Method for producing electrode material for vacuum circuit breaker, electrode material for vacuum circuit breaker and electrode for vacuum circuit breaker

Abstract

Provided are a method for producing an electrode material for a vacuum circuit breaker, whereby withstand voltage, high current interruption performance and capacitor switching performance can be improved; an electrode material for a vacuum circuit breaker; and an electrode for a vacuum circuit breaker. A contact material for an electrode for a vacuum circuit breaker has an integral structure consisting of a central member and a CuCr outer peripheral member, the central member having been produced as described above and comprising 30 to 50 wt % of Cu of a particle diameter of 20 to 150 m and 50 to 70 wt % of MoCr of a particle diameter of 1 to 5 m, while the outer peripheral member being formed of a material, which is highly compatible with the central member, shows excellent interruption performance and had high withstand voltage, and being provided outside the central member and fixed thereto.

Claims

1. An electrode material for a vacuum circuit breaker, comprising: a cup-shaped contact member fixed on an end face of a conductive rod; and a contact plate as an arcing portion, firmly fixed on an end face of said cup-shaped contact member, wherein the outer periphery of one end of said cup-shaped contact member has a plurality of slits that are slanted with respect to an axis forming an axial magnetic field type configuration, wherein said contact plate has an integrated one-body construction comprised of a central member and an outer peripheral member that is fixed firmly on the outer periphery of said central member, wherein said central member includes 30 to 50 wt % of Cu having a particle diameter of 20 to 150 m and 50 to 70 wt % of MoCr having a particle diameter of 1 to 5 m and said outer peripheral member is a CuCr material compatible with said central member.

2. The electrode material for vacuum circuit breaker according to claim 1, wherein said outer peripheral member is formed annularly using sintered alloy and said central member is formed in a disk shape using sintered alloy.

3. The electrode material for vacuum circuit breaker according to claim 2, wherein said central member has such a configuration that a circular copper plate is firmly fixed on said cup-shaped contact member side.

4. The electrode material for vacuum circuit breaker according to claim 1, said outer peripheral member is formed in a disk shape of hollow surface, and said central member is arranged in the recessed portion of the hollow surface of said outer peripheral member.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a micrograph of metal texture of the electrode material produced by the method for producing electrode material for vacuum circuit breaker by the present invention.

(2) FIG. 2 is an enlarged micrograph of the object shown in FIG. 1.

(3) FIGS. 3(a), 3(b), 3(c) are charts that indicate the results of the interruption rating test of the electrode material for vacuum circuit breaker by the present invention. The results are indicated in terms of arcing time vs. interruption current for the materials of different mixing ratio of MoCr.

(4) FIG. 4 is a schematic illustration of vertical cross sectional view of an embodiment of the electrode for vacuum circuit breaker by the present invention.

(5) FIG. 5 is a schematic illustration of vertical cross sectional view of another embodiment of the electrode for vacuum circuit breaker by the present invention.

(6) FIG. 6 is a schematic illustration of vertical cross sectional view of further another embodiment of the electrode for vacuum circuit breaker by the present invention.

(7) FIG. 7 is a chart that indicates the impulse voltage performance of the CuCr material and the CuCrMo material when the electrode separation of the electrode for vacuum circuit breaker is 12 mm.

(8) FIG. 8 is a chart that indicates the impulse voltage performance of the CuCr material and the CuCrMo material when the electrode separation of the electrode for vacuum circuit breaker is 20 mm.

EMBODIMENT 1

(9) The following explains the method for producing electrode material for vacuum circuit breaker and then the electrode material for vacuum circuit breaker. The producing of the electrode material for vacuum circuit breaker uses Mo powder and Cr powder as the chief material. Mo powder used is a commercially available Mo powder having a particle diameter of 0.8 to 6 m. Cr powder used is a thermite Cr (a metal Cr powder formed by thermite reduction) powder because an ordinary fine powder of Cr is not usable as it is easily-oxidizable. Thermite Cr powder should preferably have a particle diameter of about 40 to 80 m; however, a commercially available powder having a particle diameter of 40 to 300 m may be used. A commercially available thermite Cr powder is usable because the oxygen content of such thermite Cr powder is 500 to 1200 ppm, not over 1200 ppm.

(10) Mo powder and a thermite Cr powder are, as is detailed later, mixed together homogeneously at a mixing ratio of 1:1 or over, that is Mo:Cr=1:1 to 9:1, and satisfying the weight relation MoCr. According to the examination of an embodiment example, which is be mentioned later, preferable mixing ratio of MoCr is about 3:1. Whatever the mixing ratio is, existence of Cr, which works as an arc-resistant component, of about 5 to 15 wt % improves the high current interruption performance and the capacitor switching performance. Therefore, it becomes more suitable as an electrode material for a vacuum breaker.

(11) The method for producing the electrode material for vacuum circuit breaker by the present invention is comprised of the steps: mixing Mo powder and thermite Cr powder homogeneously, pressure molding the resultant mixture under the specified press pressure to form a molded article, press-sintering the molded article by heating to a specified temperature to form a partially sintered article; infiltrating Cu into the partially sintered article obtained in the press-sintering step by placing a thin Cu plate on the partially sintered article and heating them to a predetermined temperature so that Cu is infiltrated into the partially sintered article.

(12) To explain more specifically, preparing Mo powder and thermite Cr powder which fulfill the above-mentioned conditions, the first process mixes these materials homogeneously to obtain a mixture. In the subsequent process, which is the press-sintering step, the mixture is put in the metallic mold having a predetermined form and undergoes a short-time pressing at a pressure of 1 to 4 t/cm.sup.2 to obtain the molded article. The molded article is sintered by being maintained at a temperature of 1100 to 1200 C. for 1 to 2 hours in a heating furnace to form a partially sintered article (skeleton) of MoCr alloy.

(13) In the final process, which is the Cu infiltrating process, the partially sintered article of MoCr alloy undergoes the infiltrating process, in which a thin Cu plate, the wettability of which is highly compatible with such MoCr alloy, is placed thereon and they are maintained at a temperature of 1100 to 1200 C. for 1 to 2 hours in a heating furnace for infiltration. Thereby, Cu having several tens m of grain diameter can be infiltrated homogeneously into the fine-textured sintered base material of MoCr alloy by liquid-phase sintering.

(14) The sintering conditions, that is, the temperature is to be 1100 to 1200 C. with the retention time of 1 to 2 hours, in producing the partially sintered article can be otherwise determined for more suitable heating temperature and retention time length depending on the mixing ratio of Mo powder and thermite Cr powder. Likewise, the Cu infiltration conditions, that is, the temperature is to be 1100 to 1200 C. with the retention time being 1 to 2 hours, can be otherwise properly determined for more suitable heating temperature and retention time length depending on the degree of Cu infiltration.

(15) (Embodiment Example of Electrode Material for Vacuum Circuit Breaker and Comparison Example)

(16) Table 1 lists embodiment examples and a comparison example. The embodiment examples are electrode materials, which are listed as Samples No. 1 to No. 12, produced by the method that the present invention defines, which method is comprised of the mixing step, the press-sintering step, and the Cu infiltration step. The comparison example, which is listed as Sample No. 13, is an electrode material for vacuum circuit breaker manufactured by a conventional method using CuCr as the main constituent.

(17) TABLE-US-00001 TABLE 1 Compac- tion Contact Brinell Content Mo:Cr pressure resis- hard- Evalua- Sample (w/t %) Mixing on MoCr tance ness tion No. Cu Mo Cr ratio (t/cm.sup.2) () (HB) result No. 1 40 45 15 3:1 4 4.5 260 No. 2 30 63 7 9:1 4 7.2 197 No. 3 37 50 13 About 4 8.4 229 4:1 No. 4 41 45 14 About 3 2.6 182 3:1 No. 5 51 38 11 About 1 3.6 99 3:1 No. 6 34 33 33 1:1 4 5.2 179 No. 7 41 30 29 About 3 3.4 205 1:1 No. 8 55 23 22 About 1 3.8 158 1:1 No. 9 28 18 54 1:3 4 8.0 154 X No. 10 36 16 48 1:3 3 6.0 191 X No. 11 52 12 36 1:3 1 4.3 148 X No. 12 59 31 10 About 0 5.0 93 X 3:1 No. 13 50 50 4.8 80 X

(18) Electrode materials for vacuum circuit breakers from Samples No. 1 to No. 12 were prepared by mixing MoCr homogeneously at the mixing ratio indicated in Table 1. Except Sample No. 12, the mixture thus prepared for each of Samples No. 1 to No. 11 was press-formed by compacting at pressures of 1 t/cm2 as a minimum to 4 t/cm2 as a maximum and then sintered by being maintained at a temperature of 1150 C. for 1.5 hours in a heating furnace to form a partially sintered article of MoCr alloy. And then, a thin Cu plate was placed on the partially sintered article and they were maintained at a temperature of 1150 C. for 1.5 hours in a heating furnace for infiltration to disperse homogeneously Cu into MoCr alloy so that Cu would be contained in each sample at the weight-% content ratio as indicated in Table 1.

(19) The electrode material for vacuum circuit breaker produced by the method described above has such a texture that Cu having a particle diameter of 20 to 150 m (black portion) is dispersed in the MoCr alloy of fine texture having a particle diameter of 1 to 5 m (white portion) in which Cr is diffused and firmly fixed on Mo particles, as FIG. 1 (a micrograph of 100 magnification) and FIG. 2 (a micrograph of 500 magnification) show. It is estimated that this is a result of the infiltration of Cu into the voids generated by the diffusing and firmly fixing of Cr, on which Mo particles adhere, during infiltrating.

(20) In Samples No. 1 to No. 5 in Table 1, the mixing ratios of Mo:Cr are about 3:1, 9:1, or about 4:1; and the weights in the mixture is Mo>Cr, and the compaction pressures are different, that is, 4 t/cm2, 3 t/cm2, or 1 t/cm2. However, the contact resistances of them are lower than that of Sample No. 13, a conventional material; and the Brinell hardness of them are high. Thus, they were judged suitable () for the electrode material for vacuum circuit breaker. Samples No. 6 to No. 8 are samples the mixing of which are about 1:1, wherein the compacting pressure was varied in the same manner as those described above. Contact resistances and Brinell hardness of them were judged acceptable () for using as the electrode material for vacuum circuit breakers.

(21) However, as for electrode materials like Samples No. 9 to No. 11, the Mo:Cr mixing ratio of which is 1:3 namely the weights in the mixture is Mo<Cr, the judgments on such materials were unusable because performance were not satisfactory. Further, even for an electrode material like Sample No. 12, the Mo:Cr mixing ratio of which is 3:1 but without applying compacting pressure by a press on MoCr, the judgment on such materials was unusable (x) because performance were not satisfactory.

(22) FIGS. 3(a) to 3(c) show the results of the rating test of the CuCrMo electrode material for vacuum circuit breaker produced by the above-stated method defined in the present invention, wherein the test was performed at 36 kV with 31.5 kA. The mixing ratios of the electrode materials put under the test were as follows: 3:1 (Mo: 45 wt %, Cr: 15 wt %), 4:1 (Mo: 50.6 wt %, Cr: 12.6 wt %), and 9:1 (Mo: 63.7 wt %, Cr: 7.1 wt %). Each of them were produced by compacting pressure of 4 t/cm2. A circle in the chart represents that the test result was successful in the circuit opening (or breaking) test for examination of the performance under the conditions: closing the circuit under no-load and opening the circuit with a load connected. A square in the chart represents that the test result was successful in the circuit closing-opening test for examination of the performance under the conditions: closing the circuit with a load connected and opening the circuit with the load connected. A cross and a triangle in the chart represent that the test results in the circuit opening test and the circuit closing-opening test were not successful respectively. Where Mo content is rich, electrode materials by the present invention demonstrated successful interruption performance in the circuit opening even under a high current interruption (kA) and a long arcing time (ms) as FIGS. 3(a) to 3(c) clearly shows.

(23) Table 2 lists the results of a test on the capacitor switching performance of the materials namely a solid phase sintered CuCr material (Cu 50 wt %), which is a conventional material, and a infiltrated CuCrMo material (Mo:Cr=3:1, compacting pressure 4 t/cm2), which is a material by the present invention. The test was conducted in the manner of the circuit opening test (indicated with O) and the circuit closing test (indicated with C) under such a severe testing conditions for the comparison purpose as described in the table.

(24) TABLE-US-00002 TABLE 2 Conventional CuCr Invented CuCrMo material material Cu50 wt % Cr Mo:Cr = 3:1 4 t/cm.sup.2 Solid-phase sintered Infiltrated Count of re-arcing or 3/10 1/48 re-ignition/Test count (Test was discontinued due to frequent re-ignition) Probability of re-arcing 30% 2.1% or re-ignition Testing condition C-O C 55 kV/3x2 = 44.9 kV 4000 A-425 Hz (4.0 kA-417 Hz) 0 55 kV//3x 1.4 400 A

(25) As Table 2 shows clearly, the probability of re-arcing or re-ignition in the conventional material was 30% because the count of the re-arcing or re-ignition/test count was 3/10 until the test was discontinued due to frequent re-ignition. In contrast to this, the probability of re-arcing or re-ignition in the material by the present invention was 2.1%, that is, the count of the re-arcing or re-ignition/test count of the material was 1/48; this means that the invented material has an excellent capacitor switching performance with very low probability of re-ignition.

(26) In the producing method that the present invention defines, an electrode materials for vacuum circuit breaker is produced by a method in which Mo powder and thermite Cr powder are mixed and sintered to obtain MoCr alloy of fine texture and Cu, the wettability of which is highly compatible with the fine alloy texture, is infiltrated into voids in the alloy. This method is capable of ensuring that the quantity of Cu in the alloy is a specified certain level by dispersing uniformly Cu having several tens m of grain diameter in the fine-textured sintered base material of MoCr alloy. Thus, in contrast to the conventional electrode material of 50-50 wt % of mixing ratio of CuCr for vacuum circuit breaker, the increase in contact resistance is suppressed without lowering the interruption performance of the electrode material for vacuum circuit breaker.

(27) Further, this electrode material for vacuum circuit breaker, though it is a MoCr alloy having a composite texture that includes larger amount of the arc-resistant component, has an improved performance in the high current interruption performance because of its texture being fine. Moreover, the withstand voltage and the capacitor switching performance thereof are improved because the hardness of the contact can be enhanced.

EMBODIMENT 2

(28) Next, an electrode for vacuum circuit breaker by the present invention illustrated in FIG. 4 that uses the above-stated electrode material is explained hereunder. An electrode 10 of axial magnetic field type on the fixed side or moving side has a cup-shaped contact member 12 fixed on the end of a conductive rod 11. A part of the outer periphery of the cup-shaped contact member 12, which part is on the opposite side of the conductive rod 11, has a plurality of slits 13 that are slant with respect to the axis, which form current paths as a coil portion similarly to the conventional art. On the end face of the cup-shaped contact member 12 where the slits 13 are formed, a contact plate 14 is firmly fixed. The face of the contact plate 14 contacts with another contact plate on the other electrode to flow current; on the other hand, arcing on the face of the contact plate 14 on current interruption when electrodes open the circuit.

(29) By the present invention, the contact plate 14 is given an integrated two-parts-combined configuration. The outer portion of the plate is comprised of an outer peripheral member 21 having annular shape and the inner portion of the plate is comprised of a central member 22 having a disk-like shape; they are firmly combined to form the contact plate 14. Moreover, in such configuration, materials of the outer peripheral member 21 and the central member 22 are different. That is, the outer peripheral member 21 is produced using a high withstand voltage material with a good withstand voltage performance against IMP and the central member 22 is produced using a high current interruption capable material.

(30) As the high withstand voltage material for producing the outer peripheral member 21, a CuCr material, which is a heat resisting material, is used, wherein the CuCr material is an alloy processed so that the material includes Cr in the weight ratio range between 40 wt % or more and 60 wt % or less and has a texture in which fine grained Cr is dispersed. Discharge on the contact plate 14 due to IMP occurs in the outer periphery of the plate where the electric field intensity is high. In most cases, the concentration of the electric field usually appears in the outside area off from 80% of the diameter of the contact plate 14. Therefore, the outer peripheral member 21 is produced considering these aspects. It should be noted that a stainless steel or a CuCrMo alloy of low Mo content is also a usable material.

(31) As the high current interruption capable material for producing the central member 22, above-stated CuCrMo material, in which Cu is infiltrated into a fine-textured sintered alloy of MoCr, is used. This CuCrMo material is a sintered alloy obtained by mixing Mo and Cr followed by subsequent processes, wherein the mixing ratio in powder is Mo:Cr=1:1 to 9:1 and the weight relation is MoCr. The material includes 30 to 50 wt % of Cu having grain diameter of 20 to 150 m. and 50 to 70 wt % (MoCr) of a fine-textured MoCr alloy having particle diameter of 1 to 5 m and has a high current interruption capability. The electrode 10 of axial magnetic field type is usually intended to extinguish arc by dispersing the arc to the area within about 80% of the diameter of the contact plate 14. Therefore, the central member 22 is produced to have a diameter of 70 to 80% of the diameter of the contact plate 14.

(32) Performances of the central member 22 of the CuCrMo material and the outer peripheral member 21 of the CuCr material are such that the CuCrMo material exceeds the CuCr material in terms of the high current interruption performance and the capacitor switching performance and the CuCrMo material is inferior to the CuCr material in terms of IMP withstand voltage performance. Use of the CuCr material as a high withstand voltage material and the CuCrMo material as a high current interruption capable material are determined according to the IMP test results shown in FIG. 7 and FIG. 8.

(33) The results of IMP tests, one with a gap of 12 mm and the other with a gap of 20 mm, are shown in FIG. 7 and FIG. 8 respectively. The CuCr material, the performance of which is indicated by an open circle, does not cause flashover irrespectively of the gap distance until the testing voltage is significantly increased and the number of applied voltage is increased. This means that the material has sufficient withstand voltage performance voltage. On the other hand, the CuCrMo material, the performance of which is indicated by a filled circle, causes flashover at a far lower test voltage than that of the CuCr material and at a less number of applied voltage, indicating that the withstand voltage is low. From this, the CuCr material, which is a high withstand voltage material, is used in such a portion of the contact plate 14 as is required to have a higher withstand voltage.

(34) The contact plate 14 can be produced by a method for example wherein the outer peripheral member 21 formed in an annular shape using a sintered alloy and the central member 22 formed in a disk-like shape similarly using a sintered alloy are combined and silver brazed into a one-piece body. Or alternatively, it can be produced by a method using a metal mold wherein the outer periphery of the metal mold is filled with the CuCr powder and the central part of the same is filled with the CuCrMo powder and then filled powders are press-compacted and sintered to form a one-piece body.

(35) In the electrode 10 of axial magnetic field type, the intensity of the electric field around the outer periphery of the contact plate 14 particularly in the area outside 80% of the diameter of the contact plate becomes high at the time of arcing as stated above. This causes the concentration of the electric field, which may develop easily into the re-ignition of arc. Therefore, the outer edge of the outer peripheral member 21 is beveled to a large extent as shown in FIG. 4 for relaxation of the concentration of electric field.

(36) Since the above-stated configuration of the electrode 10 of axial magnetic field type is such that the center portion of the contact plate 14 is made of a central member of a high current interruption capable material, the use of such electrode improves the high current interruption performance and the capacitor switching performance. Further, since the outer peripheral member of a high withstand voltage material, which is highly compatible with the central member and has an excellent interruption performance, is used in the periphery where the electric field is intense, the withstand voltage performance is therefore more improved.

EMBODIMENT 3

(37) Next, an embodiment of the electrode for vacuum circuit breaker, which is another example of the present invention, is explained referring to FIG. 5. An electrode 10 of axial magnetic field type in the figure has a contact plate 14 comprised of a CuCr outer peripheral member 21 having annular shape and a CuCrMo central member 22, which are integrated into a one-piece body similarly to the example shown in FIG. 4. The central member 22 of the CuCrMo sintered alloy, a high current interruption capable material, is given a different thickness.

(38) As FIG. 5 shows, the thickness of the central member 22 of the CuCrMo sintered alloy made of a high current interruption capable material is reduced and a circular-shaped copper plate 23 having a thickness equal to the decrement in such thickness reduction is used. The CuCrMo material used in the central member 22 has a high resistance. Therefore, the member is preferred to be thin; a use with a thickness of 1 to 2 mm is realistic when an electrode consumption is taken into account. The annular-shaped CuCrMo central member 22 of sintered alloy is arranged on the circular-shaped copper plate 23 and firmly fixed thereto, and the face thereof on the copper plate 23 side is firmly fixed to the cup-shaped contact member; other features are the same as those in the construction shown in FIG. 4.

EMBODIMENT 4

(39) An embodiment of the electrode for vacuum circuit breaker, which is further another example of the present invention, is explained referring to FIG. 6. In this example, an outer peripheral member 21 of a contact plate 14 of an electrode 10 of axial magnetic field type is formed in a disk-like shape having a hollow surface using a high withstand voltage material. In the recessed portion of the hollow surface on the outer peripheral member 21, a central member 22 produced using a sintered alloy having high current interruption capability is arranged to form a one-piece body.

(40) When constructing the contact plate 14 using the CuCr outer peripheral member 21 and the CuCrMo central member 22 made of a sintered alloy, they can be produced separately followed by combining and firmly-fixing process. Instead, another producing steps are feasible, wherein the method is comprised of the steps: charging sintering alloy powder of high withstand voltage material in a mold, pressing the powder into a disk-like shape having a hollow surface, placing a sintered alloy of high current interruption capable material in the hollow surface and pressing them together, and sintering to form a one-piece body.

(41) The electrode 10 thus configured as FIG. 6 shows can also attain the same effect as the examples stated above have. Further, when both the central member 22 and the CuCr outer peripheral member 21 are produced using sintered alloy, it brings such an advantage that the contact plate 14 can be easily produced.

(42) The present invention is useful because the invention is applicable not only to those vacuum circuit breakers explained in the embodiments stated above but also to those vacuum circuit breakers having other configuration.