US3663903A

US3663903A - Tripping system for circuit breaker

Info

Publication number: US3663903A
Application number: US145175A
Authority: US
Inventors: Frank W Kussy; Gustave E Heberlein Jr
Original assignee: ITE Imperial Corp
Current assignee: Siemens Energy and Automation Inc
Priority date: 1971-05-20
Filing date: 1971-05-20
Publication date: 1972-05-16
Anticipated expiration: 1989-05-16
Also published as: CA956686A

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

United States Patent Kussy et al.

[451 May 16,1972

[54] TRIPPING SYSTEM FOR CIRCUIT BREAKER [72] Inventors: Frank W. Kussy, l-laverford; Gustave E.

Heberlein, Jr., King of Prussia, both of Pa.

ITE Imperial Corporation, Philadelphia, Pa.

22 Filed: Ma 20,1971

[21] Appl.No.: 145,175

[73] Assignee:

3,562,680 2/1971 Ozakietal ..335/16 Primary Examiner-Har0ld Broome Attorney-Ostrolenk, Faber, Gerb & Soffen 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.

16 Claims, 15 Drawing Figures Patented May 16, 1972 3,663,903

4 Sheets-Sheet l.

Patented May 16, 1972 3,663,903

4 Sheets-Sheet 2 Patented May 16, 1972 3,663,903

4 Sheets-Sheet 5 Patented May 16, 1972 4 Sheets-Sheet 4 I TRIPPING SYSTEM FOR CIRCUIT BREAKER This invention relates to circuit breakers in general, and more particularly relates to a current limiting circuit breaker 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 appeared to be an undue lag in operation since the contact operating mechanism could not move the contacts fast enough and in this current range the currents were not high enough to produce strong electrodynamic effects for rapid contact separation.

Thus, the instant invention provides a magnetic tripping means which acts in the medium fault current range to physically separate the contacts before the contact operating mechanism is effective to move the contacts. In the lower portion 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 operating mechanism 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. 1 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 currentlimiting 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 con tact opening under conditions where the magnetic tripping device exerts a mechanical force to assist the spring operating mechanism.

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

FIG. 12 isa view similar to that of FIG. with the addition of insulating barrier elements.

FIG. 13 is a cross-section taken through line 13-13 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.

FIG. 16 is a side elevation of the magnet armature looking in the direction of arrows 16-16 of FIG. 15.

Now referring to the figures. As illustrated by curve A in FIG. 1, 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 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. 10 is an end view of the contacts looking in the direction of arrows 10-10 of FIG. 8.

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 tomedium range, or typically from five to 50 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 contacts are opened at a speed that is high enough to draw and develop a high arc 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 20 achieves faster contact separation in the range of medium fault currents without adversely efi'ecting 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 20 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 to pivot 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.

The lower end of lower toggle 29 is connected by pin 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 arm 38 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 breaker 20. This current path consists of line terminal 43, conducting strap 44, stationary contact 45, bridging contact 42, stationary contact 46, conductor 47, magnet coil 48, strap 49 including bimetal heater portion 50, and load terminal 51.

With reference to FIGS. 8-13, it is seen that the shape of contact means 42 is adapted to utilize electrodynamic forces for 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 conducting block 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 l 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 formed. Magnetic flux generated by arcs 62 interact with the fluxes of currents flowing in the sections of

arms

53, 54 generally parallel to arc 62, with the result that an electrodynamic force is present, tending to elongate arcs 62 by driving them in the direction indicated by arrow 63.

As seen in FIGS. 12 and 13, insulating barrier plate 65 is positioned between

stationary contacts

45, 46 and extends into notch 66 in the contact carrying end of molded insulating auxiliary arm 39. Thus, with circuit breaker 20 open, the air path between

stationary contacts

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 in FIGS. 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 70. 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 70 upward.

Springs 76, extending between outboard pins 760 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 ears 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 70 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 40 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 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 (SeeFIG. 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 electrodynarnic 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 that 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 shifting the 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 81 or 82 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 of rod 70 located immediately above extension 82 at the lower end thereof. Extension 82 is entered into fore 83 to cooperate therewith in guiding movement of armature 73 toward and away from short center leg 84 of yoke 73.

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 conductors.

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 follows.

1. A circuit interrupter including relatively stationary contact means; movable contact means; arm means having said movable contact means mounted thereto; a releasable operating mechanism connected to said arm means for moving the mechanism when released providing a spring force to separate said movable and stationary contact means; first means effective at fault currents above a first level through said interrupter to release said operating mechanism; second means effective at fault currents above a second level to exert a mechanical force on said movable contact means separating the latter from said stationary contact means; third means effective at fault currents above a third level to exert an electrodynamic force acting to separate said contact means; said second level being between said first and third levels; at fault currents in a first range immediately above said second level said spring force and said mechanical force supplementing each other to increase speed of contact means separation above the speed of contact means separation provided solely by said spring force; at fault currents in a second range immediately above said third level said electrodynamic force supplementing said mechanical force and increasing speed of contact means separation above that provided by the combination of said spring force and said mechanical force.

2. A circuit interrupter as set forth in claim 1 in which there is a third range of currents, between said first range and said third level, in said third range of currents movement of said movable contact means to its fully open position is due essentially solely to said mechanical force.

3. A circuit interrupter as set forth in claim 2 in which at currents above said second range, movement of said movable contact means to its fully open position is due essentially solely to said electrodynamic force.

4. A circuit interrupter as set forth in claim 1 in which initial contact means separation is the result of said mechanical force at fault currents between said second and third levels, and initial contact means separation is the result of said electrodynamic force at fault currents above said third level.

5. A circuit interrupter as set forth in claim 1 in which the third means includes first and second current path sections through which currents flow in opposite directions when said contact means are in engagement; said movable contact means including said first path section; said path sections being positioned in close proximity so that magnetic fluxes generated by said currents flowing in said path sections interact to produce a substantial portion of said electrodynamic force acting to separate said contact means.

6. A circuit interrupter as set forth in claim 5 in which the stationary contact means includes first and second spaced contacts bridged by said movable contact means.

7. A circuit interrupter as set forth in claim 6 in which said movable contact means also includes generally parallel arms at opposite ends of said first path section; a movable contact at nun the free end of each of said arms engageable with said stationary contacts.

8. A circuit interrupter as set forth in claim 7 in which the arms are generally L-shaped and are disposed in planes at right angles to said path sections.

9. A circuit interrupter as set forth in claim 1 in which the second means includes an electromagnet which generates said mechanical force at fault currents above said second level.

10. A circuit interrupter as set forth in claim 9 in which operation of the electromagnet is also effective to operate said first means at fault currents above said first level.

11. A circuit interrupter as set forth in claim 1 in which said arm means comprises a main arm and an auxiliary arm; said main arm being interposed between said auxiliary arm and said operating mechanism; said movable contact means mounted on said auxiliary arm; pivot means mounting said main arm near one end thereof; said auxiliary arm being movably mounted to said main arm near the other end thereof.

12. A circuit interrupter as set forth in claim 11 in which there is an overcenter spring connected to said auxiliary arm for biasing said auxiliary arm in opposite directions about said pivot means as the line of action for said overcenter spring is shifted to opposite sides of said pivot means.

13. A circuit interrupter as set forth in claim 11 m which the second means includes an electromagnet which generates said mechanical force at fault currents above said second level operable to move said auxiliary armrelative to said main arm in contact means opening direction.

14. A circuit interrupter as set forth in claim 13 in which the auxiliary arm is pivotally mounted to said main arm, and there is a spring device acting to pivot said auxiliary arm relative to said main arm in contact means closing direction.

15. A circuit interrupter as set forth in claim 14 in which the third means includes first and second current path sections through which currents flow in opposite directions when said contact means are in engagement; said movable contact means including said first path section; said path sections being positioned in close proximity so that magnetic fluxes generated by said currents flowing in said path sections interact to produce a substantial portion of said electrodynamic force acting to separate said contact means.

16. A circuit interrupter as set forth in claim 15 in which the stationary contact means includes first and second spaced contacts bridged by said movable contact means; said moving contact means also including generally parallel arms at opposite ends of said first path section; a movable contact at the free end of each of said arms engageable with said stationary contacts; said arms being generally L-shaped and being disposed in planes at right angles to said path sections.

Claims

1. A circuit interrupter including relatively stationary contact means; movable contact means; arm means having said movable contact means mounted thereto; a releasable operating mechanism connected to said arm means for moving the latter to operate said movable contact means into and out of engagement with said stationary contact means; said operating mechanism when released providing a spring force to separate said movable and stationary contact means; first means effective at fault currents above a first level through said interrupter to release said operating mechanism; second means effective at fault currents above a second level to exert a mechanical force on said movable contact means separating the latter from said stationary contact means; third means effective at fault currents above a third level to exert an electrodynamic force acting to separate said contact means; said second level being between said first and third levels; at fault currents in a first range immediately above said second level said spring force and said mechanical force supplementing each other to increase speed of contact means separation above the speed of contact means separation provided solely by said spring force; at fault currents in a second range immediately above said third level said electrodynamic force supplementing said mechanical force and increasing speed of contact means separation above that provided by the combination of said spring force and said mechanical force.

7. A circuit interrupter as set forth in claim 6 in which said movable contact means also includes generally parallel arms at opposite ends of said first path section; a movable contact at the free end of each of said arms engageable with said stationary contacts.

13. A circuit interrupter as set forth in claim 11 in which the second means includes an electromagnet which generates said mechanical force at fault currents above said second level operable to move said auxiliary arm relative to said main arm in contact means opening direction.