CN109149371B

CN109149371B - Surge arrester

Info

Publication number: CN109149371B
Application number: CN201810688134.5A
Authority: CN
Inventors: T.迈尔; J-E.施姆茨; R.杜尔特; H.扎格比尔
Original assignee: Phoenix Contact GmbH and Co KG
Current assignee: Phoenix Contact GmbH and Co KG
Priority date: 2017-06-28
Filing date: 2018-06-28
Publication date: 2020-12-25
Anticipated expiration: 2038-06-28
Also published as: CN109149371A; DE102017114383B4; DE102017114383A1

Abstract

A surge arrester for use in a current supply device of a low-voltage network is described and shown, having a housing, having two electrodes, and having an arc chamber formed in the interior of the housing. In the case of the surge arrester according to the invention, the energy conversion in the surge arrester is reduced by providing at least one third electrode, which is likewise in contact with the arc chamber, wherein the distance of the first electrode from the second electrode is smaller than the distance of the first electrode from the third electrode, so that the at least three electrodes are arranged relative to one another in such a way that, in the event of an ignition of the spark gap, a first arc first occurs only between the first electrode and the second electrode and, in the event of a gradually increasing ionization of the arc chamber, a second arc additionally occurs also between the second electrode and the third electrode, and the first electrode and the third electrode are connected to one another directly or via electrical components.

Description

Surge arrester

Technical Field

The invention relates to a surge arrester (Ü berspannungsableiter) for use in a current supply device (Stromversorgung) of a low-voltage network, comprising a housing, comprising two electrodes and comprising an arc chamber formed in the interior of the housing, wherein the two electrodes are each in contact with the arc chamber and a spark gap (Funkenstrake) is formed between the two electrodes, so that in the event of ignition of the spark gap between the two electrodes an arc occurs and a surge current (Sto beta strom) to be discharged can flow via the low-impedance connection.

Background

When overvoltages occur which lie above the upper tolerance of the respective nominal voltage, the relevant instruments, installations and lines must be short-circuited in the shortest possible time with potential equalisation (potentiausgleich). For this purpose, different surge arresters are used depending on the location (protective area) and type of use of the equipment and the installation to be protected. In this case, the individual surge arresters are distinguished approximately by their response characteristic (ansreceverhalten) and their discharge capacity (abletiverm ribbon).

In low-voltage networks, spark gap-based surge arresters are often used to protect against overvoltages, i.e. the main component of a surge arrester is a spark gap, which responds in the event of a defined overvoltage. In the case of the ignition of the spark gap, an arc is formed here between the two electrodes. Since surge arresters with spark gaps are used in particular for protection in the event of high-energy events, for example lightning strikes (Blitzeinschlag), very high and steeply rising currents can flow through the spark gap with values in the kA range up to three bits.

Surge arresters with a spark gap as arrester have the advantage of a high surge current carrying capacity (stosstromtrgf ä highkeit) on the one hand, but have the disadvantage of a relatively high and likewise not particularly constant response voltage on the other hand. For ignition of spark gaps, therefore, different types of ignition aids (zndenhilfe) have been used for a long time, by means of which the response voltage of the spark gap or of the surge arrester is reduced.

In the case of the mentioned surge arresters (with or without the use of ignition aids), in the case of a spark gap ignited via an arc, a low-impedance connection between the two electrodes is formed, via which then first a high-energy transient surge current flows which is to be discharged. In the case of the presence of a mains voltage, however, an undesired mains free flow (netzfoldestrom) can likewise flow via this low-impedance connection, which in any case can lead to the destruction of the upstream safety device. The instruments and facilities are then protected against damage due to overvoltage, but the availability of the instruments or facilities is not yet available until the damaged safety device is replaced.

An important requirement of modern surge arresters is therefore to extinguish the arc as quickly as possible after the end of the discharge process, so that a cancellation or suppression of the mains free-wheeling likewise occurs. For this purpose, attempts are usually made to increase the arc voltage, i.e. the voltage which must be present between the two electrodes so that the arc continues to burn, to such an extent that the occurring network freewheeling is suppressed or reduced. One possibility for increasing the arc voltage consists in increasing the arc length after the response of the spark gap. Another possibility for increasing the arc voltage after the discharge process consists in the cooling of the arc by the cooling effect of the insulating material walls, the use of insulating materials which emit gas and the limitation of the arc into the narrow gap between the electrodes (Einengung).

The method of increasing the arc voltage by cooling the arc, for example, by means of a gas-emitting insulating material, is relatively strongly dependent on the level (hhine, sometimes also referred to as altitude) and duration of the surge current to be discharged. High energy events (e.g. lightning strikes) result in a strong blow of the arc through the insulating material walls emitting gas (beblastun), so that such pulses with a high energy conversion (energieumesatz) generally result in a fast suppression of the grid follow current. In the case of a short and thus low-energy event, the blowing of the arc by the rush current itself may not lead to a sufficient increase in the arc voltage, so that it only occurs with delay to suppress the grid follow current. In this case, therefore, it must be ensured by a sufficiently large arc length that the network freewheeling is reliably eliminated.

The desired increase in the arc voltage for suppressing the network freewheeling is not dependent on the method implemented for increasing the arc voltage, but has the disadvantage that, due to the increased arc voltage, an increased energy conversion takes place in the surge arrester, in particular in the arc chamber, during the discharge of the inrush current. This leads to problems, in particular, in the case of largely closed surge arresters, that is to say encapsulated, non-blown surge arresters, since the energy converted into heat can only leave the arc chamber relatively slowly. The material surrounding the arc chamber is thus subjected to very high temperatures over a relatively long time. The insulating material used for cooling and blowing the arc is particularly dangerous here. Furthermore, surge arresters must also be able to withstand the high pressures which occur in the case of surge current discharges, which requires a complex design.

DE 10338835 a1 discloses a surge arrester in which the occurrence of a mains free-wheeling is prevented in that the distance between the two electrodes is selected to be so large that the arc voltage is greater than the desired mains voltage. In order to ensure that the response voltage of the surge arrester is not too great by the relatively large spacing of the two electrodes of the spark gap, an ignition aid is provided, by means of which the desired response voltage of the surge arrester can be set. In the case of this surge arrester, the cylindrical arc chamber has a relatively small diameter, which corresponds to the diameter of the free end sides of the electrodes lying opposite one another. Furthermore, the arc chamber is almost completely surrounded by an insulating material, which not only causes cooling of the arc but also causes a limitation of the arc. Both of these, as described above, lead to a desired increase in the arc voltage, and thus, however, also to an undesirably high energy conversion in the arc chamber.

In order to dissipate the heat which is formed in the arc chamber after the arc has been ignited, in the case of the known surge arresters, cooling ducts are formed in the housing, which are connected to the arc chamber. The hot ionized gases produced by the arc in the case of a discharge process in the arc chamber can therefore be drawn out of the arc chamber and ultimately also out of the housing. In order for the gas flowing out of the housing not to have an excessively high temperature, the cooling channel must be designed such that it makes available a sufficiently long path (wegstreecke) along which the plasma flows in the housing. In the case of the surge arrester known from DE 10338835 a1, this is achieved in that the metal housing is designed in two parts and the two housing halves are arranged coaxially with respect to one another. Between the two housing parts, a cooling channel in the form of a spiral is formed, which serves for screwing the two housing parts to one another and through which the plasma can likewise flow at the same time.

In order to be able to withstand the higher pressures and temperatures occurring in the case of surge arresters, the design requirements for the housing and the material surrounding the arc chamber are very high. In particular, in order to ensure sufficient mechanical stability, the wall thickness of the two housing parts which together form the metal housing must be relatively large, which overall results in a correspondingly increased outer diameter of the housing. Furthermore, a spiral cooling channel is arranged between the two housing parts for cooling the gas flowing out of the housing, which increases the manufacturing costs of the housing parts accordingly.

Disclosure of Invention

The invention is therefore based on the object of developing a surge arrester of the type mentioned at the outset in such a way that the aforementioned disadvantages are avoided as far as possible. In particular, it should be achieved here that the energy conversion in the surge arrester is as small as possible in the event of a surge current discharge. The grid freewheeling should however be able to be eliminated reliably and as quickly as possible.

This object is achieved in the case of the surge arrester described at the outset with the features of patent claim 1 in that at least one third electrode is provided, which is likewise in contact with the arc chamber, wherein the distance a between the first and second electrodes is smaller than the distance b between the first and third electrodes, and the first and third electrodes are connected to one another directly or via an electrical component. The geometry of the surge arrester according to the invention, in which the third electrode has a greater distance from the first electrode than the second electrode, leads to the fact that, in the event of an ignition of the spark gap, a first arc is first only present between the first electrode and the second electrode and, in the event of a gradually increasing ionization of the arc chamber, a second arc is additionally also ignited between the second electrode and the third electrode.

By providing at least one third electrode in the case of the surge arrester according to the invention, the arc chamber has two regions or, in the case of more than three electrodes, likewise a plurality of regions. If the discharge is effected via a short pulse of low energy of the surge arrester according to the invention, this pulse flows through the arc between the first and second electrode. In this case, the ionization formed in the arc chamber does not progress to such an extent or the plasma cloud (plasma cloud) formed does not spread to such an extent that the arc is likewise ignited between the second and third electrodes. With increasing duration of the pulse to be discharged, however, the ionization rise in the arc chamber or the plasma cloud expands further in the direction of the third electrode, so that then an ignition of a second arc between the second electrode and the third electrode likewise occurs.

This creates a surge arrester in which, depending on the energy content of the surge current to be discharged (energy), either an arc is present only between the first and second electrodes or, in addition, a further arc is also ignited (delayed in time) between the second and third electrodes. This creates the possibility that the inrush current with a lower energy content is discharged via the arc between the first and second electrode, wherein the arc burning voltage can be selected relatively high, so that the arc can be extinguished quickly after the end of the discharge process and thus the network freewheeling can be suppressed. Since the energy content of the surge current to be discharged or its duration is very short, the energy conversion in the surge arrester is not so high despite the increased arc voltage that an impermissible load is produced and excessive wear of the material surrounding the arc chamber occurs.

If the duration of the inrush current to be discharged via the surge arrester according to the invention is, however, relatively long, this, as described above, results in the region between the second electrode and the third electrode also being ionized so strongly in the arc chamber that ignition of the arc between the second electrode and the third electrode likewise occurs. Since the first electrode and the third electrode are connected to one another directly or via an electrical component, the first arc between the first electrode and the second arc between the second electrode and the third electrode are parallel to one another, i.e. two parallel paths are obtained via which the surge current to be discharged flows. The total impedance of this parallel connection (sometimes also referred to as a parallel circuit) of the two paths is smaller than the impedance of the two individual paths, which leads to a reduction in the energy conversion in the event of a discharge of the rush current in the arc chamber.

The geometry described above, in particular the arrangement of the three electrodes with respect to one another, of the surge arrester according to the invention can be determined in practice in such a way that a low-energy pulse with a pulse shape (Impulsform) "8/20 μ s" is discharged via a first arc between the first electrode and the second electrode, while a high-energy pulse with a pulse shape "10/350 μ s" is additionally also discharged via a second arc between the second electrode and the third electrode.

In order to reliably achieve the previously described reduction of the energy conversion in the case of a rush current discharge, it must be ensured that the rush current to be discharged flows through two paths after ignition of the second arc between the second electrode and the third electrode. It should therefore be prevented by suitable design and/or circuit-technical measures that the arc is completely diverted from the first path to the second path and then only the second arc burns and the surge current is discharged only via this second arc.

According to an advantageous embodiment of the surge arrester according to the invention, the surge arrester is geometrically designed such that the distance a between the first and second electrodes is smaller than the distance c between the second and third electrodes. Alternatively or additionally, the cross section a of the arc chamber in the region between the first and second electrode can likewise be selected to be greater than the cross section C of the arc chamber in the region between the second and third electrode. The smaller cross section of the arc chamber causes a stronger constriction or confinement of the arc in this region. By means of two measures, it is thus achieved that the impedance of the current path (Strompfad) via the second spark gap between the second electrode and the third electrode is higher than the impedance of the current path via the spark gap between the first electrode and the second electrode.

According to a further embodiment of the surge arrester according to the invention, the surge arrester is geometrically designed such that the distance a between the first and second electrodes is not less than the distance c between the second and third electrodes. The distance a between the first and second electrodes is therefore smaller than or just as large as the distance c between the second and third electrodes. Alternatively or additionally, the cross section a of the arc chamber in the region between the first and second electrode can likewise be selected to be no greater than the cross section C of the arc chamber in the region between the second and third electrode. In addition, the first electrode is electrically connected to the third electrode via an impedance, so that in the case of this embodiment too it can be ensured that the impedance of the current path via the second spark gap is higher than the impedance of the current path via the first spark gap. It is thus ensured that the arc does not completely switch from the first path to the second path after ignition of the second spark gap.

Initially, it is provided that at least one third electrode is provided, the distance b of which from the first electrode is greater than the distance a of the second electrode from the first electrode. According to the invention, in addition to the third electrode, further electrodes, for example a fourth electrode and a fifth electrode, which then themselves have a larger distance from the first electrode than the preceding electrode, can likewise be provided. In this way, it is possible to achieve that, with a correspondingly longer impulse current to be discharged, an additional arc is ignited between the respectively further adjacent electrodes, i.e. for example between the third electrode and the fourth electrode, with a gradually increasing duration and thus an increasing ionization of the arc chamber. If, in this case, the further electrode is connected directly or via an electrical component to the first electrode or the third electrode, this then leads to a further reduction in the overall impedance of the ignited spark gap and thus to a reduction in the energy conversion in the arc chamber.

There are numerous possibilities of how surge arresters, and in particular the arc chamber and the individual electrodes, can be designed structurally and geometrically. According to a preferred embodiment, the first electrode is of disk-shaped design and is arranged such that it delimits the arc chamber on one side. In contrast, the second and third electrodes are each of annular design and are arranged such that they locally delimit the arc chamber radially. The arc chamber thus extends through the second and third electrodes, wherein the two electrodes are arranged one behind the other in the longitudinal direction of the arc chamber. In the case of this design and arrangement of the electrodes, the arc chamber can be of cylindrical design. Likewise, it is also possible, however, for the diameter of the arc chamber to change in the longitudinal direction, for example to decrease from the first electrode in the direction of the third electrode.

According to an alternative embodiment, the first electrode can also be of annular design, wherein the arc chamber is then bounded on the side adjacent to the first electrode by a material made of an insulating material, in particular a gas-filled insulating material. If the third electrode is likewise of annular design, in addition to the second electrode, the arc chamber is likewise bounded on the second side by an insulating material. On this side of the arc chamber opposite the first side, the opening is formed as a passage (Durchgang) to a blow-out channel (ausblastkanal, sometimes also referred to as a quenching channel) in the insulating material. In principle, it is also possible to design the third electrode not in the form of a ring but in the form of a disk, so that the arc chamber is then bounded on the second side by the third electrode. In this case, it is then preferred that in the third electrode the opening is configured as a passage to the blow-out channel.

Initially, the first electrode and the third electrode are connected to one another directly or via an electrical component. If the first electrode and the third electrode are directly conductively connected to one another, the two electrodes have the same potential. Alternatively, the first electrode and the third electrode can also be connected to one another via an electrical component, for example an impedance, wherein the control of the voltage drop (Spannungsabfall) between the first electrode and the third electrode can be achieved by the selection of the impedance. As an alternative to a linear resistor as an impedance, a non-linear resistor element can also be used as an electrical component, for example a temperature-dependent resistor, i.e. a cold conductor or a hot conductor.

Furthermore, as the electrical component via which the first electrode and the third electrode are connected to one another, a voltage switching element, for example a gas-filled surge arrester or a voltage limiting component (for example a varistor or a suppressor diode), can likewise be used. Obviously, combinations of the electrical components mentioned above are likewise conceivable.

In order to influence the flow of the thermionic gas in the arc chamber in a targeted manner, the wall surrounding the arc chamber is at least partially formed from a gas-filled insulating material, for example POM, at least in the region between the first and second electrodes. Thereby, the flow of the plasma from the first electrode to the second electrode and further to the third electrode can be adjusted, whereby it can be influenced as well when, in addition to the first arc between the first electrode and the second electrode, a second arc between the second electrode and the third electrode is ignited as well. The time of ignition of the two arcs can also be influenced via the distance of the electrodes from one another and via the shape of the arc chamber.

In addition, a further possibility for influencing the flow of the thermionic gas in the arc chamber consists in forming at least one opening in the side of the arc chamber opposite the first side. Furthermore, such openings also make it possible to achieve a targeted discharge of the plasma from the arc chamber, as a result of which the pressure in the arc chamber can be reduced in a targeted manner. Furthermore, a faster suppression of the occurring network freewheeling and an additional cooling effect can be achieved by means of one or more openings.

In order to be able to set the response voltage to a sufficiently low and constant value in the case of the surge arrester according to the invention, an ignition aid is provided according to a further advantageous embodiment of the invention. In principle, the ignition of the spark gap can be achieved in different ways. According to a preferred embodiment, an ignition aid is provided, which comprises at least an ignition element and an ignition electrode. The ignition element and the ignition electrode are in contact with the arc chamber, wherein the ignition element is electrically conductively connected to the first electrode on one side and to the ignition electrode on the other side. In addition, the ignition aid preferably also has a voltage switching element, so that the ignition aid is constructed from its basic structure in the same way as the ignition aid described in DE 10338835 a 1.

Drawings

In detail, there are a number of possibilities for designing and improving the surge arrester according to the invention. For this purpose, reference is made not only to the patent claims which follow patent claim 1, but also to the following description of two preferred embodiments in conjunction with the accompanying drawings. In the drawings:

figure 1 shows a principal illustration of a first embodiment of a surge arrester in cross section,

fig. 2 shows a schematic representation of a second exemplary embodiment of a surge arrester in section without a housing, and

fig. 3 shows a schematic representation of a third exemplary embodiment of a surge arrester in section without a housing.

Detailed Description

Fig. 1 shows a schematic representation of a first exemplary embodiment of a surge arrester 1 according to the invention in cross section. The surge arrester 1 has a housing 2 in which a first electrode 3 and a second electrode 4 are arranged and an arc chamber 5 is formed. In addition to the housing 2, which is only schematically illustrated in fig. 1, the surge arrester 1 may additionally also have an outer housing, which is made of steel, for example, so that a high compressive strength is ensured.

A spark gap is formed between the two

electrodes

3,4, which are in contact with the arc chamber 5, so that a first arc 6 occurs in the event of ignition of the spark gap between the two

electrodes

3, 4. In the case of the ignition of the spark gap, a low-impedance connection between the two

electrodes

3,4 is thus formed via the arc 6, via which a momentary surge current to be discharged can flow. For this purpose, for example, the first pole 3 is connected to a neutral conductor interface (neutralliter-anshluss) or PE interface and the second pole 4 is connected to an interface for one phase of the current supply device to be protected.

In addition to the first electrode 3 and the second electrode 4, a third electrode 7 is also provided, which is likewise in contact with the arc chamber 5. This third electrode 7 is in the case of the embodiment shown in fig. 1 directly connected to the first electrode 3 via an electrically conductive connection 8 as a return path. In contrast to this, in the case of the exemplary embodiment according to fig. 2, the first electrode 3 and the third electrode 7 are not connected to one another directly, but via an electrical component 9. The electrical component 9 can be, in particular, a resistor 9' or a voltage switching element, for example, a varistor or a gas-filled surge arrester 9 ″, as is shown in fig. 2 as an alternative.

As is evident from the schematic representation according to fig. 1 and 2, the distance a between the first electrode 3 and the second electrode 4 is smaller than the distance b between the first electrode 3 and the third electrode 7. In the longitudinal direction of the arc chamber 5, starting from the first electrode 3, the second electrode 4 is first arranged and then the third electrode 7 is arranged. Furthermore, the distance c between the second electrode 4 and the third electrode 7 is greater than the distance a between the first electrode 3 and the second electrode 4. The cross section of the arc chamber 5 is constant over its entire length, so that likewise the cross section a in the region between the first electrode 3 and the second electrode 4 is just as large as the cross section C in the region between the second electrode 4 and the third electrode 7. Both embodiments are common to the fact that the first electrode 3 is of disk-shaped design and delimits the arc chamber 5 on the first side 5 a. In contrast, the second electrode 4 and the third electrode 7 are each designed in the form of a ring, so that the two

electrodes

4,7 bound the arc chamber 5 radially with their inner surfaces.

The wall 10 of the arc chamber 5, which radially surrounds the

electrodes

4,7, is made of an insulating material, wherein at least in the region of the wall 10 between the first electrode 3 and the second electrode 4, preferably a gas-filled insulating material, for example POM. Thereby, the influence of the flow of the thermionic gas within the arc combustion chamber 5 is possible, so that the plasma is spread in the direction of the third electrode 7 after ignition of the first arc 6 between the first electrode 3 and the second electrode 4. If a short pulse of low energy is discharged via the surge arrester 1, the pulse flows through the arc 6 between the first electrode 3 and the second electrode 4. With increasing duration of the pulse to be discharged, the ionization in the arc combustion chamber 5 increases or the plasma cloud expands further in the direction of the third electrode 7, so that then additionally an ignition of the second arc 6' between the second electrode 4 and the third electrode 7 likewise takes place.

In the case of the surge arrester 1 according to the invention, depending on the energy content of the surge current to be discharged, either an arc 6 is formed only between the first electrode 3 and the second electrode 4 or, in addition, a further arc 6' is formed between the second electrode 4 and the third electrode 7, with a time delay. The inrush current with a lower energy content is thus discharged only via the arc 6 between the first electrode 3 and the second electrode 4, the arc burning voltage here being relatively high, so that the arc 6 is rapidly extinguished after the end of the discharge process and thus the grid freewheeling is effectively suppressed.

If the duration of the inrush current to be discharged is longer, this results in the ionized gas further expanding in the direction of the third electrode 7 within the arc chamber 5, so that the region between the second electrode 4 and the third electrode 7 is then likewise ionized so strongly that ignition of the second arc 6' between the second electrode 4 and the third electrode 7 occurs. The two arcs 6,6' form two parallel paths between the second electrode 4 and the first electrode 3 or between the second electrode 4 and the third electrode 7, so that the total impedance of the two paths in parallel is smaller than the impedance of the two separate paths, which leads to a reduction of the energy conversion of the impulse current in the case of a discharge in the arc chamber 5. The two arcs 6,6' then burn at a lower arc burning voltage than if only the first arc 6 burned. This leads to the fact that, in the case of high-energy pulses to be discharged, the energy transfer in the arc chamber 5 is likewise not so high that impermissible loads or even damage to the surge arrester 1 occurs.

In the case of both embodiments according to fig. 1 and 2, by making the spacing a between the first electrode 3 and the second electrode 4 smaller than the spacing c between the second electrode 4 and the third electrode 7, the impedance of the current path via the first spark gap between the first electrode 3 and the second electrode 4 is smaller than the impedance of the current path via the second spark gap between the second electrode 4 and the third electrode 7. This prevents the rush current to be discharged after ignition of the second spark gap from flowing only through the second path or the second arc 6'.

Alternatively, the impedance of the second arc 6' can also be increased by the cross section C of the arc chamber 5 in the region between the second electrode 4 and the third electrode 7 being smaller than the cross section a of the arc chamber 5 in the region between the first electrode 3 and the second electrode 4. This results in a stronger limitation of the second arc 6' and additionally also in the case of a corresponding selection of the material of the surrounding wall 10, in a targeted stronger cooling of the arc 6', both of which lead to an increase in the impedance of the second arc 6 '. This embodiment is implemented in the case of the exemplary embodiment according to fig. 3. In the case of the embodiment according to fig. 3, the spacing a between the first electrode 3 and the second electrode 4 is just as large as the spacing c between the second electrode 4 and the third electrode 7. However, it is also possible to select the distance a between the first electrode 3 and the second electrode 4 to be smaller or larger than the distance c between the second electrode 4 and the third electrode 7, as long as the impedance of the current path via the spark gap between the first electrode 3 and the second electrode 4 is not greater than the impedance of the current path via the second spark gap between the second electrode 4 and the third electrode 7.

Finally, the impedance of the second circuit can also be adjusted by selection of the electrical component 9, via which the first electrode 3 is connected to the third electrode 7. Furthermore, different materials can likewise be used for the

individual electrodes

3,4,7 or the

electrodes

3,4,7 can have different dimensions, in particular different thicknesses. Furthermore, the measures described above can also be combined with one another, i.e. for example the cross section C of the arc chamber 5 in the region between the second electrode 4 and the third electrode 7 is smaller than the cross section a of the arc chamber 5 in the region between the first electrode 3 and the second electrode 4, and additionally the first electrode 3 and the third electrode 7 are connected to one another via an impedance 9'.

In order to enable a targeted influence of the flow of the thermionic gas in the arc combustion chamber 5 and in particular a targeted removal of the hot gases from the arc combustion chamber 5, an opening 11 in a wall 10 bounding the arc combustion chamber 5 is formed on a second side 5b of the arc combustion chamber 5 opposite the first side 5a, and is connected to a blow-off channel 12. Through the openings 11 and the blow-off channels 12, the hot ionized gas can thus be discharged in a targeted manner from the arc chamber 5, whereby the pressure in the arc chamber 5 can likewise be reduced in a targeted manner. In order to achieve sufficient cooling of the hot gas before it exits from the surge arrester 1, the blow-out channel 12 preferably runs along an outer housing made of metal.

In the case of the surge arrester 1 according to the invention, the spacing a between the first electrode 3 and the second electrode 4 is selected so large that network freewheeling can be eliminated sufficiently quickly and reliably even in the case of low-energy surge currents (in which the insulating material wall 10 emits only a small amount of gas). In order to prevent the response voltage of the surge arrester 1 from becoming too high, an ignition aid 13 is provided, which has an ignition element 14, an ignition electrode 15 and a varistor 16. In this case, the ignition element 14 and the ignition electrode 15 are in contact with the arc chamber 5, the ignition element 14 being electrically conductively connected on one side to the first electrode 3 and on the other side to the ignition electrode 15.

If an overvoltage greater than the threshold voltage of the varistor 16 occurs at the surge arrester 1, a current first flows through the varistor 16, the ignition electrode 15 and the ignition element 14 to the first electrode 3. In this case, due to the low current carrying capacity of the ignition element 14, an ionization in the arc chamber 5 occurs, which causes the ignition of the first arc 6 between the first electrode 3 and the second electrode 4. Furthermore, however, other types of ignition aids (known per se from the prior art) can also be used which cause the overvoltage arrester 1 to ignite in the case of a desired response voltage.

Claims

1. A surge arrester for use in a current supply device of a low-voltage network, having a housing (2), having a first electrode (3) and a second electrode (4), and having an arc chamber (5) which is formed in the interior of the housing (2), wherein the two electrodes (3,4) are each in contact with the arc chamber (5) and a spark gap is formed between the two electrodes (3,4), so that an arc (6) occurs in the event of ignition of the spark gap between the two electrodes (3,4), so that a surge current to be discharged can flow via the low-impedance connection,

it is characterized in that the preparation method is characterized in that,

at least one third electrode (7) is provided, which is likewise in contact with the arc chamber (5), wherein three electrodes (3,4,7) are arranged one behind the other in the longitudinal direction of the arc chamber (5), and wherein the distance a of the first electrode (3) from the second electrode (4) is smaller than the distance b of the first electrode (3) from the third electrode (7),

whereby at least three electrodes (3,4,7) are arranged relative to one another such that, in the case of ignition of the spark gap, a first arc (6) firstly occurs only between the first electrode (3) and the second electrode (4) and, in the case of a gradually increasing ionization of the arc combustion chamber (5), a second arc (6') additionally likewise occurs between the second electrode (4) and the third electrode (7), and

the first electrode (3) and the third electrode (7) are connected to one another directly or via an electrical component (9).

2. Surge arrester according to claim 1, characterized in that the spacing a between the first electrode (3) and the second electrode (4) is smaller than the spacing C between the second electrode (4) and the third electrode (7) and/or the cross section a of the arc chamber (5) in the region between the first electrode (3) and the second electrode (4) is larger than the cross section C of the arc chamber (5) in the region between the second electrode (4) and the third electrode (7).

3. Surge arrester according to claim 1 or 2, characterized in that the first electrode (3) is electrically connected to the third electrode (7) via an impedance as an electrical component (9).

4. Surge arrester according to claim 1, characterized in that the spacing a between the first electrode (3) and the second electrode (4) is not smaller than the spacing C between the second electrode (4) and the third electrode (7), and/or the cross section a of the arc chamber (5) in the region between the first electrode (3) and the second electrode (4) is not greater than the cross section C of the arc chamber (5) in the region between the second electrode (4) and the third electrode (7), and the first electrode (3) is electrically connected to the third electrode (7) via an impedance as an electrical component (9).

5. Surge arrester according to claim 1 or 2, characterized in that the first electrode (3) is electrically connected to the third electrode (7) via a voltage limiting element as an electrical component (9) and/or a voltage switching element as an electrical component (9).

6. Surge arrester according to claim 1 or 2, characterized in that the first electrode (3) is disk-shaped and the arc chamber (5) is bounded on one of its sides (5a), and the second electrode (4) and the third electrode (7) are correspondingly annularly configured, locally bounding the arc chamber (5) radially and arranged one after the other in the longitudinal direction of the arc chamber (5).

7. Surge arrester according to claim 1 or 2, characterized in that the wall (10) surrounding the arc chamber (5) is at least partly composed of a gas-filled insulating material at least in the region between the first electrode (3) and the second electrode (4).

8. Surge arrester according to claim 1 or 2, characterized in that the second electrode (4) and the third electrode (7) have different dimensions or consist of different materials.

9. Arrester according to claim 6, characterized in that an opening (11) to a blow-off channel (12) is formed on a side (5b) of the arc chamber (5) opposite the side (5a), through which hot ionized gas can flow out of the arc chamber (5).

10. Surge arrester according to claim 1 or 2, characterized in that an ignition aid (13) is provided, which comprises an ignition element (14) and an ignition electrode (15), wherein the ignition element (14) and the ignition electrode (15) are in contact with the arc chamber (5) and the ignition element (14) is electrically conductively connected on one side to the first electrode (3) and on the other side to the ignition electrode (15).

11. The surge arrester of claim 5 wherein the voltage limiting element is a varistor.

12. The surge arrester of claim 5 wherein the voltage switching element is a gas-filled surge arrester.

13. The surge arrester of claim 7 wherein the gas-filled insulating material is POM.

14. Arrester according to claim 8, characterized in that the second electrode (4) and the third electrode (7) have different inner diameters or thicknesses.