US2290708A - Gas blast circuit breaker - Google Patents

Description

July 21, 1942. w. K. RANKIN 2,290,708

GAS BLAST CIRCUIT BREAKER Filed Jul 16, 1940 Fig. 1.

Inventor:

William K. l ankin.

ttorneg,

Patented July 21, 1942 GAS BLAST CIRCUIT BREAKER William K. Rankin, Lansdowne, Pa., assignor to General Electric Company, a corporation of New York Application July 16, 1940, Serial No. 345,755

Claims.

My invention relates to gas blast circuit breakers, more particularly to air circuit breakers of the cross-blast type employing an arc chute into which the arc is driven and interrupted by a high velocity blast of air or other suitable arc extinguishing gas.

In the case of heavy overload and short circuit currents, the operation of air blast circuit breakers of the aforesaid type is often accompanied by flame emission from the arc chute at the clearance point where the movable contact is withdrawn from the chute proper. This fiame may be due to incandescent particles of metal and carbon from the arc chute structure and also to combustible gases such as hydrogen and carbon monoxide which are liberated by the are heat from the arc chute walls, particularly if the chute structure is composed of a vaporizable material such as fibre. The combustible gases if sufficiently heated in the presence of oxygen will of course ignite. This ignition may even be delayed until the gases have reached the exterior of the chute where they ignite with atmospheric oxygen and burn. The resulting flame is obviously objectionable, particularly in the case of indoor stations where station operatives are present and space considerations require that the electrical apparatus be closely grouped. A comparatively small amount of flame may cause voltage breakdown of air spaces with possibly serious results.

It has been proposed that metallic cooling structure such as copper plates be placed in the path of the main exhaust gases for extracting heat sufficiently to cool the gases below the flame point. Also, it has been proposed to conduct the arc gases through long and spacious passages before exhausing to atmosphere. These methods, even though they may be feasible for cooling the main exhaust gases, have serious disadvantages in the present case since the arc chute structure would thereby be considerably more complicated and require greater space.

In accordance with my invention, the hot arc gases tending to follow the movable contact as it is being withdrawn from the arc chute during the circuit opening operation are instead diverted or blocked off at an auxiliary chamber that is in communication with the source of blast pressure. This auxiliary chamber is in the path of the movable contact as it is being withdrawn from the arc chute so that diverting or blocking of arc chamber gases at this point precludes flame emission from the arc chute along the movable contact.

My invention will be more fully set forth in the following description referring to the accompanying drawing, 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 drawing, Fig. 1 is an elevational view in section of an air blast circuit breaker embodying the present invention, and Fig. 2 is a similar fragmentary view showing another form my invention may assume.

The circuit breaker illustrated is of the crossblast type, i. e. the arc extinguishing blast is directed transversely across the arc gap, and comprises a pair of relatively movable contacts, namely a fixed contact structure l and a reciprocally movable coacting contact 2. The fixed contact l is of the so-called finger type having a plurality of pairs of contact elements 5' resiliently biased toward each other, and the contact 2 comprises a blade-like member arranged to be engaged at its opposite contact faces by the fixed contact element 5. The fixed and movable contacts are provided with arcing tips l and 2' respectively to which the current is transferred after separation of the main contact surfaces.

The separation of the contacts l and 2 takes place at the entrance portion of an insulating box-like arc chute 3 supported on an insulator 3. The entrance of the arc chute is defined by a slot-like opening at 4i and the are drawn between the arcing portions l" and 2' is parallel and adjacent to this opening so that a high velocity gas blast directed through the gas supply conduit b tends to drive the are into the arc chute. For

' the purpose of more effectively interrupting the arc, the arc chute is provided with a plurality of insulating barriers ii which extend fan-wise from the chute entrance at i to the chute exhaust portion l. The insulating barriers 6 extend edgewise across the path of the are so as to define separate diverging passages in the arc chute. Also mounted within the arc chute are a plurality of metallic cooling structures 8 which are disposed within the diverging chute passages as indicated. The cooling structures 8 are preferably composed of spaced copper plates disposed edgewise to gas fiow for extracting heat from the arc gases without materially impeding the flow of the gases. The exhaust gases can be conveniently directed from the arc chute structure by an insulating conduit 9. The are chute structure above described is specifically described and claimed in a copending application Serial No. 303,126, filed by D. C. Prince, W. K. Rankin and W. F. Skeats, forCircuit breaking apparatus and method of operating the same.

In the previous designs of this character, it had been proposed, referring more specifically to Fig. 1, to extend one of the insulating barriers 6 disposed near the end of the arc chute across the path of contact movement so as substantially to seal that end of the chute except for a slot 6' in the barrier in which the blade contact 2 is closely fitted. The space so defined between the barrier and the end of the chute was intended to provide for dissipation of the arc flame and combustible gases that might follow the movable contact as it was being withdrawn from the arc chute. However, this arrangement did not prevent flame emission at the clearance between the chute and the movable contact. This flame and hot gas emission is not only a hazard in many respects but also causes erosion of the insulation where the movable contact is guided in the chute.

I have found that this problem can be overcome by utilizing the pressure of the main blast supply so as to divert or block off the arc chamber gases. In Fig. 1 this is accomplished by shunting a small portion of the main gas blast around the end barrier 6 by way of a passage I so that the normally dead space indicated at II is traversed by an auxiliary blast tending to sweep the stray combustible gases and flame through the end chute passage I2 into the main exhaust portion. In other words, as the contacts I and 2 start to separate, the gas blast is directed into the arcing space I3 through the main blast opening 5. The arrangement of the blast opening 5' with respect to the arc path and the fixed contact structure I constitutes no part of the present invention and is disclosed and claimed in a copending application Serial No. 405,229, filed August 2, 1941, by W. L. Pease for Gas blast electric circuit breaker and assigned to the same assignee as the present invention. Normally the arc is interrupted after the arcing tip 2' has uncovered the first one or two chute passages. The are flame and combustible gases for the most part are directed into the chute before the blade contact 2 uncovers the opening 6' in the end bafiie. However, in the case of exceptionally heavy overload or short circuit currents, flame and combustible gases from the space I3 may be forced around the clearance edges of the contact 2 into the space II. In the absence of further means, these gases and flame may be expelled by the chute pressure to atmosphere as the contact 2 is being withdrawn from the chute.

In accordance with my invention, the auxiliary blast through the bypass port I0 not only clears the space II of such flame and gases but also acts as a barrier to prevent any remaining flame and gases in the space I3 from following the movable contact. In, order further to insure clearing of all flame and gases from the space I I, the arc chute structure for guiding the movable contact is provided with an insulating extension I4 which in effect is the equivalent of a contact pause prior to withdrawal of the contact from the chute.

Since the gas blast directed into the arc chute upon separation of the contacts is now efiective to expel all flame and gas into the main arc chute 3 which is particularly designed for receiving these gases, it will be apparent that the movable contact 2 can now be completely withdrawn from the chute for the purpose of forming an isolating gap in -air between the terminals of the breaker indicated at I5 and I6.

In the modification shown by Fig. 2, the hot gases and flame from the arc chamber I3 are prevented from escaping along the contact 2 by pressure means instead of the above described blast means. That is, means are provided for insuring a pressure differential between the auxiliary chamber I! through which the movable contact is drawn prior to leaving the arc chute so that gas tends to flow from the chamber I'I toward the arc chamber I3 rather than vice versa. To this end, the auxiliary chamber I1 is connected to the main gas blast conduit 5 through a passage I 0 arranged so that the pressure in the chamber I'I approximates that in the main blast conduit. The chamber I1 is otherwise sealed except of course for the contact slot opening 6 in the battle 6 and the corresponding aligned opening I8 in the outer wall of the arc chute.

In order more clearly to understand the functioning of the auxiliary chamber I'I, let it be assumed that the gas pressure in the conduit 5 at the time of the blast is approximately pounds per square inch and that the opening operation has progressed to the point illustrated by Fig. 2. At this point, the pressure in the chamber I1 is also approximately 100 pounds per square inch since the chamber at this stage of the opening operation is substantially sealed except for the baflle opening at 6' communicating with the arc chamber I 3. In view of the fact that the pressure within the arc chamber I3 is less than 100 pounds per square inch due to the free expansion of the gas as it flows into the arc chamber and into the diverging chute exhaust passages, it will be seen that'the pressure in the chamber I! more than counteracts any tendency of the arc gases and flame to flow in the direction of the movable contact. The pressure in the arc chamber I3 can also be controlled by a restriction, 1. e. an orifice of predetermined cross sectional area at the entrance to the chamber.

Since the gas blast itself from conduit 5 is relatively cool, the chamber II serves both as means for protecting the contact guiding structure from the erosive effects of the hot arc gases and as a barrier to block oil the hot gases and flame in the are chamber. I have found that this method effectively precludes emission of flame from the arc chute along the movable contact during heavy current interruptions.

It should be understood that my invention 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. An electric circuit breaker of the gas blast type comprising an insulating arc chute having an entrance portion defining an arc chamber, relatively movable contacts separable to form an arc gap in said chamber, means for directing a high velocity gas blast across said gap and into said chute to interrupt the arc therein, one of said contacts being movable through said chamber and a wall of said arc chute to open circuit position, means including an insulating barrier having an opening sufficient for passage therethrough of said contact for suppressing emission of flame from said chute wall, said barrier being spaced from said wall to form an auxiliary chamber arranged so that said contact passes through said chamber, and a passage bypassing said are chamber directly connecting said auxiliary chamber with the source of pressure for said blast.

2. An electric circuit breaker of the gas blast type comprising an insulating arc chute having an entrance portion defining an arc chamber, relatively movable contacts separable to form an arc gap in said chamber, means for directing a high velocity gas blast across said gap and into said chute to interrupt the arc therein, one of said contacts being movable through said chamber and a wall of said are chute to open circuit position, partition means spaced from said wall forming an auxiliary chamber through which said movable contact is withdrawn prior to withdrawal from said chute, said auxiliary chamber having comparatively close-fitting apertures for said movable contact, and a passage bypassing said arc chamber for connecting said auxiliary chamber to the source of blast pressure so that gas under pressure is admitted substantially simultaneously to both said are and auxiliary chambers, the gas admitted to said auxiliary chamber functioning as a barrier for hot gases and flame from said are chamber so that flame emission from the aforesaidwall of said chute is precluded.

3. An electric circuit breaker of the gas blast type comprising an insulating arc chute having an entrance portion defining an arc chamber,

relatively movable contacts separable to form an arc gap in said chamber, means for directing a high velocity gas blast across said gap and into said chute to interrupt the arc therein, one of said contacts being movable through said chamber and a wall of said are chute to open circuit position, means forming an auxiliary chamber at the chute wall through which said movable contact is finally withdrawn so that said chamber surrounds said contact, said auxiliary chamber having insulating wall structure separating it from said are chamber except for an opening sufficient for the passage therethrough of said movable contact, and a passage bypassing said are chamber connecting said auxiliary chamber with the source of pressure for said blast so that gas is admitted to said auxiliary chamber during the circuit opening operation.

4. An electric circuit breaker of the gas blast type comprising an insulating arc chute having an entrance portion and an exhaust portion, relatively movable contacts separable to form an arc gap at said entrance portion, means for directing a high velocity gas blast across said gap and into said chute to interrupt the arc therein, one of said contacts being movable through a wall of said arc chute to open circuit position exteriorly thereof, means .defining an auxiliary chamber adjacent to said chute wall arranged so that said movable contact is drawn through said chamber as it is withdrawn from said chute, said auxiliary chamber being separated by an insulating barrier from the aforesaid entrance portion in which th arc is intended to be interrupted except for an opening sufiicient for passage therethrough of said movable contact, and means for diverting auxiliary gas into said auxiliary chamber for establishing pressure therein tending to block entrance of the arc flame after withdrawal of said movable contact.

5. An electric circuit breaker of the gas blast type comprising an insulating arc chute having an entrance portion and an exhaust portion, relatively movable contacts separable to form an arc gap at said entrance portion, means for directing a high velocity gas blast across said gap and into said chute to interrupt the arc therein, one of said contacts being movable through a wall of said are chute to open circuit position, partition means in said chute through which said movable contact is withdrawn prior to withdrawal from said chute, and means for diverting an auxiliary blast of gas transversely across the path of movement of the aforesaid contact after it has been drawn through said partition.

6. An electric circuit breaker of the gas blast type comprising an insulating arc chute having an entrance portion and an exhaust portion, relatively movable contacts separable to form an are gap at said entrance portion, means for directing a high velocity gas blast transversely across said gap and into said chute to interrupt the arc therein, one of said contacts being movable through a wall of said arc chute to open circuit position exteriorly thereof, insulating structure forming at said wall an auxiliary chamber at the end where said movable contact is withdrawn from said chute, said auxiliary chamber being substantially closed except for opposite openings for said movable contact, and means for diverting auxiliary gas under pressure to said auxiliary chamber so that the gas pressure in said auxiliary chambers tends to prevent ar'c flame from entering said chamber.

7. An electric circuit breaker of the air blast type comprising an insulating arc chute having an entrance portion and an exhaust portion, a fixed and a relatively movable blade-like contact separable to form an arc gap extending across said entrance portion, means for directing a high velocity air blast transversely across said gap and into said chute to interrupt the arc therein, said blade contact being movable through a wall of said are chute to open circuit position exteriorly thereof, insulating wall structure forming an auxiliary chamber in said chute at the end where said movable contact is withdrawn from said chute, said insulating wall structure closely fitting said blade contact at upposite ends of said auxiliary chamber, and means for diverting an auxiliary blast of gas from the main blast transversely across the path of movement of said blade contact through said auxiliary chamber for clearing said chamber of gases prior to complete withdrawal of said blade contact from said chute.

8. An air blast circuit breaker comprising a fixed contact and a relatively movable blade contact separable to form an interrupting arc gap, an insulating arc chute in which said are gap is formed, means for directing a high velocity air blast across said gap and into said chute for extinguishing the arc, said chute having an exhaust opening for the blast and are gases, an insulating barrier forming with the end wall of the chute opposite to said fixed contact a separate passage communicating with said chute exhaust opening, said barrier extendmg across the path of movement of said blade contact and having an opening through which said contact is operable, the aforesaid end wall of said chute also having a similar aligned openmg for said blade contact through which said contact is moved to open circuit position exteriorly of said chute, and means for directing an auxiliary air blast into said passage transversely across the path of movement of said blade contact for clearing said passage of gases and flame prior to withdrawal of said blade contact from said chute.

9. An electric circuit breaker of the gas blast type comprising an insulating arc chute having an entrance portion defining an arc chamber, relatively movable contacts separable to form an arc gap in said chamber, means for directing a high velocity gas blast across said gap and into said chute to interrupt the arc therein, one of said contacts being movable through said chamber and a wall of said arc chute to open circuit position, partition means forming an auxiliary chamber in said chute through which said movable contact is withdrawn prior to withdrawal from said chute, said auxiliary chamber having comparatively close-fitting apertures for said movable contact, a passage for connecting said auxiliary chamber to the source of blast pressure, said auxiliary chamber being otherwise substantially sealed so that a differential pressure obtains with respect to said auxiliary and are chambers opposing flow of gas from said arc chamber to said auxiliary chamber.

10. An electric circuit breaker of the gas blast type comprising an insulating arc chute, relatively movable contacts separable to form an arc gap in said chute, means including a supply conduit for directing a cross blast of interrupting gas through said gap and into said chute for extinguishing the arc, one of said contacts being movable through a wall of said chute at one end to open circuit position exteriorly thereof, insulating structure substantially surrounding said movable contact to form at said end of the chute an auxiliary enclosure apart from said are gap, said insulating structure closely fitting said movable contact at opposite ends of said enclosure, and means forming a passage from said supply conduit so as to bypass said are gap and communicate with said auxiliary enclosure for placing the gas in the enclosed space under pressure.

WILLIAM K. RANKIN.

Images