US2875300A - Circuit interrupter - Google Patents

Description

Feb 24, 1959 s. A. BOTTONARI 2,875,300

CIRCUIT INTERRUPTER Filed Deo. 9, 1955 4 Sheets-Sheet 1 wlTNessEs INVENTOR M Samuel A. Bof'ronorl.

ATTORNE Feb. 24, 1959 s. A. BOTTON'ARI CIRCUIT INTERRUPTER 4 Sheets-Sheet 2 Filed Dec. 9, 1955 Isl NN mmm mNN Feb. 24, 1959 s. A. BoTToNARl 2,875,300

CIRCUIT INTERRUPTER Filed Deo. 9, 1955 4 Sheets-Sheet 5 Feb. 24, 1959 s. A. BOTTONARI CIRCUIT INTERRUFTER 4 Sheets-Sheet 4 Filed Deo.

United States Patent O CIRCUIT INTERRUPTER Samuel A. Bottonari, Pittsburgh, Pa., assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 9, 1955, Serial No. 552,058 12 Claims. (Cl. 20o-146) This invention relates to circuit interrupters and, more particularly, to high-speed circuit interrupters.

Modern high-power direct current systems have many large rectiers operating in parallel, and such systems are subject to a fault condition particular to mercury arc rectiiers known as arc back. This fault or arc back is caused by the occasional inability of an anode and cathode pair to withstand the inverse voltage oc curring during the normally non-conducting portion of the cycle. Reverse or back current then begins and, once started, it increases rapidly. The ultimate current is limited by the arc drop of the faulted anodecathode pair, by the resistance of the reverse current path, and by the regulation of the remainder of the direct current system. Since the direct current system is large, and resistances in the reverse current path are low, the ultimate current is relatively large.

The ultimate arc-back current is much greater than that which might be tolerated, even momentarily, by the rectifier equipment due to the mechanical stresses and overheating involved. A cathode circuit interrupter, when used for arc-back protection must, therefore, open fast enough to limit the current to a tolerable value. In order to start the limitation of fast rising fault currents the earliest possible contact separation is required, and maximum contact opening acceleration is required to obtain early are lengthening and to withstand the high voltage across the contacts during and after interruption.

In conventional circuit interrupters, the amount of time` available for sequential separation of the main and arcing contacts does not present a ditiicult problem. However, in high-speed circuit interrupters involving opening operations within l cycle, based on 60 cycle A. C. current, the problem of reducing the opening time to a minimum, yet have time to first separate the main contacts and then separatethe arcing contacts, becomes a very diflicult problem. The time used in separating the main contacts is wasted, yet conventional circuit interrupters rely on contact iiexibility to make sure that Contact pressure is maintained through the small movement of main contact follow. I have found that by increasing the main contact mass the contact follow of the main stationary contact is slowed up. Even though satisfactory contact pressure is assured by spring pressure, the spring force need not be sufficient to instantly move the large mass of the main stationary contact if the movable contact structure is tripped and moved to open position at high speed. Thus by using such an arrangement together with a movable arcing contact having a small mass and a high opening force, this contact separation time is limited essentially to the time it takes the arcing contacts to separate.

An object of this invention is to provide a circuit interrupter embodying a contact structure capable of high-speed opening operation.

Another object of the invention is to provide a circuit interrupter embodying a contact structure capable of ICS early Contact separation following a tripping operation and high acceleration in opening direction.

Another object of the invention is to provide a circuit interrupter 'embodying an improved contact structure in which the main stationary contact is movable a small amount and biased to provide contact pressure, the ratio of the mass of the main contact to the force of the biasing means being relatively high to make the main stationary contact dynamically slow in motion.

Another object of the invention is to provide a circuit interrupter embodying an improved contact structure according to the preceding paragraph in which the ratio of the mass of the moving arcing contact to the force of the accelerating spring is relatively low to provide early separation of the main contacts and high-speed opening of the contacts.

The invention, both as to structure and operation together with additional objects and advantages thereof, will be best understood from the following detailed description thereof when read in conjunction with the accompanying drawings.

ln said drawings:

Figure 1 is a side elevational view partly in section of a circuit interrupter embodying the principles of the invention;

Fig. 2 is an enlarged elevational view of the stationary contact structure;

Fig. 3 is a horizontal sectional view taken on line III-III of Fig. 2 and looking in the direction of the arrows;

Fig. 4 is an enlarged elevational view of the movable contact structure;

lFig. 5 is a sectional view taken on line V-V of Fig. 4 and looking in the direction of the arrows;

Fig. 6 is an elevational view of a modified form of the contact structure; and

Fig. 7 is a top plan View of the contact structure shown in Fig. 6.

Referring to Fig. 1 of the drawings, the circuit interrupter is mounted in a rigid metal frame comprising a base portion 11 having spaced upright frame members 13 of insulating material rigidly secured to the base portion 11 at one end and similar but shorter spaced upright frame members 15 also of insulating material rigidly secured to the base portion 11 at the opposite end thereof. The circuit interrupter also includes stationary contact means indicated generally at 17 (Figs. 1 and 2) and movable contact means indicated generally at 19, operating mechanism indicated at 21, and a trip device shown generally at 23.

The stationary contact means comprises an arcing contact member 2S (Fig. 2) secured by means of bolts 27 to the upturned end 29 of a conducting bar 31. The conducting bar 31 is rigidly supported by means of a U-shaped bracket 33 (Figs. 2 and 3), the side portions 35 of which are rigidly mounted between the spaced frame members 13 by means of bolts 37. The lefthand end of the conducting bar 31 is secured by means of bolts 39 to a horizontal portion 41 of the bracket 33. The other end of the conducting bar 31 is rigidly supported by a support bar 43 having one end secured to the conducting bar 31 by means of bolts 45 (only one being shown) and the other end rigidly secured by means of bolts 47 (only one being shown) to the bracket 33 adjacent the upper end thereof. A pair of main stationary contact bars 49 (Figs. 2 and 3) each having a contact member 51 rigidly secured to the right-hand end thereof are supported beneath the conducting bar 31 for limited movement or Contact follow relative thereto. The contact bars 49 are supported on a support plate 53 which is rigidly supported on the conducting bar 31 by means of pairs of side plates 55 and 57, the side plates beingsecured to the' conducting bar 31 and to the support plate 53 by meansA of screws 59. Ther rightf pin 63 in the support plate 53 adjacent the right-hand end thereof. The left-hand end of the bars 49 are slidably supported on the support plate 53.

The main contact bars 49 have passages'therein to circulate-a suitable fluid for cooling purposes. The contact barsl 49 have integral laterally extending projections 65, each of which is provided with a connection 67 for connecting the contact bars'to a sourceV of fluid. Thecontact bars 459 also are provided with pipes 69 for' completingA the circuit of the cooling Huid.

The contactv bars 49 are biased toward the right (Figs.V 2 and 3) by coil springs '71 coiled around the pipes 69 and compressed between theY contact bars 49 and an angular bracket 73, the upturned left end of which is rigidly vsecured by means ofV bolts 75v to a bar 77. The

bar 77 is welded or otherwise rigidly secured to the outer' end ofthe portion 41 of ithe bracket 33 and to a center ribV 79 of the bracket 33. As seenin Fig. 3, ther'side portions 81 of the bracket 73 have formed over portions 83 which engage the top surfaceV of the conducting bar 31 to rigidly support the bracket 73.

Each of the contact bars 49 is connected by means of flexible conductors S4and S6 to conducting ,blocks 88 mounted'on the conducting bar 31 by means of'bolts 90, the exible conductors 34, 86 being secured by means of bolts 92 toV the vprojections 65* of the contact bars 49 and by means ofbolts 94 to the blocks 88., The movement of the main stationary contact bars 49 is limited to a small amount by adjustable stop screws Si) (Figs. 2 and 3) which are threaded into the left-hand ends of the contact bars 49- andV locked in adjusted position by lock nuts (not shown). During an openingoperation, the ends of the stop screws St? engage the left end of the support plate 53 to limit thecontact follow.

The movable contact structure 19 (Fig. 4) comprises a main moving contact S which cooperates with the main stationaryl contact member 51 and a moving arcing contact 87 which cooperates with the stationary arcing contact 25. The main moving contact 85 is rigidly mounted on the upper end oa Contact bar 89 rigidly securedby means'of bolts 91 and 93 to a'channel-shaped contact'carrier 95. The side portions of the channelshapedcontactcarrier 95 are individually pivotally supported-at their'lower ends on spaced bars 97 and 99- by means ofspacedfpivots 161', only oneof which is shown. The bars 97 and 99 are rigidly secured'to the upright' frame`- members 13 and 15 and are joined by cross'mernbers'103'and15. Thesmoving arcing contact 87 is mounted by means of a bolt 107 on the'upper end of a `channel-shaped contact arm '1119 which is pivoted on'apinlll carried'by the side portions of the channelshaped` carrier 95;

89 by a fiexible conductor 113v having its'upper'end secured between the arcing contact 87 and thel contact arm 109 by the bolt 107 and its lower end secured to the contact bar S9 by means of a bolt 115. The arcing.

contact arm 169 is biasedin a counterclockwise direction b'y a spring` 117 surrounding the bolt 91 and compressed between the contact bar 89 and a spring seat 119 welded or. otherwiserrigidly secured to the sideportions ofthe arcing contact arm 109. A nut 121 threaded onto the right endof the bolt 91 serves as a stopfor the arcingv contact: arm109 inthe open position of,themovable contact structure. The spring 117 provides contact pres-- the uppery ends of a pair of flexible conductors123 toi thelower end ofthe movable contact bar-.89. Thelower The movable arcing contact87 is connected'to theupper'end of the movable contact barv ends of the exible conductors 123 are secured by means of a'bolt 125 to a'vconductor 127 which is, in turn, secured to a main conductor 129.

The movable contact structure 19 is biased in opening direction by means of a strong spring 131 (Fig. 1') compressed between a retainer 133 held on a spring rod 135 by means of a nut 137 threaded on one end of the rod and a ange 139 of a shock absorber 141. The other end of the rod 135 is connected to-thepivot pin 111 (Figs. 4 and 5) on the movable contact structure. The shock absorber 141- is mounted ina block 143 forming part of a bracket 145 which is secured to the bars 97 and 99. The arcing and main contacts are closely coupled to reduce-the difference between the inductance of Vthe circuit paths through these contacts. t

The movable contact structure is held in the closed position against the bias of the accelerating spring 131 (Fig. l) by means of the trip device 23 which includes aholding'magnet 147. The'holding magnetcomprises a pair of armatures 149 and 151 connectedV to opposite endsofa bar 153' by links 155; A link 157 is pivotally connected at its lower end to the mid-portion of the barl 153 andat its upper end is pivotally connected by a pivot pin 159 to onefend of a rod 161 which has its other end pivotally connected by the'pin 111 to the mov-y ing contact carrier 95. One end of a link 163 ispivotallyV connected to theV link-157 and the rod 161 by thepivot pin 159, and the other end of the link 163 is connectedby means of a pivot pin- 165 to a lever 167 which has its other end-pivoted on a fixed pivot 169. OneV endof a toggle link 171 is-pivotally connectedto the link 163 and lever 167' by the pivot pin 165, and the other endl ofl the. toggle link 171 is connected'by a knee pivot-pinV 1734 to. a: toggle link 175 lmounted on'a fixedpivot 177. In the closed position of the circuit interrupter with thearmatures 149 and 151 in their attracted positions,

Va component-of thevforce of the-accelerating spring 131 holds .'thetogglell, 1.75 in an overset position against a. fixed stop 179V and above a line drawn through the centers offthe pivots 165 and 177, thus maintaining the movable contact structure in the closed contactpositionragainstthe force. of a spring 181which tends to cause collapse-of theigtoggle 171, 175. When either of the armatures 149 or 151 is releasedby the holding magnet v147, thelink 157 andthe rod 161 are free to move inV Whenthe toggle 171, 175A collapses, a pin 183 on the` end of the toggle link Y175 opposite the. knee pin 173 movesy upwardly inan elongated slot 135 in a linl r1t7`whichV atits lower end is connected by, means ofa pin129:toy

a crank arm191. Collapse` of the toggle 171, 175 also effects vmovement of the released armatures 149er y151 to its attracted position where it is heldA upon correctionl of the abnormal circuit conditions whichl effected. itsL release. With both of the armatures 149, 151 held in theirattracted positionsby the .holding magnet, rotation oi?A the crank arm191. draws the link 187 downduring whichY movement 1 the upper end'. of' the slot 185 engages the pin 183. and resets the. toggle 171, 175V tov its. overset position and, at the same time, acting.

through the link 163.and the rod ,161 moves the movable contact structure to the closed Contact position.

The: holding4 magnet is of the typev disclosed and claimed: in copending application Serial No. 507,595,

filed May 1l, 1955, by Joseph D. Findley and assigned to the'assignee of the instant application. For this reason onlya brief description ofthe holding magnet will be' given. v

The holding magnet'comprises a U-shaped magnet yoke 193 andthree-vpolepieces .195` whichbetween themctorm:

two air gaps, one associated with each of the armatures 149 and 151. A pair of coils 197 are mounted on the legs of the U-shaped magnet yoke 193 to produce a magnetic ux that traverses the air gaps adjacent the armatures 149 and 151. The coils 197 are connected to a suitable source of electrical energy.

The main current path adjacent the holding magnet comprises s-ubstantially parallel main conductors 199 and 201 which are connected at one end to a terminal 203 and at their other ends to the conductor 127 which is connected to the moving contact structure. The current path through the interrupter extends from the terminal 203, the parallel conductors 199 and 201, the conductor 127, movable and stationary contact structures 19 and 17, axible conductors 84 and 86 to the conducting blocks 88 thence through a copper coolant pipe 205 (shown broken away for clearness) to a terminal 207. Associated with the main conductor 199 is a forward ux diverter 209 and a reverse ux diverter 211 is associated with the parallel main conductor 201.

With the holding coils 197 energized and normal current owing in the parallel conductors 199 and 201, the armatures 149 and 151 are both maintained in their attracted positions, thus holding the movable contact structure in the closed contact position. Upon a predetermined rise of current in a forward direction, the current in the main conductor 199 causes the ux to be shunted through the diverter 209 around the air gap for the armature 149, thus reducing the ux through this armature to approximately zero causing high-speed release of the armature and opening of the interrupter contacts.

When the direction of current ilow is reversed, the main conductor 201 causes the magnetic ux to be shunted through the diverter 211 around the air gap for the armature 151 reducing the magnetic flux through this armature to approximately zero and causing high-speed release of the armature 151 and opening of the contacts. The mechanism is reset and the contacts closed following an opening operation in the previously described manner.

In order to obtain main contact separation as early as possible in the opening operation the ratio of the mass of the moving stationary contact bars 49 in pounds to the force of the springs 71 in pounds is relatively large compared to previous circuit interrupters. For example, this ratio may be in the neighborhood of 1 to 10, which makes the contact bars dynamically slow. In one practical` form of the invention, the main contact bars 49, for instance, may each weigh 7.5 pounds and the springs 71 each may apply a force of 75 pounds. Also, the ratio of the mass of the movable contact structure to the force of the accelerating spring 131 is relatively small, for example, of the order of l to 200, to provide for highspeed separation of the contacts. The spring 117 provides contact pressure and ensures that the movable arcing contact 87 will separate after the main contacts separate and, in this action, the spring is assisted by the inertia of a mass of the movable arcing contact which tends to remain stationary during the opening movement until the moving contact arm 109 engages the nut 121. It will thus be seen that the inertia of the movable portion of the stationary main contacts permits the main contacts to separate quickly, for example, in less than .001 second, and the inertia of the movable arcing contact delays separation of the arcing contacts, the total contact separation time being, for example, napproximately .002 second.

In the modification of the contact structure shown in Figs. 6 and 7, the main stationary contact, in addition to the ratio of the mass to the actuating spring pressure, utilizes a gripping action caused by the flux due to parallel current paths through the contact member to further restrain the action of instant motion or contact follow of the movable portion of the main stationary contact.

The stationary contact structure shown in Fig. 6 comprises generanl a main stationary contact member 215 slidably mounted on a conducting bar 217, and a stationary arcing contact 219 rigidly secured by means of a bolt V221 to the conducting bar 217. The conducting bar 217 is rigidly supported in the same manner as the bar 31 as shown in Fig. 2. The stationary main contact member 215 is U-shaped and is divided into a plurality of resilient fingers 223 which slidably engage the upper and lower surfaces of the conducting bar 217. A contact 225 is mounted on the main contact member 215 and the contact member is biased by means of one or more springs 227 into engagement with a plurality of movable main contacts 229 which are individual contact ngers 231. The contact ngers 231 are rigidly mounted by suitable means in a movable channel-shaped switch arm 233 pivotally supported at its lower end on the bars 97, 99 (Fig. 1) 'by means of spaced pivots not shown in Fig. 6 but which are like the pivots 101 shown in Fig. 1. A movable arcing contact 235 is pivotally mounted on a pin 237 supported in the side members 239 of the channel-shaped switch arm 233 and is biased by a spring 241 into engagement with the stationary arcing con tact 219. The spring 241 is compressed between a spring seat 243 on the movable arcing contact 235 and an extension 245 of the switch member 233 and surrounds a rod 247 threaded into the movable arcing contact. The rod 247 extends through a clearance opening in the extension 245 and has a nut 249 threaded onto the outer end thereof which acts as a stop to limit the movement of the movable arcing contact 235 relative to the movable main contacts during an opening operation. The spring rod and the operating rod 161 are pivotally connected to the pin 237 in order to operate the movable switch arm 233 in the manner previously described.

The operation of the contact structure shown in Figs. 6 and 7 is similar to that of the contacts shown in Figs. l and 4. When either of the armatures 149 or 151 (Fig. l) is released in response to a rise in forward or reverse current, the accelerating spring 131 snaps the movable switch arm 233 (Fig. 6) to the openposition at high speed. Due to the relatively high ratio of the mass of the contact member 215 to the force of the springs 227 the main stationary contact member 215 tends to remain stationary while the moving main contact separates therefrom very early in the opening movement. This action is aided Aby the parallel currents owing in the fingers 223 of the main stationary contact member 215 which causes the ngers to apply a gripping force to the support bar 217 and further delays or retards the movement or contact follow of the contact member 215. The contact follow of the main stationary contact member 215 is limited by engagement of shoulders 251 (Fig. 7) on the inner ngers 223 engaging the inner end 253 of the stationary arcing contact 219.

The spring 241 ensures that the arcing contacts will separate after the main contacts separate and the spring 241 is aided by the inertia of the mass of the moving arcing contact 235 which tends to remain stationary during the opening movement. It will thus be seen that inertia plus the gripping action caused by the parallel circuits in the ngers of the main stationary contact member allows the main contacts to separate quite early in the opening operation, for example, in less than .001 second, and inertia assists the arcing contacts to remain in engagement until after the main contacts have separated a predetermined distance.

The current path between the main contacts and the current path between the arcing contacts are closely and mutually coupled to reduce the reluctance between the current paths in order to keep the sparking voltage developed as a result of transferring the current from the main contacts to the arcing contacts as low as possible to prevent pitting of the contacts and to avoid the use` of tlexible conductors.

Having described the. invention' in accordance with. the yprovisionsof the patent statutes, it is tobeunderstood 'means having a relatively largemass, stationary arcing contact means, meanssupportingfsaid stationary main. contact means for limited movement relativeto saidv stationary arcingcontact means, movable main and arcing contact means i cooperating with said stationary main and arcing contact means, biasing means vbiasing. said stationary main. contact With-a relatively light force to providecontactpressure, operating means for moving said movablecontact means to open and closed positions, and the ratio of the mass of said stationary main contact meanszto the forceof said. biasing means being relatively largey to make said. stationary main contactdynamically slow inmotion and/thereby eiect separation of said main contact means Jearly, in'` anopening operation.

. 2. InV a circuit interruptor, stationary. main contact means-having a relatively. large mass, stationary arcing contact means,rmeans supportingsaid stationary main contact means on said stationary arcing contact means for limited sliding. movement relative tosaidstationary arcing contact means, movable main andarcing contact means-cooperating with said stationary-main andarcingl contact means, biasing Vmeans biasing said stationary main contact with a relatively light. force to provide-.contact pressure, operating. means for moving said movable contact means to open. and closed positions,.and the ratio ofthe mass. of .said stationary main contact means to therforce ofsaid biasingmeans being relatively large to make said stationary main contact dynamically slow inY motion and therebyeffectseparation of said main contactrneans early in .an opening operation.

3. in a circuit interrupter, a stationaryy main contact having a relatively large mass, a stationary arcing contact, means supporting saidstationary main contact 'for limited movementrelative to said stationary arcing contact, a movable.. switch arm. having av movable main contact rigidly mounted thereon,. a movable arcing Contact mounte'don. said switch arm for limitedmovement rela# tive to said movable main contact, biasing means biasing said stationary main Contact with a relatively light force to provide contact pressure between'said main contacts,

means biasing said movable. arcing contact'to provide contact pressure, operating means biased to move saltiV movable switch arm to open position to provide highspeed lopening of said contacts, the ratio of the mass of saidstationary main contact to the force o'itsbiasing means-being relatively large to make said stationary main contact dynamically slow in motion to thereby eiect early separation of said main contacts, and the mass of said...1:novable arcing contact assisting' its biasing means to maintainlsaid arcing contacts closed until after the main contacts have separated during an Vopening operation.

4. In a circuit interruptor, stationary main contact means having a relatively large mass, stationary arcing contactrneans, means supporting said stationary main.

contact means for limited movement relative to said stationary arcing contact means, movable main and arcing ,contact means cooperating with said .stationary main and arcing contact means, the current paths through. said main contacts and said arcing. contacts being closely andV mutually` coupled to reduce. the inductance of said current paths, biasing meansbiasing said stationary main contact with a relatively `light force toprovide contact pressure, operating means formovingvsaid movable contact .means to open. and; closed positions, ,and theratio. ofrthe .mass of saidstationary main Acontact means :tothe w force. of said biasingv means being relatively large to.

make said'l stationary main contact. dynamically. slow inmotion and thereby electseparation of said main.l contact means early in an .opening operation.

5. In. acircuit .interrupten relatively movable contact meanscomprisingaa stationary arcing Contact, support means .rigidly supporting said stationary arcing. Contact, a U-shaped stationary main contact` member slidably supported von. saidsupport'means for limited movement relativeto .said .stationary arcing contact, the legsof said U-shaped main contact member applying a pressure to opposite. sides of said support means, movable. contact means comprising movable arcing and main contacts cooperating With said stationary arcing and main contacts, operating means for moving said'movable contact means toppen and closed positions, means biasing said- U-shaped stationary contact with .a relatively light force to provide contact pressure, andthe ratio of the mass of said- U-shaped'i stationary main contact to the biasing force of saidf biasing means being relatively large to make' said stationary main .contact dynamically slow in motion.

6. In a circuit interrupter, relatively movablecontact means. comprising a stationary arcing contact, support4 means rigidlyy supporting said stationary arcing contact, a U-sliaped main stationary contact member having legs engaging opposite sides of said support means slidably supporting said main contact member on said support means for limited movement relative to said stationary arcing contact, the legs of said U-shaped'stationary contact member forming parallel current paths, saidlegs. of said stationary 'main contact member applying. apredetermined pressure to opposite sides of said support means to retard movement of'said stationary main contact member, cooperating movable Contact means comprising movable arcing and main contacts, operating means for moving said'movable contact means to open and closed positions, biasingrneans biasing said U-shaped main contact member to provide contact pressure, and the legs of said U-sh'apedstationary Vmain contact memb'erbeing responsive to the' current tlowing in saidparallel current paths to increase the pressure of Vsaid legs .on said" support'member to further retardmovement of said U- shaped stationary mainfc'ontact member.

7`. In a circuit interrupter, relatively movable contact means comprising a stationary arcing contact, support means rigidly supporting said stationary arcing contact, a U-snaped main stationary contact member having legs engaging opposite sides of saidsupportmeans slidably supporting said'rnain contact member on said support means for limited movement'relative to saidvv stationary arcing contact, the legsof said U-sbaped stationary 'con'- tact member forming parallelcurrentpaths, said legs'of` said'stationary main contact member applying a predetermined pressure to opposite sides of said support meansl to retard movement of saidstationary main contact member, cooperating movable contact means comprising movable arcing and main contacts, operating means for'moving. saidmovable:contactmeanstoopen and closed posi'-` ti'ons, biasing meansbiasingsaid'U-sliaped` main contact memberto providecontact'pressure, the ratio of the mass of'said stationary main contact member to the biasing force of said biasing means being'relatively` large to make* said stationary main contact member dynamically slow in motion, andl the legs ofsaid U-shaped stationary main contactmember being responsive to the current owing in' said parallel current paths to'increase the pressure of saidV legs on said support member to Vfurther retard movement of saidl U-shaped" stationary main Contact member.'

S. In a circuit interrupter, relatively movable contact means comprising a stationary arcing contact, support means rigidly supporting said'stationary arcing Contact, a

. stationary main Contact member slidablymountedon said support member forlirnited movement relative to said' stationary,farcinggcontact, a plurality of resilient membersk members forming parallel current movable contact means comprising movable arcing and main contacts, operating means for moving said movable contact means to open and closed positions, biasing means biasing said stationary main contact to provide contact pressure, and said resilient members being responsive to the current flowing in said parallel current paths to increase the pressure of said resilient members on said support means to thereby further retard the movement of said stationary main contact member.

9. In a circuit interrupter, stationary main contact means having a relatively large mass, stationary arcing contact means, means supporting said stationary arcing contact means and supporting iXedly said stationary main contact means for movement relative to said stationary arcing contact means, stop means for limiting the movement of said stationary main contact means, movable main and arcing contact means cooperating with said stationary main and arcing contact means, biasing means biasing said stationary main contact means to provide contact pressure, operating means for etecting high-speed opening movement of said movable contact means, the mass of said stationary main contact means and the force applied thereto by said biasing means being such that said main contacts separate before any substantial movement of said stationary main contact means.

l0. In a circuit interrupter, stationary main contact means having a relatively large mass, stationary arcing contact means, means supporting said stationary main contact means for movement relative to said stationary arcing contact means, stop means for limiting the movement of said stationary main contact means, movable main and arcing contact means cooperating with said stationary main and arcing contact means, biasing means biasing said stationary main contact means to provide contact pressure, operating means for effecting high-speed opening movement of said movable contact means, the mass of said stationary main contact means and the force applied thereto by said biasing means being such that paths, cooperating 10 said main contact means separate early in the movement of said stationary main contact and before the limit of the stationary main contact movement is reached.

1l. In a circuit interrupter, stationary main contact means having a relatively large mass, stationary arcing contact means, means supporting said stationary contact means for limited contact follow, movable main and arcing contact means cooperating with said stationary main and arcing contact means, biasing means biasing said stationary main contact means to provide contact pressure, operating means for effecting high-speed opening movement of said movable contact means, and the ratio of the mass of said stationary mass contact means to the force of said biasing means being such that said main contact means separate early in the stationary main contact follow and before the limit of said main Contact follow is reached.

l2. In a circuit intelrupter, stationary main contact means having a relatively large mass, stationary arcing contact means, means supporting said stationary contact means for limited contact follow, stop means limiting said main contact follow, movable main and arcing contact means cooperating with said stationary main and arcing contact means, biasing means biasing said stationary main contact means to provide contact pressure, operating means for effecting high-speed opening movement of said movable contact means, and the ratio of the mass of said stationary mass contact means to the force of said biasing means being such that said main contact means separate early in said stationary main contact follow and before the limit of said main contact follow is reached.

References Cited in the tile of this patent UNITED STATES PATENTS 2,069,641 Bold et al. Feb. 2, 1937 2,214,471 Ludwig et al Sept. 10, 1940 2,545,341 Caswell Mar. 13, 1951 2,691,086 Milne et al. Oct. 5, 1954

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