US2629796A

US2629796A - Thermal trip mechanism for circuit breakers

Info

Publication number: US2629796A
Application number: US100025A
Authority: US
Inventors: Kern Ruth
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1949-06-18
Filing date: 1949-06-18
Publication date: 1953-02-24
Anticipated expiration: 1970-02-24

Description

R. KERN 2,

THERMAL TRIP MECHAKISM FOR CIRCUIT BREAKERS Feb. 24, 1953 Filed June 18, 1949 Fig.1.

Insu/aT/on V/ :n r? MW oe. r mK m e t m .A

F IR 8 H Patented Feb. 24, 1953 THERMAL TRIP MECHANISM FOR CIRCUIT BREAKERS Ruth Kern. Drexel Hill, Pa., assignor to General Electric Company, a corporation of New York- Application June 18, 1949, Serial No. 100,025

3 Claims. 1

This invention relates to trip units for. circuit breakers and in particular to devices that automatically trip to the open position the contacts of a circuit breaker at predetermined overload currents.

Circuit breakers of the subject class are placed directly in electrical lines and serve the function of interrupting the passage of current through the lines when, due to some variation or imperfection in the load circuit, a current equal to or greater than that at which the circuit breaker trip unit is calibrated passes through the lines.

Circuit breakers of the subject type have various operating principles, but one of the more simple types is to have a bimetallic unit operate a tripping mechanism-with an inverse time delay when the bimetallic element is heated by load current greater than that at which the circuit breaker trip unit is calibrated to trip with maximum time delay.

Thus the present invention deals primarily with a bimetallic inverse time delay tripping unit that is used to trip to the open position the contacts of a circuit breaker.

An object of this invention is to provide an improved removable single plug. contact mounted juxtaposed bimetal trip unit structure capable of calibration at different current ratings to enable interchanging bimetallic units in acircuit breaker so that the circuit breaker may'have a rated current ranging from to 200 amperes.

A further object of this invention is to facilitate the production of circuit breakers with the resultant benefits in the art by providing a means whereby one construction of circuit'breaker operates on a Wide range of rated currents.

A still further object of-this invention is to provide a simple method of interchanging.bimetallic units within a circuit breaker.

A still further object is to'provide a bimetallic un-itfor circuit breakers'which requires minimum operative space.

In its broadest form, this invention comprises a bimetallic means for tripping a circuit breaker at overload current. The said bimetallic means is readily'interchangeable allowing the same circui-t' breaker to-be used for various currents up to 200 amperes.

Further. objects and advantages of this invention will become apparent," and the invention will be better understood from" the following description referring to the accompanying drawing, and the features of novelty which characterize this invention will be pointed outwith particularity in the claims annexed to and forming a part of, this specification.

In the drawing, Fig. 1. is a front elevation, partially in section, of a circuit breaker embodying my invention.

Figs. 2, 3 and 4 are perspective views of modifications of the bimetallic unit used in the circuit breaker of Fig. 1.

In the circuit breaker l of Fig. 1, an electrical path is provided that comprises a mounting stud 2 which serves to removably mount and electrically connect both the circuit breaker and the trip unit and is located at the point where line current enters the circuit breaker, suitable securing nuts 3, a clip terminal 4, a matching prong or plug contact 5, stud B, bimetallic unit I, .pigtall 8, movable arm 9, movable contact I0, fixed contact ll, mounting stud l2 which is connected to an electric load, and corresponding nut l3.

Line current is brought into .the circuit breaker through stud 2by means of a lead (not shown) which is held in contactwith stud 2 by means of nuts 3. The current passes through stud 2, which is embedded in a plastic base I 4, to clip terminal 4 connected to stud 2. The current passes from clip terminal 4 to matching prong 5 and through stud 6, which is an integral part of the bimetallic unit I, tov pigtail 8 welded to bimetallic unit I, through movable arm 9 tocontact l0 which is rigidly recured' to the movable arm 9. The current passes from contact H] to fixed contact ll, to stud l2 and from stud 12 to an electric load (not shown) which is attached to stud l2 by means of a lead (not shown) held in place by nut l3.

The plastic base M is removably secured to the body portion I5 of the circuit breaker allowing the bod portion to be removed from the base and prong 5 to be removed from clip terminal 4. When the body portion [5 has been removed from the base plate I4, and the cover [5 from body portion IS, the bimetallic unit 1 is readily accessible.

The bimetallic unit comprises prong 5, stud 6; which is held in contact with the body portion 15 of circuit breaker I by means of nut IS, a mounting .plate 11, a bimetallic element 18, resistor I 9, series resistorZO, shunt resistor 2 l magnet 22, terminal plate 23 for pigtail 8 which is electrically connected with the movable contact arm 53 carrying contact [0.

Prong 5, an integral part or stud 6, is arranged opera-tively to engage the spring terminal 4. The contour of prong '5 is such that it may be removably secured within spring contact 4 giving secure electrical contact that allow-spassage of current from stud 2 to stud 6. Stud 6 is ri idly fastened to mounting plate H, and is the secur- 3 ing means for fastening the bimetallic unit 1 to the body portion I5 of the circuit breaker. Stud 6 is inserted through an opening 24 in the body portion of the circuit breaker and held in place by nut I6 which engages a shoulder in the body portion I5.

At point 26, one end of the bimetallic element I8 and one leg of resistor I9 are welded to the mounting plate I! as indicated in Fig. 2 of the drawing. Current flows from stud 6 through mounting plate H to point 26 where it divides. part going through bimetallic element I8 and part going through resistor I9. The current paths are joined again at point 21 Where leg 29 of resistor I9 and bimetallic element 29 join the support plate 23 as shown in Fig. 2.

The bimetallic elements I8 and 29 each comprise two strips of metal having different ccefiicients of expansion. Thus, the outer stri 39 of element I8 has a higher coefiicient of expansion than the inner strip 3|. The two strips are duplicates and rigidly secured together, in parallel juxtaposition and when heated the top of the bimetallic element bends toward a pin 32 (shown in Fig. 1) which operates a tripping mechanism (not shown) The two bimetallic elements l8 and 29 are joined by a series resistor 29and a shunt resistor 2|. In this construction, shunt resistor 2| functions as a calibrating bar. That is, the current carrying capacity or rating of the bimetallic unit can be changed by varying the position of the shunt resistor 2| alon the length of the bimetallic elements I8 and 29. The further shunt resistor 2I is positioned from series resistor 20, the greater is the current rating of the particular bimetallic unit.

Resistor I9 is of substantially uniform cross section and U-shaped, and by changing the size of its cross section, the rating of the bime allic unit can bevaried. From points 26. 21 the resistor is bent away from bimetallic elements I8 and 29, and then at points 26a it is bent again to. run parallel to them. Heat generated in the resistor I9 by current passing therethrough is radiated to the bimetallic elements uniformly since both legs of the resistor are of equal size andthe heat aids in the bending of the bimetallic elements.

An electromagnet 22 in the form of a U-shaped ferromagnetic member functions as an emergencytrip and is securely mounted on bimetallic element I8. When very high current passes through the circuit, such as that caused by a short circuit, a magnetic force is set up in the magnetby the passage of current through bimetallic element I8, to attract an armature 33 which is operatively associated with the pin 32 to cause a tripping mechanism (not shown) to function and open contact I0 away from fixed contact II. By employing the magnet 22, the contacts of the circuit breaker can be caused to open by the pull of the magnet on arm 33 before the high current has an opportunity to fuse the elements of the bimetallic unit. The magnet 22 is so designed that it does not function at rated or slightly above rated current, but does function only at current levels of the order of short circuit.

Support member 23 preferably comprises a U- shaped portion 36 that forms a mounting seat in off et alignment with the axis of the terminal plug 6 for removablyanchoring the bimetal e ement 29 of unit I in position on the bod portion I501 th circuit breaker 'I, a flat portion 31 and an upbended portion 38;. Current after leaving bimetallic element 29 and leg 28 of resistor I9 passes through the U-shaped portion 36 of support member 23 to pigtail 8 and from pigtail 8 to movable arm 9 that supports contact ID. The flat portion 31 with its offset upbent arm 38 serves the function of protecting the support plate H from the pigtail. That is, it is arranged to prevent electrical contact between support plate I! and pigtail B, and the upbent arm 36 acts as a shield between the free portion of the pigtail and the mounting plate II.

Movable contact arm 9 is electrically connected to pi tail 8 by brazing, and, is an integral part of the bimetallic unit; consequently, when a bimetallic unit is installed, a corresponding movable contact arm 9 is also installed. The contact arm 9 is mounted on suitable studs 34 and 35 which in turn are associated with the tripping mechanism (not shown) and which cause the outer end of contact arm 9 which carries contact I0 either to be brought in touch with or away from fixed contact I I.

In operation, current enters from a supply line to stud 2 through cli terminal 4 to matching prong 5, through stud Gto mounting plate I'I into bimetallic unit I through support member 23, pigtail 8 and movable arm 9 to contact I 0. When contact I0 is closed on contact II, current passes through contact I I to stud I2 to the electrical load.

Load current passing through resistor I9 and bimetallic unit I heats the elements I8 and 29, causing them to deflect, and resistor 20 approaches pin 32. The unit is constructed so that, when current at a certain percentage greater than rated passes through the bimetallic unit, enough heat is generated to cause resistor 20 to pu h against pin 32 and thereby operate a tripping mechanism that causes movable contact arm 9 and its associa ed contact I0 to move away from fixed contact II It is to be understood that suitable arc quenching means are also employed to destroy the are that extends from contact I 0 to contact lI upon opening,

If a very high current, such as that caused b short circuit, passes through bimetallic unit I, magnet 22 is energized attracting arm 33 which is operatively associated with pin 32 and causes the tripping mechanism to function and open the contacts. I 0 and I I. By use of ma net 22, the high short circuit current is interrupted before it has opportunity to'fuse the component parts of the bimetallic unit.

When it is desired to change the rating of one of the subject type circuit breakers, the body portion 15. of the circuit breaker is removed from the base portion I4 simply by pulling contact plug 5 out of socket 4. When the cover portion I5 has been removed from body portion I5, the bimetallic unit is then readily accessible and nut I6 may be removed from stud 6 allowing the bimetallic unit to be withdrawn from the body portion I5 after movable contact arm 9 has been removed from pins 34 and 35. A new bimetallic unit of a different rating is then installed in the same manner. That is, movable contact arm 9 is replaced on pins 34 and 35 and stud 6 is inserted through opening 24 and fastened in place by nut I6. The body portion I5 of the circuit breaker is then replaced on the base portion I4 of the circuit breaker with prong 5 coming into operative engagement with spring clip 4. Nuts'36 arethen-fastenedto stud 31 and the circuit breaker is again ready for operation a'ta different current rating;

Two other; types: or; bimetallic unitsewhichmre interchangeable: withtth'atshown ini Fig.2 L and Fig. 2 are-illustratedintFi'gs. 3:and14? flthedraw ing. Bimetallic units!! shown: in; Fig: -3isr of the type that" hasiarating ore-u; amperes; while bimetallic unit 40 shownln; Fig.4; theiatype that has a rating of amperes. Both bimetallic units 39. and operate the tripping. mechanism exactly as thebimetallic" unitishowrr in Figs: 1 and 2; Specifically, theKupperm'ost-bars 4| and 42 of. bimetallic units" 39:" and. 40,: respectively, press against button to trip the circuittbreal-b er. In addition; each' of the bimetallic units33 and 40 has a magnet 43 and.44, respectively, that automatically: trips the circuit in case ofi short circuit current;

Inv bimetallic unit 39;prong 5d, a stud ficiand a mounting'plate- |laiare provldediwhichare the duplicates. of: prongs: 5, 6 T and I I comprising. part of bimetallic unit 1; rigidly securedfito mounting plate" l1a-- and is joined by a seriesreslstor "inatherform of" bar 4| to bimetallicelementiwhich is theduplicate of and which is located-in spaced alignment with bimetallic element 45. Ar -supporting plate--41 is rigidly secured tothe' bottom" of bimetallic element 46'. 'This support-plated is similar to plate 23. used for bimetallic unit 1. Pigtail" 48 connects the support plate: 4-|' with armovable arm- (not shown) similar to' arm 9 shown-in Fig. 1-. The upturned: lip'= 48 of support plate-41 serves the function: of. protecting plate Na" and bimetallic element from electrical contact with' pigtail- 49'.

When bimetallic unit 39 is used to replace bi metallic unit 1, current passes from spring" clip 4 into prong 5a through stud Sarto mounting platel'la and from there into bimetallic element 45 across series resistorv 4|. and down bimetallic element 46 to support plate" '41 through pigtail 49 and the" movable contact-armrtoithei'contact.

I0 of the breaker.

The bimetallic elements 45 and45- comprise a high expansion metal on the outer side and a low expansion metal on the inner side rigidly fastened together, causing. bimetallic elements 45 and 46-tobendso that series resistor 4| ap proaches pin 32 when the bimetallic'el'ements are heated by load current passing therethrough.

If the current passing throughthe bimetallic element is greater than rated current, the element deflects to the extent that; series: resistor 4| pushes against button 32 causing themechanism to trip open contacts Hi0. and IL. If, on

the other hand, current of" the short circuit magnitude passes throughthebimetallic element 45, a magnetic attractive force is induced in magnet 43 that attracts'arm 33 of the tripping mechanism; causing contacts Illa; and II to be opened. By changing the cross section and material of the component parts of bimetallic unit 39, it can bedesigned to have a rated current of from 50 to 100 amperes.

Bimetallic unit 49, illustrated in Fig. 4 of the drawing, comprises prong 5b, stud 5b, mount Bimetallic" element" 45 1s .ment 50 with bimetallic element 6 sulating strip: 42v to deflect toward button when: the bimetallic element is heated.

A. U-shaped resistor 52 joins bimetallic" ele- The U-shaped resistor 52 comprises two legs 5| and '54 bent away from the two bimetallic elements '50'and' 55. Tnetwolegs 5| and 54 oi'the series resistor 52 in order to protect it from electrical contact with magnet 44 and trip arm 33 which is located near the U-shaped resistor.

shown in Fig. l.

A U-shaped magnet 4 is rigidly secured to bimetallic element 50. and serves the same function as 'magnets: 22' and 43 shown in Figs. 2 and 3, Specifically, it attracts tripping arm 33 when current of short circuit magnitude passes through bimetallic element 59 causing movable contact arm. 91) to separate contacts I01) and H.

A support plate 55 is rigidly secured to the lowermost portion of bimetallic element 55, and a pigtail-to conducts current from support'plate 56. to amovable contact arm similar to arm 9 Support plate 55 has an upturned portion 6| whichshields the series resistor 52 from contact with pigtail 60'. Aninsul'ating 'block 62 1s employed to prevent the upturned portion 6| ofmounting plate 55 from contacting crossbar 53 of series resistor 5| and possibly in;

terfering with operation of tripping arm 33.

When a bimetallic unit of the type shown in Fig. 4 is inserted in operative position within the 1 through support plate 55, pigtail Eli, to the movable arm and contact, through the movable contact to fixed contact H, out stud IE to the electrical load.

Heat" generated in the. bimetallic elements 50; 55 and in the series resistor 52 causes the bimetallic elements 50 and 55 to deflect so that insulating bar 42' approaches pin 32. If greater than rated current passes through the bimetallic e1ements, the insulating bar 42 presses against -'.pin 32, causing the mechanism to trip to the .open position. If current of short circuit magnitude passes through the bimetallic unit 40, magnet 44 is activated and attracts arm 33 of the tripping mechanism, causing the circuit breaker to trip to the open position.

While different modifications of the bimetallic units are shown in Figs. 2, 3 and 4, it is to be understood, however, that by varying the physical size of the component parts of each of these bi- ,jmetallic units, the current rating of each unit can be changed to handle a wide range of currents.

- Consequently, by interchanging the three units shown and by changing the physical size of the component parts, it is possible to use one circuit breaker of the type illustrated in Fig. 1 at any current rating of from 10 to 200 amperes.

Modifications of this invention will occur to those skilled in the art, and it is desired to be understood, therefore, that this invention is not to be limited to the particular arrangement enclosed, but that the appended claims are meant to cover all the modifications which do not depart from the spirit and scope of this invention.

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

1. A circuit breaker trip unit having in combination a mounting plate provided with a single projecting terminal plug contact having threaded means for removably mounting the plug and plate on the circuit breaker, a pair of duplicate bi-metallic elements carried by the mounting plate in spaced apart parallel juxtaposition and having rigid resistor means for heating the ele- I ments and for mechanically interconnecting the elements in conducting relation with only one end of one element mounted upon and electrical-- 1y connected with the mounting plate, a trip member carried by the free ends of the parallel bi-metallic elements, a flexible pigtail for connection with the circuit breaker and having a conducting terminal forming a mounting seat in offset alignment with the of the terminal plug contact and electrically and mechanically, connected with the other end of the parallel bimetallic element to effect deflection of the free ends of the bi-metallic elements in response to the heating effect of the current passing from the pigtail through the bimetallic elements and the resistor means to the terminal plug contact and thereby effect operation of the trip member in the tripping direction. 2. A circuit breaker trip unit having in combination a supporting plate provided with a single projecting terminal plug contact having threaded means for removably securing the plug and plate on the circuit breaker, a first bi-metallic element secured at one end to the mounting plate, a second bi-metallic element supported in spaced parallel juxtaposition with the one bi-metallic element and having a rigid series resistor mechanically and electrically interconnecting the other end of the one bi-metallic element with the adjacent end of the second bi-metallic element Number end of the second bi-metallic element to effect deflection of the bi-metallic elements in response to the heating effect of the current flowing from the pigtail through the elements and the resistors to the terminal plug contact and thereby effect operation of the trip member in the tripping direction.

3. A circuit breaker trip unit having in combination a mounting plate provided with a single projecting terminal, a plug contact having threaded means for removably securing the plug and plate on the circuit breaker, a pair of bimetallic elements supported by the mounting plate in spaced apart parallel juxtaposition with onlyone end of one element mounted upon and electrically connected with the mounting plate, an insulatingbar joining the other end of the one bi-metallic element with the adjacent end of the other bi-metallic element to form a trip member, a U-shaped series resistor having one end thereof electrically connected with the other end of one bi-metallic'-,.e lement and the'other end thereof with the adjacent end of the other bi-metallic element and extending in spaced apart parallel juxtaposition with the elements, a flexible pigtail having a terminal member forming amounting seat in oflset alignment with the axis of the terminal plug contact and mechanically and electrically connected with the other end of the other bi-metallic element for effecting deflection of the bi-metallic elements in responseto the heating effect of the current passing from-the pigtail through the elements in series with the U-shaped resisto'rito'the terminals and thereby effect-operation of the'trip member formed by the insulating bar in the tripping direction. I

a --RUTH KERN.

REFEREN'CES CITED The following references are of record in the file of this patent:

' UNITED STATES PATENTS Name Date 1,622,907 Getchell Mar. 29, 1927 1,838,950 Lindstrom Dec. 29, 1931 2,013,011 Sheldon Sept, 3, 1935 2,015,598 r Langfritz Sept. 24, 1935 2,050,879 Erben Aug. 11, 1936 2,052,564 Grady Sept. 1, 1936 2,074,584 Graves, Jr. Mar. 23, 1937 2,180,421 Leonard Nov. 21, 1939 2,443,090 Wise June 8, 1948 2,447,652 Jennings Aug. 24, 1948 FOREIGN PATENTS Number Country Date 427,512 Great'Britain Apr. 12, 1935