WO2003012945A1

WO2003012945A1 - Encapsulated spark-gap based surge voltage protector

Info

Publication number: WO2003012945A1
Application number: PCT/EP2002/007391
Authority: WO
Inventors: Peter Hasse; Arnd Ehrhardt; Peter Zahlmann
Original assignee: Dehn + Söhne Gmbh + Co. Kg
Priority date: 2001-08-01
Filing date: 2002-07-03
Publication date: 2003-02-13
Also published as: EP1413027A1; EP1413027B1; DE50211845D1

Abstract

The invention relates to an encapsulated spark-gap based surge voltage protector comprising large-surface, opposite lying, disk-shaped electrodes in a rotationally symmetrical arrangement in addition to an arc discharge gap which is disposed between the electrodes and which is at least partially encompassed by an impact wall. According to the invention, a first impact wall is arranged in such a way that it is directed from one of the electrodes, protruding above the spark-gap, towards the opposite electrode. A second parallel impact wall is arranged in such a way that it is radially distanced in an outward direction from the first impact wall in relation to the rotationally symmetrical structure. The existing impact walls form a meander shape through which the arc discharge pressure wave passes. Insulation paths which are protected against deposits are disposed downstream from the direction of flow, whereby the desired long-term properties and required degree of reliability of the spark gap are achieved.

Description

Encapsulated surge arrester based on foot paths

description

The invention relates to an encapsulated surge arrester based on spark gaps with large, opposing, disc-shaped electrodes in a rotationally symmetrical arrangement and an arc discharge gap between the electrodes, which is at least partially enclosed by a baffle, according to the preamble of claim 1.

Encapsulated, also triggerable spark gaps as surge arresters, preferably used as N / PE spark gaps, have been state of the art for a long time. The two most important requirements for such spark gaps, namely a high insulation capacity and very high surge current discharge properties, arise directly from their place of use with N / PE spark gaps. The key here is a high lightning current carrying capacity and high reliability, so that harmful touch voltages can be excluded in any case.

Known such spark gaps with a capacity for protection against direct lightning strikes of up to 100 kA 10/350 μs have relatively large dimensions, which is disadvantageous.

The high surge current load, the associated high material burn-up, the high dynamic loads caused by current forces, pressure, energy and temperature of the arc discharge place extremely high structural demands on encapsulated embodiments. In the case of a triggerable N / PE spark gap, in addition to the isolating gap of the main spark gap, the insulation capacity and the response voltages of two further isolating distances must be ensured at all loads. If the external dimensions of the arrester are reduced, however, this leads to an increased load on the individual components or assemblies.

DE 100 08 764 AI discloses a spark gap that can in principle be triggered less

Dimensions that can be used as an N / PE section. This spark gap has coaxial electrodes and these are connected from one side. loading Due to the structure and the principle of the migrating arc there, the performance of this spark gap remains limited in the case of surge currents due to the burn-off, the thermal and dynamic loads. is of no significant importance.

The triggerable encapsulated spark gap according to EP 0 305 077 AI is an embodiment without a ventilation opening with flat parallel main electrodes. The disadvantage of the spark gap there is based on the sliding distance between the two main electrodes, the length of which corresponds to the distance between the electrodes themselves. In the event of a high current load, this sliding path is loaded by the deposition of decomposition and erosion products, which can lead to a reduction in the insulation capacity or to a short circuit.

From the foregoing, it is an object of the invention to provide an encapsulated surge arrester based on spark gaps, in particular for use as an N / PE spark gap, which, with small dimensions and simple construction, has a high surge current discharge capacity and can be executed in a triggerable manner so that it is already in the factory different overvoltage protection levels from e.g. 1.5, 4 or 6 kV can be set without significant changes to the spark gap being necessary. Furthermore, it should be ensured that deposits due to decomposition products occur in areas which are of secondary importance for the insulation ability and thus the long-term stability of the spark gap.

The object of the invention is achieved with an encapsulated surge arrester based on spark gaps with large, opposing, disc-shaped electrodes according to the features of claim 1, the subclaims representing at least useful refinements and developments.

The design of the two main electrodes as an air spark gap ensures a high strength of the arrangement with so-called TOV loads and with long-term currents. Due to the possibility of triggering, different response voltages can be preset in the factory via an internal or external circuit. The electrodes have large-area and thus erosion-resistant arc areas, with the meandering baffle walls deflecting the hot gas flow, which is caused by the pressure wave when the spark gap is ignited. The baffle or deflecting walls partially protrude from the main separating section, so that any burning or decomposition products such as soot or the like can accumulate here without contaminating the necessary insulation sections, which are arranged between the baffles away from the direction of flow. Existing ventilation openings of small diameter ensure a slow pressure equalization in the spark gap after loading.

According to the invention, a first baffle is arranged directed from one of the electrodes, projecting beyond the main separating section, to the opposite electrode, and a second baffle is provided, radially spaced outward from the first baffle in relation to the rotationally symmetrical structure. As already mentioned, the baffle walls form a meander through which the arc discharge pressure wave has to pass. Insulation sections protected from deposits are located away from the direction of flow.

The baffle walls can have an interdigitated comb structure, which runs essentially perpendicular to the respective electrode surface.

Within the area enclosed by the first baffle, an insulating layer is provided in one of the main electrodes and the first baffle or parts thereof are designed as a conductive auxiliary or trigger electrode.

The second baffle can be part of a spacer which fixes the opposite main electrodes and which is preferably oriented in the direction of flow and has the at least one pressure equalization opening mentioned.

The spacer itself can be designed so that additional baffle or deflecting walls are formed which form meanders.

The insulating layer has a circumferential, rotationally symmetrical extension which extends beyond the surface of the corresponding main electrode that there is a flashover path for an auxiliary discharge between the trigger electrode and the main electrode, which is simultaneously oriented to the opposite main electrode.

The ratio between the distance and the diameter of the main electrodes is> 1:10 to excite diffuse arc base points.

Starting from the spacer, running radially inward and parallel and forming a gap to the main electrode surface, a so-called vaporization barrier can be provided, which can additionally have an optional offset at its free end.

In the alternative embodiment, within the area enclosed by the first baffle, there is the possibility of embedding an insulating trigger electrode in one of the main electrodes.

This insulated trigger electrode can be designed as a ring or pin electrode, which is essentially flush with or protrudes from the respective main electrode surface, the insulation additionally surrounding part of the pin electrode in a ring shape in the latter embodiment.

The main electrode surfaces can be structured to further optimize the erosion behavior. Furthermore, one of the main electrodes can form part of the arrester housing, so that the structure of the pressure-resistant encapsulation is simplified.

The invention will be explained in more detail below with the aid of exemplary embodiments and with the aid of figures.

Here show:

Fig. 1 shows a first embodiment of the encapsulated surge arrester

Spark gap base with auxiliary or trigger electrode; 2a and 2b show an embodiment analogous to that according to FIG. 1, but with additional vaporization barriers running parallel to one of the main electrodes;

3a and 3b different embodiments of auxiliary or trigger electrodes arranged in the center of one of the main electrodes;

4a and 4b an embodiment of a spark gap with a particularly high

Performance by combining a gliding path with an air flashover path or a configuration of one of the main electrodes, which is surrounded by electrically semiconducting material with or without an air gap, so that the above-mentioned sliding spark gap is formed; and

Fig. 5 is an encapsulated surge arrester with meandering baffles, but without an auxiliary or trigger electrode.

In the figures, the main electrodes are identified by the reference numerals 1 and 2. These main electrodes 1, 2 are essentially rotationally symmetrical and lie opposite one another. The main electrodes 1, 2 can have an extension directed towards one another, the parallel course and spacing of which defines the main spark gap 6.

In the embodiment according to FIG. 1, a specially designed baffle 3 takes on not only the function of the flow deflection, but also that of an auxiliary electrode, so that an initial flashover 11 occurs between the auxiliary electrode 3 fed with trigger voltage and the main electrode 2 via the insulation path 9.

The main discharge 12 takes place exclusively between the electrodes 1 and 2, specifically in the area labeled 6.

The (first) baffle starting from part 3 has the effect that the pressure wave which forms when the spark gap is triggered between the two main electrodes is broken and deflected, as a result of which the pressure surge in the downstream areas that serve to ensure insulation can be reduced.

An insulating part 4 serves for electrical insulation and at the same time represents the rollover path between the baffle / auxiliary electrode 3 and the main electrode 2. A spacer 5 keeps the two main electrodes 1, 2 at a distance. This spacer 5 comprises a plurality of baffles 10, ventilation openings 8 and insulation sections 7. After the arc has been extinguished, the ventilation openings 8 lead to the reduction of the increased internal pressure within the spark gap.

From the schematic representation of the respective figures it can be seen that the baffle walls form a meandering or interlocking comb structure, so that the gas flow is deflected several times. The actual insulation sections 7, which are decisive for the relevant electrical properties, are protected outside the flow area. Deposits that cannot be avoided due to electrode erosion do not influence the properties of these insulation sections 7.

When constructively implementing the above teaching, care must be taken that the distances between the impact walls and the respectively opposite section of the corresponding main electrode are greater than the distance 6 of the active main electrode surfaces.

With passive ignition of the spark gap, the auxiliary electrode 3 can be connected inductively or with high resistance to the main electrode 1 internally or externally. In this way, the auxiliary electrode 3 has the same potential as the main electrode 1. After flashover along the path 9, a small current flows across the auxiliary electrode, whereby the dielectric strength of the isolating path between the main electrodes is reduced, so that the arc between the main electrodes 1 and 2 Ignition is coming. This in turn relieves the auxiliary electrode 3. The auxiliary electrode 3 can be made of electrically conductive or semiconductive material.

In a further embodiment of the aforementioned passive ignition, the parts 3 and 5 can be made or consist of a single part, whereby here semiconducting material is used. In the case of passive ignition, the insulation path 9 determines the response voltage and thus essentially the protection level of the entire spark gap.

With this passive ignition, the distance 6 between the opposing main electrode surfaces can be a multiple of the distance 9, but the length of the distance 9 is to be selected as a function of the desired response voltage of the spark gap.

With active triggering, there is the possibility to choose the distances or sections 9 and 6 almost arbitrarily, the maximum possible length of the section 9 being limited by the output voltage of the trigger circuit and the maximum possible distance 6 being dependent on the energy input of the trigger circuit.

With active triggering of the spark gap, the distance 6 between the surfaces of the main electrodes 1 and 2 can thus be designed to be significantly higher than with spark gaps without auxiliary electrodes with a comparable overvoltage protection level. This and the selected version as an air spark gap ensure a high insulation capacity and a constant overvoltage protection level even under the heaviest loads.

After the discharge has been ignited with the aid of the triggering via the insulation section 9, the dielectric strength of the main section 6 is reduced so much by charge carriers formed that the arc discharge 12 ignites after a delay, whereby the trigger circuit and thus the insulation section 9 are immediately relieved.

The smaller the distance 6 and the higher the amount of trigger energy introduced, the shorter the delay until the main section 12 is fully ignited after the insulation section 9 has overturned.

In area 9, the insulation part is preferably provided with a protrusion, which increases the length and thus the energy of the ignition spark. At the same time, the charge carriers that are created are brought closer to the opposite main electrode 1, which improves the ignition of the arc 12. The wiring for passive ignition is possible inside or outside the spark gap. Corresponding high-resistance conductive or semiconducting materials, such as, for example, electrically conductive polymers or ceramics, but also resistance materials, are conceivable as internal circuitry.

In the case of external wiring, varistors, gas collectors, capacitors, coils, but also their combinations can be used. In the case of an active trigger circuit, which is preferably attached outside the spark gap, the distance between the insulation gap 9 can be selected independently of the desired overvoltage protection level.

The central extension on one or both of the main electrodes 1, 2 forms the preferred focal surface of the arc. The main electrodes 1 and 2 consist of tungsten / copper, graphite or similar erosion-resistant materials.

The large-area electrodes with a distance / diameter ratio of essentially 1:10 are characterized by diffuse and therefore low-erosion arc base points. As a result, the pressure or current load on the overall arrangement remains very low, which in turn is of decisive advantage for the desired small design.

In a further exemplary embodiment, the tendency to form a diffuse arc can be supported by lowering the pressure, by utilizing internal or external magnetic fields and by high-melting electrical materials such as graphite, silicon carbide, tungsten, molybdenum and their connections.

By using internal or external magnetic fields that are oriented in the axial or radial direction, based on the direction of current flow in the arc, it is possible to force the arc to a desirable rotation. This rotation supports the diffuse arc approach, improves the follow current behavior and reduces electrode burn-up. In addition, the diffuse arc approach reduces the arc voltage and thus reduces the energy consumption within the spark gap. At higher loads, fusible pearls are formed especially with metallic main electrodes. Due to the arc discharge pressure, these fused beads are transported away from the discharge area and settle on or behind the baffle wall, as a result of which the opposite main electrode surfaces in the active area can be kept largely free of erosion material at a distance of 6. The erosion area is in the range of essentially 75 mm ² to 1000 mm ² , the distance between the two main electrodes 1 and 2 being essentially between 0.2 mm and 4 mm.

The flank of the (first) baffle protrudes at least 0.5 mm to a maximum of 5 mm beyond the discharge gap at a distance of 6, so that the pressure which arises in the discharge gap cannot spread radially directly, but is first deflected.

Larger burn-up particles which do not slide off on the flanks of the main electrodes 1, 2 are thus thrown against the first baffle on part 3. Smaller particles are transported as described and can be deposited on the other (second) impact walls 10.

A region 7 is formed in the spacer 5, which remains almost unaffected by the pressure wave and the deposits and thus serves as the main insulation section.

Existing ventilation openings 8 ensure, after loading, a rapid reduction in the increased pressure which arises from the heated gases but also from the decomposition products, as a result of which the response behavior of the spark gap can be kept constant.

As shown in FIGS. 2a and 2b, vaporization barriers can be provided between the main electrodes 1 and 2, starting from the spacer 5. The purpose of these vaporization barriers is to create a long and thin gap 13 between the spacer 5 and at least one of the main electrodes, which gap lies outside the main direction of the propagation of the pressure and flow wave. This gap can also contain deflections due to a cranked embodiment of the vaporization barrier, as shown in FIG. 2a. The risk of contamination of this gap is therefore extremely low, is created by a further insulation section. The width of the gap should be in the range <0.2 mm, the length being at least 2 mm.

In the case of lower demands on the performance of the spark gap, a pronounced backing or an undercut in the spacer 5 can be dispensed with if the vapor barrier is dimensioned accordingly. In this case, the spacer only serves to fix the two main electrodes 1, 2 and to vent or to equalize the pressure.

It should be noted at this point that the spark gap can of course also be vented through openings in or through the electrodes or the auxiliary electrode.

With a corresponding design of the outer housing of the surge arrester, the functions mentioned above can also be carried out by this housing, eliminating the need for a separate spacer 5.

In an embodiment with special auxiliary electrodes according to FIGS. 3a and 3b, these are located quasi-centrally in one of the main electrodes, in the example shown the main electrode 2. The e.g. Pin electrode 16 is electrically isolated from the potential of main electrode 2 by insulation 15. According to FIG. 3a, the pin electrode 16 almost closes with the surface of the main electrode 2, the insulating sections 15 projecting.

In the embodiment with a reset trigger electrode 16, the insulating part 15 is designed to overlap the upper end of the pin electrode 16 in a circular shape. In the embodiment according to FIG. 3a, the trigger circuit and the distance 6 can also be ignited instead of the adjacent main electrode 2 and the opposite main electrode 1 if the trigger circuit and the spacing 6 are designed accordingly. This has the advantage that almost the entire length of the separation path between the main electrodes 1 and 2 is flipped over, as a result of which the delay time for igniting the arc 12 is minimized.

According to FIGS. 4a and 4b, in the case of spark gaps with particularly high performance, the sliding path 9 (FIG. 1) can be combined with an air gap in series between the parts 3 and the main electrode 2 to withstand greater loads to be protected. In a further variant, the main electrode 2 can also be surrounded by electrically semiconducting material, for example conductive plastic 14 with or without an air gap, via which the ignition spark then slides from the auxiliary electrode 3 to the main electrode 2.

It is in the sense of the invention that, taking into account the response voltage and the distance 6, a non-triggerable spark gap, as shown in FIG. 5, can also be realized. There is the possibility, in particular, of fulfilling the impact and deflection function with the extension 2 ′, which is part of the main electrode 2. Appropriate measures, e.g. Clearances or insulating covers, to ensure that the response distance is in the gap marked with the distance 6 even with heavy loads.

The selected rotationally symmetrical construction of the opposite main electrodes 1 and 2 advantageously allows electrical connections to be made on opposite sides. The trigger electrode can be made accessible for external wiring via an insulated bushing on or in the housing. One of the main electrodes can form part of the arrester housing, which is preferably pressed or screwed in order to achieve the desired mechanical strengths for encapsulated spark gaps.

Claims

claims

1. Encapsulated surge arrester based on spark gaps with large, opposing, disc-shaped electrodes in a rotationally symmetrical arrangement and an arc discharge gap between the electrodes, which is at least partially enclosed by a baffle, characterized in that a first baffle from one of the electrodes projects beyond the main separation zone , is arranged directed to the opposite electrode, a second baffle with respect to the rotationally symmetrical structure is provided radially spaced outward from the first baffle, the baffles forming a meander through which the arc discharge pressure wave passes, and that away from the direction of flow of deposits protected insulation sections are located.

2. Encapsulated surge arrester according to claim 1, characterized in that the baffle walls have an interdigitated comb structure and this extends essentially perpendicular to the electrode surface.

3. Encapsulated surge arrester according to claim 1 or 2, characterized in that an insulating section is provided within the area enclosed by the first baffle in one of the main electrodes and the first baffle or parts thereof are designed as conductive auxiliary or trigger electrodes.

4. Encapsulated surge arrester according to one of the preceding claims, characterized in that the second baffle is part of a spacer which fixes the main electrodes and which can have at least one pressure compensation opening oriented in the flow direction.

5. Encapsulated surge arrester according to claim 4, characterized in that the spacer comprises further meandering baffle and deflecting walls.

6. Encapsulated surge arrester according to claim 3, characterized in that the insulating layer has a circumferential rotationally symmetrical extension which extends beyond the surface of the corresponding main electrode, so that a flashover path for an auxiliary discharge between the trigger electrode and the main electrode is formed, which at the same time to the opposite main electrode is oriented.

7. Encapsulated surge arrester according to one of the preceding claims, characterized in that the ratio between the distance and the diameter of the main electrodes is> 1:10 for exciting diffuse arc base points.

8. Encapsulated surge arrester according to one of claims 4 to 7, characterized in that starting from the spacer radially inward and parallel and gap-forming to the main electrode surface, a vaporization barrier is provided, which can additionally have a crank or angled at its free end.

9. Encapsulated surge arrester according to claim 1 or 2, characterized in that an insulated trigger electrode is arranged within the area enclosed by the first baffle in the main electrode.

10. Encapsulated surge arrester according to claim 9, characterized in that the insulated trigger electrode is a pin electrode which is essentially flush with the respective main electrode surface or stands back, the insulation additionally surrounding an upper part of the pin electrode in an annular manner in the latter embodiment

11. Encapsulated surge arrester according to one of the preceding claims, characterized in that the main electrode surfaces are structured.

12. Encapsulated surge arrester according to one of the preceding claims, characterized in that the or the insulating parts consist of a gas-emitting plastic material.

13. Encapsulated surge arrester according to one of the preceding claims, characterized in that one of the main electrodes simultaneously forms part of the arrester housing.

14. Encapsulated surge arrester according to one of claims 3 to 13, characterized in that the auxiliary or trigger electrode consists of a semiconducting material.

15. Encapsulated surge arrester according to one of the preceding claims, characterized by its use as an N / PE spark gap.