US3624325A

US3624325A - Vacuum-type circuit interrupter with weld-resistant contact material consisting essentially of copper and beryllium

Info

Publication number: US3624325A
Application number: US888398A
Authority: US
Inventors: Fordyce H Horn
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1969-12-29
Filing date: 1969-12-29
Publication date: 1971-11-30
Anticipated expiration: 1988-11-30
Also published as: FR2074422A6; DE2063537A1; JPS548858B1; DE2063537C2; GB1288339A; SE381771B

Abstract

Discloses a vacuum-type circuit interrupter having a pair of contacts relatively movable into and out of engagement with each other. The contacts have their circuit-making and breaking regions formed of an alloy consisting essentially of copper and beryllium, the beryllium being present in a quantity of about 6 to 19 percent by weight of the alloy. The alloy is substantially free of additional metallic constituents that are substantially insoluble in the solid state in copper and beryllium and have effective freezing points lower than 860* C.

Description

United States Patent [72] Inventor Fordyce H. Horn, deceased late of Schenectady, N.Y. by Helen W. Horn, executrlx 888,398

Appl. No.

Attorneys-J. Wesley Haubner, William Freedman, Frank L.

Neuhauser, Oscar B. Waddell and Joseph B. Forman The portion of the term of the patent b H Flt-241987h bee o e as n ABSTRACT: Discloses a vacuum-type circuit interrupter having a pair of contacts relatively movable into and out of engagement with each other. The contacts have their circuitmaking and breaking regions formed of an allo sentially of copper and beryllium, the berylliu in a quantity of about 6 to 19 percent b y consisting esm being present WELD-RESISTANT CONTACT MATERIAL CONSISTING ESSENTIALLY OF COPPER AND y weight of the alloy. BERYLLIUM ditional metallic constituents that are substantially insoluble in the solid state in copper and beryllium and have effective freezin than 860 C.

The alloy is substantially free of ad 6 Claims, 2 Drawing Figs.

g points lower C2 4 34 m m Z M m mh "c u "M m m I L0 W d s Q U Mn. N W 5 55 VACUUM-TYPE CIRCUIT INTERRUPTER WITI-I WELD- RESISTANT CONTACT MATERIAL CONSISTING ESSEN'IIALLY OF COPPER AND BERYLLIUM BACKGROUND OF THE INVENTION This application is related to my copending application Ser. No. 562,141, filed July 1, 1966, and assigned to the assignee of the present invention, now US. Pat. No. 3,497,755.

This invention relates to a vacuum-type circuit interrupter and, more particularly, to contact structure for such an inter rupter.

The aforesaid application discloses and claims vacuum-gap electric discharge devices having arc electrodes made of a copper-beryllium alloy containing 0.1 to l 1.5 percent beryllium by weight. The purpose of the beryllium in such alloy is to serve as a getter that reacts with any oxygen present in the alloy, both during processing and during operation of the discharge device, to maintain the device essentially free of evolved oxygen during the crucial stages of its operation. The present application is also concerned with a discharge device that has arc-electrodes containing beryllium. But in the electrodes of the present application, the beryllium acts not only as a getter but as an antiweld agent, as will soon be described.

If the vacuum discharge device is a vacuum interrupter with electrodes, or contacts, movable into and out of engagement with each other, animportant requirement that must be met is that the contacts must not weld together with objectionable welds, even under the most severe operating conditions. In meeting this requirement, it is important to prevent the formation not only to those welds that are so strong that they cannot be broken except with excessive force during a subsequent opening operation but also those welds that cannot be fractured cleanly and without production of a jagged interface between the two contacts. The production of such a jagged interface leads to excessive contact wear and also to reduced dielectric strength. This antiweld requirement is especially difficult to meet in a vacuum-type circuit interrupter because the contacts of such interrupters must be extremely clean and have surfaces devoid of contaminating films. These clean surface conditions are ideal for the production of objectionable welds, which, in many cases, would be largely avoided if contaminating films were present at the interface.

One way of meeting the aforesaid antiweld requirement is to form the contacts of one of the alloys disclosed and claimed in US. Pat. No. 3,246,979-Lafferty et al., assigned to the assignee of the present invention. Each of these alloys consists essentially of a major constituent which is a good-conductivity, nonrefractory metal and a minor constituent which is a metal having a lower freezing temperature than the major con stituent and little or no solid-state solubility in the major constituent, the minor constituent being present in a quantity of a few per cent or less by weight of the alloy. Examples of such alloys are copper-bismuth, copper-lead, silver-bismuth, and silver-lead, each alloy containing a few per cent or less by weight of the second-mentioned or minor constituent. The main purpose of the minor constituent is to act as a weld-inhibiting agent that weakens any weld formed between the contacts.

While this approach is satisfactory for many vacuum interrupter applications, there are certain applications where it appears desirable to avoid the use of the low-freezing point, relatively volatile, insoluble minor constituent. The presence of this minor constituent in the contacts, in some cases, lirriits the manner in which the contacts can be processed and may interfere with realizing the maximum current and voltage interrupting performance obtainable from certain contact materials.

SUMMARY Accordingly, an object of this invention is to provide a vacuum interrupter that has contacts capable of meeting the above-described antiweld requirement and yet are free of the low-freezing point, relatively volatile, insoluble minor constituents of the aforesaid Lafferty et al. patent.

Another object is to provide the vacuum interrupter with contacts that contain beryllium to act as an effective getter of oxygen, as described in my aforesaid application, and that are also capable of meeting the object set forth in the immediately preceding paragraph.

In carrying out the invention in one form, the vacuum interrupter is provided with contacts relatively movable into and out of engagement and having their circuit-making and cricuit breaking regions made of an alloy consisting essentially of copper and beryllium, the beryllium being present in a quantity of between about 6 and 19 per cent by weight of the alloy. The alloy is substantially free of additional metallic constituents that are insoluble in the solid state in copper or beryllium and have effective freezing points lower than that of the copper-beryllium eutectic (i.e., 860 C).

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a sectional view of a vacuum-type circuit interrupter embodying one form of the invention.

FIG. 2 is an enlarged perspective view of one of the contacts of the interrupter of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT Refen'ing now to the interrupter of FIG. I, there is shown a highly evacuated envelope 10 comprising a casing 11 of a suitable insulating material, such as glass, and a pair of

metallic end caps

12 and 13, closing off the ends of the casing. Suitable seals 14 are provided between the end caps and the casing to render the envelope l0 vacuum-tight. The normal pressure within the envelope 10 under static conditions is lower than 10 mm. of mercury so that a reasonable assurance is bad that the mean free path for electrons will be longer than the potential breakdown paths in the envelope.

The internal insulating surfaces of casing 11 are protected from the condensation of arc-generated metal vapors thereon by means of a tubular metallic shield 15 suitably supported on the casing 11 and preferably isolated from both

end caps

12 and 13. This shield acts in a well-known manner to intercept arcgenerated metallic vapors before they can reach the casing 11.

Located within the envelope 10 is a pair of separable contacts l7 and 18, shown in their engaged or closed-circuit position. The upper contact 17 is a stationary contact suitably attached to a conductive rod 170, which at its upper end is united to the upper end cap 12. The lower contact 18 is a movable contact joined to a conductive operating rod 180 which is suitably mounted for vertical movement. Downward motion of the contact 18 separates the contacts and opens the interrupter, whereas return movement of contact 18 reengages the contacts and thus closes the interrupter. A typical gap length when the contacts are fully open is about one-half inch. The operating rod 18a projects through an opening in the lower end cap 13, and a flexible metallic bellows 20 provides a seal about the rod 18a to allow for vertical movement of the rod without impairing the vacuum inside the envelope 10. As shown in FIG. 1, the bellows 20 is secured in sealed relationship at its respective opposite ends to the operating rod 180 and the lower end cap 13.

All of the internal parts of the interrupter are substantially free of surface contaminants. These clean surfaces are obtained by suitably processing the interrupter, as by baking it out during its evacuation. A typical bakeout temperature is 400 C. In addition, the

contacts

17 and 18 are effectively freed of gases absorbed internally of the contact body so as to preclude evolution of these gases during high current arcing. The manner in which these internal gases are removed will be referred to in more detail hereinafter.

Although my invention is not limited to any particular contact configuration, I prefer to use the contact configuration disclosed and claimed in US Pat. No. 2,949,520, Schneider,

assigned to the assignee of the present invention. Accordingly, each contact is of a disk shape and has one of its major surfaces facing the other contact. The central region of each contact is formed with a recess 29 in this major surface and an annular circuit-making and circuit breaking area 30 surrounds this recess. These annular circuit-making and breaking areas 30 abut against each other when the contacts are in their closed position of FIG. 1, and are of such a diameter that the current flowing through the closed contacts follows a loopshaped path L, as is indicated by the dotted lines of FIG. 1. Current flowing through this loop-shaped path has a magnetic effect which acts in a known manner to lengthen the loop. As a result, when the contacts are separated to form an are between the areas 30, the magnetic effect of the current flowing through the path L will impel the arc radially outward.

As the arc terminals move toward the outer periphery of the disks l7 and 18, the arc is subjected to a circumferentially acting magnetic force that tends to cause the arc to move circumferentially about the central axes of the disks. This circumferentially acting magnetic force is preferably produced by a series of slots 32 provided in the disks and extending from the outer periphery of the disks radially inward by generally spiral paths, as is shown in FIG. 2. These slots 32 correspond to similarly designated slots in the aforementioned Schneider patent and thus, force the current flowing to or from an arc terminal located at substantially any angular point on the outer peripheral region of the disk to follow a path that has a net component extending generally tangentially with respect to the periphery in the vicinity of the arc. This tangential configuration of the current path results in the development of a net tangential force component, which tends to drive the arc in a circumferential direction about the contacts. In certain cases, the arc may divide into a series of parallel arcs, and these parallel arcs move rapidly about the contact surface in a manner similar to that described hereinabove.

As described in the introductory portion of this application, an object of this invention is to provide contacts capable of meeting severe antiweld requirements and yet free of the lowfreezing point, relatively volatile, insoluble secondary constituents of the aforesaid Lafferty et al. patent. l find that these requirements can be met by forming the circuit-making and circuit breaking portions 30 of the vacuum interrupter contacts of an alloy consisting essentially of copper and beryllium, the beryllium being present in a quantity of between about 6 and 19 percent by weight of the alloy. The alloy is free of additional metallic constituents that are insoluble in the solid state in copper and beryllium, and have freezing points lower than that of the copper-beryllium eutectic, which is 860 C. A specific alloy which has shown exceptional ability to meet these requirements is a copper-beryllium alloy consisting essentially of copper and beryllium, the beryllium being present in a quantity of 7 percent by weight of the alloy.

When the quantity of beryllium is increased beyond about l 1.5 weight percent, some of the intermetallic compound phase Be Cu is formed. The intermetallic compound is very brittle material, and its presence increases the brittleness of the overall contact material. It appears, however, that about 19 percent beryllium can be added to copper before excessive brittleness occurs. Despite the presence of the intermetallic phase when beryllium is present in amounts between I 1.5 and 19 percent, there appears to be a sufficient amount of the B phase remaining to adequately offset the brittleness of the intermetallic compound phase. Amounts of beryllium greater than about 19 percent impart so much brittleness that is becomes impractical to machine the material into contacts or to subject them to closing impacts without risking cracking.

Contacts of copper beryllium containing beryllium in the range between 6 and 19 percent have shown an exceptional resistance to cold welding, i.e., welding together under the influence of high pressure forcing the contacts together with no arcing between the contacts. For example, a series of tests have been made in which clean contacts of different materials have been forced together with 3000 pounds of force, and

then separated to fracture any weld present between them. The force required to separate them is measured. With contacts of the copper-bismuth Cu-Bi (0.5% Bi) referred to in the aforesaid Lafferty et al. patent, welds requiring approximately pounds of force for their fracture were developed. (This copper-bismuth material is believed to be the best of the contact materials disclosed in the Lafferty et al. patent.) No cold welds were formed with contacts of the following materials Cu-Be (5% Be); Cu-Be (7% Be); Cu-Be (12% Be); Cu-Be 15% Be). This freedom from substantial cold-welding is a significant advantage not only because it reduces the force necessary to separate the contacts but also because it reduces the likelihood that protuberances will be formed at the fractured weld which could impair the dielectric strength.

Another condition that can lead to contact-welding is that accompanying closing the circuit interrupter against heave currents. When the contacts are driven into closed position, they often bounce apart a short distance immediately after initial impact and then rebound toward each other, aided by the closing force applied to the movable contact. An arc is drawn when the contacts first bounce apart, and this are melts adjacent surface portions of the contacts so that when they reengage, a molten film is present at the interface. When arcing ceases following reengagement, the energy input into the contact interface drops sharply, and the film at the interface thus quickly cools to a solid state. The result is the formation of a weld between the two contacts. The higher the arcing current, the larger the surface area that will be covered by the molten film and hence the larger and stronger the weld ordinarily will be. The welds formed under these conditions will be referred to as hot welds.

For determining the relative strengths of welds that are formed under these conditions, clean contacts of various materials were driven together under high current arcing conditions, and the force required for their subsequent separation was measured. To prevent the formation of oxide or other films on the contacts, these tests were run in an inert atmosphere of argon, which provides ambient conditions with respect to oxidation closely simulating those present under high vacuum conditions. With contacts of plain copper, an opening force of 5000 pounds was typically required to fracture the weld and separate the contacts; with contacts of Cu-Bi (0.5% Bi), an opening force of -200 pounds was typically required.

With contacts of copper-beryllium (3 percent beryllium) containing 1 percent bismuth to reduce the weld strength, welds requiring an opening force of over 2000 pounds for their fracture were developed. With contacts of copper-beryllium (5 percent beryllium), welds requiring an opening force of over 3800 pounds for their fracture were developed.

But when the amount of beryllium in the copper-beryllium alloy was increased to about 7 percent by weight, only about 25 to pounds of opening force was typically required. With copper-beryllium containing about 12% Be by weight, substantially no welds were formed. With copper-beryllium containing [5% Be by weight, welds requiring as much as 500 pounds were developed. It appears from the above tests that when the percentage of beryllium in the copper-beryllium alloy exceeds about 6% Be by weight, any welds developed can typically be fractured by an opening force of less than 1000 pounds, and this is acceptable for most power circuit breaker applications. The excessive brittleness which results from increasing the beryllium content above about 19 percent by weight determines the upper limit of the beryllium content.

The above-described high resistance to the formation of both hot and cold welds is an unexpected property of the contacts of copper-beryllium having a beryllium content in the range of 6 to 19 percent by weight of the copper-beryllium. The extreme weakness of the welds formed when the berylliurn content is the range of about 7 to 13 percent by weight of the Cu-Be is especially noteworthy.

Although there is not a large difference in the forces required for fracturing welds between the above-described copper-beryllium contacts (with 6 to 19% Be) as compared to the forces required for the copper-bismuth contacts, it is most significant that the high weld resistance of the copper-beryllium material has been obtained without the need for any bismuth or other low-freezing point, high-vapor-pressure weld-inhibiting constituent which is insoluble in the other constituents. This is highly advantageous because the presence of these low-freezing point, insoluble constituents in the materi als of the Lafferty et al. patent limits the type of surface cleaning which can be employed in making the interrupter, imposes limitations on where vacuum-tight brazed joints can be located, and requires an extra step in adding the insoluble constituent. Tests made with the bismuth-free copper-beryllium alloys of my invention have also shown that increased current and voltage interrupting ability can be obtained as compared to that obtainable with copper-beryllium contacts containing bismuth, even in small quantities such as one percent by weight of the total alloy.

in referring to additional constituents that are substantially insoluble in copper and beryllium in the solid state, I am referring to additional constituents that have a solid-state solubility in copper and beryllium of less than about two per cent by weight of the alloy considered at the freezing temperature of said additional constituent. Bismuth and other weld-inhibiting metals mentioned in the aforesaid Lafferty et al. patent are examples of such additional constituents.

In preparing these contact materials, each separate constituent first should be suitably processed to free it of sorbed gases and other contaminants, as, for example, by the zonerefining process described in US. Pat. No. 3,234,35l-l-lebb, assigned to the assignee of the present invention. The constituents are then melted and appropriately mixed together while they are in the liquid state, after which the temperature is lowered to cause the constituents to solidify and form the solid alloy.

While I have shown and described a particular embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention in its broader aspects; and I, therefore, intend herein to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is: 1

l. A vacuum-type electric circuit interrupter comprising:

a. an envelope evacuated to a pressure of 10 mm. of mercury or less,

b. a pair of highly weld-resistant contacts within said envelope relatively movable into and out of engagement,

c. said contacts being substantially free of sorbed gases and contaminants,

d. said contacts having circuit-making and breaking regions formed of an alloy consisting essentially of copper and beryllium,

e. the beryllium being present in a quantity of between about 6 and 19 percent by weight of the copper-beryllium alloy,

f. said alloy being substantially free of additional metallic constituents that are substantially insoluble in the solid state in copper and beryllium and have effective freezing points lower then 860 C.

2. The vacuum-type circuit interrupter of claim 1 in which said beryllium is present in a quantity of about 7 to 13 percent by weight of the copper-beryllium alloy.

3. The vacuum-type circuit interrupter of claim 1 in which said beryllium is present in a quantity of 6 to 19 percent by weight of the copper-beryllium alloy.

4. The vacuum-type circuit interrupter of claim 1 in which said contacts are characterized by such a high resistance to hot welds that any hot welds developed therebetween can be fractured by an opening force of less than 1,000 pounds applied to one of said contacts.

5. The vacuum-type circuit interrupter of claim 2 in which said contacts are characterized b such a hi h resistance to hot welds that any hot welds deve oped there etween can be fractured by an opening force of less than 1000 pounds applied to one of said contacts.-

6. The vacuum-type circuit interrupter of claim 3 in which said contacts are characterized by such a high resistance to hot welds that any hot welds developed therebetween can be fractured by an opening force of less than 1000 pounds applied to one of said contacts.

l 0 k F

Claims

2. The vacuum-type circuit interrupter of claim 1 in which said beryllium is present in a quantity of about 7 to 13 percent by weight of the copper-beryllium alloy.
3. The vacuum-type circuit interrupter of claim 1 in which said beryllium is present in a quantity of 6 to 19 percent by weight of the copper-beryllium alloy.
4. The vacuum-type circuit interrupter of claim 1 in which said contacts are characterized by such a high resistance to hot welds that any hot welds developed therebetween can be fractured by an opening force of less than 1,000 pounds applied to one of said contacts.
5. The vacuum-type circuit interrupter of claim 2 in which said contacts are characterized by such a high resistance to hot welds that any hot welds developed therebetween can be fractured by an opening force of less than 1000 pounds applied to one of said contacts.
6. The vacuum-type circuit interrupter of claim 3 in which said contacts are characterized by such a high resistance to hot welds that any hot welds developed therebetween can be fractured by an opening force of less than 1000 pounds applied to one of said contacts.