US 3873791 A
A current limiting circuit breaker capable of interrupting a short circuit current of hundreds of thousands of amperes well short of its prospective peak amplitude utilizes a vapor-state current limiter to directly operate circuit interrupter contacts. The current limiter, connected in series with the interrupter contacts, incorporates a ram whose movement in response to vaporization and resulting expansion of the current limiting material is directly operatively coupled to open the interrupter contacts with exceptional speed.
Claims available in
Description (OCR text may contain errors)
O United States Patent [191 [111 3,873,791 Hurtle Mar. 25, 1975  CURRENT LIMITING CIRCUIT BREAKER 3,183,331 5/1965 Barkan 200/147 C Inventor: Ralph y Hurtle, West Hartford 3,389,360 6/1968 Keenan 337/114 R Conn Primary Examiner-Robert S. Macon  Assignee: General Electric Company, Attorney, Agent, or Firm-R. A. Cahill; P. L. Schlamp;
Schenectady, NY. F. L. Neuhauser 22 Fil d: No 8, 1973 1 e v 57 ABSTRACT L Appl' 4l4l A current limiting circuit breaker capable of interrupting a short circuit current of hundreds of thousands of 2] U-S-Cl- 200/144 R, 200/147 C, 337/114, amperes well short of its prospective peak amplitude 337/115 utilizes a vapor-state current limiter to directly oper-  Int. Cl. ..H01h 33/00 ate Circuit n pt n a ts. h urr nt imi  Field of Search 200/144 R, 147 R, 147 C; connected in series with the interrupter contacts, in- 337/114, 1 l5 corporates a ram whose movement in response to vaporization and resulting expansion of the current limit-  References Cit d ing material is directly operatively coupled to open the UNTED STATES PATENTS interrupter contacts with exceptional speed. 2,732,460 l/ l956 Benchemoul 337/115 R 22 Claims, 8 Drawing Figures PATENTED 3,873,791 sumaq g Ill/ 0 BACKGROUND OF THE INVENTION The expansion of electrical generation capacity necessitated by the dramatic increase in electrical power consumption has resulted in raising current availables to figures beyond the interrupting capacity of existing circuit breakers. The term current available is used in the art to refer to the magnitude of current that would flow if the source of current was connected to a zero impedance load, e.g., by short-circuiting its output terminals. Whereas current availables of 30,000 to 50,000 amperes were typical in the past, current availables of 100,000 to 300,000 amperes are presently not uncommon. The current that would actually flow in a power distribution circuit as the result of a short-circuit condition is less than the available short-circuit current due to the inevitable impedance between the source and the location in the circuit of the shortcircuit fault. Such prospective short-circuit currents nevertheless reach formidable magnitudes and must be interrupted quickly in a current limiting manner to prevent damage to the distribution circuit and the equipment connected thereto.
It is currently common practice to use current limiting fuses alone or in combination with circuit breakers to cope with short-circuit currents of such magnitudes. Fuses, while quite successful in terms of short-circuit current interruption, have the distinct disadvantage of being one-shot devices and thus must be replaced after each interruption.
Circuit breaker-current limiting fuse combinations, wherein the one-shot current limiting operation of the fuse or fuses also initiates operation of an associated actuating member adapted to trip the circuit breaker, are well known, as exemplified in US. Pat. No. 3,345,481. The same approach has been suggested in British Pat. No. 1,209,020 using a vapor-state current limiter in combination with a circuit breaker. A plunger acting in response to vaporization of the material within the limiter actuates the trip mechanism of the circuit breaker, thereby enabling the circuit breaker operating mechanism to separate the breaker contacts and thereby effect circuit interruption. The use of a vapor-state current limiter rather than a conventional fuse in combination with a circuit breaker is advantageous in that the former, if properly designed, does not self-destruct, and thus need not be replaced with each interruption. However, the action of the operating mechanism of a circuit breaker to finally effect circuit interruption is a relatively slow procedure as compared to the operation of the vapor-state current limiter. Even though the vapor-state current limiter operates to crest a short-circuit current iii current limiting fashion and reduce the current magnitude, it will sustain a so-called regulated or fuse current of considerable magnitude, possibly as high as 10,000 amperes, while the normal circuit breaker operating mechanism is acting to effect circuit interruption. Flow I of this regulated current is damaging in two ways. Firstly, it erodes the internal parts of the vapor state device, and so heats it that an auxiliary resistor must be connected in parallel with it to prevent its destruction. Secondly, the distribution circuit and the various connected loads may be heated excessively.
It is accordingly an object of the invention to provide a current limiting circuit breaker capable of safely interrupting short circuit currents of extremely high magnitudes.
A further object is to provide a current limiting circuit breaker of the above character which is selfrecoverable or selfrestoring after each interruption.
Still another object is to provide a current limiting circuit breaker of the above character having an extremely fast operating speed.
Other objects will in part be obvious and in part appear hereinafter.
SUMMARY OF THE INVENTION In accordance with the present invention, there is provided an improved current limiting circuit breaker utilizing a vapor-state current limiter to not only perform a current limiting function but also to serve as an integral part of the operating mechanism acting to separate the contacts of a circuit breaker, thereby to achieve circuit interruption in an extremely rapid manner. The vapor-state current limiter incorporates a resiliently based plunger operatively coupled to the current limiting material confined within the limiter. The plunger yields to accommodate explosive expansion of the current limiting material during current limiting operation, thus affording an economical casing design. A ram carried by the plunger extends exteriorly of the limiter casing with its external end portion operatively coupled, not with a circuit breaker trip mechanism, but directly to the movable contacts of the circuit breaker. As the plunger yields in response to vaporization of the current limiting material, the ram is stroked to open the breaker contacts with extreme abruptness.
Further in accordance with the present invention, the operative coupling between the ram and the circuit breaker movable contacts is uniquely designed to withstand the tremendous forces developed by the ram as it is stroked estimated to be about 10,000 times the force of gravity. More specifically, a resilient lever operatively coupled at one end to the ram and at its other end to a movable contact carrier assembly makes rolling contact at an intermediate location with a dowel and thus is pivoted thereabout to transform the motion of the ram into contact separating movement of the contact carrier assembly.
To prevent rebounding movement of the contact carrier assembly and consequent contact reclosure, novel retention means is provided to arrest the contact opening motion of the carrier assembly and to temporarily grasp it, thereby inhibiting return movement thereof.
Still another feature of the invention resides in the paralleling of a plurality of vapor-state current limiters the number depending on the current rating required for a particular application with only one of the current limiters being equipped with a contact operating ram. It is found that short circuit currents substantially equally divide among corresponding, parallel DESCRIPTION OF THE DRAWINGS For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:
FIG. 1 is a plan view, partially broken away, ofa current limiting circuit breaker constructed according to an embodiment of the invention;
FIG. 2 is an exploded view ofa portion of the current limiting circuit breaker of FIG. 1;
FIG. 2A is an enlarged, fragmentary view ofa portion of FIG. 2;
FIG. 3 is a side elevational view, partially broken away, of a ram-equipped, vapor-state current limiter utilized in the current limiting circuit breaker of FIG.
FIG. 4 is a longitudinal sectional view of one of paralleling vapor-state current limiters utilized in the current limiting circuit breaker of FIG. 1;
FIG. 5 is an enlarged fragmentary view of a portion of the current limiting circuit breaker of FIG. 1 illustrating the contact carrier anti-rebound assembly incorporated therein;
FIG. 6 is an enlarged sectional view taken along lines 6-6 of FIG. 1; and
FIG. 7 is a graph of current versus time, showing a short-circuit interruption performed by an embodiment of the present invention.
Like reference numerals refer to corresponding parts throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE INVENTION The current limiting circuit breaker of the invention seen in Flg. 1 comprises a line terminal block 10 for connection to a source of electrical power (not shown) and a load strap 12 for connection to a load (also not shown). The line terminal block 10 is connected to a line strap 14 by way of a ram-equipped, vapor-state current limiter, generally indicated at 16, and one or more paralleling non-ram-equipped, vapor-state current limiters; two being generally indicated at 18. Strap 14 is mounted by an insulative base in current conductive engagement with one end of a strap 22. The
other end of strap 22 is disposed in current conductive engagement with one end of still another strap 24 whose other end carries a stationary contact 26 which is elongated transversely to the plane of the drawing. The end of load strap 12 adjacent bus bar 24 also carries a similarly elongated stationary contact 28. Contacts 26 and 28 are bridged by a plurality of movable, wedge-shaped contacts 30 mounted in vertical alignment by a contact carrier assembly, generally indicated at '31.
From the description thus far, it is seen that the current path between the line terminal block and strap 14 is divided up into essentially equal current paths afforded by current limiter -l6 and the plurality of current limiters 18. From strap 14 the current. flows through straps 22 and 24. The circuit breaker stationary contacts 26 and 28, and the movable contacts 30 convey the current'frorn strap 24 to load strap 12. Movable contacts 30 which, together with stationary contacts 26 and 28, constitute the main circuit breaker contacts, are, as will be more clearly seen from the description of FIG. 2, carried by a plurality of tubular carrier members 32 reciprocated in concert by the carrier assembly 31 to effect circuit closure and interruption. The left hand ends of several of the members 32 (two out of four in the illustrated embodiment) carry wedgeshaped arcing contacts 34 operating in a secondary current path to which current flow is transferred during circuit interruption by the main contacts. This transfer is achieved by mounting the movable main and arcing contacts in the carrier members with varying degrees of lost motion such that when the carrier members 32 are reciprocated to the right, as seen in FIG. I, the main contacts are separated before the secondary current path is interrupted. The arcing contacts 34 cooperate with stationary contacts 36 and 38 carried by conductive arc runners 40 and 42, respectively. Arc runner 42 is mounted in current conducting engagement with load strap 12. It is thus seen that this secondary current path shunts the main contacts, and by the positioning of the arcing contacts the ultimate circuit interruption between line and load is effected at the entrance to an arc chute, generally indicated at 44. Since the details of arc chute 44 are not a part of the instant invention, its description herein is considered unnecessary. An arc chute suitable for use in the present invention is fully disclosed in applicants US. Pat. No. 3,5 15,829 and the disclosure of the patent is specifically incorporated herein by reference. By virtue of providing both main and arcing contacts, with the former separating first during an interruption, the main contacts are not subjected to the degrading effects of arcing and thus can be composed of or plated with quality contact material, such as silver. The arcing contacts, since they only carry appreciable current during an interruption, may be composed of a refractory conductive material.
As a feature of my invention a pair of blowout coils 45 are connected in series with each other between line terminal block 10 and strap 22, as seen in FIG. I, thus electrically paralleling current limiters 16 and 18. The resistance of the blowout coils is considerably higher than that of the current limiters under normal conditions and thus carry negligible current. This permits the A blowout coils 45 to be formed of many turns of small diameter wire. When the current limiters fire, their resistances increase dramatically and appreciable current is diverted to the blowout coils. The many turns of the blowout coils increase the electromagnetic forces tending to propel the are out into arc chute 44, thus enhancing the abruptness of the quench. This diversion of a portion of the current from the limiters to the blowout coils also assists the limiters in dissipating the energy involved in a short circuit interruption.
Current limiters l6 and 18 are for the most part identically constructed to comprise, as best seen in FIG. 4, an annular metallic casing 50 accommodating'a ceramic sleeve 52 into which is inserted a ceramic core 54. A plurality of longitudinal channels 56 are formed in angularly spaced relation at the interface of sleeve 52 and core 54, such as described and claimed in my co-pending application Ser. No. 355,693, filed Apr. 30, 1973. Channels 56, which are filled with a suitable conductive, vaporizable material, such as mercury or one of the alkali metals such as sodium, potassium, etc., may take a variety of shapes such as the bell-mount cross section illustrated in FIG. 4. The left end of core 54 is in abutting engagement with a conductive plate 58 having apertures 58a aligned with channels 56. The other end of ceramic core 54 is turned down, as indicated at 54a, for receipt in a recess 60a formed in a metallic fitting 60. The right hand end of fitting 60 is turned down to fit within a central recess 620 formed in the limiter line terminal 62. This-line terminal is threaded for bolted connection to the line terminal block as seen in FIG. 1. Intermediate terminal 62 and fitting 60 is a Bridgman seal 63 adapted to prevent leakage of current limiting material from channels 56 therepast. This current limiting material also fills the bottom of central recess 62a in terminal 62 to insure a good current conductive path between the terminal and fitting 60.
A cup-shaped end cap 64, provided with a central aperture to accommodate the extension of terminal 62 therethrough is threaded on the right end of case 50. Cap 64 longitudinally compresses a sleeve of resilient dielectric material 65 against an internal ledge 50a formed in case 50 to electrically insulate the case from terminal 62. A cup-shaped insulating plastic cap 70, such as disclosed in my US. Pat. No. 3,735,309, is formed having a re-entrant portion 70a to electrically insulate the terminal 62 from end cap 64.
Referring now to the other end of current limiter l8 seen in FIG. 4, a metallic cylinder 72 is fitted partially within the central cavity of .casing 50 in end-abutting relation with apertured disc 58. An end cap 74 is threaded on the left end of the casing 50 in closure relation with both the casing and cylinder 72. Operating within cylinder 72 is a plunger 76 backed by a gas accommodated in the space 78 between it and a pressure sealing end plug 80. A suitable seal 76a on plunger 76 and a seal 80a on end plug 80 maintain the gas confined within space 78.
The current path for current limiter 18 extends from terminal 62, electrically connected to line terminal block 10, plug 60, the current limiting material in channels 56, plate 58, and cylinder 72 to end cap 74, which serves as the load end terminal of the limiter. End cap 74 is externally threaded for receipt in a threaded bore 14a in bus bar 14 (FIG. 1), thereby completing a current path between terminal block 10 and bus bar 14. The internal wall of case 50 and the external surface of ceramic sleeve 52 are complementarily tapered, such that upon assembly of the sleeve therein, the sleeve is preloaded in compression so as to withstand the tremendous pressures generated within the current limiter as the current limiting material vaporizes in response to v excessive current. Upon vaporization, plunger 76. is reciprocated to the left as seen in FIG. 4 so as to maintain this internal pressure within manageable limits, consistent with the case design.
Current limiter 16 is identical in construction to current limiter 18 except that, as seen in FlG. 3, end cap 74'is replaced by an elongated cylinder 84 threaded on the left hand end of case 50 to accommodate a ram 86 having a plunger end 86a, equivalent to plunger 76 in current limiter 18, in operative contact with the current limiting material. Ram 86 is flanged as indicated at 86b to provide a ledge for seating one end of a compression spring 88. The other end of this spring seats against the end wall of cylinder 84 which is centrally apertured at 840 to accommodate the extension of the free end 860 of ram 86 therethrough. It will be appreciated that spring 88 performs the same function as the confined gas in space 78 of current limiter 18, Le, to pressure buffer the current limiting material fill within the current limiter. Elongated sleeve 84 extends through an aperture 146 in strap 14 and is provided with external threads to accommodate threaded engagement with a threaded bore in a plate 15 in electrically contacting engagement with strap 14 to thus provide a current path between terminal block 10 and this strap paralleling the current path afforded by each of the current limiters 18 (FIG. I).
As seen in FIG. 1, the free end 860 of ram 86 impacts against one end ofa lever 90 upon firing of current limiter 16 to reciprocate contact carrier assembly 31 from a position of circuit closure to a position of circuit interruption. Referring jointly to FIGS. I and 2, the contact carrier assembly includes a mounting cylinder 94 equipped at one end with a flange 96 facilitating mounting to straps 24 and 12. An annular cage member 98 is slidingly received within cylinder 94. Also received within cylinder 94 is a sleeve 100 in partial overlapping relation with cage 98 over the turned down external surface portion 98a thereof. Diametrically opposed pins 101 accommodated in aligned holes 98b and 100a in the cage and cylinder, respectively, lock these two members together. Diametrically opposed pins 102 fitted in apertures 10012 in sleeve 100 and projecting through elongated slots 94a in cylinder 94 permit limited telescopic movement of the sleeve and cage relative to the cylinder 94.
Accommodated within cage 98 is a holder 104 of electrically insulative material. Holder 104 has a longitudinal exterior surface profile as seen in FIG. 2A to effect a detenting action in conjunction with a garter spring 106 accommodated in an internal annular groove 98c formed in cage 98. Holder 104 is also provided with a series of axially extending through bores 104a for accommodating a pair of outboard main Contact carriers 32a and a pair of intermediate, elongated, combination arcing and main contact carriers 32b seen in FIG. 2. An elongated pin 107 extends through a transverse through bore 1041: (FIG. 2A) in holder 104 and through aligned transverse apertures 320 in the right ends of the tubular contact carriers 32a and 32b, thereby locking the carriers within the holder. The sidewall of each contact carrier 32a and 32b extending just beyond the left hand end of holder 104 is formed with transversely aligned rectangular apertures 32d into which the main, wedge-shaped contacts 30 are inserted. Springs 108 accommodated within the contact carriers between pin 107 and the respective main contacts 30 bias the main contacts to the left as seen in FIGS. 1 and 2, thereby insuring adequate contact pressure with stationary main contacts 26 and 28.
Still referring to FIGS. 1 and 2, a cylindrical insulating block 110 having a pair of axial through bores 110a is inserted on the elongated portions of contact carriers 32b beyond. the main contacts 30. A dielectric sleeve 112 is shrunk onto the oval shaped end of insulating block 110 to cover locking pin 113 inserted through aligned holes 110a and 32c to secure block 110 to carriers 32b. As seen in FIG. 1, insulating block 110 is accommodated in recesses 40a and 420 formed in arc runners 40 and 42, respectively. These recesses receive inserts 111 of oblating material which, in presence of an arc, gives off a gas which assists in forcing the are out into the arc chute 44. A seal 113 prevents arc gases from flowing back into the region of the main contacts. Sleeve 112 serves as an isolation barrier between the elongated contact carriers 32b and the stationary main contacts 26 and 28 when the contact carrier assembly is shifted to the right as seen in FIG. 1 to a circuit interrupting position. Straps 12 and 24 are recessed at 12a' and 24a, respectively, to accommodate block 110 as it is shifted to the right. The sidewall of the elongated contact carriers 32b beyond block 110 are provided with transversely aligned rectangular apertures 32f accommodating arcing contacts 34. Openings 32f accommodating arcing contacts 34 have a slightly larger longitudinal dimension than openings 32d accommodating main contacts 30, such that, upon reciprocation of the carrier assembly 31 to the right, the main contacts are engaged by the trailing edges of their respective openings prior to the engagement of the trailing edges of openings 32f with the arcing contacts. Consequently the main contacts open first and current flow is transferred to the secondary current path ultimately to be interrupted by the arcing contacts. Springs 116 accommodated in the elongated contact carriers 32b between the arcing contacts 34 and pin 113 serve to bias the arcing contacts to the left as seen in FIGS. 1 and 2. Preferably, a solid disc 117 is interposed between springs 116 and pin 113 to serve as a barrier against the passage of arc created ionized gases up the elongated contact carrier tubes to the vicinity of the main contacts.
An operating'rod 120 having a flange 122 formed in its left end, as seen in FIGS. 1 and 2, is secured to the right face of holder 104 by screws 124. Operating rod 120 is formed with an elongated transverse slot 126 for receipt of the other end of lever 90 (FIG. 1). The portion of operating rod 120 beyond slot 126 is formed with a series of annular grooves 128 which cooperate with an anti-rebound assembly, indicated generally at 130 in FIG. 1.
The anti-rebound assembly 130, as best seen in the enlargement of FIG. 5, includes a cup-shaped housing 132 having a threaded shaft 135 extending from the closed end thereof for threaded engagement in a tapped bore 136 formed in a plate 15. A lock nut 138 threaded on shaft 135 is used to facilitate fine adjustment of the longitudinal position of the housing 132. Accommodated within housing 132 are a pair of rubber discs 140 and 142 positioned against the closed end thereof. Positioned between rubber disc 142 and the inwardly turned end 132a of the housing sidewall is an annular rubber sleeve 144. Rubber disc 140 is preferably formed with a series of apertures 140a in its central portion to enhance its compressibility. When the current limiter 16 fires and the ram 86 moves to the left as seen in FIG. 1 with tremendous acceleration, estimated to be in the order of 10,000 gs, lever 90 moves the contact assembly. 92 to the right asseen in FIG. 1. The grooved end of the operating rod 120 slams against the two rubber discs 140 and 142, causing them to flow radially outwardly. Since the peripheries of these rubber discs are confined by housing 1320f the antirebound assembly, the rubber disc material flows around the end of the operating rod to compress the rubber sleeve 144. Since the rubber sleeve is confined on three sides by housing 132 and rubber disc 142, the only direction it can flow under compression is radially inwardly into the annular grooves 128 formed in operating rod 120. As a consequence, the operating rod 120 is gripped by the rubber sleeve 144, thereby preventing it from rebounding back to the left as seen in FIG. 1 and thus precluding the possibility of contact reclosure.
As seen in FIGS. 1 and 6, lever 90 is pivotally mounted intermediate its ends by a yoke 150 which is in turn mounted by plate 15. The lever passes between the spaced legs 150a of yoke 150 and is urged into rolling contact with a dowel 152 by a spring 154. Dowel 152 is mounted at its ends by the yoke legs 150a to span the gap therebetween. Spring 154 is seated at one end in a recess 150b formed in the crotch of yoke 150, while the other end of this spring is seated against the surface of lever opposite from dowel 152. A washer 156 secured to lever 90 provides recessed seating for this end of spring 154. It is seen that when current limiter 16 tires, ram 86 impacts the lower end of lever 90 as seen in FIG. 1. Lever rolls about dowel 152 causing the other end of the lever operating in actuating rod' slot 126 to reciprocate the contact carrier assembly 31 to its circuit interrupting position. Lever 90 is preferably formed of high quality spring steel so as to withstand the tremendous impacting force exerted on it by ram 86 of current limiter 16.
An annular ridge 160 having sloping or cam-shaped sides is formed on the peripheral surface of holder 104 to cooperate with garter spring 106 in releasably retaining the contact carrier assembly 31 in either its circuit closure or circuit interrupting positions. When the carrier assembly is in its circuit closure position, garter spring 106 embraces holder 104 to the right of ridge 160 as seen in FIGS. 1 and 2A. When current limiter 16 fires and its ram impacts level 90 thereby forcing the carrier assembly to the right as seen in FIG. 1, garter spring 106 expands allowing ridge 160 to pass pursuant to releasing the carrier assembly from its contact closure position. Due to the exceedingly low mass of garter spring 106, the release of the carrier assembly from its contact closure position is achieved with virtually no delay. After the circuit interrupting motion of the contact carrier assembly 31 has been arrested by the anti-rebound assembly and the force exerted on the contact carrier assembly by lever 90 has subsided due to progressive restoration of current limiter l6, garter spring 106 embraces holder 104 to the left of ridge to retain the carrier assembly in its circuit interrupt-ing position while rubber sleeve 144 in the antirebound assembly returns to its normal configuration thereby releasing its hold on the grooved end of actuating rod 120.
To restore the carrier assembly 31 to its contact closure position, a handle 170, seen in FIG. I, is manipulated to reciprocate the sleeve 100 and cage 98 combination (FIG. 2) to the right, thereby forcing the garter spring to ride over the ridge 160 on holder 104 into embracing relation therewith on the right side of the ridge. To this end, handle is suitable connected by linkage means (not shown) to a yoke having leg portions 172 formed with slotted openings 1720 in which are received the protruding ends of pins 102. It will be recalled that pins 101 interconnect the sleeve 100 and cage 98, and the reciprocation of the sleeve and cage during resetting of the current limiting circuit breaker is accommodated by the elongated slot 94a in cylinder 94 through which pins 102 extend. Once the garter spring is embracing the holder 104 to the right of its surface ridge 160, handle 170 is returned to its original position, thereby reciprocating the sleeve and cage back to the left, bringing with it holder 104 and the contact carriers 32a, 32b pinned thereto. Garter spring 106 is sufficiently strong to resist expansion such as to ride over ridge 160, and thus the cage 98 is coupled to holder 104 via garter spring 106 for conjunctive movement to the left by handle 170 to reclose the current limiting circuit breaker. To manually open the circuit breaker contacts, the handle 170 is pivoted to the right as seen in FIG. 1 to move the carrier assembly to the right; the garter spring 106, being lodged in a groove 175 (FIG. 2A) to the right of ridge 160, couples the holder 104 to the cage 98 and sleeve 100 combination.
From the foregoing description, it will be appreciated that the current limiting circuit breaker of my invention is capable of extremely rapid circuit interruption of high magnitude short-circuit currents by virtue of the direct coupling of the current limiting operation of a vapor-state current limiter to the movable contact carrier assembly of the circuit breaker. In a capacitive discharge test, (results illustrated in H0. 7), the current limiting circuit breaker of my invention has proven to be capable of cresting at 15,500 amperes (indicated at I80), an equivalent short circuit current going toward prospective peak of 100,000 amperes. Cresting occurred at 8.65 electrical degrees into the sinusoidal wave or 400 microseconds from current zero and quench was achieved in 32.4 degrees or 1.5 milliseconds (curve 182), thus demonstrating extremely rapid operation in true current limiting fashion.
A prior art circuit interrupter comprised of a vaporstate current limiter and a conventional circuit breaker utilizing a solenoid connected across the limiter and actuated in response to the rising voltage drop across the limiter to trigger the trip mechanism and initiate the opening of its contacts was tested and the results are illustrated in FIG. 7. It also crested the rising shortcircuit current at 15,500 amperes in 8.65 electrical degrees. lt quenched the are, however, in 7 milliseconds (curve 184) in contrast to a quench by my current limiting circuit breaker in 1.5 milliseconds.
Any element in an electrical circuit will generate heat as the product of its resistance and the current-squared times the duration of current flow. The latter two terms are called PT. PT thus becomes a performance term for circuit interruptersthe lower its value the better the interruption. From FIG. 7 it was calculated that during arcing the VT in the prior art circuit breaker was 2.32 that in my circuit breaker. If this large amount of PT were allowed to heat the vapor-state current limiter, the device would be destroyed. To enable the vapor-state current limiter to withstand such large 1 values, the practice has been to connect a resistor approximately the size of the vapor-state current limiter electrically in parallel to it. During arcing the limiter and the resistor have approximately equal resistance values, resulting in a division of the total current into two approximately equal magnitudes. Because my circuit breaker reduces the arcing l l' to less than half that in the prior art breaker the vapor-state current limiter in my circuit breaker does not need an auxiliary resistor. With respect to the total interruption, the prior art breaker allowed 1.68 times the FT allowed by my circuit breaker. This means that the distribution circuit and any connected loads are better protected by my circuit breaker.
It will be further appreciated from the foregoing description that the capability afforded by the current limiting circuit breaker of my invention of paralleling the ram'equipped current limiter 16 with one or more vapor-state current limiters l8 conveniently adapts one frame size to a wide range of current ratings. Thus, for example, to achieve a l,000 amp rating, a ramequipped vapor-state current limiter 16 rated at amps can be readily paralleled with nine similarly rated vapor-state limiters 18. By virtue of the inherent positive temperature coefficient characteristic of the vapor-state current limiters, current flowing from line terminal block 10 to strap 14 will substantially equally divide among the vapor-state current limiters l6 and 18, and thus their current limiting operations occur virtually simultaneously. While only a single ram-equipped current limiter is shown, it will be appreciated that, especially where heavy contacts and carrier assemblies are involved, several may be utilized, either acting in concert to open the main and arcing contacts or in tandem with one coupled to open the main contacts and the other coupled to open the arcing contacts after a short delay.
In addition, it will be appreciated that the current limiting circuit breaker of my invention affords circuit protection not only for high magnitude fault currents, such as short circuits, but also the vapor-state current limiters have the inherent capability of providing inversetime overload current protection. That is, the ram-equipped current limiter 16 responds virtually instantaneously to high level fault currents to interrupt the circuit and with inherent delay to lower level overload currents; the delay being inversely related to the overcurrent magnitude.
It will thus be seen that the objects set forth above, among those made apparent in the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
Having described my invention, what I claim as new and desire to secure by letters Patent is:
l. A current limiting circuit breaker comprising, in combination:
A. a line terminal;
B. a load terminal;
C. circuit interrupting stationary and movable contacts connected in series between said line and load terminals;
D. a carrier assembly mounting said movable contact for movement between open and closed positions relative to said stationary contacts;
E. a vapor-state current limiter having:
1. a casing;
2. at least one column of conductive, evaporable, current limiting material confined within said casing, said column being electrically connected to conduct at least a portion of the current flowing between said line and load terminals; and
3. a ram mounted by said casing for reciprocating movement, said ram having one end portion disposed within said casing in operatively coupled relationship with said column and its other end extending exteriorly of said casing, wherein said ram executes a stroke in response to vaporization and resulting expansion of a portion of the current limiting material in said column due to conduction of current exceeding a predetermined level;
F. means operatively coupling said other end of said ram to said assembly, whereby to rapidly reciprocate said assembly from said closed contact position to said open contact position in response to the execution of a stroke by said ram; and
G. anti-rebound means automatically operative to gain control of said assembly upon its arrival at said open contact position thereby to prevent return movement of said assembly toward said closed position.
2. The current limiting circuit breaker defined in claim 1, wherein said coupling means comprises a lever pivotally mounted intermediate its ends, one end thereof being acted upon by said ram, the other end thereof acting on said carrier assembly.
3. The current limiting circuit breaker defined in claiml, wherein said current limiter is electrically paralleled by at least one additional vapor-state current limiter to provide increased current rating, said additional vapor-state current limiter being operatively disassociated from said carrier assembly.
4. The current limiting circuit breaker defined in claim 1, wherein said carrier assembly includes detent means for releasably retaining said movable contact in either said open or closed positions.
5. The current limiting circuit breaker defined in claim 1, which further includes an arc chute and at least one blowout coil electrically connected in parallel with said current limiter, said blowout coil being energized upon vaporization of said current limiting material to propel an are at said contacts out into said are chute.
6. The current limiting circuit breaker defined in claim 4, wherein said carrier assembly includes:
1. a carrier mounting said movable contact,
2. a holder mounting said carrier,
3. a cage surrounding said holder,
4. said detent means including a garter spring accommodated in an internal annular groove in said cage, and
5. means forming an external annular ridge on said holder,
6. said spring embracing said holder on one side of said ridge to retain said holder in said closed contact portion and riding over said ridge upon movement of said holder relative to said cage to said open contact position to embrace said holder on the other side of said ridge, thereby to retain said holder in said open contact position.
7. The current limiting circuit breaker defined in claim 6, wherein said carrier assembly further includes means mounting said cage for manually induced movement to shift the position of said spring back to said one side of said ridge while said holder is in said open contact position, thereby to couple said cage to said holder for manually induced movement of said holder back to said closed contact position.
-8. The current limiting circuit breaker defined in claim 7, wherein said holder is formed having a surface groove adjacent said one side of said ridge, said groove accommodating spring to couple said holder to said cage for manually induced movement of said holder between open and closed contact positions.
9. The current limiting circuit breaker defined in claim 6 which includes a plurality of carriers each mounting a separate movable contact, at least one of said carriers being elongated and adapted to mount forwardly of said movable contact an arcing contact operating in a secondary current path shunting said movable and stationary contacts.
10. The current limiting circuit breaker defined in claim 6, wherein said carrier assembly further includes an actuating rod attached to said holder and engaged by said coupling means, said rod having its free end portion formed to coact with said anti-rebound means.
11. The current limiting circuit breaker defined in claim 10, wherein said anti-rebound means includes resilient means disposed to absorb the impact of said actuating rod upon movement of said carrier assembly to said open contact position, said resilient means deforming in response to impact by said actuating rod to embrace the free end portion of said actuating rod and thereby hold said carrier assembly in said open contact position.
12. The current limiting circuit breaker defined in claim 11, wherein said free end portion of said actuating rod is formed with annular grooves into which said resilient means flows to grasp and hold said actuating rod.
13. The current limiting circuit breaker defined in claim 10, wherein said coupling means includes a lever pivotally mounted intermediate its ends, said lever having one end disposed to be acted upon by said ram and its other end disposed in a slot formed in said actuating rod.
14. The current limiting circuit breaker defined in claim 13, wherein said coupling means includes a spring biasing an intermediate portion of said lever into rolling contact with the periphery of a dowel mounted transversely thereto.
15. A current limiting circuit breaker comprising, in combination:
A. movable and stationary contacts;
B. a carrier assembly mounting said movable contacts;
C. actuating means operatively coupled to reciprocate said carrier assembly from a first position where said movable contacts are in closure relation with said stationary contacts to a second position where said movable contacts are in circuit interrupting relation with said stationary contacts; and
D. anti-rebound means disposed to absorb the impact of said carrier assembly upon arrival at said second position and automatically operable to acquire temporary control of said carrier assembly such as to prevent return movement thereof toward said first position, said anti-rebound means including a resilient means capable of deforming in response to the impact of said carrier assembly to thereby embrace and hold said carrier assembly.
16. The current limiting circuit breaker defined in clain 15,-wherein said actuating means includes a vapor-state current limiter, electrically connected in series circuit with said movable and stationary contacts.
17. The current limiting circuit breaker defined in claim 15, wherein said carrier assembly mounts a member for impacting engagement with said anti-rebound means, said member having indentations formed therein, and said resilient means being positioned to flow into said indentations, thereby to grasp and hold said member.
18. The current limiting circuit breaker defined in claim 17, wherein said anti-rebound means includes a housing confining said resilient means and having an opening accommodating entry of said carrier assembly member.
19. The current limiting circuit breaker defined in claim 18, wherein said resilient means comprises a pad for absorbing the impact of said member and a gripping element deformed by said pad, said gripping element being shaped for positioning internally about said housing opening.
20. The current limiting circuit breaker defined in claim 19, wherein said member is in the form of a rod having a free end for impacting engagement with said pad, said gripping element is in the form of a sleeve, and said indentations are in the form of annular grooves formed in said rod adjacent said free end thereof.
21. The current limiting circuit breaker defined in claim 20, wherein said actuating means includes a va por-state current limiter electrically connected in series circuit with said movable and stationary contacts, said current limiter being equipped with a ram operable to execute a stroke in response to conduction of current above a predetermined level, and a lever pivotally mounted intermediate its ends, one end thereof positioned to be acted upon by said ram and the other end thereof being received in a slot formed in said actuating rod.
22. The current limiting circuit breaker defined in claim 21, wherein said vapor-state current limiter is electrically paralleled by at least one additional vaporstate current limiter to provide increased current rating, said additional vapor-state current limiter being operatively disassociated from said carrier assembly.