US3366762A - Arc controlling electrodes for switches and gaps - Google Patents

Description

Jan. 30, 1968 s. R. SMITH, JR 3,366,762

ARC CONTROLLING ELECTRODES FOR SWITCHES AND GAPS Filed April 16, 1965 3 Sheets-Sheet 1 16 16' :f 0, 8 14 20 fiZl/en/fin 570%.? S'm'ifid; 3 y jMAT'M Jan. v30, 1968 s. R; SMITH, JR 3,366,752

ARC CONTROLLING ELECTRODES FOR SWITCHES AND GAPS Filed April 16, 1965 3- Shets-Sheet 2 b WPM MSW/51775;; I

Jan. 30, 1968 Y s. R. SMITH, JR

- A RC CONTROLLING ELECTRODES FOR SWITCHES AND GAPS Filed April 16, 1965 5 Sheets-Sheet 5 United States Patent 3,366,762 ARC CONTROLLING ELECTRODES FOR SWITCHES AND GAPS Sidney R. Smith, Jr., Stockbridge, Mass., assignor to General Electric Company, a corporation of New York Filed Apr. 16, 1965, Ser. No. 448,787 9 Claims. (Cl. 200-144) ABSTRACT OF THE DISCLOSURE A circuit interrupter or gap having a cup shaped contact or electrode with a reentrant rim surrounding a second contact or electrode so as to produce an electromagnetic force on an arc between the bottom of the cup shaped electrode and the end of the other electrode so as to confine the are within the cup shaped electrode.

This invention relates to electric arcs and more particularly to their auto-confinement and control.

An example of where arc control is important is in vacuum switches, but the invention is not limited to such switches and can be used in ordinary switches or in gap devices such as are found in lightning arresters or in other electrical devices where confinement and control of an electric arc is desirable. A reason why are control is particularly important in vacuum switches is that because of the comparatively high vacuum that must be maintained their volume, and hence size, should be as small as possible. On the other hand, high energy arcs tend to spread and get out of control and vaporize the electrodes carrying metal vapor onto the insulating walls of the housing, inviting failure to interrupt. These factors, therefore, limit the interrupting capacity of a given size vacuum switch of ordinary construction. By preventing the are from spreading, the size of a vacuum switch of given interrupting ability can be substantially reduced.

An object of the invention is to provide a new and improved means for confining and controlling an electric arc.

Another object of the invention is to provide a novel electromagnetic means for self-controlling and confining an electric are.

A further object of the invention is to provide a novel arcing electrode configuration.

An additional object of the invention is to provide an improved electric switch contact configuration.

An added object of the invention is to provide a new and improved vacuum switch of increased interrupting ability per unit size.

In accomplishing the objects of the invention at least one cup shaped electrode with a re-entrant lip portion cooperates with another electrode for automatically confining by inherent electromagnetic action an are between the electrodes to the space between the electrodes. By making one of the electrodes a rod shaped contact and confining the arc to the interior of the cup shaped electrode as the other contact, the latter will also function as a metal vapor shield in a vacuum switch thus making it possible to eliminate such a shield as a separate element in vacuum switches.

The invention will be better understood from the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

In the drawings,

3,366,762 Patented Jan. 30, 1968 FIG. 1 is a perspective view of a vacuum switch employing the invention,

FIG. 2 is a longitudinal sectional view of the switch shown in FIG. 1 taken on line 2-2 of FIG. 1,

FIGS. 3, 4, 5, 6, 7 and 8 are views similar to FIG. 2 of modifications, and

FIGS. 9 and 10 are respectively orthographic and isometric half sectional views of another modification employing a pair of cup shaped electrodes or contacts.

Referring now to the drawings, and more particularly to FIG. 1, there is shown therein a vacuum switch 1 comprising by way of example a cylindrical housing 2 of suitable insulating material such as glass or ceramic material provided with metallic end caps 3 which are sealed to the ends of the housing 2 in any suitable manner so as to form a vacuum tight envelope or enclosure. Extending from the lower end of the enclosure is an electrical terminal connection 4 and extending from the upper end of the enclosure is an electrical terminal connection 5. The terminal 4 is fixed and the terminal 5 is movable by means of a bellows 6, the lower end of which is sealed to the upper end cap or plate 3 and the upper end of which is sealed to a flange 7 on the terminal connector 5.

The interior construction of the switch is shown in FIG. 2 and will be seen to consist of a cup shaped metallic or conducting electrode or contact 8 from the center of whose bottom extends outwardly the terminal connection 4. The portion of the terminal connection 5 which extends into the switch is a rod like conductive member 9 which extends into the cup electrode 8 and on the lower end of which adjacent the bottom of the cup shaped electrode 8 is an arcing electrode or contact portion 10 shown as being dumbbell shaped in cross section but, of course, being actually circular with indented central portions on both sides. Attached to the rim of the cup 8 is a metallic or conductive re-entrant inwardly extending lip portion 11 surrounding the rod 9 and extending inwardly toward the bottom of the cup member 8. The switch can be closed by moving the parts 5, 9, and 10 downwardly until part 10 contacts the bottom of the cup 8 or moving the parts 5, 9, and 10 upward until the upper edge of the part 10 engages the lower end of the inwardly extending re-entrant lip portion 11. FIG. 2 shows the switch in its open position where there is no contact between the parts 10 and the parts 8 or 11.

The operation of FIG. 2 as thus far described is as follows. Assume that the switch attained its illustrated open position by raising the arcing contact member 10 from the bottom of the cup 8. This will initially draw an are 12 which will be fed by current having a curved or kinked path in that the current will flow generally horizontally through portions of the member 10 and the bottom of the cup 8 between the rod 9 and the are 12 and between the are 12 and the terminal connection 4. As a result of this so-called current loop, the magnetic flux density on the inner side of the loop corresponding to the right-hand side of the arc 12 as viewed in FIG. 2 will be greater than the flux density on the opposite side so that an automatically produced electromagnetic force will tend to move the arc to the left as viewed in FIG. 2, i.e., clockwise about the end of the electrode or contact 10 so that the arc will successively assume positions 13, 14, 15 and 16. However, in the position 16 the arc will be fed through the re-entrant lip portion 11 which extends in the opposite direction from the Wall of the cup shaped member 8 so that the electromagnetic force will reverse and the arc will be forced back to the position 15. Then the original force which caused it to jump from position 15 to position 16 will again come into play so that the arc will rapidly jump back and forth between positions 15 and 16.

Even if the arc were to over-shoot the position 16 to a position 17 between the lip portion 11 and the rod 9, the electromagnetic force would be such as to drive the arc downward and back to position 15.

Essentially the same action would take place if the switch had come from an upward closed position where movable contact was touching the lower end of the re-entrant lip portion 11 to the open position shown in FIG. 2, except that in that case the arc would first be drawn at position 16 and would then be forced to jump to position and back and forth between those positions as already described.

The result is that the arc is confined within the cup shaped electrode or contact 8 so that little or no contact metal vaporized by heat of the arc can escape from the cup but all such vaporized metal will simply condense on the metallic surfaces within the cup. Consequently, the conventional metal shield which is normally interposed between the contacts of a vacuum switch and its insulating envelope such as the insulating cylinder 2 can be eliminated. The function of such a shield is, of course, to condense vaporized metal and prevent it from condensing on and coating the surfaces of the insulating cylinder or envelope so as to cause ultimate short circuiting or failure of the switch. It also tends to avoid weakening of the ceramic by heat shock.

If desired, means may be provided for rotating the arc about the common axis of the cup 8 and rod 9. One such means can be a conductive coil 18 for immersing the arc in a magnetic field which extends generally parallel to the common axis of the cup 8 and rod 9, this coil being connected serially in the circuit. The interaction of the horizontal component of the arc current and the vertical magnetic field will cause a tangential force to be applied to the arc, thus rotating it or spinning it about the axis of the switch. This, of course, has the desirable effect of keeping the electrodes from melting or burning away at a particular point because it does not continuously play betwen fixed spots on the electrodes.

Ordinarily, in the case of alternating current, the arc will be extinguished at the first current zero.

If desired, the rod 9 can be provided with a shield 19 for condensing what small amount of vaporized metal may escape from between the rod 9 and the lip 11.

Preferably, the radial distance between the rod 9 and the lip portion 11 is smaller than the radial distance between the lip portion 11 and the wall of the cup member 8, and preferably the axial length of the lip portion 11 is a sizable fraction of the arc chamber height.

Referring now to the modification shown in FIG. 3, the principal differences are that the movable contact 10' is more disk shaped than the dumbbell shaped contact 10 of FIG. 2, and a circular cooperating bead or raised portion is provided on the inner bottom surface of the cup shaped contact 8. This is to insure the formation of a current loop or kink which will, when the initial are 12 is formed, start it around to its ultimate alternate positions 15 and 16 as described in connection with FIG. 2. Another dilference is that in FIG. 3 the bellows 6 is mounted internally instead of externally and the shield 19 is consequently somewhat frustoconical in shape.

Referring now to the modification shown in FIGS. 4 and 5, this is generally similar to FIG. 2 except for the shape of the parts for causing arc motion. Thus while the movable contact 10" is generally similar in vertical cross section to the movable contact 10 of FIG. 3 the central inner bottom surface of the cup shaped electrode or contact 8 is dished at 21 so as to insure that an initial are drawn between the bottom of the cup 8 and the bottom of the contact 10" will be off axis so as to produce initially the required current loop or kink for moving the arc to its ultimate alternate positions 15 and 16.

Also, instead of employing the separate coil 18 shown in FIG. 2 for causing arc rotation, angularly or spirally extending slots 22 are cut in the movable contact 10 as shown by the sectional view illustrated in FIG. 5 which is a horizontal sectional view of the contact 10 taken on line 5-5 of FIG. 4. By means of these slots 22, the current flowing in the contact 1% is given a tangential component in addition to its normal radial component which it has in FIGS. 2 and 3. This tangential component of the current applies a tangential electromagnetic force to the arc causing it to spin around the vertical axis of the switch in the same way that the coil 18 of FIG. 2 causes it to spin.

If desired, this action may be supplemented or substituted for by complementary angularly or spirally extending slots 23 cut in the re-entrant lip member 11 so that in the same way current flowing to or from the are through the vertical portion of the lip member 11 will have a tangential or circumferential component for causing the arc to spin about the axis of the device. Of course, if both the movable contact 10" and the lip portion 11 are slotted, care must be taken that the slots extend in complementary angular directions so that the are spinning forces produced thereby will be in the same direction. While angularly or spirally slotting the outer walls of the cup shaped member 8 would tend to spin the arc in its transistory positions 12, 13 and 14, this is hardly necessary because the arc does not stay long enough in any one of these positions and actually it is undesirable because this would provide openings in the outer walls of the cup 8 which would allow escape of vaporized contact metal which would then coat the inner surface of the insulating envelope 2 unless a separate vapor shield were provided.

It will, of course, be understood that the coil 18 of FIG. 2 or the slots 22 of FIG. 5 or the slots 23 of FIG. 4 can be used singly or in combination in all of the various species of the invention when it is desired to cause the arc to rotate.

In the modification shown in FIG. 6, the rod 9 and/or the terminal connection 4 are made of magnetic material to influence the magnetic flux distribution near the contacts and to provide greater stiffness or electromagnetic force for moving the arc and confining it between its position 15 and 16.

In the modification shown in FIG. 7, the insulating housing 2' is shown as of generally H-shaped cross section with a metal case 24 extending around the bottom half and sealed thereto and to the bottom of the cup shaped contact 8. The opening in the crossbar of the H being sealed by the bellows 6 between which and the rod 9 there is a modified shape shield 19" if desired. The movable contact 10' is also shown of somewhat different shape, being hollow.

In the modification shown in FIG. 8 the re-entrant lip 11' fits over the rim of the cup 8 and is comparatively short because in general the length of the inwardly extending re-entrant lip is proportional to the interrupting rating of the switch, and for switches of comparatively low interrupting rating such as the one illustrated in FIG. 8 the lip 11' can be shortened. Also the movable contact 10"" consists of a plain cap fitted over the end of the rod 9 and a mating fixed contact 20' is a cap fitted over the end of the terminal connection 4 at the bottom of the cup 8. While this construction does not show any means for insuring an initial loop or kink in the current feeding an initial arc, arcs inherently have a characteristic of wandering so that even if the initial arc were exactly on the axis of the device it would move enough to create a small loop or kink which then would force it further sidewise to produce the resulting action in the are as described in connection with the previous figures particularly FIG. 2.

1n the modification shown in FIG. 9, there are two cup shaped electrodes 25 and 26 with re-entrant inwardly extending lip portions 27 and 28, respectively. They are arranged in mouth facing mouth relation and when spaced as illustrated constitute a gap so that current flowing between a terminal 29 for electrode 25 and a terminal 30 for an electrode 26 will jump the gap between them. However, they obviously may be the contacts of a switch in which case they will be relatively movable in their coaxial direction so that when they are in contact the switch will be closed and when they are separated the switch will be open. They can, of course, be located in an evacuated envelope as in the preceding figures so as to constitute a vacuum switch. It will be understood, of course, that FIG. 9 is an orthographic sectional view through the central axis and that actually the cups have re-entrant surfaces extending all around a common axis as shown by the isometric sectional view in FIG. 10. Consequently when they are separated as shown in FIG. 9 they constitute a special type of horn gap having a lateral dimension which is actually a closed re-entrant surface, this being a surface of revolution if the cups are circular in horizontal cross section. The re-entrant portions 27 and 28 are preferably provided with c0rnple mentary sloping angular or spiral cuts or slots 31 and 32 respectively for the purpose of spinning an are around the common longitudinal axis which, of course, is a central vertical axis as viewed in the drawing. The direction of rotation is as indicated by the arrowed circle at the bottom of FIG. 10.

The operation of FIG. 9 is as follows. Assume an are 33 is drawn or struck between the electrodes 25 and 2-6. This is at a point of minimum spacing and it will be seen that current flowing into and out of that arc between the terminals 29 and 30 along the sides of the cups 25 and 26 will have a loop or kink thus forcing the arc inward toward the center or common axis so that the arc will rapidly progressively assume the dashed line positions 34, 35, 36 and 37. This same action would take place regardless of where on the perimeters of the mouths of the cups 25 and 26 the are 33 initially for-ms. At the same time the arc is caused to move along this perimeter or, in other words, rotate about the common axis because the skewed teeth or cuts 31 and 32 produce tangential components in the direction of current flowing into and out of the arc. These tangential components have the same direction because the angles of skewing of the cuts or teeth are such as to take account of the directions of the current when it enters and when it leaves the arc.

Of course, the higher the arc current, the greater the electromagnetic force tending to force the arc inward toward the center and also the greater the force tending to spin it about the axis. In this manner, the arc is automatically and practically instantaneously driven inward, elongated, and cooled by the horn gap action supplemented by the spinning action so that the arc can go completely around the electrode axis many times in a half cycle of 60 cycle current.

To facilitate manufacture it is preferable to make the upper and lower halves of FIG. 9 exact duplicates as shown but this, of course, is not necessary.

The vacuum switches can, of course, be evacuated in any suitable manner such as by pumps of either the mechanical or the diffusion type or both in series or in a pumpless manner according to the method disclosed and claimed in De Santis et a1. United States Patent 2,934,392 which is assigned to the present assignee.

It will, of course, be understood that the previously used terms horizontal and vertical refer only to the drawings when they are placed in an upright position and that actually the invention in nowise depends on any particular orientation of the devices in space.

While there have been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and therefore it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

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

1. In combination, an arc confining electrode structure including a pair of spaced electrodes between which an arc is drawn, one of said electrodes being cup shaped, the other being rod shaped and extending into said cup shaped electrode through the mouth thereof to the bottom thereof, the rim of said cup shaped electrode having a reentrant lip portion extending inwardly toward the bottom thereof around said rod shaped electrode, said cup shaped electrode and re-entrant lip portion forming current paths of loop shape such that electromagnetic forces produced by current flow through the bottom of the cup shaped electrode and through the re-entrant lip portion retain all arcs within the confines of the cup shaped electrode.

2. The combination of claim 1 provided with means for rotating an arc between said electrodes about the axis of said cup and rod.

3. A combination as in claim 2 in which said means is a series of spiral cuts in at least one of said electrodes.

4. An arcing duty electric switch comprising, in combination, a cup shaped contact having a terminal extending outwardly from the center of the bottom thereof, a second contact in said cup shaped contact for engaging the bottom surface thereof, said second contact being mounted on the end of a conductive rod extending axially of the cup shaped contact out of the mouth thereof and being movable in said axial direction, the rim of said cup shaped contact having a re-entrant portion extending inwardly toward the bottom thereof, whereby current flow between said terminal and the outer end of said rod which feeds an are between said contacts will have current paths of loop shape which produce electromagnetic forces which in the case of an arc to said re-entrant portion drives said are into said cup shaped contact and in the case of an arc to the wall of said cup shaped contact drives said are in the opposite direction toward said re-entrant portion.

5. In a vacuum circuit interrupter, a circular cross section cup shaped contact having a terminal extending outwardly from the center of the bottom thereof, a circular cross section second contact in said cup shaped contact for engaging the bottom thereof, said second contact being mounted symmetrically on the end of a smaller diameter rod extending axially of said cup shaped contact out of the mouth thereof, the rim of said cup shaped contact having a re-entrant lip portion extending inwardly toward the bottom thereof, said rod being axially movable whereby an arc drawn between said contacts when they separate is driven by electromagnetic force along the Wall of the cup shaped contact toward said re-entrant lip portion but an arc to said re-entrant lip portion is driven in the opposite direction back to the wall of said cup shaped contact.

6. In a vacuum circuit interrupter, a circular cross section cup shaped contact, a circular cross section disk contact in said cup shaped contact for engaging the bottom thereof, said disk shaped contact being mounted symmetrically on the end of a rod of smaller diameter extending axially of said cup shaped contact out of the mouth thereof, the rim of said cup shaped contact having a reentrant lip portion extending inwardly toward the bottom thereof.

7. In a vacuum circuit interrupter, a circular cross section cup shaped fixed contact having an external terminal extending axially outward from the bottom thereof, a circular cross section movable disk contact for engaging flatwise between its center and its rim the inner bottom surface of said cup shaped fixed contact, a straight conductive actuating rod terminal for said movable disk con tact of smaller cross section than said disk contact connected to the center thereof and extending axially of said 3,366,762 7 8 cup shaped contact out of the mouth thereof, the rim of References Cited said cup shaped contact having a re-entrant lip portion UNITED STATES PATENTS extending inwardly toward the bottom thereof for confining withtin said cup shaped contact by electromagnetic 9 9 1935 efi action an are 'between the rim of said disk contact and the 5 3,014,108 12/ 1961 Cobi t 1, 200-144 inner surface of said cup shaped contact. 6 h 3 014 109 12/1961 Burger 2O0 144 8. A circuit interrupter as in c aim provide-d wit means for rotating an are between said contacts about the 3185797 5/1965 Pqter 200-144 axis of aid cup and rod TIUJS 9. A circuit interrupter as in claim 8 in which said 10 3,261,954 7/ 1966 Yonkers 200-144 means is a series of spiral cuts in at least one of said contacts. ROBERT S. MACON, Primary Examiner.

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