US2258226A - Electric circuit breaker - Google Patents

Description

Oct. 7, 1941. w. F. SKEATS ELECTRIC CIRCUIT BREAKER Filed Sept. 13, 1939 Inventor. WiIFred F. SKeats, y WW (9W Hi Attorney.

armed Oct. 7, 1941 2,258,226 ELECTRIC CIRCUIT BREAKER Wilfred F. Skeats, Lansdowne, Pa., assignor to General Electric Company, a corporation of New York Application September 13, 1939, Serial No. 294,644

6 Claims.

My invention relates to electric circuit breakers, particularly to circuit breakers of the fluid jet or blast type wherein an arc extinguishing fluid, such as oil, is directed under pressure through the arc gap formed upon opening of the circuit. More specifically, my invention relates to the oil blast type circuit breaker wherein arc pressure is utilized to force 011 or the like through the interrupting gap to extinguish arcing, and has for its principal object .the provision of means for appreciably increasing the interrupting capacity of this type breaker, particularly in the case of heavy overload and short circuit currents.

Where are pressure generated at an auxiliary or initially formed are is utilized to drive oil through another or interrupting are, there will also be formation of gas at the pressure generating are which may in certain cases mix with the interrupting oil blast. This gas is highly heated and therefore has poor dielectric characteristics so that its presence in the vicinity of the interrupting gap is undesirable for obvious reasons.

In accordance with the present invention, the arc pressure, while being utilized in the usual manner to effect interruption by means of a liquid blast, directs the gas formed at the pressure are away from the interrupting blast. The gas is then for practical purposes trapped until the interrupting operation has been completed.

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, the single figure thereof is an elevational view partly in section of an oil circuit breaker in the open circuit position embodying the present invention.

The oil circuit breaker illustrated by way of example is of the combined oil blast and impulse type and comprises a main casing I that is divided into a switch chamber 2 for housing the relatively movable contacts and are extinguishing structure, and a piston cylinder 3 arranged to be in communication with the switch chamber through a passage 4. The casing I which is provided with insulating supports at I' is composed of metal such as bronze for example and constitutes one terminal of the circuit breaker, the other terminal of which is suitably connected to the movable contact rod 5. This contact is slid- I ably guided for coaction with the relatively fixed contact structure in an insulating bushing 8 that is in turn suitably mounted, as indicated at I and 1', in the cover plate 8 of the switch casing.

The complete contact structure comprises a fixed butt contact 8 having a threaded extension III that is secured to a frustro-conical portion II formed on the lower wall of the switch casing. The fixed contact is therefore in direct electrical contact with one switch terminal, i. e., the metal casing I.

Interposed between the movable rod contact 5 and the fixed contact is an intermediate or floating contact I2 that is carried by an insulatin support I3 that is in turn resiliently mounted on the lower wall, as indicated at I4, of the insulating baiiie I5. The contact I2 is slidably guided in the battle as illustrated, and for practical purposes seals at all times the baffle aperture I2. In the open circuit position shown, the floating contact I2 is biased at I 4 upwardly and away from the fixed contact 8 so that a short gap (approximately separates the contacts.

When the circuit breaker is to be closed, the rod contact 5 is lowered by suitable operating means (not shown), first to engage the upper butt contact surface of floating contact I2, and subsequently upon continued movement to complete the circuit by pressing the floating contact against the fixed contact 9. The reverse order is followed upon opening of the circuit, the arc initially formed between the contacts 8 and I2 being utilized to generate pressure for assisting in interrupting the are between the contacts I2 and 5 in a manner that is now well-known in the art.

The breaker casing is filled with a suitable arc extinguishing liquid, such as oil, to the level indicated so that the baflie Ii within which are interruption takes place is practically immersed. This baflie forms two chambers within the main chamber 2, the chamber below the battle being in effect a pressure chamber, and the one above the baiile being an exhaust chamber. The baffle is provided with a cross blast passage I6 that communicates at its lower end with the pressure chamber, and after passing transversely through the arc path between the contacts I and I2, exhausts at I6 to the upper chamber. The baflle I5 is constructed of a mechanically strong insulating material and is positioned in the casing between the casing shoulder I I and an insulating sleeve I8 that is in turn firmly engaged by a positioning ring I! having adjusting means 20 secured to the casing cover 8. The lower end of the tubular insulating bushing 6 enclosing the movable contact seats on the upper wall of the battle I5 which is provided with an aligned aperture ii for the movable contact.

The structure so far described is known as the oil-blast type circuit breaker wherein two arcs are formed in series, one of said arcs being acted upon by pressure generated at the other arc. At low currents, however, additional pressure is often required and to this end the impulse feature involving a piston is added.

The cylinder 3 is provided with a piston 33 having an operating rod 23 actuated by means suitably related to the operating means for the movable contact. Such operating means form no part of the present invention and may for example be of the type disclosed and claimed in U. S. Patent 2,025,549, granted December 24, 1935 to D. 0. Prince for "Operating mechanism for electric circuit breakers." The arrangement is such that the piston is depressed as the contact is raised to open the circuit.

The piston is also provided with a resetting spring 24 seated between a stationary spider 26 and a shoulder 23' on the piston rod. A disktype one-way valve 23 coacts with the piston as illustrated for the purpose of permitting oil to flow back into the iowenpart of the casing upon the return or resetting stroke of the piston. Accordingly, when the piston 22 is driven downward from the position shown, oil is forced from the cylinder 3 through the passage 4 upwardly into the pressure chamber beneath the baifle l5, from whence it can escape only by way of the transverse blast passage it into the upper exhaust chamber.

In the case of low or moderate load currents, the oil driven solely by the piston across the are between contacts I and i2 would generally be effective to interrupt arcing within a cycle or so. However, in the case of large overload or short circuit currents, the pressure generated at the initially formed are between contacts 9 and I2 within the pressure chamber may be so great that the motion of the piston is actually reversed. In such a case, the piston is obviously ineffective and failure of the breaker may resuit.

For the purpose of utilizing the are pressure at the initially formed are to the best advantage in such a case, a valve plate 21 is mounted on the frustro-conical portion ll so that it may form a partition between the arc pressure chamber and the cylinder 3. A plurality of disk-type oneway valves 28 are mounted on the valve plate to control the openings 28' communicating with the cylinder passage 4 and the arc pressure chamber.

As shown, the valves which are slidably guided on the post supports 29 open freely when the pressure in the piston cylinder exceeds that in the arc pressure chamber, but seat tightly to close the openings 23' when the arc chamber pressure exceeds that in the piston cylinder.

Therefore, in the case of the heavy current interruptions previously referred to, the arc pressure, when it exceeds the piston pressure, causes closing of the valves 28 and drives oil from the pressure chamber through the transverse blast passage ii to interrupt the high current arc. The are pressure is therefore utilized for are interruption instead of being partially dissipated in causing reversal of the piston. It will be apparent that in other cases where the piston is eifective, the pressure generated by the initial arc serves to augment or supplement the piston pressure to aid in interrupting the arc. That is,

caused looping of the arc.

the oil blast velocity is somewhat increased. The exhaust chamber is suitably vented at 3' to the usual separating chamber (not shown).

In the case of large currents, the pressure generating arc formed between contacts 3 and i2 may be bowed or looped laterally by the magnetic forces so as to be of excessive length. This is due to the well-known magnetic effect in a looped conductor carrying current, and may cause excessive pressure in the arc chamber. For controlling the pressure generating are so that it does not appreciably exceed in length that of the gap between contacts I and it, a conducting ring 33, is employed to prevent or limit outward bowing or looping of the are beyond a certain point. The ring 33 is mounted on an insulating cylindrical spacer 3| so as to surround in spaced relation thearc gap and is composed of a metal, such as copper, and is held in position by the valve guide posts 33.

In case the arc is looped by magnetic forces into contact with the ring 33. it will be noted that the magnetic forces established by the arc current flowing at right angles from the contact I: through the ring to the valve plate act in a direction opposing the forces that originally The are control and valve arrangements above described form no part of the present invention and are fully described and claimed in a copending application, Serial No. 294,642, filed concurrently herewith by D. C. Prince for Electric circuit breaker," and assigned to the same assignee as the present invention.

When large currents are to be interrupted the gas formation due to the are heat is greater. Therefore, highly heated arc gases may be carried by the oil blast into the transverse passage I so as to cause difliculty in clearing the circuit. That is, let it be assumed that a bubble of highly heated are formed gas is passing through the passage I at the time of or slightly after a current interruption. Since this gas has comparatively low dielectric strength, the interrupting gap is poorly insulated with respect to the recovery voltage and restriking of the arc may occur either immediately or after a short interval.

This is prevented in the present case in accordance with my invention by a form of bame arrangement between the pressure generating arc and the intake of the blast passage which not only directs the gas away from the intake but tends to segregate or isolate the gas for a short time until interruption is complete. Specifically, the bailie arrangement comprises a spout or the like 32 extending beneath the bafile 15 at the intakeof the blast passage ll into the pressure chamber and ridge or lip 33 mounted on thearc control ring 33 for example at a position between the arc gap and the spout 32. The'spout 33 is offset as far as possible withrespect to the pressure generating arc and the lip 33 is preferably of crescent or semi-circular shape as illustrated so as partly to surround the pressure generating break and to shield the spout intake from the arc gases. The gases are therefore prevented from being blown directly into the spout and are temporarily pocketed and isolated beneath the bailfe at 32'. Therefore the arc gases at the break 9- are isolated with respect to the arc extinguishing liquid blast through the passage I. A small bleed vent at ii in the baflie permits the pressure chamber to reflil with oil after an interrupting operation and allows the gases trapped at 32' to escape to the top of the battle after an interrupting operation.

In certain cases, the inertia of the oil blast is such that the oil continues to move even after the piston 22 is stopped. This tends to cause a void in the region of the interrupting break in the passage IS with the result that re-ignition of the arc may occur due to the low dielectric strength at the interrupting break. I have found that this can be prevented by venting the blast passage at an intermediate point upon predetermined separation of the contacts. Specifically, this is done by providing an aperture, or apertures, indicated at 6' in the bushing 6 above the oil level so that oil from the bushing is immediately forced into the passage IS in such cases. That is, the outgoing oil blast draws oil into the interrupting gap from the bushing 6 instead of creating a momentary partial vacuum in the gap which would be the case were the vent 6' not provided. I have found that this results in improved interrupting performance.

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 oi' the fluid blast type comprising relatively movable contact structure arranged to form two breaks in series, an arc extinguishing liquid in which said breaks are formed, bafile structure for directing a liquid blast under influence of the arc pressure generated at one of said breaks through the other break to extinguish arcing, means adjacent to said pressure generating are for initially deflecting said liquid blast and the gas formed thereat, and additional means associated with said batlie for pocketing gas so deflected so that it is isolated with respect to said arc interrupting liquid blast.

2. An electric circuit breaker or the fluid blast type comprising relatively movable contact structure arranged to form two breaks in series, an arc extinguishing liquid in which said breaks are formed, baffle structure for directing a liquid blast under influence of the arc pressure generated at one of said breaks through the other break to extinguish arcing thereat, said baflie having a transverse passage communicating with the region in which said pressure generating arc is formed, means for deflecting gas generated at said pressure break away from said passage, and means forming an extension of said blast passage extending beneath said bafile into said region in offset relation to said deflecting means for isolating gas formed at said pressure generating break with respect to the interrupting liquid blast in said transverse passage.

3. An electric circuit breaker of the fluid blast type comprising relatively movable contact structure arranged to form two breaks in series, an arc extinguishing liquid in which said breaks are formed, bafiie structure for directing a liquid blast under influence of the arc pressure generated at one of said breaks through the other break to extinguish arcing thereat, a second deflecting bafile partly surrounding in generally concentric relation said pressure generating break for deflecting gas formed at said break in a direction away from said are interrupting liquid blast, and means for temporarily isolating said gas at a point near the entrance of said blast to said first-named baiiie structure.

4. An electric circuit breaker of the fluid blast type comprising relatively movable contact structure arranged to form two breaks in series, an arc extinguishing liquid in which said breaks are formed, a baille having a transverse blast passage for directing a liquid blast under influence of the arc pressure generated at one of said breaks through the other break formed in said passage to extinguish arcing, means forming an extension of said blast passage extending in a direction transversely of said baiile and into the region of said pressure generating break, said extension being appreciably offset with respect to said break, and a baflie member extending in the opposite direction disposed between said pressure generating break and said extension and ofiset with respect to said extension passage for deflecting gas formed at said pressure generating break away from the extension passage whereby said gas is isolated with respect to the arc interrupting liquid blast.

5. An electric circuit breaker of the liquid blast type comprising separable contacts, an arc extinguishing liquid in which said contacts separate, insulating means in which said contacts operate forming an enclosure for the movable contact and a blast passage traversing the arc path formed upon separation of said contacts, mechanical means for driving liquid at high velocity through said passage to interrupt the arc therein so that due to its inertia said liquid tends to evacuate said passage, and. means defined by said insulating means communicating with said passage at an intermediate point only after predetermined contact separation within said insulating means for venting it to atmospheric pressure whereby the inertia of said liquid blast is ineffective to create a partial vacuum in said passage and said passage is maintained substantially full of liquid after arc interruption.

6. An electric circuit breaker of the liquid blast type comprising fixed and movable contacts, an arc extinguishing liquid, insulating means forming a blast passage traversing the arc path formed upon separation of said contacts and enclosing the movable contact, a piston for driving liquid at high velocity through said passage to interrupt the arc therein, and an air vent in said insulating means disposed laterally of said movable contact arranged to be opened in accordance with predetermined contact opening movement to communicate with said passage at a point adjacent to said are whereby air pressure acting on said are extinguishing liquid precludes formation of a vacuum in said passage after arc interruption when said piston suddenly stops.

WILF'RED F. SKEATS.

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