US2752451A - Circuit interrupter - Google Patents

Description

June 26, 1956 J. M. WALLACE 2,752,451

cmcurr INTERRUPTER Filed Feb. 23, 1951 2 Sheets-Sheet l WITNESSES: INVENTOR 5%??? James M.Wo|loce. n U

June 26, 1956 J, WALLACE 2,752,451

CIRCUIT INTERRUPTER Filed Feb. 23, 195] Fig.2.

2 Sheets-Sheet 2 WITNESSES: INVENTOR awn 437- Jomes M.Wolloce.

United States Patent 2,752,451 Patented June 26, 1953 free CIRCUIT INTERRUPTER James M. Wallace, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, P3. a cor poration of Pennsylvania Application February 23, 1951, Serial No. 212,37

19 Claims. (Cl. 200-89) This invention relates generally to automatic reclosing circuit breakers of thetype where closely successive circuit interrupting operations have different time-current characteristics.

In automatic reclosing circuit breakers it is customary to provide for one or more substantially instantaneous openings followed by delayed openings having, in general, inverse time-current characteristics. Heretofore, it has been customary to obtain the delayed openings by using a dashpot arrangement with the operating solenoid closing or partially closing a vent in the dashpot by means of a sliding piston which is part of the operation counter.

One object of this invention is to provide in an automatic reclosing circuit breaker for using leakage flux from the operating coil for controlling venting of pressure fluid from a dashpot time delay mechanism.

Another object of my invention is to provide in an automatic reclosing circuit breaker, for modifying the operating characteristics to approach those of fuses, particularly at the higher current values.

Yet another object of my invention is to provide in an automatic reclosing circuit breaker for rendering valve means eflective to introduce time delay into the operation of the breaker during only a portion of the operating stroke.

Still another object of my invention is to provide in an automatic reclosing circuit breaker for utilizing an armature responsive to leakage flux of the operating coil for holding closed a fluid pressure valve in a time delay dashpot.

It is also an important object of my invention to provide in an automatic reclosing. circuit breaker for utilizing a magnetic valve for controlling venting from the time delay dashpot, and for rendering the valve effective in response to operation of an operation counter.

Another important object of my invention is to provide in an automatic reclosing circuit breaker for utilizing magnetic valve means to control venting of a time delay dashpot, and for rendering it effective in different degrees on different ones of closely succeeding operations.

These and other objects of this invention will become apparent upon consideration of the following detailed description of preferred embodiments thereof, when taken in connection with the attached drawings, in which:

Figure 1 is a longitudinal section view through a circuit breaker embodying this invention;

Fig. 2 is a partial longitudinal section through a circuit breaker embodying a modification of the invention, and

Fig. 3 is a sectional view taken along the line TIL-III of Fig. 2.

The circuit breaker illustratedin Fig. 1 isv contained in a metal tank 2 having an open top adapted to be covered by a hollow cover structure 4 which may be secured to tank 2 in any desired manner. Preferably, the major part of the interior of tank 2 is covered by a suitable insulating liner 3, of any desired insulatingmaterial, such as fiber or the like. The circuit breaker operating mechanism is all adapted to be mounted in cover 4, which may have supports 6 (only one of which is shown) at least partly of insulating material for supporting a supporting casting 8 and a supporting plate 10, between which a solenoid coil 12 may be mounted. Stationary contacts 14 for the breaker may in turn be suspended from supporting plate 310 by are chutes 16 of insulating material such as fiber or the like.

A bridging contact bar 18 is adapted to bridge stationary contacts 14, and is mounted on the lower end of a contact rod 22, as by a pivot 20, about which the bridging contact may have limited pivotal movement. The upper end of contact rod 22 is connected by a pair of pivoted connecting links 24 of insulating material, such as fiber or the like, to the common pivot 26 of a pair of toggle levers 28 and 30. Toggle lever 28 is adapted to be held in engagement with a pivot bracket 32 supported from cover 4 by a coil tension spring 34 secured at one end to cover 4, and at the other end engaging an opening in toggle lever 30.

In order to manually operate the circuit breaker contaste, and also to provide for a locked-open condition of the breaker, t. ere is provided a pair of toggle levers 36 and 38 connected by a knee pivot pin 40, with lever 36 being pivotally mounted in cover 4 as by a pivot pin 42, and being extended beyond this pivot pin to the exterior of cover 4 where it normally is positioned beneath a hood portion 46 integral with the cover. The handle extension 44 of lever 36 has an operating eye 43 at the outer end thereof for receiving a hook stick or similar operating member. The other toggle lever 38 is provided with a slot 5'0 at its outer end for receiving a pin 5'2 mounted between spaced supporting lugs 54 integral with cover 4. A coil compression lock-out spring 56 is mounted on toggle lever 38 so as to react between supporting lugs 54 and a shoulder provided at the inner end of a toggle lever 38. Preferably, toggle lever 38 has an inwardly and downwardly extending operating extension 58 adapted to be engaged by automatic counting means, as will be described.

For the purpose of automatically separating bridging contact 18 from stationary contacts 14 of the breaker in response to overloads, there is provided an actuating sleeve 6i) which receives an intermediate portion of contact rod 22, with the lower end of this sleeve being threaded into a solenoid core 62 of magnetic material, such as iron, having a central opening for receiving contact rod 22, and being slidably mounted in a central opening provided in coil supporting plate 10. A light coil compression spring 64 reacts between a pin 66 on contact rod 22 and solenoid core 62 to normally bias the latter to the position shown in Fig. l. Preferably, solenoid coil 12 is provided with suitable insulation covering the coil, and the interior of the coil additionally has a cylindrical dashpot sleeve 70 of insulating material, such as fiber or a molded insulating material received therein. For the purpose of limiting upward movement of actuating sleeve 6i) on contact rod 22, the latter is provided with a flange 72 adjacent the upper end thereof. The upper end of dashpot sleeve 70 is provided with an annular outlet passage 74 formed in supporting casting 8, and communicating with a laterally extending vent passage 76 also formed in the supporting casting, which opens to the interior of tank 2.

It will now be apparent that upon the passage of currents through solenoid coil 12 of a value sufficiently high to attract core 62, that the latter will be moved upwardly while stressing spring 64. Depending upon whether or not vent passage 76 is open or closed, by means to be hereinafter described, upward movement of core 62 and actuating sleeve 60 will be relatively fast (if vent passage 76 is open), or relatively slow (if vent passage 76 is closed), due to the necessity of liquid trapped within the dashpot sleeve 70 escaping through the relatively small clearances between core 62 and the opening in supporting plate when the vet passage is closed. In either case, however, spring 64 eventually becomes compressed to an extent that contact pressure spring 34 is overcome, and contact rod 22 then begins to move upwardly to separate bridging contact 18 from stationary contacts 14 in the manner previously described. In the event of any difliculty with spring 64, upward movement of core 62 and actuating sleeve 60 will eventually cause the latter to engage the flange 72 on contact rod 22 to positively separate bridging contact 18 from stationary contacts 1 When solenoid coil 12 becomes deenergized, the contacts may close in the manner previously described, except that the speed of reclosing movement will be dependent. as is the speed of contact opening movement, upon whether or not vent passage 76 is open or closed.

For the purpose of counting closely succeeding circuit interrupting operations of the circuit breaker, there is provided a cylindrical sleeve 78 mounted in an opening provided in supporting casting 8, and a counting piston 85) is adapted to be mounted in sleeve 78. The lower end of sleeve 78 is closed by a plug having a small opening controlled by a ball check valve 82, so that While fluid may be freely drawn into the lower end of sleeve 78, it cannot escape outwardly from the lower end of the sleeve. Counting piston has a reduced upwardly extending rod portion provided with a plurality of spaced flanges 84- thereon, and above this it has secured thereto an extension 36, for a purpose to be described.

A pawl lever 92 is pivoted at one end as at 94 on supporting casting 8 and has its other end engaging the top of a collar 96 secured to actuating sleeve 6%, so that the lever will be moved upwardly each time the breaker contacts separate. mounted thereon which is adapted to engage beneath flanges 84 of the counting piston to move the piston up wardly each time the breaker contacts separate.

It is believed clear that upon the occurrence of a circuit opening operation, counting piston 8i} will be moved upwardly a predetermined distance by pawl member 5 and when the breaker contacts are reclosed, counting piston 89 will remain at the position it was advanced on the preceding circuit opening operation. Counting piston 89 will return very slowly to its normal lowermost position illustrated in Fig. 1 under the force of gravity, it being retarded in such return movement by the necessity of displacing liquid drawn into the lower end of sleeve 78 when the piston was advanced, between the relatively small clearance between the piston and sleeve 73. However, if a number of circuit opening operations occur in close succession, counting piston 80 will not have time to return to its normal lowermost position shown in Fig. 1, because when the contacts reclose, they will immediately reopen, and this time pawl member 98 will engage the next lowermost flange 84 of the counting piston to advance the latter a further amount upwardly, and this will continue until the uppermost extension 86 of the counting piston engages operating extension 58 of toggle lever 33 to move the knee pivot of toggle levers 36 and 38 upwardly overcenter, whereupon the breaker contacts will be locked out in the manner previously described.

The structure thus far described is substantially identical with the breaker construction disclosed in the copending application of I, M. Wallace et al., Serial No. 787,206, filed November 20, 1947, on' Automatic Reclosing Circuit Breakers, and assigned to the assignee of this invention. For a more detailed description of the structure and operation of the breaker parts, reference may be made to the aforesaid copending application of Wallace et al.

in order to provide for one or more delayed opening after the initial one or two substantially instantaneous openings, means such as the valve member 81 may be provided for closing the vent passage 76 to render the Pawl lever 92 has a pawl member 98' dashpot action of the core 62 efiective to delay openings of the breaker. The valve member 81 may be pivotally mounted on the supporting plate 10, as by a pivot 83, being biased in a clockwise direction by a spring 85. The valve member 81 may be made of a magnetic material so as to be urged by leakage magnetic flux from the coil 12 in a counterclockwise direction to close the passage 76.

The valve member 81 may be releasab-ly latched in the position shown by a latch 87 which may be pivotally mounted on the casting 8 by a pivot 88. The latch may comprise an arm 89 disposed to engage an extension 90 on the valve member 81, and an arm 91 which may be engaged by a collar 93 on the extension 86 of the counting piston 80, after it has been stepped upwardly in response to the first one or two fast opening operations, to free the arm 89 from the extension 90.

Accordingly, when the piston has been stepped to a position where the collar 93 engages the lever 91, the valve member 81 will be released by the latch means 87. Upon reenergization of the coil 12 after the breaker recloses, the valve member 81 is attracted toward the upper casting 8, and closes the passage 76 to render the dashpot action of the core 62 efiective. Since the fluid pressure in the dashpot varies with the force on the core 62, and this force increases with reduction in the air gap between the core and the casting 8, the valve 81 may be made to open after predetermined travel of the core at any given value of load current. In this way the timecurrent curves may be made relatively faster at high values of current, it being merely a question of providing a limiting section in the valve member 81 which saturates at a predetermined flux density, so as to determine the holding force of the leakage flux on the valve member. Since the valve 81 is released when the circuit is interrupted by the opening of contacts 18 and 14, the dashpot will be freely vented. Hence, the valve 81 interposes no delay on reclosing.

in order to provide a more varied time-current characteristic, the breaker may, as shown in Figs. 2 and 3, be provided with a valve member 77 pivotally supported on the casting 8 for closing the passage 76. The valve member 77 may be freely suspended from a pivot 79. To close the valve member 77, a pair of armatures 81a and 81b may be provided. These armatures may be pivotally mounted on the plate 10 in a manner similar to that of the valve member 81 of Fig. 1, and disposed in side-by-side relation for individually urging the valve member 77 to the closed position in response to the effects of leakage flux from the coil 12.

The armatures 81a and 8112 may be provided with individual latches 87a and 87b mounted on a pivot 88 for normally rendering them inoperative. The latches 87a and 87b may be provided with arms 91:: and 91b, respectively, which may be disposed for engagement with a collar 93 on the counting piston extension 86 on successive operations of the counting piston.

In operation the passage 76 will initially be open, so that there is but little, if any, dashpot action of the core 62. Upon the third opening operation, for example, the collar 93 will engage the lever arm 91a, releasing armature 81a, which thereupon closes valve 77 under the influence of the leakage flux from the solenoid coil 12 after the breaker has reclosed, with a predetermined force which would be overcome when the oil pressure in the dashpot exceeded some predetermined value near the end of the stroke of the core 62. Upon the next operation, the lever 9112 would be actuated to release armature $1b and increase the holding force on the valve 77 after the next reclosing operation. Greater time delay would thus be effected, since the valve 77 could not open except for greatly increased values of current.

Since the valve 77 is freely pivoted, it may operate to close the passage 76 to the influx of oil during reclosing. This makes the dashpot action available for time delay on reclosing. If such time delay is not des sired, it may be obviated by the simple expedient of using a spring similar to the spring 85 of Fig. 1 to bias the valve 77 open. Likewise, if time delay on closing is desired in the circuit breaker of Fig. 1, a freely pivoted valve such as the valve 77 of Fig. 2 may be readily added to the breaker of Fig. 1.

It is believed apparent that in each of the embodiments of the invention described above, an automatic reclosing circuit breaker is provided having means for efiecting a first one or two instantaneous circuit opening operations, after which a time delay is imposed on the operations, which time delay is reduced for the higher current values so as to provide for better coordination with fuses in the system. By using the leakage flux of the solenoid coil for effecting a closing of the vent in the dashpot, the valve may be permitted to open and reduce the time delay toward the end or" the opening stroke when the pull on the core 62 increases. By using two armatures to close the valve, variations in the time delay are possible by sequentially rendering them operative and thus increasing the force eitective to maintain the valve closed.

Since certain changes may be made in the above-described construction without departing from the spirit and scope of the invention, it is intended that all the matter contained in the above description and shown in the accompanying drawings shall be considered as illustrative, and not in a limiting sense.

I claim as my invention:

1. An automatic reclosing circuit breaker comprising, separable contacts, solenoid means connected in series with said contacts and having a movable part responsive to overloads on the circuit for causing separation of said contacts, means for automatically closing said contacts following a circuit opening operation, normally ineffective time delay means, and means including a movable part operable in response to magnetic leakage flux from said solenoid means for rendering said delay means operable to delay the next circuit opening operation.

2. An automatic reclosing circuit breaker comprising, separable contacts, electroresponsive means operable in response to overloads on the circuit for causing separation of said contacts, means for automatically closing said contacts following a circuit opening operation, time delay means including a part responsive to magnetic leakage flux from said electroresponsive means to delay operation of the electroresponsive means with an inverse timecurrent characteristic, and control means normally operable to render the time delay means ineffective, said control means being responsive to a predetermined circuit opening operation for rendering said time delay means effective.

3. An automatic reclosing circuit breaker comprising, separable contacts, a solenoid coil connected in series with said contacts responsive to overload currents to attract and move a core, means actuated by said core for causing a plurality of separations of said contacts, means causing said contacts to close following separation, normally ineffective fluid dashpot means responsive to a circuit opening operation to delay circuit opening movement of said core when effective, and valve means actuated in response to energization of said solenoid coil during an opening operation for rendering the dashpot means effective only while the solenoid coil is energized so as to delay a succeeding opening operation without delaying an intervening closing operation.

4. An automatic reclosing circuit breaker comprising, separable contacts, a solenoid coil responsive to overload currents to attract and move a core, means actuated by said core for causing separation of said contacts, dashpot means operable to delay the circuit opening movement of said core, means actuated during a cycle of operation of said breaker comprising a circuit opening and succeeding closing operation for counting the number of closely successive cycles of operation, valve means operable in response to energization of said coil to render said delay means effective, releasable means disposed to render said valve means inoperative, and means actuated by said counting means for controlling said releasable means to render said valve means operable in response to the cycle of operation including said predetermined circuit openin operation for delaying a subsequent closing operation.

5. An automatic reclosing circuit breaker comprising, separable contacts, a solenoid coil responsive to overload currents to attract and move a core, means actuated by said core for causing separation of said contacts, dashpot means responsive to a predetermined circuit opening operation in any series of closely successive circuit opening operations to delay circuit opening movement of said core, means actuated during a cycle of operation of said breaker comprising a circuit opening and succeeding closing operation for counting the number of closely successive cycles of operation, vent means for said dashpot means including normally inefiective valve means disposed to be responsive to magnetic leakage flux from said solenoid coil, and means actuated by said counting means for rendering said valve means effective for closing said vent in response to energization of said coil after said predetermined circuit opening operation to increase the time delay in a subsequent operation.

6. An automatic reclosing circuit breaker comprising, separable contacts, a solenoid coil responsive to overload currents, movable means actuated by said coil for causing separation of said contacts, delay means having a part movable during a circuit opening operation to delay the circuit opening movement of said movable means, means actuated during a cycle of operation or" said breaker comprising a circuit opening and succeeding closing operation for counting the number of closeiy successive cycles of operation, and releasable control means normally preventing movement of said movable part actuated by said counting means for selectively rendering said delay means effective during circuit opening operations only, and in different degrees in different cycles of operation.

7. An automatic reclosing circuit breaker comprising, separable contacts, a solenoid coil responsive to overload currents to attract and move a core at least a predetermined distance, means actuated by said core after traveling predetermined distance for causing separation of said contacts, dashpot means responsive to a predetermined circuit opening operation in any series of closely successive circuit opening operations to delay the circuit opening movement of said core, means actuated during a cycle of operation of said breaker comprising a circuit opening and a succeeding closing operation for mounting the number of closely successive cycles of operation, valve means operable to control venting of the dashpot means, magnetic means operable to close said valve means in response to energization of said coil, and means normally operable to render said magnetic means ineffective, actuated by said counting means for rendering said valve means effective in response to the cycle of operation of said breaker.

8. An automatic reclosing circuit breaker comprising, separable contacts, a solenoid coil responsive to overload currents, means actuated by said coil for causing separation of said contacts, fiuid pressure dashpot means responsive to a predetermined circuit opening operation in any series of closely successive circuit opening operations to delay the circuit opening movement of said means, venting means for said dashpot means including valve means magnetically coupled with said solenoid coil, means actuated during a cycle of operation of said breaker comprising a circuit opening and a succeeding closing operation for countin the number of closely successive cycles of operation, and latch means actuated by said counting means for rendering said valve means operable in response to the cycle of operation including said predetermined circuit opening operation to close said venting means.

9. An automatic reclosing circuit breaker comprising, separable contacts, solenoid coil responsive to overload currents to attract and move a core at least a predetermined distance, means actuated by said core after traveling said predetermined distance for causing separation of said contacts, fluid dashpot means responsive to a predetermined circuit opening operation in any series of closely successive opening operations to delay circuit opening movement of said core, venting means for said dashpot including valve means, magnetic means including an armature magnetically coupled with said solenoid coil for operating said valve means, means actuated during a cycle of operation of said breaker comprising a circuit opening and succeeding closing operation for counting the number of closely successive cycles of operation, and releasable means actuated by said counting means for releasing said armature in response to the cycle of operation including said predetermined circuit opening operation to close said valve means and render the dashpot means effective.

10. An automatic reclosing circuit breaker comprising, separable contacts, a solenoid coil responsive to overload currents to attract and move a core at least a predetermined distance, means actuated by said core for causing separation of said contacts, dashpot means responsive to a predetermined circuit opening operation in any series of closely successive circuit opening operations to delay circuit opening movement of said core, said dashpot means having a vent for rendering it ineffective, electromagnetic operating means for closing said vent during an opening operation only, and latch means including means responsive to predetermined operation of said core to release said electromagnetic means for closing said vent.

11. An automatic reclosing circuit breaker comprising, separable contacts, means responsive to an overload on a circuit for causing separation of the contacts, means responsive to a circuit interrupting operation to automatically close said contacts, time delay means, releasable means normally rendering the time delay means ineffective, and means including parts actuated by said overload responsive means during circuit opening and closing operations respectively to effect release of said releasable means and render said time delay means effective, only after reclosure of the contacts, to delay the next circuit opening operation.

12. An automatic reclosing circuit breaker comprising, separable contacts, electromagnetic means automatically responsive to overloads on a circuit for causing separation of said contacts, means responsive to a circuit interrupting operation to automatically close said contacts, normally ineffective time delay means, and control means operable during one circuit opening operation rendering said time delay means effective for delaying a subsequent circuit opening operation, said control means having a part of a magnetic material responsive to overloads in excess of a predetermined value to render said time delay means ineffective.

13. in an automatic reclosing circuit breaker, separable contacts, electromagnetic means automatically responsive to overloads on the circuit for causing a plurality of separations of said contacts, means responsive to a circuit interrupting operation to automatically close said contacts following each separation, normally inefiective time delay means, means having a part actuated by the electromagnetic means during a first circuit opening and closing operation to render said time delay means effective only after reclosure of the contacts to delay the next circuit opening a predetermined amount Without delaying said reclosure, and additional means including a part actuated by the electromagnetic means on an opening operation after said first one responsive to said next circuit opening operation for increasing the efiectiveness of said time delay means on the following opening operation Without delaying an intervening closing operation.

14. In an automatic reclosing circuit breaker, means automatically responsive to overloads on a ciruit for causing separation of said contacts, means responsive to a circuit interrupting operation to automatically close said contacts, time delay means for delaying separation of said contacts, releasable means rendering said time delay means normally inelfective, and means including a part actuated during a circuit opening and closing operation to actuate said releasable means and render said time delay means eilective only after reclosure of the contacts to delay the next closely succeeding circuit opening operation, said actuated part being disposed to reset upon the lapse of a predetermined time after a circuit opening and closing operation without a subsequent circuit opening operation.

15. In a circuit interrupter, separable contacts, means automatically responsive to overloads on the circuit for causing separation of said contacts, means responsive to a circuit interrupting operation to automatically close said contacts, normally ineffective time delay means, and means including a movable member of magnetic material responsive solely to reclosing of the circuit after a circuit opening operation to render the time delay means eifective only after reclosing, so as to delay the next circuit opening operation without delaying the intervening reclosing operation.

16. A circuit interrupter comprising, separable con tacts, means automatically responsive to an overload on a circuit for causing separation of said contacts, means responsive to a circuit interrupting operation to automatically close said contacts, time delay means normally ineffective to delay an opening or a closing operation, and means including releasable means responsive to a predetermined opening operation responsive to reclosing of the circuit after a circuit opening operation to render the time delay means effective to delay the next circuit opening operation without delaying the intervening reclosing operation.

17. In a self-contained recloser having a fixed contact and a movable contact operating mechanism, including a movable contact, and having an engaged position in which said contacts are engaged, and a disengaged position in which said contacts are disengaged, biasing means operating on said movable contact for biasing said movable contact into engagement with said fixed contact, an electromagnet in series with said movable and fixed contacts of said contact mechanism and energizable by fault currents for instantaneously operating said contact operating mechanism to move said movable contact against the action of said biasing means to its disengaged position, said biasing means being operative following disen gagement of said contacts for operating said movable contact into engagement with said fixed contact following a circuit interruption, a time delay mechanism, a member normally rendering the time delay mechanism ineffective to control the time of operation of said movable contact, and magnetic means released by said member in response to energization of said electromagnet by the fault current which effected instantaneous opening of said contacts for operating said time delay mechanism only in response to reenergization of the electromagnet after reengagement of said contacts for rendering said time delay operative to delay said electromagnet opera tion of said contacts to disengagement.

18. in a self-contained recloser having a fixed contact and a movable contact operating mechanism including a movable contact, and having an engaged position in which said contacts are engaged, and a disengaged position in which said contacts are disengaged, biasing means operating on said movable contact for biasing said movable contact into engagement with said fixed contact,

an electromagnet in series with said movable and fixed contacts of said contact mechanism and energizable by fault current for instantaneously operating said movable contact against the action of said biasin means to its disengaged position, said biasing means being operative following disengagement of said contacts for moving said movable contact into engagement with said fixed contact following a circuit interruption, a time delay mechanism, a movable member normally rendering said mechanism ineffective to control the time of operation of said movable contact in the opening direction, and a control device for controlling the position of said member and hence operation of said time delay mechanism, including a member of a magnetic material activated by the fault current which resulted in the instantaneous disengagement of said contacts, for rendering said time delay mechanism operative only after reengagement of said contacts for rendering time delay operative to delay said electromagnet operation of said contacts to disengagement in response to a fault current condition on reengagement of said contacts and said bias operation of said contacts to engagement.

19. In a self-contained recloser having a fixed contact and a movable contact operating mechanism including a movable contact, and having an engaged position in which said contacts are engaged, and a disengaged position in which said contacts are disengaged, biasing means operating on said movable contact for biasing said movable contact into engagement with said fixed contact, an electromagnet in series with said movable and fixed contacts of said contact mechanism and energized by fault currents for instantaneously operating said movable contact against the action of said biasing means to its disengaged position, said biasing means being operative fol lowing disengagement of said contacts for operating said movable contact into engagement with said fixed contact following circuit interruption, a fluid time delay mechanism having a normally open vent rendering it ineffective to control the time of operation of said movable contact, and normally one-way valve means including a part of a magnetic material activated by the fault current which resulted in the zistantaneous disengagement of said contacts, only during the period of reengagernenr or said contacts for operating the valve means to close said vent rendering said time delay operative to delay, for a predetermined interval, said electromagnet operation of said contacts to disengagement in response to a fault current condition on reengagement of said contacts and said bias operation of said contacts to en gagement.

References Cited in the file of this patent UNITED STATES PATENTS 508,652 Thomson Nov. 14, 1893 532,537 Davis Jan. 15, 1895 1,288,017 Johnson Dec. 17, 1918 1,585,988 Hesse May 25, 1926 1,589,055 Cousins June 15, 1926 1,648,508 Schweitzer Nov. 8, 1927 2,468,498 Kyle et al. Apr. 26, 1949 2,468,851 Wallace May 3, 1949 2,549,336 Rawlins et al Apr. 17, 1951 2,560,529 Van Ryan et al July 10, 1951 2,560,831 Van Ryan et a1. July 17, 1951 2,568,155 Hubbard Sept. 18, 1951 2,573,234 Wallace et a1. Oct. 30, 1951 2,590,523 Edwards Mar. 25, 1952 2,605,327 Ranson July 29, 1952 2,626,329 Wallace et a1. Jan. 20, 1953

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