US2909633A

US2909633A - High tension oil switch

Info

Publication number: US2909633A
Application number: US639266A
Authority: US
Inventors: Donald M Umphrey
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-02-11
Filing date: 1957-02-11
Publication date: 1959-10-20
Anticipated expiration: 1976-10-20

Description

Oct. ZO, 1959 D. M. UMPHREY HIGH TENSION OIL SWITCH 2 Sheets-Sheet 1 Filed Feb. 11, 1957 ah a INVENTOR. DON/?LD M. #MM-len* Oct. 20, 1959 D. M. UMPHREY 2,909,633

` HIGHVTENSION OIL SWITCH Filed Feb. ll, 1957 2 Sheets-Sheet 2 INVENTOR.

Dvw M. UMHtEV F's- 13'??? i; 5%

United States Patent HIGH TENSION OIL SWITCH Donald M. Umphrey, Palo Alto, Calif.

Application February 11, 1957, Serial No. 639,266

8 Claims. (CI. 200-150) This invention relates to switches or circuit breakers (as herein used the terms are interchangeahle) adapted for use in high-tension power systems carrying heavy currents, and particularly to switches of the minimum oil type.

Except for so-called disconnect switches, which are not intended to be operated, when the circuits supplied through them are under load, all swtching mechanisms currently employed in high-tension power systems comprise three basic units; a pair of Contacts, connected respectively to the two sides of the circuit to be opened, an Operating mechanism for closing the Contacts to complete the circuit or separate them to break it, and some form of interrupter for quenching and deionizing the arc that is inevitably formed when the contacts are separated.

It is always desirable to interrupt the circuit at an instant of zero current occurring as soon as possible after the contacts part, but the circuit does not open until the are is quenched. The interrupter is therefore an extremely important part of the combination.

Many forms of interrupter have been devised, using, variously, air blasts for sweeping the ionzed gases resulting from the arc out of the arc path, magentic blowouts, and in oil-type switches, various means of injecting oil for deionizing, cooling, and condensing the gas. The present invention relates to oil switches, and therefore only the various factors entering into the operation of switches of this type will be discussed herein.

What happens when a high tension circuit is broken depends to a -very great eX-tent upon both the'nature of the circuit involved (i.e., whether it is primarily inductive, capacitive, or resistive) and upon the load that the circuit is carrying at the instant of the interruption. When a short circuit occurs on a power line the fault current is usually limited by the inductive reactance of the circuit to a few times normal, full load value and accordingly the voltage leads the current by nearly ninety electrical degrees. Opening the circuit suddenly with material current flowing would result in a tremendous inductive kick, which could result in many times the normal system voltage appearing across the contacts, tending to restrike the arc. This effect is minimized if the arc breaks at or near the instant of zero current, but nevertheless when it does break the full line voltage appears across the Contacts, plus a transient oscllation at the natural frequency of the system that can raise the total voltage to about double that normal to the line. To prevent the arc restriking high dielectric strength must be interposed in the arc path as soon as possible after the break. If the circuit is capacitive and is opened under very light or no load other than that required to charge the circuit, the transients resulting from opening the circuit can result in voltages several times as high as those nominally effective across the leads to be opened, and another set of conditions must be met. Moderate loads and different circuit characteristics can involve still different requirements. Circuit breakers have been built that will ice operate entirely satisfactorly to break heavy short circuits, but that fail under conditions apparently much less severe.

Oil-type circuit breakers have the advantage that the oil in which the separable contacts are immersed has a high specific heat and heat of vaporization and is therefore effective in cooling and deionizing the are. It also has a higher dielectric strength than air under atmospherec pressure. Furthermore, oil immersed parts are protected from condensing moisture and are protected from hygroscopic ionization over long periods of time.

The use of oil immersion, however, introduces problems that are mechanical and hydraulic, as well as electrical, 'and that are not always recognized in interrupter design. Oil immersion does not and in fact must not prevent the formation of the arc, which consists of a column of very hot, ionzed gas resulting from vaporizaton of the oil and the metal of the Contacts. The instant of the cycle at which the Contacts start to separate is unpredictable, and the arc must be maintained until the current approaches zero to prevent destructive voltage surges. Energy is released into the arc at a rate proportional to the square of the instantaneous current times the arc resistance. The latter is a direct function of the arc length and an inverse function of its temperature, among various other factors.

Accordingly, if the contacts start to separate at the epoch of the cycle When current is starting to rise, energy is released at a constantly increasing rate, both because of increasing length of the gap between the contacts and because of the rise of current in the cycle. If, at this stage of the operation, the arc is cooled, the resistance will rise still further and more energy will be released, to vaporize more gas and increase the pressure, sometimes to a degree that will cause an explosion of the interrupter structure. To have a high resistance arc at this instant is therefore a disadvantage. As current starts to drop toward zero, however, cooling of the arc promotes deionization and more rapid final interruption. When the gas has been deionized the effective resistance of the path to breakdown and reestablishment of the arc is a direct function of pressure.

During the high-current epoch of the cycle the hot gases tend to expand, and if the explosive efi ects mentioned are to be prevented they must be given an escape path. In so escaping they have very high velocities and considerable inertia. As a result of their nish from the arc region the pressure in the are path may subsequently drop to a very small fraction of an atmosphere so that the arc can restrike immediately following the initial break, for the rate at which pressure is generated within the arc varies substantially in phase with the are current, but the velocity imparted to the escaping gas lags the pressure and the result is frequently a rarefaction at the'instant when maximum pressure and dielectric strength are most necessary. The inertia of any mechanical relief valve would prevent its Operating fast enough to cope with the rapidly changing conditions.

The energy in the heated gas can only be dissipated through its expansion or by cooling and condensation through the absorption of its energy by heating or accelerating the surrounding oil. In the usual, tank-type of circuit breaker very large amounts of oil may be employed, frequently as much as is required to fill a railway tank car. If the breaker mechanism is immersed in such a tank there is normally ample room for the hot gases to expand and ample liqud to cool and condense them. As has been shown in a prior patent of the present inventor, however, in types of equipment where oil is injected into the are path to increase its resistance and cause an early break, there may be released into the large body of oil that such breakers require, bubbles of large size which offer relatively small surface in comparison to their Volume. Heat can be absorbed only where the vapor comes in contact with and can be condensed by the cool oil. The released bubbles first expand and then, cooled by their own expansion, contract, resulting in pressure oscillations in the device. These pressure changes occur at unpredictable phases of current flow within the arc and can lead to serious and unexpected results.

The Volume of liquid oil involved in direct cooling of the vapors is relatively small in any breaking operation. This has led to the design of so-called minimum oil types of switching mechanism. Because of the pressure eiTects discussed above and the liability of explosion in interrupting Currents resulting from heavy faults, breakers of this latter type have not come into as general use as they might, in spite of their advantages of relatively small size, and particularly their saving in oil, for they use only a very small fraction of that required in tanktype switching equipment.

The primary object of the present invention is to provide a minimum oil type of high-tension switch or circuit-breaker capable of opening high tension, high power circuits under any condition of short circuit, load, or open circuit. Contributin g to this broad purpose, among the objects of the present invention are to provide an interrupter structure and actuating equipment therefor, operative to maintain in the arc path operative conditions that change from instant to instant so as best to break the arc and prevent its restriking, irrespective of the nature of the circuit broken, to provide means for relieving excessive pressures within the interrupter under abnormal conditions of operation so that the above referred-to explosion cannot occur, to provide relief means of a type that will not lead to the formation of a region of less-than-atmospheric pressure following its operation but, instead, will raise the pressure and dielectric strength of the gases within the interrupter and prevent re-establishment of the arc, to provide a means of cooling and condensing the arc-formed gases that does not result in raising materially the resistance of the arc during periods of maximum current but that is effective in cooling and deionizing the gases as the current approaches the zero points in the alternating current cycle, to provide means for driving the condensing oil that is independent of the intensity of the arc, and to provide such driving means that is ready for instant operation as soon as the switch Contacts start to separate and is driven by the actuating mechanism that opens the circuit but that does not tend to retard the movement of the contacts and thus prolong the period during which the arc might persist or restrike. Other advantageous features of the invention will become apparent in the course of the present specification Considered broadly, the invention comprises the usual stationary contact and a contact movable to close a circuit with the stationary contact or to separate from the latter forming an arc path therebetween. An interrupter surrounds the arc path so as to form an arc chamber. The interrupter also has formed within it an exhaust passage for the escape of gases generated in the art, connected to the arc chamber by at least one and preferably several exhaust ports. Also formed in the interrupter is a nozzle terminating in an orifice adaptcd to direct a jet of oil directly into each exhaust port. Means are provided for actuating the movable contact to close or open the circuit, and a pump, Operating simultaneously with the separation of the Contacts, is connected with the jet-forming orifices in the interrupter.

In order to insure positive action and high pressure and velocity in the jets the pump preferably comprises a piston actuated by a spring. The piston is interconnected with the contact-actuating means by means of an abutment on the latter which stresses the spring when the contacts are closed. The force used to retract the piston and stress the spring can be applied by any one of the number of conventional mechanisms, such as a solenoid, a compressed air or hydraulic piston, but it is important that after the closure is complete no restraining force is applied by the actuating mechanism other than that inherent in its own inertia. When the switch is tripped, it is the spring that provides the energy to accelerate the movable contact, 'causing it to start to separate from the fixed one. At this initial phase of the opening operation the velocity of the oil is relatively low and it offers a small part of the resistance to the relaxation of the spring, most of its energy going to the acceleration of the mechanism. As the velocity increases, however, the damping of the piston increases as a power of its velocity, but it cannot restrain or retard the separating motion of the Contacts, as has occured with prior types of interconnected mechancal pump and contact mechanisms, for the abutment can leave and run ahead of the piston to permit maximum contact separation in minimum time, while the spring continues to direct the oil jets into the exhaust ports even after separation of the contacts has occurred. The action of these jets changes as conditions change within the arc chamber and can best be described after the detailed description of the preferred form of the invention, which follows.

This description is illustrated by the accompanying -drawings, wherein:

Fig. 1 is a vertical sectional view of a high-tension circuit breaker of switch of the minimum-oil type, embodying this invention; l

Fig. 2 is a plan view of the apparatus of Fig. 1, the plane of section of the first figure being indicated by the lines. 1-1 of Fig. 2;

Fig. 3 is a horizontal sectional View, on a larger scale than Fig. 1, of the interrupter embodied in the structure illustrated, the plane of section being indicated at the line 3-3 of Fig. 1;

Fig. 4 is a vertical sectional view of the same interrupter, the plane of section being indicated by the lines 4 4 of Fig. 3;

Fig. 5 is a detailed view of an oil-circulating device that may be added to the structure illustrated in Figure 1;

Fig. 6 is a horizontal sectional view, generally similar to Fig. 3, of a modified form of interrupter structure; and

Fig. 7 is a vertical sectional View through the structure illustrated in Fig. 6.

The embodiment of the invention illustrated in Fig. 1 comprises an oil reservoir 1, which forms a base upon which the entire structure rests. The top of the reservoir is closed except for a circular opening through which there extends the lower end of an insulating support column 3 that fits snugly within the opening. The support column is tubular and Bakelite laminate is a satisfactory material for its purpose.

A ridge 5, formed on the top of the reservoir 1 and surrounding the column 3 supports a flange 7, closely surrounding the support cohunn. A porcelain bushing or weather-shield 9 rests upon the flange and extends a little less than half way up the column. The bushing and support column are coaxially mounted and there is space between them that forms an annular oil passage as will be described below.

A metal contact ring 11 rests, in turn, upon the bushing 9. The ring is preferably of U-shaped cross section with the bottom of the U directed outwardly. The interior diameter of the ring is the same as that of the bushing on which it rests. A second bushing, 9', substantially identical to the bushing 9 rests, in turn, upon the contact ring 11, and an upper housing 13 is mounted on the top of the bushing 9'; the open bottom of the housing being bounded by an in-turned fiange 15 of substantially the same internal diameter as the bushing, on which the housing rests.

`bolted or welded thereto; it is provided with a downturned vent pipe 18 that permits entry or escape of air but eXcludes rain. Gaskets 19 are interposed between the weather-shield bushings and the flange 7, contact ring 11, and flange 15, respectively, and the whole outer structure is held in place by compression of heavy springs 21 hearing down on the flange from above.

The springs 21 react against an outwardly extending fiange 23 on a generally cylindrical tension ring 25. The lower ends of the tension ring are turned slightly nward to fit closely around the upper end of the column 3, where they bear against a snap-ring 27 fitted in a groove formed at the top of the column. The lower end of the column is similarly held by a snap-ring 27' hearing against the flange 7. Springs 21 therefore simultaneously tension the column 3 and conpress the outer structure, clamping the whole assembly firmly together.

The switch mechanism proper is mounted substantially entirely within the insulating column 3. Starting at the top of the column, a supporting spider 29 is firmly secured to the upper side of the flange 23. A strap 31 connects the spider to the housing 13, and the housing forms one external terminal of the switch, one side of the circuit to be controlled by it being connected, as by a strap or bus 33. A cluster of stationary spring contact fingers 35, of conventional type, is mounted centrally of the lower side of the spider and is surrounded by a tubular ring 37, extendng downward completely to enclose the contact fingers. The lower end of the ring 37 abuts against the uppermost of a series of

baflies

38, 39 and 40, the form of which can best be seen in Figs. 3 and 4.

All of the bafies have a central opening 41, extending through them, which form the arc chamber of the interrupter. For descriptive purposes, each of the bafiles can be considered as being formed of a disc of fiber or other suitable material, fitting tightly within the column 3 but with certain portions cut away from each disc. All except the top baffie 38 have an arcuate section cut away from one edge to form an oil passage 43. All except the lowest bafe 40 have portions on each side cut away to form an exhaust passage 45 that opens into the upper housing 13 through the spider 29. The intermediate bafiles are grooved part way through, on opposite faces of adjacent discs, so that the igrooves coact to form a number 'of oil passages or channels. One such channel, 47, extends transversely across the baffles forming an initial portion of the exhaust passage and this channel 47 con- -nects into the arc chamber 41 through an exhaust port 49. Opposite the exhaust port a tapered channel 51 comprises a jet-forming nozzle which directs a stream or jet of oil directly into each exhaust port 49 when pressure is applied to oil in the passage 43, as will later be described. The interrupter structure is retained in place by snap ring 53 that bears against the lower side of baffie 40, the rest of the baffles beingretained in place through the pressure applied against the spider 29 and tubular ring 37.

The moving contact, that cooperates with the fixed contact 35 to break the circuit, consists of a straight rod 55 mounted to reciprocate axially of the column 3. The contact rod 55 is Secured, by means of a fitting 56, to the upper end of an insulating actuating rod 57, which may be of wood, suitably treated, or of Bakelite tubing. The lower end of the actuating rod connects through a fitting 59 to a straight-line linkage of conventional type, later to be described.

The second external contact to the switch is made with the bus or lead 61 to the contact ring 11. This connects, in turn, through a jumper 63 and bolt 64 to a ring 65 that carries a pair of frusto-conical grading shields 66 and 67, the former extending downward from the ring while the latter extends upward. The shields are each provided 'with central apertures through which the contact rod 55 and actuating rod 57, respectively, project, and each is provided with additional apertures 69, which permit the free passage of oil through them. A similar grading shield, 67', is mounted, apex upward, in the base of the column 3. These shields serve to distribute the dielectric stresses set up when the switch is open.

A cluster of contact fingers 71, electrically continuous with the ring 65, is mounted within the shield 67, making continuous, sliding contact with the rod 55 both when it is fully extended to within the cluster 35 and when it is fully retracted. A fiexible pigtail connection could, of course, be substitutedfor the contact fingers 71, but would be more likely to fail through repeated flexing and therefore the contact cluster is preferred.

The mechanism for actuating the Contacts is mounted on a pump cylinder 73 that projects laterally from one side of the base reservoir 1. The inner end of the cylinder is surrounded by a jacket 75, forming an o il passage that connects with the space between the flange 7 and the ridge 5; one or more ports 77 connect this passage with the interior of the cylinder 73, and the passage, in turn, :connects to the space between the column 3 and the Weathershields 9 and 9' through a plurality of ports 79.

The cylinder opens directly into the reservoir. Within the cylinder a piston 83 is slidably mounted upon a reciprocating shaft 85, formed forward toward the reservoir by high energy spring 87. Check valves 88 in the piston,

normally open, close when the piston is moved forward. The piston normally bears against a head 89 on the end of shaft 85, so that forward motion of the piston carries the shaft with it.

The inner end of the shaft is pivoted to a connecting link 91 which is, in turn, pivoted to a bell-crank link 93 mounted on a fixed fulcrum 95. A second fixed fulcrum 97 carries a link 99, to the free end of which is attached link 101. The fitting 59 pivots on the other end of this last-mentioned link, while the longer end of bell crank link 93 pivots at a point between the two ends such that vertical, straight-line motion is applied to the rods 57 and 55.

The pump piston and linkage are operated by a conventional actuating mechanism 103, which may take any of several forms and the nature of which does not concern the present invention. Its function is to retract the actuating shaft and with it the piston 83. It may be operated pneumatically, hydraulically, or electrically, and its nature is ir'material as long as it will apply sufiicient force to the shaft to retract it against the pressure of the spring 87. It also incorporates a conventional release or trip mechanism which frees the shaft 85, perrnitting the spring and piston to drive it forward, thus retracting contact rod 55 and opening the switch. Such mechanisms also normally include a snubber for decelerating the moving parts during the last portion of their travel.

In placing the switch in operation it is filled with oil (including, in the term oil, any insulating liquid of low vapor-pressure and high dielectric strength which would serve the same function) at substantially the level within the housing 13 indicated at 105, it being noted that this level is well below the inner end of vent 18. Care is taken to see that all of the oil passages within the switch are completely filled and no air bubbles are included. It should be apparent that these passages comprise a complete circulating system, from the portion of the cylinder ahead of the piston 83 as it moves in response to the pressure from the spring, into the reservoir in the base, thence up through column 3 and passage 43 through the nozzles 51 and

exhaust passages

45 and 47 into the housing 13. The return passage leadsout of the housing 13 through the interspace between column 3 and the weathershields 9 and 9', through

ports

79 and 77 back behind the piston.

When the switch is closed the rod 55 extends between the fingers of cluster 35 substantially to the top of the chamber within which they are mounted. The contact rod 55 practically fills the arc chamber 41, so that 'although there is a small annular aperture surrounding the rod, which offers some opportunity for oil to enter the arc chamber and after vaporization escape through the exhau'st ports and into the housing 13, this route is very small in comparison with that through the nozzles 51 and can be neglected in considering the operation of the device.

The cross-sectional area of the nozzles is very small in comparison with those of the other passages comprising the circulatory system and hence when the switch is tripped and the piston moves forward nearly all of the pressure drop between the advancing end of the piston and the atmospheric pressure within the housing 13 takes place in the nozzles, wherein the pressure head is converted to a velocity head in the jets directed into the exhaust ports leading from the arc chamber. Disregarding skin friction, the energy expended in the nozzles rises as the square of the velocity.

When the switch is tripped the energy delivered by the spring is divided between the acceleration of the oil and that of the contact mechanism and because in the initial phase the amount of energy absorbed by the oil is small, practically all of the energy goes to the acceleration of the mechanical parts. The contact rod 55, accordingly, acquires a large part of its ultimate Velocity before breaking contact with the cluster 35. As acceleration increases, however, the pston absorbs more and more of the energy of the spring, the latter becoming somewhat less, of course, as the spring relaxes. From a point shortly after the contact separation the contact mechanism practically coasts, and almost the entire remaining energy in the spring is expended in forcing the oil through the nozzles to form the jets. Normally, the contact mechanism will not run ahead of the piston, but if the motion of the latter should be accidently checked by clogging of the oil passages or otherwise, this will not prevent continued separation of the Contacts and eventual breaking of the arc.

Even before the fixed and moving Contacts have separated, therefore, there are powerful jets of oil emerging from the nozzles 51 and directed across the eXhaust passages 47 toward the exhaust ports 49 from the arc chamber. At this phase of the operation the jets cannot enter the arc chamber, which is filled with a solid column of oil surrounding the contact rod. As a result the sole effect is to create a region of high turbulence within the exhaust port where the direction of the jet is changed and the oil diverted into the exhaust passage 47 and thence up toward the housing 13. As soon as the contacts separate, however, this condition changes; the oil in the arc path instantly vaporzes and is raised to a very high temperature, thus increasing enormously in Volume, resulting in a high pressure that first blasts the plug of oil out of the port and then follows it up with a stream of vapor movng at high velocity which meets the jet head-on and atomizes it into the bubble of escaping vapor in the passage 47. This greatly increases the surface of the oil from the jet that is exposed to the hot vapor, in an area of intense turbulence. In the hottest part of the blast from the chamber evaporation of the droplets occurs. This effect is accompanied by a large amount of cooling, both as a result of the expansion and absorption of heat by the evaporation. At greater distances from the exhaust port the vapor is further cooled and condensed on the droplets as nuclei so that by the time the mixture of vapor and oil droplets has traveled as far as the main exhaust passages 45 the amount of oil in the vapor phase is relatively small. Under ordinary circumstances all of the vapor will be condensed by the time any bubbles have reached the oil level in the housing 13, any bubbles remaining being composed of the fixed gases which result from decomposition of the oil in the intense heat of the arc.

Except as they are retarded by impact of the gas molecules emerging from the exhaust ports the particles of oil emerging from the jets retain their momentum and as a result they establish a dynamic pressure at the outlet 'of the exhaust port that approaches the pressure delivered by the pump. Accordingly, the pressure within the arc chamber is maintained at something approaching this value, but cannot materially exceed it. The jets therefore act as relief valves from the arc chamber and prevent the pressures within it from rising to a value which could explode the interrupter. During the epoch of the current cycle when the current is increasing and the Volume and temperature of the vapor within the arc are rising the oil droplets never reach the ionized vapor that forms the actual arc. They do not, therefore, increase the arc resistance and the amount of energy liberated within it, but they do cool and deionize the escaping gas or vapor very rapidly once it has left th arc path proper.

As soon as the current in the arc starts to fall, with smaller release of energy, the oil from the jet enters deeper and deeper into the exhaust ports, maintaining the pressure within the arc chamber and preventing it from dropping below atmospheric, immediately following the break, because of the momentum of escaping gas, as can happen in conventional types of interrupter. At zero current, where the arc breaks, the arc chamber is filled with either a solid column of liquid or of deionized vapor at a pressure held well above atmospheric through the injection action of the jets and the dynamic pressure from them. The previous arc path therefore offers maximum dielectric strength and hence resistance to further breakdown and restriking as the voltage of the system as a whole recovers.

It must be realized that the successive phases of the operation that have been described take place in an interval of a few milliseconds at most. Whether the arc is finally broken so that it cannot reestablish itself at the first current zero depends upon a number of factors, particularly the nature of the circuit conditions at the instant the contacts first open. If their occasion for opening is a heavy fault on a reactive circuit zero current coincides with near maximum voltage so that practically the entire voltage of the system may be available to restrike the arc before material separation of the Contacts can occur. If reactance of the circuit is capacitive, as in opening an unloaded transmission line, recovery voltage may be double or more times the normal voltage of the system, this being a particularly difficult situation to meet. A breaker that will fully and finally open a circuit under all conditions of load Within three cycles of a siXty-cycle supply is usually considered to be an extremely rapid one; the structure here shown will better this situation under almost all conditions of operation.

Many types of Operating mechanism which may be used as the element 103 include provisious for reclosing automatically after the circuit has been fully opened, so that if a fault which has caused operation is of intermittent nature and clears itself, as may be the case where the fault is a fiashover following a lightning stroke, service will be interrupted only momentarily. Automatically closing devices usually will operate to restore the circuit once or twice before finally remaining open. If any ionized gas or vapor remains in the arc path after a first operation on a contnuing fault, the second and third interruptions Will be increasingly diificult, and this fact has caused trouble in many prior circuit-breakers. It is practically impossible for it to occur with the struc ture of this invention, for as soon as the arc has finally broken the jets fill the arc chamber with a solid column of oil and a second operation takes place under almost exactly identical conditions to the first, except, perhaps, for the phase of the fault current at the instant that the Contacts separate.

The oil discharged into the housing 13 during a breaking operation is relatively hot, for it has absorbed the &909333 9 energy dissipated within the are itself. As fast as it treaches the housing, however, it returns toward the pump through the passage between the column 3 and the weather shields 9 and 9' and during this return it is dispersed against a large cooling surface.

During a breaking operation the return is rapid. The inertia of the oil surrounding the column 3 is considerable and the very rapid acceleration of the piston 83 may leave a void behind it. As the oil surrounding the column accelerates to fill the void there could result a very serious hydraulic Shock at the instant the void fills, bringing its motion to a sudden halt, which could be severe enough to break the Weather-shields 9, 9'. This is prevented by restricting the passage 77 to a value that will damp the flow of oil into the void and thus so restrict its velocity as to hold the impact resulting when p it is stopped to a safe value.

Somewhat similarly, a severe inechanical shock could result from the checking of the motion of the moving contact and its associated mechanism at the end of the opening operation. As was mentioned above, this is prevened by incorporating within the actuating mechanism 103 a dashpot or equivalent clamping device that comes into operation after the tip of the contact rod 55 has left the lower opening in the contact chamber. The mechanism is therefore gradually decelerated over the interval between the time when the tip of the rod 55 leaves the interrupter structure until it comes to rest with its tip at the level of grading shield 67.

The closing operation is more gradual and less violent than is the opening operation. In this case it is the head on the shaft 85 that drives the piston 83, instead of the reverse. The check valves 88 open during the operation, permitting relatively free flow of oil from behind the piston into the open end of the cylinder. The springs 90 are arranged to hold the check valves partially open, but these springs are light so that the valves close as soon as the piston starts to move forward when the switch is tripped.

Cooling of the current-carrying parts of the switch can usually be accomplished satisfactorily by convection. Oil heated from these parts within the column 3 rises, while that cooled in the descending channel outside of the column falls as a result of its greater density, the partially open check valves 88 permitting its return to the reservoir to repeat the cycle. At the relatively slow velocities involved in such thermosyphon action, the various restrictions in the passages impede the flow but little. During the breaking and reclosing operations this type of convection flow is supplemented by the forced flow from the pump.

The principal source of heat in the breaker is the resistance loss in the Contacts. Normally the therrnosyphon circulation is suflicent to carry ofi the heat so produced, but where usually heavy loads are carried for long periods this may not be the case. In situations where this is likely to occur the construction shown in Fig. l can be modified to provide a forced circulation in the same direction as the thermosyphon circulation just described. In this case the side of the flange 7 immediately above the aperture 77 is modified as shown in the fragmentary Figure 5, to form a housing 107 for a small motor 109 that carries, on the end of its shaft, an impeller 111 that rotates within a somewhat enlarged aperture 77' to keep the oil circulating at all times.

Figs. 6 and 7 show a slightly modified form of interrupter structure which operates on precisely the same principle as does that of Figs. 4 and 5, but differs in that the exhaust ports and jets formed between successive baflles alternate between opposite sides of the arc chamber. EXcept for the fact that each of the baflles 38', 39' has formed in it an additional passage 43' and that the grooving which forms the exhaust passages 47', exhaust ports 49' and nozzles 51' is formed on both sides of each baflle, facing oppositely with respect to the are chamber 41, there is little difierence between the structures. The modification of Figs. 6 and 7 is somewhat more compact, however, and permits more and larger oil channels and jets in an interrupter of gven size.

Although there are certain superficial similarities between interrupters built in accordance with the present invention and those of more conventional types, the apparent slight ditferences in construction lead to very important differences in operation. Many interrupter structures in the past have employed baflles, exhaust passages, and oil jets directed into the are path to increases the arc resistance and accelerate its extinction, In these prior devices the jets have been directed into the arc chamber and either directly into or parallel with the arc path itself. The back-pressure developed against the oil can, in such a case, rise to a very high value and even reverse the flow of oil, and therefore in this type of breaker conventional practice has involved some pumping means operated independently of the breaker Operating mechanism, even though a mechanical pump may be used in addition to operate when breaking light loads. One of the most usual arrangements employs an auxiliary pair of Contacts arranged to open pioto the 'main arc within the interrupter structure to form an auxiliary gap within a closed chamber, the pressure developed by vaporization of oil within the chamber energizing the jets within the body of the interrupter. With this arrangement, under very heavy shorts, the pressures can rise to extremely high values. With the present arrangement the back pressure that can be developed at the orifices of the jet-forming nozzles cannot under any circumstances rise high enough to decrease the velocity of the oil in the jets to any material degree; the arrangement that permits the Contacts to overrun the piston is primarily a safety device to permit the contacts to open in case of clogging of the oil passages or some other abnormal event.

That the rise in pressure at the nozzle orifices is relatively small should be apparent from the fact that as the gas is emitted from the exhaust ports it expands freely, first into the relatively much larger passages 47, leading in turn to the still larger passages 45, against only the relatively small hydrostatic head of the column of oil from the passages up to the surface plus the inertia of the oil displaced by the expansion. Accordingly, there may be a pressure transient during the phase of rising pressure that is effective against the nozzle orices, but it cannot be either large or continued long enough to retard the flow of oil to any material extent. The pressure in the arc chamber lags the current flow by only a few milliseconds at most, and is very nearly in phase with the current; the velocity of the emergent gases lags slightly behind the pressure. This phase of rising current and pressure is marked by intense turbulence, as the emerging blast first meets the jets head-on and its course is changed through the exhaust passages. This results in complete admixture of the resulting droplets with the vapor and continuing cooling of the gases and condensation of the vapor. t

At the instant that an opening operation starts, before the contacts have separated, oil can and does flow into the arcing charnber and up into tubular ring 37 to fill the void left by the withdrawal of the contact rod 55. The instant arcing starts, however, influx of oil into the arc chamber ceases; the vaporization of the oil and its intense heating cause it to increase in Volume much more rapidly than is necessary to fill the void left by the retreating contact rod and its only escape path is through the exhaust ports, for the pressure within the column 3 is more than adequate to prevent escape of the vapor around the rod even if it had any place to go if it did escape through this path. It Would be quite possible to run the rod into the interrupter through a seal, but the pressure gradients are such as to make this unnecessary. More and more vapor forms as the are length increases, until the current also starts to decrease and the pressure starts to fall. As soon as this occurs, however, the jets can enter first the exhaust ports, and, as energy released in the arc decreases they enter the are chamber itself first as high velocity droplets and later as a solid stream of oil. The time required for the jets to cross the exhaust passage 47 is only approximately two milliseconds. The turbulence within the arc chamber is intense. Both the turbulence and the cooling eflect of the entering oil tend to deionize the arc path with extreme rapidity. Therefore, in this decreasingcurrent phase of the operation, where the increase of arc resistance is advantageous in helping to cause an early break and prevent restriking, the jets cause the desired increase. The momentum of the jets not only conquers the momentum of the escaping gas to prevent the formation of a region of lower-than-atmospheric pressure but establishes a dynamic pressure which may be as high as several atmospheres. Since the dielectric strength of a gas is approximately in direct proportion to pressure, this greatly reduces any tendency to restrike, even if condensation within the arc path is not sufliciently rapid to interpose a solid barrier of oil between the separating Contacts. Observation of interrupters in operation has shown that when the -arc current becomes small and the arc itself stringy it sometimes loops into the exhaust ports. If this occurs with the interrupter of this invention the arc and the jets approach each other in a particularly turbulent and eflective manner. The successive lags between current and pressure, and pressure and velocity may prevent the entry of the jets into the intercontact space at the instant of zero current. it is suflicient, however, that any gas remaining uncondensed is cooled and hence deionized, and that its pressure is high. The arc is completely extinguished be'- fore the moving contact is entirely withdrawn from the interrupter.

lt will be recognized that the effects here described may differ somewhat in the order of their occurrence 'and the duration of their various phases, depending upon the nature of the circuit broken and the load on that circuit, whether normal or a heavy fault current. The arrangement, however, adapts itself to circuit conditions instantaneously to meet the eXigencies of each particular case. First, it provides a relief valve, preventing eXplosive pressures. In phases of heavy current and large evolution of vapor, it efiectively condenses the vapor evolved, but does not inject fresh oil into the arc path to cool it, increase its resistance and thus increase the energy evolved. Only when the pressure starts to fall and increased resistance becomes desirable to cause an early break is oil injected into the are itself, either within the arc chamber or looped out into the connecting passages. During the immediately following phase it eflectively prevents negative pressures. Because it thus responds to instantaneous conditions within the arc, rather than following a fixed cycle of oil injection irrespective of what is happening in the arc path, it is equally effective in opening the circuit under all conditions, whether of heavy short circuit, normal load, or the charging of a capacitive line.

One ef the reasons the device is able to accomplish these ends is that the oil pressure behind the jets is substantially constant and is not dependent upon the intensity of the dischangc. Any device that will supply the necessary pressurc and Velocity could be used in connection with the interrupter 'structure lerein disclosed with advantage over conventional types of interrupter, but in order to obtain the full advantage and completely automatic action described the relatively constant-pressure source is an important feature. Rapid and uniform separation of the Contacts is also important, however. They must not be separated so violently as to wrack the structure to pieces, nor must they be slowed by resistance to the flow of oil from the pump. T e structure shown assures that neither of these undesirable effects can occur.

Numerous modifications of the exact structure are, however, possible. The switch shown is one that would be duplicated in each leg of a polyphase circuit and employs a separate actuating mechanism and oil pump for each leg. It .is obviously possible, by only slight modifications, to use a single actuating mechanism and oil pump to actuate all three legs of a three-phase circuit, for example. The interrupter structure can be modified as to the shape and direction of the various passages within it. The foregoing description and drawings are therefore intended to be merely illustrative, and the scope of the invention defined by the following claims:

I claim:

1. A high-tension electrical switch comprising the combination of elements designated as elements (a) to (d) and defined as follows: element (a), a pair of relatively movable contact members adapted to be 'closed to complete a circuit and separated to form an are-path therebetween; element (b), means for moving at least one of said Contacts to bring the pair thereof alternatively into their closed and separated positions; element (c), an interrupter structure closely surrounding said are-path and having formed therein an exhaust passage, at least one port connecting from said are-path into said exhaust passage anda nozzle adapted to direct a jet of fluid into said port in a direction counter to flow of fluid from said arc-path into said exhaust passage; and element (d), pumping means connected to operate concurrently with element (b) to force a jet of fluid through the nozzle of element (c) as the Contacts of element (a) are separating.

2. A high-tension electrical switch comprising the combination of elements designated as elements (a) to (e) and defined as follows: element (a), a pair of relatively movable contact members adapted to be closed to complete a circuit and separated to form an are-path therebetween;

u element (b), a spring connected to separate said Contacts; element (c), contact-moving means connected to close said Contacts against the action of said spring; element (d), an interrupter structure closely surrounding said are-path and having formed therein an e'xhaust passage, at least one port connecting from said are-path into said exhaust passage and a nozzle adapted to direct a jet of fluid into said port in a direction counter to flow of fluid from said are-path into said exhaust passage; and element (e), a

'pump comprising a piston operative by relaxation of element (b) to force a jet of fluid through said nozzle of element (d).

3. A high-tension oil switch comprising the combination of elements designated as elements (a) 'to (l) and defined as follows: element (a), a base comprising an oil reservoir; element (b), a tubular insulating support column rising out of element (a) to form an oil passage leading therefrom; element (c), an upper housing mounted above element (b); element (d), stationary contact means mounted within element (c), element (e), a contact rod mounted to reciprocate substantially axially within element (b) to engage element (d) and separate therefrom to form an arc-path between elements (d) and (6); element (f), an inter'upter mounted at the top of element (b) and substantially closing the oil passage therethrough when the switch is closed, and having formed therein an axial arc-chamber surrounding said arc path, an exhaust passage opening into element (c),

`at least one eXhaust port connecting said arc-chamber and said exhaust passage and an oil passage leading from the passage within element (b) and terminating in a nozzle adapted to direct a jet of oil into said exhaust port toward said arc chamber; element (g), a pump cylnder opening into the reservoir of element (a); element (h), a piston mounted within element (g); element (i), a spring mounted to actuate said piston to force oil into said reservoir and through element (b) into the nozzle of element (f); element j), an actuating shaft slidably mounted through the axis of element (h) and having means thereon for engaging said piston to be forced forward thereby and to retIact said piston against the action of element (i); element (k), actuating means for retracting element (j); and element (l), a linkage adapted to move element (e) into contact with element (d) When element (j) is 'etracted.

4. The combinaton defined in claim 3 including, in addition, a tubular insulating weather-shield surrounding element (b) as defined in claim 3 and spaced therefrom to form an oil-duet between elements (c) and (g) of claim 3.

5. A high-tension oil switch comprising an oil reser- Voir forming a base for said switch, a tubular nsulating support column mounted on said reservoir and opening thereinto to form an oil passage, stationary contact means mounted at the top of said support column, a contact rod within said column movable axially therein alternatively to close a circuit to said contact means and to separate therefrom to establish an arc path thereto, an interrupter mounted on said support' column adjacent to said contact means so as to substantially close the oil passage through said support column and having openings formed therein to form an arc chamber surrounding said arc path, an exhaust passage opening from said arc path and a nozzle directed to inject oil from said oil passage into said arc chamber across said exhaust passage, a pump cylnder opening into said reservoir, a piston movable within said cylnder, a spring connected to advance said pston to pump oil into said reservoir and said nozzle when released, actuating means for moving said contact rod to engage said stationary contact means, and an abutment on said actuating means engaging said piston to retract it against the action of said spring, whereby upon release of said actuating means said spring will tend to cause separation of said stationa'y contact means and said rod while retardaton of said piston does not retard such separation.

6. An electric switch comprising a pair of separable contacts movable together and apart, selectively, for making and breaking an electric circuit, an interrupter structure substantially surrounding the space between said contacts as they move apart, said structure being provided with an exhaust port having an inner end and an outer end, said inner end opening directly into said space, a nozzle facing said outer end, and means forcing a continuous stream of fluid through said nozzle toward said exhaust port as said contacts separate.

7. An oil circuit breaker comprising a pair of separable contacts, an nterrupter structure defining an arc chamber between said contacts as they separate, an exhaust passage, and an exhaust port connecting said chamber to said passage, a nozzle opening into said exhaust passage opposite and facing said exhaust port, and means forcing a stream of oil through said nozzle toward said port as said contacts separate, whereby the pressure in said chamber is maintained substantially at the impact pressure of said stream of oil.

S. An oil circuit breaker comprising an interrupter structure having an axial opening therethrough definng an open-ended, cylindrical, arc chamber, having a plurality of transverse exhaust passages in non-intersecting relation to said aXial opening, and having a plurality of radial exhaust ports connecting said axial opening to said eX- haust passages, a stationary contact adjacent to one end of said axial opening, a rod-like movable contact extendable through said axial opening into engagement with said stationary contact, means for withdrawing said movable contact through said opening for separating said contacts, whereby the arc forrned between said contacts as they separate is drawn into the arc chamber, a plurality of nozzles opening into said exhaust passages opposite and facing said ports, and means for pumping oil through said nozzles into said exhaust passages as said contacts separate, whereby streams of oil are directed toward said exhaust ports and maintain the pressure within the arc chamber substantially at the impact pressure of the oil stream.

References Cited in the file of this patent UNITED STATES PATENTS 2,055,3l2 Ruppel Sept. 22, 1936 2,064,652 Flurscheim Dec. 15, 1936 2,l55,263 Flurscheim Apr. 18, 1939 2,279,040 Grosse Apr. 7, 1942 2,566,095 Scarpa Aug. 28, 1951 2,668,2l7 Vogelsanger et al. Feb. 2, 1954 2,749,4l2 McBride et al. June 5, 1956 FOREIGN PATENTS 374,500 Italy Aug. 26, 1939 646,848 Germany June 22, 1937 716,296 Germany Jan. 16, 1942 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,909,633 I October 20, 1.959

Donald M Umphrey It is hereby Certified that error appears in the printed specfica'oion of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

column 4, line 30, for "of", first occurrence, read or column 6, line 25, for "formed" read forced column 9, line 22, for prevenecl" read prevented line 55, for "usually" read --umsuall Signed and sealed this 19th day of April l90.

SEAL ttest:

KARL Ho AXLINE ROBERT c. WATSON Attesting Office' Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION October 20, 1959 Patent No. 2,909,633

Donald M.. Umphrey It is hereby Certified 'that error appears in the printed specfication of the above numbered patent requring correction and' that the said Letters Patent should read as corrected below.

Golumx 4, line 30, for "of", first occurrence, read or column 6, line 25, for formedu' read forced column 9, line 22, for

line 55, for "usually" read ---urusually-'-- read prevented "prvened" Signed and sealed this 19th day of April 1.960.

(SEAL) Attest: KARL H AXLINE ROBERT C. WATSON Commissioner of Patents Attestng Offioer