US3632926A

US3632926A - Current-limiting circuit breaker having arc extinguishing means which includes improved arc initiation and extinguishing chamber construction

Info

Publication number: US3632926A
Application number: US28258A
Authority: US
Inventors: Eldon B Heft
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1970-04-20
Filing date: 1970-04-20
Publication date: 1972-01-04
Anticipated expiration: 1989-01-04

Abstract

Current-limiting circuit breaker with arc-extinguishing means including a closed arc initiation chamber and a communicating arc-extinguishing chamber, the sidewalls of the chambers each being formed as a molded insert of high dielectric gas-generating material, the sidewalls of the arc-extinguishing chamber including means forming a controlled constriction through which the arc must pass, and diverging arc runners together with strips of material extending between the outer extremities of the arc runners, said strips comprising a material which is normally nonconductive but which becomes conductive when heated by the effect of an electric arc.

Description

United States Patent [72] Inventor Eldon B. Heft West Hartford, Conn. [21] Appl. No. 28,258 [22] Filed Apr. 20, 1970 [45] Patented Jan. 4, 1972 [73] Assignee General Electric Company Continuation of application Ser. No. 592,443, Nov. 7, 1966. This application Apr. 20, 1970, Ser. No. 28,258

a [54] CURRENT-LIMITING CIRCUIT BREAKER HAVING ARC EXTINGUISHING MEANS WHICH INCLUDES IMPROVED ARC INITIATION AND EXTINGUISHING CHAMBER CONSTRUCTION 4 Claims, 13 Drawing Figs. [52] 0.8. CI 200/144 C, 200/ 149 A [51] Int. Cl H0lh 33/00 [50] Field of Search 200/149 A, 144 C, 148 C, 150, 144, 149 [5 6] References Cited UNITED STATES PATENTS 2,345,724 4/1944 Baker et a] 200/ 148 C 2,382,850 8/1945 Bennett ,4 ZOO/148 C Primary Examiner-Robert S. Macon Attorneys-Robert T. Casey, Robert S. Smith, D. M. Schiller,

Frank L. Neuhauser and Oscar B. Waddell ABSTRACT: Current-limiting circuit breaker with arc-extinguishing means including a closed arc initiation chamber and a communicating arc-extinguishing chamber, the sidewalls of the chambers each being formed as a molded insert of high dielectric gas-generating material, the sidewalls of the arcextinguishing chamber including means forming a controlled constriction through which the arc must pass, and diverging arc runners together with strips of material extending between the outer extremities of the arc runners, said strips comprising a material which is normally nonconductive but which becomes conductive when heated by the efiect of an electric PATENTEDJA! 4m 3.632.926

SHEET 1 UF 3 INVENTOR [Lao/v 5- #:Fr

A T TORNE Y PATENTEB JAN 4 B72 SHEET 2 OF 3 a (vou's) 84( EE f I L FIG. 10

TIME

PRIOR ART F/GJI T'IME FIG. 12

//VV[NTOR [Loan 5. HEFT /{Mfi i A TTORNEY CURRENT-LIMITING CIRCUIT BREAKER HAVING ARC EXTINGUISl-IING MEANS WHICH INCLUDES IMPROVED ARC INITIATION AND EXTINGUISI-IING CHAMBER CONSTRUCTION CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation of application Ser. No. 592,443 filed Nov. 7, 1966 by the same inventor.

My invention relates to electric circuit breakers and particularly to electric circuit breakers including means for extinguishing an electric arc in a current-limiting" manner.

The term current-limiting is used herein to refer to the action of an electric circuit breaker in interrupting an electric current in such a manner than when the circuit breaker operates in a circuit of substantial voltage, such, for example, as the common commercially used voltage of 120, 240, 480 or 600 volts, and of substantial nominal current rating, (such, for example, as to 100 amperes or more), to interrupt substantial short-circuit available currents, (such! for example, as 10,000 to 100,000 or more amperes), the following relationships hold true: the actual or let-through current flowing through the circuit during the short-circuit current interruption operation of the circuit breaker never exceeds and is usually substantially less than the prospective" current. Prospective current is defined as that current which would flow in the same circuit under short-circuit conditions if the circuit breaker were to be replaced by an equivalent impedance. Such current-limiting circuit breakers are also characterized by the fact that in almost every instance, complete interruption is accomplished in substantially less than 9% cycle of a 60-cycle-per-second time wave.

It has been discovered that in order to achieve such currentlimiting interruption, the circuit breaker must function in the manner indicated as to the following three respects: (1) an arch must be drawn in extremely short time, i.e., within about 0.500 milliseconds (one-half of one-thousandth of a second) from the occurrence of the short-circuit condition, (2) theinitially created arc must be transformed into a high voltage drop arc, developing a voltage drop across it exceeding the driving line voltage of the circuit and this must occur also at extremely high speed and in not substantially more than two-thousandths of a second"(*Typica'l times in the present invention are 2 milliseconds at 1,000 amperes available and 0.7 of 1 milliseconds at 100,000 amperes available.) from the creation of the arc, and (3) the high-voltage character of the arc must be maintained without extreme or uncontrolled fluctuation or retrogressions" until the current is driven to zero and extinguished.

Prior application Ser. No. 457,557, R. L. Hurtle and H. G. Willard, filed May 21, 1965, now abandoned and replaced by application Ser. No. 768,963, filed Oct. 10, 1968 and application Ser. No. 866,083 filed Oct. 3, 1969, and assigned to the same assignee as the present invention discloses a currentlimiting circuit breaker construction capable of operating in the above-described manner and capable of providing a true current-limiting action at substantial voltages such as 250 volts and substantial nominal currents such as 100 amperes nominal current-carrying capacity and 100,000 or more am peres short-circuit current capacity. To applicants best knowledge and information, the circuit breaker constructed in accordance with the aforesaid Hurtle and Willard application is the first contact-operating circuit breaker to successfully and repeatedly interrupt short-circuit currents with true current-limiting action in circuits of commercial power voltages at substantial available short-circuit current values. Prior thereto, such interruption has been possible only by the use of current-limiting fuses.

The present invention is an improvement on the Hurtle and Willard circuit breaker, and a general object of the invention is to provide an electric circuit breaker operating on the principles set forth in the Hurtle and Willard aforesaid application and satisfying a number of specific design and performance requirements, and capable of being produced in physical sizes and in range of ampere ratings such as to make it suitable for ready adoption by circuit breaker users for use in applications where non-current-limiting circuit breakers have heretofore been used. For this purpose, such circuit breakers must comply with a number of physical and electrical requirements set up by safety code and inspection authorities and must be able to correlate with other electrical equipment in a predetermined manner.

Circuit breakers constructed in accordance with the aforesaid l-lurtle and Willard application have been found to perform remarkably well at high short-circuit current levels, as mentioned above. Short-circuit currents of relatively low levels can be adequately interrupted by conventional circuit breaker action. At certain intermediate current ranges however, above the range of conventional breakers but below the high" short-circuit range, the interrupting action of the circuit breaker of the aforementioned application has been found to be erratic. At such levels, retrogressions" have been found to occur, which, although not causing failure of the device, nevertheless cause rapid deterioration of the materials of the circuit breaker and are generally considered undesirable.

It is an object of the present invention to provide a currentlimiting circuit breaker of the type described which is capable of providing a current-limiting interrupting action throughout all ranges of available short-circuit current at least up to the specified maximum.

It is another object of the invention to provide a currentlimiting circuit breaker having a nominal capacity of amperes at 600 volts and capable of use on circuits with 100,000 amperes short-circuit current available, and having a relatively small size, such, for example, as about 4 inches wide by 4% inches high by 17 inches in length.

It is a further object of the invention to provide an electric circuit breaker of the current-limiting type which is capable of performing a current-limiting function without the occurrence of a voltage surge or spike" atthe termination of the current interruption.

It is another object of the invention to provide an electric circuit breaker having arc-interrupting means suitable for use with effective sound and shock wave muffling sounds, so as to substantially diminish the volume of sound, shock wave, and hot gases otherwise emitted from the circuit breaker upon the interruption of a high short-circuit current.

It is a general object of the invention to provide a currentlimiting circuit breaker of the type described which can be manufactured by conventional manufacturing techniques, with consistent, predictable performance characteristics and at economical cost.

A number of other objects will in part become obvious, and in part will be specificallypointed out in the following detailed description of the invention, and its scope will be pointed out in the appended claims.

In accordance with the invention, a current-limiting electric circuit breaker is provided of the basic type as set forth in the aforementioned Hurtle and Willard application, in which the current interruption is initiated by the creation of two serially related arcs which are elongated and merged into a single are which is then further elongated and maintained until the current is driven to zero, which breaker is capable of interrupting short-circuit currents with a smooth current-limiting action at all short-circuit current values from the lowest value causing operation of the high-speed opening means through the highest value which the circuit breaker is capable of interrupting.

The circuit breaker includes a pair of spaced stationary contacts having their generally planar contact surfaces inclined toward each other, and a movable bridging contact member with corresponding contact surfaces. The stationary contacts are supported in an "arc initiation" chamber having its inner wall surfaces constructed of a material having the characteristic that under the action of an electric arc, it is ablated or transformed into a gas, the gas having substantially no free carbon atoms. A suitable material is an acetal resin material, and preferably a polyoxymethylene material. Diverging arc runners extend from the stationary contacts in one direction into an arc extinction chamber. The are initiation chamber is closed in the opposite direction by a backwall, through which a contact operating rod extends. High-speed operating means, such as a magnetic solenoid, is provided for opening the movable contact at high speed.

In accordance with the invention, the arc initiation and are extinction chambers are formed so that the cross-sectional area of the space available to the are at first diminishes sharply as the arc moves away, and then increases gradually. This has the effect of retaining pressure in the arc initiation chamber for a period of time and so avoiding cavitation," which leads to are retrogressions as will be more fully described.

In addition, in accordance with the invention, the conventional arc-cooling plates" are omitted, and instead, the arc is elongated in the arc extinction chamber in a substantially straight-line condition between the arc runner tips and adjacent a slotted vent control member or bafile, to provide efiicient arc control action.

Moreover, in accordance with the invention, the spacing of the arc runner tips, and therefor the length of the arc in its most elongated condition, is made substantially greater than otherwise required, in order that the arc extinguisher may effectively coact with an effective noise and flame mufile device. The creation of excessively high voltage across the arc, and particularly the creation of a terminal voltage surge or spike is avoided despite this increased length of are, by the inclusion of sidewall strips of glass fiber-and-plastic compounds such as glass melamine which spans the space the arc runner tips at either side of the arc. It has been found that by varying the exposed surface of such strips, and concomitantly varying the exposed area of acetal resin material, the arc voltage may be adjusted and maintained at the desired level. It is speculated that the glass melamine strips diminish the terminal arc voltage spike by reason of the glass becoming partially conductive at at least the surface of the strips when heated by the action of the arc and acting as a resistor in parallel with the are to discharge any high-voltage surges.

Applicants best understanding as to how each of these aspects of structure, and other more specific aspects to be described, individually and collectively provide the advantages achieved by the applicants invention will be set forth in further detail following a detailed description of the structure of a particular embodiment of the invention.

In the drawings;

FIG. 1 is a side elevation view of the arc initiating and extinguishing portion of an electric circuit breaker constructed in accordance with the invention, a portion of the side-enclosing casing being removed to show the interior parts;

FIG. 2 is a sectional view of the arc initiating and extinguishing means of FIG. 1, taken substantially on the plane indicated by the line 22 of FIG. 1, the arc muffle portion being omitted;

FIG. 3 is an exploded perspective view of the main parts of the arc initiating and extinguishing structure of FIG. 1;

FIG. 3A is a semischematic representation of a complete circuit breaker incorporating the invention;

FIG. 4 is a diagrammatic illustration representing undesirable pressure conditions (cavitation) which it is believed may occur in a circuit breaker arc chamber, leading to undesirable results;

FIG. 5 is a diagrammatic illustration representing pressure conditions believed to occur in a circuit breaker arc chamber constructed in accordance with the present invention and believed to be desirable;

FIG. 6 is a fragmentary illustration showing a portion of the arc-extinguishing means of the circuit breaker of FIG. 1;

FIG. 7 is a view similar to FIG. 6 but showing the comparable portion of the structure of the circuit breaker of the aforesaid l-lurtle and Willard application;

FIG. 8 is a view similar to FIGS. 6 and 7 and showing a portion of the arc-extinguishing means of another embodiment of the invention;

FIGS. 9-12 are scale reproductions of oscillographic records of tests of the illustrated embodiment of the present invention and of other embodiments of the invention as described in the pertinent portions of the specification.

In the drawings, the invention is shown as incorporated in an electric circuit breaker including an arc initiating and extinguishing assembly (see FIGS. [-3) comprising a primary insulating enclosure 10 made up of two cooperating halves 10A and 108, see FIG. 2, having cooperating recesses therein and openings therethrough.

Adjoining the outlet end of the arc initiating and extinguishing assembly enclosure 10 is a muffle assembly 12 for the purpose of reducing the magnitude of sound and the temperature of the gases emitted from the arc-extinguisher enclosure 10. The construction and operation of the muffle assembly 12 is described in copending application (4lD-490), and will therefore not be described in detail here.

The enclosure 10 has a generally central, generally hourglass-shaped chamber 14 therein formed by cooperating conforming shaped recesses in each of the enclosure halves 10A and 10B. The recess 14 is made up of two parts: (I an arc initiation chamber 14A, and (2) an arc extinction chamber 14B. The chamber 14 including parts 14A and 148, has its inner sidewalls provided with inserts l8 and 20, see FIGS. 2 and 3.

The are

sideplate inserts

18 and 20 are so designed with respect to the shape and dimensions of the recess 14 that the front edges 18D and 20D respectively limit movement of these pieces within the chamber 14 by engagement with the arc tip spacer members 60, which in turn are held in place by the

arc baffle plates

48 and 50, which, like the succeeding elements are bolted in place by the bolts 63. Thus the edge surfaces 18E and 20E are spaced away from the corresponding portions of the enclosure halves 10A and 10B.

Because of this arrangement, no portion of the

sideplates

18 and 20 is placed under tension at any time. If, on the other hand, the conformance of the shape of these insert pieces with the chamber 14 were used to limit the motion of the sideplates l8 and 20 in the direction of arc movement, the

edges

18E and 20E would engage the corresponding adjacent walls of the chamber 14. The restricted or neck portion of these members would then be placed under tension by the action of the arc gases acting on the inwardly sloping sides at this point, resulting in cracking of the pieces at this point.

The main housing members 10A and 108 may be constructed of any suitable high-strength insulating material having high heat resistance, such, for example, as glass-fiber reinforced polymer or alkyd molding compound or other comparable material. The inserts l8 and 20, however, are constructed of an acetal resin material having the ablating characteristics described above. Materials which have been found suitable for this purpose, for example, include high molecular weight polyoxymethylene materials such as the material sold under the trademark Celcon" by American Celanese Corporation, and that sold under the trademark Delrin" by the Dupont DeNemours Company.

Also supported within the chamber 14, and overlying

edgewise portions

18A, 18B, and 20A, 20B of the inserts l8 and 20, are a pair of angularly shaped elongated

conductive straps

22 and 24. The

straps

22 and 24 each include a

terminal portions

22A, 24A having outgoing

terminal straps

26 and 28 connected thereto respectively. The

straps

22 and 24 also include inwardly directed or converging stationary contact support portions 228 and 24B, and outwardly diverging

arc runner portions

22C and 24C. Finally, the

straps

22 and 24 also include outer termination or are

tip portions

22D and 24D on which are inserted arc anchor" inserts 30 and 32 of high refractory material, such, for example, as tungsten carbide. Stationary contacts 25 are supported on the portions 22B, 24B of the

straps

22, 24.

.. will The

terminal portions

22A and 24A of the

straps

22 and 24 are each shielded from the internal portion 14A of the chamber 14 by means of

upstanding barriers

18C and 20C integral with the acetal resin inserts l8 and 20 respectively. In addition, the inserts l8 and 20 include shield portions 18S and 20S which shield the otherwise exposed portions of the bottom wall of the chamber 14A.

Also supported within the portion 14A of the chamber 14 is a bridging contact member 34 having a pair of

movable contacts

36 and 38 fixedly attached thereto. The bridging contact member 34 is attached by means of a yoke retaining member 40 to a movable operating rod 42 by which the contacts are operated between open and closed circuit positions in a manner to be described. The bridging contact member 34 is attached to the yoke member 40 by means of a pin 34A extending into a pair of slots 34B in the yoke member 40. The rod 42 is slidably guided by a low-friction bushing or insert 44 trapped between the housing sides A.

The outer portions of the cooperating enclosure halves 10A and 10B are cut back and serve to receive and support a bafile assembly comprising two cooperating

halves

46 and 48, (see FIGS. 2 and 3) each having a number of slots 50 cut therein providing a series of relatively wide thin exit passages for arc gas from the chamber 14 outwardly into the mufile assembly 12. The

baffle assembly

46, 48 is preferably constructed of a suitable high-strength, high-resistance insulating plastic material such, for example, as a glass-fiber filled polymer material such as glass melamine.

The cutback of the enclosure sides 10A and 108 provides a pair of shoulders or

shelves

52 and 52 against which the baffle blocks 46 and 48 are seated. The slots 50 in the

bafile members

46, 48 preferably extend therein to a distance which extends at least to the edge of the shelf 54. Thus the slots extend across the full width of the chamber 14 at its outer most portion between the

arc tips

30 and 32.

In accordance with the invention, and for a purpose to be described, the acetal resin inserts l8 and are terminated short of the battle blocks 46, 48, and a pair of

strips

58 and 60 are provided which extend between the

tips

22D and 24D of the

conductors

22 and 24, the end thereof being notched as at 60A to prevent direct contact between these strips and the

contact tips

30 and 32, for the purpose of improving the oversurface dielectric condition. Likewise the

arc runners

22 and 24 are terminated short of the baflle blocks 46 and 48.

The two halves 10A and 10B of the enclosure 10 are provided with a number of holes 62, by which these parts are securely bolted together by bolts 63 which are surrounded by suitable insulating tubing shields 64. Because of the large number and close proximity of the bolts 62 and the highstrength material used, the chamber 14 is capable of sustaining extremely high pressures therein, which pressures are estimated to exceed at least 300 pounds per square inch during the interruption of short-circuit current.

The enclosure halves 10A and 10B, and the baffle blocks 46 and 48 each include elongated semicircular grooves 68 which cooperate to provide circular holes in which elongated resilient sealing members 70 are inserted and compressed when these parts are in assembled relation. The sealing members 70 provide a means for sealing against the passage of gas under high compression from the chamber 14 outwardly through the crack between the members 10A and 10B and the corresponding portions of the bafile blocks 46 and 48. Other comparable sealing means, such as silicone plastic compounds which are plastic when first inserted and later cure" to a rubbery body may of course also be used.

The movable contact member 34 is preferably retained in the closed circuit position by operating mechanism including a biasing or contact pressure means connected to the movable contact by means which includes a breakaway-type connection, that is, one which can be defeated or released. A mechanism of the type described, is shown in semischematic form in FIG. 3A.

As shown in FIG. 3A, the mechanism illustrated includes a generally cylindrical collar member which is fixedly attached to the operating rod 42, and which has a peripheral groove 91 therein. A yoke member 92 is slidably supported on the rod 42, and is connected to the collar 90 by means of a pair of resilient spring strip fingers 93, having retum-bent end portions seated in the groove 91. The yoke member 92, and thereby the movable contact assembly including the collar 90, the rod 42, and the movable contact member 34, is moved between open and closed circuit positions by means of a pair of toggle links 94 (only one shown) each of which has one end pivotally connected by means of a pivot pin 95 to a releasable cradle member 96 which is supported on a fixed pivot pin 97 in a suitable casing or support, not shown. The other ends of the links 94 are connected to the yoke member 92 by a lost motion connection comprising a slot, not shown, in each of the links 94 receiving a pin 98 carried by the yoke member 92.

The links 94 are moved between open and closed circuit position with a snap action by means of operating spring 99 having one end connected to a pin 100 extending between the operating links and a manually operable handle member 101, the line of action of the spring 99 passing across the pivot pin 95 in the process.

The releasable member or cradle 96 is normally held by a combination armature-latch member 102 which is pivotally supported at 103 on the aforesaid support or casing. The armature-latch member 102 has a retum-bent end portion 102' which is engaged by the movable end of a bimetallic strip member 104 which has the other end rigidly mounted on a combination terminal and support member 105. The bimetallic strip 104 is further provided with a magnetic field piece 106 which is rigidly attached thereto and which serves to attract the armature member 102 upon the occurrence of predetermined high-current conditions through the bimetallic strip 104. An outgoing or load terminal member 107 is supported on the terminal strap 105. The movable end of the bimetallic strip 104 is connected by a flexible connector 108 to the solenoid winding 109. On the occurrence of extremely high short-circuit current conditions, the solenoid winding 109 causes the armature 110 to be pulled toward the field piece 111, thereby moving the contacts 34 to an open position. The solenoid winding 109 is connected by means of a conductor 112 to the contact assembly previously described which in turn is connected to line terminal 1 13.

When the armature 110 is attracted by the high-speed solenoid 109, the yoke member 90 is pulled from between the spring fingers 93, permitting the contact rod 42 and its associated contact member 34 to move without restraint by the operating spring 99 after this has occurred. The parts are also maintained in the open circuit condition by the action of the spring fingers 93 following interruption of the short-circuit current.

While one particular form of mechanism capable of use in the invention has been described for illustration purposes, it will be appreciated that more sophisticated mechanisms may be utilized, such, for example as that shown in copending application (41D-4l7), including operating means capable of generating high contact pressure, and utilizing breakaway connections capable of transmitting such higher contact pressures.

Low overload conditions, that is, for example, overloads within the range of l25 percent-300 percent of the nominal rating of the circuit breaker, cause deflection of the bimetallic strip 104 after a predetermined time, moving the movable end of the bimetallic strip 104 to the left as viewed in FIG. 3, and withdrawing the armature-latch member from the releasable member 96. This permits the releasable member 96 to rotate clockwise as viewed, moving the pivot pin 95 across the line of action of the spring 99, and reversing the bias of the spring 99 on the links 94, and rotating these links in clockwise direction, moving the yoke member 92 back toward open circuit position. Resetting of the mechanism is accomplished by engagement between a projection on the handle 101, not shown, and

the cradle member 96, by which the cradle 96 is rotated in counterclockwise direction until the latch end thereof is once again held by the armature-latch member 102.

On the occurrence of high overloads or low short-circuit current conditions, such, for example, in the range of 300-500 percent of the nominal current rating, or such other range as may be selected, the magnetic member 106 carried by the bimetallic strip 104 is sufficiently energized to attract the armature-latch member 102, rotating it clockwise about its pivot pin 103, and releasing the releasable member 96.

On the occurrence of still higher short-circuit conditions, such as those above 500 percent of the normal rating of the circuit breaker, the high-speed solenoid 109 comes into operation. The high-speed solenoid 109 remains in circuit at all times, but does not operate at lower currents since the strength of its magnetic field is not great enough to cause movement of the current-movable contact assembly 42 against the bias force of the contact-holding members 93.

Assuming the movable contact member to be in closed condition, a short-circuit condition causes energizing of the solenoid winding 109 and high-speed movement of the movable contact in the opening direction as previously described. When the contact pairs 36, 25 and 38, 25 separate, a pair of short, serially related arcs are created. The pair of short arcs are very quickly elongated and transformed into a single arc extending directly between the stationary contacts 25. This longer arc is then further elongated and moved, by the action of the general current path adjacent to it and by the repelling action of the

conductor portions

26, 28, out along the are

runners

22, 24. During this action, gases are generated from the

arc chamber sideplates

18 and 20, which maintain good dielectric or insulating conditions behind the arc and prevent restriking or retrogressions until the current is completely extinguished.

ANTICAVITATION STRUCTURE As mentioned in the introductory portion of the specification, it has been discovered by extensive testing that the circuit breaker of the aforesaid I-Iurtle and Willard application, while performing in excellent manner at extremely high shortcircuit current conditions, is subject to retrogressions at certain low short-circuit current conditions which, at least in some instances, might nevertheless lie above the values which are ordinarily interrupted by the magnetic" short-circuit interrupting means of conventional circuit breakers.

Referring to FIG. 4, there is illustrated schematically a situation which is believed to be illustrative of that causing retrogressions at certain intermediate current levels in the aforementioned I-Iurtle and Willard application structure. This difficulty is believed to arise from cavitation, that is, a region of extremely low pressure created by movement of gases away from such region at excessively high velocity as a result of action of the arc. Thus if A in FIG. 4 is considered to represent a cross section of the arc chute of a circuit breaker of the type described, the spot P may be taken as representing a cross section of the are as initially formed in the lower part of this chamber. The action of the arc in acting on the ambient air and upon the material comprising the sidewalls, causes rapid expansion of the air and generation of gases by means of volatilizing the material of the sidewalls resulting in high pressure. This high pressure creates an immediate movement of gases toward the open end of the arc chamber as indicated by the arrow D. The pressure wave moves in the direction of the arrow D as indicated by the successive diagrams B and C of FIG. 4. The movement of the gases away from the region I where the arc was initiated, at such high speed, in effect removes so much of the gas from this region I so quickly that the region I then becomes a region of extremely low pressure or in other words a pressure cavity. Because of this lowpressure region, the high-pressure gases in the upper part of the arc chamber shortly thereafter tend to surge backward as indicated in FIGS. C and D of this figure. This action is believed to be detrimental for a number of reasons. It will be recalled that one of the desired aspects of a true current-limiting circuit breaker was stated to be its ability not only to generate an arc at extremely high speed, but also to maintain a highvoltage drop condition across this arc until the current is driven to zero, without erratic action or retrogressions. For this purpose it is not sufiicient merely to generate an arc having the required voltage drop across it. In addition, the dielectric condition in the space between all conductive parts available to the current as an alternate parallel path must be maintained high enough to prevent the arc from striking across at such alternate points and therefore extinguishing in its highvoltage path. The most likely area for such striking-over to occur is the area in which the arc was first initiated.

With this in mind, it will now be observed that when the arc is initially created, a certain amount of metallic material from the contacts is necessarily vaporized, and such metallic particles or ions are, in the initial high-pressure gas, generated by the arc and accordingly, contaminate this gas. This initial high-pressure contaminated gas initially moves away from the arc initiation point at high speed, leaving the space where the arc was initially created relatively clean and with good dielectric condition.

At the same time that the contaminated gas is being moved outwardly as illustrated in FIG. B, the relatively clean, highdielectric gas which has been generated from sidewalls of the acetal resin material has filled the lower portion of the arc chamber I and created a relatively good dielectric situation at this point. If, however, cavitation occurs as illustrated in FIG. 4, some of the contaminated gas in the forefront of the wave is returned and mixed in turbulent fashion with the less contaminated gas or vapor generated from the sidewalls of the arc chamber adjacent the arc initiation point, thereby lowering the dielectric strength in this region and leading to the creation of arc retrogressions or striking-over at this point.

In accordance with the invention, the sidewalls of the chamber 14 are modified so that, proceeding from the end of the chamber where are initiation occurs at the region I in FIG. 5A, for example, the sidewalls first converge sharply because of the built-up

portions

18M, 20M, providing a narrow passage or constriction 14C. Thereafter, the walls diverge to a maximum spacing, the last portion of the sidewalls extending parallel to each other for a short distance adjacent the spacer piece 60.

It is believed that the illustrated and described construction prevents cavitation in the following manner. Referring to FIG. 5A assuming that the arc is initially created in the region I and creates a high pressure in this region, and thereafter is moved by magnetic forces outwardly and upwardly as viewed as indicated in 5B, the restriction provided by the converging walls at 14C prevents the overly rapid release of the pressure from the chamber 1. Accordingly, as the arc moves upwardly in chamber 14, the differential of the pressure between the upper and lower portions of the arc chamber is not so great as to cause the turbulent resurgence of contaminated gas as previously experienced. Since the pressure at the upper portion of the arc chamber also diminishes quickly because of the escape of the gases through the open end of the arc chamber, a more gradual and equally distributed diminishing of the pressure throughout the chamber occurs. This permits the uncontaminated gas generated from the acetal resin sidewalls of the initiation chamber to remain in this portion of the chamber and to maintain the desirable dielectric conditions here while very high voltages are being generated across the arc. Thus, for example, in circuits of 600 volts, an arc voltage of at least 1,200 volts must be attained by the arc, and voltages of at least 1,250 are commonly developed by circuit breakers constructed in accordance with the invention. Moreover, as indicated in the oscillograms reproduced in FIGS. 9-12, and in particular in FIGS. 10, 11 and 12, this high voltage is maintained for a substantial period of time while the current is driven to zero.

Referring to FIG. 9, there is reproduced an oscillographic record of a short-circuit interruption test performed on a circuit breaker of the type described herein but having an arc chamber with straight sidewalls. The curve 80 represents the current in the circuit while the curve 81 represents the voltage drop across the arc. It will be observed that under the current and voltage conditions existing, a series of 10 retrogressions 81A occurred before interruption was finally completed.

In FIG. 10 there is shown the oscillogram of a circuit interruption with a circuit breaker having a construction generally similar to that of the breaker tested in the test illustrated in FIG. 9, excepting that the sidewalls of the arc chamber were additionally provided with the described constriction adjacent the arc initiation portion of the chamber, in accordance with the present invention. In this figure, the curve 84 represents the current of the circuit, while 85 represents the arc voltage. As illustrated, under similar voltage and current conditions, the high voltage generated by the arc was maintained without retrogressions until the current was driven to zero. Note also that the interruption was completed in a substantially shorter time. This means also that the let-through energy was substantially less. This in turn means that the interrupter suffered less destructive wear and tear" and also that other circuit components in the circuit experienced less stress.

CONTROL OF ARC VOLTAGE Referring to FIGS. 6 and 7, a portion of the arc-interrupting structure of the present invention and of the aforesaid Hurtle and Willard application are shown respectively. As described in the Hurtle and Willard application, and referring to FIG. 7, the structure disclosed therein includes a pair of diverging arc runners A, 16A terminating in are tips 16A" and 15A", and a series of spaced metallic arc-cooling plates 68', together with an arc baftle member of insulating material 67' having slots 67B. The longest arc path in this structure, and the path which the are occupies just prior to extinction, is that indicated in dotted lines in FIG. 7, and extends from one of the are tips 15A to one of the end plates 68, thence across the spaces between plates from one plate to another, to the op posite end plate, and from the opposite end plate back to the other arc tip 16A". It will be observed therefore that the total are column length L, may be represented as L =2L,+(N-l )L, Where capital N equals the number of plates 68, L, represents the distance from the end arc chute plates to the adjacent arc runner tips, and L, is the distance between adjacent plates. Since each individual arc has an anode drop and a cathode drop which together total about 15 volts, the total voltage drop across this arc path may be represented as E,=l5(N+l )+eL where small 2 is the voltage drop along the column of the arc in volts per inch.

On the other hand, in a structure in accordance with the present invention as shown for example at FIG. 8, where the arc exists merely in a straight line directly between the

arc tips

22D, 24D, the voltage drop may be represented as E=l 5+eL where small e is again the voltage drop of the arc column in volts per inch, and L is the overall length of the are as marked in FIG. 8.

Consideration of these formulas would ordinarily lead to the conclusion that the voltage drop of the FIG. 8 form (the present invention) would be less than the voltage drop of the F IG. 7 form (the Hurtle and Willard application) by an amount equal to lSN volts. It has been discovered, on the contrary, however, that for the same total length of arc, (i.e., L,- of FIG. 7 equal L of FIG. 8) the voltage drop in the case of the FIG. 8 structure is very much greater than the voltage drop of the FIG. 7 structure. While the reasons for this are not completely understood, it is speculated that this may be explained by the situation being such that the portion of the space between plates which may be considered arc column" length is not as great as ordinarily supposed, perhaps, for example, because of the intrusion into this space of metallic vapor from the surface of the plates.

Whatever the explanation may be, applicant has discovered that whereas with a structure as shown in FIG. 7, a total arc length (not counting the thickness of the plates used) of Z'binches is required to provide an arc voltage drop of 1,200 volts as necessary to "override" line voltage of a GOO-volt circuit and thereby achieve current-limiting action, on the other hand, with a structure such as shown in FIG. 8, a total arc length of only 1% inches is required to do this. It will at once be observed that the structure of FIG. 8 is very much more compact than that of FIG. 7, and that space is saved not only in the direction of the arc lengthwhich is reduced by about 60 percent, but also, and equally important, in the direction at right angles to the arc length, because of the total omission of the plates 68, of about 32 percent.

It is the uniform teaching of the prior art in connection with are interruption in air that the use of spaced metallic plates is desirable for the purpose of cooling and therefore deionizing" the arc to aid in its extinction. To the extent that it may have been appreciated in the prior art that greater are voltage drop could be achieved across a given space by the omission rather than the inclusion of metallic plates (although this is nowhere suggested, to applicant's knowledge), it is believed that this was not feasible in such prior art conventional circuit breaker because the arc-extinguishing environment in which the arc was created and contained was not such as to afford a true current-limiting interruption. Since the other aspects of such interrupters did not make possible a currentlimiting interruption, the creation of such high-voltage arcs would only lead to to occurrence of retrogressions with consequent need for dissipation of increased amounts of energy in the arc, increased degradation of the arc chamber components, and probably complete failure of the device. The present applicant, on the other hand, has discovered that if the dielectric conditions are maintained in the arc chamber such as by the structure described, substantial advantages are achieved by the omission of metallic arc plate grids.

A further unsuspected advantage of omitting the metallic arc grid plates is that their omission tends to render such severe the terminal voltage spike or surge which occurs upon the extinction of the arc. It is believed that the explanation for this phenomenon is as follows. It is well understood that the anode and cathode voltage drop of an arc in air add up to about 15 volts. Stated in another way, once an are through air has been created by means of a high voltage, if the voltage is thereafter decreased, the arc cannot continue to exist if the applied voltage drops below 15 volts. If a number of such arcs are connected electrically in series, such, for example, as may be the case in a circuit breaker including a number, such as 10, spaced arc grids, the total applied voltage necessary to sustain a power are once created therein will be about 10x15, or volts. It will therefore be appreciated, that, quite apart from other considerations, as the voltage across the arc decreases toward zero, the arc in a circuit breaker having spaced metallic grids will extinguish at a higher point in the applied voltage wave (and hence at a slightly earlier point in time) than in a similar construction not including any such spaced grids. Conversely, final extinction of the arc occurs at a slightly later point in time in the situation where no intermediate grids are present. Since the current is decreasing with time, it can be said that the current will extinguish and the current will suddenly go to zero from a higher point in the decreasing current wave when intermediate grids are involved than in the comparable circuit breaker without such metallic grids.

The terminal voltage spike referred to is caused by the high rate of change of current or negative di/d! which occurs at the time of extinction of the arc. Since extinction takes place in substantially the same short space of time regardless of the current value just prior to extinction, it will be readily appreciated that a much higher rate of change of current, (di/dt),

results if extinction occurs at a time when the current is at a relatively high level.

Stated in another way, in the circuit breaker constructed in accordance with the present invention, since there is only a single anode and cathode voltage drop involved, the current is permitted to decrease to a much lower value before the sustaining voltage becomes unable to maintain the arc and the current is extinguished and immediately goes to zero. Accordingly, a much lower di/dt is involved, and the corresponding terminal voltage spike is much less.

In accordance with another aspect of the invention, the overall spacing of the

arc runner tips

22D, 24D is not established at the minimum spacing required to generate the desired arc voltage. On the contrary, a wider spacing is used, although still substantially less than the spacing which would be required if metallic plates were used. The wider spacing is utilized in order to make it possible for the arc-extinguishing assembly to cooperate in the most desirable manner with the arc muffle assembly 12. Thus it has been discovered that optimum mufiling action of the sound, shock wave, and hot arc gases requires a given optimum input opening for the muffle assembly.

When the

arc runner tips

22D, 24D are spaced at the relatively wider spacing as shown in FIG. 6, however, if no further provision were made, the resulting arc voltage and its associated terminal voltage spike would be such as to be undesirable since such a high voltage spike might cause highpotting" or "voltage puncturing at some point in the circuit. In accordance with the invention, therefore the relatively wider spacing is made possible and the tenninal voltage spike situation is nevertheless controlled, by the use of

special bridging members

58, 60 which extend between the

arc runner tips

22D, 24D. The bridging

members

58, 60 which extend at each side of the arc runner tips, are constructed of a material having a substantial portion thereof of glass. Since the presence of these pieces has been found to bring about correction of the voltage spike, it is believed that these pieces become temporarily conductive and thereby dissipate the voltage spike or surge.

FIGS. 9-12 are reproductions of oscillographic records of current and voltage conditions during each of a series of tests of current-limiting circuit breakers. FIG. 9 is an oscillographic record of the current and voltage conditions existing during a short-circuit test of a current-limiting circuit breaker constructed in accordance with the aforesaid l-Iurtle and Willard application, the line voltage and short-circuit current availability being 240 volts and 10,000 amperes respectively, at a closing power factor of 35. It will be observed that in this instance a number of arc retrogressions in all) occurred before the current was finally driven to zero.

Each of the retrogressions appearing in FIG. 9 is evidenced by a sharp drop in the voltage appearing across the arc. This indicates that the are which has once been elongated to a highvoltage condition restrikes at a previous location and at a shorter length, is once again lengthened to its high-voltage condition and once again reignites at the former location, this process being repeated a number of times. As previously stated, this action is undesirable because it causes deterioration of the conditions within the arc chute and is likely to lead to complete failure to interrupt.

It is believed that these retrogressions occurred because the device was tested at an intermediate short-circuit current availability range rather than at a high short-circuit current availability range. Thus it is a unique characteristic of a true current-limiting circuit breaker that it operates most effectively on extremely high short-circuit availability currents, and that within certain limits, the higher the amount of short-circuit current available, the quicker it is interrupted. Conversely, current-limiting interruption becomes, at least in some respects, more difiicult at low and intermediate short-circuit current availability ranges.

FIG. 10 is a reproduction of an oscillogram of a test of a circuit breaker constructed substantially similar to that tested in the test illustrated in FIG. 9, with the exception that the sidewalls of the arc chamber were constructed in accordance with the anitcavitation" structure described above, i.e., the arc chamber was made to taper inwardly sharply adjacent the arc initiation region and then to gradually widen in the direction in which the arc moves away from the arc initiation region. The circuit conditions were substantially the same as those in the test of FIG. 9. It will be observed that in this test, no retrogression occurred. In addition, the current was interrupted in a much shorter total time.

FIG. 11 is a reproduction of an oscillogram of a test of a circuit breaker substantially similar to that tested in the test illustrated in FIG. 10, with the exception that the arc-cooling grids were removed. In this figure, the curve 88 represents the current, and the curve 89,- represents the arc voltage. Again, it will be observed that no retrogressions occurred. However, it will be noted that in both the FIG. 10 and FIG. 11 tests, the voltage appearing across the arc rose very sharply just prior to complete interruption of the current. As previously mentioned, this is undesirable, since it applies a high voltage throughout the load circuit and may cause insulation puncturing, flashovers, or other undesirable phenomena.

In FIG. 12 there is illustrated a reproduction of an oscillogram of a test of a circuit breaker constructed substantially similar to that tested in the test illustrated in FIG. 11, but with the addition of two strips of glass melamine molding material, one closely adjacent each side of the path extending between the arc runner tips, that is, pieces similar to the bridging pieces 60 illustrated in the drawings, see FIG. 6 and FIG. 3. In this figure, the curve 90 represents the current, while the curve 91 represents arc voltage. It will be observed from this figure that the terminal voltage spike or surge is drastically reduced and virtually eliminated. As previously stated, it is believed that the glass included in these pieces at least on the outer surfaces exposed directly to the arc becomes partly conductive, and serves as a resistor to discharge the high voltage which tends to build up between the arc runner tips.

The glass melamine bridging means 60 are notched as indicated at 60A so that they do not directly contact the ends of the

arc runners

22C, 24C, or the arc contact tip inserts 30, 32, respectively. This is for the purpose of avoiding a continuous path between the arc runner tips of material other than acetal resin material which has been directly exposed to the action of the are. It is desirable to avoid such a continuous path in order to maintain the dielectric conditions between the arc runner tips at a required level, such, for example as to be able to withstand an applied test voltage of 2,200 volts for 60 seconds following short-circuit operation, as required by Underwriters Laboratories tests. The are runner tips are also separated from the bafile blocks 46, 48 for the same reason.

The are

bafile blocks

46, 48 are preferably constructed of glass fiber filled melamine resin compound. This material is used, rather than an acetal resin material, since it has the required strength to withstand the high shock wave generated by the interrupter, and since it has been found by test that the use of this material does not detract from the desired currentlimiting performance of the circuit breaker when constructed in accordance with the present invention. The casing halves 10A and 10B are preferably constructed of a high-strength, high-dielectric material, such, for example, as the glass fiber filled alkyd molded compound. Other materials having equally good electrical and physical characteristics may of course be utilized.

While the invention has been described in only specific embodiments, it will be readily appreciated that numerous modifications and variations may be made without departing from the spirit of the invention. It is accordingly intended by the appended claims to cover all such modifications and variations whether in substitution of materials or variation of size, dimension, etc. as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit interrupter comprising:

a. a support;

b. said support including an arc initiation chamber having a bottom wall and opposed side and end walls;

c. said support also including an arc-extinguishing chamber connected to said are initiation chamber by a passageway;

d. a pair of elongated arc runners supported on said support,

each of said are runners having a first end thereof supported adjacent said passageway, said are runners extending from said passageway into said arc-extinguishing chamber and diverging from said passageway in the direction of said arc-extinguishing chamber;

e. means for creating an electric arc in said arc initiation chamber between said first ends of said arc runners and moving said are outwardly along said diverging arc runners to a final path extending between said outer ends of 15 said outer arc runners;

f. said support comprising a first body of insulating material having relatively high strength and heat-withstanding ability, said first body of insulating material having said are initiation chamber and said arc-extinguishing chambers formed therein; and

a pair of protective insert members for said are initiation and said arc-extinguishing chambers comprising generally planar pieces of insulating material preformed separately from said first body of insulating material and conforming to the shape of said chambers and fitting closely against the otherwise exposed walls of said chambers, said inserts comprising an acetal resin compound having the characteristic of generating an arc-extinguishing gas when heated by the action of an electric are.

2. An electric interrupter as set forth in claim 1 wherein said support also includes a baffle member of insulating material extending substantially directly transversely across the outer ends of said arc runners and substantially closing the outer end wall of said arc-extinguishing chamber, said bafile member including a plurality of elongated, relatively narrow holes extending therethrough in a direction generally perpendicular to the line interconnecting said outer ends of said are runners, said bafile member comprising a high-strength plastic molding compound having high heat-withstanding ability.

3. An electric circuit interrupter as set forth in claim 1, said interrupter also comprising at least one narrow elongated strip member of insulating material carried by said first body of in sulating material and positioned so as to extend substantially the full distance between said outer ends of said diverging arc runners and parallel to and closely adjacent said final path of said arc said strip member comprising a material which is nor mally an electric insulator but which becomes conductive when heated by the action of an electric arc whereby the mag nitude of transient high voltages across said arclrunners at the instant of extinction of said are is minimized.

4. An electric circuit interrupter as set forth in claim 3 wherein said elongated strip members comprise glass fiber filled molded material.

Claims

1. An electric circuit interrupter comprising: a. a support; b. said support including an arc initiation chamber having a bottom wall and opposed side- and end walls; c. said support also including an arc-extinguishing chamber connected to said arc initiation chamber by a passageway; d. a pair of elongated arc runners supported on said support, each of said arc runners having a first end thereof supported adjacent said passageway, said arc runners extending from said passageway into said arc-extinguishing chamber and diverging from said passageway in the direction of said arc-extinguishing chamber; e. means for creating an electric arc in said arc initiation chamber between said first ends of said arc runners and moving said arc outwardly along said diverging arc runners to a final path extending between said outer ends of said outer arc runners; f. said support comprising a first body of insulating material having relatively high strength and heat-withstanding ability, said first body of insulating material having said arc initiation chamber and said arc-extinguishing chambers formed therein; and g. a pair of protective insert members for said arc initiation and said arc-extinguishing chambers comprising generally planar pieces of insulating material preformed separately from said first body of insulating material and conforming to the shape of said chambers and fitting closely against the otherwise exposed walls of said chambers, said inserts comprising an acetal resin compound having the characteristic of generating an arc-extinguishing gas when heated by the action of an electric arc.

2. An electric interrupter as set forth in claim 1 wherein said support also includes a baffle member of insulating material extending substantially directly transversely across the outer ends of said arc runners and substantially closing the outer end wall of said arc-extinguishing chamber, said baffle member including a plurality of elongated, relatively narrow holes extending therethrough in a direction generally perpendicular to the line interconnecting said outer ends of said arc runners, said baffle member comprising a high-strength plastic molding compound having high heat-withstanding ability.

3. An electric circuit interrupter as set forth in claim 1, said interrupter also comprising at least one narrow elongated strip member of insulating material carried by said first body of insulating material and positioned so as to extend substantially the full distance between said outer ends of said diverging arc runners and parallel to and closely adjacent said final path of said arc, said strip member comprising a material which is normally an electric insulator but which becomes conductive when heated by the action of an eLectric arc whereby the magnitude of transient high voltages across said arc runners at the instant of extinction of said arc is minimized.