Vacuum Circuit Interrupter

1. Field of the Invention

The present invention relates to a vacuum interrupter having a highly evacuated vessel containing a pair of electrode contacts which are in contact with each other when the vacuum interrupter is closed and with one of the electrode contacts being separated from the other electrode contact when the vacuum interrupter is open, an arc shielding member surrounding both the electrode contacts so as to prevent generation of metal vapor due to arcing between the electrode contacts during the opening and closing operation, and a cylindrical insulating envelope with metallic end plates located at the ends of the insulating envelope in which the pair of electrode contacts and the arc shielding member are contained in a highly evacuated state.

2. Statement of the Prior Art

A conventional vacuum interrupter comprises:

(1) an insulating envelope having a metallized portion covered by a metal suitable for hermetically brazing each of upper and lower ends thereof;

(2) a first metallic end plate brazed to the upper end of the insulating envelope;

(3) a second metallic end plate brazed to the lower end of the insulating envelope;

(the insulating envelope, first metallic end plate, and second metallic end plate constituting a vacuum vessel)

(4) a stationary electrode holder extending through the center of the first metallic end plate and brazed thereat to the first metallic end plate;

(5) a movable electrode holder extending through the center of the second metallic end plate so as to move vertically with one end thereof brazed to one end of a bellows whose other end is brazed to the center of the second metallic end plate;

(6) a stationary electrode contact brazed to the inner end of the stationary electrode holder;

(7) a movable electrode contact brazed to the inner end of the movable electrode holder; and

(8) a cylindrical arc shielding member extended so as to surround both the stationary and movable electrode contacts, one end thereof being brazed to the second metallic end plate.

In such a conventional vacuum interrupter, the insulating envelope is formed of ceramics or crystallized glass (which is also called Devitro ceramics, glass ceramics, or devitrified glass). Such a material has a higher mechanical strength and superior heat resistance of 600.degree. C. or more. The end plates to be brazed to the insulating envelope have a thermal expansion coefficient different from that of the insulating envelope. After brazing a residual stress is, therefore, generated so that the insulating envelope may be destroyed since its mechanical strength is weaker than that of the end plates.

To cope with the problem described above, each end plate is formed of an alloy of iron and nickel (abbreviated Fe-Ni alloy) or iron, nickel, and cobalt (abbreviated Fe-Ni-Co alloy). Such alloys have substantially the same thermal expansion coefficient as ceramic or crystallized glass. A brazing alloy of 72% of silver and 28% of copper equal in solidus and liquidus temperature is frequently used as the brazing agent. If a brazing alloy including a component of silver is used, the brazing alloy penetrates and diffuses into the Fe-Ni alloy or Fe-Ni-Co alloy of the end plates to cause cracking, so that the reliability of the hermetic seal is lowered in the vacuum interrupter. Consequently, brazing alloys including silver cannot be used. Fe-Ni and Fe-Ni-Co alloys are magnetic materials and each end plate is positioned perpendicularly with respect to each electrode holder through which a current passes so that the magnetic flux passes perpendicularly through each end plate and the amount of induced flux is increased and a large eddy current is developed in each end plate. Consequently, each end plate exhibits a considerable temperature rise due to eddy current losses. This is particularly noticeable in the case of a vacuum interrupter with a large current rating. Furthermore, the use of cobalt is expensive and therefore an Fe-Ni-Co alloy is also expensive. As compared with the Fe-Ni-Co alloy, the Fe-Ni alloy is inexpensive but the difference of thermal expansion coefficient from that of ceramics or crystallized glass is relatively large and residual stresses will be easily generated.

With the above-described problems in mind, it is an object of this invention to provide a less expensive vacuum interrupter for electric power, which avoids large temperature rises in the metallic end plates and avoids failure of the vacuum vessel of the vacuum interrupter when using a brazing metal including an alloy of silver and another brazing metal.

To achieve the present invention, there is provided a vacuum interrupter having a vacuum vessel comprising: (a) a first metallic end plate made of corrosion-free copper at the edge thereof, brazed to one metallized end of an insulating envelope; (b) a second metallic end plate also made of corrosion-free copper at the edge thereof, brazed to the other metallized end of the insulating envelope; (c) a stationary electrode holder extending through the first metallic end plate and having a stationary electrode contact brazed at the inner end thereof; (d) a movable electrode holder extending through the second metallic end plate so as to move in a given direction and having a movable electrode contact at the inner end thereof; (e) a bellows made of an iron and chromium alloy, with one end brazed to the movable electrode holder and the other end to the second metallic end plate; and (f) an arc shielding member made of the iron and chronium alloy or of copper, located within the insulating envelope so as to surround both the stationary and movable electrode contacts, one end brazed to the second metallic end plate.

All of the objects, features, and advantages of the present invention will be understood from a reading of the specification taken with the claims and drawings in which:

FIG. 1 shows an axial cross-sectional view of a conventional interrupter in the closed state;

FIG. 2 shows an axial cross sectional view of a vacuum interrupter of a first preferred embodiment in accordance with the principles of the present invention with the electrode contacts in their closed position;

FIG. 3 shows a vertically sectioned perspective view of the end plate located around the movable electrode holder of the vacuum interrupter of the first preferred embodiment shown in FIG. 2;

FIG. 4 shows a graph representing the relationship between the temperature and the tensile strength and elongation rate of annealed copper;

FIG. 5 shows an axial cross-sectional view of a vacuum interrupter of a second preferred embodiment in accordance with the principles of the present invention with the electrode contacts in their closed position;

FIG. 6 shows an axial cross-sectional view of the end plate located around the movable electrode holder of the vacuum interrupter of the second preferred embodiment shown in FIG. 5;

FIG. 7 shows an axial cross-sectional view of a vacuum interrupter of a third preferred embodiment in accordance with the principles of the present invention with the electrode contacts in their closed position;

FIG. 8 shows a vertically sectioned perspective view of the second metallic end plate located around the movable electrode holder of the vacuum interrupter of the third preferred embodiment shown in FIG. 7;

FIG. 9 shows an axial cross-sectional view of a vacuum interrupter of a fourth preferred embodiment in accordance with the principles of the present invention with the electrode contacts in their closed position;

FIG. 10 shows an axial cross-sectional view of a vacuum interrupter of a fifth preferred embodiment in accordance with the principles of the present invention with the electrode contacts in their closed position;

FIG. 11 shows a partially sectioned perspective view of the first metallic end plate located around the stationary electrode holder of the vacuum interrupter of the fifth preferred embodiment shown in FIG. 10;

FIG. 12 shows a partially sectioned perspective view of the second metallic end plate located around the movable electrode holder shown in FIG. 10;

FIG. 13 shows an axial cross-sectional view of a vacuum interrupter of a sixth preferred embodiment in accordance with the principles of the present invention with the electrode contacts in their closed position;

FIG. 14 shows an axial cross-sectional view of a vacuum interrupter of a seventh preferred embodiment in accordance with the principles of the present invention with the electrode contacts in their closed position;

FIG. 15 shows a partially sectioned perspective view of the second metallic end plate located around the movable electrode holder of the vacuum interrupter shown in FIG. 14;

FIG. 16 shows an axial cross-sectional view of a vacuum interrupter of an eighth preferred embodiment in accordance with the principles of the present invention with the electrode contacts in their closed position;

FIG. 17 shows a partially sectioned perspective view of the second metallic end plate located around the movable electrode holder shown in FIG. 16;

FIG. 18 shows an axial cross-sectional view of a vacuum interrupter of a ninth preferred embodiment in accordance with the principles of the present invention with the electrode contacts in their closed position;

FIG. 19 shows an axial cross-sectional view of a vacuum interrupter of a tenth preferred embodiment in accordance with the principles of the present invention with the electrode contacts in their closed position;

FIG. 20 shows a sectioned perspective view of the arc shielding member of the vacuum interrupter of the tenth preferred embodiment shown in FIG. 19;

FIG. 21 shows a sectioned perspective view of the bellows of the vacuum interrupter of the tenth preferred embodiment shown in FIG. 19;

FIG. 22 shows a sectioned perspective view of the arc shielding member of a vacuum interrupter of an eleventh preferred embodiment in accordance with the principles of the present invention;

FIG. 23 shows a sectioned perspective view of the bellows of a vacuum interrupter of the eleventh preferred embodiment in accordance with the present invention; and

FIG. 24 shows an axial cross-sectional view of part of a vacuum interrupter of a twelfth preferred embodiment in accordance with the present invention particularly indicating the brazing position for a single brazing operation.

Referring first to FIG. 1, a conventional vacuum interrupter VI is shown including:

(a) an insulating envelope 1 having a metallized layer 2 at each end thereof, the metallized layer 2 being previously metallized on each end with a suitable metal to provide a hermetic seal after brazing;

(b) a first metallic end plate 3 located on the upper end of the insulating envelope 1 brazed to the corresponding metallized layer 2 of the insulating envelope 1 (all brazing being shown at numerals 11);

(c) a second metallic end plate 4 located on the lower end of the insulating envelope 1, brazed to the corresponding metallized layer 2 of the insulating envelope 1;

(d) a stationary electrode holder 5 having a portion brazed to a central hole in the first metallic end plate 3 and extending vertically into the vacuum vessel formed by the first and second metallic end plates 3 and 4 and insulating envelope 1;

(e) a movable electrode holder 6 having an upper end brazed to a bellows 7, which bellows is brazed to a central hole in the second metallic end plate 4 and extends vertically into the vacuum vessel;

(f) a stationary electrode contact 8 brazed to the inner end of the stationary electrode holder 5;

(g) a movable electrode contact 9 brazed to the inner end of the movable electrode holder 6; and

(h) a cylindrical arc shielding member 10 located within the vacuum vessel so as to surround the stationary and movable electrode contacts 8 and 9.

In FIG. 1, each numeral 11 indicates in a dotted marks or solid line, denotes the places where a brazing is performed to provide hermetic seals and form the vacuum interrupter.

In such a vacuum interrupter as described above, the insulating envelope 1 is formed of ceramic material or devitro ceramics (hereinafter referred to as a crystallized glass) because of its greater mechanical strength and superior heat resistance of 600.degree. C. or more. If, however, the thermal expansion coefficient of the end plates 3 and 4 is considerably different from that of the material used for the insulating envelope 1, a residual stress is generated so that the insulating envelope 1 may break since the mechanical strength of the insulating envelope 1 is weaker than that of the end plates 3 and 4. Therefore, the end plates 3 and 4 are made of an alloy of iron and nickel (hereinafter referred to as an Fe-Ni alloy) or of iron, nickel, and cobalt (hereinafter referred to as an Fe-Ni-Co alloy). Although a brazing metal is used consisting of 72% silver and 28% copper equal in solidus liquidus temperature and which is easy to braze, a brazing metal including silver penetrates and diffuses into the Fe-Ni or Fe-Ni-Co alloy used for these metallic end plates. Consequently, the hermetic reliability of the vacuum interrupter is reduced. For this reason, it is inconveniently impossible to use such a brazing metal including silver.

Since Fe-Ni and Fe-Ni-Co alloys are magnetic materials and the end plates 3 and 4 are disposed perpendicularly with respect to the corresponding electrode holders 5 and 6, magnetic flux passes perpendicularly into the end plates 3 and 4 increasing the induced magnetic flux. Consequently, each end plate 3 and 4 develops a large amount of eddy current and an abrupt rise in temperature arises due the eddy currents. This problem becomes more noticeable as the current rating of the vacuum interrupter increases. Furthermore, Fe-Ni-Co alloy is expensive due to the high price of cobalt. As compared to a Fe-Ni-Co alloy, Fe-Ni alloy is inexpensive but the difference of the thermal expansion coefficient from ceramics or crystallized glass is relatively large so that residual stresses in the ceramics or crystallized glass are generated easily.

With reference to the drawings of FIGS. 2 through 24, preferred embodiments of the vacuum interrupter in accordance with the principles of the present invention will be described hereinafter.

FIG. 2 and 3 show a vacuum interrupter of the first preferred embodiment according to the present invention.

In FIG. 2, numeral 12 denotes an insulating envelope made of the same material as described with FIG. 1, with upper and lower ends which have metallized layers 12a that are made of a metal which is suitable for forming a hermetical seal by brazing. The temperature range within which vacuum brazing is possible is from 600.degree. C. to 1050.degree. C. or more (hereinafter the contents of brackets indicate the possible vacuum brazing temperature range described above). Numerals 13 and 14 denote a first and second metallic end plate each brazed to the corresponding end of the insulating envelope 12. Each end plate 13 and 14 is formed of corrosion-free copper (600.degree. C. to 1200.degree. C. or more). In addition, the first metallic end plate 13 has substantially the same profile as the second metallic end plate 14; that is, an inwardly bent recess 13a or 14a at the center of each end plate 13 and 14 having a hole 13c or 14c in each recess 13a or 14a respectively, and another inwardly bent recess 13b or 14b near the edge of each end plate 13 or 14 attached to each metallized layer 21 of the insulating envelope 12. It will be seen that the end plates 13 and 14 and the insulating envelope 12 constitute a vacuum vessel. Numerals 15 and 16 denote a stationary electrode holder and movable electrode holder, respectively. These holders 15 and 16 are made of corrosion-free copper Cu. The stationary electrode holder 15 is inserted through the hole 13c and brazed to the recess 13a of the stationary end plate 13 by a flange 15a of the stationary electrode holder 15. The movable electrode holder 16 is inserted through the hole 14c of the second metallic end plate 14 so as to move in its axial direction. Numeral 17 denotes a bellows, an upper end of which is connected to the upper part of the movable electrode holder 16 by brazing. The lower end of bellows 17 is connected to the edge of the recess 14a of the second metallic end plate 14 by brazing. Numerals 18 and 19 denote a stationary electrode contact and a movable electrode contact respectively, brazed to the inner end of the stationary electrode holder 15 and to the inner end of the movable electrode holder 16, respectively. Each electrode contact 18 and 19 is formed of a copper alloy (600.degree. C. to 1050.degree. C. or more), a silver alloy (600.degree. C. to 900.degree. C. or more), or a beryllium alloy (600.degree. C. to 1200.degree. C. or more). Numeral 20 denotes an arc shielding member made of an alloy of iron and chromium (hereinafter referred to as a Fe-Cr alloy), e.g., stainless steel (900.degree. C. to 1200.degree. C. or more) or copper (600.degree. C. to 1050.degree. C. or more). Each numeral 21 denotes a brazed joint. It will be appreciated from FIG. 2 that the brazed joint 21 using the brazing material is sandwiched between each metallized layer 12a of the insulating envelope 12 and metallic end plate 13 and 14. It should be noted that the lower limit of the brazing temperature range is 600.degree. C. because of the limitations of the vacuum brazing material used and the lowest temperature in the deoxidation of the base metal. Furthermore, it should be noted that the higher limit of the brazing temperature range is, e.g., 1200.degree. C. or more, since a value of more than the higher limit, e.g., more than 1200.degree. C. is possible for brazing but in actual practice, the value of the indicated higher temperature limit is assumed to be the higher limit of the brazing temperature range.

In the vacuum interrupter described above, the end plates 13 and 14 are formed of copper for the following reason:

Whereas the thermal expansion coefficient of copper is 16.7.times.10.sup.-6 /.degree.C., that of the ceramics or crystallized glass forming the insulating envelope 12 is from 7 to 9.times.10.sup.-6 /.degree.C. (the thermal expansion coefficient of the aluminous ceramics used commonly is approximately 8.times.10.sup.-6 /.degree.C. and of the Fe-Ni and Fe-Ni-Co alloys are from 4.5 to 5.5.times.10.sup.-6 /.degree.C. Therefore, if the insulating envelope 12 is brazed to the end plates 13 and 14, residual stress may be developed after brazing due to the difference between the thermal expansion coefficients so that the insulating envelope 12 may break.

When the insulating envelope 12 and the first and second metallic end plates 13 and 14 are, however, brazed under a vacuum pressure below 10.sup.-4 Torr and at a temperature ranging from 600.degree. C. to 1050.degree. C., it has been indicated that a hermetic seal can be performed by brazing without failure, the mechanical life of the closing and opening operations is 0.5 million or more times, and that ambient temperatures from -40.degree. C. to 100.degree. C. can be sufficiently endured. The reason for this is that the end plates are annealed during the brazing operation.

FIG. 4 shows the relationship between the temperature, tensile strength, and elongation of annealed copper. The tensile strength decreases as the temperature rises, whereas the elongation rate increases as the temperature rises. Therefore, annealed copper easily deforms plastically. After the brazing at a temperature from 600.degree. C. to 1050.degree. C., the brazing metal is solidified to form a hermetic seal between the insulating envelope 12 and each end plate 13 and 14. When the temperature decreases, the end plates 13 and 14 deform plastically so that thermal stress between each end plate 13 and 14 and the insulating envelope 12 is not developed and neither the insulating envelope 12 nor the brazed joints 21 are broken. When the temperature further decreases and drops below approximately 200.degree. C., each end plate 13 and 14 is transformed from plastic deformation to elastic deformation so that the annealed copper of each end plate 13 and 14 takes the same state as under a hardened treatment, and increases its mechanical strength. If the brazing between the insulating envelope 12 and each plate 13 and 14 is performed under an reducing atmosphere, such as hydrogen, the brazing is further facilitated. In this case, a getter material for adsorbing hydrogen is required to be installed within the insulating envelope 12. It will be seen that each end plate 13 and 14 can be manufactured easily by pressing. It will also be seen that two recesses 13a and 13b or 14a and 14b are provided in each end plate 13 and 14 so that an increase of axial mechanical strength and a relaxation of diametrical thermal stress and mechanical stress can be achieved.

When the vacuum interrupter described above is manufactured, the brazing temperature is required to be 900.degree. C. or more since the bellows 17 (and the arc shielding member 20) is formed of a Fe-Cr alloy. In this case, if each stationary and movable electrode contact 18 and 19 is formed of a copper alloy or beryllium alloy, a single brazing operation permits the brazing of all the members of the vacuum interrupter under a vacuum pressure below 10.sup.-4 Torr and at a temperature from 900.degree. C. to 1050.degree. C.

As an alternative, the brazing of the bellows 17 and the arc shielding member 20 with other corresponding members is performed in a hydrogen atmosphere or under a vacuum pressure below 10.sup.-4 Torr at a temperature ranging from 900.degree. C. to 1050.degree. C. After inspection of each brazed joint, brazing with other corresponding members may be performed at a temperature ranging from 600.degree. C. to 900.degree. C. and under a vacuum pressure below 10.sup.-4 Torr.

FIGS. 5 and 6 show a vacuum interrupter of a second preferred embodiment according to the present invention.

Numerals 22 and 23 denote first and second metallic end plates made of corrosion-free copper, respectively. The first metallic end plate 22 is provided with a hole 22a at its center through which the stationary electrode holder 24 is inserted and to which the holder 24 is brazed as shown by numeral 21 and a plurality of recesses 22b are provided on the first end plate 22 with a given angular distance to engage with the circumference of the insulating envelope 12. The second metallic end plate 23 is provided with a hole 23b at its center through which the movable electrode holder 16 is inserted, a lip 23a bending inwardly from the hole 23b to which the bellows 17 is brazed, and a plurality of recesses 23c with a given angular distance around the circumference thereof to engage with the insulating envelope 12. The stationary electrode holder 24 is made of corrosion-free copper. Other constructions, actions and manufacturing methods are the same as in the first preferred embodiment described hereinbefore.

FIGS. 7 and 8 show a vacuum interrupter of a third preferred embodiment according to the present invention. Numeral 25 denotes an insulating envelope made of ceramics or crystallized glass. The insulating envelope 25 is provided with a circular groove 25a and 25b at each end thereof where a metallized layer 25c is formed; with the first groove 25a at the upper end and the second groove 25b at the lower end. Numerals 26 and 27 denote a first metallic end plate and second metallic end plate, respectively. At the center of the first metallic end plate 26 is a hole 26a through which the stationary electrode holder 24 is inserted into the vacuum vessel and to which the holder 24 is brazed as indicated by numeral 21. A lip 26b, which is inwardly bent at substantially a right angle, is brazed into the circular groove 25a and to the metallized layer 25c of the insulating envelope 25. In addition, the second metallic end plate 27 is provided with a hole 27a at the center thereof to which the bellows 17 is fitted and brazed and through which the movable electrode holder 16 is inserted so as to move in its axial direction. A circular recess 27b is formed along the periphery of the hole 27a so as to be fitted and brazed to the circular end indicated by numeral 21, of the arc shielding member 20. A lip 27c, which is bent inward is formed at the periphery of the second end plate 27 so as to be fitted and brazed in the circular groove 25b to the metallized layer 25c of the insulating envelope 25. Since in the vacuum interrupter of this construction the edge of the first and second metallic end plates 26 and 27 is brazed to the circular grooves 25a and 25b respectively, the voltage withstanding characteristics of the vacuum circuit interrupter is improved during an open state of the electrode contacts and plastic deformation of the first and second metallic end plates 26 and 27 is made easier. The other constructions, actions, and manufacturing methods are substantially the same as those in the preferred embodiments described above.

FIG. 9 shows a fourth preferred embodiment according to the present invention. In FIG. 9, numeral 28 and 29 denote a first and second metallic end plate, respectively, made of corrosion-free copper. The first metallic end plate 28 is provided with a hole 28a at the center thereof through which the stationary electrode holder 24 is inserted and to which the holder 24 is brazed as indicated by numeral 21. The second end plate 29 has a hole 29a at the center thereof through which the movable electrode holder 16 is inserted so as to be able to move in its axial direction, a lip 29b at the center thereof bent inward to be brazed with the lower end of the bellows 17, a step 29c to which the lower end of the arc shielding member 20 is brazed, and a lip 29d bent inward along the periphery thereof so as to be fitted and brazed to the groove 25b provided at the lower end of the insulating envelope 25. In this vacuum interrupter VI, the steps 28b and 29c are provided in each end plate 28 and 29 respectively so that a reinforcement of axial mechanical strength and relief of radial stress can be achieved. The constructions, actions, and manufacturing methods are substantially the same as those in the other preferred embodiments described before.

FIGS. 10, 11, and 12 show a fifth preferred embodiment according to the present invention. In FIG. 10, numerals 30 and 31 denote first and second metallic end plates respectively which are partially bent inwardly and made of corrosion-free copper. The first metallic end plate 30 is provided with a hole 30a through which the stationary electrode holder 34 is inserted and to which the holder 24 is brazed as indicated by numeral 21, a plurality of elongated radial recesses 30b at a given angular distance from each other, and a lip 30c protruding inward from the periphery portion thereof to extend into the circular groove 25a of the insulating envelope 25 so as to be brazed therewith.

Similarly, the second metallic end plate 31 is provided with a hole 31a at the center thereof through which the movable electrode holder 16 is inserted so as to be able to move in its axial direction, a lip 31b bent inward from the hole 31a at the end of which the lower end of the bellows 17 is brazed, a plurality of relatively small recesses 31c at a given angular distance from each other to which the lower end of the arc shielding member 20 is brazed, and a lip 31d along the periphery which is bent inward to fit into the circular groove 25b to be brazed to the metallized portion 25c. In the vacuum interrupter VI each end plate 30 and 31 is bent toward the inside of the vacuum vessel at the edge 31d so that the strength of each end plate 30 and 31 increases. The other constructions, actions, and manufacturing methods are substantially the same as those in the other preferred embodiments.

FIG. 13 shows a sixth preferred embodiment according to the present invention. In FIG. 13, numeral 32 denotes an insulating envelope made of ceramics or crystallized glass at the outer peripheral surface of each end of which a metallized layer 32a is formed. Numerals 33 and 34 denote first and second metallic end plates made of corrosion-free copper, respectively. The first end plate 33 is provided with a hole 33a at the center thereof through which the stationary electrode holder 24 is inserted and to which it is brazed and a lip 33b bent slightly toward the outer peripheral surface of the insulating envelope 32 and to be brazed to the metallized layer 32a. Similarly, the second metallic end plate 34 is provided with a hole 34a at the center thereof through which the movable electrode holder 16 is inserted so as to be able to move in its axial direction, a lip 34b bent inward from the hole 34a at the upper end of which the bellows 17 is brazed, a plurality of recesses 34c at a given angular distance from each other so as to be brazed to the lower end of the arc shielding member 20, and a lip 34d bent upward to be brazed to the metallized layer 32a provided on the peripheral surface of the lower end of the insulating envelope 32. In this vacuum interrupter, a compression force is applied to the insulating envelope 32 due to the contraction of each end plate 33 and 34 after brazing. The ceramics material used in the insulating envelope 32 has, in particular, a larger strength against a compression force so that the vacuum interrupter VI is constructed as described above.

FIGS. 14 and 15 show a seventh preferred embodiment according to the present invention. In FIG. 14, numerals 35 and 36 denote first and second metallic end plates which are substantially flat discs made of corrosion-free copper, respectively. The first end plate 35 is provided with a hole 35a at the centre thereof through which the stationary electrode holder 24 is inserted and to which the holder 24 is brazed, and a flange 35b at the periphery thereof to which the metallized layer 12a of the insulating envelope 12 is brazed. On the other hand, the second metallic end plate 36 is provided with a hole 36a with at least one step through which the movable electrode holder 16 is inserted so as to be able to move in its axial direction and to which the lower end of the bellows 17 is brazed, a circular groove 36b provided coaxially with the hole 36a into which the lower end of the arc shielding member 20 is inserted and brazed to the lower end thereof, and a flange 36c at the periphery thereof to which the metallized layer 12a of the insulating envelope 12 is brazed. The first and second end plates 35 and 36 are formed by pressing or cutting. In this vacuum interrupter, both end plates 35 and 36 have so thick a wall that a sufficient strength can be provided without particular convex and concave indentations in either of the end plates 35 and 36. The other constructions, actions, and manufacturing methods are substantially the same as those in the preferred embodiments described above.

FIGS. 16 and 17 show a eighth preferred embodiment according to the present invention. In FIG. 16, numerals 37 and 38 denote first and second metallic end plates of relatively flat thick disks made of corrosion-free copper, respectively. The first metallic end plate 37 is provided with a hole 37a through which the stationary electrode holder 24 is inserted and to which the holder 24 is brazed as indicated by numeral 21, and a plurality of recesses 37b at the periphery thereof with which the internal end surface of the insulating envelope 12 is engaged. Similarly, the second metallic end plate 38 is provided with a hole 38a at the centre thereof through which the movable electrode holder 16 is inserted so as to be able to move in its axial direction, a plurality of recesses 38b near the hole 38a to which the lower end of the bellows 17 is brazed, and a plurality of recesses 38c along the periphery thereof to which the arc shielding member 20 is brazed. In this vacuum interrupter each end plate 37 and 38 is considerably thicker so that only relatively small diameter recesses 37b, 38b, and 38c need by provided. The other constructions, actions, and manufacturing methods are substantially the same as those in the other preferred embodiments described above.

FIG. 18 shows a ninth preferred embodiment according to the present invention. In FIG. 18, numeral 39 denotes a stationary end plate having an integrally formed stationary electrode holder 39a made of corrosion-free copper. Since there is no need to braze the stationary electrode holder 39a to the stationary end plate 39 the number of brazed joints are thereby reduced.

FIGS. 19 to 21 show a tenth preferred embodiment according to the present invention. In FIG. 19, numerals 40 and 41 denote first and second metallic end plates made of corrosion-free copper. The first end plate 40 is provided with a hole 40a at the center thereof through which the stationary electrode holder 40 is inserted and to which the holder 40 is brazed as indicated by numeral 21, and a circular recess 40b at the periphery thereof to which the inner surface of the upper end of the insulating envelope 12 is brazed. Similarly, the second metallic end plate 41 is provided with a hole 41a at the center thereof through which the movable electrode holder 16 is inserted so as to be able to move in its axial direction, a lip 41b around the hole 41a to which the lower end of the bellows 17 is brazed, and another circular recess 41c around the periphery thereof at the inner edge of which the lower end of the arc shielding member 20 is brazed and to the outer edge of which the lower end of the insulating envelope 12 is attached. When this vacuum interrupter VI is manufactured, the ends of the bellows 17 to be brazed and those of the arc shielding member 20 made of Fe-Cr alloy and having a high brazing temperature must be sintered after nickel plating 42 as is shown in FIGS. 20 and 21 and all the parts to be brazed at 21 are at a temperature ranging from 600.degree. C. to 900.degree. C. and under a vacuum pressure below 10.sup.-4 Torr.

FIGS. 22 and 23 show a eleventh preferred embodiment according to the present invention. In this embodiment, the ends of the bellows 17 and arc shielding member 20 are to be brazed are previously brazed with an auxiliary brazing metal made of copper at a temperature ranging from 900.degree. C. to 1050.degree. C. and under a vacuum pressure below 10.sup.-4 Torr. After the brazing operation described above, the brazing of the ends of the bellows 17 and arc shielding member 20 with other corresponding members of the vacuum interrupter VI is carried out at a temperature ranging from 600.degree. C. to 900.degree. C. and under a vacuum pressure below 10.sup.-4 Torr.

FIG. 24 shows a twelfth preferred embodiment according to the present invention. In this embodiment, the brazing of the lower ends of the bellows 17 and the arc shielding member 20 to the corresponding surfaces of the second end plate 41 and the other end of the bellows 17 with a brazing auxiliary member 44 is carried out at a temperature ranging from 900.degree. C. to 1050.degree. C. and under a vacuum pressure below 10.sup.-4 Torr. After the brazing operation described above, the brazing of the other members to the corresponding members described above as indicated also by numeral 21 is carried out at a temperature ranging from 600.degree. C. to 900.degree. C. and under a vacuum pressure below 10.sup.-4 Torr.

As described hereinbefore in the vacum interrupter according to the present invention each end plate is made of copper so that the brazing of each end plate with other corresponding members can be carried out at a temperature ranging from 600.degree. C. to 1050.degree. C. and under a vacuum pressure below 10.sup.-4 Torr in a hydrogen atmosphere using an arbitrary brazing metal since cracks do not develop in a copper member using a brazing metal including silver. In addition, copper is a non-magnetic material, so that a large eddy current is not generated due to magnetic flux caused by a flowing current and, therefore, the consequent rise in temperature does not appear in the end plates. It will, therefore, be appreciated that it is advantageous to use end plates made of copper instead of a Fe-Cr alloy in the vacuum interrupter. Furthermore, each end plate made of copper is easily shaped by means of pressing and is less expensive then if made of a Fe-Ni or Fe-ni-Co alloy. Although end plates made of copper have a considerably different thermal expansion coefficient from that of the insulating envelope made of ceramic or crystallized glass, such end plates are easily deformed due to the annealing treatment during brazing. Therefore, thermal stress generated between the end plate and insulating envelope is absorbed by the plastic deformation of each end plate so that the insulating envelope and the brazed joints will not be broken. Furthermore, the annealed copper is transformed from plastic deformation to elastic deformation when the temperature of the annealed copper drops below 200.degree. C. after brazing. At this time, each end plate exhibits a hardened state so that each end plate increases its mechanical strength and can withstand the impact generated when the vacuum interrupter is opened or closed.

It will be understood by those skilled in the art that the foregoing description is in terms of preferred embodiments of the present invention wherein various changes and modifications may be made without departing from the spirit and scope of the present invention, which is to be defined by the appended claims.