US2310728A - Electric circuit breaker - Google Patents

Description

WWW/WM Feb. 9, 1943.

P. BARTLETT ELECTRIC CIRCUIT BREAKER Filed Sept. 4, 1941 66$ PHISSUHE Inventor- Per-c3 Bartlett,

Hi5 Attorney.

Patented Feb. 9, 1943 ELECTRIC CIRCUIT BREAKER Percy Bartlett, Springfield, Pa., assignor to Generai Electric Company, a corporation of New York Application September 4, 1941, Serial No. 409,515

9Claims.

My invention relates to electric circuit breakers. more particularly to those of the magnetic blowout type having an insulating arc chute into which the arc is driven by the magnetic blowout field and extinguished, and has for its principal object the provision of an improved circuit breaker of the aforesaid type that is particularly effective in interrupting heavy current power arcs and in suppressing flame emission from th arc chute during such interruptions.

The use of magnetic blowout air circuit breakers for interrupting power circuit at distribution voltages such as 5000 volts has been made possible by improved arc chute construction. In one well-known form of magnetic blowout air circuit breaker, the arc is greatly lengthened and attenuated within the arc chute and. cooled' throughout its length. This results in a rapid increase of the arc stream resistance so that the current is correspondingly decreased and the power factor greatly improved thereby facilitating interruption at a current zero. However, it has been found in the case of particularly heavy overload and short circuit currents that the blowout field drives the are through the chute with such force and so quickly that the arc may actually be expelled from the chute exhaust portion. In other words, the arc is blasted through the chute before it has had sufilcient time to be cooled by the arc chute walls. Consequently, the resistance of the arc stream has not increased sufliciently to bring about interruption.

In accordance with my invention, the back pressure at the arc chute exhaust portion is caused to increase in response to gas pressures incident to high current arcs so that the arc itself, in the case of such high current interruptions, is retained for a longer time within the chute. By so slowing up the movement of the are through the chute, the heat transfer from the arc stream to the chute walls is greatly improved and the arc is cooled with consequent increase of the arc resistance. Interruption of the 1 are is therefore greatly facilitated.

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. l is an elevational view, partly in section, of an air circuit breaker of the magnetic blowout type embodying my invention; Fig. 2 is a perspective view of arc chute structure shown in Fig. 1 for increasing the arc chute back pressure; Figs. 3 and 4 are sectional views, similar to F18. 1, showing a modifled form of my invention in the open and closed positions thereof respectively; and Figs. 5 and 6 are similar views of another form of my invention also in the open and closed positions respectively.

Th air circuit breaker illustrated by Fig. 1 is shown for example in a form that is particularly adaptable'for central stations and sub-stations wherein the circuit breaker unit can be bodily disconnected from the stationary circuit. This form of circuit breaker is generally incorporated in metal-clad structure for vertical movement therein. However, since this feature forms no part of the present invention a complete disclosure thereof is omitted in the interest of clearness.

The circuit interrupter comprises essentially means for opening the circuit to form the interrupting arc and are extinguishing structure. Specifically, the circuit opening means comprises a relatively fixed contact I and a movable contact 2 that is pivotally mounted at 3 on one of the circuit breaker studs and is operated by means of a reciprocally movable rod 4. The operating rod is suitably connected to an actuating mechanism (not shown) for operating the movable contact between closed and open circuit positions. The contacts I and 2 are electrically connected to the lower ends of the breaker lead. in conductor studs 5 and 6 respectively which also serve as the breaker terminals. Accordingly, when the breaker is connected in series in a power circuit and the contacts I and 2 are separated, an arc may form across the gap indicated. 1

For the purpose of interrupting this power arc, an arc extinguishing structure, such as the arc chute generally indicated at 'I is mounted with respect to the contact structure so as directly to receive the power are which is under the influence of the magnetic blowout fields produced by the coils 8 and 9. The switch contacts and the magnetic blowout structures can assume any preferred form and comprise no part of the present invention so that a brief description will be suflicient. The magnetic blowout coils 8 are electrically connected to the conductor stud 5 and to the conducting arc runners 8' so that the arc current (as the arc travels along the runners) flows through the blowout coils as well-known in the art.

, Normally th current is carried in the closed circuit position of the breaker by the spring bi-- breaker.

, ased contact I, thecurrent being shunted to the arcing contact at l upon opening of the As the arc is drawn 'by the movable contact 2, it is transferred to the arc runner I when it passes the position indicated by Fig. 1 so that the blowout coil 9, which is electrically connected as indicated at 9" to the conductor stud t is now also connected in series withthe arc current. Accordingly. the blowout coilsare energized at an early stage to influence the arc in a well-known manner-,1. e. to drive it into the chute in an ever-expandingloop. It will be apparent of course that the blowout field can be utilized in themost emcient manner by disposing iron pole pieces cooperating with the blowout coils in the conventional manner at the outer opposite sides of the arc chute.

The are chute itself may comprise any suitable structure for interrupting the arc, preferably by lengthening and attenuating it within restricted insulating passages so that the resistance of the arc stream is greatly increased. In the wellknown form of arc chute indicated by Fig. 1, Y

' at its inner side facing the other wall is provided with a plurality of parallel rib-like fins or ridges, such as indicated at ill. The ridges are preferably integral with the side walls of.

chute, the above-described zigzag arc passage simply opening into the venting structure at the chute exhaust. The eflfective venting area is the same for both small and large currents.

In certain large current interruptions, the magnetic blowout field maybe so strong, as previously explained, that the arc is driven too hurriedly through the chute with the result that it is not sufllciently cooled to increase its resistance to the interrupting point. When this happens, the arc may go beyond even the chute exhaust or flash over exteriorly of the chute causing failure of the breaker. In any event, considerable flame is projected from the chute tending to cause failure of the breaker and damage to adjacent equipment even though the arc is eventually interrupted.

For the purpose of retarding or throttling the movement of large current arcs within the chute while also providing adequate venting area for small or moderate current, arcs, I provide pressure responsive means disposed at the chute exhaust for automatically restricting or decreasing the eflective venting area when the gas pressure accompanying large current are builds up to a predetermined extent within the chute. This restriction of the venting area also materially the chute which are suitably joined and clamped together ashalves of the chute. The height and spacing of the ridges are such that when the side walls are clamped together, the ridges are interleaved in spaced relation with respect to each other, i, e. in staggered relation, so as to form a restricted zigzag passage having alternating salients into which the arc is driven at the entrance l2 of the arc chute. As clearly shown by Fig. 1, which illustrates but half the arc chute in detail, namely the side wall iii, the

ridges longitudinally extend parallel in spaced relation from the chute entrance to the chute exhaust, so that the salient height of the ridges is in a direction transverse to the direction of movement of the are as it moves through the chute.

As the arc is driven into the zigzag space defined by the interleaving ridges, the cross-section of the arc is reduced as the are more and more assumes a serpentine form. If a heavy current are is to be interrupted, interruption may not occur until the arc has been moved well into the chute. Up to the point of interruption, the

. of the zigzag path becomes greater. The are is thereby greatly lengthened and attenuated concurrent with very eflective cooling as it approaches the exhaust part of the chute due mainly to the large cooling surfaces of the ridges.'

,A magnetic blowout air circuit breaker of the character so far described is specifically disclosed in Letters Patent No. 2.293,513, issued August 18, 1942, to L. J. Linde for Electric air circuit breaker," and assigned to the same assignee as the present invention.

In the aforesaid patent there is illustrated meansfor suppressing and confining within the chute heavy overload or short circuit arcs. In this arrangement, the grid-like structure also freely vents are gases generated within the reduces the likelihood of flame-throw from the chute.

Specifically, this may be accomplished for example by relatively movable grid-like members normally biased apart to provide quite free venting, but arranged so that the venting area is appreciably reduced when the grids are moved together by gas pressure. Referring particularly to the form of my invention shown by Figs. 1 and 2, the arc throttling means generally indicated at l3 comprises a pair of relatively movable insulating members or plates I4 and I5 having slot-like apertures as indicated by Fig, 2-

These apertured plates or grids are suitably mounted within the arc chute at the exhaust end and are normally biased apart as indicated in Fig. 1 by springs l6 seated in recesses it formed in the insulating grids. In the open or extended position of the throttling device for free venting, the grid I4 is near the ends of the arc barriers forming the zigzag arc passage. In the case of a heavy current interruption, theexplosive-like generation of gas withinthe chute moves the grid it toward the grid l5 against the bias of springs l5 so that the transversely ex-- tending apertures or slots M in the grid I4 and the longitudinally extending apertures or slots 15' in the grid I5 are partly restricted due to the non-registering positions thereof so that the exhaust venting area is materially reduced. This restriction in the venting area causes such increase in back pressure that the movement of the are through the chute is materially slowed down with consequent improved interrupting performance of the breaker.

It will be noted that the grid [5 is not provided with apertures at its center portion It". The resulting high back pressure at the center of the chute'is useful in retarding the central crest of the are which often precedes the ends of the arc at the arc runners on opposite sides of the chute. It will be apparent that it is within the scope of my invention to design the slots I4 and I5 so as to vary the back-pressure in any desired manner along the entire exhaust portion of the chute in accordance with the arc chute characteristics.

In the modification of my invention shown by Figs. 3 and 4, the insulating grids l1 and II are arranged in the manner of Fig. 1 and provided with a number of holes I1 and I8 respectively in semi-registering relation. The holes of each grid are substantially equally spaced so that when the grids are forced together as shown by Fig. 4 the venting area is restricted substantially uniformly approximately fifty per cent across the exhaust portion.

In the form of my invention shown by Figs. 5 and 6, a grid i9 substantially similar to the grid II is likewise provided with equally spaced hoies'lt' whereas the coacting grid '20 is provided with unequally spaced holes 20' so as to vary in Vernier-manner the venting area. This is best shown by Fig. 6 wherein the grid holes (8' at the center of the chute are practically closed of! by the grid 20, and the holes 20' in the grid 2| at opposite ends of the chute exhaust are restricted a comparatively small amount by the grid l9. With this arrangement, the are also is throttled at its center more severely than at its opposite ends as in the case of Fig. 2.

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 interrupter of the magnetic blow-out type comprising means for opening the circuit to form an interrupting arc, an arc extinguishing structure into which said arc is directed by a blow-out field, said extinguishing structure having an exhaust opening for venting arc gases generated within said extinguishing structure, and means at said exhaust opening for restricting the gas venting area in response to predetermined gas pressure generated by arcing within said extinguishing structure, said restricting means being acted upon immediately by said gas pressure so that the movement of said arc through said structure is retarded by the resulting back pressure at said exhaust opening.

2. An electric circuit breaker of the magnetic blow-out type comprising relatively movable contacts separable to form an interrupting gap, an arc chute into which the arc at said gap is directed by a blow-out field, said chute having extinguishing structure for restricting and cooling the arc stream and an exhaust opening for venting arc gases generated within said chute, and throttling means disposed at said exhaust opening operable to restrict the gas venting area in response to predetermined increase of the gas pressure generated by arcing within said chute, said throttling means being acted. upon immediately by said gas pressure thereby maintaining said are longer within said chute in heat exchange contact with said are extinguishing structure.

3. An electric circuit interrupter comprising means for opening the circuit to form an interrupting are, an insulating arc extinguishing structure into which said arc is directed, said extinguishing structure having a restricted arc passage for facilitating heat transfer from the arc stream, said passage terminating in an exhaust opening for venting arc gases generated within said extinguishing structure, and throttling means at said exhaust opening for'decreasing the effective gas venting area in accordance with predetermined arc pressure generated by 76 arcing within said extinguishing structure thereby increasing the back-pressure at said opening, retarding the movement of said arc through said are e and increasing the amount of heat transferred from said are stream.

4. An electric circuit breaker comprising relatively movable contacts separable to form an interrupting gap, an arc chute, magnetic blow-out means for driving the arc at said gap into said chute, said chute having extinguishing structure for cooling the arc stream and an exhaust opening for venting arc gases generated within said chute, and throttling means disposed in said exhaust opening, said throttling means normally freely venting said arc chute and operableto decrease the gas venting area in response to predetermined increase of the gas pressure within said chute incident to large current arcs so as to hold the large current arc longer within said chute in contact with said arc extinguishing structure.

5. An electric circuit breaker comprising relatively movable contacts separable to form an interrupting gap, an arc chute, magnetic blow-out means for driving the are at said gap into said chute, said chute having extinguishing structure for cooling the arc stream and an exhaust opening for venting arc gases generated within said chute, and relatively movable grid-like members disposed at said exhaust opening, said members being normally biased freely to vent said arc chute, said members also being arranged to restrict the gas venting area when moved with respect to each other in accordance with heavy current arcs so as to increase the chute backpressure and hold the heavy current arc longer within said chute in contact with said are extinguishing structure.

6. An electric circuit breaker comprising relatively movable contacts separable to form an interrupting gap, an arc chute into which the arc at said gap is driven, said chute having extinguishing structure for cooling the arc stream and an exhaust opening for venting arc gases generated within said chute, throttling means including a pair of relatively movable apertured members disposed in superposed relation at said exhaust opening, the apertures of said members being in non-registering relation, and means for biasing apart said members so that normally the arc chute is freely vented, at least one of said members being movable toward the other to restrict the gas venting area in response to predetermined increase of the gas pressure within said chute so as to increase the chute back pressure during large current interruptions and hold said are longer within said chute in contact with said are extinguishing structure.

'I. An electric circuit breaker comprising relatively movable contacts separable to form an interrupting gap, an arc chute, magnetic blowout means for driving the are at said gap into said chute, said chute having arc runners at opposite ends thereof,- extinguishing structure intermediate said runners for cooling the arc stream and an exhaust opening for venting arc gases generated within said, chute, and throttling means normally freelyi 'tenting said chute disposed at said exhaust opening, said throttling means operable to restrict the gas venting area in response to predetermined increase of the gas pressure within said chute incident to large current arcs, said throttling means ,being arranged to gradate said venting area so that said exhaust opening is vented more freely at the arc runner ends of guishing structure for restricting and cooling.

the arc-stream and an exhaust opening for venting are gases generated within said chute, and throttling means including a pair of relatively movable apertured members disposed in superposed relation at said exhaust opening, said members being normally biased apart freely to vent said chute, the apertures of one of said members being in non-registering Vernier-like relation with respect to the apertures of the other member, said members being moved relatively toward each other in response only to high gas pressure .incident to a large current are thereby increasing the chute back-pressure and holding the large current are longer within said chute in contact with said are extinguishing structure.

9. An electric circuit breaker comprising relatively movable contacts separable to form an interrupting gap, an arc chute,'magnetic blowout means for driving the are at said gap into said chute for extinguishing the are, said are chute having an exhaust opening for venting arc gases generated within said chute, and throttling means normally freely venting said chute at said exhaust opening, said throttling means being controlled in accordance with heavy current interruptions so as to restrict the venting area opposite the central or intermediate portion of the are more than the venting-area opposite the extremities of said are.

PERCY BARTLETT.

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