US2442190A - Electric circuit interrupter - Google Patents

Description

May 25, l948- R. M. BENNETT ELECTRIC CIRCUIT INTERRUPTER Filed March 23, 1945 Inventor: Robert M Berwrjett,

b Zai/05j@ y is Attorney Patented May 25, 1948 ELECTRIC CIRCUIT INTERRUPTER Robert M. Bennett, ter County,

. Company, a

Birmingham Township, Ches- Pa., asslgnor to General Electric corporation of New York Application March 23, 1945, Serial No. 584,412

(Cl. 20G-148) Claims.

My invention relates to electric circuit interrupters and more particularly to electric circuit interrupter employing a blast of iluid such as air, to extinguish the arc ldrawn between relatively separable contacts.

Gas blast circuit breakers which have been extensively used in recent years generally are of two kinds, the so-called cross blast breaker and the axial blast breaker. The cross blast breaker is typified by the disclosure of United States Letters Patent 2,284,842, Prince et al., assigned to the same assignee as the present application, while the arial blast breaker is typified by Rankin Patent 2,306,186, granted December 22, 1942, and assigned to the same assignee as the present application. The axial blast breaker lends itself very well for high voltage outdoor application, but the current limit of an axial blast breaker is relatively low compared to that of a cross gas blast breaker. It would be desirable to provide a gas blast circuit breaker with the high 'current carrying ability of the cross gas blast breaker and the high voltage capacity of an axial blast breaker.

it is an object of my invention to provide a new and improved :duid blast circuit interrupter.

it is another object of my invention to provide a high voltage gas blast circuit breaker or the cross gas blast type wherein higher currents may be interrupted than in high voltage circuit brealyu ers used .bereitcroreu another object of my invention is to prou vide' high speed, high voltage, high interrupting capacity fluid blast circuit breaker of improved construction.

Further objects and advantages of my invena polyphase circuit breaker.

relatively movable l arcing contacts, as will become apparent from the following description. 2 is preferably mounted on a pair of suitable insulators 3 and 'l and one end of the interrupting unit is connected to the line terminal indicated at 5. The other end of the interrupting unit 2 is preferably connected by a conductor 8 with a set of isolating contacts comprising the movable contact arm 'l which engages with a stationary contact t connected to line terminal il. The isolating or disconnecting contacts are supported on suitable insulators ill and ii.

As illustrated in thedrawing, the interrupting unit 2 is horizontally arranged which is particularly advantageous from the standpoint oi pro- The interrupting unit tection from the weather, as will become apparent tion Will become apparent as the following description proceeds 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 specication.

For a. better understanding of my invention reference may be had to the accompanying drawing in which Fig. 1 is a somewhat schematic elevational view of an electric circuit interrupter embodying my invention; Fig. 2 is an enlarged view partly in section of a portion of Fig. 1; Fig. 3 is an enlarged sectional view of a portion of Fig. 2, and Fig. fi is a view taken on line 4 4 of Fig. 3.

Referring now to the drawing, there is illustrated an electric circuit breaker generally indicated at l in Fig. 1, comprising an arc extinguishing or circuit interrupting unit generally indicated at 2. It will be understood that my invention is applicable either to a single phase o1- where this is material a from the following description. Such horizontal construction requires more ground space, and vertical arrangement can be employed. It should be understood, therefore, that the horizontal arrangement disclosed is by way of example only.

My invention is particularly concerned with the construction of interrupting unit 2 which embodies-the cross blast principle of arc interruption. Cross blast circuit breakers have an advantage where high speed operation is desired5 as contrasted with nozzle type interrupters which require the Contact to move through a nozzle or? appreciable length before interruption can place. .ln a cross blast breaker, on the other hand, the fluid blast is effective the instant the contacts part. The problem of increasing the voltage rating of. cross blast circuit interrupters has been under extensive consideration for some time. Previous attempts to increase the voltage rating of the cross blast interruptor have generally involved increasing the stroke of the contacts.` It is now recognized that with contacts of reasonable size indefinite increase in contact separation simply produces bad distribution of voltage between the contacts. The voltage drop is concentrated mainly at the tips of the contacts and the maximum gradient is reduced very little by increasing the contact separation. Also, increasing the contact separation has another undesirable effect. It increases the voltage stress in the immediate neighborhood in such a way that failures occur through joints in the insulating structure and as a consequence thereof the size of the insulating structure must be increased so that the design is uneconomical. With my arrangement, a very compact design is permitted with little or no chance of failure of the insulatlng structure.

As illustrated in Fig. 2, the interrupting unit 2 of my invention is of the multibreak type comprising a. plurality of serially arranged sets of arcing or interrupting contacts I2 and I3. In Fig. 2 only two sets of arcing contacts are indicated, but it should be understood that more than two or only one may be utilized, depending upon the voltage rating of the circuit interrupter. Each set of interrupting contacts is arranged in an arc confining chamber comprising a laminated structure made up of members I4, I5, I6, I1, I8, I9 and 20. Only one of the arc confining structures will be described associated with the contacts I2 and I3, since they are all identical and the corresponding parts will be designated by the same reference numerals in the drawing. The laminated structures defining the arc confining chambers are spaced from each other by suitable insulating means such as the porcelain insulator 2|. Similarly, insulators 22 and 23 are provided at either end of the arc extinguishing unit to space the laminated, arc confining structures from the supporting insulators 3 and 4 respectively. The insulators 2|, 22 and 23, all preferably formed of a. weather resistant material, such as porcelain, and the laminated arc confining structures described above are assembled into a unitary structure as shown in Fig. 2 by means of bolts 24 formed of insulating material. The laminations I4 to 20, inclusive, and the insulators 2i, 22 and 23 are provided with aligned openings through which bolts 24 may extend.

The assembly of insulating members held together by bolts 24 are supported from insulators 3 and 4 by conducting angle members 25 and 28, respectively. The insulating bolts 24, which may be wood rods, or the like, extend through conducting angle members 25 and 26.

Insulators 2l and 22 and laminations I4 to 20, inclusive, of each laminated arc confining structure are provided with aligned openings so as to define a fluid passageway 21 extending from the end of interrupting unit 2 adjacent conducting member 25 to the arcing contacts farthest removed from insulator 3. Fluid passageway 21 is preferably connected by means of a conduit 28 to a source of fluid under pressure (not shown) and suitable means, such as a blast valve (also not shown), controls the flow of fluid to passageway 21.

The relatively movable arcing contacts associated with each laminated arc confining structure, each comprises a pair of stationary cupshaped members 29 arranged with their axes disposed substantially along the axis of interrupting unit 2. The arclng contacts i2 and i3 are adapted to move into cup-shaped members 291 but are biased by means of spring enclosed within cup-shaped members li into contacting engagement, es shown in Fig. 3. It will be obvious that the contacts i2 and i3 are very light and movement thereof is quite limited, preferably being less than an inch. Such a cnstruction enables high speed operation to be obtained both by virtue of the light weight and the short distance through which movement takes place. Contact i2 of the aro confining structure adje cent insulator 3 is connected by a conductor 3E, which is illustrated as a flexible conductor, to conducting member 25. Contact it, associated with the arc confining structure adjacent insulator 3, is connected by means of. iexible conductor 32 with the contact of the arc conflning structure adjacent insulator 4. Also contact I3 of the arc confining structure adjacent insulator 4 is connected by means of a. nexible conductor (not shown) with conducting angle member 26. It should be understood that sultable passageways in insulators 2|. 22 and 28 will be provided for these flexible conductors.

At this stage of the description, it will be understood that a blast of pressure fluid, released into the conduit 28, flows along the passageway 21 and is effective both to separate the so-called retracting arcing contacts I2 and I3 and' to blast to extinction the arcs drawn therebetween. Before the blast is shut ofi, thereby permitting the spring-biased arcing contacts to reclose, the isolating contact arm 1 is caused to swing open so that a safe isolating gap is provided whereby current is effectively prevented from flowing through the circuit breaker from line terminal 5 to line terminal 9.

The laminations I4 to 20, inclusive, of the laminated arc confining structures comprise a pair of outer laminations I4 and 20 which are identical in construction and two sets of laniim nations I5 and I9 and I5 and I8, the members of each set also being identical with each other. The laminations IS and I8 are constructed in the manner clearly disclosed in Fig. 4, and are provided with an upper circular portion and a lower downwardly extending portion. The opening defining passageway 21 and the opening through which contacts I2 and I3 extend are interconnected by a radially extending passage- Way 33. This cutout passageway continues below the contact opening where it diverges into a relatively wide exhaust opening 34. The central lamination I1 is provided with a similar cutout radial passageway 33 which continues below the contact opening for but a short distance where it terminates abruptly, thereby providing a barrier or partition portion 35 so that the arc drawn between the relatively separable contacts is forced against the transverse edge of barrier portion 35 by the fluid blast. The barrier portion 35 of lamination I1 extends considerably below the lowermost extensions of the other laminations.

Laminations I5 and I9 do not have the passageway or cutaway portion 33 interconnecting the opening for the relatively movable contacts and the opening defining passageway 21. The lower portions thereof, however, are cut away as indicated at 36 so as to provide a larger exhaust area for the fluid blast.

In order to provide for further cooling the exhaust gases flowing on either side of the baffle or partition portion 35 of lamination il, I pref" erably provide a plurality of parallel arret'. cooling plates (il formed of copper or other good heat conducting material.

Preferably the iaminations it to 2E? are ienne-d of a suitable gas evolving, insulating mate such as ber, methyl :nethacrylate and the lil: fn certain cases it might be desirable use a semi-resistance material.

Although laminar construction for insulating intelrupter structure possesses certain advantages of which, among others, may be cited the benefit of using high dielectric materials which commonly are available only in sheet form, and the facility by which complex intera nal pockets or passages may be fashioned therein; nevertheless, such laminar construction attended by offsetting disadvantages, particu larly the hazard ci' interlaminar voltage breaw down. For example, in the embodiment shown by the drawing and assuming that a iluid blast has just extinguished the arcs. the high voltage stress in the region of the separated contacts is seeking to re-establish an arc through the path of least impedance between the separated contacts.' Such a breakdown path (neglecting the presence of the grooves 38) is most likely to be a detour from contact to contact radially outwards through one interlaminar Joint, raxially or longitudinally along a short creepage path on the surface of an adjacent insulated bolt 24, then radially inwards through another interlaminar joint; because breakdown across the shortest direct path across the vseparated contacts is precluded by the continued blast of fresh high pressure high dielectric extinguishing fluid rushing through the contact gap. 'I'his interlaminar breakdown hazard threatens even though the laminations are cemented together, for cemented joints invariably are electrically weaker than the insulating material per se.

In order to reduce or eliminate the above described hazard of interlaminar breakdown, the

laminations i4 to 20 and the insulators 2|, 22-

and 23 are provided with a substantially circumferential groove 38, as shown in Figs. 3 and 4. 'Ihis circumferential groove completely surrounds the relatively movable contacts insofar as laminations i4 and 20 are concerned and almost completely surrounds the relatively movable contacts insofar as the other laminatlons are concerned. Grooves 38 are connected with the passageway 2l so as to be lled with air or other uid at high pressure during the circuit interrupting operation. These grooved, compressed air seals between each of the joints concentrically surrounding the region of high volt age stress interpose a high strength dielectric barrier directly in the way of each of the weaker breakdown paths. In an electrical seal oi this type, it might be supposed that the increased dielectric strength of the interlaminar `joint is simply a measure of the actual linear increase in creepage length provided by the walls of the groove. This, however, is not the case, for it should be recognized that creepage breakdown strength is also commensurate to the dielectric strength of the medium to which the surface of the material is exposed. For example, it is known that a. breakdown voltage value along a unit length of a given material, say maple wood in free air, is increased a number of times when the same wood is immersed in insulating oil. Accordingly, the `breakdown strength oi the grooves additional creepage length is increased commensurate to the intensity o1 the blast pressure admitted into the channel formeel by the grooves and which may be several times the normal creepage breakdown strength of the insulating materials surface in free air. Obviously, for achieving maximum effect, a groove 38 is required in each of the two abutting surfaces of the laminar joint which coact to form a single hollow channel or insulating seal that cuts through the plane of the joint. The grooves 38 should be designed so that the breakdown value due to creepage around the walls of the grooved sections approximates that of the breakdown value due to puncture radially across the groove gap. From the foregoing explanation, it will be obvious that v the provision of grooves alone; i. e., filled only with free air, will increase the dielectric strength only in proportion to the actual linear increase in the creepage length afforded by the groove walls: but that when the grooved channels are charged with compressed iluid during the interrupting process in accordance with my invention, the dielectric strength of the seal is thereby increased in accordance with the increase in dielectric strength of the iluid due to the latters compressed state and which phenomenon is well known in the art. While other high dielectric strength fluids. such as oil or insulating compound, could be used to fill the channel seals thereby improving the breakdown strength of a laminar joint `using a seal filled only with free air; we prefer to use the more practical momentarily charged pressure gas seal in accordance with the chosen embodiment of the patent drawing. vIn this embodiment, the highest voltage stress is applied through the laminar joints consequent to the opening of the interrupting contacts I2 and I3 when, immediately following the circuit interruption, the recovery voltage is endeavoring to break through'the path of least impedance from contact to contact as previously stated. Accordingly, it will be appreciated that the admittance of pressure fluid into the grooves 38, concurrently with supplying pressure fluid for opening the contacts, provides an advantageous arrangement whereby the .breakdown strength of the joints is appropriately increased in immediate anticipation o the increase in applied voltage stress about to occur in the joints. It is desirable to keep the grooves 38 as narrow as possible consistent with the desired dielectric strength of the seal., thereby minimizing the bursting force, introduced by the admittance of fluid pressure to the seal, which tends to separate the laminations one from another. Mom ii'ig. e, it will be observed that the insulating channels formed by the coacting grooves 3u branch out from the longitudinal fluid supply conduit 2l whereby fresh un-ionized uid is introduced to the seals at 'the beginning of each interruption; also that the entrances to the seals are remote from the exhaust passages about the cooling plates 3l? so that the pressure fluid in the lseals ttl continues uri-ionized and substantially unaected by the arc products, thereby maintaining the high dielectric property of the seal during the continuance of the blast.

it will loe obvious with the arrangement described above the interrupting unit is especially adapted for outdoor application since the downwardly opening exhaust passages for the laminated arc confining structures areA protected from the weather. If desired, a suitable shield may be provided for protecting the upper portion of each laminated structure.

It will be obvious that with my arrangement the number of interrupting contacts can 'be in-n creased with a consequent increase in voltage that :may be satisfactorily interrupted. Such a construction is particularly advantageous from the standpoint of testing the circuit breaker' since it may be tested more nearly at its actual rating by applying the test to a single set of arcing contacts. Also with the cross blast construction very high currents may be interrupted and the relatively light contacts provide for very high speed operation.

In viewv of the detailed description included above, the operation of the circuit interrupter embodying my invention Will be obvious to those skilled in the art and no further discussion will be included herein. It should be understood that suitable means for operating and controlling isolating contact arm 1 will be provided such for example as the arrangement disclosed and claimed in copending Boisseau et al., application, Serial No. 565,834, filed November 30, 1944, and assigned to the same assignee as the present application.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, aim ln the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

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

1. In a fluid blast electric circuit interrupter comprising a pair of relatively separable arcing contacts, an arc confining chamber comprising a laminated structure with openings through the laminations for said relatively separable contacts, and means including a groove in the adjacent surfaces of said laminations for defining a channel between each of said laminations, said channel being spaced from said arcing chamber and disposed athwart the path of voltage stress existing when said contacts are separated for increasing the surface creepage path along the adjacent surfaces of said laminations and from one to the other of said contacts ln a direction substantially parallel to said adjacent surfaces so as to increase the dielectric strength of said chamber.'

2. In a fluid blast electric circuit interrupter comprising a plurality of serially arranged cross blast interrupting sections, means for supplying a blast of are-extinguishing fluid to said sections, a pair of relatively separable arcing contacts associated with each interrupting section, an arc confining chamber foreach interrupting section comprising a laminated structure with openings through the laminations for accommodating said relatively separable contacts, means for supporting said interrupting sections in spaced relationship mechanically, means for connecting said contacts in series electrically, and means for increasing the electrical breakdown strength between adjacent surfaces of said laminations in a, direction substantially parallel thereto, comprising grooves in said adjacent surfaces defining cavities substantially surrounding each chamber and connected to said fluid supply means, said cavities being disposed in spaced relation from each chamber in the planes defined by the adjacent surfaces of said laminations.

3, In a fluid blast electric circuit interrupter comprising a plurality of interrupting sections, means for supplying a blast of arc-extinguishing fluid to said sections, a pair of relatively separable arcing contacts associated with each in.- terrupting section, an arc confining chamber for each interrupting section comprising a laminated structure with openings through the laminations i o1: accommodating said relatively separable con tacts, a groove in the adjacent surfaces of said laminations and in spaced relation from each chamber, means for supporting said interrupting sections in spaced relationship mechanica-ily, means for connecting said contacts in series electrically, and means including said fluid supply means for injecting a supply of fluid under pressure to said grooves between said laminations to improve the dielectric strength of said interrupting sections ln a direction substantially parallel to the adjacent surfaces or said laminations.

4. In a fluid blast electric circuit interrupter comprising a pair of relatively separable arcing contacts, an arc confining chamber comprising a laminated structure with openings through the laminations for said relatively separable contacts, means defining a fluid passageway through said laminations through which fluid under pressure may be supplied for the fluid blast at said contacts, and means for increasing the dielectric strength of said chamber in a direction substantially parallel to the adjacent surfaces of said laminations, comprising grooves in the adjacent surfaces ot said laminations connected to said fluid passageway and defining channels between said laminations which substantially surround said arc-confining chamber and which are spaced from said chamber.

5. In a fluid blast electric circuit interrupter comprising a pair of relatively separable arcing contacts, an arc confining chamber comprising a laminated structure with openings through the laminations for said relatively separable contacts, means defining a fluid passageway through said laminations through which fluid under pressure may be supplied for the fluid blast at said contacts, and a fluid seal in the joint between each of said laminations to increase the Voltage breakdown strength through each said joint comprising a narrow substantially circular groove on each face of each of said laminations surrounding said relatively movable contacts, said grooves being connected t0 said fluid passageway so as to be filled with fluid under pressure when fluid under pressure is supplied to said passageway.

6. In a fluid blast electricl circuit interrupter comprising a pair of relatively separable arcing contacts, an arc confining chamber comprising a-lam'inated'structure with openings through the laminations for said relatively separable contacts,-means-deflning a fluid passageway through said laminations through which fluid under pressure may be supplied for the fluid blast at said contacts, and a fluid seal in the joint between each of said laminations to increase the voltage breakdown strength through each said joint comprising a narrow substantially circular groove on each face of each of said laminations with the grooves on adjacent faces of adjacent disks being coincident, said grooves being connected to said fluid passageway so as to be filled with fluid when fluid under pressure is supplied to said passageway.

7. In a fluid blast electric circuit interrupter having a pair of relatively separable arcing contacts, a plurality of juxtaposed laminations havlng surface grooves and openings therein, said openings defining an arc-confining' chamber in which said contacts are mounted, means for producing a blast of fluid in said chamber when said contacts are separated to extinguish the arc drawn therebetween, and means for improving the dielectric strength of said chamber at the juxtaposed surfaces of said laminations in a direction substantially parallel thereto comprising cavities defined by opposing grooves in adjacent laminations, said cavities being spaced from said chamber, and means connecting said fluid supply means and said cavities for supplying a quantity of fluid under pressure to said cavities during a circuit-interrupting operation.

8. Irfan electrical device, an insulating structure interposed between points of substantially diierent potential, said structure comprising e. pair of insulating members having surfaces disposed in abutting relationship is :roem e, jeins therebetween, end means for increasing the electrical breakdown ereepsge path thzough seid joint in a 'iireetion substantially parallel to the abutting surfaces of said insulating members comprising an elsngeed groove :in et least one of said surfaces disposed a'thwsl't the psx-ii of Bruitage stress through said Jsint, said groove being spaced imm the edges si said joint.

i?. In an -feleetiieai device, an insulating structure interposed 'tween points of substantially different potential, seid struesure comprising e, pair si insulating members having surfaces dispose-fi in abutting relationship te om s. join-L therebetween, means for increasing she electrical breakdown strength threughsaid joint in e. fiirectnn substantially parallel te the abutting sur- :fs-ces oi' said insulating members comprising en elongated muove in ai: least one of said suriaees disposed athwsrt the path oi vnltage stress through said Joint between the points nf different potential, said groove being spaced from the edges of said joint, and means for charging said groove with uuid under pressure.

lil. 1n an eleetrlcai device, an insulating structure interposed between points of substantially different potentiel, said structure comprising s.

` other of seid insulating mem-bess, and means for suppiying said esi/ity with fluid under me@ suren Zilli.

STATES PATENTE Numbei Name Dass Lilwi ilhitney et al Nov. 20, i934 2,0%,729 Beiersdorf Ges. 12, i937 2,253l96 Paul Aug. 19, 194i 2,304,529 Beker Dec. 8, 21942 2,31%@ Ludwigs et si Mar. 9, 1943 2,331,441 Then et ai Oct. l2, i943 2,498,673 Gsmbitts Aug. EL i946

Images