DE2515392A1 - ELECTRIC CONTACT - Google Patents

Description

GERMAN GOLD AND SILVER SCHEIDEAESTALT YORMALS ROESSLER 6000 Frankfurt am Main, Weißfrauenstrasse 9

Electric contact

The invention "relates to silver / tin oxide electrical contacts with fibrous tin oxide structure for switching high electrical Currents "with relatively small magnetic blowing field strengths, especially for switching devices with characteristic currents of 40 - 400 A with a blowing field strength of 50 to 500 Gauss.

In switchgear of electrical power engineering is used for Switch-on and switch-off currents of approx. 50 - 3000 A are widely used today, the contact material silver / cadmium oxide with 10 - 20 Gew .- ^ CdO used. Also contact materials with others Oxide additives have been known per se for a long time. For example, in DiC-PS 860 525, a contact material produced by sintering is used of silver and lead oxide mentioned, in US-PS 2,539,298 additions of lead oxide, thallium oxide, copper oxide, Beryllium oxide and thorium oxide referred to as silver contacts and additives in GB-PS 661 147 and DT-PS 807 416 of tin oxide. The metal oxides in these composites reduce the tendency of the contact pieces to weld together and before especially the material wear as a result of the switch-on or switch-off arcs. As a manufacturing process for these materials come essentially selective internal oxidation or powder metallurgy question, whereby an isotropic Distribution of the 2nd phase results.

In practice, however, except for silver / cadmium oxide, none of the materials mentioned has prevailed to any significant extent can.

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According to the state of knowledge of the professional world (e.g. Yuan-Shou Shen, RH Krock: "A Study on the E _r osion Modes of AgIOCdO-Contact. Material" in the Proceedings of the 7th International Conference on Electrical Contact Phenomena, 1974, pages 31-35 ) the effect of the oxide additives to silver in the concentrations usually used, which reduces switching erosion, is based on the fact that they evaporate, sublime or dissociate in the area of the arc roots, ie in the area of the highest energy density. The energy required for this is taken from the arc, which cools it and reduces the evaporation loss of the base material, in this case silver 900 ° C) from the arc. The amount of heat absorbed by other oxides, such as Cu ^ O, MnO, Sb ₂ O ^, SnO ₂ and ZnO, up to 900 ° C only corresponds to their heat content and is thus about a power of ten lower than with cadmium oxide.

Table 1 below gives a comparative review about the "cooling effect" to be expected according to the state of knowledge oxidic additives. Here the values (inKcal / cnr) were on standardized the value valid for CdO.

Table 1

oxide rel. Cooling effect
Kcal / cm '' CdO 1 CuO 0.17 MnO 0.16 Sb ₂ O ₃
PbO 0.14
0.21 SnO ₂ 0.14 ZnO 0.18

609 8 44 / Ό447

According to the values in this table, there should not be a more effective extinguishing additive "for electrical contacts as CdO. This prediction is supported by the widespread use of silver / cadmium oxide materials in electrical Circuit technology confirmed.

The known silver / cadmium oxide materials, however, still show a noticeable loss of burn-off when switching the corresponding Contacts, especially at high rated currents and relatively low magnetic blowing field strengths. This will the service life of these contact pieces is severely limited.

There has therefore been no lack of attempts in the past to reduce these burn-off losses. For example, it is known from DT-OS 1 640 007 to improve the burn-up ratios, and thus the burn-up loss, by embedding a material with good electrical conductivity, such as silver or copper, in a second material, forming a large number of individual current paths. whose boiling or sublimation temperature is at least 10 fo below the Siedebzw. Sublimation temperature of the electrically conductive material is. But even these materials did not produce fully satisfactory results with regard to the burning behavior.

It is also known (DT-OS 25 10 784), electrical contacts Rope with good ductility from silver / metal oxides by extrusion, the metal oxide being wood fiber-like Structure. Preferably here Silver / cadmium oxide is used and the semi-finished product is deformed into contact rivets, so that the possible wood-fiber-like structure is strongly disturbed in the area of the rivet head and adapts to the flow of material during the deformation. To the burning behavior no information is given to these contacts.

It was therefore an object of the present invention to find electrical contacts made of a combination of materials that have a noticeably lower erosion loss than the known contacts

60 98A kl 0 4 k 7

made of silver / cadmium oxide or other metal oxides, in particular for switching devices with rated currents of 40 to 400 Ampere with magnetic blowing field strengths of about 50 to 500 G-outside.

According to the invention, this object was achieved in that electrical contacts are used which are at least in the contact layer Made of a composite material of silver and fibrous embedded tin oxide exist, the fibrous deposits in the contact layer parallel to each other and are arranged perpendicular to the switching plane.

It was very surprising for the person skilled in the art that the invention electrical contacts with the special combination of materials and microstructure such a favorable combustion • show that, according to the current state of knowledge, there should be no better materials than silver / cadmium oxide *

The advantages of the electrical contacts according to the invention can be demonstrated by the following holding tests (Table 2):

^ one-part powder (-ü60 / um particle size) of the oxides CdO, CUpO, In ₂ O. ,, MnO, SbpO ,, SnOp and ZnO were each filled into silver tubes (12/10 mm diameter) and with these to wires of 0, 5 mm in diameter drawn. In the next stage, a large number of such wires were bundled and drawn together again to form a wire 0.5 mm thick. This was repeated several times to select a material was present, ij ^ which the oxide phase is in fiber form (diameter of the single fiber 5 / Ui) was present, wherein the volume content of each oxide was uniformly 15 $>.

Cylindrical contact pieces with a diameter of 8 mm and a thickness of 5 mm were made with the arrangements outlined in Fig Oxide fibers switched relative to the switching plane under the following test conditions.

6098U / 04A7,

Voltage TJ = 220 V, 50 Hz

Current I = 100 - 2200 A

Power factor cos (ß = 0.35 + 0.05

Blow field induction B = 100 and 100 G

Lookout moment = 0 ° (0.1 ms after the natural

Current zero crossing)

Sehalt number N = 200

Switching frequency h = 12 cycles / min

Separation speed ^va _us = 0 »4 m / s

Separation distance a = 0.4 mm

Contact force = 5 kp

(before separating)

Vertical contact piece arrangement, anode on top.

The magnetic blown field is created in the switching device essentially by self-excitation and is determined by the Cut-off current and the structural design of the device.

Loss of weight of the contact pieces (consumption) determined after every 200 switching operations.

The burn-up values listed in Table 2 are the mean value from numerous switching operations, They are calculated from the sum of the anodic and cathodic weight losses.

Figure Ia shows a fiber structure of the oxide inclusions perpendicular to the switching plane, while in the figures Ib and Ic the oxide fibers lie parallel to the switching plane.

6Q9 8 44 / O44 7

(Table 2

as as 39a

material .- - Ag / CdO - • • V Test current 700 Blow field Burn-off [κ {? b).; .. c) ft f7 "X I ΤΛ, - () [a] 1000 M. 23 - 22 - . 1400 with Kojatakt'stückanordnimg 79 · 7/4. Asr / SnO 1800 100 a). 130 125 "2 7OO 100 11 215 206 - - 1000 100 • 5s '70 67 1400 100 68 140 ■ 131 -1800 1000 118 272 250 Ag / Cu ~ O 7OO 1000 55 412 404 '1000 1000. 74 34 30th 1400 1000 14-3 82. 82 '- 1800 100 221 ·. 172 178 7OO 100 20th 255. . 240. . · 1000 100 75 76 70 1400 .100. Ί46. 151 160 1800 1000 233 263 " 254 7OO ' . 1000 55 402 398 1000 1000 13c 32 28 1400 . 1000 234. 117 "- ■ 115 1800 100 373. 409 385 ■ 7OO 100 24 653 • 1000 . 100 113 23Ο 217 ~ 1400 100 293. 560. 532 1800 1000 508 1092 1112. · ^: 7OO 1000 169 - 2090 2132 "1000 1000 '+95 . 34 35 . 1400 . 1000 1003 74- - 82 - '1800 100 1865 156 163 7OO 100 · 27 316 375 1000 100 91 27 '30 1400 ' 100 190 103 97 1800 ■ 1000 -405 '.. 429- -434 1000 18th 603 ' 575 1000 77 1000 261. 522

609844/0447

to table 2

"Material ■ - - Test current Blow field Burn-off C ^m E- b) .- - c) LA] [Gj. .52 ~ 50 - with contact piece arrangement M95 . 193 Ag / KaO 700- 100. a) 531 544 1000 100 43 844 860 1400 100 190 132 127 1800 100 482 350 317 700 1000 812 1144 1093 - 1000 1000 112 2412 2301 - ■ 1400 1000 325 ■ 31 27 1800 1000 1056 ■ 150 137 Ag / SboO, 700 100 1865 253 270 1000 100 26 ' . 450 4-53 1400 100 '114 135 -120 ■ 1800 ■ 100 243 . 406 393 700 1000 412 903 885 - 1000 1000 .114 1970 1907 ■ 1400 - ■ 1000 377 25th . 27 . 1800 1000 752 84 79 Ag / ZnO 700 100 1850 125 134 1000 100 42 317 324 (^ r. 7) 1400 100 221 48 40 . 1800 - 100 569 112 120 . 700 1000 853 312 319 1000 1000 112 804 776 1400 - 1000 341 1800 1000 893 1604

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- 8 The following can be seen in Table 2:

In all of these synthetically produced and structurally identical fiber materials, an influence of the fiber orientation on the size of the material burn can be seen. Materials with the oxides CdO, CUpO, Ιη ,, Ο. ,, MnO, Sb 0, and SnOp have slightly lower erosion values for fibers lying perpendicular to the button than for fibers lying parallel to the button. Only in the case of ZnO is this the other way round. However, while this phenomenon makes with Cu "0, _9, O. ,, MnO, SbpO-, and even at CdO hardly noticeable, the burn-up values for Snop in arrangement of the fibers are perpendicular to the shifting plane only about half as high as in an arrangement parallel to the switching plane. In addition, the erosion values of the contacts according to the invention are significantly below those of silver / cadmium oxide.

For better illustration, the erosion values of Ag / SnOp and Ag / CdO (each with 15 vol. $ Oxide = 10.5 wt Fig. Ia and Ib. The advantage of using Ag / SnO instead of Ag / CdO with a structure according to Ia becomes particularly great with increasing test current strength with weaker magnetic fields, ie with switching devices with weak magnetic self-blowing of the arc. The switch-off burn-off was investigated in the current strength range of approx. 700 - 1800 A. This test current range corresponds in AC4 operation (starting of motors with squirrel cage, jogging, counter-current braking, reversing) with in and out currents in the amount of 6 times the nominal current, a nominal current range of approx. 100 - 300 A. That is why it is used in switching devices particularly favorable for this current range, Ag / SnO _? -Contact in the special structure and arrangement to be used instead of Ag / CdO.

fi09844 / 0447

These particularly favorable properties of the invention electrical contacts with regard to the erosion behavior were extremely surprising for the person skilled in the art, since after the theoretical Findings and according to previous practical tests, silver / cadmium oxide should be the best contact material, regardless of a fiber structure and a special one 3? Ace arrangement.

The following examples show further manufacturing processes for the electrical contacts according to the invention:

Example 1 ;

Finely divided powders (^ -60 / μm particle size) of SnO ₂ and Ag were mixed with one another in various weight ratios (see Table 3), compacted into bolts with a diameter of 25 mm, sintered and compacted by hot extrusion to form rods with a thickness of 8 mm. Here the alignment of the SnO ₂ inclusions also takes place to form fiber-like aggregates, while this is not the case with the extrusion of Ag / CdO mixtures, as can be seen from Figures III and IV, Figure III showing an extruded Ag / CdO material .Shows, and Figure IV a likewise extruded Ag / Sn0 ₂ ~ material, both at a magnification of 400: 1.

Table 3 Heating temp. 4- C ⁰ Cj Pressure) BhO ₂ content 800 (^ kp / mm J [ G _e w. -Io} 840 64 10 870 65 12th 900 70 14th 920 74 18th 80 • 24

) Compression ratio

= 10 / l

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Cylindrical contact pieces of 8 mm diameter, whereby also in this case the fiber-like orientation of the SnOp inclusions perpendicular to the button, were under the previous test conditions, but in an extended Test current strength range from 220 A to 2200 A, examined for their appearance burn-up.

Figures V and VI show the burn-up values measured on these extruded materials with SnO contents of 10-24% by weight in a logarithmic representation. For comparison, the corresponding data for Ag / CdO with 12 $ CdO are also entered. Figure V applies to a magnetic blowing field strength of 100 Gauss. Under these conditions, the extruded Ag / SnO materials are clearly superior to Ag / CdO at test currents above approx. 250 A, ie at nominal currents of 7 40 A. With large blowing field strengths (1000 Gauss) the same applies above approx. 600 A test current, ie from approx. 400 A nominal current, as can be seen from Fig. VI.

Example 2 ;

The finely divided powder (· <16Ο / um particle size.) Of SnO "and xig in the weight ratio 89.5 $ Ag, 10.5 ° i SnO ₂ (= 15 vol 96

₂ ) were mixed, compacted and then extruded with a compression ratio of 30: 1 to form profiles with a cross-section of 17 × 17 mm. Contact pieces 3 mm thick were sawn off the rods and used to equip three-pole AC contactors. In these cases, too, the contact pieces were soldered on in such a way that the SnO "fibers were perpendicular to the switching plane. The contact pieces were switched with the conditions given in Table 4 until the first of the 12 contact pieces (double break of fixed and moving bridge contacts, 3-phase) of a contactor failed due to material wear. The switching numbers achieved in this way are given in Table 4 in comparison with Ag / CdO of the same composition and production.

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80-98447-044 7

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The electrical contacts according to the invention are "special" advantageous for nominal currents of 40 to 400 amperes and magnetic Blow field strengths from 50 to 500 Gauss. Of course, they can also be used with higher rated currents and blowing field strengths Find.

Table 4- Device and test data

line current 250 A

Nominal service life of the contact pieces: · 50,000 switching operations

Test voltage:

Inrush current: Inrush current:

Cosk: 0.4

Switching frequency: 250Zh

Duty cycle: ■ 80 ms

Result:

580 V; 50 Hz

1000 A, blowing field strength approx. 250 G

1000 A '-.

Kbnt aktwerk 10 material achieved number of operations AgZSnO ₂ 10 148,000
I7O.5OO '
165,000 AgZCdO .5 % 53,000
67,5OO
'63,000

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6 0 9 8 4 4 / G 4 4 7

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The results presented in the examples clearly demonstrate the technical port step achieved by Ag / SnOp in comparison to Ag / CdO, which has hitherto been used exclusively for such purposes.

A particularly favorable erosion behavior of the electrical contacts according to the invention is obtained when the diameter of the tin oxide fibers is 1 to 15 μm. The preferred range for the tin oxide content is between 12 and 18% by weight .

60984Α / Ό4Α7

Claims (2)

- "13 - Claims 1.) Electrical contact, especially for switching devices with nominal currents of 40 to 400 amperes with a magnetic one Blowing field strength of 50 to 500 Gauss, at least in the contact layer made of a composite material consists of silver and tin oxide embedded in fibrous form, characterized in that the fibrous tin oxide deposits are arranged in the contact layer parallel to one another and perpendicular to the switching plane. 2. An electrical contact according to claim 1, characterized e g indicates that the fiber thickness of the incorporated Zinnoxidfasern 1-15 / .mu.m. 3 «Electrical contact according to claim 1 and 2, characterized in that the tin oxide content is 12 to 18 wt .- ^. PL / Dr Bre-P
7.4.1975 609844AO A4 7