US2987596A - Scavenging means for air blast circuit breaker - Google Patents

Description

H. FORWALD SCAVENGING MEANS FOR AIR BLAST CIRCUIT BREAKER Filed Nov. 23. 1959 INVEN TOR.

June 6, 1961 United States Patent.

2,987,596 r I SCAVENGING MEANS FOR AIR BLAST CIRCUIT BREAKER Haakon Forwald, Ludvika, Sweden, assignor to Allmanna, Svenska Elektriska Aktieholaget, Vasteras, Sweden, 11 Swedish corporation 7 Filed Nov. 23, 1959, Ser. No. 854,648 I Claims priority, application Sweden Dec. 6, 1958 2 Claims. (Cl. 200-148) This invention relates to air blast circuit breakers and more particularly relates to a scavenging means for eliminating ionized gas particles from the arc extinguishing stream of gas or air.

Air blast circuit breakers having a hollow contact through which an air jet or gas jet is passed during arc interruption conditions are well known to those skilled in the art. Conventionally, the movable contact is a hollow member which is so arranged that during contact separation of the movable contact and its cooperating contact, a jet of air or gas is passed through the hollow movable contact and is brought to play upon the arc to cool the arc and to remove ionized gas produced in the arcing area. To assist in permitting the escape of previously ionized gas, it has been the practice to provide exhaust means which communicate between areas external to the interrupting chamber and an area adjacent to the inlet openings of the movable contact. Thus, ionized gas which expands due to the high temperature of the arc can pass outwardly through these exhaust vents.

The principal reason for this type of arrangement is that when the arc current is relatively high, there is a very high back pressure generated by the ionized gas or air for'cooling the arc. Because of this, it has been found that the only time there is a substantial flow of cooling gas through the hollow contact is for a short interval prior to the point at which the arc current passes through zero and for a short interval before the current reaches the aforementioned relatively high value.

Therefore, ionized gas will be stored in the inlet portion of the air blast means during equal pressure intervals so that when the current decreases and a flow of cooling gas is possible, the arc will not be exposed to a blast of fresh unionized gas, but will be exposed to this previously ionized gas which is stored at the inlet of the extinguishing gas source. In providing the aforementioned exhaust between the inlet of the extinguishing gas source and the external atmosphere, it is possible for this ionized gas which would be stored at the inlet to escape to areas external to the interrupting chamber so that when it is possible for an air blast to proceed, this air blast will consist of unionized gas.

The main disadvantage in providing these channels communicating between the air blast inlet and areas external of the interrupting chamber is that there will be a large volume of interrupting or fresh gas which is lost through these channels under air blast conditions so that a smaller portion of the unionized gas is available for the actual arc interruption and a correspondingly larger source of interrupting fluid is needed.

The principal object of the present invention is to retain the advantages of the scavenging channels which permit the ionized gases to drain out of the interrupting chamber under high counter-pressure conditions and to substantially decrease the loss of unionized gas provided for are interrupter through these same scavenging channels.

Another object of the present invention is to provide a novel interrupting chamber having improved ionized gas scavenging provisions which will not cause a substantial loss of compressed air for the air blast operation.

Patented June 6, 1961 "ice A further object of this invention is to substantially improve the interrupting characteristics of an air blast circuit breaker by scavenging a substantial amount of ionized products through channels which pr sent a relatively high impedance to cool unionized gas.

These and other objects of the invention will become apparent from the following description when taken in connection with the drawing, which shows a cross-sectional view of a typical air blast circuit breaker interrupter chamber adapted in accordance with the present invention.

In the present invention, I have found that the scavenging exhaust channels connecting the air blast inlet area and areas external of the interrupting chamber can be adapted with a selective grid means which will readily pass hot ionized gas and at the same time will present a substantial impedance to the flow of cool unionized gas. By way of example, the exhaust passages may contain cooling grids formed of a grid comprising a number of narrow channels which may be formed by closely spaced plates or concentrically positioned closely spaced rings. However, any type of means forming a plurality of narrow paths can be provided in the exhaust ports.

In the accompanying drawing which shows one embodiment of the present invention, the interrupting chamber includes a tubular insulator 1 which carries a stationary contact 2 in the usual manner well known to those skilled in the art. A hollow movable contact 3 which is movable into and out of engagement with respect to stationary contact 2 is carried in a piston 4 which is movable within a cylinder 5. The cylinder 5 may be of metallic material and is mounted at the upper end of insulator 1 as illustrated in the drawing. An arcing contact 6 is also carried by cylinder 5 in the standard manner. Piston 4 is biased downwardly to a contact engaged position with respect to stationary contact 2 by biasing spring 7.

In order to move piston 4 upwardly and to a contact disengaged position, a contact operating means of any desired construction may be provided. In a typical application, compressed air can be introduced to the bottom of piston 4 through annular opening 1a in insulator 1 to force piston 4 and thus movable contact 3 upwardly against the bias of spring 7. The air blast for extinguishing the are drawn when contacts 2 and 3 are disengaged is derived from the compressed gas coming through the annular opening 1a in tubular insulator 1. This compressed gas may be delivered from any convenient source having a conventional control therefor. The path of the compressed air through insulator 1 is illustrated by the arrows which show the air as flowing through the centre of hollow contact 3 and outwardly of the interrupter through the central opening in outlet channel 8 and through annular opening 9 which communicates with channel 8 through open portions 9a and 9b.

In this structure, when piston 4 is moved upwardly under the action of the compressed air introduced through channel In, an arc is drawn between contacts 2 and 3. At the same time, however, a strong blast of air which is compressed under piston 4 will flow through the previously sealed opening of contact 3 whereby the arc illustrated by the shaded line from arcing contact 6 to stationary contact 2 is moved from contact 3 to arcing contact 6.

Also, as shown in the drawing, the air blast will flow down the central opening 8 in stationary contact 2 to blow the arc a short way downwardly in the contact 2. The arc thereby generates a high counter-pressure in the inlet opening of channel 8 which pressure varies with the arc current intensity and, under high current intensity conditons, is greater than the pressure of the cool unionized aeezees gas under piston 4 so that the ionized gas will remain stored in the inlet of channel 8.

As previously mentioned, this led to the problem that when the high counter-pressure decreases with decreased current intensity, the hot ionized gas stored in the inlet openings will be swept upwardly through the opening in contact 3 and downwardly along the arc portions in channel 8 whereby the arc is supplied with hot ionized gas rather than the cool unionized gas blast required to extinguish the arc. It has been further previously brought out that this problem was solved by providing auxiliary openings which communicate between areas adjacent the inlet of channel 8 and areas external of the interrupting chamber, which will permit the high pressure ionized gas to drain away from the inlet so that it will not be subsequently brought through the are when the pressure of the air blast exceeds the counter-pressure of the ionized gas.

This, however, raises a new problem since the forming of a parallel path for the cooling unionized gas blast causes a large consumption of compressed air needed for extinguishing the arc.

In accordance with the invention, a cooling grid 10 is placed in the outlet channel 9. In the drawing, the cooling grid is comprised of a plurality of concentric tubes closely spaced with respect to one another to form narrow annular openings. The cooling grid 16 shown in the drawing could, of course, take many diiferent forms. For example, it could be a solid member having holes drilled therein in an axial direction to provide a plurality of small cross-sectional area channels. The cooling grid 10 operates to present an extremely large cooling surface to the hot ionized gas. Furthermore, because of the small grid spacing, the grid will present a relatively high flow resistance to cold air while presenting a relatively low resistance to hot ionized gas which has a lower viscosity than cold air.

A further reason which permits the selective action of grid 10 to proceed in a highly efiicient manner is that when the hot gases flow out of the grid, they are cooled so that their volume is decreased to provide a partial vacuum. This will cause a still greater flow of hot gases into the grid. The cooling air which is to be used for the air blast action, however, will not be cooled to the same degree since it is already at a low temperature and Consequently, the decrease in volume of the cold in the cooling grid will be lower than that of the hot gas whereby the flow resistance of the cooling grid against cold air will be higher than the flow resistance of the hot ionized gas.

In view of this action of grid 10, it will be apparent that under high current intensity conditions causing a high pressure adjacent the inlet opening of channel 8 due to hot ionized gas, that this gas will be scavenged through cooling grid 10 in channel 9. At the same time, the gas or air entering the interrupting chamber through channel 1a and which is the cooling air or gas for extinguishing the arc will be substantially blocked by grid 10 whereby the consumption of compressed gas is kept within practical limitations in spite of use of venting channels such as channel 9.

In the foregoing, I have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specific disclosure herein, but only by the appended claims.

I claim:

1. In an air blast circuit breaker having an interrupting chamber, cooperative contacts at least one of which is movable between engaged and a disengaged position, and gas blast means for directing a blast of cool gas on the are drawn by said cooperating contacts when said contact is moved to said disengaged position, said gas blast means including an opening in one of the contacts, exhaust means communicating between areas adjacent the arc and areas external to said interrupting chamber, a venting channel having at least its inlet separate from said exhaust means communicating between areas adjacent the arc and areas external to the interrupting chamber and containing at its entrance selective cooling grid means for exerting a relatively low flow resistance to hot ionized gas and a relatively high flow resistance to relatively cool unionized gas, said grid permitting venting of hot ionized gas during relatively high current intensity intervals of said arc without substantial loss of gas of said blast of cool gas.

2. In a device as claimed in claim 1, said venting channel being concentrically arranged with respect to one of said pair of cooperating contacts, said grid means being positioned in said concentric portion of the area adjacent said are.

References Cited in the tile of this patent UNITED STATES PATENTS 2,051,478 Hampton et al Aug. 18, 1936 2,284,842 Prince et a1. June 2, 1942 2,302,592 Amer Nov. 17, 1942 2,333,598 Strom Nov. 2, 1943 2,526,387 Milliken Oct. 17, 1950 FOREIGN PATENTS 597,533 Germany May 26, 1934 676,353 Germany June 2, 1939

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