US3786214A

US3786214A - Interleaving-rod type vacuum interrupter having two breaks in series between each pair of rods

Info

Publication number: US3786214A
Application number: US00325181A
Authority: US
Inventors: J Sofianek
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1973-01-19
Filing date: 1973-01-19
Publication date: 1974-01-15
Anticipated expiration: 1991-01-15
Also published as: FR2214953A1; CA958054A; DE2358120A1; JPS49103172A; GB1437108A

Abstract

A vacuum-type electric circuit interrupter comprises interleaving rod electrodes of alternating polarity arranged in a ring pattern and a tubular metal shield disposed around the ring of rod electrodes and normally electrically isolated from the rod electrodes. The tubular shield comprises metal partitions projecting from regions radially outside the ring radially inward into the spaces between immediately-adjacent rod electrodes, thereby dividing each of these spaces into two series-related arcing gaps respectively disposed on opposite sides of each of said metal partitions.

Description

United States Patent 1 Sofianek [4 Jan. 15, 1974 [5 INTERLEAVlNG-ROD TYPE VACUUM 3,670,123 6/1972 Luehring 200/144 B INTERRUPTER HAVING TWO BREAKS IN 3,702,911 11/1972 Schonhuber 200/144 B SERIES BETWEEN EACH PAIR OF RODS [75] Inventor: Joseph C. Sofianek, Broomall, Pa.

[73] Assignee: General Electric Company,

Philadelphia, Pa.

[22] Filed: Jan. 19, 1973 [21] App]. No.: 325,181

52 US. Cl 200/144 B [51] Int. Cl. HOlh 33/66 5 8] Field of Search 200/144 B [56] References Cited UNITED STATES PATENTS 2,897,322 7/1959 Reece 200/144 B 3,321,598 5/1967 Streater.. 200/144 B 3,643,047 2/1972 Rich 200/144 B Primary ExaminerRobert S. Macon Att0rney.l. Wesley Haubner et al.

[5 7] ABSTRACT A vacuum-type electric circuit interrupter comprises interleaving rod electrodes of alternating polarity arranged in a ring pattern and a tubular metal shield disposed around the ring of rod electrodes and normally electrically isolated from the rod electrodes. The tubular shield comprises metal partitions projecting from regions radially outside the ring radially inward into the spaces between immediately-adjacent rod electrodes, thereby dividing each of these spaces into two series-related arcing gaps respectively disposed on opposite sides of each of said metal partitions.

11 Claims, 3 Drawing Figures BACKGROUND This invention relates to a vacuum-type electric circuit interrupter of the type comprising interleaving rod electrodes of alternating polarity arranged in a ring pattern, as is described and claimed in U.S. Pat. No. 3,679,474-Rich, assigned to the assignee of the present invention. More particularly, the invention relates to a vacuum interrupter of that type in which two gaps in series are provided between each pair of adjacent rod electrodes.

The following additional prior art is of interest with respect to this invention: US. Pat. Nos. 2,897,322-Reece; 3,185,798-Titus; 3,l85,799- Greenwood et a]; 3,321 ,598-Streater; 3,372,258-Porter; and 3,643,047-Rich.

The interrupter of the aforesaid Rich US. Pat. No. 3,679,474 comprises two spaced-apart primary electrode assemblies, each comprising a common base and a plurality of rod electrodes extending normal to the base. The electrode assemblies are positioned so that the rod electrodes of the two assemblies form a ring of rod electrodes in which the rod electrodes of one assembly interleave with those of the other assembly. The rod electrodes about said ring alternate in polarity, and each pair of immediately-adjacent rod electrodes are separated by an arcing gap therebetween. During an interrupting operation, across these arcing gaps there are established diffuse arcs which can carry relatively high currents without the formation of anode spots.

Rich attributes this ability to carry high currents without forming anode spots to the ability of this interrupter configuration to limit to a very low level the body force F that acts on the conduction paths through the arc discharge across each inter-electrode gap. The tendency to cause the conduction paths between a pair oppositely-poled arc-electrodes to bunch together and develop a high current density which results in formation of an anode spot appears to be directly related to the body force F. By keeping F low, this tendency to bunch is kept correspondingly low.

While prior vacuum interrupters of this interleavingrod type can interrupt exceptionally high currents, their voltage-handling capacity has been limited by the fact that only a single gap is present between each pair of adjacent rods. If, following clearance at current zero,

any of these gaps should arc-over in response to a voltage transient applied between the terminals of the interrupter, a complete circuit is developed between the terminals of the interrupter via the arcing path; and through this complete circuit, high current can flow, resulting in conditions which delay, or even prevent, successful interruption.

If two gaps in series are present between each pair of rods, the likelihood of an arcing path developing between the rods is substantially reduced, and the chances for successful interruption are substantially improved.

SUMMARY Thus, an object of my invention is to provide an interleaving-rod type vacuum interrupter having two arcing gaps in series between each pair of adjacent rods.

Another object is to divide the space between each pair of adjacent rod electrodes into two series-related gaps by structurally simple means, the v presence of which does not greatly increase the size of the inter-' rupter.

In my interrupter, there is a set of separable contacts located in a position disposed centrally of the ring of rod electrodes. When the interrupter is in closed position, current passes therethrough via these contacts. Interruption is initiated by separating the contacts to form an arc therebetween. The arcing products developed by the arc are propogated radially outward into the gaps between the rods, and this causes the gaps to ignite and develop low arc-voltage discharges thereacross to which the interrupter circuit is transferred from the are initially formed betweenthe contacts.

Another object of my invention is to provide two gaps in series between each pair of adjacent rod electrodes by means of a structurally simple arrangement that readily lends itself to use in an interrupter in which interruption is initiated by separable contacts surrounded by the ring of rod electrodes.

In carrying out my invention in one form I provide around the ring of interleaving rod electrode members a tubular metal shield that is normally electrically isolated from both electrode assemblies. This shield comprises metal partitions projecting from regions radially outside said ring radially inward into the spaces between immediately-adjacent electrode members of said electrode assemblies, thereby dividing each of said spaces into two series-related arcing gaps respectively disposed on opposite sides of each of said metal partitions. These arcing gaps share the voltage applied between adjacent rod electrode members when the recovery voltage builds up between said electrode members at current zero at the end of an arcing period.

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. 1 is a side elevational view, partly in section, of a vacuum interrupter embodying one form of the invention.

FIG. 2 is a sectional view along the line 2-2 of FIG. 1.

FIG. 3 is a sectional view similar to that of FIG. 2 except showing a modification of the interrupter of FIG. 1

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a vacuum interrupter 10 that comprises an upper electrode assembly l1 and a lower electrode assembly 12 that are joined in hermetically sealed relationship to opposite ends of a cylindrical insulating casing 13 to form a hermetically sealed envelope 14. The interior of this envelope 14 is evacuated to a pressure of 10 torr or lower. Upper electrode assembly 11 comprises a metal base plate, or disc, 15 and a plurality of downwardly depending electrodes 16 suitably joined to the base plate, as by brazing. Lower electrode assembly 12 comprises a metal base plate, or disc, 17 and a plurality of upwardly depending electrode members 18 brazed thereto. Preferably, each of the electrode members is a cylindrical rod having a smooth external surface, as

is described and claimed in the aforesaid Rich US. Pat. No. 3,679,474.

The rods of each electrode assembly extend parallel to each other, as shown in FIG. 1, and are arranged in a circular pattern, circumferentially spaced from each other about the circle, as shown in FIG. 2. Referring to FIG. 2, the electrode assemblies are positioned so that the rods of one assembly interleave with the rods of the other assembly and together form a ring of circumferentially spaced rods, with the rods alternating in polarity about the ring. The

rods

16 and 18 are of a high purity, nonrefractory metal such as suitably degassed copper or steel.

For protecting the insulating casing 13 from arcing products generated during an interrupting operation, a metallic shield 23 comprising a body portion 19 of tubular form is provided. This shield body 19 surrounds the ring of electrodes in spaced relationship to the rods and is supported on the insulating casing 13 by means of a flange 20 suitably joined to the shield and extending radially outward therefrom. Flange 20 is positioned between upper and lower halves of the casing and is joined to these halves by suitable seals 21. The shield 23 is so located and shaped that a substantially equal capacitance is present between the shield and each of the electrode assemblies when the interrupter is open, thus maintaining the shield at a potential substantially midway between that of the two electrode assemblies when the interrupter is open.

For carrying current through the interrupter when the interrupter is closed, a pair of separable contacts 30 and 32 are provided. These contacts are located generally centrally of the ring formed by the

rod electrode

16, 18. Contact 30 is a stationary contact fixed to the lower end of a stationary contact rod 34, and contact 32 is a movable contact fixed to the upper end of a movable contact rod 36. The stationary contact rod 34 extends through upper base plate and is joined thereto by a suitable brazed joint forming a vacuumtight seal between the rod and the base plate. The movable contact rod 36 extends freely through an opening in the lower base plate 17, and a flexible metal bellows 38 provides a seal between base plate 17 and rod 36 that permits the rod to move freely in a vertical direction with respect to the base plate. In the illustrated interrupter, a metal tube 39 is shown surrounding the bellows 38, and this tube is connected by suitable vacuum tight joints at its opposite ends with the bellows 38 and the base plate 17.

When the interrupter is to be operated to interrupt the circuit therethrough, movable contact rod 36 is driven in a downward direction from its position of FIG. 1 by a suitable operator (not shown). This separates contact 32 from contact 30, thereby establishing a gap between the contacts. Establishment of this gap causes an arc to be developed across the gap; and in this arc vaporizes contact material, which material is expelled radially outwardly into the spaces between

adjacent rod electrodes

16 and 18. No arcs are initially present across the spaces between the electrodes, but when the arcing products enter these spaces, the dielectric strength of the spaces is drastically reduced, and the spaces are broken down by the voltage then present thereacross. This breakdown of the spaces between the rods results in an arc discharge between each adjacent pair of opposite polarity rods.

In the interrupter of my invention, the arc discharge space between each pair of rod electrodes is divided into two separate series-related arcing gaps by providing a plurality of metal partitions 40 constituting a part of shield 23. These partitions 40 are preferably in the form of metal plates 41 of planar configuration disposed in radially extending vertical planes that include the central longitudinal axis of the interrupter. Each plate 41 is suitably attached at its radially-outer edge to the tubular portion 19 of the shield, as by brazing or welding. Along the radially-inner edge of each plate 41, there is a metal rod 43 of circular cross section extending vertically along the length of the plate 41. This rod 43 is suitably joined to its associated plate 41, as by welding or brazing, or being integrally formed therewith and provides the partition with a rounded inner edge that serves to reduce electrical stress concentration in this region. In a preferred form of the invention, the partition 40 extends radially inward from the tubular portion 19 of the shield to a reference line located radially inward of a reference circle 45 along which the radially innermost surfaces of the rod electrodes are located. Since the tubular shield portion 19 is at substantially mid-potential, as above described, the partitions 40 which are electrically connected to the tubular portion 19 are also at substantially mid-potential.

The metal partitions 40 serve the important purpose of increasing the breakdown voltage between each adjacent pair of

opposite polarity rods

16 and 18 when the usual recovery voltage builds up across the interrupter following a current zero at the end of an arcing period. In each of the spaces between a pair of

rod electrodes

16 and 18, there are two series-related gaps, one between rod 16 and the partition 40 and the other between the partition 40 and the rod 18. Since the partition 40 is at a potential substantially midway between that of the

electrodes

16 and 18, substantially half the total voltage across the interrupter is applied to each gap. In a vacuum, the total breakdown voltage of two series-related gaps, each subject to half the applied voltage, is substantially greater than that of a single gap of the same total length subject to the full applied voltage. Hence, the total breakdown voltage across the two gaps present between each pair of

electrodes

16, 18 is substantially greater than that present when the partition 40 is absent.

Between the distal end of each upwardly-projecting rod electrode 18 and the adjacent upper end plate 15, there is a space across which a spark-over will establish a continuous electrical path through the interrupter. In the illustrated embodiment, each of these end spaces is divided into two series-related end gaps by a metal cap that extends generally horizontally from the tubular portion 19 of the shield to the radially innermost edge of the partition 40 across the top of the compartment that surrounds rod 18. Thus, this space adjacent the distal end of each rod electrode 18 is also divided into two series-connected gaps across each of which half the total voltage appears. This relationship results in improved dielectric strength in this region.

Between the lower end plate 17 and the distal end of each of the downwardly projecting rod electrodes 16, there is a corresponding metal cap 52 that divides this space into two series-related end gaps, each bearing approximately half the total applied voltage.

For further protecting the insulating casing 13 from arcing products generated during an interrupting operation, I provide a plurality of

auxiliary shields

70, 71, 72, and 73 adjacent the insulating casing 13 and surrounding the main shield 23. Each of these auxiliary shields is a tubular metal member disposed concentrically of the casing 13 in a position adjacent a glass-tometal seal in the casing. Auxiliary shields 70 and 73 project inwardly of the interrupter from

base plates

15 and 17, respectively, and are electrically connected to their associated base plates. Auxiliary shields 71 and 72 project in opposite directions from central flange and are electrically connected to the flange. These auxiliary shields are radially spaced from the insulating casing 13 and from the main shield portion 19 and serve to intercept and condense any arcing products escaping from the region within the main shield portion 19 before these arcing products can reach the insulating casing 13. The auxiliary shields also serve to shape the electric field so as to reduce electrical stresses on the glass-to-metal seals.

FIG. 3 shows a modified form of the invention in which the partitions 40, instead of being planar in configuration, are curved so as to have an inner surface that is generally concentric with respect to the cylindrical surface of the adjacent rod electrode. Each pair of adjacent partitions is welded together along a vertical seam 62 so as to form about each rod electrode a generally cylindrical housing or compartment that is open at 63 for about 90 of its periphery to the central portion of the interrupter where the contacts 30, 32 are located. An advantage of this design of FIG. 3 is that the electric field between each rod electrode and the metal housing or compartment surrounding the rod electrode is generally uniform in view of the generally concentric uniformly-spaced relationship of these parts. This uniformity of the electric field contributes to a higher breakdown voltage between the rod electrodes and the surrounding compartments.

In FIG. 3, the tubular portion of the shield that surrounds the entire ring of rod electrodes can be thought of as being constituted almost entirely by the partitions 40. Metal caps corresponding to 50 and 52 in the embodiment of FIG. 1 are also present in the embodiment of FIG. 3,

In both of the illustrated embodiments, it will be noted that the arcs formed across the arcing gaps between the rod electrodes extend generally circumferentially of the interrupter. This results in the body force F on each are being limited to a low value, as is explained in the aforesaid Rich patent, thus enabling the arcs to carry relatively high currents without developing anode spots and also limiting to a low value the arc voltage developed by each arc. The relatively low level of the arc voltage developed by the circumferentiallyextending arcs plays an important role in enabling these arcs to be established and maintained in preference to the single arc between the contacts 30, 32. There is a strong tendency for such a single arc to persist in preference to multiple arcs over an alternate path if arcing via said alternate path will result in the development of a higher total arc voltage than is developed by the single are. In my interrupter, the tendency for the single arc to persist is greatly reduced because the sum of the arc voltages developed by the series-related circumferentially-extending arcs is less than that which would be developed by a single arc burning between the contacts 30, 32.

In order to reduce the likelihood that the recovery voltage will establish a breakdown across the gap between the contacts 30 and 32, I provide the interrupter with an unusually long stroke. In one embodiment of the invention, for example, the stroke is of such a length that the full gap between the contacts 30 and 32 is approximately 2 inches in length, which is appreciably greater than the total length of the two arcing gaps between adjacent opposite-

polarity rod electrodes

16 and 18.

To further reduce the likelihood that the recovery voltage will establish a breakdown between contacts 30, 32, I make the gaps between each of the contacts and the radially-inner edges of the partitions equal to or greater than the length of the arcing gaps between the rod electrodes and the partitions 40. This discourages breakdowns across these contact-to-shield gaps, the occurrence of which could develop into an are between the contacts 30 and 32.

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

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A high-current vacuum circuit interrupter comprising:

a. a hermetically sealed envelope evacuated to a pressure of 10' tort or less,

b. a first primary arc-electrode assembly comprising a first plurality of spaced-apart substantially parallel rod electrode members having arcing surfaces disposed within said envelope,

0. a second primary arc-electrode assembly comprising a second plurality of spaced-apart substantially parallel rod electrode members having arcing surfaces disposed within said envelope and interleaving in alternate sequence between the spaced electrode members of said first arc-electrode assembly, said first and second pluralities of electrode members being positioned so as to form a ring of electrode members within said envelope with spaces between immediately adjacent electrode members, said members alternating in polarity about said ring, e. a tubular metallic shield surrounding said ring and electrically isolated from both of said electrode assemblies when no current is passing through said interrupter via said electrode members, said shield comprising metal partitions projecting from regions radially outside said ring radially inward into the spaces between immediately adjacent electrode members of said electrode assemblies, thereby dividing each of said spaces into two seriesrelated arcing gaps respectively disposed on opposite sides of each of said metal partitions,

g. and means for causing electric arcs to be established in said series-related arcing gaps during a circuit interrupting operation,

h. said arcing gaps being arranged to share the voltage applied between adjacent rod electrode members when the recovery voltage builds up between i said electrode members at current zero at the end of an arcing period.

2. The interrupter of claim 1 in which:

a. the rod electrode members of said first assembly are connected at their proximal ends to a common metal base toward which the rod electrode members of said second assembly project,

b. an end space is present between the distal end of each of said second-assembly rod electrode members and said common base,

0. metal caps are provided dividing each of said end spaces into two series related end gaps on opposite sides of the associated metal cap,

d. said metal caps each constitute a portion of said shield and are electrically connected to the portion of said shield surrounding said ring of electrodes.

3. The interrupter of claim 2 in which:

a. said second-assembly rod electrode members at their proximal ends are connected to a second common metal base toward which said firstassembly rod electrode members project,

b.'additional end spaces are present between the distal ends of said first-assembly rod electrode members and said second common base,

0. second metal caps are provided dividing each of said additional end spaces into two series-related end gaps on opposite sides of the associated second p! d. said second metal caps each constitute a portion of said shield and are electrically connected to the portion of said shield surrounding said ring of electrodes.

4. The interrupter of claim 1 in which said partitions extend radially inward past a reference circle that includes the radially innermost surfaces of said rod electrode members.

5. The interrupter of claim 1 in which the arcing surfaces of each of said rod electrode members are smooth cylindrical surfaces.

6. The interrupter of claim 1 in which said shield, including said partitions, is shaped to form about each rod electrode member a metal compartment having an internal surface substantially uniformally spaced from the outer surface of the rod electrode member located therein.

7. The interrupter of claim 5 in which said shield, including said partitions, is shaped to form about each rod electrode membera metal compartment having an internal surface substantially concentric with an substantially uniformally spaced from the cylindral surface of the rod electrode member located therein.

8. The interrupter of claim 1 in which:

a. said means for causing electric arcs to be established comprises a pair of separable contacts located in the space surrounded by said ring of rod electrode members,

b. said contacts are engageable to carry current through said interrupter and are separable to establish an inter-contact gap across which an arc is formed,

c. said inter-contact gap freely communicates with the series-related arcing gaps on opposite sides of said metal partitions so that arcing products from said inter-contact gap are propagated into said series-related arcing gaps to cause arc discharges to form across said series-related arcing gaps.

9. The interrupter of claim 8 in which when said contacts are fully separated, said interrupter has an intercontact gap of a length greater than the sum of the length of the two series-related arcing gaps on opposite sides of each of said partitions.

10. The interrupter of claim 8 in which there is a contact-to-shield gap between each of said contacts and the radially inner edge of each of said partitions, said contact-to-shield gaps having a length at least as great as the length of each of said series-related arcing gaps.

11. The interrupter of claim 1 in which each of said partitions is of a generally planar form and includes at its radially-inner end an edge that is enlarged and rounded to reduce electric stress concentrations thereadjacent.

Claims

1. A high-current vacuum circuit interrupter comprising: a. a hermetically sealed envelope evacuated to a pressure of 104 torr or less, b. a first primary arc-electrode assembly comprising a first plurality of spaced-apart substantially parallel rod electrode members having arcing surfaces disposed within said envelope, c. a second primary arc-electrode assembly comprisiNg a second plurality of spaced-apart substantially parallel rod electrode members having arcing surfaces disposed within said envelope and interleaving in alternate sequence between the spaced electrode members of said first arc-electrode assembly, d. said first and second pluralities of electrode members being positioned so as to form a ring of electrode members within said envelope with spaces between immediately adjacent electrode members, said members alternating in polarity about said ring, e. a tubular metallic shield surrounding said ring and electrically isolated from both of said electrode assemblies when no current is passing through said interrupter via said electrode members, f. said shield comprising metal partitions projecting from regions radially outside said ring radially inward into the spaces between immediately adjacent electrode members of said electrode assemblies, thereby dividing each of said spaces into two series-related arcing gaps respectively disposed on opposite sides of each of said metal partitions, g. and means for causing electric arcs to be established in said series-related arcing gaps during a circuit interrupting operation, h. said arcing gaps being arranged to share the voltage applied between adjacent rod electrode members when the recovery voltage builds up between said electrode members at current zero at the end of an arcing period.

2. The interrupter of claim 1 in which: a. the rod electrode members of said first assembly are connected at their proximal ends to a common metal base toward which the rod electrode members of said second assembly project, b. an end space is present between the distal end of each of said second-assembly rod electrode members and said common base, c. metal caps are provided dividing each of said end spaces into two series related end gaps on opposite sides of the associated metal cap, d. said metal caps each constitute a portion of said shield and are electrically connected to the portion of said shield surrounding said ring of electrodes.

3. The interrupter of claim 2 in which: a. said second-assembly rod electrode members at their proximal ends are connected to a second common metal base toward which said first-assembly rod electrode members project, b. additional end spaces are present between the distal ends of said first-assembly rod electrode members and said second common base, c. second metal caps are provided dividing each of said additional end spaces into two series-related end gaps on opposite sides of the associated second cap, d. said second metal caps each constitute a portion of said shield and are electrically connected to the portion of said shield surrounding said ring of electrodes.

7. The interrupter of claim 5 in which said shield, including said partitions, is shaped to form about each rod electrode member a metal compartment having an internal surface substantially concentric with an substantially uniformally spaced from the cylindral surface of the rod electrode member located therein.

8. The interrupter of claim 1 in which: a. said means for causing electric arcs to be established comprises a pair of separable contacts located in the space surrounded by said ring of rod electrode members, b. said contacts are engageable to carrY current through said interrupter and are separable to establish an inter-contact gap across which an arc is formed, c. said inter-contact gap freely communicates with the series-related arcing gaps on opposite sides of said metal partitions so that arcing products from said inter-contact gap are propagated into said series-related arcing gaps to cause arc discharges to form across said series-related arcing gaps.