US2382850A - Gas blast electric circuit breaker - Google Patents

Description

Aug; 14, 1945. M ENNETT 2,382,850

GAS BLAST ELECTRIC CIRCUIT BREAKER Filed June 16, 1942 v 2 Sheets-Sheet 1 2 z If? 2 A! l 6 W i /74 I /74 M l I I l e: i /f I 1 I a rm: I

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3 Inventor:

Robert M. Bennett.

His Attorney.

Aug.'.14; 1945.

R. M. BENNETT GAS BLAST ELECTRIC CIRCUIT BREAKER 2 Sheets-Sheet 2 Filed June 16, 1942 Inventor.

Robert M. Bennett, by .X/awy W His Attorney.

Patented Aug. 14, 1945 GAS BLAST ELECTRIC CIRCUIT BREAKER Robert M. Bennett, Ithan, Pa., assignor to General Electric Company, a corporation of New York ' Application June 16, 1942, Serial No. 447,281

7 Claims.

My invention relates to gas blast electric circuit breakers, more particularly to those of the cross-blast type wherein a supply of gas under pressure is directed at high velocity transversely across the arc path to drive the are into an extinguishing structure or are chute, and. has for its principal object the provision of an improved circuit breaker of the aforesaid type that is more effective and efficient in its application of 'the interrupting blast to the arc stream for extinguishing the arc and preventing restriking thereof after interruption at a current zero.

This application is a continuation-in-part of my application Serial No. 411,303, filed September 18, 1941, forv Gas blast electric circuit breaker.

My invention will be more fully set forth in the following description referring to the accompanying drawings, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawings, Fig. 1 is an elevational view in section of a gas blast electric circuit breaker embodying the present invention, Fig. 2 is a view taken along the line 2-2 of Fig. 1, Fig. 3 is an enlarged detail view in plan of the diffusing means at the entrance of the blast passage looking at the section indicated by the arrows at 33, Fig. 4 is a partial view in section of a modified form of my invention, and Figs. 5 and 6 are views taken along the section lines 55 and 6-6, respectively, of Fig. 4.

In Fig. 1, there is shown by way of example an air. circuit breaker of the cross-blast type in the closed circuit position thereof having relatively movable contacts comprising fixed contact structure I and a coacting reciprocally guided rod or blade-like contact 2 hereinafter more fully described. The fixed contact is electrically connected as indicated to one line terminal of the breaker at 3 and the movable blade contact is also connected by sliding engagement as indicated to the other line terminal at 4. The blade contact 2 is movable by suitable actuating means (not shown) preferably along a generally rectilinear path to make and break the circuit with' respect. to the fixed contact I although it will be apparent that the blade may, if desired, be arcuate in form and move longitudinally along an are instead of a straight line. v

For the purpose of extinguishing the are formed between the contactswhen the power circuit is opened by separation of the breaker contacts, an insulating arc chute 5 is arranged with respect to the contacts so thatthe arc is drawn at the entrance portion or throat" of the chute opposite a gas blast supply conduit 6. The conduit 6 is suitably connected through a blast control valve (not shown) to a source of compressed gas, such as air, comprising for example a storage tank and compressor equipment, also not shown.

The arc-chute 5 defines a narrow, diverging space into which the arc is driven and extinguished by the interrupting blast and is formed by diverging end walls I and 8 and comparatively closely spaced parallel side walls Band In (Fig. 2) together with a bottom wall I I through which the blast passage extends. The walls'of the chute are composed of a mechanically strong insulating material, such as a molded laminated structure. The exhaust end of the chute opens. into a laterally extending conduit I2 which directs the heated blast gases away from the circuit breaker proper.

The chute also includes a plurality of insulating arc barriers I3 that are disposed edgewise to the arc path with the barrier width transversely of the arc path so as to form diverging gas passage leading to the exhaust conduit. Spaced cooling plates M are located in the path of the hot gases flowing through the chute. The barriers extend fairly close to the arc path as indicated and are composed of a vaporizable insulating material such as hard fibre that does not lose its insulating characteristics in the presence of the are as disclosed and claimed in Letters Patent No. 2,284,- 842 issued June 2, 1942, to D. C. Prince et al. for Circuit breaking apparatus, and assigned to the same assignee as the present invention.

The are chamber or space in which the arc is drawn is formed, as previously stated, at the entrance oi the chute between the blast supply conduit 6 and the arc barriers I3 and constitutes an elongated chamber I5 having at one end the fixed contact I and at the opposite end an opening I6 formed in the sidewall 8. This opening is in close fitting registry with the movable contact 2 which can move exteriorly of the chute to a safe isolating distance. The side wall 8 is also provided with a sleeve-like extension 8' forming a fluid-seal pocket 8 through which the contact moves for confining the arc flame to the chute interior. The are formed between the separated contacts may extend longitudinally of the chamber as is evident from Fig. 1 so as to be directly across the path of the gas blast as it is directed into the chute.

In the cross blast circuit breakers heretofore used, the chamber I5 was in general formed either as a comparatively narrow slot, the insulating sidewalls of which lay fairly closel along the sides of the blade contact as disclosed in the Prince et al. patent above referred to, or, in the case of higher voltages, such as voltages appreciably in excess of kv., with the chamber sidewalls spaced appreciably from the contact blade a distance dependent on the line voltage and other factors. In this latter arrangement, the arc chamber has a cross-sectional area considerably larger than that of the blade contact.

An arc chamber design of this latter character is disclosed and claimed in my Letters Patent No. 2,284,856, issued June 2, 1942, for Gas blast electric circuit breaker" and assigned to thesame assignee as the present invention.

In this type of arc chamber, high current carrying and interrupting capacity requires that the cross section of copper for the blade contact be sufficiently large toprevent overheating and this in turn calls for a larger cross-sectional area for the arc chamber. However, when the cross-sectional 'area of the chamber, and also its length, become quite large as compared with the blast passage opening leading from the gas supply conduit, the 'arc -in certain high current interruptions may restrike when the recovery voltage appears across the breaker terminals after actual interruption at a current zero. Such failures were characterized by delayed restriking, 1. e., momentary interruption and clearing of the circuit for from 50 to 300 microseconds foliowedby relgnition of the arc. This particular restriking 'or failure to clear the circuit is somewhat unusual in that it "is quite unpredictable and is apparently caused by hot gases or conducting particles oi contact material that are trapped in the arc chamber and blown into the contact space after momentary interruption at a current zero. It is also possible that this restriking phenomenon may in addition involve a momentary lessening in intensity of the interrupting blast.

I have found that this restriking of the arc can 'be prevented and the breaker made more efficient in promptly and positively clearing the circuit after interruption at a current zero by providing means for diffusing or spreading the flow of "the interrupting gas substantially at, or a short distance up-stream with respect to the point of transverse application of the interrupting blast to the arc stream so that the gas flow enters the arc chamber along substantially its entire up-stream side. This diifused and more uniform flow of the interrupting gas entering the arc chamber is believed to improve the interrupting performance of the breaker by eliminating turbulence and dead spots of hot arc gases that tend to decrease the dielectric strength of the space separating the contacts at the moment oi interruption, which might be the case were the gas supply conduit to open directly into an arc chamber of appreciable size, or be oilset with respect to a portion thereof, or both. Instead, the difiusing means of my invention provides a smooth, even flow of gas at high velocity entirely throughout the so-called throat or are chamber.

I have also found that the interrupting gas blast is more eflectlvely applied when -a cushioning or surge chamber is used "in the gas line close behind "the orifice or orifices leading to the arc chamber I5. This appears to resulting. more uniform and eflicientcontrol of the intwmpting blast, probably by surge-chamber action in maintaining the gas flow along the supply line during very brief intervals when the arc chamber back-pressure tends to stop or reverse the gas flow.

The transient nature of air 01' gas flow makes it very difiicult to describe just what takes place. In the specific form of cross blast circuit breaker disclosed, the arc chute passages are substantially shut off or restricted in respect to the incoming blast when the contacts are touching and while a heavy current are is being initially drawn. During this period the air flow is comparatively low and consequently the air pressures in the supply line upstream from the arc tend to rise to high values approaching the main supply or tank pressure. At the moment the arc is interrupted and full air flow takes place, a substantial pressure drop occurs across the supply line and especially across the blast control valve so that the pressure at the entrance to the arc chute drops rapidly to a'va'lue determined by the steady state of flow of air. The surge chamber immediately behind the orifice venting area tends to prevent this rapid decrease in supply pressure because the additional air stored therein must be exhausted before -a return to normal flow conditions can take place. Although the total volume of this chamber is not large compared to that of the supply conduit, it should be noted that the crucial period during which clearing or restriking are in the balance is measured in microseconds and 'a small volume oi interrupting gas stored for delivery at the right instant to the arc gap may be capable of determining the difference between success and failure of the breaker.

Referring more particularly to 'a specific embodiment of my invention, the diffusing means and surge chamber are indicated at i'! and Ha respectively between the gas supply conduit 0 and the arc chamber 1'5. The diffuser can convem'ently comprise a perforated plate or guidlike structure having apertures ll of suitable size and spacing as indicated by Fig. 3 which shows the plan view of the diiluser. The diffuser plate at l I is suitably mounted in the chute between theend plate I l and the block-like members 18 forming the side walls of the arc chamber i5 as best shown by Fig. 2.

The surgechamber l'la is conveniently formed by removing insulating material from the diffuser plate I! and the end plate H asshown so that-the chamber defined thereby is materially larger in cross-sectional area than either the supply conduit 6 or the diffuser or orifice areas. The chamber is located close behind the orifice means I1.

The blade contact 2 in the specific instance has not only an appreciable copper cross-sectional area but also is of hollow construction in the specific example shown for most efficient handling of large alternating power currents. The blade is provided with a ridge 2' at its lower side that extends along the entrance of a restricted passage i5 formed by the blocks 18 leading from the arc chamber to the chute passages The contact ridge portion 2' coacts with the elongated finger contatcs -l' of the fixed contact structure so that thearc is initially 'l'orm'ed and drawn through the chamber near the restricted passage i5 and adjacent to the edges l-"Z' of the insulat' ing barriers i3. Due to the large total crosssectional area of the blade contact I, the crossseotional area of the chamber l5 will-also necessarily be quite large, even in the case-of designs wherein the chamber sidewalls lie close to the contact blade. The restricted passage leading from the arc chamber is not dependent on the 'width of the chamber itself and is designed to provide for most efiicient and economical use of the interrupting gas supply for driving the arc against the barrier edges and into the chute passages for extinguishing it.

The operation of the circuit breaker above described is as follows: When the blade contact 2 is moved toward the right to open the circuit, the interrupting gas is also admitted to the conduit 6. As the blade portion 2' separates from the fixed contact fingers l the'arc is drawn across the'opening of the first chute passage substantially concurrent with the blast of gas which passes through the surge chamber Fla and the difiuser or orifice means l1, across the arc chamber and the arc stream to drive or loop the are into the first chute passage. As the blade contact continues to move toward the right, successive chute passages are uncovered and the arc is driven by'the blast against the edges of the barriers and also looped into the other chute passages. Generally the arc is interrupted before more than two or three passages are uncovered by the blade, and often at the first passage. At the moment of current interruption, the gas blast tends to sweeep the'hot arc gases and products from't'he chamber into the chute passages and to replace them with fresh gas of.comparative1y high dielectric strength. This is a critical moment in the interrupting operation, since any appreciable impairment of the dielectric strength of the space separating the contacts due to the presence of conducting gases or particles, inomentary failure of the gas blast, or other causes might cause restriking of the are as the recovery voltage appears. Such. restriking might result in failure of and damage tothe circuit breaker.

By means of the surge chamber Ila and the diffuser or orifice means I1, I provide for more uniformity in the application and dielectric strength of the gas that is interposed between the separated contacts after interruption at a current zero so that restriking of the arc is less likely to occur. When a perforated plate such as I! having av plurality of apertures I1 is employed in the manner shown in Figs. 1 and 2, a plurality of gas jets are provided along the direction of movement of the contact 2. This uniform control of the gas'flow along substantially the entire upstream side of the arc chamber is indicated by the flow-direction arrows in Figs. 1 and'2. This clearly shows how dead spaces at the right end of the chamber, for example, are avoided which otherwise might exist if the main blast flow were directed somewhat to the left of that portion of thechamber. In general, this has been the case in prior designs since it is quite impracticable to provide a gas supply conduit of large cross-sectional area for delivering interruptinggas at sufficient pressure. With my improvement a gas blast breaker of the cross blast type is more reliable and efficient in the interruption of particularly heavy power currents, both at moderate and high voltages, and in addition prevents restriking of the are at a lower operating gas pres sure.

I have also found that the surge chamber apparently intercepts or traps particles of carbon and contact metals, such as copper and tungsten, blown back from the arc chamber that would otherwise be deposited on the inner sidewalls of the gas supply conduit a material distance back. from the arc chamber. Such a deposition of conducting material would in time cause a voltage-breakdown and flashover along the supply conduit to ground.

In the modification of my invention shown by Figs. 4, 5 and 6 the arc chamber and orifice vent-- ing area are designed for different interrupting conditions although the basic principle is the same. Sincethe circuit breaker in general can be essentially the same as shown by Figs. 1 and 2 it-will be sufiicient toindicate similar structure by similar reference numerals.

- Referring now to Fig. 4 whichshows the circuit breaker closed, the blast line, as in the previous instance includes a surge chamber lla located immediately upstream from the orifice venting area at 20. Inthis case, the orifice venting area constitutes a single slot-like opening formed in the insulating orifice plate l"! extending longitudinally of the length of the arc chamber and positioned centrally of the upper side thereof as shown by Figs. 5 and 6. I Th chamber lla can be suitably formed by cuttin away portions of the insulating plates H and I! as indicated so that the cross sectional area of the chamber is, as is obvious from the drawings, at least twice as great as either'the venting areas of the orifice 20 or the supply'conduit 6.

This combined arrangement is also effective more uniformly and efficiently to apply the interrupting blast to the arc path and is superior in interrupting performance to prior designs wherein the arc chute'is directly connected to a conv'entional supply conduit.

It will be understood that my invention is not limited to the specific form and shape of'the orifice venting'area, or to a specific size and shape of the surge chamber, and that my invention is also applicable to gas blastcircuit breakers of moderate current interrupting capacity and is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may. occur to one skilled in the art without departing from, the spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A gas blast circuit breaker comprising an arc-chute having an entrance portion including an arc chamber, relatively movable contacts separable in said chamber to form an arc gap, means containing interrupting gas under pressure prior to separation of said contacts, a conduit for directing said interrupting gas under pressure into said chamber and transversely across said gap to drive the arc into said chute for extinguishing it, said conduit having a gas supply opening that is smaller than the upstream side of said chamber,

and diffusing means disposed at said upstream side between said conduit and are gap for pro ducing a pluralit of gas jets along the direction of movement of said relatively movable contacts for insuring substantially uniform and even fiow of interrupting gas through substantially the entire length and width of said upstream side and said chamber and the arc gap therein, said last mentioned means reducing the effective area of the entrance to said chamber by at least onehalf.

2. A gas blast circuit breaker comprising an arc chute having an entrance portion defining an elongated arc chamber, relatively movable contacts separable in said chamber to form an arc gap, means containing interrupting gas under pressure prior to separation of said contacts, a conduit having a gas supply opening opposite the longitudinal axis of said chamber for directing said interrupting gas under pressure into vsaid chamber and transversely across said 'saptodrive the are into said chute tor extinguishing it, and diffusing means including a perforated plate comprising a plurality of apertures extendin along the upstream side of said chamber and interposed with respect to said conduit opening and are gap tor providing uniform and even fiow of interrupting gas throughout the length and width of; said chamber and the arc gap therein, said perforated plate providing an orifice area or less than 50% of the area at the entrance to said chamber.

3. A gas blast circuit breaker oomprisingmeans defining an arc chamber, relatively movable contacts separable to formlan arcgap in said-chamber, means containing interrupting gas under pressure prior to separation of said contacts, a conduit for supplying said interrupting gas under pressure to said chamber, means interposed with respect to said gas supply conduit and said are gap for directing a gas blast transversely through said gap to extinguish the arc and star improving the effectiveness of said blast in clearing the circuit, including means defining a. long narrow orifice disposed with its long dimensioniextending along the path of movement of said relatively movable contacts and positioned substantially at the entrance to said are chamber and a surge chamber disposed in the blast line a short distance upstream from said orifice, said surge chamber being at least twice as large in cross sectional area, as either the venting areas .of said orificeor said supply conduit.

4. A gas blast circuit breaker comprising means defining an arc chamber, relatively movable contacts separable to form an arc gap inrsai chamber, means containing interrupting as under pressure prior to separation of said contacts, means for directing said interrupting gas under pressure transversely through said gap to extinguish the are including a gas supply conduit, orifice means disposed substantiall :at the entrance to said are chamber spaceand arranged to produce a cross blast of gas all along the path of movement of said relatively movable contacts at the entrance to said are chamber and a surge chamber disposed immediately between said oriflee means and gas supply conduit, said surge chamber being adjacent to said are chamber at the upstream side thereof and being at least twice as large in cross sectional area as either the venting areas of said orifice means or said supply conduit.

5. A gas blast circuit breaker comprising means defining an arc chamber, relatively movable contacts separable in said chamber to form an arc gap, means containing interrupting gas under pressure prior to separation of said contacts, means including a conduit for directin said interrupting gas under pressure transversely through said gap to extinguish the are, means comprising a perforated plate including a plurality of apertures in the path of said interrupting gas adjacent to said are gap for insuring substantially uniform distribution of gas flow throughout the arc chamber space and said are gap, and a chamber having a cross sectional area at least twice as large as either the'cross sectional venting areas of said conduit or said flow distribution means directly interposed in the blast line immediately upstream from said flow distribution means.

6. A gas blast circuit breaker comprising an arc chute having at its entrance portion a narrow elongated arc chamber, said chute having a gas exhaust portion arranged to communicate with said are chamber, a blade-like contact mounted for reciprocal movementwithin and longitudinally of said are chamber, a fixed contact at one end of said chamber arranged to be engaged by said blade contact for controlling the circuit, means containing interrupting gas under pressure prior to separation of said contacts, a gas supply conduit for directing said interrupting gas under pressure to said are chamber, said blade contact substantially shutting off or restricting the flow of gas to the exhaust portion of said chute from said supply conduit when said contacts are in engagement, means defining an orifice ventin area for the interrupting blast at the entrance to said chamber comprising a perforated plate including a plurality of apertures, and a chamber in the blast supply line located immediately upstream from said arc chamber and said orifice venting area, said chamber being at least twice as large in cross sectional area as either the venting areas of said orifice or said supply conduit.

7. A gas blast circuit breaker comprising an arc chute having at its entrance portion a narrow elongated arc chamber, said chute having a m exhaust portion arranged to communicate with said are chamber, a blade-like contact mounted for reciprocal movement within and longitudinally of said are chamber, a fixed contact at one end of said chamber arranged to be engaged by said blade contact for controlling the circuit, means containing interrupting gas under pressure prior to separation of said contacts, a gas supply 0011-, duit for directing said interrupting gas under pressure to said are chamber, said blade contact substantially shutting off or restricting the flow of gas .to the exhaust portion of said chute from said supply conduit when said contacts are in engagement, means defining a narrow slot-like orifice venting area for the interrupting blast at the entrance to said are chamber, said slot-like orifice extending longitudinally of the length ofsaid arc chamber so as to produce a blast of gas all along the path of movement of said blade-like contact at the entrance to said are chamber, and a chamher in the blast supply line located upstream from said are chamber and said slot-like orifice venting area, said chamber being at least twice as large in cross sectional area as either the venting areas of said slot-like orifice or said supply conduit.

ROBERT M. BENNETT.

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