US3700842A

US3700842A - Vacuum interrupter contacts and method for making the same

Info

Publication number: US3700842A
Application number: US201465A
Authority: US
Inventors: Edward A Attia
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1971-11-23
Filing date: 1971-11-23
Publication date: 1972-10-24
Anticipated expiration: 1989-10-24
Also published as: DE2257258A1; JPS4860270A; GB1378399A; CA963944A

Abstract

A vacuum type electric circuit interrupter comprises a glass envelope, stainless steel end plates, a pair of relatively movable studs with a contact on each within the envelope, and shielding means within the envelope. Each stud and its associated contact are integrally formed of an alloy comprising by weight 0.4 to 0.6 percent tellurium, 0.007 to 0.012 percent phosphorus and the balance O.F.H.C. copper (oxygen free high conductivity copper which is 99.95 percent pure copper). The integrally formed stud and contact are subjected to a treatment wherein it is: raised slowly to 500*C. and held there for approximately 1/2 hour; exposed to ultra-pure hydrogen and raised slowly to about 900*C.; exposed to a vacuum and raised to about 975*C. to effect brazing of components thereto; lowered to about 500*C. in the vacuum and held there to cause effusion of certain gases; and cooled in the vacuum prior to final assembly.

Description

United States Patent 1 3,700,842 Attia Oct. 24, 1972 VACUUM INTERRUPTER CONTACTS [57] ABSTRACT gigg FOR MAKING THE A vacuum type electric circuit interrupter comprises a glass envelope, stainless steel end plates, a pair of rela- [72] inventor: Edward A. Attla, Milwaukee, Wis. tively movable studs with a contact on each within the envelope, and shielding means within the envelope. [73] Asslgnee' a izgg z' C l Each stud and its associated contact are integrally formed of an alloy comprising by weight 0.4 to 0.6 Flledi 1971 percent tellurium, 0.007 to 0.012 percent phosphorus [211 App] No: 201,465 and the balance O.F.H.C. copper (oxygen free high conductivity copper which is 99.95 percent pure copper). The integrally formed stud and contact are [LS- CI' C, B, subjected to a treatment wherein is: raised lowly to [5 Int. Cl. ..Holh and there for approximately hour; ex [58] Field Of Search ..200/166 C, 144 B; 75/ 153 posed to ultrapure hydrogen and raised slowly to about 900C; exposed to a vacuum and raised to [56] References Cited about 975C. to effect brazing of components thereto; UNITED STATES PATENTS lowered to about 500C. in the vacuum and held there n to cause effusion of certain gases; and cooled in the 3,502,465 3/1970 Naka ima ..200/144 B X vacuum prior to fi l assemb]y 3,463,892 8/1969 Wesoloski ..200/ 144 B 3,596,027 7/1971 Okutomi ..200/144 B 6 Claims, 1 Drawing Figure Primary Examiner-H. 0. Jones Attorney-Robert C. Jones et al.

III

Ill/A PATENTEDnm 24 I972 SUMMARY OF THE INVENTION 1 Field of the Invention This invention relates generally to electrical circuit interrupters. More particularly, it relates to improved vacuum circuit interrupters and similar devices (all hereinafter called vacuum interrupters) and to improved methods for making such interrupters.

2. Description of the Prior Art Vacuum interrupters are used in the electrical power industry to interrupt power circuits in the event of fault conditions. Though compact in size, vacuum interrupters are adapted to handle relatively high voltages and currents. Vacuum interrupters comprise a sealed envelope, sometimes ceramic, in which a high vacuum, on the order of -7 Torr, is maintained and wherein one or more pairs of .relatively movable contacts are disposed. In some types of vacuum interrupters each contact is mounted on the end of a current carrying member such as an electrically conductive elongated rod or stud. The studs are in axial alignment with each other and at least one stud is axially movable to efiect contact opening and closing. Usually, a cylindrical metal (thin molybdenum, copper, or nickel) shield is disposed within the envelope and surrounds the contacts to prevent metal vapor and particles from being deposited on the inside of the envelope during arcing between the contacts and shorting out the tube.

In practice 'the contacts were formed by vacuum casting of O.F.l-I.C. or suitable contact alloys and the contacts were brazed to the ends of the contact studs.

Heretofore, the studs were usually made of high purity copper designated as O.F.H.C. (oxygen free high conductivity) copper which is 99.95 percent pure. However, during manufacture of a typical vacuum interrupter it was subjected to brazing at high temperatures (900C.) and bake-out (for example, at about 400C. for 10 to 16 hours) and the O.F.H.C. copper studs became fully annealed and dead soft. Consequently, great care was needed in handling the vacuum interrupters during manufacture, shipping and field use to prevent sudden jolts from bending the studs to a position where they pierced the shield, broke the envelope, or became misaligned.

Such vacuum interrupters were costly and complicated to manufacture and were sometimes unreliable in use for the following reasons. The commercially available O.F.H.C. copper used for the contacts needed to undergo a costly vacuum casting process to remove remaining impurities existing in O.F.H.C. copper. The use and treatment of commercial materials for a vacuum interrupter, especially the contacts, has several advantages. One is the elimination of costly vacuum cast material, reducing necessary machining of contacts and holder, elimination of brazing 'of contacts to holders, and providing holders with high strength in comparison to O.F.H.C. Cu. In particular, the elimination of a braze joint between the contact and holder has the advantage, in addition to cost reduction, of eliminating an arc play and attachment hazard. Due to the susceptibility of braze materials for contamination with high gas content and high vapor pressure elements, braze joints are generally known to be favorable arc play and attachment regions.

It is desirable, therefore, to provide improved vacuum interrupters and methods for making the same.

BACKGROUND OF THE INVENTION The present invention concerns an improved vacuum interrupter or circuit breaker capable of interrupting high current (on the order of up to IOKA) and a method for making such an interrupter.

A vacuum interrupter in accordance with the invention comprises a glass envelope joined to metallic end plates, preferably stainless steel, by expansion sleeves, preferably of Kovar metal (iron, nickel, cobalt alloy). A pair of relatively movable contacts having integrally formed studs are mounted in the envelope. Preferably, one contact is stationary and is secured to and extends through one end plate and the other contact is axially movable in an opening through the other end plate by flexible sealing means, such as bellows, preferably made of inconel metal. Shielding means, preferably formed of nickel, are provided to shield the inner surface of the glass envelope and the bellows from infringement of arcing by-products. Preferably, the shield means for shielding the envelope is floating shield or a shield maintained at mid-potential but it could be one electrically connected to either one of the end plates.

In accordance with the invention, each contact and stud is integrally formed, as by making or forging, from commercially available high strength (as compared to O.F.H.C. copper), high conductivity material, such as an alloy comprising 0.4 to 0.6 percent Te (tellurium), 0.007 to 0.012 percent P (phosphorus) and the balance O.F.H.C. copper which is 99.95 percent pure. In further accordance with the invention, the combined contact and stud and certain components brazed thereto (i.e., the bellows and bellows shield and end plates) subjected to heat treatment to remove impurities and effect structural changes in accordance with the following method:

I. Raise temperature slowly to 500 C. and hold there for approximately, /2 hour;

2. Expose to ultra pure hydrogen and raise tempera ture slowly to 900 C.; 3. Expose to a vacuum and raise temperature to about 975 C.;

4. Lower temperature to about 500 C. and hold until certain gases effuse;

5. Cool in the vacuum;

6. Assemble above treated parts and other components, weld and pump down vacuum in tube;

7. Spark condition finally assembled vacuum interrupter;

8. Bake-out by raising interrupter from ambient to 400C. over a 16 hour period and hold there for 4 hours while pumping out to maintain vacuum.

OBJECTS OF THE INVENTION A vacuum interrupter and the method of making it in accordance with the invention has numerous ad vantages. For example, commercially available materials requiring more economical treatment are used. Thus, costly vacuum casting is eliminated and necessary machining procedures on the contact and stud are reduced. Brazing of the contact to the stud is eliminated thereby reducing costs and eliminating a possible source of contamination and a potential region for are hang-up. Furthermore, the stud portion of the integrally formed contact and stud has higher physical strength in comparison to O.F.H.C. copper. Consequently, a vacuum interrupter economically competitive and having equal or greater reliability is provided. Other objects and advantages of the invention will hereinafter appear.

DRAWINGS The accompanying drawing illustrates a preferred- DESCRIPTION OF THE PREFERRED EMBODIMENT The Vacuum Interrupter Referring to the drawing, there is shown a vacuum interrupter comprising an envelope 12 made of electrical insulating material such as borosilicate glass and having

end plates

13 and 15, preferably made of stainless steel.

Plates

13 and 15 are joined by welding to sleeves l7 and 19, respectively, and the latter are sealed to glass envelope 12. The interior of envelope 12 is understood to be maintained at a relatively high vacuum. The vacuum interrupter further comprises a pair of relatively movable contacts 14 and 16 (shown in open position) which are integral with a pair of

studs

18 and 20, respectively. In the embodiment shown stud 18 supports the stationary contact and is therefore, rigidly mounted in sealed relationship in envelope 12. Stud 20 supports the movable contact and is movably mounted in sealed relationship in envelope 12 by means of a bellows 22, preferably made of Inconel metal and brazed to plate 15. A cylindrical shield 24, preferably made of nickel is mounted on plate 13 and extends around the

contacts

14 and 16. A disk type shield 26, preferably of nickel, is brazed to a shoulder on stud 20 to protect the bellows 22 from the arc products.

Arc shield 24 is a floating type shield and attains during interruption any potential of the anode and the potential of the cathode. If preferred, the shield could be of a type which attains during interruption, a midpotential value so that the potential difference between the shield and one of the electrodes is equal to the potential difference between the shield and the other electrode, or the shield could be connected to any one of the end plates. A shield which is floating or at midpotential is preferred.

The Purification Treatment In accordance with the

invention contacts

14 and 16 which are integrally formed with

studs

18 and 20, respectively, as by forging or machining, are made of commercially available material such as AMT EL metal which is produced by the addition of a master alloy of tellurium and phosphorus, to oxygen free copper. In an actual embodiment the contacts and studs (hereinafter called electrodes) were machined from a rod of AMTEL metal 1% inch in diameter.

AMTEL metal is an alloy comprising about 0.4 to 0.6 percent Te, 0.007 to 0.012 percent P with the remainder O.F.H.C. Cu and is manufactured by AMAX COPPER, INC., N.Y., N.Y.

It has been discovered that, for purposes of the present invention, this alloy is superior to O.F.H.C. copper which contains about 100 ppm of metallic impurities and about 200 ppm of gaseous impurities, mainly oxygen in free or combined form and hydrogen.

Cu-Te in the alloy, as compared to O.F.H.C. copper, possesses better anti-weld properties and better mechanical properties (impact values, toughness and softening temperatures). Also, due to the high vapor pressure of Te, Cu-Te possesses better chopping properties. The depression of the electrical conductivity to about 90 percent IACS, due to the presence of Te, is considered only a minor disadvantage.

However, commercial Cu-Te contains between -120 'ppm phosphorus. While this amount of phosphorus is beneficial to improve the workability and counteract the oxidizing tendencies during handling and forming, it is objectionable as a constituent of a vacuum interrupter contact. This is because the majority of phosphorus will be present in the Cu matrix in the form of P 0 This may decompose on arcing, thus releasing oxygen and impairing the vacuum integrity inside the interrupter. It should also be noted that phosphorus, as well as any other high vapor pressure contaminant, e.g., sulfur, could influence the interruption ability of the contact. The purification treatment, therefore, decomposes the oxides, depresses the concentration of high vapor pressure components, and also reduces the concentration of the soluble gases to an acceptable level 10 pp Broadly considered the method in accordance with the present invention for the purification of Cu-Te containing P consists of the following heat treatment and other steps:

a. Deoxidation of the material under investigation by the free active component, phosphorus.

b. Transfer of the nonsoluble phosphorus oxides to positions, in the matrix, where they can be readily reduced.

c. Reduction of the oxides and the elimination of their by-products.

d. Suppression of the concentration of the soluble gases.

The furnace used for heat treatment and brazing of a vacuum interrupter in accordance with the invention is understood, for example, to be a vacuum-controlled atmosphere cold wall furnace furnished with a mass spectrometer, an ion gauge, moisture gauge, and a chromotograph. The solid state purification treatment is combined with the braze process in a single thermal cycle, which makes the purification treatment economical. The electrodes (comprising the

contacts

14 and 16 and the

studs

18 and 20, respectively) with the

end plates

13 and 15 and other parts (e.g. bellows 22) which required treatment or braze are assembled in the vacuum-controlled atmosphere furnace. The furnace is then pumped down to 10 Torr and the treatment cycle started. This cycle consists of the following steps.

1. The temperature is raised slowly to 500 C and held for approximately V2 hour. Raising the temdaries. Cu Te particles are apparently unaffected by this treatment. it is possible, however, that grain boundaries become enriched with Cu Te particles. The mass spectrometer analysis during this stage shows that there is slight increase in the concentration of water vapor, hydrogen, carbon monoxide and carbon dioxide and high mass hydrocarbons, of the chemical composition C,,l-l,,. These effects are traceable to the decomposition of the surface contaminants. After '6 hour of holding at 500 C the residual gases are mainly water (60 percent) and hydrogen percent). Longer holding does not produce any significant change in the concentration of the residuals. Metallographic observations show that in comparison to the untreated samples, the treated samples possess a more refined grain matrix and the insoluble particles (possibly P 0 and Cu Te are mainly confined to the grain boundaries.

2. Ultra pure hydrogen (0, below i ppm and dew point less than -l00 C) is admitted and the temperature is raised slowly to 900 C. During this treatment hydrogen will diffuse into the treated parts reducing the oxides including the phosphorus oxides, and forming water vapor. This treatment also reduces other oxides in the treated parts, as well as the oxides in the braze material. Chromotographic analysis shows that, if hydrogen is admitted to the furnace and the pressure allowed to build to about 1 atmosphere, the concentration of methane, CH increases with time indicating the reduction of carbon or carbon compounds. The moisture gauge shows an increase with time of the water vapor component indicating the reduction of oxides. To render this treatment more effective, the partial pressure of H 0 and CH in the furnace atmosphere is reduced by passing a stream of H through the furnace to the vacuum system while maintaining a dynamic reducing atmosphere inside the oven. The analysis equipment during this process shows at first an increase in percentage concentration of CH, and H 0, then the concentration decreased to an asymptotic value after prolonged holding at 900 C. It is also possible that some reduction of free phosphorus takes place, during this stage, through the formation of phosphorus hydrogen gaseous compounds, e.g.,

. In the third stage of the treatment the furnace is evacuated and the temperature raised to about 975 C to allow the braze material to flow to the required joints. During brazing the mass spectrometer indicates an increase in the residual components of H CH and CO. Heating in vacuum at such high temperature also, to some extent, apparently reduces the concentration of high vapor pressure elements; phosphorus, for example.

4. In the next and final stage of treatment the temperature is lowered to 500 C and held there to allow the gases above the solubility limit to efiuse from the treated materials. Mass spectrometer analysis shows that H, is the major effusing gaseous component during this treatment. When the eifusing rate is insignificantly small the power to the furnace is interrupted and the treated parts left to cool in vacuum.

Assembly and Final Processing After the aforedescribed treatment, the treated partswith the shield and envelope are assembled as shown in the drawing and seals are provided by Plasma-Arc- Welding. The interrupter is then connected to the exhaust processing station, as by means of a pinch-off tube 28, and a processing cycle hereinafter described is started.

1. The vacuum interrupter is subjected to an initial surface spark arc conditioning using 60 Hz high voltage arcing between the

contacts

14 and 16. This is done by first valving off the ion pump thus holding the interrupter in static low pressure 5 X 10) system. The interrupter is then immersed in an oil bath and connected to the secondary of a high voltage transformer. The alternating potential difference between the contacts, at a V4 inch gap, is increased slowly. After 15 minutes of conditioning treatment at high voltage levels, the power is interrupted. The conditioning process is divided into two stages. A stage, below 25 KV, characterized by small changes in the partial pressure of the residual gases and a second stage, above 25 KV, characterized by relatively large changes in the partial pressure. At the end of the conditioning process (after exposure to 50 KV) in an actual embodiment, the residual gases were found to be approximately 32 percent CH 20 percent high mass hydrocarbons, 20 percent hydrogen, l5 percent CO, 8 percent H 0, 3 percent AR and 2 percent C0 2. Subsequent to the spark arc conditioning the interrupter is placed in an oven and a bake-out treatment commenced. The temperature of the oven is raised slowly from ambient temperature to 400 C over a period of 16 hours followed by a holding period, at 400 C, for 4 hours. The ion and sublimation pumps are used all the time during the bake-out, whereas a cryogenic pump was activated when the temperature was in excess of 300 C.

It appears that in the temperature range of 50-l 00 C, water vapor is the most significant released gaseous component.

In the temperature range l00-200 C, the gas release rate of water vapor drops, whereas an increase occurs in the release rate of H C0, C0 and hydrocarbons.

In the temperature range 200 300 C, there are fast changes in the release rate of most of the residual gaseous components. At the end of this temperature range H and H 0 are the major residuals with concentrations of about 40 percent and 35 percent of the total residuals respectively.

Above 300 C, and with cryogenic pumping, the concentration of H 0, hydrocarbons and CO drops significantly. The percentage composition of CO shows a little increase followed by a decrease. The percentage composition of H shows a significant increase to about 70 percent of the total residuals at 400 C.

Holding for 4 hours at 400 C resulted in a small increase in the H concentration and small decrease in the concentration of all the other residuals.

At the end of the bake-out treatment the power to the oven was interrupted and the interrupter is allowed to cool slowly. The pinch-off tube 28 is pinched off at approximately 150 C.

It should be noted that the shield and the glass envelope are not thermally treated in any way. The only treatment they receive is degreasing in organic solvents. The methane and other high mass hydrocarbons released during hi-potting can be, to some extent, traced to the contamination of these surfaces.

Tests of a vacuum interrupter in accordance with the present invention demonstrated clearly that it was capable of interrupting successfully currents up to 8 9 KA r.m.s.

CONCLUSION The use and treatment of commercial materials for a vacuum interrupter, especially the contacts, has several advantages. One is the elimination of costly vacuum cast material, reducing necessary machining of contacts and holder, elimination of brazing of contacts to holders, and providing holders with high strength in comparison to O.F.H.C. Cu. In particular, the elimination of a braze joint between the contact and holder has the advantage, in addition to cost reduction, of eliminating an arc play and attachment hazard. Due to the susceptibility of braze materials for contamination with high gas content and high vapor pressure elements, braze joints are generally known to be favorable arc play and attachment regions. All these advantages are important in promoting the utilization of vacuum interrupters.

While the invention disclosed herein is depicted as applied to one of several types of vacuum interrupters, it will be apparent to those skilled in the art that it is applicable to other types of vacuum interrupters and other types of devices. Furthermore, while the alloy is disclosed herein as the material of which the studs are made, it is apparent that the alloy could be used for other electrical current carrying components within vacuum interrupters or other devices which are subjected to the aforedescribed heat treatment during manufacture.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a vacuum interrupter, an envelope wherein a high vacuum is maintained, and a pair of relatively movable current carrying members within said envelope, a stud of at least one of the current carrying members being made of a copper-telluriumphosphorous alloy.

2. A vacuum interrupter according to claim 1 wherein said alloy comprises about 0.4 to 0.6 percent tellurium, about 0.007 to 0.012 percent phosphorous and the balance O.F.l-l.C. copper.

3. A vacuum interrupter .according to claim 2 wherein said current carrgiibg member is heat treated as follows: raised to about 0 C. m a vacuum; exposed to hydrogen and raised to about 900 C.; exposed to a vacuum and raised to about 975 C.; lowered to about 500 C.; and cooled in a vacuum.

4. A vacuum interrupter according to claim 1 wherein said current carrying member comprises a contact making portion and an integrally formed stud portion.

5. A method of making a vacuum interrupter comprising an envelope wherein a high vacuum is maintained and a pair of relatively movable current carrying members, at least one current carrying member having a contact portion and an integrally formed stud portion, said current carrying member being fabricated from a commercially available alloy comprising copper-tellurium and phosphorous, comprising the steps of: heating said member to deoxidize it by means of the phosphorous therein; further heating said member to transfer nonsoluble phosphorous oxides to positions in the matrix wherein they are reducible; reducing said oxides and eliminating their by-products; and suppressing the concentration of soluble gases.

6. A method according to claim 5 wherein said steps include the steps of: heating said member slowly to about 500 C. in vacuum; exposing said member to hydrogen and further heating it to about 900 C.; exposing said member to a vacuum and further heating it to about 975 C.; lowering the temperature of said member in a vacuum to about 500 C.; and cooling said member in a vacuum to ambient temperature.

Claims

2. A vacuum interrupter according to claim 1 whErein said alloy comprises about 0.4 to 0.6 percent tellurium, about 0.007 to 0.012 percent phosphorous and the balance O.F.H.C. copper.

3. A vacuum interrupter according to claim 2 wherein said current carrying member is heat treated as follows: raised to about 500* C. in a vacuum; exposed to hydrogen and raised to about 900* C.; exposed to a vacuum and raised to about 975* C.; lowered to about 500* C.; and cooled in a vacuum.

6. A method according to claim 5 wherein said steps include the steps of: heating said member slowly to about 500* C. in vacuum; exposing said member to hydrogen and further heating it to about 900* C.; exposing said member to a vacuum and further heating it to about 975* C.; lowering the temperature of said member in a vacuum to about 500* C.; and cooling said member in a vacuum to ambient temperature.