US3544747A - Gas-blast circuit-breakers operating with extinguishing gas consisting of or comprising a fluorinated compound - Google Patents

Description

United States Patent Inventor Rintje Boersma Ilarmelen, Netherlands AppLNo; 691,012 Filed Dec. 15, 1967 Patented Dec. 1, 1970 Assignee N.V.COQ

Utrecht, Netherlands a Dutch limited liability company Priority Dec. 28, 1966 Netherlands 6618237 Pat. 1]

GAS-BLAST CIRCUIT-BREAKERS OPERATING WITH EXTINGUISHING GAS CONSISTING OF OR COMPRISING A FLUORINATED COMPOUND 11 Claims, 2 Drawing Figs.

200/144, 200/149 Int. Cl 1-l0lh 33/60 Field of Search 200/ 1 48.7,

144.3, 148.5, 148, 149.1, (Cursory) Primary Examiner-Robert S. Macon Artorneylmirie, Smiley, Snyder and Butrum ABSTRACT: The portions of a gas blast circuit breaker employing a fluorinated insulating gas, such as the contacts and parts adjacent thereto and surfaces of the extinguishing chamber, which are disposed in close adjacency to the are produced by opening the contacts, are made of a sintered tungsten-nickel alloy consisting essentially of from 95-99] percent tungsten and the balance nickel. These portions are also coated in part with carbon.

GAS-BLAST CIRCUIT-BREAKERS OPERATING WITH EXTINGUISHING GAS CONSISTING OF OR COMPRISING A FLUORINATED COMPOUND The invention relates to a gas-blast circuit breaker, in which the electric arc setup during the switching-off process is extinguished by a blast of gas consisting of or comprising a fluorinated compound, such as sulfur hexafluoride,

It is known that the extinguishing action of certain gaseous fiuorinated compounds is very much stronger than that of air or nitrogen, so that for the extinguishing process considerably less gas is required However, a disadvantage of these fluorinated compounds is that they dissociate under the infiuence of the electric arc and that several dissociation products thereof are very aggressive and are apt to attack the 'materials used in the circuit breaker and are liable to form compounds with several metals among these materials which settle in powdered form within the confines of the circuit breaker. These powdered substances can be very hygroscopic so that, for instance during inspection of the inner parts of the circuit breaker, water vapour contained in the air is taken up and thereby forms a conductive layer on the surface of the insulators. Additionally, corrosive agents such as hydrofluoric acid may be formed. It has already been proposed to conduct the flow of gaseous and powdered switching products, immediately after their having passed the arc-extinguishing chamber, through filters which render the aggressive products chemically harmless and collect the powdered substances, but in that case the switching contacts, the arcing contacts and the walls of the arc-extinguishing chamber of the circuit breaker are often soon covered with a chemically aggressive layer, so that a circuit breaker of this kind will have to be opened and cleaned directly after it has been switched off. Moreover, in such a circuit breaker the filters are mounted in the vicinity of the live parts of the circuit breaker which makes the replacement of the filter material difficult. Furthermore, these filters must have large filtering areas since the quantity of gas used to extinguish the arc must be passed through said filters in the very short space of time involved in the switching process. Such filters require a considerable enlargement of the dimensions of the circuit breaker.

An object of the invention is to avoid entirely or almost entirely the disadvantages of the known circuit breakers of the mentioned kind. It is characterized in that at least each of the surfaces of the circuit breaker parts lying, during the switching-off process, within the active radiation field of or which come into contact with the arc and/or the constituents of the very hot gas mixture produced by dissociation of a part of the extinguishing gas heated by said are, is constituted of material which guarantees that at the pressures and the temperatures obtaining on said surfaces during the switching process, only negligible or almost negligible quantities of deleterious gaseous or solid products are formed. The invention is based on the recognition that great advantages can be achieved if the circuit breaker parts, such as the arcing contacts and the wall parts of the arc-extinguishing chamber which lie in the direct vicinity of the arc and the parts at greater distances from the electric are are manufactured of or clad with materials whichform with said dissociation products mainly nonaggressive products. Those very few aggressive products which may appear either remain gaseous under the I circumstances obtaining in the circuit breaker or, if solid, are

of negligible quantity and in the form of powdered metal fluorides which are either nonhygroscopic or substantially nonhygroscopic. The result thereof is that in many cases the filters may be omitted or, if still desired, may be mounted on the grounded side in or outside the circuit breaker, since the concentration of the gaseous aggressive products which are found in the circuit breaker after the breaking operation is so small that said products do not appreciably affect the relevant parts thereof so that they are allowed to stay longer in the lowpressure container of the circuit breaker. The powdered products are themselves insulators and since they cannot take up moisture under normal circumstances they do not affect the insulating conditions within the circuit breaker. The filters may be made much smaller than the known filters because instead of being located near the circuit contacts which require them to be of such large size as is capable of handling the high mass rate of gas flow effected during circuit breaking, they are located remote from the circuit breaker and are not required to handle this high rate of gas flow. Instead, a filter if used effects its action at the much reduced rate involved in returning the gas through the pump to the high-pressure container.

To realize the idea of the invention the surfaces of at least those circuit breaker parts which, during the switching-off process, come into contact or are liable to come into contact with the arc may be constituted by a sintered alloy of tungsten and nickel in the ratio lying between :5 percent and 99.710? percent. Under the influence of the electric arc these alloys form with the dissociation products of the extinguishing gas extremely small quantities of permanently gaseous tungsten hexafluoride, which is aggressive only in cooperation with water vapour, as well as powdered nickel fluoride which is insulating in its dry state and only slightly hygroscopic in the presence of atmospheric water vapour contents. ln the presence of the very small quantity of water vapour which during operation is contained in the circuit breaker these products cannot appreciable affect the materials and the insulating condition of the circuit breaker.

Advantageously, the surfaces of at least those circuit breaker parts which, during the switching-off process, lie within the active radiation field of the arc and/or of the very hot gas mixture produced by dissociation of a part of the heated extinguishing gas and/or come into contact with said hot gas mixture are constituted by carbon. To that end the metals used for the said circuit breaker parts may be covered with a thin layer of carbon. Thencarbon is evaporated from said layer by the radiation and the thermal action of the electric arc and the dissociation products of the extinguishing gas and permanently gaseous fiuorinated carbon compounds are formed which are neither aggressive nor hygroscopic, so that they need not be filtered out or discharged in another manner.

The invention makes the provision of gas-blast circuit breakers in the mentioned kind possible, of which the operation is stable and the dimensions are considerably reduced owing to the possibility of using small filters or to omit same.

If the gas-blast circuit breaker constructed in accordance with the invention comprises, as is usual, 21 first container for more compressed extinguishing gas, a second container for less compressed extinguishing gas, a switching chamber, through which said containers are in communication with one another during the switching-off process only, a conduit connected to both containers, said conduit comprising a pump to pump the extinguishing gas from the second container back to the first one, and at least one filter to neutralize and and/or to collect the aggressive or otherwise injurious products formed by dissociation of the extinguishing gas and by the attack of materials used in the circuit breaker by the disintegration products of said gas, said filter is preferably mounted on the suction side of the pump whereat it may be grounded, beyond the pressure side of the pump in the second or the first container, or outside the circuit breaker. Then the replacement of the filter material is very much facilitated.

The invention will be elucidated with the aid of the drawing. In the drawing: I

FIG. 1 is partly an axial sectional view, partly an elevational view of a gas-blast circuit breaker constructed in accordance with the invention; and

FIG. 2 is on a larger scale an axial sectional view of the switching element of said circuit breaker.

ln the drawing 1 designates an electrically grounded metal tank, in which an inner wall consisting of insulators 2, 3, 4 and contact rings 5, 6 are provided. The space 7 between the tank and said inner wall is filled with a gaseous, liquid, viscous or solid insulating material of great dielectric strength. Mounted in the thus formed double-walled casing is the switching element which is kept in place by insulators 8, 9 and provided with electrically conductive contact holders 10, 11, The latter are electrically conductively connected with the contact rings 5, 6 through connecting contact 12, 13. Connected to these contact rings 5, 6 are the connecting conductors 14, 15 for the connection with the outer circuit. This circuit breaker serves only to break the circuit. To keep the circuit interrupted and to close same an isolator switch (not shown) connected in series with this circuit breaker must be provided.

It appears from FIG. 2 that mounted between the contact holders 10, 11 is a cooler made of perforated metal tubes 16, 17, 18, 19 and an insulator 20. The contact holder supports an arc-extinguishing chamber 22 surrounded by a metal wall 21 which is constricted at 23 and rests with a flange 24 upon the insulator 20. Said contact holder also supports a contact block 25 provided with resilient contacts 26 which permanently connect an axially movable switching rod 27 operated by an operation mechanism (not shown) with the block 25. To makeand break the circuit the switching rod 27 cooperates with a fixed contact supported by the contact holder 11. This fixed contact consists of a contact block 28 provided with resilient contacts 29. Mounted within said contact block 28 is an axially movable arcing contact 31 which is loaded by a spring 30.

Provided in the wall 21 of the arc-extinguishing chamber 22 are several discharge openings 32 which, in the closed condition of the circuit breaker, are closed by an annular sliding valve 33 mounted around said wall 21. This annular sliding valve is opened by springs 34 during the switching-off process and closed during the closing of the circuit breaker by a ring 35 connected with the switching rod 27.

The circuit breaker is normally closed. In that condition the switching rod 27, the arcing contact 31, the annular sliding valve 33 and the ring 35 are in the positions shown in dotted lines. The circuit breaker operates with an extinguishing gas consisting of one or more fiuorinated compounds, e.g. nexafluoride which, in the closed condition of the circuit breaker, is contained in, the arc-extinguishing chamber 22 and in the circuit breaker spaces 36 and 37 under compression, say under a pressure of atm. and in the circuit breaker spaces 38, 39 under lower compression, say under a pressure of 3 atm. During the switching-off process the arcing contact 31 follows the switching rod 27 through a part of the switching stroke until the arcing contact is pushed against the stop'ring 40. Thereafter the switching rod 27 is removed from the arcing contact 31 and an electric are 41 is established. Just before the separation of the switching rod and the'arcing contact the openings 32 are opened, so that the extinguishing gas is able to flow with great force out of the extinguishing chamber 22 and, through the narrow opening 42, out of the circuit breaker spaces 36 and 37 to the circuit breaker spaces 38, 39 to extinguish the electric arc. lmmediately after the extinction of the arc the circuit breaker is closed again and the used extinguishing gas is pumped by means of a pump 44 from the circuit breaker spaces 38, 39 back to the circuit breaker spaces 36, 37 and the arc-extinguishing chamber 22 through a conduit 43 which is provided outside the circuit breaker.

In accordance with the invention those parts which are liable to be hit by the arc, namely, the free ends of the switching rod 27 and the arcing contact 31, the wall parts 45, 46, 47, 48 of the arc-extinguishing chamber and the upper surface 49 of the fixed contact 28, 29, are clad with a layer 50 consisting of a sintered alloy of tungsten and nickel in the ratio lying between 95:5 percent and 99.7103 percent whereas the remaining wall portions of the arc-extinguishing chamber and the remaining area of the upper surface of the fixed contact are covered by a layer of carbon 51. The reason for these covering layers is already explained heretofore.

Furthermore, filters 52 are provided in the conduit 43 to render the injurious products produced by the switching process harmless and to collect said products. These filters are also mounted outside the circuit breaker, i.e.; on the electrically grounded side thereof, so that they are accessible at any time. These filters may also be positioned on the pressure side of'the pump in the conduit 43 or in the circuit breaker spaces 39101137 near the bottom of the grounded tank 1.

c arm:

1. A gas-blast circuit breaker in which the electric are setup during the switching-off process in a region ofa switching and arc-extinguishing chamber is extinguished by a blast of gas forced through said chamber and consisting of or comprising a fluorine-containing compound, such as sulfur hexafluoride,

and in which at least all electricallyconductive solid parts eonstituting wall surfaces bounding and facing said region of said chamber are made from an alloy of -997 percent tungsten and 5-0.3 percent nickel.

2. A gas-blast circuit breaker as claimed in claim 1, in which electrically conductive solid parts forming portions of the walls of said switching and arc-extinguishing chamber and constituting wall surfaces which adjoin said wall surfaces constituted by the said tungsten-nickel alloy, are made from carbon.

3. In a gas-blast circuit breaker of the type including a body presenting a chamber, a pair of relatively movable contacts in said chamber, means for opening said contacts whereby an arc is drawn therebetween, and means for blasting a flow of insulating gas through said chamber to extinguish the are, the improvement wherein:

said insulating gas is a gas selected from the group consisting of fluorinated compounds and mixtures thereof; and at least those portions of said chamber and said contacts which are liable to be hit by the arc being constructed of a sintered tungsten-nickel alloy consisting essentially of from 95-997 percent tungsten and the balance nickel.

4. In the gas-blast circuit breaker according to claim 3 wherein said insulating gas is sulfur hexafluoride.

5. In the gas-blast circuit breaker as defined in claim 4 wherein secondary portions of said chamber more remote from the arc are coated with carbon.

6. In the gas-blast circuit breaker as defined in claim 3 wherein secondary portions of said chamber more remote from the arc are coated with carbon.

7. In the gas-blast circuit breaker as defined in claim-3 including support bodies through which said contacts project, the surfaces of said support bodies adjacent said contacts also being formed of said sintered tungsten-nickel alloy.

8. In the gas-blast circuit breaker as defined in claim 7 wherein secondary portions of said chamber and portions of said surfaces of the support bodies more remote from the are are coated with a carbon.

9. In the gas-blast circuit breaker according to claim 8 wherein said insulating gas is sulfur hexafluoride.

10. In the gas-blast circuit breaker as defined in claim 3 wherein said body includes inner wall portions defining first and second'chambers and a constricted portion joining said chambers, said constricted portion including a pair of oppositely directed frustoconical wall portions having their apices joined by a tubular wall portion, a contact support in said first chamber including an end wall portion in spaced opposition to one of said frustoconical wall portions and having one of said contacts projecting therefrom in axial alinement with said tubular wall portion but terminating in spaced relation thereto, the other of said contacts extending from said second chamber and through said constricted portion into engagement with said one contact, a guide for said other contact having an end wall disposed in spaced opposition to the other of said frustoconical wall portions means for withdrawing said other contact through said tubular wall portion to a position on the opposite side thereof from said one contact whereby an arc is drawn between said contacts which is enclosed by said tubular wall portion, said frustoconical wall portions, said tubular wall portions, and said end wall portions being those portions of the chamber constructed of said alloy.

11. In the gas-blast circuit breaker as defined in claim 10 wherein said guide and said support include sidewall portions leading to said end wall portions thereof and which are constructed of graphite.

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