US3704435A - Tripping system for circuit breaker - Google Patents

Abstract

A current limiting circuit breaker is constructed to achieve more rapid tripping in the medium fault current range by utilizing a magnetic tripping device which imparts physical motion to the movable contact under particular fault current conditions. In the lowest fault current range above the thermal tripping range the magnetic tripping unit automatically operates or releases the spring operating mechanism thereby causing contact separation. As fault current increases the magnetic tripping means is effective to assist the operating mechanism to physically move the movable contact, and at still higher currents the magnetic tripping means moves the movable contact to its fully open position before any movement is imparted to the movable contact by the spring operating mechanism. As fault currents increase still further, electrodynamic forces assist the magnetic means to physically move the movable contacts, and in the very highest fault current range electrodynamic operation moves the movable contact essentially to its fully opened position, before the magnetic trip means for the operating mechanism is active in moving the movable contact.

Description

[54] TRIPPING SYSTEMFOR cmcmr- BREAKER [72] Inventors: Frank W. Kussy, Haverford; Gustave E. Heberlein, Jr., King-0f Prussia, both of Pa.

[73] Assignee: I-T-E Imperial Corporation, Philadelphia, Pa.

[22] Filed: Dec. 20, 1971 [21] Appl. No.: 209,853

Related US. Application Data [62] Division or Ser. No. 145,175, May 20, 1971,

Pat. No. 3,663,903.

521 uscn ..3s5/255,335/17e 51 rm. c1. .Htllh 3/52 58 newer Search ..335/258, 261, 279,255,281, ass/19,174

[56] I References Cited UNITED STATES PATENTS 2,829,319 4/1958 McCleskey ..-...335/25s 2,570,062 10/1951 Kesselring ..335/19 [15] 3,7 ill f ,35 [451 Nov. 28, E972 57 TRACT A current limiting circuit breaker is constructed to achieve more rapid tripping in the medium fault current range by utilizing a magnetic tripping device which imparts physical motion to the movable contact under particular fault current conditions. In the lowest fault current range above the thermal tripping range the magnetic tripping unit automatically operates or releases the spring operating mechanism thereby causing contact separation. As fault current increases the magnetic tripping means is effective to assist the operating mechanism to physically move the movable contact, and at still higher currents the magnetic tripping means moves the movable contact to its fully open position before any movement is imparted to the movable contact by the spring operating mechanism. As fault currents increase still further, electrodynamic forces assist the magnetic means to physically move the movable contacts, and in the very highest fault current range electrodynamic operation moves the movable contact essentially to its fully opened position, before the magnetic trip means for the operating mechanism is active in moving the movable contact.

3 C, 16 Drawing Figures TRIPFING SYSTEM FOR CIRCUIT BREAKER This is a divisional application of Ser. No. 145,175, filed May 20, 1971, now US. Pat No. 3,663,903.

This invention relates to circuit breakers in general, and more particularly relates to a current limiting circuitbreaker having means to increase the speed of contact separation in the medium fault current range.

In current limiting circuit breakers of the. prior art utilizing electrodynamic effects for current limiting action, in the range of medium fault currents there apcontact operating mechanism is effective to move the contacts. In the lowerportion of this range the magnetic tripping means and the contact operating means complement one another in bringing about contact separation. However, in the upper portion of this range,

contact separation is essentially completed before the contact operatingmechanism acts to separate the contacts. Above this latter range electrodynamic effects assist the magnetic tripping means to separate the contacts, and at still higher currents electrodynamic effects operate the movable contact essentially to its fully opened position before either the tripping mechanism or the contact operating mechanism is effective to move the movable contact.

Accordingly, a primary object of the instant invention is to provide a novel construction for a current limiting circuit breaker.

Another object is to provide a circuit breaker of this type in which the speed of contact separation in the medium fault current range is increased.

Still another object is to provide a circuit breaker of this type in which there is a novel magnetic tripping means that is effective to physically move movable contacts upon the occurrence of predetermined fault currents.

A further object is to provide a circuit breaker of this type in which there is coordination between an overcenter spring operated mechanism, an electromagnetic tripping device, and electrodynamic means to achieve a relatively smooth tripping characteristic.

A still further object is to provide a circuit breaker having a tripping electromagnet with a novel armature construction.

These objects as well as other objects of this invention will become readily apparent after reading the following description of the accompanying drawings in which:

FIG. I is a graph showing a comparison between the tripping characteristics of a current limiting circuit breaker constructed in accordance with the instant invention'and a current limiting circuit breaker of the prior art.

FIG. 2 is a side elevation of a molded case current limiting circuit breaker constructed in accordance with teachings of the instant invention, with the near side of the housing removed to reveal the essential operating and current carrying elements.

FIG. 3 is a fragmentary portion of FIG. 2, illustrating contact opening due solely to action of the spring operating mechanism.

FIG. 4 is a fragmentary portion of FIG. 3, illustrating contact opening under conditionswhere the magnetic tripping device exerts a mechanical force to assist the spring operating mechanism.

FIG. 5 shows the elements of FIG. 4 when contact opening is due solely to mechanical'forces developed by the magnetic tripping means.

FIG. 6 is a fragmentary portion of FIG. 3, illustrating contact opening under conditions where electrodynamic forces assist the mechanical force of the magnetic tripping means.

FIG. 7 shows the elements of FIG. 6 under conditions where contact separation is due solely to electrodynamic forces.

FIGS. 8 and 9 are perspectives of the movable stationary contacts looking at opposite sides thereof.

FIG. III is an end view of the contacts looking in the direction of arrows ltl lll of FIG. 8-

FIG. I1 is an end view ,of the contacts looking in the direction of arrows 11-11 of FIG. 9.

FIG. 12 is a view similar to that of FIG. '10 with the addition of insulating barrier elements.

FIG. 13 is a cross-section taken through line III-I3 of FIG. 12 looking in the direction of arrows 13-13.

FIG. 14 is an enlarged view of the operating magnet under normal load current conditions.

FIG. 15 is a side elevation of the magnet yoke and armature under fault current conditions. contacts FIG. 16 is a side elevation of the magnet armature looking in the direction of arrows 16l6 of FIG. I5.

Now referring to the figures. As illustrated by curve A in FIG. I, the tripping characteristic of prior art molded case current limiting circuit breakers is generally divided into two regions C and D. In the first region C the magnetic trip device of the breaker releases a latch, permitting energy stored in the operating springs to open the contacts. In region C, fault currents are in the low to medium range, or typicallyfrom 5 to 5th times the maximum continuous current rating of the breaker, and very little current limitation takes place because contact opening speed is relatively slow.

In the second region D, the fault currents are higher than in region C, and the circuit breaker contacts are opened independently of the circuit breaker operating mechanism. The major share of current limitation takes place in region D since the contacts are opened before current has reached the maximum available peak. At this time the onntacts are opened at a speed that is high enough to draw and develop a high are voltage which opposes the driving voltage of a system until current arrives at zero.

As will hereinafter be seen, circuit breaker or circuit interrupter 20 (FIG. 2), constructed in accordance with the instant invention, has a tripping characteristic illustrated by curve B. The differences between curves A and B are due to the fact that circuit breaker 2t) achieves faster contact separation in the range of medium fault currents without adversely effecting tripping at low fault currents or very high fault currents.

Circuit breaker 20 of FIG. 2 is a multi-phase unit, only one phase of which is illustrated in the drawings. In particular, circuit breaker 2% includes molded insulating compartmented hollow base 21 having removable molded insulating cover 22 with opening 23 through which manual operating handle 24 extends. Handle 24 controls operation'of a standard type overcenter spring operating mechanism 25 which operates automatically upon the occurrence of predetermined fault conditions. Mechanism 25 includes main operating tension spring 26 connected between handle 24 and knee 27 of the toggle-formed by links 28, 29.-Upper link 28 is pivotally connected at 31 to cradle 32. The latter is mounted at one end topivot 33 and at its other end is provided with latch tip 34 engageable by latch 36 of a standard type automatic trip mechanism 35. The latter includes thermal or bimetal tripping means (not shown) which provides delayed tripping under low fault conditions in the region over which curve portion E extends. v The lower end of lower toggle 29 is connected by pi 37 to the main contact ,arm portion 38 which is pivotally mounted on a center extending through insulating tie bar 41. .Pivot pin 40 connects auxiliary movable contact arm 39 to the end of main armi38 remote from tie bar 41. Bridging contact 42 (FIG. .8) is mounted to auxiliary arm 39 at the left end thereof and provides a part of the main current path through circuit trodynamic forces fro bringing about separation of bridging contact 42 from stationary contacts 45, 46 under severe fault conditions. In particular, bridging contact 42 is a modified U-shaped member including spaced parallel generally L-shaped arms 53, 54 joined by web or connecting section 52. The free ends of arms 53 54 carry movable contacts 55, 56, respectively, which overlie and are engageable with stationary contacts 45, 46. Conductor 47 is connected at one end to conductingblock 57 which supports stationary contact 46. The portion 47a of conductor 47 that extends parallel and adjacent to bridging contact connecting section 52 is rigidly held with respect to base 21.

Thus, currents I flow in opposite directions in conductors 52 and 47a so that magnetic fluxes accompanying such currents interact to produce an electrodynamic force indicated by double-headed arrows 61. Because conductor section 47a is rigidly held, this electrodynamic force moves bridging contact 42 upward with respect to FIG. 8, thereby separating movable contacts 55, 56 from stationary contacts 45, 46. As the separation takes place, electric current arcs 62 are tacts 45 and 46 is a path having a narrow U-shaped section defined by the space between insulating barrier 65 and the boundary surfaces of notch 66. It is noted that inFIGS. 2-10, insulating barrier 65 is not shown nor is an arc chute shown. These elements are not present in order that the elements shown in these Figures may be illustrated with a greater degree of clarity.

Under overload conditions where current exceeds the current required for thermal tripping overcenter spring operating mechanism 25 is operated through the action of trip bar 67 releasing latch 36 which in turn releases latch tip 34 of cradle 32. Rod 67 is pivotally mounted at 68, and is biased in a clockwise direction by tension spring 69. The right end of rod 67, with respect to FIG. 2, extends into trip unit 35 for releasing latch 36, and the left end of rod 67 extends into the space between adjustable collars 71, 72 mounted on trip rod 76. The latter extends upward from magnet armature 73 which constitutes the movable part of the magnetic frame also including stationary yoke 74.

Spring 69 acting through rod 67 in engagement with collar 71 biases rod upward.

Springs 76, extending between outboard pins 76a of auxiliary arm 39 and pin 76b extending through the bifurcated sections of main arm 38, have a line of action shiftable to opposite sides of pin 40. When the line of action of pin 40 is below pin 40 (FIG. 2) auxiliary arm 39 is biased counterclockwise and springs 76 provide contact pressure. Counterclockwise movement is limited by inwardly extending vears 38a which engage the right end of auxiliary arm-39. When the line of action of springs 76 is moved above pin 40 (FIG. 12) arm 39 is biased clockwise with this movement being limited by housing protrusion 77.

Under normal current conditions the current through coil 48 does not generate sufficient flux to move armature 73 against the upward force exerted by spring 69. When current through circuit breaker 20 is in the range indicated by the first tripping step in FIG. 1, armature 73 is attracted to yoke 74 with a force sufficient to move rod 76 downward so that collar 71 moves the left end of trip rod 67 downward, pivoting the latter counterclockwise and releasing latch 36 so that the energy stored in main spring 26 is effective to pivot contact arm 38, 39 thereby separating contact bridge 32 from stationary contacts 45, 46 (FIG. 3).

In the range of currents indicated by the second tripping step in FIG. 1, during the delay in operation of mechanism 25 lower collar 72 engages the right end of auxiliary arm 39 and physically pivots the latter about pin 49 with respect to main arm 38. This relative motion between main and auxiliary arms 38, 39 is increased as mechanism 25 moves main arm 38 in its opening stroke, and in so doing moves pin 40 upward with respect to FIG. 4 relative to roller collar 72. Thus, in the second tripping step, contact opening is achieved through the complementary action of both mechanism 25 and the physical force exerted by magnet 73, 74.

In the third tripping step of FIG. 1 the force exerted by magnet 73, 74 is so great that the speed of movement of rod 79 causes collar 72 in engagement with auxiliary arm 39 to move contact bridge 32 to full contact separation position before spring operated mechanism 25 has had time to move main arm 38 a substantial distance if at all (See FIG. 5).

' In the fourth tripping step illustrated in FIG. 1, the conditions prevailing in the third tripping step (See FIG. 5) are exaggerated to the point where before main arm 38 is moved by mechanism 25 the engagement of collar 72 with auxiliary arm 39 begins to separate contact bridge 42 from stationary contacts 45, 46. However, before complete separation takes place due to the mechanical action of magnet 73, 74, the electrodynam ic force described in detail in connection with FIGS. 8-11 comes into play to assist in opening the contacts. Thus, in the fourth tripping step the mechanical force exerted by magnet 73, 74 is complemented by the electrodynamic force acting between conductor 47 and bridging contact 42 to bring about rapid separation of the circuit breaker contacts.

In the fifth tripping step of FIG. 1, the current magnitude is so high tat even before spring mechanism 25 of magnets 73, 74 is effective to cause contact separation, bridging contact 32 is moved to its fully opened position of FIG. 12 through the action of the electrodynamic force acting between bridging contact connecting section 55 and conductor section 47a. This electrodynamic force pivots'auxiliary arm 39 clockwise against the force of springs 76 thereby. moving pins 76a upward and shiftingthe line of action for springs 76. When this line of action moves above pin 40, or overcenter, springs 76 aid the electrodynamic force to separate contacts 45, 46, 55, 56.

As seen in FIGS. 14-16, armature 73 is constructed in a manner to reduce the weight thereof, thereby permitting increased speed of operation. That is, the groups of arrowed generally circular lines 91, 92 illustrate the loop paths for flux when magnet 73, 74 is energized. Since the shaded area 73a of armature 73 is not included. in either flux path 91 or 92 through stationary generally E-shaped yoke 74, the upper surface of armature 73 is cut away to provide a V-shaped notch in the shaded area 73a, thereby substantially reducing the weight of the iron laminations forming armature 73. These laminations are riveted to the flared out portion 81 at the lower end of rod 70.

Thus, it is seen that the instant invention provides a novel construction for a molded case current limiting circuit breaker, in which more rapid tripping action is obtained in the medium fault current range by utilizing mechanical forces of the tripping electromagnet to physically move the movable contact. The characteristic tripping'curve for the breaker constructed in accordance with this invention is relatively smooth in that in various fault current ranges there is complementary action between the opening forces exerted by the spring operating mechanism, the tripping electromagnet, and the electrodynamic forces generated by currents flowing in opposite directions in adjacent conduc: tors.

Although there have been described preferred embodiments 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 herein, but only by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as fol- 1? An electromagnet including a magnetic frame and a coil means for: generating lines of magnetic flux in said frame as current flows in said coil means; said frame including a stationary part and a movable armature forming loop path means where said lines of magnetic flux are located; biasing means urging said armature away from said stationary part to a position wherein there is a substantial gap between said stationary part and one end of said armature and with said coil means energized said magnetic flux lines providing an attracting force moving said armature to close said gap; said armature having a cutaway section located at its other end and disposed where said lines of magnetic flux would not be located had said cutaway section not been removed.

2. An electromagnet as set forth in claim 1 in which the magnetic frame includes first, second and third parallel legs; said second leg positioned between said first and third legs; said loop path means including a first and a second loop path; said first loop path including said first and second legs and said second loop path including said second and third legs; said armature constituting at least a portion of said second leg; said gap being at one end of said armature; said cutaway section being at the other end of said armature.

3. An electromagnet as set forth in claim 2 in which the cutaway section is substantially V-shaped.

Claims (3)

1. An electromagnet including a magnetic frame and a coil means for generating lines of magnetic flux in said frame as current flows in said coil means; said frame including a stationary part and a movable armature forming loop path means where said lines of magnetic flux are located; biasing means urging said armature away from said stationary part to a position wherein there is a substantial gap between said stationary part and one end of said armature and with said coil means energized said magnetic flux lines providing an attracting force moving said armature to close said gap; said armature having a cutaway section located at its other end and disposed where said lines of magnetic flux would not be located had said cutaway section not been removed.

2. An electromagnet as set forth in claim 1 in which the magnetic frame includes first, second and third parallel legs; said second leg positioned between said first and third legs; said loop path means including a first and a second loop path; said first loop path including said first and second legs and said second loop path including said second and third legs; said armature constituting at least a portion of said second leg; said gap being at one end of said armature; said cutaway section being at the other end of said armature.

3. An electromagnet as set forth in claim 2 in which the cutaway section is substantially V-shaped.

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