Vacuum interrupter

Abstract: A vacuum interrupter of more inproved large current interrupting capability and dielectric strength is disclosed. The interrupter has a pair of separable contact-electrodes (5, 6), a vacuum envelope (4) electrically insulating and enclosing the pair therewithin, a contact-making portion (14) of material of 20 to 60% IACS electrical conductivity being a part of one contact-electrode (6) of the pair, a magnetically arc-rotating portion (13) of material of 2 to 30% IACS electrical conductivity secured to the contact-making portion (14) so as to be apart from the other contact-electrode (5) when the contact-­ electrodes (5, 6) are into engagement, and means, which include a plurality of slots extending radially and circumferen­ tially of the magnetically arc-rotating portion (13) and being apart from each other, for magnetically rotating arc estab­ lished between the contact-electrodes (5, 6) on an arcing sur­ face of the contact-electrode (6).

Description: The present invention relates to a vacuum interrupter comprising a pair of separable contact electrodes, at least one of which consists of a generally disc-shaped arc-rotating portion for magnetically rotating an arc formed on separation of said contact electrodes and a contact-making portion projecting from an arcing surface of the arc-rotating portion at a central portion of the arc-rotating portion, wherein the electrical conductivity of the arc-rotating portion is around 17.27% IACS and is lower than the electrical conductivity of the contact-making portion of around 50% IACS; wherein a plurality of slots are formed in the arc-rotating portion, each of which extends radially and circumferentially of the arc-rotating portion, and wherein the contact electrodes are enclosed in a vacuum-tight manner in a vacuum envelope which is electrically insulating. A vacuum interrupter of this general kind is known, for example from EP-A-00 76 659, from US-A-3,182,156, from US-A-3,828,428 and from DE-OS 25 22 832, although these documents do not disclose the specific conductivity values for the arc-rotating and contact making portions. The document "Wissenschaftlichelektrische Hochleistungstechnik" Heft 17, Dec. 1976 comprises a collection of articles which disclose the specific conductivity values of 10 m/Ohm m² (17.27% IACS) for an FeCu 70/30 arc-rotating portion and 29 m/Ohm m² (50% IACS) for a Mo/Cu 55/45 contact-making portion but does not establish a general rule relevant to conductivities of the arc-rotating and contact-making portions. The preamble of claim 1 and the identical preambles of claims 3 and 5 are based on the prior art recited in this latter document. In such vaccum interrupters a first lead rod is secured by brazing to the central portion of the backsurface of one of the contact electrodes and is electrically connected to an electric power circuit outside of the envelope. The contact-making portion of the said one of the contact electrodes is provided at the central portion of the surface thereof. In operation the said contact electrode drives an arc established between it and the other contact electrode radially outwardly and circumferentially. This occurs due to an interaction between the arc and a magnetic field which is produced by arc current flowing radially and outwardly from the contact-making portion of the said one contact electrode during separation of the contact electrodes, and by virtue of the slots. Consequently, the said one contact electrode prevents excessive local heating and melting of the contact electrodes, thus enhancing the large current interrupting capability and dielectric strength of the vacuum interrupter. In practice the contact electrode itself is generally required to consistently satisfy the following requirements: i) achieving high large-current interrupting capability, ii) achieving high dielectric strength, iii) achieving both high small leading-current interrupting capability and high small lagging-current interrupting capability, iv) achieving a low degree of current chopping, v) possessing low electrical resistance, vi) possessing excellent anti-welding capability, and vii) possessing excellent anti-erosional capability. However, a contact electrode which consistently satisfies all the above requirements has not yet been provided in the present state of the art. By way of example a contact electrode is known from US-A-3,246,979 of which the arc-rotating portion is made of copper and of which the contact-making portion is made of a Cu-Bi alloy such as Cu-0.5Bi alloy consisting of copper and 0.5% bismuth by weight. Another contact electrode is known from US-A-3,811,939 in which the arc-rotating portion is made of copper and in which the contact-making portion is made of Cu-W alloy such as a 20Cu-80W alloy consisting of 20% copper by weight and 80% tungsten by weight. With the contact electrodes specified above, the low mechanical strenght of copper, i.e., tensile strength of about 196.1 MPa (20 kg/mm²) causes the arc-rotating portion to be made of thick and heavy shape so that the arc-rotating portion can resist deformation due to the mechanical impact and the electromagnetic force from the large current which is applied to the pair of contact electrodes when a vacuum interrupter is closed and opened. However, this thick and heavy shape increases the size of the vacuum interrupter. Additionally, the segments of the arc-rotating portion defined by the slots (hereinafter, referred to as fingers) cannot be lengthened because of their mechanical performance in order to enhance the magnetic arc-rotating force and the large-current interrupting capability. Additionally, the fingers are much eroded by excessive melting and evaporation thereof due to a large current arc because copper and Cu-0.5Bi alloy are soft, because their vapor pressures are considerably higher than that of tungsten and because their melting points are considerably lower than that of tungsten. Recently the requirement has arisen to provide a vacuum interrupter of the same size as or smaller than the conventional which much enhances large current interrupting capability and dielectric strength to cope with increasing demands of an electric power supply network. Thus an object of the present invention is to provide a vacuum interrupter of the arc-rotating type which possesses high large-current interrupting capability and dielectric strength. Another object of the present invention is to provide a vacuum interrupter of the arc-rotating type which possesses high resistance against mechanical impact and electromagnetic force from a large-current arc, and therefore long period durability. In order to satisfy these objects a first embodiment of the present invention provides, starting with a vacuum interrupter of the initially named kind, that said arc-rotating portion of at least one of the contact electrodes is made of a complex metal consisting of 30 to 70% copper by weight and 30 to 70% by weight of non-magnetic stainless steel and has 2 to 30% IACS electrical conductivity, and said contact-making portion of the one contact electrode is made of material of 20 to 60% IACS electrical conductivity, the conductivity of the arc-rotating portion being always lower than the conductivity of the contact-making portion. In accordance with a second embodiment the present invention provides, starting with a vacuum interrupter of the initially named kind, that said arc-rotating portion of at least one of the contact electrodes is made of complex metal consisting of 30 to 70% copper by weight and 30 to 70% magnetic stainless steel by weight and has 2 to 30% IACS electrical conductivity, and said contact-making portion of the one contact electrodes is made of material of 20 to 60% IACS electrical conductivity, the conductivity of the arc-rotating portion being always lower than the conductivity of the contact-making portion. Attention should also be drawn to four other prior art patent specifications. EP-A-101 024, which has only to be regarded under the aspect of novelty, discloses contact materials which are closely similar to the materials used for the contact making portion of the electrodes of the vacuum interrupter of the present application. However, EP-A-101 024 does not disclose the specific contact electrode of the present specification, namely a contact electrode having an arc-rotating portion and a contact-making portion and is thus clearly also silent as to the possibility of obtaining improved performance by selecting a specific range of conductivity for the arc-rotating portion. EP-A-101 024 also discloses infiltrating processes for producing contact material for a vacuum interrupter by powder metallurgy, said infiltrating processes being similar to those described in the present specification. EP-A-77 157 which also has only to be regarded under the aspect of novelty, discloses an electrical contact structure for a vacuum interrupter in which the electrical contact is coaxially joined to the inner end portion of the associated contact rod via a disc-shaped electric current bypassing conductive member having an outer radius substantially equal to that of the electrical contact. The current bypassing conductive member may comprise a plurality of petals extending in the outer direction from the joining position in a spiral manner to produce a magnetic driving force. The reference does not disclose the conductivities of the electrical contact or of the current bypassing conductive member. The electrical contact comprises a substantially disc-shaped semi-resistor including a plurality of portions of low electrical conductivity and a plurality of portions made of metal or ceramics each having a high electrical conductivity and serving as a major current flowing portion penetrated in said semi-resistor in the direction of the thickness of the semi-resistor and separated from each other. The portion of low electrical conductivity can comprise stainless steel or iron and the stainless steel may comprise material of an austenitic or ferritic structure. In addition to the abovementioned prior art attention is drawn to two references concerned with contact electrodes of the arc-diffusing type rather than of the arc-rotating type. As is known contact electrodes of the arc-diffusing type operate with an axial magnetic field, whereas contacts electrodes of the arc-rotating type operate with a transverse magnetic field. In DE-A-29 47 090 the contact-making portion is a copper-chromium alloy of high electrical conductivity and is supported on a backing or support disc of low electrical conductivity. This support disc is however not responsible for producing arc-rotation nor does it have an arcing surface. The ring-like structure behind the backing disc and the contact-making poriton is of high electrical conductivity and serves to generate the axial magnetic field. In EP-A-119 563, which also has only to be regarded under the aspect of novelty, the axial magnetic field is generated by a coil and the arc-diffusing portion is not slotted. Further advantageous developments of the invention are set forth in the dependent claims 2 to 19. Embodiments of the invention will now be described in further detail by way of example only and with reference to the accompanying drawings in which: Figure 1 is a sectional view through a vacuum interrupter of the arc-rotating type according to the present invention. Figure 2 is a plan view of a movable contact-electrode of Figure 1. Figure 3 is a sectional view taken along the line III-III of Figure 2. Figure 4 is a diagram illustrative of a relation between the number of times N of a large-current interruption and the ratio P of the withstand voltage of a vacuum interrupter after large-current interruption relating to the withstand voltage of the vacuum interrupter before large-current interruption. Figures 5A to 5D all are photographs taken by an X-ray microanalyzer of the structure of a first example C₁ of a complex metal constituting the contact-making portion of a contact electrode, in which: Figure 5A is a secondary electron image photograph of the structure. Figure 5B is a characteristic X-ray image photograph of molybdenum. Figure 5C is a characteristic X-ray image photograph of chromium. Figure 5D is a characteristic X-ray image photograph of infiltrant copper. Figure 6A to 6D all are photographs taken by the X-ray microanalyzer of the structure of a second example C₂ of a complex metal constituting the contact-making portion of a contact electrode, in which: Figure 6A is a secondary electron image photograph of the structure. Figure 6B is a characteristic X-ray image photograph of molybdenum. Figure 6C is a characteristic X-ray image photograph of chromium. Figure 6D is a characteristic X-ray image photograph of infiltrant copper. Figure 7A to 7D all are photographs taken by the X-ray microanalyzer of the structure of a third example C₃ of a complex metal constituting the contact-making portion of a contact electrode in which: Figure 7A is a secondary electron image photograph of the structure. Figure 7B is a characteristic X-ray image photograph of molybdenum. Figure 7C is a characteristic X-ray image photograph of chromium. Figure 7D is a characteristic X-ray image photograph of infiltrant copper. Figure 8A to 8D all are photographs taken by the X-ray microanalyzer of the structure of a fourth example A₄ of a complex metal constituting the arc-rotating portion of a contact electrode, in which: Figure 8A is a secondary electron image photograph of the structure. Figure 8B is a characteristic X-ray image photograph of iron. Figure 8C is a characteristic X-ray image photograph of chromium. Figure 8D is a characteristic X-ray image photograph of infiltrant copper. Figures 9A to 9D are all photographs taken by the X-ray microanalyser of the structure of a seventh example A₇ of a complex metal constituting the arc-rotating poriton of a contact electrode, in which: Figure 9A is a secondary electron image photograph of the structure. Figure 9B is a characteristic X-ray image photograph of iron. Figure 9C is a characteristic X-ray image photograph of chromium. Figure 9D is a characteristic X-ray image photograph of infiltrant copper. Figure 10A to 10E all are photographs taken by the X-ray microanalyzer of the structure of a tenth example A₁₀ of a complex metal constituting the arc-rotating portion of a contact electrode, in which: Figure 10A is a secondary electron image photograph of the structure. Figure 10B is a characteristic X-ray image photograph of iron. Figure 10C is a characteristic X-ray image photograph of chromium. Figure 10D is a characteristic X-ray image photograph of nickel. Figure 10E is a characteristic X-ray image photograph of infiltrant copper. As shown in Figure 1, a vacuum interrupter of a 1st embodiment of the present teaching includes a vacuum envelope 4, the inside of which is evacuated to, e.g. a pressure of no more than 13.4 mPa (10⁻⁴ Torr) and a pair of stationary and movable contact electrodes 5 and 6 located within the vacuum envelope 4. Both the contact-electrodes 5 and 6 are of the arc-rotating type. The vacuum envelope 4 comprises, in the main, two insulating cylinders 2 of glass or alumina ceramics of the same shape which are serially and hermetically associated by welding or brazing to each other by means of metallic sealing rings 1 of Fe-Ni-Co alloy or Fe-Ni alloy at the adjacent ends of the insulating cylinders 2, and by means of a pair of metallic end plates 3 of austenitic stainless steel hermetically associated by welding or brazing to both the remote ends of the insulating cylinders 2 via metallic sealing rings 1. A metallic arc shield 7 of a cylindrical form which surrounds the contact electrodes 5 and 6 is supported on and hermetically joined by welding or brazing to the metallic sealing rings 1 at the adjacent ends of the insulating cylinders 2. Further, metallic edge-shields 8 which moderate the electric field concentration at the edges of the sealing metallic rings 1 at the remote ends of the insulating cylinders 2 are joined by welding or brazing to the pair of metallic end plates 3. An axial shield 11 and a bellows shield 12 are provided on respective stationary and movable lead rods 9 and 10 which are secured by brazing to the respective stationary and movable contact electrodes 5 and 6. The arc shield 7, edge shield 8, axial shield 11 and bellows shield 12 all are made of austenitic stainless steel. The contact electrodes 5 and 6 have the same construction and the movable contact electrode 6 will be described hereinafter. As shown in Figures 2 and 3, the movable contact electrode 6 consists of a magnetically arc-rotating portion 13 and an annular contact-making portion 14 which is secured by brazing to the surface of the arc-rotating portion 13 around the center thereof. The arc-rotating portion 13 is made of material of 10 to 20%, preferably 10 to 15% IACS (an abbreviation of International Annealed Copper Standard) electrical conductivity. For example, the latter material may be a complex metal of about 294 MPa (30 kg/mm²) tensile strength consisting of 50% copper by weight and 50% austenitic stainless steel by weight, e.g., SUS304 or SUS316 (at JIS, hereinafter, at the same). The arc-rotating portion 13, which is generally disc-shaped, is much thinner that the arc-rotating portion of a conventional type of vacuum interrupter. As shown in Figure 2, the arc-rotating portion 13 includes a plurality (in Figure 2, eight) of spiral slots 16 and a plurality (in Figure 2, eight) of spiral fingers 17 defined by the slots 16. The surfaces of the fingers 17, which slant slightly from the center of the arc-rotating portion 13 to the periphery thereof, serve as an arcing surface. A circular recess 18 is provided at the center to the arc-rotating portion 13. A circular recess 19, the diameter of which is larger than that of the movable lead rod 10, is provided at the center of the surface of the arc-rotating portion 13. The contact-making portion 14, an outer-diameter of which is equal to that of the circular recess 19, is fitted into the circular recess 19 and brazed to the arc-rotating portion 13. The contact-making portion 14 projects from the surface of the arc-rotating portion 13. A boss 20 is provided at the center of the backsurface of the arc-rotating portion 13. The contact-making portion 14 is made of material of 20 to 60% IACS electrical conductivity, e.g., a complex metal consisting of 20 to 70% copper by weight, 5 to 70% chromium by weight and 5 to 70% molybdenum by weight. A process for producing the complex metal will be hereinafter described. In this embodiment, the contact-making portion 14 exhibits substantially the same electrical contact resistance due to its thin thickness, as a contact-making portion of Cu-0.5Bi alloy. A current conductor 15 which, on the surface thereof, is brazed ot the boss 20, is made of material of electrical conductivity much higher than that of the material for the arc-rotating portion 13, e.g., of copper or copper alloy. The current conductor 15 is shaped to a thickened disc having a diameter larger than that of the movable lead rod 10 but slightly smaller than the outer-diameter of the contact-making portion 14. The backsurface of the current conductor 15 is brazed to the inner end of the movable lead rod 10. Under the presence of the current conductor 15, most of the current conducted by the movable lead rod 10 flows not in a radial direction of the arc-rotating portion 13 of low electrical conductivity but in that of the current conductor 15 and an axial direction of the arc-rotation portion 13 to the contact-making portion 14. Consequently, the amount of Joule heating in the arc-rotating portion 13 is much reduced. A perforamnce comparison test was carried between an embodiment of the present teaching, and a conventional vacuum interrupter of the arc-rotating type. The former interrupter includes a pair of contact electrodes each consisting of a contact-making portion which is made of a complex metal consisting of 50% copper by weight, 10% chromium by weight and 40% molybdenum by weight and an arc-rotating portion which is made of a complex metal consisting of 50% copper by weight and 50% SUS304 by weight. This embodiment of the present invention is also refered to later as embodiment 19, the contact-making portion comprising materail later designated C₁ and the arc-rotating portion comprises material later designated A₁₀. The conventional interrupter used for comparison purposes includes a pair of contact electrodes each consisting of a contact-making portion which is made of Cu-0.5Bi alloy, and an arc-rotating portion which is made of copper. Results of the performance comparison test will be described as follos: In the specification, amounts of voltage and current are represented in rms value if not otherwise specified. 1) Large current interrupting capability The large-current interrupting capability of the vacuum interrupter of the first embodiment of the present teaching was improved by at least 10% over that of the conventional vacuum interrupter and was more stable than the large current interrupting capability of the conventional vacuum interrupter. 2) Dielectric strength "Withstand voltages" of the vacuum interrupter of the first embodiment of the present teaching and of the conventional vacuum interrupter were measured, in accordance with JEC-181 test method, with a 3.0 mm gap between the contact-making portions of the first embodiment of the present teaching but with a 10 mm gap between the contact-making portions of the conventional vacuum interrupter. In this case, both vacuum interrupters exhibited the same withstand voltage. Thus, the vacuum interrupter of the present invention possesses a little more than 3 times the dielectric strenght of the conventional vacuum interrupter. Figure 4 shows the results of comparative performance measurements for the two interrupters. In Figure 4, the abscissa represents the number of times N (times) of an interruption of large-curreng of rated 84 kV and 25 kA, while the ordinate represents the ratio P (%) of withstand voltage after large-current interruption to withstand voltage therebefore. Moreover, in Figure 4, the line A indicates the relation between the number of times N of the interruption and the radio P for the 1st embodiment of the vacuum interrupter of the present teaching, while the line B indicates the same relation for the conventional vacuum interrupter. As apparent from Figure 4, the dielectric strength after large-current interruption of the vacuum interrupter of the 1st embodiment of the present teaching is much higher than that of the conventional vacuum interrupter. 3) Anti-welding capability The anti-welding capability of the contact electrodes of the 1st embodiment of the present teaching amounted to 80% of the anti-welding capability of those of the conventional vacuum interrupter. However, such decrease is not actually significant. If necessary, the disengaging force applied to the contact electrodes may be slightly enhanced. 4) Lagging small current interrupting capability The current chopping value of the vacuum interrupter of the 1st embodiment of the present teaching amounted to 40% of that of the conventional vacuum interrupter, so that chopping surge is almost insignificant. The value was maintained even after engaging and disengaging of the contact electrodes more than 100 times for interrupting lagging small current. 5) leading small current interrupting capability The vacuum interrupter of the 1st embodiment of the present teaching was formed to be capable of interrupting twice the charging current of the conventional vacuum interrupter of condenser or unload line. Performances of the vacuum interrupter of the 1st embodiment of the present teaching are thus higher than those of the conventional vacuum interrupter with respect to large-current interrupting capability, dielectric strength, lagging small current interrupting capability and leading small current interrupting capability. In particular, the ratio of dielectric strength after large-current interruption to that therebefore for the vacuum interrupter of the 1st embodiment of the present teaching is much higher than for the conventional vacuum interrupter. Other embodiments of the present invention will be described hereinafter in which each of the materials for the arc-rotating portions 13 and contact-making portions 14 of the pair of stationary and movable contact electrodes 5 and 6 as shown in Figure 1 is changed or varied. Processes for producing the complex metal are known, may be classified in two categories, and will be described generally with reference to a complex metal consisting of 20 to 70% copper by weight, 5 to 40% chromium by weight and 5 to 40% iron by weight. The process of one category comprises the step of diffusion-bonding a powder mixture consisting of chromium powder and iron powder into a porous matrix and the step of infiltrating the porous matrix with molten copper (hereinafter, referred to as an infiltration process). The process of the other category comprises the step of press-shaping a powder mixture consisting of copper powder, chromium powder and iron powder into a green compact and the step of sintering the green compact below the melting point of copper (about 1083°C) or at at least the melting point of copper but below the melting point of iron (about 1537°C) (hereinafter, referred to as a sintering process). The infiltration and sintering processes will be described hereinafter. Each metal powder was of a size of no more than 149 µm (minus 100 meshes). The first infiltration process First of all a predetermined amount (e.g., an amount of one final contact electrode plus a machining margin) of chromium powder and iron powder which are respectively prepared 5 to 40% by weight and 5 to 40% by weight but in total 30 to 80% by weight at a final ratio, i.e. of the electrode material including copper, are mechanically and uniformly mixed. Secondly, the resultant powder mixture is placed in a vessel of a circular section made of material, e.g., alumina ceramics, which interacts with none of chromium, iron and copper. A copper bulk is placed on the powder mixture. Thirdly, the powder mixture and the copper bulk are heated while being held in a nonoxidizing atmosphere, e.g., a vacuum of at highest 6.67 mPa (5×10⁻⁵Torr) at 1000°C for 10 min (hereinafter, referred to as the chromium-iron diffusion steps), thus resulting in a porous matrix of chromium and iron. Then, the resultant porous matrix and the copper bulk are heated while being held under the same vacuum at 1100°C for 10 min, which leads to the molten copper infiltrating the porous matrix (hereinafter, referred to as the copper infiltrating step). After cooling, the result is the desired complex metal for the arc-rotating portion. The second infiltration process Firstly, chromium powder and iron powder are mechanically and uniformly mixed in the same manner as in the first infiltration process. Secondly, the resultant powder mixture is placed in the same vessel as that in the first infiltration process. The powder mixture is heated while being held in a nonoxidizing atmosphere, e.g., a vacuum of at highest 6.67 mPa (5×10⁻⁵ Torr), or in hydrogen, nitrogen or argon gas at a temperature below the melting point of iron, e.g., within 600 to 1000°C for a fixed period of time, e.g., within 5 to 60 min, thus resulting in a porous matrix consisting of chromium and iron. Thirdly, a copper bulk is placed on the porous matrix and the porous matrix and the copper bulk are heated while being held in the same nonoxidizing atmosphere, e.g., in a vacuum of at highest 6.67 mPa (5×10⁻⁵ Torr), as that of the chromium-iron diffusion step, or in another nonoxidizing atmosphere, at a temperature of at least the melting point of copper but below the melting point of the porous matrix for a fixed period of time, e.g., within about 5 to 20 min, which leads to molten copper infiltrating the porous matrix. After colling, the result is a desired complex metal for the arc-rotating portion 13. In the second infiltration process, the copper bulk is not placed in the vessel in the chromium-iron diffusion step, so that the powder mixture of chromium powder and iron powder can be heated to form the porous matrix while being at a temperature of at least the melting point (1083°C) of copper but below the melting point (1537°C) of iron. In the second infiltration process the chromium-iron diffusion step may also be performed in various nonoxidizing atmospheres, e.g., hydrogen, nitrogen or argon gas, and the copper infiltration step may be performed under evacuation to effect vacuum degassing of the complex metal for the arc-rotating portion 13. In both the described infiltration processes, vacuum is preferably selected as the nonoxidizing atmosphere rather than other nonoxidizing atmospheres, because degassing of the complex metal for the arc-rotating portion 13 can be concurrently performed during head holding. However, even if deoxidizing gas or inert gas is used as a nonoxidizing atmosphere, the resultant material has actually no failure as a complex metal for the arc-rotating portion 13. In addition, the heat holding temperature and the period of time for the chromium-iron diffusion step is determined by taking into account conditions of the vacuum furnace or other gas furnace, the shape and size of the porous matrix to be produced and its workability so that the properties desired for a complex metal for the arc-rotating portion 13 are achieved. For example, a heating temperature of 600° determines a heat holding period of 60 min or a heating temperature of 1000°C determines a heat holding period of 5 min. The particle size of the chromium particles and of the iron particles may be minus 60 meshes, i.e., no more than 250 µm. However, the lower the upper limit of the particle size, the more difficult it generally is to uniformly distribute each metal particle. Further, it is more complicated to handle the metal particles, and, when used, they necessitate a preteatment because they are more liable to be oxidized. On the other hand, if the particle size of each metal article exceeds 250 µm (60 meshes), it is necessary to make the heat holding temperature higher or to make the heat holding period of time longer as the diffusion distance of each metal particle increases, which leads to lower productivity of the chromium-iron diffusion step. Consequently, the upper limit of the particle size of each metal particle is determined in view of various conditions. According to both the infiltration processes, the particle size of each metal particle is made no more than 149 µm (minus 100 meshes) because the particles of chromium and iron can be more uniformly distributed to cause better diffusion bonding thereof, thus resulting in a complex metal for the arc-rotating portion possessing better properties. If chromium particles and iron particles are badly distributed, then drawbacks of both metals will not be offset by each other and advantages thereof will not be developed. In particular, the more the particle size of each metal particle exceeds 250 µm (60 meshes), the larger is the porportion of copper in the surface region of an arc-rotating portion, which contributes to lower the dielectric strength of the contact electrode. Alternatively chromium particles, iron particles and chromium-iron alloy particles which have been granulated larger appear in the surface region of the arc-rotating portion, so that the drawbacks of chromium, iron and copper respectively are more apparent but not the advantages thereof. The sintering process Firstly, chromium powder, iron powder and copper powder which are prepared in the same manner as in the first infiltration process are mechanically and uniformly mixed. Secondly, the resultant powder mixture is placed in a preset vessel and press-shaped into a green compact under a preset pressure, e.g., of 196.1 to 490.4 MPa (2,000 to 5,000 kg/cm²). Thirdly, the resultant green compact which is taken out of the vessel is heated while being held in a nonoxidizing atmosphere, e.g., a vacuum of at highest 6.67 mPa (5×10⁻⁵ Torr), or hydrogen, nitrogen or agon gas at a temperature below the melting point of copper, e.g., at 1000°C, or at a temperature of at least the melting point of copper but below the melting point of iron, e.g., at 1100°C for a preset period of time, e.g., within 5 to 60 min. The green compact is thus sintered into the complex metal of the arc-rotating portion. In the sintering process, the conditions of the nonoxidizing atmosphere and the particle size of each metal particle are the same as those in both the infiltration processes, and the conditions of the heat holding temperature and the heat holding period required for sintering the green compact are the same as those for producing the porous matrix from the powder mixture of metal powders in the infiltration processes. Structures of the complex metals for the contact-making portion 14 which are produced according to substantially the same process ad the first infiltration process above, will be described hereinafter with reference to Figures 5A to 5D, Figures 6A to 6D and Figures 7A to 7D which are photographs taken by the X-ray microanalyzer. Example C₁ of a complex metal for the contact-making portion possesses a composition consisting of 50% copper by weight, 10% chromium by weight and 40% molybdenum by weight. Figure 5A shows a secondary electron image of a metal structure of example C₁. Figure 5B shows a characteristic X-ray image of distributed and diffused molybdenum, in which distributed grey insular agglomerates indicate molybdenum. Figure 5C shows a characteristic X-ray image of distributed and diffused chromium, in which distributed grey or white insular agglomerates indicate chromium. Figure 5D shows a characteristic X-ray image of infiltrant copper, in which white parts indicate copper. Example C₂ of a complex metal for the contact-making portion 14 possesses a composition consisting of 50% copper by weight, 25% chromium by weight and 25% molybdenum by weight. Figures 6A, 6B, 6C and 6D show similar images to those of Figures 5A, 5B, 5C and 5D, respectively. Example C₃ of a complex metal for the contact-making portion 14 possesses a composition consisting of 50% copper by weight, 40% chromium by weight and 10% molybdenum by weight. Figures 7A, 7B, 7C and 7D show similar images to those of Figures 5A, 5B, 5C and 5D, respectively. As apparent from Figures 5A to 5D, Figures 6A to 6D and Figures 7A to 7D, the chromium and molybdenum are uniformly distributed and diffused into each other in the metal structure, thus forming many insular agglomerates. The agglomerates are uniformly bonded to each other throughout the metal structure, thus resulting in the porous matrix consisting of chromium and molybdenum. Interstices of the porous matrix are infiltrated with copper, which results in a stout structure of the complex metal for the contact-making portion 14. Measurements which were carried out on examples C₁, C₂ and C₃ possessed 40 to 50% IACS electrical conductivity and 120 to 180 Hv hardness. The Figures 8A to 8D and Figures 9A to 9D show structures of the complex metals for the arc-rotating portion. According to the 1st to 18th embodiments of the present teaching (further particulars of which will be given later), the arc-rotating portions are made of a complex metal consisting of 30 to 70% magnetic stainless steel by weight and 30 to 70% copper by weight. For example, ferritic stainless or martensitic stainless steel is used as a magnetic stainless steel. As a ferritic stainless steel, SUS405, SUS429, SUS430, SUS430F or SUS434 may be listed. As a martensitic stainless steel, SUS403, SUS410, SUS416, SUS420, SUS431 or SUS440C may be listed. The complex metal above consisting of 30 to 70% magnetic stainless steel and 30 to 70% copper by weight, possesses at least 294 MPa (30 kg/mm²) tensile strength and 180 Hv hardness. This complex metal possesses 3 to 30% IACS electrical conductivity when a ferritic stainless steel is used, and 4 to 30% IACS electrical conductivity when a martensitic stainless steel is used. Complex metals for the arc-rotating portion 13 of the 1st to 18th embodiments of the present invention were produced by susbtantially the same process as the first infiltration process. The contact-making portions 14 of the contact electrodes of 1st to 18th embodiments are made of the same complex metal as those described previously. The contact-making portions of the contact electrodes of the 1st and 2nd comparison interrupters (which will be fully defined later) are made of Cu0.5Bi alloy. The contact-making portions of the contact electrodes of 3rd and 4th comparison interrupters are made of 20Cu-80W alloy. The structures of the complex metals for the arc-rotating portion which were produced by susbtantially the same process as the first infiltration process, will now be described with reference to Figures 8A to 8D and Figures 9A to 9D which are photographs taken by the X-ray microanalyzer. Example A₄ of a complex metal for the arc-rotating portion possesses a composition consisting of 50% ferritic stainless steel SUS434 and 50% copper by weight. Figure 8A shows a secondary electron image of a metal structure of example A₄. Figure 8B shows a characteristic X-ray image of distributed iron, in which distributed white insular agglomerates indicate iron. Figure 8C shows a characteristic X-ray image of distributed chromium, in which distributed grey insular agglomerates indicate chromium. Figure 8D shows a characteristic X-ray image of infiltrant copper, in which white parts indicate copper. As apparent from Figures 8A to 8D, the particles of ferritic stainless steel SUS434 are bonded to each other, resulting in a porous matrix. Interstices of the porous matrix are infiltrated with copper, which results in a stout structure of the complex metal for the arc-rotating portion. Example A₇ of a complex metal for the arc-rotating portion possesses a composition consisting of 50% martensitic stainless steel SUS410 by weight and 50% copper by weight. Figures 9A, 9B, 9C and 9D show similar images to those of Figures 8A, 8B, 8C and 8D, respectively. Structures of the complex metals of Figures 9A to 9D are similar to those of Figures 8A to 8B. Example A₅ of a complex metal for the arc-rotating portion possesses a composition consisting of 70% ferritic stainless steel SUS434 by weight and 30% copper by weight. Example A₆, of 30% ferritic stainless steel SUS434 by weight and 70% copper by weight. Example A₈, of 70% martensitic stainless steel SUS410 by weight and 30% copper by weight. Exemple A₉, of 30% martensitic stainless steel SUS410 by weight and 70% copper by weight. Examples A₅, A₆, A₈ and A₉ of the complex metal for the arc-rotating portion were produced by substantially the same process as the first infiltration process. Measurements of IACS electrical conductivity which were carried out on examples A₄ to A₉ of the complex metal for the arc-rotating portion and examples C₁ to C₃ above of the complex metal for the contact-making portion established that: Example A₄, has 5 to 15% IACS electrical conductivity Example A₅, has 3 to 8% Example A₆, has 10 to 30% Example A₇, has 5 to 15% Example A₈, has 4 to 8% Example A₉, has 10 to 30% Example C₁, has 40 to 50% Example C₂, has 40 to 50% Example C₃, has 40 to 50%. Respective measurements of tensile strength and hardness established that example A₄ of the complex metal for the arc-rotating portion possessed 294 MPa (30 kg/mm²) tensile strength and 100 to 180 Hv hardness. Examples A₄ to A₉ of the complex metal for the arc-rotating portion 13 and examples C₁ to C₃ of the complex metal for the contact-making portion 14 were respectively shaped to the same shapes as those described previously and tested. Results of the tests will be described hereinafter. The description will be made with reference to a vacuum interrupter in accordance with the 1st embodiment which includes a pair of contact electrodes each consisting of an arc-rotating portion 13 made of example A₄, and a contact making portion 14 made of example C₁. The arc-rotating portion 13 and the contact-making portion 14 of a contact electrode of a 2nd embodiment are made of examples A₄ and C₂ respectively. Those of a 3rd, of examples A₄ and C₃. Those of a 4th, of examples A₅ and C₁. Those of a 5th, of examples A₅ and C₂. Those of a 6th, of examples A₅ and C₃. Those of a 7th, of examples A₆ and C₁. Those of an 18th, of examples A₆ and C₂. Those of a 9th, of examples A₆ and C₃. Those of a 10th, of examples A₇ and C₁. Those of an 11th, of examples A₇ and C₂. Those of a 12th, of examples A₇ and C₃. Those of a 13th, of examples A₈ and C₁. Those of a 14th, of examples A₈ and C₂. Those of a 15th, of examples A₈ and C₃. Those of a 16th, of examples A₉ and C₁. Those of a 17th, of examples A₉ and C₂. Those of a 18th of examples A₉ and C₃. Those of a 1st comparative, of example A₄ and Cu-0.5Bi alloy. Those of a 2nd comparative, of example A₇ and Cu-0.5Bi alloy. Those of a 3rd comparative, of example A₄ and 20Cu-80W alloy. Those of a 4th comparative, of examples A₇ and 20Cu-80W alloy. When the performances of the vacuum interrupters of the 2nd to 18th embodiments differ from those of the 1st embodiment, then the points of difference will be specified. 6) Large current interrupting capability Interruption tests which were carried out at an opening speed within 1.2 to 1.5 m/s under a rated voltage of 12 kV, however, a transient recovery voltage of 21 kV according to JEC-181, established that the test vacuum interrupters interruped, 45 kA current. Moreover, interruption tests at an opening speed of 3.0 m/s under a rated voltage of 84 kV, however, a transient recovery voltage of 143 kV according to JEC-181, established that the test vacuum interrupters interrupted 35 kA current. Table 1 below shows the results of the large current interrupting capability tests on vacuum interrupters of the 1st to 18th embodiments and vacuum interrupters of the 1st to 4th comparatives. 7) Dielectric strength In accordance with the JEC-181 test method, impulse withstand voltage tests were carried out with a 30 mm inter-contact gap. The results showed 280 kV withstand voltage against both positive and negative impulses with ±10 kV deviation. After 10 times interrupting 45 kA current of rated 12 kV, the same impulse withstand voltage tests were carried out, thus establishing the same results. After 100 times continuously opening and closing a circuit through which 80A leading small current of rated 12 kV flowed, the same impulse withstand voltage tests were carried out, thus establishing substantially the same results. Table 2 below shows the results of the tests of the impulse withstand voltage at a 30 mm inter-contact gap which were carried out on the vacuum interrupters of the 1st and 4th embodiments of the present invention, and on the 1st and 3rd comparatives. 8) anti-welding capability In accordance with the JEC rated short time current test, current test, current of 25 kA was flowed for 3s through the stationary and movable contact electrodes 5 and 6 which were forced to contact each other under 1275N (130 kgf) force. The stationary and movable contact electrodes 5 and 6 were then separated without any failures with 1961N (200 kgf) static separating force. The increase of electrical contact resistance then stayed within 2 to 8%. In accordance with the JEC short time current test, current of 50 kA was flowed for 3s through the stationary and movable contact electrodes 5 and 6 which were forced to contact each other under 9807N (1,000 kgf) force. The stationary and movable contact electrodes 5 and 6 were then separated without any failures with a 1961N (200 kgf) static separating force. The increase of electrical contact resistance then stayed zero or at most 5%. Thus, the stationary and movable contact electrodes 5 and 6 actually possess good anti-welding capability. 9) Lagging small current interrupting capability In accordance with the lagging small current interrupting test standard of JEC-181, a 30A test current of 84× 1.5 √3 kV was flowed through the stationary and movable contact electrodes 5 and 6. Current chopping values had 3.9A average (however, a standard deviation δ n =0.96 and a sample number n=100). In particular, the current chopping values of the vacuum interrupters of the 2nd, 5th, 8th, 11th, 14th and 17th embodiments had a 3.7A (however, δ n =1.26 and n=100) average, and the current chopping values of the vacuum interrupters of the 13th, 16th, 19th, 22nd, 24th and 28th embodiments had a 3.9A (however, δ n =1.50 and n=100) average. 10) Leading small current interrupting capability In accordance with the leading small current interrupting test standard of JEC-181, a test leading small current of 84× 1.25 √3 kV and 80A was flowed through the stationary and movable contact electrodes 5 and 6. Under that condition a continuous 10,000 times opening and closing test was carried out. No reignition was established. The following limits were apparent with respect to the composition ratio of magnetic stainless steel in the complex metal for the arc-rotating portion of the 1st ot 18th embodiments. Magnetic stainless steel below 30% by weight significantly decreased the dielectric strength and the mechanical strength and durability of the arc-rotating portion 13, so that the arc-rotating portion 13 had to be thickened. On the other hand, magnetic stainless steel above 70% by weight significantly lowered interruption performance. Figures 10A to 10E show structures of the complex metals used for the arc-rotating portion 13 of the 29th to 27th embodiments of the present teaching. Arc-rotating portions 13 of the 19th to 27th embodiments are made of a complex metal consisting of 30 to 70% austenitic stainless steel by weight and 30 to 70% copper by weight. SUS304, SUS304L, SUS316 or SUS316L may, for example, be used as an austenitic stainless steel. The complex metal consisting of 30 to 70% austenitic stainless steel by weight and 30 to 70% copper by weight possesses 4 to 30% IACS electrical conductivity, at least 294 MPa (30 kg/mm²) tensile strength and 100 to 180 Hv hardness. The complex metals for the arc-rotating portion 13 of the 19th to 27th embodiments were produced substantially by the first infiltration process. The contact-making portions 14 of th 19th to 27th embodiments are made of complex metals of the same composition as those described previously. Structures of the complex metals for the arc-rotating portion, which were produced by substantially the same process as the first infiltration process, will be described hereinafter with reference to Figures to 10E which are photographs taken by the X-ray microanalyzer. Example A₁₀ of a complex metal for the arc-diffusing portion possesses a composition consisting of 50% austenitic stainless steel SUS304 by weight and 50% copper by weight. Figure 10A shows a secondary electron image of a metal structure of example A₁₀. Figure 10B shows a characteristic X-ray image of distributed iron, in which distributed white insular agglomerates indicate iron. Figure 10C shows a characteristic X-ray image of distributed chromium, in which distributed grey insular agglomerates indicate chromium. Figure 10D shows a characteristic X-ray image of distributed nickel, in which distributed grey insular agglomerates indicate nickel. Figure 10E shows a characteristic X-ray image of infiltrant copper, in which white parts indicate copper. As apparent from Figures 10A to 10E, the particles of austenitic stainless steel SUS304 are bonded to each other, resulting in a porous matrix. Interstices of the porous matrix are infiltrated with copper, which results in a stout structure of the complex metal for the arc-rotating portion. Example A₁₁ of a complex metal for the arc-rotating portion possesses a composition consisting of 70% austenitic stainless steel SUS304 by weight and 30% copper by weight. Example A₁₂ of a complex metal for the arc-rotating portion possesses a composition consisting of 30% austenitic stainless steel SUS304 by weight and 70% copper by weight. Measurements of IACS electrical conductivity which were carried out on examples A₁₀ to A₁₂ of the complex metal for the magnetically arc-rotating portion established that: Example A₁₀, has 5 to 15% IACS electrical conductivity Example A₁₁, has 4 to 8%. Example A₁₂, has 10 to 30%. Examples A₁₀ to A₁₂ of the complex metal for the arc-rotating portion 13 and examples C₁ to C₃ of the complex metal for the contact-making portion 14 were respectively shaped to be the same as those described previously and were tested as before. Results of the test will be described hereinafter. The description will be specifically made with respect to the vacuum interrupter of a 19th embodiment which includes a pair of contact electrodes each consisting of an arc-rotating portion 13 made of example A₁₀, and a contact-making portion 14 made of example C₁. The arc-rotating portion and the contact-making portion of a contact electrode of a 20th embodiment are made of examples A₁₀ and C₂ respectively. Those of a 21st are made of examples A₁₀ and C₃. Those of a 22nd are made of examples A₁₁ and C₁. Those of a 23rd are made of examples A₁₁ and C₂. Those of a 24th are made of examples A₁₁ and C₃. Those of a 25th are made of examples A₁₂ and C₁. Those of a 26th are made of examples A₁₂ and C₂. Those of a 27the are made of examples A₁₂ and C₃. When performances of the vacuum interrupters of the 20th to 27th embodiments differ from those of the 19th, then points of difference will be specified. 11) Large current interrupting capability Interruption tests which were carried out at an opening speed within 1.2 to 1.5 m/s under a rated voltage of 12 kV, however, a transient recovery voltage of 21 kV according to JEC-181, established that the test vacuum interrupters interrupted 43 kA current. Moreover, interruption tests at an opening speed of 3.0 m/s under a rated voltage of 84 kV, however, a transient recovery voltage of 143 kV according to JEC-181, established that the test vacuum interrupters interrupted 32 kA current. Table 3 below shows the results of the large current interrupting capability tests which were carried out on the vacuum interrupters of the 19th to 27th embodiments. Table 3 also shows those of vacuum interrupters of 5th and 6th comparatives which include a pair of contact electrodes each consisting of a arc-rotating portion and a contact-making portion each having the same sizes as those of the contact electrodes of the 19th to 27th embodiments. The arc-rotating portion and the contact-making portion of the 5th comparative are respectively made of example A₁₀ and 20Cu-80W alloy. Those of the 6th comparative are made of example A₁₀ and Cu-0.5Bi alloy. 12) Dielectric strength In accordance with JEC-181 test method, impulse withstand voltage tests were carried out with a 30 mm inter-contact gap. The vacuum interrupters showed 280 kV withstand voltage against both positive and negative impulses with ±10 kV deviation. After 10 times interrupting 43 kA current of rated 12 kV, the same impulse withstand voltage tests were carried out, thus establishing the same results. After 100 times continuously opening and closing a circuit through which 80A leading small current of rated 12 kV flowed, the same impulse withstand voltage tests were carried out, thus establishing substantially the same results. Table 4 below shows the rsults of the tests of the impulse withstand voltage at a 30 mm inter-contact gap which were carried out on the vacuum interrupters of the 19th embodiment and on the 5th and 6th comparatives. 13) Anti-welding capability The same as in the item 8). 14) Lagging small current interrupting capability In accordance with the lagging small current interrupting test of JEC-181, a 30A test current of 84× 1.5 √3 kV was flowed through the stationary and movable contact electrodes 5 and 6. Current chopping values had a 3.9 average (however, δ n =0.96 and n=100). In particular the current chopping values of the vacuum interrupters of the 20th, 23rd and 26th embodiments had 3.7A average (however, δ n =1.26 and n=100), and those of the 21st, 24th and 27th embodiments had a 3.9A average (however δ n =1.50 and n=100). 15) Leading small current interrupting capability The same as in the item 10). The following limits were apparent with regard to the composition ratio of austenitic stainless steel in the complex metals for the arc-rotating portion of the 19th to 27th embodiments. Austenitic stainless steel below 30% by weight significantly decreased the dielectric strength and the mechanical strength and durability of the arc-rotating portion 13, so that it had to be thickened. On the other hand, austenitic stainless steel above 70% by weight significantly lowered interruption performance. The arc-rotating portions 13 of the 28th to 30th embodiments are each made of a complex metal consisting of a porous structure of austenitic stainless steel including many holes extending in the axial direction through the arc-rotating portions 13 at an areal occupation ratio of 10 to 90%, with copper or silver infiltrating the porous structure of the austenitic stainless steel. The complex metal possesses 5 to 30% IACS electrical conductivity, at least 294 MPa (30 kg/mm²) tensile strength and 100 to 180 Hv hardness. Complex metals for the arc-rotating portion of the 28th to 30th embodiments were produced by the following processes: The third infiltration process At first, a plurality of pipes of austenitic stainless steel, e.g., SUS304 or SUS316 and each having an outer-diameter within 0.1 to 10 mm and an inner diameter within 0.01 to 9 mm are heated at a temperature below a melting point of the austenitic stainless steel in a nonoxidizing atmosphere, e.g., a vacuum, or hydrogen, nitrogen or argon gas, thus bonded to each other so as to form a porous matrix of a circular section. Then, the resultant porous matrix to the circular section is placed in a vessel made of material, e.g., alumina ceramics, which does not interact with austenitic stainless steel, copper or silver. All the bores of the pipes are infiltrated with copper in the nonoxidizing atmosphere. After cooling, the result is a desired complex metal for the arc-rotating portion. The fourth infiltration process In place of the pipes in the third infiltration process, a plate of austenitic stainless steel which includes many holes directed vertically to the surfaces of the plate at an areal occupation ratio of 10 to 90% is used as a porous matrix. A desired complex metal for the arc-rotating portion was produced using the same subsequent steps as for the third infiltration process. Contact-making portions of the 28th to 30th embodiments are made of the complex metal fo the same composition as that of previous embodiments. Example A₁₃ of a complex metal for the arc-rotating portion possesses a composition consisting of 60% austenitic stainless steel SUS304 by weight and 40% copper by weight. Example A₁₃ of the complex metal for the arc-rotating portion 13 and examples C₁ to C₃ above of the complex metal for the contact-making portion were respectively shaped to be the same as those of the arc-rotating portion 13 and the contact-making portion 14 described previously and tested as a pair of contact electrodes. The results of the tests will be described hereinafter. The description will be made with respect to the 28th embodiment of the vacuum interrupter which includes a pair of contact electrodes each consisting of an arc-rotating portion made of example A₁₃, and a contact-making portion made of example C₁. The arc-rotating portion and the contact-making portion of the contact electrode of the 29th embodiment are made of examples A₁₃ and C₂ respectively. Those of the 30th embodiment are made of examples A₁₃ and C₃ respectively. When performances of the vacuum interrupters of the 29th and 30th embodiments differ from those of the 28th embodiment, then the points of difference will be specified. 16) Large current interrupting capability Interruption tests which were carried out at an opening speed within 1.2 to 1.5 m/s under a rated voltage of 12 kV, however, a transient recovery voltage of 21 kV according to JEC-181, established that the test vacuum interrupters interrupted 45 kA current. Moreover, interruption tests at an opening speed of 3.0 m/s under a rated voltage of 84 kV, however, a transient recovery voltage of 143 kV according to JEC-181, established that the test vacuum interrupters interupted 30 kA current. Table 5 below shows the results of the large current interrupting capability tests which were carried out on the vacuum interrupters of the 28th to 30th embodiments 17) Dielectric strength In accordance with JEC-181 test method, impulse withstand voltage test were carried out with a 30 mm inter-contact gap. The results showed 250 kV withstand voltage against both positive and negative impulses with ±10 kV deviation. After 10 times interrupting 45 kA current of rated 12 kV, the same impulse withstand voltage tests were carried out, thus establishing the same results. After continuously 100 times opening and closing a circuit through which 80A leading small current of rated 12 kV flowed, the same impulse withstand voltage tests were carried out, thus establishing substantially the same results. 18) Anti-welding capability The same as in the item 8). 19) Lagging small current interrupting capability The same tests as in the item 9) established that the vacuum interrupters of the 28th, 29th, and 30th embodiments of the present invention had respective 3.9A (δ n =0.96 and n=100), 3.7A(δ n 1.26 and n=100) and 3.9A (δ n =1.50 and n=100) averages of current chopping value. 20) Leading small current interrupting capability The same as in the item 10). In the complex metal for the arc-rotating portion of the 28th to 30th embodiments an areal occupation ratio below 10% for the holes of axial direction inth plate of austenitic stainless steel significantly decreased the current interrupting capability, on the other hand, an areal occupation ratio above 90% thereof significantly decreased the mechanical strength of the arc-rotating portion and the dielectric strength of the vacuum interrupter. The vacuum interrupters of the 28th to 30th embodiments possess better improved high current interrupting capability than the other embodiments. A vacuum interrupter in accordance with the present, teaching in which a contact-making portion of a contact electrode is made of a complex metal consisting of 20 to 70% copper by weight, 5 to 70% chromium by weight and 5 to 70% molybdenum by weight, and in which the arc-rotating portion of the contact electrode is made of the materials given below, possesses improved large current interrupting capability, dielectric strength, anti-welding capability, and lagging and leading small current interrupting capability, than a conventional vacuum interrupter of the magnetic arc-rotating type: Material for the arc-rotating portion: austenitic stainless steel of 2 to 3% IACS electrical conductivity, at leas 481 MPa (49 kg/mm²) tensile strength and 200 Hv hardness, e.g., SUS304 or SUS316, ferritic stainless steel of about 2.5% IACS electrical conductivity, at least 481 MPa (49 kg/mm²) tensile strength and 190 Hv hardness, e.g., SUS405, SUS429, SUS430, SUS430F or SUS434, martensitic stainless steel of about 3.0% IACS electrical conductivity, at least 588 MPa (60 kg/mm²) tensile strength and 190 Hv hardness, e.g., SUS403, SUS410, SUS416, SUS420, SUS431 or SUS440C a complex metal of 3 to 25% IACS electrical conductivity consisting of a 29 to 70% austenitic stainless steel by weight, 1 to 10% molybdenum or tungsten by weight, and a balance of copper, a complex metal of 3 to 25% IACS electrical conductivity consisting of a 29 to 70% ferritic stainless steel by weight, 1 to 10% molybdenum or tungsten by weight, and a balance of copper, a complex metal of 3 to 30% IACS electrical conductivity consisting of a 29 to 70% martensitic stainless steel by weight, 1 to 10% molybdenum or tungsten by weight, and a balance of copper, a complex metal of 3 to 30% IACS electrical conductivity consisting of a 29 to 70% austenitic stainless steel by weight, molybdenum and tungsten amounting in total to 1 to 10% by weight and either one amounting to 0.5% by weight, and a balance of copper, a complex metal of 3 to 30% IACS electrical conductivity consisting of a 29 to 70% martensitic stainless steel by weight, molybdenum and tungsten amounting in total to 1 to 10% by weight and either one amounting to 0.5% by weight, and a balance of copper, and a complex metal of 3 to 25% IACS electrical conductivity consisting of a 29 to 70% ferritic stainless steel by weight, molybdenum and tungsten amounting in total to 1 to 10% by weight and either one amounting ot 0.5% by weight, and a balance of copper. The complex metals listed above are produced by processes substantially the same as the first, second, third or fourth infiltration or sintering processes.

Claims: A vacuum interrupter comprising a pair of separable contact electrodes (5, 6), at least one of which consists of a generally disc-shaped arc-rotating portion (13) for magnetically rotating an arc formed on separation of said contact electrodes and a contact-making portion (14) projecting from an arcing surface of the arc-rotating portion (13) at a central portion of the arc-rotating portion (13), wherein the electrical conductivitiy of the arc- rotating portion (13) is around 17.27 % IACS and is lower than the electrical conductivity of the contact-making portion (14) of around 50 % IACS; wherein a plurality of slots (16) are formed in the arc-rotating portion, each of which extend radially and circumenferentially of the arc-rotating portion (13), and wherein the contact electrodes (5, 6) are enclosed in a vacuum-tight manner in a vacuum envelope which is electrically insulating, characterized in that said arc-rotating portion (13) of at least one (6) of the contact electrodes (5, 6) is made of a complex metal consisting of 30 to 70 % copper by weight and 30 to 70 % by weight of non-magnetic stainless steel and has 2 to 30 % IACS electrical conductivity, and said contact- making portion (14) of the one contact electrode (6) is made of material of 20 to 60 % IACS electrical conductivity, the conductivitiy of the arc-rotating portion (13) being always lower than the conductivitiy of the contact-making portion (14). A vacuum interrupter as defined in claim 1, wherein said arc-rotating portion (13) is made of material of 10 to 15 % IACS electrical conductivity. A vacuum interrupter comprising a pair of separable contact electrodes (5, 6), at least one of which consists of a generally disc-shaped arc-rotating portion (13) for magnetically rotating an arc formed on separation of said contact electrodes and a contact-making portion (14) projecting from an arcing surface of the arc-rotating portion (13) at a central portion of the arc-rotating portion (13), wherein the electrical conductivitiy of the arc- rotating portion (13) is around 17.27 % IACS and is lower than the electrical conductivity of the contact-making portion (14) of around 50 % IACS; wherein a plurality of slots (16) are formed in the arc-rotating portion, each of which extend radially and circumenferentially of the rac-rotating portion (13), and wherein the contact electrodes (5, 6) are enclosed in a vacuum-tight manner in a vacuum envelope which is electrically insulating, characterized in that said arc-rotating portion (13) of at least one (6) of the contact electrodes (5, 6) is made of a complex metal consisting of 30 to 70 % copper by weight and 30 to 70 % magnetic stainless steel by weight and has 2 to 30 % IACS electrical conductivity, and said contact-making portion (14) of the contact electrode (6) is made of material of 20 to 60 % IACS electrical conductivity, the conductivitiy of the arc-rotating portion (13) being always lower than the conductivitiy of the contact-making portion (14). A vacuum interrupter as defined in claim 3, wherein said arc-rotating portion (13) is made of a complex metal consisting of 30 to 70 % copper by weight and 30 to 70 % ferritic stainless steel by weight. A vacuum interrupter as defined in claim 3, wherein said arc-rotating portion (13) is made of a complex metal consisting of 30 to 70 % copper by weight and 30 to 70 % martensitic stainless steel by weight. A vacuum interrupter as defined in claim 3, claim 4 or claim 5, wherein said contact-making portion (14) is made of a complex metal consisting of 20 to 70 % copper by weight, 5 to 70 % chromium by weight and 5 to 70 % molybdenum by weight. A vacuum interrupter as defined in claim 2, wherein said non-magnetic stainless steel is an austenitic stainless steel of 2 to 3 % IACS electrical conductivity. A vacuum interrupter as defined in claim 4, wherein said ferritic stainless steel has about 2.5 % IACS electrical conductivity. A vacuum interrupter as defined in claim 5, wherein said martensitic stainless steel has about 3.0 % IACS electrical conductivity.

Inventors: KASHIWAGI YOSHIYUKI, KITAKIZAKI KAORU, NODA YASUSHI, KASHIWAGI, YOSHIYUKI, KITAKIZAKI, KAORU, NODA, YASUSHI
Applicants: MEIDENSHA ELECTRIC MFG CO LTD, KABUSHIKI KAISHA MEIDENSHA
Application year: 1984
Main classification: H01H1
IPC codes: H01H1, H01H33