RS66508B1 - Overvoltage protection device including multiple varistor wafers - Google Patents

Description

Description

FIELD OF INVENTION

[0001] This invention relates to devices for circuit protection and, in particular, to devices and methods for overvoltage protection.

BACKGROUND OF THE INVENTION

[0002] Frequently, an excessive value of voltage or current is applied over service lines that deliver electrical power to residential units and commercial or institutional facilities. Such excess voltage or current surges (transient overvoltages and surge currents) can occur from lightning strikes, for example. The above events can be of particular concern in telecommunications distribution centers, hospitals and other facilities where equipment damage caused by power surges and/or power surges and resulting power outages can incur very high costs.

[0003] Usually, sensitive electronic equipment can be protected from transient overvoltages and surge currents by using surge protective devices (SPD). For example, a brief reference is made to Figure 1, which shows a system incorporating conventional surge and surge protection. The overvoltage protection device 12 can be installed at the power input of the equipment 50 to be protected, which is usually protected from excessive surge currents at the time of failure. A typical type of SPD device failure is a short circuit. The most commonly used overcurrent protection is a combination of internal thermal disconnectors that protect the device from overheating due to increased leakage currents and external fuses to protect the device from higher fault currents. Various SPD technologies can avoid the use of internal thermal disconnectors, since, in case of failure, they change their mode of operation to low ohmic resistance. Consequently, the device can withstand significant short-circuit currents. In this regard, there may not be an operational need for internal thermal disconnects. Furthermore, in addition to the above, some designs that have the ability to withstand even higher short-circuit currents can also be protected only by the main circuit fuse in the installation, without the need for a separately assigned branch circuit fuse.

[0004] Brief reference is now made to Figure 2, which is a block diagram of a system incorporating conventional overvoltage and overcurrent protection. As shown, a three-phase line may be connected in the electrical network, thereby supplying power to one or more transformers 66, which may supply three-phase power to a circuit breaker 68. Three-phase power may be provided to one or more distribution panels 62. As shown, the three line voltage lines, three-phase power, may be labeled L1, L2, and L3 and the neutral line may be labeled N. In some embodiments, the neutral line N may be conductively connected to earth.

[0005] Some embodiments include surge protection devices (SPDs) 15 . As shown, each of the SPD devices 15 may be connected between the respective lines L1, L2, L3 and neutral (N). The SPD 15 can protect other equipment in the installation, such as the distribution panel among others. In addition, SPD devices can be used to protect all equipment in the event of a surge of longer duration. However, such a condition may force the SPD to carry a limited current for an extended period of time, which may lead to the SPD overheating and possibly tripping (depending on the energy endurance the SPD can absorb and the level and duration of the overvoltage condition). A typical operating voltage of the SPD device 15 in the example shown may be around 400 V (for phase-to-phase voltage systems of 690 V L-L). In this sense, SPD devices 15 act as insulators and thus do not conduct current under normal operating conditions. In such embodiments, the operating voltage of the SPD device 15 is substantially higher than the normal phase voltage, to ensure that the SPD device 15 continues to act as an isolator, even in cases where the system voltage increases due to overvoltage conditions, which may occur as a result of neutral conductor loss or other power system problems.

[0006] In the case of occurrence of surge current in, for example, L1 line, the protection of the load device of the power system must necessarily ensure the passage of current to the ground for the excessive value of the surge current. The inrush current can generate a transient overvoltage between line L1 and neutral N. Since the transient overvoltage significantly exceeds the operating voltage of SPD 15, SPD 15 becomes conductive, allowing excess current to flow from line L1 through SPD 15 to neutral N. After the inrush current has been conducted to neutral N, the overvoltage condition ends and SPD 15 can become non-conductive again. However, in some cases, one or more of the SPD devices 15 may begin to allow leakage current to flow even at voltages lower than the operating voltage of the SPD device 15. Such conditions may occur in the event of deterioration of the SPD device.

[0007] As mentioned above, devices for protecting equipment from overvoltage or current shocks (transient overvoltages and surge currents) can include integrated varistors (for example, metal oxide varistors (eng. Metal oxide varistors - MOV) and/or silicon carbide varistors).

US2013/0335869A1 describes a surge protection device including first and second electrically conductive electrode members and a varistor member.

US 2015/103462 A1 describes a surge protection device having a metallic safety element.

US 2016/276821 A1 describes devices for protection against overvoltages, excessive surge currents and electric arcs.

CA 2,098,365 A1 describes surge arresters which are particularly suitable for the secondary protection of distribution transformers with low voltage, high energy, varistor disks.

BRIEF OVERVIEW OF THE INVENTION

[0008] A surge protection device is provided as required in the appended claims.

[0009] These and other objects and/or aspects of the present invention are explained in detail in the specification set forth ahead.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to provide a better understanding of the implementation of the proposed invention, the accompanying drawings are included, are included and form an integral part of the specification. The drawing figures illustrate some embodiments of the proposed invention and, together with the description, serve to explain the principles of the proposed invention.

Figure 1 is a block diagram of a system incorporating conventional surge protection. Figure 2 is a block diagram of a system incorporating conventional surge protection. Figure 3 is a perspective view of the surge protection device.

Figure 4 is an exploded perspective view of the surge protection device of Figure 3.

Figure 5 is a cross-sectional view of the surge protection device of Figure 3, along axis 5-5 of Figure 3.

Figure 6 is a perspective view of the varistor circuit, which forms part of the surge protection device of Figures 3.

Figure 7 is an exploded perspective view of the varistor circuit of Figure 6.

Figure 8 is a cross-sectional view of the varistor assembly of Figure 6, along axis 8-8 of Figure 6.

Figure 9 is a schematic diagram representing the electrical circuit of the varistor circuit of Figure 6.

Figure 10 is a perspective view of the surge protection device.

Figure 11 is an exploded perspective view of the surge protection device of Figure 10.

Figure 12 is a cross-sectional view of the surge protection device of Figure 10, along axis 12-12 of Figure 10.

Figure 13 is a cross-sectional view of the surge protection device.

Figure 14 is a cross-sectional view of the surge protection device.

Figure 15 is a perspective view of the surge protection device.

Figure 16 is a cross-sectional view of the surge protection device of Figure 15, along axis 16-16 of Figure 15.

Figure 17 is a cross-sectional view of a surge protection device according to embodiments of the invention.

Figure 18 is an exploded perspective view of the surge protection device of Figure 17.

Figure 19 is a cross-sectional view of the surge protection device of Figure 17, along axis 19-19 of Figure 17.

Figure 20 is a top view of the cavity filling member forming part of the surge protection device of Figure 17.

Figure 21 is a cross-sectional view of a surge protection device according to other embodiments of the invention.

DETAILED DESCRIPTION OF THE IMPLEMENTATION OF THE INVENTION

[0011] Figures 17-21 show embodiments in accordance with the claimed invention. Figures 3-16 show some of the features of the claimed invention and provide an understanding of the claimed invention. The proposed invention will now be described in more detail below, 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 shown enlarged for clarity. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments shown herein; more specifically, these embodiments are described in order to provide a thorough and comprehensive view of the invention, and the scope of the invention is fully conveyed to those skilled in the art.

[0012] It will be understood that when an element is designated as being "joined" or "connected" to another element, it may be directly joined or connected to another element or certain intermediate elements may be present. Conversely, when an element is marked as "directly connected" or "directly connected" to another element, there are no intermediate elements present. Similar elements are marked here with similar numbers.

[0013] In addition, spatially relative terms, such as "under," "below," "over," "above," and the like may be used herein for ease of description, to represent one element or characteristic relationship to another element(s) or characteristic(s), as shown in the figures. It is understood that spatially relative terms are intended to include different orientations of the device in use or operation with the orientation shown in the figures. For example, if the device in the images is facing up, elements that are marked "under" or "under" other elements or features will then point "over" the other elements or features. Therefore, the term from the example "below" can include both direction over and under. The device may be oriented differently (rotated 90 degrees or in other positions) and spatially relative descriptions are then interpreted accordingly.

[0014] Well-known functions or constructs may not be described in detail for the sake of brevity and/or clarity.

[0015] As used herein, the term "or/and" includes one or all combinations of one or more related items.

[0016] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the invention. As used herein, the singular forms are intended to include the plural as well, unless the context clearly indicates otherwise. It will further be understood that the terms "comprises" and/or "consisting of", when used in this specification, indicate the presence of said features, integers, steps, operations, elements, and/or components, but do not exclude the presence or addition of one or more features, integers, steps, operations, elements, components, and/or groups thereof.

[0017] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It will further be understood that terms such as those defined in commonly used dictionaries are to be interpreted to have a meaning consistent with their meaning in the context of the relevant technical field and shall not be construed in an idealized or overly formal sense, unless expressly defined herein.

[0018] As used herein, "monolithic" means an object that is single, of one piece, formed or composed of material without joints or seams.

[0019] As used herein, the term "wafer" refers to a layer having a thickness that is relatively small compared to its diameter, length, or width.

[0020] Referring to Figures 1-9, a modular surge protection device (SPD) or surge protection device is shown herein and designated 100. In accordance with some embodiments, the surge protection device 100 is used as an SPD in an electrical circuit, as discussed earlier. For example, surge protection device 100 may be used in place of SPD device 12 in the system of Figure 1 or in place of SPD device 15 in the system of Figure 2.

[0021] The surge protection device 100 is configured as a unit or module, which has a longitudinal axis A-A (Figure 5). The surge 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 safety clamp 128B, a fusible member 132, insulating sleeve 134.

[0022] The overvoltage protection device 100 further includes a varistor circuit 150, according to embodiments of the proposed 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 .

[0023] The surge protection device 100 may further include an integrated safety mechanism, arrangement, feature, or system 102. The failure protection system 102 is adapted to prevent or prevent overheating or thermal breakdown of the surge protection device, as explained in more detail below.

[0024] Components 122, 124, 128A-C, which together form a housing assembly 121, which defines a sealed, closed chamber 126. Components 122, 124, 128A-E, 132 and 150 are located axially between the housing 122 and the electrode 124, along the longitudinal axis A-A in the closed chamber 126.

[0025] The housing 122 has an electrode wall 122A and an integral cylindrical side wall 122B, which extends from the electrode wall 122A. Side wall 122B and electrode wall 122A form a chamber or cavity 122C communicating with opening 122D. Threaded post 122E extends axially outwardly from electrode wall 122A.

[0026] Electrode wall 122A has an inwardly facing, substantially flat contact surface 122G. An annular slot 122H for the clamp is formed on the inner surface of the side wall 122B. According to some embodiments, the housing 122 is made of aluminum. However, any suitable conductive metal can be used. According to some embodiments, the housing 122 is one piece and, in some embodiments, monolithic. Housing 122, as illustrated, is cylindrical in shape, but may be shaped differently.

[0027] The internal electrode 124 has a head 124A, which is placed in the cavity 122C and an integrated shaft 122B, which is directed outwardly through the opening 122D.

[0028] The head 124A has a generally flat contact surface 124C, which faces the contact surface 122G of the electrode wall 122A. A pair of integral, annular, axially spaced flanges 124D extend radially outwardly from shaft 124B and define an annular, laterally open groove 124E therebetween. A threaded bore 124F is formed in the end of the shaft 124B, to accept a screw for securing the electrode 124 to the busbar, for example. An annular, laterally open groove 124G is formed on the shaft 124B.

[0029] According to some embodiments, the electrode 124 is made of aluminum. However, any suitable conductive metal can be used. According to some embodiments, the electrode 124 is one piece and, in some embodiments, monolithic.

[0030] Electrodes 122, 124, insulating ring 128C, and end cap 128A together define a closed chamber 126, which contains fusible member 132 and varistor assembly 150.

[0031] 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 about 1 to 15 mm.

[0032] The fusible member 132 is annular and is placed on the electrode 124 in the groove 124E. The fusible member 132 is spaced from the side wall 122B by a distance sufficient to electrically isolate the fusible member 132 from the side wall 122B.

[0033] The fusible member 132 is made of a fusible, electrically conductive material. According to some embodiments, the fusible member 132 is formed of a metal. According to some embodiments, the fusible member 132 is formed from an electrically conductive metal alloy. According to some embodiments, the fusible member 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 can be used.

[0034] According to some embodiments, the fusible member 132 is selected so that its melting point is greater than the prescribed maximum standard operating temperature. The maximum standard operating temperature may be the highest temperature expected in fusible Article 132, during normal operation (including surge operation, within the values designed for the system's range), but not during operation that, if left unchecked, would result in thermal breakdown. According to some embodiments, the fusible member 132 is formed of a material having a melting point in the range of 80 to 160 °C and, according to some embodiments, in the range of about 130 to 150 °C. According to some embodiments, the melting point of the fusible member 132 is at least 20 °C less than the melting point of the housing 122 and the electrode 124 and, according to some embodiments, at least 40 °C less than the melting point of those components.

[0035] According to some embodiments, the fusible member 132 has an electrical conductivity in the range of 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 about 1 x 10<6>S/m to 3 x 10<6>S/m.

[0036] Three varistor wafers 152, 154, 156 and two interconnecting elements 160, 162 are axially stacked in the chamber 126, between the head 124 of the electrode and the electrode wall 122 and form the varistor assembly 150. The interconnecting members 160, 162 electrically interconnect the wafers 152, 154, 156 and electrodes 122, 124, in the manner represented by the schematic electrical diagram in Figure 9.

[0037] According to some embodiments, each varistor trigger 152, 154, 156 is a varistor wafer (ie wafer or thin disk). In some embodiments, each of the varistor wafers 152, 154, 156 is circular in shape and has a substantially uniform thickness. However, the varistor wafers 152, 154, 156 may be shaped differently. The thickness and diameter of the varistor wafers 152, 154, 156 will depend on the varistor characteristics desired for a particular application.

[0038] In some embodiments, each varistor wafer 152, 154, 156 has a ratio of diameter D1 to thickness T1 of at least three. In some embodiments, the thickness T1 (FIG. 8) of each of the varistor wafers 152, 154, 156 ranges from about 0.5 to 15 mm. In some embodiments, the diameter D1 (FIG. 8) of each of the varistor wafers 152, 154, 156 is in the same range of about 20 to 100.

[0039] The varistor assembly 152 has first and second opposite, generally planar contact surfaces 152U, 152L and a peripheral screw 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.

[0040] The varistor material can be any suitable material conventionally used for varistors, i.e. a material that exhibits a non-linear resistance characteristic with applied voltage. It is desirable that the resistance becomes very low when the prescribed voltage value is exceeded. The varistor material can be doped metal oxides or silicon carbide, for example. Suitable metal oxides include zinc oxide compounds.

[0041] Each varistor wafer 152, 154, 156 may include a wafer of varistor material that is coated on both sides with a conductive coating 157, so that the exposed coating surfaces serve as contact surfaces 152U, 152L, 154U, 154L, 156U, 156L. The coating can be a metallized form consisting of aluminum, copper or silver, for example. Conversely, clean surfaces of the varistor material may serve as contact surfaces 152U, 152L, 154U, 154L, 156U, 156L.

[0042] Interconnecting members 160, 162 are electrically conductive. Interconnect member 160 includes a pair of axially spaced disc-shaped contacts as portions 160U, 160L, connected by a bridge 160B. Interconnect member 162 includes a pair of axially spaced disc-shaped contacts as portions 162U, 162L, connected by a bridge 162B.

[0043] According to some embodiments, each contact portion 160U, 160L, 162U, 162L is substantially flat, relatively thin, and wafer- or disc-shaped. In some embodiments, each contact portion 160U, 160L, 162U, 162L has a ratio of diameter D2 (Figure 8) to thickness T2 (Figure 8) of at least 15. In some embodiments, the thickness T2 of each contact portion 160U, 160L, 162U, 162L is in the range of about 0.1 to 3 mm. In some embodiments, the diameter D2 of each contact portion 160U, 160L, 162U, 162L is in the range of about 20 to 100 mm.

[0044] According to some embodiments, none of the contact portions 160U, 160L, 162U, 162L have any cavities extending through the thickness of the contact portion.

[0045] In some embodiments, the width W3 (Figure 6) of each bridge 160B, 162B is in the range of about 2 mm to 10 mm. The cross-section of each bridge 160B, 162B should be large enough to withstand the short-circuit current that may flow through the SPD device following a possible failure of one or more of the varistor wafers 152, 154, 156.

[0046] According to some embodiments, the interconnecting members 160, 162 are formed of copper. However, any suitable electrically conductive metal can be used. According to some embodiments, the connecting members 160, 162 are of one piece and, in some embodiments, monolithic.

[0047] In the varistor assembly 150, the varistor wafer 154 is placed or nested in a sandwich between the varistor wafers 152, 156, the varistor wafers 152, 154, 156 are placed or nested in a sandwich between the interconnecting members 160, 162, and the interconnecting members 160, 162 are mutually intertwined, as shown in Figures 6 and 8. The contact portion 160U engages the contact surface 152U. The contact part 162U engages the contact surfaces 152L and 154U. The contact part 162L engages the surface 156L. Each mentioned form of engagement forms a close physical and mechanical contact between the identified contact parts of the interconnecting members and the varistor contact surfaces. Each of the mentioned forms of engagement forms a direct electrical connection or connection between the identified contact parts of the interconnecting members and the varistor contact surfaces. The contact portions 160U and 162L form or serve as the external electrode contact surfaces of the varistor assembly 150.

[0048] Each bridge 160B, 162B includes a pair of tab sections 163 (extending radially outward from the contact portions 160U, 160L or 162, 162L) and a connection section 165 that extends axially connecting the tab sections 163 and are radially spaced from adjacent peripheral edges of the varistor wafers 152, 154, 156. In some embodiments, each connection section 165 is located a distance D3 (FIG. 8) from adjacent peripheral edges of the varistor wafers 152, 154, 156. In some embodiments, the distance D3 is in the range of about 0.5 to 15 mm.

[0049] According to some embodiments, and as shown, there are no electrical insulators inserted between the components 152, 154, 156, 160, 162.

[0050] In some embodiments, the varistor wafers 152, 154, 156 are mutually secured by a bonding agent 164. According to some embodiments, the bonding agent 164 is located and secures adjacent varistor wafers 152, 154, 156 at their peripheral edges. In some embodiments, the bonding means 164 is formed as a plurality of discrete, spaced portions or points of the bonding means 164. Bonding is used to hold the components of the varistor assembly 150 in place during shipping and assembly of the surge protection device 100.

[0051] In some embodiments and as shown in Figures 5, 6 and 7, the bonding means 164 includes a portion or portions of the bonding means 164', located within the bridges 160, 162B, between each bridge 160B, 162B and adjacent edges of the varistor wafers 152, 154, 156. In such a way, these portions of the bonding means 164' may serve as electrical insulators, electrically isolating the bridges 160B, 162B, from the edges of the varistor wafers 152, 154, 156.

[0052] According to some embodiments, the binding agent 164 is an adhesive agent. As used herein, adhesive refers to adhesives or other adhesives derived from natural and/or synthetic sources. The adhesive is a polymer that binds to the surfaces to be bonded (eg, the edge surfaces of the varistor wafers 152, 154, 156). The adhesive may be any suitable adhesive. In some embodiments, the adhesive 164 secures the varistor wafers 152, 154, 156 at their peripheral edges and is discretely distributed in the form of zones or dots located at the peripheral edges.

[0053] In some embodiments, the adhesive 164 is either cyanoacrylate-based, or epoxy resin-based. Suitable cyanoacrylate-based adhesives may include Permabond 737 adhesive available from Permabond Engineering Adhesives, Inc of the United States of America.

[0054] In some embodiments, the adhesive has a high operating temperature, above 40 °C, does not contain any solvents, and has a high dielectric strength (eg, 5 kV/mm).

[0055] In some embodiments, the outer edges of each coating 157 are radially inserted from the outer edge of the varistor wafers 152, 154, 156, and the outer edge of each contact portion 160U, 160L, 162U, 162L is radially inserted from the outer edge of the layer 157.

[0056] In other embodiments, the varistor wafers 152, 154, 156 are mechanically secured and electrically directly connected to the respective contact portions 160U, 160L, 162U, 162L with electrically conductive solder.

[0057] The varistor assembly 150 may be assembled as follows, in accordance with embodiments of the invention.

[0058] Interconnecting members 160, 162 may be pre-bent into the shapes shown in Figure 7.

[0059] In some embodiments, each contact portion 160U, 160L, 162U, 162L covers and engages at least 40% of the corresponding area of the paired varistor wafer 152U, 152L, 154U, 154L, 156U, 156L.

[0060] The varistor wafers 152, 154, 156 and the interconnect members 160, 162 are placed and interlaced according to the order and relationship shown in Figures 6 and 8. This assembly can be fitted or placed, after assembly, in a fixed manner so as to laterally align the varistor wafers 152, 154, 156 and the interconnect members 160, 162 to each other. In some embodiments, the varistor wafers 152 , 154 , 156 and the interconnect members 160 , 162 are substantially coaxially aligned.

[0061] Aligned components 152, 154, 156, 160, 162 are axially pressure loaded, pressed or clamped together (eg, using a fixing means or additional external clamping or loading device) and are in close contact. A bonding agent 164 is then applied to the outer edges 152E, 154E, 156E of the varistor wafers 152, 154, 156, at the locations mentioned earlier, and bonding is performed. This forms the varistor assembly 150. After the bonding agent 164 has cured, the external load is removed from the varistor assembly 150.

[0062] The insulating sleeve 134 is tubular in shape and generally cylindrical. In some embodiments, the insulating sleeve 134 is formed from a high temperature polymer and, in some embodiments, a high temperature thermoplastic. In some embodiments, the insulating sleeve 134 is formed from polyetherimide (PEI), such as ULTEM<TM> thermoplastic, available from SABIC of Saudi Arabia. In some embodiments, the insulating sleeve 134 is formed from unreinforced polyetherimide.

[0063] According to some embodiments, the insulating sleeve 134 is formed of a material having a melting point greater than the melting point of the fusible member 132. According to some embodiments, the insulating sleeve 134 is formed of a material having a melting point in the range of about 120 to 200 °C.

[0064] According to some embodiments, the material of the insulating sleeve 134 can withstand a voltage of 25 kV per millimeter of thickness.

[0065] According to some embodiments, the insulating sleeve 134 has a thickness in the range of about 0.1 to 2 mm.

[0066] Spring coupling 128E surrounds shaft 124B. Each spring coupling 128E includes a cavity that receives a shaft 124B. The lowermost spring coupling 128E abuts the upper side of the head 124A. In some embodiments, the clearance between the spring coupling cavity and the shaft 124B is in the range of about 0.015 to 0.035 inches. The spring coupling 128E may be formed from a resilient material. According to some embodiments and as shown, the spring coupling 128E is a wave or spring washer (as shown) or a Belleville washer, formed from spring steel. Although two spring couplings are shown, more or fewer may be used. The spring can be arranged in different ways, such as in series, parallel or series and parallel.

[0067] A flat metal washer 128D is located between the uppermost spring coupling 128E and the isolation ring 128C with a shaft 124B passing through a cavity formed in the washer 128D. The washer 128D is intended to distribute the mechanical load of the upper spring coupling 128E, to prevent the spring coupling 128E from cutting into the insulating ring 128C.

[0068] The insulating ring 128C covers and abuts the washer 128D. Insulating ring 128C has a main ring body and a cylindrical top flange or collar extending upwardly from the main body ring. The cavity accepts the shaft 124B. In some embodiments, the clearance between the cavity and the shaft 124B is in the range of about 0.025 to 0.065 inches. An open groove is formed upwards and outwards, in the upper corner of the ring of the main body.

[0069] The insulating ring 128C is primarily made of a dielectric or electrically insulating material, which has a high melting point and combustion temperature. The insulating ring 128C can be formed from polycarbonate, ceramic or high temperature polymer, for example.

[0070] End cap 128A covers and abuts insulating ring 128C. End cap 128A has a cavity that receives shaft 124B. In some embodiments, the distance between the cavity and the shaft 124B is in the range of about 0.1 to 0.2 inches. End cap 128A may be formed from aluminum, for example.

[0071] Clamp 128B is elastic and in the form of a serrated ring. Clamp 128B is partially received in slot 122H and partially extends radially toward the inner wall of housing 122 to limit axial movement of end cap 128A. Clamp 128B may be formed from spring steel.

[0072] O-ring 130B is placed in groove 124G so that it is sandwiched between shaft 124B and isolation ring 128C. The O-ring 130A is placed in a groove in the insulating ring 128C so that it is sandwiched between the insulating member 128C and the side wall 122B. When installed, O-rings 130A, 130B are compressed so that they are opposed to form a seal between adjacent mating surfaces. In the event of a surge or failure, byproducts such as hot gases and fragments from the varistor wafers 152, 154, 156 may fill or disperse into the cavity of the chamber 126. The exit of these products from the surge protection device 100, through the opening 122D of the housing, may be limited or prevented by the O-rings 130A, 130B.

[0073] O-rings 130A, 130B can be formed from the same or different materials. According to some embodiments, the O-rings 130A, 130B are made of a resilient material, such as an elastomer. According to some embodiments, the O-rings 130A, 130B are made of rubber. O-rings 130A, 130B may be formed from fluorocarbon rubber, such as VITON<TM>, available from DuPont. Other rubbers can also be used, such as butyl rubber. According to some embodiments, the rubber has a hardness of about 60 to 100 Shore.

[0074] The electrode head 124A and the housing end wall 122A are constantly connected or loaded by a varistor assembly 150 along the loading or clamping axis C-C (Figure 5) in the F direction, to ensure a tight and uniform engagement between the above-defined contact contact surfaces. This aspect of the unit 100 can be appreciated by considering the method according to the proposed invention, for assembling the unit 100, as described above. In some embodiments, the C-C clamping axis substantially coincides with the A-A axis (Figure 5).

[0075] The components 152, 154, 156, 160, 162, 164 are assembled as shown earlier 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 interface member 162 engages the contact surface 122G of the end wall. 122A.

[0076] O-rings 130A, 130B are installed in their respective cavities.

[0077] The head 124A is inserted into the cavity 122C, such that the contact surface 124C engages the upper contact surface or part 160U of the interface member 160.

1

[0078] Spring couplings 128E are strung along shaft 124B. Washer 128D, insulating ring 128C, and end cap 128A are threaded down shaft 124B and over spring couplings 128E. A jig tool (not shown) or other suitable device is used to press down the end cap 128A by moving the spring coupling 128E. While the end cap 128A is still under pressure from the jig tool, the clamp 128B is pressed into the slot 122H. Clamp 128B is then released allowing it to return to its original diameter, partially filling the slot and partially extending radially inwardly into the cavity from slot 122H. Clamp 128B and slot 122H thereby serve to maintain the load on end cap 128A, for partial deflection of spring coupling 128E. The load of the end cap 128A to the insulating ring 128C and from the insulating ring to the spring couplings is in turn transferred to the head 124A. In this manner, the varistor assembly 150 is sandwiched (clamped) between the head 124A and the electrode wall 122A.

[0079] When the surge protection device 100 is assembled, the housing 122, electrode 124, insulating member 128C, end cap 128A, clamp 128B, O-rings 130A, 130B together form a single housing or housing assembly 121 containing the components in the chamber 126.

[0080] In the assembled surge protection device 100, the large flat contact surfaces of the components 122A, 124A, 152, 154, 156, 160, 162 can ensure reliable and stable electrical contact and connection between components during surges or surge currents. Head 124A and end wall 122A are mechanically biased by these components to provide a tight and uniform engagement between the mating contact surfaces.

[0081] Advantageously, the surge 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.

[0082] The construction of the surge protection device 100 provides a load in the form of pressure on the varistor wafers 152, 154, 156 in one modular unit. The surge protection device 100 provides adequate electrical interconnection between the electrodes 122, 124 and the varistor wafers 152, 154, 156, while maintaining a compact form factor and providing adequate thermal energy dissipation from the varistor wafers 152, 154, 156.

[0083] The construction of the surge protection device 100 provides a safe mode of operation in the event of a device failure. During use, one or more varistor wafers 152, 154, 156 may be damaged by overheating and may arc within the housing assembly 121. The housing assembly 121 may contain damage (eg, debris, gases, and heat spikes) within the surge protection device 100 such that the surge protection device 100 fails in a safe manner. In this way, the surge protection device 100 can prevent or reduce any damage to adjacent equipment (eg, switchgear in a cabinet) and endangering personnel. In this way, the surge protection device 100 can increase the safety of equipment and personnel.

[0084] In addition, the surge protection device 100 provides a fail-safe mechanism in the event of the end of service life in one of the multiple varistor wafers 152, 154, 156. In the event of failure of the varistor wafers 152, 154, 156, a fault current will flow between the corresponding phase conductor and the neutral conductor. As is well known, a varistor naturally has a rated switching voltage VNOM (often known as the "cut-off voltage" or simply "varistor voltage"), at which the varistor begins to conduct current. Below the voltage value VNOM, the varistor will not pass current. Above the VNOM value, the varistor will conduct current (ie leakage current or inrush current). VNOM varistor voltage is usually determined as the measured voltage across the varistor with a DC current value of 1 mA.

[0085] As is known, the varistor has three modes of operation. In the first, normal mode of operation (discussed earlier), up to the value of the rated or nominal voltage, the varistor is practically an electrical insulator. In the second, normal mode of operation (also discussed earlier), when the varistor is exposed to an overvoltage, it temporarily and reversibly becomes an electrical conductor during the overvoltage condition and returns to the first mode of operation thereafter. In the third mode of operation (the so-called end of technical or working life), the varistor is effectively worn out and becomes a permanent, irreversible electrical conductor.

[0086] A varistor also has a natural switching voltage VC (sometimes referred to simply as "switching voltage"). The switching voltage VC is defined as the maximum voltage measured on the varistor, when a certain value of current is applied to the varistor, over time according to the standard protocol.

[0087] In the case where there are no overvoltage conditions, the varistor wafers 152, 154, 156 provide high resistance, so that the current does not flow through the overvoltage protection device 100 since it appears electrically as an open circuit. That is, no current usually passes through the varistor. Under inrush current conditions (typically transients; e.g., lightning) or overvoltage conditions or cases (typically longer in duration than inrush current conditions) when voltages greater than VNOM occur, the resistance of the varistor wafer rapidly decreases, allowing current to flow through the surge protection device 100 and form a bridge for current flow to protect other components attached to the electrical system under consideration. Normally, the varistor recovers from these events without significantly overheating the surge protection device 100 .

[0088] A varistor has several failure modes. Failure modes include: 1) the varistor fails as a short circuit; 2) the varistor fails as a linear resistance. Varistor failure to short circuit or linear resistance can be caused by conditions of single or multiple current surges of sufficient magnitude and duration or single or multiple continuous overvoltage events, which conduct a sufficient amount of current through the varistor.

[0089] A short circuit failure typically manifests as a localized cavity or spot of breakdown (herein known as a failure spot), extending through the thickness of the varistor. These failure sites form a path for current to flow between the two electrodes, of low resistance but high enough to form ohmic losses and cause the device to overheat, even under low fault current conditions. A sufficiently large value of the fault current through the varistor can melt the varistor in the area of the fault and generate an electric arc.

[0090] Failure of a varistor into a linear resistance form can cause limited current conditions through the varistor, leading to heat build-up. This heat build-up can lead to catastrophic thermal runaway and the device temperature can exceed the specified maximum temperature. For example, the maximum allowable temperature for the external surfaces of the device can be set by code or standard, in order to prevent burning of adjacent components. If the leakage current is not interrupted for a certain period of time, overheating will lead to the eventual failure of the varistor in the form of a short circuit, as defined earlier.

[0091] In some cases, the current through a failed varistor can also be limited by the power supply system (eg, by ground resistance in the system or in applications of photovoltaic (photo-voltaic - PV) power sources, where the fault current depends on the possibility of electricity generation at the time of failure), leading to a progressive rise in temperature, even if the varistor failure is a short circuit. There are cases where a limited leakage current flows through the varistor, due to prolonged overvoltage conditions, which occur due to power system failure, for example. These conditions can lead to a temperature rise in the device, as in a situation where there is a failure of the varistor as a linear resistance and can possibly lead to a failure of the varistor, either as a linear resistance or as a short circuit, as described earlier.

[0092] As mentioned earlier, in some cases the surge protection device 100 may be in an "end-of-life" or end-of-life state, in which the varistor wafers 152, 154, 156 are consumed in whole or in part (ie, in an "end-of-life" state), leading to failure in an end-of-life state. When the varistor reaches its end of life, the surge protection device 100 becomes essentially a short circuit, with a very low, but not zero, ohmic resistance. As a result, in the end-of-life or end-of-life condition, the fault current will constantly flow through the varistor, even under no overvoltage conditions. In that case, the fusible member 132 can function as a fail-safe mechanism, by bridging the failed varistor and creating a low-ohmic permanent short circuit between the terminals of the surge protection device 100, in the manner described in U.S. Pat. Patent No. 7,433,169.

[0093] The fusible member 132 is adapted and configured to operate as a thermal switch for an electrical short circuit current occurring on the associated surge protection device 100, around the varistor wafers 152, 154, 156, to prevent or reduce heat generation in the varistors. In this way, the fusible member 132 can function as a switch that bridges the varistor wafers 152, 154, 156 and prevents the overheating and catastrophic failures described earlier. As used herein, the fail safe system is activated or “triggered” upon the occurrence of the conditions necessary to initiate operation of the fail safe system, as described for the short circuit of electrodes 122A, 124A.

[0094] When heated to the threshold temperature, the fusible member 132 will flow and thereby bridge the electrical electrodes 122A, 124A. The fusible member 132 thereby diverts the current appearing on the surge protection device 100 to bridge the varistors 152, 154, 156, so that the current causing the heating of the varistors ceases. The fusible member 132 can thus serve to prevent or prohibit thermal runaway (caused or generated in the varistors 152, 154, 156), without the need to interrupt the current through the surge protection device 100.

[0095] More specifically, the fusible member 132 initially has the configuration shown in Figure 5 so that it does not electrically connect the electrode 124 and the housing 122, except through the head 124A. After the heat rise occurs, the electrode 124 is thereby heated. Fusible member 132 is also heated directly and/or by electrode 124. During normal operating conditions, the temperature of fusible member 132 remains below its melting point, so that fusible member 132 remains in a solid state. However, when the temperature of the fusible member 132 exceeds its melting point, the fusible member 132 melts (fully or partially) and flows by gravity into a second configuration, which is different from the first. The fusible member 132 bridges the short circuits of the electrode 124 to the housing 122 to bridge 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 side wall 122B of the housing, through the fusible member 132. According to some embodiments, at least some of these flow paths do not include the varistor wafers 152, 154, 156.

[0096] According to some embodiments, the surge protection device 100 is adapted in such a way that, when its fusible member 100 is activated, the conductivity of the surge protection device 100 is at least as great as the conductivity of the power line and external cables connected to the device.

[0097] Protective electrical devices, according to some embodiments of the proposed invention, can provide a number of advantages, in addition to those described earlier. Devices can be formed to have a relatively compact form factor. The devices can be retrofitted, for installation in places where surge protection devices of a similar type do not have electrical circuits, as described here. In detail, the proposed devices may have the same dimensions as the previous devices.

[0098] There are applications where SPD devices are required to have a lower residual voltage, at the same nominal operating voltage. For example, this is required for some applications in telecommunications, intended for -48 Vdc systems. If using an SPD that includes a varistor (eg, MOV), typical

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the constant operating voltage Vc for such a varistor is 100 Vdc. However, such an SPD will have a residual voltage Vres of about 300 V or more. To better protect the equipment in the system, it would be advantageous to use SPDs with a residual voltage Vres that is much lower than these levels (ie close to 100 V).

[0099] Usually, in order to reduce the residual voltage of SPD devices, manufacturers use technology other than varistor technology, such as SAD technology or TVS diodes. These technologies have a significantly lower residual voltage, compared to MOV varistors, for the same constant operating voltage Vc. For example, TVS diodes for this application may have a residual voltage of 100 V. But SAD and TVS diodes usually cannot conduct inrush currents of the significant amount of energy expected in such applications. For this reason, many manufacturers use a larger number of SAD and/or TVS diodes in parallel, in order to achieve greater endurance on the transferred energy, during the conduction of surge currents.

[0100] In the surge protection device 100, the varistor wafers 152, 154, 156 are connected in electrical parallel, in order to reduce the residual voltage Vres of the surge protection device 100.

[0101] In some embodiments, each of the varistor wafers 152, 154, 156 is rated for a voltage of 60 Vdc (constant operating voltage Vc), instead of 100 Vdc, which is typical for such applications. Furthermore, the use of three varistors in parallel reduces the switching voltage of the SPD device at a given inrush current (compared to the use of a single varistor), since each varistor will conduct only a part of the total inrush current (the switching voltage will depend on the conducted inrush current, a higher conducted inrush current causes a higher switching voltage of the varistor). For telecommunications applications (nominal voltage of -48 Vdc) the resulting residual voltage is about 140 V at a surge current of 5 kA.

[0102] In some embodiments, the surge protection device 100 is used in DC electrical systems and, in some embodiments, in protective electrical circuits of telecommunications equipment on a -48 Vdc system. The device 100 may also be used in an AC or other DC system.

[0103] Reducing the nominal voltage of the varistor wafers 152, 154, 156 makes the varistor wafers 152, 154, 156 thinner and more sensitive to significant temperature variations. Therefore, how the varistor wafers are placed and assembled within the surge protection device 100 is very important.

[0104] As mentioned earlier, in some embodiments of the varistor wafers, the varistor wafers 152, 154, 156 may be secured to the interconnect members 160, 162 and/or to each other using solder. However, the use of solder can destroy the varistor wafer. The high temperature required to melt the solder material and the different elastic coefficients between the varistor material and the solder can create microcracks in the varistor. The stress on the varistor, caused by the electrodes, can also cause cracks in the varistor wafer. These cracks, as well as paste or impurities entering the cracks, can progressively damage and thus cause the varistor to fail. Ingress of paste can create a conductive path at the edge of the crack that increases the leakage current, which can lead to failure of the varistor wafer. The risks are of particular concern in the case of relatively thin (eg, less than 2 mm) ceramic varistors.

[0105] Further, in order to avoid mechanical damage caused to the varistor due to different thermal expansion between the varistor and the interconnect members 160, 162, the shape of the contact parts of the interconnect member should be round with a cavity in the middle. The cavity can reduce the even distribution of current across the surface of the varistor. The cavity may also reduce the energy tolerance of the varistor during inrush currents, as this will greatly reduce the heat dissipation capabilities of the varistor and increase the resistance and overall strength of the stack forming the varistor assembly 150.

[0106] As mentioned above, in some embodiments, the varistor wafers 152, 154, 156 are stacked in parallel and bonded or bonded together with an adhesive 164 at their edges 152E, 154E, 156E. The adhesive 164 on the edges 152E, 154E, 156E provides a compact assembly for transport and manipulation in the manufacture of the varistor assembly 150 and the device 100.

[0107] Moreover, the adhesive 164 solves the problems mentioned above. The adhesive holds the varistor wafers 152, 154, 156 and interconnect members 160, 162 together, for operation without introducing heat, solder, and paste, which can cause microcracks and introduce conductive paths as discussed earlier.

[0108] The adhesive allows the use of contact portions 160U, 160L, 162U, 162L of interconnect members, which do not include voids within their peripheral portions (ie electrodes having a full face surface). As a result, the varistor assembly 150's energy endurance during surge situations is increased. The contact resistances between the varistor wafers 152, 154, 156 and the interconnect members 160, 162 are reduced. This reduces the residual voltage during surges.

[0109] According to some embodiments, the areas involved between each of the electrode contact surfaces and the varistor contact surfaces are at least one square inch.

[0110] According to some embodiments, the bridged electrodes (eg, electrodes 122 and 124) apply a load to the varistor along the C-C axis in the range of about 2000 lbf and about 26000 lbf (8896 N and 115654 N), depending on the contact area.

[0111] According to some embodiments, the combined thermal mass of the housing (eg, housing 122) and electrode (eg, electrode 124) is substantially greater than the thermal mass of each of the varistors nested therebetween. The greater the ratio between the thermal mass of the housing and electrodes and the thermal mass of the varistor, the better the varistors will be preserved during exposure to surge currents and TOV phenomena and therefore the technical life of the SPD device will be longer. As used herein, the term "thermal mass" means the product of a specific heat of a material or materials of an object multiplied by the mass or masses of the material or materials of the object. That is, the thermal mass is the amount of energy required to raise one gram of material or more of the object's material by one degree Celsius of the mass of the material or more of the object's material. According to some embodiments, the thermal mass of at least one electrode head and electrode wall is substantially greater than the thermal mass of the varistor. According to some embodiments, the thermal mass of at least one electrode head and electrode wall is at least twice the thermal mass of the varistor, and, according to some embodiments, at least ten times greater. According to some embodiments, the combined thermal mass of the head and electrode wall is substantially greater than the thermal mass of the varistor, according to some embodiments at least two times greater than the thermal mass of the varistor, and, according to some embodiments, at least ten times greater.

[0112] As discussed earlier, the spring coupling 128E is a disk washer (Belleville washer) or a wave washer. A plate or wave washer can be used to apply a relatively large load, without requiring a large axial space. However, other types of bridging can be used in addition to or instead of a plate washer or wave washer. Suitable alternative means include one or more coil springs or coil washers.

[0113] The varistor assembly 150 includes three varistors and two interconnecting members. However, the varistor assembly, according to further embodiments, may include more than three varistors stacked and connected in electrical parallel, as described. For example, a varistor circuit may include five varistors stacked and connected in electrical parallel with three interconnecting members.

[0114] In accordance with Figures 10-12, a modular surge protection unit 200 is shown, according to further embodiments of the invention. The surge protection device 200 can be used in the same sense and for the same purpose as the surge protection device 100, except that the unit 200 is generally functionally equivalent to the function of the two surge protection devices 100.

[0115] The surge protection unit 200 includes a housing assembly 221 and two SPD internal sets of components or sub-modules 211, 212.

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[0116] Housing assembly 221 includes a first electrode or housing 223 and a cover 226. Housing 223 is one piece and, in some embodiments, monolithic. The housing 223 is formed from an electrically conductive metal, such as aluminum. Housing 223 includes two integral housing electrode wall portions 222 . Each housing electrode portion 222 includes an electrode wall 222A, a side wall 222B, a cavity 222C, and a top opening 222D, according to features 122A, 122B, 122C, and 122D, respectively, of the device 100.

[0117] Cover 226 is substantially plate-shaped and has a profile that matches housing 223. Cover 226 has two electrode openings 226A and six clamping holes 226B, which are defined herein. According to some embodiments, the cover 226 is formed from an electrically conductive material. In some embodiments, the cover 226 is formed of metal and, according to some embodiments, of aluminum.

[0118] Each of the SPD device submodules 211, 212 includes electrodes 224, a fusible member 232, an insulating sleeve 234, and a varistor assembly 250, corresponding to components 124, 132, 134, and 150, respectively, of the device 100. Each SPD submodule 211, 212 further includes an elastomeric insulating member. 239.

[0119] The insulating members 239 are formed from an electrically insulating, elastic, elastomeric material. In some embodiments, the insulating members 239 are formed of a material having a hardness of about 60 to 85 Shore A. In some embodiments, the insulating members 239 are formed of rubber. According to some embodiments, the insulating members 239 are formed of silicone rubber. Suitable materials for the insulating members 239 may include KE-5612G or KE-5606 silicone rubber available from Shin-Etsu Chemical Co. Ltd.

[0120] Each SPD sub-module 211, 212 is located in a corresponding housing cavity 222C. Cover 226 is attached to housing 223 with screws 5. Cover 226 includes SPD submodules 211, 212 and axially compresses elastomeric insulators 239. SPD submodule 211 and their electrode wall 222A form a first surge protection device, corresponding to device 100. SPD submodule 212 and electrode wall 222A form a second surge protection device, corresponding to device 100. 100.

[0121] When the unit 200 is assembled, the insulating member 239 of each SPD sub-module 211, 212 is nested between the cover 226 and the upper electrode flange 224D and axially pressed (ie, axially loaded and elastically deformed from its relaxed state), so that the insulating member 239 serves as a bridging member and applies a constant axial pressure or load to the electrode 224 and cover 226. The insulating member 239 also serves to electrically isolate the housing 223 from the electrode 224. The pressed insulating member 239 may also form a seal that restricts or prevents byproducts of overvoltage events, such as hot gases and fragments of the varistor wafers of the varistor assembly 250, from exiting the unit 200 through the corresponding opening 222D of the housing.

[0122] The varistor assemblies 250 may provide the same advantages in the unit 200 as previously discussed for the varistor assembly 150. Each varistor assembly 250 includes an adhesive 264 that corresponds to the adhesives 164, 164'.

[0123] In other embodiments, SPD submodules 211 , 212 may use separate springs and isolation rings, as shown in accordance with device 100 .

[0124] In further embodiments, each SPD sub-module 211 , 212 may include a single varistor wafer instead of the multi-varistor varistor assembly 250 .

[0125] Figure 13 shows a modular surge protection device 300, according to further embodiments of the invention. The surge protection device 300 can be used in the same way and for the same purpose as the surge protection device 100. The surge protection device 300 is constructed in the same manner as the surge protection device 100, except as follows.

[0126] The surge protection device 300 includes a varistor assembly 350, which corresponds to the varistor assembly 150, except as follows. Varistor assembly 350 includes five varistor wafers 352, 353, 354, 355, 356, for interconnect members 360, 362, 366, 368, and bonding means 364. Varistor wafers 352, 353,

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354, 355, b correspond to and are formed in the same manner as the varistor wafers 152, 154, 156. Interconnecting members 360, 362, 366, 368 correspond to and are formed in the same manner as the interconnecting members 160, 162. The connecting means 364 correspond to the connecting means 164, 164'. Five varistor wafers 352, 353, 354, 355, 356 are axially stacked, connected and connected in electrical parallel with four interconnecting members 360, 362, 364, 368.

[0127] Figure 14 shows a modular surge protection unit 400, according to further embodiments of the invention. The surge protection device 400 can be used in the same way and for the same purpose as the surge protection device 100. The surge protection device 300 is constructed in the same manner as the surge protection device 100, except as follows.

[0128] The surge protection device 400 includes a varistor assembly 450, which corresponds to the varistor assembly 150, except as follows. The varistor assembly 450 includes two varistor wafers 452, 454, two interconnect members 460, 462, bonding means 464, and an electrically isolated 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 way as the connecting members 160, 162. The connecting means 464 correspond to the connecting means 164, 164'. Insulating wafer 457 is formed as an electrically insulating material. Suitable electrical insulating materials may include ULTEM<TM>1000, a thermoplastic available from SABIC, mica or polyester film, such as DYFILM<TM>polyester film, available from Coverna of Italy, for example. Two varistor wafers 452, 454 are axially nested and connected in electrical parallel by two interconnecting members 460, 462. An insulating wafer 457 is axially placed or nested between the varistor wafers 452, 454, to prevent a short circuit between the facing varistor wafers 452, 454'.

[0129] Figures 15 and 16 show a modular surge protection device 500. The surge protection device 500 can be used in the same way and for the same purpose as the surge protection device 100.

[0130] The surge protection device 500 is constructed as one half of the unit 200 (Figure 12). Device 500 includes housing assembly 521 , which is half of housing assembly 221 , and SPD internal component set 512 , which corresponds to submodule 212 .

[0131] Referring to Figures 17-20, a modular surge protection device 600 is shown, according to embodiments of the invention. The surge protection device 600 can be used in the same way and for the same purpose as the surge protection device 100. The surge protection device 600 is constructed in the same manner as the surge protection device 100, except as follows.

[0132] The surge protection device 600 includes a varistor assembly 650, which corresponds to the varistor assembly 150, except as follows. Varistor assembly 650 includes three varistor wafers 652, 654, 656 and two interconnect members 660, 662. Varistor wafers 652, 654, 656 correspond to and are formed in the same manner as varistor wafers 152, 154, 156. Interconnect members 660, 662 correspond to and are formed in the same manner as interconnect members 160, 162. Varistor wafers 652, 654, 656 are axially stacked and connected in electrical parallel to interconnect members 660, 662, as discussed earlier for device 100.

[0133] The surge protection device 600 further includes an electrically isolated cavity filling member or bushing 636. The bushing 636 includes side walls 636A, which define a passageway 636B. Passage 636 extends from upper opening 636C to lower opening 636D. A pair of laterally opposed axially extending receiving channels 636E are defined in the inner cavity 636F of the side wall 636A.

[0134] The sleeve 636 is tubular and has an outer surface 636G which is generally cylindrical. In some embodiments, the sleeve 636 is formed from a high temperature polymer and, in some embodiments, a high temperature thermoplastic. In some embodiments, the sleeve 636 is formed from polyetherimide

1

(PEI), such as ULTEM<TM>thermoplastics, available from SABIC of Saudi Arabia. In some embodiments, the sleeve 636 is formed from an electrically insulating ceramic.

[0135] According to some embodiments, the sleeve 636 is formed of a material having a melting point greater than the melting point of the fusible member 632. According to some embodiments, the sleeve 632 is formed of a material having a melting point in the range of about 120 to 200 °C.

[0136] According to some embodiments, the sleeve material 636 has a voltage withstand of 25 kV per mm of thickness.

[0137] According to some embodiments, the sleeve sidewall 636A has a nominal thickness T5 (Figure 20) of at least 2 mm, in some embodiments at least 4 mm, and in some embodiments in the range of about 2 to 15 mm. According to some embodiments, the depth D5 of each channel of receiver 636E is at least 1 mm and, in some embodiments, ranges from about 1 to 12 mm.

[0138] The inner chamber 627 of the housing assembly 621 of the surge protection device 600 includes a first subchamber 627A and a second subchamber 627B in fluid communication with the first subchamber 627A. Prior to melting the fusible member 632, the electrode 624 and the fusible member 632 occupy the first subchamber 627A. The varistor assembly 650 occupies the central space of the second subchamber 627B, so that the remaining tubular cavity or volume 627C of the gap, the second subchamber 627B, remains unoccupied by the varistor assembly 650. The gap volume 627C is the space or volume that extends radially between the varistor assembly 650 and the inner surface 622H of the sidewall of the electrode 622B 622 cases. Cavity filler sleeve 636 occupies gap volume 627C and surrounds varistor assembly 650 .

[0139] The receiver recesses or channels 636E and the bridges 660B, 662B of the interconnecting members 660, 662 are relatively large and assembled so that each of the bridges 660B, 662B is received and placed in one of the respective receiving channels 636E. The remainder of the inner surface 636F of the sleeve generally conforms to the peripheral profile of the varistor wafers 652, 654, 654.

[0140] Thus, as can be appreciated from Figures 17 and 19, the inner surface 636F generally corresponds to the outer shape of the varistor assembly 650. The cylindrical outer surface 636G generally corresponds to the inner shape of the surface 622H of the inner electrode wall 622 of the housing. In some embodiments, 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.

[0141] The varistor wafers 652, 654, 656 are relatively thick, so that the overall height of the varistor assembly 650 is increased relative to the height of the varistor assembly 150, for example. As a result, the gap cavity or volume 627C surrounding the varistor assembly 650 is relatively large. In addition, the bridges 660B, 662B project radially outward, beyond the peripheral edges of the varistors 652, 654, 656. Since the inner surface 622H of the housing electrode 622 is cylindrical, the required clearance between the bridges 660B, 662B and the inner surface 622B creates relatively large clearances around the rest of the varistor assembly 650.

[0142] If there were no sleeve 636 to fill the gap, this large gap volume 627C could compromise the intended operation of the fusible member 632 and the safety mechanism 602. In detail, the volume of the melted fusible member 632 may not be sufficient to bridge the electrodes 622 and 624, in order to short-circuit these electrodes 622 and 624, depending on directing device 600 when the fusible member 632 is molten. The spacer sleeve 636 occupies the gap volume 627C and thereby reduces or limits the amount or volume of the fusible member 632 that can flow into the gap volume 627C when the fusible member becomes molten. In this way, the cavity filling member 636 ensures that a greater and reliably sufficient amount of the molten fusible member is retained in the first sub-chamber 627A to make simultaneous contact with the two electrodes 622, 624.

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[0143] In some embodiments, the cavity filler sleeve 636 occupies at least 50 percent of the volume of the gap 627C and, in some embodiments, at least 80 percent. In some embodiments, the cavity filler sleeve 636 has a volume in the range of about 100 mm<3>to 100000 mm<3>and, in some embodiments, a volume of about 21000 mm<3>

[0144] While the illustrated cavity filling member 636 is configured as a one-piece tubular sleeve having axially spaced receiving channels 636E, which are defined herein, other configurations and constructions may be used. For example, the 636E channels can be replaced with radial bores, which do not extend to the edges of the sleeve. The cavity-filling member 636 may be replaced by two or more cavity-filling members configured and arranged to occupy the volume of the gap 627C to the degree and dimensions contemplated herein. The two or more cavity filling members may be axially stacked and may surround the varistor assembly 650 by less than 360 degrees.

[0145] In accordance with Figure 21, a modular surge protection device 700 is shown, according to further embodiments of the invention. The 700 surge protection device can be used in the same way and for the same purposes as the 600 surge protection device. The 700 surge protector is constructed in the same manner as the 600 surge protector, except as follows. Device 700 includes varistor assembly 750, which corresponds to varistor assembly 650, and cavity filling member 736 corresponds to cavity filling member 636.

[0146] The surge protection device 700 includes an elastomeric insulating member 739, which corresponds to the elastomeric insulating member 239 (Figure 12). The insulating member 739 is nested between the cover 726 and the upper flange 724D of the electrode and is axially pressed (ie, axially loaded and elastically deformed from its relaxed state), so that the insulating member 739 serves as a bridging member and applies a constant pressure or load to the electrode 724 and the cover 726, as described in accordance with unit 200.

[0147] It will be appreciated that the various aspects described herein may be used in various combinations. For example, an elastomeric insulating member, corresponding to elastomeric insulating member 239, may be used in place of the spring and end insulating members (eg, insulating member 128C) of the surge protection device 100, 300, 400, 600. The varistor assemblies of each device 100-700 may be replaced with a varistor assembly of another of the devices 100-700 (eg, a five-wafer varistor assembly 350 or a two-wafer varistor assembly 450 may be used in place of the varistor assembly 650 in device 600).

[0148] Those of ordinary skill in the art may make numerous changes and modifications, having regard to the advantages of the disclosed disclosure, without departing from the scope of the invention. In view of this, it must be understood that the illustrated embodiments are set forth for the purpose of example only, and should not be construed as limiting the invention as defined by the following claims.

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Claims (14)

Patent claims 1. The surge protection device (600) includes: a first electrode member (622); a second electrode member (624); a varistor (652, 654, or 656) interposed between and electrically connected to each of the first and second electrode members; an electrically conductive fusible member (632), wherein the fusible member responds to heat in the surge protection device by melting and forming an electrical short across the first and second electrode members; and a cavity filling member (636) surrounding at least a portion of the varistor, wherein the cavity filling member is formed of an electrically insulating material; whereby the surge protection device includes a sidewall (626B) defining a chamber (627), the chamber including a first subchamber (627A) and a second subchamber (627B) in fluid communication with the first subchamber; the fusible member is placed in the first subchamber (627A); the varistor is placed in the second sub-chamber (627B) and a gap volume (627C) is defined between the varistor and the side wall in the second sub-chamber; a cavity-filling member is disposed in the gap volume to restrict the flow of the fusible member into the gap volume (627C); and varistor (652) is the first varistor wafer; characterized in that the surge protection device includes: a second varistor wafer (654 or 656) formed from the varistor material; and an electrically conductive interconnect member (660 or 662) connecting the first and second varistors in electrical parallel between the first and second electrode members (622, 624); wherein the first and second varistor wafers are axially stacked between the first and second electrode members (622, 624); the cavity filling member (636) includes a receiver recess (636E); and a portion (660B or 662B) of the interconnect member extends outwardly beyond the first and second varistor wafers and is located in the recess (636E) of the receiver. 2. The surge protection device according to Claim 1, wherein the cavity filling member (636) is formed of electrically insulating ceramics. 3. The surge protection device of Claim 1, wherein the cavity filling member (636) occupies at least 50 percent of the gap volume. 2 4. The surge protection device of Claim 1, wherein the cavity filling member (636) includes a tubular cavity filling sleeve surrounding the varistor wafer (652, 654, or 656). 5. Overvoltage protection device according to Claim 4, wherein: the cavity filling sleeve (636) includes an inner surface (636F) that generally conforms to the outer shape of the varistor (652, 654, or 656); and the cavity filler sleeve (636) includes an outer surface (636G) that generally conforms to the shape of the inner wall surface of the sidewall (622B). 6. Overvoltage protection device according to Claim 5, wherein: the gap between the inner surface (636F) of the cavity filler sleeve and the varistor (652) is less than 2 mm; and the clearance between the outer surface (636G) of the cavity filler sleeve and the inner wall surface of the sidewall (622B) is less than 0.5 mm. 7. The surge protection device of Claim 4, wherein the cavity filling sleeve (636) includes a sleeve sidewall (636A) having a nominal thickness (T5) of at least 2 mm. 8. The surge protection device according to Claim 4, wherein the sleeve (636) for filling the cavity is in one piece. 9. The surge protection device of Claim 1, wherein the receiver recess (636E) is an axially extending channel defined in the inner surface (636F) of the cavity filling member (636). 10. The surge protection device of Claim 1, wherein the recess (636E) of the receiver has a depth (D5) in the range of about 1 to 12 mm. 11. The surge protection device of Claim 1, wherein the cavity filling member (636) is formed of high temperature thermoplastic. 12. The surge protection device of Claim 1, wherein the cavity filling member (636) is formed of a material having a melting point in the range of about 120 to 200 °C, or wherein the cavity filling member (636) is formed of a material capable of withstanding a voltage of 25 kV per mm of thickness. 13. The surge protection device of Claim 1, wherein the cavity filling member (636) has a volume in the range of about 100 mm<3> to 100000 mm<3>. 14. Surge protection device according to Claim 1, wherein: the first electrode member (622) includes an electrode housing including a side wall (622B) and an end wall (122A) integral with the side wall; the side wall (622B) and the end wall (122A) together define the chamber (627); the second electrode member (624) extends into the chamber (627); and the housing electrode is formed from one piece of metal.