Surge protection device, circuit, module, and system including the surge protection device, circuit, and module

Abstract

A surge protection device (SPD) includes a first electrical terminal, a second electrical terminal, and an overvoltage protection circuit connected between the first and second electrical terminals. The overvoltage protection circuit includes a gas discharge tube and a current management circuit connected in series to the gas discharge tube. The current management circuit includes a varistor and a resistor connected in parallel between a first node of the current management circuit and a second node of the current management circuit.

Description

Technical Field

[0001] The present invention relates to a surge protection device, and more particularly, to a surge protection device including a varistor. Background Art

[0002] Often, excessive voltage or current is applied across the supply lines that deliver electrical power to residential as well as commercial and institutional facilities. Such excessive voltage or current spikes (transient overvoltages and surge currents) can be caused, for example, by lightning strikes. These events can be of particular concern in telecommunications distribution centers, hospitals, and other facilities, where equipment damage caused by overvoltages and / or current surges is unacceptable and the resulting downtime can cause significant losses.

[0003] Generally, surge protection devices (SPDs) can be used to protect sensitive electronic equipment from transient overvoltages and surge currents. For example, an overvoltage protection device can be installed at the power input of the equipment to be protected, and the overvoltage protection device typically protects the equipment from overcurrent damage when the equipment fails. The typical failure mode of an SPD is a short circuit. The overcurrent protection commonly employed is a combination of an internal thermal disconnector and an external fuse. The internal thermal disconnector is used to protect the device from overheating due to increased leakage current, and the external fuse is used to protect the device from higher fault currents. Different SPD technologies can avoid using an internal thermal disconnector because, in the event of failure, these technologies change their operating mode to a low ohmic resistance.

[0004] In the case of a surge current in line L (e.g., a voltage line of a three-phase power circuit), protecting the power system load device may require providing a current path to ground for the excess current of the surge current. The surge current can generate a transient overvoltage between line L and the neutral line N (the neutral line N can be conductively connected to a ground ground PE). Since the transient overvoltage significantly exceeds the operating voltage of the SPD, the SPD will change, thereby allowing the excess current to flow from line L through the SPD to the neutral line N. Once the surge current has been conducted to the neutral line N, the overvoltage condition terminates, and the SPD can become non-conductive again. However, in some cases, one or more SPDs can start to allow conduction of leakage current even at voltages below the operating voltage of the SPD. This condition can occur in the case of SPD degradation. Summary of the Invention

[0005] According to some embodiments of the inventive concept, a surge protection device (SPD) includes a first electrical terminal, a second electrical terminal, and an overvoltage protection circuit connected between the first and second electrical terminals. The overvoltage protection circuit includes a gas discharge tube and a current management circuit connected in series to the gas discharge tube. The current management circuit includes a varistor and a resistor connected in parallel between a first node and a second node of the current management circuit.

[0006] In some embodiments, the current management circuit further includes an inductor connected in series with the resistor between the first and second nodes of the current management circuit.

[0007] In some embodiments, the inductor includes a surface mount device (SMD) inductor.

[0008] In some embodiments, the inductor has an inductance in the range from about 1 μH to about 1 mH.

[0009] In some embodiments, the overvoltage protection circuit further includes a thermal disconnector mechanism connected in series to the gas discharge tube and the current management circuit. The thermal disconnector mechanism is configured to electrically disconnect the first electrical terminal from the second electrical terminal in response to a thermal event.

[0010] In some embodiments, the resistor includes an axial resistor and has a resistance in the range from about 1 kΩ to 50 MΩ.

[0011] In some embodiments, the resistor includes a radial resistor and has a resistance in the range from about 1 kΩ to 50 MΩ.

[0012] In some embodiments, the resistor includes a surface mount device (SMD) resistor and has a resistance in the range from about 1 kΩ to 50 MΩ.

[0013] In some embodiments, the varistor has a peak current rating of about 20 kA and a peak voltage rating of about 300 V.

[0014] In some embodiments, the gas discharge tube has a DC spark discharge voltage rating of about 500 V at a voltage rise of 100 V / s, and a discharge current rating of about 20 kA.

[0015] In some embodiments, the varistor has a clamping voltage level associated therewith, and the clamping voltage level exceeds the ambient voltage level associated with the first electrical terminal.

[0016] In some embodiments, the current management circuit is configured to facilitate: in response to a transient overvoltage event associated with a first electrical terminal, transitioning a gas discharge tube from a non-conductive state to a conductive state by causing the voltage across the gas discharge tube to exceed the spark discharge voltage associated with the gas discharge tube.

[0017] In some embodiments, the current management circuit is configured to facilitate, in response to the termination of a transient overvoltage event, dissipating the associated energy by causing the voltage across the gas discharge tube to be less than the arc voltage associated with the gas discharge tube, and transitioning the gas discharge tube from a conductive state to a non-conductive state.

[0018] In some embodiments, the first electrical terminal is configured to be connected to a line, and the second electrical terminal is configured to be connected to a common reference voltage.

[0019] In some embodiments, the line is an alternating current (AC) or direct current (DC) power line.

[0020] In some embodiments, the line is a communication line configured to transmit a communication signal.

[0021] In some embodiments, the communication signal is an RF communication signal.

[0022] In some embodiments, the SPD includes a second gas discharge tube connected in parallel with the first gas discharge tube between the current management circuit and the first electrical terminal.

[0023] In some embodiments, the SPD includes a base and an SPD module. The base is configured to be mounted on a DIN rail. The SPD module is configured to be removably mounted on the base. When the SPD module is mounted on the base, the SPD module and the base together form a DIN rail SPD assembly. The SPD module includes: a module housing; first and second electrical terminals mounted on the module housing; a gas discharge tube disposed in the module housing; and a current management circuit disposed in the module housing.

[0024] In some embodiments, the SPD module includes a thermal disconnector mechanism positioned in a ready configuration, wherein a varistor is electrically connected to the second electrical terminal. The thermal disconnector mechanism is repositionable to electrically disconnect the varistor from the second electrical terminal. The thermal disconnector mechanism includes: an electrode electrically connected to the varistor in the ready configuration; and a solder fixing an electrical conductor into electrical connection with the varistor in the ready configuration. The solder is fusible in response to overheating in the SPD module. The thermal disconnector mechanism is configured to electrically disconnect the electrical conductor from the varistor and thereby disconnect the varistor from the second electrical terminal when the solder melts.

[0025] According to some embodiments, the SPD module includes an indicator mechanism configured to provide an alert that the SPD module has failed when the thermal disconnector mechanism disconnects the overvoltage clamping element from the second electrical terminal.

[0026] In some embodiments, the indicator mechanism includes: a local alert mechanism including: a window in the module housing; an indicator member movable relative to the window between a ready position and an indicating position; and an indicator spring configured to force the indicator member from the ready position to the indicating position when the thermal disconnector mechanism disconnects the varistor from the second module electrical terminal.

[0027] According to some embodiments, the SPD is an SPD module including: a module housing including first and second electrodes, wherein the first electrode includes a first electrical terminal and the second electrode includes a second electrical terminal; and a gas discharge tube and a varistor, the gas discharge tube and the varistor being axially stacked between the first and second electrodes in the module housing.

[0028] In some embodiments, the first electrode includes a housing electrode including an end wall and an integral side wall that together define a cavity, the second electrode extends into the cavity, and the gas discharge tube and the varistor are disposed in the cavity.

[0029] According to some embodiments, the housing electrode is integrally formed of metal.

[0030] In some embodiments, the SPD includes a biasing device that applies an axial compressive load to the gas discharge tube and the varistor.

[0031] In some embodiments, the SPD includes a conductive fusible member. The fusible member melts in response to heat in the overvoltage protection device and forms an electrical short circuit path across the first and second electrode members.

[0032] In some embodiments, the varistor includes a varistor disc.

[0033] In some embodiments, the SPD includes: a first internal electrode axially sandwiched between the varistor disc and the first electrode; and a second internal electrode axially sandwiched between the varistor disc and the second electrode; wherein the resistor is electrically connected to the first and second electrodes in the module housing.

[0034] According to some embodiments, the resistor is laterally positioned beside the outer edge of the varistor disc.

[0035] In some embodiments, the resistor is axially positioned under the varistor disc.

[0036] In some embodiments, the resistor is configured to discharge the capacitance of the varistor in response to a voltage surge event across the first and second electrical terminals.

[0037] In some embodiments, the resistor is a resistive material layer mounted on the varistor.

[0038] From reading the following drawings and detailed description of the preferred embodiments (such description is merely illustrative of the present invention), those skilled in the art will understand additional features, advantages, and details of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings forming a part of the specification illustrate embodiments of the present invention.

[0040] Figure 1 and Figure 2 are electrical schematic diagrams of an overvoltage protection circuit for an SPD according to some embodiments of the present inventive concept.

[0041] Figure 3 and Figure 4 are voltage and current curves of a GDT and a varistor respectively in response to a transient overvoltage event according to some embodiments of the present inventive concept.

[0042] Figure 5 is according to some embodiments of the present inventive concept including Figure 6 an electrical schematic diagram of a circuit of an SPD assembly.

[0043] Figure 6 is a top front perspective view of an SPD assembly mounted on a DIN rail according to some embodiments of the present inventive concept.

[0044] Figure 7 and Figure 8 are exploded perspective views of an SPD module forming part of Figure 6 the SPD assembly according to some embodiments of the present inventive concept.

[0045] Figure 9 is along Figure 6 the line 9-9 taken Figure 7 a cross-sectional view of the SPD module of

[0046] Figure 10 is Figure 7 a first side elevation view of the SPD module of

[0047] Figure 11 is where the cover is removed Figure 7 a relative side elevation view of the SPD module of

[0048] Figure 12 is Figure 7 a front perspective view of the SPD module of

[0049] Figure 13 A cross-sectional view of a base component that is part of an SPD component forming Figure 6 the

[0050] Figure 14 A rear perspective view of a fragment of an SPD module in an SPD component according to another embodiment of the inventive concept and in which its cover is removed for Figure 6 the

[0051] Figure 15 is Figure 14 an enlarged rear perspective view of a fragment of the SPD module of

[0052] Figure 16 A perspective view of a fragment of an SPD module in an SPD component according to another embodiment of the inventive concept and in which its cover is removed for Figure 6 the

[0053] Figure 17 A perspective view of an SPD module used in a circuit according to another embodiment of the inventive concept for Figure 5 the

[0054] Figure 18 is Figure 17 an exploded perspective view of the SPD module of

[0055] Figure 19 is a cross-sectional view of the SPD module taken along line 19-19 of Figure 17 and Figure 17 for

[0056] Figure 20 is Figure 17 a perspective view of a fragment of the SPD module of

[0057] Figure 21 illustrating an attachment configuration of a resistor for forming part of the SPD module of Figure 17 the

[0058] Figure 22 A perspective view of a fragment of an SPD module in an SPD component according to another embodiment of the inventive concept and in which its cover is removed for Figure 6 the

[0059] Figure 23 is Figure 22 a perspective view of a varistor, a metallization layer, and a resistance layer forming part of the SPD module of

[0060] Figure 24 is alongFigure 22 taken along line 24-24 of Figure 22 Fragment cross-sectional view of the SPD module of

[0061] Figure 25 is a perspective view of an overvoltage clamping element subassembly according to another embodiment.

[0062] Figure 26 is Figure 25 Bottom perspective view of the overvoltage clamping element subassembly of

[0063] Figure 27 is taken along Figure 25 line 27-27 of Figure 25 Fragment cross-sectional view of the overvoltage clamping element subassembly of DETAILED DESCRIPTION

[0064] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. In the drawings, for the sake of clarity, the relative sizes of regions or features may be exaggerated. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art.

[0065] It will be understood that when an element is referred to as being "coupled" or "connected" to another element, it can be directly coupled or connected to the other element, or intervening elements may also be present. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, there are no intervening elements. Throughout the text, the same numbers refer to the same elements.

[0066] In addition, spatial relative terms, such as "under", "below", "beneath", "above", "on", etc., may be used herein for ease of description to describe the relationship of one element or feature to other element(s) or feature(s) as illustrated in the drawings. It will be understood that, in addition to the orientation depicted in the drawings, the spatial relative terms are intended to encompass different orientations of the device in use or operation. For example, if the device in the drawings is flipped, an element described as "under" or "beneath" other element(s) or feature(s) will then be oriented "above" the other element(s) or feature(s). Thus, the exemplary term "under" can encompass both an orientation of above and under. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatial relative descriptors used herein are to be interpreted accordingly.

[0067] For brevity and / or clarity, well-known functions or constructions may not be described in detail.

[0068] As used herein, the expression "and / or" includes any and all combinations of one or more of the associated listed items.

[0069] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the invention. As used herein, unless clearly indicated otherwise in the context, the singular forms "a", "an" and "the" are intended to include the plural forms as well. It will also be understood that the terms "comprises" and / or "comprising", when used in this specification, specify the presence of the stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or their groups.

[0070] All terms used herein, unless otherwise defined, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will also be understood that terms such as those defined in a general dictionary should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formalized sense unless clearly so defined herein.

[0071] As used herein, "monolithic" means an object formed of a single integral part or composed of a material without joints or seams. Alternatively, an integral object can be a composition composed of a plurality of parts or components fixed together at joints or seams.

[0072] Gas discharge tubes (GDTs) and metal oxide varistors (MOVs) can be used in surge protection devices (SPDs), but both GDTs and MOVs have advantages and disadvantages in shunting current away from sensitive electronic components in response to an overvoltage surge event. For example, an MOV has the advantage of rapidly responding to a surge event and being able to dissipate the power associated with the surge event. However, an MOV has the disadvantages of having increased capacitance relative to a GDT and even allowing leakage current to pass through it under ambient conditions. An MOV may also have a reduced expected lifetime relative to a GDT. A GDT may have the advantages of having extremely low to no leakage current, minimal capacitance, and an increased expected lifetime relative to an MOV. However, a GDT is not as sensitive to a surge event as an MOV. Additionally, when a GDT is triggered and transitions into an arc region in response to a surge event, the GDT may remain in a conductive state if the ambient voltage on the line connected to the GDT exceeds the arc voltage. Some embodiments of the inventive concept stem from the recognition that an SPD may include an overvoltage protection circuit that includes both a GDT and a current management circuit that includes an MOV. The GDT can mitigate the current leakage problem associated with the MOV, which can extend the operating lifetime of the MOV. The current management circuit that includes the MOV can help trigger the GDT in response to a transient overvoltage event, while the MOV provides improved energy dissipation and voltage clamping for one terminal of the GDT to eliminate the hold current of the GDT and allow the GDT to reset to a non-conductive state after the transient overvoltage event.

[0073] Reference Figure 1 , in which an overvoltage protection circuit 600 according to some embodiments of the inventive concept is shown. The overvoltage protection circuit 600 can be used in embodiments of the SPD components and modules described herein, such as the Figure 6 - 21 SPDs 100, 200, 300, 400, and 500 according to some embodiments of the inventive concept.

[0074] The overvoltage protection circuit 600 includes a thermal disconnector mechanism 605, a GDT 610, and a current management circuit 620 connected in series between a first electrical terminal L and a second electrical terminal C. The first electrical terminal L can be configured for electrical connection to a line, such as Figure 5 lines L1, L2, L3, and N, or other types of physical electrical transmission media. According to various embodiments of the inventive concept, the electrical terminals can be electrically connected to lines configured to carry alternating current (AC) signals, direct current (DC) signals, and / or communication signals. In some embodiments, the communication signal can be a radio frequency (RF) communication signal. The second electrical terminal C can be configured for electrical connection to a common reference voltage source, such as a ground voltage.

[0075] A GDT is a sealing device that contains a gas mixture trapped between two electrodes. The gas mixture becomes conductive after being ionized by a high-voltage spike. The high voltage that causes the GDT to transition from a non-conductive high-impedance state to a conductive state is called the spark discharge voltage of the GDT. The spark discharge voltage is typically expressed as the rate of rise of voltage with respect to time. For example, a GDT can be rated to have a DC spark discharge voltage of 500V at a rate of rise of 100V / s. When the voltage across the terminals of the GDT experiences an increase that exceeds its spark discharge voltage, the GDT will transition from the high-impedance state to a state called the glow region. The glow region refers to the time region in which the gas in the GDT begins to ionize and the current flowing through the GDT begins to increase. During the glow region, the current through the GDT will continue to increase until the GDT transitions into a virtual short circuit called the arc region. The voltage generated across the GDT when it is in the arc region is called the arc voltage and is typically less than 100V. The GDT takes a relatively long time to trigger the transition from the high-impedance state to the arc region state, in which it acts as a virtual short circuit. Thus, relatively high voltage transients may not be transferred to ground or other reference terminals and can be passed on to other circuits. In Figure 3 are shown voltage and current curves of the GDT, represented by S(t), in response to a transient overvoltage event. As Figure 3 shown, the current through the GDT remains approximately zero until the voltage across the GDT reaches the spark discharge voltage level (which is 1000V in this example) at time T E . The GDT then transitions into the arc region, in which it acts as a virtual short circuit to allow current to pass through, and has an arc voltage of 50V.

[0076] A varistor, such as a metal oxide varistor (MOV), still conducts a relatively small amount of current caused by the reverse leakage of the diode junction when in its normally non-conductive state. This leakage current may generate enough heat to use a device such as a thermal disconnect mechanism 605 to reduce the risk of damaging components of the overvoltage protection circuit 600. When a transient overvoltage event occurs, the varistor will conduct little current until the clamping voltage level is reached, at which point the varistor will act as a virtual short circuit. Typically, the clamping voltage is relatively high (e.g., several hundred volts), such that when the varistor passes a high current due to a transient overvoltage event, a relatively large amount of power can be dissipated. In Figure 4 are shown voltage and current curves of the varistor, represented by S(t), in response to a transient overvoltage event. As shown in Figure 4 , the varistor at time T VThe voltage is clamped at 500V here and at the same time serves as a virtual short circuit to allow current to surge through the device in response to the overvoltage event S(t). Once the overvoltage event S(t) drops below the clamping voltage level, the voltage generated across the varistor drops below the clamping voltage level. Compared with the GDT, the varistor has a relatively short transition time from the high impedance state to the virtual short circuit state, which corresponds to the time taken for the voltage generated across the varistor to reach the clamping voltage level.

[0077] Return to Figure 1 , if the GDT 610 is used without the current management circuit 620, the GDT 610 may take a relatively long period of time to transition to the arc region where it serves as a virtual short circuit. In contrast, if the GDT 610 and the current management circuit 620 are replaced with a varistor, the lifespan of the varistor may be shortened because it may carry more leakage current in response to the ambient electrical signals carried on the first electrical terminal L. Additionally, the capacitance of the varistor generally increases with the current-carrying capacity of the varistor. The GDT has a relatively low capacitance compared to the varistor. Therefore, for higher frequency applications (such as radio frequency (RF) applications, etc.), the GDT can provide improved performance in the SPD device compared to the varistor. However, the response time of the varistor is usually very fast, typically in the nanosecond range, while the GDT generally allows more energy to pass through (i.e., through the main line without diversion) over a longer period of time (e.g., a fraction of a microsecond) before tripping at the exceeded spark discharge voltage. Figure 1 The overvoltage protection circuit 600 can provide operational benefits associated with both the GDT and the varistor.

[0078] The thermal disconnector mechanism 605 can be configured to disconnect the GDT 610 and the current management circuit 620 from the first electrical terminal L in response to an increase in temperature that may cause damage to the GDT 610 of the SPD that can be incorporated into the overvoltage protection circuit 600 and / or the current management circuit 620 or other components of the SPD. Examples of thermal response mechanisms 151 and 432 are described below with reference to Figure 11 and Figure 19 respectively.

[0079] The current management circuit 620 includes a varistor 625 and a resistor R1 connected in parallel.

[0080] During ambient conditions on the first electrical terminal L, the GDT 610 conducts a very small current, thereby reducing the leakage current through the varistor 625. Accordingly, heat generated in the SPD including the overvoltage protection circuit 600 can be reduced, the likelihood that the thermal disconnector mechanism 605 is activated to disconnect the GDT 610 and the current management circuit 620 from the first electrical terminal can be reduced, and the lifespan of the varistor 625 can be increased.

[0081] The varistor 625 clamps the voltage across the nodes of the current management circuit 620 to a clamping voltage. The varistor 625 can be configured to have a clamping voltage that exceeds the ambient voltage level on the first electrical terminal L. This allows the varistor 625 and the resistor R1 to eliminate the continuous current received through the GDT 610 and allows the GDT 610 to transition out of the arc region and reset back into a non-conductive state. For example, if the arc voltage of the GDT 610 is 50V and the ambient line voltage is 120V, then in the absence of the varistor 625, when the signal on the first electrical terminal is in the ambient state after a transient overvoltage event has terminated, the GDT 610 will remain in the arc region and continue to transfer current. The varistor 625 clamps the bottom terminal of the GDT 610 to a clamping voltage level of, for example, 500V, which is generated across the varistor 625 from the transient overvoltage event. When the transient overvoltage event has passed and the ambient line voltage returns to 120V at the first electrical terminal L, the GDT 610 will have -331V 最大 generated across its terminals, thereby terminating the continuous current through the GDT 610 and causing the GDT 610 to reset back into a non-conductive state. The voltage across the GDT 610 would be at -670V 最大 at the negative cycle of the ambient voltage in the absence of the resistor R1 and would be up to 170V 最大 in the presence of the resistor R1 because the resistor R1 discharges the capacitance of the varistor 625. As described above, the varistor can be characterized by having a greater capacitance than the GDT. Once the transient overvoltage event has terminated, the resistor R1 can discharge the charge associated with the capacitance of the varistor 625.

[0082] Now referring Figure 2 to Figure 1operate in a similar manner to their corresponding counterpart components described. The current management circuit 720 differs from the current management circuit 620 in that an inductor L1 is included and is in series with a resistor R1. Since an inductor tends to resist changes in current, the inductor L1 allows the current through the resistor to increase over time based on a time constant given by R1xL1. Thus, the inductor L1 can protect the resistor R1 from high current surges caused by transient overvoltage events on the line electrically connected to the first electrical terminal L.

[0083] According to various embodiments of the inventive concept, Figure 1 and Figure 2 the resistor R1 in can be embodied as an axial resistor, a radial resistor, a surface mount device (SMD) resistor, and / or a combination thereof.

[0084] In some embodiments, the inductor L1 has an inductance in the range from about 1 µH to about 1 mH. The inductor L1 can be embodied as a discrete device and / or specifically as an SMD device.

[0085] In some embodiments, Figure 1 the varistor 625 of and Figure 2 the varistor 725 of have a peak current rating of about 20 kA, a peak voltage rating of about 300 V, and a clamping voltage of about 1500 V. According to various embodiments of the inventive concept, the varistor 625 and the varistor 725 can be embodied as the varistors 132 and 452 described below. Each of the varistors 625 and 725 can be embodied as one or more varistors connected in series or in parallel.

[0086] In some embodiments, the resistor R1 has a resistance in the range from about 1 kΩ to 50 MΩ, and in some embodiments, a resistance of about 1 MΩ.

[0087] In some embodiments, Figure 1 the GDT 610 of and Figure 2 the GDT 710 of have a pulse sparkover voltage rating of about 1400 V at a rate of rise of about 5 kV / µs and a discharge current rating of about 20 kA. The GDT 610 and the GDT 710 can be embodied as the GDTs 140 and 440 described according to various embodiments of the inventive concept. Each of the GDTs 610 and 710 can be embodied as one or more varistors connected in series or in parallel.

[0088] as described below according to various embodiments of the inventive concept Figure 1 and Figure 2The resistor R1 can be embodied as resistors 180, 280, 480, and 580. Figure 2 The inductor L1 can be embodied as inductor 386 described below according to various embodiments of the inventive concept.

[0089] Accordingly, embodiments of the inventive concept can provide an SPD including an overvoltage protection circuit and a current management circuit, the overvoltage protection circuit including a GDT, and the current management circuit including a varistor. The GDT can mitigate the current leakage problem associated with the varistor, which can extend the operating life of the varistor. The current management circuit including the varistor can help trigger the GDT in response to a transient overvoltage event, while the varistor provides improved energy dissipation and voltage clamping for a terminal of the GDT to eliminate the GDT holding current after the transient overvoltage event and allow the GDT to reset to a non-conductive state.

[0090] Reference Figure 6 - 13 , in which a transient voltage surge suppression (TVSS) or surge protection device (SPD) assembly 101 and an SPD system 103 according to an embodiment of the present invention are shown. The SPD assembly 101 and the system 103 include an SPD module 100 and a chassis or base 50. The SPD module 100 can be plugged into the base 50.

[0091] The SPD module 100 includes Figure 1 an electrical overvoltage protection circuit 600. The SPD module 100 can also be modified to further include an inductor corresponding to the inductor L1, such that the modified SPD module 100 includes Figure 2 an overvoltage protection circuit 700.

[0092] According to some embodiments and as shown, the SPD assembly 101 is configured, sized, and shaped for mounting on a support rail 92 (e.g., a DIN (Deutsches Institut für Normung) rail 92 as shown in Figure 6 ) and compliant with corresponding applicable DIN requirements or standards. The DIN rail 92 can be fixed (e.g., by screws 99 or other fasteners) to a suitable support structure such as a wall W (e.g., the rear wall of an electrical supply cabinet). The base 50 can be removably mounted on the DIN rail 92. The pluggable surge protection device (SPD) module 100 can then be removably mounted on the base 50.

[0093] In some embodiments, the maximum dimensions of the SPD assembly 101 comply with at least one of the following DIN (Deutsches Institut für Normung) standards: DIN 43 880 (December 1988). In some embodiments, the maximum dimensions of the assembly 101 comply with each of these standards.

[0094] According to some embodiments and as shown, rail 92 is a DIN rail. That is, rail 92 is a type of rail sized and configured to meet the DIN specifications for rails used to mount modular electrical devices.

[0095] The DIN rail 92 has a rear wall 93 and an integral longitudinal flange 95 that extends outwardly from the rear wall 93. Each flange 95 includes a forwardly extending wall 95A and an outwardly extending wall 95B. The walls 93, 95 together form a longitudinally extending front central channel 94 and an opposing longitudinally extending rear edge channel 96. Mounting holes may be provided that extend completely through the wall 93 and are adapted to receive fasteners 99 (e.g., threaded fasteners or rivets) for securing the rail 92 to a support structure (e.g., a wall or panel). The DIN rail 92 defines a DIN rail plane E-F and has a longitudinal axis F1-F1 that extends in the plane E-F. This type of DIN rail may be referred to as a "top hat" support rail.

[0096] According to some embodiments, the rail 92 is a 35 mm (width) DIN rail. According to some embodiments, the rail 92 is formed of metal and / or composite or plastic materials.

[0097] The assembly 100 has a DIN rail device assembly axis A-A ( Figure 6 ) that extends transversely to the axis F1-F1 of the DIN rail 92 and, in some embodiments, extends substantially perpendicular to the axis F1-F1 of the DIN rail 92. In some embodiments, the DIN rail mounting assembly axis A-A extends transversely to the plane E-F of the DIN rail 92 and, in some embodiments, extends substantially orthogonally to the plane E-F. As used herein, "front" or "distal" refers to the end that is further from the DIN rail 92 when the assembly 101 is mounted on the DIN rail 92, and "rear" or "proximal" refers to the end that is closer to the DIN rail 92.

[0098] The base 80 ( Figure 6 and Figure 13 ) includes a housing 82. The housing 82 includes a rear section 83A, an upper leg or section 83B, and a lower leg or section 83C. The housing 82 defines an enclosed cavity. According to some embodiments, the housing 82 is formed of an electrically insulating polymer material. The housing 82 may be formed of any suitable one or more materials. In some embodiments, the housing 82 is formed of a rigid polymer material or metal (e.g., aluminum). Suitable polymer materials may include, for example, polyamide (PA), polypropylene (PP), polyphenylene sulfide (PPS), or ABS.

[0099] The DIN rail receiver channel 82F is defined in the rear side of the rear section 83A. The integral rail hook feature 82H is positioned on one side of the channel 82F, and the spring-loaded DIN rail latch mechanism 82G is mounted on the other side of the channel 82F. As is known in the art, the feature and components 82F, 82G, 82H are sized and configured to securely and releasably mount the base 80 on a standard DIN rail 92.

[0100] The receiver slot 83D is defined in the front side of the base 80 by the sections 83A - C. The receiver slot 83D has a front opening and is open on either side. The receiver slot 83D extends axially along the axis A - A from the opening and is terminated by the front side of the rear section 83A.

[0101] Base terminal electrical connector assemblies 84, 86 are mounted in each of the upper and lower sections 83B, 83C. Each connector assembly 84, 86 includes a cable clamping connector 85A and a terminal contact connector socket 85B. Cable ports 82C are defined in each of the upper and lower sections 83B, 83C to receive the ends of the cables CL, CP into the corresponding cable clamping connectors 85A. A screwdriver port 82I is provided in each section 83B, 83C to receive a screwdriver for operating a threaded member (e.g., a screw) 85D of the associated cable clamping connector 85A.

[0102] Upper and lower contact openings 82E are defined in the front side or wall of the rear section 83A.

[0103] A switch 88 is disposed in the housing 82. The switch 88 includes a spring-loaded remote control pin 88A that projects forward from the front side of the rear section 83A. The switch 88 also includes switch electronics that are mounted on a PCB and connected to the control pin 88A and an output electrical connector.

[0104] As discussed in more detail below, the SPD module 100 includes a housing 110, an overvoltage clamping element subassembly 130 disposed in the housing 110, an integral thermal disconnector mechanism 151, an integral indicator mechanism 170 (including a local alarm mechanism 107 and a remote alarm mechanism 108), a first fail-safe mechanism 102, and a second fail-safe mechanism 104. The SPD module 100 also includes potting P (shown only in Figure 9 ), a first electrical contact member 166, and a second electrical contact member 168.

[0105] The housing 110 includes an inner housing member or frame 114 and an outer housing body member or cover 112 that together form the housing 110. The housing 110 defines an inner cavity or chamber.

[0106] The front indicator opening or window 112B is provided in the front wall of the cover 112. As discussed below, the indicator window 112B can be used to visually indicate a change in the state of the module 100.

[0107] The frame 114 includes a partition wall 116A that separates the cavity of the housing 110 into opposing cavities 118A and 118B. Electrical conductor or electrode slots 120 are defined in the partition wall 116A and connect these cavities.

[0108] The housing members 112, 114 can be formed from any suitable one or more materials. In some embodiments, each of the housing members 112, 114 is formed from a rigid polymer material. Suitable polymer materials can include, for example, polyamide (PA), polypropylene (PP), polyphenylene sulfide (PPS), or ABS.

[0109] In some embodiments and as shown, the overvoltage clamping element subassembly 130 includes a varistor 132, a first electrode 134 (also referred to herein as the "ground electrode"), a second electrode 136 (also referred to herein as the "disconnect electrode"), two gas discharge tubes (GDTs) 140, GDT electrodes or contact plates 142, and a resistor 180.

[0110] The varistor 132 has opposing contact surfaces 132A, 132B. Metallization layers 133 can cover the contact surfaces 132A, 132B.

[0111] The thickness of each varistor 132 and the diameter of its contact surfaces 132A, 132B will depend on the varistor characteristics desired for a particular application. In some embodiments, the varistor 132 has a width W1 ( Figure 10 ) to thickness T1 ( Figure 9 ) ratio of at least 2. In some embodiments, the thickness T1 of the varistor 132 ranges from about 0.75 to 15 mm.

[0112] The varistor material of the varistor 132 can be any suitable material conventionally used for varistors, i.e., a material that exhibits a non-linear resistance characteristic as a function of the applied voltage. In some embodiments, the varistor 132 is a metal oxide varistor (MOV). In some embodiments, the resistance becomes very low when a specified voltage is exceeded. The varistor material can be, for example, a doped metal oxide or silicon carbide. Suitable metal oxides include zinc oxide composites.

[0113] The first or ground electrode 134 includes a peripheral portion 134A, crossing or support legs 134B, an integral terminal protrusion 134C, and an integral resistor connection protrusion 134D. Portions 134A and 134B together form a contact portion. The ground electrode 134 is conductive. In some embodiments, the ground electrode 134 is formed of metal. Suitable metals may include nickel brass or copper alloys such as CuSn6 or Cu-ETP. In some embodiments, the ground electrode 134 is integral (composite or monolithic), and in some embodiments, the ground electrode 134 is monolithic.

[0114] The second or disconnect electrode 136 includes a peripheral portion 136A and a terminal protrusion 137. Portion 136A forms a contact portion, and the terminal protrusion 137 forms an extension portion.

[0115] The terminal protrusion 137 has a substantially planar contact surface 137A that defines a protrusion plane. In some embodiments, the protrusion plane is transverse to the plane defined by the contact surface 132B, and in some embodiments is substantially orthogonal to the plane defined by the contact surface 132B.

[0116] The disconnect electrode 136 is conductive. In some embodiments, the disconnect electrode 136 is formed of metal. Suitable metals may include nickel brass or copper alloys such as CuSn6 or Cu-ETP. In some embodiments, the disconnect electrode 136 is integral (composite or monolithic), and in some embodiments, the disconnect electrode 136 is monolithic.

[0117] The resistor 180 corresponds to Figure 1 or Figure 2 resistor R1. The resistor 180 may be a through-hole resistor that includes a resistor body 182 and opposing leads 184A, 184B. The resistor 180 may be an axial lead resistor as shown in Figure 8 or have another configuration (e.g., a radial lead resistor).

[0118] The resistor lead 184A is mechanically and electrically connected to the protrusion 134D. The resistor lead 184B is mechanically and electrically connected to the metallization layer 133 of the contact surface 132B. In some embodiments, the leads 184A and 184B are soldered to the protrusion 134D and the metallization layer 133 of the surface 132B.

[0119] A suitable through-hole resistor for the resistor 180 may include the metal film resistor type HVR3700001004JR500 rated at 1 MΩ available from Vishay Intertechnology, Inc. in the United States.

[0120] The ground electrode 134 and the disconnect electrode 136 are mounted on the outer surfaces 132A and 132B of the varistor 132. More particularly, the ground electrode 134 is soldered to the metallization layer 133 of the contact surface 132A, and the disconnect electrode 136 is soldered to the metallization layer 133 of the contact surface 132B, such that the electrodes 134 and 136 are electrically connected to the contact surfaces 132A and 132B, respectively.

[0121] The terminal protrusion 137 serves as an electrical conductor that extends laterally through the hole 120 in the frame 114. A section of the terminal protrusion 137 protrudes laterally beyond the lateral extension distance defined by the surface 132B of the varistor 132.

[0122] The overvoltage clamping element subassembly 130 is contained within the cavity 118A such that the terminal protrusion 137 extends through the slot 120 and into the cavity 118B. The other unoccupied space within the cavity 118A is filled with potting P.

[0123] Each GDT 140 includes a body 140A and anode and cathode terminals 140B and 140C at opposite ends of the body 140A. As is known in the art, the body 140A contains an anode, a cathode, and a spark gap chamber.

[0124] In some embodiments and as shown, each GDT 140 is cylindrical. An annular electrical insulator (e.g., ceramic) may surround the body 140A between the terminals 140B, 140C.

[0125] In some embodiments, the body 140A includes an enclosed or hermetically sealed chamber or unit that contains a selected gas. The terminals 140B, 140C are electrically connected to the gas (e.g., through corresponding electrode portions that are in fluid contact with the contained gas). Below a specified spark discharge voltage, the GDT 140 is electrically insulating between the terminals 140B, 140C. When the voltage applied across the terminals 140B, 140C exceeds the specified spark discharge voltage, the contained gas is ionized to cause current to flow through the gas (by the Townsend discharge process) and thus between the terminals 140B, 140C. Accordingly, depending on the applied voltage, the GDT 140 will selectively be electrically insulating or conductive. The voltage required to initiate and sustain conduction (discharge) will depend on the design characteristics of the GDT 140 (e.g., geometry, gas pressure, and gas composition).

[0126] In some embodiments, each GDT 140 has a surge current and energy withstand capacity that is at least as great as that of the MOV varistor disc 132 used (combined) in series with the GDT 140.

[0127] Suitable GDTs may include Class I and Class II GDTs. Suitable GDTs may be rated at impulse currents from 5 kA to 100 kA and at maximum continuous operating voltages from 60 V to 1200 V. Suitable GDTs may include a GDT of the surge arrester type A80 - A500XTP rated at 500 V available from TDK - EPC Corporation of Japan.

[0128] The contact plate 142 is conductive. In some embodiments, the contact plate 142 is formed of metal. Suitable metals may include nickel brass or copper alloys such as CuSn6 or Cu - ETP.

[0129] The contact plate 142 is mechanically fixed and electrically connected to the ground electrode 134, for example, by solder. The anode terminal 140B of each GDT 140 is mechanically fixed and electrically connected to the contact plate 142, for example, by solder.

[0130] The first electrical contact member 166 ( Figure 7 ) includes a base 166A and an integral U - shaped modular terminal connector 166B. The cathode terminal 140C of each GDT 140 is mechanically fixed and electrically connected to the base 166A, for example, at the joint J1 ( Figure 12 ) by brazing or soldering.

[0131] The GDT 140 is thus electrically connected in parallel between the varistor 132 and the contact member 166.

[0132] When forming the joint J1 during manufacturing, the relative positions of the ground electrode 134 and the base 166A can be adjusted or changed. For example, the lateral position of the contact member 166 relative to the ground electrode 134 can be adjusted and then fixed (e.g., by brazing or soldering) to accommodate varistors 132 of different thicknesses. This floating contact or joint can allow the use of the same ground electrode 134 to assemble varistors 132 of different thicknesses.

[0133] The contact member 166 can be formed of any suitable one or more materials. In some embodiments, the contact member 166 is formed of metal. Suitable metal materials may include, for example, nickel brass, CuSn 0.15, CuSN 6, CuP 0.008. In some embodiments, the contact member 166 is integral and, in some embodiments, monolithic.

[0134] The thermal disconnector mechanism 151 includes a disconnect spring 150 and a solder layer 159.

[0135] The disconnect spring 150 includes a cantilevered free leg. The free leg includes a lower portion 154A and an upper contact portion 154B. The contact portion 154B includes an inner contact surface facing the terminal protrusion 137. A weak region 156 is located in the spring 150 between the lower portion 154A and the contact portion 154B. The weak region 156 may include a notch defined in the side edge of the spring 150. Accordingly, the spring 150 has a reduced cross-sectional area at the weak region 156.

[0136] The spring 150 may be formed of any suitable one or more conductive materials. In some embodiments, the spring 150 is formed of metal. Suitable metal materials may include, for example, CuSn 0.15 alloy (bronze), nickel brass, CuSn6, Cu-ETP, oxygen-free copper. According to some embodiments, the spring 150 has a restoring force in the range from about 5 N to 50 N in the ready position ( Figure 11 ). According to some embodiments, the spring 150 has a conductivity of at least 14 nΩ·m (at 20 °C).

[0137] The second electrical contact member 168 ( Figure 7 ) includes an integral U-shaped modular terminal connector 168B. The spring 150 is fixed to the contact member 168 (e.g., by a rivet). The contact member 168 may be formed of any suitable one or more materials. In some embodiments, the contact member 168 is formed of metal. Suitable metal materials may include, for example, nickel brass, CuSn 0.15, CuSN 6, CuP 0.008. In some embodiments, the contact member 168 is integral and, in some embodiments, monolithic.

[0138] The solder 159 may be formed of any suitable one or more materials. In some embodiments, the solder 159 is formed of metal. Suitable metal materials may include, for example, 58Bi42Sn.

[0139] According to some embodiments, the solder 159 is selected such that its melting point is greater than a specified maximum standard operating temperature but less than or equal to a specified disconnect temperature. The maximum standard operating temperature may be the expected maximum temperature in the solder 159 during normal operation (including handling overvoltage surges within the design range of the module 100). The specified disconnect temperature is the temperature at which the solder 159 is intended to release the spring 150 to actuate the first fail-safe mechanism 102.

[0140] According to some embodiments, the solder 159 has a melting point in the range from about 109 °C to 160 °C, and in some embodiments has a melting point in the range from about 85 °C to 200 °C.

[0141] The indicator mechanism 170 includes a swing arm 172, an indicator shuttle or member 174, and an indicator spring 176. The indicator member 174 is slidably fixed to a track or the front wall of the frame 116 to slide along the indicator axis I-I ( Figure 11 ).

[0142] The indicator spring 176 is elastically stretched such that it exerts a continuous pulling force on the swing arm 172.

[0143] When the module 100 assembly is in the ready configuration as shown in Figure 9 - 11 , the disconnect spring 150 is elastically bent, deformed, or deflected such that it continuously exerts a biasing load on the solder 159 to pull away from the terminal protrusion 137 in the release direction DR.

[0144] In the ready configuration, the swing arm 172 is locked by the disconnect spring 150 in the position shown in Figure 11 . The indicator spring 176 is elastically extended or stretched such that it continuously exerts a biasing load to pull the swing arm 172 in the pivot direction DP (i.e., toward the front wall 116B). The indicator member 174 is thus fixed in the ready position, where the indicator surface of the indicator member 174 is not aligned with the window 112B and is not visible through the window 112B.

[0145] The circuit formed by the module 100 is schematically represented as an overvoltage protection circuit 600 and a circuit 700 in Figure 1 and Figure 2 respectively.

[0146] The system 101 can be used according to the method of the present invention as follows.

[0147] Referring to Figure 5 , Figure 5 an exemplary circuit 15 in which one or more SPD assemblies 101 can be used is shown. The SPD assembly 101 can be mounted on a DIN rail 92 ( Figure 6). The illustrated circuit 15 is a three-phase system using a "3 + 1" protection configuration. In the illustrated circuit 15, there are three SPD components 101 (denoted as S1, S2, and S3 respectively), and each SPD component is connected between the corresponding lines L1, L2, L3, and N (i.e., L-N). An additional SPD module SPE is connected between N and PE (i.e., N-PE). The SPD module SPE can be connected to PE through a local grounding terminal EBB (e.g., an equipotential bonding busbar). The SPD module SPE can also be an SPD component 101 as described herein. Each of the lines L1, L2, L3 can be provided with a main circuit breaker or fuse FM and an external disconnector, such as an auxiliary fuse FS between the line and its SPD components S1, S2, S3. In other embodiments, one or more of the SPD components S1, S2, S3, SPE can have a configuration different from that of the SPD component 101 disclosed herein.

[0148] The operation of the SPD component S1 and the conditions or transient overvoltage events on line L1 will be described hereinafter. However, it will be understood that this description applies equally to the SPD components S2, S3 and the lines L2, L3.

[0149] In use, as shown in Figure 6 , the base 80 is mounted on the DIN rail 92. The DIN rail 92 is received in the channel 82F and fixed by the hook 82H and the latching mechanism 82G.

[0150] The cables CL, CP (shown in dashed lines in Figure 6 ) 82C are inserted through the cable ports and fixed in the clamping connectors 85A. In some embodiments, the cable CL is connected to the line L1, and the cable CP is connected to the protective ground (PE).

[0151] Then, the module 100 is axially inserted or pushed into the receiver slot 83D through the front opening along the axis A-A in the insertion direction. As shown in Figure 6 , the module 100 is pushed back into the receiver slot 83D until the rear end of the module 100 substantially engages the front side of the rear housing section 83A.

[0152] The insertion of the module 100 into the slot 83D causes the terminals 166B and 168B to be inserted into the sockets 85B of the connector assemblies 84 and 86 along the insertion axis I-I.

[0153] Since the thermal disconnector mechanism 151 is in its ready position, the indicator member 174 is held in the retracted position ( Figure 11). Additionally, when the module 100 is inserted into the receiver slot 83D, the remote control pin 88A is thereby pressed by the end of the cover port 122 of the swing arm 172. Thereby, the module 100 provides feedback via the pressed remote control pin 88A that the module 100 has been placed in the base 80 and that the module 100 is in its ready or operational (non-failed) condition.

[0154] By performing the operations opposite to the foregoing procedures, the module 100 can be released and removed from the base 80. The foregoing steps of installing the module 100 or other suitably configured modules in the base 80 and removing them from the base 80 can be repeated multiple times. For example, in the case where the varistor 132 of the module 100 deteriorates or is damaged or no longer has the appropriate specifications for the intended application, the module 100 can be replaced with a new or suitably constructed module.

[0155] In the case where the varistor 132 fails, a fault current will conduct between the corresponding line (e.g., Figure 5 line L1) and the neutral line N. As is well known, a varistor has an inherent 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 VNOM, the varistor will effectively not conduct current. Above VNOM, the varistor will conduct current (i.e., leakage current or surge current). The VNOM of a varistor is typically specified as the measured voltage across the varistor in the case of a 1 mA DC current.

[0156] As is well known, a varistor has three operating modes. In the first normal mode (discussed above), the varistor is effectively an electrical insulator until the nominal voltage. In the 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 then returns to the first mode. In the third mode (the so-called end-of-life mode), the varistor is effectively depleted and becomes a permanently non-reversible electrical conductor.

[0157] The varistor also has an inherent clamping voltage VC (sometimes simply referred to as the "clamping voltage"). According to the standard protocol, the clamping voltage VC is defined as the maximum measured voltage across the varistor when a specified current is applied to the varistor over time.

[0158] In the absence of overvoltage conditions, the varistor 132 provides a high resistance such that approximately no current flows through the module 100, as if it were electrically open. That is, typically each varistor approximately does not conduct current. In the case of an overcurrent surge event (usually transient; e.g., lightning strike) or an overvoltage condition or event exceeding VNOM (usually of longer duration compared to an overcurrent surge event), the resistance of the varistor disc rapidly decreases, thereby allowing current to flow through the module 100 to form a shunt path for current flow in order to protect other components of the associated electrical system. Typically, the varistor recovers from these events without the module 100 overheating significantly.

[0159] 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 resistor. The failure of the varistor to a short circuit or to a linear resistor can be caused by conducting a single or multiple surge currents of sufficient magnitude and duration or by a single or multiple consecutive overvoltage events that will drive sufficient current through the varistor.

[0160] A short circuit failure typically manifests as a local pinhole or perforated site (in this document, a "failure site") extending through the thickness of the varistor. This failure site forms a path for current flow between two low-resistance electrodes, but the resistance is high enough to generate ohmic losses and cause the device to overheat even at low fault currents. A large enough fault current through the varistor can melt the varistor in the region of the failure site and generate an arc.

[0161] The failure of the varistor as a linear resistor will result in limited current conduction through the varistor, which will lead to heat accumulation. This heat accumulation may lead to catastrophic thermal runaway, and the device temperature may exceed the specified maximum temperature. For example, a maximum allowable temperature for the outer surface of the device can be set by a code or standard to prevent adjacent components from burning. If the leakage current is not interrupted at certain time intervals, overheating will ultimately cause the varistor to fail to a short circuit as defined above.

[0162] In some cases, the current through a failed varistor can also be limited by the power system itself (e.g., the ground resistance in the system or in a photovoltaic (PV) power supply application, where the fault current depends on the power generation capacity of the system at the moment of failure), resulting in a gradual accumulation of temperature, even if the varistor failure is a short circuit. For example, due to an extended overvoltage condition caused by a power system failure, there are cases where a limited leakage current flows through the varistor. Additionally, the varistor will exhibit some leakage current at voltages below a threshold at which the varistor becomes substantially conductive. These conditions can lead to temperature accumulation in the device, such as when the varistor has failed as a linear resistor and can potentially cause the varistor to fail as a linear resistor or as a short circuit as described above.

[0163] As discussed above, in some cases, module 100 can present an "end-of-life" mode in which the varistor 132 is fully or partially depleted (i.e., in an "end-of-life" state), resulting in an end-of-life failure. When the varistor reaches its end of life, module 100 will essentially become a short circuit with a very low but non-zero ohmic resistance. Thus, under end-of-life conditions, even in the absence of an overvoltage condition, a fault current will continuously flow through the varistor.

[0164] Depending on the state of varistor 132 and external event conditions, SPD assembly 101 has several operating modes.

[0165] In some modes, the first fail-safe mechanism 102 operates by heating solder 159 until the solder melts and allows the elastic spring load of spring 150 to cause contact portion 154B to pull away from terminal protrusion 137 and thereby break the electrical continuity with electrode 136. The varistor 132 is thereby electrically disconnected from contact member 168, creating an open circuit between terminals 166B, 168B.

[0166] In some modes, the second fail-safe mechanism 104 operates by heating spring 150 at weak region 156 until the weak region is sufficiently thermally softened to allow the load of spring 150 to cause spring 150 to break at weak region 156. Contact portion 154B may remain bonded to terminal protrusion 137 by solder 159, but lower portion 154A pulls away from contact portion 154B and thereby breaks the electrical continuity with electrode 136. The varistor 132 is thereby electrically disconnected from contact member 168, creating an open circuit between terminals 166B, 168B.

[0167] During normal operation (referred to herein as mode 1), module 100 operates as an open circuit between line cable CL and PE cable CP. The thermal disconnector mechanism 151 remains in the ready position ( Figure 11), where the contact portion 154B of the disconnecting spring 150 is bonded to the terminal protrusion 137 by solder 159 and is in electrical continuity with the terminal protrusion 137. In this normal mode, the varistor 132 is an insulator (and thus the SPD module 100 is also an insulator) until the nominal clamping voltage VNOM. In this mode, the fail-safe mechanisms 102, 104 are not actuated (i.e., the thermal disconnector 151 remains in the ready position ( Figure 11 ).

[0168] In the case of a transient overvoltage or surge current in line L1, protection of the power system load device may require providing an overcurrent path for the surge current to ground. The surge current can generate a transient overvoltage between the line cable CL and the PE cable CP, which can overcome the isolation of one or both of the varistor 132 and the GDT 140. In this event and mode (referred to herein as mode 2), the varistor 132 is subjected to an overvoltage exceeding VNOM and temporarily and reversibly becomes a low-resistance electrical conductor. Similarly, the GDT 140 is subjected to a transient overvoltage exceeding its breakdown voltage and temporarily and reversibly becomes a low-resistance electrical conductor. Then, the GDT 140 and the varistor 132 will transfer, shunt, or allow a high surge current or pulse current to flow from the line cable CL through the base connector 84, through the contact member 168, through the spring 150, through the solder 159, through the terminal protrusion 137, through the electrode 136, through the varistor 132, through the electrode 134, through the GDT 140, through the GDT electrode 142, through the contact member 166, and through the base connector 86 and reach the protective ground cable CP.

[0169] In mode 2, the fail-safe mechanism 102 does not operate because the overvoltage event duration is short and the heat generated by the surge current is not sufficient to melt the solder 159.

[0170] In mode 2, the fail-safe mechanism 104 does not operate because the heat generated in the spring 150 is not sufficient to weaken the weak area 156 to the breaking point.

[0171] If the surge or pulse current is below the maximum surge / pulse current rated for the SPD module 100, the external fuse FS will not blow and the varistor 132 should remain functional. In this case, since the fail-safe mechanisms 102, 104 have not tripped, the SPD module 100 can remain in place for future overvoltage events.

[0172] If the surge or pulse current exceeds the maximum surge / pulse current rated for the SPD module 100, the fuse FS will typically blow or trip. The varistor 132 can also fail internally as a short circuit (with a pinhole) or with a limited resistance. In this case, the operating mode will be the failure mode described below for Mode 3, 4, or 5.

[0173] In the third mode (Mode 3), the varistor 132 is in an end-of-life mode, where there is a low leakage current between line L1 and PE. The varistor 132 fails as a linear resistor. This type of varistor failure can be the result of multiple surge / pulse currents. The leakage current generates heat in the varistor 132 due to ohmic losses. In some cases, the leakage current occurs during normal operation and is low (from approximately 0 to 0.5 A). The heat generated in the varistor 132 gradually deteriorates the varistor 132 and accumulates over an extended duration.

[0174] In Mode 3, the fail-safe mechanism 102 operates. More particularly, heat (e.g., from ohmic losses in the varistor 132) is transferred from the varistor 132 to the electrode 136 and then to the solder 159. Over an extended period of time (e.g., in the range from approximately 60 seconds to 48 hours), heat accumulates in the solder 159 until the solder 159 melts. The melted solder 159 releases the spring 150 into an open or released configuration to disconnect the circuit in the SPD module 100. This prevents the varistor 132 from catastrophically overheating.

[0175] In Mode 3, the fail-safe mechanism 104 does not operate because the heat generated in the spring 150 is not sufficient to weaken the weak area 156 to the breaking point.

[0176] In Mode 3, the SPD module 100 must be replaced because the fail-safe mechanism 102 has tripped.

[0177] In the fourth mode (Mode 4), the varistor 132 is in good condition (i.e., not in an end-of-life condition), but there is a temporary overvoltage (TOV) event where the voltage across terminals 166B, 168B forces the varistor 132 to conduct an increased surge current (typically, in the range from approximately 0 to 10 A). This current accumulates heat over a certain duration (e.g., in the range from approximately 5 seconds to 120 minutes), which is shorter than the duration of the surge current that triggers the fail-safe mechanism 102 in Mode 3 but much longer than the pulse current conducted through the varistor 132 in Mode 2.

[0178] In Mode 4, the fail-safe mechanism 102 trips (i.e., the spring 150 is released by the solder 159) so as to disconnect the circuit passing through the SPD module 100 in the same manner as described for Mode 3.

[0179] In Mode 4, the fail-safe mechanism 104 does not operate because the heat generated in the spring 150 is not sufficient to weaken the weak area 156 to the breaking point.

[0180] In Mode 4, the SPD module 100 must be replaced because the fail-safe mechanism 102 has tripped.

[0181] In the fifth mode (Mode 5), the varistor 132 is in an end-of-life mode as a short circuit or a linear resistor, which allows the conduction of the current from the power supply to pass through it. The value of the conducted current can be between approximately 10 amperes and the maximum short-circuit current of the power supply, which should be lower than the short-circuit current rating of the SPD module 100. This depends on the specific configuration of the electrical equipment and the severity of the varistor failure.

[0182] For Mode 5, there are two mechanisms to protect the SPD module 100: namely, the external fuse FS and the fail-safe mechanism 104 as described above. For current levels between 10 amperes and a medium current level (usually five times the rating of the external fuse FS), the fail-safe mechanism 104 is triggered. For higher current levels, the external fuse FS will trip first to protect the SPD 100. For example, for current levels up to 1000 A, the SPD 100 can be protected by the fail-safe mechanism 104, and for current levels up to 25 kA, a 200 A external fuse FS is used to protect the SPD 100.

[0183] In Mode 5, for medium currents, the current level is not high enough to cause the external fuse FS to trip within a reasonable amount of time (e.g., in the range from about 50 ms to 5000 ms). In addition, the fail-safe mechanism 102 is too slow and cannot protect the SPD module 100. By the time the fail-safe mechanism 102 trips, significant internal damage will be caused to the SPD module 100.

[0184] Therefore, in Mode 5, the fail-safe mechanism 104 trips to disconnect the circuit passing through the SPD module 100. More specifically, the current heats the spring 150 at the weak area 156 until the load on the spring 150 causes the spring 150 to break at the weak area 156 and create the necessary distance between the electrodes to eliminate the associated arc. The varistor 132 is thereby electrically disconnected from the contact member 168, creating an open circuit between the terminals 166B and 168B. Only the fail-safe mechanism 104 operates in time and disconnects the SPD 100 before any internal damage occurs.

[0185] Alternatively, a fuse FS with a lower rating can be used, such that the fuse FS will trip much faster and protect the SPD 100 even at medium current levels. For example, a 10 A fuse FS can be used and the fail-safe mechanism 104 can be omitted. On the other hand, however, such a lower-rated fuse FS will trip at surge / pulse currents below the level that the SPD 100 can actually withstand. Thus, by using the fail-safe mechanism 104, the performance of the SPD 100 is extended with respect to surge / pulse currents.

[0186] The release of the disconnect spring 150 (by actuating either the fail-safe mechanism 102 or the fail-safe mechanism 104) as described above also actuates the local alarm mechanism 107. The displacement of the spring 150 along the release direction DR disengages the swing arm 172 from the spring 150. The swing arm 172 is driven by a spring 176 in the pivot direction DP ( Figure 11 ) from the locked position ( Figure 11 ) to the indicating position. The indicator member 174 is thereby driven by the spring 176 to slide along the front wall in the signaling direction DS ( Figure 11 ). The indicator member 174 is thereby displaced to the alarm position as shown, in which the indicator surface 174A is aligned with and visible through the front window 112B of the module housing 110. The indicator surface 174A has a distinctly different visual appearance through the front window 112B compared to the housing indicator surface 116C, thereby providing a visual alarm or indication such that an operator can easily determine that the local alarm mechanism 107 has been activated. For example, the housing indicator surface 116C and the indicator surface 174A can have distinctly different colors (e.g., green and red). In this way, the local alarm mechanism 107 can provide a convenient indication that the module 100 has assumed its open-circuit configuration or state.

[0187] The release of the swing arm 172 as described above also actuates the remote alarm mechanism 108. In the ready position of the module 100, the end of the switch arm 172 covers the rear opening of the frame such that the switch pin 88A of the base 80 is maintained in compression. The swing arm 172 pivots away from the rear opening, such that the switch pin 88A is thereby allowed to extend further into the module 100 to the alarm signal position. The remote pin 88A is connected to switch electronics or a sensor that detects the displacement of the pin 88A and provides an electrical signal via a connector to a remote device or terminal. In this way, the remote alarm mechanism 108 can provide a convenient remote indication that the module 100 has assumed its open-circuit configuration or state.

[0188] As discussed above, the thermal disconnect mechanism 151 responds to a temperature rise in the SPD module 100 when current flows through the varistor 132 and disconnects the varistor 132 from the power line. Generally, the thermal disconnect mechanism 151 can be configured to desirably balance the response of the SPD component 100 and the fuse FS to pulsed or surge current with the response to leakage current. The failure mode of the varistor 132 can be one of the modes discussed above, for example: a gradual degradation of the varistor 132 that will result in an increased leakage current (e.g., 0 - 0.5 A) during normal operation; a temporary overvoltage (TOV) event that will result in an increased conduction of the leakage current (e.g., 0.5 A - 10 A); or a short circuit of the varistor 132, which may result in significant current conduction (several amperes up to the full prospective short-circuit current of the power line, e.g., up to 200 kArms).

[0189] When the varistor 132 has an expanded leakage or surge current conduction (modes 3 and 4 discussed above), then the varistor 132 will gradually overheat over an extended period of time. Eventually, the thermal disconnect mechanism 151 will respond to the temperature rise of the varistor 132 transmitted through the electrode protrusion 137 to the solder joint. How quickly the thermal disconnect mechanism 151 will respond to this event on a given temperature profile of the varistor 132 depends on the materials of the components of the thermal disconnect mechanism 151 and the melting point of the solder 159. These parameters can be selected to adjust the response of the thermal disconnect mechanism 151 to different event profiles or event types.

[0190] In addition, the reaction time of the thermal disconnect mechanism 151 should not be too fast because in the case where the varistor 132 conducts a surge current with increased energy, the varistor 132 will overheat and the disconnect mechanism 151 may trip even if the varistor 132 is intact. Therefore, it is desirable or necessary to fine-tune the reaction time of the thermal disconnect mechanism 151. Thus, for proper operation during all types of events / exposures that the SPD module 100 may face, the selection of the materials and shapes of the elements that make up the thermal disconnect mechanism 151 is important and may be critical because the reaction time depends on this selection.

[0191] During a sudden failure of the varistor 132 to short circuit, the current through the varistor 132 can reach from a medium value (a few kA) up to the maximum short-circuit current of the power line. For medium current values, the weak point 156 of the thermal disconnector will usually overheat, melt, and disconnect the current via the second fail-safe mechanism 104. This is done because the weak point 156 of the thermal disconnector mechanism 151 has a reduced cross-sectional area with a higher resistance. The selection of the material for the weak area 156 is also important for its fast response time because in such an event, the second fail-safe mechanism 104 of the thermal disconnector mechanism 151 must react very quickly. The second fail-safe mechanism 104 does not respond to surge currents, so there is no lower limit to its response time. Additionally, if the second fail-safe mechanism 104 does not react quickly enough, the SPD module 100 may be damaged due to the high current conducted. Further, during these events, the solder 159 will not melt because the first fail-safe mechanism 102 takes a relatively long time to react (a few seconds), while the second fail-safe mechanism 104 operates faster, and the weak point 156 will melt within a few milliseconds (ms).

[0192] When the short-circuit current is high enough, then the SPD module 100 is protected by the external fuse FS. Usually, when the short-circuit current is sufficient to trip the fuse FS, the external fuse FS will trip. When the short-circuit current is not sufficient to trip the fuse FS, the thermal disconnector mechanism 151 (either the first fail-safe mechanism 102 or the second fail-safe mechanism 104) will trip.

[0193] The series arrangement of the GDT 140 with the varistor 132 can provide substantially leak-free operation. In the absence of surge current, the GDT 140 will remain non-conductive and will thus prevent the conduction of leakage current through the varistor 132. In the case of a surge, the varistor 132 will clamp and conduct, allowing the GDT 140 to turn on and conduct. When the surge subsides, the varistor 132 will return to its highly electrically insulating state, causing the arc extinction of the GDT 140. In this way, the varistor 132 can cut off the prolonged continuous current that would otherwise cause the failure of the GDT 140.

[0194] The potting P can provide strength and vibration resistance to the SPD module 100 and has a lower usage cost compared to epoxy resin. The potting P can provide heat absorption to cool the varistor 132 and the GDT 140.

[0195] In some embodiments, module 100 is a Type I surge protection device (SPD). In some embodiments, module 100 complies with IEC 61643-11 for SPD (Clause 8.3.4.4) "Additional energy rate test for testing Type I" based on the impulse discharge current waveform defined in Clause 8.1.1 of IEC 61643-11, which impulse discharge current waveform is commonly referred to as the 10 / 350 microsecond ("µs") current waveform ("10 / 350 µs current waveform"). The 10 / 350 µs current waveform may characterize a current wave in which the maximum current (100%) is reached at approximately 10 µs and the current is 50% of the maximum value at approximately 350 µs. Under the 10 / 350 µs current waveform, according to one or more standards, the charge Q and specific energy W / R transferred to the SPD should be related to the peak current. For example, the IEC61643-11 parameters for Type I SPD testing are illustrated in Table 1 as follows:

[0196] Table 1 Parameters for Type I SPD Testing

[0197] <![CDATA[Within 50 μs I imp (kA)]]> Q (As) within 5 ms W / R (kJ / Ω) within 5 ms 25 12.5 156 20 10 100 12.5 6.25 39 10 5 25 5 2.5 6.25 2 1 1 1 0.5 0.25

[0198] It is desirable that the SPD module has a small form factor. In particular, in some applications, it is desirable that the SPD modules each have a size of 1TE according to DIN standard 43871 published on November 1, 1992. According to some embodiments, module 100 has a maximum width W9 of approximately 18 mm parallel to the axis F1-F1 ( Figure 6 ).

[0199] Reference Figure 14 and Figure 15 , which show a modular overvoltage protection device or surge protection device (SPD) module of another embodiment of the present invention and is labeled 200. For purposes of explanation, only certain internal components of module 200 are shown in Figure 14 and Figure 15 . Except as follows, module 200 is constructed, used, and operated in the same manner as module 100.

[0200] The SPD module 200 includes Figure 1 overvoltage protection circuit 600.

[0201] The disconnect electrode 236 includes an integral contact protrusion 236B.

[0202] Module 200 includes a PCB resistor assembly 281 in place of resistor 180. The PCB resistor assembly 281 includes resistor 280, printed circuit board (PCB) 282, and solder 285.

[0203] The PCB 282 includes a non-conductive substrate 283 having conductive layers 284A, 284B thereon. The conductive layers 284A, 284B can be copper foil tracks deposited or laminated onto the outer surface of the substrate 283. The substrate 283 can be formed of any suitable material such as, for example, glass epoxy resin. A relatively shallow groove 283A is defined in one side edge of the substrate 283. A relatively deeper groove 283B is defined in the opposite side edge of the substrate 283.

[0204] The resistor 280 can be a surface mount device (SMD) resistor. Suitable SMD resistors include the thick film high voltage chip resistor type CHV2512-FX-1004ELF rated at 1 MΩ available from Bourns, Inc. of the United States. The resistor 280 includes a resistor body 280A and opposite electrical terminals 280B, 280C. The resistor 280 is mechanically attached to the PCB 282 such that the terminals 280B and 280C are electrically connected to the conductive layers 284A and 284B, respectively. In some embodiments, the terminals 280B and 280C are attached and electrically connected to the conductive layers 284A and 284B by solder 285.

[0205] The contact protrusion 234D of the ground electrode 234 is placed in the groove 283D. The contact protrusion 236B of the disconnect electrode 236 is placed in the groove 283A. The contact protrusion 236B is mechanically fixed and electrically connected to the conductive layer 284A by solder 285. The contact protrusion 234D is mechanically fixed and electrically connected to the conductive layer 284B by solder 285. In this way, the terminal 280B is electrically connected to the electrode 236, and the terminal 280C is electrically connected to the electrode 234.

[0206] The groove 283B enables the components of the module 200 to be conveniently configured for varistors 232 of different thicknesses. Varistors of different thicknesses can be used for different voltage protection levels. Varistors of different thicknesses require different spacings between the electrodes 234, 236 and different clearances between the protrusions 234D, 236B. During manufacturing, this variation can be accommodated by sliding the protrusion 234D laterally in the direction DL into the groove 283B as needed and then fixing and electrically connecting the protrusion 234D to the copper layer 284B using solder 285.

[0207] Reference Figure 16 , which shows a modular overvoltage protection device or surge protection device (SPD) module according to another embodiment of the present invention and labeled 300. For explanatory purposes, only certain internal components of the module 300 are shown in Figure 16 . The module 300 is constructed, used, and operates in the same manner as the module 200, except as follows.

[0208] Module 300 may include an overvoltage protection circuit 700 according to some embodiments of the inventive concept. Figure 2 Module 300 includes an inductor 386 mounted on a PCB 382 in electrical series with a resistor 380. The inductor 386 corresponds to Figure 2 inductor L1 of the overvoltage protection circuit 700.

[0209] The inductor 386 may be a surface mount device (SMD) inductor coil. Suitable SMD inductor coils include the Wirewound chip inductor CC453232 series type 331KL available from Bourns, Inc. of the United States. The terminals of the inductor 386 may be attached and electrically connected to the conductive layer of the PCB 382 by solder.

[0210] Reference Figure 17 - 20 shows a modular surge protection device (SPD) or overvoltage protection device according to additional embodiments of the present invention and labeled as 400. According to some embodiments, the overvoltage protection device 400 is used as an SPD in the circuit as described above. For example, the overvoltage protection device 400 may be used to replace one or more of the SPDS1, S2, S3 in Figure 5 system 15.

[0211] The overvoltage protection device 400 includes Figure 1 the overvoltage protection circuit 600. Alternatively, the device 400 may be modified to include an inductor corresponding to Figure 2 inductor L1, in which case the modified device 400 will include Figure 2 the overvoltage protection circuit 700.

[0212] The overvoltage protection device 400 is configured as a unit or module having a longitudinal axis B-B ( Figure 17 ). The overvoltage protection device 400 includes a first electrode or housing 422, a piston-shaped second electrode 424, two spring washers 428E, a flat washer 428D, an insulating ring member 428C, two O-rings 430A, 430B, an end cap 428A, a fixing clip 428B, a fusible member 432, a varistor 452, a GDT 440, a first internal electrode 460, a second internal electrode 462, a resistor 480, an electrical insulator 486, and a GDT contact member 442. The varistor 452, internal electrodes 460, 462, resistor 480, and insulator 486 form an overvoltage clamping element subassembly 450.

[0213] The overvoltage protection device 400 may further include an integral fail-safe mechanism, device, feature, or system 402. As discussed in more detail below, the fail-safe system 402 is adapted to prevent or inhibit overheating or thermal runaway of the overvoltage protection device.

[0214] Components 422, 424, 428A - C together form a housing assembly 423, which defines a sealed enclosed chamber 426. Components 428A - E, 432, 460, 452, 462, 442, 440, 480, and 486 are axially disposed between the housing 422 and the electrode 424 in the enclosed chamber 426 along the longitudinal axis B - B.

[0215] The housing 422 has an end electrode wall 422A and an integral cylindrical side wall 422B extending from the electrode wall 422A. The side wall 422B and the electrode wall 422A form a chamber or cavity 422C that communicates with an opening 422D. A threaded post 422E projects axially outward from the electrode wall 422A. The inner side of the electrode wall 422A includes a circular recess 422F configured to receive the terminal 440B of the GDT 440.

[0216] The electrode wall 422A has an inward - facing substantially planar contact surface 422G. An annular clamping groove 422H is formed in the inner surface of the side wall 422B. According to some embodiments, the housing 422 is formed of aluminum. However, any suitable conductive metal can be used. According to some embodiments, the housing 422 is integral and in some embodiments is monolithic. The housing 422 is illustrated as cylindrical, but can be of a different shape.

[0217] The inner electrode 424 has a head 424A disposed in the cavity 422C and an integral shaft 424B that projects outward through the opening 422D.

[0218] The head 424A has a substantially planar contact surface 424C that faces the contact surface 422G of the electrode wall 422A. A pair of integral annular axially - spaced flanges 424D extend radially outward from the shaft 424B and define an annular laterally - open groove 424E therebetween. A threaded hole is formed in the end of the shaft 424B to receive a bolt, for example, for fixing the electrode 424 to a bus bar.

[0219] According to some embodiments, the electrode 424 is formed of aluminum. However, any suitable conductive metal can be used. According to some embodiments, the electrode 424 is integral and in some embodiments is monolithic.

[0220] An annular gap is radially defined between the closest adjacent surfaces of the head 424A and the side wall 422B. According to some embodiments, the gap has a radial width in the range from about 4 to 45 mm.

[0221] The fusible member 432 is annular and is mounted on the electrode 424 within the recess 424E. The fusible member 432 is spaced apart from the sidewall 422B by a distance sufficient to electrically isolate the fusible member 432 from the sidewall 422B.

[0222] The fusible member 432 is formed of a thermally fusible conductive material. According to some embodiments, the fusible member 432 is formed of a metal. According to some embodiments, the fusible member 432 is formed of a conductive metal alloy. According to some embodiments, the fusible member 432 is formed of a metal alloy from the group including aluminum alloys, zinc alloys, and / or tin alloys. However, any suitable conductive metal may be used.

[0223] According to some embodiments, the fusible member 432 is selected such that its melting point is greater than a specified maximum standard operating temperature. The maximum standard operating temperature may be the expected maximum temperature in the fusible member 432 during normal operation (including handling overvoltage surges within the design range of the system) rather than during operation that would result in thermal runaway if not suppressed. According to some embodiments, the fusible member 432 is formed of a material having a melting point in the range from about 80 to 460 °C and according to some embodiments in the range from about 110 to 160 °C. According to some embodiments, the melting point of the fusible member 432 is at least 20 °C less than the melting points of the housing 422 and the electrode 424, and according to some embodiments, at least 40 °C less than the melting points of those components.

[0224] According to some embodiments, the fusible member 432 has a conductivity in the range from about 0.5×40 6 Siemens per meter (S / m) to 4×40 7 S / m and according to some embodiments in the range from about 4×40 6 S / m to 3×40 6 S / m.

[0225] The varistor disc 452 and the two internal electrodes 460, 462 are axially stacked in the chamber 426 between the electrode head 424 and the electrode wall 422. The internal electrodes 460, 462 electrically interconnect the disc 452, the resistor 480, and the electrodes 422, 424 in the manner represented in the Figure 1 schematic electrical diagram. The varistor disc 452, the internal electrodes 460, 462, the resistor 480, and the insulator 486 form the subassembly 450.

[0226] According to some embodiments, the varistor 452 is a varistor chip (i.e., is in the shape of a sheet or a disc). In some embodiments, the varistor chip 452 is circular in shape and has a substantially uniform thickness. However, the varistor chip 452 can be formed in other shapes. The thickness and diameter of the varistor chip 452 will depend on the varistor characteristics desired for a particular application. Additionally, the varistor chip 452 can be replaced with a plurality of axially stacked varistor chips.

[0227] In some embodiments, the varistor chip 452 has a diameter D4 to thickness T4 ratio of at least 3. In some embodiments, the thickness T4 of the varistor chip 452 ( Figure 19 ) is in the range from about 0.5 to 15 mm. In some embodiments, the diameter D4 of the varistor chip 452 ( Figure 19 ) is in the range from about 20 to 100 mm.

[0228] The varistor chip 452 has first and second opposite, substantially planar contact surfaces 452U, 452L and a peripheral edge 452E.

[0229] The varistor material can be any suitable material conventionally used for varistors, i.e., a material that exhibits non-linear resistance characteristics as a function of the applied voltage. Preferably, the resistance becomes very low when a specified voltage is exceeded. The varistor material can be, for example, a doped metal oxide or silicon carbide. Suitable metal oxides include zinc oxide compounds.

[0230] The varistor chip 452 can include a sheet of varistor material coated on either side with a conductive coating such that the exposed surfaces of the coating serve as the contact surfaces 452U, 452L. The coating can be a metallization coating formed of, for example, aluminum, copper, or silver. Alternatively, the bare surfaces of the varistor material can serve as the contact surfaces 452U, 452L.

[0231] The internal electrodes 460, 462 are conductive. Each internal electrode 460, 462 includes a contact portion 460A and an integral connecting protrusion 460B that extends radially outward from the peripheral edge of the contact portion 460A. Each protrusion 460A can include a hole 460C (e.g., a through hole).

[0232] According to some embodiments, each contact portion 460A is substantially planar, relatively thin, and is in the shape of a sheet or a disc. In some embodiments, each contact portion 460A has a diameter to thickness ratio of at least 15. In some embodiments, the thickness of each contact portion 460A is in the range from about 0.1 to 3 mm. In some embodiments, the diameter of each contact portion 460A is in the range from about 20 to 100 mm.

[0233] According to some embodiments, each contact portion 460A does not have any through holes extending through the thickness of the contact portion.

[0234] According to some embodiments, the internal electrodes 460, 462 are formed of copper. However, any suitable conductive metal can be used. According to some embodiments, the internal electrodes 460, 462 are integral and in some embodiments are monolithic.

[0235] As shown in Figure 19 , the varistor sheet 452 is sandwiched or clamped between the internal electrodes 460, 462. The contact portion 460A of the internal electrode 460 engages the contact surface 452U. The contact portion 460A of the internal electrode 462 engages the contact surface 452L. Each such engagement forms a tight physical or mechanical contact between the identified internal electrode contact portion and the varistor contact surface. Each such engagement forms a direct electrical connection or coupling between the identified interconnect member contact portion and the varistor contact surface.

[0236] In some embodiments, each internal electrode contact portion 460A covers and engages at least 40% of the surface area of the corresponding mating varistor sheet surfaces 452U, 452L.

[0237] Resistor 480 corresponds to Figure 1 resistor R1. Resistor 480 can be a through-hole resistor that includes a resistor body 482 and opposing leads 484A, 484B. Resistor 480 can be an axial lead resistor as shown in Figure 18 , or have another configuration (e.g., a radial lead resistor).

[0238] Resistor lead 484A is mechanically and electrically connected to the protrusion 460B of electrode 460. Resistor lead 484B is mechanically and electrically connected to the protrusion 460B of electrode 462. In some embodiments, leads 484A and 484B are soldered to protrusion 460B. In some embodiments, the ends of leads 484A, 484B are placed in the holes 460C of protrusion 460B and soldered in place.

[0239] A suitable through-hole resistor for resistor 480 can include the metal film resistor type HVR3700001004JR500 rated at 1 MΩ available from Vishay Intertechnology, Inc. of the United States.

[0240] The resistor leads 484A, 484B, and the protrusion 460B are covered by an electrical insulator 486. In some embodiments, the insulator 486 is an electrically insulating epoxy resin. In some embodiments, the insulator 486 is an electrically insulating heat-shrinkable thermoplastic. In some embodiments, the insulator 486 covers each of the leads 484A, 484B from its protrusion 460A to the entire resistor body 482, and also covers the protrusion 460A.

[0241] The GDT 440 is sheet-shaped or disc-shaped and includes a body 440A and opposing electrical terminals 440B and 440C on opposing major faces of the body 440A and an annular electrical insulator (e.g., ceramic) surrounding the body 440A between the terminals 440B, 440C. In some embodiments and as shown, the outsides of the terminals 440B, 440C are substantially flat and planar, or include substantially flat or planar circular or annular contact regions. According to some embodiments, the ratio of the diameter of the GDT 440 to its thickness is in the range from about 4 to 15. According to some embodiments, the thickness of the GDT 440 is in the range from about 3 mm to 8 mm. In some embodiments, the diameter of the GDT 440 is in the range from about 20 mm to 40 mm. In some embodiments, the GDT 440 has a surge current and energy withstand capacity that is at least as great as that of the MOV varistor disc 452 used in series with the GDT 440 in the same SPD 400. Suitable GDTs can include the Flat gas discharge tube type 3L30-25 rated at 600V available from Varsi of Slovenia or the D20-A800XP from TDK-EPC Corporation of Japan (EPCOS).

[0242] The body 440A includes an enclosed or hermetically sealed chamber or unit in which a selected gas is contained. The terminals 440B, 440C are electrically connected to the gas (e.g., through respective electrode portions in fluid contact with the contained gas). Below a specified spark discharge voltage, the GDT 140 is electrically insulating between the terminals 440B, 440C. When the voltage applied across the terminals 440B, 440C exceeds the specified spark discharge voltage, the contained gas is ionized to cause current to flow through the gas (by the Townsend discharge process) and thus flow between the terminals 440B, 440C. Thus, depending on the applied voltage, the GDT 440 will selectively be electrically insulating or conductive. The voltage required to initiate and sustain conduction (discharge) will depend on the design characteristics of the GDT 440 (e.g., geometry, gas pressure, and gas composition).

[0243] The GDT contact member 442 is a disc-shaped insert. The lower side of the member 442 includes a circular recess 442A configured to receive the terminal 440B of the GDT 440. The upper side of the member 442 is substantially planar to closely mate with the internal electrode 462. According to some embodiments, the GDT contact member 442 is formed of aluminum. However, any suitable conductive metal may be used. According to some embodiments, the GDT contact member 442 is integral and in some embodiments is monolithic.

[0244] The spring washer 428E surrounds the shaft 424B. The lowest spring washer 428E abuts the top face of the joint 424A. The spring washer 428E may be formed of an elastic material. According to some embodiments and as shown, the spring washer 428E is a wave washer (as shown) or a conical washer formed of spring steel. Although two spring washers 428E are shown, more or fewer spring washers may be used. The springs may be provided in different stacking arrangements, such as in series, in parallel, or in series and in parallel.

[0245] The flat metal washer 428D is clamped between the highest spring washer 428E and the insulator ring 428C, wherein the shaft 424B extends through the hole formed in the washer 428D. The washer 428D is used to distribute the mechanical load of the upper spring washer 428E to prevent the spring washer 428E from cutting into the insulator ring 428C.

[0246] The insulator ring 428C covers the washer 428D and abuts the washer 428D. The insulator ring 428C has a body ring and a shaft ring or a cylindrical upper flange extending upward from the body ring. The insulator ring 428C is preferably formed of a dielectric material or an electrically insulating material having a high melting and combustion temperature. The insulator ring 428C may be formed of, for example, polycarbonate, ceramic, or a high-temperature polymer.

[0247] The end cap 428A covers the insulator ring 428C and abuts the insulator ring 428C. The end cap 428A may be formed of, for example, aluminum.

[0248] The clip 428B is partially received in the groove 422H and extends radially inwardly partially from the inner wall of the housing 422 to limit the outward axial displacement of the end cap 428A. The clip 428B may be formed of spring steel.

[0249] The O-ring 430B is positioned in the groove in the electrode 424 such that it is captured between the shaft 424B and the insulator ring 428C. The O-ring 430A is positioned in the groove in the insulator ring 428C such that it is captured between the insulating member 428C and the sidewall 422B. When installed, the O-rings 430A, 430B are compressed such that they are biased against the adjacent mating surfaces and form a seal between the adjacent mating surfaces. In an overvoltage or failure event, by-products such as hot gas and debris from the varistor disc 452 can fill or disperse into the chamber 426 of the cavity. These by-products can be restricted or prevented from escaping from the overvoltage protection device 400 through the housing opening 422D by the O-rings 430A, 430B.

[0250] The O-rings 430A, 430B can be formed of the same or different materials. According to some embodiments, the O-rings 430A, 430B are formed of an elastic material such as an elastomer. According to some embodiments, the O-rings 430A, 430B are formed of rubber. The O-rings 430A, 430B can be formed of a fluorocarbon rubber such as VITON™ available from DuPont. Other rubbers such as butyl rubber can also be used. According to some embodiments, the rubber has a hardness between approximately 60 and 100 Shore A hardness.

[0251] The module 400 can be assembled according to the method of the present invention as follows.

[0252] The subassembly 450 can be pre-assembled. The varistor disc is axially stacked with the internal electrodes 460, 462 and clamped between the internal electrodes 460, 462. In some embodiments, the varistor disc 452 and the internal electrodes 460, 462 are substantially coaxially aligned. The mating surfaces of the varistor disc 452 and the internal electrodes 460, 462 can be welded or brazed together. In some embodiments and as shown in Figure 20 the resistor body 482 is laterally positioned radially outside (with respect to the axis B-B) the side of the varistor 452. The resistor leads 484A, 484B are brazed to the contact projections 460B. The insulator 486 is applied to the leads 484A, 484B and the projections 460B.

[0253] The GDT 440 is placed in the cavity 422C such that the terminal 440B is received in the recess 422F and engages the contact surface 422G of the end wall 422A.

[0254] The GDT contact member 442 is placed on the GDT 440 in the cavity 422C such that the terminal 440C is received in the recess 442A and makes good electrical contact with the contact member 442.

[0255] The varistor 452, resistor 480, and internal electrodes 460, 462 (whether pre-assembled into the sub-assembly 450 or not) are placed in the cavity 422C such that the lower contact surface of the internal electrode 462 engages the upper surface of the GDT contact member 442.

[0256] The O-rings 430A, 430B are installed in their respective grooves.

[0257] The head 424A is inserted into the cavity 422C such that the contact surface 424C engages the upper contact surface of the contact portion 460A of the interconnect member 460.

[0258] The spring washer 428E slides downward along the shaft 424B. The washers 428D, insulator ring 428C, and end cap 428A slide downward along the shaft 424B and are positioned on the spring washer 428E. A clamp (not shown) or other suitable device is used to force the end cap 428A downward, thereby deflecting the spring washer 428E. The clamp 428B is installed in the slot 422H to maintain the load on the end cap 428A such that the spring washer 428E is partially deflected. The load from the end cap 428A onto the insulator ring 428C and from the insulator ring to the spring washer is then transmitted to the head 424A. In this way, the sub-assembly 450 is clamped between the head 424A and the electrode wall 422A.

[0259] The electrode head 424A and the housing end wall 422A are continuously biased or loaded along the direction F along the loading or clamping axis C-C ( Figure 19 ) onto the varistor 452, internal electrodes 460, 462, GDT contact member 442, and GDT 440 to ensure a firm and uniform engagement between the interacting contact surfaces identified above. In some embodiments, the clamping axis C-C is substantially coincident with the axis B-B ( Figure 17 ).

[0260] In the assembled overvoltage protection device 400, the large planar contact surfaces of the components 422A, 424A, 452, 460, 462, 442 can ensure reliable and consistent electrical contact and connection between the components during an overvoltage or surge current event. The head 424A and the end wall 422A are mechanically loaded onto these components to ensure a firm and uniform engagement between the mating contact surfaces.

[0261] In a single modular unit, the design of the overvoltage protection device 400 provides compressive loading on the varistor disc 452 and the GDT 440. The overvoltage protection device 400 provides suitable electrical interconnection between the electrodes 422, 424, varistor disc 452, and GDT 440 while maintaining a compact form factor and providing appropriate thermal dissipation of the energy from the varistor disc 452.

[0262] The construction of overvoltage protection device 400 provides a safe failure mode for the device. During use, one or more of the varistor discs 452 may be damaged by overheating, and an arc discharge may occur inside the housing assembly 424. The housing assembly 424 can contain damage (e.g., debris, gas, and immediate heat) within the overvoltage protection device 400, causing the overvoltage protection device 400 to fail safely. In this way, the overvoltage protection device 400 can prevent or reduce any damage to adjacent equipment (e.g., switching device equipment in a cabinet) and harm to personnel. In this way, the overvoltage protection device 400 can enhance the safety of equipment and personnel.

[0263] Additionally, overvoltage protection device 400 provides a fail-safe mechanism in response to an end-of-life mode in the varistor discs 452. In the event of failure of the varistor discs 452, as discussed above regarding varistor 132 of SPD 100, a fault current will conduct between the corresponding line and neutral line. More particularly, when the varistor 452 reaches its end-of-life state, the overvoltage protection device 400 will essentially become a short circuit with a very low but non-zero ohmic resistance. Thus, under end-of-life conditions, even in the absence of an overvoltage condition, a fault current will continuously flow through the varistor 452. In this case, the fusible member 432 can operate as a fail-safe mechanism to bypass the failed varistor and form a permanent low-ohmic short circuit between the terminals of the overvoltage protection device 400 in the manner described in U.S. Patent No. 7,433,169, the disclosure of which is incorporated herein by reference.

[0264] The fusible member 432 is adapted and configured to operate as a thermal disconnector to electrically short-circuit the current applied to the associated overvoltage protection device 400 around the varistor disc 452 to prevent or reduce heat generation in the varistor. In this way, the fusible member 432 can operate as a switch to bypass the varistor disc 452 and prevent overheating and catastrophic failure as described above. As used herein, an automatic fail-safe system is "triggered" when conditions occur that cause the automatic fail-safe system to operate as described to short-circuit electrodes 422A, 424A.

[0265] When heated to a threshold temperature, the fusible member 432 will flow to bridge and electrically connect electrodes 422A, 424A. The fusible member 432 thereby redirects the current applied to the overvoltage protection device 400 around the varistor disc 452, stopping the current-induced heating of the varistor. The fusible member 432 can thus be used to prevent or inhibit thermal runaway (caused by or occurring in varistor 452) without requiring interruption of the current through the overvoltage protection device 400.

[0266] More particularly, the fusible member 432 initially has a first configuration as shown in Figure 19 such that the fusible member 432 is not electrically coupled to the electrode 424 and the housing 422 except through the header 424A. In the event of a heat accumulation event, the electrode 424 is thereby heated. The fusible member 432 is also heated directly and / or by the electrode 424. During normal operation, the temperature in the fusible member 432 remains below its melting point such that the fusible member 432 remains in solid form. However, when the temperature of the fusible member 432 exceeds its melting point, the fusible member 432 melts (in whole or in part) and flows by gravity into a second configuration that is different from the first configuration. The fusible member 432 bridges or shorts the electrode 424 to the housing 422 to bypass the varistor disc 452. That is, one or more new direct flow paths are provided from the surface of the electrode 424 to the surface of the housing sidewall 422B through the fusible member 432. According to some embodiments, at least some of these flow paths do not include the varistor disc 452.

[0267] According to some embodiments, the overvoltage protection device 400 is adjusted such that when the fusible member 432 is triggered to short-circuit the overvoltage protection device 400, the conductivity of the overvoltage protection device 400 is at least as great as the conductivity of the feed and outlet cables connected to the device.

[0268] According to some embodiments, the bonding area between each electrode contact surface and the varistor contact surface is at least one square inch.

[0269] According to some embodiments, depending on the surface area of the varistor, the biasing electrodes (e.g., electrodes 422 and 424) apply a load in the range from 2000 lbf to 26000 lbf to the varistor along the axis C-C.

[0270] According to some embodiments, the combined thermal mass of the housing (e.g., housing 422) and the electrodes (e.g., electrode 424) is substantially greater than the thermal mass of each of the varistors trapped therebetween. The greater the ratio of the thermal mass of the housing and electrodes to the thermal mass of the varistors, the better the varistors will be preserved during exposure to surge current and TOV events and thus the longer the life of the SPD. As used herein, the term "thermal mass" means the product of the specific heat of one or more materials of an object multiplied by the mass or masses of one or more materials of the object. That is, thermal mass is the amount of energy required to raise one gram of one or more materials of an object by one degree Celsius multiplied by one or more masses of one or more materials in the object. According to some embodiments, 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. According to some embodiments, the thermal mass of at least one of the electrode head and the 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 the electrode wall is substantially greater than the thermal mass of the varistor, according to some embodiments, at least twice the thermal mass of the varistor, and according to some embodiments, at least ten times greater.

[0271] As discussed above, spring washer 428E is a disc or wave washer. Disc or wave washers can be used to apply relatively high loads without requiring a large amount of axial space. However, other types of biasing devices can be used in addition to or instead of disc or wave washers. Suitable alternative biasing devices include one or more coil springs or helical washers, or elastomeric spring members.

[0272] Module 400 includes one varistor 452. However, an SPD module according to further embodiments can include two or more varistors electrically stacked in series.

[0273] Reference Figure 21 , in which a modular overvoltage protection device or surge protection device (SPD) module showing additional embodiments of the present invention is shown and labeled 500. For purposes of explanation, only certain internal components of module 500 are shown in Figure 21 . Module 500 is constructed, used, and operated in the same manner as module 400 except as follows.

[0274] In module 500, resistor 580 is axially mounted below the varistor 552 (i.e., axially mounted between internal electrode 562 and electrode wall 422A ( Figure 19 )) rather than beside the varistor 552 laterally as in module 400.

[0275] Reference Figure 22 - 24, which shows a modular overvoltage protection device or surge protection device (SPD) module of another embodiment of the present invention and is labeled 800. For purposes of explanation, only certain internal components of module 800 are shown in Figure 22 - 24 . Except as follows, module 800 is constructed, used, and operated in the same manner as module 100.

[0276] The SPD module 800 includes Figure 1 the overvoltage protection circuit 600.

[0277] The SPD module 800 includes an overvoltage clamping element assembly 830. The overvoltage clamping element sub-assembly 830 includes a varistor 832, a first electrode 834, a second electrode 836, two gas discharge tubes (GDTs) 840, and GDT electrodes or contact plates 842, which correspond to the varistor 132, the first electrode 134, the second electrode 136, the GDT 140, and the GDT electrode 142 (see, for example, Figure 8 and Figure 12 ). The overvoltage clamping element sub-assembly 830 further includes a resistive material layer 880 instead of the resistor 180.

[0278] The varistor 832 has opposing contact surfaces 832A, 832B. The peripheral side edge surface 832C surrounds the varistor 832 and separates the contact surfaces 832A, 832B. Corresponding metallization layers 833A, 833B cover the contact surfaces 832A, 832B.

[0279] The resistive layer 880 includes a first strip, leg, or section 882, a second strip, leg, or section 884, and a bridging strip, leg, or section 886 that extends between, abuts, and electrically connects each of the sections 882, 884.

[0280] The resistive layer 880 wraps around the varistor 832 such that the bridging section 886 spans the side edge 832C and portions 882A, 884A of the first section 882 and the second section 884, respectively overlapping and joining the metallization layers 833A and 833B. The metallization layers 833A and 833B in turn are in electrical contact with the electrodes 834 and 836, respectively. In this way, the resistive layer 880 electrically connects the electrode 834 to the electrode 836 through the resistive layer 880. The resistive layer 880 is thus electrically parallel with the varistor 832 between the electrodes 834, 836.

[0281] The resistive layer 880 can be a thin film resistive layer. The resistive layer 880 can be a thick film resistive layer. In some embodiments, the resistive layer 880 is a resistive paste layer. The resistive paste can include an alumina substrate (90% or more by weight) mixed with other materials. The composition can vary. According to some embodiments, the material of the resistive paste has a viscosity in the range from about 100 to 200 Pascal-seconds before the material is screen printed and fired. Suitable resistive pastes include the 4300-series resistors available from the Research Triangle Park DuPont Microcircuit Materials in North Carolina, USA.

[0282] In some embodiments, the resistive layer 880 is formed of a resistor (e.g., paste) having a sheet resistance in the range from about 1 Ω / square to 1 MΩ / square.

[0283] In some embodiments, the resistive layer 880 is bonded to the surfaces 832A, 832B, 832C and the metallization layer 833. In some embodiments, the resistive layer 880 is directly bonded to the surfaces 832A, 832B, 832C and the metallization layer 833. In some embodiments, it is adhesively and directly bonded to the said surfaces.

[0284] The size of the resistive layer 880 can be selected to obtain desired electrical properties. In some embodiments, the resistive layer 880 has a thickness T3 in the range from about 2 μm to 1000 μm ( Figure 24 ), and in some embodiments has a thickness T3 in the range from about 50 μm to 90 μm.

[0285] In some embodiments, the resistive layer 880 has a width W3 in the range from about 1 mm to 20 mm ( Figure 23 ).

[0286] In some embodiments, the overvoltage clamping element assembly 830 includes a plurality of resistive layers 880 mounted on the varistor 832 and electrically parallel to the varistor 832.

[0287] The resistive layer 880 can be mounted on the varistor 832 using any suitable technique. Suitable techniques can include, for example, printing or deposition (e.g., vapor deposition, sputtering or vacuum deposition).

[0288] Reference Figure 25 - 27 is made to, in which an overvoltage clamping element sub-assembly 950 according to a further embodiment is shown. The sub-assembly 950 can be used in place of the sub-assembly 450 of the SPD 400 ( Figure 18). The sub-component 950 includes a varistor 952 corresponding to the varistor 452 and opposing metallization layers 953U and 953L. The sub-component 950 also includes a resistive layer 980 that replaces the resistor 480. The internal electrodes 460, 462 of the sub-component 450 can be omitted.

[0289] The varistor 952 has opposing contact surfaces 952U, 952L. The peripheral side edge surface 952E surrounds the varistor 952 and separates the contact surfaces 952U, 952L.

[0290] The corresponding metallization layers 953U and 953L cover the contact surfaces 952U and 952L. In some embodiments and as shown in Figure 25 - 27 , each metallization layer 953U, 953L covers the entirety of its surface 952U, 952L and has a terminal peripheral metallization edge 954. The peripheral metallization edge 954 is located at the corner 956 defined between the side edge surface 952E and the contact surfaces 952U, 952L, or radially outward beyond the corner 956. The peripheral passivation layer 955 ( Figure 27 ) can cover the side edge surface 952E. The passivation layer 955 can be a glass material that surrounds the entire circumferential portion of the side surface 952E.

[0291] The resistive layer 980 includes a strip 986 that has opposing axial terminal edges or ends 986U and 986L.

[0292] The resistive layer 980 covers the varistor 952 such that the strip 986 spans the side edge 952E and the ends 986U and 986L respectively engage and make electrical contact with the peripheral edges 954 of the metallization layers 953U and 953L. The metallization layers 953U and 953L in turn make electrical contact with the electrode head 424A and the GDT contact member 442 ( Figure 18 ). In this way, the resistive layer 980 electrically connects the electrode 424 to the electrode 422 through the resistive layer 980. The resistive layer 980 is thus electrically in parallel with the varistor 952 between the electrodes 422, 424.

[0293] In some embodiments, the resistive layer 980 is bonded to the edge surface. In some embodiments, the resistive layer 980 is directly bonded to the surfaces 952E and the metallization layers 953U, 953L. In some embodiments, the resistive layer 980 is adhesively directly bonded to the edge surface 952E.

[0294] In some embodiments, the sub-component 950 includes a plurality of resistive layers 980 mounted on and electrically in parallel with the varistor 952.

[0295] The resistive layer 980 can be formed using the same materials, dimensions, properties (including sheet resistance), and techniques as discussed above for the resistive layer 880.

[0296] The metallization layers 133, 833A, 833B, 953U, 953L can be formed of any suitable metal (such as aluminum, copper, or silver). In some embodiments, the metallization layers are bonded (e.g., adhesively bonded) to the respective surfaces of the varistors 132, 852, 952 covered by the metallization layers. In some embodiments, each of the metallization layers 133, 833A, 833B, 953U, 953L has a thickness in the range from about 10 μm to 100 μm (e.g., the thickness T4 in Figure 24 ).

[0297] Without departing from the spirit and scope of the present invention, and considering the benefits of this disclosure, those skilled in the art can make many changes and modifications. Therefore, it must be understood that the illustrated embodiments are set forth only for purposes of example and that the illustrated embodiments should not be regarded as limiting the present invention as defined by the following claims. Accordingly, the following claims are to be understood to cover not only the combination of elements literally set forth, but also all equivalent elements for performing substantially the same function in substantially the same way to obtain substantially the same result. The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and what incorporates the basic idea of the present invention.

Claims

1. A surge protection device module, comprising: A first electrical terminal; A second electrical terminal; An overvoltage protection circuit connected between the first electrical terminal and the second electrical terminal, the overvoltage protection circuit comprising: A first gas discharge tube; And A current management circuit connected in series to the first gas discharge tube, the current management circuit comprising a varistor and a resistor connected in parallel between a first node of the current management circuit and a second node of the current management circuit, The current management circuit further comprises an inductor connected in series with the resistor between the first node and the second node of the current management circuit, the inductor configured to resist changes in current and protect the resistor from high current surges caused by transient overvoltage events on the line electrically connected to the first electrical terminal; and The varistor is connected in parallel with the series combination of the resistor and the inductor between the first node and the second node of the current management circuit.

2. The surge protection device module according to claim 1, wherein A first terminal of the resistor is directly connected to the first node, a first terminal of the inductor is directly connected to the second node, and a second terminal of the resistor and a second terminal of the inductor are directly connected to each other respectively.

3. The surge protection device module according to claim 1, wherein, The inductor comprises a surface mount device (SMD) inductor.

4. The surge protection device module according to claim 1, wherein, The inductor has an inductance in the range from 1 µH to 1 mH.

5. The surge protection device module according to claim 1, wherein The overvoltage protection circuit further comprises: A thermal disconnector mechanism connected in series to the first gas discharge tube and the current management circuit, the thermal disconnector mechanism configured to electrically disconnect the first electrical terminal from the second electrical terminal in response to a thermal event.

6. The surge protection device module according to claim 1, wherein, The resistor comprises an axial resistor and has a resistance in the range from 1 kΩ to 50 MΩ.

7. The surge protection device module according to claim 1, wherein The resistor comprises a radial resistor and has a resistance in the range from 1 kΩ to 50 MΩ.

8. The surge protection device module according to claim 1, wherein, The resistor comprises a surface mount device (SMD) resistor and has a resistance in the range from 1 kΩ to 50 MΩ.

9. The surge protection device module according to claim 1, wherein, The varistor has a peak current rating in the range of 20 kA and a peak voltage rating of 300 V.

10. The surge protection device module according to claim 1, wherein, The first gas discharge tube has a spark discharge voltage rating of 500 V and a discharge current rating of 20 kA.

11. The surge protection device module according to claim 1, wherein, The varistor has a clamping voltage level associated therewith that exceeds the ambient voltage level associated with the first electrical terminal.

12. The surge protection device module according to claim 11, wherein The current management circuit is configured to contribute to dissipating the associated energy by causing the voltage across the first gas discharge tube to be less than the arc voltage associated with the first gas discharge tube in response to the termination of the transient overvoltage event, thereby causing the first gas discharge tube to transition from a conductive state to a non-conductive state.

13. The surge protection device module according to claim 12, wherein, The first electrical terminal is configured to be connected to a line, and the second electrical terminal is configured to be connected to a common reference voltage.

14. The surge protection device module according to claim 13, wherein, The line is an alternating current (AC) power line or a direct current (DC) power line.

15. The surge protection device module according to claim 13, wherein, The line is a communication line configured to transmit communication signals.

16. The surge protection device module according to claim 15, wherein, The communication signal is an RF communication signal.

17. The surge protection device module according to claim 1, comprising a second gas discharge tube, which is connected in parallel with the first gas discharge tube between the current management circuit and the first electrical terminal.

18. The surge protection device module according to claim 1, comprising: a base configured to be mounted on a DIN rail; and a surge protection device module configured to be removably mounted on the base, wherein when the surge protection device module is mounted on the base, the surge protection device module and the base together form a DIN rail surge protection device assembly, and the surge protection device module comprises: a module housing; first and second electrical terminals mounted on the module housing; the first gas discharge tube provided in the module housing; and the current management circuit provided in the module housing.

19. The surge protection device module according to claim 18, wherein, The surge protection device module comprises: a thermal disconnector mechanism positioned in a ready configuration, wherein the varistor is electrically connected to the second electrical terminal, and the thermal disconnector mechanism is repositioned to electrically disconnect the varistor from the second electrical terminal, and the thermal disconnector mechanism comprises: an electrical conductor electrically connected to the varistor in the ready configuration; and a solder fixing the electrical conductor to be electrically connected to the varistor in the ready configuration, wherein: the solder can be melted in response to overheating in the surge protection device module; and the thermal disconnector mechanism is configured to electrically disconnect the electrical conductor from the varistor, and thereby disconnect the varistor from the second electrical terminal when the solder is melted.

20. The surge protection device module according to claim 19, wherein, The surge protection device module comprises an indicator mechanism configured to provide an alarm that the surge protection device module has failed when the thermal disconnector mechanism disconnects the overvoltage clamping element from the second electrical terminal.

21. The surge protection device module according to claim 20, wherein, The indicator mechanism comprises a local alarm mechanism, which comprises: a window in the module housing; an indicator member movable relative to the window between a ready position and an indicating position; and, an indicator spring configured to force the indicator member from the ready position to the indicating position when the thermal disconnector mechanism disconnects the varistor from the second electrical terminal.

22. The surge protection device module according to claim 1, wherein, The surge protection device module comprises: a module housing including a first electrode and a second electrode, wherein the first electrode includes a first electrical terminal, and the second electrode includes a second electrical terminal; and the first gas discharge tube and the varistor are axially stacked between the first and second electrodes in the module housing.

23. The surge protection device module according to claim 22, wherein: the first electrode includes a housing electrode, which includes an end wall and an integral side wall that jointly define a cavity; the second electrode extends into the cavity; and the first gas discharge tube and the varistor are provided in the cavity.

24. The surge protection device module according to claim 23, wherein, The housing electrode is integrally formed of metal.

25. The surge protection device module according to claim 22, comprising: a biasing device that applies an axial compressive load to the first gas discharge tube and the varistor.

26. The surge protection device module according to claim 22, comprising: A conductive fusible member, wherein the fusible member melts in response to heat in the overvoltage protection device and forms an electrical short-circuit path across the first and second electrode members.

27. The surge protection device module according to claim 22, wherein, The varistor includes a varistor chip.

28. The surge protection device module according to claim 27, comprising: A first internal electrode axially sandwiched between the varistor chip and the first electrode; And, A second internal electrode axially sandwiched between the varistor chip and the second electrode; Wherein the resistor is electrically connected to the first and second electrodes in the module housing.

29. The surge protection device module according to claim 27, wherein, The resistor is laterally positioned beside the outer edge of the varistor chip.

30. The surge protection device module according to claim 27, wherein, The resistor is axially positioned under the varistor chip.

31. The surge protection device module according to claim 1, wherein The resistor is configured to discharge the capacitance of the varistor in response to a voltage surge event across the first and second electrical terminals.

32. The surge protection device module according to claim 1, wherein, The resistor is a resistive material layer mounted on the varistor.

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