DE2012453C3 - Gas discharge surge arrester, preferably with a noble gas filling - Google Patents

Description

1/4

The electrode material is iron, the diameter (D ₂ ) of the cylinder electrode being at least 3 mm.

5. Gas discharge surge arrester according to one of claims 1 to 4, characterized in that that the metallic parts of the vacuum-tight housing in the transition area to the annular Insulating body (3) are much thinner than in the other areas of the housing.

In (I + a ₂

and that the coaxial hollow electrode (1) made of a second, electrically conductive material (k) has an inner diameter (D _u ) which is greater than the diameter (D ₂ ) of the cylinder electrode (2) by at most Id equal to 2 mm its outer diameter (D ^), which is at most 15 mm, over the diameter (D ₂ ) of the cylinder electrode by the relationship

with d is set as the distance between the cylinder electrode (2) and the hollow electrode (1), the

Factor A is a quotient 1-iiSa.l from two products

\ ^c t /

is determined on the one hand by the temperature coefficient α (1 / ° C) of the electrical resistance and the specific electrical resistance ρ ₀ (ίϊ · cm) of the respective electrode material and on the other hand by the mean specific heat c (-sfi) and the specific gravity γ ( -jb ·) of the respective electrode material, where AT also indicates the respective temperature difference between the operating temperature and the melting temperature of the electrodes and finally J (A) is the maximum current intensity with f (s) as the mean duration of the current flow.

2. Gas discharge surge arrester according to claim 1, characterized in that the cylinder electrode and the hollow electrode are made of the same material, the outer diameter (D ₁₁₁₁ ) of the hollow electrode over the diameter (D ₂ ) of the cylinder electrode (2) with the relationship

i - (D ₂ + Idf> D)

(3)

is fixed.

3. Gas discharge surge arrester according to claim 2, characterized in that the factor t · J ^{2 is} determined by the maximum current strength of the strongest known lightning strikes with / = 10OkA and an average duration of ί = 10 ~ ⁴ s to ti ² = 10 ⁶ As is.

4. Gas discharge surge arrester according to claim 3, characterized in that the The invention relates to a gas discharge surge arrester with a vacuum-tight housing, preferably with a noble gas filling, in which a solid cylinder electrode carrying an end cap facing a coaxially surrounding hollow electrode, which is in the form of a hollow cylinder with an end wall and having an annular insulating body together with the end cap of the cylinder electrode forms the vacuum-tight housing.

Such surge arresters are well known (compare, for example, the German Patent specification 7 14 139, although contrary to the embodiments common today, the hollow electrode does not yet form part of the vacuum-tight housing). In addition to small dimensions and These surge arresters are supposed to have the following additional costs, some of which are low production costs have conflicting properties. The surge arrester is said to be atmospheric High amperage discharges, d. H. Can derive lightning. It must have current pulses of up to 20 μβ duration and endure currents up to 10OkA several times. On the other hand, currents must also be lower Size, but can be derived over longer periods of time, for example in the case of an inductive influence of telecommunication lines or a contact .of telecommunication lines with power lines. In both types of loads (short-term exposure to high currents, long-term exposure to relatively low currents) it is required that the arrester responds extremely quickly. Just If the ignition takes place immediately with the onset of the overvoltage, the system to be protected is also effectively protected,

In addition to the short response time, so-called »failsafe« properties are required. This means, that the surge arrester then, if it despite its ability, both AC loads as well as enduring lightning loads, overloading, causing a safe short circuit got to. This is only achieved if, in the event of an overload, the electrodes of the surge arrester melt together before the arrester would leak. One that is definitely brought about in the event of an overload Short circuit is very important because then the device to be protected is temporary is not operational, but no overvoltages can penetrate the device. The point of failure is easy and reliable to find.

Surge arresters, in which a short circuit is brought about, are known per se. For this are however, additional construction elements are required, such as B. bimetal strips (compare the

German Auslegeschrift 12 86191) or a switching device, the Z. B. from an easily fusible or easily atomized metal or from a with Heating metal-separating substance or can consist of a bimetallic body (compare German patent 6 68 589).

The object of the invention is therefore to create a surge arrester with "fail-safe" properties, in which no additional structural elements are required to cause a short circuit and which has small dimensions, which can handle both short-term loads with high currents and long-term loads with relatively withstands low currents and which responds extremely quickly. For this purpose it is proposed according to the invention in a gas discharge surge arrester of the type mentioned at the beginning that the cylinder electrode consists of a first electrically conductive material (z) and has a diameter

V1 / 4

0.625 in (I-Ha ₂

and that the coaxial hollow electrode consists of a second, electrically conductive material (k) and its inner diameter D _{ki is} at most 2d equal to 2 mm greater than the diameter D _{2 of} the cylinder electrode and its outer diameter D _ka , which is at most 15 mm the diameter D _{2 of} the cylinder electrode by the relationship

(D + IdY> D ²

- (D ₂ + ld) > D ₂

^. _{) n (1}

" _K. ,, _Tk) )

where d is defined as the distance between the cylinder electrode and the hollow electrode, the factor A being a

quotient

C- γ

made up of two products, the one hand

from the temperature coefficient ri (l / ° C) of the electrical Resistance and the specific electrical resistance ρ (ü ■ cm) of the respective electrode material and on the other hand from the middle special

fish heat c (-57Ο and the specific gravity γ (- ^ t) of the respective electrode material are formed, with IT also indicating the respective temperature difference between the operating temperature and the melting temperature of the electrodes and finally J (A) the maximum current intensity with t ( s) is the mean duration of the current flow.

In a gas discharge surge arrester according to the invention, the cylinder electrodes and the hollow electrode are usually made of the same material. In this case, the rule for dimensioning the hollow electrode is simplified as a function of the diameter D _{1 of} the cylinder electrodes to the relationship

If one assumes that iron is a particularly suitable electrode material and that the maximum current strength of the strongest lightning bolts ^{does not exceed 10OkA and their average duration 10 ~ 4} s, the diameter of the cylinder electrode must be at least 3 mm according to the invention.

The metallic parts of the vacuum-tight housing of a gas discharge cover according to the invention Voltage arresters are particularly useful in the transition area to the annular insulating body Thinner-walled than in the other areas of the housing. This way it is between the electrodes on the one hand and the insulating body on the other hand achieved a thermal brake that causes the im Operation of the gas discharge surge arrester

ίο Any heat generated by the electrodes does not change immediately transfers to the insulator. This guarantees with absolute certainty that in the event of an overload actually the cylinder electrode melts before the gas discharge surge arrester possibly a crack in the insulating body could cause a leak due to thermal effects.

On the basis of an exemplary embodiment shown in the drawing, the invention is intended to include in the following further features are explained in more detail.

ίο The drawing shows a gas discharge surge arrester in longitudinal section shown, which consists essentially of a hollow electrode 1, a cylinder electrode 2 and an insulating body 3 consists. The hollow electrode 1 forms together with a

2 $ by the cylinder electrode 2 carried end cap 4 and the annular insulating body 3 a vacuum-tight housing which is filled with noble gas. The metallic parts of this vacuum-tight housing are substantially thinner-walled in the transition areas 5, 6 to the annular insulating body 3 than in the other areas of the housing. The purpose of this measure is to protect the insulating body 3 from overheating which may arise from the electrodes 1 and 2 in the event of an overload.

The surge arrester shown should primarily have a small design. In practice, this means that the outer diameter D _{ka of} the hollow electrode 1 must not exceed 15 mm. Any excess diameter of an over-

40. surge arresters because of the high proportion space requirement, which is the sum of all gas-filled surge arresters in modern systems.

. borrowed the entire space occupies, under no circumstances permitted. However, a correspondingly small design raises the problem that high current surges (lightning bolts) could cause the electrodes to melt or even evaporate immediately. It has been shown that undesired melting of the electrodes 1 'is safely avoided if the following dimensioning specified according to the invention for the outer diameter D _{2 of} the cylinder electrode 2 is adhered to:

0.625 In (HO ₂ -ZiT ₁ )

Thereby means

A =

Cy

t = time (s),

J = current flowing through the electrode (A),
ρ ₀ = specific resistance of the electrode material at the initial temperature (Ω cm),
u = temperature coefficient of the electrical

Resistance of the electrode material sq

IT = temperature increase from initial temperature (ambient temperature) to
Melting point of the electrode (° C),

c = mean specific heat of the electrode material (r ^ g),

γ = specific weight of the electrode material (- ^ j

speaking time of the surge arrester should be guaranteed. In consideration of these two according to the invention For boundary conditions, the following general design rule applies to the relationship between the dimensions of cylinder electrode 2 on the one hand and hollow electrode 1 on the other hand:

D ₁ - diameter of the cylinder electrode 2,
D _ka = diameter of the hollow electrode 1,
z, k = indices for the physical properties of the cylindrical electrode (z) and the hollow electrode ¹ (k).

In a practical embodiment, iron is used as the electrode material. If one uses the physical properties of iron in the given solution for the dimensioning of the diameter D _{1 of} the cylinder electrode 2 and one further assumes that the strongest known lightning bolts in no case exceed 100 kA and a duration of 100 μβ, D _{1 results} than equal to or greater than 2.94 mm or rounded up to 3 mm. The starting temperature was assumed to be 20 ° C.

So that a gas discharge surge arrester according to the invention reliably causes a short circuit before it is destroyed in the event of an overload, it is essential for the invention that the hollow electrode 1 withstands higher heating than the cylinder electrode 2. Only then is it ensured that the cylinder electrode 2 the hollow electrode 1 does not melt through, so does not receive any holes. The distance d of the hollow electrode 1 from the cylinder electrode 2 must not be greater than 1 mm if a sufficiently short specification for the dimensioning of the outer cross-section D _{ka of} the hollow electrode 2 is considerably simplified if, as is customary in practice, the The inner and outer electrodes are made of the same electrode material (ζ = ic). You then get the relationship

D \ "- (D _z + 2d) ² > D ² _z ,

where again d is assumed to be at most 1 mm.

A gas discharge surge arrester according to the invention has the essential advance that it has the following properties despite its small dimensions with absolute certainty has:

The gas discharge surge arrester can withstand short-term high-intensity discharges (Lightning) as well as long-term alternating current loads. When overloaded, the Uberleiter goes into one safe short-circuit over, and before a destruction of its vacuum envelope (clear short-circuit condition). When exposed to a shock wave, the surge arrester ignites so quickly that it closes protective system in no case suffers damage.

1 sheet of drawings

Claims (1)

Patent claims: 1. Gas discharge overvoltage continue with a vacuum-tight housing, preferably filled with inert gas, in which a massive end cap the supporting cylinder electrode faces a coaxially surrounding hollow electrode, which is designed in the form of a hollow cylinder with one end wall and with an annular one The insulating body, together with the end cap of the cylinder electrode, forms the vacuum-tight housing, characterized in that the cylinder electrode (2) consists of a first, electrical conductive material (z) a diameter