EP2375426B1 - Varistor including an electrode with jag portion forming a pole and lightning including such a varistor - Google Patents

Description

The present invention relates to the general technical field of equipment protection devices or electrical installations against overvoltages, especially against transient overvoltages, due for example to a lightning strike. The present invention relates more particularly to a device for protecting an electrical installation against transient overvoltages, such as a varistor arrester, for low voltage electrical installations.

It is known to ensure the protection of an electrical installation against overvoltages using devices including at least one overvoltage protection component, in particular one or more varistors and / or one or more spark gaps. For single-phase installations, it is usual to use a varistor connected between the phase and the neutral while a spark gap is connected between neutral and earth. For three-phase installations, it is usual to have varistors between the different phases and / or between each phase and the neutral and a spark gap between neutral and earth. For electrical installations operating under direct current, for example for installations of photovoltaic generators, it is also resorted to varistors and possibly spark gaps.

In case of failure of the protection component, these devices comprise a disconnection system for isolating the protection component of the electrical installation for safety. In particular, in the case of varistors, it is conventional to provide thermal protection. The thermal protection or thermal disconnector serves to disconnect the varistor of the electrical installation to be protected in case of overheating of the varistor, for example above 140 ° C. This excessive heating of the varistor is due to the increase of the leakage current - generally a few tens of milliamperes - through it because of its aging. In this case, it is called thermal runaway of the varistor.

The thermal disconnector is often a low temperature solder now in place a movable contact forming element through which the varistor is connected to the electrical installation, this conductive element being elastically constrained towards the opening. The fusion of the weld results in the displacement of the moving contact under the effect of the elastic stress, which causes the disconnection of the varistor. Thermal disconnectors of this type are described in particular in EP-A-0 716 493 , EP-A-0 905 839 and EP-A-0 987 803 .

These overvoltage protection devices, and in particular their thermal disconnector, can be confronted with various constraining situations during their use, which are dependent in particular on the type of electrical network to which they are connected.

First, their thermal disconnector must have a breaking capacity sufficient to effectively disconnect the protective component in case of thermal runaway thereof. This constraint is more delicate in the case of installations operating under direct current, since there is no periodic transition to zero voltage volt, as is the case in alternating current, contributing to the extension of the electric arc generated at the opening of the moving contact.

The electrical circuit of the protection devices must also be able to withstand the stresses resulting from electric shocks such as the lightning currents for which they are intended. These electrical shocks are transient overvoltages of large amplitude (several thousand volts) and short duration (from the microsecond to the millisecond). These overvoltages induce in particular electrodynamic forces and temperature rises which mechanically solicit the various conductive parts constituting the protection device. Despite these mechanical stresses, the electrical circuit ensuring the connection of the protective component to the electrical installation must remain closed. In particular, the mechanical stresses must not cause the opening of the thermal disconnector by tearing of the hot-melt solder. The ability of the device to meet this constraint is verified by the applicable standards, in particular for low-voltage AC installations, in section 7.6 ( load test ) of the standard IEC 61643-1, 2nd ed., 2005-03 (noted below IEC paragraph 7.6 ) or paragraph 37 ( Surge testing ) of the standard UL 1449, 3rd ed., 29.09.2006 (noted below UL paragraph 37 ). For direct current installations such as photovoltaic generator installations, for example, see section 6.6 ( Loaded operating tests ) of the photovoltaic guide. UTE C 61-740-51 of June 2009 (noted below UTE paragraph 6.6 ).

Furthermore, the electrical circuit of the protection device connecting the protection component to the electrical installation can be subjected to very high currents at the rated voltage of the electrical installation, especially in the case of installations supplied by the power supply network. AC voltage. This is the case when the varistor of the protection device experiences a failure by short circuit. In this case, disconnection of the faulty varistor is caused by specific protection against short circuits such as a fuse or circuit breaker. Given the reaction time of this specific protection, the electrical circuit the protection device, including the thermal disconnector, shall not cause a start of fire within this time, given the importance of the short-circuit currents supplied by the electrical supply network. The ability of the device to satisfy this constraint is verified for installations powered by low-voltage alternating current, for example in section 7.7.3 ( Short-circuit withstand ) of the standard. IEC 61643-1, 2nd ed., 2005-03 (noted below IEC paragraph 7.7.3 ).

The overvoltage protection device is still likely to be powered by a temporary overvoltage related to an anomaly in the power supply voltage of the electrical installation or in the event of a short-circuit failure of a varistor. there are at least two branches connected in series between the lines of the supply network. In such a case, the varistor becomes busy and likely to be traversed by a very high current given its low independence, current which is more or less the current short circuit that can provide the power supply network of the Electrical Installation. Faced with such a situation, the protective device should not cause a fire.

The ability of the protection device to satisfy this constraint is verified for low-voltage AC installations, for example in paragraph 39 ( Current testing ) of the standard. UL 1449, 3rd ed., 29.09.2006 (noted below UL paragraph 39) ), or for photovoltaic generator installations, for example in section 6.7.4 (end-of-life tests) of the photovoltaic guide UTE C 61-740-51 of June 2009 (noted below UTE paragraph 6.7.4 ).

US 2006245125 A1 The present invention relates to overvoltage protection devices for circuits and electrical equipment.

EP 2278605 A1 relates to a device for protecting an electrical installation against transient overvoltages, in particular due to lightning strikes

US 6252488 B1 relates to metal oxide varistors (MOVs) containing fusible materials which melt before the MOVs can start a thermal exhaust.

US 5781394 A relates to an overvoltage suppressor such as a metal oxide varistor (MOV) comprising a short-circuit mechanism.

DE 102008048644 A1 relates to an overvoltage protection device comprising one or more overvoltage limiting elements connected in parallel.

These protection devices must therefore, depending on the case, meet many constraints. The present invention aims above all to contribute to a reliable disconnection in case of thermal disconnection for surge protection devices to have a small footprint.

For this, the invention proposes a varistor according to claim 1.

According to a variant, said connection pole portion is connected to the remainder of the plate over at least 80% of its perimeter and more preferably over its entire perimeter.

According to a variant, said projecting portion forming a connection pole is formed by stamping the plate.

According to a variant, said brazing surface is located at least 0.1 mm, and more preferably at least 0.3 mm, above the level of the electrical insulation coating.

According to a variant, said projecting portion forming a connection pole is situated inside an imaginary circle centered on said main face of the block and having a diameter equal to 75% of the diameter of the inscribed circle of the main face of the block. .

According to a variant, the conductive plate is centered on said main face of the block.

According to a variant, the remainder of the conductive plate around the projecting portion forming a connection pole, is full.

Alternatively, the surface of the plate in contact with said main face of the block has an area that is at least half of the area of the main face of the block.

According to a variant, the brazing surface is parallel to said main face of the block.

Alternatively, the varistor is fully coated by the electrical insulation coating through which also emerges the other connection poles.

The invention further proposes a set of varistors assembled into a compact mass, comprising at least two varistors, at least one of which is the previous varistor, in which the two varistors are electrically connected to each other and have a common pole, the set of varistors being fully encapsulated by the electrical insulation coating through which the poles of connection of the varistors emerge.

The invention also proposes a device for protecting an electrical installation against transient overvoltages according to claim 11.

According to one variant, the device comprises at least two terminals for connecting the device to the electrical installation and in which the moving contact is a blade extending mainly in a plane parallel to said main face of the varistor block and mainly facing of this main face, the blade and one of the connection terminals forming part of one and the same piece.

According to one variant, the part of which the blade and said one of the two connection terminals have an IACS conductivity of greater than or equal to 70%, preferably greater than or equal to 90%, even more preferably greater than or equal to 95%.

Alternatively, the portion of the blade held on the brazing surface of said pole protruding portion is connected to the remainder of the blade by local restriction of the section of the blade to concentrate heat released by the varistor. one of the varistors of said assembly at the level of the hot-melt solder.

The invention further proposes a cartridge according to claim 15.

• figure 1, une vue en perspective d'une cartouche de protection d'une installation électrique basse tension, embrochée sur une embase montée sur un rail DIN ;
• figure 2, des vues de face et de profil avec cotes dimensionnelles de la cartouche de la figure 1, embrochée sur l'embase ;
• figure 3, un schéma de principe du volume intérieur défini par le boîtier de la cartouche de la figure 2 avec vues de profil et de face et munis de cotes dimensionnelles ;
• figure 4 , un schéma de principe illustrant à l'intérieur de la cartouche le contact mobile du dispositif de protection en position fermée ;
• figures 5 et 6, un schéma de principe de l'intérieur de la cartouche avec le boîtier de la cartouche ouvert illustrant le contact mobile du dispositif de protection en position ouverte et un schéma de la partie du boîtier enlevée ;
• figure 7, une vue de face de la varistance susceptible d'être logée avec le reste du dispositif de protection dans la cartouche de la figure 1 ;
• figures 8A, 8B ett 8C, une vue en perspective de différents modes de réalisation de l'électrode de la varistance ;
• figure 8D, une vue de profil de l'électrode de la varistance de la figure 8C ;
• figures 9 et 10, une vue de profil et en perspective de la pièce de contact électrique de la figure 6A ;
• figures 11A et 11B, une vue en coupe d'un mode de réalisation du dispositif de protection et son schéma équivalent électrique ;
• figures 12A et 12B, une vue en coupe d'un mode de réalisation du dispositif de protection avec déconnecteurs thermiques dédoublés et son schéma équivalent électrique ;
• figures 13A et 13B, une vue de face et de profil d'un composant de protection destiné à être logé dans le volume intérieur de la cartouche en figure 1 ;
• figures 14A, 14B, 14C, 15A, 15B et 16A, des vues de différents modes de réalisation du dispositif de protection avec deux composants de protection
• figure 16B, le schéma équivalent électrique du mode de réalisation de la figure 16A ;
• figure 17A et 17B, une application d'un mode de réalisation du dispositif de protection avec un composant de protection comprenant deux blocs non linéaires pour une installation photovoltaïque et une vue en coupe de ce mode de réalisation.

Other features and advantages of the invention will appear on reading the following detailed description of the embodiments of the invention, given by way of example only and with reference to the drawings which show:

• figure 1 , a perspective view of a protective cartridge of a low-voltage electrical installation, plugged on a base mounted on a DIN rail;
• figure 2 , front and side views with dimensional dimensions of the cartridge of the figure 1 , skewered on the base;
• figure 3 , a schematic diagram of the interior volume defined by the case of the cartridge of the figure 2 with side and side views and dimensional dimensions;
• figure 4 a block diagram illustrating inside the cartridge the movable contact of the protective device in the closed position;
• Figures 5 and 6 a schematic diagram of the interior of the cartridge with the open cartridge case illustrating the movable contact of the protection device in the open position and a diagram of the part of the housing removed;
• figure 7 , a front view of the varistor may be housed with the rest of the protective device in the cartridge of the figure 1 ;
• Figures 8A, 8B andt 8C, a perspective view of various embodiments of the varistor electrode;
• figure 8D , a profile view of the electrode of the varistor of the Figure 8C ;
• Figures 9 and 10 , a profile and perspective view of the electrical contact piece of the Figure 6A ;
• Figures 11A and 11B , a sectional view of an embodiment of the protection device and its electrical equivalent diagram;
• Figures 12A and 12B , a sectional view of an embodiment of the protection device with split thermal disconnectors and its electrical equivalent diagram;
• Figures 13A and 13B , a front and side view of a protective component intended to be housed in the interior volume of the cartridge in figure 1 ;
• Figures 14A, 14B, 14C , 15A, 15B and 16A , views of different embodiments of the protective device with two protective components
• figure 16B , the electrical equivalent diagram of the embodiment of the figure 16A ;
• Figure 17A and 17B , an application of an embodiment of the protection device with a protection component comprising two non-linear blocks for a photovoltaic installation and a sectional view of this embodiment.

The invention relates to a varistor, comprising at least two connection poles and a block having a non-linear electrical resistance whose value varies as a function of the voltage applied to the two connection poles. The block is for example based on metal oxide, the varistor then forms a varistor metal oxide called MOV (of the English Metal Oxide Varistor). The varistor further comprises a conductive plate forming a contact electrode with the block, said conductive plate being arranged on a main face of the block. This conductive plate has a projecting portion forming one of the connection poles of the varistor. In other words, the projecting part forming one of the poles is not an insert on the conductive plate, but on the contrary, the projecting part forming one of the poles comes from material with the rest of the conductive plate. Thus the protruding portion and the conductive plate are part of one and the same piece.

The varistor further comprises an electrical insulation coating applied at least on the assembly formed by the main face of the block on which the conductive plate is arranged. Furthermore, the protruding plate part forming a connection pole emerges out of the electrical insulation coating. This pole portion then has a solder surface that extends above the level of the electrical insulation coating for electrical connection of the pole. In addition, said projecting portion forming a connection pole is connected to the remainder of the plate over at least half of its perimeter.

The above varistor can be used as a protection component of a protection device of an electrical installation against transient overvoltages which can advantageously have the following characteristics. It comprises, in addition to the varistor, a thermal disconnector, comprising a movable contact capable of passing from a closed position to an open position to disconnect the varistor.

The movable contact of the thermal disconnection is held in the closed position by a hot melt solder fixing the movable contact on the protruding portion brazing surface forming a connection pole of the varistor. The thermal disconnector is then provided to move the movable contact into the open position when the hot melt solder melts. Finally the movable contact is provided to move from the closed position to the open position, parallel to said main face of the block of the varistor and away from the electrical insulation coating of the varistor.

The movement of the movable contact parallel to the main face of the block of the varistor provides a small footprint of the protection device, as demonstrated later in the description.

The arrangement of the pole protruding and emerging from the electrical insulation coating ensures that the moving contact, initially in the closed position ie welded to the brazing surface of the pole, performs the movement parallel to the main face of the block of the varistor while remaining away from the insulating coating. Thus the movement towards the open position takes place without friction of the contact mobile on the electrical insulation coating which improves the breaking capacity, as demonstrated in more detail later in this document. The arrangement of the pole protruding and emerging from the electrical insulation coating of the varistor thus allows the protection device to benefit from an improved breaking capacity in a small footprint.

Linking the pole portion to the remainder of the plate over at least 50% of the perimeter of the pole provides effective thermal conduction from the plate to the pole. Thus the varistor described above leads to an improvement in the reaction time of the varistor, which is the time elapsing between the beginning of the heating of the varistor and the temperature increase of the pole of the varistor. The improvement of this reaction time limits the current flowing through the varistor at the time of the thermal disconnection to a leakage current of the varistor not having too much intensity compared to the improved breaking capacity of the device.

The arrangement of the pole projecting and emerging from the electrical insulation coating of the varistor with a link to the remainder of the plate on at least half of the perimeter of the pole makes it possible to obtain that the protection device has, in a small space, a breaking capacity sufficient to cut the electric currents passing through the varistor at the time of the thermal disconnection. The varistor thus ensures reliable disconnection in the event of thermal disconnection for overvoltage protection devices having a small footprint.

The figure 1 represents in perspective a protective cartridge 20 of a low voltage electrical installation. The protective cartridge 20 comprises the protection device described above. This protective cartridge 20 is plugged into a base 82 intended to be mounted on a standard DIN panel rail. The racking of the cartridge 20 on a base 82 facilitates the connection of the protective device to the low voltage electrical installation to be protected. As standard, a low-voltage electrical installation is understood to mean rated rated equipment up to 1000 V AC or up to 1500 V DC. Fixing on a DIN rail is standard for such electrical installations. The overvoltage protection device described is also suitable for the protection of photovoltaic generator installations.

The common use of DIN rail cartridges and bases, in the low voltage field, imposes a compact design constraint on overvoltage protection devices. The Figures 2A and 2B respectively illustrate one of the main faces of the cartridge 20 and the edge of the cartridge 20. The cartridge 20 intended to house the protection device has outside dimensions AxBxC less than or equal to 57 x 50.5 x 17.6 mm.

The Figures 3A and 3B schematically illustrate the internal volume 21 defined by the housing of the cartridge 20 housing the protective device. The figure 3A shows a section of the housing according to one of the main faces of the housing. The figure 3B shows a section of the case according to the edge of the case. The cartridge 20 intended to house the protection device, thus has an internal parallelepipedal volume 21 having dimensions C'xA'xB 'less than or equal to 15 x 42 x 43 mm.

In the following are described various features of the protective device for obtaining a compact protective device capable of being housed in the interior volume 21 defined above.

According to figure 4 , the cartridge 20 houses the protective device comprising a varistor 30 as a protective component and a conductive blade 44 forming a moving contact of a thermal disconnector. Alternatively the movable contact can be formed by a braid or a wire, to ensure the connection of the protective component to the electrical installation. The protection device 30 comprises two terminals 38 and 48 for connecting the device to the electrical installation. The varistor 30 has two poles each connected to a respective one of the terminals 38 and 48. The figure 4 represents the protection device with the blade 44 in the closed position, the blade 44 being electrically connected to the pole 34 (visible on the figure 5 ) of the varistor 30. The pole 34 thus constitutes a fixed contact of the thermal disconnector. The pole 34 is connected to the terminal 48 by means of the blade 44. Furthermore, the blade 44 is biased elastically by a torsion spring 50. The connection of the terminals 38 and 48 to the electrical installation to be protected is carried out, in this example, via the base 82 previously described with reference to the figure 1 . The terminals 38 and 48 may take the form of male terminals as pins. The figure 5 represents the same protection device with the blade 44 in the open position. The blade 44 is then disconnected from the pole 34 of the varistor 30. In this position, the pole 34 of the varistor 30 is no longer connected to the terminal 48.

The Figures 5 and 6 illustrate cartridge 20 of the figure 1 with the housing 20 of the cartridge open. The housing is composed of an upper flange 23 represented in figure 6 and a lower flange 24 shown in figure 5 . The compactness of the protective device allows forming with the lower flange 24 an "equipped cradle". The figure 5 represents the blade 44 in the disconnected state.

The thermosensitive element of the thermal disconnector is a hot-melt solder 70 by which the blade 44 is at the pole 34 of the varistor 30. This solder is still visible on the pole 34 of the varistor 30 on the figure 5 . The solder 70 provides the electrical connection between the blade 44 in the closed position and the terminal 34 until the protective component 30 reaches the threshold temperature (e.g. 140 ° C) which is indicative of a failure of the varistor 30. When the varistor 30 reaches the threshold temperature, the solder 70 melts and the end of the blade 44 which was connected to the pole 34 of the varistor 30, away from the latter under the action of the spring 50. Therefore, the electrical connection between the blade 44 and the pole 34 is broken.

It is desirable to provide that the protective device can cope with temporary overvoltages without risk of explosion or fire, at least if the protective device is likely to be subject to such surge conditions temporary. In particular, it may be designed to meet the tests required by UL paragraph 39 or UTE 6.7.4. For this, the applicant recommends an approach to ensure a very rapid thermal disconnection of the varistor 30. Indeed, in these situations of temporary overvoltages, the current through the varistor increases gradually until the varistor goes short circuit franc.

The passage time of the varistor 30 in short circuit depends in particular on the ratio between the temporary overvoltage and the maximum permissible operating voltage by the varistor and the electrical behavior of the varistor (variation of the resistivity of the varistor as a function of the voltage applied to it). On the one hand, when the ratio between the temporary overvoltage and the maximum permissible voltage of the varistor 30 is high, the passage time of the short-circuited varistor 30 is small. On the other hand, when the behavior of the varistor is very strongly non-linear (the resistivity of the varistor varies very sharply with the increase in the voltage applied to it), the passage time of the varistor 30 shorted is low. It is then possible to choose the varistor according to these different characteristics to increase the free-passage time in the operating conditions of the varistor. The transient phase of current increase is accompanied by an increase in temperature of the varistor 30, during the passage time of the varistor in short circuit. The thermal disconnector is designed to disconnect in the transient phase the behavior of the varistor before the current flowing through it becomes too high to be cut by the thermal disconnector. This implies a quick detection of the increase of the temperature of the varistor.

Different technical characteristics contribute to obtaining this quick disconnect.

Thus, the pole 34 is preferably arranged on one of the main faces of the protection component 30. Such a main face of the protection component is represented by the shaded area 32 on the Figures 4 and 5 . The figure 7 shows the varistor 30 viewed perpendicularly to the plane of its main face 32. The pole 34 is advantageously disposed inside a central zone on the main face 32. This central zone is represented fictitiously by a circle 86 dotted on the figure 7 . The central zone may thus be located inside an imaginary circle 86 centered on said main face 82 of the block 80 and having a diameter equal to 75% of the diameter of the inscribed circle of the main face 82 of the block 80. the pole 34 on the main face 32 in the central zone ensures rapid capture by the hot melt solder 70 of the increase in the temperature of the varistor 30 during the transient phase where the current flowing therethrough. Indeed, the runaway of the varistor 30 causes an increase in temperature first in the deteriorated areas of the varistor 30. These deteriorated areas correspond to areas of the varistor 30 with uncontrolled design defects. The location of these zones is not known a priori , so that the thermal runaway of the varistor begins in an indeterminate zone. The arrangement of the pole 34 in the central zone thus ensures that the pole 34 is statistically closest to the zone where the thermal runaway of the varistor begins.

Then, the pole 34 of the varistor 30 may advantageously extend along the main face 32, and not projecting perpendicular thereto. Thus the solder 70 is formed on the pole 34 at a brazing surface which is parallel to the main face 32 of the varistor 30. The solder 70 then has its thickness in the direction perpendicular to the main face of the protective component . Consequently, the solder assembly 70 is as close as possible to the varistor 30 and provides it with instantaneous communication of the temperature of the varistor 30. This measurement is advantageous compared with conventional solutions in which the pole of the protection component forming a fixed contact of the thermal disconnection extends in a plane perpendicular to the main face of the protection component. The solder is then made in this perpendicular plane and a portion of the solder is kept away from the protective component. When the protection component fails, the solder is first thermally stressed in its near part of the protective component, the increase in temperature of the varistor arriving with a delay at the part of the solder furthest from the component of the protection 30, which has the disadvantage of slowing the thermal disconnection.

Furthermore, the speed of the thermal disconnection can be further improved by the design of the varistor 30, more precisely by the design of its electrode forming the pole of the varistor which serves to transmit the heat released by the varistor to the thermosensitive element thermal disconnector.

From this point of view, it is advantageous that the electrode of the varistor is formed by a conductive plate 84, represented in FIG. figure 7 . The varistor 30 then further comprises a block 80, whose figure 7 shows only the main face 82. The block 80 has an electrical resistance whose value varies as a function of the voltage applied to the block 80. This block 80 constitutes the active part of the varistor 30 and makes it possible to limit the overvoltages by exhibiting a resistance. low for overvoltages of strong amplitudes such as those occurring during lightning strikes. The conductive plate 84 is arranged on a main face 82 of the block 80. The main faces of the block 80 correspond to the main faces of the varistor 30. The plate 84 has a projecting portion forming one of the poles 34 of connection of the varistor. In other words, the protruding portion forming one of the poles 34 is not an insert on the conductive plate 84, but instead, the protruding portion forming one of the poles 34 is made of material with the rest of the plate Conductive 84. Thus the projecting portion and the conductive plate are part of a single piece. Similarly, a second pole 36 of the varistor 30 may be constituted by a projecting portion of a conductive plate arranged on another main face of the block 80, the varistor 30. In the remainder of the document, only the constitution of the pole 34 by the projecting portion of the plate 84 is described.

The varistor 30 then comprises an electrical insulation coating applied to the assembly formed by the main face 82 of the block 80 and the plate 84. The assembly formed by the main face 82 of the block 80 and the plate 84 is thus isolated electrically from its surrounding environment, including the movable contact of the protective device. Preferably the assembly formed of the block 80 and the plate 84 are entirely covered by the electrical insulation coating through which the different connection poles of the varistor also emerge to allow an electrical connection to be made with the rest of the device. protection, particularly with blade 44.

The projecting portion forming the pole 34 may emerge out of the electrical insulation coating so as to allow an improvement in breaking capacity as described in more detail later in this document.

The projecting portion forming the pole 34 may be connected to the rest of the plate 84 on at least half of its perimeter so as to improve the speed of the disconnection. Indeed, during the deterioration of the varistor 30 subjected to temporary overvoltages, the leakage current of the varistor 30 increases until the varistor 30 passes in short-circuit franc. This transient phase of increase of leakage current is accompanied by an increase in temperature of the varistor 30. This temperature increase is gradual. The temperature first increases at the heart of block 80 of the varistor 30 in areas with inhomogeneities. The increase in temperature then propagates by conduction throughout the block 80 of the varistor to the outer faces of the block and in particular to the main face 82 of the block 80. The arrangement of the conductive plate 84 on the main face 82 of block 80 allows a minimum propagation time of the temperature increase from the defective zones of the block 80 to the electrode plate 84 of the varistor 30. On the one hand the plate 84 is electrically conductive allowing the plate to form an electrode. On the other hand, the plate 84 is thermally conductive to ensure a rapid propagation of the rise in temperature to the pole 34 of the varistor 30 after the temperature rise has reached the plate 34. The conductive plate is advantageously made of copper. The connection of the protruding portion forming the pole 34 to the remainder of the plate 84 over at least half of the perimeter of the pole 34 ensures an effective thermal conduction from the plate 84 to the pole 34, and whatever the location of the zones of the block 80 having defects with respect to the pole 34. Finally the varistor previously described allows a reduction in the reaction time of the varistor, which is the time between the first deteriorations of zones of the block 80 of the varistor and the temperature rise of the pole 34 of the varistor 30.

The figure 8A illustrates a possible embodiment of the pole portion 34. This pole portion 34 is connected to the remainder of the plate 84 on its dimension sides D. The dimension sides E of the pole portion 34 have been cut from the plate 84 and then not participate in thermal conduction.

The Figure 8B , illustrates another possible embodiment of the pole portion 34. In this embodiment, the pole portion 34 is disposed on the edge of the plate 84.

All these embodiments of the pole portion 34 have a connection with the remainder of the plate over at least half of the perimeter of the pole 34.

Advantageously, the part of the connection pole plate is connected to the remainder of the plate 84 over at least 80% of its perimeter to ensure better thermal conduction.

Even more preferably, the pole portion 34 may be connected to the remainder of the plate 84 throughout its perimeter, as illustrated by FIG. Figure 8C . The heat, due to the temperature increase of the block 80 and captured by the plate 84, is then thermally conducted at the pole 34 by the entire of its perimeter. Thermal transfer and speed of disconnection are improved.

All these embodiments of the pole portion 34 have been obtained by stamping the plate 84. The stamping is a manufacturing technique for obtaining, from a flat sheet of thin sheet metal, an object whose form is not developable. In the embodiment of the figure 8A , the plate 84 has been cut beforehand so as to facilitate the deformation of the plate 84.

The formation of one of the poles of the varistor plate stamping 84 ensures a continuity of material between the portion of the plate arranged on the main face 82 of the block 80 and the stamped portion.

The part of the plate 84 forming pole 34 of the plate 84 can also be arranged at the central zone of the block 80 which corresponds to the central zone delimited by the circle 86 represented in FIG. figure 7 , allowing a speed of disconnection as previously demonstrated. For a similar purpose, the conductive plate 84 may be centered on said main face 82 of the block 80.

The remainder of the conductive plate 84 around the projecting pole portion 34 may be solid. The remainder of the plate 84 then has no recess material or hole inside the surface delimited by its outer perimeter. Being free of holes, the plate 84 has a large sensing surface of the temperature increase of the block 80 to improve the speed of the thermal disconnection. For the same purpose, it can also be provided that the surface of the plate 84 arranged in contact with the main face 82 of the block 80 has an area which is at least half the area of the main face 82 of the block 80.

The plate 84 preferably has a thickness less than or equal to 0.7 mm so as to limit the amount of material to be heated before the increase in temperature reaches the pole 34. The plate 84 preferably has a greater thickness or equal to 0.3 mm so as to allow the plate to withstand the mechanical stresses mentioned later in this document.

Another measure is to choose for the hot-melt solder 70 a low-melting temperature alloy to ensure rapid disconnection of the blade 44. A low melting temperature of the solder 70 allows to quickly obtain an opening of the thermal disconnector. The tin / indium alloy In ₅₂ Sn ₄₈ is particularly preferred because it has a liquidus temperature at 118 ° C., whereas the alloys conventionally used have a liquidus temperature that is generally greater than 130 ° C. In addition, this alloy complies with the European RoHS Directive 2002/95 / EC ( Restriction of the use of certain Hazardous Substances in Electrical and Electronic Equipment ).

Yet another measure is to optimize the shape of the blade 44. Figures 9 and 10 illustrate, respectively seen in profile and in perspective, a preferred embodiment of the blade 44 of the figure 5 . The blade 44 has a portion 42 intended to be welded to the pole 34 by the solder 70. The portion 42 is connected to the remainder of the blade 44 by a local restriction 58 of the section of the blade 44. This restriction 58 of the blade 44 allows to concentrate the heat released by the protective component 30 at the portion 42 - and therefore at the level of the solder 70 - because the diffusion of heat from the portion 42 to the rest of the blade 44 is limited by the local restriction 58. As a result, the increase in temperature of the solder 70 is faster during the temperature increase of the varistor 30. The speed of the opening of the thermal disconnector is increased.

The surface of the portion 42 advantageously corresponds to the section of the solder 70. The section of the solder 70 is chosen according to the mechanical considerations mentioned below.

The portion 42, as well as the solder 70 preferably have a disc shape to allow a better homogeneity of the heating of the solder 70. The portion 42 can thus be characterized by a mean diameter of this disc. It is preferable that the local restriction 58 has a length of less than 80% of the average diameter of the portion 42 to provide a substantial concentration effect on the solder 70 of the heat emitted by the varistor 30. It is even more advantageous than the restriction The length of the local restriction 58 referred to above is the smallest distance separating two opposite edges of a main face of the blade 44: this length is less than 70% of the average diameter of the portion 42. referenced 'L' on the figure 9 .

The local restriction 58 is disposed near the solder 70 so as to limit the thermal energy losses between the local restriction 58 and the solder 70. The distance from the local restriction 58 to the solder 70 can be estimated by the ratio between the surface of the solder 70 (i.e., the section of the solder previously described) and the surface of the portion 42 (represented by hatching and to the right of the restriction 58 on the figure 9 ). This ratio is preferably greater than 70%, and more preferably greater than 80%.

The previously described features each contribute to increasing the speed of thermal disconnection. They can be implemented independently of one another. It is possible to use only some of them or all according to the desired speed of disconnection. These measures make it possible in particular to meet the requirements of UL paragraph 39 and / or UTE 6.7.4. The fact of combining all these measures is particularly advantageous in the case where the protection device is designed to meet the particularly stringent requirements of the UL paragraph 39 standard.

The protection device is also advantageously designed to have an improved breaking capacity. Such improved breaking capacity can be useful both in the case of a thermal disconnection at the nominal voltage only in the case of a temporary overvoltage as in the tests of the UL standard paragraph 39 and / or the UTE guide paragraph 6.7.4.

Different technical characteristics contribute to obtaining an improved breaking capacity.

Thus, the protection device may comprise an arc reduction or suppression member that is formed during blade movement 44 to the open position. Such an arc reduction or suppression device is particularly useful for electrical installations powered by direct current. Such members are for example constituted by electrical means (such as a capacitor 22), electronic means, electromechanical means (such as an arc extinguishing chamber), or mechanical means (such as an insulating shutter coming from interpose between the movable contact and the fixed contact, by elastic stress or by gravity). When the capacitor 22 is used, it is arranged in parallel with the thermal disconnector to reduce the voltage of the electric arc formed during the displacement of the blade 44 to the open position. In this sense, Figure 11B represents the electrical diagram corresponding to the protective device of the figure 11A which represents it schematically in cross section.

Then, for DC or AC powered installations, the protection device may have a second thermal disconnector as illustrated by the Figure 12A and 12B . The second disconnector is formed of a movable contact 64 and a fixed contact 36 on the same varistor 30. The fixed contact 36 corresponds to the figure 12A at the second pole of the varistor 30. The movable contact 64 can be made by a blade similar to the blade 44 of the first thermal disconnector. In accordance with Figures 12A and 12B , the protection component is associated with the two thermal disconnectors, that is to say that the two thermal disconnectors and the protective component are connected in series. Thus, the presence of the second thermal disconnector on the same varistor makes it possible to increase the breaking capacity of the proposed protection device, since the isolation distances between the moving contact and the fixed contact (s) of the two thermal disconnectors come from add up. In this embodiment, the disconnection of the first thermal disconnector is followed by the disconnection of the second thermal disconnector only when the electric current continues to flow through the protection component despite the first disconnection. Alternatively, the two thermal disconnectors can be mechanically interconnected to coordinate the disconnection of the second disconnector and the disconnection of the first disconnector. The mechanical coordination of the two thermal disconnectors is for example carried out using a mechanical coordination member or mechanism. made of insulating material. As illustrated by figure 12B which represents the equivalent electrical scheme of the protection device of the figure 12A capacitors 22 in parallel with each of the thermal disconnectors may also be provided in order to further improve the breaking capacity.

Moreover, as illustrated on the figure 5 , the protection device may comprise a torsion spring 50 for elastically biasing the blade 44 from the closed position to the open position. In such an embodiment, when the varistor 30 reaches the threshold temperature, the solder 70 melts and releases the blade 44 which is driven to the open position due to elastic biasing by the spring 50. The use of a 50 separate spring blade 44 allows a calibration of the opening speed of the blade 44 and a precise orientation of the biasing force of the blade 44. In conventional systems, the movable contact blades of a thermal disconnector are elastically stressed because of the intrinsic elasticity of the blades. The elasticity is intrinsically linked to the blade, so it is difficult to predict a large opening speed of the blade without changing the geometry of the blade. In the protective device proposed with the spring 50, the spring 50 can be sized to drive the blade 44 to the open position with a large opening speed without changing the blade geometry 44 which can then be defined solely according to the other considerations. Furthermore, the choice of a high opening speed of the thermal disconnector increases the breaking capacity of the disconnector.

As illustrated in Figures 9 and 10 , the blade 44 comprises a support 56 for the spring 50, for transmitting the bias of the spring 50 to the blade 44. As illustrated in FIGS. Figures 4 and 5 , the blade 44 extends in a first plane parallel to the main face 32 of the varistor 30 with a movement of the blade 44 between the closed position and the open position taking place mainly in this first plane. With reference to the figure 5 it is thus possible to obtain a large isolation distance D between the moving contact - that is to say the blade 44 - and the fixed contact - that is to say the pole 34 - of the thermal disconnector. Thus the insulation distance for a thermal disconnector can be substantially greater than 5 mm and reach at least 10 mm.

In addition, such a movement of the blade 44 in a plane parallel to the main face 32 also makes it possible to obtain a compact protection device that can be accommodated in the cartridge 20. In conventional solutions of thermal disconnectors consisting of a blade of disconnection, the movement of the blade to the open position is a movement carried out perpendicularly to the main face of the protective component. In such devices, the increase in the disconnection distance is achieved by increasing the thickness of the device (i.e. the dimension of the device in the direction perpendicular to a main face of the protection component), which affects its compactness.

The movement of the blade 44 parallel to the main face 32 of the varistor 30 is confined in a volume based on 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 thus having the largest dimensions of the varistor 30, results in the possibility of obtaining a large breaking distance inside the volume confining the movement. of the blade 44. The thickness of this volume being small, the compactness of the protective device is close to the compactness of the varistor 30. This embodiment of the blade 44 is particularly advantageous when the protective device comprises a second disconnector thermal on the same varistor as previously described. This second thermal disconnector is then connected in series to the first thermal disconnector via the varistor. We then obtain a compact design in accordance with the figure 12A .

With reference to the figure 8D and as previously described, the electrode 84 of the varistor 30 may advantageously have the protruding part forming pole 34. This pole portion 34 emerges out of the electrical insulation coating such as the brazing surface for the electrical connection of the pole and stamped extends above the level of the electrical insulation coating, as represented by the figure 12A .

The arrangement of the portion of the pole plate 84 projecting and emerging from the electrical insulation coating ensures that the movable contact blade 44 moves to the open position parallel to the main face 32 of the varistor 30 while remaining at a distance from the insulating coating. The movement to the open position is thus performed without friction of the blade 44 on the insulating coating. The absence of friction of the blade 44 on the insulating coating provides a good speed of disconnection without trailing liquefied residue of solder 70 on the main face 32 of the varistor 30. On the one hand a good speed of disconnection thermal disconnector contributes to the improvement of the breaking capacity of the disconnector. On the other hand, the prevention of the formation of a liquefied solder streak 70 makes it possible to ensure that the insulation distance provided by the thermal disconnector in the open state is effectively equal to the distance separating the blade 44 and pole 34, thus improving the breaking power.

The arrangement of the portion of the plate 84 projecting to form the pole 34 furthermore makes it possible to isolate the blade 44 electrically from the insulation coating. electric without using an additional partition. The protection device can thus be made so that only an air gap separates the main face 32 of the blade 44 during its movement from the closed position to the open position. The absence of additional partition between the blade 44 and the main face 32 of the varistor 30 further reduces the size of the protective device.

For the same purpose of improving the breaking capacity, the pole portion 34 has its brazing surface at least 0.1 mm above the level of the electrical insulation coating. Even more preferably, the brazing surface is at least 0.3 mm from the level of the electrical insulation coating.

The electrical insulation coating preferably has a thickness of between 0.1 mm and 1 mm. Even more preferably, the thickness is greater than or equal to 0.6 mm to allow improved electrical insulation of the varistor 30 relative to the remainder of the protection device.

The characteristics described above each contribute to increasing the breaking capacity. They can be implemented independently of one another. It is possible to use only some of them or all according to the desired breaking capacity

The protective device is still advantageously designed to reliably withstand the shock currents, in particular to meet the tests of IEC standards paragraph 7.6 or UL paragraph 37, or the UTE paragraph 6.6 guide as appropriate.

The realization of the braze 70 in the plane of the main face 32 of the varistor 30 already described effectively withstands the electrodynamic forces due to lightning shock. The resistance of the solder 70 to the mechanical tearing of the electrodynamic forces can be adapted by increasing the cross section of the solder 70, more particularly by increasing the surface of the solder 70 welded to the pole 34 - that is to say by increasing the brazing surface of the pole portion 34 -. In conventional solutions, the brazing section extends in a plane perpendicular to the main face of the protection component. Sizing the section of the solder relative to the electrodynamic forces causes an increase in the thickness of the entire protective device (that is to say in the direction perpendicular to the main face of the protective component). In the protective device proposed with the solder 70 made in the plane of the face 32 at the pole 34 disposed on the face 32, the increase in the section of the solder 70 is in the plane of the face 32. L increase of the section of solder 70 for resistance to efforts electrodynamics is then limited by the requirement of compactness of the protective device. One can thus choose to obtain a section of the solder 70 greater than or equal to 50 mm ² , or even greater than or equal to 100 mm ² without impacting the compactness of the protection device to be housed in the cartridge 20 as previously defined. Even for surfaces of weld section as important, the speed of the disconnection is satisfactory with the various features already described.

With reference to the figure 9 , the blade 44 may be integral with a flexible portion 46. This flexible portion 46 forms a bend 46 (or a lyre) about an axis perpendicular to the plane of the figure 9 . This bend 46 allows movement of the blade 44 between the open position and the closed position. In the event of shock currents flowing through the protection device, the electrodynamic forces bias the opening of the flexible elbow 46. Such an opening urging of the elbow 46 causes a biasing of the blade 44 to the open position. In other words, the electrodynamic forces stress the solder 70 in shear. However, as described above, the solder 70 can be sized to withstand stresses such as shearing without deteriorating the compactness of the device. The flexible elbow 46 thus contributes to both the compactness of the protective device and its resistance to shock currents.

The shearing stress of the solder 70 also makes it possible to overcome problems encountered during a tensile stressing of the solder. Indeed in a tensile situation of the solder, the stresses in the solder may not be evenly distributed. The portion of the braze with the highest stresses then begins to deteriorate locally creating a start of the braze which decreases the effective section of the solder facing the traction. It is then in a situation of cleavage where the most stressed portion of the solder gradually causes tearing of all the solder. The shear stress of the proposed solder allows a more uniform distribution of the stresses in the solder 70 avoiding a situation equivalent to the tensile cleavage.

The elbow material 46 preferably has a low elastic resistance (Re). A low elastic resistance allows the bend 46 to absorb some of the energy by opening plastically. The absorption of a portion of the energy due to the electrodynamic effects makes it possible to limit the stress on the solder 70. The elastic resistance is conventionally approached by the plastic deformation stress at 0.2% (denoted Rp0.2). When the material used for the elbow is Cu-a1 copper as discussed in more detail later, the latter has an advantageously low Rp0.2, namely 250 MPa (N.mm ^-2 ).

The use of the tin / indium alloy In ₅₂ Sn ₄₈ for the solder 70 makes it possible to obtain a shear strength of the order of 11.2 MPa (N.mm ^-2 ). is a good resistance compared to the alloys conventionally used for brazing. Thus a conventional alloy such as Bi ₅₈ Sn ₄₂ has a shear strength of the order of 3.4 MPa only. Consequently, it is possible to limit the supply of material for producing solder 70 by reducing the section of solder 70, for example to a surface area of 25 mm ² while having a satisfactory mechanical shear strength.

As illustrated on Figures 9 and 10 , the blade 44 may comprise a stiffening zone 52 of the part 40. The bending inertia of the blade 44 is thus increased so that the biasing engagement of the blade 44 by the spring 50 or by the electrodynamic forces is substantially exclusively pure shear. The sizing of the solder 70 for the resistance to the shock currents is thus facilitated. However, a low flexural inertia can be provided between the portion 42 of the blade 44 which is welded to the pole 34 and the restriction 58. This makes it possible to compensate for the dimensional clearances during the assembly of the different parts of the protection device without having to deform the blade 44 to weld it to the pole 34.

The portion 42 of the blade 44, intended to be welded to the pole 34 by the solder 70, is preferably tinned. The tinning of the portion 42 allows an improvement in the quality of the solder resulting in a better mechanical strength thereof, including impact currents.

The previously described characteristics 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 one another. It is possible to use only some of them or all according to the desired mechanical strength.

Because of the compactness, a varistor 30 with larger dimensions can be accommodated within cartridges of the dimensions mentioned in relation to the FIGS. 2A, 2B, 3A and 3B . In particular, the varistor 30 may have a greater thickness, which allows a service voltage of the higher varistor. In other words, the protection device can be adapted for an installation operating at a higher voltage, for example between 500 and 1000 V in the case of installations with photovoltaic generators to be compared with the 230 V or 400 V usual for the networks of alternative power supply in Europe. The Figures 13A and 13B respectively illustrate front and side, the dimensions A ", B", C "of a varistor 30 which can be accommodated in the cartridge 20 with the rest of the proposed compact protection device.The dimensions A" and B "of the varistor 30 is typically 35mm.) The varistor 30 can have a thickness C "up to 9mm. The varistor 30 with a thickness of 9 mm has an operating voltage of the order of 680 V and exhibiting a leakage current of the order of 1 mA. under a voltage of 1100 V DC. The compactness of the protection device then makes it possible to use it for a voltage range of 75 V to 680 V. In particular, it allows the use of the protection device for the protection of photovoltaic generator installations.

According to a compact preferred embodiment of the double thermal disconnector protection device and with reference to the figure 12A the two poles 34 and 36 of the varistor 30 are arranged on opposite main faces of the varistor 30. The first electrical disconnector which comprises the blade 44 connected by hot-melt soldering to the first pole 34 of the varistor 30, is produced as previously described. . The second thermal disconnector comprises a blade 64 forming a movable contact thermofusibly soldered to the second pole 36 of the varistor 30. This second disconnector advantageously has the same characteristics as the first disconnector which have been previously described. According to this embodiment, the varistor 30 is associated with two thermal disconnectors, that is to say that the two thermal disconnectors and the protection component are connected in series, which allows to increase the breaking capacity in case failure of the protection component.

The protective device is still advantageously designed to safely withstand the case where the varistor 30 short-circuits below the nominal operating voltage while specific short-circuit protections - such as a fuse or circuit breaker external to the device - intervene. In particular, it is intended to meet the IEC standard paragraph 7.7.3. The difficulty comes from the fact that these external protections have a certain reaction time during which the protective device is traversed by high currents. The protective device must not explode or start a fire during this time.

For this, the applicant recommends an approach to limit the heating of the conductive parts of the protective device, in particular its thermal disconnector. Indeed, the short-circuit current is such that it causes a heating of these parts by Joule effect. Uncontrolled heating of the various parts of the protective device can then lead to the melting of one of the parts constituting a possible fire start before the external devices cut off the current.

Different characteristics contribute to limiting the heating of the parts of the protective device.

Thus, as illustrated by figures 5 , 9 and 10 , the blade 44 and the terminal 48 are part of a single piece to form the piece 40. The piece 40 can be obtained by stamping, bending or folding of a rolled sheet. Since the piece 40 is not obtained by assembling several pieces, but constitutes only one, the current flowing through the workpiece 40 of the terminal 48 to the blade 44 does not encounter any electrical contact resistance or Welding. This absence of contact resistance or welding limits the heating of the workpiece 40 when it is traversed by currents of high intensity.

In addition, the part 40 is preferably made of copper with a purity sufficient to have an international annealed copper standard (IACS) conductivity greater than 70%. The IACS conductivity of a part corresponds to the ratio between a resistivity of 1.7241 μΩ.cm and the resistivity of the part, the IACS conductivity is dimensionless. Therefore, the piece 40 has a low electrical resistivity and thus ensures the passage of electric current while limiting its heating. From this point of view, it is advantageous if the purity of the copper is such that its IACS conductivity is greater than or equal to 90% or even 95%. It is even more advantageous to use copper having a purity of 99.9%, that is to say that has a 100% IACS conductivity, which is the case of copper Cu-a1 (or Cu-ETP, also called electrolytic copper ). The electrical resistivity of the part 40 can thus be less than or equal to 1.7241 μΩ.cm and can very effectively limit the heating of the part 40 subjected to short-circuit currents. In conventional solutions, blades with intrinsic elasticity were commonly used to form the moving contact of the thermal disconnector. But only copper alloys provide sufficient intrinsic elasticity, but at the expense of the resistivity is significantly higher. In the proposed protection device, the use of a resilient bias external to the blade 44 (by the spring 50 in our example) allows the blade 44 to be made with a copper of sufficient purity to substantially limit its heating during the tests. short circuits.

The part 40 preferably has a minimum section designed to allow the continuous passage without deterioration of a short circuit current to which the protective device can be exposed. Furthermore, the piece 40 preferably has a thickness of 0.4 mm to 0.6 mm to provide the flexibility of the elbow 46 discussed above. The thickness of the sheet used to obtain the piece 40 may be equal to 0.5 mm.

Furthermore, it is advantageous that the blade 44 has - outside the portion 42 - a significant heat exchange surface with the ambient air, but without detriment to the compactness of the device. For this, the main faces of the blade 44 extend parallel to the main face 32 of the varistor 30. The blade 44 thus ensures a function of cooling fin, which further improves the resistance of the workpiece 40 to short-circuit currents.

More generally, the part 40 may comprise zones of maximum cross-section to dissipate the heat obtained by Joule effect with a substantially constant thickness, which makes it possible to increase the contact surface of the part 40 with the ambient air and thus to limit the heating during the passage of the short-circuit current. The maximum section of the piece 40 is preferably provided at the blade 44, between the elbow 46 and the part 42 or the constriction 58.

An increase in the width of the part 40 can also be provided between the bend 46 and the terminal 48. Figures 9 and 10 thus illustrate a cooling fin 54. This cooling fin 54 makes it possible in particular to limit the temperature rise of the flexible elbow 46 during passage of the short-circuit current. The bend 46 may indeed have a minimum section of the workpiece 40 for reasons of shaping the workpiece 40, or for considerations of sufficient flexibility of the bend 46.

The fact that the blade 44 is thus provided with an exchange surface that limits the heating of the part 40 makes it possible to locally reduce the minimum section of the part 40 previously mentioned, given the temporary nature of the short circuit. It is thus possible to realize the restriction 58 with a length less than or equal to 5.5 mm, or even 5 mm, remaining below this point of the minimum section of the part 40 as previously defined.

The material of the part 40 is preferably bare at the pin 48 to limit the welding 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 previously described characteristics each contribute to increasing the resistance to short-circuit currents, in particular as verified by the IEC standard paragraph 7.7.3. They can be implemented independently of one another. It is possible to use only some of them or all according to the importance of short-circuit currents that can be provided by the power supply network of the installation to be protected.

According to one embodiment, provision may be made to have two protective components in the same cartridge 20.

The Figures 14A and 14B represent the protection device comprising two varistors 30 each with a respective thermal disconnector comprising a blade 44a connected to the pole 34 of the corresponding varistor. The figure 14A represents the protective device with the two thermal disconnectors in closed position. The Figure 14B represents the protection device with the two thermal disconnectors in the open position. The figure 14C represents schematically in cross section such an embodiment of the protective device. The blades 44a are thus each welded to one of the varistors 30 at one of their main faces. The other main faces of the varistors are connected together so as to produce a parallel connection of the varistors 30.

The Figures 15A and 15B represent an alternative embodiment of the protection device comprising two varistors 30 each with a respective thermal disconnector formed of a blade 44b connected to the pole 34 of the corresponding varistor. The figure 15A represents the protection device with the two thermal disconnectors in the closed position. The figure 15B represents the protection device with the two thermal disconnectors in the open position.

In the embodiments of Figures 14A, 14B, 14C , 15A and 15B the varistors 30 are arranged next to each other in the same plane parallel to the main faces of the varistors. With reference to the figure 14C the thickness of each varistor 30 is thus similar to the thickness of the varistor 30 in the embodiments of the protection device with a single varistor. The operating voltage of the protection device remains the same.

The realization of each thermal disconnector in these embodiments with two protection components may be as described above. The blades 44a or 44b are made in a manner similar to the preceding description. With reference to Figures 14A to 14C , the blades 44a and the terminal 48 are preferably parts of one and the same piece 40a so as to provide a resistance to short-circuit currents as previously described. With reference to Figures 15A and 15B , the blades 44b and the terminal 48 are preferably parts of one and the same piece so as to provide a resistance to the currents of short circuits as previously described. In the variant of Figures 14A and 14B , the blades 44 are elastically constrained by a single torsion spring 50a while in the variant of Figures 15A and 15B the blades 44 are elastically constrained each by a respective torsion spring made with a single wire 50b. Other numerical references of Figures 14A, 14B, 14C , 15A and 15B are the same as those used for the previously described embodiments.

The figure 16A represents another alternative embodiment of the protection device comprising two varistors 30 each with a thermal disconnector formed of a respective blade 44 connected to a pole 34 of the respective varistor. In this variant, the varistors 30 are arranged one above the other in the direction of the thickness of the cartridge 20. The compactness conferred by the previously described characteristics of the thermal disconnector makes it possible to realize such an embodiment with interesting operating voltages for the varistors 30.

In these two-component protection variants illustrated in FIGS. Figures 14A, 14B , 15A, 15B and 16A , the protection device may have an electrical diagram in accordance with that shown in figure 16B . Thus these variants correspond to an electrical assembly where a single thermal disconnector is provided for each varistor considered. These embodiments then do not correspond to the series connection of a protection component with two thermal disconnectors of this protection component. Alternatively, to these variants of Figures 14A, 14B , 15A, 15B and 16A it may be provided to add, for each varistor considered, a second thermal disconnect connected in series to the first thermal disconnector via the varistor. With reference to the figure 16B this second thermal disconnector may, for example, be common to both varistors being disposed on the common part of the electrical branches connected to the terminal 38 (embodiment not shown).

As illustrated on the figure 16B a capacitor 22 may be arranged in parallel with the two thermal disconnectors to improve the breaking capacity, especially when using direct current.

The presence of this additional varistor in the same internal volume 21 of the cartridge 20 ensures continuity of service and protection when one of the varistors, end of life, has been disconnected. The disconnection of one of the varistors by a thermal disconnector can be signaled to the user of the electrical installation using a display element known per se. The user is notified of the arrival at the end of life of one of the protective components of the cartridge 20, with a surge protection function still provided by the second varistor the time for the user to replace the cartridge 20 . The figure 5 illustrates a possible embodiment of the display element 26 of the state of one of the thermal disconnectors.

Thanks to the compactness of the thermal disconnector previously described, the protection devices of the Figures 14A, 14B , 15A, 15B and 16A, 16B can be in a cartridge 20 with the dimensions as defined above.

According to one embodiment, it may be provided to have a plurality of varistors in the same protection component. These varistors can be connected in series and / or in parallel with each other according to the applications. The varistors are then assembled into a compact mass, comprising at least two varistors. In the case where it is intended to associate several varistors in series and / or in parallel, the term "protection component", the block disposed between two successive electrical poles and formed of a varistor or at least two varistors interconnected.

The Figure 17B illustrates an alternative embodiment of a double protection component 30 composed of two blocks 80 having a non-linear electrical resistance. These two blocks 80 form two varistors. The dual protection component 30 further comprises an electrode 98 forming a common pole of the varistors for electrically connecting the two varistors together. The electrode 98 thus connects a pole of the first block 30 to a pole of the second block 80. The other poles 34 of the blocks 80 are connected to movable contacts 44 of thermal disconnectors electrically connected to the terminals 38 and 48 of the protection device such as previously described. The set of varistors - that is to say the combination of the two blocks 80 - is entirely covered by the electrical insulation coating 88 through which emerges the connection poles of the varistors including the electrode 98. Such an embodiment the double protection component realizes the combination of two varistors in parallel, because of the intermediate potential taken by the electrode 98. The two blocks 80 of varistors being separated by a pole electrode 98, this embodiment with a Double protection component is to be distinguished from the previous embodiment, where several varistors are associated with each other between two successive poles, thus forming a single protection component.

This embodiment of the dual protection component is particularly useful for photovoltaic installation protection. The Figure 17A illustrates a photovoltaic installation comprising a photovoltaic panel 90. This panel 90 generates an electrical voltage between the son 95 and 96. A bypass son 95 and 96 (not shown) then retrieves the electrical current generated by the photovoltaic system. In order to ensure the overvoltage protection of this installation, each of its son 95 and 96 can be connected to one of the terminals 48 and 38 of the protection device comprising the previous double protective component 30. The electrode 98 of the double protection component 30 is connected to the earth 94 via a spark gap 92. Each of the wires 95 and 96 is thus connected to the ground via a respective varistor and the earth. a spark gap 92 common.

In this embodiment, a single thermal disconnector is provided for each protection component considered. This embodiment therefore does not correspond to the series connection of a protection component with two thermal disconnectors of this protection component. As an alternative to this embodiment, it may be provided to add, for a varistor considered, a second thermal disconnect connected in series to the first thermal disconnector through the varistor. With reference to the Figure 17B this second thermal disconnector may, for example, be common to both varistors by ensuring the disconnection of the electrode 98 (embodiment not shown). In this alternative embodiment, for each protection component considered, the two thermal disconnectors and the corresponding protection component are connected in series.

Embodiments of multiple protection components 30 are possible by the combination of a larger number of varistors in series or in parallel. One embodiment of the multiple protection component 30 thus consists in the superposition of several blocks 80 having a non-linear electrical resistance by connecting the blocks 80 by electrodes 98 in a manner similar to the embodiment illustrated by FIG. Figure 17B . All of these blocks 80 may be coated with the electrical insulation coating 88 previously described (such embodiments are not shown). According to an example of this embodiment, a triple protection component 30 may be formed by the superposition of three blocks 80 separated by electrodes 98. This triple protection component then has four poles, including two electrodes 98, for carrying out the differential voltage surge protection of a three-phase electrical installation. Each block 80 of varistors being separated by a pole electrode 98, this embodiment with a triple protection component is to be distinguished from the embodiment with a single protection component for which several varistors are associated with each other between two successive poles. According to the embodiment of a triple protection component, at most only one thermal disconnector is provided for each protection component considered. This embodiment therefore does not correspond to the series connection of a protection component with two thermal disconnectors of this protection component. As an alternative to this embodiment, it may be provided to add, for a protection component considered, a second thermal disconnect connected in series to one of the first thermal disconnectors via one of the blocks. Such an embodiment can be obtained by arranging a second thermal disconnector at one of the electrodes 98 (embodiment not shown). In this alternative embodiment, for at least one protection component considered, the two thermal disconnectors and the corresponding protection component are connected in series.

According to one embodiment, it may be provided that the protection device has more than two terminals for connection to the electrical installation to be protected. Such an embodiment of the invention corresponds, for example, to the use of a multiple protection component 30 with a number of poles greater than two such that the embodiment described with reference to the Figures 17A and 17B .

The characteristics described above, taken together or only some of them, make it possible to provide transient overvoltage protection devices which can satisfy both IEC and UL standards, as well as the UTE guide which have been mentioned more above. Each of these features may, independently of one another or in combination, be implemented in the protection device according to the desired level of performance. The protection device thus produced benefits from the advantages associated with the characteristics previously described and which it incorporates.

These characteristics make it possible in particular to provide protection devices provided for a nominal operating voltage up to 690V AC at 50 Hz or 60 Hz and up to 895V DC and to provide protection against lightning strikes. nominal current (Imax) of 40kA for an 8/20 shock wave according to the IEC standard and against 20kA rated current cracks (In) for an 8/20 shock wave according to the UL standard. These performances can be obtained with a single varistor chosen appropriately. The maximum rated voltage can easily be increased by assembling one or more of these varistors in series.

Claims (15)

1. A varistor comprising:

   - at least two connection poles (34, 36);

   - a block (80) having non-linear electric resistance whose value varies in relation to the voltage applied to the two connection poles (34, 36);

   - a conductive plate (84) forming a contact electrode with the block, said conductive plate (84) being arranged on a main face (82) of the block (80) and having a projecting part forming one of the connection poles; and

   - a covering of electrical insulation (88) applied at least to the assembly formed by the main face (82) of the block (80) and the conductive plate (84) arranged on said main face of the block,
   and wherein

   - said projecting part forming a connection pole emerges from the covering of electrical insulation and exhibits a soldering surface for its electric connection, said soldering surface extending above the level of the covering of electrical insulation; and

   - said projecting part forming a connection pole being part of one and the same part with the conductive plate (84) is connected to the remainder of the plate (84) over at least one half of its perimeter.
2. The varistor according to claim 1, wherein said part forming a connection pole is connected to the remainder of the plate (84) over at least 80 % of its perimeter and more preferably over its entire perimeter.
3. The varistor according to claim 1 or 2, wherein said projecting part forming a connection pole (34) is formed by stamping the plate (84).
4. The varistor according to any of claims 1 to 3, wherein said soldering surface lies at least at 0.1 mm, more preferably at least at 0.3 mm above the level of the covering of electrical insulation (88).
5. The varistor according to any of claims 1 to 4, wherein the said projecting part forming a connection pole lies inside an imaginary circle (86) centred on said main face (82) of the block (80) and having a diameter equal to 75 % of the diameter of the inscribed circle on the main face of the block.
6. The varistor according to any of claims 1 to 5, wherein the conductive plate (84) is centred on said main face (82) of the block (80) and/or wherein the remainder of the conductive plate (84) around the projecting part forming a connection pole (34) is solid.
7. The varistor according to any of claims 1 to 6, wherein the surface of the plate (84) in contact with said main face (82) of the block (80) has a surface area which is at least one half of the surface area of the main face (82) of the block (80).
8. The varistor according to any of claims 1 to 7, wherein the soldering surface lies parallel to said main face (82) of the block (80).
9. The varistor according to any of claims 1 to 8 which is entirely covered with the covering of electrical insulation (88) through which the other connection pole(s) (36) also emerge.
10. An assembly of varistors assembled in a compact mass, comprising at least two varistors of which at least one conforms to any of claims 1 to 9, wherein the two varistors are electrically connected together and have a common pole (98), the assembly of varistors being entirely covered with the covering of electrical insulation (88) through which the varistor connection poles (34, 36, 98) emerge.
11. A device for protecting an electric installation against transient overvoltage comprising:

    - a varistor (30) according to any of claims 1 to 9 or an assembly of varistors according to claim 10;

    - a thermal disconnector comprising a movable contact (44,64) able to move from a closed position to an open position to disconnect the varistor or one of the varistors of said assembly;

    wherein the movable contact (44) is held in closed position by a heat-meltable solder joint (70) fixing the movable contact (44) on the soldering surface of said projecting part forming the connection pole (34) of the varistor, the thermal disconnector being designed to cause the movable contact (44) to move to the open position when the heat-meltable solder joint melts, and
    wherein the movable contact (44) is designed to move from the closed position to the open position parallel to said main face (82) of the block (80) of the varistor (30) and at a distance away from the covering of electrical insulation (88) of the varistor.
12. The protective device according to claim 11, comprising at least two terminals (38, 48) to connect the device to the electric installation, and wherein the movable contact (44) is a leaf member principally extending over a plane parallel to said main face (82) of the block (80) of the varistor (30) and principally opposite this main face (82), the leaf member and one of the connection terminals (38, 48) belonging to one and the same part (40).
13. The protective device according to claim 12, wherein the part (40) to which the leaf member (44) and said one of two connection terminals (48) belong have an IACS conductivity of 70 % or higher, preferably of 90 % or higher and further preferably of 95 % or higher.
14. The protective device according to claim 12 or 13 wherein the part (42) of the leaf member (44) held on the soldering surface of said projecting part forming the pole (34) is connected to the remainder of the leaf member (44) via a local restriction (58) of the cross-sectional area of the leaf member (44) to concentrate the heat, released by the varistor (30) or one of the varistors of said assembly, at the point of the heat-meltable solder joint (70).
15. A cartridge comprising:

    - a housing (23, 24),

    - a protection device against overvoltage according to any of claims 11 to 14, and

    - pins for connecting the protective device to an electric installation to be protected,

    wherein the protective device is housed in the housing and the pins protrude outside the housing, the housing (23, 24) defining an inner parallelepiped volume (21) in which the protective device is housed, the maximum dimensions of the inner volume being 15x42x43 mm.

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