US3859487A

US3859487A - Electric switch for aerodynamic acceleration of a plasma

Info

Publication number: US3859487A
Application number: US353651A
Authority: US
Inventors: Bertold Berberich
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1970-06-13
Filing date: 1973-04-23
Publication date: 1975-01-07
Anticipated expiration: 1992-01-07

Abstract

The quenching chamber of an electric switch has a quenching channel with a portion between the switch contacts and the quenching plates having a cross-section in the configuration of a nozzle transverse to the direction of movement of the switch contacts and to the plane of movement of the light arc.

Description

United States Patent [111 3,859,487 Berberich 1 Jan. 7, 1975 1 ELECTRIC SWITCH FOR AERODYNAMIC [56] References Cited ACCELERATION OF A PLASMA UNITED T S PATENTS [75] Inventor: Bertold Berberich, Erlangen, 2,829,221 4/1958 Ramrath 200/148 C Germany 3,031,552 4/1962 Stewart 200/147 B [73] Assignee: Siemens Aktiengesellschaft, Berlin, FOREIGN PATENTS OR APPLICATIONS Germany 1,057,680 5/1959 Germany 200/144 R [22] Filed: Apr. 23 1973 506,135 12/1954 ltaly 200/147 B [21] P N05 353,651 Primary ExaminerRobert S. Macon Related s Application Data Attorney, Agent, or Firm-Herbert L. Learner [63] Continuation of Ser. No. 151,260, June 9, 1971.

[57] ABSTRACT l l Foreign Application Priority Data The quenching chamber of an electric switch has a June 13, 1970 Germany 2029252 quenching channel with a portion between the switch T contacts and the quenching plates having a cross- [52] US. Cl. 200/144 R, 200/ 148 C section in the configuration of a nozzle transverse to [51] Int. Cl. H01h 33/08 the direction of movement of the switch contacts and [58] Field of Search 200/148 C, 144 R, 144 C,

l ll

to the plane of movement of the light are.

9 Claims, 3 Drawing Figures ELECTRIC SWITCH FOR AERODYNAMIC ACCELERATION OF A PLASMA This is a continuation of application Ser. No. 151,260, filed June 9, 1971.

DESCRIPTION OF THE INVENTION The invention relates to an electric switch. More particularly, the invention relates toan electric switch with an accelerated light arc.

The invention relates to an electric switch, particularly for low voltage circuits, comprising a quenching chamber which contains switch contacts movable relative to each other,'between which a light are is drawn, and which is sealed transversely to the direction of movement of the switch contacts, by insulating members. The quenching chamber further comprises quenching plates toward the front edges of which the light arc moves. In the direction of movement of the switch contacts, the chamber contains wall portions of electrically conducting material along which the roots of the arc move.

High voltage switches for alternating current usually switch during zero passage of the current. Their quenching chambers are designed to prevent arc-back or reignition of the arc following the zero current passage. Switches of this type should not switch too fast, due to the voltage peaks which may result and their effect upon the power system.

By contrast, low voltage switches are so designed that they are able to quench the arc in the shortest possible time. Theseswitches are therefore able to solve the general problem of increasing the light arc voltage above the driving voltage. This is accomplished by elongation or cooling of the light arc. Low voltage switches may also be designed so that they comply with both requirements. The light are is blown away between the switch contacts, by magnetic or air blowing or fanning and is elongated thereby. To accomplish this, known switches were provided with so called blow-out coils which create an external magnetic field which acts upon the arc. The utilization of the blow-out coils may make the switches much more expensive, under certain circumstances. In a special structure of the switches, the arc may also be blown away between the contacts by the intrinsic magnetic field which is formed by the arc itself.

German Pat. No. 735,603 discloses a switch with movable switch contacts where the roots of the arc are at a standstill. The wall of the quenching chamber, whose lower end is sealed, emits gas due to the heat of the arc, which provides the gas with a high pressure that serves for quenching the arc. The pressure wave of the gas is reflected at the bottom of the blow-out tube and impinges again upon the arc. The cross-section of the chamber is shaped in the form of a nozzle in the direction of movement of the'switch contacts and in the direction of movement of the pressure wave to permit the passage of the reflected pressure wave.

In another embodiment, this switch includes, above the switch contacts, an insulating member which is so designed that a nozzle-shaped passage point forms on both sides of the insulating member.'This arrangement facilitates the passage of the air-pressure wave, and the light are is elongated by the blowing away of the arc.

German Pat. No. l,006,928 discloses a switch with switch contacts which are movable relative each other, between which a light arc is drawn which moves along electrically-conducting portions of the wall of the chamber. The electrically conductive portions are resistors which are bent in the shape of horns and which form a nozzle-shaped cross-section in the quenching chamber in the plane of movement of the travelling light arc. The quenching chamber also comprises quenching plates directly above the switch contacts or moved back somewhat between the resistors. The quenching plates are of lamination or sheet type whose shape is similar to the resistors abutting the chamber wall. This configuration of the quenching chamber is designed to stop or check the air blast current and to promote the cooling as well as the deionization of the chamber area or space. The partitions or bridges of such switches may also extend into the quenching chamber in the form of a wedge and may be made of ceramic. The wedges form wedge chambers which provide a quenching field intensity of approximately 5 to 10 volts per cm.

German Published Application No. 1,021,054 shows that it is also possible to place the quenching plates at the end of a quenching chamber. The light are is drawn between contacts which are movable in relation to one another, and travels along electrically conductive portions of the chamber, which expands above the switch contacts, toward the quenching plates. The quenching plates are positioned transversely to the longitudinal direction of the light are. Due to the quenching plates of electrically conductive material, the voltage drop of the light are is additionally increased through the voltage loss of the root points of the arc at individual plates which function as intermediate electrodes. The chamber comprises switch contacts whose mutually facing surfaces have the shape of horns which facilitate the initiation of the drive of the arc, and thus it entrance into the chamber, and whose wall comprises electrically conductive portions in the direction of movement of the contacts. The are is accelerated there, and im pinges at great speed upon the electrically conductive portions positioned in parallel in the direction of movement of the are. A rather great bending or curving of the are between individual quenching plates causes each component arc, and thus the entire light are, to be considerably elongated.

A special design of the quenching plates provides a loop formation of the component arcs between the individual quenching plates. The loop can only be formed, however, with a specific minimum spacing or distance between the individual quenching plates. The quenching chamber requires a considerable amount of space, due to such a requirement, and entails great expense because of the special processing of the plates. The long light arc is additionally cooled by the plates and, due to its resultant diminished conductivity, absorbs a considerably higher voltage. The quenching plate chamber is more effective, the more plates it contains.

On the other hand, a greater distance between the quenching plates facilitates the entrance of the light arc into said plates. A DC are makes it possible, at higher current intensity for the arc to remain at the lower edges of the quenching plates without dividing itself, and to destroy the chamber as soon as a predetermined minimum distance between the plates is not attained. From these opposite requirements, a relatively large plate distance may be obtained in the known switches. Such quenching plate chambers in switches with a I high light are speed during the entrance of the arc into the quenching plates provides a correspondingly wide expansion of the component light are between the quenching plates, and that a very high light are speed also permits the entrance of the are between quenching plates spaced a very small distance from each other. The invention emanates from the knowledge that the light are may be additionally aerodynamically accelerated in the chamber. In addition to air blowing or fanning, magnetic fanning of the light are is also known. During magnetic fanning, the componentof the L- rentz force is influenced by the blow-out winding in the direction of movement of the arc. By contrast, the invention uses features known from aerodynamics for accelerating the plasma.

In this connection, reference has been made to the well known work Handbook of Fluid Dynamics, 1st edition, 1961, McGraw Hill Book Co. Inc. NY., see

I pages 27-18 to 2720, particularly 27.43 and 27.44.

The following factors influencing plasma movements have to be considered: nozzle cross-section A, electrical conductivity a, magnetic flow density B, electric field intensity E, pressure P, adiabatic exponent -y and the converted heat 0. With an increase in travel distance x, in flow dirction,.the change in speed is defined as du/dr 0 and the changein Mach number being defined by dM/dx 0.

To accomplish this, and in accordance with the invention, the quenching channel has a nozzle shaped cross-section constriction between the switch contacts and the quenching plates transverse to the direction of movement plane of the switch contacts and transverse to the movement plane of the plasma, which enters behind the nozzle mouth, between the quenching plates.

For very high travel or movement speeds, particularly above Mach 1, the cross-section is preferably designed as a Laval nozzle; a nozzle of the aforementioned type, having a cross-section which expands again following the constriction. In this type of quenching chamber, the light arc is limited by the electricallyficonductive parts of the chamber wall; i.e., guide rails or tracks, and; is aerodynamically accelerated without external means, and enters into the quenching plates at high speeds, where it absorbs a high voltage even without loop formation. It follows from the above, that an essential criteria for the success of the present invention, relates to proper nozzle profile; that is, the nozzle which forms the cross-section of the chamber walls must be capable of functioning in accordance with the laws of aerodynamics, i.e., rated for aerodynamic acceleraation. Obviously for flowrates somewhat below Mach 1, nozzle profile need only be rated for thermodynamic acceleration. The quenching plates are spaced a small distance from each other. Such switches can provide quenching field intensities of 200 volts per cm and higher. The nozzle also prevents a return travel of the light are to the switch contacts; thus preventing the occurrence of arc-backs.

The distance between the quenching plates in the switch of the invention is maintained small.

The loop formation in the known switches provides an increased voltage of thecomponent light arcs, which occurs in addition to the increase in voltage due to cooling of the plates. In the switch of the invention, the cooling effect of the plates is also of consequence. The cooling effect is increased by the small distance between the quenching plates down to less than 1 mm, the considerably shorter length of the component light arcs, and the high impingement'speed of the light are upon the quenching plates. The increase in voltage due to loop formation is compensated in the switch of the invention by intensive aerodynamic cooling which is provided in addition to the cooling by the quenching plates, and which usually increases upon an increase in the speed of impingement. The entrance of arcs into the quenching plates spaced from each other by such small distances is made possible by the increase in the speed of movement. The number of plates, and thus the number of component arcs, may be increased accordingly at the same chamber width. This affords a correspondingly higher quenching voltage. The suddenly increased light are voltage produces during its entrance into the quenching plates correspondingly diminished quenching periods, and thus short switching periods of the switch.

In orderthat the invention may be readily carried into effect, it will now be described with reference to the accompanying drawings, wherein:

FIG. 1 illustrates a cross-section of an embodiment of the switch of the invention with a quenching channel in the direction of movement of the switch contacts;

FIG. 2 is a section, taken along the lines II-II of FIG. 1, through the quenching channel, perpendicular to the direction of movement of the switch contacts; and

FIG. 3 is a sectional view of another embodiment of the quenching chamber.

In the FIGS., the same components are identified by the same reference numerals.

In FIG. 1, 'an electric switch used, for example, for a direct current of about 300 to 3,000 amperes and a voltage of 320 volts, comprises

switch contacts

2 and 2. A quenching chamber 5 has a chamber wall having electrically conductive portions 4 and 4 for the light arc which limit the quenching channel. A plurality of quenching plates 6 are provided in the quenching chamber. The direction of movement of the switch contacts 2 and 2' is indicated by a double-headed arrow. One of the

switch contacts

2 and 2 is usually fixed in position and the other is movable. The electrically conductive portions are at the same potential as the corresponding switch contacts 2 and 2'.

Each of the switch contacts is connected to a corresponding one of a pair of DC terminals P and N. Each of the quenching plates 6 may comprise a 1 mm thick iron sheet or plate. The quenching plates 6 are equidistantly spaced from each other at a distance of about 0.5 to 2.5 mm. preferably approximately 0.7 to 2 mm, and particularly approximately 0.8 to 1.2 mm. across the width b of the quenching channel of the quenching chamber which is about 30 mm. The maximum length h of the quenching plates is about 35 mm.

A favorable effect upon the entrance of the light are into the quenching plates is obtained in a known manner by making the lower edges or the edges of the quenching plates 6 facing the switch contacts, uneven. This is accomplished, for example, by shifting alternate quenching plates back by a few millimeters, preferably about 5 mm. The laterally extending electrically conducting portions 4 and 4 preferably comprise copper or copperplated members.

The profile of the quenching plates 6 and the nozzletype design of at least one part of the quenching channel 5., between the

switch contacts

2 and 2 and said quenching plates is limited, as shown in FIG. 2, traversely in the direction of movement of said switch contacts by insulating

plates

8 and 8. The quenching channel 5 is formed in the shape of a nozzle by inserts l and 10' of electrically insulating material. The inserts 10 and 10' preferably comprise a workable ceramic or synthetic material. The surfaces of the inserts l0 and 10 which face each other or the center of the quenching channel have the profile of a Laval nozzle, for especially high speeds of movement or travel of the arc, particularly above Mach 1. A recess, hole, indentation, or the like, 12 is formed in the edge of each quenching plate facing the switch contacts 2 and 2'. The recesses'l2 facilitate the entry of the light are into the quenching plates 6.

In a modification of the embodiment-of FIG. 2, in which the inserts and 10 form the nozzle profile, the insulating plates or walls of the chamber and the inserts 10 and 10' may be produced as an integral unit. Under certain circumstances it may be advantageous not to design the entire chamber area between the

switch contacts

2 and 2 and the quenching plates 6, in form of a nozzle. If the nozzle formed by the inserts l0 and 10 ends at a predetermined distance from the quenching plates 6, then the aerodynamic acceleration of the light are by said nozzle, is still effective between the mouth of said nozzle and said quenching plates. It is not important for the effect of the nozzle formed by the inserts 10 and 10' that said nozzle begin at the upper ends of the ends of the

switch contacts

2 and 2 facing the quenching plates 6.

The nozzle-shaped design of the quenching channel of the invention provides low switching periods. The switching period is essentially determined by the duration of the light arc, that is, the period from the onset of opening the switch contacts 2 and 2' until the termination of the flow of current. In the illustrated embodiment of a DC switch for approximately 300 to 3,000 amperes rated current, the quenching chamber has a depth 0 of about 10 mn and a small distance between the quenching plates 6. The nozzle diameter at its narrowest point a is approximately 0.5 to 3 mm, preferably about 0.8 to 2 mm, and particularly approximately 1 mm. This design of the quenching chamber helps to obtain a quenching voltage of about 300 to 400 volts and a quenching field intensity of about 100 to 150 volts per cm. This switch requires only about 0.5 millisecond to quench a direct current of about 2,000 amperes.

In an embodiment of the switch of the invention for a short-circuit alternating current up to about 20,000 amperes at a net voltage of 220 volts and a frequency of 50 Hertz, the quenching plates 6 are spaced from each other by a small distance of about 1 mm, for example. Each quenchirig plate has a small thickness of, for example, about 0.5 mm. The narrowest nozzle diameter of the Laval nozzle of FIG. 2 is preferably approximately 1 to 2 mm, more preferably approximately 1.5 mm. This type of switch provides a quenching voltage of at least 300 volts, and thus a quenching field intensity of greater than volts per cm. This switch quenches the light arc at a current of about 2,000 to 3,000 amperes in approximately 0.3 to 0.5 millisecond. The switching period of the switch of the invention is so short, due to the reduced quenching time, that the switching of an alternating current produces a currentlimiting effect.

In an embodiment of the switch having requirements for the switching time which are not as high, so that its light are duration is therefore somewhat longer, an entrance speed of less than Mach 1 is sufficient for the light arc, during its impingement upon the quenching plate. In such operating conditions, a normally converging nozzle may suffice for the aerodynamic acceleration of the light are, in place of the illustrated Laval nozzle.

A particularly slight expansion and compact construction is provided for the quenching chamber by a nozzle whose mouth extends into the recesses, openings, holes, cutouts, or the like, 12 formed in the quenching plates 6. In this case, each of the quenching plates 6 may be provided with an additional lateral cutout, not shown in the drawing, or said quenching plates may extend into the

inserts

10 and 10 forming the nozzle in their areas facing the quenching plates 6. Furthermore, the areas of the inserts l0 and 10 facing the quenching plates 6 may be provided with an appropriate lateral cutout for said quenching plates, as shown in the embodiment of FIG. 3.

In the embodiment of FIG. 3, the quenching chamber walls 14 and 14' between the quenching plates 6 and the switch contacts 2 and 2' are of electrically insulating material and are formed in the shape of a nozzle.

The quenching voltage of the switch is essentially determined by the thickness of each quenching plate, the spacing between the quenching plates, and the number of quenching plates. If a predetermined chamber width diminishes the thickness of the quenching plates and/or the spacing between said plates, the quenching field intensity may also be increased accordingly.

The nozzle-shaped design of the cross-section of the quenching channel not only helps to reduce the period during which the voltage increases, but also helps to reduce the scattering or straying of the voltage. This also reduces the switching time.

While the invention has been described by means of specific examples and in specific embodiments, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

I claim:

1. An electric switch having a quenching chamber including: a chamber wall; switch contacts movable relative to each other and between which a light arc is drawn; insulating members disposed transversely to the direction of movement of said switch contacts; quenching plates, against which said light are is moved across conductive portions of said chamber wall; and a quenching channel, said quenching channel having a nozzle shaped constriction disposed between said switch contacts and said quenching plates, transversely to the plane of movement of said switch contacts; said constriction having a cross-section rated for aerodynamic acceleration of said light arc, which arc is urged to enter behind the mouth of said nozzle between said quenching plates.

2. An electric switch as claimed in claim 1, wherein said quenching channel is provided with a cross-section having a nozzle shaped constriction followedby an expansive portion, disposed in the light are travel direction.

3. An electric switch as claimed in claim 1, wherein the cross-section of the quenching channel has the configuration of a Laval nozzle.

4. An electric switch as claimed in claim 1, wherein the distance between adjacent quenching plates is 0.7 to 2.0 mm.

5. An electric switch as claimed in claim 1, wherein the distance between adjacent quenching plates is 0.8 to 1.2 mm.

6. An electric switch as claimed in claim 5, wherein the nozzle has a minimum diameter of 0.8 to 2.0 mm and the quenching chamber has a width of approximately 30 mm for a direct current of approximately 300 to 3,000 amperes.

7. An electric switch as claimed in claim 5, wherein the nozzle has a minimum diameter of l to 2 mm and the quenching chamber has a width of approximately 20 mm for a short-circuit alternating current up to approximately 20,000 amperes at a voltage of approximately 220 volts and a frequency of 50 Hertz.

8. An electric switch as claimed in claim 6, wherein the nozzle has a diameter of approximately 1.0 mm.

9. An electric switch as claimed in claim 7, wherein the nozzle has a minimum diameter of approximately

Claims

1. An electric switch having a quenching chamber including: a chamber wall; switch contacts movable relative to each other and between which a light arc is drawn; insulating members disposed transversely to the direction of movement of said switch contacts; quenching plates, against which said light arc is moved across conductive portions of said chamber wall; and a quenching channel, said quenching channel having a nozzle shaped constriction disposed between said switch contacts and said quenching plates, transversely to the plane of movement of said switch contacts; said constriction having a cross-section rated for aerodynamic acceleration of said light arc, which arc is urged to enter behind the mouth of said nozzle between said quenching plates.

2. An electric switch as claimed in claim 1, wherein said quenching channel is provided with a cross-section having a nozzle shaped constriction followed by an expansive portion, disposed in the light arc travel direction.

7. An electric switch as claimed in claim 5, wherein the nozzle has a minimum diameter of 1 to 2 mm and the quenching chamber has a width of approximately 20 mm for a short-circuit alternating current up to approximately 20,000 amperes at a voltage of approximately 220 volts and a frequency of 50 Hertz.

9. An electric switch as claimed in claim 7, wherein the nozzle has a minimum diameter of approximately 1.5 mm.