US3679851A - Autoextinguishing interrupters - Google Patents

Abstract

The invention relates to a self-extinguishing interruptor in which one of the contacts is mounted in the upstream portion of an insulating tube. It is characterized in that the total section of the passage of the conduit or conduits which feed the compressed gas to the tube is limited to a value equal to or less than the section of the passage of the neck of the tube.

Description

United States Patent 1151 3,679,851

Latour et al. [4 1 July 25, 1972 [54] AUTOEXTINGUISHING 7 References Cited INTERRUPTERS UNITED STATES PATENTs [721 lnvenmm Grenoble France; Gimmo 2,781,435 2/1957 i-ieilmann et al ..2oo/1 so 0 Fumlsfllll, Bersamo, Italy 2,957,063 10/1960 Leeds ..200/148 A Assignee: s Milianowlcz ...-200/l48 A Milan, My FOREIGN PATENTS OR APPLICATIONS [221 Film 700,729 12/1940 Germany ..200/i48 A [21] Appl. No.2 48,118

Primary Examiner-Robert S. Macon Attorney-Karl F. Ross [30] Foreign Application Priority Data June 23, 1969 France ..6920971 [57] ABSTRACT The invention relates to a self-extinguishing interrupter in [52] U.S. Ci ..200/ 148 A, 200/150 G hi one of the contacts is mounted in the upstream portion [51] Int. Cl. ..H01h 33/70 -an in la ing t be- It is ch racterized in that the total sec- [58] Field of Search ..200/148 A, 150 G tion of the p g of h conduit r n i whi h fe d th compressed gas to the tube is limited to a value equal to or less than the section of the passage of the neck of the tube.

6 Claim, 6 Drawing figures EF/ 2 l I I I I 47 2 1 1 I /z z I, I Z .24 1/! PATENTED JUL 25 m2 SHEET 2 OF 4 ATTORNEY ATENTH] JUL 2 5 m3 BEST AVAILABLE COPY 3 6 7 9 8 5 l SHEEI3UF l l i /6,3 I v I I I I I I F I I 1/; 5 1/ 2 /Z a? .1 9;? (z, I V- 5 Q g |/l\ I I will). RIM! ATTORNEY PATENTED I972 3.679.851 sumuufa FIG. 4

FIG. 4A

INVENTORS 10/0 25 .4 4 o (J /4 c ma Fu/ m 4L1 ATTORNEY AUTOEXTINGUISI-IING INTERRUP'I'ERS FIELD OF THE INVENTION BACKGROUND OF THE INVENTION lnterrupters for high-voltage alternating current are known in which one of the contacts is mounted in the upstream portion of an insulating tube near its neck. This tube communicates through a conduit with a mechanical piston-cylinder arrangement attached to the contacts such that, when they separate, a blast of compressed gas is forced across the breaking space. The whole device is generally mounted in a housing containing the necessary gas, for example sulfur hexafluoride. Such interrupters are called autopneumatic or autoextinguishing." The breaking arc which forms between the contacts is thus affected by a stream of gas which extinguishes it if the otherwise necessary extinguishing conditions are present.

It is well known that the most favorable instantfor extinguishing an arc is that which for SO-cycle alternating current takes place 100 times a second at the instant when the current is zero (zero passage) between the polarity changes inherent in the sinusoidal waveform. During the few microseconds which precede or which follow this instant the arc is fragile because it is entirely without heat and, if at this moment a sufficiently insulating gaseous barrier can be placed in its path, it will not reform and its extinction will be definitive.

Building of an efficient insulating gaseous barrier requires in every case that the extinguishing gas retain all of its dielectric qualities. It is impossible to extinguish satisfactorily an arc with a gas made conductive by heating or mixing with ionic vapors. It is precisely this phenomenon which in conventional interrupters limits the interruption capacity, i.e., the arc-current amplitude that the interrupter can overcome. In effect, for large arc currents the enormous heat released by the arc has the effect of:

l. dilating the extinguishing gas,

2. disassociating it into its atomic elements,

3. volatilizing the walls of the tube, and

4. volatilizing the metal of the contacts.

These four effects are additive to form a volume of gas or of vapor which is too great to evacuate completely from the neck of the tube. The result is that a rather large portion of this gaseous mass, whose temperature is high and whose dielectric properties are almost nonexistent, is forced into the conduit upstream of the tube, toward the cylinder-piston arrangement.

Obviously this back-blast action only lasts for a few milliseconds corresponding to the portion of the current sinusoid above critical value close to zero passage. Below this level, i.e., in the portion of the sinusoid close to zero current, the back-blast stops and is replaced by the gaseous extinguishing puff in the normal direction. In the arcing space between the contacts the arc extinction is commenced by a preliminary evacuation of the gases previously driven back which, due to their high temperature and their highly ionized state, act as an electrical conductor or at best as an insulator without any appreciable dielectric character. If this evacuation is not carried out completely before the drop to zero of the current, no interruption of the arc can be obtained. In every case the backblast causes the insulating gas precompressed in the cylinderpiston arrangement to be late in penetrating the path of the arc. The less this penetration is delayed, the greater will be the time available for building a gaseous insulating barrier in the arc path. The result of these considerations, we have found, is that it is very important to reduce as much as possible the quantity of gas driven back.

In addition the reduction or suppression of back-blast gases is not simple because, due to the origins of the gas components, thedisturbing effects can vary considerably.

Thus, on the one hand, those vapors derived from the volatilization of the contacts (usually made of refractory metals or alloys) are very strongly ionized because of their very high temperature and the intimate contact they share with the arc. Such vapors which are practically conductive are thus completely undesirable in the intercontact gap which is to be made as nonconducting as possible.

On the other hand, the gases formed by the volatilization of the insulating tube usually made of an organic material such as polytetrafluoroethylene (Teflon) are much cooler and in addition, because of their electronegative characteristics, regain very quickly their dielectric strength. Their eventual presence in the arc gap is thus much less prejudicial than is that of the metallic vapors.

OBJECTS OF THE INVENTION It is an object of the present invention to provide interrupters which are of equal size as the known types of devices and which have considerably larger interruption capacities.

It is another object of the present invention to provide an interruptor, switch or circuit breaker of improved design and in which the disadvantages of earlier devices of this type are avoided.

Yet another object of our invention is to provide a circuit breaker for high-voltage alternating-current systems of the plug-and-socket type with improved arc-extinguishing means of the gas-blast type.

BRIEF SUMMARY OF THE INVENTION Its operation principle is based on the selective elimination of the ionized gas or vapors which are driven back (in the known devices) into the upstream tube or nozzle while in the half period which precedes its passage to zero the current intensity passes a certain critical value.

According to the invention, this result is obtained by limiting the total section of passage of the conduit or conduits. which are concentric to the contacts and bring the compressed gas to the tube, to a size between 1 and l/3.5 times the size of the section of passage of the neck of the tube.

This proposition may seem paradoxical taking into account that itis present practice, in order to reduce the charge losses and to obtain the most energetic arc extinction, to provide the gas-feed conduit with an effective cross-sectional area largely greater than that of the neck of the tube. But this prior practice apparently has failed to consider the importance of the thermal phenomena which happen once a highpower are forms.

In fact the invention attains the surprising and unexpected result of doubling, even tripling the breaking power of the known devices while nevertheless reducing the gas blast by arrangement whose essential role is that of reducing the quantity of gas fed back by operating in a selective manner on the most conductive vapors.

The invention envisages also several auxiliary means which can eventually be combined with the means described above for further increasing efiiciency. In particular the limitation of section described above can be obtained by means of a body filling the gap left between the principal contact and the arcing contact.

Another means according to the invention for making the evacuation of the driven-back gas quicker comprises the provision of an auxiliary channel communicating with the compression cylinder and opening obliquely into the channel leading the gas to the tube.

In order to accelerate the evacuation of the conducting metallic vapors the invention also provides, at the base of the arcing electrode, holes connected to a conduit opening to the exterior of the compressor cylinder-piston arrangement.

Finally, to limit the mixture of incoming gases with the metallic vapors which have been blown back, vanes are mounted in the grooves separating the contact fingers.

From the foregoing, it is evident that our present invention is based upon the discovery that the delay in arc extinction can be avoided or reduced and the extinguishing gas rendered effective more rapidly by dimensioning the arc-extinguishing duct between the aforementioned neck or constriction and the inlet of the extinguishing gas of a flow cross-section C 0.2850 where c is the flow cross-section of the neck or constriction and C is the flow cross-section of the gas-blast chamber between the extinguishing-gas inlet and the arc gap. When reference is made herein to the flow cross-section of the neck or constriction, it should be understood that it is intended to so designate the narrowest portion of the gas-blast duct from the arcing electrode outwardly, i.e., away from the extinguishing-gas inlet and, when reference is made to the effective flow cross-section of the chamber between the extinguishing-gas inlet and the arc gap, it is the narrowest portion of this chamber which is to be so dimensioned.

In more general terms, therefore, the self-extinguishing circuit breaker of the present invention comprises a fixed contact and a movable contact shiftable axially with respect to the fixed contact, the contacts being preferably of the plug-andsocket type in which one of the contacts is received within the other and is embraced thereby. The contacts are disposed with annular clearance in a tube defining the gas-blast chamber which has a mouth open axially away from the direction of displacement of the movable contact in the circuit-opening direction. To restrict damage to the circuit-closing and circuitopening contacts, the movable contact is formed as an arcing electrode which projects beyond the movable contact in the direction of the stationary contact so that the circuit-breaking arc is concentrated between the arcing electrode and the fixed switch contact. Ahead of the arcing electrode, the inner wall of the tube and, consequently, the wall of the gas-blast chamber projects inwardly to define a neck or constriction having the effective flow cross-section c noted earlier, this constriction being disposed between the arcing electrode and the fixed contact. In other words, the constriction lies along that portion of the gas-blast chamber in which the circuitopening arc is formed.

As we have also noted earlier, the tube and movable-contact assembly is provided with a piston arrangement designed, upon retraction of this assembly, to drive the arc-extinguishing gas into this chamber and through the tube and constriction. The inlets from the piston-and-cylinder arrangement may be constituted by one or more ports communicating with the chamber at the base of the movable contact and arcing electrode so that the tube and assembly housing define a duct extending along the movable contact and arcing electrode and communicating axially with the chamber in the region of the arcing electrode. This duct, according to the present invention, has at its most constricted portion, the effective crosssection C formed by a filler body whose external diameter is substantially equal to the internal diameter of the socket contact and is dimensioned to so constrict the duct as to achieve the aforestated relationship of the flow cross-section. Preferably the filler body or bodies extend axially over a substantial portion of the duct between the extinguishing-gas inlet and the arcing electrode. The term substantial portion is here intended to designate an axial length of at least one third of the length of the duct.

Advantageously, the movable contact is a multifinger contact of the socket type, i.e., is constituted by a cylindrical array of contact fingers adapted to hug the tubular fixed plug contact, the interior of which receives the arcing electrode. The latter, which is coaxially and spacedly surrounded by the fingers of the movable contact, projects beyond the fingers into the region in which the duct described earlier communicates with the gas-blast chamber.

DESCRIPTION OF THE DRAWING The invention will be better understood with the help of the description and the drawing which follow, which description and drawing are evidently given only by way of example excluding no other embodiments.

In the drawing:

FIG. 1 shows an axial section through an interrupter of the known type according to the generic definition given at the beginning of this text;

FIG. 2 shows in axial section, an interrupter according to the invention,

FIG. 2A is a section along line IIA IIA of FIG. 2;

FIGS. 3 and 4 show in axial section, auxiliary means of different forms applied in combination with the principal feature of the invention; and

FIG. 4A is a section along line IVA IVA of FIG. 4.

SPECIFIC DESCRIPTION The interrupter of the known type shown in FIG. 1 comprises a fixed tubular contact 1 cooperating with an annular mobile contact formed by an array of elastic contact fingers 2 surrounding an arcing electrode 3. In the closed position the contact 1 is surrounded by the contact fingers 2 while the electrode 3 fits into the tubular part of the contact I. Electrode 3 and contact 2 are fixed on a cylinder 4 slidable on a piston 5 fixed by means of a control rod 6 which also projects from the conductor for the current. The upper end of the cylinder has an insulating tube 7 or nozzle (FIG. I) which completely surrounds the contacts and which, by means of holes or orifices 8 formed in the end of the cylinder 4, can receive the gases compressed by the cylinder-piston arrangement. The lower bore of the tube 7 forms with the annular contact 2 a gap 9 that forms a first passage for the compressed gases; a second passage 10 is formed by the gap left between the body of the arcing contact 3 and the fingers 2 of the annular contact; finally a third passage 11 is made by the spaces separating the annular contact fingers 2 from one another. The whole of the interrupter is fixed in a housing (not shown) containing a compressed gas, for example sulfur hexafluoride (SF In order to best regulate the charge losses and to thus obtain through the neck of the tube 7 the most energetic blast, it is the current practice to dimension the three passages 9, I0 and 11 such that the sum of their cross-sectional areas is substantially greater to that of the passage of the neck 12 of the tube 7.

In the absence of arc this practice would be entirely justified. But when an arc 13 corresponding to a high-voltage alternating current is drawn between the contacts considerable counter pressures come into play such that an important portion of the gases or vapors produced by the arc are driven back toward the base of the figure, toward the cylinder-piston arrangement (back-blast). As the current amplitude which is sinusoidal drops to change direction and approaches zero the back blast disappears and is replaced by a blast in the normal direction. In any case, before the fresh gases can pass into the breaking gap and act as a dielectric barrier the hot backblast gases must have been already entirely evacuated.

More particularly disadvantageous to an efficient dielectric regeneration are the metallic vapors bursting in every direction from the end of the arcing electrode 3 which vapors, unable to escape completely through the neck 12 of the tube 7, descend in the passage 10 toward the compressing cylinderpiston arrangement. The high conductivity of these vapors due to their high temperature and to their strongly ionized state prevents any dielectric regeneration in the gap between the contacts as long as, under the effect of blowing in the normal direction, they have not been completely evacuated.

FIGS. 2 and 2A show the application of the invention to the known apparatus of FIG. I. In FIG. 2 the arcing electrode is provided with a thickened part 14 that completely fills the gap 20 which separates the annular contact fingers 2 with the exception of the upper region 15 necessary for the penetration of the contact I. The passage 10 of FIG. I is also shown almost entirely eliminated. In addition the inside bore 16 of the tube 7 and bore 17 of the support which follows it is reduced such that it defines with the annular contact 2 and the gaps between the contact fingers 2 a total passage section smaller in crosssectional area than the section of the passage of the neck 12 of the tube 7 preferably greater than to l/ 3.5 times the section of passage of the neck (i.e., 10 C l/3.5 c), the nozzle diverges in opposite axial directions away from the constriction.

Under the effect of the thermal radiations of the arc, the inside walls of the insulating tube 7 vaporize and envelop every part of the end of the arcing electrode 3 so that it is the metallic vapors which escape. Due to the restriction formed by the thickening l4 and the reduced dimensions of the passages, the totality of the gases and vapors disengaged cannot be driven back unlike the situation with the prior-art system. The result is a rise in the pressure upstream of the neck 12 which has the effect of carrying the excess gases and vapors toward the mouth. Due to the position of the arcing electrode 3 immediately adjacent the neck 12 of the tube 7 it is essentially and selectively the metallic vapors issued from the electrode which are evacuated by the neck 12, pushed by the gases freed by the walls of the tube 7. The only gases driven back thus come uniquely from the volatilization of the material forming the tube and from the expansion of the preexisting gases. All these products are at temperatures much lower than those of the metallic vapors issued from the arcing electrode. Their insulating and deionizing power is thus considerably greater, along with their electronegative characteristics so to get them veritable electron capturers." At the instant when the electric current goes toward zero and when the blowing again assumes its normal direction of flow toward the exit of the tube, the first gaseous products which come into the gap between contacts, even though they are not all fresh, are at least electronegative gases free from all metallic vapor and perfectly capable of creating a dielectric barrier. This easily explains why the breaking power of the system of this invention is augmented considerably.

FIG. 3 shows an improvement on the preceding device. In this Figure the annular contact 2 is surrounded by a frustoconical body 18 which, with the contact 2, defines a passage 19 situated in the continuation of the passage 20 leading the gas to the tube 7. The passage 19 communicates with the compressing cylinder-piston assembly by means of orifices or holes 21. In addition the piece 18 defines with the support 22 of the tube 7 an auxiliary canal 23 communicating with the compression cylinder 4 through holes or orifices 24 and opening obliquely into the channel 20 conducting gases to the tube 7. When the gases originating in the tube are driven back toward the compressor cylinder 4 they only take the channel 19 which. due to its position, does not impose on them any deviation in their path unlike the auxiliary channel 23 whose obliqueness denies them access. At the moment when the blowing resumes its escape direction toward the outlet of the tube 7 the gases which have crossed the channel 19 can, by their acquired speed, follow their path toward the cylinder, the auxiliary channel 23 assuming alone the feeding of the tube 7 with fresh gases which have not had the time to mix with the driven-back gases. A large portion of the driven-back gases is thus hindered to go back into the neck of the tube before the fresh gases can arrive there. Thus, the delay in arrival for these fresh gases in the breaking gap is shortened.

FIG. 4 is another improvement on the device shown in FIG.

2. In FIGS. 4 and 4A the thickened portion 25 of the arcing electrode has a conduit 26 which, following the control rod 27, opens to the exterior of the compressing assembly. Into this conduit 26 open the holes 28 opening at the base of the arcing electrode 3 in the region 29 into which the fixed contact penetrates. This permits, thus, a portion of the metallic vapors disengaged from the arcing electrode 3 to be evacuated definitively to the exterior without passing through the neck 12 of the tube 7. The dielectric regeneration of the intercontact gap is facilitated.

In order to limit the mixing of gases with the metallic vapors driven back into the holes 28, vanes 30 fixed in the grooves se arating the contact fingers 2 can be provided.

t goes without saying that the invention is applicable to many forms of execution other than those shown in the accompanying drawings. In particular the tube can have a different shape and, for example, in a known manner can include adjacent its neck radially extending holes or can present on the surface of its diverging orifice circular grooves intended to improve its functioning.

We claim:

1. A circuit breaker for high-voltage alternating current, comprising an insulating nozzle defining an axially extending arc-extinguishing nozzle chamber; a pair of contacts disposed in said nozzle chamber, one of said contacts being movable relative to the other of said contacts axially to interrupt an electric circuit between said contacts; inlet means coupled with the movable contact for forcing an arc-extinguishing gas through said nozzle chamber upon opening of said circuit, said nozzle chamber being formed at an intermediate location along the length with a constriction ahead of said arc-extinguishing gas through said nozzle chamber and between both said contacts in an open-circuit position thereof; and means defining an axially extending duct connecting said inlet means with said nozzle chamber and having a flow cross-section traversed by said are extinguishing gas which is between I and l /35 time the cross-section of said constriction.

2. The circuit breaker defined in claim 1, further comprising an arcing electrode coupled with said movable contact and extending therebeyond in the direction of the other contact, said constriction being located ahead of said electrode, said movable contact coaxially surrounding said electrode and the lastmentioned means including a filler body in the gap between said electrode and said movable contact.

3. The circuit breaker defined in claim 2 wherein said inlet means include a gas displacement cylinder operable upon movement of said movable contact and provided with at least one opening for introducing said arc-extinguishing gas axially through said duct and along said movable contact, and said body.

4. The circuit breaker defined in claim 3 wherein the means defining said duct is formed with at least one passage extending from said cylinder and opening into said duct obliquely thereto.

5. The circuit breaker defined in claim 3 wherein said electrode is formed with at least one passage extending away from said chamber and communicating with the exterior for venting back-blast ionized gas from said chamber.

6. The circuit breaker defined in claim 3 wherein said body is provided with a plurality of generally radial vanes extending between said fingers.

Claims (6)

1. A circuit breaker for high-voltage alternating current, comprising an insulating nozzle defining an axially extending arc-extinguishing nozzle chamber; a pair of contacts disposed in said nozzle chamber, one of said contacts being movable relative to the other of said contacts axially to interrupt an electric circuit between said contacts; inlet means coupled with the movable contact for forcing an arc-extinguishing gas through said nozzle chamber upon opening of said circuit, said nozzle chamber being formed at an intermediate location along the length with a constriction ahead of said arc-extinguishing gas through said nozzle chamber and between both said contacts in an open-circuit position thereof; and means defining an axially extending duct connecting said inlet means with said nozzle chamber and having a flow cross-section traversed by said arc extinguishing gas which is between 1 and 1/35 time the cross-section of said constriction.

2. The circuit breaker defined in claim 1, further comprising an arcing electrode coupled with said movable contact and extending therebeyond in the direction of the other contact, said constriction being located ahead of said electrode, said movable contact coaxially surrounding said electrode and the last-mentioned means including a filler body in the gap between said electrode and said movable contact.

3. The circuit breaker defined in claim 2 wherein said inlet means include a gas displacement cylinder operable upon movement of said movable contact and provided with at least one opening for introducing said arc-extinguishing gas axially through said duct and along said movable contact, and said body.

4. The circuit breaker defined in claim 3 wherein the means defining said duct is formed with at least one passage extending from said cylinder and opening into said duct obliquely thereto.

5. The circuit breaker defined in claim 3 wherein said electrOde is formed with at least one passage extending away from said chamber and communicating with the exterior for venting back-blast ionized gas from said chamber.

6. The circuit breaker defined in claim 3 wherein said body is provided with a plurality of generally radial vanes extending between said fingers.

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