US2679561A

US2679561A - Circuit breaking device

Info

Publication number: US2679561A
Application number: US293919A
Authority: US
Inventors: Thompson Harry
Original assignee: Telemecanique Electrique SA
Current assignee: Telemecanique SA
Priority date: 1951-09-19
Filing date: 1952-06-17
Publication date: 1954-05-25
Anticipated expiration: 1971-05-25
Also published as: BE510633A; FR1042303A; GB743178A

Description

May 25, 1954 H. THOMPSON CIRCUIT BREAKING DEVICE Filed June 17, 1952 2 Shets-Sheet l .May 25,1954

H. THOMPSON 2,679,561

CIRCUIT BREAKING DEVICE Filed June 17, 1952 2 Sheets-She et 2' Patented May 25, v1954 .Harry Thompson, Nanterre,

France, assignor to .Telemcanique Electrique (Socit Anonyme), Seine, France, a company of France Application June 17, 1952, Serial No. 293,919

Claims priority, application France September 19, 1951 4 'Claims.

In 'cir'cuit break'ing devices having solid contacts, each of "the movable contacts is pressed against the corresponding fixed contact, generally'byaspring force. Now, principally by reason of the necessity for extinguishing the arc which is set up between the contacts at the instant when they are opened, the direction in which the .movable contact is opened is towards the outside of the loop 'formed by the conductors leading to the contacts, so that "the consequent electromagnetic forcesset up by the current in these conductors tend to separate the contacts. These forces, which areproportional to the square of the current,.-assume .such a value in the event of .a short-circuit .thatit tends to annul the contactpressure, so that all the conditions favourable to the fusing of the contact studs are presentinsuch an event.

The currents which the device is capable of interrupting thus have an upper limit which may belower than thepossible values of the short-circuit currents met with in practice which results in serious difliculties.

In order to overcome these difiiculties, the present invention has-for an object to provide a device for compensating for the electromagnetic repulsion force acting on the movable contacts of circuit breakers.

According to the invention, a member through which thecurrentvfiows and on which a movable contactis mounted is subjected, in the direction of a co-operating fixed contact, to the magnetic action of .an electromagnet in which the magnetomotive forceis set u'pby the actual current which flows through the said contacts.

.Inone embodiment of the invention, the member on which the \movable'contact is mounted is secured to a magnetic armature adapted to be attracted by the electromagnet in the direction of the fixed contact.

Thus, as long as the magnetic material of the .electromagnet and of the armature has not .reached saturation, the said attraction, which tends to bring the contacts together, follows the samelaw as the repulsion force which tends to separate these contacts, whereby the said repulsion force is compensated .for. f i The electromagnet and its armature preferably form a magnetic circuit in which, by reason of theconsiderablecurrents concerned, the magnetomotive force "is produced by currentpassing through one of the conductors leading to the contacts and forming part of the loop formed by the electric circuit.

The simplest constructions are'obtained by 2 using, as the conductor producing the magnetomotive force, the member on which the movable contact is mounted. If the induction is insuffi cient, this conductor could obviously be made to form one or more turns around one of the branches of the magnetic circuit.

In order to set upfforces of electromagnetic origin on the member on-which the movab'le contact is mounted, it is not essential to provide't'his movable member with an armature, because the current which passes through it imparts magnetic. properties thereto. The electromagnet may therefore act directly on the said conductor.

To this end, according to a further feature of the invention, the member on which the movable contact is mounted passes atleast once through an air gap in a magnetic element by which it is partially surrounded and which constitutes the core of the electromagne't, and the said member is movable in relation to the said element in the said air gap in a direction parallel to the surfaces defining the air gap, the said element being so positioned that the relative movement of the member on which the movable contact is mounted takes place in the direction in which the contacts move towards one the magnetic flux generated in the said element by thecurrent flowing through the said member increases.

Calculations and experience show, in this case also, that the current flowing through thememher on which the movable contact is'mounted-sets up on this member an attractive force proportional to the square of the current, which tends to urge the contacts one against the other,

This phenomenon is readily explained by the fact that a current flowing through an electric circuit develops, on each of the elements of the said circuit, forces which tend to displace or deform this element in the direction'of an increase according to the forces which are tor by an increase in "the magnetic flux which surrounds it.

Briefly, owing to the local concentration, produced by means of a suitably disposed electroof the poles of the contactor the manner hereinbefore described.

magnet, of a part of by the current the contactor, the effects of the remainder of this magnetic fiux on the member supporting the movable contact are counteracted.

In a preferred embodiment of the invention, the member on which the movable contact is mounted is pivoted to the movable part of the contactor and the core of the electromagnet is also mounted on this part.

Thus, the attractive force created by the electromagnet not only does not oppose the opening of the contacts, but promotes it. In fact, when the contacts touch one another, the member supporting the movable contact is held fast and the attractive force therefore tends to drive the movable part of the contactor in the opposite direction, that is to say, in the direction of the opening of the contactor. Under these conditions, both with a view to increasing the contact pressure and in order to promote this phenomenon, it may be desirable to so dimension the device according to the invention as to overcompensate for the electromagnetic repelling forces acting on the contacts, which are inherent in the design of contactors.

In the accompanying drawing, there is shown by Way of non-limitative example, two embodiments of the invention. In the drawing:

Figure 1 shows in side view, partly in diagrammatic form, a unipolar contactor according to the invention, the contactor being in the closed position.

Figure 2 is a partial view similar to that of Figure 1 showing the contactor in the open posi tion.

Figure 3 is a section taken along the line III-III of Figure 1.

Figure 4 is a side view similar to that of Figure 1, showing a modified form of construction, and

Figure 5 is a section taken along the line V-V of Figure 4 and drawn to an enlarged scale.

The contactor shown in Figures 1, 2 and 3 comprises two fixed terminals I and 2, in and lead out conductors 3 and 4 are connected. The terminal 2 is secured to a rigid right-angled member 5 which carries a fixed contact stud 5, while the terminal I is connected by a flexible conductor 1 to an arm contact stud 9 is mounted. on a pin IE in a U-shaped element ll of magnetic metal which, by means of a plate l2 and bolts I3, is fixedly secured to an insulating shaft [4 of the contactor. The said shaft, which is of rectangular section, comprises cylindrical portions Ma which are journalled in bearings not shown. The shaft is adapted to be rotated by an electromagnet, diagrammatically illustrated at l5, which acts on an armature l6 secured to the said shaft.

The arm 8 is acted upon by a spring I! surrounding a bolt 58 extending both through the U-shaped element and the said arm, a nut IS on the said bolt permitting adjustment of the force excited by the spring H. The thrust of the spring is transmitted to the arm 8 by a plate 29 of magnetic material, the edges of which tie opposite the arms of the U-shaped element H. Stops 2| prevent any possible contact between the edges of the plate and those of the U-shaped element.

It will be understood that a multipolar contactor may be constructed in a similar manner, each being arranged in the magnetic flux developed in the circuit which is formed by to which lead 8 on which a movable The arm 8 is pivoted The contactor hereinbefore described operates in the following manner:

Starting from the open position illustrated in Figure 2, when the electromagnet I5 is energised, the movable equipment, that is to say, all the parts mounted on the shaft l4, pivots about the axis 0-0 in a direction which moves the movable stud 9 towards the fixed stud 6. After the studs 6 and 9 have come into contact one with the other, the remainder of the travel of the movable equipment produces compression of the spring l1, thereby exerting pressure on the two contacts. The contactor is held operated by the magnet 15 and current passes from the conductor 3 to the conductor 4.

By reason of the fact that the various parts through which this current flows are arranged in loop form, the arm 8 in particular is subjected to an electromagnetic force which tends to move it away from the fixed contact 6. For intense values of current as in the case of a short-circuit, this force may become equal to that of the spring 11, whereby the contact pressure would be nullifled and fusing of the contacts would be promoted. However, the current flowing through the arm 3 produces in the magnetic circuit formed by the U-shaped element H and the plate 20 a magnetomotive force which acts on the plate 2| across the air gaps 22 to attract the plate towards the element H and thus compensate for the said repulsion force between the contacts.

This attractive force, which tends, by reaction, to drive the element H in a clockwise direction as viewed in Figure 1, also combines with an external force, acting on the movable equipment in such manner as to cause opening of the contacts. The movement of this equipment, in the case of tripping due to excess current, is therefore accelerated, which accelerated movement assists in. preventing fusing of the contacts.

In the constructional example illustrated, the said external force is provided by a return member (not shown) of the movable equipment, which acts in opposition to the attraction of the electromagnet IS, the energisation of which is interrupted at the instant of the short-circuit. The contact opening force may also be supplied by other mechanical means or electromagnetically as in the case of circuit breakers for example.

The stops 2| limit the compression stroke of the spring i'l against the U-shaped element and also increase the reluctance of the magnetic circuit consisting of the U-shaped element H and the plate 263, so that although the current may be sufficient to exert a strong pull at the instant when the contacts are closed, the elements H and it do not stick, which might interfere with the operation of the device.

The modified construction illustrated in Figures 4 and 5 is similar in its broad form to the construction illustrated in Figures 1, 2 and 3, and the corresponding members bear the same reference numerals. However, the arm 8 has no plate 20.

In this case, the air gap is formed by the distance separating the internal faces of a U-shaped element 23. When the current flows through the arm 3, the magnetic field set up by this current is, as in the previously described construction, concentrated in the U-shaped element and the lines of force of this field extend across an air gap 24 from one inner face tc the other of the U-shaped element, perpendicularly to these faces.

It will be seen that, regardless of the direction of the current in the arm 8, this arm is subjected, by reason of this field, to a force which tends to move it inwards, towards the web of the u-shaped element, that is to say in a direction which tends to apply the contacts 6 and 9 one against the other.

It should be noted that the movement of the arm 8 in the direction of this force tends to increase the surface of the air-gap subjected to the magnetic field, that is to say, to reduce the stituted by the arm 8.

In the constructional example illustrated, the outer face of the arm 8 lies fiush with the edges of the U-shaped position. However, the arm may also project from the U-shaped element.

In order to increase the forces exerted on the arm 8, it is desirable to reduce the size of the air gap 24, which necessitates the use of movable arms the cross-section of which is elongated in the direction of movement of the movable contact towards the fixed contact.

While the width of the air gaps 22 of Figures 1, 2 and 3 is variable and comparatively small, the air gap 24 (Figure 5) remains constant and is fairly large. The reluctance of the magnetic circuit in the second construction described may therefore be greater than in the first.

Consequently, with equal current strength in the arm 8, saturation of the magnetic circuit may be less rapidly reached, so that it is possible for the repulsion between the the higher currents. Converse- 1y, this compensating force, which is always proportional to the square of the current, is lower ing the leverage of this force, that is to say, by disposing the U-shaped element H at as great a distance as possible from the pivot of the arm 8 without interfering with the disposition of the contacts.

The construction illustrated in Figure 4 affords a further advantage. A stop 25 is provided on the element ll so that when the contacts become worn, the travel of the movable contact under compression is limited by the stop 25. This does not however substantially modify the action of the compensating force, while the limit of travel by means of the stop Zl, in the case or the construction of Figures 1 to 3, affects the air gap 22 and therefore the desired compensation.

It will be noted that in the constructions illustrated,

the movable arm The construction siderably simplified,

that the core of the pivoting axis thereof and member independent of the support of the movable arm. Similarly, in the case of Figure 1, the armature secured to the arm could have the sole function of co-operating with this core.

It will be likewise understood that modifications may be made in the constructions hereinbefore described, as for example by substitution of equivalent technical means, without departing from the scope of the present invention.

What I claim is:

1. A circuit-breaker comprising a fixed contact element; a p-ivotally mounted structure movable towards and away from said fixed contact element, including a U-shaped magnetic core having legs extending away from said fixed contact element; a movable contact arm pivotally connected to said structure and extending at least partly between the legs of said core; a contact element located on said arm beyond said core with respect to pivotal connection between said structure and said arm, adapted to make contact with said fixed contact element; and resilient means interposed between said structure and said arm for urging said arm towards said fixed contact element.

2. A circuit-breaker as claimed in claim 1,

wherein said movable contact arm carries a magnetic armature cooperating with the ends of the legs of the magnetic core.

3. A circuit-breaker as claimed in claim 1, wherein said resilient means comprises a coilspring, one end or which engages said movable contact arm while the other end engages an adjustable stop carried by said structure.

4. A circuit-breaker comprising a fixed contact element; an insulating pivotally mounted structure movable with respect to said fixed element into a contact-making and a contactbreaking position, respectively towards and away from said fixed element; a magnetic U haped member secured to said insulating structure and having flanges extending perpendicularly to the References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Re. 18,630 Van Sickle Oct. 18, 1932 1,395,327 Aalborg Nov. 1, 1921 1,753,650 Gay Apr. 8, 1930 2,590,523 Edwards Mar. 25, 1952