US2518195A - High-voltage electric circuit interrupter - Google Patents

Description

Aug. 8, A1950 l w. F. sKEATs HIGH VOLTAGE ELECTRIC CIRCUIT INTERRUPTER Filed July 19, 1946 .LSEFSI u A l \\\\\\.../vl.. M 7 3 .if nl: 0 ./l 7 l uw 2 ITQehbol-z Wi IFT-ed. F. Ske ats,

by H is Attorn e5 .Y

Patented Aug. 8, 1950l mau-VOLTAGE ELECTRIC cmcUrr rN'rEaaUr'rEn Wilfred F. sima, Lansdowne, ra., signor to General Electric Company, a corporation of New York Application July 19, 1946, Serial No. 684,810

6 Claims. (Cl. 20o-150) My invention relates to electric circuit interrupters for high voltage circuits, and particularly to high speed circuit breakers of the liquid blast type for opening high voltage alternating current power circuits within a few half cycles.

More specifically my invention is a further development andan improvement upon the multi-break interrupter disclosed in U. S. Patent 2,i64,i75 granted on an application filed by E. J. Frank and assigned to the same assignee as the present application.

In this type of interrupter, the movable con- .tact structure draws a plurality of arcs in series simuitaneousiy within a substantially enclosed casing which is immersed in a tank of insulating such as oil, some of the series'arcs having no immediate venting means so that they generate pressure areas Within the connes of the casing which are effective to blast streams of extinguishing liquid through expulsion ports positioned close to the other series arcs in the interrupting circuit. The ported series arcs accordingly are extinguished by the blasts of cli that are set up by the unvented series arcs se that the circuit is interrupted prior to the subsequent establishment of an isolating gap, the latter being effected by the separation of a moyable contact arranged external to the interrupter easing, but Within the enclosing tank. The very e'iiective above described interrupting process, whereby an arc that is drawn close to an xpulsion port within an cil confining chamber is extinguished by the blast caused by a pressure established adjacent to the arc, is generally reierred to and recognized as oil blast action.

in such an oil blast interrupter, it will be obuicus thatits interrupting capacity is limited-by the physical strength of the casing to resist with.. out rupture internal pressures generated under all conditions of interrupting the highest currents within its proper rating. Another, and less obvious, interrupting limit is encountered when the current and voltage condition of the circuit being interrupted is such that the current magnitude causes the formation of a gas lbubble at a generating break which is large enough to closely approach, or even to coalesce with, the

bubble formed at the associated interrupting break. In this event, the high voltage of the circuit can cause a breakdown through the relaa contact, so that a failure of the circuit breaker to interrupt the circuit becomes imminent.

It is known in the art to provide expulsion ports,` similar and equal, opposite each of the series arcs in a plural break interrupter, whereby the gas bubble at each break is permitted equal sidewise relief through closely adjacent confining walls. Although such an arrangement provides for the immediate relief of excessive gas pressure and lessens the above mentioned merger hazard of the gas bubbles, this benefit is achieved at the expense of the oil blast action, for it will be apparent that any preponderating blasting eifect of one arc over the other is mainly fortuitous, especially where the twin breaks are established simultaneously. it will be apparent that, by venting all the gas bubbles immediately to the outer tank, the greater portion of these bubbles, which virtually are reservoirs of energy, escape beyond control so that they are rendered impotent for contributing further toward the interrupting process within the casing.

Also known in the art is the provision of relief ports or valves, auxiliaryA expansion chambers and the like for circuit interrupting chambers for h the purpose of venting harmfui excessive pressures which may be generated during the interruption oi' heavy current circuits such as occur toward the upper limits of a circuit breaker's interrupting capacity.

in contradistinction to the` above mentioned known art, and in accordance with my invention, I provide a relief vent in the wall of an interrupter casing suicien'tly near to a pressure generating arc so that a limited local quantity of oil is readily displaced from the casing, thereby permitting the bubble 'to expand therein for sustaining the oil blast action while, at the same time, the bubble functions further as a resilient internal cushion for relieving the casing walls of any subsequent sudden surges of pressure during the interrupting process. I furthermore locate the relief vent or vents so as to minimize the hazard of the bubble coalescing with other gas bubbles or from bridging gaps between conducty ing parts at dierent potentials within the casing.

It is therefore an object of my invention to provide a. liquid blast circuit interrupter with venting means which permits the escape of liquid while retaining Kthe pressure generating gas bubble effectively within the casing.

It is another object of my invention to provide a liquid blast circuit interrupter with venting means for modifying the conformation of the .3 I blast producing gas bubble in a predetermined advantageous manner.

It is a further object of my invention to provide a liquid blast circuit interrupter with simple inexpensive means for controlling the magnitude and conformation of the pressure generating gas bubble whereby the circuit interrupting characteristics are improved.

The advantages of my invention will become apparent from the following description referred to in 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.

breaker, the latter of which comprises a lpair or` such interrupters which depend xedly from the top cover (not shown) of an enclosing tank 2 by means of a pair of symmetrically inclined conductor bushings. one of which is indicated by 3.

The pair of interrupters I are immersed well below the oil level indicated toward the top of tank 2 and are electrically connected in series when the lift rod d is in the upper or closed posi- .tion as shown, and in which position the conj ducting switch bladert interconnects the conducting structures within the interrupters I,

the casing l by a plurality of headless screws I2 radially disposed around the cylindrical wall of the casing. A like metallic cylindrical shell I3 may be provided for electro-statically shielding the throat region of the interrupter I.

For the purpose of forming a plurality of breaks in series within. the casing l, contact structure mounted for limited movement is disposed therein comprising plural contact bridging members I il, which are resiliently mounted about a strong central axial member I of insulating materialhaving a reduced cylindrical guide portion It which extends above the members short square-sectioned body at its upper end and which is threaded at its lower end for uniting to it a light iianged contact Il which abuttingly ccI operates with the rod contact 6 for establishing the isolating gap, already referred to, subsequent to the interrupting process within the casing.

thereby completing a closed circuit through the breaker unit from the external or line terminal (not shown) of the bushing 3 to the correspond.- ing external line terminal of the opposite bushing. In a triple pole circuit breaker, as is well understood in the art, three of the above-described single pole breaker units would be arranged in spaced relationship and a common operating mechanism would be provided for lowering or raising the lift rods t in unison for effect- -ing a circuit opening or closing operation respectively in the three phases.

When the breaker is tripped to open, the lift rod 4 and its switch blade 5 are moved downwardly at high speed. During the initial part of this opening movement, internal members respond automatically to draw and extinguish a series of arcs within the interrupters I as will be described later, and continued downward movement of the blade 5 then establishes a pair of isolating gaps between the blade rod contacts 6 and the interrupters I. The length of -these gaps and the spacing of the interrupters i within the oil-iilled tank 2 arefsuch as to preclude the possibility of electrical breakdown from bushing to bushing under any voltage conditions that might .arise while the breaker remains in the open circuit condition.

' The interrupter I comprises a cylindrical casing 1 composed of a mechanically strong insulatving material such as bonded laminated paper Concentrically disposed about the tensioned axial member I5 is a series of suitable insulating l spacers and washers secured in compressive relationship between the shoulder of the altrovee mentioned square-sectioned body of member i5 and the shoulder of anged butt contact Il. Ace cordingly, it will be clearly observable from the drawing that the movable element of the contact structure within casing 'l comprises the axial member I5, the lower butt contact il and the various elements carried thereby, including the two similar bridging contacts Il. This movable element is guided for axial reciprocable move ment within the casing, both at its upper end by virtue of guide portion It sliding within the bore of adapter e, and at its lower end by spacer I8 sliding `within the throat oi? guide member Ii. It will be evident that when the blade 5 moves down to effect a circuit opening operation. the movable element of each interrupterwill follow in abutting relationship to rod contacts t under the bias of opening spring i9 until arrested by the engagement of washer 2@ against a stack of shock-absorbent washers shown lying on the inner surface of the throat guide member II. A suitable wipe distance is aorded each of the movable contacts Id relative to the movable ele= ment by means of a shoulder formed by washer 2i, while a compression spring 22 below each contact I4 provides adequate contact pressure when in the closed continuous current carrying position.

In this embodiment of my invention, the xed contact structure Within the casing l comprises an upper conducting and contact member 23, which is mechanically and electrically connected to the adapter casting 8, an intermediate conducting and contact member 24, and a lower conducting and contact member 25 which, as shownl may be an extension of the ring-like member IIii these several conductor-contacts being secured as necessary to the casing wall by insulated screws 25. It will be clear from the drawing that the current path through each clcxsed interrupter from the bushing stud to the switch blade 5 is via adapter 8, upper conductor 23, upper bridging contact I4, intermediate conductor 26, lower bridging lcontact I d, lower conductor 25, throat guide member I I, iieXible conductors 21, butt contact I'I and rod contact 6. It will also be evident that during the opening movement, when the movable contact element moves downwardly, four series arcs will be drawn from the fixed contacts, one at each end of each of the two bridging contacts I4. Such an arrangement is known as a four-break interrupter, and it will be clear to those skilled in the art that a structure such as that described above might be adapted for a twobreak or a six-break interrupter by providing a lesser or greater number of conductors and contacts in accordance with the desired voltage rating of the particular circuit breaker involved. Where conductor-contacts extend adjacent the path of the arc, as is the case for members 24 and 25, they may be shielded from the arc by protective insulating sheathings 28 and 29. The abutting or wiping portions of the ilxed and movable conductors and contacts preferably are provided with conventional arc resistant metal facings as depicted in the drawing. O

The structure described thus far is not my invention but is disclosed and claimed in a concurrently filed application Serial Number 684,813 of T. R. Coggeshall and assigned to the same assignee as the present application.

Referring again to the specic embodiment shown in the drawing; of the four series arcs drawn at the four breaks in accordance with the downward opening movement of the movable contact element, two of these are interrupting arcs which are drawn longitudinally downward and closely adjacent to an expulsion port member Bil of arc resistant insulating material secured to the side wall of the casing 'Ihese renewable port members may be provided with a set of horiaantal slots as shown, for arc splitting in known manner, and which register with corresponding and larger openings inthe casing wall. The remaining two arcs, one drawn at the left-hand end of the upper bridging contact id and the other at the right end of the lower contact i4, constitute the pressure generating arcs for producing the oil blast action, the improved control of which is the main object of my invention.

For controlling the amount of gas generated at each of the pressure generating breaks, I provide a pair of known so-called arcing plates 3i, which are bolted to and depend from either side of each of the pressure generating fixed contacts and which lie closely adjacent to the path of the pressure generating end of contact i4 as shown best by the transverse section of Fig. 2. These renewable arcing plates 3| preferably are faced with a strip of arc resistant metal on their inner surfaces as indicated in the drawing. The purpose of the arcing plates is to control the eiective length of the pressure generating arc by providing a regulated short gap between the separating pressure generating contacts for a predetermined distance (or time) of the interrupting stroke. The length of the arcing plates 3i is such as to maintain a short generating arc during the arcing period adequate for the interruption of heavy currents, while allowing nevertheless, some eX- tension of this arc toward the end of the stroke to provide for those light current interrupting conditions where insuillcient pressure for interruption would be generated by the short lateral arc. It will be observed that the opposite end of contact M rides in the vertical groove of the channel-sectioned port member 30 so that the contact cannot rotate during its travel to vary unduly the controlled side gap distance Vto the arclng plates 3| I have found that even with the use of the arcing plates 3| as described above, and particularly at fast opening speeds, it is possible to draw an undesirably long initial pressure generating arc whose roots tend to adhere at the center of area of the coacting contact surfaces and which position is one of equilibrium with respect to magnetic forces. To prevent any dwell in this undesirable condition, I bifurcate the end of contact I4, as clearly shown at 34 in Fig. 2, so that the pressure generating arc perforce is initiated to one side or other of the coacting contact surfaces. In such an off-center position with respect to the central balanced current path, the arc thus drawn is inherently unstable and will be urged magnetically by this off-side loop effect to move further off-center so as to quickly assume the short predetermined gap distance across to the nearest side plate 3|. Because the pressure generating arc may form unpredictably on either side of the bifurcated contact end, it is advantageous to provide an arcing plate in ilanking relationship on each side of the contact, as shown, for effecting the rapid transition of the arc from its initially drawn longitudinal path to the nearest of the two lateral arc gaps.

In addition to control'ng the blast generating bubble with respect to the amount of gas generatedl I further improve the breakers interrupting characteristics by providing means for causing the bubble to expand within the casing to provide internal cushioning, this expansion extending in a transverse direction with respect to the bubble iormed about the associated interrupting break for minimizing the already described bubble merger hazard. For this purpose I provide one or more vents 32 through the wall of casing 1, arranged adjacent to and spaced from each of the pressure generating breaks, as best shown by Fig. 2. These vents are quite different from the arc expulsion ports in member 30 opposite the interrupting break, for the prime purpose of vents 32 is to permit the egress from the casing of a local mass of the oil lying adjacent to the pressure generating break. Hence, oil ilows relievingly from the casing through the vents 32 substantially in accordance with the severity of the arcs, especially those nearest the vents and which produce the gas generating bubble. The latter accordingly is permitted limited expansion enabling it to serve as an effective cushion against ,sharp pressure surges which might be due to vagaries of the interrupting arc and random flow conditions at the ports '3U in the casing, While at the same time serving as an energy reservoir for sustaining the internal oil blast action. t will be apparent that by positioning the vents 32 in sidewise relation to the pressure generating break as shown in Fig. 2 I cause the bubble to elongate in the wake of the expelled oil in a direction that will minimize the hazard of the bubble merging with other bubbles or of bridging the gap between conducting parts at different potentials. Only in exceptional cases where a high current interruption produces excessive internal pressure will gas from the pressure generating bubble be relievingly ejected into the surrounding tank 2 through the vents 32.

The longitudinal positioning of the vents 32 in the casing wall is properly selected with respect to the interrupting break to suit the local internal conditions of the interrupting structure.

For example. in the embodiment shown, I prefer to position the vents at the approximate level of the tips of arcing plates 3| as best shown by Fig. l. In this position the vent tends to counteract the natural tendency of the bubble to float upward, thereby maintaining it substantially in the region of the associated interrupting break. In one application of my invention to a wellknown commercial type of oil circuit breaker, it is not practicable to provide a vent hole 32 on 7 each side of the interrupting break so that one of the pair shown by Fig. 2 is omitted, while the remaining one is enlarged correspondingly; nevertheless, numerous tests reveal that this modification produces the same marked improvement as the embodiment shown in comparison to similar'interrupters, which lack the simple but eifective venting means of my invention. Conversely, in place of the single vent 32 on one or both vsides of the interrupting break, I might providel a plurality of smaller vent holes for effecting some other predetermined advantageous distortion of the pressure generating bubble away from its associated interrupting break bubble. From tests made on interrupters embodying my invention, I have found that best results are achieved by making the total cross-section of the relief vents approximately half that of the expulsion ports at the opposite side of the casing.

This empirical ratio will vary to some extent de pending on the proximity of the vents to the pressure generating break, the diameter of the vent holes, the thickness of the casing wall, and other related iiow factors.

Conseivably, the voltage conditions of the internal contact structure of an interrupting unit might be such that the bubble distending vent of my invention is necessitated by only one of the pressure generating breaks so that it might be advantageous to omit the local relief vent entirely from other of the pressure generating breaks.

In view of the above detailed description and analysis it is believed that only the following brief review of the operation of the interrupter is necessary. Responsive to a tripping impulse, the blade 5, with the movable contacts within the interrupters l in follow-up engagement is unlatched and moves downwardly at high speed under the accelerating influence of springs I9 and 22. In the initial opening movement, each contact i 4 separates from the xed contact structure to draw a pair of arcs, one at each end of the moving contact. The interrupting arc of this pair is drawn from one end of contact M across the expulsion ports in the renewable port member` 30, while a lesser arc whose effective length is modified by arcing plates 3| and whose generated gas bubble is influenced by the adjacent vent 32, is established at the opposite end of contact lf3. The resulting controlled oil blast action within casings 'I is eiective to extinguish the interrupting arcs, whose products of arcing are driven through the expulsion ports `into the low pressure region in the tank 2, ordinarily before the rod contacts 6 of the blade 5 separate from their coacting isolating contacts l1. Continued downward movement of blade 5 to its fully open position interposes adequately 'safe isolating gaps in the breaker circuit. After interruption, the casings 'I rell with oil from the tank, oil iiowing back through the several ports and vents, while residual gas may escape through suitable vents 33 in the top of the casing.

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 None 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 liquid blast type comprising a confining chamber, a first pair of relatively movable contacts in said with said breaker, a second pair of relatively movable contacts in said chamber for drawing a pressure generating arc therebetween, an arc extinguishing liquid within said chamber, an expulsion port in said chamber positioned close to said rst pair of contacts, andventing means in a wall of said chamber positioned close to and on opposite sides of said second pair of contacts for causing the expanding pressure generating gas bubble formed by the arc drawn between said second pair of contacts to distend within said chamber in a transverse direction with respect to the bubble formed by the arc drawn between said rst pair of contacts.

.2. An electric circuit breaker of the liquid blast type comprising a confining chamber, a rst pair of relatively movable contacts in said chamber for interrupting the circuit associated with said breaker, a second pair of relatively movable contacts in said chamber for drawing a pressure generating arc therebetween, an arc extinguishing liquid within said chamber, an electrode electrically connected to one of said second pair of contacts and spaced from the path of relative movement so that transfer of the arc to said electrode from the contact electrically connected therewith is facilitated, an expulsion port in said chamber positioned close to said rst pair of contacts, and venting means in a wall of said chamber positioned close to and on opposite sides of said second pair of contacts for causing the expanding pressure generating gas bubble formed by the arc drawn between said second pair vof contacts to distend within said chamber in a transverse direction with respect to thebubble formed by the arc drawn between said first pair of contacts. I

3. An electric circuit breaker of the liquid blast type comprising a pressure conning chamber immersed in an arc extinguishing liquid, a first pair of relatively movable contacts in said chainber for interrupting the circuit associated with said breaker, a second pair of relatively movable contacts in said chamber for drawing a pressure generating arc therebetween, an expulsion port in the wall of said casing positioned close to said first pair of contacts for causing a flow of liquid' between said first pair of contacts to extinguish the arc drawn therebetween in response to pressure within said chamber during a circuit interrupting operation, one of said second pair of contacts being bifurcated to prevent the are drawn between said second pair of contacts from assuming a magnetically stable central path between said second pair of contacts, arcing electrodes electrically connected to one of said second pair of contacts and disposed on opposite sides of the path of relative movement between said second pair of contacts, said arcing electrodes being spaced from the path of relative movement between said second pair of contacts by a distance substantially less than the length of said electrodes in the direction of relative movement between said contacts, and venting means in said casing close to and on opposite sides of the point of formation of the arc drawn between said second pair of contacts. l

4. An electric circuit breaker of the liquid blast type comprising a pressure confining chamber immersed in an arc extinguishing liquid, a first pair of relatively movable contacts in said chamberA for interrupting the circuit associated with said breaker, a second pair of relatively movable contacts in said chamber for drawing a pressure generating arc therebetween, an expulsion port in the wall of said casing positioned close to said first pair of,contacts for causing a iiow of liquid between said rst pair of contacts to extinguish the arc drawn therebetween in response to pressure Within said chamber during a circuit interrupting operation and venting means in a wall of said chamber close to and on opposite sides of said second Apair of contacts for causing the expanding gas bubble formed by the pressure generating arc drawn between said second pair of contacts to distend within said chamber in a direction transverse to an imaginary line connecting the gas bubble formed at said ilrst pair of contacts and that formed at said second pair of contacts during a circuit interrupting operation, the total cross-sectional area of said expulsion port being substantially greater than that of said venting means.

5. A multibreak circuit interrupter of the liquid blast type comprising a pressure conning casing immersed in an arc extinguishing liquid, xed contact structure mounted within said casing, a plurality of movable bridging contacts, each separable from said fixed contact structure to produce a pair of series arcs in the interrupting circuit, a pressure relieving vent in said casing close to the point of formation of one of said arcs, an expulsion port in said casing adjacent to the point of formation of the other of said arcs, the distance between said vent and the point of formation of the arc adjacent thereto being substantially greater than the distance between said port and the point of formation of the arc adjacent thereto and the cross-sectional area of said expulsion port being substantially greater than that of said vent.

6, An electric circuit breaker of the fluid blast Y lishing a pressure producing arc, one of said contacts being bifurcated to 4prevent the arc drawn between said contacts from assuming a magnetically stable central path between said contacts, and arcing electrodes electrically connected to one of said contacts and disposed on opposite sides of the path of relative movement between said contacts, said arcing electrodes being closely spaced with respect to the path of relative movement between said contacts so that transfer of the arc to one of said electrodes from the contact connected therewith is facilitated.

WILFRED F. SKEATS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 967,281 White Aug. 16, 1910 1,551,514 Hilliard Aug. 25, 1925 1,820,927 Whitney et al Sept. 1, 1931 1,998,941 Perino Apr. 23, 1935 2,098,801 Erben Nov. 9, 1937 2,159,829 Hobson May 23, 1939 2,164,175 Frank June 27, 1939 2,192,772 'MacNeill Mar. 5, 1940 2,224,611 Skeats Dec. 10, 1940 2,271,989 Prince Feb. 3, 1942 f 2,323,642 Baker July 6, 1943 FOREIGN PATENTS Number Country Date :ef- '-f-e---FE-f

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