US2385008A - Circuit interrupter - Google Patents

Description

- ;p'1s,1945.' w. M. LEEDS ETA'L 2,385,908

I I CIRCUIT INTERRUPTER Filed Sept. 17, 1942 Q 5 Sheets-Shae; l

WITNESSES:

, INVENTORS 'M'nt/Irqp M Leads 022d Earl 27mm Pflater'.

p 1945. w. M. LEEDS ETAL- 2,385,008

I cmcurr INTERRUP'I'ER Filed Sept. 17, 1942 5 Sheets-Sheet 2 INVENTORS' 'wzmbrapmLeeas and Benja n wh EBuker.

f mo Sept- 1945- w. M. LEEDS ETAL 2,385,008

C IRCUIT INTERRUPTER Filed Sept. 17, 1,942 I 5 Sheets- Sheet 3 WITNESSES:

Ben amin PBaker:

INVENTORS I Winthrop M Leeds and i Se t. 18, 1945.

w. M. LEEDS ETAL GIRCUIT INTERRUPTER Filed Sept. 17, 1942 5 Sheets-Sheet 4 Wag/7611b Material Mayne/i0 INVENTORS lhrop fiZLeeds and Ben gain PBaken, 62

WITNESSES:

ATTORNEY Sept. 1945- Y w M. LEEDS ETAL 2,335,003

0 IRCUIT INTERRUFTER Filed Sept. 17, 1942 5 Sheets-Sheet 5 z ,25. v H 1 1 7 26. E427 112 Mag/7227b Mag/1627's Mala/"1a! Material WITNESSES: INVENTORS Patented Sept. 18, 1945 CIRCUIT INTERRUPTER Winthrop M. Leeds, Wilkinsburg, and Benjamin P. Baker, Turtle Creek, Pa., assignors to Westinghousc Electric Corporation, East Pittsburgh,

Pa., a corporation of Pennsylvania Application September 17, 1942, Serial No. 458,660

8 Claims.

This invention relates to circuit interrupters in general and, more particularly, to circuit interrupters which efiect arc extinction by a blast of arc extinguishing fluid.

Certain features of the invention are described and claimed in applicants divisional application, filed January 27, 1945, Serial Number 574,856, entitled Circuit interrupters" and assigned to the assignee of the instant application.

An object of the present invention is to provide an improved arc extinguishing structure in which a pressure generating arc and an interrupting are are established and which provides, a more efifective flow of arc extinguishing fluid from said pressure generating arc to said interrupting arc to effectively quench the latter.

Another object is to provide an improved contact structure in which flexible current carrying shunts are avoided and in which a single biasing means serves to not only bias a cooperating contact away from the stationary contact, but also to provide the desired contact pressure when the stationary and cooperating contacts are in abutting relation. I

Another object is to provide an improved intermediate contact structure in which a single compression spring not only biases the intermediate contact away from the stationary contact when the breaker is in the open circuit position, but also furnishes the requisite contact pressure in the closed circuit position.

Another object is to provide an improved circuit interrupter in which the intermediate contact is successively pivotal about .two fulcrum points.

Another object is to provide an improved interrupting structure in which a concentrated blast of fluid is employed both for rapid arc lengthening and for scavenging purposes.

Another more specific object is to provide an improved circuit interrupter in which an arc is established, and in which a fluid blast isconcentrated and directed against the initially formed portion of said are which tends to lengthen the same at a greater ratethan the rate of separation of the movable contacts, and to provide means to prevent such lengthening until relatively low instantaneous values of arcing current. It will be readily apparent that such a concentrated fluid blast will build up the dielectric strength in the relatively short gap between the contacts to prevent restrlking in this region after the greatly lengthened arc itself has been extinguished;

l The term fluid as used in the specification and in the appended claims includes gases, liquids and vapors.

It will b readily apparent to one skilled in the art that our invention is applicable to circuit interrupters operating in gaseous mediums, such as air, as well as in liquid mediums. However, for purposes of illustration, and not by way of limitation, we illustrate our invention as applied to circuit interrupters of the liquid immersed type.

Further objects and advantages will become apparent upon a reading of the following specification taken in conjunction with the drawings,

in which:

Figure 1 is an elevational View, partly in cross section, of a circuit interrupter embodying our invention;

Fig. 2 is an enlarged fragmentary elevational view, partly in cross section, of one of the arc extinguishing structures shown in Fig. 1;

Fig. 3 is a plan view in cross section taken on the line 33 of Fig. 2;

Fig. 4 is an inverted plan view in cross section taken on the line 44 of Fig. 2;

Figs. 5 through 12 are plan and side views of plates used in the are extinguishing structure of Fig. 2;

Figs. 13 andl4 are enlarged fragmentary elevational views showing various positions of the intermediate contact of Fig. 2;

Fig. 15 is an enlarged elevational view in cross section through another circuit interrupting structure embodying our invention;

Fig. 16 is a, plan view in cross section taken on the line XVIXVI of Fig. 15;

' Fig. 17 is a plan view in cross section of a circuit interrupting structure, not shown, but similar to the circuit interrupting structure of Fig. 15, illustrating a further embodiment of our invention;

Figs. 18 through 2.0 illustrate various intermediate positions of the intermediate contact used in the interrupting structure of Fig. 15;

Figs. 21 through 24 show various positions of a different intermediate contact structure which may beemployed in any of the circuit interrupting structures shown in the drawings; and

Figs. 25 through 36 showenlarged plan and sideviews of insulating plates used in the interrupting structures shown in Figs. 15 and 1'7.

Referring to the drawings, and more particularly to Figure 1, the reference numeral I designates a tank filled with a' suitable arc extinguishing liquid 2, such as oil, in which are immersed a plurality, in this instance two, are extinguishing structures 3 supported by the two stationary contact structures 4 and the insulating bushings 5 in a conventional manner. An insulating operating rod 6, carrying at its lower end a conducting bridging member I, is adapted for longitudinal reciprocating motion through the cover 8 of the tank I and operated by an external operating mechanism, not shown, to effect the opening and closing of the circuit interrupter. It will be apparent that the circuit interrupter is connected into the external circuit by the line terminals 9. Hence the electrical circuit through the interrupter consists briefly of the left hand line terminal 9, the left hand stationary 'contact structure 4, the conducting bridging memher I, the right hand stationary contact structure 4 and the right hand line terminal 9 as viewed in Fig. l.

The dot and dash lines designated by the reference numeral I indicate the position of the conducting bridging member 'I when the circuit interrupter is in the opencircuit position.

Referring to Fig. 2, which shows an enlarged elevational view in cross section of the left hand are extinguishing structure 3 shown in Fig. 1, it will be observed that there is provided a stationary contact I I, an intermediate contact structure generally designated by the reference numeral I2 and a lower movable contact I3 constituting the upstanding portion of the conducting bridging member I. When the circuit. interrupter is to be closed the conducting bridging member I is raised by the insulating operating rod 6 to bring the movable contact I3 upward to engage the intermediate contact structure I2 in a manner shown in Fig. 14.

The intermediate contact structure I2 comprises a lever I4, at the left hand end of which is a. contacting portion I which is adapted to engage the stationary contact I I. At the right hand end of the lever I4 is secured a pin I6 which operates in slots I! provided in upstanding brackets I8. A stud I9, rigidly secured to an insulating plate 20 with a cap 2I at its upper end, car ries a compression spring 22 which serves to bias the lever I4 downward away from the stationary contact II. A contacting portion 23 of the lever I4 engages the movable contact I3 in the closed circuit position of the interrupter as shown more clearly in Fig. 13.

It will be apparent that upward motion of the movable contact I3 will produce abutting engagement between the movable contact I3 and the contact portion 23 of the lever I4 to first cause a clockwise rotation of the lever I4 about the pin i6 when the pin I6 is at the lower end of the slots IT as more clearly shown in Fig. 14. This clockwise rotation of the lever I4 continues until the contact portion I5 strikes the stationary contact I I, at which time the lever I4 rotates in a counterclockwise direction about the stationary contact II as a pivot point until the pin I6 nearly reaches the top of the slots IT as clearly shown in Fig. 13.

When it is desired to open the interrupter the movable contact I3 is drawn downward to permit a clockwise rotation of the lever I4 about the stationary contact I I as a fulcrum point until the pin I6 reaches the lower end of the slots IT, at which time the lever I4 begins a counterclockwise rotation about the pin I6 as a fulcrum point until the lever I4 rests on the insulating plate 20. At this point in the opening operation the movable contact I3 withdraws from the contacting portion 23 of the intermediate contact structure I2.

It will be apparent that upon opening of the breaker under load a pressure generating are 24 will be drawn between the stationary contact II and the contact portion I5 of the lever I4. Further opening movement will draw an interrupting are 25 between the contact portion 23 of the lever I4 and the movable contact I3.

- The interrupting are 25 is drawn in an interrupting structure comprising a plurality of suitably shaped insulating plates held together by the insulating studs 26. The insulating plates form a pressure generating chamber 21, a conduit generally designated by the reference numeral 28, a plurality of flow passages 29, an arc slot generally designated by the reference numeral 30, a very restricted arcing slot 3I and a plurality of vent passages 32.

Referring more particularly to Figs. 5 through 12, the reference numeral 33 (see Figs. 9 and 10) designates an insulating insert plate formed with a plurality of apertures 34 for the reception of the insulating studs 26, an aperture 35, a relatively widened slot 36 which communicates with an adjacently disposed relatively narrow slot 31 and a U-shaped insert 38 of magnetic material, such as iron, the purpose for which will appear more clearly hereinafter.

Immediately above and below the insert plate 33 is a guard plate 39 (see Figs. 7 and 8) also composed of insulating material having the same configuration as the insert plate 33 and having the function of protecting the U-shaped magnetic insert 38 from the interrupting are 25. Adjacent to the insulating guard plates 39 are a plurality, in this instance three, pocket plates 40 containing apertures 34 for the reception of the insulating studs 26 and also having an enlarged aperture M which communicates by passage 42 with a plurality, in this instance four, pockets 43, as more clearly shown in Figs. 5 and 6. A vent passage 44 connects the right hand pocket 43, as viewed in Fig. 5, to the region outside of the pocket plate 40.

The bottom plat in the stack is designated by the reference numeral 45 and is more clearly shown in Figs. 11 and 12. It is formed of insulating material and contains apertures 34 for the reception of the insulating studs 28 and also has formed therein an elongated slot 46 to accommodate the motion of the movable contact I3. The elongated slot 46 is beveled at 41 to facilitate the guiding of the movable contact I3 during the closing operation of the breaker.

When the several insulating plates are assembled on the insulating studs 26 they will form the pressure generating chamber 21, the conduit 28, the plurality of flow passages 29, the relatively wide arcing slot 30, the plurality of relatively narrow arcing slots 3| and a plurality of vent passages 32. When the circuit interrupter is opened the pressure generating are 24 will react upon the oil disposed in the pressure generating chamber 21 to close the check valve 48 (see Fig. 2) and to force oil through the conduit 28, through the plurality of flow passages 29 (the movable contact I3 not serving as a. valve to close off the flow passages 29), through the relatively widened arcing slot 30, and out through the vent passages 32.

During relatively high instantaneous values of arcing current the cross section of the interrupting are 25 will be too large to permit it to be forced into the relatively narrow arcing slots 3|,

although the flow of oil through the flow passages '28 will tend to carry the interrupting arc 25 to the right toward the vent passages 32. The magnetic inserts 38 will bias the interrupting are 25 to the left, as viewed in Fig. -2, with a force approximately proportional to the square of the instantaneous value of arcing current through the interrupting arc 25. During this time when the interrupting are 25 is biased by the magnetic inserts 38 away from the relatively narrow restricted arcing slots 3| the flow of oil through the flow passages 29 will be such as to freely pass by on both sides of the arc column, since the passage 42 in the pocket plates 40 (see Fig. is sufficiently wide to permit a relatively free passage of oil past the interrupting are and out through the vent passages 32.

When, however, the instantaneous value of arcing current through the interrupting are 25 falls to a relatively low value, that is, approaching a current zero on the alternating current wave, the magnetic biasing force exerted toward the left by the magnetic inserts 38 will correspondingly decrease to permit the oil flow through the how passages 29 to carry the interrupting are 25 into the plurality of constricted arcing slots 3| where it will be blasted by a transverse flow of oil and gas particles to eflect its extinction. It will be noticed that during relatively low instantaneous values of arcing current the cross section of the interrupting are 25 will be sufflciently small to permit it to be forced into the constricted arcing slots 3| where it is held in a centralized and relatively fixed position to be effectively acted upon by the flow of oil and gas particles.

It will be observed that the method of are extinction thus far described disturbs the continuity of the interrupting are 25 very little during the peak of the alternating current wave, yet brings into play efiective deionizing conditions at or near a current zero when extinction is most easily effected. I

It will be noted that in the provision of the particular intermediate contact structure I2 described a number of advantages result. First, there is a rolling motion between the movable contact l3 and the contact portion 23 of the lever I4 to prevent any welding between the movable contact 13 and the contact portion 23. The rolling motion is also present between the stationary contact I I and the contact portion l5 of the lever M. No flexible shunts are necessary, the current passing directly from the movable contact [3 through the contacting portion 23, the

'lever I4, the contacting portion 15 to the station- 1 ary contact II, the latter being preferably fixed in position. The particular arrangement of the compression spring 22 eliminates the necessity for resiliently mounting the stationary contact H since the compression spring 22 produces the desired contact pressure and takes up the shock on closing.

It will be observed that the pockets '43 located in the pocket plates 40 (see Fig. 5) provide a plentiful supply of arc extinguishingliquid adjacent the widened arcing slot 30 and also adjacent the relatively narrow arcing slots 3| which may be acted upon by the interrupting are 25 to provide additional transverse blasts of oil and gas particles.

In the open circuit position of the interrupter, shown by the dotted lines I 8 inFig. l, the -mov able contact I3 is withdrawn from the are extinguishing structure 3 to provide an isolating break. Also, fresh arc extinguishing liquid is thus permitted to enter the enlarged slot 46 in the bottom insulating plate 15 (see Fig. 11), through the vent passage 32 and through the check valve 88 to provide a fresh supply of arc extinguishing liquid for the next circuit opening operation of the circuit interrupter.

Some features of the above method of are extinction are described and broadly claimed in Patent 2,138,382 which issued November 29, 1938 to Winthrop Leeds and Ennio Ortensi and which was assigned to the Westinghouse Electric 8: Manufacturing Company.

In the interrupter shown in 15 a pressure generating are 11 (see Fig. 18) is drawn between th stationary contact 18 and the upper 'contacting portion 18 of the intermediate contact structure generally designated by the reference numera1 80. intermediate contact structure 81] comprises a U-shaped bracket 8| rigidly secured to a metallic support plate 82 by screws 83 (see Fig. 20). The U-shaped bracket 8! serves as an upper seat for a compression spring 84, the lower end of which is seated in a recess 85 provided in the intermediate contact 88 to bias the latter towards its lower position as more clearly shown in Fig. 19. The right hand end of the intermediat contact 86 is pivotally mounted by a pin 81 which is movable in slots 88 provided in two upstanding brackets 89 also rig-idly secured to the metallic support plate 82. The movable contact I3 engages a lower contacting portion 90 of the intermediate contact 85.

Referring to Fig. 15, which shows the interrupter in the closed circuit position, it will be apparent that downward motion of the movable contact [3 will result in the intermediate contact 86 pivoting about the stationary contact 18 as a first fulcrum point while the pin 81 moves down in the slots 88 by the biasing action exerted by the compression spring 84. This movement continues until the pin 81 reaches the lower end of the slots 88, at which time the intermediate contact 86 rotates in a counterclockwise direction about the pin 81 as a second fulcrum point, as more clearly shown in Fig. 18. When the intermediate contact 86 has rotated sufliciently in a counterclockwis direction about the pin 81 so that it strikes the metallic support plate 82, continued downward movement of the movable contact l3 draws an interrupting arc 9! as more clearly shown in Fig. 19.

It will be observed that with the intermediate contact structure 80 shown there is no need for flexible shunts, a rolling action between the contact surfaces prevents welding, and a single compression spring 84 provides not only a biasing means to bias the intermediate contact structure 80 to its open circuit position, but also provides contact pressure for the contacts in the closed circuit position. It will further be noticed that both in the intermediate contact structure l2 in Fig. 2 and 80 in Fig. 15 the construction is such that the motion of th intermediate contact substantially prevents fluid flow between the pressure generating chamber and the interrupting chamber other than by the fluid conduits provided.

For example, in Fig. 15 the lower contacting portion 90 substantially fills theslot 92'provided in the insulating partition 93 separating the pressure generating chamber 94 from the interrupting chamber 95.

An alternativ intermediate contact arrangement which may be used either in the interrupter shown in Fig. 15 or in any of the other interrupters shown in the drawings is the construction shown in Figs. 21 through 24. Referring more particularly to Figs. 21 through 24, it will be observed that we have provided a U-shaped upstanding bracket 99 which serves as an upper seat for compression springs 91, the lower end of which are seated in a recess 98 provided in the intermediate contact 99. The intermediate contact 99 is pivotally supported by a pin I03 to two links IUI which are pivotally mounted at their left hand ends by the pins I92, I63 to the U-shaped bracket 96 (see Fig. 24).

It will be apparent that the pin I is analogous to the pin 81 in Fig. 15, but instead of being guided in the slots 88 as was the case in Fig. 15 the pin ISO is guided by the links IIII. The movement of the intermediate contact 99 is the same as the movement of the intermediate contact 86 in the intermediate contact structure 80 shown in Fig. 15; that is, upward movement of the movable contact I3 first causes it to engage the lower contacting portion I04 of the intermediate contact 99 to cause a clockwise rotation of the intermediate contact 99 about the pin It!) as a fulcrum until the contact portion I05 of the intermediate contact 99 engages the sta-- tionary contact I05.

Further upward motion of the movable contact I3 causes a counterclockwise rotation of the intermediate contact 99 about the stationary contact I86 as a fulcrum and further compressing the compression springs 91 to produce the desired final contact pressure. Again all flexible shunts can be eliminated, the rolling motion between the contact surfaces prevents welding and a single compression spring serves the dual purpose of an opening biasing means and also as a contact pressure maintaining means. The lower contacting portion I04 substantially fills the slot I98 in the insulating partition plate I69 to prevent fluid flow through the slot I08, nus rendering more effective the fiuid flow through the conduit provided for connecting the pressure generating chamber with the interrupting chamber.

Referring particularly to the interrupter shown in Fig. it will be observed that the pressure generating arc 'I'I (see Fig. 18) creates pressure in the pressure generating chamber 94 to cause fiuid flow through the conduit |I0 into the interrupting chamber 95 and out the vent passages III.

An insert insulating plate I I2 having the configuration shown in Fig. 33 is provided. The insulating insert plate I|2 contains apertures 34 for the reception of the insulating studs 26 and an elongated slot II3, the right hand end of which narrows to a constriction I I4. A U-shaped insert ||5 composed of magnetic material, in this instance iron, is imbedded in the insulating insert plate H2. Immediately above and below each insulating insert plate H2 is an insulating guard plate H6 having the same configuration as the insulating insert plate H2 and shown more clearly in Fig. 29.

The purpose of the insulating guard plate H6 is to protect the magnetic insert I|5 from the action of the interrupting arc 9| drawn in the interrupting chamber 95. Adjacent each insulating guard plate IIE are a plurality, in this instance three, insulating vent plates II! the configuration of which is more clearly shown in Fig. 25. It will be observed that each insulating vent plate II'I contains apertures 34 for the reception of the insulating studs 25 and an enlarged slot I I8 which narrows at I I9 and leads to a vent opening I20. When the several insulating plates are assembled on the insulating studs 26 the interrupting arc 9| will be established in an elongated arcing slot generally designated by the reference numeral I2| in Fig. 16.

The several plates in the lower portion of the interrupting chamber 95 are in the same grouping as those in the upper portion of the interrupting chamber 95 and are similar in configuration except that the slots H3 and H8 in these lower plates terminate adjacent the movable contact I3 to concentrate and direct the blast from the conduit ||l| between the main contacts.

The operation of the interrupter shown in Fig. 15 will now be explained. When it is desired to open the interrupter the movable contact I3 is moved downward to permit the intermediate contact 88 to rotate in a clockwise direction about the stationary contact I8 as a fulcrum until the pin 81 strikes the bottom of the slots 83, at which time the intermediate contact 86 rotates in a counterclockwise direction about the pin 81 as a fulcrum until the intermediate contact 86 strikes the metallic support plate 82. When this occurs the movable contact I3 will separate from the lower contacting portion 90 to draw an interrupting arc 9| (see Fig. 19). The interrupting arc 9| will be drawn in the elongated arcing slot I2I (see Fig. 16) where it will be acted upon by two forces. One of the forces will be the concentrated oil flow from the pressure generating chamber 94 through the conduit III] and into the elongated arcing slot |2| toward the vent passages III.

The other force will be the magnetic biasing force exerted by the magnetic inserts ||5 tending to cause the interrupting arc 9| to move to the left, as viewed in Fig. 15, during relatively high instantaneous values of arcing current. It will therefore be apparent that during the peak of the alternating current wave the interrupting arc 9| will be biased away from the constriction I|4 provided in the insulating guard plates |I6 (see Fig. 29) and the insulating insert plates I I2 (see Fig. 33) to permit a relatively free passing of oil past the interrupting arc 9| while it is in the enlarged portion of the elongated arcing slot I2I.

When the instantaneous value of arcing current falls to a relatively low value the magnetic biasing force exerted toward the left by the magnetic inserts |I5 will correspondingly decrease to permit the concentrated fiuid blast through the conduit III) to carry the interrupting arc 9| to the right as viewed in Fig. 15 to position it in the constriction II4 provided in the insulating guard plates I I6 and insulating insert plates IIZ. It will be noted that the portion 9Ia (see Fig. 15) of the lower plates causes a concentrated directed blast of oil from the conduit I II) to move the lower terminal of the interrupting arc 9Idown the side of the movable contact I3 to rapidly lengthen the same during low instantaneous values of arcing current. In this position the interrupting arc 9| is subjected to very eifective extinguishing conditions caused by the liquid and gas flow through the narrowing portion I|9 provided in the vent plates H! (see Fig. 25). It will be observed that the interrupting arc 9| is held in a relatively fixed position at the constriction I I4 where the fluid flow tends to converge on the arc because of the narrowing which is more clearly shown in Fig. 2'7.

portion II9 provided in the vent plates In, this occurring at or near a current zero when the magnetic biasing force exerted by the magnetic inserts H5 is relatively small. Extinction of the interrupting arc 9I soon follows, and the movable contact I3 is withdrawn from the interrupting structure to effect an isolating gap. In the open circuit position fresh oil enters through the vent passages III and through the slot I22 in the bottom insulating plate I22a through which the movable contact I3 was drawn. It will be noted that the concentrated and directed blast of oil through the conduit IIO scavenges the relatively short distance between the movable contact I3 and the contacting portion 99 to prevent restriking in the relatively short gap after the relatively lengthened arc 9| has been extinguished.

Fig. 17 shows a modified construction of the interrupter shown in Fig. 15. Fig. 17 represents a plan view in cross section of an interrupter similar to that just described in connection with Fig. 15 except that the conduit IIO in the insulating plate 93 is omitted and in its place longitudinal passages I23 (see Fig. 17) are provided in each plate making up the lower portion of the modified arc extinguishing structure. Fig. 35 illustrates the type of insulating insert plate which may be used in such a modified construction and is represented by the reference numeral I24. The insulating insert plate I24 has openings I25 to form the passages I23 shown in Fig. 17. Insulating plate I24 also contains apertures 34 to accommodate the insulating studs 26, an elongated slot II3 and a constriction I14, An insert I26 composed of a suitable magnetic material, in this instance iron, is formed to such a shape as to accommodate the openings I25. Immediately above and below the insulating insert plate I 24 is an insulating guard plate I21, the configuration of which is more clearly shown in Fig. 31. The insulating guard plate I2I contains apertures 34 for the insulating studs 26, openings I25, an elongated slot H3 and a constriction II4. Again the insulating guard plate I21 protects the insulating insert plate I24 from the effect of the interrupting arc. Immediately adjacent to each insulating guard plate I2! is an insulating flow plate I28, the configuration of This insulating flow plate I28 is similar to the vent plate I ll shown in Fig. 25 except that it contains flow passages I29 which lead from the openings I25 to the enlarged slot II8.

It will be apparent that with the conduit III'I (see Fig. 15) omitted the oil flow from the pressure generating chamber 94 (see Fig. 15) will flow down through the passage I23 and only the flow plates I28 will permit flow into the enlarged slot IIII provided in the flow plates I28. During the peak of the alternating current wave the interrupting arc 9I (see Fig. 19) will be drawn to the left, as viewed in Fig. 17, to a position where the flow coming through the flow passages I29 in the flow plates I28 (see Fig. 27) interferes very little with the continuity of the interrupting arc 9|. This reduces the are energy and internal pressure in the arc extinguishing structure. When, however, the instantaneous value of arcing current falls to a relatively low value, the magnetic inserts I26 will exert little biasing force on the interrupting arc 9| and will permit it to return to the place where it was initially drawn, that is between the opposed flow passages I29 (see Fig. 17) at which position it receives the full effect of a transverse flow of oil which tends to carry the interrupting arc 9| to the right, as viewed in Fig. 17, to the constriction II4, the flow converging on the interrupting arc 9I in this position as defined by the narrow portion H9 in the flow plates I28. The strong deionizing action in the arc space eifectively builds up dielectric strength at current zero so that the arc cannot restrike, thus interrupting the circuit.

It will be apparent to one skilled in the art that our invention is readily applicable not only to liquid immersed circuit interrupters but also to circuit interrupters operating in a gaseous medium, such as air. The insulating plates described in connection with the various embodiments of our invention may be made of a suitable gas evolving material to facilitate the interruption of the interrupting arc. Consequently, any of the'interrupters previously described could be operated in air with the insulating plates com-- posed of a suitable gas evolving material such as horn fiber or boric acid. Merely for purposes of illustration, and not by way of limitation, we have described our invention as embodied in various forms of oil immersed circuit interrupters.

The broader aspects of holding an interrupting are by magnetic means away from vents provided along an elongated arcing slot during the peak of the alternating current wave is described and broadly claimed in a patent application filed March 19, 1942, Serial No. 435,380, by Benjamin P. Baker, now Patent 2,303,524 which issued December 1, 1942 which was assigned to the assignee of the instant application.

Although we have shown and described specific structures, it is to be understood that the same were only for purposes of illustration and that changes and modifications may be made therein by those skilled in the art without departing from the spirit and scope of the appended claims.

We claim as our invention:

1. In a circuit interrupter, a stationary contact, an intermediate contact, a movable contact, said intermediate contact comprising a lever member having a first fulcrum point operative before said intermediate contact engages said stationary contact, said lever member also having a second fulcrum point at said stationary contact during the final closing operation, and the movable contact causing the actuation of the intermediate contact.

2. In a circuit interrupter, a first contact, a second contact cooperable with the first contact, the second contact comprising a lever member successively pivotal about both its ends during the closing operation, and a third contact cooperable with the second contact.

3. In a circuit interrupter, a first contact, a second contact cooperable with the first contact, the second contact comprising a lever member successively pivotal about both its ends during the closing operation, a third contact cooperable with the second contact, and biasing means acting on the lever member intermediate the ends thereof.

4. In a circuit interrupter, a relatively stationary contact, a relatively movable contact cooperable with the relatively stationary contact, the relatively movable contact comprising a lever member having a first fulcrum point operative before the relatively movable contact en- I gages the relatively stationary contact, the lever member also having a second fulcrum point at the relatively stationary contact during the final closing operation, and a second movable contact cooperable with the relatively movable contact.

5. In a circuit interrupter, a relatively stationary contact, a relatively movable contact cooperable with the relatively stationary contact, the relatively movable contact comprising a lever member having a first fulcrum point operative before the relatively movable contact engages the relatively stationary contact, the lever member also having a second fulcrum point at the relatively stationary contact during the final closing operation, a second movable contact cooperable with the relatively movable contact, and biasing means acting on the lever member intermediate the ends thereof.

6. In a circuit interrupter, relatively stationary contact means, movable lever-shaped contact means pivotally mounted, a second movable contact cooperable with the first-mentioned movable contact, and a single biasing means to bias the movable lever-shaped contact means away from the relatively stationary contact means in the open circuit position of the interrupter, the single biasing means also serving to maintain pressure between the relatively stationary contact means and the movable lever-shaped contact means in the closed circuit position of the interrupter.

7. In a circuit interrupter, relatively stationary contact means, movable lever-shaped contact means pivotally mounted at a movable pivot point and having a contact portion engageable with said relatively stationary contact means, a second movable contact cooperable with the firstmentioned movable lever-shaped contact means to engage it at a point spaced along the lever from its point of engagement with said relatively stationary contact means, and a single biasing means acting on the movable lever-shaped contact means at a point outside the portion of the lever extending between its two contact engaging points in a direction to bias the movable lever-shaped contact means away from the relatively stationary contact means in the open circuit position of the interrupter, the single biasing means also serving to maintain pressure between the relatively stationary contact means and the movable lever-shaped contact means in the closed circuit position of the interrupter.

8. In a circuit interrupter, relatively stationary contact means, movable lever-shaped contact means pivotally mounted adjacent one end at a movable pivot point and having its other end engageable with said relatively stationary contact means, a, second movable contact cooperable with the first-mentioned movable levershaped contact means to engage it at a point intermediate its ends, and a single biasing means acting on the movable lever-shaped contact means between the point of engagement of said second movable contact and said movable pivot in a direction to bias the movable lever-shaped contact means away from the relatively stationary contact means in the open circuit position of the interrupter, the single biasing means also serving to maintain pressure between the relatively stationary contact means and the movable lever-shaped contact means in the closed circuit position of the interrupter.

WINTHROP M. LEEDS. BENJAMIN P. BAKER.

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