Patent Application
20120086540
This application claims priority under 35 U.S.C. §119 to French Patent Application No. 1052736 filed in France on Apr. 9, 2010, the entire content of which is hereby incorporated by reference in its entirety.
The present disclosure relates to the general technical field of devices for protecting equipment or electrical installations from overvoltages, such as from surges, due for example to a lightning strike. The present disclosure also relates to devices for protecting an electrical installation from surges, such as a varistor lightning arrestor, for low-voltage electrical installations.
It is known that the protection of an electrical installation from overvoltages can be achieved by using devices including at least one component for protection from overvoltages, for example one or more varistors and/or one or more spark gaps. For single phase installations, it is known to use a varistor connected between the phase and the neutral and a spark gap connected between the neutral and the ground. For three-phase installations, it is known to position varistors between the different phases and/or between each phase and the neutral and a spark gap between the neutral and the ground. For electrical installations operating under direct current, for example for photovoltaic generator installations, varistors and possibly spark gaps can be used.
In the event of failure of the protection component, these known devices include a disconnection system serving to isolate the protective component from the electrical installation as a safety measure. For example, in the case of varistors, it is known to provide thermal protection. The thermal protection or thermal disconnector can disconnect the varistor from the electrical installation to be protected in the event of excessive heating of the varistor, for example beyond 140° C. This excessive heating of the varistor is due to the increase of the leakage current—generally several tens of milliamperes—due to its aging, which is known as thermal runaway of the varistor.
The thermal disconnector often comprises (e.g., consists of) a low-temperature weld that keeps a conductive element in place to form a mobile contact through which the varistor is connected to the electrical installation, when the conductive element is elastically stressed towards the opening. The fusion of the weld results in the mobile contact moving under the effect of the elastic stress, which causes the disconnection of the varistor. Thermal disconnectors of this type are described in EP-A-0 716 493, EP-A-0 905 839, and EP-A-0 987 803, each of which is hereby incorporated by reference in its entirety.
These known devices which protect against overvoltages, and their thermal disconnector, can be faced with different restrictive situations during their use. The restrictive situations can depend, for example, on the type of electrical grid to which they are attached.
First, their thermal disconnector should have a sufficient interrupting capacity to effectively disconnect the protection component in case of thermal runaway. This constraint can be more delicate in the case of installations operating under direct current, given that there is no periodic passage at zero volts, as with alternating current. The alternating current contributes to the extension of the electric arc generated at the opening of the mobile contact.
The electrical circuit of the protective devices shall also be able to support the constraints resulting from electrical shocks, such as the lightning currents for which they are provided. These electric shocks can be surges with a significant amplitude (e.g., several thousand volts) and short duration (e.g., from a microsecond to a millisecond). These overvoltages, for example, can cause electrodynamic stresses and temperature increases that mechanically stress the different conductive pieces making up the protection device. Despite these mechanical stresses, the electrical circuit ensuring the connection of the protective component to the electrical installation should remain closed. In particular, the mechanical stresses should not cause the thermal disconnector to turn on via pulling out of the thermofusible braze. The ability of the device to meet this constraint can be verified by the applicable standards, for example, in installations supplied with low-voltage alternating current, in paragraph 7.6 (operating duty tests) of standard IEC 61643-1, 2nd ed., 2005-03 (hereafter noted IEC paragraph 7.6), or paragraph 37 (Surge testing) of standard UL 1449, 3rd ed., 09.29.2006 (hereafter noted UL paragraph 37). For direct current installations such as photovoltaic generator installations, examples include paragraph 6.6 (Operating duty tests) of photovoltaic guide UTE C 61-740-51 dated June 2009 (hereafter UTE paragraph 6.6).
Moreover, the electric circuit of the protective device connecting the protective component to the electrical installation can be subject to very high currents under the nominal voltage of the electrical installation, for example in installations powered by the alternating voltage grid. This example occurs when the varistor of the protection device experiences a power outage by short circuit. In this case, the disconnection of the failing varistor is caused by a specific protection from short circuits such as a fuse or a circuit-breaker. Given the reaction time of this specific protection, the electric circuit of the protection device, including the thermal disconnector, should not cause any fire outbreak in that period of time, given the significance of the short circuit currents provided by the electrical power grid. The ability of the device to satisfy this constraint can be verified for installations powered with low-voltage alternating current, for example in paragraph 7.7.3 (Short circuit withstand) of standard IEC 61643-1, 2nd ed., 2005-03 (hereafter noted IEC paragraph 7.7.3).
The device for protection from overvoltages can also be capable of being powered by a surge related to an anomaly in the voltage of the power grid of the electrical installation, when a power outage caused by a short circuit of a varistor if there are at least two varistors serially connected between the lines of the power grid. In such a case, the varistor turns on and can pass a very high current given its low independence. The current is more or less the short circuit current that the power grid of the electrical installation can supply. Faced with such a situation, the protective device should not cause a fire to start.
The ability of the protective device to satisfy this constraint can be verified for installations supplied with low-voltage alternating current, for example in paragraph 39 (Current testing) of standard UL 1449, 3rd 3d., Sep. 29, 2006 (hereafter noted UL paragraph 39), or for photovoltaic generator installations, for example in paragraph 6.7.4 (End of life tests) from photovoltaic guide UTE C 61-740-51 dated June 2009 (hereafter noted UTE paragraph 6.7.4).
These protective devices should therefore, depending on the case, meet a number of constraints. The present disclosure sets forth exemplary embodiments which can improve the resistance of protective devices to overvoltages in situations where the protective component, for example regarding a varistor, reaches the end of its life by short circuit under nominal voltage, this situation being taken into account by standard IEC paragraph 7.7.3, as mentioned above. Indeed, specific protection from overvoltages can have a relatively long reaction time, in the vicinity of a second or more. There is a risk that during this period of time, the passage of a high intensity current in the protective device may cause the formation of an uncontrolled electric arc in the device protecting from overvoltages. Such an uncontrolled arc can then initiate a fire outbreak in the electrical installation.
A protective device for protecting an electrical installation from surges is disclosed. The protective device comprises two connection terminals for connecting the device to an electrical installation to be protected; and a protective component protecting against overvoltages, said protective component being electrically connected to the two connection terminals. The protective device includes a thermal disconnector that comprises a conductive contact blade maintained in a first position in which the contact blade ensures an electrical connection between the protective component and one of the two connection terminals. The thermal disconnector being provided for making the contact blade go to a second position when the temperature of the protective component exceeds a predetermined temperature threshold in which second position said electrical connection is open, wherein the contact blade and said one of the two connection terminals are part of a single and same piece.
Other features and advantages of the disclosure will appear upon reading the following detailed description of exemplary embodiments of the disclosure, provided solely for information and with reference to the appended drawings, as follows:
An exemplary protective device is disclosed for protecting an electrical installation from surges. The protective device comprises two connection terminals for connecting the device to the electrical installation to be protected, a protective component protecting against overvoltages, where the protective component is electrically connected to the two connection terminals. The protective device also includes a thermal disconnector comprising a conductive contact blade maintained in a first position in which the contact blade ensures an electrical connection between the protective component and one of the two connection terminals, where the thermal disconnector being provided to make the contact blade go to a second position when the temperature of the protective component exceeds a predetermined threshold in which second position said electrical connection is open. The contact blade and said one of the two connection terminals are part of a single and same piece.
According to an exemplary alternative, the protective component protecting from overvoltages can be a varistor.
According to an exemplary alternative, the device can include a member reducing or eliminating electric arcs forming during movement of the contact blade from the first position towards the second position, the reducing or eliminating member can be chosen from the group of arc reducing or eliminating members comprising electric means, electronic means, electromechanical means, and mechanical means.
According to an exemplary alternative, the piece to which the contact blade and the one of the two connection terminals belong has an IACS conductivity greater than or equal to for example 70%, preferably greater than or equal to for example 90%, still more preferably greater than or equal to for example 95%.
According to an exemplary alternative, the piece to which the contact blade and said one of the two connection terminals belong can be made from copper with a copper content greater than or equal to 99.9%.
According to an exemplary alternative, the piece formed by the contact blade and the one of the two connection terminals can include a flexible part intermediate between the contact blade and the terminal to allow the contact blade to move relative to the terminal, between the first position and the second position.
According to an exemplary alternative, the contact blade can be elastically stressed towards the second position, the thermal disconnector comprising a thermosensitive element in thermal contact with the protective component, the thermosensitive element maintaining the contact blade in the first position up to the predetermined temperature threshold and releasing the contact blade when the temperature of the protective component exceeds the predetermined threshold.
According to an exemplary alternative, the thermosensitive element can be a thermofusible braze by which the contact blade is welded to a pole of the protective component.
According to an exemplary alternative, the part of the contact blade welded to the pole by the thermofusible braze can be connected to the rest of the contact blade by a local restriction of the section of the blade to concentrate the heat given off by the protective component at the thermofusible braze.
According to an exemplary alternative, the contact blade can extend primarily in a first plane parallel to one of the main faces of the protective component, the movement of the contact blade between the first position and the second position being done mainly in the first plane.
According to an exemplary alternative, the part of the contact blade welded to the pole of the protective component can be tinned.
According to an exemplary alternative, the device can comprise a second thermal disconnector to disconnect the protective component from the electrical installation when the temperature of the protective component exceeds a predetermined threshold.
The disclosure also relates to an exemplary device for protecting an electrical installation from surges. The protective device can comprise a component for protecting from overvoltages and two connection terminals for connecting the device to the electrical installation to be protected. The protective component is electrically connected to the two connection terminals. The protective component can for example be a varistor. It will be understood that this can be a block of several varistors connected to each other serially or in parallel.
An exemplary device can also comprise a thermal disconnector comprising a conductive contact blade. The conductive contact blade can be kept in a first position, called the closed position, in which the contact blade ensures an electrical connection between the protective component and one of the two connection terminals. The thermal disconnector is provided to make the contact blade go to a second position, called the open position, when the temperature of the protective component exceeds a predetermined threshold. When the contact blade is in the second position, the electrical connection between the protective component and the one of the two connection terminals is then on.
Furthermore, the conductive contact blade and the one of the two connection terminals can be part of a single and same (common) piece. In the event of a failure of the protective component by short circuit, the short circuit current supplied by the power grid under nominal voltage then passes through the protective device and flows through said single-unit piece comprising the connection terminal and the conductive contact blade without encountering contact or weld electrical resistance. This absence of contact or weld electrical resistance can limit the heating of the piece when it is passed through by this short circuit current, which can have a very high intensity. Limiting the heating of the piece can contribute to limiting the risk of destruction thereof by melting, which would be likely to cause the creation of uncontrolled electric arcs able to cause a fire outbreak. The single-unit piece comprising the connection terminal and the conductive contact blade can thus contribute to maintaining the passage of the current through the protective device reliably, at least for the time needed for outside overvoltage protection to interrupt the current. The proposed overvoltage protection device thereby can have improved resistance to short circuit currents.
The current use of cartridges and bases for a DIN rail, in the low-voltage field, can impose a compact design constraint of the devices for protecting from overvoltages.
Described below are various exemplary features, which enable the protective device to have a compact structure, thereby allowing it to be housed in the inner volume 21.
The thermosensitive element of the thermal disconnector can be a thermofusible braze 70 via which the contact blade 44 is at the pole 34 of the varistor 30. This braze can be visible on the pole 34 of the varistor 30 as shown in
In the exemplary embodiments of the present disclosure, the protective device can face surge situations without a risk of explosion or fire outbreak, at least if the protective device is likely to be subjected to such surge conditions. For example, the exemplary embodiments can be designed to satisfy the tests provided by the UL standard, paragraph 39 or by the UTE guide, paragraph 6.7.4. To this end, the disclosed exemplary embodiments provide fast thermal disconnection of the varistor 30. In these surge situations, current passing through the varistor increases gradually until the varistor goes into a steady-state short-circuit.
The time the varistor 30 spends in short circuit can depend, for example, on a ratio between the surge and the maximum operating voltage allowable by the varistor and the electric behavior of the varistor (e.g., variation of the resistivity of the varistor as a function of the voltage applied to it). On one hand, when the ratio between the surge and the maximum allowable voltage of the varistor 30 is high, the time spent by the varistor 30 in short circuit is low. On the other hand, when the behavior of the varistor is strongly non-linear (e.g., the resistivity of the varistor varies very sharply with the increase of the voltage applied to it), the time spent by the varistor 30 in short circuit is low. It is then possible to choose the varistor as a function of these different features to increase the time spent in steady-state short circuit under the in use conditions of the varistor. The current surge phase can be accompanied by an increase in the temperature of the varistor 30, during the time spent by the varistor in short circuit. The exemplary thermal disconnector can be designed to ensure a disconnection in the transitional phase of the behavior of the varistor before the current passing through it becomes too high to be able to be interrupted by the thermal disconnector. This design involves a fast detection of the increase in the temperature of the varistor.
Various technical characteristics of the exemplary embodiments of the present disclosure contribute to obtaining this fast disconnection.
The pole 34 can be arranged on one of the main faces of the protective component 30. Such a main face of the protective component is shown by the cross-hatched area 32 in
The pole 34 of the varistor 30 can advantageously extend along the main face 32, and not protrude perpendicular thereto. As a result, the braze 70 is done on the pole 34 at a brazing surface that is parallel to the main face 32 of the varistor 30. The braze 70 has its thickness in a direction perpendicular to the main face of the protective component. As a result, the entire braze 70 is as close as possible to the varistor 30 and can establish immediate communication with it regarding the temperature of the varistor 30. This measure can be advantageous relative to known solutions in which the pole of the protective component forming the fixed contact of the thermal disconnector extends in a plane perpendicular to the main face of the protective component. The braze can extend along the perpendicular plane and part of the braze can be kept at a distance from the protective component. When the protective component fails, the braze is first stressed thermally in a portion closest to the protective component. The delay of a temperature increase of the varistor arriving at the portion of the braze that is farthest from the protective component 30, which can slow the thermal disconnection.
Moreover, the speed of thermal disconnection can also be improved by the exemplary varistor 30 of the present disclosure, through the electrode forming the pole of the varistor, which serves to transmit the heat given off by the varistor to the thermosensitive element of the thermal disconnector.
Thus, the electrode of the varistor can be formed by a conducting plate 84, as shown in
The varistor 30 can include an electrically insulating coating applied on the assembly formed by the main face 82 of the block 80 and the plate 84. Thus, the assembly formed by the main face 82 of the block 80 and the plate 84 can be electrically insulated from its surrounding environment, including the mobile contact of the protective device. In an exemplary embodiment, the assembly formed by the block 80 and the plate 84 can be completely coated with the electrically insulating coating through which the different connection poles of the varistor also emerge to produce an electrical connection with the rest of the protective device, for example, with the contact blade 44.
The protruding part forming the pole 34 can emerge outside the electrically insulating coating to allow an improvement of the interrupting capacity as described below.
The protruding part forming the pole 34 can be connected to the rest of the plate 84 on at least half of its perimeter to improve the speed of the disconnection. During the deterioration of the varistor 30 subjected to surges, the leakage current of the varistor 30 increases until the varistor 30 goes into steady-state short circuit. This transitional phase for increase of the leakage current is accompanied by an increase in the temperature of the varistor 30. This temperature increase can be gradual. The temperature first increases in the core of the block 80 of the varistor 30 in areas having homogeneity flaws. The temperature increase can spread by conduction in the entire block 80 of the varistor up to the outer faces of the block for example, up to the main face 82 of the block 80. The arrangement of the conducting plate 84 on the main face 82 of the block 80 can allow a minimum propagation time of the temperature increase from the defective areas of the block 80 up to the plate 84 forming the electrode of the varistor 30. The plate 84 has an electrically conductive characteristic, allowing the plate to form an electrode. The plate 84 also has a thermally conductive characteristic to ensure a rapid propagation of the temperature increase to the pole 34 of the varistor 30 after the temperature increase has reached the plate 34. The conducting plate can be made of copper. The connection of the protruding part forming the pole 34 to the rest of the plate 84 over at least half of the perimeter of the pole 34 ensures effective thermal conduction from the plate 84 towards the pole 34, despite the location of the areas of the block 80 having defects relative to the pole 34. Over time, a decrease in the reaction time of the varistor can be observed. This is the time that elapses between the first deteriorations of areas of the block 80 of the varistor and the temperature increase of the pole 34 of the varistor 30.
All of these embodiments forming the pole 34 have a connection with the rest of the plate over at least half of the perimeter of the pole 34.
For example, the part of the plate forming the connection pole can be connected to the rest of the plate 84 over at least 80%, for example, of its perimeter to ensure better thermal conduction.
In another example, the part forming the pole 34 can be connected to the rest of the plate 84 over its entire perimeter, as illustrated in
All of these embodiments of the part forming the pole 34 were obtained by drawing of the plate 84. Drawing is a manufacturing technique to obtain, from a planar and thin sheet of metal, an object whereof the shape cannot be developed. In the embodiment of
The formation of one of the poles of the varistor by drawing the plate 84 can establish continuity between the part of the plate arranged on the main face 82 of the block 80 and the drawn part.
The part of the plate 84 forming the pole 34 of the plate 84 can also be arranged at the central zone of the block 80 that corresponds to the central zone delimited by the imaginary circle 86 drawn in
The rest of the conducting plate 84 around the protruding part forming the pole 34 can be solid. The rest of the plate 84 then does not have any material recess or hole inside the surface delimited by its outer perimeter. By not having holes, the plate 84 can have a significant surface for picking up the temperature increase of the block 80 to improve the speed of the thermal disconnection. With the same aim, the surface of the plate 84 can be arranged to be in contact with the main face 82 of the block 80 to have an area that is at least half the area of the main face 82 of the block 80.
In an exemplary embodiment, the plate 84 can have a thickness smaller than or equal to 0.7 mm so as to limit the amount of material to be heated before the temperature increase reaches the pole 34. The plate 84 can preferably have a thickness greater than or equal to 0.3 mm, for example, to allow the plate to withstand the mechanical stresses as described in the present disclosure.
Another measure comprises (e.g., consists of) choosing, for the thermofusible braze 70, an alloy with a low melting temperature to establish a quick disconnection of the contact blade 44. A low melting temperature of the braze 70 can be used to quickly obtain a covering of the thermal disconnector. In an exemplary embodiment, the tin/indium alloy In52Sn18 can be used because it has a liquidus temperature at 118° C. while the alloys traditionally used have a liquidus temperature generally greater than 130° C. Moreover, this alloy complies with European directive 2002/95/CE, called RoHS (Restriction of the use of certain Hazardous Substances in electrical and electronic equipment).
Still another measure comprises (e.g., consists of) optimizing the shape of the connecting blade 44.
The surface of the part 42 can correspond to the section of the braze 70. The section of the braze 70 can be chosen as a function of the mechanical considerations described below.
The part 42, as well as the braze 70, can have a disc shape to allow better homogeneity of the heating of the braze 70. The part 42 can thus have an average diameter of this disc. In an exemplary embodiment, the local restriction 58 can have a length smaller than 80% of the average diameter of the part 42 to establish a sensitive concentration effect on the braze 70 of the heat given off by the varistor 30. In another exemplary embodiment, the local restriction can have a length smaller than 70% of the average diameter of the part 42. The length of the aforementioned local restriction 58 can extend by the shortest distance separating two opposite edges of a main face of the contact blade 44: this length is referenced ‘L’ in
The local restriction 58 can be arranged near the braze 70 to limit the losses of thermal energy between the local restriction 58 and the braze 70. The distance from the local restriction 58 to the braze 70 can be estimated by the ratio between the surface of the braze 70 (e.g. the section of the braze previously described) and the surface of the part 42 (shown by cross-hatching and to the right of the restriction 58 on
The exemplary characteristics previously described each can contribute to increasing the speed of the thermal disconnection, can be implemented independently of each other, in any suitable combination depending on the desired disconnection speed. These measures can be used to meet the specification of the UL standard paragraph 39 and/or of the UTE guide paragraph 6.7.4. Combining all of these measures can be used to meet the particularly strict specifications of the UL standard, paragraph 39.
In an exemplary embodiment, the protective device can be designed to have an improved interruption capacity. The improved interruption capacity can be useful both in the case of a thermal disconnection under nominal operating voltage and in the case of a surge such as in the tests of UL standard paragraph 39 and/or the UTE guide paragraph 6.7.4.
Different technical characteristics can contribute to obtaining an improved interrupting capacity.
Thus, the protective device can comprise a member for reducing or eliminating arcs forming during the movement of the contact blade 44 towards the open position. Such an arc reduction or elimination member can be useful for electrical installations powered with direct current. Such members are for example made up of electrical means (such as a capacitor 22), electronic means, electromechanical means (such as an arc extinction chamber), or mechanical means (such as an insulating flap inserted between the mobile contact and the fixed contact, by elastic stress or by gravity). When the capacitor 22 is used, it can be positioned parallel to the thermal disconnector to reduce the voltage of the electric arc forming during the movement of the contact blade 44 towards its open position. In this sense,
Moreover, as illustrated in
As illustrated in
Moreover, such a movement of the contact blade 44 in a plane parallel to the main face 32 can also allow obtaining a compact protective device that can be housed in the cartridge 20. In traditional solutions of thermal disconnectors formed by a disconnection contact blade, the movement of the contact blade towards the open position can be a movement in a direction perpendicularly to the main face of the protective component. In such devices, the increase of the disconnection distance goes through the increase of the thickness of the device (i.e. the dimension of the device in the direction perpendicular to a main face of the protective component), which damages its compactness.
The movement of the contact blade 44 parallel to the main face 32 of the varistor 30 can be confined in a volume having for base the main face 32 of the varistor and having a small thickness relative to the dimensions of the varistor. Such a movement of the blade 44 along the main face 32 of the varistor 30, and therefore having larger dimensions than the varistor 30, causes the possibility of obtaining a substantial interruption distance inside the volume confining the movement of the contact blade 44. The thickness of this volume being small, the compactness of the protective device can be close to the compactness of the varistor 30. This embodiment of the contact blade 44 can be particularly advantageous when the protective device comprises a second thermal disconnector on the same varistor as previously described. A compact design is then obtained according to
With reference to
The arrangement of the part of the plate 84 forming the pole 34 protruding and emerging from the electrically insulating coating ensures that the contact blade 44, forming the mobile contact, performs a movement towards the open position, in a manner parallel to the main face 32 of the varistor 30 while remaining at a distance from the insulating coating. The movement towards the open position is thus done without friction of the contact blade 44 on the insulating coating. The absence of friction of the contact blade 44 on the insulating coating can obtain a good disconnection speed without dragging liquefied residue from the braze 70 on the main face 32 of the varistor 30. In one example, a good disconnection speed of the thermal disconnector can contribute to improving the interruption capacity of the disconnector. In another example, preventing the formation of a trail of liquefied braze 70 can establish that the clearance procured by the thermal disconnector in the on state is indeed equal to the distance separating the contact blade 44 and the pole 34, thereby improving the interruption capacity.
The arrangement of the part of the plate 84 protruding to form the pole 34 can also electrically insulate the blade 44 from the electrically insulating coating without using an additional separating partition. The protective device can thus be made such that only an air blade separates the main face 32 from the contact blade 44 during its movement from the closed position towards the open position. The absence of an additional separating partition between the contact blade 44 and the main face 32 of the varistor 30 can further reduce the bulk of the protective device.
With the same aim of improving the interruption capacity, the part forming the pole 34 can have its braze surface at least 0.1 mm above the level of the electrically insulating coating. In an exemplary embodiment, the braze surface can be preferably situated at least, for example, 0.3 mm from the level of the electrically insulating coating.
In an exemplary embodiment, the electrically insulating coating can have a thickness between 0.1 mm and 1 mm. In another exemplary preferred embodiment, the thickness is greater than or equal to 0.6 mm to allow an improved electrical insulation of the varistor 30 relative to the rest of the protective device.
The previously described characteristics each contribute to increasing the interruption capacity. They can be implemented independently of each other, and in any combination depending on the desired interruption capacity.
The protective device can be designed to reliably withstand shock currents, for example, to pass the tests in standards IEC paragraph 7.6 or UL paragraph 37, or the UTE guide paragraph 6.6 depending on the case.
The production of the braze 70 in the plane of the main face 32 of the varistor 30 already described can withstand the electrodynamic stresses due to the lightning strike. The resistance of the braze 70 to the mechanical pulling out of electrodynamic forces can be adapted by increasing the section of the braze 70, for example, by increasing the surface of the braze 70 welded to the pole 34—(e.g., by increasing the brazing surface of the part forming the pole 34). In known solutions, the section of the brazing extends in a plane perpendicular to the main face of the protective component. The dimensioning of the section of the braze relative to the electrodynamic forces can cause an increase in the thickness of the entire protective device (i.e. in the direction perpendicular to the main face of the protective component). In the protective device proposed with the braze 70 made in the plane of the face 32 at the pole 34 arranged on the face 32, the increase in the section of the braze 70 is done along the plane of the face 32. The increase of the section of the braze 70 for resisting electrodynamic forces is not limited by the compactness requirement of the protective device. As a result, a section of the braze 70 that is larger than or equal to 50 mm2, for example, or even larger than or equal to 100 mm2, for example, can be obtained without affecting the compactness of the protective device to be housed in the cartridge 20 as previously described. Even for surfaces with a fairly substantial weld section, the speed of the disconnection can be satisfied with the different characteristics already described.
With reference to
The shearing stress of the braze 70 can eliminate problems encountered during a traction stress of the braze. Indeed, in a situation involving traction of the braze, the strains in the braze may not be uniformly distributed. The part of the braze with the strongest strains can deteriorate locally, creating a start of the braze that decreases the effective section of the braze faced with the traction. There is then a cleavage situation where the most stressed part of the braze can gradually cause the entire braze to be pulled out. The shearing stress of the proposed braze allows a more uniform distribution of the strains in the braze 70, avoiding a situation equivalent to traction cleavage.
In an exemplary embodiment the material of the bend 46 can have a low elastic resistance (Re). A low elastic resistance allows the bend 46 to absorb part of the energy by opening in a plastic manner. The absorption of part of the energy due to the electrodynamic effects can limit the stress of the braze 70. The elastic resistance can be approached by the plastic deformation strain at 0.2% (noted Rp0.2). When the material used for the bend is copper Cu-al as discussed in more detail below, the latter has an Rp0.2 that is low, e.g., 250 MPa (N·mm-2)).
The use of the tin/indium alloy In52Sn18 for the braze 70 can obtain a shearing resistance in the vicinity of 11.2 MPa (N·mm-2), which constitutes a good resistance compared to the alloys traditionally used for the braze. A known alloy such as Bi58Sn42 has a shearing resistance in the vicinity of only 3.4 MPa. As a result, the material contribution for the production of the braze 70 can be limited by decreasing the section of the braze 70 for example to an area of 25 mm2 while having a satisfactory mechanical shearing resistance.
As illustrated by
In an exemplary embodiment, the part 42 of the contact blade 44, intended to be welded to the pole 34 by the braze 70, can be tinned. The tinning of the part 42 can improve the quality of the braze causing better mechanical resistance thereof, for example, to the shock currents.
The exemplary characteristics previously described each contribute to increasing the mechanical resistance to shock currents while allowing a compact implementation of the protective device. They can be implemented independently of each other, and in any suitable combination depending on the desired mechanical resistance.
Due to the compactness, a varistor 30 with larger dimensions can be housed within cartridges having the dimensions mentioned relative to
According to an exemplary embodiment, as shown in
In an exemplary embodiment, the protective device can be designed to resist, in complete safety, the varistor 30 experiencing a short circuit under nominal operating voltage for the time that specific short circuit protection—such as a fuse or circuit-breaker outside the device—intervenes. For example, it is provided to be able to satisfy standard IEC paragraph 7.7.3. The difficulty comes from the fact that this external protection has a certain reaction time during which high currents pass through the protective device. The protective device should not explode or trigger a fire during that time.
To achieve this objective, the conductive pieces of the protective device are limited, for example, in its thermal disconnector. Indeed, the short circuit current can cause heating of these pieces by the Joule effect. Uncontrolled heating of the different pieces of the protective device can lead to the melting of one of the pieces, constituting a possible fire outbreak before the external devices cut the current.
Different characteristics contribute to limiting the heating of the pieces of the protective device.
Thus, as illustrated by
In an exemplary embodiment, the piece 40 can be made of copper with a sufficient purity to have an IACS (international annealed copper standard) conductivity greater than 70%. The IACS conductivity of a piece corresponds to the ratio between a resistivity of 1.7241 μΩ·cm and the resistivity of the piece, the IACS conductivity does not have dimensions. As a result, the piece 40 has a low electrical resistivity and therefore can establish the passage of the electrical current while limiting its heating. From this perspective, it can be advantageous for the purity of the copper to be such that its IACS conductivity is greater than or equal to 90%, or even 95%, for example. In another exemplary embodiment, copper such as Cu-al (or Cu-ETP are electrolyte copper), having a purity of 99.9%, and an IACS conductivity of 100% can be used. The electrical resistivity of the piece 40 can be less than or equal to 1.7241 μΩ·cm, for example, and limit the heating of the piece 40 subject to short circuit currents. In known solutions, contact blades were used with an intrinsic elasticity to form the mobile contact of the thermal disconnector. However, while copper alloys procure a sufficient intrinsic elasticity, this elasticity is to the detriment of the resistivity, which is substantially higher. In an exemplary embodiment, the protective device, uses an elastic stress outside the contact blade 44 (by the spring 50 in our example) to produce a contact blade 44 with copper having a sufficient purity to substantially limit its heating during short circuit tests.
In an exemplary embodiment, the piece 40 can have a minimal section provided to allow the continuous passage, without deterioration, of a short circuit current to which the protective device can be exposed. Moreover, in another exemplary embodiment, the piece 40 can have a thickness of 0.4 mm to 0.6 mm, for example, to provide the flexibility of the bend 46 discussed above. The thickness of the sheet used to obtain the piece 40 can be equal to 0.5 mm.
Moreover, the contact blade 44 can have, outside the part 42, a substantial heat exchange area with the ambient air, but without compromising the compactness of the device. Thus, the main faces of the contact blade 44 can extend parallel to the main face 32 of the varistor 30. The contact blade 44 thereby acts as a cooling fin, which further improves the resistance of the piece 40 to short circuit currents.
The piece 40 can include zones with a maximum section to dissipate the heat obtained by the Joule effect with a substantially constant thickness, which can increase the contact surface of the piece 40 with the ambient air and limit the heating during the passage of the short circuit current. The maximum section of the piece 40 can be provided at the contact blade 44, between the bend 46 on one hand and the part 42 on the other, or if applicable the constriction 58.
An increase in the width of the piece 40 can also be provided between the bend 46 and the terminal 48.
The fact that the contact blade 44 can be provided with an exchange surface limiting the heating of the piece 40 can locally decrease the minimum section of the piece 40 previously mentioned, given the temporary nature of the short circuit. It is thus possible to produce the restriction 58 with a length smaller than or equal to 5.5 mm, or even 5 mm, for example, while staying, at that location, below the minimum section of the piece 40 as previously defined.
In an exemplary embodiment, the material of the piece 40 can be bare at the broaching 48 to limit the weld effect with the elastic couplings of the base 82 through which the protective device is electrically connected to the electrical installation to be protected.
The exemplary characteristics described above can each contribute to increasing the resistance to short circuit currents, for example, as verified by standard IEC paragraph 7.7.3. These characteristics can be implemented independently of each other, and in any suitable combination depending on the significance of the short circuit currents likely to be provided by the supply grid of the installation to be protected.
According to an exemplary embodiment, two protective components can be provided in the same cartridge 20.
In the embodiments of
The production of each thermal disconnector in these embodiments with two protective components can be in accordance with the preceding description. The contact blades 44a or 44b can be made in a manner similar to the preceding description. With reference to
In these embodiments with two protective components 30 illustrated in
As illustrated in
The presence of this additional varistor in the same inner volume 21 of the cartridge 20 can establish the continuity of service and protection when one of the varistors, having reached the end of its life, has been disconnected. The disconnection of one of the varistors by a thermal disconnector can be indicated to the user of the electrical installation via a viewing element known in itself. The user is notified that one of the protective components of the cartridge 20 has reached the end of its life, with a function protecting against overvoltages still being ensured by the second varistor for the time it takes the user to replace the cartridge 20.
Owing to the compactness of the thermal disconnector previously described, the protective devices of
According to an exemplary embodiment, the thermal disconnector can be provided to include a plurality of varistors in the same protective component. These varistors can be connected serially and/or in parallel to each other depending on the applications. The varistors can then be assembled in a compact mass that comprises at least two varistors.
This exemplary embodiment of the protective component can be useful for protecting photovoltaic installations.
Other exemplary embodiments of the protective component 30 can include associating a larger number of varistors serially or in parallel. One embodiment of the protective component 30 can include (e.g., consist of) superimposing several blocks 80 having a non-linear electrical resistance by connecting the blocks 80 via electrodes 98 in a manner similar to the embodiment illustrated in
According to another exemplary embodiment, the protective device can have more than two terminals for connecting to the electrical installation to be protected. Such an embodiment of the disclosure, for example, corresponds to the use of the protective component 30 with a number of poles greater than two such as the embodiment described with reference to
The characteristics described above, considered all together or in any suitable combination as described, can produce devices for protecting against surges that can meet both the IEC and UL standards, as well as the UTE guide mentioned above. Each of these characteristics can, independently of the others or in combination, be implemented in the protective device according to the desired performance level. The protective device can produce benefits from the advantages associated with the characteristics previously described and that it incorporates.
These characteristics can be used to produce protective devices provided for a nominal operating voltage of up to 690V, for example, in alternating current under 50 Hz or 60 Hz and up to 895 V, for example, in direct current and having protection from lightning strikes with a nominal current (Imax) of 40 kA, for example, for a shock wave 8/20 according to the IEC standard and from lightning strikes with a nominal current (In) of 20 kA for a shock wave 8/20 according to the UL standard. These performances can be obtained with a single varistor chosen appropriately. The maximum nominal voltage can easily be increased by assembling one or several of these varistors serially.
Thus, it will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1052736 | Apr 2010 | FR | national |
