US3356818A

US3356818A - Contact assembly for a vacuum interrupter

Info

Publication number: US3356818A
Application number: US550731A
Authority: US
Inventors: Sugawara Hiroyuki
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1965-05-17
Filing date: 1966-05-17
Publication date: 1967-12-05
Anticipated expiration: 1984-12-05

Description

5, 1967 HIROYUKI SUGAWARA 3,356,818

CONTACT ASSEMBLY FOR A VACUUM INTERRUPTER Filed May 17, 1966 United States Patent 3,356,818 CONTACT ASSEMBLY FOR A VACUUM INTERRUPTER I-Iiroyuki Sugawara, Hitachi-shi, Japan, assignor to Hitachi, Ltd., Tokyo-to, Japan Filed May 17, 1966, Ser. No. 550,731 Claims priority, application Japan, May 17, 1965,

9 Claims. (Cl. 200-166) ABSTRACT OF THE DISCLOSURE The present disclosure relates to an improved contact structure for a vacuum interrupter which is based on the concept that a transference of an arc can be accomplished by a self induced magnetic transference force whose effect is enhanced by a change in curvature of the contact surfaces, and is especially useful for interruption of large AC currents by an interrupter of minimum size. The improved contact structure is comprised by a first electrode having a frusto-conical portion and a centrally located projecting end portion, with the frusto-conical portion defining a tapered contact face thereon. The projecting end portion is provided with a curved face the radius of curvature of which is shorter than that of the contact face of the frusto-conical portion. The contact structure is further comprised by a second electrode having a funnel-shaped portion and a closed-ended sleeve portion extended from the funnel-shaped portion at the bottom thereof. The funnel-shaped portion defines a complementary tapered contact face which coacts with that of the frusto-conical portion of the first electrode. The width of the contact faces is sufficienly large to provide an initial self induced magnetic transferring force to an are formed therebetween. The closed-ended sleeve portion defines a hollow cavity which opens into the bottom of the funnel-shaped portion and operatingly encloses the projecting end portion of the first electrode.

This invention relates to an improved contact structure for a vacuum interrupter which is especially useful for interruption of a large A.C. current by an interrupter of minimum size.

When a large A.C. current is interrupted, the developed arc should be transferred away from the contact face of the contact electrodes and eliminated as far as possible. For this purpose, a conventional interrupter is provided means for transferring the arc magnetically. Such magnetic arc transfer means generally are either of the selfmagnetizing type or the magnctizable type. The former utilizes the A.C. current to be interrupted as a source for the magnet means, and the latter utilizes a separate current source. They are, however, both complex in the structure thereof and further involve many difficulties such as, for example, maintaining high vacuum in an evacuated vessel, providing good electrical insulation in vacuum, manufacture of contact electrodes of a material which give off only a minimum amount of interfering gas, obtaining a suflicient mechanical strength for the contact electrodes, and manufacture within a vacuum bulb.

The present invention is established after many experiments and studies in dynamic'characteristics of arcs in vacuum.

The object of this invention is to provide a new and improved contact assembly for a vacuum interrupter utilizing a new type of structure for creating an arc transferring force.

Another object is to provide a new contact assembly having a new shaped contact electrode.

3,356,818 Patented Dec. 5, 1967 A further object is to provide an improved contact assembly that is especially fit for interruption of a large A.C. current with an interrupter of minimum size.

Before describing the present invention, the following facts should be recognized as a background of this invention.

Within a range of about 12-13 ka. of A.C. current to be interrupted, the arc eliminating condition should be varied in accordance with the amount of the A.C. current to be interrupted and the contact shape of the contact electrodes.

In case that a contact face has a circular shape, the following formula defines a boundary condition whether a small current arc or a large current are is developed:

in which (mm) is the diameter of the circular contact face and I (ka.) is the current.

On the other hand, where a contact face is a round band shape, the condition is provided as follows:

in which d (mm) is the width of the band face.

In case of either shape, a small current are would be developed if the width of the contact face exceeds the critical amount defined in Formulas I and II. Otherwise, a large current are would be developed. Therefore, if a circular shape contact face is more than 25 (mm) in diameter, it would be sufficient to be used for interrupting a current of 5 ka. with a small current arc.

A small current arc, in general, is defined as'a plurality of unit arcs of amperes each having a column shape of 10* (cm) in diameter. They repel one another and scatter zig-zag on the contact face; however, they have a tendency to move toward contact portions which have the shortest distance between the open contact faces. Moreover, each such contact portion should have enough area so that a small current are may scatter thereon as defined in Formula I or II. V

On the other hand, a large current are is defined to be a column of 7-9 (mm.) in diameter. This are would melt contact electrodes at the arc sustaining portions thereof if allowed to continue to exist between two portions for too great a period of time. Where such melting occurs, it interferes with the recovery of electric insulation between the separated contact electrodes, even if a gas evacuated metal is used as the electrode material, and this results in rendering the interrupter inoperable. Therefore, the arc should be transferred from one face portion to another on the contact face, not only to cool the contact face portions on which the arc is standing, but also to prevent the electrode from being melted too much. a

One of the most significant facts on which the present invention relies is the inventors experimental finding that a large current are may be transferable towards a sharply curved electrode portion, i.e., a portion having a short radius of curvature. During experiments of the inventor, the transference of an arc was found to'be much more influenced by the change ofcurvature of contact surface than by thechange of distance between contact electrodes. This transferring force on the arc was found to be produced by the change in curvature of the contact force and could be made to be bigger than the magnetic force of a conventional magnetic arc-drive system.

The large current are has a large inertia of transference thereof, so that it will not move easily at the starting time thereofand will. not stop easily once it is moving.

The large current are transfers linearly, so'that if the path on the surface along which the arc transfers should be curved, its transference might be interfered with. Therefore, the path, along which the arc transfers, should be straight.

In order to make the are move at a desired rate, it may be advisable to provide a difference in curvatures at different surface portions along the arc transferring path so as to tailor the transference force requirements.

Now the principle of this invention will be described by referring to the following detailed description when read in conjunction with the accompanying drawing, in which the single figure illustrated is a sectional view of one embodiment of this invention.

In this figure, 1 and 2 are a pair of physically separable contact electrodes disposed in an evecuated space and fabricated from a gas evacuated conductive metal. The electrode 1 is formed in a funnel shape having a tapered inside face 3, a bottom end portion 7 and an an nular top end portion 16. From the bottom end portion 7, a cylindrical sleeve portion 9 with a closing end 11 is integrally formed to provide a bore at the bottom of the funnel portion. The annular top end portion 16 is provided with an annular edge 13. This electrode 1 is connected to an electric conductor 14 for connection to a source of electric current in the usual manner.

The other electrode 2 is formed to have a frustoconical portion with a tapered face 4 thereon and a projecting end portion 6 at the center thereof. This electrode 2 is connected to an electric conductor 15. The tapers of respective faces 3 and 4 are provided to be the same, and the respective electrodes 1 and 2 are arranged to operatingly provide a face-to-face contact by the contact faces 3 and 4.

The widths or heights of the contact faces 3 and 4 are advised to be more than 12 mm., preferably 15-18 mm. Such widths are required for the following reasons. First, in case of interruption of less than 12-13 ka., the are becomes a small current are and requires a sufficient contact area as defined by the Formula II. Second, in case of interruption of a large current, the arc becomes a large current are and a continuous change in curvature of the contact surface for a sufiicient distance is required for providing an initial self produced magnetic transferring force to the arc to cause the arc to be moved from between the contact surfaces, 3 and 4 toward the projecting end portion 6 and into the bore 5.

The projecting end portion 6 is extended integrally from the top portion of frustoconical portion of the electrode 2. The top end of the projecting end portion 6 is shaped to form a spherical surface having a minimum radius of curvature. The projecting end portion 6 may be axially elongated. The curvature of the peripheral surface of the projecting end portion 6 is defined by a certain radius of curvature which may be longer than the minimum radius of curvature of the top spherical face 10 but shorter than that of the contact face 4.

Both the contact electrodes 1 and 2 are reciprocally moved axially by a controller, not shown. When the contact faces 3 and 4 are separated to interrupt AC. current, an arc would be developed therebetween. Where the arc is a small current are, a plurality of unit arc columns are transferred towards the bore 5 by a magnetic force originated by the current to be interrupted. Where the arc is a large current arc, an arc column is centripetally forced to move closer to the projecting end portion 6 By the difference in radius of curvature at contact face portions as discussed above. Also, as the two contact electrodes 1 and 2 separate, the distance between the contact faces 3 and 4 increases while the distance between the peripheral surface of projecting end portion 6 and the inside surface of bore portion 5 remains the same. This results in further forcing the are into bore portion 5. The annular edge portion 13 is formed to prevent any evaporated metal from spattering on an outer vacuum vessel, not shown.

According to this invention, the arc is caused to be transferred into the bore portion 5 as the two contacts 1 and 2 physically separate, so that spattering of evaporated metal is almost entirely included within the inside space of bore 5 rather than between the contacting electrode faces 3 and 4. Hence, proper operation of the interrupter is assured. As a further consequence, the vacuum vessel in which the contacts are disposed may be formed in a small size, and this contributes to minimizing the size of the over-all interrupter.

From the foregoing description, it can be appreciated therefore that the invention makes available a new and improved vacuum interrupter which is especially useful for interruption of a large A.C. current by an interrupter of minimum size.

Having described one embodiment of a vacuum interrupter constructed in accordance with the invention, it is believed obvious that other modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiment of the invention described which are within the full intended scope of the invention as defined by the appended claims.

I claim:

1. A contact assembly for a vacuum interrupter, comprising:

a first electrode having a frusto-conical portion and a centrally located projecting portion, said frusto-conical portion defining a tapered contact face thereon, said projecting portion providing a curved face the radius of curvature of which is shorter than that of said contact face of said frusto-conical portion, and

a second electrode havingv a funnel-shaped portion and a closed-ended sleeve portion extended from said funnel-shaped portion at the bottom thereof, said funnel-shaped portion defining a complementary tapered contact face to that of said frusto-conical portion of said first electrode, said frusto-conical portion and said funnel-shaped portion operatingly contacting one another at the contact faces the width of the contact faces being sufficiently large to provide an initial self induced magnetic transferring force to an arc formed therebetween, and said closed-ended sleeve portion defining therein a hollow cavity which opens into the bottom of said funnel-shaped portion and operatingly encloses therein said projecting portion of said first electrode the projecting portion of said first electrode being spaced-apart from the walls of the enclosing hollow cavity a fixed distance which is relatively short in comparison to the width of the contact faces.

2. A contact assembly as defined in claim 1, in which said projecting portion is in the form of a cylindrically shaped rod having a certain length and a spherically shaped end atop thereof, and said sleeve portion is formed in a surrounding cylinder portion closed at one end thereof and integrated to the bottom of said funnel-shaped portion at the other end thereof, said rod being centrally disposed in said cylinder and spaced apart therefrom a constant distance during closure of the contact faces of the assembly.

3. A contact assembly as defined in claim 1, in which said funnel-shaped portion further includes an annular edge portion extending from an upper end thereof.

4. A contact assembly as defined in claim 2, in which said funnel-shaped portion further includes an annular edge portion extending from an upper end thereof.

5. A contact assembly as defined in claim 2, in which the peripheral surface of the projecting end portion has a radius of curvature which is longer than the minimum radius of curvature of the spherically shaped end thereof and is shorter than the radius of curvature of the complementary tapered contact faces.

6. A contact assembly as' defined in claim 5 in which said funnel-shaped portion further includes an annular edge portion extending from an upper end thereof.

7. A contact assembly for a vacuum interrupter according to claim 1, in which the width of the contact faces is more than 12 mm.

8. A contact assembly for a vacuum interrupter according to claim 1 in which the width of the contact faces has a value which is more than 15 mm. and less than 18 9. A contact assembly for a vacuum interrupter, comprising:

a first electrode having a frusto-conic'al portion and a centrally located projecting portion, said frusto-conical portion defining a tapered contact face thereon, and

a second electrode having a funnel-shaped portion and a closed-ended sleeve portion extended from said funnel-shaped portion at the bottom thereof, said funnel-shaped portion defining a complementary tapered contact face to that of said frusto-conical portion of said first electrode, said frusto-conical portion and said funnel-shaped portion operatingly contacting one another at the contact faces, the width of the contact faces being sufiiciently large to provide an initial self induced magnetic transferring force to an arc formed therebetween, and said closed-ended sleeve portion defining therein a hollow cavity which opens into the bottom of said funnel-shaped portion and operatin'gly encloses therein said projecting portion of said first electrode.

References Cited UNITED STATES PATENTS ROBERT S. MACON, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

H. O. JONES, Assistant Examiner.

Claims

9. A CONTACT ASSEMBLY FOR A VACUUM INTERRUPTER, COMPRISING: A FIRST ELECTRODE HAVING A FRUSTO-CONICAL PORTION AND A CENTRALLY LOCATED PROJECTING PORTION, SAID FRUSTON-CONICAL PORTION DEFINING A TAPERED CONTACT FACE THEREON, AND A SECOND ELECTRODE HAVING A FUNNEL-SHAPED PORTION AND A CLOSED-ENDED SLEEVE PORTION EXTENDED FROM SAID FUNNEL-SHAPED PORTION AT THE BOTTOM THEREOF, SAID FUNNEL-SHAPED PORTION DEFINING A COMPLEMENTARY TAPERED CONTACT FACE TO THAT OF SAID FRUSTO-CONICAL PORTION OF SAID FIRST ELECTRODE, SAID FRUSTO-CONICAL PORTION AND SAID FUNNEL-SHAPED PORTION OPERATINGLY CONTACTING ONE ANOTHER AT THE CONTACT FACES, THE WIDTH OF THE CONTACT FACES BEING SUFFICIENTLY LARGE TO PROVIDE AN INITIAL SELF INDUCED MAGNETIC TRANSFERRING FORCE TO AN ARC FORMED THEREBETWEEN, AND SAID CLOSED-ENDED SLEEVE PORTION DEFINING THEREIN A HOLLOW CAVITY WHICH OPENS INTO THE BOTTOM OF SAID FUNNEL-SHAPED PORTION AND OPERATINGLY ENCLOSES THEREIN SAID PROJECTING PORTION OF SAID FIRST ELECTRODE.