EP3413320B1 - Überspannungsschutzvorrichtung mit mehreren varistorwafern - Google Patents
Überspannungsschutzvorrichtung mit mehreren varistorwafern Download PDFInfo
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- EP3413320B1 EP3413320B1 EP18190872.4A EP18190872A EP3413320B1 EP 3413320 B1 EP3413320 B1 EP 3413320B1 EP 18190872 A EP18190872 A EP 18190872A EP 3413320 B1 EP3413320 B1 EP 3413320B1
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- varistor
- overvoltage protection
- protection device
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Classifications
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- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01C—RESISTORS
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01C—RESISTORS
- H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
-
- 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
- H01C7/001—Mass resistors
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- 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
- H01C7/102—Varistor boundary, e.g. surface layers
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- 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
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- 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
- H01C7/123—Arrangements for improving potential distribution
Definitions
- the present disclosure relates to circuit protection devices and, more particularly, to overvoltage protection devices and methods.
- FIG. 1 is a system including conventional overvoltage and surge protection.
- An overvoltage protection device 12 may be installed at a power input of equipment to be protected 50, which is typically protected against overcurrents when it fails.
- Typical failure mode of an SPD is a short circuit.
- the overcurrent protection typically employed is a combination of an internal thermal disconnector to protect the device from overheating due to increased leakage currents and an external fuse to protect the device from higher fault currents.
- Different SPD technologies may avoid the use of the internal thermal disconnector because, in the event of failure, they change their operation mode to a low ohmic resistance.
- the device can withstand significant short circuit currents.
- some embodiments that exhibit even higher short circuit withstand capabilities may also be protected only by the main circuit breaker of the installation without the need for a dedicated branch fuse.
- FIG. 2 is a block diagram of a system including conventional surge protection.
- a three phase line may be connected to and supply electrical energy to one or more transformers 66, which may in turn supply three phase electrical power to a main circuit breaker 68.
- the three phase electrical power may be provided to one or more distribution panels 62.
- the three voltage lines of the three phase electrical power may designated as LI, L2 and L3 and a neutral line may be designated as N.
- the neutral line N may be conductively coupled to an earth ground.
- each of the SPDs 15 may be connected between respective ones of LI, L2 and L3, and neutral (N).
- the SPD 15 may protect other equipment in the installation such as the distribution panel among others.
- the SPDs may be used to protect all equipment in case of prolonged overvoltages. However, such a condition may force the SPD to conduct a limited current for a prolonged period of time, which may result in the overheating of the SPD and possibly its failure (depending on the energy withstand capabilities the SPD can absorb and the level and duration of the overvoltage condition).
- a typical operating voltage of an SPD 15 in the present example may be about 400V (for 690V L-L systems).
- the SPDs 15 will each perform as an insulator and thus not conduct current during normal operating conditions.
- the operating voltage of the SPD's 15 is sufficiently higher than the normal line-to-neutral voltage to ensure that the SPD 15 will continue to perform as an insulator even in cases in which the system voltage increases due to overvoltage conditions that might arise as a result of a loss of neutral or other power system issues.
- devices for protecting equipment from excess voltage or current spikes may include including varistors (for example, metal oxide varistors (MOVs) and/or silicon carbide varistors).
- varistors for example, metal oxide varistors (MOVs) and/or silicon carbide varistors.
- CA 2,098,365 A1 describes a surge arrester for protecting distribution transformers from damage which may arise from lightning-induced surge currents entering the secondary windings from the transformer's low voltage side.
- the surge arrester has voltage dependent varistors which are retained in position by a spring clip.
- EP 1 798 742 A1 describes an overvoltage protection device including first and second electrically conductive electrode members and a varistor member.
- US 3,863,111 describes a surge protective device with a plurality of polycrystalline varistor elements in a stack configuration.
- an overvoltage protection device includes a first electrode member, a second electrode member, and a varistor assembly.
- the varistor assembly may include a plurality of varistor wafers each formed of a varistor material; and at least one electrically conductive interconnect member connecting the varistor wafers in electrical parallel between the first and second electrode members.
- the varistor wafers may be axially stacked between the first and second electrodes.
- the plurality of varistor wafers includes first, second and third varistor wafers
- the at least one interconnect member includes at least first and second interconnect members connecting the varistor wafers in electrical parallel between the first and second electrode members.
- the first interconnect member contacts and electrically connects each of the first electrode member and the first, second and third varistor wafers
- the second interconnect member contacts and electrically connects each of the second electrode member and the first, second and third varistor wafers.
- each of the first, second and third varistor wafers includes opposed planar contact faces
- each of the first and second interconnect members includes two spaced apart, planar contact portions and a bridge portion extending between and electrically connecting the contact portions, and the contact portions engage the planar contact faces.
- each contact portion engages at least 40 percent of each contact face engaged thereby.
- each varistor wafer has a thickness in the range of from about 0.5 mm to 15 mm.
- each varistor wafer includes metallization layers forming opposed planar contact faces of the varistor wafer.
- the overvoltage protection device includes a bonding agent bonding at least two of the varistor wafers in the varistor assembly to one another.
- the bonding agent is at least one of cyanoacrylate-based adhesive and epoxy-based adhesive.
- the bonding agent is bonded to peripheral edges of the varistor wafers.
- the bonding agent includes a plurality of circumferentially spaced apart bonding agent masses bonded to the peripheral edges of the varistor wafers.
- the first electrode includes a housing electrode including an end wall and an integral sidewall collectively defining a cavity, the second electrode extends into the cavity, and the varistor assembly is disposed in the cavity.
- the housing electrode is unitarily formed of metal.
- the overvoltage protection device includes a biasing device applying an axially compressive load to the varistor assembly.
- the overvoltage protection device includes a biasing device applying an axially compressive load to the varistor assembly.
- the overvoltage protection device includes an electrically conductive meltable member, wherein the meltable member is responsive to heat in the overvoltage protection device to melt and form an electrical short circuit path across the first and second electrode members.
- the overvoltage protection device includes a void filling member surrounding at least a portion of the varistor assembly, wherein the void filling member is formed of an electrically insulating material.
- the void filling member includes a receiver recess and a portion of the interconnect member extends outwardly beyond the plurality of varistors and is disposed in the receiver recess.
- the first electrode includes a housing electrode including an end wall and an integral sidewall collectively defining a chamber
- the chamber includes a first subchamber and a second subchamber in fluid communication with the first subchamber
- the meltable member is disposed in the first subchamber
- the varistor assembly is disposed in the second subchamber and a gap volume is defined between the varistor assembly and the sidewall
- the void filling member is disposed in the gap volume to limit a flow of the meltable member into the gap volume.
- the void filling member occupies at least 50 percent of the gap volume.
- the varistor assembly includes an insulator wafer axially interposed and stacked between at least two of the plurality of varistor wafers.
- the first electrode is a unitary housing electrode
- the housing electrode includes first and second cavities
- the varistor assembly is disposed in the first cavity
- the overvoltage protection device further includes a second varistor assembly and a third electrode member.
- the second varistor assembly is disposed in the second cavity.
- the second varistor assembly includes: a plurality of varistor wafers each formed of a varistor material; and at least one electrically conductive interconnect member.
- the varistor wafers of the second varistor assembly are axially stacked between the housing electrode and the third electrode.
- the at least one interconnect member of the second varistor assembly connects the varistor wafers of the second varistor assembly in electrical parallel between the housing electrode and the third electrode.
- a varistor assembly includes: a plurality of varistor wafers each formed of a varistor material; at least one electrically conductive interconnect member connecting the varistor wafers in electrical parallel; and a bonding agent bonding at least two of the varistor wafers in the varistor assembly to one another.
- the varistor wafers and the at least one interconnect member are axially stacked.
- the bonding agent is at least one of cyanoacrylate-based adhesive and epoxy-based adhesive.
- the bonding agent is bonded to peripheral edges of the varistor wafers.
- the bonding agent includes a plurality of circumferentially spaced apart bonding agent masses bonded to the peripheral edges of the varistor wafers.
- a method for forming a varistor assembly includes: providing a plurality of varistor wafers each formed of a varistor material; providing at least one electrically conductive interconnect member; axially stacking the varistor wafers and the at least one interconnect member such that the at least one interconnect member connects the varistor wafers in electrical parallel; thereafter applying an axial load to the varistor wafers and the at least one interconnect member; and thereafter bonding at least two of the varistor wafers in the varistor assembly to one another using a bonding agent.
- an overvoltage protection device includes a first electrode member, a second electrode member, a varistor, an electrically conductive meltable member, and a void filling member.
- the varistor is interposed between and electrically connected to each of the first and second electrodes.
- the meltable member is responsive to heat in the overvoltage protection device to melt and form an electrical short circuit path across the first and second electrode members.
- the void filling member surrounds at least a portion of the varistor.
- the void filling member is formed of an electrically insulating material.
- the overvoltage protection device includes a sidewall defining a chamber, the chamber including a first subchamber and a second subchamber in fluid communication with the first subchamber.
- the meltable member is disposed in the first subchamber.
- the varistor assembly is disposed in the second subchamber and a gap volume is defined between the varistor assembly and the sidewall.
- the void filling member is disposed in the gap volume to limit a flow of the meltable member into the gap volume.
- the void filling member occupies at least 50 percent of the gap volume.
- 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. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted 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 exemplary term “under” can encompass both an orientation of over and under. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
- monolithic means an object that is a single, unitary piece formed or composed of a material without joints or seams.
- wafer means a substrate having a thickness which is relatively small compared to its diameter, length or width dimensions.
- a modular surge protective device (SPD) or overvoltage protection device according to embodiments of the present invention is shown therein and designated 100.
- the overvoltage protection device 100 is used as an SPD in an electrical circuit as discussed above.
- overvoltage protection devices 100 may be used in place of the SPD 12 in the system of FIG. 1 or in place of the SPDs 15 in the system of FIG. 2 .
- the overvoltage protection device 100 is configured as a unit or module having a lengthwise axis A-A ( FIG. 5 ).
- the overvoltage protection device 100 includes a first electrode or housing 122, a piston-shaped second electrode 124, four spring washers 128E, a flat washer 128D, an insulating ring member 128C, two O-rings 130A, 130B, an end cap 128A, a retention clip 128B, a meltable member 132, and an insulator sleeve 134.
- the overvoltage protection device 100 further includes a varistor assembly 150 according to embodiments of the present invention.
- the varistor assembly 150 includes a first varistor member 152, a second varistor member 154, a third varistor wafer 156, a first internal interconnect member 160, a second internal interconnect member 162, and a bonding agent 164.
- the overvoltage protection device 100 may further include an integral fail-safe mechanism, arrangement, feature or system 102.
- the fail-safe system 102 is adapted to prevent or inhibit overheating or thermal runaway of the overvoltage protection device, as discussed in more detail below.
- the components 122, 124, 128A-C collectively form a housing assembly 121 defining a sealed, enclosed chamber 126.
- the components 122, 124, 128A-E, 132 and 150 are disposed axially between the housing 122 and the electrode 124 along the lengthwise axis A-A, in the enclosed chamber 126.
- the housing 122 has an end electrode wall 122A and an integral cylindrical sidewall 122B extending from the electrode wall 122A.
- the sidewall 122B and the electrode wall 122A form a chamber or cavity 122C communicating with an opening 122D.
- a threaded post 122E projects axially outwardly from the electrode wall 122A.
- the electrode wall 122A has an inwardly facing, substantially planar contact surface 122G.
- An annular clip slot 122H is formed in the inner surface of the sidewall 122B.
- the housing 122 is formed of aluminum. However, any suitable electrically conductive metal may be used.
- the housing 122 is unitary and, in some embodiments, monolithic.
- the housing 122 as illustrated is cylindrically shaped, but may be shaped differently.
- the inner electrode 124 has a head 124A disposed in the cavity 122C and an integral shaft 122B that projects outwardly through the opening 122D.
- the head 124A has a substantially planar contact surface 124C that faces the contact surface 122G of the electrode wall 122A.
- a pair of integral, annular, axially spaced apart flanges 124D extend radially outwardly from the shaft 124B and define an annular, sidewardly opening groove 124E therebetween.
- a threaded bore 124F is formed in the end of the shaft 124B to receive a bolt for securing the electrode 124 to a busbar, for example.
- An annular, sidewardly opening groove 124G is defined in the shaft 124B.
- the electrode 124 is formed of aluminum. However, any suitable electrically conductive metal may be used. According to some embodiments, the electrode 124 is unitary and, in some embodiments, monolithic.
- the electrodes 122, 124, the insulating ring 128C and the end cap 128A collectively define an enclosed chamber 126 containing the meltable member 132 and the varistor assembly 150.
- An annular gap is defined radially between the head 124A and the nearest adjacent surface of the sidewall 122B. According to some embodiments, the gap has a radial width in the range of from about 1 to 15 mm.
- the meltable member 132 is annular and is mounted on the electrode 124 in the groove 124E.
- the meltable member 132 is spaced apart from the sidewall 122B a distance sufficient to electrically isolate the meltable member 132 from the sidewall 122B.
- the meltable member 132 is formed of a heat-meltable, electrically conductive material. According to some embodiments, the meltable member 132 is formed of metal. According to some embodiments, the meltable member 132 is formed of an electrically conductive metal alloy. According to some embodiments, the meltable member 132 is formed of a metal alloy from the group consisting of aluminum alloy, zinc alloy, and/or tin alloy. However, any suitable electrically conductive metal may be used.
- the meltable member 132 is selected such that its melting point is greater than a prescribed maximum standard operating temperature.
- the maximum standard operating temperature may be the greatest temperature expected in the meltable member 132 during normal operation (including handling overvoltage surges within the designed for range of the system) but not during operation which, if left unchecked, would result in thermal runaway.
- the meltable member 132 is formed of a material having a melting point in the range of from about 80 to 160 °C and, according to some embodiments, in the range of from about 130 to 150 °C.
- the melting point of the meltable member 132 is at least 20 °C less than the melting points of the housing 122 and the electrode 124 and, according to some embodiments, at least 40 °C less than the melting points of those components.
- the meltable member 132 has an electrical conductivity in the range of from about 0.5 x 10 6 Siemens/meter (S/m) to 4 x 10 7 S/m and, according to some embodiments, in the range of from about 1 x 10 6 S/m to 3 x 10 6 S/m.
- the three varistor wafers 152, 154, 156 and the two interconnect members 160, 162 are axially stacked in the chamber 126 between the electrode head 124 and the electrode wall 122 and form the varistor assembly 150.
- the interconnect members 160, 162 electrically interconnect the wafers 152, 154, 156 and the electrodes 122,124 in the manner represented in the schematic electrical diagram of FIG. 9 .
- each varistor wafer 152, 154, 156 is a varistor wafer (i.e., is wafer-or disk-shaped).
- each varistor wafer 152, 154, 156 is circular in shape and has a substantially uniform thickness.
- varistor wafers 152, 154, 156 may be formed in other shapes. The thickness and the diameter of the varistor wafers 152, 154, 156 will depend on the varistor characteristics desired for the particular application.
- each varistor wafer 152, 154, 156 has a diameter D1 to thickness T1 ratio of at least 3. In some embodiments, the thickness T1 ( FIG. 8 ) of each varistor wafer 152,154,156 is in the range of from about 0.5 to 15 mm. In some embodiments, the diameter D1 ( FIG. 8 ) of each varistor wafer 152, 154, 156 is in the range of from about 20 to 100 mm.
- the varistor wafer 152 has first and second opposed, substantially planar contact surfaces 152U, 152L and a peripheral edge 152E.
- the varistor wafer 154 has first and second opposed, substantially planar contact surfaces 154U, 154L and a peripheral edge 154E.
- the varistor wafer 156 has first and second opposed, substantially planar contact surfaces 156U, 156L and a peripheral edge 156E.
- the varistor material may be any suitable material conventionally used for varistors, namely, a material exhibiting a nonlinear resistance characteristic with applied voltage. Preferably, the resistance becomes very low when a prescribed voltage is exceeded.
- the varistor material may be a doped metal oxide or silicon carbide, for example. Suitable metal oxides include zinc oxide compounds.
- Each varistor wafer 152, 154, 156 may include a wafer of varistor material coated on either side with a conductive coating 157 so that the exposed surfaces of the coatings serve as the contact surfaces 152U, 152L, 154U, 154L, 156U, 156L.
- the coatings can be metallization formed of aluminum, copper or silver, for example.
- the bare surfaces of the varistor material may serve as the contact surfaces 152U, 152L, 154U, 154L, 156U, 156L.
- the interconnect members 160, 162 are electrically conductive.
- the interconnect member 160 includes a pair of axially spaced apart, disk-shaped contact portions 160U, 160L joined by a bridge portion 160B.
- the interconnect member 162 includes a pair of axially spaced apart, disk-shaped contact portions 162U, 162L joined by a bridge portion 162B.
- each contact portion 160U, 160L, 162U, 162L is substantially planar, relatively thin and wafer- or disk-shaped.
- each contact portion 160U, 160L, 162U, 162L has a diameter D2 ( FIG. 8 ) to thickness T2 ( FIG. 8 ) ratio of at least 15.
- the thickness T2 of each contact portion 160U, 160L, 162U, 162L is in the range of from about 0.1 to 3 mm.
- the diameter D2 of each contact portion 160U, 160L, 162U, 162L is in the range of from about 20 to 100 mm.
- each contact portion 160U, 160L, 162U, 162L does not have any through holes extending through the thickness of the contact portion.
- each bridge portion 160B, 162B is in the range of from about 2 mm to 10 mm.
- the cross-sectional area of each bridge portion 160B, 162B should be large enough to withstand the short circuit current that may flow through the SPD after a possible failure of one or more of the varistor wafers 152,154,156.
- the interconnect members 160, 162 are formed of copper. However, any suitable electrically conductive metal may be used. According to some embodiments, the interconnect members 160, 162 are unitary and, in some embodiments, monolithic.
- the varistor wafer 154 is interposed or sandwiched between the varistor wafers 152, 156, the varistor wafers 152, 154, 156 are interposed or sandwiched between the interconnect members 160, 162, and the interconnect members 160, 162 are interleaved with one another as shown in FIGS. 6 and 8 .
- the contact portion 160U engages the contact surface 152U.
- the contact portion 160L engages the contact surfaces 154L and 156U.
- the contact portion 162U engages the contact surfaces 152L and 154U.
- the contact portion 162L engages the contact surface 156L.
- Each said engagement forms an intimate physical or mechanical contact between the identified interconnect member contact portions and varistor contact surfaces.
- Each said engagement forms a direct electrical connection or coupling between the identified interconnect member contact portions and varistor contact surfaces.
- the contact portions 160U and 162L form or serve as the outer electrode contact surfaces of the varistor assembly 150.
- Each bridge portion 160B, 162B includes a pair of tab sections 163 (extending radially outwardly from the contact portions 160U, 160L or 162, 162L) and an axially extending connecting section 165 connecting the tab sections 163 and radially spaced apart from the adjacent peripheral edges of the varistor wafers 152, 154, 156.
- each connecting section 165 is located a distance D3 ( FIG. 8 ) from the adjacent peripheral edges of the varistor wafers 152, 154, 156.
- the distance D3 is in the range of from about 0.5 to 15mm.
- the varistor wafers 152, 154, 156 are secured to one another by the bonding agent 164.
- the bonding agent 164 is located at and secures the adjacent varistor wafers 152, 154, 156 at their peripheral edges.
- the bonding agent 164 is provided as a plurality of discrete, spaced apart patches or spots of the bonding agent 164. The bonding is used to keep the components of the varistor assembly 150 in place during transportation and assembly of the overvoltage protection device 100.
- the bonding agent 164 includes a bonding agent portion or portions 164' located within the bridge portions 160, 162B between each bridge portion 160B, 162B and the adjacent edges of the varistor wafers 152, 154, 156. In this way, these bonding agent portions 164' can serve as electrical insulators that electrically insulate the bridge portions 160B, 162B from the edges of the varistor wafers 152, 154, 156.
- the bonding agent 164 is an adhesive.
- 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 (e.g., the edge surfaces of the varistor wafers 152, 154, 156).
- the adhesive may be any suitable adhesive.
- adhesive 164 is secures the varistor wafers 152, 154, 156 at their peripheral edges and are discrete, spaced apart patches or spots located about the peripheral edges.
- the adhesive 164 is a cyanoacrylate-based adhesive or an epoxy-based adhesive.
- Suitable cyanoacrylate adhesives may include Permabond 737 adhesive available from Permabond Engineering Adhesives, Inc. of the United States of America.
- the adhesive has a high operating temperature, above 40 °C, does not contain any solvent, and has a high dielectric strength (e.g., above 5kV/mm).
- each coating 157 is radially inset from the outer periphery of the varistor wafer 152, 154, 156, and the outer periphery of each contact portion 160U, 160L, 162U, 162L is radially inset from the outer periphery of the coating 157.
- the varistor wafers 152, 154, 156 are mechanically secured and electrically directly connected to the respective contact portions 160U, 160L, 162U, 162L by an electrically conductive solder.
- the varistor assembly 150 can be assembled as follows in accordance with embodiments of the invention.
- the interconnect members 160, 162 may be pre-bent into the shapes shown in FIG. 7 .
- each contact portion 160U, 160L, 162U, 162L covers and engages at least 40% of the surface area of the corresponding mating varistor wafer surface 152U, 152L, 154U, 154L, 156U, 156L.
- the varistor wafers 152, 154, 156 and the interconnect members 160, 162 are stacked and interleaved in the order and relation as shown in FIGS. 6 and 8 .
- This assembly may be assembled in or placed, after assembly, in a fixture to laterally align the varistor wafers 152, 154, 156 and the interconnect members 160, 162 with respect to one another.
- the varistor wafers 152, 154, 156 and the interconnect members 160, 162 are substantially coaxially aligned.
- the aligned components 152, 154, 156, 160, 162 are axially compressively loaded, pressed or clamped together (e.g., using the fixture or an additional external clamping or loading device) and into intimate contact.
- the bonding agent 164 is then applied to the peripheral edges 152E, 154E, 156E of the varistor wafers 152, 154, 156 at locations as discussed above, and cured.
- the varistor assembly 150 is thus formed. Once the bonding agent 164 has cured, the external loading device is removed from the varistor assembly 150.
- the insulator sleeve 134 is tubular and generally cylindrical. According to some embodiments, the insulator sleeve 134 is formed of a high temperature polymer and, in some embodiments, a high temperature thermoplastic. In some embodiments, the insulator sleeve 134 is formed of polyetherimide (PEI), such as ULTEMTM thermoplastic available from SABIC of Saudi Arabia. In some embodiments, the insulator member 134 is formed of non-reinforced polyetherimide.
- PEI polyetherimide
- ULTEMTM thermoplastic available from SABIC of Saudi Arabia.
- the insulator member 134 is formed of non-reinforced polyetherimide.
- the insulator sleeve 134 is formed of a material having a melting point greater than the melting point of the meltable member 132. According to some embodiments, the insulator sleeve 134 is formed of a material having a melting point in the range of from about 120 to 200 °C.
- the insulator sleeve 134 material can withstand a voltage of 25 kV per mm of thickness.
- the insulator sleeve 134 has a thickness in the range of from about 0.1 to 2 mm.
- the spring washers 128E surround the shaft 124B. Each spring washer 128E includes a hole that receives the shaft 124B. The lowermost spring washer 128E abuts the top face of the head 124A. According to some embodiments, the clearance between the spring washer hole and the shaft 124B is in the range of from about 0.015 to 0.035 inch.
- the spring washers 128E may be formed of a resilient material. According to some embodiments and as illustrated, the spring washers 128E are wave washers (as shown) or Belleville washers formed of spring steel. While two spring washers 128E are shown, more or fewer may be used. The springs may be provided in a different stack arrangement such as in series, parallel, or series and parallel.
- the flat metal washer 128D is interposed between the uppermost spring washer 128E and the insulator ring 128C with the shaft 124B extending through a hole formed in the washer 128D.
- the washer 128D serves to distribute the mechanical load of the upper spring washer 128E to prevent the spring washer 128E from cutting into the insulator ring 128C.
- the insulator ring 128C overlies and abuts the washer 128D.
- the insulator ring 128C has a main body ring and a cylindrical upper flange or collar extending upwardly from the main body ring.
- a hole receives the shaft 124B.
- the clearance between the hole and the shaft 124B is in range of from about 0.025 to 0.065 inch.
- An upwardly and outwardly opening peripheral groove is formed in the top corner of the main body ring.
- the insulator ring 128C is preferably formed of a dielectric or electrically insulating material having high melting and combustion temperatures.
- the insulator ring 128C may be formed of polycarbonate, ceramic or a high temperature polymer, for example.
- the end cap 128A overlies and abuts the insulator ring 128C.
- the end cap 128A has a hole that receives the shaft 124B. According to some embodiments, the clearance between the hole and the shaft 124B is in the range of from about 0.1 to 0.2 inch.
- the end cap 128A may be formed of aluminum, for example.
- the clip 128B is resilient and truncated ring shaped.
- the clip 128B is partly received in the slot 122H and partly extends radially inwardly from the inner wall of the housing 122 to limit outward axial displacement of the end cap 128A.
- the clip 128B may be formed of spring steel.
- the O-ring 130B is positioned in the groove 124G so that it is captured between the shaft 124B and the insulator ring 128C.
- the O-ring 130A is positioned in the groove in the insulator ring 128C such that it is captured between the insulating member 128C and the sidewall 122B.
- the O-rings 130A, 130B are compressed so that they are biased against and form a seal between the adjacent interfacing surfaces.
- byproducts such as hot gases and fragments from the varistor wafers 152, 154, 156 may fill or scatter into the cavity chamber 126. These byproducts may be constrained or prevented by the O-rings 130A, 130B from escaping the overvoltage protection device 100 through the housing opening 122D.
- the O-rings 130A, 130B may be formed of the same or different materials. According to some embodiments, the O-rings 130A, 130B are formed of a resilient material, such as an elastomer. According to some embodiments, the O-rings 130A, 130B are formed of rubber.
- the O-rings 130A, 130B may be formed of a fluorocarbon rubber such as VITONTM available from DuPont. Other rubbers such as butyl rubber may also be used. According to some embodiments, the rubber has a durometer of between about 60 and 100 Shore A.
- the electrode head 124A and the housing end wall 122A are persistently biased or loaded against the varistor assembly 150 along a load or clamping axis C-C ( FIG. 5 ) in directions F to ensure firm and uniform engagement between the above-identified interfacing contact surfaces.
- This aspect of the unit 100 may be appreciated by considering a method according to the present invention for assembling the unit 100, as described below.
- the clamping axis C-C is substantially coincident with the axis A-A ( FIG. 5 ).
- the components 152,154,156,160,162,164 are assembled as described above to form the varistor assembly 150.
- the varistor assembly 150 is placed in the cavity 122C such that the lower contact surface or portion 162L of the interconnect member 162 engages the contact surface 122G of the end wall 122A.
- the O-rings 130A, 130B are installed in their respective grooves.
- the head 124A is inserted into the cavity 122C such that the contact surface 124C engages the upper contact surface or portion 160U of the interconnect member 160.
- the spring washers 128E are slid down the shaft 124B.
- the washer 128D, the insulator ring 128C, and the end cap 128A are slid down the shaft 124B and over the spring washers 128E.
- a jig (not shown) or other suitable device is used to force the end cap 128A down, in turn deflecting the spring washers 128E. While the end cap 128A is still under the load of the jig, the clip 128B is compressed and inserted into the slot 122H. The clip 128B is then released and allowed to return to its original diameter, whereupon it partly fills the slot and partly extends radially inward into the cavity from the slot 122H.
- the clip 128B and the slot 122H thereby serve to maintain the load on the end cap 128A to partially deflect the spring washers 128E.
- the loading of the end cap 128A onto the insulator ring 128C and from the insulator ring onto the spring washers is in turn transferred to the head 124A. In this way, the varistor assembly 150 is sandwiched (clamped) between the head 124A and the electrode wall 122A.
- the housing 122, the electrode 124, the insulating member 128C, the end cap 128A, the clip 128B, and the O-rings 130A, 130B collectively form a unit housing or housing assembly 121 containing the components in the chamber 126.
- the large, planar contact surfaces of the components 122A, 124A, 152, 154, 156, 160, 162 can ensure reliable and consistent electrical contact and connection between the components during an overvoltage or surge current event.
- the head 124A and the end wall 122A are mechanically loaded against these components to ensure firm and uniform engagement between the mating contact surfaces.
- the overvoltage protection device 100 integrates three varistor wafers 152, 154, 156 in electrical parallel in the same modular device, so that energy can be shared between the varistor wafers 152, 154,156 during electrical conduction.
- the design of the overvoltage protection device 100 provides compressive loading of the varistor wafers 152, 154, 156 in a single modular unit.
- the overvoltage protection device 100 provides suitable electrical interconnections between the electrodes 122, 124 and the varistor wafers 152, 154, 156, while retaining a compact form factor and providing proper thermal dissipation of energy from the varistor wafers 152, 154,156.
- the construction of the overvoltage protection device 100 provides a safe failure mode for the device.
- one or more of the varistor wafers 152, 154, 156 may be damaged by overheating and may generate arcing inside the housing assembly 121.
- the housing assembly 121 can contain the damage (e.g., debris, gases and immediate heat) within the overvoltage protection device 100, so that the overvoltage protection device 100 fails safely.
- the overvoltage protection device 100 can prevent or reduce any damage to adjacent equipment (e.g., switch gear equipment in the cabinet) and harm to personnel. In this manner, the overvoltage protection device 100 can enhance the safety of equipment and personnel.
- the overvoltage protection device 100 provides a fail-safe mechanism in response to end of life mode in one of more of the varistor wafers 152, 154, 156.
- a fault current will be conducted between the corresponding line and the neutral line.
- a varistor has an innate nominal clamping voltage VNOM (sometimes referred to as the "breakdown voltage” or simply the "varistor voltage") at which the varistor begins to conduct current. Below the VNOM, the varistor will not pass current. Above the VNOM, the varistor will conduct a current (i.e., a leakage current or a surge current).
- the VNOM of a varistor is typically specified as the measured voltage across the varistor with a DC current of 1mA.
- a varistor has three modes of operation. In a first normal mode (discussed above), up to a nominal voltage, the varistor is practically an electrical insulator. In a second normal mode (also discussed above), when the varistor is subjected to an overvoltage, the varistor temporarily and reversibly becomes an electrical conductor during the overvoltage condition and returns to the first mode thereafter. In a third mode (the so-called end of life mode), the varistor is effectively depleted and becomes a permanent, non-reversible electrical conductor.
- the varistor also has an innate clamping voltage VC (sometimes referred to as simply the "clamping voltage").
- the clamping voltage VC is defined as the maximum voltage measured across the varistor when a specified current is applied to the varistor over time according to a standard protocol.
- the varistor wafer 152, 154, 156 provides high resistance such that no current flows through the overvoltage protection device 100 as it appears electrically as an open circuit. That is, ordinarily the varistor passes no current.
- an overcurrent surge event typically transient; e.g., lightning strike
- an overvoltage condition or event typically longer in duration than an overcurrent surge event
- the resistance of the varistor wafer decreases rapidly, allowing current to flow through the overvoltage protection device 100 and create a shunt path for current flow to protect other components of an associated electrical system. Normally, the varistor recovers from these events without significant overheating of the overvoltage protection device 100.
- Varistors have multiple failure modes.
- the failure modes include: 1) the varistor fails as a short circuit; and 2) the varistor fails as a linear resistance.
- the failure of the varistor to a short circuit or to a linear resistance may be caused by the conduction of a single or multiple surge currents of sufficient magnitude and duration or by a single or multiple continuous overvoltage events that will drive a sufficient current through the varistor.
- a short circuit failure typically manifests as a localized pinhole or puncture site (herein, "the failure site") extending through the thickness of the varistor.
- This failure site creates a path for current flow between the two electrodes of a low resistance, but high enough to generate ohmic losses and cause overheating of the device even at low fault currents.
- Sufficiently large fault current through the varistor can melt the varistor in the region of the failure site and generate an electric arc.
- a varistor failure as a linear resistance will cause the conduction of a limited current through the varistor that will result in a buildup of heat. This heat buildup may result in catastrophic thermal runaway and the device temperature may exceed a prescribed maximum temperature.
- the maximum allowable temperature for the exterior surfaces of the device may be set by code or standard to prevent combustion of adjacent components. If the leakage current is not interrupted at a certain period of time, the overheating will result eventually in the failure of the varistor to a short circuit as defined above.
- the current through the failed varistor could also be limited by the power system itself (e.g., ground resistance in the system or in photo-voltaic (PV) power source applications where the fault current depends on the power generation capability of the system at the time of the failure) resulting in a progressive build up of temperature, even if the varistor failure is a short circuit.
- the power system itself
- PV photo-voltaic
- the overvoltage protection device 100 may assume an "end of life” mode in which a varistor wafer 152, 154, 156 is depleted in full or in part (i.e., in an "end of life” state), leading to an end of life failure.
- the overvoltage protection device 100 will become substantially a short circuit with a very low but non-zero ohmic resistance.
- a fault current will continuously flow through the varistor even in the absence of an overvoltage condition.
- the meltable member 132 can operate as a fail-safe mechanism that bypasses the failed varistor and creates a permanent low-ohmic short circuit between the terminals of the overvoltage protection device 100 in the manner described in U.S. Patent No. 7,433,169 , the disclosure of which is incorporated herein by reference.
- the meltable member 132 is adapted and configured to operate as a thermal disconnect to electrically short circuit the current applied to the associated overvoltage protection device 100 around the varistor wafers 152, 154, 156 to prevent or reduce the generation of heat in the varistors. In this way, the meltable member 132 can operate as switch to bypass the varistor wafers 152, 154, 156 and prevent overheating and catastrophic failure as described above.
- a fail-safe system is "triggered" upon occurrence of the conditions necessary to cause the fail-safe system to operate as described to short circuit the electrodes 122A, 124A.
- the meltable member 132 When heated to a threshold temperature, the meltable member 132 will flow to bridge and electrically connect the electrodes 122A, 124A. The meltable member 132 thereby redirects the current applied to the overvoltage protection device 100 to bypass the varistors 152, 154, 156 so that the current induced heating of the varistor ceases. The meltable member 132 may thereby serve to prevent or inhibit thermal runaway (caused by or generated in a varistor 152, 154, 156) without requiring that the current through the overvoltage protection device 100 be interrupted.
- the meltable member 132 initially has a first configuration as shown in FIG. 5 such that it does not electrically couple the electrode 124 and the housing 122 except through the head 124A. Upon the occurrence of a heat buildup event, the electrode 124 is thereby heated. The meltable member 132 is also heated directly and/or by the electrode 124. During normal operation, the temperature in the meltable member 132 remains below its melting point so that the meltable member 132 remains in solid form. However, when the temperature of the meltable member 132 exceeds its melting point, the meltable member 132 melts (in full or in part) and flows by force of gravity into a second configuration different from the first configuration.
- the meltable member 132 bridges or short circuits the electrode 124 to the housing 122 to bypass the varistor wafers 152, 154, 156. That is, a new direct flow path or paths are provided from the surface of the electrode 124 to the surface of the housing sidewall 122B through the meltable member 132. According to some embodiments, at least some of these flow paths do not include the varistor wafers 152, 154,156.
- the overvoltage protection device 100 is adapted such that when the meltable member 132 is triggered to short circuit the overvoltage protection device 100, the conductivity of the overvoltage protection device 100 is at least as great as the conductivity of the feed and exit cables connected to the device.
- Electrical protection devices may provide a number of advantages in addition to those mentioned above.
- the devices may be formed so to have a relatively compact form factor.
- the devices may be retrofittable for installation in place of similar type surge protective devices not having circuits as described herein.
- the present devices may have the same length dimension as such previous devices.
- an SPD having a lower residual voltage at the same nominal operating voltage. For example, this is a requirement for some telecom applications rated for - 48 Vdc systems.
- a varistor e.g., an MOV
- a typical continuous operation voltage Vc for such a varistor is 100 Vdc.
- this SPD will have a residual voltage Vres of around 300V or more. It would be beneficial for the better protection of the equipment to use SPDs with a residual voltage Vres much lower than these levels (i.e., close to 100V).
- SADs or TVS diodes typically have a much lower residual voltage than MOVs for the same continuous operating voltage Vc.
- a TVS diode for this application may have a residual voltage of 100 V.
- SADs and TVS diodes typically cannot conduct the surge currents of significant energies that are expected in such applications. For that reason, many manufacturers have used multiple SADs and/or TVS diodes in parallel to achieve higher energy withstand capabilities during surge current conduction.
- the varistor wafers 152, 154, 156 are connected in electrical parallel to reduce the residual voltage Vres of the overvoltage protection device 100.
- each varistor wafer 152, 154, 156 is rated for 60 Vdc (continuous operating voltage; Vc) instead of 100 Vdc that is typical for this application.
- Vc continuous operating voltage
- the use of three varistors in parallel reduces even further the clamping voltage of the SPD at a given surge current (as compared to using a single varistor), as each varistor will conduct only a fraction of the overall surge current (the clamping voltage depends on the conducted surge current, the higher the conducted surge current the higher the clamping voltage of the varistor).
- the resultant residual voltage is around 140 V at a surge current of 5 kA.
- the overvoltage protection device 100 is used in a DC power system and, in some embodiments, in a protection circuit of -48Vdc telecommunications equipment.
- the device 100 may also be used in AC or other DC applications.
- the reduction of the rated voltage of the varistor wafers 152, 154, 156 makes the varistor wafers 152, 154, 156 thinner and sensitive to significant temperature variations. Therefore, how the stack of varistor wafers is held in place and assembled inside the overvoltage protection device 100 is important.
- the varistor wafers varistor wafers 152, 154, 156 may be secured to the interconnect members 160, 162 and/or each other using solder.
- solder may damage the varistor wafer.
- the high temperature required to melt the soldering material and the different coefficients of elasticity between the varistor material and the solder may create micro cracks in the varistor.
- Loading on the varistor wafer by electrodes may also cause cracks in the varistor wafer. These cracks as well as flux or impurities that intrude into the cracks can progressively damage and thereby derate the varistor.
- Intruding flux may create a conductive path on the edge of a crack that increases leakage current, which can lead to failure of the varistor wafer.
- These risks are particularly of concern in the case of relatively thin (e.g., less than about 2 mm) ceramic varistor wafers.
- the shape of the interconnect member contact portions should be round with a hole in the middle.
- the hole may decrease the uniform distribution of the current over the surface of the varistor.
- the hole may also reduce the energy withstand capability of the varistor during surge currents, as it will significantly decrease the heat shrink capabilities of the varistor and increase the contact resistance and overall strength of the stack forming the varistor assembly 150.
- the varistor wafers 152, 154, 156 are stacked in parallel and bonded or adhered together by adhesive 164 on their edges 152E, 154E, 156E.
- the adhesive 164 on the edges 152E, 154E, 156E provides a compact assembly for transport and manipulation in production of the varistor assembly 150 and the device 100.
- the adhesive 164 rectifies the above mentioned issues.
- the adhesive holds the varistor wafers 152, 154, 156 and the interconnect members 160, 162 together for handling without introducing heating, solder and flux that may cause micro cracks and introduce conductive paths as discussed above.
- the adhesive permits the use of the contact portions 160U, 160L, 162U, 162L of the interconnect members that do not include holes within their peripheries (i.e., are full face electrodes).
- the energy withstand capability of the varistor assembly 150 during surge events is increased.
- the contact resistances between the varistor wafers 152, 154, 156 and the interconnect members 160, 162 are reduced.
- the expected residual voltage during surges is thereby reduced.
- the areas of engagement between each of the electrode contact surfaces and the varistor contact surfaces are each at least one square inch.
- the biased electrodes (e.g., the electrodes 122 and 124) apply a load to the varistors along the axis C-C in the range of from about 2000 lbf and about 26000 lbf (8896N and 115654N) depending on its surface area.
- the combined thermal mass of the housing (e.g., the housing 122) and the electrode (e.g., the electrode 124) is substantially greater than the thermal mass of each of the varistors captured therebetween.
- thermal mass means the product of the specific heat of the material or materials of the object multiplied by the mass or masses of the material or materials of the object.
- the thermal mass is the quantity of energy required to raise one gram of the material or materials of the object by one degree centigrade times the mass or masses of the material or materials in the object.
- the thermal mass of at least one of the electrode head and the electrode wall is substantially greater than the thermal mass of the varistor.
- the thermal mass of at least one of the electrode head and the electrode wall is at least two times the thermal mass of the varistor, and, according to some embodiments, at least ten times as great.
- the combined thermal masses of the head and the electrode wall are substantially greater than the thermal mass of the varistor, according to some embodiments at least two times the thermal mass of the varistor and, according to some embodiments, at least ten times as great.
- the spring washers 128E are Belleville or wave washers. Belleville or wave washers may be used to apply relatively high loading without requiring substantial axial space. However, other types of biasing means may be used in addition to or in place of the Belleville or wave washers. Suitable alternative biasing means include one or more coil springs or spiral washers.
- the varistor assembly 150 includes three varistors and two interconnect members. However, varistor assemblies according to further embodiments may include more than three varistors stacked and connected in electrical parallel as described. For example, a varistor assembly can include five varistors stacked and connected in electrical parallel by three interconnect members.
- the overvoltage protection unit 200 can be used in the same manner and for the same purpose as the overvoltage protection device 100, except that the unit 200 is generally operationally equivalent to two if the overvoltage protection devices 100.
- the overvoltage protection unit 200 includes a housing assembly 221 and two SPD internal component sets or submodules 211, 212.
- the housing assembly 221 includes a first electrode or housing 223 and a cover 226.
- the housing 223 is unitary and, in some embodiments, monolithic.
- the housing 223 is formed of an electrically conductive metal such as aluminum.
- the housing 223 includes two integral housing electrode wall portions 222.
- Each housing electrode portion 222 includes an electrode wall 222A, a sidewall 222B, a cavity 222C, and a top opening 222D corresponding to the features 122A, 122B, 122C and 122D, respectively, of the device 100.
- the cover 226 is substantially plate-shaped and has a profile matching that of the housing 223.
- the cover 226 has two electrode openings 226A and six fastening bores 226B defined therein.
- the cover 226 is formed of an electrically conductive material.
- the cover 226 is formed of a metal and, in some embodiments, are formed of aluminum.
- the SPD submodules 211, 212 each include an electrode 224, a meltable member 232, an insulator sleeve 234, and a varistor assembly 250 corresponding to the components 124, 132, 134, and 150, respectively, of the device 100.
- Each SPD submodule 211, 212 further includes an elastomeric insulator member 239.
- the insulator members 239 are formed of an electrically insulating, resilient, elastomeric material. According to some embodiments, the insulator members 239 are formed of a material having a hardness in the range of from about 60 Shore A to 85 Shore A. According to some embodiments, the insulator members 239 are formed of rubber. According to some embodiments, the insulator members 239 are formed of silicone rubber. Suitable materials for the insulator members 239 may include KE-5612G or KE-5606 silicone rubber available from Shin-Etsu Chemical Co. Ltd.
- Each SPD submodule 211, 212 is disposed in respective one of the housing cavities 222C.
- the cover 226 is secured to the housing 223 by bolts 5.
- the cover 226 captures the SPD submodules 211, 212 and axially compresses the elastomeric insulators 239 thereof.
- the SPD submodule 211 and its electrode wall 222A form a first overvoltage protection device corresponding to the device 100.
- the SPD submodule 212 and its electrode wall 222A form a second overvoltage protection device corresponding to the device 100.
- each SPD submodule 211, 212 is captured between the cover 226 and the electrode upper flange 224D and axially compressed (i.e., axially loaded and elastically deformed from its relaxed state) so that the insulator member 239 serves as a biasing member and applies a persistent axial pressure or load to the electrode 224 and the cover 226.
- the insulator member 239 also serves to electrically insulate the housing 223 from the electrode 224.
- the compressed insulator member 239 can also form a seal to constrain or prevent overvoltage event byproducts, such as hot gases and fragments from the varistor wafers of the varistor assembly 250 from escaping the unit 200 through the corresponding housing opening 222D.
- the varistor assemblies 250 can provide the same advantages in the unit 200 as discussed above for the varistor assembly 150.
- Each varistor assembly 250 includes adhesive 264 corresponding to the adhesive 164,164'.
- the SPD submodules 211, 212 can employ separate springs and insulating rings as described with regard to the device 100.
- each SPD submodule 211, 212 can include a single varistor wafer in place of the multi-varistor varistor assembly 250.
- a modular overvoltage protection device 300 according to further embodiments of the invention is shown therein.
- the overvoltage protection unit 300 can be used in the same manner and for the same purpose as the overvoltage protection device 100.
- the overvoltage protection device 300 is constructed in the same manner as the overvoltage protection device 100, except as follows.
- the overvoltage protection device 300 includes a varistor assembly 350 corresponding to the varistor assembly 150, except as follows.
- the varistor assembly 350 includes five varistor wafers 352, 353, 354, 355, 356, four interconnect members 360, 362, 366, 368, and bonding agents 364.
- the varistor wafers 352, 353, 354, 355, 356 correspond to and are formed in the same manner as the varistor wafers 152, 154, 156.
- the interconnect members 360, 362, 366, 368 correspond to and are formed in the same manner as the interconnect members 160, 162.
- the bonding agents 364 correspond to the bonding agents 164, 164'.
- the five varistor wafers 352, 353, 354, 355, 356 are axially stacked, bonded and connected in electrical parallel by the four interconnect members 360, 362, 366, 368.
- the overvoltage protection device 400 can be used in the same manner and for the same purpose as the overvoltage protection device 100.
- the overvoltage protection device 300 is constructed in the same manner as the overvoltage protection device 100, except as follows.
- the overvoltage protection device 400 includes a varistor assembly 450 corresponding to the varistor assembly 150, except as follows.
- the varistor assembly 450 includes two varistor wafers 452, 454, two interconnect members 460, 462, bonding agents 464 and an electrical insulator wafer 457.
- the varistor wafers 452, 454 correspond to and are formed in the same manner as the varistor wafers 152, 154, 156.
- the interconnect members 460, 462 correspond to and are formed in the same manner as the interconnect members 160, 162.
- the bonding agents 464 correspond to the bonding agents 164, 164'.
- the insulator wafer 457 is formed of an electrically insulating material.
- Suitable electrical insulating materials may include ULTEMTM 1000 thermoplastic available from SABIC, mica, or polyester film such as DYFILMTM polyester film available from Coveme of Italy, for example.
- the two varistor wafers 452, 454 are axially stacked and connected in electrical parallel by the two interconnect members 460, 462.
- the insulator wafer 457 is axially interposed or stacked between the varistor wafers 452, 454 to prevent short circuiting between the opposing faces of the varistor wafers 452, 454.
- a modular overvoltage protection device 500 according to further embodiments of the invention is shown therein.
- the overvoltage protection device 500 can be used in the same manner and for the same purpose as the overvoltage protection device 100.
- the overvoltage protection device 500 is constructed as one half of the unit 200 ( FIG. 12 ).
- the device 500 includes a housing assembly 521 that is one half of the housing assembly 221 and an SPD internal component set 512 corresponding to the submodule 212.
- a modular overvoltage protection device 600 according to further embodiments of the invention is shown therein.
- the overvoltage protection device 600 can be used in the same manner and for the same purpose as the overvoltage protection device 100.
- the overvoltage protection device 600 is constructed in the same manner as the overvoltage protection device 100, except as follows.
- the overvoltage protection device 600 includes a varistor assembly 650 corresponding to the varistor assembly 150, except as follows.
- the varistor assembly 650 includes three varistor wafers 652, 654, 656 and two interconnect members 660, 662.
- the varistor wafers 652, 654, 656 correspond to and are formed in the same manner as the varistor wafers 152, 154, 156.
- the interconnect members 660, 662 correspond to and are formed in the same manner as the interconnect members 160, 162.
- the varistor wafers 652, 654, 656 are axially stacked and connected in electrical parallel by the interconnect members 660, 662 as discussed above for the device 100.
- the overvoltage protection device 600 further includes an electrically insulating void filling member or sleeve 636.
- the sleeve 636 includes a side wall 636A defining a through passage 636B.
- the passage 636 extends from an upper opening 636C to a lower opening 636D.
- a pair of laterally opposing, axially extending receiver channels 636E are defined in the inner surface 636F of the side wall 636A.
- the sleeve 636 is tubular and has an outer surface 636G that is generally cylindrical.
- the sleeve 636 is formed of a high temperature polymer and, in some embodiments, a high temperature thermoplastic.
- the sleeve 636 is formed of polyetherimide (PEI), such as ULTEMTM thermoplastic available from SABIC of Saudi Arabia.
- the sleeve 636 is formed of non-reinforced polyetherimide.
- the sleeve 636 is formed of an electrically insulating ceramic.
- the sleeve 636 is formed of a material having a melting point greater than the melting point of the meltable member 632. According to some embodiments, the sleeve 636 is formed of a material having a melting point in the range of from about 120 to 200 °C.
- the sleeve 636 material can withstand a voltage of 25 kV per mm of thickness.
- the sleeve side wall 636A has a nominal thickness T5 ( FIG. 20 ) of at least 2 mm, in some embodiments at least 4 mm, and in some embodiments in the range of from about 2 to 15 mm.
- the depth D5 of each receiver channel 636E is at least 1 mm and, in some embodiments, in the range of from about 1 to 12 mm.
- the internal chamber 627 of the housing assembly 621 of the overvoltage protection device 600 includes a first subchamber 627A and a second subchamber 627B in fluid communication with the first subchamber 627A.
- the electrode 624 and the meltable member 632 Prior to melting of the meltable member 632, the electrode 624 and the meltable member 632 occupy the first subchamber 627A.
- the varistor assembly 650 occupies a central volume of the second subchamber 627B such that a remaining tubular void or gap volume 627C of the second subchamber 627B remains unoccupied by the varistor assembly 650.
- the gap volume 627C is the space or volume extending radially between the varistor assembly 650 and the inner surface 622H of the sidewall 622B of the housing electrode 622.
- the void filling sleeve 636 occupies the gap volume 627C and surrounds the varistor assembly 650.
- the receiver recesses or channels 636E and the bridge portions 660B, 662B of the interconnect members 660, 662 are relatively sized and assembled such that each of the bridge portions 660B, 662B is received and seated in a respective one of the receiver channels 636E.
- the remainder of the sleeve inner surface 636F generally conforms to the peripheral profiles of the varistor wafers 652, 654, 654.
- the inner surface 636F generally conforms to the outer shape of the varistor assembly 650.
- the cylindrical outer surface 636G generally conforms to the inner shape of the inner wall surface 622H of the housing electrode 622.
- the gap between the inner surface 636F and the varistor wafers 652, 654, 654 is less than 2 mm. In some embodiments, the gap between the outer surface 636G and the inner wall surface 622H is less than 0.5 mm.
- the varistor wafers 652, 654, 656 are relatively thick so that the overall height of the varistor assembly 650 is increased as compared to that of the varistor assembly 150, for example. As a result, the gap void or volume 627C surrounding the varistor assembly 650 is relatively large. Additionally, the bridge portions 660B, 662B project radially outwardly beyond the peripheral edges of the varistors 652, 654, 656. Because the inner surface 622H of the housing electrode 622 is cylindrical, the required spacing between the bridge portions 660B, 662B and the inner surface 622B creates relatively large gaps around the remainder of the varistor assembly 650.
- this large gap volume 627C could compromise the intended operation of the meltable member 632 and the fail-safe mechanism 602.
- the volume of the melted meltable member 632 may not be sufficient to bridge the electrodes 622 and 624 to short circuit the electrodes 622, 624, depending on the orientation of the device 600 when the meltable member 632 is melted.
- the spacer sleeve 636 occupies the gap volume 627C and thereby reduces or limits the amount or volume of the meltable member 632 that can flow into the gap volume 627C when the meltable member 632 becomes molten. In this way, the void filling member 636 ensures that a greater and reliably sufficient quantity of the melted meltable member is retained in the first subchamber 627A to make simultaneous contact with the two electrodes 622, 624.
- the void filling sleeve 636 occupies at least 50 percent of the gap volume 627C and, in some embodiments, at least 80 percent. In some embodiments, the void filling sleeve 636 has a volume in the range of from about 100 mm 3 to 100,000 mm 3 and, in some embodiments, the volume is about 21,000 mm 3 .
- void filling member 636 is configured as a unitary, tubular sleeve having axially extending receiver channels 636E defined therein, other configurations and constructions may be employed.
- the channels 636E may be replaced with radially extending bores that do not extend to the ends of the sleeve.
- the void filling member 636 may be replaced with two or more void filling members that are configured and arranged to occupy the gap volume 627C to the degree and with the dimensions discussed above.
- the two or more void filling members may be axially stacked and or may each surround the varistor assembly 650 by less than 360 degrees.
- the overvoltage protection device 700 can be used in the same manner and for the same purpose as the overvoltage protection device 600.
- the overvoltage protection device 700 is constructed in the same manner as the overvoltage protection device 600, except as follows.
- the device 700 includes a varistor assembly 750 corresponding to the varistor assembly 650, and a void filling member 736 corresponding to the void filling member 636.
- the overvoltage protection device 700 includes an elastomeric insulator member 739 corresponding to the elastomeric insulator member 239 ( FIG. 12 ).
- the insulator member 739 is captured between the cover 726 and the electrode upper flange 724D and axially compressed (i.e., axially loaded and elastically deformed from its relaxed state) so that the insulator member 739 serves as a biasing member and applies a persistent axial pressure or load to the electrode 724 and the cover 726, as described with regard to the unit 200.
- an elastomeric insulator member corresponding to the elastomeric insulator member 239 can be used on place of the springs and end insulator members (e.g., insulator member 128C) of the overvoltage protection devices 100, 300, 400, 600.
- the varistor assemblies of each device 100-700 can be replaced with a varistor assembly of another one of the devices 100-700 (e.g., the five-wafer varistor assembly 350 or the two-wafer varistor assembly 450 can be used in place of the varistor assembly 650 in the device 600).
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- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Manufacturing & Machinery (AREA)
- Thermistors And Varistors (AREA)
- Emergency Protection Circuit Devices (AREA)
Claims (14)
- Überspannungsschutzvorrichtung (100), umfassend:eine Varistoranordnung (150), umfassend:eine Vielzahl von Varistorwafers (152, 154, 156) wobei jeder aus einem Varistormaterial geformt ist;zumindest ein elektrisch leitfähiges Verbindungselement (160, 162), das die Varistorwafers elektrisch parallel geschaltet verbindet; undein Bindemittel (164, 164'), das zumindest zwei der Varistorwafers in der Varistoranordnung aneinander bindet;wobei die Varistorwafers und das zumindest eine Verbindungselement axial gestapelt sind;ein erstes Elektrodenelement (122); undein zweites Elektrodenelement (124);wobei das zumindest eine elektrisch leitfähige Verbindungselement den/die Varistorwafer(s) elektrisch parallel geschaltet zwischen den ersten und zweiten Elektrodenelementen verbindet oder verbinden; undwobei die Varistorwafers axial zwischen den ersten und zweiten Elektroden gestapelt sind.
- Überspannungsvorrichtung nach Anspruch 1, wobei das Bindemittel (164, 164') zumindest eins aus einem Klebstoff auf Cyanacrylatbasis und einem Klebstoff auf Epoxidbasis ist.
- Überspannungsschutzvorrichtung nach Anspruch 1 oder Anspruch 2, wobei das Bindemittel (164, 164') an periphere Kanten (152E, 154E, 156E) der Varistorwafers geklebt wird und/oder wobei das Bindemittel (164, 164') eine Vielzahl von zirkumferenziell beabstandeten Bindemittelmassen einschließt, die an die peripheren Kanten der Varistorwafers geklebt sind.
- Überspannungsvorrichtung nach irgendeinem der Ansprüche 1 bis 3, wobei das Bindemittel (164, 164') eine Vielzahl von zirkumferenziell beabstandeten Bindemittelmassen einschließt, die an die peripheren Kanten der Varistorwafers geklebt sind.
- Überspannungsschutzvorrichtung nach irgendeinem vorhergehenden Anspruch wobei:jeder der Varistorwafers (152, 154, 156) entgegengesetzte planare Kontaktflächen (152U, 152L, 154U, 154L, 156U, 156L) einschließt;jedes der Verbindungselemente (160, 162) zwei beabstandete, planare Kontaktabschnitte (160U, 160L, 162U, 162L) und einen Brückenabschnitt (160B, 162B) einschließt, der sich zwischen den Kontaktabschnitten erstreckt und diese elektrisch verbindet; unddie Kontaktabschnitte in jeweilige der planaren Kontaktflächen der Varistorwafers eingreifen;optional wobei jeder Kontaktabschnitt zumindest in 40 Prozent jeder Kontaktfläche eingreift, die dadurch in Eingriff gebracht wird.
- Überspannungsschutzvorrichtung nach irgendeinem vorhergehenden Anspruch wobei jeder Varistorwafer Metallisierungsschichten (157) einschließt, die entgegengesetzte planare Kontaktflächen des Varistorwafers formen.
- Überspannungsschutzvorrichtung nach irgendeinem vorhergehenden Anspruch wobei die Varistoranordnung (450) einen Isolatorwafer (457) einschließt, der axial zwischen zumindest zwei der Vielzahl von Varistorwafers (452, 454) gelegt und gestapelt ist.
- Überspannungsschutzvorrichtung nach irgendeinem vorhergehenden Anspruch wobei:die Vielzahl von Varistorwafers erste, zweite und dritte Varistorwafers (152, 154, 156) einschließt; unddas zumindest eine Verbindungselement zumindest erste und zweite Verbindungselemente (160, 162) einschließt, welche die Varistorwafers elektrisch parallel geschaltet zwischen den ersten und zweiten Elektrodenelementen verbinden.
- Überspannungsschutzvorrichtung nach Anspruch 8, wobei:das erste Verbindungselement (160) jedes des ersten Elektrodenelements (122) und der ersten, zweiten und dritten Varistorwafers (152, 154, 156) kontaktiert und elektrisch verbindet; unddas zweite Verbindungselement (162) jedes des zweiten Elektrodenelements (124) und der ersten, zweiten und dritten Varistorwafers (152, 154, 156) kontaktiert und elektrisch verbindet.
- Überspannungsschutzvorrichtung nach irgendeinem vorhergehenden Anspruch wobei:die erste Elektrode (122) eine Gehäuseelektrode einschließt, die eine Endwand (122A) und eine integrale Seitenwand (122B) einschließt, die zusammen einen Hohlraum (122C) definieren;sich die zweite Elektrode (124) in den Hohlraum erstreckt;die Varistoranordnung im Hohlraum angeordnet ist; unddie Gehäuseelektrode einheitlich aus Metall geformt ist.
- Überspannungsschutzvorrichtung nach irgendeinem vorhergehenden Anspruch, die einschließt:eine Vorspannvorrichtung (128E), die eine axiale Druckbelastung auf die Varistoranordnung anwendet; und/oderein elektrisch leitfähiges, schmelzbares Element (632), wobei das schmelzbare Element auf Wärme in der Überspannungsschutzvorrichtung anspricht, um zu schmelzen und einen elektrischen Kurzschlusspfad über die ersten und zweiten Elektrodenelemente zu formen.
- Überspannungsschutzvorrichtung nach Anspruch 11, die ein Hohlraumfüllelement (636) einschließt, das zumindest einen Abschnitt der Varistoranordnung umgibt, wobei das Hohlraumfüllelement aus einem elektrisch isolierenden Material geformt ist;
wobei das Hohlraumfüllelement (636) eine Aufnahmevertiefung (636E) und einen Abschnitt (660B) der Verbindung (660) einschließt, die sich nach außen über die Vielzahl von Varistoren (652, 654, 656) hinaus erstreckt und in der Aufnahmevertiefung angeordnet ist. - Überspannungsschutzvorrichtung nach Anspruch 12, wobei:die erste Elektrode (622) eine Gehäuseelektrode einschließt, die eine Endwand und eine integrale Seitenwand (622B) einschließt, die zusammen eine Kammer (627) definieren;die Kammer eine erste Unterkammer (627A) und eine zweite Unterkammer (627B) in Flüssigkeitsverbindung mit der ersten Unterkammer einschließt;das schmelzbare Element (632) in der ersten Unterkammer angeordnet ist;die Varistoranordnung (650) in der zweiten Unterkammer angeordnet ist und ein Spaltvolumen (627C) zwischen der Varistoranordnung und der Seitenwand definiert ist; unddas Hohlraumfüllelement (636) im Spaltvolumen angeordnet ist, um einen Fluss des schmelzbaren Elements in das Spaltvolumen zu begrenzen;optional wobei das Hohlraumfüllelement (636) zumindest 50 Prozent des Spaltvolumens einnimmt.
- Überspannungsschutzvorrichtung nach Anspruch 8 oder irgendeinem vom Anspruch 8 abhängigen Anspruch, wobei:die erste Elektrode (223) eine einheitliche Gehäuseelektrode ist, wobei die Gehäuseelektrode erste und zweite Hohlräume (222C) einschließt;die Varistoranordnung (250) im ersten Hohlraum angeordnet ist; unddie Überspannungsschutzvorrichtung ferner einschließt:eine zweite Varistoranordnung (250), die im zweiten Hohlraum angeordnet ist, wobei die zweite Varistoranordnung einschließt:eine Vielzahl von Varistorwafers, wobei jeder aus einem Varistormaterial geformt ist; undZumindest ein elektrisch leitfähiges Verbindungselement; und ein drittes Elektrodenelement,wobei die Varistorwafers der zweiten Varistoranordnung axial zwischen der Gehäuseelektrode und der dritten Elektrode gestapelt sind; undwobei das zumindest eine Verbindungselement der zweiten Varistoranordnung die Varistorwafers der zweiten Varistoranordnung elektrisch parallel geschaltet zwischen der Gehäuseelektrode und der dritten Elektrode verbindet.
Priority Applications (5)
Application Number | Priority Date | Filing Date | Title |
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PL18190872T PL3413320T3 (pl) | 2017-10-27 | 2018-08-25 | Urządzenie zabezpieczające przed przepięciem zawierające wiele płytek warystorowych |
SI201830133T SI3413320T1 (sl) | 2017-10-27 | 2018-08-25 | Prenapetostna zaščitna naprava, ki vključuje več rezin varistorja |
RS20201341A RS61022B1 (sr) | 2017-10-27 | 2018-08-25 | Uređaj prenaponske zaštite sa više varistorskih vafera |
EP20174839.9A EP3716296A3 (de) | 2017-10-27 | 2018-08-25 | Überspannungsschutzvorrichtung mit mehreren varistorwafern |
HRP20201798TT HRP20201798T1 (hr) | 2017-10-27 | 2020-11-10 | Uređaj za zaštitu od prenapona, uključujući više varistorskih pastila |
Applications Claiming Priority (1)
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US15/795,986 US10707678B2 (en) | 2016-12-23 | 2017-10-27 | Overvoltage protection device including multiple varistor wafers |
Related Child Applications (2)
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EP20174839.9A Division EP3716296A3 (de) | 2017-10-27 | 2018-08-25 | Überspannungsschutzvorrichtung mit mehreren varistorwafern |
EP20174839.9A Division-Into EP3716296A3 (de) | 2017-10-27 | 2018-08-25 | Überspannungsschutzvorrichtung mit mehreren varistorwafern |
Publications (3)
Publication Number | Publication Date |
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EP3413320A2 EP3413320A2 (de) | 2018-12-12 |
EP3413320A3 EP3413320A3 (de) | 2019-07-24 |
EP3413320B1 true EP3413320B1 (de) | 2020-08-12 |
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EP18190872.4A Active EP3413320B1 (de) | 2017-10-27 | 2018-08-25 | Überspannungsschutzvorrichtung mit mehreren varistorwafern |
EP20174839.9A Pending EP3716296A3 (de) | 2017-10-27 | 2018-08-25 | Überspannungsschutzvorrichtung mit mehreren varistorwafern |
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EP20174839.9A Pending EP3716296A3 (de) | 2017-10-27 | 2018-08-25 | Überspannungsschutzvorrichtung mit mehreren varistorwafern |
Country Status (11)
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EP (2) | EP3413320B1 (de) |
CN (2) | CN109727739B (de) |
CY (1) | CY1123713T1 (de) |
DK (1) | DK3413320T3 (de) |
ES (1) | ES2827702T3 (de) |
HR (1) | HRP20201798T1 (de) |
HU (1) | HUE051788T2 (de) |
PL (1) | PL3413320T3 (de) |
PT (1) | PT3413320T (de) |
RS (1) | RS61022B1 (de) |
SI (1) | SI3413320T1 (de) |
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CN117081023B (zh) * | 2023-08-21 | 2024-02-06 | 济南雷盾电子技术有限公司 | 一种免维护充电桩电源防雷器 |
Family Cites Families (10)
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US3863111A (en) * | 1973-06-29 | 1975-01-28 | Gen Electric | Polycrystalline varistor surge protective device for high frequency applications |
US5130884A (en) * | 1986-10-28 | 1992-07-14 | Allina Edward F | Parallel electrical surge-protective varistors |
US5608596A (en) * | 1990-10-16 | 1997-03-04 | Cooper Power Systems, Inc. | Surge arrester with spring clip assembly |
CA2098365A1 (en) * | 1992-06-30 | 1993-12-31 | Robert William Smith | Surge arrester with spring clip assembly |
US7433169B2 (en) * | 2005-12-15 | 2008-10-07 | Raycap Corporation | Overvoltage protection devices including wafer of varistor material |
DE102009004704B4 (de) * | 2008-09-17 | 2015-03-12 | Dehn + Söhne Gmbh + Co. Kg | Überspannungsableiter mit einer Schalteinrichtung zum Auslösen einer Abtrenneinrichtung |
JP5493065B2 (ja) * | 2011-03-24 | 2014-05-14 | 音羽電機工業株式会社 | バリスタ装置およびその製造方法 |
DE102012004678A1 (de) * | 2012-03-12 | 2013-09-12 | Phoenix Contact Gmbh & Co. Kg | Überspannungsschutzgerät |
US8743525B2 (en) * | 2012-06-19 | 2014-06-03 | Raycap Intellectual Property, Ltd | Overvoltage protection devices including wafer of varistor material |
US10447023B2 (en) * | 2015-03-19 | 2019-10-15 | Ripd Ip Development Ltd | Devices for overvoltage, overcurrent and arc flash protection |
-
2018
- 2018-08-25 EP EP18190872.4A patent/EP3413320B1/de active Active
- 2018-08-25 PL PL18190872T patent/PL3413320T3/pl unknown
- 2018-08-25 RS RS20201341A patent/RS61022B1/sr unknown
- 2018-08-25 ES ES18190872T patent/ES2827702T3/es active Active
- 2018-08-25 PT PT181908724T patent/PT3413320T/pt unknown
- 2018-08-25 SI SI201830133T patent/SI3413320T1/sl unknown
- 2018-08-25 HU HUE18190872A patent/HUE051788T2/hu unknown
- 2018-08-25 DK DK18190872.4T patent/DK3413320T3/da active
- 2018-08-25 EP EP20174839.9A patent/EP3716296A3/de active Pending
- 2018-10-26 CN CN201811257996.9A patent/CN109727739B/zh active Active
- 2018-10-26 CN CN202210907190.XA patent/CN115116683A/zh active Pending
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2020
- 2020-10-29 CY CY20201101020T patent/CY1123713T1/el unknown
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Also Published As
Publication number | Publication date |
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ES2827702T3 (es) | 2021-05-24 |
CN109727739A (zh) | 2019-05-07 |
SI3413320T1 (sl) | 2020-11-30 |
CN115116683A (zh) | 2022-09-27 |
EP3716296A2 (de) | 2020-09-30 |
PT3413320T (pt) | 2020-10-26 |
EP3413320A3 (de) | 2019-07-24 |
HUE051788T2 (hu) | 2021-03-29 |
PL3413320T3 (pl) | 2021-01-25 |
CN109727739B (zh) | 2022-08-09 |
EP3716296A3 (de) | 2020-10-21 |
RS61022B1 (sr) | 2020-12-31 |
DK3413320T3 (da) | 2020-11-09 |
EP3413320A2 (de) | 2018-12-12 |
CY1123713T1 (el) | 2022-03-24 |
HRP20201798T1 (hr) | 2021-01-08 |
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