US3836740A

US3836740A - Vacuum type circuit interrupter having improved contacts

Info

Publication number: US3836740A
Application number: US00249990A
Authority: US
Inventors: R Hundstad
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1972-05-03
Filing date: 1972-05-03
Publication date: 1974-09-17
Anticipated expiration: 1991-09-17
Also published as: DE2321753A1; GB1423581A; JPS4941860A; CA979958A; CH567794A5; JPS5778538U

Abstract

A vacuum type circuit interrupter comprising cup-shaped electrodes for improved arc movement during circuit interruption. The contact structures of the vacuum-type circuit interrupter are shaped so that when an arc is established between the contacts during circuit interruption the current path through the contacts to the arc is substantially perpendicular to the arc, for improved arc movement. The arc is initiated at the primary contacting surfaces during circuit interruption and is moved rapidly around the contact area thereby preventing the contact area from being grossly eroded.

Description

United States Patent [1 1 Hundstad VACUUM TYPE CIRCUIT INTERRUPTER HAVING IMPROVED CONTACTS Richard L. Hundstad, Pittsburgh, Pa.

Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

Filed: May 3, 1972 Appl. No: 249,990

Inventor:

US. Cl. 200/144 B, 200/ 166 H Int. Cl. II0lh 33/66 Field of Search ZOO/144 B, 166 81-1 I References Cited UNITED STATES PATENTS 5/1963 Smith, Jr. 200/166 BH X 1/1968 Smith, Jr. 200/144 B 3,546,406 12/1970 Frink ZOO/144 B 3,622,724 11/1971 Sofianek 200/144 B FOREIGN PATENTS OR APPLICATIONS 1,410,884 8/1965 France 200/144 B [451 Sept. 17, 1974 France 200/144 B Great Britain 200/144 B Primary Examiner-Robert S. Macon Attorney, Agent, or Firm-l-l. G. Massung ABSTRACT 11 Claims, 13 Drawing Figures LIB 29 i 1 r' I 44 I ///K// PAIENIEDSEPI 1 3.836.740

sum 2 or 3 may VACUUM TYPE CIRCUIT INTERRUPTER HAVING IMPROVED CONTACTS CROSS-REFERENCE TO RELATED APPLICATIONS This application is related to US. Patent Office Ser. No. 416,470 filed Nov. 16,- 1973, which is a continuation of Ser. No. 249,992, filed May 3, 1973 now abandoned, assigned to the same assignee asthe presentapplication.

BACKGROUND OF THE INVENTION formed therebetween and current will continue to flow through this are until the arc is extinguished which on an alternating current circuit will normally occur near the first current-zero.- The contact surface must support the are from its initiation at the time of electrode separation until its extinction at approximately current zero. While the arc isbeing sustained the contacts are subjectedto very intense heat. This arc energy causes melting, erosion and general deterioration of the contact. surfaces. To minimize deterioration of the contact-surfaces it is customary to move the are around the contact surfaces. Such are movement tends to minimize theamount of metallic vapors or particles generated by the are, from the contact surfaces, duringcircuit interruption. This are movement is usually accomplished by self-induced magnetic. fieldsas explained in prior art'U.S. Pat. No. 3,089,936 issued May 14, 1963 to S. R. Smith, Jr., and US. Pat. No, 3,417,216 issued Dec. 17, 1968 to SR. Smith, Jr.

SUMMARY OF THE INVENTION in a third direction. The direction in which the arc will move is, perpendicular to the current flow in the arc,

and perpendicular; to the magnetic field component which isat a right angle to currentflow in the arc. In a self-induced magnetic field straight parallel rails with current entering and exiting through corresponding ends produces the greatest unbalance in the magnetic field distribution and therefore the greatest magnetic field todrivean arcin aspecific predetermined direction. The contact assembly in the'present invention is designed so that the current conducting path through the contacts approximate straight parallel rails, for most effective are movement.

The contacts of the present invention are generally cup-shaped in design and in this respect resemble prior art cup-shaped designs such as US. Pat. No, 3,089,936 and US. Pat. No. 3,417,216, however, the embodiments here disclosed have significant advantages over prior art contacts. One of the main advantages of sthe present invention stemsfrom the current carrying path through the contacts, which approximates straight parallel rails for effective are movement. The embodiments disclosed in the present application make very effective use of the self-induced magnetic field in moving the arc over the contact surface and thereby distributing the are energy over the entire contact surface.

In one embodiment of the invention a pair of relatively movable cup-shaped contacts are disposed in a vacuum interrupter, the contacts have annular mating ridges which are divided into a plurality of contact surfaces. The contact surfaces are formed so as to approximate parallel rails to produced maximum unbalance in the magnetic field distribution and rapid arc movement. The are will extend axially of the contacts, and the current path in the contact surfaces will extend substantially perpendicular to the arc, for most of the arc travel. Current flowing in the contact surfaces perpendicular to the arc will produce an intense magnetic field on the one side of the arc tending to move the arc rapidly around the annular contact ridge.

In a second embodiment of the invention, the contacts are cup-shaped with an inward facing lip portion forming an annular ring which is the contact surface. The annular ring is slotted thereby dividing it into a plurality of contacts surfaces. The slots are angled so as to drive the arc in a combined azimuthal and radial inward direction. The angles of the slots cut in the annular ring and the amount by which the lip of the cup extends radially inward are factors which can be used to establish the angular velocity of the arc and its radial position. The are is thus driven inwardly and rotates rapidly around the inner periphery of the annular contacts surface until it is extinguished. Forcing the arc in an inward direction is a very important feature since it has been found experimentally that current interruption limits are usually reached when the arc interacts with the shield. This embodiment of the present invention tends to confine the arc to the inner electrode space and thereby prevent the are from interacting with the arc shield. By so confining the arc, the volume of the interrupter can be used more effectively and the radial distance separating the contacts and the main shield can be reduced.

In a third embodiment of the invention multiple contact surfaces are attached at intervals around a discshaped electrode, each of these contact surfaces extend formed therebetween current flowing through the contact surfaces flows perpendicular to the arc to move the are rapidly inward and around the inner periphery of the annular ring formed by the contact surfaces.

All embodiments of this invention can be constructed to provide small relative motion between the contact surfaces when the contacts are closed so as to increase the number of contact points and thereby reduce contact resistance. The rigidity of the contact surfaces can be controlled by varying wall thickness, the angle of the slots or slot spacing.

All disclosed embodiments of this invention also have the stress concentration feature described in detail in Ser. No. 416,470, for weld breaking.

BRIEF DESCRIPTION OF THE DRAWINGS Other advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a sectional view of a vacuum circuit interrupter comprising a contact structure of one embodiment of the invention;

FIG. 2 is an enlarged top view of the contact structure shown in FIG. 1; a

FIG. 3 is a side view of the contact structure shown in FIG. 2;

FIG. 4 is a sectional view taken along the line IVIV of FIG. 2;

FIG. 5 shows a pair of contacts of the type illustrated in FIG. 2 facing each other as they are disposed in a vacuum interrupter;

FIG. 6 is a side view of a contact structure illustrating a second embodiment of the invention;

FIG. 7 is a top view of the contact shown in FIG. 6;

FIG. 12 is a sectional view of thevcontact shown in FIG. along theline XII-XII; and

FIG. 13 is a side view of a pair of contacts of the type shown in FIG. 10 as they are disposed in a vacuum interrupter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and to FIG. 1 in particular there is shown a vacuum-type circuit interrupter 16. The vacuum circuit interrupter 16 comprises a highly evacuated tubular envelope 18 formed from glass or suitableceramic material and a pair of

metallic end caps

20 and 22 closing off the ends of the insulating envelope 18. Suitable seals 24 are provided between the end caps 20 and 22 and insulating envelope 18to render the inside of the insulating envelope l8 vacuum tight. The pressure within the envelope 18 undernormal operating conditions is lower than 10" torr to assure that the mean free' path for electrons will be longer than the potential breakdown path within the envelope Located within the insulatingenvelopel8 are apair of relatively movable electrodes or

contacts

26 and 28 as shown in FIG. 1 in their opencircuit position. When the

contacts

26 and 28 are separated there is'formed an arcing gap 30 therebetween. The upper contact 26 is a stationary contact secured to a conducting rod 32 by a suitable means, such as welding or brazing. The conducting rod 32 is rigidly joined to the stationary end cap 20 by asuitable means, such as welding or brazing. The lower contact 28 is a movable contact and isjoined to a conductive operating rod 34 by a suitable means, such as welding or brazing. The operating rod 34 is'l'suitably mounted for movement along the longitudinal axis of the insulating envelope 18. The operating rod- 34 projects through an opening 36 in the bellows end cap 22 as shown in FIG. 1. A metal bellows 38 is secured in sealing relationship at its respective opposite ends to the operating rod 34 and to the opening 36 in the bellows end cap 22. The flexible metallic bellows 38 provides a seal about the operating rod 34 to allow for movement of the operating rod 34 without impairing the vacuum within the envelope l8.

Coupled to the lower end of the operating rod 34 is a suitable actuating means (not shown) for driving the movable contact 28 upward into engagement with the stationary contact 26 so as to close the interrupter 16. The closed position of the movable contact 28 is indicated by the dotted line 29. The actuating means is also capable of returning the movable contact 28 to its open position, during circuit interruption. The circuit opening operation will entail a typical gap length 30, when the contacts are fully separated, of approximately onehalf inch.

When the

contacts

26 and 28 are separated during circuit interruption an arc is formed in the arcing gap 30 between the

electrodes

26 and 28. The are which is formed between the

contacts

26 and 28 vaporizes some of the contact material, these vapors and particles are disposed from the arcing gap 30 toward the insulating envelope 18. The internal insulating surfaces of the insulating envelope 18 are protected from the condensation of these are generated metallic vapors and particles by means of a tubular metallic shield 40 which is suitably supported on the insulating envelope 18, and preferably electrically isolated from both ends caps 20 and 22. This shield 40 acts to intercept and to condense arc generated metallic vapors and particles before they can reach the insulating envelope 18. To further reduce the chances for vapor or particles reaching the insulating envelope 18, by bypassing the shield 40, a pair of end shields 42 and 44 are provided at opposite ends of the main central shield 40. The speed with which the vapors, generated during arcing, are removed determines the steady state operating condition during arcing, and also the recovery capability of the unit. If the vapor is not quickly removed high voltage transients may cause the arc to reignite, after it has been extinguished, resulting in failure of the interrupter 16. The arc, interacting with the main shield 40-and melting a hole therethrough, is the cause of many of the failures noted in vacuum interrupters 1 6.

Referring now to.FIGS., 2, 3'and 4 there, is shown a v contact structure28 embodying the teachings of the present invention. Electrode 28 is generally cup-shaped with an inward facing lip portion 47 which forms an annular contact ring 46. The annular contact ring*46 lies in a plane which is perpendicular to the sides or walls 48 of the cup-shaped electrode 28. The annular contact ring 46 is divided into aplurality of contact surfaces 50.

The contact surfaces 50 are formed by cutting slots 52 through the inward facing lip 47 and wall 48 of the cupshaped electrode 28. The slots 52 can also be cut completely through the cup-shaped electrode 28. That is slots 52, as shown in FIG. 4, can be extended through the bottom portion 49 of the cup-shaped contact 28.

The contact 28 is thus made up of multiple contact surfaces 50 which are perpendicular to the walls 48 of the contacts 28. The slots 52 made in the contact 28 are angled so as to make the contact surface 50 point in a somewhat circumferential or azimuthal direction. Thus, any arc 54, .as shown in FIG. 5, which is formed when the

electrodes

26 and 28 are separated during current intertuption is driven in a combined azimuthal (circumferential) and radial inward direction. This tends to confine the are 54 to the inner .electrode or arcing gap space and thereby prevents the are 54 from interacting with the arc shield 40.

The angle of the slots 52 cut in the cup-shaped contact 28 and the amount by which the annular contact ring .46 extends radially inward, are factors which can be used to establish the angular velocity and the radial position of the are 54. Note that the slots 52 in contact 26 are opposite those in contact 28 so that when

contacts

26 and 28 are disposed in a vacuum interrupter 16, face-to-face as shown in FIG. 5, they tend to move the arc in the same direction.

Contacts

26 and 28 are positioned so that the contact surfaces 50 of contacts 26 and '28 face each other and approximate straight parallel rails so as to produce the greatest unbalance in the magnetic field distribution and therefore the greatest magnetic force to drive the arc in a specified predetermined direction. The current path through contact 28 is up the contact wall 48 and through one of the contact surfaces 50 to the arc 54, so that the current path in the contact surface 50 is at substantially a right angle to the longitudinal axis of the are 54. During circuit interruption when an arc is formed between

contacts

26 and 28 the arc is driven inward and rotates rapidly around the inner periphery 58 of the annular ring 46 until the are 54 is extinguished, which occurs on an alternating current circuit at approximately the first current zero.

Referring now to FIGS. 6, 7, 8 and 9 there is shown a contact structure 60 illustrating a second embodiment of the invention. The contact 60 is generally cupshaped with an annular contact surface 63 which is divided into multiple contact surfaces 64. The walls 66 of the cup-shaped contact 60 are formed so that current flowing to the are 54 during circuit interruption must flowthrough the contact surfaces 64 perpendicular to the axis of the are 54. Current flow to the contact surfaces 64 is through a restricted portion 68 so that current flowing in the contact surfaces 64 flows at substantially a right angle to the are 54. As shown in FIG. 9

contact 62 is a mirror image of contact 60. The contacts 60 and 62 are disposed in a vacuum interrupter 16 so that the contact surfaces 64 approximate parallel rails, and during circuit interruption the are 54 is driven rapidly around the annular contact surface 63, in the direction indicated by arrow'65, until it is extinguished. Current to the are 5.4 during the major portion ,of the arc travel must flow through the contact surfaces 64 at substantially a right angle to the axis of the are 54 to produce a greater unbalance in a magnetic field dis- .tribution and'therefore a greater magnetic field to drive the arc in a more predetermined or controlled direction than in the prior arc contact structures.

Referring now to FIGS. l0, l1, l2 and 13 there is shown a third embodiment of the invention on a contact structure'72. Contact 72 has a disc-shaped portion 73 with contact surfaces 76 attached at points 78 around the outer perimeter of the disc-shaped portion 73. Contact surfaces 76 can be made integral with the disc-shaped portion 73, or contact portion 76 can be attached to the disc-shaped portion 73 by a suitable means, such as welding or brazing. The contact surfaces 76 are attached to the disc-shaped surface 73 at points 78, and at other areas are separated from the surface 73 by a slight gap. The contact surfaces 76 point in a generally radially inward and circumferential direction.

.Contact 74 as shown in FIG. 13 is a mirror image of the contact 72 through a plane perpendicular to the longitudinal axis of the operating rod 34 and the stationary rod 32 and located midway between contacts 72 and 74. An arc 54 forms during circuit interruption and is driven rapidly inward and around the inner edge 80 of the contact surfaces 76. The contact surface 76 are in a plane which is parallel to the top of the discshaped portion 73. As shown in FIG. 13 the contact surfaces 76 of contacts 72 and 74 face each other so as .to approximate straight parallel rails. Current flowing through the contact surfaces 76 to the arc 54 flows at right angles to the are 54 so as to produce the greatest unbalance in the self-induced magnetic field distribution and therefore to move the arc most efficiently in a specified direction. The are 54 moves around the contacts 72 and 74 in the direction indicated by arrow 65. This construction of contact 72 drives the arc in a combined azimuthal (circumferential) and radial inward direction. The arc 54 is generally confined to the inner electrode or arcing space 30 and is thereby prevented from interacting with the arc shield 40. This is very important since it has been determined experimentally that current interruption limits are reached when the arc 54 interacts with the shield 40. In most cases a hole is melted in the arc shield 40 and the interrupter 16 fails. By a partial confinement as suggested by this embodiment the volume of the interrupter can be used more effectively. The radial distance separating the contacts 72 and 74 and the arc shield 40 can be reduced. In this embodiment of the invention the contact surfaces 76 are separated from each other by slots 84, and are separated from the disc-shaped portion 73 of the electrode 72 by gaps 86. The configuration of these

separations

84 and 86 and the amount by which the contact surfaces 76 project toward the center of the disc-shaped portion 73, beyond the attachment point 78, are factors which can be used in establishing the angular velocity of the are 54 and its radial inward position.

The contact structures, disclosed in this invention have several advantages, for instance the contact surfaces 50, 64 and 76 can be supported for slight relative motion so as to increase the number of contact points and thereby reduce contact resistance when the interrupter 16 is closed. Another advantage of

contacts

28 and 72 is that the arc 54 is forced radially inward and is prevented from interacting with the arc shield 40. All

contacts configurations

28, 60 and 72 effectively employ stress concentration to aid in breaking any welds which might occur between the contacts. Yet another important advantage of all these designs is that the current through the

contacts

28, 60 and 72 and the are 54 must travel through the contact surfaces 50, 64 and 76, respectively, perpendicular to the axis of the arc 54 and this produces a greater unbalance in the self-induced magnetic field distribution and therefore a greater magnetic field to drive the arc in a specified direction than prior art contacts.

Since numerous changes may be made in the abovedescribed apparatus different embodiments of the invention may be made without departing from the spirit and scope thereof. It is intended that all the matter conan annular contact and arcing portion having a relatively thin cross-sectional area and being divided into a plurality of contact and arcing surfaces; contact support means for supporting each contact and arcing surface from one end only and for positioning said annular contact and arcing portion slightly above said disc-shaped portion by a distance less than the thickness of said annular contact and arcing portion; and each of said contact and arcing surfaces connected to said flat circular base portion near the outer periphery and extending from the connection in a radially inward and circumferential direction so that the arc formed during circuit interruption is moved radially inward and rotated around the inner diameter of said annular contact and arcing portion. 2. A vacuum interrupter as claimed in claim 1 wherein:

said plurality of contact and arcing surfaces of said annular contact and arcing portion lie in a common plane so that when said vacuum circuit interrupter is closed with the second contact-in engagement with the first contact the entire annular contact and arcing portion of the first contact engages the entire annular contact and arcing portion of the second contact and when said vacuum interrupter is in the open position with the first contact separated from the second contact an arcing gap having a uniform length is formed therebetween. 3. A vacuum interrupter as claimed in claim 2 wherein most of the contact support means for each contact and arcing surface is positioned beneath the preceding contact and arcing surface whereby the current flow through the contact and arcing surfaces during arcing must be substantially parallel to said flat circular base portion and perpendicular to any arc formed during circuit interruption. I I

4. A vacuum" interrupter .as claimed in claim 3 wherein:v l Y I each of saidv contact support means is joined to said flat circular base portion in a trapezoidal shaped"- figuration with two sides of the trapezoid extending generally radially inward a'distance from the outer periphery of said flat circular base portion less than the radially inward spacing of said annular contact and arcing portion; and

with the outer side of the trapezoid running parallel and in alignment with the outer periphery of said flat circular base portion.

5. A vacuum interrupter as claimed in claim 2 wherein said annular contact and arcing portion has an inner diameter which is greater than the radius of said flat circular base portion.

6. A vacuum interrupter as claimed in claim 2 wherein said annular contactand arcing portions have an outer diameter which is approximately equal to the outer diameter of said flat circular base portion.

7. A vacuum interrupter as claimed in claim 3 wherein said contact support means for supporting each contact and arcing surface from one end only is resilient to allow each of said contact and arcing surfaces to flex slightly and provide that complete contact is made at each contact and arcing surface when the first contact and second contact are in engagement.

8. A vacuum interrupter as claimed in claim 4 wherein, the contact areas where each of said contact support means joins said flat circular base portion define an annular ring with the contact support means joined to the flat'circular base portion at discreet intervals on the defined annular ring and the area of the annular ring covered by said contact support means joining to said flat circular base portion is substantially less than the area defined by the annular ring.

9. A vacuum interrupter as claimed in claim 1 wherein said contact support means supports said contact and arcing portion above said disc-shaped portion by a distance less than the length of the arcing gap.

tion.

Claims

1. A vacuum interrupter having a first contact and a second contact being relatively movable with respect to the first contact between a closed position in engagement with the first contact and an open position separated from the first contact to form an arcing gap therebetween across which an arc is formed during circuit interruption wherein each contact comprises: a flat circular base portion having a solid disc shape; an annular contact and arcing portion having a relatively thin cross-sectional area and being divided into a plurality of contact and arcing surfaces; contact support means for supporting each contact and arcing surface from one end only and for positioning said annular contact and arcing portion slightly above said disc-shaped portion by a distance less than the thickness of said annular contact and arcing portion; and each of said contact and arcing surfaces connected to said flat circular base portion near the outer periphery and extending from the connection in a radially inward and circumferential direction so that the arc formed during circuit interruption is moved radially inward and rotated around the inner diameter of said annular contact and arcing portion.

2. A vacuum interrupter as claimed in claim 1 wherein: said plurality of contact and arcing surfaces of said annular contact and arcing portion lie in a common plane so that when said vacuum circuit interrupter is closed with the second contact in engagement with the first contact the entire annUlar contact and arcing portion of the first contact engages the entire annular contact and arcing portion of the second contact and when said vacuum interrupter is in the open position with the first contact separated from the second contact an arcing gap having a uniform length is formed therebetween.

3. A vacuum interrupter as claimed in claim 2 wherein most of the contact support means for each contact and arcing surface is positioned beneath the preceding contact and arcing surface whereby the current flow through the contact and arcing surfaces during arcing must be substantially parallel to said flat circular base portion and perpendicular to any arc formed during circuit interruption.

4. A vacuum interrupter as claimed in claim 3 wherein: each of said contact support means is joined to said flat circular base portion in a trapezoidal shaped figuration with two sides of the trapezoid extending generally radially inward a distance from the outer periphery of said flat circular base portion less than the radially inward spacing of said annular contact and arcing portion; and with the outer side of the trapezoid running parallel and in alignment with the outer periphery of said flat circular base portion.

6. A vacuum interrupter as claimed in claim 2 wherein said annular contact and arcing portions have an outer diameter which is approximately equal to the outer diameter of said flat circular base portion.

8. A vacuum interrupter as claimed in claim 4 wherein, the contact areas where each of said contact support means joins said flat circular base portion define an annular ring with the contact support means joined to the flat circular base portion at discreet intervals on the defined annular ring and the area of the annular ring covered by said contact support means joining to said flat circular base portion is substantially less than the area defined by the annular ring.

10. A vacuum interrupter as claimed in claim 1 wherein said contact support means supports said contact and arcing portion above said disc-shaped portion by a distance less than one-fourth of an inch.

11. A vacuum interrupter as claimed in claim 1 wherein said contact support means supports said contact and arcing portion above said disc-shaped portion by a distance less than the radius of said base portion.