DE1946777U - SURGE ARRESTERS. - Google Patents

Description

PArB 13732 * -S, 6.6fi

Electric; Corporation
t Pittsburgh

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- 62/8015

Surge arresters

For this application, the priority is taken from the corresponding.xi American patent application Sei * .No. 113 878

claimed from May 31, 1961.

That deals with surge arresters, in particular with improved training in order to be able to use these corona certificates to suppress.

If a. surge arrester becomes dirty on the surface of its outer housing, a noticeable reduction in the internal flashover voltage can be observed. This decrease

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The internal overlap stress results from a change in the stress gradient on internal parts. If the surface of a surge arrester housing becomes contaminated, the surge arrester essentially forms a large capacitor. One surface of this capacitor is formed by the contaminated outer surface and the other by the outer inner parts of the arrester. The changes in the voltage gradient on the inner parts are the result of capacitive currents flowing through the porcelain wall between the contaminated surface and the inner parts «

The amount of reduction in the breakdown voltage depends on the size of the capacitive current. Under normal conditions. ■ When hoisting with a clean and dry porcelain surface, the resistance is very high »It approaches the value infinitely. If the surface of the arrester becomes soiled, the resistance value drops. “It can drop to a short-circuit value _; go «The resistance of the porcelain surface can fluctuate anywhere between the limits" infinite "and" Hull ". A change in the voltage gradient is also due to the fact that the surface resistance can not only change uniformly over the entire surface, but part of the surface can have a resistance value close to zero, while other parts still have an almost infinite resistance .. The voltage at any point on the arrester surface changes with the surface contamination. It follows that as a result of the change in resistance on the surface of the porcelain case, a potential difference between

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the soiled outer surface and inner parts in Longitudinal direction of the arrester comes about.

The amount of the capacitive current that flows through the porcelain wall depends, among other influencing factors, on the distance between the two parts acting as capacitor plates, the area of the two plates and the potential difference between the plates. Due to the flowing capacitive currents, a corona arises around the inner arrester parts. The extent of the coronary phenomena depends directly on the size of the current. away. The corona has the. Effect of apparently bringing the two plates closer to each other. This shortening of the distance between the two plates in turn leads to a stronger formation of the corona phenomena. The process can be repeated * until a flash occurs on some of the inner parts of the arrester, which causes the arrester to respond. If the pollution is very high, the arrester "may not be able to interrupt the leakage current. In this case, the arrester will fail.

The area of the plate covered by the contaminated surface is formed depends on the size of the pollution. the .Area of the other plate from the inner arrester parts. may vary with the extent of the corona phenomena. The formation of corona discharges leads to, ■ effective enlargement of the plate and thus brings a ■

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larger area. As the corona discharge continues to develop, the effective distance between the two is also reduced. These two effects lead to an increase in the capacitive current. The capacitive current in turn causes further corona discharges. If these circumstances occur during: -. _: . persist for a relatively long period of time, a median voltage flashover can form in the arrester and. to . contribute to the possibility of the arrester failing. Depending on,; Depending on the degree of pollution, the corona discharge can progress so far that the response voltage of the arrester is reduced by 20 to -JOfo. The difficult problem of contamination of the surge arrester can therefore be solved by bringing the corona phenomena inside the arrester under control. - ..

The primary goal of the E is to provide an arrestor that contains electronegative gas in order to eliminate polarity to suppress the surface degradation: are to be traced back.

Another goal is to create one ^; . Over voltage arrester, in which the effect of surface pollution is reduced by reducing the formation of coronary discharges on inner parts of the arrester. For this purpose, an electronegative gas is provided as a means for suppressing the discharges.

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Further goals and advantages of the B- result from the the following detailed descriptions in context. with the drawings o it shows

Figure 1 shows a partial section of an arrester according to, Figure 2 is a schematically simplified representation of the.

In short, it comprises a surge arrester of the valve type with a number of electrodes that form a spark gap. The spark gap is housed in a sealed capsule. The arrester also includes a number of resistance blocks with a non-linear characteristic arranged together with the spark gap capsule. Under certain circumstances, one or more columns of resistance blocks and spark gap capsules can be arranged next to one another. Furthermore, each column can only consist of resistor blocks, only spark gaps or a combination of the two. The entire column of the inner elements is in This in turn is arranged in a larger insulating cylinder, which can consist of porcelain or another weatherproof material ien the response voltages of the spark gap can be changed. The outer housing is also sealed "to prevent the entry of moisture 'or other contaminants that the resistor blocks damage ^könn-: th The free space in the outer porcelain cylinder which is not occupied by the grant Ä.b'Xeit. , is with an electron negative gas with an extraordinarily heavy molecule, for example;:; _ν> % ^ ν ^ τ.ΐί '| _: ; ί _: - ^ _: - 5 - -

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Sulfur hexafluoride gas (SFg), filled. The electronegative which is used to suppress corona discharges kept away from the spark gap itself by the fact that this is in is housed in a separately closed capsule.

In a preferred embodiment of the idu shown in the drawings for purposes of illustration, the arrester comprises a generally cylindrical housing TO. The housing 10 is preferably made of porcelain. But it can also be made of other suitable weatherproof insulating materials. The housing 10 is provided with a metallic armature 12 at each end. The fitting 12 is cemented onto the housing 10 at 14 with cement or fastened in another suitable manner. A seal 16 between each of the two fittings 12 and the housing 10 provides a tight seal for the inner housing 10. A terminal 18 can be provided on the upper fitting 12 to connect the arrester to a line 13 or another device to be protected. The same lower connection, not shown, is provided for connecting the arrester to earth.

The surge arrester assembly carried by the housing 10 ', consists of one or more columns 20 of diverter elements. If there are several pillars, the individual ones Columns in the housing are preferably connected in series, if there is more than one column 20 of arrester elements, the columns are either one above the other or next to one another in the

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Housed porcelain case. The arrester elements include Spark line arrangements 22 and resistor blocks 24 with non-linear Resistance curve. The resistor blocks can be from be of the usual type and consist, for example, of silicon carbide. Any combination of spark gap arrangements can be used in a column: 22 and resistor blocks 24 are combined.

The spark gap arrangement 22 can be configured, for example, as indicated in U.S. Patent 2,858,476 is. In the exemplary embodiment, it consists of a number of individual spark gaps 26, which are in a porcelain tube 28 as Column are arranged. Each of the individual spark gaps 26 consists of a flat electrode plate 29 and a deformed one Electrode 30 with a circular rib that connects to the electrode 29 together form an annular spark gap space 31 ο The electrodes 29 and 30 are supported by an annular spacer 32 supported against each other from a material of great resistance. In the space that is joined by the ribs Adjacent electrodes 30 is formed, a permanent magnet 34 can be arranged. The permanent magnet creates a magnetic field in the spark gap, emerge that a movement of the arc; » which makes it easier to extinguish it. * Depending on the voltage required, any number of spark gaps can be used 26 are combined in the tube 28 with conductive intermediate pieces to form a column. The conductive spacers, not shown are to be inserted at the top and bottom of the column, if necessary. The ends of the porcelain tube 28 can be closed with metallic end caps 36, which with

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be connected to the porcelain in a suitable manner, for example by soldering onto a metallic coating on the porcelain, as indicated up to 38. In order to keep the individual spark gap arrangements 26 in contact with one another and with the band caps 36, means not shown in the figure are provided.

The resistor blocks 24 can be formed by any suitable resistors with a non-linear characteristic. They are "preferably made of granular silicon carbide, which is brought into the desired size and shape with the aid of sodium silicate as a binder and baked in a known manner to form resistor blocks. The column of resistor elements shown in FIG Spark gap arrangement 22 and a number of resistor blocks 24. The elements are connected in series and arranged as a column in a tube 39 made of a suitable mechanically strong insulating material.

The free tree between the insulating housing 10 and the Isolierstoffrohr 39 is filled with a substance that corona phenomena suppressed. One such substance is, for example, sulfur hexafluoride gas suitable. It is used in the embodiment. In addition, gases or gas mixtures or other substances are used, their ability to reduce corona phenomena suppress, which are equivalent to those of sulfur hexafluoride. Essentially all are electronegative gases

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or electron-absorbing substances that are heavy Molecule on.

The sulfur hexafluoride gas suppresses corona phenomena that develop when the outer surface of the housing TO is contaminated. This avoids a reduction in the flashover voltage in the contaminated state. What is essential here, however, is that the sulfur hexafluoride gas or a similar electronegative gas remains excluded from the area of the point line arrangement in the housing 28. This is important because sulfur hexafluoride gas and other electronegative Gases lead to the suppression of an arc and are suitable for extinguishing or interrupting electric arcs as well as suppressing the formation of arcs. The presence of sulfur hexafluoride gas in the space of the spark gap would therefore change the normal response voltage; and other electrical properties of the spark gap. Bs however, it is desirable that the electrical properties of the spark gap are not affected by the means for suppressing the corona n Corona phenomena in the arrester are used. This should prevent undesirable effects of the pollution. This goal will be achieved dex tlberschlagskennlinie without modification. Up until now, however, it was so that a drastic reduction in the internal flashover resistance could be observed when an arrester became dirty.

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The following table shows the effect of pollution a surge conductor. As can be seen, there is a significant reduction in the flashover voltage in one dirty trap »

Arrester - öOHz response change - öOHz response reduction rated voltage voltage in clean alternating voltage of the response and dry state in dirty voltage in

Condition ok

37 KV 85 KV 63 KV . 26 fo 60 KV 132 KV 99 KV 25 Φ 121 KV 282 KV 178 KV 29 fo 121 KV * 25a KV 227 KV 12 io -1 sr kv 310 KV 200 KV 35 1 °

*): 121 KV arresters with

It should be noted that the table of the measurements given above represents a considerable improvement in the maintenance of information the ^ overshoot characteristics. for the arrester that shows with SFg grass is filled »This follows from the information for the Arrester with a nominal voltage of 121 KV.

The process that occurs when the breakdown voltage of a contaminated arrester is reduced can best be understood with the aid of FIG. Under normal conditions (in an even and dry state), the resistances of the boron eÜanÄer surface, which in FIG. 2 with R ₁ , R ₂ , R ₅ , '- iß | And Hr are designated, very large. Their value is almost infinite. If the arrester surface is soiled, the resistance decreases

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worth. It can decrease down to the value of a short circuit. In other words, the resistance of the porcelain surface can be anywhere between the limits of infinite resistance and zero resistance. The resistance can also be unevenly variable over the entire surface. This further complicates the process. Eiii part of the surface can have a value near zero, another, on the other hand, have near infinity. The voltage at any point on the arrester changes directly with the Resistance on the dirty surface.

The real mechanism of reducing the internal flashover voltage arises from a change in the stress gradient on internal parts. The change is the result of capacitive ■ currents flowing through the porcelain wall between the contaminated surface and the inner parts. In FIG. 2, the capacitances between the soiled surface and the inner parts C., C ₂ , G ₃ , G. and G, - are designated. The currents through these capacitances are denoted by i., ± 2 * ΐ-ζ * i-λ ^un ^ ^ s. The size of the capacitive currents depends, among other things, on the following:

1. the dielectric constant of the material that separates the two plates,

2. the potential difference between the two plates,

3. the area of the two plates,

4. the distance between the two plates.

From a separate consideration of the four above factors

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it turns out that some are fixed and cannot be influenced, others, on the other hand, can be controlled. For example, this is the dielectric constant of the material between the two plates once the arrester has been built and sealed. The potential difference between the two plates depends on the size of the dirty surface. It can be for everyone Instantaneous value of time can be regarded as a fixed value. The face of the one plate that is exposed to the soiled surface is formed depends on the degree of pollution. she can can also be regarded as fixed. The face of the other Plate, which is formed from the inner parts, fluctuates on the other hand with the size of the corona phenomena. The formation of Corona increases the size of the internal conductive parts and represents an enlargement of the surface. The distance between the two plates also fluctuates with the strength of the corona discharges. As the corona builds up, the distance between plates is reduced.

From the above considerations it can be seen that the two points best suited for influencing in the plane of the inner plate, and in the distance of the two Plates exist because both values depend on the size of the corona. The greatest part of the reduction in the field tension si & h results from the build-up of corona on the inner ones

: -sf ⁹

Divide. The strength of the corona depends directly on the size of the charging currents and the size of the currents is directly a puncture the corona development. When corona phenomena arise

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on the inner parts becomes the effective area of the condenser increased and the effective distance between the two plates " decreased. Both effects lead to an increased charging current- = This in turn causes further corona discharges.

Depending on the severity of the contamination, the corona effect can progress to such an extent that a reduction in the ablation response voltage of 20 to 30% occurs. If this condition persists for a relatively long period of time, then. the arrester triggers at low voltage. This adds to the possibility of trap failure. Based on this theory, electronegative gases such as sulfuric hexafluoride gas are inserted into the arrester housing. Sulfur hexafluoride gas has long been known for its insulating and arc-quenching properties. In addition, sulfur hexafluoride gas also has the ability to suppress corona phenomena. Properties that play a role in the suppression of ■ corona are the very large, heavy SFglolectll and its ability to store electrons «

The build-up of corona on the internal parts of the arrester will by using SFg as a means of suppressing the Corona influenced - at the same time, however, the flashover properties are affected the spark gaps of the arrester are not changed.

A special exemplary embodiment was used to explain shown and described. Various other embodiments are also possible within the scope of the invention.

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This is how the! It columns can be arranged side by side of arrester elements e.g. also in an arrester as well as in an arrester with a multi-part outer porcelain housing be used. In both cases, the influence of pollution is equally critical and an influencing factor this effect achievable. Furthermore, two or more of the arresters described can also be installed in series in a single housing switched or two arrangements can be attached to one another.

2 figures

3 claims

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Claims (2)

1. Surge arrester for high voltage with a closed Housing that has a voltage-dependent resistor and a spark gap connected in series with this contains and with an electronegative gas, preferably sulfur hexafluoride (SF>), is filled, characterized in that the spark gap is encapsulated in a gastight manner in order to protect the electronegative Keep gas away. 2. Surge arrester according to claim 1, characterized in that the electrodes of the spark gap in a ,, in particular from ■ Porcelain existing insulating tube are arranged, its Front sides are sealed gas-tight by metal caps. 3ο surge arrester according to claim 1, characterized in that that the encapsulated spark gap with the voltage-dependent resistor to a column in the arrester housing one above the other is stacked » - 15 -