US3028466A - Electric circuit interrupter of the liquid-break type - Google Patents

Description

April 3, 1962 v. E. PHILLIPS ELECTRIC CIRCUIT INTERRUPTER OF THE LIQUID-BREAK TYPE Filed May 28, 1959 2 Sheets-Sheet 1 L nnunr l Inventor: Virgel E. Phi||ips,| b His Attorneg.

V. E. PHILLIPS April 3, 1962 ELECTRIC CIRCUIT INTERRUPTER OF THE LIQUID-BREAK TYPE Filed May 28, 1959 2 Sheets-Sheet 2 I co/vrncr cor/mars MO TION PART BEG/NS m n 2 7 VI ne IS- w M H: b w w w w F g.6. E X

His Attorn e9.

United States Patent 3,028,466 ELECTRIC CIRCUIT INTERRUPTER OF THE LIQUID-BREAK TYPE Virgel E. Phillips, Springfield, Pa., assignor to General Electric Company, a corporation of New York Filed May 28, 1959, Ser. No. 816,630 9 Claims. (Cl. 200-450) This invention relates to a circuit interrupter of the liquid-break type and, more particularly, to a circuit interrupter of this type which has an exceptional ability to successfully interrupt capacitance currents, particularly in the higher current range.

It has been found that pressurizing the fluid within an interrupter materially aids in the successful interruption of capacitance currents. In order to obtain the desired pressure level within the interrupter during capacitance current interruptions, interrupters have been provided with one or more pressure-responsive exhaust valves in combination with a pump communicating with the interrupter. When circuit interruption is initiated, the pump applies a force to the fluid within the interrupter, and the exhaust valves substantially block the liquid from flowing through the exhaust ports of the interrupter, thereby resulting in a pressure build-up within the interrupter.

I have found that it is most important that the pressure within the interrupter be built up to a relatively high level within a very short time after the contacts part. Any appreciable delay in such presstue build-up results in lower dielectric strength in the interrupter during a possibly-critical interval, with the result being that a harmful restrike across the contacts might occur which could result in an excessive voltage build-up. In view of the desirability of a high rate of pressure build-up. I have constructed my interrupter in such a manner that possible gas traps within the interrupter have been largely eliminated so that the free space within the interrupter is substantially entirely filled with liquid. This has resulted in a more rapid rate of pressure build-up because any gas trapped within the interrupter had tended to act as a compressible cushion delaying the desired pressure build-up.

Although the above approach has been highly effective in minimizing restrikes when interrupting relatively light or medium range capacitance currents, e.g., less than about 100 amperes, I have found that it is not as effective as desired when the capacitance currents are of a higher value, e.g., 200 or more amperes. Restrikes have occurred with undue frequency in spite of the high rate of pressure build-up.

An object of the present invention is to materially lessen the frequency of such restrike occurrences when interrupting relatively high capacitance currents with a pressurized interrupter of the type that is normally liquidfilled.

Another object is to substantially increase the dielectric strength of the fluid within the interrupter during the transient low pressure interval that I have found to occur after the initial pressure peak has been reached, yet with-' out harmfully delaying or interfering with the action of the pump during initial pressure build-up.

In carrying out my invention in one form, I provide a housing containing arc-extinguishing liquid in which circuit-interrupting arcs are adapted to be established. The housing is provided with an exhaust passage for venting arcing products to its exterior. During the usual capacitance current interruption, the housing is substantially closed-off by means including a normally-closed pressure-responsive exhaust valve in the exhaust passage. A pump operable upon the establishment of a capacitance current are builds up and maintains a pressure within the housing to aid in extinguishing the arc. The

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pump is assisted in its pressure-maintenance function by a bufier device submerged within the arc-extinguishing liquid. This buffer device contains a volume of gas which is compressed by pressures developed within the housing during initial operation of the pump, and this compressed gas responds to a transient drop in pressure following a pressure peak by expanding and thus increasing the instantaneous pressure within the housing to a level substantially exceeding the pressure that would be developed without the buffer device. The buffer device has a limited area orifice that reduces the flow of pressurized fluid into compressing relationship relative to the gas volume to such an extent that the pump can initially build up pressure at a rate and to a level sufficiently high to substantially maintain the ability of the interrupter to prevent restrikes during initial pressure build-up as compared to a corresponding interrupter without the buffer device. The interrupter is further constructed in such a manner that just prior to an interrupting operation, the free internal space within the housing outside of the buffer device is substantially entirely filled with the arcextinguishing liquid.

For a better understanding of my invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side elevational view partly in section showing a circuit interrupter embodying one form of my invention.

FIG. 2 is a one-line circuit diagram illustrating the use of a circuit interrupter for interrupting capacitance currents.

FIG. 3 is a graphical representation of certain voltage and current relationships occurring during capacitance current interruptions.

FIG. 4 is in enlarged detailed view, partly in section, of a portion of FIG. 1.

FIG. 5 is a graphical representation of certain pressure, current and voltage relationships occurring during a capacitance current interruption.

FIG. 6 illustrates a modified form of the invention.

Referring now to FIG. 1, the interrupter 1 shown therein is of the general type described and claimed in Patent No. 2,749,412 McBride et al., assigned to the assignee of the present invention. This interrupter 1 is mounted, along with another similar interrupter (not shown) inside a relatively large oil-filled enclosing tank.

The two interrupters are electrically connected by a reciprocable blade contact 2 of conventional form, such as shown for examplein US. Patent 1,548,799 Hilliard, assigned to the assignee of the present invention.

The interrupter 1 is supported within the oil-filled tank from an insulating bushing structure 3 having a conductor stud to which an adapter 4 is suitably secured in a known manner. Adapter 4 is arranged to cooperate with suit able tie bolts (not shown) which structurally interconnect the interrupter unit 1 and the adapter 4.

The interrupter 1 comprises a tubular insulating casing 5 enclosing a plurality of pairs 8, 9 of separable interrupting contacts which are electrically connected in series. The upper pair 8 of separable contacts comprises a relatively fixed contact assembly 10 and a relatively movable rod-type contact 11. The fixed contact assembly 10 is preferably of the conventional cluster-type comprising a plurality of fingers urged radially inwardly by suitably resilient means (not shown). In a corresponding manner, the lower pair 9 of contacts comprises a similar fixed contact assembly 12 and a relatively movable contact 13. The pairs of interrupting contacts 8 and 9 are electrically connected in series by means of suitable current transfer contacts 14 and the transversely-extending contact support casting 15. For supporting the movable contacts 11 and 13 and for interrelating them for 3 simultaneous movement so as to draw a pair of simultaneously-occurring arcs, there is provided a common crosshead 16 of conducting material to which the lower rod contact 13 is directly secured and to which the upper rod contact 11 is suitably fixed by means of an interconnect ing insulating rod 17.

In order to complete the electrical circuit through the interrupter and to provide an isolating contact arrangement for the interrupter, there is provided on the head 16 an external contact button '18 which cooperates with an isolating contact 19 secured to the movable switch blade 2 to form a pair of isolating contacts. From the above description, it will be apparent that the electrical circuit through the interrupter extends from the adapter 4 through the conductor 20, through the upper inerrupting contacts 10, 11, through the current transfer contacts 14 and the casting 15, then through the lower interrupting contacts 12, 13, the crosshead 16, the contact button "18, the isolating contact 19, and finally through the switch blade 2 and to the cooperating interrupter (not shown), which is disposed at the opposite end of the switch blade 2.

A circuit-opening operation is produced by driving the switch blade 2 rapidly downward. This allows suitable compression springs 6 to force the crosshead 16 together with the contacts 11 and 13 rapidly downward so as to draw a pair of circuit-interrupting arcs in the regions where these contacts part from their mating stationary contacts. After a predetermined downward movement, the crosshead 16 is blocked by suitable stop means (not shown) from following the switch blade 2. The switch blade 2 however, continues moving downwardly and, as a result, establishes an isolating break between the contacts 18 and 19 in a conventional manner.

The compression springs 6, it will be noted, bear at their upper end against a stationary plate 7. This plate 7 and the adapter 4 act to enclose the interior of the interrupter 1 at its respective lower and upper ends.

Adjacent to the serially-related interrupting contacts 8 and 9 are a pair of arc-extinguishing units in the form of bafile stacks 21 and 22. Baflie stack 21 is formed of a plurality of superposed apertured baflie plates 23 of insulating material which together provide a central interruptin'g passageway 24 and a plurality of verticallyspaced, angularly-aligned exhaust passages 25 radiating therefrom. The exhaust passages are preferably formed by slotting certain of the baffle plates 23 in a well-known manner. When a high current arc, say, of short circuit proportions, is drawn within the passageway 24- 'in respouse to separation of contacts and 11, the arc reacts with the surrounding oil to produce pressure within the oil filled casing 5, and such pressure is elfective to force a blast of dielectric fluid and are products through the slots or exhaust passages 25 and out the registering exhaust port 26 formed in the adjacent wall of casing 5. The pressure and flow conditions present during this interval aid in extinguishing the arc. The lower baffle stack 22 generally corresponds to the bafiie stack 21 except that baflle stack 22 is provided with an opening 27 through which reciprocates the insulating portion of the upper rod contact 11.

For controlling the flow of fluid through the exhaust passages 25, 26, there is provided a pressure-responsive exhaust valve 100 for each of the arc extinguishing units 21 and 22. These exhaust valves are preferably constructed as described and claimed in the application S.N. 717,892, Schneider, now Patent No. 2,927,181, assigned to the assignee of the present invention. Each of these exhaust valves 100 comprises a tubular valve body 102 which is suitably clamped to the casing 5, as by means of a nut 104 on the exterior of the tubular body 102. When the nut 104 is tightened, it acts to force a shoulder 106 formed on the tubular housing 102 into clamping engagement with a recessed portion f rmed in he interior of casing 5.

For controlling the flow of fluid through the hollow valve body, there is disposed therewithin a pivotallymounted valve member in the form of a metallic vane or flapper 110. This vane is fixed to a pivotally-mounted shaft 112 which extends horizontally across the bore of the valve body at an off center location, which, in FIG. 1, is shown as being closer to the bottom inner surface of the valve body than to the top inner surface. Preferably, the shaft 112 is of a rectangular cross section, and the shaft-receiving opening in the valve member 110 is of a similar shape so as to preclude relative rotation between these parts. This shaft 112 is suitably journaled at its opposite'ends within the walls ofthe valve body 102 so as to allow for pivotal motion of the shaft 112 on the valve body.

Located externally of the valve body 102 are crank arms which are suitably fastened to the shaft 112 at opposite ends thereof. Each of the vanes 110 is urged into its closed position of FIG. 1 by means of a tension spring 116 which interconnectes the outer ends of the crank arms 115. This tension spring 116 extends about the top exterior of the valve body 102 and is suitably anchored to the valve body 102 adjacent to top surface of the valve body. The means for anchoring the spring 116* to the valve body preferably comprises a lug 118 which is fastened to the valve body 102, as by suitable screws. The lug comprises a curved flange extending about a portion of the spring periphery, as shown in FIG. 1, and thereby preventing movement of the top portion of the spring 116 axially along the valve body 102.

When the pressure within the interrupter exceeds a predetermined value, it forces the valve member 110 counterclockwise about the axis of pivot shaft 112 thereby opening the central exhaust passageway through the valve body 102 and allowing fluid to flow therethrough. As is pointed out in greater detail in the aforementioned Schneider application, the resilient means 115, 116 exerts a generally decreasing force on the valve member 110 as it travels away from its closed position toward its fullyopen position. This follows from the fact that the effective moment arm through which tension spring 116 acts on the vane 110 becomes progressively smaller as the vane 110 moves from its closed position toward its fully open position.

In its fully-open position the vane 110* bears against a suitable stop 121, which is so located that it blocks opening movement of the vane prior to the crank arms 115 reaching a dead center position relative to the spring 116. As a result, the spring 116 still exerts a closing bias on the vane 110 when the vane is fully open and is, accordingly, capable of restoring the vane to closed position when the pressure within the interrupter falls below a predetermined level.

A basic function of the exhaust valves 100 is to restrict the exhaust ports during those low current interruption which generate relatively small quantities of gases. Without the valves, the liquid displaced by these gases would be dissipated so quickly through the large exhaust ports that no appreciable pressure build up would occur within the interrupter, which is a condition that would tend to interfere with interrpption, especially of capacitance currents. A pump 30, soon to be described, is provided for pressurizing the fluid within the interrupter during low current interruptions, but its effectiveness in this regard would be substantially impaired by the absence of any material downstream restriction in the exhaust ports, which would be the case if the valves 100 were not present. With the exhaust valves 100 present, how: ever, the pump 30 produces a pressure build-up which greatly aids in interrupting the lowcurrent arc. There is some minor leakage out of the interrupter during pump operation but not enough to materially interfere with the desired "pressure build-up. For this reason, I refer to my interrupter as being substantially closed-oft during the time the valves 100 are closed.

When a higher current are, say, of 500 or more amperes, is established within the interrupter 1, the arc generates suflicient pressure to force each of the valve members 110 out of its closed position into its fully-open position. Such higher current arcs are capable of generating suflicient pressure and flow to effect are extinction without reliance upon any downstream restriction, as is present when the valves are closed. The valves, in opening widely during such interruptions help to prevent excessive pressure rises within the interrupter.

As soon as the interrupting operation for relatively high currents has been completed, the pump 3% operates to scavenge the interrupter 1 of any ionized gases remaining after the interruption so as to prepare the interrupter for possible reclosure followed by another interruption. To this end, the pump 30 forces a flow of fresh insulating liquid through the arc extinguishing unit via thepassageways 31 and 25, 26 and the exhaust valves 100, all in a manner soon to be described in greater detail.

The pump 30, which is structurally similar to a corresponding pump described in the aforementioned Mc- Bride patent, comprises a cylinder 32 suitably secured to the interrupter casing and connected with the passageways 31 by means of ducts 43. The pump 30 also comprises an impulse piston 35 which is spring biased downwardly by a compression spring 36. The compression spring 36 is mounted between a stationary part 37 and a stop 39 fixed to the piston rod 40, which in turn is fixed to the piston 35. The compression spring 36 is held charged during the time the interrupter is closed by means of a plunger 39a fixed to the switch blade 2 and abutting against the stop 39. However, when the switch blade 2 is driven downwardly to open the interrupter, the restraint of the plunger is removed and the spring 36 is free to begin driving the piston 35 downwardly against the opposition of the oil disposed therebeneath.

During high current interruptions the spring 36 is ineffective to produce substantial downward movement of the piston 35 until after the high current arcs are extinguished. This is the case because these high current arcs generate sufiicient pressure to overcome the action of the spring 36. It is only when these pressures subside that the pump becomes effective to impel liquid through the arc extinguishing unit.

For protecting the pump 30 from high arc-generated pressures, the ducts 43 are preferably provided with check valves 44 disposed in each of the ducts 43. These check valves are adapted to cooperate with valve seats 45 located within each of the ducts. The valves are free to slide on their centrally disposed spindles 46 which are supported from the valve seats by suitable spiders. These valves freely permit fluid flow therethrough from the pump 30 except when the pressure produced by the arcs drawn by the contacts 11 and 13 predominates. Under such conditions, the valves close automatically to protect the pump from objectionable arc-generated back pressures.

A type of low current interruption that provides an extremely severe test for an interrupter is that encountered when opening predominantly capacitive circuits. This type of interruption is depicted in FIG. 2 where a circuit breaker 10 is shown disposed between a capacitive load C and a source S. Assume first that the breaker is in closed position and that alternating power is flowing between the source S and the capacitive load C. The current I flowing through the circuit breaker contacts will lead the terminal voltage E of the source by 90 degrees inasmuch as the load is substantially entirely capacitive. This phase relationship is depicted in FIG. 3. If the breaker is tripped toward open position and its contacts part at an instant A in FIG. 3, arcing will take place until a first current zero is reached at an instant B (when the voltage E is at its crest value). At this instant B, the voltage level E at the capacitor C side of the breaker 10 is equal to the voltage level E at the source side of the breaker. Hence there is then essentially no voltage across the breaker contacts. Thereafter, the source voltage E begins reversing, but the capacitor voltage E remains at approximately the crest value due to the energy storage properties of the capacitor C. This results in a voltage E being established across the breaker contacts.

Interruption at the first current zero B is effected by the interrupter with comparative ease at a relatively short contact-separation. This is the case because there is no appreciable voltage E across the breaker contacts for several hundred microseconds after the instant B. This interruption, however, might be only temporary because as the source voltage E continues reversing toward its opposite crest value, the voltage E across the breaker contacts approaches double this crest value. It is under such conditions and during this interval that an arc is likely to restrike across the partially-separated contacts. Such restrikes, being of an oscillatory nature, can produce seriously high voltages of a possibly harmful value. In referring to restrikes in this application, I am referring to those current resumptions which occur more than onequarter cycle after a current zero such as shown at B. A reignition occurring before this time usually does not result in excessive voltages being built-up.

By employing the pressure-responsive exhaust valves in combination with the pump 30, it has been possible to greatly decrease the frequency with which such restrikes have occurred (in comparison to the same interrupter without the valves). The pressures developed by the coaction of the pump 30 and the valves 100 have raised the dielectric strength between the parting contacts to a relatively high level capable in most cases of withstanding the voltage E impressed across the contacts after a current zero. I have found that in order to prevent a restrike, it is most important that this pressure he built up to a relatively high level before the restrikeproducing voltage can be developed. Depending upon the point in the current wave at which the contacts are parted, such voltages can be developed even in one-fourth cycle after the contacts part. In view of the desirability of a high rate of pressure build-up, the interrupterof the present invention is constructed in such a manner that possible gas traps within the interrupter have been substantially eliminated so that the free space within the interrupter is substantially entirely filled with liquid. Thus, with one exception soon to be described, no substantial amount of residual gas is present within the interrupter to act as a cushion to delay pressure build-up. This, in combination with the fact that the exhaust ports are substantially closed off by the valves 100, has resulted in a very rapid rate of pressure build-up in my interrupter.

The above approach has been highly effective in minimizing restrikes when interrupting relatively light or medium range capacitance currents, e.g., less than about 100 amperes. I have found, however, that it is not as effective as desired when the capacitance currents are of a higher value, e.g., 200 or more amperes but not of sufficient value or duration to open the valves 100. For such currents, restrikes have occurred with undue frequency despite the high rate of pressure build-up.

I have overcome this problem by equipping my pressurized interrupter with a special gas-filled buffer device, which is shown at 50 in FIGS. 1 and 4. This buffer device St comprises a cup-like metallic member 52 provided with a centrally disposed recess 54 filled with a suitable gas such as air. The gas is maintained within the recess by means of a resilient diaphragm 53 secured between the cup 52 and an orificed cover 55 provided for the cup. The cover 55 is clamped against the rim of the cup 52 by suitable bolts 57 peripherally spaced about the cover. Several of these bolts extend entirely through the cup and are threaded into the casting 15 to hold the buffer device in position within the interrupter.

The cover 55 is provided with a limited area orifice 56 through which oil from the interrupter is forced first in one'direction and then in an opposite direction during a circuit interrupting operation. Oil flow into the buffer device 50 through the orifice 56 deforms the diaphragm 53, as shown by the dotted lines in FIG. 4, and compresses the gas within the recess 54. Expansion of the gas after such compression forces oil out of the buffer device through the orifice 56 and tends to return the diaphragm to its original position. The diaphragm isolates the oil of the interrupter from the air within the recess 54 and thereby prevents absorption of the air by the oil.

I have found that, without the butter device 50 present, the pressure developed within the interrupter during the interruption of relatively high capacitance currents quickly reaches a peak value exceeding the pressure developed at a corresponding instant with no load or light capacitance currents. I have found, however, that as the current decreases to zero and is interrupted, the gas generated by arcing begins to cool and in so cooling causes the interrupter pressure transiently to fall to a value considerably lower than the no load pressure at a corresponding instant. This low value of pressure can prevail at the time when high dielectric strength is most needed to prevent. restrikes, i.e., between one-fourth and one-half cycle after current zero. With insufiicient dielectric strength to withstand the voltage prevailing during this critical interval, a harmful restrike occurs. The above described pressure relationships are illustrated by FIG. where pressure inside the interrupter (and certain other quantities) are plotted against time as an abscissa. The dotted line curve NL represents the no load pressures, and the dot-dash curve G represents the pressures developed while switching approximately 200 amperes of capacitance current without the buffer device 50. In the depicted interruptions, almost a full half cycle of current I flowed until the instant B was reached. Thereafter, the voltage E across the contacts began building up. One-fourth of a cycle after the instant B, the pressure within the interrupter is at a low value, with the result being a restrike occurring at X as broadly described earlier in this paragraph.

The butter device 50 of the present application acts to raise the instantaneous pressure prevailing during the time the pressure is receding from its peak value and thus acts to raise the dielectric strength during this critical interval, thereby lessening the chances for a restrike. In this regard, the initial pressure build-up by the pump forces a small amount of oil from the interrupter into the buffer device through the orifice 56 thus compressing the air within the buffer device. When the pressure recedes from its peak, the compressed air acts to force oil back through the orifice 56 thereby materially increasing the pressure otherwise prevailing. The type of pressure conditions prevailing with the butter device present are illustrated by the curve H of FIG. 5, where it can be seen that during the critical interval extending from one-fourth to one-half cycle after B, the pressure is substantially above that prevailing without the buffer device as illustrated by the curve G.

By limiting the area of the orifice 56 on my buffer device, I am able to effect the desired increase in pressure during the critical interval without harmfully interfering with the rate at which pressure builds up within the interrupter. In this regard, the limited area of the orifice limits the amount of oil flowing into the butter device to a value which does not harmfully interfere with the rate of pressure build-up inside the interceptor. Thus, if the contacts should be separated at some point in the current wave that necessitated an immediate high dielectric strength, say one fourth cycle after contact separation, there would still be suflicient pressure available to prevent a restrike despite the presence of butter device 50.

In interrupters of the general type shown in the drawing (having from one to four breaks and capacitance current interrupting ability up to 600 amperes), my tests and calculations indicate that the orifice area should be be- 5 tween 0.1 and 1.0 square inch and the compressible volume of the butter device between 1 and 18 cubic inches. In general, the larger the volume of gases generated by a given interrupter during capacitance current interruption, the larger should be the orifice area and the larger should be the volume (within the above-described area and volume ranges). The ratio of the volume in cubic inches to the area in square inches should be between 3 and 20. In an orifice area of a size appreciably exceeding 1.0 square inch is utilized, then the butter device will detrimentally delay the pressure build-up, whereas an area appreciably smaller than 0.1 will not allow sufiicient oil to flow into the buffer device to render it eifective when the pressure is subsiding from its peak. Similarly, a

volume of excess or insuificient size will render the butter device ineffective during the time the pressure is subsiding from its peak.

It is preferable to provide a butter device such as 50 for each break of the interrupter and to locate such bufier devices as close as possible to the arcing regions, but if for some reason this is not practical, then a single butter device communicating with the fluid at all of the arcing regions may be employed. The dimensions specified hereinabove are for a single buffer device for the entire interrupter. If a plurality of buffer devices are utilized, then the recommended dimensions should be divided by the number of buffer devices used. If a buffer device is to be utilized for each break, the butler device 50 could serve as the buffer device for break 9 and a similar buffer device at 50a could serve as the buffer device for break 8. Locating the buffer devices near the arcing regions is desirable in that this proximity lessens the amount and mass of oil which the gas pockets, in expanding during the low pressure interval, must displace toward the arcing region in order to perform their desired pressure-maintenance function.

It is to be noted that the buffer device 5th is positioned with the recess 54 disposed above the diaphragm rather than below it. This positioning helps to prevent any loss of air in the event that the diaphragm should develop a leak and, thus helps to assure continued availability of the gas volume in the buffer device 50.

Although I prefer to use a flexible diaphragm for effecting isolation between the liquid in the interrupter and the gas pocket in the buifer device, it is possible to use, as an alternative to the diaphragm, a piston disposed between the liquid and the gas. Such a device is shown in FIG. 6 Where the butter device is shown as comprising a cup-like member 76 having a smooth cylindrical bore 72 in which a piston 74, corresponding to the diaphragm 55, is slidably mounted. The piston is disposed internally of an orifice 76 provided in a cover 77 for the buffer device. The orifice area and the compressible volume of the modified buffer device are substantially the same as those set forth in connection with FIGS. 1 and 4. Likewise the modified bufier device would be located in the same locations as the device of FIGS. 1 and 4.

While I have shown and described particular embodiments 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, intend in 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 an electric circuit interrupter for interrupting capacitance currents, a housing containing arc-extinguisl1- ing liquid, means for establishing a circuitinterrupting are within said housing, means defining an exhaust passage for venting arcing products from the region of said are to the exterior of said housing, means for substantially closing off said housing during certain capacitance current interruptions comprising a normally-closed pressure-responsive exhaust valve located in said exhaust passage,

r 9 r a pump operable upon establishment of a capacitance current are within said housing to bulid up a pressure within said housing, a buffer device submerged within said liquid and containing a pocket of gas which is compressed by the pressure developed within said housing during initial operation of said pump, said compressed gas expanding in response to a transient drop in pressure following a pressure peak to increase the instantaneous pressure Within said interrupter to a level substantially exceeding the pressure that would be developed without said buffer device, said buffer device comprising means defining a limited area orifice for reducing the flow of pressurized liquid into compressing relationship relative to said gas pocket to such an extent that the pump can initially biuld up pressure within said housing at a rate and to a level sufficiently high to substantially maintain the ability of the interrupter to prevent restrikes during initial pressure build-up as compared to a corresponding interrupter without the bufier device, said housing having its free internal space outside of said buffer device substantially entirely filled with said arc-extinguishing liquid just before an interrupting operation.

2. In an electric circuit internupted or interrupting capacitance currents, a housing containing arc extinguishing liquid, means for establishing a circuit interrupting arc within said housing, means defining an exhaust passage for venting arcing products from the region of said are to the exterior of said housing, means for substantially closing old said housing during certain capacitance current interruptions comprising a normally-closed pressure responsive exhaust valve located in said exhaust passage, a pump operable upon establishment of a capacitance current are within said housing to build up a pressure within said housing, a bufier device submerged within said liquid and containing a pocket of gas which is compressed by the pressure developed within said housing during initial operation of said pump, said compressed gas expanding in response to a transient drop in pressure following a pressure peak to increase the instantaneous pressure within said interrupter to a level substantially exceeding the pressure that would be developed without said buifer device, said butter device comprising means defining a limited area orifice for reducing the flow of pressurized liquid into compressing relationship relative to said gas volume, said orifice having an area of between 0.1 and 1.0 square inch, said pocket of gas having a compressible volume of between one and 18 cubic inches, the ratio of said volume to said area being between 3 and 20, said housing having its free internal space outside of said buffer device substantially entirely filled with said are extinguishing liquid just prior to an interrupting operation.

3. In an electric circuit interrupter for interrupting capacitance currents, a housing containing arc-extinguishing liquid, means for establishing a circuit interrupting are within said housing, means defining an exhaust passage for venting arcing products from the region of said are to the exterior of said housing, means for substantially closing off said housing during certain capacitance current interruptions comprising a normally-closed pressure-responsive exhaust valve located in said exhaust passage, a pump operable upon establishment of a capacitance current are within said housing to build up a pressure within said housing, a plurality of butter devices submerged Within said liquid and each containing a pocket of gas which is compressed by the pressure developed within said housing during initial operation of said pump, said compressed gas expanding in response to a transient drop in pressure following a pressure peak to increase the instantaneous pressure within said housing to a level substantially exceeding the pressure that would be developed Without said buffer devices, said buffer devices each comprising means defining a limited area orifice for reducing the flow of pressurized liquid into compressing relationship relative to said gas pocket to such an extent that the pump can initially build up pressure with-in said interrupter at a rate and to a level sufficiently high to substantially maintain the ability of the interrupter to prevent restrikes during initial pressure build-up as compared to its corresponding interrupterwithout the buffer device, said housing having its free internal space outside of said buffer devices substantially entirely filled with said arcextinguishing liquid just prior to an interruption.

4. The interrupter of claim 3 in which the total orifice area of said buffer devices is between 0.1 and 1.0 square inch, the total compressible volume of the gas pockets in said bufier devices is between 1 and 18 cubic inches, and the ratio of said total volume to said total area is between 3 and 20.

5. The interrupter of claim 3 in which there is provided means for establishing at least one additional circuit interrupting arc in said housing and in which each of the arcing regions within said housing has one of said butter devices located closely thereadjacent.

6. The interrupter of claim 3 in which there is provided means for establishing at least one additional circuit-interrupting arc in said housing and in which at least one of the arcing regions has one of said butler devices located closely thereadjacent.

7. The interrupter of claim 1 :in which said buffer device includes a resilient diaphragm isolating said gas packet from said arc-extinguishing liquid and disposed between said orifice and said gas pocket.

8. The interrupter of claim 1 in which said buffer device includes a slidable piston isolating said gas pocket from said arc-extinguishing liquid and disposed between said orifice and said gas pocket.

9. The interrupter of claim 3 in which'at least one of said buffer devices include-s a resilient diaphragm isolating said gas pocket from said arc-extinguishing liquid and disposed between said orifice and said gas pocket.

References Cited in the file of this patent UNITED STATES PATENTS 2,061,945 Koppelmann et al Nov. 24, 1936 2,160,673 Prince May 30, 1939 2,749,412 McBride et a1. June 12, 1956 2,927,181 Schneider Mar. 1, 1960 FOREIGN PATENTS 626,525 Germany Feb. 28, 1936 518,314 Great Britain Feb. 23, 1940

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