US3891814A

US3891814A - Apparatus for arc quenching

Info

Publication number: US3891814A
Application number: US334936A
Authority: US
Inventors: Walter Hertz; Jurgen Mentel; Jan Stroh
Original assignee: Siemens Corp
Current assignee: Siemens AG; Siemens Corp
Priority date: 1972-02-28
Filing date: 1973-02-22
Publication date: 1975-06-24
Anticipated expiration: 1992-06-24
Also published as: CH550478A; DE2209388A1; NL7301006A; JPS4899661A; IT979526B; SU511881A3; DE2209388B2; DE2209388C3; DE7207479U; CS167376B2; DD103338A5; FR2174062B1; FR2174062A1

Abstract

An improved method and apparatus for extinguishing the arc in a gas flow circuit breaker of the type in which one or more of the contacts is designed as a nozzle. The end surface of the nozzle and a portion of its inner surface are insulated so that the arc will be drawn inside the nozzle to a point from which current will flow in a direction so as to generate a magnetic field which will tend to force the arc into the center of the nozzle thereby resulting in quicker extinguishing action.

Description

United States Patent |191 Hertz et al.

|451 June 24, 1975 [54] APPARATUS FOR ARC QUENCHING [75] Inventors: Walter Hertz; Jrgen Mentel; `lan Stroh, all of Erlangen, Germany [73] Assignee: Siemens Aktiengesellschaft, Munich,

Germany [22] Filed: Feb. 22, 1973 [2l] Appl. No.: 334,936

[30] Foreign Application Priority Data Feb. 28, 1972 Germany 2209388 [52] U.S. Cl 200/148 R; 200/147 R; 20C/275 [51] lnt. Cl.. HOlh 33/60 [58] Field of Search 20G/148 R, 147 R, 275, 20G/148 R, 144 B, 148 B [56] References Cited UNITED STATES PATENTS 3,210,505 10/1965 Porter 200/144 B 3,274,365 9/1966 Beatty 2001148 B 3,327,081 6/1967 Pflanz 20D/144 B 3,417,216 12/1968 Smith, Jr. 20D/144 B 3,471,666 10/1969 Barkan 200/148 B FOREIGN PATENTS OR APPLICATlONS 646,031 6/1937 Germany A'lIIIIIIII/ :2;

961.906 4/ 1957 Germany 972,025 5/1959 Germany 1,212,617 3/1966 Germany l,2l7,926 1/1971 United Kingdom 1,227,833 4/1971 United Kingdom 1,965,853 6/1971 Germany 20C/148 R 117,076 6/1943 Australia 200/148 R 1,197,156 7/1965 Gennany .i 2001148 R Primary Examiner-Robert S. Macon Attorney, Agent, or Firm-Kenyon & Kenyon Reilly Carr & Chapin 5 7 ABSTRACT An improved method and apparatus for extinguishing the are in a gas flow circuit breaker of the type in which one or more of the contacts is designed as a nozzle. The end surface of the nozzle and a portion of its inner surface are insulated so that the arc will be drawn inside the nozzle to a point from which current will ow in a direction so as to generate a magnetic field which will tend to force the arc into the center of the nozzle thereby resulting in quicker extinguishing action.

14 Claims, 4 Drawing Figures l APPARATUS FOR ARC QUENCl-IING BACKGROUND OF THE INVENTION This invention relates to circuit breakers in general in more particularly to a method and apparatus for interrupting the arc formed in a quenching medium-flow breaker.

There are various types of circuit breakers which have been used in the art for switching large currents. One class of breakers are known as quenching medium flow circuit breakers, and are generally of the gas flow type although oil may also be used as a quenching medium. These circuit breakers may be designed as dualpressure breakers, blast piston breakers, and also as free-jet air blast breakers. One such breaker is shown in the German published Pat. application No. l,2l2,6l7. The breaker disclosed therein is a cornpressed gas circuit breaker in which the electrodes comprise two coaxial nozzle tubes which are arranged at a fixed distance apart from each other. The nozzles of each of the two electrodes are divided into segments by slots extending in the axial direction. A common air blast valve is provided for the two contacts. In normal operation a bridging contact member at the outer cylindrical surface completes the circuit between the two electrodes. When the circuit breaker operates the bridging contact member moves and serves to draw the arc between the contacts. The contact fingers of this bridging contact member are arranged inside a tubular body which is open on one side and which at the same time is the movable blast valve. The bridging contact member causes the arc to be drawn at the outer cylindrical surface between two opposing end faces of the electrodes. The arc is then blown into the nozzleshaped contacts by the gas stream. The segments cause the current to flow radially inward toward the arc and thereby create a magnetic field which tends to cause the arc to travel inward. This effect is only achieved, however, if the arc is drawn from a segment on one nozzle to the segment on the other nozzle which opposes it. It is possible under some conditions that the arc will burn between two segments which are not opposing, in which case the magnetic force is reduced. If the arc burns from a segment on one nozzle to a segment on the other nozzle which is shifted from it by substantially 180, the magnetic forces will not act radially inward but instead outward and the entering of the arc into the nozzle will be impeded.

Another type of circuit breaker in which quenching is accomplished by a flowing pressure medium is disclosed in the German published Pat. application l,055,643. In the arrangement shown therein two individual metallic nozzles are arranged a fixed distance from each other. In this case the nozzles are not the current carrying electrodes but are used only for the feeding of the flowing quenching medium. The current carrying electrodes are arranged concentric to and inside the nozzles and are movable with respect to each other along the nozzle axis. The arc is then drawn between these two electrodes. The nozzle bodies are lined at their surface, at least in the region of their narrowest cross section, with an insulating layer to prevent the arc which has been drawn between the switching contacts from passing to the nozzle bodies.

SUMMARY OF THE INVENTION The contact arrangement of the present invention facilitates the entrance of the base of the arc into the inner portions of at least one nozzle shaped contact through the use of magnetic forces generated within the contacts and thus improves the quenching ability of the breaker. ln general terms the invention is based on the discovery that the magnetic forces resulting from the arc current can be used very effectively for moving the base points of the arc and the arc column if the current is properly directed. This is particularly significant since the magnetic forces are by nature volume forces, which act on all of the arc, while the forces of a quenching medium such as air can only attack the surface areas of the arc. In addition it has been discovered that the current being interrupted will generate a magnetic force which increases with the square of the current. ln practical terms this means that in situations where it is desired to interrupt or switch a large current, which in former breakers would have required an air flow exceeding the velocity of sound thus making the task impossible, the increased force effect of the magnetic field now makes such switching possible.

In addition, when interrupting large currents in the order of for example, l0() kiloamperes and more, there is a backup effect which occurs in the prior art circuit breakers which is caused by the arc clogging the discharge openings in the nozzle and reducing the mass flow rate of the quenching medium. This then results in a decrease of the forces of the quenching medium on the arc and its base points and slows quenching time. The apparatus and method of the present invention overcome this difficulty through the use of magnetic forces which act upon the arc and its base point. Thus, even if clogging of the nozzles occurs at high currents, the high current will generate an increasingly larger force which will still tend to cause the arc and the base to be pushed in the desired direction toward the nozzle center for fast quenching.

The current which achieves these advantages, i.e. that which generates a magnetic force in an inward radial direction, is obtained by causing the base of the arc to be drawn inside the entrance of the nozzle. The nozzle has a shape such that the current will then flow in a direction opposite to that of the current flow in the arc thereby providing the required magnetic force.

The preferred apparatus for practicing the method of the present invention comprises two opposing nozzle shaped electrodes having contact surfaces on the inside. A bridging electric electrode concentric with and inside the two nozzles, electrically connects their inner surfaces and upon operation of the circuit breaker draws the arc from the inside of one nozzle to the inside of the other. To assure that the base points of the arc are located inside the nozzles rather than at its outer edges, the surfaces of the electrodes, their outer opposing end faces and a portion of their inner surface are coated with an insulating material. By thus causing the base of the arc to be inside the nozzle, a curved path through the nozzle which will provide the desired magnetic field results. A second embodiment of the invention includes the forming of spiral paths on the end faces of the electrode to further enhance the characteristics of the magnetic field and to Cause rotation of the base points of the arc. Also shown is a third embodiment in which only one nozzle type electrode is used.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a first preferred embodiment of the invention showing two opposing nozzles in a cross sectional view.

FIG. 2 is a cross sectional view illustrating a second embodiment of the invention in which spiral current paths are used and in which the nozzles have replaceable contacts.

FIG. 3 is an end view ofthe nozzle of FIG. 2 showing the electrode arrangement to obtain the spiral path.

FIG. 4 is a cross sectional view ofa third embodiment of the invention in which only a single nozzle type electrode is used.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a cross sectional view illustrating a first ernbodiment of the present invention. The upper electrode 2 is formed to shape a nozzle having an entrance portion 6 and a mouth portion 10. Similarly the lower electrode 4 has an entrance portion 8 and a mouth portion l2. The two nozzles thus constructed form the path through which the quenching medium will flow for quenching the arc. The quenching effect of the flow will be similar to that described in the above referenced German published application and will not be discussed in detail herein. Each of the electrodes is covered on its outside by an insulating material designated 16 for

electrode

2 and 18 for electrode 4. This insulation extends around the end of the respective electrodes and coats a portion of the inside of the nozzle in the vicinity ofthe nozzle opening. In addition, it is preferable to also coat the inner surfaces of the electrodes in the vicinity ofthe nozzle opening with an insulating material indicated collectively as 22 for

electrode

2 and 24 for electrode 4.

The electrodes 2 and 4, particularly at their end portions, may be divided into individual segments similar to the segmenting of the contacts in German application No. l,2l2,6l7 referenced above. This may be done by slotting the electrodes 2 and 4 and filling in these slots with insulating material much in the manner to be described below in connection with FIGS. 2 and 3. The slots 27 should extend at least to the depth of the nozzle mouth opening designated respectively as and l2. The number of slots may be two, three or more as desired.

A contact member designated by the numeral 25 will have been making contact between the inner surfaces of the electrodes 2 and 4 prior to the switching action. Contact member 25 will preferably be of tubular design and will be mechanically connected to the breaker tripping mechanism in a manner well known in the art. When switching action occurs, the contact member 2S will be drawn from a position where it contacts the electrodes 2 and 4 to the position shown on the drawings. In doing so, it will draw the arc designated as 26 between electrodes 4 and 2. Because the insulating

material

16 and 18 is extended over the ends of the nozzles 2 and 4 partially into the

sections

6 and 8, the arc will be drawn at least partially inside each of the nozzles. The insulation 22 and 24 prevents the arc from jumping from the inner portion of the electrodes to the outer walls. Thus, the current must follow the curved paths designated respectively as 28 and 32 on the electrodes 2 and 4. For proper operation, the depth of the insulation on the inner portion of the contact designated on the figure as b should be at least equal to or greater than the dimension shown as a, the thickness of the electrode at its end.

As a result of the arcs being drawn inside the nozzles 2 and 4, and the current following the curved paths designated as 28 and 32, magnetic forces are generated as soon as the arc is drawn. The magnetic forces thus generated will tend to repel the arc in the direction indicated by the arrow 34. This results in a tendency for the base points of the arc to move even further into the nozzle toward the

mouth portions

10 and 12. In turn, because of the longer current path, this will result in a greater magnetic force in the same direction, thereby continually providing positive reinforcement of the effect. These forces operate in conjunction with the quenching medium, which is flowing into the nozzles in a manner well known in the art, to move the arc toward the axis of the two nozzles for fast and efficient quenching. Even if a large current is being interrupted, which can tend cause the arc to wander outside the center region because of clogging of the quenching medium, the magnetic forces are still present independent of the quenching medium and will keep the arc stabilized within the nozzle section.

The

current loops

28 and 32 generate a magnetic field which has a tangential direction at the end faces ofthe electrodes 2 and 4. If for some reason, for example, turbulent flow of the quenching medium, the arc is driven toward the outside of the nozzle ends, this force directed toward the axis of the electrodes will act on the arc at these regions and drive it back into the interior of the electrodes. The portions of the current flowing in the outer part of the electrodes designated respectively as 36 and 38 will, of course, produce a magnetic field which is opposite to that produced by the currents in the

paths

28 and 32. However, at the arc 26 this magnetic force will be of much less magnitude than that generated in the opposite direction by the current in

paths

28 and 32 and will have little effect on the arc 26, i.e. the net force will still be so as to tend to force the arc 26 toward the axis of the electrodes.

The insulating

materials

16 and 18 and 22 and 24 may consist of. for example` a heat resisting plastic, ceramic material or casting resin.

A second embodiment which offers further advantages is illustrated by FIGS. 2 and 3. ln these figures, parts which are essentially the same as those of FIG. 1 are given identical reference numerals. Also, only one electrode is shown although it will be recognized that in operation a pair of electrodes such as shown in FIG. 1 will be used. In this embodiment as is evident from the view of FIG. 2, the end surface of the electrode contains a flat portion. lt is constructed in this manner to permit the cutting of slots into the electrode as illustrated more clearly by FIG. 3. On FIG. 3, which shows the end prior to coating with the outer insulating 16, the slots in the electrode are designated by the

numerals

40, 41, 42 and 43. The electrode conducting portions are designated as 44, 45 and 46 and 46 a. In general, the slots are cut so that the conducting portions of the electrode follow an essentially spiral path such as shown by the current path 48. This arrangement will produce magnetic forces which reinforce the forces de` scribed above in connection with the

current paths

28 and 32. The current l flowing in the right hand side of the electrode 2 of FIG. 2 will enter the end portion of the electrode segment 46 at a point designated as 47. It will follow the path shown by the line 48 on FIG. 3

and will exit from the electrode section 46 at a point designated as 49, shown on both figures, at the opposite side of the electrode 2 on its inner surface. In the illustrated embodiment, the section 47 where the current enters and the section 49 where it exits are approximately 180 from each other. This angle is not critical and other angles may be used. The result of this arrangement is that the current in the area of point 47 will generate a magnetic field which attracts the arc 26 whereas the current in the portion 49 will generate a current which repels the arc 26 in the same manner as it was repelled by the field generated by the current at point 28 in FIG. l. The repelling force generated at point 49 and the attracting force generated by the current at 47 will each tend to draw the arc 26 toward the center axis of the nozzle. Thus, this arrangement reinforces the magnetic forces tending to draw the arc toward the center for better quenching. In contrast, the current 36 in the embodiment of FIG. l, which is equivalent to the current at 47 here, detracted from the magnetic force generated by the current at point 28 of FIG. 1.

The rotation of the current path by approximately 180 as shown on FIGS. 2 and 3 will also generate a magnetic field which runs in the axial direction of the electrodes 2 and 4. A field such as this may make the arc 26 unstable under certain conditions. To overcome this effect the second electrode may be slotted such that its current paths are rotated in the opposite sense, preferably by the same angle. In this way the directions of the two magnetic fields generated by the electrodes are opposite and in the space between the electrodes 2 and 4 a type of field, known as a cusp field, with predominately radial components will be produced. The arc will be set into rotation by the magnetic forces of this field but it cannot be driven outward. This results in an arc which is stabilized along the axis of the electrodes 2 and 4 and which has base points which rotate from one electrode section to another. The rotating effect of the base points is beneficial in that the burn off of the electrodes will thereby be reduced.

The beneficial effects obtained by rotating the current path in the end faces of the electrodes 2 and 4 can be enhanced by additional rotations in integral 360 increments. This may be done by additional slotting of the ends or by continuing the slots in a helical fashion along the outer walls of the cylindrical surfaces of the electrodes 2 and 4. With this arrangement the axial field in the nozzle is amplified and the rotation effect on base points of' the arc is increased. The nozzle mouth opening can be provided with replaceable contacts commonly known as burn-off fingers 50 as shown on FIG. 2. These are supported by a lip on the inner portion ofthe electrode 2 and by an additional lip in the insulation 54. They are held in place by springs designated as 5l and 52. There may be a single burn-off finger 50 provided for each segment of the electrode or, depending on the width of the electrode segments, two or more fingers may be provided for each section as illustrated by the two fingers 50 associated with each segment on FIG. 3. Also shown on FIG. 2 is a collector electrode 56. This electrode will pick up the arc if the quenching and magnetic forces have moved it beyond the entrance parts of the

nozzle

6 and 8. Such collector electrodes and their use are well known in the art.

An embodiment of the invention in which a single nozzle type electrode is used is shown in FIG. 4. The

second electrode comprises a switching tube 60 which serves the dual purposes of being a switching contact and of drawing the arc between the nozzle electrode 2 and itself. When switching occurs, the electrode 60 is withdrawn through an opening in a partition 68 which is used to control the flow of the quenching medium. The flow direction of this medium is indicated by the

arrows

62, 63, 64, 65, and 68. The arc 26 will be influenced both by the quenching medium and by the magnetic effects generated by the current in nozzle 2 as described above. The partition 68 may be insulating material or may also be metal. The hole therethrough acts as a flow nozzle and may be shaped to have a definite profile, e.g. it may be of cylindrical or conical shape or may also take the shape of a Laval jet.

Similarly, the nozzle profile of the electrodes 2 and 4 may also be shaped differently depending on the particular application, e.g. cylindrically, as a Laval jet, divergent, or also convergent. It is only essential that the insulation extend over the end portions of the electrodes 2 and 4 into the mouth of the nozzle so that a current loop, such as

loop

28 and 32 shown on FIG. l is produced. This result may also be accomplished by a separate body of insulating material arranged in front of the end faces of the electrodes 2 or 4 or insulating material arranged between the two nozzle tubes. The only requirement is that the arc be caused to have its base points inside the nozzles to obtain the

currents

28 and 32 as shown on FIG. 1.

The slots shown and described in connection with FIG. 3 or the slotting described in connection with FIG. l may be accomplished by sawing or milling the slots into the nozzle conductors 2 and 4. After the sawing or milling, the slots may then be filled in with insulation as described in connection with FIGS. 2 and 3. A further method of accomplishing the same purpose is to fill in the slots with a material of lower conductivity. For example, the conducting portions 44 to 46 of FIG. 3 could comprise copper while the insulating parts 40 to 43 could be made of a material such as graphite. Further, the slots need not be cut completely through the conducting material but instead be grooved areas of reduced cross section so that the current will tend to flow in the paths of greater cross section. These groove portions may be filled or not filled as desired with insulating material or a material of lower conductivity.

Thus, an improved method of arc quenching in nozzle type electrodes and apparatus for performing the arc quenching, in which the base of the arc is caused to be drawn inside the nozzle of the electrode so that the current in the nozzle follows a curved path which will generate a magnetic field tending to force the arc into the center of the nozzle, has been shown. Although specific embodiments have been shown and described, it will be obvious to those skilled in the art that various modifications may be made without departing from the spirit of the invention which is intended to be limited solely by appended claims.

What is claimed is:

l. In a quenching medium f'low circuit, breaker where at least one of the contacts is in the form of a nozzle tube comprising a cylindrical tube of a conductive material having a looped end consisting of a portion of the tube looped inside the tube to form a nozzle, wherein the improvement comprises; insulating means covering the outer surface of the cylindrical tube at least in the vicinity of the looped end, covering the looped end, and covering a small portion of the inside nozzle adjacent to the looped end for a distance equal to or greater than the thickness of said tube at said looped end, the portion of the outer surface being covered for a distance which is sufficiently greater than the small inside nozzle portion covered so that an arc is drawn inside said nozzle whereby a current path through said looped end will be followed to set up magnetic forces tending to extinguish the arc.

2. The invention according to claim l wherein said insulating means comprise a layer of insulating material deposited on the surface of the nozzle tube.

3. The invention according to claim 2 wherein both contacts are in the form of nozzle tubes arranged opposite each other on a common axis and further including a bridging contact member whose outside diameter is at least as large as the smallest inside diameter of said nozzle tubes and is movable along said axis inside said nozzles1 whereby said bridging contact member may be used to draw an arc between the two contacts.

4. A contact arrangement according to claim 3 wherein the looped end in nozzle tube is divided into segments at its end face by slots extending from the end of the nozzle tube to the depth of the nozzle mouth opening and filled with insulating material.

5. The invention according to claim 4 wherein said slots are filled with a material of different electrical conductivity.

6. The invention according to claim 5 wherein the segments are arranged to form spiral-like conducting paths` thereby causing current to enter the nozzle end at one angular position about the nozzle axis and leave the nozzle end at another angular position displaced therefrom.

7. The invention according to claim 6 wherein the angular displacement is substantially 8. The invention according to claim '7 wherein said spiral-like paths are constructed so as to cause the current to travel substantially 180 plus at least one additional integral multiple of 360 between entering and exiting the nozzle end.

9. The invention according to claim 8 wherein the twist of the segments on one nozzle end is opposite to that on the other nozzle end. whereby a cusp field which will tend to rotate the arc base points will result.

l0. The invention according to claim 9 wherein the twist on the nozzle ends is continued in helical fashion on the outer sides of the cylindrical tube.

11. The invention according to claim l0 wherein the segments in the nozzle end are formed by slots cut in the conducting material.

12. The invention according to claim l1 wherein said slots are filled with a material of different electrical conductivity.

13. The invention according to claim ll wherein at least the inner portions of the nozzles are provided with replaceable burn off fingers.

14. The invention according to claim 7 wherein said segments in the nozzle end are separated by a material ot' lower electrical conductivity.

*it Ik 1k It

Claims

1. In a quenching medium flow circuit, breaker where at least one of the contacts is in the form of a nozzle tube comprising a cylindrical tube of a conductive material having a looped end consisting of a portion of the tube looped inside the tube to form a nozzle, wherein the improvement comprises; insulating means covering the outer surface of the cylindrical tube at least in the vicinity of the looped end, covering the looped end, and covering a small portion of the inside nozzle adjacent to the looped end for a distance equal to or greater than the thickness of said tube at said looped end, the portion of the outer surface being covered for a distance which is sufficiently greater than the small inside nozzle portion covered so that an arc is drawn inside said nozzle whereby a current path through said looped end will be followed to set up magnetic forces tending to extinguish the arc.

2. The invention according to claim 1 wherein said insulating means comprise a layer of insulating material deposited on the surface of the nozzle tube.

3. The invention according to claim 2 wherein both contacts are in the form of nozzle tubes arranged opposite each other on a common axis and further including a bridging contact member whose outside diameter is at least as large as the smallest inside diameter of said nozzle tubes and is movable along said axis inside said nozzles, whereby said bridging contact member may be used to draw an arc between the two contacts.

6. The invention according to claim 5 wherein the segments are arranged to form spiral-like conducting paths, thereby causing current to enter the nozzle end at one Angular position about the nozzle axis and leave the nozzle end at another angular position displaced therefrom.

7. The invention according to claim 6 wherein the angular displacement is substantially 180*.

8. The invention according to claim 7 wherein said spiral-like paths are constructed so as to cause the current to travel substantially 180* plus at least one additional integral multiple of 360* between entering and exiting the nozzle end.

9. The invention according to claim 8 wherein the twist of the segments on one nozzle end is opposite to that on the other nozzle end, whereby a cusp field which will tend to rotate the arc base points will result.

10. The invention according to claim 9 wherein the twist on the nozzle ends is continued in helical fashion on the outer sides of the cylindrical tube.

11. The invention according to claim 10 wherein the segments in the nozzle end are formed by slots cut in the conducting material.

12. The invention according to claim 11 wherein said slots are filled with a material of different electrical conductivity.

13. The invention according to claim 11 wherein at least the inner portions of the nozzles are provided with replaceable burn off fingers.

14. The invention according to claim 7 wherein said segments in the nozzle end are separated by a material of lower electrical conductivity.