, and the trigger device includes a plurality of the trigger resistors each disposed in a respective one of the grooves.

In some embodiments, the gas discharge tube assembly further includes an outer resistor that electrically connects the first trigger end electrode to the second trigger end electrode, and is not exposed to the cells.

In some embodiments, the outer resistor is mounted on an exterior of the housing.

According to some embodiments, the trigger resistor includes an inner surface facing the inner electrodes and including the interface surface, and the gas discharge tube assembly further includes an electrically insulating resistor protection layer bonded to the inner surface between the inner surface and the inner electrodes.

According to some embodiments, the gas discharge tube assembly includes an integral primary GDT connected in series with the multi-cell GDT. The primary GDT is operative to conduct current in response to an overvoltage condition across the gas discharge tube assembly and prior to conduction of current across the plurality of spark gaps of the multi-cell GDT.

In some embodiments, the primary GDT is electrically connected to the trigger resistor such that current is conducted through the trigger resistor when the primary GDT conducts current.

According to some embodiments, the primary GDT is located in the GDT chamber, and the GDT chamber is hermetically sealed.

In some embodiments, the GDT chamber is hermetically sealed, the primary GDT includes a primary GDT chamber that is hermetically sealed from the GDT chamber, and the primary GDT chamber contains a primary GDT gas that is different from the gas in the GDT chamber.

According to some embodiments, the GDT chamber is hermetically sealed.

In some embodiments, the housing includes a tubular housing insulator, and at least one reinforcement member positioned in the housing insulator between the inner electrodes and the housing insulator.

According to some embodiments, the at least one reinforcement member includes a plurality of locator slots, and the inner electrodes are each seated in a respective one of the locator slots such that the inner electrodes are thereby held in axially spaced apart relation and are able to move laterally a limited displacement distance.

According to some embodiments, the inner electrodes are substantially flat plates.

In some embodiments, the trigger resistor is formed of a material having a specific electrical resistance in the range of from about <NUM> micro-ohm-meter to <NUM>,<NUM> ohm-meter.

In some embodiments, the trigger resistor has an electrical resistance in the range of from about <NUM> ohm to <NUM> ohms.

According to some embodiments, the interface surface of the trigger resistor is nonhomogeneous and porous.

In some embodiments, the multi-cell GDT has a main axis and the inner electrodes are spaced apart along the main axis, the trigger resistor extends along the main axis, a plurality of laterally extending, axially spaced apart surface grooves are defined in the interface surfaces of the trigger resistor, and the surface grooves do not extend fully through a thickness of the trigger resistor, so that a remainder portion of the trigger resistor is present at the base of each surface groove and provides electrical continuity throughout a length of the trigger resistor.

According to some embodiments, each surface groove has an axially extending width in the range of from about <NUM> to <NUM>.

In some embodiments, the gas discharge tube assembly includes a thermal disconnect mechanism responsive to heat generated in the gas discharge tube assembly to disconnect the gas discharge tube assembly from a circuit.

In some embodiments, the gas discharge tube assembly includes an integral test gas discharge tube (GDT). The test GDT includes a test GDT electrode and a test GDT chamber. The test GDT chamber is in fluid communication with the GDT chamber to permit flow of the gas between the GDT chamber and the test GDT chamber.

One or more embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:.

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. In the drawings, the relative sizes of regions or features may be exaggerated for clarity.

It will be understood that when an element is referred to as being "coupled" or "connected" to another element, it can be directly coupled or connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, there are no intervening elements present.

In addition, spatially relative terms, such as "under", "below", "lower", "over", "upper" and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. For example, if the device in the figures is turned over, elements described as "under" or "beneath" other elements or features would then be oriented "over" the other elements or features. Thus, the example term "under" can encompass both an orientation of over and under.

As used herein the expression "and/or" includes any and all combinations of one or more of the associated listed items.

As used herein, a "hermetic seal" is a seal that prevents the passage, escape or intrusion of air or other gas through the seal (i.e., airtight). "Hermetically sealed" means that the described void or structure (e.g., chamber) is sealed to prevent the passage, escape or intrusion of air or other gas into or out of the void or structure.

As used herein, "monolithic" means an object that is a single, unitary piece formed or composed of a material without joints or seams.

With reference to <FIG>, a modular, multi-cell gas arrestor or gas discharge tube (GDT) assembly <NUM> according to embodiments of the invention is shown therein. The GDT <NUM> includes a housing insulator <NUM>, a first outer or terminal electrode <NUM>, a second outer or terminal electrode <NUM>, a primary GDT end electrode <NUM>, a first trigger end electrode <NUM>, a second trigger end electrode <NUM>, a set E of inner electrodes E1-E21, seals <NUM>, bonding layers <NUM>, a pair of locator members <NUM>, a bonding agent <NUM>, a pair of trigger covers or devices <NUM>, and a selected gas M.

As discussed in more detail below, the GDT assembly <NUM> includes a separated or primary GDT <NUM> and a multi-cell main or secondary GDT <NUM>.

The trigger devices <NUM> and the trigger end electrodes <NUM>, <NUM> together form a trigger system <NUM>.

The housing insulator <NUM> is generally tubular and has axially opposed end openings 114A, 114B communicating with a through passage or cavity <NUM>. The housing insulator <NUM> also includes an annular locator flange <NUM> proximate, but axially spaced apart from, the opening 114A. The housing insulator <NUM> and the cavity <NUM> are rectangular in cross-section.

The housing insulator <NUM> may be formed of any suitable electrically insulating material. According to some embodiments, the insulator <NUM> is formed of a material having a melting temperature of at least <NUM> degrees Celsius and, in some embodiments, at least <NUM> degrees Celsius. In some embodiments, the insulator <NUM> is formed of a ceramic. In some embodiments, the insulator <NUM> includes or is formed of alumina ceramic (Al<NUM><NUM><NUM>) and, in some embodiments, at least about <NUM>% Al<NUM><NUM><NUM>. In some embodiments, the insulator <NUM> is monolithic.

The housing insulator <NUM> and the terminal electrodes <NUM>, <NUM> collectively form an enclosure or housing <NUM> defining an enclosed GDT chamber <NUM>. The chamber <NUM> is rectangular in cross-section. The inner electrodes E1-E21, the locator members <NUM>, the electrodes <NUM>, <NUM>, <NUM>, the trigger devices <NUM>, and the gas M are contained in the chamber <NUM>. The trigger end electrode <NUM> divides the GDT chamber <NUM> into a secondary chamber 108A and a primary GDT chamber <NUM>.

The housing <NUM> has a central lengthwise or main axis A-A, a first lateral or widthwise axis B-B perpendicular to the axis A-A, and a second lateral or heightwise axis C-C perpendicular to the axes A-A and B-B.

The first terminal electrode <NUM> is mounted in intimate electrical contact with the primary GDT end electrode <NUM>. As discussed hereinbelow, the electrodes <NUM>, E1-E21, and <NUM> are axially spaced apart to define a plurality of gaps G (twenty-two gaps G) and a plurality of cells C (twenty-two cells C) between the electrodes <NUM>, E1-E21, and <NUM>. Additionally, the primary GDT end electrode <NUM> and the first trigger end electrode <NUM> are axially spaced apart to define a primary GDT gap GP and a primary GDT cell CP between the electrodes <NUM> and <NUM>. The electrodes <NUM>, <NUM>, E1-E21, and <NUM>, the gaps G, GP, and the cells C, CP are serially distributed in spaced apart relation along the axis A-A.

Each locator member <NUM> includes a body <NUM> having a plurality of integral ribs defining locator slots <NUM>. Opposed integral locator protrusions <NUM> project laterally outward from the body <NUM>.

The locator members <NUM> may be formed of any suitable electrically insulating material. According to some embodiments, the locator members <NUM> are formed of a material having a melting temperature of at least <NUM> degrees Celsius and, in some embodiments, at least <NUM> degrees Celsius. In some embodiments, each locator member <NUM> is formed of a ceramic. In some embodiments, each locator member <NUM> includes or is formed of alumina ceramic (Al<NUM><NUM><NUM>) and, in some embodiments, at least about <NUM>% Al<NUM><NUM><NUM>. In some embodiments, each locator member <NUM> is monolithic.

The terminal electrodes <NUM>, <NUM> are substantially flat plates each having opposed, substantially parallel planar surfaces <NUM>. The electrodes <NUM>, <NUM> may be formed of any suitable material. According to some embodiments, the electrodes <NUM>, <NUM> are formed of metal and, in some embodiments, are formed of molybdenum or Kovar. According to some embodiments, each of the electrodes <NUM>, <NUM> is unitary and, in some embodiments, monolithic.

The terminal electrodes <NUM>, <NUM> are secured and sealed by the bonding layers <NUM> over and covering the openings 114A, 114B. The bonding layers <NUM> along with the seals <NUM> thereby hermetically seal the openings 114A, 114B. In some embodiments, the bonding layers <NUM> are metallization, solder or metal-based layers. Suitable metal-based materials for forming the bonding layers <NUM> may include nickel-plated Ma-Mo metallization. Suitable materials for the seals <NUM> may include a brazing alloy such as silver-copper alloy.

The trigger end electrodes <NUM>, <NUM> are substantially flat plates each having opposed, substantially parallel planar surfaces <NUM>. The electrodes <NUM>, <NUM> may be formed of any suitable material. According to some embodiments, the electrodes <NUM>, <NUM> are formed of metal and, in some embodiments, are formed of molybdenum or Kovar. According to some embodiments, each of the electrodes <NUM>, <NUM> is unitary and, in some embodiments, monolithic.

The primary GDT end electrode <NUM> is a substantially flat plate having opposed, substantially parallel planar surfaces <NUM>. The electrode <NUM> may be formed of any suitable material. According to some embodiments, the electrodes <NUM> is formed of metal and, in some embodiments, is formed of molybdenum or Kovar. According to some embodiments, the electrode <NUM> is unitary and, in some embodiments, monolithic.

The inner electrodes E1-E21 are substantially flat plates with opposed planar faces <NUM>.

According to some embodiments, each of the electrodes E1-E21 has a thickness T1 (<FIG>) in the range of from about <NUM> to <NUM> and, in some embodiments, in the range of from about <NUM> to <NUM>. According to some embodiments, each electrode E1-E21 has a height H1 in the range of from about <NUM> to <NUM> and, in some embodiments, in the range of from <NUM> to <NUM>. According to some embodiments, the width W1 of each electrode E1-E21 is in the range of from about <NUM> to <NUM>.

The electrodes E1-E21 may be formed of any suitable material. According to some embodiments, the electrodes E1-E21 are formed of metal and, in some embodiments, are formed of molybdenum, copper, tungsten or steel. According to some embodiments, each of the electrodes E1-E21 is unitary and, in some embodiments, monolithic.

The side edges of the electrodes E1-E21 are seated in opposed slots <NUM> of the locator members <NUM>, and the electrodes E1-E21 are thereby semi-fixed or floatingly mounted in the chamber <NUM>. As discussed above, the inner electrodes E1-E21 are serially positioned and distributed in the chamber <NUM> along the axis A-A. The electrodes E1-E21 are positioned such that each electrode E1-E21 is physically spaced apart from the immediately adjacent other inner electrode(s) E1-E21. The locator members <NUM> thereby limit axial displacement (along the axis A-A) and lateral displacement (along the axis B-B) of each electrode E1-E21 relative to the housing <NUM>. Each electrode E1-E21 is also captured between the trigger devices <NUM> to thereby limit lateral displacement (along axis C-C) of the electrode E1-E14 relative to the housing <NUM>.

The primary GDT end electrode <NUM> is secured in position by and axially captured between the locator flange <NUM> and the first terminal electrode <NUM>.

The first trigger end electrode <NUM> is secured in position by and axially captured between the locator flange <NUM> and the ends of the locator members <NUM> and the trigger devices <NUM>. The first trigger end electrode <NUM> is thereby axially spaced apart from the primary GDT end electrode <NUM>.

In this manner, each electrode <NUM>, <NUM>, E1-E21, and <NUM> is positively positioned and retained in position relative to the housing <NUM> and the other electrodes <NUM>, <NUM>, E1-E21, and <NUM>. In some embodiments, the electrodes <NUM>, <NUM>, E1-E21, and <NUM> are secured in this manner without the use of additional bonding or fasteners applied to the electrodes E1-E21 or, in some embodiments, to the electrodes <NUM>, <NUM>, E1-E21, and <NUM>. The electrodes <NUM>, <NUM>, E1-E21, and <NUM> may be semi-fixed or loosely captured between the housing insulator <NUM>, the locator members <NUM>, and the trigger devices <NUM>. The electrodes <NUM>, <NUM>, E1-E21, and <NUM> may be capable of floating relative to the housing insulator <NUM>, the locator members <NUM>, and/or the trigger devices <NUM> along one or more of the axes A-A, B-B, C-C to a limited degree within the housing <NUM>.

The trigger covers or devices <NUM> may be constructed in the same manner. One of the trigger devices <NUM> will be described below, it being understood that this description likewise applies to the other trigger device <NUM>.

Each trigger device <NUM> includes a substrate <NUM>, a plurality of inner trigger resistor layers or resistors <NUM>, an outer supplemental resistor layer or resistor <NUM>, and a pair of metal contacts <NUM>.

The substrate <NUM> includes a secondary wall or body <NUM> and a pair of laterally opposed integral flanges <NUM>. A recess 154A is defined in each flange <NUM>. Axially extending inner recesses or grooves <NUM> are defined in the inner side of the body <NUM>. An axially extending outer recess or groove <NUM> is defined in the outer side of the body <NUM>. The body <NUM> has axially opposed end edges 153A, 153B. The grooves <NUM>, <NUM> each extend from edge 153A to edge 153B.

The substrate <NUM> may be formed of any suitable electrically insulating material. According to some embodiments, the substrate <NUM> is formed of a material having a melting temperature of at least <NUM> degrees Celsius and, in some embodiments, at least <NUM> degrees Celsius. In some embodiments, the substrate <NUM> is formed of a ceramic. In some embodiments, the substrate <NUM> includes or is formed of alumina ceramic (Al<NUM><NUM><NUM>) and, in some embodiments, at least about <NUM>% Al<NUM><NUM><NUM>. In some embodiments, the substrate <NUM> is monolithic.

Each inner trigger resistor <NUM> is an elongate layer or strip having a lengthwise axis I-I, which may be substantially parallel to the axis A-A. The opposed ends 160A and 160B of each resistor <NUM> are located at the end edges 153A and 153B, respectively, of the substrate <NUM> so that each resistor <NUM> is substantially axially coextensive with the body <NUM>. Each resistor <NUM> extends continuously from end 160A to end 160B and from end 153A to end 153B. Each resistor <NUM> is seated in a respective one of the grooves <NUM> such that an inner interface surface <NUM> of the resistor <NUM> is substantially coplanar with an inner surface 153C of the body <NUM>.

As discussed below, each trigger resistor <NUM> includes a plurality of axially spaced apart and serially distributed surface grooves <NUM> defined in the interface surface <NUM> of the resistor <NUM>. The grooves <NUM> extend lengthwise transverse to the axis I-I. The grooves <NUM> do not extend through the full thickness T3 of the resistors <NUM>, so that a remainder portion <NUM> of each resistor <NUM> remains at the bottom of each groove <NUM>. The remainder portions <NUM> provide continuity throughout the length of the resistor <NUM>.

The trigger resistors <NUM> may be formed of any suitable electrically resistive material. According to some embodiments, the inner resistors <NUM> are formed of a mixture of aluminum and glass. However, the resistors <NUM> may be formed of any other suitable electrically resistive material.

According to some embodiments, the trigger resistors <NUM> are formed of a material having a specific electrical resistance in the range of from about <NUM> micro-ohm-meter to <NUM>,<NUM> ohm-meter.

According to some embodiments, each of the trigger resistors <NUM> has an electrical resistance in the range of from about <NUM> to <NUM> ohms.

According to some embodiments, each of the trigger resistors <NUM> has a cross-sectional area (in the plane defined by axes B-B and C-C) in the range of from about <NUM> to <NUM><NUM>.

According to some embodiments, each of the trigger resistors <NUM> has a length L3 (<FIG>) in the range of from about <NUM> to <NUM>.

According to some embodiments, each of the trigger resistors <NUM> has a thickness T3 (<FIG>) in the range of from about <NUM> to <NUM>.

According to some embodiments, each of the trigger resistors <NUM> has a width W3 (<FIG>) in the range of from about <NUM> to <NUM>.

According to some embodiments, the width W4 (<FIG>) of each groove <NUM> is in the range of from about <NUM> to <NUM> and, in some embodiments, is in the range of from about <NUM> to <NUM>.

According to some embodiments, the length L4 of each groove <NUM> extends across the entire width W3 of its resistor <NUM>. In this case, the grooves <NUM> divide or partition the interface surface <NUM> into a series of discrete interface surface sections 161A (<FIG>).

According to some embodiments, each groove <NUM> has a depth T4 (<FIG>) in the range of from about <NUM> to <NUM>. According to some embodiments, each remainder portion <NUM> has a thickness T5 (<FIG>) in the range of from about <NUM> to <NUM>.

According to some embodiments, the spacing W5 (<FIG>) between each adjacent groove <NUM> is in the range of from about <NUM> to <NUM>.

The outer resistor <NUM> is an elongate layer or strip having a lengthwise axis J-J, which may be substantially parallel to the axis A-A. The opposed ends 164A and 164B of the resistor <NUM> are located at the end edges 153A and 153B, respectively, of the substrate <NUM> so that the resistor <NUM> is substantially axially coextensive with the body <NUM>. The resistor <NUM> extends continuously from end 164A to end 164B and from end 153A to end 153B. The resistor <NUM> is seated in the outer groove <NUM>.

The outer resistor <NUM> may be formed of any suitable electrically resistive material. According to some embodiments, the outer resistor <NUM> is formed of a mixture of aluminum and glass. The resistor <NUM> may be formed of other suitable electrically resistive materials.

According to some embodiments, the outer resistor <NUM> is formed of a material having a specific electrical resistance in the range of from about <NUM> ohm-meter to <NUM>,<NUM> ohm-meter.

According to some embodiments, the outer resistor <NUM> has an electrical resistance in the range of from about <NUM> to <NUM>,<NUM> ohms.

According to some embodiments, the outer resistor <NUM> has a cross-sectional area (in the plane defined by axes B-B and C-C) in the range of from about <NUM> to <NUM><NUM>.

According to some embodiments, the outer resistor <NUM> has a length L6 (<FIG>) in the range of from about <NUM> to <NUM>.

According to some embodiments, the outer resistor <NUM> has a thickness T6 (<FIG>) in the range of from about <NUM> to <NUM>.

According to some embodiments, the outer resistor <NUM> has a width W6 (<FIG>) in the range of from about <NUM> to <NUM>.

Each contact <NUM> is U-shaped and includes a body 170A and opposed flanges 170B collectively defining a channel 170C. Each contact <NUM> is mounted on the trigger device <NUM> over an end edge 153A, 153B such that the end edge 153A, 153B is received in the channel 170C, the body 170A spans the end face of the substrate <NUM>, and the flanges 170B overlap and engage the inner and outer sides of the substrate <NUM>.

The contacts <NUM> maybe formed of any suitable material. In some embodiments, the contacts <NUM> are formed of metal such as nickel sheet.

The bonding agent <NUM> is bonded to and bonds together the locator members <NUM> and the substrates <NUM>.

According to some embodiments, the bonding agent <NUM> is an adhesive. As used herein, adhesive refers to adhesives and glues derived from natural and/or synthetic sources. The adhesive is a polymer that bonds to the surfaces to be bonded. The adhesive <NUM> may be any suitable adhesive. According to some embodiments, the bonding agent <NUM> is a glue. Suitable adhesives may include silicate adhesive.

In some embodiments, the adhesive <NUM> has a high operating temperature, above <NUM>.

The gas M may be any suitable gas, and may be a single gas or a mixture of two or more (e.g., <NUM>, <NUM>, <NUM>, <NUM>, or more) gases. According to some embodiments, the gas M includes at least one inert gas. In some embodiments, the gas M includes at least one gas selected from argon, neon, helium, hydrogen, and/or nitrogen. According to some embodiments, the gas M is or includes helium. In some embodiments, the gas M may be air and/or a mixture of gases present in air.

According to some embodiments, the gas M may comprise a single gas in any suitable amount, such as, for example, in any suitable amount in a mixture with at least one other gas. In some embodiments, the gas M may comprise a single gas in an amount of about <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% by volume of the total volume of gas present in the chamber <NUM>, or any range therein. In some embodiments, the gas M may comprise a single gas in an amount of less than <NUM>% (e.g., less than <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>%) by volume of the total volume of gas present in the chamber <NUM>. In some embodiments, the gas M may comprise a single gas in an amount of more than <NUM>% (e.g., more than <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>%) by volume of the total volume of gas present in the GDT chamber <NUM>. In some embodiments, the gas M may comprise a single gas in an amount in a range of about <NUM>% to about <NUM>%, about <NUM>% to about <NUM>%, or about <NUM>% to about <NUM>% by volume of the total volume of gas present in the chamber <NUM>. In some embodiments, the gas M comprises at least one gas present in an amount of at least <NUM>% by volume of the total volume of gas present in the chamber <NUM>. According to some embodiments, the gas M comprises helium in an amount of at least <NUM>% by volume of the total volume of gas present in the chamber <NUM>. According to some embodiments, the gas M comprises at least one gas present in an amount of about <NUM>% or more by volume of the total volume of gas present in the chamber <NUM>, and, in some embodiments, in an amount of about <NUM>% by volume of the total volume of gas present in the chamber <NUM>.

According to some embodiments, the gas M may comprise a mixture of a first gas and a second gas (e.g., an inert gas) different from the first gas with the first gas present in an amount of less than <NUM>% by volume of the total volume of gas present in the chamber <NUM> and the second gas present in an amount of at least <NUM>% by volume of the total volume of gas present in the chamber <NUM>. In some embodiments, the first gas is present in an amount in a range of about <NUM>% to about <NUM>% by volume of the total volume of gas present in the chamber <NUM> and the second gas is present in an amount of about <NUM>% to about <NUM>% by volume of the total volume of gas present in the chamber <NUM>. In some embodiments, the first gas is present in an amount of about <NUM>% by volume of the total volume of gas present in the chamber <NUM> and the second gas is present in an amount of about <NUM>% by volume of the total volume of gas present in the chamber <NUM>. In some embodiments, the second gas is helium, which may be present in the proportions described above for the second gas. In some embodiments, the first gas (which may be present in the proportions described above for the first gas) is selected from the group consisting of argon, neon, hydrogen, and/or nitrogen, and the second gas is helium (which may be present in the proportions described above for the second gas).

In some embodiments, the pressure of the gas M in the chamber <NUM> of the assembled GDT <NUM> is in the range of from about <NUM> to <NUM>,<NUM> mbar at <NUM> degrees Celsius.

According to some embodiments, the relative dimensions of the insulator <NUM>, the electrodes <NUM>, <NUM>, E1-E21, <NUM>, the trigger devices <NUM>, and the locator members <NUM> are selected such that the electrodes E1-E21 are loosely captured between the substrate <NUM> and the insulator bottom wall <NUM> to permit the electrodes <NUM>, <NUM>, E1-E21, <NUM> to slide up and down (along axis C-C) a small distance. In some embodiments, the permitted vertical float distance is in the range of from about <NUM> to <NUM>. In other embodiments, the substrates <NUM> fit snuggly against or apply a compressive load to the electrodes E1-E21.

The locator members <NUM> prevent contact between the inner electrodes E1-E21 and the trigger electrodes <NUM>, <NUM>. According to some embodiments, the minimum width W7 (<FIG>) of each gap G (i.e., the smallest gap distance between the two electrode surfaces forming the cell C) is in the range of from about <NUM> to <NUM>.

The locator flange <NUM> prevents contact between the electrodes <NUM>, <NUM>. According to some embodiments, the minimum width W8 (<FIG>) of the primary GDT gap GP (i.e., the smallest gap distance between the two electrode surfaces forming the cell CP) is in the range of from about <NUM> to <NUM>.

The GDT assembly <NUM> may be assembled as follows.

The inner electrodes E1-E21 are seated in the slots <NUM> of the locator members <NUM> to form a subassembly. The trigger members <NUM> are installed over the locator members <NUM> such that the protrusions <NUM> are received in the recesses 154A. The trigger devices <NUM> are positioned such that the interface surfaces <NUM> of the trigger resistors <NUM> face the edges of the inner electrodes E1-E21 and the top and bottom open sides of the spark gaps G between the inner electrodes E1-E21. More particularly, the interface surfaces <NUM> are contiguous with the cells C between the inner electrodes E1-E21 and define, in part, the cells C.

The bonding agent <NUM> (e.g., liquid glue) is then applied at the side joints between the locator members <NUM> and the trigger devices <NUM> to bind these components into a subassembly <NUM>.

The subassembly <NUM> and the trigger end electrodes <NUM>, <NUM> are inserted into the cavity <NUM> through the opening 114B. The primary GDT end electrode <NUM> is inserted into the cavity <NUM> through the other opening 114A. The bonding layers <NUM> and seals <NUM> are heated to bond the terminals <NUM>, <NUM> to the insulator <NUM> over the openings 114A, 114B and hermetically seal the openings 114A, 114B. According to some embodiments, the seals <NUM> are metal solder or brazings, which may be formed of silver-copper alloy, for example.

In some embodiments, the components of the GDT assembly <NUM> are disposed in an assembly chamber during the steps of sealing the openings 114A, 114B. The assembly chamber is filled with the gas M at a prescribed pressure and temperature. As a result, the gas M is thereafter captured and contained in the chamber <NUM> of the assembled GDT assembly <NUM> at a prescribed pressure and temperature. The prescribed pressure and temperature are selected such that the gas M is present at a desired operational pressure when the GDT assembly <NUM> is installed and in use at a prescribed service temperature.

The trigger resistors <NUM> are electrically connected on both ends 160A, 160B with trigger end electrodes <NUM>, <NUM> by the contacts <NUM>. In practice, small gaps may be present between contacts <NUM> and the trigger end electrodes <NUM>, <NUM> is allowed. In some embodiments, these gaps are each smaller than <NUM> and, in some embodiments, are in the range of from about <NUM> to <NUM>.

In use and operation, the first terminal <NUM> may be connected to a line or phase voltage of a single or multi-phase power system and the second terminal <NUM> may be connected to a neutral line of the single or multi-phase power system. The total arcing voltage of the modular, multi-cell GDT assembly <NUM> generally corresponds to the sum of the arcing voltage of individual series connected single cell GDTs and thus exceeds the peak value of the system voltage. As such, when the modular, multi-cell GDT assembly <NUM> is in conduction mode, the current flowing therethrough will be generally limited to the current corresponding to a surge event, such as lightning, and not from the system source.

Under normal (i.e., non-conducting) conditions, since no current is flowing through the primary GDT <NUM>, then no current is flowing through the resistors <NUM>, <NUM> or the multi-cell secondary GDT <NUM>, and the voltage across the GDT assembly <NUM> is the same as the line-neutral voltage at the second terminal <NUM>.

The operation of the GDT assembly <NUM> may be loosely regarded as having five steps. When an overvoltage is applied to the system, the overvoltage will be applied to the primary GDT <NUM>. Since the primary GDT <NUM> is electrically connected to the second terminal <NUM> by the trigger resistors <NUM> and/or the outer resistors <NUM> and the primary GDT <NUM> is therefore at the same potential as the second terminal <NUM>, the primary GDT <NUM> reacts to the high voltage and begins to conduct electrical current through the trigger resistors <NUM> and/or the outer resistors <NUM>. As a result, at the beginning of the surge, a first spark is formed in/across the cell CP of the primary GDT <NUM> and current passes through the trigger resistors <NUM> and/or the outer resistors <NUM>. In some embodiments, the resistance of each trigger resistor <NUM> is chosen such that the specific resistance of each trigger resistor <NUM> is high enough to be able to conduct (and limit) high current without damage. In some embodiments, the resistance of each trigger resistor <NUM> is in the range of from about <NUM> to <NUM> ohms.

As discussed below, the outer resistors <NUM> may be especially important at the beginning of the surge, when the current is small and is conducted through the outer resistors <NUM>. The provision of the outer resistors <NUM> provides additional time for the arcs to form between the inner electrodes E1-E21 and through the multi-cell secondary GDT <NUM> as described herein. When the current through the GDT assembly <NUM> becomes higher, typically only a relatively small portion of this current will be conducted through the outer resistors <NUM>.

In the second step, during the conducting of the current through the trigger resistors <NUM>, the current generates small sparks along the interface surfaces <NUM> of the trigger resistors <NUM>. In some embodiments, the material and formation of the resistors <NUM> is selected to promote this phenomenon, as discussed herein (e.g., using slightly non-homogenous material with some porosity). As discussed and illustrated, the interface surfaces <NUM> at which sparks are generated is located adjacent, immediately adjacent, and/or contiguous with the cells C. As a result, the sparking on the trigger resistors <NUM> moves between the resistors <NUM> and the inner electrodes E1-E21 and into the gaps G and cells C between the inner electrodes E1-E21.

In the third step, this sparking on the trigger resistors <NUM> in turn promotes, induces or establishes electrical arcing between the facing inner electrodes E1-E21. After a very short time (typically <NUM> ns or less), stable arcing or sparks are generated or formed between all of the inner electrodes E1-E21 (i.e., across each of the cells C), thereby generating sparks across each of the cells C of the multi-cell secondary GDT <NUM>.

In the fourth step, the secondary impulse current is then conducted through arcs between the inner electrodes E1-E21. The overvoltage is thus applied to the multi-cell secondary GDT <NUM>.

Substantially all of the arcs between the inner electrodes E1-E21 may be formed in the same time period (i.e., rather than strictly sequentially from first inner electrode E1 to last inner electrode E21). The time required to make all of the arcs is shortened by the resistors <NUM> and the response is quicker. In some embodiments, the arcs are formed between all of the electrodes <NUM>, E1-E21, <NUM> within a period of less than <NUM> and, in some embodiments, less than <NUM>.

In some embodiments, the current may only flow through the trigger resistors <NUM> until the multi-cell secondary GDT <NUM> begins to conduct, which may be a very short period of time. For example, current may only flow through the resistors <NUM> for a time interval that is less than <NUM> microsecond.

In the fifth step, at the end of the current impulse, the GDT assembly <NUM> extinguishes the current through the GDT assembly <NUM>. Once the overvoltage condition ceases, the GDTs <NUM>, <NUM> cease to conduct because the peak value of the system voltage is less than the total arcing voltage of the modular, multi-cell GDT assembly <NUM>.

The extinguishing step may be accomplished even when the terminal electrodes <NUM>, <NUM> are permanently connected to the network voltage. The extinguishing step is enabled by the provision by the GDT assembly <NUM> of a sufficiently high total arc voltage, which is made possible by the incorporation of multiple GDTs in the GDT assembly <NUM>. For example, a simple GDT (two electrodes, one arc) may have an arc voltage around <NUM> V. A multi-cell GDT assembly <NUM>, on the other hand, may have for example, twenty-one inner electrodes (and twenty arcs) with a resulting arc voltage around 400V. If the number of cells is high enough, the follow current through the GDT assembly <NUM> from network will be practically zero. The short circuit prospective current of the network i(i.e., the maximum available current from the network) can be very high (e.g., above <NUM> kArms). If the arc voltage of the GDT assembly <NUM> was low, the follow through current through the GDT assembly <NUM> would be high and would damage the GDT assembly <NUM>. However, with its relatively high arc voltage as discussed above, the GDT assembly <NUM> will be able to interrupt network currents without damage.

Reference is now made to <FIG>, which is an electrical schematic circuit of the modular, multi-cell GDT assembly <NUM>. As illustrated, in the electrical schematic context, the modular, multi-cell GDT assembly <NUM> may function in the same manner as a plurality of single cell GDTs that are arranged serially between terminals <NUM> and <NUM>. For example, the primary GDT end electrode <NUM> and the first trigger electrode <NUM> may function as a first single cell GDT<NUM> (the primary GDT <NUM>); the first trigger electrode <NUM> and the inner electrode E1 may function as a second single cell GDT<NUM> that is serially connected to the first single cell GDT<NUM>; the inner electrode E1 and the inner electrode E2 may function as a third single cell GDT<NUM> that is serially connected to the second single cell GDT<NUM>; and so on to the final inner electrode E21 and the trigger end electrode <NUM>, which form a final single cell GDT<NUM> in the series.

Each trigger device <NUM> may include more or fewer inner trigger resistors <NUM>. In some embodiments, the cross-sectional area of each trigger resistor <NUM> is greater than <NUM><NUM>. In some embodiments, the cross-sectional area of each resistor <NUM> is in the range of from about <NUM><NUM> to <NUM><NUM>. The number of trigger resistors <NUM> may be as low as one. In some embodiments, each trigger device <NUM> includes a plurality of resistors <NUM> and, in some embodiments, at least one trigger resistor <NUM>. The inventors have found that a higher trigger resistor cross-sectional area (for example, <NUM><NUM> or more) and a greater number of trigger resistors <NUM> (for example, <NUM> to <NUM> trigger resistors) provide better response time and better stability in use. In some embodiments, the GDT assembly <NUM> includes fewer trigger resistors <NUM> each having greater cross-section areas. In some embodiments, the optimal thickness of each trigger resistor is in the range of from about <NUM> to <NUM>.

The width W8 (<FIG>) of the gap GP of the primary GDT <NUM> can be selected to define the prescribed spark-over voltage of the primary GDT <NUM>. The spark-over voltage of the primary GDT <NUM> is also substantially the same as the prescribed spark-over voltage of the entire GDT assembly <NUM> because the current through the primary GDT <NUM> is short-circuited to the other trigger end electrode <NUM> (and, in turn, to the second terminal electrode <NUM>) through the trigger resistors <NUM>. In some embodiments, small gaps may be permitted or present between some parts of the GDT assembly <NUM> in order to ease assembly. For example, gaps may be present between the trigger end electrodes <NUM>, <NUM> and the contacts <NUM> or between the contacts <NUM> and the resistors <NUM>. These gaps may increase the spark-over voltage of the overall GDT assembly <NUM>. However, if the gaps are small (e.g., less than <NUM> and, in some embodiments, in the range of from about <NUM> to <NUM>), the spark-over voltage of the entire GDT assembly <NUM> will be only slightly increased over the spark-over voltage of the primary GDT <NUM> and typically will not significantly affect the intended operation of the GDT assembly <NUM>.

The trigger resistors <NUM> need to conduct high current and they need to have some resistance (typically in the range of from <NUM> to <NUM> ohms). If specific resistance is low (e.g., metals), the resistors <NUM> need to be thin layers and at high current they will be damaged. The current capability is improved if, for a resistor of a given resistance, the cross-sectional area (and mass) of the resistor <NUM> is increased. Further, the resistor <NUM> is preferably very immune to high temperature plasma, which is formed between inner electrodes E1-E21 and is in direct contact with resistors <NUM>. As discussed herein, in some embodiments, the resistors <NUM> are non-homogenous with some porosity to generate sparks on their interface surfaces <NUM> for ignition of arcs between the inner electrodes E1-E21 (in the cells C). The resistors <NUM> may be formed of graphite, which can reach proper resistance and cross-sectional area. However, graphite typically will not survive in contact with plasma, and may be damaged by sparks on the interface surfaces <NUM>.

In some embodiments, in order to address the aforementioned objectives and concerns, the resistors <NUM> are formed of a material including a combination of aluminum and glass. In some embodiments, the aluminum and glass material of the resistors <NUM> is sintered into the grooves <NUM> to form the resistors <NUM>. The aluminum and glass material can be sintered at high temperature to form trigger resistors <NUM> with all of the desired properties. Advantageously, the resistors <NUM> of this type can be formed to have selected different specific resistances, depending on the design criteria of a given GDT assembly <NUM> (e.g., by deliberately selecting and using corresponding different weight ratios of aluminum and glass). In some embodiments, the composition of the resistors <NUM> includes at least <NUM>% by weight of aluminum and at least <NUM>% by weight of glass.

As discussed above, the non-homogeneity and porosity of each trigger resistor <NUM> (in particular, the interface surface <NUM> thereof) helps to establish electrical arcs between the inner electrodes E1-E21. Additionally, the narrow cross-wise grooves <NUM> will promote or create arcs between the inner electrodes E1-E21.

In some embodiments, the grooves <NUM> are formed in the resistors <NUM> by laser cutting the resistors <NUM>. The depth T4 of laser cut grooves <NUM> is less than the thickness T3 of the trigger resistor <NUM> and the groove width W4 (<FIG>) should be in the range of from about <NUM> to <NUM>. In some embodiments, the number of grooves <NUM> is similar to number of inner electrodes (about <NUM>, for example). Due to the small width W4 of the grooves <NUM>, the final resistance of each resistor <NUM> is still very similar to the resistance of the initial resistor without cut grooves <NUM>. But the grooves <NUM> cause formation of small electrical arcs that accelerate and stabilize ignition of arcs between inner electrodes E1-E21.

Another benefit of the grooves <NUM> is that the grooves <NUM> also extinguish current through the trigger resistors <NUM>. When current through a resistor <NUM> is high, only a small part of the current is conducted through the resistor <NUM> at each groove <NUM> (i.e., through the remainder portion <NUM> below the groove <NUM>) because the cross-sectional area of the remainder portion <NUM> is much smaller than the cross-sectional areas of the resistor <NUM> between the grooves <NUM>. So the other part of the current is conducted through arcing from one side of each groove <NUM> to the other side of the groove <NUM>. Practically that means, when current through a resistor <NUM> is high, the arcs start to limit the current. This may provide two advantages. The trigger resistors <NUM> are less loaded, and also the current at the end of surge through the resistors <NUM> is smaller. Less loading means more stable condition of resistors and longer life time. Smaller current after surge means easier extinguishing of follow current from network.

The contacts <NUM> can help to ensure reliable and consistent operation of the GDT assembly <NUM>. In practice, the sintering process of forming the trigger resistors <NUM> may not be a very accurate process. For this reason, unwanted gaps can be established between trigger resistors <NUM> and the trigger end electrodes <NUM>, <NUM>. If the gap is too broad, then additional voltage will be required for ignition of the GDT assembly <NUM> and, consequently, the protection level provided by the GDT assembly <NUM> will be diminished. The metal contacts <NUM> help to ensure good electrical continuity between the resistors <NUM> and the trigger end electrodes <NUM>, <NUM> by contacting each and conducting current therebetween. In some embodiments, each contact <NUM> is formed in the shape of a letter U, the U-shaped contact <NUM> is placed over an end edge 153A of the substrate <NUM>. The resistor layers <NUM>, <NUM> are then mounted on the substrate <NUM> over and in contact with the flanges 170B of the contact <NUM>. In some embodiments, the resistor layers <NUM>, <NUM> are sintered onto the substrate <NUM> and the flanges 170B.

The trigger resistors <NUM> are exposed to very high temperatures of plasma, which is formed during high current surges through the GDT assembly <NUM>. In addition, the trigger resistors <NUM> need to conduct high current in the initial stage of the surge. The damage to the trigger resistors <NUM> can cause slower response before first spark formation. For formation of first spark (i.e., the spark across the spark gap GP of the primary GDT <NUM>), the GDT assembly <NUM> needs a voltage on the first and second terminal electrodes <NUM>, <NUM> that is at least equal to the spark-over voltage of the primary GDT <NUM>. But if the trigger resistors <NUM> are damaged, they may not make a sufficient short circuit from the trigger end electrode <NUM> to the trigger end electrode <NUM>, and the first response can be delayed thereby.

This potential problem is addressed by the additional outer resistor <NUM> on the back or outer side of each substrate <NUM>. The outer side of the substrate <NUM> may be regarded as the safe side because it is not exposed to hot plasma and the outer resistor <NUM> therefore cannot be damaged by plasma. The resistance of each outer resistor <NUM> can be higher than that of the trigger resistors <NUM>. For example, the resistance of each outer resistor <NUM> can be in the range of from about <NUM> to <NUM> ohms. Due to this, the currents through the outer resistors <NUM> are not very high and the outer resistors <NUM> can survive surges without significant damage. High resistance is allowed for the outer resistors <NUM> because the outer resistors <NUM> are needed only at the beginning of surge when total current is low. After a short time period, most of current is then conducted through trigger resistors <NUM>.

In order to fix the inner electrodes E1-E21 in stable positions, it is preferable to use at least two properly shaped rigid insulator members. In the example GDT assembly <NUM>, the inner electrodes E1-E21 are inserted between two ceramic locator members <NUM> and covered by two ceramic trigger devices or covers <NUM>. After assembling of the parts <NUM>, <NUM> and E1-E21 together, the resulting subassembly may be very difficult to handle without breaking up. This problem is addressed by the bonding agent (adhesive) <NUM>, which can be safely used in production of the GDT assembly <NUM>. In some embodiments, the glue <NUM> is a dense liquid of alumina fine powder mixed with potassium or sodium silicate.

In order to perform properly and consistently, the hermetically sealed GDT assembly <NUM> should not leak gases into or out of the chamber <NUM>. Even if only a small leak of gas occurs due to a crack in the housing insulator <NUM>, the GDT assembly <NUM> may not be useful any longer. Such cracks may be induced by forces applied to the ceramic housing insulator <NUM> or high temperature gradients. These forces would be experienced if the inner electrodes E1-E21 were in direct contact with the ceramic housing insulator <NUM>. In this case, the housing insulator <NUM> would be exposed to hot plasma during high current surges. Also these forces would be experienced if the housing insulator <NUM> were in contact with the metal inner electrodes E1-E21, which can become very hot. At very high surge currents, some melting of the inner electrodes E1-E21 may be presented. The high temperatures of plasma and the inner electrodes, and also thermal expansion of the inner electrodes E1-E21, could cause cracks in the ceramic housing insulator <NUM>. In addition, during impulses highly ionized plasma is generated in the cells C, which causes high gas pressures, which would press directly on the housing insulator <NUM>.

To address or prevent these problems, the inner electrodes E1-E21 are packed from all lateral sides into the additional reinforcement components <NUM>, <NUM>, each of which include a ceramic body or substrate. The ceramic trigger device substrates <NUM>, with the help of the ceramic locator members <NUM>, protect the ceramic housing insulator <NUM> against dangerous conditions of high temperatures. In practice, there may typically be a small gap (e.g., less than <NUM> and, in some embodiments, in the range of from about <NUM> to <NUM>) between the ceramic trigger device substrates <NUM> and the housing insulator <NUM>. With this double wall structure approach, the temperature gradient and pressure forces on the housing insulator <NUM> are reduced or minimized.

Advantageously, the plurality of spark gaps G, GP are housed or enveloped in the same housing <NUM> and chamber <NUM>. The plurality of cells C and spark gaps G defined between the electrodes <NUM>, <NUM>, E1-E21, <NUM> are in fluid communication so that they share the same mass or volume of gas M. By providing multiple electrodes, cells and spark gaps in one common or shared chamber <NUM>, the size and number of parts can be reduced. As a result, the size, cost and reliability of the GDT assembly <NUM> can be reduced as compared to a plurality of individual GDTs connected in series.

Moreover, the trigger devices <NUM> are housed or enveloped in the same housing <NUM> and chamber <NUM> as the electrodes <NUM>, <NUM>, E1-E21, <NUM>, and are likewise in fluid communication with the same mass of gas M. As a result, the size, cost and reliability of the GDT assembly <NUM> can be reduced as compared to a plurality of individual GDTs connected in series with an external trigger circuit.

The floating or semi-fixed mounting of the electrodes <NUM>, <NUM>, E1-E21, <NUM> in the housing <NUM> can facilitate ease of assembly.

The performance attributes of the GDT assembly <NUM> can be determined by selection of the gas M, the pressure of the gas M in the chamber <NUM>, the dimensions and geometrics of the electrodes <NUM>, <NUM>, E1-E21, <NUM>, the geometry and dimensions of the housing <NUM>, the sizes of the gaps G, GP, and/or the electrical resistances of the resistors <NUM>, <NUM>.

With reference to <FIG>, a GDT assembly <NUM> according to further embodiments is shown therein. <FIG> shows only a subassembly <NUM> of the GDT assembly <NUM> including the inner electrodes E1-E24 and a pair of opposed trigger covers or devices 250A, 250B. The GDT assembly <NUM> may be constructed and operate in the same manner as the GDT assembly <NUM> except that, in the GDT assembly <NUM>, the locator members <NUM> are integrated into the trigger device 250A.

More particularly, the lower trigger device 250A includes a substrate 252A. The substrate 252A includes a body 253A and flanges 254A. Ribs and corresponding locator slots <NUM> are defined in the inner sides of the flanges 254A. The inner electrodes E1- E24 are seated and retained in the slots <NUM> in same manner as they are seated in the slots <NUM> of the GDT assembly <NUM>.

The upper trigger device 250B includes a substrate 252B. The substrate 252A includes a body 253B and flanges 254B. The upper trigger device 250B is mounted on the inner electrodes E1- E24 and the lower trigger device 250A such that the flanges 254B are seated in axially extending channels 254C defined in the lower trigger device 250A.

The substrates 252A, 252B may be formed of the same material(s) as described for the substrate <NUM>. In some embodiments, each substrate 252A, 252B is monolithic.

The trigger devices 250A, 250B also provide a double wall structure (along with the surrounding wall of the insulator housing <NUM>, not shown in <FIG>) and the corresponding benefits discussed above.

As illustrated in <FIG>, a GDT assembly as described herein (e.g., the GDT assembly <NUM>) may have fewer, wider inner grooves <NUM> and inner resistor layers <NUM>. As also illustrated in <FIG>, a GDT assembly as described herein (e.g., the GDT assembly <NUM>) may have more than one outer groove <NUM> and more than one outer resistor layer <NUM>.

With reference to <FIG>, a GDT assembly <NUM> according to further embodiments is shown therein. The GDT assembly <NUM> may be constructed and operate in the same manner as the GDT assembly <NUM> except as discussed below. The GDT assembly <NUM> includes a housing insulator <NUM>, seals <NUM>, bonding layers <NUM>, a first terminal electrode <NUM>, and a second terminal electrode <NUM> corresponding to the components <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, respectively, of the GDT assembly <NUM>. The GDT assembly <NUM> includes a multi-cell secondary GDT <NUM> corresponding to the multi-cell secondary GDT <NUM>. The secondary GDT <NUM> has trigger end electrodes <NUM>, <NUM> corresponding to the electrodes <NUM>, <NUM>.

The GDT assembly <NUM> includes a primary GDT <NUM> in place of the primary GDT <NUM> of the GDT assembly <NUM>. The primary GDT <NUM> functions generally in the same manner and for the same purpose as the primary GDT <NUM>, but may provide certain advantages in operation.

The primary GDT <NUM> includes an inner electrode <NUM>, an outer shield electrode <NUM>, a connection medium (e.g., brazing alloy) <NUM>, an annular first insulator member <NUM>, an annular second insulator member <NUM>, and the gas M.

The inner post electrode <NUM> has the form of a cylindrical post. The post electrode <NUM> has an outer end surface 372A and a cylindrical side surface 372B. The inner end of the inner electrode <NUM> is electrically and mechanically connected directly to the trigger end electrode <NUM> by the brazing alloy <NUM>.

The outer shield electrode <NUM> has the form of a cylindrical cup defining an inner cavity 374C. The outer shield electrode <NUM> includes a planar end wall 374A and an annular side wall 374B. The shield electrode <NUM> is seated in a cavity <NUM> formed in the end of the housing insulator <NUM>. The shield electrode <NUM> is axially captured and positioned relative to the post electrode <NUM> by the first terminal electrode <NUM> and an integral ledge 313A of the housing insulator <NUM>.

The electrodes <NUM>, <NUM> are thereby maintained with the post electrode <NUM> disposed in the cavity 374C. A gap G3 is defined between the end surface 372A and the end wall 374A. A gap G4 is defined between the circumferential surface 372A and the side wall 374B. In this way, a GDT chamber or cell CP3 is formed in the cavity 374C between the electrodes <NUM>, <NUM>. The cell CP3 is filled with the gas M.

The first insulator member <NUM> is mounted around an inner base of the post electrode <NUM> between the trigger end electrode <NUM> and the circumferential surface 372A. The second insulator member <NUM> mounted around an inner base of the post electrode <NUM> between the first insulator member <NUM> and the circumferential surface 372A.

In some embodiments, the insulator members <NUM>, <NUM> are formed of the same material(s) as described above for the substrates <NUM>.

The electrodes <NUM>, <NUM> may be formed of any suitable material. According to some embodiments, the electrodes <NUM>, <NUM> are formed of metal. According to some embodiments, the electrodes <NUM>, <NUM> are formed of a metal including copper-tungsten alloy. According to some embodiments, the electrodes <NUM>, <NUM> are formed of a metal including at least <NUM>% by weight of copper-tungsten alloy. According to some embodiments, the electrodes <NUM>, <NUM> are each unitary and, in some embodiments, monolithic.

In the case of a primary GDT employing two flat electrodes (e.g., the primary GDT <NUM> including flat electrodes <NUM> and <NUM>), the flat electrodes work properly at low current impulses. But at high current impulses, such a primary GDT may not extinguish as needed. The cylindrically shaped primary GDT <NUM> addresses this problem by providing more stable operation and improve extinguishing of follow current.

The first insulator member <NUM> prevents sparking directly between the shield electrode <NUM> and the trigger end electrode <NUM>. The second insulator member <NUM> prevents formation of a conductive layer of evaporated electrode material between the post electrode <NUM> and the shield electrode <NUM>.

With reference to <FIG>, a GDT assembly <NUM> according to further embodiments is shown therein. The GDT assembly <NUM> may be constructed and operate in the same manner as the GDT assembly <NUM> except as discussed below. The GDT assembly <NUM> includes a multi-cell secondary GDT <NUM> corresponding to the multi-cell secondary GDT <NUM> and the multi-cell secondary GDT <NUM>.

The GDT assembly <NUM> includes a primary GDT <NUM> in place of the primary GDT <NUM> of the GDT assembly <NUM>. The primary GDT <NUM> functions in the same manner and for the same purpose as the primary GDT <NUM>, but can be more easily preassembled for assembly with the multi-cell secondary GDT <NUM> and the housing insulator <NUM> to form the GDT assembly <NUM>.

The primary GDT <NUM> includes an inner electrode <NUM>, an outer shield electrode <NUM>, a first bonding layer 419A (e.g., metallization), a second bonding layer 419B (e.g., metallization), a first connection medium 418A (e.g., brazing alloy), a second connection medium 418B (e.g., brazing alloy), an annular first insulator member <NUM>, an annular second insulator member <NUM>, and a gas M2.

The components <NUM>, <NUM>, and <NUM> may be constructed in the same manner as the components <NUM>, <NUM>, and <NUM> of the primary GDT <NUM>. The bonding layers 419A, 419B may be formed of the same materials as described for the bonding layers <NUM>. The connection mediums 418A, 418B may be formed of the same materials as described for the seals <NUM>.

The insulator member <NUM> corresponds to the insulator member <NUM> except that the insulator member <NUM> includes a base 477B and an integral extended annular flange 477A. The bonding layers 419A, 419B are disposed on the end faces of the flange 477A and the base 477B.

The end face of the flange 477A is bonded to the inner end face 474D of the side wall of the shield electrode <NUM> by the bonding layer 419A and the connection medium 418A. The insulator member <NUM> is captured between the insulator member <NUM> and an enlarged head of the post electrode <NUM>. The inner end of the post electrode <NUM> is bonded to the insulator member <NUM> by the bonding layer 419B and the connection medium 418B. The bonding layer 419B forms a seal between the insulator member <NUM> and the side perimeter of an endmost section of the post electrode <NUM>. The connection medium 418B is melted to make a seal between the components 419B, <NUM>. The inner end face 472C of the post electrode <NUM> is held in close contact with the trigger end electrode <NUM>. A chamber or cell CP3 is defined within the shield electrode <NUM> and the insulator member <NUM>. The cell CP3 is filled with the gas M2.

In some embodiments, the flange 477A is bonded to the shield electrode <NUM> as described, with the insulator member <NUM> and the post electrode <NUM> captured therein, to form a module or subassembly <NUM> as shown in <FIG>. The preassembled subassembly <NUM> is then inserted into a cavity <NUM> of the housing insulator <NUM> and the electrode <NUM> makes contact with the trigger end electrode <NUM>. A small gap (e.g., less than <NUM>, and in some embodiments, in the range of from about <NUM> to <NUM>) may be present between the post electrode <NUM> and the trigger end electrode <NUM>.

In some embodiments, the subassembly <NUM> is provided with a small gap or hole to allow gases to leak into and out from the cell CP3. In some embodiments, the cell CP3 is filled through the hole or gap with the same gas M as the chamber <NUM> of the multi-cell secondary GDT <NUM> (i.e., the gas M2 is the gas M).

In some embodiments, the subassembly <NUM> is formed such that the chamber or cell CP3 is hermetically sealed. In this case, the connection layers 418A, 418B (e.g., brazing alloys) may be selected to have higher melting points than the seals <NUM> (e.g., brazing alloys). The chamber CP3 is thus sealed from the multi-cell GDT chamber <NUM>. The chamber CP3 is filled with a different gas mixture M2 than the gas mixture M used in the chamber <NUM> of the multi-cell secondary GDT <NUM>. The benefit of this is that the manufacturer can use special gases for gas M with relatively higher arc voltage in the multi-cell secondary GDT <NUM> to ensure better extinguishing, while using different gas M2 in the primary GDT <NUM> to optimize the spark-over voltage of primary GDT <NUM>.

With reference to <FIG>, a GDT assembly <NUM> according to further embodiments of the invention is shown therein. The GDT assembly <NUM> may be constructed and operate in the same manner as the GDT assembly <NUM> except as discussed below. The GDT assembly <NUM> includes a multi-cell secondary GDT <NUM> corresponding to the multi-cell secondary GDT <NUM> and the multi-cell secondary GDT <NUM>.

The GDT assembly <NUM> includes a primary GDT <NUM> in place of the primary GDT <NUM> of the GDT assembly <NUM>. The primary GDT <NUM> functions in the same manner and for the same purpose as the primary GDT <NUM>. The primary GDT <NUM> can be preassembled for assembly with the multi-cell secondary GDT <NUM> and the housing insulator <NUM> to form the GDT assembly <NUM>. The GDT assembly <NUM> includes a bonding layer 519C and a connection medium 518C that seals the primary GDT <NUM> to the housing insulator <NUM>.

The primary GDT <NUM> includes a terminal electrode <NUM>, a base electrode <NUM>, an inner electrode <NUM>, an outer shield electrode <NUM>, a first bonding layer 519A (e.g., metallization), a second bonding layer 519B (e.g., metallization), a first connection medium 518A (e.g., brazing alloy), a second connection medium 518B (e.g., brazing alloy), an annular first insulator member <NUM>, an annular second insulator member <NUM>, and a gas M3.

The components <NUM>, <NUM>, and <NUM> may be constructed in the same manner as the components <NUM>, <NUM>, and <NUM> of the primary GDT <NUM>. The bonding layers 519A, 519B may be formed of the same materials as described for the bonding layers <NUM>. The connection mediums 418A, 518B may be formed of the same materials as described for the seals <NUM>.

The insulator member <NUM> corresponds to the insulator member <NUM> except that the integral extended annular flange 577A of the insulator member <NUM> circumferentially surrounds the shield electrode <NUM> and extends axially to the outer end of the shield electrode <NUM>. The bonding layers 519A, 519B are disposed on the end faces of the flange 577A and the base 577B.

The end face of the flange 577A is bonded to an inner end face of the terminal electrode <NUM> by the bonding layer 519A and the connection medium 518A. The insulator member <NUM> is captured between the insulator member <NUM> and an enlarged head of the post electrode <NUM>. The end face of the base 577B is bonded to the base electrode <NUM> by the bonding layer 519B and the connection medium 518B. The inner end face 572C of the post electrode <NUM> is directly secured and electrically connected to the base electrode <NUM> by the bonding layer 519B and the connection medium 518B. When the GDT assembly <NUM> is assembled, the base electrode <NUM> is in electrical contact with the trigger end electrode <NUM>.

A chamber or cell CP4 is defined within the shield electrode <NUM> and the insulator member <NUM>. The cell CP4 is filled with the gas M3.

In some embodiments, the flange 577A is bonded to the terminal electrode <NUM> as described, with the insulator member <NUM> and the post electrode <NUM> captured therein, and base electrode <NUM> is bonded to the insulator member <NUM>, to form a module or subassembly <NUM> as shown in <FIG>. The preassembled subassembly <NUM> is then bonded to the housing insulator <NUM> by bonding the base electrode <NUM> to the housing insulator <NUM>. Alternatively, the base electrode <NUM> can be bonded to the insulator <NUM> after the base electrode <NUM> has been bonded to the insulator <NUM>. The housing <NUM> and the remainder of the multi-cell secondary GDT <NUM> may be preassembled to form a secondary GDT subassembly <NUM>. The primary GDT subassembly <NUM> may thereafter be mounted on the secondary GDT subassembly <NUM> as described above (i.e., by first bonding the base electrode <NUM> to the insulator member <NUM>, or by first bonding the base electrode to the housing <NUM>). A seal 518D (e.g., brazing alloy) between the base electrode <NUM> and the housing <NUM> hermetically seals the housing chamber <NUM>.

In some embodiments, the subassembly <NUM> is formed such that the chamber or cell CP4 is hermetically sealed. In some embodiments, the cell CP4 is filled with the same gas M3 as the multi-cell GDT <NUM>. For example, the primary GDT <NUM> may be assembled in same gas-filled manufacturing chamber as all other components so that the same gas is captured in both the chamber CP4 and the housing chamber <NUM>.

In some embodiments, the chamber CP4 is filled with a different gas mixture M3 than the gas mixture M used in multi-cell secondary GDT <NUM>, and the gases M, M3 may be selected to provide benefits as discussed above with regard to the GDT assembly <NUM>.

Accordingly, the GDT assembly <NUM> incorporates two different chambers (i.e., chamber CP4 for the primary GDT <NUM>, and chamber <NUM> for the multi-cell secondary GDT <NUM>). The primary GDT <NUM> can be preassembled and easily soldered or brazed on the base electrode <NUM>.

Compared to the GDT assemblies <NUM>, <NUM>, the GDT assembly <NUM> may allow much faster temperature increase if the GDT assembly <NUM> fails. That is, the primary GDT <NUM> will heat faster than the primary GDT <NUM>, for example. In this case, the GDT assembly <NUM>, <NUM>, <NUM> will normally go to short circuit. The temperature will increase faster on the outer surface of the externally mounted primary GDT <NUM> than on the outer surface of the housing of the overall GDT assembly <NUM>, <NUM>, <NUM>. This effect can be used to more quickly signal that the GDT assembly has failed or to more quickly actuate a disconnect mechanism that disconnects the GDT assembly from network.

For example, as shown in <FIG>, the GDT assembly <NUM> can be connected to a line L of the network by a disconnect mechanism <NUM>. In some embodiments, the disconnect mechanism <NUM> is a thermal disconnect mechanism that responds to the heat generated in the GDT assembly <NUM> to disconnect the GDT assembly <NUM> from a circuit. In the illustrated embodiment, the disconnect mechanism <NUM> includes a spring contact 579A and meltable solder 579B securing an end of the spring contact to the terminal electrode <NUM>. When the GDT assembly <NUM> fails (e.g., the multi-cell secondary GDT <NUM> short-circuits internally), the primary GDT <NUM> will quickly heat up until the solder 579B melts sufficiently to release the spring contact 579A (which is biased or loaded away from the terminal electrode <NUM>). The GDT assembly <NUM> is thereby disconnected from the line L.

<FIG> shows a GDT assembly <NUM> according to further embodiments in exploded view. The GDT assembly <NUM> is constructed and operates in the same manner as the GDT assembly <NUM>, except as follows.

The GDT assembly <NUM> includes a multi-cell secondary GDT <NUM> and a primary GDT <NUM>.

The multi-cell secondary GDT <NUM> is of the same construction and operation as the multi-cell secondary GDT <NUM>. The secondary GDT <NUM> is embodied in a subassembly 29A that includes an outer electrode <NUM> corresponding to the base electrode <NUM>.

The primary GDT <NUM> is embodied in a preassembled module or subassembly 28A in place of the subassembly <NUM>. The primary GDT <NUM> may be of the same construction and operation as the primary GDT <NUM>, except that the primary GDT <NUM> includes a base electrode <NUM> in place of the base electrode <NUM>. The primary GDT <NUM> is mechanically and electrically connected to the secondary GDT by bonding (e.g., soldering) the base electrode <NUM> to the outer electrode <NUM>. The base electrode <NUM> of the subassembly 28A conforms to the shape of the insulator member <NUM> and the terminal electrode <NUM>. Other shapes for the electrodes <NUM>, <NUM> may be used.

With reference to <FIG>, a trigger device <NUM> according to further embodiments is shown therein. The trigger device <NUM> may be constructed and operate in the same manner as the trigger device <NUM> except as discussed below.

The trigger device <NUM> includes a substrate <NUM> and a plurality of inner trigger resistor layers or resistors <NUM> corresponding to the substrate <NUM> and the resistors <NUM>.

The trigger device <NUM> further includes a plurality or set <NUM> of resistor protection layers <NUM> covering the inner sides of the resistors <NUM>. The resistor protection layers <NUM> collectively form an electrically insulating layer covering major surfaces of the resistors <NUM> that would otherwise be exposed to the GDT chamber <NUM> and the gas M contained therein.

In some embodiments, each resistor protection layer <NUM> is disposed in direct contact with one or more of the inner surfaces <NUM> of the resistors <NUM>. In some embodiments, each resistor protection layer <NUM> is bonded to one or more of the inner surfaces <NUM> of the resistors <NUM>.

In some embodiments, each resistor protection layer <NUM> is an elongate layer or strip that extends transversely across the trigger device <NUM> and covers portions of a plurality of the resistors <NUM>. In some embodiments, each resistor protection layer <NUM> extends transversely (relative to the longitudinal axis I-I) across the trigger device <NUM> and covers portions of all of the resistors <NUM>.

The layer <NUM> includes a plurality of axially spaced apart and serially distributed channels or gaps <NUM> defined between the adjacent edges of the resistors <NUM>. The gaps <NUM> extend lengthwise transverse to the axis I-I. Each gap <NUM> is aligned with a respective one of the resistor grooves <NUM> so that the groove <NUM> is exposed through the gap <NUM>.

In use, the resistors <NUM> of the GDT assembly <NUM>, for example, may be exposed to hot plasma. In some cases (e.g., strong current impulses), the plasma can damage the resistors <NUM> and change the electrical conductivity of the resistors <NUM>. In operation, the resistor protection layers <NUM> serve to protect the resistors <NUM> from the plasma.

The gaps <NUM> enable the surfaces of the resistors <NUM> exposed within the grooves <NUM> to contact the gas within the chamber of the gas discharge tube assembly. This can enable the gas discharge tube assembly to achieve a short response time in the case of an overvoltage.

In some embodiments, each resistor protection layer <NUM> has a thickness T9 (<FIG>) of at least about <NUM>, in some embodiments, in the range of from about <NUM> to <NUM>, and, in some embodiments, in the range of from about <NUM> to <NUM>.

In some embodiments, each resistor protection layer <NUM> has a width W9 (<FIG>) of at least about <NUM> and, in some embodiments, in the range of from about <NUM> to <NUM>.

In some embodiments, the width W11 (<FIG>) of each gap <NUM> is substantially the same as the width W10 (<FIG>) of the adjacent groove <NUM>.

The protection layers <NUM> are formed of an electrical insulator (i.e., a substantially electrically nonconductive or insulating material). The protection layers <NUM> are formed of a material having a lower electrical conductivity value than the electrical conductivity of the resistors <NUM>. In some embodiments, the electrical conductivity of the material of the resistors <NUM> is at least <NUM> times the electrically conductivity of the protection layers <NUM>.

In some embodiments, the protection layers <NUM> include potassium or sodium silicate. In some embodiments, the protection layers <NUM> include alumina fine powder. The alumina may improve stability because alumina powder is very stable at high temperatures (e.g., temperatures caused by plasma).

The protection layers <NUM> may be mounted on the resistors <NUM> using any suitable technique. In some embodiments, the protection layers <NUM> are deposited on the resistors <NUM>. In some embodiments, an enlarged layer (e.g., a single layer) of the electrically nonconductive material is mounted on the resistors <NUM>, and the gaps or channels <NUM> are then cut into the nonconductive layer. In some embodiments, the gaps or channels <NUM> are laser cut into the nonconductive layer.

With reference to <FIG>, a surge protective device (SPD) module <NUM> according to embodiments of the invention is shown therein. The SPD module <NUM> includes a GDT assembly <NUM> according to further embodiments of the invention is shown therein. However, it will be appreciated that the SPD module <NUM> may include a GDT assembly according to other embodiments (e.g., the GDT assembly <NUM> or <NUM>) in place of the GDT assembly <NUM>. It will also be appreciated that the GDT assembly <NUM> may be used in other applications (e.g., not in an SPD module).

The GDT assembly <NUM> is constructed and operates in the same manner as the GDT assembly <NUM>, except as discussed below. The GDT assembly <NUM> includes a multi-cell secondary GDT <NUM> (corresponding to the secondary GDT <NUM>) and a primary GDT <NUM>.

The multi-cell secondary GDT <NUM> is of the same construction and operation as the multi-cell secondary GDT <NUM>. The secondary GDT <NUM> is embodied in a subassembly 29B that includes an outer electrode <NUM> corresponding to the outer electrode <NUM> and the base electrode <NUM>.

The primary GDT <NUM> is embodied in a preassembled module or subassembly 28B. The subassembly 28B is constructed and operates in the same manner as the subassemblies <NUM> and 28A (<FIG>), except as follows.

The primary GDT <NUM> includes a terminal electrode <NUM>, a base electrode <NUM>, an inner post electrode <NUM>, a first or outer bonding layer 819A (e.g., metallization), a second or outer bonding layer 819B (e.g., metallization), a first connection medium 818A (e.g., brazing alloy), a second connection medium 818B (e.g., brazing alloy), a third connection medium 818C (e.g., brazing alloy), an annular first insulator member <NUM>, an annular second insulator member <NUM>, a third annular insulator member <NUM>, and a gas M.

The subassembly 28B can be used and installed on the multi-cell secondary GDT <NUM> by bonding (e.g., soldering) the base electrode <NUM> to the outer electrode <NUM> as described above with regard to the subassembly 28A. For example, the primary GDT <NUM> may be mechanically and electrically connected to the secondary GDT <NUM> by soldering the base electrode <NUM> to the outer electrode <NUM>.

The multi-cell secondary GDT <NUM> is embodied in a subassembly 29B that includes an outer electrode <NUM> corresponding to the base electrode <NUM>. The multi-cell secondary GDT <NUM> is of the same construction and operation as the multi-cell secondary GDT <NUM>, except as follows.

The secondary GDT <NUM> further includes a housing insulator <NUM>, seals <NUM> (e.g., brazing alloy), locator members <NUM>, a set E of inner electrodes, a terminal electrode <NUM>, a first trigger end electrode <NUM>, and a second trigger end electrode <NUM>, corresponding to components <NUM>, <NUM>, <NUM>, E, <NUM>, <NUM>, and <NUM> of the GDT assembly <NUM>.

When the GDT assembly <NUM> is assembled, the base electrode <NUM> of the primary GDT <NUM> is in electrical contact with the outer electrode <NUM>. The outer electrode <NUM> is in turn in electrical contact with a conductive (e.g., metal) spacer <NUM>. The spacer <NUM> is in turn in electrical contact with the trigger end electrode <NUM>. The chamber <NUM> is hermetically sealed by the seals <NUM> between the outer electrodes <NUM>, <NUM> and the ends of the housing insulator <NUM>.

It will be appreciated that the GDT assembly <NUM> thus includes a trigger system <NUM> that operates in the same manner as the trigger system <NUM>. However, the trigger system <NUM> differs from the trigger system <NUM> of the GDT assembly <NUM> in that the trigger system <NUM> includes an outer supplemental resistor layer or resistor <NUM>. In some embodiments and as shown, the outer resistor <NUM> is provided in place of the resistor <NUM> (i.e., no corresponding outer resistor is provided within the insulator housing on a side of the trigger devices opposite the inner electrodes).

The outer resistor <NUM> is an elongate layer or strip seated in an outer groove <NUM> in the exterior surface 810A of the housing insulator <NUM>. The outer resistor <NUM> has a lengthwise axis J-J, which may be substantially parallel to the lengthwise axis A-A of the secondary GDT <NUM>. The resistor <NUM> is substantially axially coextensive with the housing insulator <NUM>.

The opposed ends 864A and 864B of the resistor <NUM> extend beyond the ends of the housing <NUM> and overlap the terminal electrodes <NUM> and <NUM> (corresponding to terminal electrodes <NUM> and <NUM>, respectively). The outer resistor <NUM> extends continuously from end 864A to end 864B. The ends 864A and 864B engage and are bonded to the terminal electrodes <NUM> and <NUM>, respectively, to electrically connect the outer resistor <NUM> to the terminal electrodes <NUM> and <NUM> in the same manner the outer resistor <NUM> is electrically connected to the terminal electrodes <NUM> and <NUM> in the GDT assembly <NUM>.

In use, the outer resistor <NUM> operates in the same manner as described above for the outer resistor <NUM> to conduct current between the primary GDT <NUM> and the terminal electrode <NUM>. However, the outer resistor <NUM> located outside of the secondary GDT chamber <NUM> containing the gas M can provide benefits over the resistor <NUM> located in the chamber <NUM>.

In the case of the resistor <NUM>, it is possible to develop bad contacts between two or more of the terminal electrodes <NUM>, <NUM>, the trigger end electrodes <NUM>, <NUM>, and the metal contacts <NUM>. Gaps may be introduced between these parts during assembly or during surge impulses. These gaps extend the response time of the primary GDT <NUM> because small sparks must be created to connect the electrical path between the primary GDT and the terminal electrode <NUM> at the outset of an overvoltage event. Consequently, the effective protection level of the GDT assembly can be too high.

With the outer resistor <NUM> on the outside of the insulation housing <NUM> i(e.g., ceramic), this problem can be reduced or eliminated. By locating the outer resistor <NUM> on the insulation housing <NUM>, onto which the electrodes <NUM> and <NUM> are affixed, the reliable contact between the outer resistor <NUM> and the electrodes <NUM> and <NUM> can be more easily ensured. As a result, more reliable electrical continuity between the electrodes <NUM> and <NUM> through the resistor <NUM> can be provided.

The outer resistor <NUM> may be formed of any suitable electrically resistive material. According to some embodiments, the outer resistor <NUM> is formed of a graphite-based paste or similar material. However, the outer resistor <NUM> may be formed of any other suitable electrically resistive material.

According to some embodiments, the outer resistor <NUM> has an electrical resistance in the range of from about <NUM> to <NUM> ohms.

The width and thickness of the outer resistor <NUM> may depend on the material and desired resistance. According to some embodiments, the outer resistor <NUM> has a width in the range of from about <NUM> to <NUM>, and a thickness in the range of from about <NUM> to <NUM>.

The outer resistor <NUM> can be located in any suitable location on the outer surface of the housing <NUM>. More than one outer resistor <NUM> may be provided on the housing <NUM>.

Outer resistors corresponding to outer resistor <NUM> can also be incorporated into the GDT assemblies <NUM>, <NUM>.

The multi-cell secondary GDT <NUM> is also provided with a test gas discharge tube (GDT) <NUM>. The test GDT <NUM> includes a metal outer test electrode <NUM>, an electrically insulating (e.g., ceramic) ring <NUM>, and a through hole <NUM> defined in the outer electrode <NUM>. The ring <NUM> is bonded to the outer electrode <NUM> over the hole <NUM> by metallization <NUM> and brazing alloy <NUM>. The test electrode <NUM> is bonded to the ring <NUM> by metallization <NUM> and brazing alloy <NUM>.

The test electrode <NUM> and the ring <NUM> define a test GDT chamber 880A. The test GDT chamber 880A is in fluid communication with the secondary GDT chamber <NUM>. As a result, the gas M contained in the secondary GDT chamber <NUM> can flow into and out of the test GDT chamber 880A, and the same gas M is thus shared between the chambers 880A, <NUM>.

The test electrode <NUM> and the outer electrode <NUM> serve as opposed spark gap terminals to generate a spark across the test GDT chamber 880A. In order to test the secondary GDT <NUM>, an overvoltage is applied across the test GDT <NUM> and the spark over voltage of the test GDT <NUM> is measured. This may be accomplished by contacting the two test leads to the test electrode <NUM> and the outer electrode <NUM>, respectively, and applying the overvoltage across the leads.

The test GDT <NUM> can solve a practical problem associated with the secondary GDT <NUM> or similar designs. Because the outer electrodes <NUM> and <NUM> are connected in short circuit by the outer resistor <NUM> (and/or by a resistor <NUM> (<FIG>) or equivalent), it is very difficult to check and determine whether the proper gas is contained in the chamber <NUM>. The hole <NUM> enables the GDT <NUM> to contain the same gas M in both cells (i.e., the main chamber <NUM> and the test GDT chamber 880A). According to some embodiments, the measured voltage is between the outer electrode <NUM> and the test electrode <NUM>. The distance between these electrodes may be about <NUM>.

If the gas in the chambers <NUM>, 880A is not the prescribed gas or a gas mixture within a prescribed acceptable range, the measured spark over voltage of the test GDT <NUM> will be different than a reference spark over voltage. In particular, if the gas in the test chamber 880A is or includes an excessive amount of ambient air, the measured spark over voltage will be much higher than when the appropriate gas mixture M is contained in the chamber 880A. Ambient air may be introduced into the chamber <NUM>, and thereby the chamber 880A, by a leak in a seal of the GDT assembly <NUM>. The manufacturer can predetermine and assign a prescribed acceptable range of test spark over voltage for the secondary GDT <NUM>. The secondary GDT <NUM> would then be identified as defective when the measured spark over voltage is outside the prescribed range.

Test GDTs corresponding to the test GDT <NUM> can also be incorporated into the GDT assemblies <NUM>, <NUM>.

The SPD module <NUM> further includes a housing <NUM> within which the GDT assembly <NUM> is mounted. The housing <NUM> may take other forms and the module <NUM> will typically include a cover (not shown) that envelopes the contents of the housing <NUM>, including the GDT assembly <NUM>. In some embodiments, the SPD module <NUM> is a plug-in module configured to be mounted in a base (not shown).

The SPD module <NUM> includes an electrical conductive (e.g., metal) terminal member <NUM>. The terminal member <NUM> includes contact portion or plate 50B and an integral first contact terminal 50A. The contact portion or plate 50B engages the outer terminal <NUM>. The contact terminal 50A extends from the housing <NUM>.

The SPD module <NUM> further includes a thermal disconnect mechanism <NUM>. The thermal disconnect mechanism <NUM> includes an electrically conductive spring <NUM> that is secured at one end by a contact portion 46B to the primary GDT electrode <NUM> by meltable solder <NUM>. The other end of the spring <NUM> includes an integral terminal contact 46A of the module <NUM>. When the GDT assembly <NUM> fails (e.g., the multi-cell secondary GDT <NUM> short-circuits internally), the primary GDT <NUM> will quickly heat up until the solder <NUM> melts sufficiently to release the spring contact 46B,which is spring biased or loaded away from the terminal electrode <NUM>. The GDT assembly <NUM> is thereby disconnected from the line connected to the terminal contact 46A.

The SPD module <NUM> also includes a failure indicator mechanism <NUM>. The failure indicator mechanism <NUM> includes a swing arm <NUM>, a biasing feature (e.g., a spring) <NUM>, and an indicator member <NUM>. The spring <NUM> tends to force the swing arm, and thereby the indicator <NUM>, in a direction I away from a ready position (when the contact portion 46B is secured by the solder <NUM> to the electrode <NUM>; as shown in <FIG>) toward a triggered position that indicates to an observer that the module <NUM> has failed. The swing arm <NUM> is held in the ready position by the secured spring <NUM>, and released by the spring <NUM> when the spring is released from the electrode <NUM> by overheating of the electrode <NUM>.

While the GDT assemblies (e.g., GDT assemblies <NUM>-<NUM> and <NUM>) have been shown and described herein having certain numbers of inner electrodes (e.g., electrodes E1-E21), GDT assemblies according to embodiments of the invention may have more or fewer inner electrodes. According to some embodiments, a GDT assembly as disclosed herein has at least two inner electrodes defining at least three spark gaps G and, in some embodiments, or at least three inner electrodes defining at least four spark gaps G. According to some embodiments, a GDT assembly as disclosed herein has in the range of from <NUM> to <NUM> (or more) inner electrodes. The number of inner electrodes provided may depend on the continuous operating voltage the GDT assembly is intended to experience in service.

Claim 1:
A gas discharge tube assembly (<NUM>) comprising:
a multi-cell gas discharge tube (GDT) (<NUM>) including:
a housing (<NUM>) defining a GDT chamber (<NUM>);
a plurality of inner electrodes (E1-E21) located in the GDT chamber;
a trigger resistor (<NUM>) located in the GDT chamber (<NUM>); and
a gas (M) contained in the GDT chamber (<NUM>);
wherein the inner electrodes are serially disposed in the chamber in spaced apart relation to define a series of cells (C) and spark gaps (G); and
characterised in that:
the trigger resistor includes an interface surface (<NUM>) exposed to at least one of the cells; and
the trigger resistor is responsive to an electrical surge through the trigger resistor to generate a spark along the interface surface and thereby promote an electrical arc in the at least one cell.