US2829217A - Current responsive control device - Google Patents

Description

M. B. FORNWALT CURRENT RESPONSIVE CONTROL DEVICE Filed May 25, 1954 April 1, 1958' Inventor: Porn alt, K im orneg.

nited States Patent CURRENT RESPONSIVE CONTROL DEVlCE Mas B. Fornwalt, Springfield, Pa., assignor to General Electric Company, a corporation of New York Application May 25, 1954, Serial No. 432,078

12 Claims. (Cl. ZUB-94) This invention relates to current-responsive control devices and, more parti-cularly, to an electromagneticallyoperated, current-responsive trip device for a circuit breaker.

A convenient manner of operating an electroresponsive device in response to predetermined current conditions in an electrical conductor is to provide the device with a magnetizable core mounted about the conductor. Such a core when sutciently magnetized in response to predetermined current conditions in the conductor can be utilized to attract an armature, which upon actuation, will perform a preselected control function. In most prior arrangements, Where the conductor is one of a plurality of closely spaced conductors, the magnetization of the core has been appreciably influenced, not only by current conditions in the one conductor about which the core is mounted, but also by current conditions in the adjacent conductors. In such prior arrangements, where the electroresponsive device has been calibrated to respond in a predetermined manner to predetermined current conditions in the one conductor, this calibration has been detrimentally effected by varying current conditions in the adjacent conductors. As a result, incorrect or unpredictable operation of the electroresponsive device frequently has occurred. An example of such a situation is present in a circuit breaker which has a plurality of conductive poles about each of which is mounted a U-shaped magnetizable core of a current-responsive trip device for tripping the breaker. if the trip device is calibrated to operate in a preselected manner iu response to predetermined fault currents in the pole about which it is mounted, it is most desirable that the device always respond in the same preselected manner. Since current conditions in the adjacent conductors may vary widely, depending upon the type of fault encountered, the operation of the device should be essentially independent of current conditions in adjacent poles. Unless this independence is achieved, `the trip device Will not respond consistently in the desired manner.

Accordingly, Where a current-responsive control device is provided with a magnetizable core mounted about one conductor of a plurality of closely spaced conductors, it is an object of my invention to arrange the core and the one conductor in such a manner that the response of the device depends only upon predetermined current conditions within the one conductor and is essentially independent of current conditions in the adjacentconductors.

Where the current-responsive device is the calibrated, time-delayed tripping device of a circuit breaker, it is an object of this invention to maintain the same timedelayed tripping characteristics in spite of varying current conditions in the adjacent conductors.

It is 'a further object of my invention to provide a simple and sturdy arrangement for mounting the core so that it will be capable of producing the above-mentioned desired results.

in accordance with one form of my invention, there asian? armature movable toward said core in response to current flowing through said stud in excess of a predetermined value is arranged to perform a preselected control function.

For a better understanding of my invention, reference may be had to the accompanying drawing in which Fig. l is an elevational view showing a current-responsive circuit breaker trip device embodying my invention. Fig. 2

is a plan view, partly in section, of the trip device of Fig. l. Fig. 3 illustrates an arrangement in which a trip device such as shown in Figs. l and 2 is applied to each of the three closely spaced poles of 'a circuit breaker.

i have illustrated my invention as applied to a timedelayed electro-magnetic trip device of a circuit breaker. Since the circuit breaker mechanism forms no part of the present invention, l have shovyn only such parts of the breaker as are required for an understanding of my invention. Referring more particularly to Figs. l and 3, i have shown a circuit breaker it) comprising a rotatable trip shaft il having trip members 12, 12a, and 12b suitably secured thereto. When the trip shaft il. is rotated sufciently in a counterclockwise direction (as seen in Fig. l) by a force applied to any one of the trip members 12, 12a or 12b, the shaft 11 acts to release a suitable latch (not shown). This latch, upon release, permits the breaker to open under the iniluence of suitable open-ing springs (not shown). A conventional form of such a latched-closed, biased-opened circuit breaker is shown in U. S. Patent 2,549,441, issued to l. A. Favre and assigned to the assignee of the present invention.

Each pole of the circuit breaker comprises an elongated terminal conductor, or stud, such as 1S about which is mounted magnetizable U-shaped core 16 of a trip device i7. As may be seen more clearly in Fig. 2, the stud 15 is formed in two parts 18 and 19 which are secured together by bolts 20 threaded into suitable apertures in part 19. The composite stud structure comprises transversely-spaced, longitudinally-extending segments 2l and 22 and a transversely-extending portion 23 electrically interconnecting the segments. The U- shaped core 16 is mounted in a position in which its bight portion 27 extends longitudinally of the stud 15 and its legs 24 straddle the transversely-extending stud portlon 23. As is evident from Fig. 3, the composite stud l5 may be thought of as having staggered, transverselyextending, longitudinally-spaced recesses 23a and 23b which receive the legs 24 of the U-shaped core. The recess 23a of Fig. 3 has, opposite its mouth, an end wall which faces toward the adjacent stud 15u, and the recess 23b has, opposite itsmouth, an end wall 29 which faces away from the adjacent stud 15a. For ixedly mounting the core in this position, the core and the segment 22 are provided with registering openings receiving suitable bolts 2S. The openings in segment 22 are threaded so that the correspondingly threaded bolts 25 may be tightened to clamp the core firmly against the segment 22.

For actuating the trip shaft 11 in response to predetermined current conditions in the stud l5, a pivotally mounted armature structure 39 is provided. ln the ilassegni? lustrated embodiment of my invention, this armature structure 3h comprises a pair of independently-movable armatures 3l. and 32 mounted to pivot about a trans` versely-extendiug shaft 33. This shaft 33, which is suitably supported on the extended legs 34 of a pair of spaced U-shaped frame members secured to the laminated cores i6, carries a suitable sleeve 33a for spacing the armatures 3l and 32.

As shown in Fig. l, the armatures 3l and 32 are biased to a disabled position against a stop 35 by means of gravity and by means of calibrated springs 39, d3, and 56 forming a part of a timing mechanism 36, which is enclosed by a housing 36a. These springs and the timing mechanism are described in greater detail hereinafter. The housing 36a is joined to the core by suitable support brackets 36b so that the composite trip device constitutes a unitary structure which may be assembled as a unit about the stud 1S.

Under normal current conditions in the stud 15, the biasing force provided by gravity and the above-mentioned springs will maintain the armatures 3l and 32 in the disabled position of Fig. 1. However, should abnormal current conditions, such as overcurrent, take place in the stud l5, the core i6 will be sufficiently magnetized to attract at least one of the armatures with a force great enough to overcome the forces biasing the armature structure to the disabled position. As the armature moves toward the core 16, its outer end will contact the trip member l2 thereby rotating the trip shaft 1l counterclockwise to unlatch and trip open the circuit breaker.

ln order to provide for electrical system coordination, it is customary in many circuit breaker applications to retard the circuit breaker tripping operation 'for a predetermined period of time which varies inversely with the magnitude of the overcurrent. This inverse time element is provided in the illustrated embodiment of my invention by retarding the motion of the pivotal armatures 3i and 32 so that the speed of their clockwise tripping movement in response to the attraction of the magnetized core tti varies directly with the magnitude of the current. ln the illustrated embodiment, three stages of time delay are provided, in general, by means of an escapernent mechanism 37 coupled to one armature 32 and a dashpot mechanism 38 resiliently coupled to the other armature 3l. As will appear more clearly hereinafter, the escapement mechanism 3'7 is eiective to provide a relatively short inverse time delay in the movement olf armature 32 to the attracted position when the stud l5 is energized by currents within a predetermined intermediate range of values. For such intermediate currents, the other armature 31 is delayed by means of the dashpot 38 to respond at a slower rate than armature Accordingly, the escapement-retarded armature 32 alone trips the breaker for this intermediate range of currents. lt is to be understood that the speed at which the armature 32 moves varies directly with the magnitude of the current, so that an inverse time element is provided for this intermediate range of currents.

For predetermined values of current below this intermediate range, the dashpot-retarded armature 3l, rather than the escapement-retarded armature, is effective to trip the breaker. More particularly, for such low current conditions, the attractive force provided by the magnetic core lo is insutlcient to overcome the force of calibrating spring d3 associated with the escapement-retarded armature .32 but is sufficient to overcome the forces restraining the dashpot-retarded armature 31. As a result, under such low current conditions, the dashpot-retarded armature ic alone elective to trip the breaker. lt is to be understood that the speed at which the dashpot-retarded armature 3l moves varies directly with the magnitude of the current, so that an inverse time element is provided for this lower range of currents.

For currents above the intermediate range, the armature 3l is permitted to move to its attracted position substantially instantaneously by means of a yielding connecticn provided by a break-away spring 39, to be described in greater detail hereinafter. Duripg currents in the lower and intermediate range, the break-away spring 39, in effect, forms a positive coupling between arma- 31 ci the dashpot piston dl). But for higher currents, the attractive forces on the armature are sutlicient to stretch the spring 39 and permit the armature 31 to ore-ak away from the restraint of the retarded dashpot piston dil and to move substantially instantaneously into the attracted position.

For utilizing the escapeinent mechanism 37 to retard the armature 3l, these parts are coupled together by means including a pivotally-mounted crank 40a having one end coupled to armature 32 through a link 44, which is pivotally connected to the armature 32. The other end of the crank 40a is coupled to escapement wheel 41 by means of a rack 42 and pinion 42a. A tension spring 43 connected to the crank 40a provides a force which biases the armature 32 toward the droppedout position of Fig. l. Suitable means (not shown) are provided for adjusting the tension of spring 43 whereby the response of armature 32 to predetermined current conditions may be suitably calibrated.

For utilizing the dashpot 33 to retard the armature 3l these parts are coupled together by a linkage 5G. This linkage 5l) comprises a crank 51, which is pivotally mounted on a xed pivot 52 and has one end suitably coupled to dashpot piston dil. The other end of the crank 5i is coupled through spring 39 to a link 53, which in turn, is pivotally joined at its upper end to armature 3i. The lower end of link 53 is carried by a support arm 5ft, which is freely pivoted on pivot 52. The break-away spring 39 normally urges the crank Sl to pivot counteclockwise about its pivot S2 and into a position wherein a stop 55 on the crank 51 abuts against support arm 54. Thus, it will be apparent that when the armature 3l is attracted to core 16, the resulting downward movement of the link 53 is transmitted by the spring 39 to the crank 51 in a manner thereby the crank moves clockwise about its pivot 52. This clockwise movement is retarded by the dashpot 38 whereby to provide the desired time-delayed tripping.

For all currents up to a predetermined limit, the spring 39 acts as an essentially rigid link and thus, the armature 31 moves as a unit with the retarded dashpot piston 4t). However, for currents above this limit, the armature 31 moves the link 53 downward with suicient speed and force to stretch the spring 39 so as to permit the armature to move essentially free of `restraint from dashpot 38, whereby to permit an instantaneous response of armature 31.

For biasing the armature 31 to its dropped-out position, a spring 56 is provided. The tension of this Spring 56 can 'be adjusted 'by means of an adjusting nut 57, whereby the response of armature 31 to predetermined current conditions may be suitably calibrated. Suitable means, not shown, are also provided for adjusting the tension of break-away spring 39 whereby further calibration of the armature may be carried out. Heretofore, where current responsive trip devices of the general type shown in the drawing have been utilized, it has been customary to mount the U-shaped core about the elongated stud in such a manner that the legs of the corc are disposed in a plane perpendicular to the longitudinal axis of the stud. In such arrangements, where the stud is one of a plurality of closely-spaced conductors, serious diflculties have arisen in maintaining the trip device precisely calibrated to respond only to current conditions- 1n the one stud. Varying current conditions in the adja.

cent conductors have detrimentally affected this calibration of the trip device and have resulted in unpredictable operation thereof. Constructing and arranging the maogegaan? netic core of the stud in accordance with the present invention makes it possible to maintain this calibration of the trip device constant and essentially independent of current conditions in the adjacent conductors. For example, once the springs 39, 43 and 56 of my trip device have been adjusted to provide predetermined operation in accordance with current values in stud 15, this calibration will be maintained and will be essentially independent of current conditions in the adjacent conductors. In accordance with the present invention the U-shaped core is disposed in a plane which is generally perpendicular to the plane in which similar cores have previously been disposed. As may Abe seen in Fig. 3, each of the cores 16, 16a, and 16h of the respective trip devices 17, 17a and 17b is disposed in a plane which extends longitudinally with respect to the elongated conductive studs 15, a and 15b. For example, referring to Fig. 3, the core 16 can be considered as being disposed in a plane A-A which extends longitudinally with respect to its associated stud 15. This plane A-A, in which the two legs of the core are disposed, is referred to hereinafter as the major plane of the core. This major plane is also disposed generally perpendicular to a reference plane that contains the longitudinal axes of the adjacent conductive studs. For a given spacing of the conductors, this disposition permits the cores to be spaced a maximum distance from each other and from the adjacent conductors. Also with my arrangement, each stud serves as a shield which tends to conne the stray flux from its associated core Vand essentially prevents such flux from linking with an adjacent core. This shielding effect together with the maximum-spacing eifect effectively reduces the flux linkage between adjacent poles to a value which is negligible. Accordingly, my trip device may be calibrated to perform in a predetermined manner in response to predetermined current conditions in its stud, and this calibration will be maintained essentially independent of current conditions in the adjacent studs. Thus in Fig. 3 the current-responsive trip unit 17b is essentially independent of current conditions in studs 15 and 15a. Accordingly, irrespective of the current conditions in studs 15 and 15a, when the current in stud 15b exceeds a predetermined value the armature structure (not shown) of trip unit 17b will always respond in a predetermined manner to actuate the trip member 12b and trip breaker. Similarly, trip unit 17a, which is arranged to actuate trip member 12a, will respond only to current conditions in stud 15a, and trip unit 17 only to current conditions in stud 15. Thus, each of the trip units 17, 17a and 17b may be calibrated to respond to predetermined current conditions in its particular stud and this calibration will be unaffected 'by varying current conditions in adjacent studs.

It will be apparent that this high degree `of reliability has been obtained by the use of a stud 15 which is of a simple and sturdy construction. Stud parts 18 and 19 are of a simple conliguration which facilitates fabrication and assembling together of these parts. Additionally, since the stud is formed in two parts, the trip device may be easily assembly about the stud as a complete precalibrated unit. For example, before the stud part 19 is attached to stud part 18, I can assemble the trip unit 17 about the transversely-extending stud portion 23 and then mount this sub-assembly upon a test iixture corresponding to stud part 18. The springs 39, 43 and 56 may then be adjusted to provide the desired calibration. In view of the essentially complete independence of each trip unit from current conditions in adjacent conductors, this adjustment or precalibration may be performed with the assurance that the precalibration will be preserved in the completed circuit breaker. The subassembly is then detached from the test fixture and, thereafter, may be mounted upon the stud part 18 at any desired time without any further calibration being required.

While I have described and illustrated a preferred embodiment of my invention, it should be understood that I do not intend to be restricted solely thereto but l do intend to cover all modications thereof which will 'be apparent to one skilled in the art and which come Within the spirit and scope of my invention.

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

l. In a device having a control element actuable to perform a preselected control function, a plurality of closely-spaced, generally-parallel, elongated conductive studs having their longitudinally-extending central regions disposed in a predetermined reference plane, one of said elongated conductive studs comprising longitudinally-extending, transversely-spaced segments and a transversely-extending portion electrically interconnecting said segments, a magnetizable U-shaped core having a bight portion extending longitudinally of said one stud and a pair of `spaced legs straddling said transversely-extending portion whereby said core is arranged to be magnetized by current flowing through said one stud, said core having a major plane in which its two legs are disposed, said major plane being generally perpendicular to said reference plane, a magnetizable armature movable toward said core in response to current flowing through said one stud in excess of a predetermined value, and means responsive to said armature movement for actuating said control element.

2. In a device having a control element actuable to perform a preselected control function, a pair of closelyspaced, generally-parallel, elongated conductive studs, one of said studs having staggered transversely-extending longitudinally-spaced recesses, one of said recesses having an end wall facing toward the other of said studs and the other of said recesses having an end wall facing away from said other stud, a magnetizable U-.shaped core having a pair of spaced legs disposed within said recesses whereby said core is arranged to be magnetized by current flowing through said one stud, and a magnetizable yarmature movable toward said core in response to current flowing through said one stud in excess of a predetermined value, and means responsive to said armature movement for actuating said control element.

3. In a device having a control element actuable to perform a preselected control function, a pair of closelyspaced, generally-parallel, elongated conductive studs having their longitudinally-extending central regions disposed in a predetermined reference plane, one of said conductive studs having a portion extending transversely thereto, a magnetizable U-shaped core having a pair of spaced legs straddling said transversely-extending portion whereby said core is arranged to be magnetized by current flowing through said one stud, said core having a major plane in which its two legs are disposed, said major plane extending longitudinally of said one stud and being generally perpendicular to said reference plane, an armature movable toward said core in response to current flowing through said one stud in excess of a predetermined value, and means responsive to said armature movement for actuating said control element.

4. In a circuit breaker having a trip element actuable to trip thebreaker, a plurality of closely-spaced, generally-parallel, elongated conductive studs having their longitudinaly-extending central regions disposed in a predetermined reference plane, one of said conductive studs having a portion extending transversely thereto, a magnetizable U-shaped core having a bight portion extending longitudinally of said one stud and a pair of spaced legs straddling said transversely extending portion whereby said core is arranged to be magnetized by current flowing through said one stud, said bight portion and said two legs being disposed in a plane which extends generally perpendicular to said reference plane, a magnetizable armature movable toward said core in response to current flowing through said one .stud in excess of a predetermined value, and means responsive to said armature movement for actuating said trip element.

5. In a circuit breaker trippable to interrupt current owing in a circuit extending through said breaker, said circuit including a plurality of closely-spaced, generallyparallel, elongated conductive studs having their longitudinally extending central regions disposed in a predetermined reference plane, one of said elongated studs comprising longitudinally-extending, transversely-spo-ced segments and a transversely-extending portion electrically interconnecting said segments, a magnetizable U-shaped core having a pair of spaced legs straddling said transversely-extending portion whereby said core is arranged to be magnetized by current flowing through said one stud, .said core having a major plane in which said two legs are disposed, said major plane extending longitudinally of said one stud and generally perpendicular to said reference plane, a magnetizable armature movable toward said core in response to current flowing through said one stud in excess of a predetermined value, and means responsive to said armature movement for tripping said breaker.

6. in a control arrangement comprising a pair of closely-spaced, generally-parallel elongated conductive studs, one of said studs including longitudinally-extending, transversely-spaced segments and a transversely-extending portion eiectrically interconnecting said segments, one of said segments being located adjacent the other of said studs and the other of said segments being located at a greater distance from said other stud, a magnetizable U-shaped core having a pair ot' spaced legs straddling said transversely-extending portion whereby said core is arranged to be magnetized by current owing through said one stud, said core having a major plane in which its two legs are disposed, said major plane extending longitudinally of said one stud, and a magnetizable armature movable toward said one core in response to current flowing through said one stud in excess of a predetermined value.

7. ln a control arrangement comprising a plurality of closely-spaced, generally-parallel, elongated conductive studs, one of said studs having staggered, transverselyextending, longitudinally-spaced recesses, one of said recesses having an end wall facing toward the other of said studs and the other of said recesses having an end wall facing away from said other stud, a magnetizable U-shaped core having a pair of spaced legs disposed within said recesses whereby said core is arranged to be magnetized by current flowing through said one stud, and a magnetizable armature movable toward said core in response to current flowing through said one stud in excess of a predetermined value.

S. A current-responsive assembly including a pair of closely-spaced, generally-parallel elongated conductive studs having their longitudinally-extending central regions disposed in a predetermined reference plane, one of said studs comprising two portions, one of said stud portions comprising a longitudinally-extending segment and a transversely-extending segment joined thereto, the other of said stud portions comprising a longitudinally-extending segment, means for detachably securing said transversely-extending segment to the longitudinally-extending segment of said other portion, a magnetizable U- shaped core having a bight portion extending longitudinally of said stud and a pair of spaced legs straddling said transversely-extending segment whereby said core is arranged to be m'agnetized by current flowing through said one stud, said core having a major plane in which its two legs are disposed, said major plane being generally perpendicular to said reference plane, and an armature movable toward said core in response to current flow through said one stud in excess of a predetermined value.

9. The assembly of claim 8 in which the other of said studs is generally identical to said one stud, another core mounted about said other stud and disposed in a plane generally parallel to the core of said one stud.

10. In combination, a plurality of closely-spaced elongated conductive studs each including longitudinally-extending, transversely-spaced segments and a transverselyextending portion electrically interconnecting said segments, the longitudinally-extending central regions of said uds being disposed in a predetermined reference plane, a phtrality ot magnetizable U-shaped cores each having a pair of spaced legs straddling one of said transverselyextending stud portions whereby each of said cores is arranged to be magnetized by current owing through the associated stud about which it is mounted, each of said cores having a major plane in which its two legs are disposed, said major planes extending longitudinally with respect to said studs and disposed generally perpendicular to said reference plane and a plurality of magnetizable armatures each of which is mounted adjacent one of said cores and is movable toward said one core in response to current liowing through the associated stud in excess of a predetermined value.

ll. In a circuit breaker trippable to interrupt current llowing in a circuit extending through said breaker, said circuit including a plurality of closely-spaced elongated studs having their longitudinally-extending central regions disposed in a predetermined reference plane, each comprising longitudinally-extending, transversely-.spaced segments and a transversely-extending portion electrically interconnecting said segments, a magnetizable U-shaped core associated with each of said studs, each of said cores having a pair of spaced legs straddling said transverselyextending portion of said stud whereby said core is arranged to be magnetized by current flowing through said stud7 each of said cores having a major plane in which its two legs are disposed, said major planes extending longitudinally with respect to said studs and disposed generally perpendicular to said reference plane, a magnetizable armature associated with each of said cores and movable toward said core in response to current i'lowing through the associated stud in excess of a predetermined value, and means responsive to said armature movement for tripping said breaker.

l2. In an electro-responsive control arrangement comprising a pair of elongated conductors mounted in closelyspaced, generally-parallel relationship, the longitudinally-extending central regions of said conductors being disposed in a predetermined reference plane, at least one of said conductors comprising spaced, longitudinally-extending segments and a transversely-extending portion electrically interconnecting said segments, a current-responsive device sensitive to current in said one conductor mounted about said transversely-extending portion with the major plane of said device extending longitudinally of said one conductor and in non-intersecting relationship with adjacent portions of the other of said conductors, said major plane being generally perpendicular to said reference plane.

References Cited in the lile of this patent UNlTED STATES PATENTS 2,000,442 Healis May 7, 1935 2,027,221 Bostwick lan. 7, 1936 2,043,306 Sandin June 9, 1936 2,144,501 Lingal Ian. 17, 1939 FOREIGN PATENTS 252,697 Great Britain Nov. 4, 1926 142,860 Switzerland Jan. 2, 1931

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