US3453566A - Automatic current limiting circuit breaker - Google Patents

Description

July 1, 1969 YASUO KASAHARA AUTOMATIC CURRENT LlMl'IINU CIRCUIT BREAKER Filed Jan. 23, 1967 Sheet Fig.2

Y Asuo KASAHARA AUTOMATIC CURRENT LIMITING CIRCUIT BREAKER Filed Jam; 23, 1967 July 1, 1969 Sheet Fig.3

I July 969 YAsuo KASAHARA 3,453,566

Filed Jan. 25, 1967 AUTOMATIC CURRENT LIMITING CIRCU IT BREAKER Sheet 3- of6 y 1969 YASUO KASAHARA 3,453,566

AUTOMATIC CURRENT LIMITING CIRCUIT BREAKER Filed Jan. 23', 1967 Sheet 4 of 6 I I0 I') gn I202) .July1,l969 YASUO KASAHARA 3,453,566

. AUTOMATIC CURRENT LIMITING CIRCUIT BREAKER Filed Jan. 23, 1967 Sheet \3' of e July 1, 1969 YASUO KASAHARA AUTOMATIC CURRENT LIMITING CIRCUIT BREAKER Filed Jan. 23, 1967 Sheet United States Patent '0 US. Cl. 33516 6 Claims ABSTRACT OF THE DISCLOSURE An automatic circuit breaker having a lock-trip mechanism, said mechanism including a magnet, a conductor made of electrically conductive magnetic substance to carry load current therethrough, said conductor being attracted by the magnet under normal conditions to lock the breaker as closed, and a bias means to apply a bias force to the lock-trip mechanism in opposition to the magnetic attraction, whereby under conditions of Overcurrent, the magnetic attraction is diminished in recoverable fashion to separate the conductor from the magnet for tripping the breaker.

This invention relates to an electric circuit breaker, more particularly to an automatic circuit breaker capable of making accurate and high speed interruption of overcurrent and adaptable for trip free operation with ease.

In order to simplify the complicated structure of conventional current limiting circuit breakers for distribution system and to provide a novel circuit breaker having a high reliability at a low cost, the inventor proposed use of magnetic shunt material, as disclosed in his US. Patent No. 3,226,507 as well as his US. Patent No. 3,373,383.

In the course of continued studies on such circuit breakers, the inventor has noticed the fact that magnetic attraction acting between a magnet and an electrically conductive magnetic substance member attracted by said magnet is diminished instantaneously, say in about 10 milliseconds for a 50 cycle alternating current, upon application of a large current through the member, and the inventor has succeeded in providing a novel circuit breaker of compact form at low cost based on said fact.

Therefore, an object of the present invention is to provide a novel circuit breaker by taking advantage of a phenomenon that magnetic attraction acting between an electrically conductive magnetic substance member and a magnet is greatly reduced upon passage of a large current through said member.

Another object of the present invention is to provide an automatic circuit breaker including a lock-trip means having a permanent magnet, a movable straight conductor made of electrically conductive magnetic substance and attracted to said permanent magnet under normal conditions, and a bias spring acting on the conductor, wherein under conditions of overcurrent through the conductor, the magnetic attraction acting on the conductor becomes smaller than a bias force of the bias spring to move the conductor away from the permanent magnet.

It is an object of the present invention to provide a double pole four terminal circuit breaker including a lock-trip means having a pair of fixed straight conductors made of electrically conductive magnetic substance, a movable permanent magnet attracted to said fixed conductors under normal conditions, and a bias spring acting on said permanent magnet, wherein under conditions of overcurrent through the conductors, the magnetic attraction acting on the permanent magnet becomes smaller 3,453,566 Patented July 1, 1969 than a bias force of the bias spring to move the permanent magnet away from the fixed conductors.

Salient features of the circuit breaker according to the present invention are as follows:

(1) High speed interruption of overcurrent in less than 1 cycle of commercial power frequency (to be referred to as a cycle hereinafter) is possible.

In most conventional circuit breakers, interruption of overcurrent is carried out in two steps, i.e., tripping of a lock means locking main contacts of the breaker and moving or separating the main contacts to interrupt the overcurrent at the contacts. With such a two step mechanism, mechanical inertia of both the lock means and the contacts as well as movable supporting structures thereof acts to slow down the speed of the interrupting operation and to hamper high speed interruption, such as interruption within 1 cycle.

On the other hand, in the circuit breaker according to the present invention, a light weight movable conductor member, e.g., an electrically conductive magnetic substance member, is adapted to act both as a tripping element and as a carrier of a light weight movable contact of the switching means thereof, thereby the inertia of the movable member of the lock-trip means is greatly reduced and at the same time a single step operation for overcurrent interruption is made possible. For instance, it has been confirmed by experiment that a large overcurrent can be interrupted in /2 of a cycle with the circuit breaker of the invention.

(2) Durability of the circuit breaker is high, because "adverse mechanical and electromechanical effects of overcurrent on various parts of the breaker are prevented by the high speed interruption.

In some of conventional circuit breakers having magnetic locking means, conductor means for carrying load current is held stationary adjacent to magnet means thereof even after the opening of the main contacts of the breaker. Hence, a follow current succeeding the opening of the main contacts, such as an arc current through the contacts, tends to exert adverse eifects on some parts of the circuit breaker.

On the other hand, according to the present invention, the very conductor carrying the overload current is moved quickly away from the magnet means. Consequently, there is no danger of exerting adverse elfects to the magnet means due to the overload current. Such interruption of the overload current and isolation of the overload carrying conductor from the magnet means are made possible only by the circuit breaker of the present invention including an electrically conductive magnetic substance member. More particularly, the danger of such adverse efiects can be further reduced by mounting movable contact of the switching means on the aforesaid movable conductor member.

Generally speaking, if a permanent magnet is used in the magnet means of the magnetic lock-trip means, the large overcurrent carried by a conductor adjacent to the magnet means tends to demagnetize permanently the magnetization of such permanent magnet. However, it has been confirmed by experiment that there is no possibility of such permanent demagnetization in the circuit breaker of the present invention. The inventor believes that the distance between the conductor and the permanent magnet is increased rapidly before the magnetomotive force produced by such overcurrent increases as high as the coercive force of the permanent magnet.

(3) It has been confirmed by experiments that the tripping speed of the circuit breaker of the present invention is substantially unafiected by the polarity of the overcurrent to be interrupted thereby. Thus, quick interruption within /2 of a cycle is made possible.

(4) Closing time of the circuit breaker is very short. This is possible because the mass of the movable member can be very small. Furthermore, the magnetic attraction between the fixed part and the movable part of the switching means also acts to shorten the closing time. The aforesaid single step operation of the present invention is also favorable for shortening the closing time.

The operation of the circuit breaker is stable and affected very little by the presence of mechanical vibrations.

In the circuit breaker of the present invention, the difference between the magnetic locking force and the bias force can be made very large while ensuring quick and reliable overload current interruption. Thereby, the effective locking force, which is equivalent to the aforesaid difference of the two forces, can be made large to make the locking action free from any adverse effects due to vibrations.

(6) The circuit breaker is simple in construction and inexpensive to manufacture.

(7) The circuit breaker can be easily made in so-called trip free type. In conventional circuit breakers, it has been necessary to provide some additional equipments, such as coils, ratchets, etc., in order to make them trip free. However, the circuit breaker of the present invention can be made trip free with ease.

(8) The magnetic flux for locking the contact means can be also used for extinction of arc.

For a better understanding of the invention, reference is made to the accompanying drawings, in which:

FIG. 1 is a vertical sectional view of a circuit breaker according to the present invention;

FIG. 2 is a side view of the circuit breaker shown in FIG. 1;

FIGS. 3A to 3C are sectional views taken on the line III-III of FIG. 1, illustrating different forms of a permanent magnet and an electrically conductive magnetic substance member usable in the circuit breaker of the invention;

FIGS. 4a to 4 are a series of diagrammatic illustrations of the sequence of interrupting operation of the circuit breaker of FIG. 1;

FIGS. 5A and 5B are respectively an elevation and a plan view of a four terminal double pole circuit breaker according to the present invention;

FIGS. 6A and 6B are diagrammatic illustrations showing different embodiments of the present invention;

FIGURES 7A and 7B are diagrammatic illustrations showing an additional embodiment of the present invention.

Similar parts and similar devices are represented by the same reference numerals and symbols throughout the drawings.

Referring to FIGS. 1 and 2 illustrating a trip free type circuit breaker according to the present invention, refference numeral 1 designates a base of the circuit breaker, 2 a cover of the same, 3 an operating pin planted at the top of a permanent magnet M, 30 an operating knob engageable with said pin 3 and movable on the surface of the cover 2 along a guide 3b formed thereon, 4 a pivot pin to hold rotatably the permanent magnet M adjacent to an electrically conductive magnetic substance member 14, 4a another pivot pin to hold rotatably said magnet M, 6 a movable contact mounted on the free end of the magnetic substance member 14 and cooperating with a fixed contact 7 secured to one of terminals 11 and 12, say the terminal 12, and 8 a bias spring to apply a bias force to the magnetic substance member 14 in opposition to the magnetic attraction between the permanent magnet M and the member 14. A lock-trip means generally designated by 13 includes the electrically conductive magnetic substance member 14, which is flat bar-shaped in this particular embodiment, the pivoted permanent magnet M, and a bias spring 8.

The permanent magnet M can be magnetized in any suitable polarity. For instance, the permanent magnet M is so magnetized as to produce the S pole along the lower edge thereof in parallel with the magnetic substance member 14, while producing the N pole along the upper edge thereof, as shown in FIG. 3A. The present invention is not restricted to such polarity alone, but it is also possible to use any suitable polarities, such as applying a pair of pole pieces on opposite vertical surfaces of the permanent magnet M so as to produce the S pole in one of the pole pieces while producing N pole in the other pole piece, as shown in FIG. 3B.

Preferable material for the electrically conductive magnetic substance member 14 is magnetic shunt material or soft ferrite, as disclosed in the US. Patent No. 3,226,507, which has reversible thermal variation characteristics of permeability, however, it is also permissible to form it with any other suitable magnetic substance, such as soft iron, or with a permanent magnet. If a high electric conductivity is required to such member 14, then it can be formed as a composite member consisting of an electrical conductor element 14b, say a copper element, and magnetic substance element 14a, such as soft ferrite, as shown in FIG. 3C.

The permanent magnet M is preferably made of magnetic substance having reversible thermal variation characteristics of spontaneous magnetization, such as Al-Ni-Co alloys (Alnico V), barium ferrite, etc. However, the permanent magnet M can be also formed with other magnetic substance having no such specific characteristics or it can be an electromagnet, provided that the aforesaid electrically conductive magnetic substance member 14 is made of magnetic substance having reversible thermal variation characteristics of permeability and that the circuit breaker is not required to have time delay characteristics for interrupting a comparatively small overload current.

In operation, when the circuit breaker is closed, the circuit carrying the load current is traced from the terminal 11, through the magnetic substance member 14 and the then closed contacts 6 and '7, and to the other terminal 12. Under the conditions as shown by solid lines in FIG. 1, the magnetic substance member 14 is attracted by the permanent magnet M to lock the circuit breaker at the closed position to complete the aforesaid circuit carrying the load current. Upon moving the operating knob 3a to the right from the position as shown in FIG. 1, the permanent magnet M is rotated around the pivot pin 4 in a clockwise direction by the mechanical engagement between the knob 3a and the operating pin 3 thereof, and after travelling through the gap, the lower right edge of the permanent magnet M is brought into direct contact with the magnetic substance member 14 to force its free end downwards. As the permanent magnet M is further rotated by moving the operating knob 3a to its extreme right position, FIG. 1, the movable contact 6 is moved away from the fixed contact 7 to open the circuit breaker. As the operating knob 3a is moved leftwards from its extreme right position, FIG. 1, the movable contact 6 is again brought into engagement with the fixed contact 7 in the similar manner to the aforesaid opening but in the opposite sequence.

It is preferable to provide a suitable click means to the operating knob 311, so that the knob can be held securely at either one or both ends of its operative stroke.

The circuit breaker of the invention is tripped rather slowly with suitable time delay for a comparatively small overcurrent and instantaneously for a comparatively large overcurrent, such as a heavy fault current. The slow tripping with time delay is carried out by taking advantage of the thermal reversible reduction of magnetization of the permanent magnet M due to the heat generated by the overcurrent or of similar thermal reversible reduction of permeability of the electrically conductive magnetic substance member 14 caused by the same heat. Since the time necessary for reduction of the aforesaid magnetization or the permeability to a predetermined level depends on the rate of heat generation from the conductor member 14, which rate is in turn related to the magnitude of the overcurrent, it is possible to obtain any desired time delay characteristics by selecting proper balance of heat generation in and heat dissipation from the conductor member 14 in relation with the overcurrent flowing therethrough.

The instantaneous tripping of the circuit breaker, which will be described in detail hereinafter, is an outstanding feature of the present invention. According to experiments made on the circuit breaker of FIG. 1, it has been proved that when a large overcurrent, such as about 1,000 percent of the rated continuous current carrying capacity of the breaker, is forced to flow through the conductor member 14, the member 14 is separated from the permanent magnet M extremely quickly or instan-' taneously, and the movable contact 6 is subsequently moved away from the fixed contact 7 to interrupt the overcurrent. The aforesaid 1,000 percent of the rated current was taken as an example, and the present invention is not restricted to such magnitude of the overcurrent, but for instance, it is possible to design or manufacture a circuit breaker capable of instantaneous interruption of overcurrent of considerably smaller magnitude, say about 500 percent of the rated continuous current carrying capacity. As will be described hereinafter, the interruption of such large overcurrent can be greatly facilitated with a suitable arc extinguishing chamber, and the overcurrent is interrupted quickly responsive to opening of the circuit between the contacts 6 and 7.

A short circuit test was made on the circuit breaker of FIGS. 1 and 2 by passing a 50 cycle alternating current of 1,600 amperes R.M.S. at 100 volts through the conductor member 14, and the behavior of the circuit breaker for such large current was recorded by a movie film at a rate of 10,000 frames a second. FIGS. 4a to 4] show schematic. views, prepared by copying different views selected from the movie film, in which the permanent magnet M is magnetized with polarity as shown by FIG. 3B and the time taken from the closing of the breaker to each view is as shown in Table I.

TABLE I Time taken from FIGURE: closing (ms) 4a 0 4b 1.0 40 2.4 4d 3.8 4e 5.2 4f 6.6

It is apparent from FIGS. 4a to 4 and Table I that with the circuit breaker of the invention, a large overcurrent can be interrupted very quickly. In fact, in the case of the aforesaid test, the large overcurrent was interrupted in about /3 of a cycle (20 ms.) after the breaker was closed.

Such high speed interruption is, of course, due to the fact that the mass of the electrically conductive magnetic substance member 14 or the movable element of the breaker is very small, but the exact mechanism of napid reduction in the magnetic attraction between the magnet M and the magnetic substance member 14 responsive to the large current passing through the magnetic substance member 14 is not known yet. The inventor assumes that the behavior of magnetic domains of the magnetic substance member 14 may be disturbed due to the passage of an extremely large current therethrough.

It was also confirmed by the test that the magnitude of the magnetization of the permanent magnet M is not affected by the large current and the circuit breaker can be used repeatedly. The reason for such unaffectedness of the permanent magnet M by the large current through the magnetic substance member M is due to the fact that the magnetic substance member 14 from the permanent magnet M before the magnetomotive force at the permanent magnet M due to the large current through the magnetic substance member 14 is increased to the level of coercive force of the magnet M, and to the fact that large current itself is interrupted by the circuit breaker.

Referring to FIG. 1 again, when the circuit breaker is opened automatically by moving the magnetic substance member 14 to a position away from the permanent magnet M, the magnetic attraction between the magnet M and the member 14 is so reduced that the member 14 is kept at said position away from the magnet M to hold the movable contact 6 separated from the fixed contact 7. In order to close the breaker thus opened, it is necessary to move the operating knob 3a once to its open position for resuming the locking action between the permanent magnet M and the magnetic substance member 14, and then the operating knob is moved toward the left, FIG. 1, to its closed position. If the fault conditions or overload conditions are not removed prior to the aforesaid reclosing, the circuit breaker is opened again in the aforesaid manner, and thus so-called trip-free mechanism is incorporated into the circuit breaker with ease.

With the circuit breaker of the invention, it is preferable to mount the contacts 6 and 7 in an arc extinguishing chamber for quick interruption of any arc current following the high speed opening of the contacts. In FIG. 1, a bifurcated arc extinguishing wall 9 is mounted on the inside surface on the cover wall 2, and arc extinguishing ridges are also secured to the inside surface of the cover wall 2.

Thus, according to the present invention, there is provided a circuit breaker having a lock-trip mechanism comprising a magnet and an electrically conductive magnetic substance member placed opposite to said magnet so as to be attracted thereby for reliable locking and high speed tripping responsive to occurrence of faulty or overload conditions. Thus, the aim of limiting overcurrent magnitude to a low level by means of a high speed tripping action can be achieved.

Furthermore, the construction of the circuit breaker of the present invention, more particularly, mounting of a movable contact directly onto a movable member of the tripping mechanism in conunction with actuation of the cooperating member of the tripping mechanism by .an operating lever, has made it possible to provide a simple and reliable trip free mechanism.

The construction of the circuit breaker of the invention shown in FIGS. 1 and 2 can be easily modified for a double pole circuit breaker.

FIGS. 5A and 5B show an automatic double pole type current limiting circuit breaker embodying the present invention. In this double pole breaker, two electrically conductive magnetic substance members 14a and 1412, one for each pole, are used. Thus, an automatic two pole current limiting circuit breaker of very simple construction can be provided.

Referring to the figures, the reference numeral 1 represents the base plate of the circuit breaker, 2 a cover, and 11, 11' and 12, 12' two pairs of terminals, the former pair being connected to an electric power source means at one end of the base plate while the latter pair being connected to a load at the opposite end of the base plate.

In this particular embodiment shown in FIGS. 5A and 5B, the member 14a made of electrically conductive magnetic substance is secured to the base plate so as to be inserted in the electric circuit between the terminals 11 and 12, and the other member 14b made of the same substance is secured to the base plate so as to be inserted in the electric circuit between the terminals 11' and 12.

Instead of the bias spring 8 of FIG. 1, elastic conductor members 8 and 8' having movable contacts 6 and 6' secured thereon are connected to each of the electrically conductive magnetic substance members 14a and 14b at is moved away one end thereof respectively through connectors 29 and 29'. Stationary contacts 7 and 7 are connected to the terminals 11 and 11' so as to cooperate with said movable contacts 6 and 6' respectively. The elastic conductor means 8 and 8' are biased in a direction to interrupt the circuit between the contacts 6 and 7 and another circuit between the contacts 6' and 7, respectively. Instead of the elastic conductor members, it is permissible to use separate biasing means, such as springs, in order to apply the aforementioned bias to the movable contacts in the direction to interrupt said circuits.

It is apparent to those skilled in the art that the double pole circuit breaker of FIGS. A and 5B can be used as a single pole circuit breaker by short circuiting one of the two members 14a and 14b, say the member 14 thereof.

For simplicity, the operation of the circuit breaker of FIGS. 5A and 58 will now be described by referring only to the switching circuit including the contacts 6 and 7, but it should be understood that One can obtain a double pole circuit breaker by adding another switching circuit including contacts 6' and 7' between the terminal 11' and the element 14b.

In order to close the circuit between the contacts 6 and 7, the movable contact 6 is urged toward the stationary contact 7 by a spherical press means 5 mounted to the lower end of a lever 15a pivotally supported by a pin 17 secured to a bracket 18. The pivoted lever 15a is in turn connected to a lock lever 31 through a link means 16. A sphere 5a is secured to the tip end of the press means 5 to minimize the friction between the press means and the elastic conductor member 8 holding the movable contact 6.

In this embodiment of the invention, the pivoted lever 15a is made short and adapted to make a large angular displacement for a given angular stroke of the lock lever 31 to actuate the circuit breaker. Thereby, when the circuit breaker is opened, the clearance between the contacts 6 and 7 and the corresponding clearance between the magnetic substance elements 14a and 14b and a permanent magnet M can be made considerably large.

In FIGS. 5A and SE, a pivot shaft 4 of the lock lever 31 is supported by a pair of brackets 21. The upper end of a link 16 is pivotally connected to the pivoted lever 15a by a pin 19, while the lower end thereof is pivotally connected to the lock lever 31 by another pin 24. The permanent magnet M is secured to the free end of the lock lever 31. The two electrically conductive magnetic substance members 14a and 14b are disposed substantially in parallel with each other, and the permanent magnet M is attracted to the members under normal conditions. A knob 22 is secured to the lever 15a to facilitate opening and closing of the circuit between the contacts 6 and 7.

The operation of the circuit breaker of FIGS. 5A and 5B is essentially the same as that of the circuit breaker of FIG. 1, namely, the movable contact 6 is retained in contact with the cooperating stationary contact 7 as long as the current through the electrically conductive magnetic substance member 14 is smaller than a certain predeter mined rated value, while it is moved away from the stationary contact 7 with a proper time delay for an overload current within a predetermined range and instantaneously for a heavy short circuit current.

It the double pole circuit breaker of FIGS. 5A and 5B is utilized in a DC. network or in a single phase A.C. network, the electrically conductive magnetic substance members 14a and 14b carry the load current in opposite directions. It is apparent to those skilled in the art that the double pole circuit breaker of FIGS. 5A and 5B can be easily modified to a single pole circuit breaker by removing the second pair of terminals 11', 12', together with the related conductors and ope-rating means.

In the embodiments of the present invention described in the foregoing, the switching means comprises a stationary contact and a movable contact, however, it is pos- 8 sible to form the switching means with a pair of movable contacts, in which case, the current interrupting capacity of the circuit breaker is increased responsive to the increased relative speed of the two contacts. FIGS. 6A

and 6B show such embodiment of the invention.

Referring to the figures, contacts 6 and 7 are mounted on elastic conductor members 8a and 8b respectively, which are biased in the directions to be away from each other, e.g., upwards and downwards respectively. An electrically conductive substance member 14 is inserted to the circuit between terminals 11 and 12, so that the electric circuit in the circuit breaker may be traced from the terminal 11, through a lead wire 10', an elastic conductor member 8b, the contact 7 secured to the free end of the conductor member 8b, the contact 6, an elastic conductor member 8a carrying said contact 6 at the free end thereof, a lead wire 9, the electrically conductive magnetic substance member 14, and a lead wire 10, to the terminal 12.

The magnetic substance member 14 in this embodiment is made in a horseshoe shape by utilizing electrically conductive magnetic material, such as soft iron or cast material for permanent magnets. One leg of the horseshoe-shaped member carries the load current in one di rection, while the other leg of the element carries the same current in the opposite direction. If it is desired to use magnetic substance having a low electric conductivity, such as hard ferrite and soft ferrite, then the member 14 can be made as a composite member either by laminating said magnetic substance on an electrically conductive element, for instance a copper sheet, or by shaping the member 14 with the mixture of the ferrite powder particles and copper powder particles. Aluminium and iron can be also used in conjunction with ferrite to improve the electric conductivity of the magnetic substance member 14 in the aforementioned manner.

There are provided two lock levers 31a and 31b pivoted by shafts 4a and 4b, respectively, and two magnets M and M are mounted at free ends of the levers 31a and 311; respectively. One of the magnets, say M,,, is adapted to cooperate with one leg of the horseshoe shaped magnetic substance member 14, while the other one of the magnets, say M may cooperate with the other leg of the member 14. The lock levers 31a, 31b are connected through a link means 16a, 16b to pivoted levers 15a, 15b respectively. Press means 50, 5d are secured to the pivoted levers 15a, 15b in the proximity of the pivot shafts 17a, 17b thereof, respectively, so that the free ends of the elastic conductor members 8a and 811 may be urged toward each other by means of spherical members 5a and 5b secured to the tip ends of the press means 50 and 5d, respectively. There is provided an operating knob (not shown) at a suitable location of the circuit breaker to manually complete and interrupt the circuit between the contacts 6 and 7.

The magnets M and M of this embodiment can be made of the same material as that for the corresponding magnet M of the preceding embodiments described hereinbefore referring to FIGS. 1 to '53.

With the circuit breaker shown in FIGS. 6A and 6'B, if the current flowing through the magnetic substance member 14 is less than a certain predetermined value, then the magnets M and M are pulled toward the member 14 and retained in contact therewith. The magnetic attraction between the member 14 and the magnets M, M acts to keep the contacts 6 and 7 at the positions to complete the circuit between them through the lock levers 31a and 31b, 1inks.16a and 16b, pivoted levers 15a and 15b, and press means 50 and 5d, while overcoming the elastic bias forces applied to the contacts by the resilient conductor members 8a, 8b. Thus, the circuit between the contacts 6 and 7 can be locked as closed.

It is apparent to those skilled in the art that upon increase of the current through the magnetic substance member 14 in excess of a certain predetermined value, for instance by overloading or short circuiting, then the aforementioned magnetic attraction in the look-trip mechanism 13 is reduced in the same manner as in the preceding embodiments, and hence, the locking force acting on the contact means 6 and 7, which is in proportion to the magnetic attraction, is surpassed by the elastic bias force applied by the elastic conductor members 8a and 812. Thus, any overcurrent in excess of a predetermined value can be interrupted by the circuit breaker.

With the arrangement shown in FIGS. 6A and 6B, both contacts 6 and 7 are displaced from each other very quickly for interruption of an overcurrent therethrough, and hence, the relative speed of the contacts in the opening operation becomes twice as fast as that in the preceding embodiments. Thus, the decay of the contact is reduced, and the reliability and the durability of the circuit breaker can be greatly improved.

In the particular embodiment shown in FIGS. 7A and 7B, an electrically conductive magnetic substance member 14 is made of two separate sections 41 and 42 having electrical contact means 6 and 7 secured thereon respectively. One of the two sections, say 41 is movable to complete the circuit between the electrical contacts 6 and 7 at one position thereof and to interrupt said circuit through said contacts at another position thereof. A magnet M is inserted into the space between the two sections of the magnetic substance member 14 in a swayable manner. With such construction of the circuit breaker, separate supporting means for the contacts 6 and 7 can be eliminated and the overall mechanism of the circuit breaker can be greatly simplified.

Referring to FIGS. 7A and 7B, 1 is a base, 11 and 12 terminals, 41 a movable section of the magnetic substance member 14 pivotally supported by a shaft 43' at the lower end thereof, 6 a movable contact secured to the tip end of the section 41, and 42 a fixed section of the member 14 having a stationary contact 7 secured to the top end thereof so as to be engageable with the movable contact 6. The movable section 41 is biased in a direction away from the fixed section by means of a spring 44, and connected to the terminal 11 by a lead wire 10.

When the circuit through the contacts 6 and 7 is closed, the movable section '41 takes a position substantially in parallel with the fixed section 42, and the electric current flowing in the two sections through the contacts '6 and 7 produces a force acting on the two sections in a direction to separate them away from each other.

The movable section 41 is made of magnetic substance, so that it may be attracted by the magnet M and locked thereto. The magnet M can be held stationary during normal operation of the circuit breaker, as will be described in detatil hereinafter. Thereby, the movable contact 6 carried by the section 41 can be locked in contact with the statioinary contact 7 held by the fixed section 42 to complete the electric circuit through the contact means 6 and 7, while overcoming both the elastic force of the spring 44 and the electromagnetic force due to an electric current through the sections 41 and 42.

It is of course permissible to form the movable section 41 as a composite member comprising an electric conductor element to carry an electric current at a low loss and a magnetic substance element to cause the above locking etfects.

In the embodiment of FIGS. 7A and 7B, there are provided a pivoted operative knob 45 having the magnet M formed as an integral part thereof and a permanent magnet 46 atfixed to the base 1 in such a manner that the magnetic attraction between the permanent magnet 46 and the magnet M acts to lock the operating knob 45 as attracted by the permanent magnet 46.

Under overcurrent conditions, the movable member 41 is rotated away from the magnet M to open the circuit between the contacts 6 and 7 in the same manner as the preceding embodiments. In order to reclose the circuit breaker, it is necessary to turn the operating knob 45 away from the permanent magnet 46 until the movable section 41 is attracted to the magnet M held by the knob 45. Then, as the operating knob 45 is turned back to the permanent magnet 46, the movable section 41 is also brought back to the fixed section 42 for reclosing the circuit between the contacts 6 and 7.

If the overcurrent conditions are sustained at the time when the circuit breaker is reclosed, the movable section 41 will be again separated from the fixed portion 42 for interrupting the overcurrent by opening the circuit between the contacts 6 and 7, as described above. Thus, the so-called trip free operation is ensured.

The normal on-off operation of the circuit breaker can be carried out by turning the operating handle 45 toward and away from the permanent magnet 46.

What I claim is:

1. An automatic circuit breaker comprising, a casing, at least one magnet pivotally secured to said casing so as to selectively assume a first and a second position, a pair of external-circuit-connecting means mounted on said casing, a conductor electrically connected to one of said external-circuit-connecting means and having at least one straight portion made of magnetic substance, said straight conductor portion disposed in the proximity of said magnet so as to be magnetically attracted by said magnet, a first contact connected to the other one of said externalcircuit-connecting means, a second contact secured to said conductor, said second contact engaged with said first contact so as to complete a circuit between said pair of external-circuit-connecting means through said conductor when said magnet is at said first position with said straight conductor portion attracted thereto, and a bias spring means producing a bias force tending to separate said straight conductor portion and said magnet from each other, whereby said circuit between said external-circuit connecting means is completed and interrupted for a load current by selectively placing said magnet at said first and said second positions, respectively, while upon occurrence of an overcurrent, the magnetic attraction between said magnet and said straight conductor portion is reduced and surpassed by said bias force, resulting in separation of said magnet and said straight conductor portion from each other to disengage said first contact from said second contact for interrupting said circuit between said eX- ternal-circuit connecting means.

2. An automatic circuit breaker comprising, a casing, a magnet pivotally secured to said casing so as to selectively occupy a first and a second angular position, a pair of external-circuit-connecting means mounted on said casing, a straight conductor electrically connected to one of said external-circnit-connecting means and pivotally secured to said casing in the proximity of said magnet, said straight conductor made of magnetic substance so as to be normally attracted by said magnet, a stationary contact electrically connected to the other one of said external-circuit-connecting means, a moving contact secured to said straight conductor, said moving contact engaged with said stationary contact so as to complete a circuit between said external-circuit-connecting means through said straight conductor when said magnet is at said first position with said straight conductor attracted thereto, and a bias spring biasing said straight conductor away from said magnet, whereby a circuit between said external-circuit-connecting means is completed and interrupted for a load current by selectively turning said magnet to said first and said second positions, respectively, while upon occurrence of an overcurrent, the magnetic attraction between said magnet and said straight conductor is reduced and surpassed by the force of said bias spring to force the straight conductor away from said magnet for interrupting said circuit between said externalcircuit-connecting means.

3. An automatic circuit breaker comprising, a casing, a magnet pivotally secured to said casing so as to selec- 1 1 tively occupy a first and a second position, a pair of external-circuit-connecting means mounted on said casing, a conductor electrically connected to one of said pair of external-circuit-connecting means and having a straight portion made of magnetic substance and a resilient conductor portion connected in series with said straight portion and secured to said casing at one end thereof, said straight conductor portion disposed in the proximity of said magnet so as to be magnetically attracted by said magnet, a stationary contact connected to the other one of said external-circuit-connecting means, a moving contact secured to the opposite end of said resilient conductor portion, and a lever operatively connected to said magnet and adapted to urge said moving contact to said stationary contact so as to complete a circuit between said external-circuit-connecting means through said conductor when said magnet is at said first position with said straight conductor portion attracted thereto, said resilient conductor portion biasing said magnet away from said straight conductor portion through said lever, whereby said circuit between said external-circuit-connecting means is completed and interrupted for a load current by selectively placing said magnet at said first and said second positions, respectively, while upon occurrence of an overcurrent, the magnetic attraction between said magnet and said straight conductor portion is reduced and surpassed by said biasing force, resulting in separation of said magnet from said straight conductor portion to disengage said moving contact from said stationary contact for interrupting said circuit between said external-circuit-connecting means.

4. An automatic circuit breaker according to claim 3 and further comprising a second pair of external-circuitconnecting means, a second conductor extending between said second pair of external-circuit-connecting means and having a straight portion and a resilient portion identical to those of said conductor, a second stationary contact secured to one of said second pair of external-circuit-connecting means, a second moving contact secured to said resilient portion of said second conductor so as to be engageable with said second stationary contact, and a second lever operatively connected to said magnet and adapted to urge said second moving contact to said second stationary contact when said magnet is at said first position, wherein said magnet is attracted to and separated from said straight portions of said first and second c-onductors simultaneously, whereby said automatic circuit breaker acts as a double pole circuit breaker.

5. An automatic circuit breaker comprising, a casing, a first and a second lever pivotally secured to said casing at one end thereof so as to selectively assume a first and a second angular position, respectively, a first and a second magnet secured to the free ends of said first and second lever, respectively, a pair of external-circuit-connecting means mounted on said casing, a conductor electrically connected to one of said external-circuit-connecting means and having a pair of series-connected straight portions and a biased portion connected in series to said straight portions, said straight portions secured to said casing in the proximity of said first and second magnets and made of magnetic substance so as to magnetically attract said first and second magnets, said biased portion secured to said casing at one end thereof and related to said first lever so as to bias said first magnet away from said straight portion, a first contact mounted on the opposite end of said biased portion, a second biased conductor member electrically connected to the other one of said external-circuit-connecting means and secured to said casing at one end thereof, said second biased conductor member related to said second lever so as to bias said'second magnet away from said straight portions, and a second contact mounted on the opposite end of said second biased conductor member, said first lever urging said first contact toward said second contact when said first lever is at said first angular position with said first magnet attracted to one of said straight portions, said second lever urging said second contact toward said first contact when said second lever is at said first position with said second magnet attracted to the other one of said straight portions, said biased portion of said conductor biasing said first contact away from said second contact, said second biased conductor member biasing said second contact away from said first contact, whereby a circuit between said external-circuit-connecting means is completed and interrupted for a load current by turning said first and second levers to said first and second positions, respectively, while upon occurrence of an overcurrent, the magnetic attraction between said magnets and said straight conductor portions is reduced and surpassed by said bias ing force to force the magnets away from the straight conductor portions for interrupting said circuit between said external-circuit-connecting means.

6. An automatic circuit breaker according to claim 2 and further comprising a second permanent magnet secured to said casing, wherein said stationary contact is mounted at the top of a conductor plate issuing from said casing with a certain angular relation therewith, said pivotally secured magnet is attracted by said second permanent magnet at said first position while being separated therefrom at said second position thereof, and said straight conductor portion extends in parallel with said conductor plate when said pivotally secured magnet is at said first position with said straight conductor portion attracted thereto.

References Cited UNITED STATES PATENTS 1,687,515 10/1928 Roberson 335-18 2,467,720 4/ 1949 Austin 335-18 2,911,502 11/1959 Edsall 200-116 3,127,488 3/ 1964 Bodenschatz 335-16 3,215,799 11/1965 Clausing 335-18 3,218,406 11/1965 Gornperts 335-154 OTHER REFERENCES IBM Technical Disclosure Bulletin, J. W. Berkman, vol. 4, No. 11, April 1962.

BERNARD A. GILHEANY, Primary Examiner.

H. BROOME, Assistant Examiner.

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