US3858076A

US3858076A - Vacuum-type circuit interrupter with interleaving spiral electrodes

Info

Publication number: US3858076A
Application number: US00359497A
Authority: US
Inventors: G Mitchell
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1973-05-11
Filing date: 1973-05-11
Publication date: 1974-12-31
Anticipated expiration: 1991-12-31
Also published as: JPS5031368A; CA978247A; BR7403805D0

Abstract

A vacuum-type circuit interrupter comprises spaced-apart first and second electrode members, each comprising a metal sheet in the form of a spiral wound in turns about a longitudinal axis via a path that progressively recedes from said longitudinal axis as it winds thereabout. The longitudinal axes of the spirals are generally parallel to each other and their turns interleave in spaced relationship to each other, thus defining an interelectrode gap of spiral form between the electrode members. Means is provided for forcing most of the current flowing through a discharge across the gap to follow a path through the electrodes that enters one of the electrodes at the outer end of its spiral and leaves the other at the inner end of its spiral.

Description

1 States Patent 1 Mitchell [451 Dec. 31, 1974 [75] Inventor: Graham R. Mitchell, Willingboro,

[73] Assignee: General Electric Company,

Philadelphia, Pa.

[22] Filed: May 11, 1973 [21] Appl. No.: 359,497

[52] US. Cl. 313/217, 200/144 B, 313/231 [51] 1111. C1. 11-1101j 17/04 [58] Field of Search..... 200/144 B, 166 C; 313/217,

3,471,736 10/1969 Rich 313/217 Primary Examiner-H. A. Dixon Attorney, Agent, or Firm-William Freedman; J. Wesley Haubner [57] ABSTRACT A vacuum-type circuit interrupter comprises spacedapart first and second electrode members, each comprising a metal sheet in the form of a spiral wound in turns about a longitudinal axis via a path that progressively recedes from said longitudinal axis as it winds thereabout. The longitudinal axes of the spirals are generally parallel to each other and their turns interleave in spaced relationship to each other, thus defining an interelectrode gap of spiral form between the electrode members. Means is provided for forcing most of the current flowing through a discharge across the gap to follow a path through the electrodes that enters one of the electrodes at the outer end of its spiral and leaves the other at the inner end of its spiral.

8 Claims, 5 Drawing 1F igures BACKGROUND This invention relates to a vacuum-type circuit interrupter and, more particularly, relates to a vacuum circuit interrupter of the type that has an interelectrode gap across which there is established a diffuse arc which can carry relatively high currents without the formation of anode spots.

Examples of vacuum circuit interrupters of this type are disclosed in U.S. Pat. Nos. 3,679,474-Rich; 3,471,733-Rich; 3,471,734-Rich; and 3,471,736-Rich, all of which are assigned to the assignee of the present invention. Other prior art of interest is: U.S. Pat. Nos. 3,309,555-Lee et al.; 3,225,167-Greenwood; 2,056,609-Journeaux; and Japenese pat. No. 13164/1961.

Rich attributes the ability of certain vacuum interrupters to carry high currents through an arc discharge without forming anode spots to their ability to limit to a very low level the body force that acts on the conducticm paths through the arc discharge. The body force F is so limited by severely limiting the density? of the magnetic field component that extends transversely of the conduction paths through the are discharge. This follows because the body force is determined by:

where J is the current density and B is the flux density of the transverse magnetic field component.

Certain of the rior electrode configurations that limit the density B of the transverse magnetic field to a low level are characterized by limited surface areas over which the terminals of the arc discharge can spread out, e.g., the overlapping rod configuration of the above-mentioned U.S. Pat. No. 3,679,474-Rich. This necessitates using a relatively large number of overlapping pairs of rods for high current interrupters and, even then, the effective surface area is not as large as might be desired.

SUMMARY An object of my invention is to provide an electrode configuration that is capable of limiting the transverse magnetic field to a relatively low density and yet pro vides exceptionally large surface areas over which the arc discharge can spread out.

Another object is to achieve the immediately preceding object with an electrode configuration that makes especially effective use of a cylindrical volume, such as is typically present within the usual vacuum interrupter envelope.

In carrying out the invention in one form, I provide a highly evacuated envelope and spaced-apart first and second electrode members within the envelope. Each of these electrode members comprises a metal sheet in the form of a spiral wound in turns about a longitudinal axis via a path that progressively recedes from said longitudinal axis as it winds thereabout, the width of the sheet extending generally parallel to said longitudinal axis. The spirals are so positioned that their longitudinal axes are generally parallel to each other and their turns interleave in spaced relationship to each other, thereby defining an interelectrode gap of spiral form between said electrode members. Means is provided within said envelope for supplying an electron-ion plasma to said interelectrode gap, thus establishing a discharge across said gap. Means is also provided for forcing most of the current that flows through said discharge to follow a path through said electrodes that enters one of the electrodes at the outer end of its spiral and leaves the other of the electrodes at the inner end of its spiral.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. I is a sectional view through a triggered vacuum gap device embodying one form of my invention.

FIG. 2 is a sectional view taken along the line 2-2 of FIG. ll.

FIG. 3 is a diagrammatic view of a portion of FIG. 2 during the arcing period of the device of FIG. 2.

FIG. 4 is a sectional view in simplified form ofa vacuum switch with separable contacts embodying another form of the invention.

FIG. 5 is a sectional view along the line 44 of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawing, there is shown a vacu umtype circuit interrupter 10 comprising a sealed envelope llll evacuated to a pressure of 10 torr or lower. The envelope 111 comprises a cylindrical casing 12 of insulating material and a pair of metal end caps 13 and 114 suitably sealed to the opposite ends of casing 12.

The interrupter of FIG. I is a vacuum gap device comprising a pair of spaced-apart

electrode members

17 and 18. Each of the electrode members comprises a metal sheet in the form of a spiral wound in turns about a longitudinal axis extending longitudinally of envelope lll. The longitudinal axis of the spiral of electrode T7 is shown at 19 in FIG. 2 and that of the spiral of electrode 18 is shown at 20 in FIG. 2. The width of each sheet, which is the dimension extending between the top and bottom of envelope Ill, extends generally parallel to the longitudinal axis of its spiral. The thickness dimension of each sheet may be thought of as that dimension extending normal to the longitudinal axis of the spiral. The above-described width dimension is much greater than the thickness dimension. It will be apparent from the drawing, especially FIGS. 2 and 5, that the turns of each spiral electrode follow a path that generally progressively recedes from the longitudinal axis of the spiral as it winds thereabout.

The electrode members 17 and llS are so positioned that the longitudinal axes of their spirals are generally parallel to each other and their turns interleave in spaced relationship to each other, thus defining between the electrodes an interelectrode gap 22 of spiral form.

The end caps 13 and T4 serve as spaced-apart electrical terminals of the vacuum interrupter. The outer electrode 17 is electrically connected to upper end cap 13 through a conductive support element 25; and the inner electrode 1% is electrically connected to the lower end cap M through a conductive support ele ment 26. Conductive support element 25 is a short pin of high-conductivity metal such as copper suitably brazed at its opposite ends to end cap 13 and electrode 17. The other conductive support element 26 is also a short pin preferably of copper brazed at its opposite ends to end cap 14 and electrode 18. For reasons which will soon be explained, conductive pin 25 is located at the outer end of its spiral electrode 17, and the other conductive pin 26 is located at the inner end of its spiral electrode 18.

Conductive pins

25 and 26, in addi tion to serving as electrical connectors, also help to support their associated electrodes on their associated end caps.

Each electrode is further supported on its associated end cap by a plurality of spacers of low-conductivity material, such as shown at 27 and 28 in FIGS. 1 and 2. Spacers 27 help to support electrode 17 on upper end cap 13, and spacers 28 help to support electrode 18 on lower end cap 14. These

spacers

27 and 28 can be either of insulating material, as shown in FIGS. 1 and 2, or of a low-conductivity metal such as stainless steel. Because these

spacers

27 and 28 are of lowconductivity material, nearly all the current that flows between each electrode and its associated end cap is forced to follow a path through the highly-

conductive pin

25 or 26, as the case may be. To minimize the current flowing through each

spacer

27 or 28, the spacer is preferably provided with one or more circumferential grooves. The presence of such grooves reduces the likelihood that the outer surface of the spacer will become completely coated with metallic condensate from arcing products and also increases the resistance of the spacer if it is of metal.

The vacuum interrupter of FIGS. 1 and 2 is a normally non-conducting device that can be rendered conductive by developing an arc discharge between its

electrodes

17 and 18. The interrupter comprises a main gap 22 that normally has a high dielectric strength normally capable of withstanding the high voltage normally present between the

electrodes

17 and 18. For initiating an arc discharge between the

electrodes

17 and 18, I provide a trigger assembly 30 which, upon operation, develops a supply of electron-ion plasma that is injected into the main gap 22 between

electrodes

17 and 18. When this plasma enters the main gap, it drastically lowers the dielectric strength of the gap causing a dielectric breakdown of the gap, followed by an arc discharge across the gap. Current flows through the arc discharge until a natural current zero is reached, at which time the vacuum interrupter recovers its dielectric strength and prevents further current flow therethrough, thus interrupting the circuit. The abovementioned trigger assembly 30 can be of a conventional form and is therefore only briefly described. For more details of such a trigger assembly reference may be had to U.S. Pat. No. 3,465,162-Lafferty, assigned to the assignee of the present invention.

In general, the trigger assembly comprises a pair of

trigger electrodes

32 and 34 separated by a scored ceramic disc 35. When an electrical pulse is applied between the

electrodes

32 and 34 by a pulse source 36, a spark develops across the left hand surface of the ceramic disc. This spark vaporizes and ionizes some of the trigger electrode material, developing a conducting electron-ion plasma that is projected through an orifice 39 into the main gap 22.

In FIGS. 1 and 2, the trigger assembly isshown positioned outside the outer spiral electrode 17 but communicating with the main gap 22 through an opening 39 in the outer electrode 17. Positioning the trigger assembly in this location enables the plasma from the trigger to be injected directly into the main gap 22, thus aiding the trigger in initiating an arcover promptly when desired. It is to be understood that additional trigger assemblies (not shown) can be provided, if needed, to supply additional plasma for initiating an are discharge at the. desired instant.

By locating one of the terminal pins 25 at the outer end and the other terminal pin 26 at the inner end of the

spiral electrodes

17 and 18 respectively, I am able to reduce the density of any component of magnetic field extending transversely of an arc discharge between the electrodes. This can be best explained by referring to FIG. 3, where an arc discharge is shown at 40. Assuming that electrode 17 is the anode and 18 is the cathode, current enters the arc discharge 40 by following a path through electrode 17 in the direction of arrow 42 and leaves the arc discharge by following a path through electrode 18 in the direction of arrow 43. Since these current paths are in the same direction, the magnetic fields around each conductor are essentially canceled out in the central region between the two conductors, thus leaving a region of low magnetic field in the central region between the two conductors. A diagram similar to this is shown in the above mentioned Rich U.S. Pat. No. 3,679,474, where it is explained in more detail how the arc discharge assumes such a configuration as illustrated and how the magnetic field in the central region between the conductors is generally canceled out.

Although the transverse magnetic field is substantially reduced by the effect described in the immediately preceding paragraph, it is to be understood that this is a somewhat idealized picture of the flux cancellation. The current flowing in the other turns of the two spirals does develop some transverse magnetic field in the portion of gap 22 illustrated in FIG. 3; but at any rate, there is a substantial reduction in the net transverse magnetic field as a result of locating the terminal connections of one spiral at an opposite end of the spiral from the terminal connection of the other spiral.

An important feature of my electrode configuration is the exceptionally large surface areas that are provided for the terminals of the arc discharge to spread out over. In this respect, the entire outer surface of the inner spiral 18 and the entire inner surface of the outer spiral 17 are available for the terminals to spread out over. These surfaces extend along spiral paths from the extreme outer end to the extreme inner end of the two spirals and also extend over most of the length of the cylindrical space within the cylindrical casing 12. Since almost this entire cylindrical space is filled with arcing surfaces, it will be apparent that a near maximum utilization of the cylindrical space for arcing surfaces is being made.

It will be apparent that from most parts of the arcing gap 22 there are no straight line paths leading to the insulating casing 12 that are not intercepted by surfaces of the

electrodes

17 and 18. These surfaces act to inter cept and condense almost all the arcing products before they can reach casing 12. This relationship greatly reduces the need for a separate vapor condensing shield along the inner surface of the casing 12, and in some applications it is possible to dispense entirely with such a shield. In the embodiment of FIG. 1, however, I have included such a shield to provide extra assurance against vapor deposition on casing 12. This shield,

which is shown at S ll, is a tubular metallic member supported on the casing l2 and electrically isolated from both end caps 13 and M.

In a preferred form of my invention, the length of the main gap 22 as measured between the two electrodes 17 and I3 is substantially uniform over the major portions of the areas of the electrodes that are exposed to arcing. Although this gap length may in limited areas be greater than this substantially uniform value, it should not be substantially lower than the uniform value. The generally uniform gap length encourages spreading out of the arc discharge over the extensive electrode surfaces.

FIGS. 4 and 5 show the invention applied to a vacuum switch instead of a vacuum gap device. The switch of FIGS. 4 and 5 is a normally-closed device through which current can flow via a set of normally-closed separable contacts oil and 62. Contact 60 is a stationary contact fixed to the lower end of a conductive contact rod 63, and contact 62 is a movable contact fixed to the upper end of a conductive contact rod 64. Contact rod 64 is vertically movable and extends through the lower end of the interrupter, and a flexible bellows 65 therearound provides a vacuum-tight seal that allows the rod to be moved vertically without impairing the vacuum in the envelope. When the switch is to be opened, contact rod 6% is driven downwardly, separating contact 62 from contact (6th, thereby establishing an arc therebetween. The are vaporizes and ionizes some of the contact material, thus developing an electron-ion plasma which is projected radially outward into the gap 22 between the spiral electrodes l7 and 18. The dielectric strength of the gap 22 is drastically reduced by the plasma and the gap is broken down by the voltage than present between the

electrodes

17 and 18. This breakdown results in an arc discharge between the electrodes which corresponds to the arc discharge described in connection with FIGS. 1 and 2.

Although not shown, it is to be understood that the contact 6% and62 could be provided with suitable are running extensions for driving the are into closer proximity with the gap 22 to promote ignition of the gap by the plasma from the contacts 60 and ea.

In the embodiment of FIGS. 4 and 5, the contacts 60, 62 are located in a central position where they are surrounded by the spiral electrodes I7 and 18. The electrodes terminate at their inner ends in positions angularly spaced by greater than 90 degrees from each other to facilitate entry of plasma from the inter-contact space into the interelectrode gap at the start of interruption.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects; and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

I claim:

l. A vacuum-type circuit interrupter comprising:

a. a highly evacuated envelope provided with spacedapart opposed electrical terminals for connection to an electric circuit,

b. spaced-apart first and second electrode members within said envelope respectively electrically connected to said spaced-apart terminals and between which a high voltage is applied during circuit inter ruptlon,

b,. each of said electrode members comprising a metal sheet in the form ofa spiral wound in turns about a longitudinal axis via a path that generally progressively recedes from said longitudinal axis as the path winds about said axis, said sheet hav ing a width much greater than its thickness; the width of the sheet extending generally parallel to said longitudinal axis and the thickness of the sheet extending generally normal to said longitudinal axis,

b said spirals being so positioned that their longitudinal axes are generally parallel to each other and their turns interleave in spaced relationship to each other, thereby defining an interelectrode gap of spiral form between said electrode members,

0. means within said envelope for supplying an electron-ion plasma to said interelectrode gap for causing the voltage between said electrodes to establish an arc discharge across said interelectrode gap,

d. and means for forcing most of the current that flows through said discharge to follow a path extending between said terminals through said electrodes that enters one of the electrodes from its associated terminal near the outer end of its spiral and leaves the other of the electrodes for its associated terminal near the inner end of the spiral of said other electrode.

2. The vacuum-type circuit interrupter of claim I in which:

a. said means of (d) comprises a first highconductivity connection between the outer end of said one electrode and one of said terminals and means for preventing most of said current from flowing between said one electrode and said one terminal other than through said first high conductivity connection,

b. said means of (d) further comprises a second highconductivity connection between the inner end of said other electrode and the other of said terminals and means for preventing most of said current from flowing between said other electrode and said other terminal other than through said second high-conductivity connection.

3. The vacuum type circuit interrupter of claim I in which said envelope has a generally cylindrical internal volume, the longitudinal axis of said cylindrical volume being generally parallel to the longitudinal axes of said spirals.

4 The vacuum-type circuit interrupter of claim I in which said means for supplying an electron-ion plasma to said gap comprises a trigger assembly located adjacent said gap, said trigger assembly including a trigger gap that is sparked-over to generate said plasma.

5. The vacuum-type circuit interrupter of claim I in which said interelectrode gap is of substantially uniform length over the major portions of the areas of said electrodes exposed to arcing.

6. The vacuum type circuit interrupter of claim I in which said substantially uniform length is the minimum spacing between said electrodes when the interrupter is in an open condition.

7. The vacuum type circuit interrupter of claim l in combination with a pair of separable contacts operable when engaged to carry current across said gap, separation of said contacts developing an arc therebetween that acts as a generator of said electron-ion plasma.

8. The vacuum type circuit interrupter of claim 7 in which said contacts are located in a central position where they are surrounded by said spiral electrode

Claims

1. A vacuum-type circuit interrupter comprising: a. a highly evacuated envelope provided with spaced-apart opposed electrical terminals for connection to an electric circuit, b. spaced-apart first and second electrode members within said envelope respectively electrically connected to said spacedapart terminals and between which a high voltage is applied during circuit interruption, b1. each of said electrode members comprising a metal sheet in the form of a spiral wound in turns about a longitudinal axis via a path that generally progressively recedes from said longitudinal axis as the path winds about said axis, said sheet having a width much greater than its thickness, the width of the sheet extending generally parallel to said longitudinal axis and the thickness of the sheet extending generally normal to said longitudinal axis, b2. said spirals being so positioned that their longitudinal axes are generally parallel to each other and their turns interleave in spaced relationship to each other, thereby defining an interelectrode gap of spiral form between said electrode members, c. means within said envelope for supplying an electron-ion plasma to said interelectrode gap for causing the voltage between said electrodes to establish an arc discharge across said interelectrode gap, d. and means for forcing most of the current that flows through said discharge to follow a path extending between said terminals through said electrodes that enters one of the electrodes from its associated terminal near the outer end of its spiral and leaves the other of the electrodes for its associated terminal near the inner end of the spiral of said other electrode.

2. The vacuum-type circuit interrupter of claim 1 in which: a. said means of (d) comprises a first high-conductivity connection between the outer end of said one electrode and one of said terminals and means for preventing most of said current from flowing between said one electrode and said one terminal other than through said first high-conductivity connection, b. said means of (d) further comprises a second high-conductivity connection between the inner end of said otHer electrode and the other of said terminals and means for preventing most of said current from flowing between said other electrode and said other terminal other than through said second high-conductivity connection.

3. The vacuum type circuit interrupter of claim 1 in which said envelope has a generally cylindrical internal volume, the longitudinal axis of said cylindrical volume being generally parallel to the longitudinal axes of said spirals.

4. The vacuum-type circuit interrupter of claim 1 in which said means for supplying an electron-ion plasma to said gap comprises a trigger assembly located adjacent said gap, said trigger assembly including a trigger gap that is sparked-over to generate said plasma.

5. The vacuum-type circuit interrupter of claim 1 in which said interelectrode gap is of substantially uniform length over the major portions of the areas of said electrodes exposed to arcing.

6. The vacuum type circuit interrupter of claim 1 in which said substantially uniform length is the minimum spacing between said electrodes when the interrupter is in an open condition.

7. The vacuum type circuit interrupter of claim 1 in combination with a pair of separable contacts operable when engaged to carry current across said gap, separation of said contacts developing an arc therebetween that acts as a generator of said electron-ion plasma.

8. The vacuum type circuit interrupter of claim 7 in which said contacts are located in a central position where they are surrounded by said spiral electrode members.