EP2631927B1 - Method for shutting down an electric arc, method and device for protecting a facility against overvoltages - Google Patents

Description

The invention relates to the general technical field of the protection of equipment or electrical installations against overvoltages, in particular against transient overvoltages, due for example to a lightning strike. The present invention more particularly relates to a method of cutting an electric arc in a spark gap and a method of protecting an electrical installation against transient overvoltages using the method of breaking an electric arc. The invention further relates to a device for protecting an electrical installation against transient overvoltages.

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. Such devices are commonly referred to as lightning arresters. 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.

The use of a spark gap as an overvoltage protection device can pose a problem of current management of the spark gap. Indeed, because of the initiation of the spark gap, a current can continue to flow through the spark gap initiated and even after the end of the transient overvoltage. This current is maintained by the voltage source of the electrical installation to be protected. This current then corresponds to a current that we want to stop by cutting the arc formed in the spark gap. This problem of current cut-off is particularly relevant in the case of electrical installation operating in direct current such as a photovoltaic power generation installation.

In the field of surge arresters, various breaking systems are proposed.

In the case where an arc is formed between two electrodes at the end of the life of varistors, there are disposable cleavage systems including a mechanical short-circuit of the arc and a short-circuit current management by fuse.

In the case of using a spark gap as arrester, arcs are formed repeatedly between the electrodes of the spark gap, preventing the use of unsuitable disposable cleavage systems. The cutting of arcs forming repeatedly also corresponds to a need for other equipment whose purpose is more generally to cut a current due to a fault, or to any external action. Multi-purpose clipping systems are then proposed for equipment such as contactors, circuit breakers or switches as for spark gap arresters.

The systems proposed are essentially based on an enlargement of the distance between the electrodes between which the arc is formed or on the separation of the arc into a multiplicity of arcs. In both cases, the breaking of the arc is achieved by raising the so-called arc voltage to a sufficiently high value so that the voltage of the source is no longer able to maintain this arc voltage. Thus, when the voltage of the source is high, multipurpose breaking systems must allow an expansion of the distance between the electrodes all the more important or a separation into a multiplicity of arcs all the more important. For high operating voltages likely to be encountered in photovoltaic installations, for example between 500 and 1000V or even up to 1500V because of the continuous nature of the current, the adaptation of the preceding systems to the breaking of such voltage levels can lead to significant dimensional constraints. Or arrester devices, are usually contained in cases said "mountable" DIN rail. These housings do not exceed 17.5mm in width and 92mm in length, and are then too small to meet such dimensional constraints.

DE 102 45 144 B3 discloses a method of breaking an electric arc formed between two main electrodes, comprising moving the formed electric arc to an electrode located in an intermediate position between the two main electrodes and separating the two-phase electric arc. secondary arcs between the main electrodes and the intermediate electrode.

There is therefore a need for an electric arc cutting method allowing a smaller size of the devices implementing it.

• le déplacement de l'arc électrique formé vers une électrode située dans un positionnement intermédiaire entre les deux électrodes principales ;
• la séparation de l'arc électrique formé en deux arcs électriques secondaires entre les électrodes principales et l'électrode intermédiaire, un interrupteur à semi-conducteur normalement ouvert reliant l'électrode intermédiaire à une des électrodes principales ;
• la fermeture de l'interrupteur à semi-conducteurs pour éteindre l'arc électrique secondaire entre les deux électrodes que l'interrupteur à semi-conducteurs relie ;
• l'ouverture de l'interrupteur à semi-conducteurs pour éteindre l'autre arc électrique secondaire.

For this purpose the invention proposes a method of cutting an electric arc formed between two main electrodes, the method comprising:

• moving the formed electric arc to an electrode located in an intermediate position between the two main electrodes;
• separating the electric arc formed into two secondary electric arcs between the main electrodes and the intermediate electrode, a normally open semiconductor switch connecting the intermediate electrode to one of the main electrodes;
• closing the semiconductor switch to extinguish the secondary electric arc between the two electrodes that the semiconductor switch is connecting;
• opening the semiconductor switch to turn off the other secondary electric arc.

According to a variant, the method comprises a delay after the separation of the arc formed in two second electric arcs to prevent the reformation of an arc between the two main electrodes at the closing of the semiconductor switch.

Alternatively, the method includes a timer after closing the semiconductor switch to prevent reformation, upon opening of the semiconductor switch, of the off arc between the intermediate electrode and the semiconductor switch. one of the main electrodes.

The invention also proposes a method of protecting an electrical installation against transient overvoltages, the method implementing the breaking of an electric arc according to the preceding cutoff method in the event of occurrence of a transient overvoltage in the electrical installation to be protected causing the formation of a first electric arc between the two main electrodes, the main electrodes being connected to the electrical installation to be protected.

According to one variant, the electrical installation to be protected is an electrical installation connected to a low-voltage electrical distribution network.

According to a variant, the electrical installation to be protected is an electrical installation operating under direct current, preferably a photovoltaic power generation installation.

• deux bornes de connexion du dispositif à l'installation électrique à protéger ;
• une première électrode principale et une deuxième électrode principale, chaque électrode principale étant reliée à l'une respective des bornes de connexion ;
• une électrode située dans un positionnement intermédiaire entre la première électrode principale et la deuxième électrode principale ;
• un interrupteur à semi-conducteurs normalement ouvert reliant l'électrode intermédiaire à la première électrode principale ;
• un circuit de commande de l'interrupteur à semi-conducteurs, le circuit de commande étant prévu pour assurer successivement la fermeture de l'interrupteur, puis l'ouverture de l'interrupteur, après qu'un arc électrique formé entre les électrodes principales soit divisé en deux arcs par l'électrode intermédiaire.

The invention also proposes a device for protecting an electrical installation against transient overvoltages, comprising:

• two connection terminals of the device to the electrical installation to be protected;
• a first main electrode and a second main electrode, each main electrode being connected to a respective one of the connection terminals;
• an electrode located in an intermediate position between the first main electrode and the second main electrode;
• a normally open semiconductor switch connecting the intermediate electrode to the first main electrode;
• a control circuit of the semiconductor switch, the control circuit being provided for successively closing the switch, and then opening the switch, after an electric arc formed between the main electrodes is divided into two arcs by the intermediate electrode.

Alternatively, the semiconductor switch is an insulated gate bipolar transistor or a metal oxide gate field effect transistor.

According to one variant, the control circuit provides a delay between the division of the electric arc into two arcs by the intermediate electrode and the closing of the switch and / or between the closing of the switch and the opening of the switch. 'light switch.

According to a variant, the electrodes are fixed, the two main electrodes being positioned opposite one another from a first side to a second side, and forming a spark gap; and the intermediate electrode extending partially between the two main electrodes from the second side.

According to a variant, the device comprises a device for triggering an arc between the main electrodes in the event of occurrence of a transient overvoltage on the electrical installation to be protected, the tripping member comprising an arc triggering electrode. on the first side of the main electrodes.

According to a variant, the intermediate electrode has a corner end portion on the side where the intermediate electrode extends between the two main electrodes.

According to a variant, the device comprises a magnet arranged to move, in the direction from the first side to the second side, an electric arc formed between the main electrodes of the spark gap and / or the main electrodes being diverging from the first side towards the second side.

According to a variant, the device comprises an additional connection terminal and an additional spark gap formed by two additional electrodes, one of the additional electrodes being connected to the additional terminal and the other of the additional electrodes being connected to one of the two connection terminals. from the device to the electrical installation.

According to a variant, the device is especially designed for the implementation of the preceding method.

• figure 1, une représentation schématique des différentes phases d'un mode de réalisation du procédé de coupure proposé et mis en oeuvre sur un éclateur ;
• figure 2, un graphique temporel de l'évolution des diverses grandeurs électriques lors de la mise en oeuvre du procédé schématisé en figure 1 ;
• figure 3, une vue en coupe d'un mode de réalisation du dispositif proposé de protection contre les surtensions ;
• figure 4, un schéma électrique d'un mode de réalisation du circuit de commande d'un interrupteur à semi-conducteurs du dispositif de protection de la figure 3 ;
• figure 5, une représentation schématique d'un mode de réalisation du dispositif de protection proposé avec un aimant ;
• figures 6 et 7, des vues éclatées d'un mode de réalisation préféré du dispositif proposé de protection dans une cartouche "montable" sur un rail DIN ;
• figure 8, une représentation schématique d'un mode de réalisation préféré du dispositif de protection avec une borne supplémentaire de connexion.

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 schematic representation of the different phases of an embodiment of the proposed cutting method and implemented on a spark gap;
• figure 2 , a temporal graph of the evolution of the various electrical quantities during the implementation of the process schematized in figure 1 ;
• figure 3 , a sectional view of an embodiment of the proposed device for protection against overvoltages;
• figure 4 , a circuit diagram of one embodiment of the control circuit of a semiconductor switch of the protection device of the figure 3 ;
• figure 5 , a schematic representation of an embodiment of the proposed protection device with a magnet;
• Figures 6 and 7 exploded views of a preferred embodiment of the proposed protection device in a "mountable" cartridge on a DIN rail;
• figure 8 , a schematic representation of a preferred embodiment of the protection device with an additional connection terminal.

The invention relates to a method of cutting an electric arc. The method is implemented for a first main electrode and a second main electrode between which an arc to be cut is likely to form as a result of a defect, an external action or an external event, such as a lightning strike or the separation of moving contacts in a mechanical switch.

A semiconductor switch connects the intermediate electrode to the first main electrode. A semiconductor switch is a switch formed by the superposition of doped semiconductor layers. Thus a semiconductor switch corresponds to a switch whose closed or open character is enabled by a semiconductor operating in switching between letting the current flow or interrupting it. As a result, unlike a mechanical switch, the semiconductor switch has no moving contact or moving mechanical part whose movement makes the transition between the closed state and the open state and ensures the interruption of current by the distance separating the movable contact and the fixed contact. The semiconductor switch then ensures the interruption of current without causing arc creation in contrast to a mechanical switch. The semiconductor switch may be a bipolar gate transistor (also known as " Insulated Gate Bipolar Transistor " abbreviated as "IGBT ") or a metal oxide gate field effect transistor (better known as English " Metal Oxide Semiconductor Field Effect Transistor " abbreviated as "MOSFET" or "MOS ").

The figure 1 shows a schematic representation of different phases of the proposed cleavage process. According to this schematic representation, the method is implemented on a spark gap 20 formed in particular of the main electrodes previously described and also comprising the intermediate electrode and the semiconductor switch described above. According to figure 1 , the main electrodes 24 and 28 are positioned facing one another from a first side (referenced by a P surrounded) towards a second side (referenced by a D surrounded), the intermediate electrode 26 extending partially between the two main electrodes from the second side D.

The proposed breaking process is implemented after the formation of a first electric arc 62 between the two main electrodes 24 and 28. The first electric arc 62 between the two main electrodes 24 and 28 is also designated by the term "electric arc formed "62. Following the formation of the first electric arc 62, the method comprises the displacement of the electric arc 62. According to the figure 1 the arc 62 is moved from the first side P to the second side of the gap D. According to the embodiment illustrated by the figures, the displacement of the arc is facilitated by the fact that the main electrodes 24 and 28 diverge. from the first side P to the second side D. Alternatively or in addition to the divergence of the electrodes 24 and 28, but always in order to facilitate the movement of the arc, a magnet may be provided which is described in FIG. following the description.

When the electric arc 62 is moved to the level of the intermediate electrode 26, the method comprises separating the first electric arc 62 into two second electric arcs 64 and 68. Each of the two second electric arcs 64 and 68 is also designated by the term "secondary electric arc" 64 or 68. The intermediate electrode 26 preferably has a floating potential. The second electric arc 64 is formed between the first main electrode 24 and the intermediate electrode 26 while the second electric arc 68 is formed between the second main electrode 28 and the intermediate electrode. The steps of the method before the separation of the arc 62 into arcs 64 and 68 correspond to the phase referenced 32. figure 1 , the arc 62 is represented several times in positions taken successively during its displacement.

After the separation of the arc 62 into arcs 64 and 68, the second arcs can also be moved in the direction of the first side P to the second side D (from the left to the right according to the figure 1 ). The steps of separation into two arcs 64 and 68 and displacement of the two arcs 64 and 68 correspond to the phase referenced 34. According to the figure 1 , the arcs 64 and 68 are represented several times in positions taken successively during their displacement.

The method then comprises closing the semiconductor switch to extinguish the second electric arc 64 between the intermediate electrode 26 and the first electrode 24. The closing of the switch causes the short circuit of the arc 64 by setting to the same potential of the first main electrode 24 and the intermediate electrode 26. Due to the short circuit, the current flowing in the arc 64 passes entirely into the switch which causes the extinction of the This step of the method corresponds to the referenced phase 36.

After the extinction of the arc 64, the method comprises the opening of the semiconductor switch to turn off the other second arc 68. Indeed, the opening of the switch causes the isolation of the intermediate electrode 26 by relative to the first main electrode 24. These electrodes 24 and 26 are no longer connected by the switch or by the arc 64 previously extinguished, the current flowing through the arc 68 can no longer flow until to the main electrode 24 except to recreate an electric arc. For this, the voltage between the intermediate electrode 26 and the main electrode 24 must be greater than the breakdown voltage of the air gap that separates these electrodes 24 and 26. It is useful to note that the breakdown voltage d an air gap is greater than the holding voltage of an already formed arc passing through the same blade. If the voltage of the source can be sufficient to maintain an initially formed arc between 24 and 26, the source voltage is insufficient to allow the breakdown of this same air space, that is to say insufficient to allow the formation of a new arc between 24 and 26. The distance between the electrodes 24 and 26 is chosen accordingly. Then the opening of the switch causes the extinction of the arc 68. This process step corresponds to the referenced phase 38.

After the implementation of the proposed method, the continuation current is completely cut off because of the extinction of the two arcs 64 and 68. The arc cutting provided by the proposed method is carried out without increasing the holding voltage of the current. arc in the spark gap, unlike the spark gaps of the prior art. Thus according to this method, it is no longer necessary to cause the arc holding voltage to exceed the voltage of the source by splitting the arc many times or increasing the size of the arc. The proposed method can therefore be implemented in a spark gap having only isolation distances between these different electrodes which are only sufficient to prevent the formation of a new arc with the voltage of the source of the installation. Since the forming voltage of a new arc is much greater than the holding voltage of an already formed arc, the proposed method allows the distances between the electrodes of the spark gap to be reduced. Ultimately, the spark gap implementing the method can have a limited space while ensuring the interruption of the electric arc maintained by high voltage sources.

• une des électrodes principales 24 et 28 peut être un contact mobile d'interrupteur mécanique alors que l'autre des électrodes principales 24 et 28 est un contact fixe ;
• l'électrode intermédiaire 26 peut aussi être mobile par rapport aux électrodes principales 24 et 28, avec un mouvement corrélé ou décorrélé du mouvement des électrodes principales l'une par rapport à l'autre.

The positioning of the electrodes according to figure 1 corresponds to electrodes fixed relative to each other, the main electrodes forming a spark gap. It may be alternatively provided that, in non-illustrated embodiments, the electrodes are movable relative to each other, for example:

• one of the main electrodes 24 and 28 may be a moving switch mechanical contact while the other of the main electrodes 24 and 28 is a fixed contact;
• the intermediate electrode 26 may also be movable relative to the main electrodes 24 and 28, with a correlated or decorrelated movement of the main electrodes relative to each other.

In these alternative embodiments with moving electrodes, the implementation of the method also allows the reduction of the maximum spacing distances between the electrodes. Ultimately, the device with mobile electrodes implementing the method can also have a limited space while ensuring the interruption of the electric arc maintained by high voltage sources.

The cutting method described above can be particularly advantageous when it is used in a more general method of protecting an electrical installation against transient overvoltages.

In the field of protection against transient overvoltages, for example due to a lightning strike, it is possible to provide a spark gap at the terminals of an electrical installation, as a surge arrester. The formation of an electric arc in the spark gap during transient overvoltage allows the limitation of the voltage across the electrical installation to be protected. However, at the end of the transient overvoltage event, this electric arc can be maintained by the voltage source of the electrical installation to be protected. This maintenance of the arc disturbs the return to normal operation of the installation. The implementation of the preceding cut-off method in an overvoltage protection method then makes it possible to cut off the current in succession even for high source voltages while limiting the size of the protection device implementing the protection method.

The proposed method allows protection of electrical installations, including electrical installations connected to a low voltage electrical distribution network.

As standard, an electrical installation connected to a low-voltage electrical distribution network is understood to mean a low-voltage electrical installation of rated voltage effective up to 1,000 V AC or up to 1,500 V DC except very low voltage electrical equipment. Very low voltage electrical equipment may be defined as equipment having an effective rated voltage of less than 12 V AC or DC. Thus the electrical installation to be protected may be an electrical installation operating at a voltage between 12V and 1000V AC and between 12V and 1500V continuously. Such very low voltage electrical equipment is not directly connected to a low voltage electrical network. In other words, the proposed method of protecting an electrical installation connected to a low-voltage electrical network is distinguished from a method of protecting microelectronic components against overvoltages.

Among the electrical installations connected to a low-voltage electrical distribution network, the protection method is particularly used for electrical installations operating under direct current, for example for a photovoltaic power generation installation. The implementation of the cut-off method in a method of protecting an installation against overvoltages makes it possible in particular to cut following currents maintained by a DC voltage source of 1500V such as in photovoltaic power generation installations.

The figure 2 shows a time chart of the evolution of the various electrical quantities during the implementation of the preceding cut-off method for the purpose of protection against overvoltages of an electrical installation operating under direct current.

The origin of the times of the figure 2 corresponds to the beginning of a transient surge such as a lightning strike. According to this figure 2 the time axis can then be cut into the previously described phases 32, 34, 36 and 38.

During phase 32, an arc is formed due to the overvoltage across the main electrodes 24 and 28 of the spark gap 20. The voltage across the main electrodes is represented by the curve 50. During such an overvoltage, the spark gap limits the voltage 50 to the starting voltage of the arc in the spark gap. This arc allows the flow of a current 40 between the main electrodes 24 and 28. At the beginning of the phase 32, the current 40 then corresponds to a lightning current 48 which is the major part of the current associated with the transient overvoltage. This lightning current 48 is positive or negative depending on the polarity of the transient overvoltage, the lightning for example may be positive or negative discharge. After the transient overvoltage, the current 40 and the voltage 50 drop. The formed electric arc 62 can be maintained and flow away current supplied by the voltage source of the electrical installation to be protected. The current 40 then corresponds to the following current 42 and the voltage 50 corresponds to the voltage maintaining the arc 62 between the main electrodes 24 and 28.

During the transient overvoltage and then after the current flow, the arc 62 is moved to the intermediate electrode 26. The electrodes 24 and 28 are, in this example, divergent on the side D of the intermediate electrode 26 , the displacement of the arc 26 towards the intermediate electrode causes an increase in the voltage of the arc after the transient overvoltage. Indeed, the tension of the arc depends on one hand on the length of the arc and on the other hand on its number of feet, here two: one at the electrode 24 and the other at the the level of the electrode 28. This increase in the tension 50 continues with the displacement of the arc 62 until the arc 62 is separated in the two arcs 64 and 68 by the intermediate electrode 26.

Then enters the phase 34. At the time of the separation of the arc 62 into two arcs 64 and 68, the voltage 50 across the main electrodes 24 and 28 increases sharply due to the increase in the number of feet of arcs that goes from two to four: two feet for each of the arcs 64 and 68. The separation of the arc 62 into two arcs 64 and 68 also corresponds to the appearance of a voltage 52 between the intermediate electrode 26 and the electrode 24. When the device is symmetrical in the plane of the intermediate electrode 26, the voltage 52 corresponds to half of the voltage 54 between the electrodes 24 and 28. This voltage 52 is maintained until the closing of the semiconductor switch. However, the voltage 52 may be slightly increased with the voltage 54 because the arcs 64 and 68 continue to be moved between diverging electrodes to the D side.

When the semiconductor switch is closed, phase 36 is entered. Closing the semiconductor switch causes a short circuit to be formed between the electrode 26 and the electrode 24. current flowing through the switch corresponds to the current previously flowing through the arc 64 shorted, that is to say that the current 46 corresponds to the following current 42. The voltage 52 between the intermediate electrode 26 and the electrode 24 vanishes and the arc 64 is cut. The voltage 50 between the electrodes 24 and 28 is then decreased and goes from the voltage 54 to the voltage 56.

It may be useful to provide a delay between the separation of the first arc 62 and the closing of the semiconductor switch. Such a delay corresponds to the duration of the phase 34. This delay makes it possible to ensure that when the switch is closed, the current flowing through the spark gap corresponds to a consecutive current 42 and no longer to a lightning current 48. Thus it is avoided that the lightning current 48 can pass through the semiconductor switch which would damage the semiconductors of the switch. On the other hand, regardless of the use of the breaking method for the purpose of overvoltage protection, the delay of the duration of the phase 34 contributes to preventing the reformation of an arc between the two main electrodes 24 and 28 at closing. of the semiconductor switch. Indeed, the duration of this delay can be chosen to ensure, before closing the switch, the deionization of the air initially ionized by the first arc 62.

Following the closing of the semiconductor switch, it goes into phase 38, opening the same switch. The current 46 passing through the switch is then zero and the following current 42 can no longer flow between the intermediate electrode 26 and the main electrode 24. This causes the extinction of the arc 68, the voltage between the main electrodes then becomes equal to the voltage of the source of the electrical installation and the current 40 passing through the spark gap is zero. Next stream 42 is thus cut. A time delay can be provided between closing and opening the semiconductor switch to prevent the reformation of the arc between the intermediate electrode 26 and the first main electrode 24 at the opening of the semiconductor switch. Indeed, the duration of this delay can be chosen to ensure, before the opening of the switch, the deionization of the air initially ionized by the arc 64. Such a timing corresponds to the duration of the phase 36.

The invention further relates to a device for protecting an installation against transient overvoltages. The device comprises two terminals for connecting the device to the electrical installation to be protected. With reference to the figure 1 , the device further comprises the first main electrode 24 and the second main electrode 28. The main electrodes can form the spark gap 20 between them. These two main electrodes 24 and 28 are then positioned opposite one another from the first side P to the second side D. Each main electrode is connected to a respective one of the connection terminals (described in the following section). the description).

The device further comprises the intermediate electrode 26 located in an intermediate position between the main electrodes 24 and 28. When the main electrodes form the spark gap 20, the intermediate electrode extends partially between the two main electrodes from the second side D. The device comprises the normally open semiconductor switch and connecting the intermediate electrode 26 to the first main electrode 24.

The device further comprises a control circuit 78 of the semiconductor switch. The assembly formed by the semiconductor switch and the control circuit 78 is referenced 70 in figure 1 . The control circuit 78 is provided for closing and successively opening the switch after the electric arc 62 formed between the main electrodes 24 and 28 is divided into two secondary arcs 64 and 68 by the intermediate electrode 26. The control circuit 78 is thus capable of controlling the device so that, following the formation of the arc 62 between the main electrodes 24 and 28, the steps of the previously described method are implemented. The protection device proposed can then have a compact design. For example, the protective device may be in the form of a DIN rail mountable housing with a length not exceeding 92 mm. The figure 3 shows a sectional view of such an embodiment of the proposed device 90 for protection against overvoltages, the device 90 comprising an outer housing 92 corresponding to a housing "mountable" DIN rail. The DIN rail mountable housing 92 includes a DIN rail mounting interface 96 (not shown).

In general, the proposed device may be specially designed for the implementation of one of the embodiments of the above methods.

Thus in the proposed device, the control circuit 78 can provide the time delay before the closing of the switch and / or between the closing of the switch and the opening of the switch. Back to the figure 2 to provide these delays and the control of the semiconductor switch, the control circuit 78 may be supplied by a portion 44 of the following current 42 passing through the intermediate electrode 62.

• Lorsque la tension 52 de l'arc 64 apparaît (au début de la phase 34), un condensateur C₁ se charge à travers la résistance R₁. En fonction de l'étalonnage de C₁ et R₁, on obtient le temps de charge souhaité pour C₁ permettant la temporisation voulue de la phase 34. Lorsque la charge du condensateur C₁ permet d'atteindre la tension inverse d'une diode Zener DZ₁, la diode Zener devient passante entraînant l'apparition d'une tension aux bornes d'une résistance R₂. La tension aux bornes de la résistance R₂ permet la commutation du thyristor T₁ dans l'état passant. L'IGBT voit alors une tension à sa grille faisant passer l'IGBT à l'état passant, ce qui limite la tension de l'arc 64 à une tension V_CEsat de l'IGBT. L'IGBT étant alors passant, l'arc 64 disparaît mais un courant circule encore dans l'éclateur par l'intermédiaire de l'IGBT. Autrement dit, la partie 72 du circuit de commande 78 assure la commande en fermeture de l'IGBT. On entre dans la phase 36.
• Après le moment où l'IGBT est devenu passant, le condensateur C₁ maintient la tension de commande et charge un condensateur C₂ par l'intermédiaire d'une résistance R₄. En fonction de l'étalonnage de C₂ et R₂, on obtient le temps de charge souhaité pour C₂ permettant la temporisation voulue de la phase 36. Lorsque le condensateur C₂ atteint la tension inverse d'une diode Zener DZ₂, la diode Zener DZ₂ devient passante. Cela entraîne l'application d'une tension aux bornes d'une résistance R₅, permettant la commutation du thyristor T₂ dans l'état passant. L'IGBT est alors court-circuité et l'IGBT passe de l'état passant à l'état bloqué. Le courant de suite est coupé par l'ouverture de l'IGBT et l'arc 68 s'éteint. Autrement dit, la partie 74 du circuit de commande 78 assure la commande en ouverture de l'IGBT. On entre dans la phase 38.
• A la suite de l'extinction de l'arc 68, les condensateurs C₁ et C₂ se déchargent respectivement dans des résistances R₃ et R₆.

The figure 4 shows a circuit diagram of an embodiment of the control circuit 78 of the semiconductor switch. The assembly 70 is thus connected to the intermediate electrode 26 and to the main electrode 24. The semiconductor switch is in the form of an IGBT. R _L represents the resistance of the conductive lines. The assembly 70 operates as follows:

• When the voltage 52 of the arc 64 appears (at the beginning of the phase 34), a capacitor C ₁ is charged through the resistor R ₁ . As a function of the calibration of C ₁ and R ₁ , the desired charging time for C ₁ is obtained allowing the desired delay of the phase 34. When the charge of the capacitor C ₁ makes it possible to reach the reverse voltage of a diode Zener DZ ₁ , the Zener diode becomes conductive causing the appearance of a voltage across a resistor R ₂ . The voltage across the resistor R ₂ makes it possible to switch the thyristor T ₁ in the on state. The IGBT then sees a voltage at its gate passing the IGBT to the on state, which limits the voltage of the arc 64 to a voltage V _CEsat of the IGBT. The IGBT is then passing, the arc 64 disappears but a current still flows through the spark gap via the IGBT. In other words, the portion 72 of the control circuit 78 provides the closing control of the IGBT. We are entering phase 36.
• After the moment when the IGBT has become on, the capacitor C ₁ maintains the control voltage and charges a capacitor C ₂ via a resistor R ₄ . As a function of the calibration of C ₂ and R ₂ , the desired charging time for C ₂ is obtained allowing the desired delay of phase 36. When capacitor C ₂ reaches the reverse voltage of a Zener diode DZ ₂ , the Zener diode DZ ₂ becomes busy. This causes the application of a voltage across a resistor R ₅ , allowing the switching of the thyristor T ₂ in the on state. The IGBT is then bypassed and the IGBT switches from the off state to the off state. The current in a row is cut off by the opening of the IGBT and the arc 68 goes out. In other words, the portion 74 of the control circuit 78 provides the opening control of the IGBT. We are entering phase 38.
• As a result of the extinction of the arc 68, the capacitors C ₁ and C ₂ discharge respectively into resistors R ₃ and R ₆ .

A varistor V ₁ is provided to ensure the protection of the IGBT by eliminating the eventual peak of lightning current associated with the overvoltage in the case where there is still an overvoltage at the time of the separation of the arc 62 into arcs. 64 and 68. In general, in all the embodiments described above, the positioning of the intermediate electrode 26 on the D side of the main electrodes can be adjusted to ensure a desired time delay of the duration of the phase. phase 32 may thus correspond to a sufficiently long duration for the surge episode, for example due to a lightning strike, to be completed before the start of phase 34.

Back to the figure 4 diodes D ₁ , D ₂ and D _{3 are provided} to protect the circuit 78 by forcing the direction of the current. Thus the portion 76 of the control circuit 78 provides protection for the IGBT.

According to one embodiment, the semiconductor switch may comprise a plurality of IGBTs arranged in parallel with each other, for example two IGBTs in parallel. Such an IGBT parallel arrangement allows the semiconductor switch thus formed to flow a greater current current in a row than the semiconductor switch having a single IGBT. Such an embodiment is particularly advantageous for uses of the proposed device relating to the protection of photovoltaic installations capable of supplying currents of high intensity, such as an intensity greater than 1000 A. According to this embodiment, the circuit of FIG. command 78 illustrated in figure 4 can be used alone for the parallel control of the plurality of IGBTs.

In the particular case of the circuit illustrated in figure 4 a current limiting resistor R _p can be arranged in series with the diode D1. R _p has a resistance large enough to limit the intensity of the current flowing through the control circuit 78 to a level below the threshold intensity of the arc-holding current 68. In other words, the limiting resistor R _p prevents the flow of current from the arc 68 to the electrode 24 through the control circuit 78. Thus, the limiting resistor R _p contributes to the extinction of the arc 68, at the moment of the transition between phases 36 and 38, that is to say at the moment when the IGBT which flowing the stream of continuation 42 of the arc 68 is opened, the arc 64 having been extinguished by the prior closure of the IGBT.

In general, depending on the embodiment chosen for the control circuit 78, any other means for limiting the intensity of the current flowing through the control circuit 78 may be provided to limit such intensity to a level below the control current. threshold intensity of the current maintaining the arc 68 in the proposed device. According to a preferred embodiment, the choice of the intensity limiting means results from a compromise between limiting the intensity of the control circuit and obtaining a level for this intensity which is sufficient to operate. the control circuit of the semiconductor switch.

According to a preferred embodiment, the device may comprise a magnet arranged to move the electric arc 62 from the first side P to the second side D. The magnet may correspond to the assembly of opposite poles of separate permanent magnets. The figure 5 shows a schematic representation of an embodiment of the protective device proposed with the magnet 80. This magnet 80 is formed by the assembly of two opposite poles of separate permanent magnets 82 and 84. The gap between the magnets 82 and 84 may be held by any suitable member such as air gaps 86. The magnet 80 is arranged to generate magnetic field lines 88 passing through the spark gap 20 which are perpendicular to both the direction of extension of the arc. 62 and the direction of the desired movement of the arc 62. The orientation of the magnet 80 conditions the movement of the arc 62 from the P side to the D side.

In a general case of a device without a magnet, the electric arc formed in the device moves under the effect of its own energy. The greater the intensity of the current flowing through the arc, the easier the movement of the arc is. In contrast, when the intensity of the current flowing through the arc is too small, the arc 62 may present difficulties to move under the sole effect of its own energy. However for some electrical installation including photovoltaic power generation facilities, the current can follow very low values. Indeed, the following current of a photovoltaic power generation installation can have several values between a value near zero (night) and a maximum value (the cloudless day). These short current values, such as currents of the order of 0.5A, may not be sufficient for the operation of the breaking systems based solely on the movement of the arc under its own energy. The use of the magnet in the device 90 then makes it possible to facilitate the movement of the arc 62 even in the case of a low current intensity. Such an embodiment of the device 90 makes it possible to obtain a device for protecting an electrical installation against overvoltages, independently of the value of the following current. Alternatively or in addition the main electrodes 24 and 28 of the device may be divergent from the first side P towards the second side D, as illustrated in figures 1 and 3 . The divergence of the main electrodes contributes, like the magnet, to the displacement of the electric arc 62 from P to D.

Alternatively or additionally, the intermediate electrode 26 may have a corner end portion on the side where the intermediate electrode 26 extends between the two electrodes 24 and 28. The wedge end of the intermediate electrode is then the end of the electrode that is closest to the D side of the main electrodes 24 and 28. According to the figure 3 such a wedge end portion 66 may have a triangular shape. The corner end of the intermediate electrode 26 makes it possible to present surfaces of the electrode 26 which are parallel to the electrodes 24 and 28, when the electrodes 24 and 28 are divergent. The production of such parallel surfaces contributes to facilitating the displacement of the arc 62 from the P side to the D side when the arc 62 separates into the two arcs 64 and 68. Indeed, when entering the phase 34, these parallel surfaces limit the increase of the voltage across the main electrodes 24 and 28 due to the non-increase in the distance to be traveled by the arcs between the electrodes 24 and 28.

The Figures 6 and 7 show exploded views of a preferred embodiment of the protective device proposed in the cartridge 92 "mountable" on DIN rail. The figure 6 shows an exploded view of the right side of the device 20 while the figure 7 shows an exploded view of the left side of the device 20. The figure 6 allows the viewing of the spark gap 20 formed by the electrodes 24, 26 and 28. The cartridge or the housing 92 is formed in four parts. Two middle portions of the cartridge 92 allow the formation of an envelope around the spark gap 20. The two other parts of the cartridge 92 are the two end portions of the cartridge 92. These extremal parts ensure the formation of an envelope around magnets 82 and 84. According to this embodiment illustrated in figure 7 , the end portion of the cartridge 92 which forms the envelope of the magnet 82 houses the assembly 70 formed by the IGBT and the control circuit 78.

The figure 8 illustrates the two connection terminals 98 and 94 of the device 90 to the electrical installation to be protected. The electrode 24 is connected to the terminal 94 while the electrode 28 is connected to the terminal 98.

The figure 8 also shows a schematic representation of a preferred embodiment of the protection device and which is an improvement of the embodiment illustrated by the Figures 6 and 7 . According to figure 8 , the device 90 comprises an additional terminal 198 in addition to the two connection terminals 98 and 94. Still according to this figure the device 90 comprises a spark gap 120 additional to the spark gap 20 previously described. This spark gap 120 includes two additional electrodes 124 and 128. The electrode 128 is connected to the additional terminal 198 while the electrode 124 is connected to the electrode 24. According to this embodiment this additional spark gap 120 may be free of intermediate electrode. The electrodes 124 and 128 of the additional spark gap 120 may also diverge between a first side P and a second side D. The device 90 with the additional terminal 198 may be connected to three separate conductors of the electrical installation to be protected. Thus the device 90 can provide a Y-mode of protection between two active conductors of the electrical installation to be protected and a ground conductor.

When the electrical installation to be protected is a DC - operated installation, the two active conductors are respectively the polarity conductor + and the polarity conductor -. It is estimated that in 60% of the installations of this type, the polarities + and - are floating relative to the earth. For the remaining installations where one of the active conductors is connected to the earth, it is estimated that it is the polarity + conductor that is connected to the earth in 95% of the cases. Thus when using the device 90 in the Y-protection mode, the terminals 98 and 198 are preferably connected to the polarity-and + conductors respectively, while the terminal 94 can be connected to the earth. According to this connection diagram, for the vast majority of installations operating under direct current, the spark gap 20 with the intermediate electrode 26 is connected between the ground and an active connector not connected to the ground. This allows the device 90 to provide effective Y protection with a break in current for the vast majority of DC-powered installations.

In the case of a single-phase electrical installation operating on alternating current, one of the two protected active conductors may be the phase while the other of the two protected active conductors may be the neutral.

In a symmetrical embodiment of the device 90 as illustrated in FIG. figure 8 , another terminal 194 may be provided at the connection of the electrode 124 to the electrode 24. However, this terminal 194 is at the same potential as the terminal 94.

Still referring to the figure 8 , the embodiment of the device 90 with the additional terminal 198 can be housed in a housing 92 "mountable" on DIN rail having a width L less than or equal to three times the standard width of 17.5mm of the housings "mountable" rail DIN. In one embodiment of the device without additional terminal, the device 90 may comprise a housing 92 "mountable" on a DIN rail having a width less than or equal to twice the standard width of 17.5 mm of the boxes "mountable" on DIN rail .

The device 90 in the various embodiments described above may comprise a device for triggering an arc between the electrodes 24 and 28, or 124 and 128 where applicable. The figure 8 illustrates such a trigger member 22. The trigger member 22 may comprise an arc triggering electrode on the P side of the spark gap 20, where appropriate on the P side of the spark gap 120. Thus, the electrode The trigger is positioned on the side of the main electrodes where the formation of an electric arc is easiest during the occurrence of an overvoltage. As a result, such an electrode for triggering an electric arc differs from the intermediate electrode described above.

Claims (15)

1. A method of extinguishing an electric arc formed between two main electrodes, the method comprising:

   moving the formed arc to an electrode (26) located in an intermediate position between the two main electrodes (24,28);

   separating the formed electric arc (62) into two secondary electric arcs (64, 68) between the main electrodes (24, 28) and the intermediate electrode (26),

   characterized in that

   a normally open semiconductor switch connecting the intermediate electrode (26) to one of the main electrodes (24);

   closing the semiconductor switch to extinguish the secondary electric arc (64) between the two electrodes (24, 26) connected by the semiconductor switch;

   opening the semiconductor switch to extinguish the other secondary electric arc (68).
2. The method of extinguishing according to claim 1, the method comprising a delay after the separation of the formed arc (62) into two secondary electric arcs (64, 68) to prevent the reformation of an arc between the two main electrodes (24, 28) upon closing of the semiconductor switch.
3. The method of extinguishing according to claim 1 or 2, the method comprising a time delay after the closing of the semiconductor switch to prevent reformation, upon opening of the semiconductor switch, of the arc extinguished between the intermediate electrode (26) and one of the main electrodes (24).
4. A method of protecting an electrical installation against transient overvoltages, the method implementing the extinguishing of an electric arc according to the method of one of claims 1 to 3 in the event of occurrence of a transient overvoltage in the electrical installation to be protected causing the formation of a first electric arc (62) between the two main electrodes (24, 28), the main electrodes (24, 28) being connected to the electrical installation to be protected.
5. A method of protecting an electrical installation according to claim 4, the electrical installation to be protected being an electrical installation connected to a low voltage electrical distribution network.
6. A method of protecting an electrical installation according to claim 5, the electrical installation to be protected being an electrical installation operating under direct current, preferably a photovoltaic power generation installation.
7. Device for protecting an electrical installation against transient overvoltages, comprising:

   two terminals (94, 98) for connecting the device to the electrical installation to be protected;

   a first main electrode (24) and a second main electrode (28), each main electrode (24, 28) being connected to a respective one of the connection terminals (94, 98);

   an electrode (26) located in an intermediate position between the first main electrode (24) and the second main electrode (28);

   characterized in that it comprises:

   a normally open semiconductor switch connecting the intermediate electrode (26) to the first main electrode (24);

   a circuit (78) for controlling the semiconductor switch, the control circuit being provided for successively closing the switch and then opening the switch after an electric arc (62) formed between the main electrodes is divided into two arcs (64, 68) by the intermediate electrode (26).
8. Device according to claim 7, wherein the semiconductor switch is an insulated gate bipolar transistor or a metal oxide gate field effect transistor.
9. Device according to claim 7 or 8, wherein the control circuit provides a time delay between the division of the electric arc into two arcs by the intermediate electrode and the closing of the switch and/or between the closing of the switch and the opening of the switch.
10. Device according to one of claims 7 to 9, wherein the electrodes (24, 26, 28) are fixed, the two main electrodes (24, 28) being positioned opposite one another from a first side (P) to a second side (D), and forming a spark gap; and the intermediate electrode (26) extending partially between the two main electrodes (24, 28) from the second side (D).
11. Device according to claim 10, comprising an arc tripping member (22) between the main electrodes (24, 28) in case of occurrence of a transient overvoltage on the electrical installation to be protected, the arc tripping member (22) having an arc triggering electrode from the first side (P) of the main electrodes (24, 28).
12. Device according to claim 10 or 11, wherein the intermediate electrode (26) has a corner end portion (66) at the side (D) where the intermediate electrode (26) extends between the two main electrodes (24, 28).
13. Device according to one of claims 10 to 12, comprising a magnet (80) arranged to move in the direction from the first side (P) to the second side (D), an electric arc being formed between the main electrodes (24, 28) of the spark gap (20) and/or the main electrodes diverging from the first side (P) to the second side (D).
14. Device according to one of claims 10 to 13, comprising an additional connection terminal (198) and an additional spark gap (120) formed by two additional electrodes (124, 128), one (128) of the additional electrodes being connected to the additional terminal (198) and the other (124) of the additional electrodes being connected to one (94) of the two connection terminals of the device (90) to the electrical installation.
15. Device according to one of claims 7 to 14, specially designed for the implementation of the method according to one of claims 4 to 6.

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