DE2539013B2 - Material for extinguishing chambers - Google Patents

Description

2 ZnO ■ 3 B ₂ O ₃ ■ 3 y H ₂ O

and the silicone resin comprising the monobasic monomer according to the structural formula

CH ₃ -, -SiO

contains is

5. Material for arc chambers according to claim 4, characterized in that the Compound constitutes at least 40% by weight of the material.

6. Material for arcing chambers according to claim 4, characterized in that the connection is at least 50% by weight of the material matters.

7. Material for arcing chambers according to claim 4, characterized in that the compound makes up about 65% by weight of the material.

The discovery concerns a material for fire chambers.

For example, from the "Siemens-Zeitschrift" 38th) edition, April 1964, issue 4. Pages 225 to 228, it is known to use sulfur hexafluoride (SFh) as a material for arc quenching in switches. This gas is chemically inactive, non-flammable and non-toxic; <·% Is also strongly electronegative, i.e. its molecules have a high degree of slow ability Capturing electrons and binding them to yourself, what for rapid arc extinction is essential. Since SFa

is gaseous, a high-pressure container must be assigned to the switch, which is to be heated ^{at outside temperatures below approx. +13 0 C}

ι ο Material naturally not possible.

From US-PS 38 81 165, however, it is known to use tungsten oxide (WO ₃ ) J as a material for arcing chambers in such a way that it is either bound to a ceramic cement or another Carrier in the form of an upper cover applied to parts of extinguishing chamber walls or one Synthetic resin binder, such as methyl methacrylate, is processed into extinguishing chamber parts. Under the auspices of the heat generated by the arc is then used Gaseous tungsten trioxide is released, which has a high Has electron affinity and therefore accelerates arc quenching. Tungsten trioxide bound with methyl methacrylate is, however, a material that can due to a relatively high proportion of coal

2ϊ atoms of matter

The object of the invention is therefore to create a material for arcing chambers that is suitable for Arc protection shields, arc chamber parts, housings for electrical devices and the like

jo used or in the form of overcoats on such Parts to be used and which is characterized by even better arc-extinguishing properties To solve this problem, the material for

r> arcing chambers according to the invention such that

a) it emits electronegative extinguishing gas under the effect of an arc,

4 (i b) it from a non-toxic, boiling, sublimation or decomposition temperature of a maximum of 2000 Grade C compound of an element from the group of silver, platinum, gold, tantalum, copper, Cobalt rhenium, boron, palladium, antimony, tellurium,

Zinc and selenium, as well as a silicone resin as a binder

consists,

c) the individual chemical elements of which have a first ionization voltage that is equal to or greater than than that of silver (7.54 e V),

-) (i d) and of its atoms a maximum of 15% carbon atoms are.

It should be noted that it is known in principle from DE-PS 8 33 386, especially in one

*> *> so-called hard gas switch, the gas-emitting switch room walls using organic silicon compounds, in particular silicones build up in order to be as free of soot as possible because of the lower carbon content of these substances

Wed to achieve surface evaporation of the material. Urea, melamine resin or low molecular chain hetero compounds are used as fillers that release gas under the action of heat, in whose chains the carbon atoms are above

h- »nitrogen atoms or oxygen atoms with each other are connected. The arc-extinguishing properties of this material are in comparison with those at the beginning materials mentioned are significantly lower.

Further refinements of the invention are the subject matter of subclaims,

The invention is based on the following fundamental considerations underlying;

The arc interruption requires manufacture of conditions which promote recombination exceeding ionization. The problem consists in knowing the basic factors that determine the course of these two processes, ionization and recombination.

One of the factors to consider when selecting materials with arc extinguishing properties is the initial ionization voltage (ionization potential) of each of the constituent materials. The first ionization voltage of an element is the amount of energy that is necessary to transport an electron away from a neutral atom of the element into infinity. The first ionization voltage for silver is 7.54 eV, while the first ionization voltage for aluminum is 538 eV Energy difference of one electron volt is 7730 ⁰ K.

Another factor to consider when choosing materials with arc extinguishing properties must is the extent to which the evolved gases are electro-negative. This is in turn a Measure of the affinity of an atom of an element for electrons. Whom: the arc current is zero approaching, it is advisable to put an eleki-O-negative gas in the arc quenching chamber, the difference between cooling and slowing down the electrons captures These electrons would otherwise be accelerated by the increasing, recurring voltage and then cause further ionization and possibly flashback.

For this, the boiling, sublimation or decomposition temperature is an additional factor. During the few microseconds that the current passes through zero in an AC system before and after, the arc temperature decreases rapidly until it reaches the temperature of the arc quenching chamber walls, which during the quenching process on the boiling point, Sublimation or decomposition temperature persists. The lower the boiling temperature of the material of the arc extinguishing chamber walls is, the higher the recombination of the ionized particles of the gas that occurs.

Endothermic processes develop their effectiveness especially with zero electricity. The energy that is in one endothermic process is absorbed, which to a modest extent in the arc extinguishing chamber expires, can approximate the energy that by the wake of the electric arc in the Arc extinguishing chamber is introduced. This effect, through a favorable, appropriately If the boiling point is supported, it contributes significantly to the success of the arc extinguishing.

When an arc-extinguishing material decomposes to release free carbon, it can this carbon can be oxidized to carbon dioxide. The process is exothermic; the timing its process is bad because the exothermic formation of carbon dioxide takes place just when the

ίο

The arc current approaches zero and the temperature drops as the recombination of ions and dissociated molecules begin. Deposits of free carbon can also cause knee walkways and dielectric defects. However, restricting the arc-extinguishing materials to those τα that do not contain any carbon would mean limiting the choice of materials too narrowly. It has been found that the number of carbon atoms as a percentage of the total number of atoms of an arc extinguishing material should not exceed a value of about 15%. It has also been found that hydrogen is a useful component of the gas medium surrounding an arc, especially when the special application makes it necessary to force the arc to move through a transverse magnetic field.

An endothermic decomposition process corresponds to an exothermic process during formation. It is therefore advisable to choose materials whose formula structure is such that the probability of new formation after decomposition is small. Aluminum oxide (Al ₂ O ₃ ) and boron oxide (B ₂ O ₃ ) are materials with such a formula structure. However, aluminum oxide is undesirable as an arc-extinguishing material because the ionization voltage of aluminum is low and the boiling temperature of aluminum oxide is too high 264 and 30 71666, both of which recommend alumina as a good arc extinguishing material.

The first ionization voltage of each of the components of a suitable new spark-extinguishing material must accordingly be greater than or equal to 7.54 eV, which corresponds to the first ionization voltage of silver. The atomic concentration of carbon in the material should not be greater than about 15%. The boiling, sublimation or decomposition temperature of the material should be as low as possible with regard to compatibility with the other requirements, preferably of 2000 ° C. The decomposition of the material should take place in a strongly endothermic process; the more endothermic, the better. The decomposition products of the material should be as electronegative as possible with regard to compatibility with the other requirements. The material should also have a formula structure such that the rate of regression after decomposition is negligibly small in the vicinity of the zero crossing of the alternating current, as is the case for 3 ₂ O ₃ or HjBOj. The material should also be non-toxic, non-corrosive, incombustible, easy to work and use, and dimensionally and chemically stable under normal operating conditions. Finally, it should have good thermal conductivity for an electrically insulating material, which is preferably greater than 0.001 calories per second per square centimeter per degree Celsius per centimeter,

Oxides, borides, borates, silicates and the ammonium complexes of the elements, their first ionization voltage is equal to or greater than that of silver (7.54 eV) are generally considered to be arc-quenching materials suitable, as are their hydrated forms. A preferred selection of such elements, whose first ionization voltage in brackets

is added are; Tantalum (7.70 eV), copper (7.72 eV), Cobalt (7.86 eV), rhenium (7.87 eV), iron (7.90 eV), Tungsten (7.98 eV), silicon (8.15 eV), boron (8.29 eV), Palladium (8.30 eV), antimony (8.64 eV), tellurium (9.01 eV), zinc (9.39 eV) and selenium (9.75 eV), these substances can also be used as fillers in suitable resins, provided that the more atomic The carbon concentration does not exceed the nominal limit of 15%. Silicone resins are quite suitable The use of resins becomes mandatory when the filler material is not in its pure form can be used. So z. B. pure silicon dioxide should not be used because its Boiling temperature is too high, while the use of pure boric acid is impossible because it is water soluble and therefore dimensionally unstable; these materials are, however, when used in suitable resins are quite useful.

Beryllium (9.32 eV), arsenic (9.81 eV) and mercury (10.43 eV) have ionization voltages higher than that of Silber Hegen; however, these elements are toxic and therefore undesirable sulfates, nitrates and halogens are also unsuitable because they are toxic.

Silver, platinum or gold oxides, borates and silicates with or without ammonium complexes would be suitable as arc extinguishing materials per se, but would be expensive.

As a particularly suitable material with arc extinguishing Properties has been shown to be a material that consists of 55.8% by weight

2 ZnO 3 B ₂ O ₃

H ₂ O

and 44.2% by weight of a dimethyl silicone resin, that is, a basic silicone resin containing a basic monomer which is represented by the following Structural formula is given:

-CH, -,

SiO-1 — CH ₃ -

is composed

Claims (4)

Patent claims: 1. Material for extinguishing chambers, a) the electronegative under the influence of the arc Emits extinguishing gas, b) that from a non-toxic compound with a boiling, sublimation or decomposition temperature of a maximum of 2000 degrees C. an element from the group silver, platinum, gold, tantalum, copper, cobalt, rhenium, boron, Palladium, antimony, tellurium, zinc and selenium, as well as a silicone resin as a binder, c) the individual chemical elements of which have a first ionization voltage that is the same or greater than that of silver (7.54 e V), d) and of whose atoms a maximum of 15% are carbon atoms. 2. Material for arcing chambers according to claim 1, characterized in that it has such a structural formula structure that the after the exothermic regression occurring after the endothermic decomposition is negligible 3. Material for arcing chambers according to claim 1 or 2, characterized in that it has a specific thermal conductivity of at least 1/250 joules per second square centimeter per ⁰ C per centimeter 4. Material for arc chambers according to one of the preceding claims, characterized in that the compound has the formula