- ^* ' The present invention relates to a vacuum 5 interrupter of high mechanical strength in which an arc is stably and uniformly distributed on surfaces of electrodes, and electro-magnetic repulsive force generated at the time of applying a large current is reduced. 10 BACKGROUND OF THE INVENTION

Usually, as shown in Fig. 1, a vacuum interrupter comprises a vacuum container (1) closed with end plates (21), (22), a pair of electrodes (30), (40) facing to each other and conductive rods (5), (6) provided through 15 said end plates (5), (6), and in which a bellows (7) is mounted on one electrode (6) to be movable in the axial direction without affecting air-tightness , and said electrodes (30), (40) are detachable and can be connected to each other. Further, a shield (8) is 20 provided to acquire evaporated metals. Said conductive rod (6) is driven by a drive mechanism not shown for switching operation of an electric circuit.

In such type of vacuum interrupter, it is well known that interruption performance can be improved by 25 stably and uniformly distributing the arc on the surfaces of the electrodes by applying a magnetic field in parallel to the arc, particularly when interrupting a large current arc. It is also known that when said electrodes (30), (40) are in a closed state, an 30 electro-magnetic repulsive force is generated due to the large current application, and a small gap is formed between said electrodes (30), (40), thereby generating a ₄ local arc which brings about welding or deteriorates the electrode surfaces, finally lowering withstand voltage 35 performance.

To meet the aforesaid interruption of large current arc and to reduce the electro-magnetic repulsive

force when applying a large current, a further vacuum interrupter has been proposed as shown in Fig. 2(a)-(c) (Japanese laid-open Patent Publication (unexamined) No.57-3327). Fig. 2 (a) is a side view showing an example of arrangement of electrodes in such prior vacuum interrupter, Fig. 2 (b) is a plan view in the direction of the arrow b-b, and Fig. 2 (c) is a plan view in the direction of the arrow c-c. In these drawings, reference numerals (50), (60) designate bridge conductors respectively fixed on the ends of the bridge conductors (5), (6). These bridge conductors (5), (6) are rectangular and projecting parts (51), (52), (61), (62) are respectively formed on both ends thereof. Numerals (30), (40) disignate a pair of electrodes connected electrically to each bridge conductor (50),

(60) on their outer peripheral back sides respectively. As shown in Fig.2 (b), (c), circular arc-shaped grooves (33), (34), (43), (44) serving as high resistance areas are formed on each electrode (30), (40) by cutting at required distances, thus circular arc-shaped electrode parts (31), (32) and (41), (42) serving as outside parts of the electrodes partitioned by these grooves (33), (34) and (43), (44) are formed. Said bridge conductor (50) is so arranged as to cross the grooves (43), (44), and the projecting parts (51), (52) and (61), (62) are electrically and mechanically connected to substantially central parts of said circular arc-shaped electrode parts (31), (32) and (41), (41).

Gaps between said bridge conductors (50), (60) and the electrodes (30), (40) are desired to be as small as possible, but it is necessary that the gaps are in a range in which the electrodes (30), (40) do not come in contact with the bridge conductors (50), (60) when the electrodes are butted to each other bringing about elastic deformation due to a mechanical force applied. The aforesaid electrode (30) and the bridge conductor (50) are respectively of the same configuration as the

electrode (40) and the bridge conductor (60), but the electrode (40) and the bridgre conductor (60) are so arranged as to face to the electrode (30) and the brdige conductor (50) by 90° respectively being deviated by 90° therefrom.

According to this prior art, when an opening operation is performed by an operation mechanism not shown, an arc is formed between the electrodes (30), (40), and a current i passes from the conductive rod (5) toward the conductive rod(6j. In this step, when an arc is formed between a point A of the electrode (30) and a point A' of the electrode (40), the current i passes from the conductive rod (5) to the arc point A by way of the bridge conductor (50), the projecting part (51) thereof, the circular arc part (31) of said electrode

(30) and a gap B between the grooves (33), (34). That is, a substantial one turn is formed by a current loop (5) →- (50) -* (51) →- (31) →- B→- A is formed. Since the (51) →.

(31) →- B →- A is a loop formed by the electrode itself, the loop is near the point A and a strong axial magnetic field is generated. In the same manner, the current i passes from the point A' of the other electrode (40) to the conductive rod (6) by way of a gap C between the grooves (43), (44) of the electrode (40), the circular arc-shaped electrode part (41), the projecting part ( 6j) and the bridge conductor ( 60. ) . That is, one turn is further formed by a current loop A ¹ - ^* - C ->- (41 ) -* (61)→- (60) →- ( 6) is further formed, and a magnetic field of the same axial direction as the foregoing loop is generated. Thus, a strong combined magnetic flux in the axial direction acts in parallel to the arc A-A ¹ as indicated by the arrow Φ in Fig. 2(a), effectively preventing emission and diffusion of ionized metals from the arc to outside, acquiring a sufficient amount of plasma particles and stabilizing the arc. In the event that an accidental large current should pass in the closed state, an electro-magnetic repulsive force is generated

at the contact points due to concentration of the current and acts to separate the electrodes (30), (40), but since the current direction from the projecting part (51) to the gap B in the electrode (30) is same as that from the gap C to the projecting part (61) in the other electrode (40), the circular arc-shaped electrode parts (31), (41) are strongly attracted to each other. Actually, in the closed state of said electrodes (30), (40), a lot of contact points are distributed in the electrode surfaces and a quite strong electro-magnetic attractive force is generated on all areas of the circular arc-shaped electrode parts (31), (32) and (41), (42), and therefore the electro-magnetic repulsive force due to the current concentration at the contact points are effectively prevented.

Thus, the electrode contact force applied to said electrodes (30), (40) can be greatly reduced by means of the operation mechanism not shown, and and the operation mechanism can be small-sized and light-weighted. According to the prior vacuum interrupter arranged as above, however, a serious problem exists in that, in the arc formed between the electrodes (30), (40), when the arc current is so large as to extend to the high resistance areas, i.e., the areas near the grooves (33), (34), (43), (44), the one turn current loop cannot be formed and the magnetic field necessary for the stable and uniform distribution of the arc is not formed.

It is, therefore, an object of the present invention to overcome the above-discussed problems of the conventional vacuum interrupter and to provide a novel vacuum interrupter, in which one turn is formed by an electric current loop generated in the electrodes, and a strong axial magnetic field can be generated while interrupting an eddy current passage. DISCLOSURE OF THE INVENTION

In order to achieve the foregoing object, there is provided according to the present invention a vacuum

interrupter, in which at least one of a pair of electrodes is provided with first high resistance areas formed passing through from a contact surface to a back side thereof at specified distances from a peripheral edge of the electrode and facing to each other and second high resistance areas extending from ends of the first high resistance areas toward a center of said electrode being not connected to each other, and in which outside parts of the electrode between the first high resistance areas and said peripheral edge are elctrically connected to a conductive rode on said back side of the electrode by way of a bridge conductor arranged over the first high resistance areas so that one turn is formed by a current loop passing through the electrode when an arc is formed anywhere on the electrode, preventing generation of an eddy current and generating a strong axial magnetic field thereby. BRIEF DESCRIPTION OF THE DRAWINGS' In the drawings forming a part of the present application,

Fig. 1 is a sectional view showing a prior vacuum interrupter;

Fig. 2 shows an electrode structure of the prior - vacuum interrupter, and wherein (a) is a side view; and (b), (c) are plan views;

Fig. 3 shows an electrode structure in accordance with an embodiment of the present invention, and wherein (a) is a side view; and (b), (c) are plan views;

Fig. 4 shows another embodiment of the present invention, and wherein (a) is a sectional view ; and (b) is a plan view;

Figs. 5 and 6 are plan view respectively showing further embodiments of the present invention;

Fig. 7 shows an electrode structure of a vacuum interrupter in accordance with a further embodiment of the present invention, and wherein ( ^* a) is a side view; and (b), (c) are plan views;

Fig. 8 shows a further embodiment of the invention, and wherein (a) is a sectional view; and (b) is a plan view;

Figs. 9 and 10 are plan views respectively showing further embodiments of the present invention;

Fig. 11 shows an electrode structure of in accordance with a further embodiment of the invention, and wherein (a), (d) are sectional views; and (b), (c) are plan views; Fig. 12 shows a further embodiment of the present invention, and wherein (a) is a sectional view; and (b) is a plan view and

Figs. 13 and 14 are plan views respectively showing further embodiments of the present invention. BEST MODES OF CARRYING OUT THE INVENTION

Referring now to the drawings, an embodiment of the present invention is described hereinafter. Fig. 3 (a) is a side view showing an electrode structure of a vacuum interrupter in accordance with an embodiment of the present invention, Fig. 3 (b) is a plan view in the direction of the arrow b-b in Fig. 3 (a), and Fig. 3 (c) is a plan view in the direction of the arrow c-c in Fig. 3 (a).

In the drawings, reference numerals (33), (34), (43), (44) denote high resistance areas formed on each electrode (30), (40) passing through from the contact surface to the back side thereof at specified distances from peripheral edges of the electrode (30), (40), and in this embodiment, the high resistance areas are arranged symmetrical to the center of each electrode forming a pair of grooves not connected to each other. Numerals (35) to (38), (45) to (48) denote second high resistance areas extending from both ends of the first high resistance areas (33), (34), (43), (44) toward the center of each electrode (30), (40), and in this embodiment, the second high resistance areas are linear grooves formed substantially perpendicular to bridge

conductors (50), (60). Each electrode (30), (40) is partitioned by the first and second high resistance areas (33) ^ (38), (45) 0, (48), thereby current passages (53), (54), (55), (56) toward outside parts (31), (32), (41), (42) of the electrodes (30), (40) and center parts thereof are formed. In this embodiment, width of each current passage (53) 56) is narrower than that of the bridge conductors (50), (60). The bridge conductors (50), (60) are arranged over the first high resistance areas (33), (34), (41), (42) to electrically and mechanically connect the outside parts (31), (32), (41), (42) to conductive rods (5), (6). The electrode (30) and the bridge conductor (50) are of the same configuration as the electrode (40) and the bridge conductor (50) respectively in this embodiment, but the electrode (40) and the bridge conductor (60) are so arranged as to face to the electrode (30) and the bridge conductor (50) respectively being deviated by 90° therefrom. According to the vacuum interrupter in the embodiment described above, when opening operation is performed by an operation mechanism not shown, an arc is formed between the electrodes (30), (40). In this step, when a current i passes from the conductive rod (5) toward the conductive rod (6) and the arc is formed between a point A of one electrode (30) and a point A' of the other electrode (40), the current i passes from the conductive rod (5) to the arc point A by way of the bridge conductor (50), the projecting part (51), the outside part (31) and the current passage (53). That is, a complete one turn is formed by a current loop (50) (51 ) -* (31)-* (53) A, and wherein since the (51)-- (31)-* (53)→-A is a loop formed by the electrode itself and situated near the arc point A, a strong axial magnetic field is generated. In the same manner, the current i passes from the other point A' of the electrode (40) to the conductive rod (6) by way of the current passage

(55), the outside part (41), the projecting part (61) and the bridge conductor (60). That is, a complete one turn is formed by the current loop A' -* (55) -* (41) -* (61) •* (60) -* ( 6) and the same axial magnetic field as the foregoing current loop is formed. Thus, a strong combined axial magnetic flux acts in parallel to the arc A-A' indicated by the arrow Φ in Fig. 3 (a), emission and diffusion of ionized metals to outside are effectively prevented and the arc is stabilized by acquiring a sufficient amount of plasma particles. In this connection, there is the possibility that an eddy current is generated in the electrodes (30), (40) generating a magnetic field in the reverse direction and reducing the effective axial magnetic field thereby, but in accordance with the present invention, since the passage of such eddy current is completely intercepted by the second high resistance areas (35) (38), (45) (48), the generation of the magnetic field in the reverse direction can be prevented without taking any particular measure to cope with the eddy current.

Fig. 4 (a), (b) shows another embodiment of the present invention, and wherein a thin electrode structure is attained by interposing a reinforcing member (57) between the brdige conductor (50) and the electrode (30) considering that electrode materals of high conductivity such as copper, silver used in general have disadvantages in view of mechanical strength and cost saving. An inside part (39) of the elctrode (30) is slightly projected to prevent application of mechanical force to the outside parts (31), (32) of the electrode and arm parts of the bridge conductor (50) when performing opening and closing. A material such as stainless steel of less conductivity than the electrode material is preferably used as the reinforcing member (57). It is also satisfiable to form the inside part (39) of the electrode (30) of an electrode material resistant to welding and high pressure, while forming

the outside parts (31), (32) of ordinary copper.

Although the inside part of the electrode is projected and further the reinforcing member is added in the foregoing embodiment, it is satisfiable that either one of such arrangements is employed.

Although only one electrode (30) and one bridge conductor (50) are shown in Fig. 4(a), (b), it is further satisfiable to have a structure in which both or either of the facing electrodes and the bridge conductors is arranged as shown in Fig. 4 (a), (b).

Although the arrangement in accordance with the present invention is applied to a pair of electrodes disposed in the vacuum container (1) in the foregoing embodiment, it is also satisfiable to aplly such arrangement to either one electrode. The axial magnetic field can be generated even when the first high resistance areas (33), (34) are formed linear as is done in the embodiment of Fig. 5 instead of being circular arc-shaped. - It is further preferable that, as shown in Fig. 6, the bridge conductor (50) is divided into three parts and the first high resistance areas are arranged to cross them, thereby increasing the area of generating the axial magnetic field. ^' In this case, the electrodes facing to each other are desired to be deviated by 60° from each other. It is further preferable that the bridge conductor is divided into more than three parts and the first high resistance areas are arranged to cross them. The high resistance areas in the embodiments described above can be formed by filling the groove (33) (38), (43) (48) with a high resistance material.

Referring now to Fig. 7, a still further embodiment is described hereunder. Fig. 7 (a) is a side view showing an elctrode structure of a vacuum interrupter in accorance with the embodiment of the present invention, Fig. 7 (b) is a plan view in the direction of the arrow b-b, and Fig. 7 (c) is a plan

view in the direction of the arrow c-c in Fig. 7 (a). In these drawings, reference numerals (33), (34), (43), (44) denote grooves for the first high resistance areas in the same manner as the preceding embodiment in Fig. 3 (a) to (c), but in this embodiment the grooves do not pass through the contact surfaces of the elctrodes (30), (40), and the grooves hve a certain depth from the back sides of the electrodes (30), (40) toward the contact surfaces and are formed at a certain distance from the peripheral edges of the electrodes (30), (40). In the same manner, reference numerals (35) -- (38), (45) '- (48) denote the second high resistance areas, but they do not pass through from the contact surfaces of the electrodes (30), (40) toward the back sides, and the grooves have a certain depth from the back sides of the electrodes

(30), (40) toward the contact surfaces. Numerals (59), (69) denote circular third high resistance areas formed inside the electrodes extending from the first high reistance areas (33), (34), (43), (44) toward the electrode peripheral edges and they are grooves in this embodiment.

According to the vacuum interrupter of this embodiment described above, when an opening operation is performed by an operation mechanism not shown, an arc A is formed between the electrodes (30), (40). This arc A is formed on all surfaces of the electrodes (30), (40) when the arc current is very large. In this step, the current i to passing from the conductive rod (5) toward the conductive rod (6), first passes from said conductive rod (5) being divided into two currents passing reversely to each other as shown in Fig. 7 (a), then passes through the circular arc-shaped electrode parts (31), (32) by way of the projecting parts (52), (53) as shown in Fig. 7 (b), and after passing through the the current passages (53) and (54) of the second high resistance areas (35), (37) and (36), (38), reaches the arc point A by way of the detachable connection

surface of the electrode (30). That is, four pairs of one turns are formed by four current loops (50) →- (51) -*

⁽ 31) - 53) →-A. (50) -* (51) - ^»■ (31) -* (54) -* A, ( 50) -* (52) +

(32) →- (53) →-A and ( 50) * (52 ) ÷ ( 32 ) -* ( 54 ) →- A. Since the loops (51) -*A and (52) -* A are formed by the electrode itself, these loops are near and a strong axial magnetic field is generated.

In the same manner, as shown in Fig. 7 (c), in the other electrode (40), the current i coming from the contact surfaces passes through the current passages (55) and (56) being divided into two currents, then passes through the circular arc-shaped electrode parts (41), (42) in the reverse direction, and after passing through the projecting parts (61) and (62), reaches the conductive rod (6) by way of the bridge conductor (60). That is, four pairs of one turns are formed by four current loops A -* ( 55 ) - ( 41 ) →- ( 61 ) * ( 60 ) -* ( 6 ) , A* (55) + (41) -* (62) -* (60) -* (6) , A→- (56) -* (42) -* (61) -* (60) ÷ (6) and A →- ( 56 ) -» ^• ( 42 ) - ^► ( 62 ) ^■ * ( 60 ) -» ^• ( 6 ) , and the ^' .axial magnetic field of the same direction as the preceding loops are further generated by each of them. Furthermore, the axial magnetic fields generated by each loop are in reverse directions one another as shown in Fig. 7 (b) - (c) and the magnetic fields in the center part of the elctrode axis are mutually offset. As a result, a residual magnetic flux affecting the extinction of ionized metals in the arc can be reduced. Accordingly, when a large current arc is formed, a strong axial magnetic field acts on almost all over the contact surfaces of the electrodes in parallel to the arc, thereby the arc is stably and uniformly distributed. Moreover, since the high resistance areas

(33) . (38) , (43) . (48), (59), (69) are not exposed on the contact surfaces and do not come in contact with the arc, local melting due to arc energy concentration can be effectively prevented.

A yet further embodiment of the present invention

is shown in Fig. 8 (a), (b), and wherein a thin electrode structure is attained by interposing a reinforcing member (57) between the brdige conductor (50) and the electrode (30) considering that electrode materals of high conductivity such as copper or silver used in general have disadvantages in view of mechanical strength and cost saving. An inside part (39) of the elctrode (30) is slightly projected to prevent application of mechanical force to the outside parts (31), (32) of the electrode and arm parts of the bridge conductor (50) when performing opening and closing. A material such as stainless steel of less conductivity than the electrode material is preferably used as the reinforcing member (57). It is also satisfiable to form the inside part (39) of the electrode (30) of an electrode material resistant to welding and high pressure, while forming the outside parts (31), (32) of ordinary copper. Although only one electrode (30) and one bridge conductor (50) are shown in Fig. 8(a), (b), it is further satisfiable to have a structure in which both or either of the facing electrodes and the bridge conductors is arranged as shown in Fig. 4(a), (b).

Although the arrangement in accordance with the present invention is applied to a pair of electrodes disposed in the vacuum container (1) in the foregoing embodiment, it is also satisfiable to aplly such arrangement to either one electrode.

The axial magnetic field can be generated even when the first high resistance areas (33), (34) are formed linear as is done in the embodiment of Fig. 9 instead of being circular arc-shaped.

It is further preferable that, as shown in Fig. 10, the bridge conductor (50) is divided into three parts and the first high resistance areas are arranged to cross them, thereby increasing the area of generating the axial magnetic field. In this case, the electrodes facing to each other are desired to be deviated by 60°

from each other. It is further preferable that the bridge conductor is divided into more than three parts and the first high resistance areas are arranged to cross them. The high resistance areas in the embodiments described above can be formed by impregnating a high resistance material in the groove (33) (38), (43) (48).

Referring now to Fig. 11, a still further embodiment is described hereunder. Fig. 11 (a) is a side view showing an elctrode structure of a vacuum interrupter in accorance with the embodiment of the present invention, Fig. 11 (b) is a plan view in the direction of the arrow b-b in Fig. 11 (a), Fig. 11 (c) is a plan view in the direction of the arrow c-c in Fig. 11 (a) and Fig. 11 (d) is an explanatory sectional view showing one electrode in Fig. 11 (a). In these drawings, reference numerals (103), (104), (123), (124) denote the first high resistance areas formed on each electrode (10), (20) facing to one another, passing through from the facing surfaces to back sides and keeping certain distances from the peripheral edges of the electrodes (10), (20), i.g., at about 20% of the diameter. In this embodiment, the first high resistance areas are formed of a grooves consisting of a pair of circular arc-shaped parts (103a), (104a), (123a), (124a) arranged substantially symmetrical to the center of each elcetrode and not connected to one another, and a linear parts (103b), (103c), (104b), (104c), (123b), (123c), (124b), (124c) extending from both ends of the circular arc toward the center of each electrode substantially perpendicular to the bridge conductors (50), (60) and not connected to one another. Numerals (107), (108) denote the second high resistance areas provided inside the first high resistance areas (103), (104), (123), (124), and, as shown in Fig. 11 (d), these second high resistance areas pass through the electrodes (10), (20) connecting an annular high resistance area of which

outer diameter is Dj, on the electrode back sides to an annular resistance area of which outer diameter is D ₂ (where D _x > D ₂ ) on the electrode facing sides. In the second high resistance areas of this embodiment, parallel annular parts (107a), (108a) are formed on the elctrodes back sides, while inclined annular parts (107b), (108b) are formed on the electrode facing sides toward the center of the electrode in continuation to the parallel annular parts (107a), (108a). The second high resistance areas are actualy formed of annular hollow grooves coaxial with the first high resistance areas (103), (104), (123), (124). Numerals (113), (133) denote contactors each projecting in a form of a ring of which inner diameter is D ₃ , i.e., concaves (114), (134) with their diameter D ₃ are formed on the center. The electrodes (5), (6) are connected to back sides of the contactors (113), (134) by way of cylindrical conductive members (115), (135) with their outer diameter ^' Ot for electical connection to the outside of the vacuum container. Since there is a relation of D_ > Dit between this outer diameter O n of the conductive members (115), (135) and the inner diameter D ₃ of the contactors (113), (133), the contactors (113), (133) come in contact with each other outside the diameter D n . Usually, these contactors (113), (133) are made of an alloy of low melting point material such as bismuth and copper of which mechanical strength is not high, and therefore in order to prevent the electrodes (10), (20) from deformation and breakage when they are opened and closed, reinforcing members (116), (136) of low conductivity and high mechanical strength as compared with a copper material, etc. are fixed to the back sides of the contactors (113), (133). Since the electrodes (10), (20) are disposed on the outer peripheries of the contactors (113), (133), the elctrodes are insulated from the contactors (113), (133) with high insulation material as compared with the spacing portion or copper

material forming the second high resistance areas (107), (108). Each electrode (10), (20) are partitioned by the first high resistance areas (103), (104), (123), (124) respectively. The bridge conductors (50), (60) are respectively arranged on the back sides of the electrodes over the first high resistance areas (103), (104), (123), (124) so that the electrode outside parts (10), (20) and (131), (132) are electrically and mechanically connected to the conductive rods (5), (6). In this embodiment, the electrodes (10), (20) are formed of an alloy of copper and chromium.

The electrode (30) and the bridge conductor (50) are of the same configuration as the electrode (40) and the bridge conductor (50) respectively in this embodiment, but the electrode (40) and the bridge conductor (60) are so arranged as to face to the electrode (30) and the bridge conductor (50) respectively being deviated by 90° therefrom. This is because a magnetic field formed by the- current passing through one electrode is in the same direction as a magnetic field formed by the current passing through the other electrode.

The vacuum interrupter arranged as above described performs a following operation. Since only the contactors (113), (133) are in contact state when turned on, the current passage is formed by the conductive rod (5), the conductive member (115), the contactors (113), (133), the conductive member (135) and the conductive rod (6) in order. In this step, the outer diameter DM. of the conductive members (115), (135) and the inner diameter D ₃ of the contactors (113), (133) are in the relation of D ₃ ≥ D-+ , the current does not pass linearly but is curved between the conductive members (115), (135) and the contactors (113), (133), thereby an arc formed after opening the electrodes being easily transferred. Further, as compared with the prior arts, since the current does not

pass through the electrodes (10), (20) and the bridge conductors (50), (60) during the current application, generation of Joule's heat is reduced. A Heat generated on the contact surfaces of the contactors (113), (133) is promptly discharged outside the vacuum container by way of the conductive members (115), (135).

When performing an opening operation, the current passes as indicated by the broken line in Fig. 11 (a) and an arc is formed between a point A of the contactor (113) and a point A' of the contactor (133). Since a force extruding the arc from the surfaces of the contactors (113), (133) outward is applied to the arc, the arc is transferred across the second high resistance areas (107) to ignite between points B, B ¹ on the surfaces of the electrodes (10), (20). In this step, since there is a difference between the outer diameter D _x of the back side of the electrode and the outer diameter D ₂ of the facing side, i.e., -Di > D ₂ in the second high resistance areas (107), (108), in addition to the cdurrent outwardly curved at the contactors

(113), (133), the inclined annular parts (107b), (108b) are formed on the facing sides, the arc is easily transferred from between the points A-A' to between the points B-B'. When the arc is ignited between the points B-B' of the electrodes (10), (20), the current i passes from the cunductive rod (5) to the point B by way of the bridge conductor (50), projecting part (111), outside part (10) of the elctrode and through between the liner parts (103c), (104c) in the first high resistance areas. The current i further passes from the point B' to the bridge conductor (60) through between the linear parts (123b), (124b) in the first high resistance areas and by way of the outside part (131) of the electrode and projecting part (141). That is, each one turn is formed by the current loop (50)+ (111)+ (101)+ B and B' + (131)+ (141)÷ (60) , and an axial magnetic field is generated. As a result,

an arc is stably and uniformly distributed on the surfaces of the electrodes, enabling interruption of large current thereby.

Fig. 12 (a), (b) are a sectional view and a plan view in the direction of the arrow b-b of a portion near one electrode of a vacuum interrupter in accordance with a yet further embodiment of the present invention. In this embodiment, each first high resistance area is formed into one circular arc and the bridge conductor (50) is transformed according to such configuration of the first high resistance areas. The applied current does not pass through the electrode (10) and the bridge conductor (50) and Joule's heat is not generated, either, in this embodiment. Accordingly the electrode (10) can be connected to the bridge conductor (50) at only one point in the projecting part (111). As a result, the current passing outside part of the first high resistance areas (104) is increased more than the foregoing embodiment, and it is possible to generate a stronger axial magnetic field resulting in improvement of the interruption performance.

Although only one electrode (30) and one bridge conductor (50) are shown in Fig. 12 (a), (b), it ^' is further satisfiable to have a structure in which both or either of the facing electrodes and the bridge conductors is arranged as shown in Fig. 12 (a), (b).

Although the arrangement in accordance with the present invention is applied to a pair of electrodes disposed in the vacuum container ( 1 ) in the foregoing embodiment, it is also satisfiable to aplly such arrangement to either one electrode. The axial magnetic field can be generated even when the first high resistance areas (33), (34) are formed linear as is done in the embodiment of Fig. 10 instead of being circular arc-shaped. it is further preferable that, as shown in Fig. 13, the bridge conductor (50) is divided into three

parts and the first high resistance areas are arranged to cross them, thereby increasing the area of generating the axial magnetic field. In this case, the electrodes facing to each other are desired to be deviated by 60° from each other considering the direction of the magnetic field. It is further preferable that the bridge conductor is divided into more than three parts and the first high resistance areas are arranged to cross them. The high resistance areas in the embodiments described above can be formed by filling the groove (33) - ^* - (38), (43) '- (48) with a high resistance material. In addition, it is satisfiable that the first high resistance areas have no linear parts perpendicular to the bridge conductors and toward the center of each electrode.

POSSIBILITY OF INDUSTRIAL UTILIZATION The present ^' invention can be utilized for vacuum interrupters.