US3551622A - Alloy materials for electrodes of vacuum circuit breakers - Google Patents

Description

Q United States Patent 11113 551 22 [72] inventors Hisasuke Takeuchi; [56] References Cited l'fgdatipshlilTgda; Tsuneyoshi Takasuna, UNITED STATES PATENTS 1248.924 12/1917 Sandell ZOO/166C l 1 2.137.283 8/1938 Hensel et al ZOO/166C e gfi ofsen 603,739 2,358,326 9/1944 Hensel m1. ZOO/166C Dec 22 1966 now abandoned whichisa 2,975,256 3/1961 Lee et a1. ZOO/144(2) Q 7 9 7 continuatiomimpa" ofsen No 353,614 3,414,351 2/1966 Hebb 200/144(...) Mar. 20, 1964, now abandoned. FOREIGN PATENTS [45] Patented Dec. 29, 1970 406,614 3/1965 Japan 75/153 [73] ASSlgI'lBfi Hitachi, Ltd. OTHER REFERENCES Tokyo P fJ Hackh 5 Chemical Dictionary; Third Edition revised by Jug g' rgg; lius Grant; McGraw-Hill Book Co.. copyright 1944; page 220; Pnomy 2: copy in Scientific Library or Group 2177 [31 No. 38/ 13436 Primary Examiner-Robert K. Schaefer [54] ALLOY MATERIALS FOR ELECTRODES OF VACUUM CIRCUIT BREAKERS 144.2; 75/153(Cursory), 159(lnquired); 252/500 Assistant Examiner-Robert A. Vanderhye A1ror11eyCraig Antonelli, Stewart & Hill copper rich phase and an iron-group-element rich phase,.

wherein the alloys have lower chopping current and larger dielectric strength than that of copper contacts.

ALLOY MATERIALS FOR ELECTRODES OF VACUUM CIRCUIT BREAKERS CROSS-REFERENCES TO RELATED APPLICATIONS Thepresent application is a continuation application of ap plication Ser. No. 603,739, filed Dec. 22, 1966 which in turn' is a continuation-in-part of application Ser. No. 353,614, filed in the US. Patent Office on Mar. 20, 1964.

BACKGROUND OF THE INVENTION represented by a chopping phenomenon encountered in interdestroyed. An electrode for operation in a vacuum environment is required to produce the smallest possible amount of gas therefrom, independent of the magnitude of current bringing forth the chopping phenomenon. Thisis an important requisite for the persistence of satisfactorily high performance and long service'life of a vacuum circuit breaker because emission of included gas from the surface of the electrode by the action of the electrical are will lower the degree of vacuum in a vessel containing the electrode-therein. Furthermore, a

metal having a high vapor pressure will evaporate to impair the electrical insulation in the vessel. I

Contact materials for vacuum circuit breakers heretofore proposed in the art includesingle substances of copper, silver,

tungsten, molybdenum, tin, indium, lead. antimony and the 2 g- SUMMARY'OE THE INVENTION With a view to eliminate the above drawbacks of prior art contact materials and vacuum circuit'breakers using such electrode contacts therein, the present invention provides a vacuum circuit breaker adapted for making and breaking an electric circuit in a vacuum atfi pressure ofabput la0 m m.- Hg. or less, said vacuum circuit breaker having electrodes made of alloys which consist essentially of at least one iron group element selected from the group consisting of iron, cobalt and nickel, the essential balance being copper and a very small amount of gaseous impurities."

According to the prior art, it has been said that electrode contact materials should contain elements such as bismuth and antimony, which have a higher vapor pressure than tin; in 1 order to effectively reduce the chopping current. In melting alloys containing elements having a relatively high vapor pressure, that is, elements liable to be vaporized, it is impossible to make the degree of vacuum extremely high and as a result it is inevitable that certain fractions of gaseous components remain in the electrode. in contrast tosuch prior difficulty, the

' electrode contact alloys employed in the present invention like, and copper-bismuthalloys, silver-bismuth alloys, copperv antimony alloys, silver-antimony alloys, and the like. These prior contact materials have however. been defective in the following points:

a. Copper and silver have a high chopping current and a low dielectric strength. I Tungsten and molybdenum have a chopping current remarkably greater than that of copper and have an interrupting ability remarkably poorer than that of copper.

c. Tin, indium, lead and antimony have a satisfactorily low chopping current, but they have a low interrupting ability as well as a remarkablylowdielectric strength.

Cu-Bi alloys, Ag-Bi alloys, Cu-Sb alloys andAg Sb alloys containing a relatively large amount of bismuth and antimony inorder to minimize the chopping current have a. dielectric strength lower than that of copper and are easily consumed, hence have a short contact life.

An object of the present invention is to provide electrode contact materials especially suitable for use in vacuum circuit breakers for operation in a high tension circuit and to thereby attain remarkable improvements in the performance ofcircuit breakers of the kind described by the use of such electrode contact materials.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples while indicating preferred embodiments of the invention, are given can be melted at a further higher degree of vacuum and yet have a low chopping current characteristic.

The alloys comprising copper and the other components including iron, nickel andcobalt employed i'n'the practice of the present invention can be melted in a high vacuum, for example, at a pressure ofless than about l0 mm. Hg. by means of high-frequency induction heating or by means of bombardment by an electron beam. As a result of the above manner of melting, measurement of amounts of gases such as H O- and N in the electrode contact materials revealed that a Cu 10 percent Bi alloy, melted in the above-described high vacuum of the order of 10.- mm. Hg. or less contained onl y 5 to 7 p.p.m. of such included gases against to 200 p.p.m. in the case of the same alloy melted in an open atmosphere. Mel ting...

of a Cu 10 percent Bi alloy in a higher vacuum such asabout 10 mm, Hg. is difficult because bismuthvaporizes and the compositionideviates from the desired value.

Melting in a high-frequency induction furnace is advantageous in that alloys ofhomogeneous nature can be easily obtained by the stirring effect. Bombardment by an electron beam is also advantageous in its high degassing andrefining effect which leads to production of sound ingots. lnany event,

the alloys of copper ,and other components including iron,

nickel and cobalt made by any of these two methods have a composite structure consisting of a copper-rich phase of high electric and thermal conductivity and another .phase of low electric and thermal conductivity, and inclusion of gases can be minimized. It is to be .understood that the composition ratio between copper and other components, iron, nickel and DESCRIPTION OF THE PREFERRED EMBODlMENTS The invention will now be explainedin detail with reference to table 1 showing typical examples of experiments made on the alloy ofthe present invention containing'various compositions. Electrode contact alloys used in the experiments were of high purity which were melted and degassed in a high vacuum. Opposite electrode contact portions were brought into contact with each other at a Contact area of l2 millimeters in diameter and, during the experiments, pressure in the envelope is maintained at 10-- mm. Hg. or below such as 10- or lOlO- mm. Hg.

The amount of addition of'the elements such as iron, nickel and cobalt with respect to copper is an important factor in order to obtain an optimum composition for use as electrodes of vacuum circuit breakers, and varies depending on the carrying current fed across the electrodes, the short circuit current, the dielectric strength between the electrode contacts, the contact force and the separating force of the electrode contact portions, and the shape and structure of the electrode curs under the same conditions in the case of electrode contacts with a nickel content of 15 percent.

Generally. the alloy of copper-nickel system shows a homogeneous single phase according to its equilibrium phase diagram. but the present electrode contact material. for use in TABLE LRESULTS OF INTERRUPTION TESTS MADE ON VACUUM CIRCUIT BREAKERS HAVING ELECTRODE CONTACTS F ALLOYS OF Cu Fe, Ni, 00 SYSTEM Dielectric strength Chopping current kv./i mm. (A) Electrode contact intermaterial composlelectrode Maximum Mean Interrupting N on-weldlng tion, percent distance value value ability characteristic Test No.2

Pure Cu 36-50 22-27 11-12 Medium Good.

Ll. Cu-3 Fe.. About 50.... 9. 8 Cu- Fe.. d 8. 2 Cu-IO Fe. 6. 7 3. ell- Fe 6. 9 3. Cu- Fe... 54.5 6. 4 d Cu-40 Fe 62.0 6.6 8.1 do...... Bad.

1.2 Cu-3 Ni About 50.... 9.8 6.0 Medium Good.

d 9. 6 5. d Do.

8. 0 5. Slightly bad (Judi) Ni 53.0 6. 6 4. ad.

1.3 Cu-3 Co About 50... 9. 4 6. Medium Good.

d 9. 0 6. d Do.

7.8 5. Slightly bad 8. 4 3. Do.

1.4 Ctr-1.5 Fe-L5 00-. 9. 6 4. 8 Good.

(in-5.0 Fe-5.0 Co 8.0 4.7 Do. Cu-7.5 Fe7.5 00.. 7. 2 3. 9 Do. Cu-l5.0 Fe-15.0 Co- 48 6. 5 3. 1 Slightly bad.

L5 Cu-1 Fe-i Ni-! 00... About 50.... 8.2 5.5 .....do... Good.

Cu-5 Fe-5 Ni-5 Co do 6. 6 3. 2 do Do.

- has a composite structure of a copper-rich phase of high electric conductivity and an iron-rich phase of low thermal conductivity. Therefore. it is considered that. when such alloy is used as electrode contacts of a vacuum circuit breaker, the value of the chopping current becomes markedly lowerthan that of pure copper. Electrodes of the copper-iron alloy containing 40 percent by weight of iron therein have a poor nonwelding characteristic. and welding and sticking takes place when a current of 8 kiloamperes (peak) is made to pass across the electrode contacts which are closed by a contact force. for example. of 39 kilograms. However. no welding and sticking occurs under the same conditions in case of electrode contacts of the copper-iron alloy containing 20 percent by weight of iron therein. This is considered to be attributable to the fact that the iron-rich phase of low thermal conductivity is excessiveiy fonned in the copper-iron alloy with 40 percent iron therein. resulting in the reduction in the thermal conductivity and the increase in the contact resistance. Therefore. the maximum iron contentpreferable in the electrode contact alloy of a copper-iron system is in the order of about 20 percent by weight.

1.2 In the alloy of copper-nickel system. it will be seen that. by the addition of 3 percent by weight of nickel, that chopping current has 'a mean value which is approximately one-half of the case of pure copper. and thus the addition of nickel to copper has a noticeable effect. When the nickel content in the copper-nickel alloy is increased to percent. electrode contacts with such alloy composition show a poor nonwelding characteristic and welding and sticking takes place when a current of 8 kiloamperes (peak) is made to pass across the electrode contacts which are closed by a contact force of. for example. 39 kilograms. Howevei no welding and sticking oca vacuum circuit breaker. has the composite structure of a two phase mixture since the electrode contact material is subjected to melting and ingot making in a high vacuum. Or more precisely, the alloy so treated has a cast structure in which a nickel-rich phase is developed in the form of dendrite in a copper-rich matrix, and the copper-nickel alloy apparently has a structure of a two phase mixture. It is considered that a copper-nickel alloy system possesses the sufficient chopping characteristic required for electrode contacts of a vacuum cir cuit breaker because the copper-nickel alloy has the structure which is actually the mixture of the phases of different physical properties, that is, the copper-rich phase of high electrical and high thermal conductivity and the nickel-rich phase of low electrical and low thermal conductivity.

1.3 In the alloy of a copper-cobalt system. it will be seen that the addition of 3 percent by weight of cobaltis effective to reduce a mean value of the chopping current to approximately one-half of the value of pure copper, and thus a sub stantial effect is obtained by the addition of cobalt to copper. The copper-cobalt alloy has a composite structure of a cobaltrich phase and a copper-rich phase and it has been recognized that the copper-cobalt alloy with such structure. when used as electrode contacts, has a satisfactory effect on the chopping current as in the cases of the copper-iron alloy and the coppernickel alloy. Further, it has been found that the copper-cobalt alloy containing 30 percent by weight of cobalt therein is suffciently usable as electrode contacts of a vacuum circuit breaker although this alloy has a slightly poor nonwelding characteristic.

1.4 in an attempt to find out an effect of addition of two elements among iron. nickel and cobalt to copper. the ternary alloy of copper-iron-cobalt system was selected as a typical example. As a result of tests made on this electrode contact material. it was proved that, with electrode contacts of the ternary alloy having the content of any two elements ranging from 3 to 30 percent by weight. the chopping current is reduced to a value less than one-half of the case with pure copper, and the interrupting ability as well as nonwelding characteristic thereof is so excellent that the electrode contacts are quite suitable for incorporation in a vacuum circuit breaker. It is considered that the ternary alloy electrode contact material shows such prominent effect in its chopping current characteristic because of a composite structure of a copper-rich phase of high electrical and high thermal conductivity and a second and a third phase consisting essentially of the specified additive elements.

l.5 Tests were similarly made with a quarternary alloy in which all of three elements. iron, nickel and cobalt. were simultaneously added to copper and a total amount of the elements added was varied in a range of 3 to percent by weight. As a result of the tests. the simultaneous addition of these three elements was proved to be quite effective to improve the chopping current characteristic, interrupting ability and nonwelding characteristic.

It will thus be understood that, in the alloys of copper with iron. nickel and cobalt. generated arcing energy is small owing to a low arc voltage of the phases rich in the additive elements and the rate of dielectric recovery in a vacuum is high owing to a high dielectric strength of such phases. Therefore, vacuum circuit breakers having electrodes of the inventive alloy have an improved interrupting ability.

The present invention thus relates to a vacuum circuit breaker characterized by the provision of make-break electrode contacts made from a compound of copper and one or more elements selected from the group consisting of iron,

nickel and cobalt. Particularly, the vacuum circuit breaker of the present invention has a dielectric strength of the order of about 50 kilovolts (at interelectrode distance of l millimeter), low chopping current, good interrupting ability, little electrode consumption, and satisfactory nonwelding characteristics, even with an excessive current in the short circuit of electrodes. From the foregoing description, it will be apparent that the most practical effect can be developed with a vacuum circuit breaker having an electrode contact material made from an alloy consisting essentially of copper and containing about 10 percent by weight of iron, nickel and/or cobalt.

As a summary, the alloys provided by the invention have a substantial composite structure consisting of one phase that is a copper-rich phase of a high electric and thermal conductivity and another phase that is an iron group element-rich phase of a low electric and thermal conductivity, and thus the electrode contacts made of said alloys in a vacuum circuit breaker have very low chopping current characteristics, large dielectric strength, and the vacuum circuit breaker has high interrupting characteristics.

Since modifications of this invention will be apparent to those skilled in the art, it is not desired to limit the invention to the exact constitution shown and described. Accordingly, all suitable modifications and equivalents may be resorted to which fall within the scope of the appended claims.

We claim:

I. A vacuum circuit breaker adapted for making and breaking an electrical circuit in a vacuum comprising an envelope evacuated to a pressure not greater than about 10- mm. Hg, and a pair of electrode contacts made of alloys which consist essentially of from about 3 to percent by weight of at least one iron group element selected from the group consisting of iron, nickel, and cobalt, the balance being copper and a very small amount of gaseous impurities, said alloys having a substantially composite structure of a copper rich phase of high electric and thermal conductivity and an iron-group-element rich phase of low electric and thermal conductivity.

2. A vacuum circuit breaker adapted for making and breaking an electrical circuit in a vacuum comprising an envelope evacuated to a pressure not greater than about l0 mm. Hg., and a pair of electrode contacts made of alloys which .consist essentially of from about 3 to 30 percent by weight of at least one element selected from the group consisting of iron, nickel, and cobalt, the balance being copper and a very small amount of gaseous impurities, wherein said alloys have less than about strength as that of copper electrode contacts.

3. vacuum circuit breaker adapted for making and breaking an electrical circuit in a vacuum comprising an envelope evacuated to a pressure not greater than about l0 mm. H g.. and a pair of electrode contacts made of alloys which consist essentially of from about 3 to 30 percent by weight of at least one iron group element selected from the group consisting of iron, nickel, and cobalt, the balance being copper and a very small amount of gaseous impurities, said alloys having a substantially composite structure of a copper rich phase of high electric and thermal conductivity and an iron-group-element rich phase of low electric and thermal conductivity, wherein said alloys have less than about one-half of the chopping current of the typical mean value of that of copper electrode contacts and at least the same dielectric strength as that of copper electrode contacts. v g

4. A vacuum circuit breaker according to claim 1, wherein said element is iron and is present in said alloy in an amount of about} to 20 percent by weight. g

5. A vacuum circuit breaker according to claim 1, wherein said element is nickel and is present in said alloy in an amount a ut? 2. Pe n y we h 6. A vacuum circuit breaker according to claim 1, wherein said element is cobalt and is present in said alloy in an amount of about 3 to 30 percent by weight.

7. A vacuum circuit breaker according to claim 1, wherein said alloy contains two of said elements in an amount of about 3 to 30 percent by weight.

8. A vacuum circuit breaker according to claim 7, wherein said two elements are iron and cobalt.

9. A vacuum circuit breaker according to claim 1, wherein said alloy contains all three of said elements in an amount of about 3 to l5 percent by weight.

10. A vacuum circuit breaker adapted for making and breaking an electrical circuit in a vacuum which comprises an envelope evacuated to a pressure not greater than about l0- mm. Hg., and a pair of electrode contacts made of alloys which are prepared by melting metals by electron beam bombardment and cooling them to produce a solid composite structure, said alloys consisting essentially of from about 3 to 30 percent by weight of at least one iron group element selected from the group consisting of iron, nickel and cobalt, the balance being copper and a very small amount of gaseous impurities, said alloys having a substantially composite structure of a copper rich phase of high electric and thermal conductivity and an iron-group-element rich phase of low electric and thermal conductivity, wherein said alloys also have less than about one-half of the chopping current of the typical mean value of that of copper electrode contacts and at least the same dielectric strength as that of copper electrode contacts.

11. A vacuum circuit breaker adapted for making and breaking an electrical circuit in a vacuum which comprises an envelope evacuated to a pressure not greater than about 10- mm. Hg, and a pair of electrode contacts made of alloys which are prepared bymelting metals in a high-frequency induction furnace and cooling them to produce a solid composite structure, said alloys consisting essentially of from about 3 to 30 percent by weight of at least one iron group element selected from the group consisting of iron, nickel and cobalt, the balance being copper and a very small small amount of gaseous impurities, said alloys having a substantially composite structure of a copper rich phase of high electric and thermal conductivity and an iron-group-element rich phase of low electric and thermal conductivity, wherein said alloys also have less than about one-half of the chopping current of the typical mean value of that of copper electrode contacts and at least the same dielectric strength as that of copper electrode contacts.