US 3612939 A
Description (OCR text may contain errors)
United States Patent Inventor Mario Rabinowitz Menlo Park, Calif. App]. No. 712,790 Filed Mar. 13, 1968 Patented Oct. 12, 1971 Assignee Westinghouse Electric Corporation Pittsburgh, Pa.
MOLECULAR SIEVE FOR VACUUM CIRCUIT INTERRUPTER 9 Claims, 6 Drawing Figs.
US. Cl 313/146, 313/174, 200/144 B, 417/48 Int. Cl 1101] 19/70 Field of Search 313/ 146,
174, 176,178, 179; ZOO/144.2; 206/0.4
 References Cited UNITED STATES PATENTS 1,941,567 1/1934 Marti 200/144 2,882,244 4/1959 Milton...... 206/0.4 2,900,800 8/1959 Loveday 206/0.4 X 3,014,107 12/1961 Cobine et al..... 200/144 3,090,852 5/1963 Greenwood 313/174 X 3,133,224 5/1964 Reid 313/176X 3,163,734 12/1964 Lee 200/144 3,305,656 2/ 1967 Devins 200/ 144 Primary ExaminerRoy Lake Assistant Examiner-Palmer C. Demeo Attorneys-A. T. Stratton, C. L. McHale and Willard R. Crout ABSTRACT: A vacuum-type circuit interrupter has a molecular-sieve shielding structure surrounding the arc gap to sorb vapors and gases during interruption and during the normal closed position of the interrupter.
PAIENTEDUET 12 Ian SHEET 1 OF 2 MOLECULAR SIEVE FOR VACUUM CIRCUIT INTERRUPTER This invention relates to a vacuum-type circuit interrupter and, more particularly, to a molecular-sieve structure, which acts as an improved shield for condensing and removing the vapors and gases generated during arcing, for efficiently sorbing, trapping, or scattering incident particles and photons, and for removing gases which may permeate or leak into the interrupter vessel.
One of the problems inherent in the operation of a vacuum circuit interrupter is related to its ability to maintain a high vacuum for a long period of time. Gas is released from the contacts during arcing. Another source of gas which is significant over long-time durations is leakage at seals as well as the permeation of gases through the interrupter vessel materials. Another problem, associated with the operation of a vacuum circuit interrupter, is the ability of the shielding structure, which surrounds the arc, to efficiently condense, sorb, trap, or scatter away from the arc particles, such as clumps, vapors and gases, and photons which are incident upon it. (The word particles will be used to denote atoms, molecules and aggregates of atoms.) Otherwise, if these are reflected back into the arc gap by the shielding structure, the arc may not extinguish, or may reignite if it does extinguish. My invention is directed at a combined solution of these problems.
Generally, vacuum-type alternating-current circuit interrupters consist of separable contacts in an evacuated chamber at less than torr pressure. An arc is drawn between the contacts as they are separated to initiate current interruption. The arc is primarily maintained in metal vapor vaporized from the contact material, and in part from gases liberated from the surfaces and interior volume of the contacts. If the contacts and the are are not too hot, and not too much gas has been released and accumulated, the arc will tend to extinguish as a natural current zero is approached.
If the arc is to remain extinguished from this time on, the gap must recover dielectric strength at a greater rate than the increasing voltage transient, as Slepian has previously described it (J. Amer. Inst. Elect. Engrs, 47(l928)706), or the arc will restrike. Whether or not the dielectric strength of the gap will increase sufiiciently fast, depends to a great extent upon the rate at which metallic vapor and gas is removed from the gap, and the temperature of the metallic vapor, gas, and contact surfaces. Of course, electrical breakdown can also occur in other interior regions of the interrupter when the dielectric strength in these regions is reduced due to the presence of arc-generated vapors and gas.
When particles and photons are reflected back into the are from the surrounding shielding structure, the probability that the arc will be successfully extinguished is diminished. The presence of matter in the form of metal-clumps, metallic atoms, or gas in the interelectrode space reduces the dielectric strength of the gap compared to vacuum. Hence, if the shielding structure returns particles to the gap, it is impairing the gaps ability to quickly recover dielectric strength. When photons are reflected back into the arc, they can excite atoms into higher energy states-making it easier to ionize themand the reflected photons can also photoionize excited atoms. Reflected photons incident on the negative electrode can produce photoelectrons at its surface. Thus, if the shielding structure reflects photons back into the arc, they can also impair the rate of dielectric recovery.
Accordingly, a general object of my present invention is to provide a molecular-sieve structure for removing gases released from the contacts during arcing.
Another object is to provide a molecular-sieve structure for removing gases entering the interrupter vessel by leakage at seals, as well as permeation of gases through vessel materials.
Another general object of this invention is to increase the rate of recovery of dielectric strength in the arcing gap by efficiently sorbing, trapping, or scattering arc-generated particles, atoms, and photons that are incident on the molecular-sieve shielding structure.
Another object of this invention is to decrease the probability of dielectric breakdown throughout the interior of the interrupter resulting from arc-generated particles rebounding from the shielding structure, by efficiently sorbing and trapping these particles in the molecular-sieve structure.
Another object of this invention is to increase the interrupting capacity of a vacuum-type circuit interrupter made of gassy materials.
Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:
FIG. 1 is a vertical sectional view taken through a low-temperature molecular-sieve vacuum-type circuit interrupter, the contact structure being shown in the closed-circuit position;
FIG. 2 is a vertical sectional view taken through a vacuumtype circuit interrupter illustrating the use of the molecularsieve shielding structure for use at standard operating temperature;
FIG. 3 is a horizontal sectional view taken along the line III-III of the interrupter of FIG. 2.
FIG. 4 is a vertical sectional view of a modified-type of lowtemperature molecular-sieve circuit interrupter, the contact structure being shown in the closedcircuit position;
FIG. 5 is a fragmentary vertical sectional view of a vacuumtype circuit interrupter illustrating a modified type of molecular-sieve shielding structure for use at standard operating temperature; and,
FIG. 6 is a vertical sectional view of a liquid-metal vacuum circuit interrupter embodying the molecular-sieve shielding structure, the solid electrode being shown in the closed-circuit position with the liquid metal.
Porous molecular-sieve materials, such as zeolites, activated carbon, sintered porous-metal bodies such as are used for filters, and metallic felt are known to readily sorb large quantities of gas. Their capacity for sorbing gas, as well as the rate at which they sorb gas, is greatly increased at low temperatures. For ultrahigh vacuum use, a temperature of about 450 C., or higher, is sufficient to drive off gases and vapors from these materials to make them highly sorbing.
At low temperatures, the pumping speed and holding capacity for gas of these molecular-sieve materials is phenomenal. At many laboratories, vacuum pressures as low as 10"torr have been produced, starting from 10 torr using nothing but any of the well-baked molecular-sieve materials at liquid nitrogen temperature (l95.8 C.). In one experiment, a 10-inch diameter by IO-inch high cylinder containing 12 pounds of zeolite (Linde molecular-sieve type 5A) was activated by baking, and then precooling. When opened to a 3 l2-liter chamber, the pressure in the chamber was reduced from atmospheric pressure to 0.1 torr in 10 minutes. A liter chamber was evacuated from atmospheric pressure to 10 torr using three such molecular-sieve cylinders in stages. In another experiment, using only baked precooled activated anthracite charcoal, a 2-liter vacuum chamber was evacuated to 109 torr within 24 hours after starting at atmospheric pressure. Even at normal operating temperatures, all of the abovementioned molecular-sieve materials have sufficient pumping speed and capacity to be significant for a vacuum circuit interrupter.
The term molecular-sieve" material as used here and in the claims refers to a highly sorbing materials by reason of their microscopic porosity. The term sorption" is used, rather than adsorption, or absorption, since it is frequently difficult to distinguish clearly between the two. Although adsorption is primarily a surface phenomena, it is often accompanied by a deeper penetration of a vapor or gas into the body of the solid adsorbent. This deeper penetration is akin to the formation of a solid solution, which is commonly referred to as absorption. The broader term sorption" is intended to cover both phenomena. The following table lists examples of several suitable molecular-sieve materials. The zeolites are of clothrate structure and have given outstanding results in practicing the present invention.
sorb carbon monoxide, and they sorb water more strongly electrostatic attraction of the cations. The more unsaturated the molecule, the more polarizable it is, and the more strongly primarily on the following four variables: (1) the rate at which the material being sorbed can diffuse to the activated crystals size can range from less than 10 A. to over 100,000 A. in
TABLE OF SOME MOLECULAR SIEVE MATERIALS Pore diameter, Sorbeut Description angstrom Form Zeolite-Linde type 3A Aluminum potassium silicate. -3 Pellets. Zeolite-Linde type 4A Aluminum sodium silicate 4. 2-4. 75 Do. Zeolite-Liude type 5A Aluminum calcium silicate. 5. 0-5. 6 Do. Zeolite-Lmde type 13X Aluminum sodium silicate. 10 Activated charcoal Anthracite charcoal Granules Reforming catalyst 0.35% platinum on alumina 1 -32 Pellets 1 Average.
The inorganic zeolites of clothrate structure are known to be highly sorbing materials. X-ray diffraction studies in the early 1930s revealed the zeolites to be crystalline materials having within each crystal a system of precisely arrayed cavities and pores. In addition to naturally occurring mineral zeolites, a number of zeolite compounds have been synthesized, see U.S. Pat. No. 3,181,231. The zeolites have the ability, depending on the size of their pores, to readily sorb, slowly sorb, or completely exclude certain molecules. This sievelike selectivity, based on molecule size, plus a selective preference for polar or polarizable molecules, results from the fact that the pores of any particular type of zeolite are uniform in size, of molecular dimensions, and contain exposed cations.
Crystalline zeolites have a basic formula of M ,,,O-Al,O -x SiO yH O, where M is a cation of n valence. The zeolite species differ in chemical composition, crystal structure, and sorption properties, but are basically a class of crystalline aluminosilicates. For example, Types 4A and 13X have the following unit cell formulas:
Type 13X: Na [(AlO (SiO ,,]-276H O. The water of hydration is removed by heating, when the crystals are made ready for use. The synthetic zeolites are supplied in a pellet or bead form, which contains about 20 percent inert clay binder. The cations are probably responsible for the very strong and selective sorptive forces, which are characteristic of the zeolites. In general, the elasticity and kinetic energy of incoming molecules allows easy passage of molecules up to 0.5 angstroms larger than the free diameter of the aperture in the zeolite, larger molecules being excluded.
The very strong sorptive forces in zeolites seem to be due primarily to the cations, which are exposed in the crystal lattice. These cations act as sites of strong localized positive charge which electrostatically attract the negative end of polar molecules. The greater the dipole moment of the molecule, the more strongly it will be attracted and sorbed. Polar molecules are generally those which contain 0, S, Cl, or N atoms, and are asymmetrical. For example, zeolites readily than any other material.
Under the influence of the localized, strong positive charge on the cations, molecules can have dipoles induced in them.
The polarized molecules are then sorbed strongly due to the it is sorbed.
The rate at which a given gas is sorbed on zeolite depends within the pellets or beads; (2) the relative size of the ,molecules and the zeolite pores; (3) the strength of the sorptive forces between the zeolite and the sorbate; and (4) the temperature.
. The processes by which the other molecular-sieve materials operate are similar to that of zeolite, but perhaps not as well understood. A high degree of porosity is common to all the one type) is a complex network of pores of varied shapes and sizes. The shapes include cylinders, rectangular cross sections, as well as many irregular shapes and constrictions. The pore diameter. The pore-size distribution depends, in part, on the source materials used, and on the method and extent of activation. The sintered porous-metal filters are made by sintering powdered metal. The limits of their pore size and uniformity attainable by present techniques have not been fully determined as yet. They are readily available in the 10,000 A. pore range.
In addition to the above-mentioned molecular-sieve materials, there are others, such as activated alumina, silica gel, and reforming catalysts. The latter are usually a highly sorbing metal, such as platinum on alumina. These reforming catalysts are difficult to adequately degas. However, once degassed, they are extremely effective sorbents even at room temperature. Using a platinum on alumina reforming catalyst at room temperature, the pressure of a 2liter vacuum chamber was reduced to 4X10" torr starting with the chamber at 3 l0 torr pressure. However, the previously mentioned group of molecular-sieve materials are far superior and are preferred for this invention, although the latter group are suitable for some purposes, and may also be used.
The amount and kinds of gases evolved during arcing largely depends on the processing and degree of purification of the contacts. For fairly gas-free contacts containing a gas-impurity level of about one part in one million, the following gases have been observed to evolve during arcing: CH CO, H 0 H, and C0 The molecular-sieve materials are well suited to sorb all of these gases. These gases, together with a small amount of water vapor, are the main constituents of the residual gas in high and ultrahigh vacuum systems. The addition of molecular-sieve materials to these vacuum systems greatly reduces the amounts of these gases.
Helium and some hydrogen most commonly permeate into sealed vacuum vessels over long periods of time. When there is leakage in the vessel, such as at seals and welds, nitrogen and oxygen leak in readily Helium diffuses through glass at a fairly slow rate, which decreases with decreasing temperature and which depends upon the type of glass used. For example, Corning 1720 glass has a permeation rate l0 lower than ordinary borosilicate glass. The helium permeation rate through lead borate glasses tends to be low. The permeation rate of all gases is lowest through crystalline materials. Hence, an all ceramic-metal sealed vacuum interrupter vessel should have the lowest permeation rate for gases.
Even though the leakage and permeation rates are very low, the time duration may be quite great. Since a given interrupter may be in the field with only a few high-fault current interruptions in the course of 50 years or more, it would be rather inefticient, if its operational life were limited by leakage and permeation of gases.
Permeation of gases through metals seems to occur by diffusion of the gas atoms along interstitial sites in the metal lattice. The mechanism appears to be that of absorption, i.e. solution of the gas on the high-pressure side of the metal, with subsequent diffusion primarily through interstitial sites, and to a lesser extent along grain boundaries. The rare gases, such as helium, neon, and argon, and polyatomic molecules do not noticeably diffuse through metals. The diffusion rate depends upon both the particular gas and upon the metal. Hydrogen diffuses more readily than other gases through most metals. Diffusion rates have also been measured for other gases such as nitrogen, oxygen, and carbon monoxide.
One way to solve the problem of the leakage and permeation of gases into a sealed vacuum interrupter vessel would be to have the vessel inside one or more other sealed vacuum vessels. However, this is not only expensive, but does not solve the problem of removing the gases evolved during arcing. Another solution might be to operate a pump connected to the vessel. However, this is also expensive, and has its difficulties. The use of getter materials, as has been previously proposed, is limited to pumping only during arcing when the getter material is heated.
The solution to this problem according to this invention is to dispose molecular-sieve material in the interrupter to produce continuous sorption of gases in the vacuum interrupter vessel, regardless of their origin. lt is inexpensive, simple to incorporate in a vacuum interrupter, and provides other advantages, which will be described shortly. Although the molecular-sieve materials operate most efficiently at low tem peratures, their presence in a vacuum interrupter is advantageous at standard operating temperatures for sorbing gases.
There is another sense, besides that of sorption, in which the collection of pellets, beads, granules and/or chunks surrounding the arc in the form of a shielding structure will act as a sieve. For convenience, the word beads will be used to also denote small beads, pellets, granules, chunks, etc. By placing a cylindrical array of beads around the arc, a sievelike trap is formed for particles and photons.
The rough surface and pockets formed by the cylindrical array of beads helps to trap particles and photons coming from the arc, and helps to reduce their reflection back into the arc. Particles and photons are trapped in rebounding among the beads, rather than back into the arc. The lowered photon reflectivity helps to absorb the radiated energy from the are, so that less is reflected back into the are. This helps to cool the arc. When photons are reflected back into the arc, they can excite atoms in the are into higher energy states, making it easier to ionize them. The reflected photons can also photoionize excited atoms. The reflected photons can also produce photoelectrons at the surface of the negative electrode. Thus, reducing particle and photon reflection, helps to extinguish the arc.
The fact that the beads are loose and therefor free to move around behind a confining screen, allows them to take up the energy and momentum of the incident particles more effectively than a rigid shield, which action also acts to decrease the reflection of these particles back into the arc.
When the beads are made of poor electrically conducting material, such as zeolite, activated alumina, and activated carbon, the production of photoelectrons at the shielding structure is greatly reduced. Although these photoelectrons contribute only a minute fraction of the total current, their presence can reduce the dielectric strength between the shielding structure and the electrodes.
The irregular surface presented by the beads also causes scattering of particles and photons so that those which are not sorbed, or otherwise trapped among the beads, are scattered more effectively in directions other than back into the are, as would occur from a smooth cylindrical shield around the arc. The irregular surface presented by the beads, also decreases the power input per unit area at a given radius from the arc by providing an increased effective area exposed to the arcing products, as opposed to a smooth cylindrical shield of the same radius.
As has been described, the use of porous highly-sorbing molecular-sieve beads performs two valuable functions in a vacuum-type circuit interrupter. A large effective surface area is provided for sorption of gases. And a large, irregular geometrically efficient surface is provided for trapping and scattering incident particles and photons. This results in an increase in rate of recovery of dielectric strength by decreasing particle density in the arc gap, and decreasing the production of photoelectrons, photoionization, and photoexcitation.
With reference to the foregoing principles, attention is now directed to the accompanying drawings, which illustrate different embodiments of the invention.
Referring now to FIG. 1, there is shown a low-temperature vacuum-type circuit interrupter 10 having a molecular-sieve shielding structure 11. As shown, there is provided a relatively stationary tubular contact 12 cooperable with a movable tubular contact 14, the latter being reciprocally actuated in a vertical direction by a suitable operating mechanism, not shown, which is attached to, and actuates the conducting tubular operating rod portion 16. As shown, the two contacts l2, 14 make separable abutting engagement and, for example, may separate a distance of one-half inch in interrupting currents, which may be as high as 30,000 amperes.
To insure a highly evacuated state within the vacuum chamber 118, such as of the order of 10'' torr, the operating rod 16 is sealed, as at 16a, to the lower end of a flexible metallic bellows 20. A bellows shield 17 protects the bellows 20 from metallic vapor emitted during arcing. The flexible metallic bellows 20 will insure a permissible vertical operating movement of the movable contact 14, while at the same time maintaining a highly evacuated state within the vacuum chamber 18. It will be noted that the upper end of the flexible metallic bellows 20 is secured in sealing relationship to an upper metallic end cap 24, as at 20a. The operating rod 16 is guided by the insulated sleeve 26. The sleeve 26 is made of insulating material, such as polytetrafluoroethylene, sold under the trade name Teflon, so that current will not be conducted through the bellows 20. Otherwise, the bellows 20 may rupture when carrying high currents.
A casing structure 30 may be provided, comprising an upper insulating tubular portion 32, which is sealed, as at 32a, to a downwardly extending flange portion 24a of the upper end cap 24. ln addition, the insulating tubular portion 32 may be sealed, as at 32b, to the upper end of a tubular metallic casing member 40, which is hermetically sealed, as at 40a, to a surrounding tubular housing member 44. All joints are hermetically sealed. The housing member 44 has an inwardly extending lower cap portion 440, which is hermetically sealed, as at 44b, to an insulator 45, which in turn is hermetically sealed, as at 45a, to the tubular supporting rod portion 12a of the lower stationary contact structure 12. The insulator 45 makes hermetic seals at all joints. The insulator 45 is protected from the condensation of metal-vapor upon it by means of the umbrellalike shield 46 immediately above it.
When the contacts are not sufficiently free of gases dissolved in the material, gas-producing contaminants, and sorbed gases, all of which can be liberated during arcing, the interrupting ability of most vacuum interrupters is greatly impaired. A vacuum interrupter constructed in accordance with the present invention has an increased interrupting capacity over a vacuum interrupter which does not employ this molecular-sieve including the performance of an interrupter limited by the gas content of the contacts. This increased performance results form the fact that the released gas is quickly sorbed or trapped in the molecular-sieve structure 11, which surrounds the are, thus maintaining a high vacuum.
A gas-impurity level in the contacts of one part in 10 million or less, has been found satisfactory in ordinary vacuum-type circuit interrupters. With such highly gas-free contacts, the arcing characteristics and interrupting performance of a vacuum interrupter is primarily determined by the electrode material. Construction of a vacuum interrupter in accordance with the present invention, in which the arcing gap is surrounded by a molecular-sieve shielding structure 11, increases the interrupting capacity of a highly gas-free interrupter by reducing the reflection of particles and photons from the shielding structure back into the arc gap.
The arc, which is established across the arcing gap between the separable contacts 12, 14, vaporizes some of the contact material. Arc-generated particles are driven in all directions from the arcing region. The internal insulating surfaces of the tubular insulating casing portion 32 are protected from the condensation of arc-generated metallic vapors thereon by means of the tubular metallic end-shield 50, and also by the condensation, sorption, and trapping provided by the interiorly disposed molecular-sieve shielding structure 11 surrounding the arc gap. This shielding structure 11 comprises an interior cylindrical screen 11a, behind which are disposed the relatively loose molecular sieve beads 64, an exterior cylindrical supporting metallic casing 66 to confine the beads 64, and a second exterior cylindrical metallic casing 68 to confine the coolant 69.
As has been pointed out previously, the molecular-sieve materials are most efi'ective at low temperatures, although they provide sufficient pumping speed and holding capacity at room temperature to be of value in a vacuum-type circuit interrupter. It is the intent of this invention, in its broader aspects, to include both the normal operating temperature and the low-temperature applications. Additional benefits derived from low-temperature operation of a vacuum-type circuit interrupter are disclosed and claimed in the copending application of Mario Rabinowitz, filed Mar. 14, 1966, Ser. No. 534,239, now U.S. Pat. No. 3,440,376, and assigned to the assignee of the present invention. Both ordinary temperature and low-temperature operation will be described in this specification. In accordance with the principles as set forth herein, and in the above copending patent application, the shielding structure 11 and the contacts 12, 14 are cooled to a relatively low temperature, preferably below 30 C. Various coolants 69 may be employed. The following table lists a number of suitable coolants 69.
TABLE OF SOME COOLANTS Boiling Point at Coolant Chemical Symbol l Atmosphere Liquid Ammonia NH 33.3 C. Liquid Radon R, 6l.8 C. Dry Ice CO, -78.5 C.(sublimates) Liquid Xenon Xe -l07. I C. Liquid Krypton Kr l52.9 C. Liquid Argon A -l85.7 C. Liquid Nitrogen N, l95.8 C. Liquid Neon Ne 245.9 C. Liquid Helium 11 He 268.9 C.
Liquid oxygen and liquid hydrogen with boiling points of I 83.0 C., and -252.8 C., respectively were not included in the above table because they are potentially explosive.
The coolant 69 may enter the space 70 interiorly of the lower relatively stationary contact structure 12 by means of an inlet port 72, and may be exhausted by an outlet port 74. Likewise, the coolant 69 may enter the space 80 interiorly of the upper hollow tubular movable contact 14 by means of a suitably provided inlet port 90, and exhausted by a suitable outlet port 92. In addition, the space 97 immediately behind the molecular-sieve beads 64, as determined by the metallic cylindrical walls 66 and 68, ma be supplied by coolant 69 from an inlet port 96 and the coolant 69 utilized in the annular space 97 exhausted by means of an outlet port 98.
By a circulation of the coolant 69, the temperature of the contacts 12, 14 and of the molecular-sieve shielding structure 11 may be maintained at the low temperature provided by the coolant 69. The annular space 100, surrounding the metallic casing 68, is at the same high-vacuum pressure as the interior 18 of the interrupter by means of communicating holes 101a, 101b, 102a and 102b. The communicating holes 102 are in the form of tubes, which make hermetic seals with the easings 66 and 68. This evacuated space 100 provides heat insulation for the interior cold metallic casing 68. Cooling may also be provided by thermoelectric effect, by use of powdered dry ice, or by other means.
The vacuum-type circuit interrupter 10 is ideally suited for minimizing the power density incident on the shielding structure 11, which surrounds the are. There is no limitation here on the diameter of the interrupting chamber and shielding structure, as is the case with other designs due to a practical limit on the diameter of the isolating insulator. Hence, for a given molecular-sieve material 64, the diameter of the molecular-sieve shielding structure 11 can easily be made large enough to keep the power density incident upon it below some critical value. This critical power density is primarily determined by the properties of the particular molecular-sieve material 64 being used. In general, it is desirable to keep the power density below a value that will give rise to a temperature of not more than 200 C., to the surface of the shielding structure 11 that faces the arc.
FIG. 2 illustrates a modified-type vacuum circuit interrupter 103 operating at standard temperature with a molecular-sieve structure 120 similar to that described in connection with FIG. 1. There is provided a relatively stationary solid contact 112 cooperable with a movable solid contact 114, the latter being reciprocally actuated in a vertical direction by a suitable operating mechanism, not shown, which is attached to and actuates the conducting operating rod portion 116. As shown, the two contacts 112, 114 make separable abutting engagement. The operating rod 116 is sealed, as at 116a, to the lower end of a flexible metallic bellows 20.
A casing structure 118 may be provided comprising an upper insulating tubular portion 32, which is sealed, to a downwardly extending flange portion 24a of the upper end cap 24. In addition, the insulating tubular portion 32 may be sealed to the upper end of a tubular metallic casing member 40, which is sealed to the surrounding housing member 44. The housing member 44 has an inwardly extending lower cap portion a, which is sealed to the insulator 45. The insulator 45 is, as before, sealed to the supporting rod portion 112a of the lower contact structure 112.
The internal insulating surfaces of the tubular insulating casing portion 32 are protected from the condensation of arcgenerated metallic vapors thereon by means of the tubular metallic end-shield 50, and also by the condensation, sorption, and trapping provided by the interiorly-disposed molecularsieve shielding structure surrounding the arc gap, and generally designated by the reference numeral 120. This shielding structure 120 comprises an interior cylindrical screen 122 with triangular channels 123 (FIG. 3), behind which are disposed the relatively loose molecular-sieve beads 64. The exterior housing 44 of the interrupter, together with the screen 122, confine the beads 64.
FIG. 3 shows a horizontal cross-sectional view of the interrupter 103 of FIG. 2 taken along the line Ill-Ill of FIG. 2. This view clearly illustrates the triangular channels 123 in the screen 122. These channels 123 provide an effectively larger surface area exposed to the arc than an ordinary cylindrical screen of the same diameter. This further reduces the power density to the molecular-sieve shielding structure 120. It also provides a larger area for sorption, and a more effective geometry for trapping and scattering of incident particles and photons.
When activated carbon granules are used around the arc, either singly or together with the other molecular-sieve materials, as an integral part of the shielding structure 120, an additional reduction in the reflection of photons is obtained due to the very color (black) of carbon. Black objects absorb light in all wavelengths and have a greatly lower reflectivity than shiny metal surfaces, which commonly surround the arc in the form of a cylindrical condensing shield. A great deal of energy is emitted in the form of radiation from metal-vapor 11 steradians, and the arc is 40 percent absorbing, the following approximate percentages of emitter radiant energy will be reabsorbed by the are:
First Reflection: 2V5 reabsorbed; 32% passes through Second Reflection: 7% reabsorbed; I01: panes through Third Reflection: 2% reabsorbed; 3% passes through.
First Reflection: 4% reabsorbed; 6% passes through Second Reflection: 0.2% reabsorbed; 0.4% passes through Third Reflection: 0.01% reabsorbed; 0.02%
Therefore, for a molecular-sieve shielding structure 120, as embodied in this invention, only about 4.2 percent of the emitted radiation would be recovered by the arc after three reflections. This is a negligible amount compared to what would otherwise be reabsorbed by the arc. In addition, there is also a similar gain from the reduction in the reflection of particles back into the are that the molecular-sieve shielding structure 60 provides.
Referring now to FIG. 4 of the drawings, there is shown another low-temperature vacuum circuit interrupter 130, cmbodying an inverted type of molecular-sieve structure 131. In this case, the molecular-sieve material 64 is not directly exposed to the are, as it was in the interrupters of FIGS. l and 2. In this type of application, the molecular-sieve material is present primarily to sorb gases generated during arcing, and gases, which leak into or otherwise permeate the interrupter vessel.
Except for the inversion of the molecular-sieve material 64, the general construction of the interrupter of FIG. 4 is much the same as that illustrated in FIG. 1. The molecular-sieve shielding structure 131 is modified so that the screen 62 is farthest from the arc gap, with the molecular-sieve material 64 being next to the screen, and confined by the metallic cylindrical casing 136. The coolant 69 is confined in the annular space 135 between the casing 136 and the innermost cylindrical casing 137. Communicating holes 101a, 101b, 102a, 102b, 103a, 103b, 103a, and 103d are provided to communicate the interior vacuum region 18 with the annular vacuum space 100, which surrounds the screen 62. The communicating holes 102 and 103 are in the form of tubes which make hermetic seals with the casings 136 and 137.
FIG. illustrates, in fragmentary fashion, an inverted molecular-sieve structure for use at standard operating temperatures. There is shown the vacuum circuit interrupter 140, similar in construction to the interrupter 103 of FIG. 2. The molecular-sieve shielding structure 60 is modified from that of FIG. 2, so that the screen 62 is farthest from the arc gap, with the molecular-sieve material 64 being next to the screen and confined by the cylindrical casing 66. Communicating holes such as 101, 103 and 104 are provided to communicate the interior vacuum region 18 with the annular vacuum space 100, which surrounds the screen 62. As in the case of FIG. 4, the molecular-sieve material 64 is not directly exposed to the arc, and is primarily present to sorb gases generated during arcing, and gases which leak into or otherwise permeate the interrupter vessel.
Referring now to FIG. 6, there is shown a liquid-metal vacuum-type circuit interrupter 150, embodying a molecularsieve shielding structure 120. The general construction is similar to that of the interrupter of FIG. 2. The stationary contact is replaced by a pool of liquid metal 153, such as gallium, into which the solid movable contact 151 dips. As shown, the solid contact 151 dips all the way to the bottom of the liquidmetal pool 153 and makes contact with the liquid metal 153 and the bottom of the liquid-metal well 160. A thin film of liquid metal rs present between the contact 151 and the bottom of the well 160, which reduces contact resistance and additionally prevents welding. The contact 151 bottoms on the well 160 so that the interrupter can easily remain closed, if required, during a high overload current. For interruption, the movable contact 151 moves up out of the liquid metal 160. A small interrupter of this type has easily interrupted currents exceeding 16,000 amperes RMS.
Although various liquid metals may be used, gallium and its alloys are preferred. This is described and set forth more fully in the copending application by Mario Rabinowitz and Russell E. Fox, filed Oct. 14, I965, Ser. No. 496,008 now US. Pat. No. 3,462,573, and assigned to the assignee of the present invention.
While I have shown and described specific embodiments of my invention, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may be readily made therein by those skilled in the art without departing from the spirit and 'scope of my invention.
I claim as my invention:
1. A vacuum-type circuit interrupter including means defining an evacuated envelope, a pair of relatively movable contacts separable to establish an arcing gap therebetween disposed within said evacuated envelope and a molecularsieve shielding structure within the envelope and surrounding the arcing gap for maintaining the vacuum and providing for a high consistent level of arc interruption capability.
2. The vacuum-type circuit interrupter of claim 1, wherein the molecular-sieve shielding structure comprises loose beads.
3. The combination of claim 1, wherein the molecular-sieve shielding structure is cooled to a very low temperature.
4. A vacuum-type circuit interrupter including means defining an evacuated envelope, a pair of relatively movable contacts that are separable to establish an arcing gap therebetween disposed within said evacuated envelope, and a molecular-sieve material therein to sorb gases entering the interrupter vessel by leakage at seals or otherwise permeating the vessel.
5. The vacuum-type circuit interrupter of claim 4 wherein the molecular-sieve material comprises loose beads.
6. The combination of claim 4 wherein the molecular-sieve material is cooled to a very low temperature.
7. A vacuum-type circuit interrupter including means defining an evacuated envelope, a pair of relatively movable contacts that are separable to establish an arcing gap therebetween disposed within said evacuated envelope, and a shielding structure surrounding the arc gap containing loosely held beads, pellets, granules, and/or chunks for condensing, sorbing, trapping, and/or efficiently scattering arc-generated particles and/or photons.
8. The combination according to claim 7 wherein the beads, etc. are of low reflectivity material to further reduce the reflection of photons back into the are.
9. The combination according to claim 7 wherein the beads, etc. are made of a poor or nonconducting material to reduce the production of photoelectrons at the shielding structure.