US3558991A

US3558991A - Circuit breaker with high speed tripping system

Info

Publication number: US3558991A
Application number: US756479A
Authority: US
Inventors: Thomas P Brandt Jr; Frank J Pokorny
Original assignee: ITE Imperial Corp
Current assignee: ABB Inc USA
Priority date: 1968-08-30
Filing date: 1968-08-30
Publication date: 1971-01-26
Anticipated expiration: 1988-01-26
Also published as: DE1944062B2; FR2016634A1; GB1232721A; DE1944062A1

Abstract

A HIGH SPEED TRIPPING SYSTEM FOR A CIRCUIT BREAKER PARTICULARLY USEFUL FOR CURRENT LIMITING APPLICATIONS DURING A SHORT CIRCUIT INTERRUPTION. THE TRIPPING SYSTEM INCLUDES AN ELECTRONIC SENSING SUBSYSTEM WHICH RAPIDLY SENSES THE OCCURRENCE OF SHORT CIRCUIT FAULTS AND ENERGIZES AN IMPULSE COIL IN RESPONSE THERETO WHICH IN TURN ROTATES A BREAK-AWAY LATCH TO PERMIT THE MOVABLE CONTACT ARM OF THE BREAKER TO RAPIDLY ROTATE TO ITS OPEN CIRCUIT POSITION FREE OF THE RELATIVELY HIGH MASS RESTRAINING AND/OR CLOSING MECHANISM NORMALLY ASSOCIATED THEREWITH.

Description

Jan. 26, 1971 K T. RfBRAND'nJR.; ETAL 3,558,991 -j CIRGUT BREAKER WITH HIGH SPEED TRIPPING SYSTEM l Filed 11mg.'` so, 196e y a sheets-sheet 2 United States Patent Oce 3,558,991 Patented Jan. 26, 1971 3,558,991 CIRCUIT BREAKER WITH HIGH SPEED TRIPPING SYSTEM Thomas P. Brandt, Jr., Swarthmore, and Frank J. Pokorny, Hatboro, Pa., assignors to I-T-E Imperial Corporation, Philadelphia, Pa., a corporation of Dela- Wale Filed Aug. 30, 1968, Ser. No. 756,479 Int. Cl. H02h 1/00; H0111 77/ 00 U.S. Cl. 317-58 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to circuit breakers and more particularly to a tripping system thereof which permits extremely rapid interruption.

The growing electrical distribution industry constantly requires new high capacity power supplies, the output levels of which reach magnitudes previously thought unattainable. One of the most important elements in these systems is the circuit breaker which protects the entire system and the various components being operated thereby in the event of overloads and short circuit fault conditions. Furthermore, because of the magnitudes of current flowing in these higher rated distribution systems, circuit breakers must be designed to be much quicker acting than those presently available.

The instant invention is in fact directed to a quickacting circuit breaker which is particularly useful in the higher rated systems coming into extensive use in the electrical distribution industry. By means of a novel high speed tripping system, to be described in greater detail, the circuit breaker can be of minimum size, compact construction, reliable over extended periods of use, and have such high speed tripping characteristics as to be especially useful for current limiting applications during the occurrence of short circuit fault conditions in a line or lines being monitored.

To accomplish the above noted objects, the instant invention proposes a tripping system which, upon the occurrence of predetermined fault conditions, will free the movable contact of the circuit breaker from the conventional restraining and/or closing mechanism normally associated therewith such that the movable contact arm can rapidly snap open under the inuence of the opening springs free of the relatively high inertial parts of the restraining system. Thus in a conventional breaker, the movable contact arm used to interrupt current, is conventionally restrained or latched against the bias of the opening springs by means of a jack shaft and other parts rotatable therewith. When a fault is sensed, the aforenoted restraining mechanism, customarily a toggle arrangement, collapses such that its parts rotate with the movable contact arm during the opening sequence. Because the opening springs must rotate relatively heavy portions of the restraining mechanism, in addition to the movable contact arm, the opening sequence is relatively slow.

In contradistinction thereto, in the instant invention,

upon the occurrence of the prescribed faults, there are provided means to immediately free the movable contact arm of the breaker from the remainder of the restraining mechanism whereby only the mass of the movable contact arm and the linkage intimately associated therewith, need be rotated by the opening springs, thereby materially increasing the speed of the opening operation.

In a preferred embodiment of the instant invention, the high speed tripping system, although applicable for initiating rapid interruption in response to any type of fault, is preferably utilized to initiate interruption in response to short circuit current faults where the need for quick opening is especially acute. To this end the invention includes an electronic sensing subsystem for quickly detecting the presence of a short circuit fault in the circuit being protected. Such subsystem preferably comprises a Hall crystal located in the eld generated by the current ilow through the conductor being monitored. The output of the Hall crystal, upon reaching a predetermined magnitude, actuates an electronic switching circuit which discharges a capacitor storage tripping supply to energize an impulse tripping coil which rotates a break-away latch to free the movable contact arm for independent rotation.

Accordingly, it is an object of the instant invention to provide a high speed tripping ssytem for a circuit breaker which is of reduced size, simple construction, reliable over long periods of use, and of such high speed operating characteristics as to be particularly useful to current limiting applications during short circuit fault conditions. y

Another object of the instant invention is to provide such a lhigh speed tripping system which includes means for freeing the rotatable contact ar-m of a circuit breaker from the relatively heavy and complex restraining mechanism normally associated therewith in response to predetermined current conditions flowing in the line being protected.

Another object of the instant invention is to provide such a tripping system for a circuit breaker which frees the movable contact arm from the relatively complex and heavy mechanism normally associated therewith, such that the opening springs of the circuit breaker need only rotate the movable contact arm of the breaker and essential linkage elements associated therewith in order to effectuate circuit interruption.

Yet another object of the instant invention is to provide such a high speed tripping mechanism for a circuit breaker which employs a novel electronic sensing subsystem utilizing a Hall crystal, the output of which is response to current ilow in such a manner as to eliminate the necessity of current transformers previously utilized in such circuit breakers to provide an indication of current ow.

Yet another object of the instant invention is to provide such a circuit breaker with a high speed tripping system which can be utilized in combination with conventional circut breakers in such a way as to add extremely quickacting tripping characteristics to the relatively slower tripping characteristics of the existing breaker.

These and other objects, and a further understanding of the instant invention will be had by referring to the following description and drawings, in which:

FIG. l is a somewhat schematic side view of a circuit breaker embodying the instant invention; and

FIG. 2 is an exploded, perspective detailed view of a portion of the high speed tripping 4mechanism of the instant invention.

Turning to FIG. l, there is shown a circuit breaker 10 incorporating the high speed tripping system of the instant invention. As conventional, the breaker includes an upper and lower primary conductor 412 and '14, respectively, which are to be electrically connected in the line being protected. The upper conductor 12 terminates in a stationary contact arrangement I16 including a main and arcing contact surface 18 and 20, respectively. The lower conductor 14 is provided with a pivot 22 at one extremity, about which is rotatable the movable contact arm 24 of the breaker.

The movable contact arm 24 includes main and arcing surfaces 26 and 28, respectively, which cooperate in a well known manner with contact surfaces 18 and 20, respectively, to assure that upon circuit interruption, that is,`rotation of the movable contact arm 24 in a counterclockwise direction, the main contact surfaces 18 and 26 will separate prior to the separation of arcing contacts 20 and 28. In this manner an arc which is nally drawn across the separating arcing contacts 20 and 28 will be transferred to the

arc runners

30 and 32, respectively, whereby such arc may rise into the arc chute 34 to be expeditiously extinguished with the aid of arc plates such as 36. Preferably, and as illustrated in FIG. 1, the delayed separation of the arcing contacts 20 and 28 with respect to the main contacts 18 and 26 is etfectuated by providing that the movable arcing contact 28 be situated on a sub-portion 37 of the movable contact arm 24 continually biased clockwise about a pivot point 38 by a spring 40.

The movable contact arm 24 is linked by means of a pull rod 42. to one end 44 of a contact operating lever arm 46 which, as best shown in FIG. 2, is provided with an enlarged central aperture 48 such that it is freely rotatable with respect to a pivotal axis constituted by the jack shaft 50. The contact operating lever arm is normally biased in a counterclockwise direction, as viewed in FIG. 1, by an opening spring 52, one end of which 54 bears against a xed stop 56 while the second end of which 58 bears against the contact operating lever arm at a point above the pivotal axis defined by the jack shaft 50. Thus, in order to maintain the movable contact arm 24 in the closed circuit position of FIG. 1, a restraining system 60, to be immediately described, is necessitated. Furthermore, such restraining system must be defeatable when it is desired to trip the breaker.

It is to be appreciated that the defeatable restraining system 60, illustrated in FIG. 1, is not the only type of restraining system which can be utilized to counteract the bias of the opening spring 52. As will be more fully appreciated, the only essential operating characteristics of a restraining system such as 60 is that in normal operation it maintains or latches the movable contact arm 24 in a closed circuit position and that upon being defeated, the entire restraining mechanism or portions thereof can be collapsed or otherwise made movable, in which case the opening springs will be free to rotate contact operating le'ver arm 46 and hence the movable contact arm 24, and additionally those portions of the restraining system 60 which previously presented a rigid obstruction to such movement.

In the embodiment illustrated, the restraining mechanism includes a support plate 62 which is keyed to and rotatable with the jack shaft 50. As best illustrated in FIG. 2, one end 64 of the support plate 62 pivotally carries a latch 66. As will be explained, the latch 66 is an integral portion of a high speed releasing system, the function of which will be explained in greater detail. For the immediate purposes of describing the restraining system 60, it is sufficient to note that latch 66 is normally biased by a spring 68 in a clockwise direction with respect to FIG. 2 such that one end 70l thereof is normally in blocking relationship with respect to a roller 72 carried on the second end 74 of the contact operating lever arm 46. Thus it will be appreciated, that as far as described, with the opening spring S2 biasing the contact operating lever arm 46 in a counterclockwise direction, as viewed in FIG. 2, there will be a rigid linking arrangement through the roller 72, latch 66, the support plate 62 and the jack shaft 50-such that if the contact operating lever arm 46 were rotated in a counterclockwise direction the jack shaft 50 would be similarly rotated.

However, it is to be appreciated that also keyed to and rotatable with the jack shaft 50 is a cam member 76 having a cammed surface 78 engaged by a following roller 80 carried by a bell-crank type of lever 82 pivotally mounted on one end 84 of an L-shaped link 86 pivotally mounted on a xed pivot pin 88. As viewed in FIG. l, the bell-crank type lever `82 lwould tend to rotate clockwise about the pivot 84, and indeed the L-shaped lever 86 would tend to rotate counterclockwise about the xed pivot 88 (from the bias of the opening spring 52 transmitted through the aforenoted rigid linking arrangement and cammed surface 718) were it not for a second bellcrank type lever 90 pivotally mounted at 92, such that one end 94 thereof prevents movement of the bell-crank lever 82 and the L-s'haped link 86. Thus it will now be appreciated that the restraining system 60, including all of the aforenoted parts, does in fact counteract the bias developed by the opening spring 52 and thereby retain the movable contact arm 24 in a closed circuit position of FIG. 1.

As noted previously, in order that the circuit breaker provide the basic function of circuit interruption, there must be some means for defeating the above described restraining mechanism. To this end, most circuit breakers include some means for manually tripping the circuit breaker and additionally customarily include some means for automatically tripping the circuit breaker upon the occurrence of predetermined conditions within the line to which the primary conductors 12 and .14 are connected. Thus it is well known to provide some type of current sensing means which will detect the presence of overload currents in the line being monitored and, upon the occurrence of a predetermined magnitude, produce as an output some type of motion which can be utilized to initiate the tripping operation.

The circuit breaker of FIG. l preferably includes such a current sensing means (not shown) which might comprise, for example, a magnet and armature trip device, the armature of which would be moved upon the occurrence of a predetermined current occurring within the line '12, 14, Upon the occurrence of such armature movement, a latch 94, shown in FIG. l, is rotated out of engagement with a roller '96 provided on the second end 98 of the second bell-crank lever 90. Once this occurs, the bell-crank lever 90 is free to rotate such that the L-shaped lever 86 and the bell-crank lever 82 are free to rotate counterclockwise and clockwise, respectively, and consequently the cam member 76, and the rigid arrangement comprising the jack shaft 50, support plate 62 and the contact operating lever arm 46 (through the latch 66) is free to rotate in a counterclockwise direction under the bias of the opening spring 52 to rotate the movable contact arm 214 counterclockwise to its open circuit position.

For the purpose of presenting a complete description of the typical operation of a circuit breaker, it should be pointed out that circuit breakers are additionally provided with some sort of closing mechanism for rotating the movable contact arm back to the closed circuit position after the fault which initiated interruption has been cleared. Thus the breaker of FIG. 1 would be additionally provided with closing mechanism (not shown) which could, if desired, rotate the bell-crank type lever 82 in a counterclockwise direction such that the roller 80 bearing against the cam surface 78 would rotate the cam member 76 which eventually (through the jack shaft 50, support plate 62, latch 66 and roller 72) would rotate the `contact operating lever arm 46 and hence the movable contact arm 24 against the bias of opening spring 52 to return the breaker to the closed circuit position. In this connection it might be pointed out that a prop latch such as 99 may be conveniently provided to prevent a closing operation unless the fault has been cleared.) Thus a portion of the restraining system which was previously utilized to maintain the breaker in the closed position may simultaneously function as a portion of the closing mechanism used after a circuit interruption to recomplete the circuit.

Returning once again to the opening operation, it becomes apparent that because various members of the restraining mechanism (which as noted above might also comprise a portion of the closing system) are rotated during an opening sequence, and because such members are of relatively high mass to add durability to the breaker, a great deal of the natural bias of the opening spring 52 is expended in rotating parts other than those intimately associated with the movable contact arm 24. Thus with many parts of high mass to rotate, the opening sequence is a relatively slow operation. However, since the above described opening cycle is primarily used in interrupting overcurrents which are not instantly harmful, this relatively slow opening operation can be tolerated within the normal ranges of overcurrents expected in the lines being protected.

However, when it comes to protecting against short circuit fault conditions, and especially when the line is conducting ultra-high currents coming into extensive use in the distribution industry, it is imperative that the opening operation be materially quickened. To this end, the instant invention, as is to be immediately described below, provides a quick-acting tripping system which, upon the occurrence of predetermined short circuit fault conditions occurring in the line, will bring about circuit interruption much quicker than was heretofore possible.

To this end the instant invention provides that upon the occurrence of a high current fault condition, the movable contact arm 24 (and the contact operating lever arm 46) will be freed and allowed to rotate independent of those portions of the restraining mechanism 60 which customarily are rotated during what is conveniently classified as the semi-high speed tripping operation described above. To effectuate such independent motion of the contact arm 24, the instant invention includes a trip coil 100, which, as will be further explained, is energized in response to the occurrence of a short circuit fault flowing in the line 12, 14. The trip coil 100 includes a member 102 which would be linked to the armature of the coil (not shown), which member 102 strikes the latch 66 and rotates it counterclockwise against the bias of spring 68 in response to energization of the coil 100. When the latch 66 is rotated counterclockwise, the aforementioned rigid arrangement which was effectuated between the contact operating lever arm 46 and the support plate 62 (through the engagement of the end 70 of the latch 66 and the roller 72) is defeated such that the contact operating lever arm 46 is now free to rotate independently about the jack shaft 50 under the influence of the opening spring 52. Thus all of the energy of the opening spr-ing 52 is applied ysolely to the contact operating lever arm 46 and hence to the movable contact arm 24 to rapidly snap the movable contact arm 24 to its open circuit position in a much shorter time than the contact arm is opened when the spring must rotate not only the contact operating lever arm 46 but all of the various elements such as 80, 86, etc., of the restraining mechanism 60. Since the contact arm 24 and the contact operating lever arm 46 have been rotated independently of the restraining mechanism 60, other means (not shown) are provided to trip the restraining mechanism so that it may be properly reset to allow the closing mechanism to close the contacts at a subsequent time.

In its preferred embodiment, the sensing system for energizing the impulse trip coil 100 upon the occurrence of predetermined short circuit fault conditions, takes advantage of the well known Hall effect which permits the development of an electrical potential when a magnetic field is applied transversely to a current in a suitable material. Thus current flow through the line 12, 14, generates a magnetic field about the conductor 14 which is conveniently concentrated by means of an iron structure 104 which has located in its gap a Hall crystal of suitable type, 106, which is excited with a constant current source (not shown). Thus in accordance with the well known Hall effect, the crystal 106 supplies a signal which will be proportional to a magnetic field in turn proportional to the current owing through the line 14. This signal is amplied by DC amplifier 108 and used to actuate or turn on an electronic switch of suitable design, 110, at predetermined levels of forward and reverse current. When such predetermined fault levels are reached, the electronic switch will serve to connect a capacitor storage tripping supply 112 to the impulse trip coil 100 which, as noted previously, will initiate the high speed tripping operation. Thus there has been described a high speed tripping system for a circuit breaker, typically of the DC type, which permits the movable contact arm of such breaker to be freed and rotated to its open circuit position independently of the restraining and/or closing mechanism normally provided in such breakers. The high speed opening operation afforded by the instant invention permits breakers employing the invention to have higher interrupting capabilities than previously possible, With increased interrupting capabilities, smaller circuti breakers can be utilized to service equipment previously requiring higher rated breakers. For example, in one situation it was found that a 4000 kw. rectifier in a singled ended substation required an 8000 amp. main breaker and a 3000 amp. feeder breaker for adequate short circuit capabilities. Using circuit breakers embodying the instant invention, it was found that the same protection could be afforded using a 6000 amp. main breaker and a 1200 amp. feeder breaker for substantial reductions in size and cost.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure here, but, only the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A circuit breaker for interrupting the flow of current through a conductor upon the occurrence of predetermined conditions, said circuit breaker comprising:

a stationary contact;

a movable contact rotatable between a closed circuit and an open circuit position with respect to said stationary contact;

bias means for rotating said movable contact between closed and open circuit positions;

defeatable restraining means for normally preventing rotation of said movable contact means, said restraining means including members which are rotated in response to rotation of said movable contact under the bias of said means when said restraining means is defeated in response to lirst predetermined conditions;

release means for permitting said -movable contact to rotate to its open circuit position independent and free of said members of said restraining means in response to occurrence of second predetermined conditions;

whereby said bias means need not overcome the mass of said members in rotating said movable contact to its open circuit position;

wherein said movable contact is linked to a contact operating lever arm freely rotatable on a first rotatable axis, and further including support means rigidly mounted on said first rotatable axis and rotatable therewith, said release means including a latch carried by said support means, said latch normally preventing rotation of said contact operating lever arm independent of said support means, energization of said release means rotating said latch out of the path of rotation of said contact operating lever arm such that said contact operating lever arm and said movable contact can rotate free of said support means and said first rotatable axis.

2. The circuit breaker of claim 1, and further including camming means rigidly mounted on said rst rotatable axis and rotatable therewith, said camming means constituting one of said members of said restraining means which is rotated in response to rotation of said movable contact arm when said restraining means is defeated, whereby with said latch in blocking relationship with respect to said contact Operating lever arm, rotation of said contact operating lever arm will cause rotation of said support means which, through said iirst rotatable axis, will bring about rotation of said camming means, and when said latch is moved out of blocking relationship with respect to said contact operating lever arm, said contact operating lever arm will be free to rotate independent of said camming means and the remainder of said restraining means.

3. The circuit breaker of claim 1, and further including sensing means for monitoring the current flow in said conductor, said second predetermined condition being when said current reaches a predetermined magnitude.

4. The circuit breaker of claim 3, and further including a normally non-energized trip coil which efectuates rotation of said latch when energized, energy storage means for energizing said trip coil, and switching means for permitting said energy storage means to energize said trip coil when said predetermined magnitude of current is sensed.

5. The circuit breaker of claim 3, wherein said sensing means is a crystal device located in the magnetic iield generated by said conductor, said crystal device producing an output signal which is proportional to the current liowing in said conductor.

References Cited UNITED STATES PATENTS 3,064,163 ll/1962 Smith 3l7-60 3,384,845 5/1968 Johnson 335-16X 3,384,846 5/1968 Heft 335--16 3,391,357 7/1968 Heft 335-16 JAMES D. TRAMMELL, Primary Examiner H. FENDELMAN, Assistant Examiner UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Paf-ent N0' 3,558,991 DMEMMLFLQZL Inventorfs) Thomas F. Brandt, Jr. et al It is certified that error appears in the above-identified pate-n and that said Letters Patent are hereby corrected as shown below:

In the first and second sheets of drawings containing Figures l and 2 at the top thereof, the inventor, "T. R. BRANDT, JR." should be listed as T. F. BRANDT, JR.

Column l, line 4 the inventor, "Thomas P. Brandt Jr." should be listed as `Thomas F. Brandt, Jr

Signed and sealed this 16th day of November 1 971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Paten