US3469216A - High speed current limiting circuit breaker utilizing electromagnetic repulsion - Google Patents

Description

p 23, 1969 TOKUO SHIRAISHI 3. 69, 6

HIGH SPEED CURRENT LIMITING CIRCUIT BREAKER UTILIZING ELECTROMAGNETIC REPULSION Filed July 10, 1967 2 Sheets-Sheet 1 p 3, 69 TOKUO SHIRAISHI 3,469,216

HIGH SPEED CURRENT LIMITING CIRCUIT BREAKER UTILIZING ELECTROMAGNETIC REPULSION Filed July 10, 1967 2 Sheets-Sheet 2 United States Patent 3,469,216 HIGH SPEED CURRENT LIMITING CIRCUIT BREAKER UTILIZING ELECTROMAGNETIC REPULSION Tokuo Shiraishi, Tokyo, Japan, assignor to Nikko Electric Mfg. Co., Ltd., Tokyo, Japan, a corporation of Japan Filed July 10, 1967, Ser. No. 652,248 Claims priority, application Japan, July 12, 1966, 41/ 45,116 Int. Cl. H01h 3/28 US. Cl. 335-195 3 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention The present invention relates to circuit breakers of a high current breaking capacity adapted for use in a low voltage electric circuit, and more particularly relates to a circuit breaker of the type specified in which a movable contact is disengaged from the cooperating contact instantaneously upon occurrence of severe overload conditions so as to limit the overload current by the formation of arc, and the movable contact, once disengaged, is quickly moved away from the cooperating contact to a distance required for breaking the short-circuit current, in spite of attenuation of said short-circuit current, and which therefore is completely free from melt bonding of the contacts upon re-closure of the same.

Description of the prior art With the capacity of power source facilities becoming larger in recent years, there has been an increasing demand for a circuit breaker which has a larger current breaking capacity. However, since prior circuit breakers have a limited current breaking capacity, it is the common practice at the present time to use a current limiting fuse and a circuit breaker in cascade connection wherever a breaking capacity greater than that of the presently available circuit breakers is required. There has also been developed the so-called current limiting circuit breaker, as disclosed in US. Patent 3,127,488 and US. Patent 3,277,407, in which the circuit breaker itself is designed to perform a current limiting action so as to increase the current breaking capacity. The former method, however, has the drawback that the device is complicated in construction and inconvenient in use due to the current limiting fuse incorporated therein, whereas the latter has not yet progressed to such a level as to ensure positive and safe current breaking action. The conventional current limiting circuit breakers comprise two parallel movable contact arms of conductive material and are designed such that these two contact arms are operated electromagnetically to cause disengagement of one contact from the coopcrating contact with no time delay, there achieving shortcircuit current limiting action and, after the disengagement, the other movable contact arm on the upper side is brought into a full open position before they are brought into engagement again to close the circuit. With such circuit breakers, however, it is very difficult from the time standpoint to move one contact arm away from the other before the latter returns to a closed position and even a slight delay in the opening movement of the upper movable contact arm, caused by friction of some components in a complicated tripping mechanism, will result in re-closure and melt-bonding of the contacts, thus possibly causing a serious accident. In general, ordinary circuit breakers having no current limiting action are capable of completely breaking a short-circuit current occurring in an associated circuit, so that the short-circuit current is interrupted even when the disengagement of the contacts is delayed somewhat. In case of current limiting circuit breakers, however, such delay results in no current limiting action, thus inducing dangerous conditions, and further melting of the contacts due to arc during opening operation provides a better condition for melt-bonding of the contacts when they are brought into engagement again. According to another method employed heretofore,

. the movable contact arms are locked in their open positions when they are opened to a certain degree. Such a method is still unsatisfactory because, when the contact arms are not opened to the locking positions, the contacts are closed again resulting in melt-bonding of the same, as in the case of circuit breakers of the type mentioned previously. This is because the electromagnetic repulsive force acting between the two parallel movable contact arms decreases as the distance between said arms increases, while at the sme time a spring supplying a contact pressure for the contacts is compressed progressively, rendering the pivotal opening movement of the contact arms difficult, and therefore the contact parting distance is limited. For example, the 400 A. circuit breaker commonly used in industry requires about 10 kg. of contact pressure for each pole. This pressure is large enough to resist the rotational movement of the movable contact arm caused by electromagnetic repulsion and dangerous conditions are induced particularly when a short-circuit current is relatively low and hence the repulsive force acting between the contact arms is small.

SUMMARY OF THE INVENTION In view of the above, the present invention contemplates the provision of an improved current limiting circuit breaker which obviates the aforementioned drawbacks of the conventional current limiting circuit breakers and which operates in a positive manner. The concept of the present invention is particularly advantageously applied to circuit breakers which are required to have a large current breaking capacity. According to the present invention, there is provided a circuit breaker in which the movable contact arms are fully opened in their disengaged positions and the lower movable contact arm is retained in the open position by means of a locking mechanism, so that circuit breaking action is achieved even when the opening of the upper movable contact arm is delayed for some reason, and which therefore is highly reliable and is completely free from melt-bonding of the contacts upon re-closure which has been experienced with the conventional circuit breakers.

More specifically, the present invention provides a circuit breaker of the type in which two movable contact arms, arranged in opposed parallel relation in a closed state and each carrying at their end extremities a contact, are opened by an electromagnetic repulsive force acting therebetween upon occurrence of an overload current such as short-circuit current. The present invention is characterized in that at least one of said movable contact arms is connected by way of a first spring to one end of an auxiliary movable arm which is rotatable about a pivot pin and has the other end secured to a molded base 3 p of a casing by way of a second spring. The said first spring is stronger than said second spring, whereby, when the contacts are in the closed position, said first spring imparts a contact pressure to the movable contacts while supplying biasing force for the auxiliary movable arm to retain said movable contact arm in an engaging position. When the contacts are to be opened by electromagnetic repulsive force, said movable contact arm is released -from engagement with said movable arm as the former makes a pivotal downward movement, causing the biasing force of said first spring to drop off and thereby providing for less consumption of the repulsion energy. The said auxiliary movable arm is also rotated under the action of the second spring to lock said movable contact arm in its open position so as to prevent premature return movement of said movable contact arm to a closed position. According to the present invention, therefore, the contact opening action can be effected smoothly to bring the contacts to a full open position and premature re-closing of the contacts can be avoided.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a vertical cross section, partly broken away, of a circuit breaker according to the present invention, with only one pole shown;

FIGURE 2 is a vertical cross section, similar to FIG- URE 1, of another embodiment of the inventive circuit breaker;

FIGURES 3, 4 and are views illustrating the operation of the circuit breaker shown in FIGURE 2, in which FIGURE 3a shows the circuit breaker in a closed position; FIGURE 4a shows a lower movable contact arm in an open position and FIGURE 5a shows the lower movable contact arm in a reset position after circuit breaking action of both the upper and lower movable contacts has been achieved, and FIGURES 3b, 4b and 5b are enlarged views of the essential portions in the corresponding FIG- URES 3a, 4a and 5a respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings and particularly to FIG. 1, the upper and lower movable contact arms 3 and 4 made of a conductive material and carrying contacts 5 and 6 respectively at their end extremities, are disposed in parallel relation in a closed state within acase consisting of a molded base 1 and a molded cover 2.

The lower movable contact arm 4 is pivotally mounted to the molded base 1 at pivot 7. An auxiliary movable arm 10 is also pivotally mounted to the base 1 at pivot 9, and a coil spring 12 is provided between a projection 8 formed at the free end portion of the movable contact arm 4 on the side opposite to the contact 6 and a projection 11 formed on the upper side of the left-hand end portion of the auxiliary movable arm 10 with an insulator cap mounted thereon. The spring 12 serves to bias the movable contact arm to rotate clockwise about the pivot 7 to provide a contact pressure for the lower movable contact 6, while concurrently biasing said auxiliary movable arm 10 to rotate counterclockwise about the pivot 9. The movable contact arms 3 and 4 are held in the closed position by a detent device described hereafter. Another coil spring 16 is mounted between approximately the center of the lower edge of the right half portion of the auxiliary movable arm 10 and the base 1. This spring 16 is weaker than the spring 12 and serves to bias the auxiliary movable arm 10 to rotate counterclockwise about the pivot 9. When the upper and lower movable contact arms 3 and 4 are in a closed position, therefore, a notch 14 formed at the end of the downwardly extending portion 13 of the lower movable contact arm 4, engages a roller 15 provided at the right-hand end of the auxiliary movable arm 10 under the relative biasing forces of said springs 12 and 16'. The other end of the lower movable contact arm 4 is connected to a flexible braid 18 which in turn is connected to a conductor 17 leading to a power source terminal. The upper movable contact arm 3 is pivotally mounted on a cross bar 19 common to all poles and is also connected to a conductor 21 through a flexible braid For opening and closing the upper movable contact arm 3, a manual operating handle 22 is provided whichis operatively connected to said movable contact arm at pivot 24 through the component links of a contact arm operating mechanism generally indicated at 23.

.An electromagnetic tripping mechanism, generally indicated at 25, is provided responsive to an overload current, which includes an electromagnetic coil 26 having 7 one end connected to the conductor 21 and the other end to a load terminal 27. In the circuit breaker described above, as well as in the conventional ones, protection of the associated circuit upon occurrence of normal overload or short circuit conditions, is achieved by the disengagement of the upper movable contact arm 3 from the cooperating lower movable cotnact arm 4. When, however, a severe overload condition occurs due to short circuiting, the lower movable contact arm 4 makes an instantaneous pivotal movement about the pivot 7 against the biasing force of spring 12, under the electromagnetic repulsive force induced by the overload current flowing through the parallel upper and lower movable contact arms 3 and 4 in opposite directions. The downwardly extending portion 13 of the lower movable contact arm 4, therefore, is displaced in the direction of the arrow shown in FIGURE 1, releasing the roller 15 on the auxiliary movable arm 10 from engagement with the notch 14 in. said downwardly extending portion 13. The auxiliary movable arm 10 is permitted to rotate in a counterclockwise direction under the relative biasing forces of springs 16 and 12, with the roller 15 rolling on the sloped edge 13' of the downwardly extending portion 13 of the lower movable contact arm 4, to the position indicated by the dotted circle. Due to such rotation of the auxiliary movable arm 10, the force of the spring 12 is reduced to almost nothing and thus the resistance energy of the spring 12, which has prevented the downward pivotal movement of the lower movable contact arm 4, is eliminated. The lower movable contact arm 4, therefore, is set free from the restraining force of spring 12 and makes a downward pivotal movement to the position indicated by the dotted line with no wasteful consumption of the repulsion energy and permits the short-circuit current to form an arc. Thus, the lower movable contact arm 4 will not return to the closed position again. The contact pressure and wipe between the contacts 5 and 6 are provided by the spring 12 which biases the lower movable contact arm 4 to rotate clockwise. During the contact closing operation, which is effected by means of the manual operating handle 22, the lower movable contact arm 4 is slightly moved counterclockwise due to the wiping action. According to the present invention, however, since the roller 15 of the auxiliary movable arm 10 follows up the displacement of the notch 14 in the lower movable contact arm 4, the engagement between said notch and said roller is not released by such slight counterclockwise rotation of the lower movable contact arm. The engagement is released promptly to enable said lower movable contact arm to be locked in an open position, only when the lower movable contact arm 4 is rotated under electromagnetic repulsive force more than by said wiping action. Resetting of the lower movable contact arm 4, after having once been locked in the open position, may beeasily achieved by the provision of unlocking means, such as a push-button, although the manner in which it is effected is not described herein.

Now, another embodiment of the present invention will be described hereunder with reference to FIG. 2.

According to this embodiment, similar to the preceding embodiment, upper and lower movable contact arms 30 and 31, respectively made of a conductive material and carrying at their end extremities contacts 32 and 33 respectively, are disposed in a case in parallel relation in a closed state, said case being composed of a molded base 28 and a molded cover 29. The lower movable contact arm 31 and an auxiliary movable arm 34 are pivotally mounted to a fixed frame member 36 at a common pivot 35. The auxiliary movable arm 34 carries thereon an integral pin 37 which is loosely received in an aperture 38 formed in the lower movable contact arm 31 and also in an arcuate slot 39 formed in the fixed frame member 36. Between the end extremities of the lower movable contact arm 31 and the auxiliary movable arm 34 is mounted a coil spring 40 which biases said movable arms apart from each other but only to such an extent as allowed by the amount of play of the pin 37 in said aperture 38 which is just slightly larger than said pin. The amount of the play is determined such that it is sufficient for a suitable contact pressure to be produced between the contacts 32 and 33 and also for the lower movable contact arm 31 to bring the auxiliary movable arm 34 into a released position under electromagnetic repulsion. The pin 37 has one end of a coil spring 42 connected thereto, the other end of which is connected to a pin 41 provided on the right-hand portion of the fixed frame member 36. This spring 42 serves to bias the auxiliary movable arm 34 to rotate in a counterclockwise direction. The movable contact arms 30 and 31 are held in the closed position by a detent device described hereafter. Provided at the right lower portion of the fixed frame member 36 is a movable frame member 45 which is pivotally mounted to said fixed frame member at pivot 59. The movable frame member 45 carries at its end extremity a roller 43 and is biased to rotate clockwise by a torsion spring 46. Thus, the roller 43 is held in engagement with a square notch 44 formed in the auxiliary movable arm 34. The other end of the lower movable contact arm 31 is connected to a conductor 47, leading to a source terminal, by way of a flexible braid 48. The upper movable contact arm 30 is pivotally mounted on a cross bar 49 common to all poles, which cross bar is supported by the base 28, though not shown in FIGURE 2. The other end of the upper movable contact arm 30 is connected to a flexible braid 50 which in turn is connected to a conductor 51.

A manual operating handle 52 for opening and closing the upper movable contact arm 30 is operatively connected to said upper movable contact arm at pivot 53 by way of the component links in a contact arm operating mechanism generally indicated at 57. Also disposed in the case, as overload responsive means, is an electromagnetic tripping mechanism generally indicated at 54, which includes an electromagnetic coil 55 which is electrically connected to the conductor 51 at one end and to a load terminal 56 at the other end. In the circuit breaker described above, alike in the conventional ones, protection of the associated circuit, upon occurrence of normal overload or short-circuit current condition, is achieved by the disengagement of the upper movable contact arm 30. When, however, a severe overload condition occurs, the lower movable contact arm 31 makes an instantaneous pivotal movement in a counterclockwise direction about the pivot 35 against the bias of the spring 40, under the electromagnetic repulsion caused by the current flowing through said parallel upper and lower movable contact arms 30 and 31. The amount of this pivotal movement corresponds to the amount of play between the pin 37 and the aperture 38. The lower movable contact arm 31, as shown in FIG. 3b, has a cam surface 58 formed at the right lower portion thereof for engagement with the roller 43. This cam suface 58 depresses the roller 43 during the counterclockwise rotation of the lower movable contact arm 31, so that the movable frame member 45 is caused to rotate counterclockwise about a pin 59, with the result that the square notch 44 in said auxiliary movable arm 34 is disengaged from the roller 43. The auxiliary movable arm 34, therefore, is permitted to rotate in a counterclockwise direction under the electromagnetic repulsion as well as the relative forces of spring 42 and compression spring 40. In this case, since the lower movable contact arm 31 is loosely mounted on the pin 37, which is integral with the auxiliary movable arm 34, it also rotates counterclockwise along with the rotating auxiliary movable arm. Thus, it will be understood that, when the lower movable contact arm 31 has once compressed the spring 40 under the electromagnetic repulsion, causing the roller 43 to be released from engagement with the square notch 44 in the auxiliary movable arm 34, it may be brought into a full open position with no wasteful consumption of the electromagnetic repulsion energy. As stated previously, the fixed frame member 36 is formed therein with the arcuate slot 39 which is concentric with the pin 35, and the pin 37 on the auxiliary movable arm 34 makes a rotational movement within said arcuate slot 39 in sliding contact with the peripheral edge thereof. It will thus be seen that the range of rotational movement of said pin 37 and hence the auxiliary movable arm 34 is defined by said arcuate slot 39.

FIGS. 3a and b show the positions of the lower movable contact arm 31 and the associated parts thereof in the initial stage of the circuit breaking operation. In these figures, it will be seen that the pin 37 is located at the left end extremity of the arcuate slot 39. When the lower movable contact arm 31 is fully opened by the electromagnetic repulsion as shown in FIGS. 4a and b, the pin 37 is located at the right end extremity of the arcuate slot 39.

Now, when the lower movable contact arm 31 is desired to be reset upon completion of the opening of the upper movable contact arm 30 successively after the action of electromagnetic repulsion, the manual operating handle 52 is turned to the OFF position in the direction of the arrow. In this case, since a link 61 integral with the operating handle 52 is operatively connected with the lower movable contact arm 31 and auxiliary movable arm 34 by means of a link 65 through the engagement of a pin 66 at one end of said link 65 with a hole 62 at one end of the link 61 and the engagement of a pin 64 at the other end of said link with arcuate slots 63 formed in both of said movable arms, as shown in FIG. 5a, the lower movable contact arm 31 and auxiliary movable arm 34 are rotated clockwise about the pin 35 by said link 65, and thus the lower movable contact arm 31 is reset in a closed position, with the square notch 44 engaged with the roller 43. Then the manual operating handle 52 is turned counterclockwise, whereupon the upper movable contact arm 30 is reset in its engaging position by way of the component links of the contact operating mechanism 57, which links are not shown completely. During this operation, the lower movable contact arm 31 and auxiliary movable arm 34 are held in their reset positions, since the pin 64 is loosely received in the arcuate slots 63, and thus the circuit is closed. A slight counterclockwise rotation of the lower movable contact arm 31 with respect to the auxiliary movable arm 34, which is allowed by the play between the integral pin 37 on the auxiliary movable arm and the aperture 38 in the lower movable contact arm, is prevented by the biasing force of the spring 40 mounted between said lower movable contact arm and said auxiliary movable arm. Consequently, the lower movable contact 33 is held in pressure contact with the upper movable contact 32.

As may be understood from the description herein, the circuit breaker according to the present invention is capable of instantaneously breaking the associated circuit, upon occurrence of a large capacity short-circuit current, by the cooperation of the upper and lower movable contact arms, the lower movable contact arm thus disengaged from the upper movable contact arm being locked positively to permit the high short-circuit current to form an are, thereby limiting the overload current, and the distance between both contacts being further increased for safety 7 by the successive movement of the upper movable contact arm away from the lower movable contact arm. The inventive circuit breaker is advantageous in that it is small in size, is economic and positive in operation and has a high breaking capacity.

What is claimed is:

1. A high speed current limiting circuit breaker comprising two movable contact arms arranged in opposed parallel relation in a closed state and respectively having contacts at their end extremities, said arms being opened by utilizing the electromagnetic repulsion produced between said two arms upon occurrence of an exceedingly high current, such as a short-circuit current, characterized in that a roller is provided at one end of an auxiliary movable arm said roller being engaged in a notch in a downwardly extending end portion of the movable contact arm rotated by the electromagnetic repulsion produced between said two arms, said roller engaging said notch of said movable contact arm while the contact pressure of the movable contact exists, but when said movable contact arm is slightly rotated by the electromagnetic repulsion, and thereby the contact pressure of the movable contact has become zero, said roller is so adapted as to be disengaged from the notch of said movable contact, and by this disengagement the auxiliary movable arm being rotated, the pressure of a first spring is made zero and at the same time the roller of the auxiliary arm is urged against the sloped edge of the movable contacts to thereby prevent repeated arc loss produced between the contacts whereby a large interrupting capacity is obtained. 7

2. A high speed current limiting circuit breaker comprising two movable contact arms arranged in opposed parallel relation respectively having contacts at their end extremities, said arms being opened by utilizing an electromagnetic repulsion produced between said two arms upon occurrence of an exceedingly high current, such as a short-circuit current, characterized in that a first spring is mounted between one end of the movable contact and one end of an auxiliary movable arm rotating about a pivot and a second spring is interposedly aflixed between the other end of said auxiliary movable arm and a molded base, whereby when the contacts are closed a compressive force is imparted by said first spring so as to apply a contact pressure to the movable contact and at the same time a biasing force is applied to the auxiliary movable contact, and wherein a roller is provided at the other end of said auxiliary movable arm, said roller being maintained in engagement with a notch provided in downwardly extending end portion of the movable contact arm, and when said movable contact is rotated slightly by an electromagnetic repulsion produced upon occurrence of a short-circuited current by an amount corresponding to the wiping of the contact, the roller of said auxiliary movable arm is disengaged from the notch of the movable contact arm and thereby the resisting pressure of the first spring preventing the repulsing rotationof the movable contact arm due to the electromagnetic repulsion disappears suddenly whereby highspeed current limiting interruption is accomplished making the consumption of the electromagnetic repulsion energy acting on said movable contact arm small, and said movable contact arm once opened is engaged with said roller with the sloped,edge of said contact arm locked thereto, thereby providing a suflicient distance between the contact of said movable contact arm opened by the operation of a trip device that may arise successively and the contact provided on said repulsive movable contact arm independently of the attenuation of the short-circuit current and thereby preventing repeated arc loss produced between the contacts, whereby a large interrupting capacity being obtained.

3. A high speed current limiting circuit breaker including two movable contact arms arranged in opposed parallel relation in a closed state, said arms being provided with contacts at their extremities, and said arms being opened by the electromagnetic repulsion produced between said arms upon the occurrence of an exceedingly high current, such as a short circuit current, wherein the improvement comprises:

a movable auxiliary arm associated with a first of said contact arms, said arms being movable together away from the second contact arm; 7

spring means positioned between the auxiliary arm and said first contact arm for normally urging said movable contact arms into engagement with each other, and for urging the auxiliaryarm and the first contact arm apart; I

detent means positioned in engagement with one of said auxiliary and first contact arms for preventing said first contact arm and said auxiliary arm from moving apart under the influence of said spring means, said 1 detent means being released upon a small movement of said first movable arm due to electromagnetic repulsion between the two movable contact arms; and a'second spring means for moving said first contact arm and said auxiliary arm away from the second contact arm upon release of said detent means to thereby prevent repeated arc loss produced between the contacts, whereby a large interrupting capacity is obtained.

References Cited UNITED STATES PATENTS 3,317,866 5/1967 Hanafusa -s 335l6 3,343,108 9/1967 Murai- 335--16 BERNARD A. GILHEANY, Primary Examiner H. BROOME, Assistant Examiner "US. Cl. X.R.' 335-516

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