DE1024595B - Arc-proof insulating body - Google Patents

Description

GERMAN

It is well known that a considerable amount of energy is released in electrical switching devices in the event of short-circuit disconnections, the so-called switching work, which is performed by the parts of the switching device surrounding the switching-off arc Overheating and burn-off endangered. To counter this risk, it has been proposed to use the cut-off arc to move the endangered parts along with the help of a magnetic blown field, so that its Heat emission is distributed over a relatively large surface. Furthermore, switching arrangements have become known, in which the arc is forced by magnetic fields, in a stack from across the arc standing metal plates to circle. The metal plates split the arc into a series of partial arcs which are axially cooled and deionized by the metal plates. With a number of switching devices however, the arrangement of magnetic blown fields or stacks of plates to increase the on The surface participating in the cooling of the arc is not possible for reasons of space or price. In such Cases is based on the formation of insulating bodies that occur in the immediate vicinity of switching operations Arcs are arranged or have to be arranged, special care must be taken. You will in such cases try to keep the switching work small. Beyond that, however, it may be necessary be to provide suitable means for the rapid dissipation of the heat generated from the switching arc in order to avoid that the insulator is gradually destroyed. In many cases, the short-circuit safety of a switching device depends largely on the effectiveness of heat dissipating agents.

Naturally, insulating bodies that consist entirely of insulating material have a low thermal conductivity. In the event of a brief shutdown process, they are therefore only heated in a thin surface layer (penetration depth a few thousandths of a millimeter, max. a few centimeters). The energy from such a thin layer can be absorbed before the surface reaches the melting point is therefore in most cases too small, so that the insulating body melts and evaporates on the stressed surface. This is evident from the following rough considerations about the heating of an insulating body by a cut-off arc emerged.

The power delivered by the arc to the surface of the insulating body per unit area (cm ² ) is P. In the case of brief heating, as is the case with shutdown processes, it can be assumed to a good approximation that the temperature gradient in the insulating body

-j— = -, - , where χ is the distance from the surface

d χ λ

and λ means the thermal conductivity of the insulating body. The temperature thus falls in the insulator from the arc-proof insulator

^J Applicant:

FKG Fritz Kesselring Gerätebau AG,
Bactitobel, Weinfelden (Switzerland)

Representative: Dipl.-Ing. R. Barckhaus, patent attorney,
Erlangen, Eichenweg 10

Claimed priority:
Switzerland from August 19, 1952

Dr. Erwin Wettstein and Rudolf Kläui, Zurich (Switzerland), have been named as inventors

Temperature # _{0 of} the stressed surface decreases linearly and reaches the ambient temperature in an ab-

stand x _a = - - = £ - (depth of penetration). When the temperature & ₀ on the surface has reached the melting temperature - & _{s of} the insulating body, the following energy is stored in the heated layer:

W = c X _n .

2P

where c is the specific heat of the insulating body per unit volume. The factor indicates

thus the erosion resistance of the insulator.

On the other hand, the stored energy is equal to the energy released by the arc in the corresponding time Δ t

W = At-P (2)

The comparison of the two formulas (1) and (2) shows that the higher the erosion resistance, the higher the arc power or a longer arc duration is permissible without exceeding the melting point of the insulating body will.

In certain switchgear it is an absolute requirement that any burn-up be avoided, i. H. that the temperature of the insulating body is kept below the melting temperature. This applies e.g. B. to for Switching devices in which there is a liquid conductor through which the current to be switched flows, the

709 880/513

when crossing a due to its type and arrangement given response current evaporates, whereby an interruption of the flowing through this conductor Stromes is brought about. Such switching devices contain a filled with the liquid conductor Switching channel in which an arc occurs when the system is switched off. You can show that practically the entire arc heat from the surface of the liquid conductor during the shutdown process surrounding insulating body must be added.

For a long time, attempts have been made to replace the solid fusible link of the fuses with a liquid conductor, especially made of mercury, which should be easier to regenerate after a shutdown. Despite many proposals, such protective devices with mercury conductors have not yet been introduced. Obviously difficulties have arisen, presumably mainly with the required short-circuit protection related.

How difficult it is to meet the short-circuit safety requirement becomes clear when comparing the situation with the fuses. While a fuse with a nominal value of 500 V, 25 A, thanks to the sand filling, has a cooling surface of 15 ... 35 cm ² , which can also melt, the channel surface is only around 0.10 with appropriate protective devices with mercury conductors. .0.15 cm ² per cm of canal length and must not reach the melting point.

Using an example that is correct in terms of magnitude, it should be shown that opaque channel walls made of insulating material are unable to carry away the heat generated by the arc. The switching channel has a diameter of 0.4 mm. Its surface is therefore 0.125 cm ² per cm of length. In the event of a short-circuit shutdown, the arc has an average power of 10 kW per cm of duct length, corresponding to P = 80 kW per cm ^{2 of} duct surface. The arc duration is At = 3 ms. The insulating body would have to absorb the energy P-Ai = 240 Ws / cm ² per cm ^{2 of} duct surface. If the insulating body z. B. consists of steatite, which has a thermal conductivity λ = 0.023 W / cm ° C, a specific heat c = 2.2 Ws / cm ³ ° C and a melting temperature $ _s = 1600 ° C, but the same can be achieved until the Melting point on the channel surface according to formula (1) only absorb an energy W = 0.815 Ws / cm ^2. The penetration depth is 5 μ .. It can be seen that the actual heat absorption of the insulating body is far too low. Even with the use of corundum, which of the insulating materials probably has the highest erosion resistance, the heat absorption can only be increased by a factor of 10, so in the present example it is still more than a factor of 10 too small.

At higher powers, it is useful to magnetically or the arc in a manner known per se to move pneumatically along the stressed surface.

The present invention now aims to provide an arc-resistant insulating body which is the solution of the mentioned problem with regard to its use in a switching device of the type described as well for switching devices in which similar difficulties arise. The inventive Insulating body is characterized in that it for the purpose of rapid dissipation of the arc heat from the endangered Surface away into the interior of the insulating body as a composite body in the direction of the electrical voltage stress stacked, mutually electrically insulated plates made of one material is formed with a higher thermal conductivity than the insulating material located between the plates. The plates of higher thermal conductivity protect the surface stressed by the arc against destruction by heat, by making the heat generated by the arc at least partially perpendicular to the dissipate the stressed surface into the interior of the insulating body. Under electrical stress is both the voltage gradient of a switching arc occurring along the surface of the insulating body as well as a recurring voltage on the insulating body after the arc has been extinguished, for example to understand.

In order to ensure effective heat dissipation, the thermal conductivity of the plates used for heat dissipation should be at least ten times that of the insulating material. A material whose thermal conductivity is at least 0.5 W / cm ⁰ C is advantageously used for this purpose. In addition, the choice of materials with good thermal conductivity is restricted by a certain lower limit for the erosion resistance defined earlier. In the table below, some materials with the relevant characteristic values are given, which have proven to be favorable for the present purpose. The insulating materials steatite and corundum are also listed for comparison.

Thermal conductivity
capability
λ
W / cm ⁰ C Specific
warmth
C.
Ws / cm × ^{1 0} C Melting point
>%
⁰ C Burn-off
strength
λ c &, * λ
(kW) ² · s / cm ⁴ steatite
corundum
nickel
Pure iron
platinum
copper
molybdenum
money
tungsten
Composite metal Wo / Cu. 0.023
0.065
0.59
0.65
0.70
3.93
1.45
<1.45
1.60
1.53 2.2
4.2
3.9
3.6
2.86
3.45
2.72
2
2.72
3.0 1600
2 050
1452
1528
1770
1083
2,600
3,900
3 380
3,380,1,080 0.065
0.57
2.42
2.73
3.15
7.95
13.3
<22
25th
25.7 / 2.65

As can be seen from the table, they have charring resistance. In addition, however, are also suitable

the materials tungsten, carbon, molybdenum and one of the metals copper, platinum, iron, especially technical

a copper-soaked tungsten skeleton built up pure iron and nickel as heat-conducting materials

Sintered material (composite metal) a particularly high 70 quite well, with the iron already from economic

5 6

Reasons are given preference in certain cases. This covering can be made of a metal oxide,

should. All of these materials have a burn-off z. B. aluminum oxide exist. The plates 1 can

strength of over 1 (kW) ² s / cm ⁴ , which value as well as phosphated, enamelled, anodically oxidized

lower limit for practically usable solutions to be painted on or varnished,

can be taken. 5 Under certain circumstances it may be useful, e.g. B. off

The use of the insulator in a mercury price reasons that serve to dissipate heat

steam atmosphere, e.g. B. in a mercury interrupter, parts only on the stressed surface with a

conditionally, in addition to the required erosion resistance, material must also be provided whose erosion resistance matches the one here

a high mercury vapor resistance. The requirements set for the structure are sufficient. This measure has

of the insulating body used material for warmth io besides the technical advantage that at the stressed

Derivation should be a material with a very high melting point, especially in the case of the surface on the surface

of the insulating body as a result of an arc prevailing and otherwise a material with a very high thermal conductivity

Temperature no connection with the mercury capacity can be used, so that the burn-up

enter, which the heat dissipation significantly strengthen these composite parts even higher

worsens. Of the materials listed in the table, 15 values were achieved than with uniform materials

Molybdenum, nickel and pure iron are now sufficient. As materials with a high melting point

this further requirement is sufficient. insulating materials can also be used.

With regard to the structural design of the insulating FIGS. 3 and 4 show insulating bodies constructed in this way are numerous bodies within the scope of the invention. The heat dissipating plates 5, which in Solutions possible. 20 example according to FIG. 3 again by insulating plates 2

With reference to the drawing, some are separated from each other below, exist in this case

Embodiments and an application example of the preferably made of copper and are on the surface

Subject of the invention described. In the drawing z. B. with tungsten or another high melting point

show the material occupied. The thickness of the covering 6 is chosen so

Fig. 1 to 5 some embodiments of layered 25 that when the melting point is reached at the claimed

Insulating body, th surface of the copper part has its own melting

Fig. 6 has not yet reached a protective device with a liquid conductor as a point. Practically comes a strength

Shutdown device with a layered insulating body that extends the covering from a few tenths of a millimeter to a maximum

Forms channel material. a few millimeters in question. In the case of FIG

In all of the figures, the insulating body is initially in a 30, the heat-dissipating plates 5 with a

Cross-section provided in the direction of the electrical voltage-insulating coating 4; then the

stress, which is indicated by a double arrow covering 6 applied from the high-melting material,

is presented, layed out. This ensures that the insulation layer is opposite

The insulating body according to FIG. 1 is set back from a number of the stressed surface and plates 1, which in the direction of the stress 35 must withstand less high temperatures.
separated from one another by plates 2 of insulating material. In the embodiment of Figure 5, the insulating material is constructed. The plates 1 consist of a material body designed as a hollow body, in the bore 9 of which the arc occurs with a higher thermal conductivity than the insulating material. The heat dissipating plates 7 ability. Plates made of mica can be used as insulating material, for example made of copper and are placed on the surface that is not subject to quartz, special glasses, ceramics or oxide ceramics, ie on the outside. The heat generated from a along the surface of the insulating plates 2 and act as cooling flags of the insulating body 3 (dotted The current flowing in the bore 9 tends to be indicated) will penetrate through the plates 1 into the electrically conductive plates 7. The at least partially perpendicular to the claimed longitudinal resistance of the arrangement would thereby be derived down-surface. Set by a suitable choice of material 45. In certain cases it is advisable to counteract this tendency for the plates 1 (see table above) by using the cover material that, due to this effective heat form, is formed by pressed-in rings 8 in such a way as to derive the temperature at the claimed that the base material and the cover material only remain in one area of the insulating body below the melting temperature - the doors of the plate materials that run perpendicular to the stress. Touch to increase the 50 line (circular line along the circumference). In other cases, hollow rivets such. B. made of nickel, in that the plates 7 serving for heat dissipation are riveted.

Plates 1 on the stressed surface over which FIG. 6 shows an example of an application of the insulating material protruding. In order to avoid that the body according to the invention arcs in a protective device instead of burning over the entire surface, 55 (e.g. line or motor protection switch) with mercury in from plate to plate (which naturally also has good silver conductors (cf. German patent 944024) .These electrical conductors are) burning short arcs on the outside of the protective device has roughly the shape of a part, the thickness d of the plates 1 is to be chosen so that an ordinary fuse cartridge and contains the following condition is met: a ceramic insulating body 12 two partly with

60 mercury-filled chambers 13 and 14. Chamber 14 is partially formed by the iron electrode 15, of

E ■ d < TJa + U _k (3) which is led out through an insulating end wall 16 of the contact pin 17. The two chambers 13 and 14 are connected to one another by a channel 18.

E means the voltage gradient in the light- 65 It is formed by a hole in the insulating body 19,

bogen, U _a the anode and U _k the cathode. which is constructed according to FIG. 3, for example. The end

For example, at U _a + U _k = 16.5 V and £ = 165 V / cm, the chamber 13 also forms a resilient membrane 20

a maximum thickness d = 1 mm is permissible. stable end positions, which together with the connection

In the embodiment according to FIG. 2, the lugs 21 are on the part of the chamber 13 forming

Plates 1 with an electrically insulating covering 4 70 iron electrode 22 is attached. Opposite the canal

The inlet opening in the chamber 13 is on the membrane 20 a push button 23 made of insulating material is arranged, which is guided in the cylindrical insulating piece 24. The space of the chambers 13 and 14 not filled by the mercury contains a gas which is mixed with mercury does not form compounds and has good arc-extinguishing properties, e.g. B. hydrogen.

For a protection device with a nominal current of 10 A and a nominal voltage of 500 V, one will use a channel about 30 mm long and about 0.3 mm in diameter. The thermally conductive Plates are about 0.3 mm thick and spaced about 0.1 mm apart.

It can be seen that the switching work occurs primarily in switching channel 18. The hardest are those Conditions in the event of a short-circuit shutdown. Today's official regulations write a test short circuit current of 1500 A, that of a large capacity battery with a DC voltage of 550 V. is delivered. The arc power per cm of channel length is approximately 10 kW / cm; the arc lasts some ms. These values of arc power and duration are the estimate made in the introduction based on the heat absorption capacity of various insulating bodies. It's from the ones there It can be seen that insulating materials withstand the thermal stress caused by the short-circuit disconnection arc have not grown that, on the other hand, the insulators listed in the table with the meet the highest burn resistance of the load.

The application of the insulating body according to the invention is in no way related to that described with reference to FIG. 6 Limited example, such insulating bodies can be used wherever there is a large thermal Stress caused by a cut-off arc occurs, for example in mercury interrupter tubes, automatic Switches, periodic interrupters, in particular mercury interrupters, and generally in switching devices with compact design, in particular switching devices with liquid conductors.

Claims (21)

Patent claims: 1. Arc-resistant insulating body, along the surface of which an arc occurs and against the same can give off heat to a dangerous extent, characterized in that the same for the purpose of rapid dissipation the arc heat away from the endangered surface into the interior of the insulating body as a composite body from stacked against each other in the direction of the electrical voltage stress electrically insulated plates made of a material with opposite that located between the plates Insulating material higher thermal conductivity is formed. 2. Insulating body according to claim 1, characterized in that the serving for heat dissipation Panels are made of a material whose thermal conductivity is at least ten times greater than that of the insulating material. 3. Insulating body according to claim 1, characterized in that the plates serving for heat dissipation consist of a material whose thermal conductivity is at least 0.5 W / cm ⁰ C. 4. Insulating body according to claim 1, characterized in that the plates used for heat dissipation consist of a material, at least on the claimed surface, whose erosion resistance is at least 1 (kW) ² s / cm ⁴ . 5. Insulating body according to claim 4, characterized in that that the plates used for heat dissipation are made of one of the materials tungsten, carbon, Copper and platinum are made. 6. Insulating body according to claim 4, characterized in that the serving for heat dissipation Plates consist of a sintered material. 7. Insulating body according to claim 6, characterized in that one of an impregnated with copper Tungsten skeleton built up sintered material is used. 8. Insulating body according to claim 4 for use in a mercury vapor atmosphere, characterized characterized in that the plates serving for heat dissipation at least on the stressed surface consist of a material that is also at the surface of the insulating body as a result of a The temperature of the arc does not form a connection with the mercury, which is the cause of heat dissipation significantly worsened. 9. Insulating body according to claim 8, characterized in that the serving for heat dissipation Plates are made from one of the materials iron, nickel and molybdenum. 10. Insulating body according to claim 1, characterized in that that the plates used for heat dissipation are separated from one another by insulating plates are. 11. Insulating body according to claim 10, characterized in that that the insulating plates are made of mica. 12. Insulating body according to claim 1, characterized in that that the plates used for heat dissipation have an electrically insulating coating are provided. 13. Insulating body according to claim 12, characterized in that that the plates are provided with a covering made of aluminum oxide. 14. Insulating body according to claim 1, characterized in that that the plates used for heat dissipation on the stressed surface over the Insulating material protrude. 15. Insulating body according to claim 4, characterized in that the serving for heat dissipation Plates are covered on the stressed surface with a material that is opposite to the base material has a higher melting point. 16. Insulating body according to claim 15, characterized in that that the plates used for heat dissipation are made of copper and with one of the in the claims 5 and 6 mentioned materials are occupied. 17. Insulating body according to claim 8, characterized in that the serving for heat dissipation Plates are covered on the stressed surface with a material that is opposite to the base material has a higher mercury vapor resistance. 18. Insulating body according to claim 17, characterized in that that the plates used for heat dissipation are made of copper and with one of the im Claim 9 mentioned materials are occupied. 19. Insulating body according to claim 1, wherein the plates are provided on the claimed surface with a cover material, characterized in that The base material and the cover material are only perpendicular to the electrical voltage stress touch the running line. 20. Insulating body according to claim 1, characterized in that the plates on the not claimed Surface protrude over the insulating material and act as cooling flags. 21. Isoherkörper according to claim 1, characterized in that the thickness of the thermally conductive plates is smaller than the ratio of anode and cathode fall to the arc gradient. Considered publications: German patent specifications No. 624 777,626 424,637 744, 658 697.764026; Austrian Patent No. 164163; Swiss patent specification No. 262 091. 1 sheet of drawings