Patent Description:
Frequently, excessive voltage or current is applied across service lines that deliver power to residences and commercial and institutional facilities. Such excess voltage or current spikes (transient overvoltages and surge currents) may result from lightning strikes, for example. The above events may be of particular concern in telecommunications distribution centers, hospitals and other facilities where equipment damage caused by overvoltages and/or current surges is not acceptable and resulting downtime may be very costly.

Typically, sensitive electronic equipment may be protected against transient overvoltages and surge currents using surge protective devices (SPDs). For example, an overvoltage protection device may be installed at a power input of equipment to be protected, which is typically protected against overcurrents when it fails. Typical failure mode of an SPD is a short circuit. The overcurrent protection typically used is a combination of an internal thermal disconnector to protect the SPD from overheating due to increased leakage currents and an external fuse to protect the SPD from higher fault currents. Different SPD technologies may avoid the use of the internal thermal disconnector because, in the event of failure, they change their operation mode to a low ohmic resistance.

SPDs may use one or more active voltage switching/limiting components, such as a varistor or gas discharge tube, to provide overvoltage protection. These active voltage switching/limiting components may degrade at a rapid pace as they approach the end of their operational lifespans, which may result in their exhibiting continuous short circuit behavior. Referring now to <FIG>, an electrical power supply installation or circuit <NUM> P<CIT> / <CIT>/ <CIT> from <CIT>(<CIT>) including a conventional SPD configuration includes an SPD <NUM> in series with an external fuse <NUM> connected in parallel across sensitive equipment. The SPD <NUM> is designed to protect the sensitive equipment from overvoltages and current surges and includes a metal oxide varistor (MOV) <NUM> and thermal disconnector <NUM>.

In the example SPD configuration <NUM> shown in <FIG>, the SPD <NUM> is connected in series with a standard external fuse <NUM> and is also connected upstream to the power source via a second fuse or circuit breaker <NUM>. Conventional fuses, however, may not be able to withstand large surge currents and/or overvoltages generated by, for example, lightning events. As a result, they might blow or trip in response to such events. To achieve the desired high surge current rating, a fuse size typically has to be relatively large. In addition, the voltage applied to the sensitive equipment may be relatively high as it is the sum of the voltage across the SPD <NUM> (VSPD), and the voltages developed across the connecting cables VL1 and VL2. The external fuse/circuit breaker design may also increase installation costs due to the use of large discrete components in the design.

Document <CIT> discloses a bimetallic fuse that is useful to help keep hurtful voltage surges from developing.

Document <CIT> discloses a fused surge protection device comprising an overvoltage protection circuit and a fuse.

A fused surge protective device module is provided by claim <NUM>. Further advantageous embodiments are provided by the dependent claims.

The accompanying drawings, which form a part of the specification, illustrate inter alia embodiments of the present invention.

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

It is noted that aspects described with respect to one embodiment may be incorporated in different embodiments although not specifically described relative thereto. That is, all embodiments and/or features of any embodiments can be implemented separately or combined in any way and/or combination. Moreover, other apparatus, methods, and systems according to embodiments of the inventive concept will be or become apparent to one with skill in the art upon review of the following drawings and detailed description. It is intended that all such additional apparatus, methods, and/or systems be included within this description, be within the scope of the present inventive subject matter, and be protected by the accompanying claims.

As used herein, a unitary object can be a composition composed of multiple parts or components secured together at joints or seams.

Some embodiments of the inventive concept stem from a realization that fuses or circuit breakers used to protect surge protective devices (SPDs) from short circuit currents when they fail by disconnecting them from the circuit have generally very high current ratings. These high current ratings may allow the fuses or circuit breakers to handle high impulse voltages and/or impulse currents from overvoltage events, such as lightning strikes, when configured in series with the SPD between the power line and ground or handle ongoing current when provided inline in the power line. To achieve such high current ratings, the fuses and/or circuit breakers may be large and require additional expense in installation due to being a discrete component from the SPD.

According to some embodiments of the inventive concept, an overvoltage protection circuit may be connected in series with a bimetallic fuse element to form, in combination, a fused SPD circuit. In some embodiments, the fused SPD circuit is provided in the form of a fused SPD unit or module, wherein the overvoltage protection circuit and the bimetallic fuse element are each integrated in the fused SPD unit or module. In some embodiments, the bimetallic fuse element is a bimetallic strip.

The fused SPD circuit may include a thermal disconnector device along with the overvoltage protection circuit and the bimetallic fuse element. In some embodiments, the thermal disconnector device is integrated in the fused SPD unit or module along with the overvoltage protection circuit and the bimetallic fuse element.

The overvoltage protection circuit of the fused SPD circuit may include one or more active voltage-switching/limiting components, such as a varistor or gas discharge tube.

The bimetallic strip may be configured to mechanically open the circuit through deformation of the bimetallic strip within a specified time period in response to a minimum short circuit current received therethrough from the overvoltage protection circuit (referred to herein as the "minimum SPD short circuit current"). For example, in a power line application, the minimum SPD short circuit current expected through the overvoltage protection circuit may be in a range from 300A - 1000A. This minimum SPD short circuit current may be called a trigger current threshold. The short circuit current through the overvoltage protection circuit and the bimetallic fuse element may also be called a trigger current. A standard for protecting SPDs from short circuit current events may be that the SPD be disconnected from the circuit within <NUM> seconds of the SPD short circuit current event. Thus, when used in the example power line application, the bimetallic fuse assembly may be configured such that the bimetallic strip deforms within <NUM> seconds to open the circuit in response to an SPD short circuit current of at least 300A. The bimetallic strip element after deforming will quickly evaporate due to arcing between the electrodes of the bimetallic fuse device.

In some embodiments, the bimetallic fuse element forms a part of a bimetallic fuse device or assembly. The bimetallic fuse device may include an electric arc extinguishing agent, such as SiO2, to terminate the arcing. The SiO2 may be provided in the form of sand or powder.

The bimetallic fuse device may also be configured to handle very large SPD surge impulse currents that are generated due to overvoltage or current surge events, such as lightning strikes. An SPD may be required to re-direct a surge impulse current of up to <NUM> kA, which lasts between <NUM> to <NUM>, to ground. The bimetallic fuse device, according to some embodiments of the inventive concept, may conduct such high currents for up to <NUM> without the bimetallic strip element deforming to open the circuit.

The bimetallic fuse device may conduct relatively low currents therethrough corresponding to the leakage current associated with a varistor in an overvoltage protection circuit. These leakage currents may be relatively low, such as, for example, 1A - 15A. The bimetallic fuse device may be configured so that the bimetallic fuse element does not deform to open the circuit before the overvoltage protection circuit heats up sufficiently that a thermal disconnector opens the circuit to terminate the leakage current.

With reference to <FIG>, a bimetallic fuse device or assembly <NUM> according to some embodiments is shown therein. The fuse assembly <NUM> may be provided, installed and used as a component in a protection circuit of a power supply circuit as described above with reference to <FIG> in place of the fuse <NUM>, for example, to form a protected power supply circuit <NUM> as shown in <FIG>.

In some embodiments, the fuse assembly <NUM> is integrated into a fused surge protective device (SPD) unit or module <NUM> including an overvoltage protection circuit (OPC) <NUM>, as illustrated in <FIG> and <FIG>. In this case, the fuse assembly <NUM> operates as an integrated backup fuse. In some embodiments, the fused SPD module <NUM> is configured to mount on a DIN rail <NUM> as shown in <FIG>, for example. In other embodiments, the fuse assembly <NUM> may be provided, installed and used as an individual component in a protection circuit of a power supply circuit (e.g., not physically integrated in a module with the OPC <NUM>).

With reference to <FIG>, the fused SPD module <NUM> includes the fuse assembly <NUM>, a module housing <NUM>, a first electrical terminal <NUM>, a second electrical terminal <NUM>, the OPC <NUM>, and a thermal disconnector <NUM>. The fuse assembly <NUM>, the OPC <NUM>, and the thermal disconnector <NUM> are disposed in the housing <NUM>, and are electrically connected between the terminals <NUM> and <NUM> to form a fused SPD electrical circuit <NUM>.

The OPC <NUM> may be any suitable overvoltage protection circuit. In some embodiments, the OPC <NUM> includes an active voltage-switching or active voltage limiting component (referred to herein as a "voltage-switching/limiting component) <NUM>.

In some embodiments, the OPC <NUM> is a varistor-based overvoltage protection circuit and the voltage-switching/limiting component <NUM> is a varistor. In some embodiments, the voltage-switching/limiting component <NUM> is a metal oxide varistor (MOV)).

In some embodiments, the voltage-switching/limiting component <NUM> is a gas discharge tube (GDT).

The voltage-switching/limiting component <NUM> may also be another type of voltage-switching/limiting surge protective device. Other types of voltage-switching/limiting component <NUM> that may form, or form a part of, the OPC <NUM> may include spark gap devices, multi-cell GDTs (e.g., as disclosed in <CIT>and <CIT>), diodes, or thyristors.

The OPC <NUM> may include or consist of only a single voltage-switching/limiting component <NUM>. In some embodiments, the OPC <NUM> includes or consists of only the active voltage-switching/limiting component(s) <NUM> and associated electrical connections, if any.

The OPC <NUM> may include a plurality of voltage-switching/limiting components <NUM>. The OPC <NUM> may include one or more voltage-switching/limiting components <NUM> in combination with other electrical components. In some embodiments, the OPC <NUM> includes multiple varistors (connected in electrical parallel or series between the module terminals), multiple GDTs (e.g., connected in electrical series), and/or both varistor(s) and GDT(s) (e.g., connected in electrical series with the varistor(s)), and/or other circuit elements, such as resistors, inductors, or capacitors.

Gas discharge tubes (GDTs) and metal oxide varistors (MOV) may be used in surge protection devices, but both GDTs and MOVs have advantages and drawbacks in shunting current away from sensitive electronic components in response to overvoltage surge events. For example, MOVs have the advantage of responding rapidly to surge events and being able to dissipate the power associated with surge events. But MOVs have the disadvantages of having increased capacitance relative to GDTs and passing a leakage current therethrough even in ambient conditions. MOVs may also have a decreased lifetime expectancy relative to GDTs. GDTs have the advantage of having extremely low to no leakage current, minimal capacitance, and an increased lifetime expectancy relative to MOVs. But GDTs are not as responsive to surge events as MOVs. Moreover, when a GDT fires and transitions into the arc region in response to a surge event, the GDT may remain in a conductive state if the ambient voltage on the line to which the GDT is connected exceeds the arc voltage. The GDT may mitigate current leakage issues associated with the MOV, which may extend the working life of the MOV.

A GDT is a sealed device that contains a gas mixture trapped between two electrodes. The gas mixture becomes conductive after being ionized by a high voltage spike. This high voltage that causes the GDT to transition from a non-conducting, high impedance state to a conducting state is known as the sparkover voltage for the GDT. The sparkover voltage is commonly expressed in terms of a rate of rise in voltage over time. For example, a GDT may be rated so as to have a DC sparkover voltage of <NUM> V under a rate of rise of <NUM> V/s. When a GDT experiences an increase in voltage across its terminals that exceeds its sparkover voltage, the GDT will transition from the high impedance state to a state known as the glow region. The glow region refers to the time region where the gas in the GDT starts to ionize and the current flow through the GDT starts to increase. During the glow region, the current through the GDT will continue to increase until the GDT transitions into a virtual short circuit known as the arc region. The voltage developed across a GDT when in the arc region is known as the arc voltage and is typically less than <NUM> V. A GDT takes a relatively long time to trigger a transition from a high impedance state to the arc region state where it acts as a virtual short circuit.

A varistor, such as a MOV, when in a generally non-conductive state still conducts a relatively small amount of current caused by reverse leakage through diode junctions. This leakage current may generate a sufficient amount of heat that a device, such as the thermal disconnector <NUM>, is used to reduce the risk of damage to components of the fused SPD <NUM>. When a transient overvoltage event occurs, a varistor will conduct little current until reaching a clamping voltage level at which point the varistor will act as a virtual short circuit. Typically, the clamping voltage is relatively high, e.g., several hundred volts, so that when a varistor passes a high current due to a transient over voltage event a relatively large amount of power may be dissipated. In contrast to a GDT, a varistor has a relatively short transition time from a high impedance state to the virtual short circuit state corresponding to the time that it takes for the voltage developed across the varistor to reach the clamping voltage level.

The thermal disconnector <NUM> may be any suitable thermal disconnector device configured and positioned to disconnect the OPC <NUM> (and thereby the voltage-switching/limiting component <NUM>) from the terminal <NUM> in response to heat generated by the OPC <NUM> (for example, by the voltage-switching/limiting component <NUM>). The thermal disconnector <NUM> may include a spring-loaded switch having a solder connection that is melted or softened by excess heat from the OPC <NUM> (e.g., generated by an MOV <NUM> thereof) to permit the switch to open.

With reference to <FIG>, the fuse assembly <NUM> has a first end 200A and an opposing second end 200B. The fuse assembly <NUM> includes a fuse assembly housing <NUM>, a first electrode <NUM> (at the end 200A), a second electrode <NUM> (at the end 200B), a partition wall <NUM>, a fastener <NUM>, an electric arc extinguishing agent <NUM>, a plug <NUM>, an indicator mechanism <NUM>, and a bimetallic fuse link or element <NUM>. The housing <NUM>, the partition <NUM>, and the electrodes <NUM>, <NUM> define a main chamber <NUM> and an adjacent auxiliary chamber <NUM>.

The housing <NUM> and the partition wall <NUM> may be formed of any suitable electrically insulating material. In some embodiments, the housing <NUM> and the partition wall <NUM> are formed of ceramic.

The electrodes <NUM>, <NUM> may be formed of any suitable electrically conductive metal. In some embodiments, the electrodes <NUM>, <NUM> are formed of copper, brass, stainless steel, aluminum copper (AlCu) or tungsten copper (WCu). The electrodes <NUM>, <NUM> may be formed of a base metal as stated above with additional surface plating (galvanization) of nickel or tin.

The electric arc extinguishing agent <NUM> may be formed of any suitable material. In some embodiments, the arc extinguishing agent <NUM> is a flowable media. In some embodiments, the arc extinguishing agent is flowable granules. In some embodiments, the electric arc extinguishing agent <NUM> is silica granules (silicon dioxide). The granule size and packing may be selected to optimize the performance of the extinguishing agent <NUM> as described herein. The main chamber <NUM> is filled with the agent <NUM> through a fill opening 212B in the electrode <NUM>, and then sealed with the plug <NUM>.

The indicator mechanism <NUM> includes an electrically resistive wire <NUM>, a metallic indicator member or pin <NUM>, and a preload spring <NUM> located in the auxiliary chamber <NUM>. The indicator mechanism <NUM> is assembled such that the resistive wire <NUM> is attached (e.g., welded) at one end 232A to the electrode <NUM>, and is attached at its opposing end 232B to the indicator pin <NUM>. The spring <NUM> is supported by extrusions on the housing <NUM> in a compressed state such that the spring <NUM> applies tension to the wire <NUM> and biases the indicator pin <NUM> towards the electrode <NUM>. The end of the pin <NUM> is inserted in an indicator opening 212C in the electrode <NUM> and makes electrical contact therewith. When the resistive wire <NUM> disintegrates, as discussed below, the spring <NUM> forces the pin <NUM> to slide outwardly through the opening 212C to provide a visible or mechanical indication or alert.

In some embodiments, the resistive wire <NUM> has a wire diameter in the range of from about <NUM> to <NUM>. In some embodiments, the resistive wire <NUM> is formed of a resistive material having a resistance in the range of from about <NUM> to <NUM> Ohm/cm for wire diameters in the range of from about <NUM> to <NUM>.

The auxiliary chamber <NUM> may remain unfilled with the agent <NUM>. In other embodiments, the partition <NUM> may be omitted and the indicator mechanism <NUM> may be located in the main chamber <NUM>.

The fuse element <NUM> is a bimetallic strip having opposed first and second ends 242A, 242B. The strip includes an elongate connecting body or leg <NUM>, an integral first tab <NUM> on the first end 242A, and an integral second tab <NUM> on the second end 242A. Holes 254A and/or cutouts 254B may be defined in the strip <NUM>.

The bimetallic fuse element <NUM> includes a first or inner metal band or layer <NUM> and a second or outer metal band or layer <NUM> mated (e.g., face to face) with the inner metal layer <NUM> along the length of the fuse element <NUM>. The inner metal layer <NUM> and the outer metal layer <NUM> are formed of different metal compositions from one another. More particularly, the outer metal layer <NUM> is formed of a metal having a higher coefficient of thermal expansion than that of the inner metal layer <NUM>. When the fuse element <NUM> is heated, the different rates of thermal expansion between the metal layers <NUM>, <NUM> will cause the fuse element <NUM> to bend or deform in a deformation direction B.

In some embodiments, the bimetallic fuse element <NUM> further includes a third metal band or layer <NUM> mated (e.g., face to face) with the inner metal layer <NUM> or the outer metal layer <NUM> (as illustrated in <FIG>) along the length of the fuse element <NUM>. In some embodiments, the third metal layer <NUM> is formed of a metal having a higher electrical conductivity than the metals or alloys forming the inner metal layer <NUM> and the outer metal band or layer <NUM>.

The metal layers <NUM>, <NUM> may be formed of any suitable metals. In some embodiments, the inner metal layer <NUM> (i.e., the low expansion side layer) is formed of FeNi36 nickel alloy, and the outer metal layer <NUM> (i.e., the high expansion side layer) is formed of FeNi22Cr3 nickel alloy.

In some embodiments, the fuse element <NUM> has a specific thermal curvature in the range of <NUM> x <NUM>-<NUM> to <NUM> x <NUM>-<NUM> [K-<NUM>] and a specific resistance in the range of <NUM> x <NUM>-<NUM> to <NUM> x <NUM>-<NUM> [Ω m].

In some embodiments, the fuse element <NUM> has a strip width W1 (<FIG>) in the range of from about <NUM> to <NUM>.

In some embodiments, the fuse element <NUM> has a strip length L1 (<FIG>) in the range of from about <NUM> to <NUM>.

In some embodiments, the fuse element <NUM> has a strip thickness T1 (<FIG>) in the range of from about <NUM> to <NUM>.

In some embodiments, the outer metal layer <NUM> of the fuse element <NUM> has a layer thickness T2 (<FIG>) in the range of from about <NUM>/<NUM> to <NUM>/<NUM> times the thickness T1.

In some embodiments, the inner metal layer <NUM> of the fuse element <NUM> has a layer thickness T3 (<FIG>) in the range of from about <NUM>/<NUM> to <NUM>/<NUM> times the thickness T1.

In some embodiments, the third metal layer <NUM> of the fuse element <NUM> has a layer thickness T4 (<FIG>) in the range of from about <NUM> to <NUM> times the thickness T1.

In some embodiments, the bend in the fuse element <NUM> between the first tab <NUM> and the leg <NUM> has a radius R1 (<FIG>) in the range of from about <NUM> to <NUM> times the thickness T1.

In some embodiments, the bend in the fuse element <NUM> between the second tab <NUM> and the leg <NUM> has a radius R2 (<FIG>) in the range of from about <NUM> to <NUM> times the thickness T1.

In some embodiments, the tab <NUM> is bent at an angle in the range of from about <NUM> to <NUM> degrees relative to the leg <NUM> and at a bending radius in the range of from about <NUM> to <NUM> times the thickness T1, and the tab <NUM> is bent at an angle in the range of from about <NUM> to <NUM> degrees relative to the leg <NUM> and at a bending radius in the range of from about <NUM> to <NUM> times the thickness T1.

The end 242A of the fuse element <NUM> is secured, anchored or affixed to the first electrode <NUM> by the fastener <NUM> (e.g., nut and bolt, screw, rivet, or weld), which may extend through an opening 212A in the electrode <NUM>. The tab <NUM> is thereby held in electrical contact with the interior surface <NUM> of the electrode <NUM>.

The opposing end 242B of the fuse element <NUM> is held with the tab <NUM> in electrical contact with the interior surface <NUM> of the second electrode <NUM>. The tab <NUM> may be lightly loaded against the surface <NUM> (e.g., by a small elastic deflection of the fuse element <NUM>), but the end 242B is not affixed to the electrode <NUM>. That is, the end 242B is free.

The fuse element <NUM> is generally surrounded by the agent <NUM> that fills the main chamber <NUM>.

The fuse assembly <NUM> and the fused SPD assembly <NUM> may operate as follows in service.

According to some embodiments of the inventive concept, the fused SPD <NUM> may be configured to operate under four different conditions: <NUM>) normal operation; <NUM>) an overvoltage or current surge event in which the fused SPD <NUM> is designed to shunt an SPD surge impulse current to ground; <NUM>) an ambient leakage current event associated with the OPC <NUM> (e.g., associated with diode junctions of a varistor <NUM> of the OPC <NUM>); and <NUM>) a short circuit event in which the voltage-switching/limiting component <NUM> of the OPC <NUM> degrades at the end of its lifecycle and begins acting or operating as a short circuit.

The fuse assembly <NUM> is constructed and installed with the fuse assembly <NUM> in the configuration shown in <FIG>. The electrodes <NUM> and <NUM> are electrically connected by the fuse element <NUM>, which makes electrical contact with the electrodes <NUM> and <NUM> via the tabs <NUM> and <NUM>, respectively. The terminal <NUM> is electrically connected to the Line (L) of the circuit <NUM>, and the terminal <NUM> is electrically connected to the Ground (G) of the circuit <NUM> (<FIG>).

As discussed above, during normal operation, the SPD OPC does not let current through, and the fuse assembly <NUM> therefore is not supplied with a current. The fuse assembly <NUM> remains in the configuration shown in <FIG>.

As discussed above, when an overvoltage or current surge event applies a surge impulse current to the circuit <NUM>, the OPC <NUM> will effectively become a short circuit, and the fuse assembly <NUM> is supplied with an SPD surge impulse current. The voltage-switching/limiting component <NUM> (e.g., varistor or GDT) of the OPC <NUM> is designed to shunt the surge impulse current associated with such events to ground to protect sensitive equipment. The SPD surge impulse current may be on the order of tens of kA, but will typically last only a short duration (in the range of from about tens of microseconds to a few milliseconds).

The fuse element <NUM> is capable of conducting this SPD surge impulse current without disintegrating or deforming the fuse element <NUM>. The fuse assembly <NUM> remains in the configuration shown in <FIG>. The fuse assembly <NUM> therefore will not interrupt the SPD surge impulse current, and will remain usable for further operation. Accordingly, the bimetallic fuse assembly <NUM> may be configured to carry the SPD surge impulse current therethrough without the bimetallic fuse element <NUM> deforming to open the circuit. In some embodiments of the inventive concept, the bimetallic fuse assembly <NUM> may be configured to carry therethrough an SPD surge impulse current of up to 25kA for a time of up to <NUM>, a 25kA <NUM>/<NUM> impulse waveform, and/or 25kA <NUM>/<NUM> impulse waveform without the bimetallic fuse link or element <NUM> deforming to open the circuit.

As discussed above, when the voltage-switching/limiting component <NUM> (e.g., varistor or GDT) of the OPC <NUM> fails with a relatively small SPD leakage current (i.e., an ambient leakage current event associated with a varistor <NUM>), the fuse assembly <NUM> is supplied with the SPD leakage current. However, the fuse element <NUM> is capable of conducting this SPD leakage current for a minimum leakage current time threshold without disintegrating or deforming the fuse element <NUM> to open the circuit. The fuse assembly <NUM> remains in the configuration shown in <FIG>. The fuse assembly <NUM> therefore will not interrupt the SPD leakage current, and will remain usable for further operation. The voltage-switching/limiting component <NUM> (e.g., MOV) may further degrade and generate progressively more heat until the thermal disconnector <NUM> responds to the heat by opening and interrupting the current through the circuit <NUM>. This leakage current is lower than the SPD short circuit trigger current for the bimetallic fuse assembly <NUM>. The leakage current in a power line application may be in a range from about 1A - 15A. When the leakage current from the varistor is excessive it may cause heat buildup resulting in the thermal disconnector <NUM> opening the circuit to terminate the leakage current. The minimum leakage current time threshold may be set to be greater than a time at which the thermal disconnector <NUM> would open the circuit to terminate the leakage current.

As discussed above, the voltage-switching/limiting component <NUM> (e.g., varistor or GDT) of the OPC <NUM> may fail as a short circuit in a manner and under circumstances that cause the OPC <NUM> to supply the fuse assembly <NUM> with a relatively high SPD short circuit current (e.g., in the range of from about hundreds of amps to tens of kA). This may occur when a varistor <NUM> of the OPC <NUM> degrades, for example and acts as a short circuit.

The bimetallic fuse assembly <NUM> is configured to open based on the minimum short circuit current that the SPD is expected to deliver when the SPD fails as a short circuit, which is based on the application. The minimum expected short circuit current may be called a threshold short circuit current or a trigger current of the bimetallic fuse assembly <NUM> (i.e., the prescribed trigger current threshold for which the fuse assembly <NUM> is rated or designed). In a power line application, for example, the minimum expected short circuit current or trigger current may be in a range of 300A - 1000A.

In response to the SPD short circuit current exceeding the prescribed trigger current of the fuse assembly <NUM>, the fuse element <NUM> will disconnect from the electrode <NUM> and interrupt the current through the fuse assembly <NUM>. More particularly, the trigger current heats the bimetallic fuse element <NUM>. In response, the differentially expanding layers <NUM> and <NUM> cause the second end 242B and the tab <NUM> of the fuse element <NUM> to bend or deflect away from the second electrode <NUM> in the direction B (as shown in <FIG>). In this manner, the fuse element <NUM> draws the tab <NUM> (and thereby the fuse element <NUM>) out of electrical contact with the electrode <NUM>. The granulated extinguishing agent <NUM> is flowable and permits the fuse element <NUM> to deform in this manner.

Thus, for a power line application, the bimetallic fuse assembly <NUM> may be configured such that the bimetallic fuse element <NUM> deforms once the SPD short circuit current or trigger current has flowed through the fuse for not greater than a maximum short circuit response time threshold. In power line applications, this maximum short circuit response time threshold may be set by regulation or standard to <NUM> seconds.

Once the fuse element end 242B has been displaced from the electrode <NUM>, electrical arcing will occur between the end 242B and the electrode <NUM>. This arcing causes a portion of the fuse element end 242B to quickly evaporate or disintegrate. The fuse element 242B is thereby shortened or truncated so that it terminates at an end 242C (<FIG>).

The extinguishing agent <NUM> (e.g. SiO2), the loss of material from the fuse element <NUM>, and/or the spatial distance between the end of the fuse element <NUM> will then cause the electrical arcing to terminate, cease or be extinguished. The fuse assembly <NUM> is now open and the current therethrough has been interrupted.

In some embodiments, the fuse assembly <NUM> is thereby irreversibly and permanently tripped to an open, current interrupting state. That is, the triggered and tripped fuse assembly <NUM> is non-resetting and non-resettable.

In some embodiments, this non-resetting and non-resettable feature is achieved in whole or in part by the disintegration of the end 242B of the fuse element <NUM>, as illustrated in <FIG>, for example. The loss of material from the end 242B ensures that the fuse element <NUM> can no longer make contact with the electrode <NUM> or come within sufficient proximity to the electrode <NUM> to enable arcing.

In some embodiments, this non-resetting and non-resettable feature is achieved in whole or in part by interference from the extinguishing agent <NUM>. In some embodiments, the arcing described above also causes a portion 226A of the extinguishing agent <NUM> adjacent the fuse element <NUM> to fuse or otherwise harden or lose flowability, as illustrated in <FIG>, for example. When the fuse element <NUM> cools (after cessation of the trigger current), the bimetallic fuse element <NUM> may tend to unbend (i.e., return to its original shape). The stiffened or rigidified extinguishing agent <NUM> prevents or inhibits the fuse element <NUM> from unbending back to a position in which the fuse element <NUM> would make contact with the electrode <NUM> or come within sufficient proximity to the electrode <NUM> to enable arcing.

The indicator mechanism <NUM> is configured such that the trigger current also disintegrates the resistive wire <NUM>. This permits the indicator pin <NUM> to pop up through the opening 212C and alert an operator that the fuse assembly <NUM> has been tripped.

In other embodiments, the fuse assembly may have a different form factor. Also, the indicator mechanism may be omitted. For example, <FIG> show an exemplary fuse assembly <NUM> according to further embodiments wherein the fuse housing is cylindrical and no indicator mechanism is provided. The fuse assembly <NUM> has a first end 300A and an opposing second end 300B. The fuse assembly <NUM> includes a fuse assembly housing <NUM>, a first electrode <NUM> (at the end 300A), a second electrode <NUM> (at the end 300B), a fastener <NUM>, an electric arc extinguishing agent <NUM>, a bimetallic fuse link or element <NUM>, and a main chamber <NUM> corresponding to the housing <NUM>, the first electrode <NUM>, the second electrode <NUM>, the fastener <NUM>, the electric arc extinguishing agent <NUM>, the bimetallic fuse element <NUM>, and the main chamber <NUM>, respectively.

Referring to <FIG>, a fused SPD circuit <NUM>, and a fused SPD module <NUM> forming the circuit <NUM>, according to further embodiments of the inventive concept are shown therein. The fused SPD module <NUM> includes the fuse assembly <NUM>, a module housing <NUM>, a first electrical terminal <NUM>, a second electrical terminal <NUM>, an OPC <NUM>, and a thermal disconnector <NUM>. The fused SPD circuit <NUM> and fused SPD module <NUM> may be constructed and operate as described for the circuit <NUM> and module <NUM>, except as follows.

The OPC <NUM> includes both a varistor (e.g., MOV) <NUM> and a GDT <NUM>. The varistor <NUM> and the GDT <NUM> are provided in electrical series with the fuse assembly <NUM> and, in some embodiments, with the thermal disconnector <NUM>.

With reference to <FIG>, a bimetallic fuse device or assembly <NUM> according to further embodiments is shown therein. The fuse assembly <NUM> may be constructed, installed and used in the same manner as described for the fuse assembly <NUM>, except as discussed below. For example, the fuse assembly <NUM> may be used in place of the fuse assembly <NUM> in the fused SPD module <NUM>.

The fuse assembly <NUM> has a first end 500A and an opposing second end 500B. The fuse assembly <NUM> includes a fuse assembly housing <NUM>, a first electrode <NUM>, a second electrode <NUM>, electrode fasteners <NUM>, fuse element fasteners <NUM>, <NUM>, an electric arc extinguishing agent <NUM>, and a bimetallic fuse link or element <NUM>. The housing <NUM> and the electrodes <NUM>, <NUM> define a fuse chamber <NUM>.

The housing <NUM> may be formed of any suitable electrically insulating material. In some embodiments, the housing <NUM> is formed of ceramic.

The electric arc extinguishing agent <NUM> may be formed of any suitable material. In some embodiments, the arc extinguishing agent <NUM> is a material as described for the extinguishing agent <NUM> (e.g., a flowable media, such as silica granules). The fuse chamber <NUM> is filled with the agent <NUM>.

The fuse element <NUM> is a bimetallic strip having opposed first and second ends 542A, 542B. The strip includes, an integral first tab or base section <NUM> on the first end 542A, a first elongate connecting body, section, branch or leg <NUM>, a second elongate connecting body, section, branch or leg <NUM>, and integral tabs 544A, 545A. Each leg <NUM>, <NUM> extends from a first leg end 543A joined to the base section to an opposing second leg end 543B from which a respective tab 544A, 545A extends at the second end 542B. Mounting holes <NUM> are defined in the base section <NUM> and each of the tabs 544A, 545A.

In some embodiments and as shown, the fuse element <NUM> includes the legs <NUM>, <NUM>, the base section <NUM> and the tabs 544A, 545A in the form of a unitary strip. In other embodiments, the fuse element <NUM> may be configured as two (or more, if more than two legs are provided) bimetallic strips, each including a respective one of the legs.

The base section <NUM> is secured, anchored or affixed to the first electrode <NUM> by the fastener <NUM> extending through the hole <NUM> therein. In some embodiments, the fastener <NUM> is a rivet. The base section <NUM> may be affixed to the first electrode <NUM> using other techniques such as a nut and bolt, a screw, or a weld. The base section <NUM> is thereby held in electrical contact with the interior surface of the electrode <NUM>.

The tabs 544A, 545A are secured, anchored or affixed to the second electrode <NUM> by the fastener <NUM> extending through the hole <NUM> therein. In some embodiments, the fastener <NUM> is a rivet. The tabs 544A, 545A may be affixed to the second electrode <NUM> using other techniques such as a nut and bolt, a screw, or a weld). The tabs 544A, 545A are thereby held in electrical contact with the interior surface of the electrode <NUM>.

The bimetallic fuse element <NUM> includes a first or inner metal band or layer <NUM> (<FIG>) and a second or outer metal band or layer <NUM> mated (e.g., face to face) with the inner metal layer <NUM> along the length of the fuse element <NUM> (including along the lengths of the legs <NUM>, <NUM>). The inner metal layer <NUM> and the outer metal layer <NUM> are formed of different metal compositions from one another.

In some embodiments, the inner metal layer <NUM> is formed of a metal having a higher coefficient of thermal expansion than that of the outer metal layer <NUM>. In this case, when the fuse element <NUM> is heated, the different rates of thermal expansion between the metal layers <NUM>, <NUM> will cause the leg <NUM> to bend or deform in a deformation direction B1 and/or will cause the leg <NUM> to bend or deform in a deformation direction B2. Alternatively, the outer metal layer <NUM> may be formed of a metal having a higher efficient of thermal expansion than that of the inner metal layer <NUM>, so that the legs <NUM> and <NUM> bend or deform in directions opposite the directions B1 and B2, respectively, when the fuse element <NUM> is heated.

The metal layers <NUM>, <NUM> may be formed of metals as described herein for the metal layers <NUM>, <NUM>.

The legs <NUM>, <NUM> each include a plurality of preformed weak points <NUM> therein. The weak points <NUM> may be formed by cutouts <NUM> defined in the legs <NUM>, <NUM>. In some embodiments (e.g., as shown in the drawings), the cutouts <NUM> are defined in the side edges of the legs <NUM>, <NUM>.

In some embodiments, there are at least three weak points <NUM> defined in each leg <NUM>, <NUM>. In some embodiments, the number of weak points <NUM> defined in each leg <NUM>, <NUM> is in the range of from <NUM> to <NUM>. In other embodiments, there may be as few as one weak point <NUM> defined in each leg <NUM>, <NUM>. The cutouts <NUM> reduce the widths of the legs <NUM>, <NUM> at the locations of the weak points <NUM> along the lengths of the legs <NUM>, <NUM>.

In some embodiments, the width W3 (<FIG>) of the fuse element <NUM> is in the range of from about <NUM>/<NUM> to <NUM>/<NUM> of the width W4 (<FIG>) of the chamber <NUM>.

In some embodiments, the width W5 (<FIG>) of each leg <NUM>, <NUM> at the weak points <NUM> is in the range of from about <NUM>/<NUM> to <NUM>/<NUM> of the width W6 (<FIG>) of each leg <NUM>, <NUM>.

In some embodiments, the height H7 (<FIG>) of each cutout <NUM> is in the range of from about <NUM>/<NUM> to <NUM>/<NUM> of the width W6 of each leg <NUM>, <NUM>.

In some embodiments, the fuse element <NUM> has a specific resistance in the range of <NUM> x <NUM>-<NUM> to <NUM> x <NUM>-<NUM> Ωm.

The fuse assembly <NUM> and the fuse element <NUM> can be used in the same manner as described herein for the fuse assembly <NUM> and the fuse element <NUM>. However, instead of bending out of contact with the electrode <NUM> as described for the fuse element <NUM>, the legs <NUM>, <NUM> disintegrate or break apart at a weak point <NUM> in a midsection of each leg <NUM>, <NUM>. Once a leg <NUM>, <NUM> has broken, electrical arcing will occur between the opposed ends of the leg <NUM>, <NUM> at the break. This arcing causes a portion or portions of the fuse element <NUM> at these opposed ends to quickly evaporate or disintegrate. The extinguishing agent <NUM> (e.g., SiO2), the loss of material from the fuse element <NUM>, and/or the spatial distance between the opposed ends of the leg <NUM>, <NUM> at the break will then cause the electrical arcing to terminate, cease or be extinguished. Once both legs <NUM>, <NUM> have been transformed in this manner, the fuse assembly <NUM> is open and the current therethrough has been interrupted.

In some embodiments, the fault current will initially generate heat in, arcing at and disintegration of the fuse element <NUM> at one of the weak points <NUM> in one of the legs <NUM>, <NUM>. The fault current may then cause the fuse element <NUM> to begin arcing and disintegrating at other weak points <NUM> in the same leg <NUM>, <NUM>. The current will also then cause the other leg <NUM>, <NUM> to begin arcing and disintegrating at one or more weak points <NUM> therein. The disintegration of each leg <NUM>, <NUM> will propagate along the leg <NUM>, <NUM> toward the electrodes <NUM>, <NUM> until the arcing in the leg <NUM>, <NUM> is terminated by the extinguishing agent <NUM> and/or spatial distance between the opposed ends of the leg <NUM>, <NUM>. In some cases, most of each leg <NUM>, <NUM> will be disintegrated, and in some embodiments substantially all of each leg <NUM>, <NUM> will be disintegrated, depending on the amplitude of the fault current.

In some embodiments, the bimetallic legs <NUM>, <NUM> will bend or deform (e.g., in directions B1, B2) in response to the heat generated in the legs <NUM>, <NUM> by the surge current flowing therethrough. This bending or deformation can assist in spacing apart the opposed ends of leg <NUM>, <NUM> at a break (e.g., occurring at a weak point <NUM>) to extinguish arcing. However, in other embodiments, the electrodes <NUM>, <NUM> may be fully disconnected by the disintegration of the leg <NUM>, <NUM> before the leg <NUM>, <NUM> bends or deforms, or before the extent of the bending or deformation can appreciably contribute to the disconnection.

It will be appreciated that the bimetallic fuse element <NUM> provides two parallel branches (i.e., the two legs <NUM>, <NUM>) for the flow of current through the fuse assembly <NUM>. In other embodiments, the bimetallic fuse element <NUM> may include more than two (e.g., three, four, or more) legs corresponding to and secured in the same manner as the legs <NUM>, <NUM> that each provide a parallel branch for the flow of current through the fuse assembly <NUM>. The provision of two or more branches <NUM>, <NUM> increases the overall effective cross-sectional area of the fuse element <NUM>. This increased cross-sectional area can serve to increase the surge current rating of the fuse assembly <NUM>.

With reference to <FIG>, a fused surge protective device (SPD) unit or module <NUM> according to further embodiments is shown therein. The fused SPD module <NUM> includes the fuse assembly <NUM> integrated therein. However, in other embodiments, the fuse assembly <NUM>, the fuse assembly <NUM>, or another bimetallic fuse assembly according to embodiments of the invention may be used in place of the fuse assembly <NUM> in the fused SPD module <NUM>.

The fused SPD module <NUM> includes a module housing <NUM>, a first module electrical terminal <NUM>, a second module electrical terminal <NUM>, an overvoltage protection circuit (OPC) assembly <NUM>, a thermal disconnector <NUM>, an indicator mechanism <NUM>, and the fuse assembly <NUM>. The thermal disconnector <NUM>, the OPC assembly <NUM>, and the fuse assembly <NUM> are disposed in the housing <NUM>, and are electrically connected in series between the module terminals <NUM> and <NUM> to form a fused SPD electrical circuit <NUM>. It will be appreciated that the fused SPD electrical circuit <NUM> corresponds to the fused SPD electrical circuit <NUM> (<FIG>). It will be appreciated that the OPC <NUM>, the thermal disconnector <NUM>, the indicator mechanism <NUM>, the fuse assembly <NUM>, and the fused SPD assembly <NUM> function and operate in the same manner as described herein for the OPC <NUM>, the thermal disconnector <NUM>, the indicator mechanism <NUM>, the fuse assembly <NUM>, and the fused SPD module <NUM>, except as discussed below.

The module housing <NUM> includes a module frame <NUM> and a module cover <NUM>. The components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are mounted on or in the module frame <NUM>, and this subassembly is covered by the module cover <NUM>. The module electrical terminals <NUM>, <NUM> project from the base of the housing <NUM>. In use, the fused SPD module <NUM> can be mounted on a cooperating base assembly such that the module electrical terminals <NUM>, <NUM> make mechanical and electrical contact with associated terminals of the base assembly.

The OPC assembly <NUM> includes an overvoltage protection circuit <NUM>. In some embodiments, the OPC assembly <NUM> is a multi-cell GDT assembly. In some embodiments, the OPC assembly <NUM> is a multi-cell GDT assembly as disclosed in <CIT>or <CIT>. However, it will be appreciated that other types and configurations of overvoltage protection circuits and active voltage-switching/limiting components may be used in or in place of the multi-cell GDT <NUM>.

The illustrative multi-cell GDT assembly <NUM> includes a primary GDT 646A and a secondary multi-cell GDT 646B. The multi-cell GDT assembly <NUM> has a first terminal <NUM> and a second terminal <NUM>. The primary GDT 646A and the secondary multi-cell GDT 646B are connected in electrical series between the terminals <NUM>, <NUM>, for example, as disclosed in <CIT>.

The fused SPD module <NUM> includes a first terminal member <NUM> including the first module terminal <NUM> and electrically connecting the first module terminal <NUM> to the terminal <NUM>.

The fused SPD module <NUM> includes a second terminal member <NUM> including the second module terminal <NUM> and electrically connecting the second electrode <NUM> of the fuse assembly <NUM> to the second module terminal <NUM>.

The terminal <NUM> of the multi-cell GDT <NUM> is electrically connected to the first electrode <NUM> of the fuse assembly <NUM> by the thermal disconnector <NUM>, which is electrically conductive (e.g., metal). More particularly, a first end 650A of the thermal disconnector <NUM> is fastened to the fuse electrode member <NUM>. An opposing end 650B of the thermal disconnector <NUM> is affixed to the terminal <NUM> by a meltable bonding agent <NUM> such as a solder.

A leg or spring contact <NUM> is retained by the bonding agent <NUM> in an elastically deflected position such that the spring force of the spring contact <NUM> tends to pull the end 650B away from the terminal <NUM>. In use, when the GDT assembly <NUM> fails (e.g., the multi-cell secondary GDT 646B short-circuits internally), the primary GDT 646A will quickly heat up until the solder <NUM> melts sufficiently to release the spring contact <NUM>, which is spring biased or loaded away from the terminal <NUM>. The GDT assembly <NUM> is thereby disconnected from the fuse assembly <NUM>.

The indicator mechanism <NUM> includes an indicator member <NUM>, a preload spring <NUM>, a resistive wire <NUM>, a ferrule <NUM>, a resistor <NUM>, an indicator strip <NUM>, an electrical connector member <NUM>, a local indicator window <NUM> (defined in the cover <NUM>), and a remote indicator opening <NUM> (defined in the base of the frame <NUM>).

The resistive wire <NUM> may be constructed as described for the resistive wire <NUM>. A retention cap 670A is affixed to the upper end of the resistive wire <NUM> and interlocked with the indicator member <NUM>. In the ready (non-failed) configuration, the resistive wire <NUM> is in tension and retains the indicator member <NUM> in a ready position against the load of the spring. When the resistive wire <NUM> disintegrates and breaks (as discussed herein), the indicator member <NUM> is thereby released to translate in direction E (<FIG>).

The resistive wire <NUM> is mechanically braced in tension, and electrically connected to the resistor <NUM>, by the ferrule <NUM>. The opposing lead of the resistor <NUM> is electrically connected to the second module terminal <NUM> by an integral connection feature or tab <NUM> of the second terminal member <NUM>.

The electrical connector member <NUM> (e.g., formed of metal) electrically connects the resistive wire <NUM> to the terminal <NUM> of the GDT assembly <NUM>. An electrical insulator <NUM> may be provided to increase the breakdown voltage between the electrical connector member <NUM> and portions of the GDT assembly <NUM> at a different potential than the terminal <NUM>. It will be appreciated that the resistive wire <NUM> is connected between the GDT assembly <NUM> and the second module terminal <NUM> in electrical parallel with the bimetallic fuse element <NUM> (<FIG>) of the fuse assembly <NUM>. The resistor <NUM> limits current flow through the resistive wire <NUM>.

The fused SPD circuit <NUM> and fused SPD module <NUM> operate as described for the circuit <NUM> and module <NUM>, except that the indicator mechanism <NUM> will be triggered or actuated under the same conditions as discussed herein for the indicator mechanism <NUM>.

The indicator mechanism <NUM> is configured such that, under conditions where the trigger current through the fuse assembly <NUM> opens (i.e., the bimetallic fuse element <NUM> disintegrates), the trigger current also disintegrates the resistive wire <NUM>. The indicator member <NUM> is thereby released to translate in direction E under the force of the spring <NUM>. This movement of the indicator member <NUM> causes the indicator member <NUM> to move to a position underneath the window <NUM>, thereby providing a local visible alert to a user that the module <NUM> has failed or tripped.

This movement of the released indicator member <NUM> also draws the indicator strip <NUM> up through a channel <NUM> in the module frame <NUM> in direction F (<FIG>). In this way, an end section 676A of the indicator strip <NUM> is pulled away from a position over the opening <NUM>, thereby uncovering the opening <NUM>. The uncovering of the opening <NUM> can permit a switch of the base assembly to move into the module <NUM> through the opening <NUM>. The switch can in turn be connected to a remote monitoring circuit associated with the base assembly. In this manner, the indicator mechanism <NUM> can provide a remote alert to a user that the module <NUM> has failed or tripped.

Embodiments of the inventive concept have been described above with respect to the fuse assembly <NUM> and the fuse assembly <NUM> including a bimetallic fuse element or link <NUM> or <NUM> as shown, for example, in <FIG> and <FIG>. According to some embodiments of the inventive concept, the bimetallic fuse element or link <NUM> or <NUM> may comprise one or more fusible elements or legs that each comprise one or more metal alloys. The one or more metal alloys in each element or leg may have a specific resistance in a range of <NUM> x <NUM>-<NUM> Ωm - <NUM> x <NUM>-<NUM> Ωm, which is greater than that of materials used in conventional fuses, such as copper, aluminum, and the like. The shape of each element or leg may be configured to provide the fuse element or link <NUM>, <NUM> with an overall resistance in the range of <NUM> mΩ - <NUM> mΩ. Thus, according to some embodiments of the inventive concept, a fuse element <NUM>, <NUM> comprising a metallic alloy material as described above may be used in a fuse assembly <NUM>, <NUM>, which provides a continuous current conduction of <NUM> A without overheating above a dT of <NUM> - <NUM> and a surge impulse current rating of <NUM> kA in response to a <NUM>/<NUM> surge current pulse shape (i.e., a rise time of <NUM> and a decay time to <NUM>% of peak value of <NUM>. The fuse assembly <NUM> and/or <NUM> may have an arc voltage associated therewith that is in a range of about <NUM> - <NUM> V in accordance with IEC <NUM>-<NUM>. TABLE <NUM> set forth below provides a summary that compares electrical characteristics of a fuse assembly <NUM>, <NUM> including a bimetallic/monolithic fuse element <NUM>, <NUM>, according to some embodiments of the inventive concept, with both a conventional small fuse and a conventional big fuse. As can be seen from TABLE <NUM>, the conventional small fuse may have similar specific resistance and overall fuse resistance, but it does not provide a similar impulse surge current rating. Similarly, the large or big fuse may have a similar surge impulse surge current rating, but does not provide a similar specific resistance or overall total resistance.

Like reference numbers signify like elements throughout the description of the figures.

It will be understood that, although the terms "first," "second," etc. may be used herein to describe various elements, these elements should not be limited by these terms. Thus, a first element could be termed a second element without departing from the teachings of the inventive subject matter.

Claim 1:
A fused surge protective device (SPD) module (<NUM>; <NUM>), comprising:
a first electrical terminal (<NUM>);
a second electrical terminal (<NUM>);
an overvoltage protection circuit (<NUM>) connected between the first electrical terminal and the second electrical terminal; and
a bimetallic fuse (<NUM>; <NUM>) including a bimetallic fuse element (<NUM>; <NUM>) connected in series with the overvoltage protection circuit between the first and second electrical terminals;
wherein the bimetallic fuse element includes:
a first metal layer (<NUM>; <NUM>) having a first coefficient of thermal expansion; and
a second metal layer (<NUM>; <NUM>) having a second coefficient of thermal expansion;
wherein the first coefficient of thermal expansion is greater than the second coefficient of thermal expansion;
wherein the bimetallic fuse element is configured to disintegrate in response to a current flowing through the bimetallic fuse element to thereby disconnect the first electrical terminal from the second electrical terminal;
wherein the bimetallic fuse element is configured to bend in a deformation direction (B), due to the difference in the coefficients of thermal expansion of the first and second metal layers, in response to heat generated in the bimetallic fuse element by the current flowing through the bimetallic fuse element; and
wherein said bending assists in extinguishing electrical arcing from the bimetallic fuse element.