US3702980A

US3702980A - Circuit breaker

Info

Publication number: US3702980A
Application number: US149167A
Authority: US
Inventors: Yasuo Kasahara
Original assignee: Nakatani KK
Current assignee: Nakatani KK
Priority date: 1971-06-02
Filing date: 1971-06-02
Publication date: 1972-11-14
Anticipated expiration: 1989-11-14

Abstract

A permanent magnet and a conductor of magnetic material which is attracted by the magnet are arranged in biased relationship to each other so as to move away from each other. Current flow occurs through the conductor in substantial alignment with the direction of that portion of magnetic flux emanating from the magnet that passes through the conductor. When the current has a great magnitude such as short circuit current, the magnet and the conductor are pulled apart. The resulting movement of the conductor is effective to interrupt the current path. At least one pole of the magnet is attached with a magnetizable member for increasing the speed of interruption.

Description

United States Patent 1 3,702,980 Kasahara [451 Nov. 14, 1972 4] CIRCUIT BREAKER Primary Examiner-Harold Broome 72 I W t r: Y KHBMH T k J Attorney-William D. Hall, Elliot 1. Pollock, Fred C. 1 n o asuo 0 yo apan Philpitt, George Vande Sande, Charles F. Steininger [73] Ass1gnee: Kabushikikalsha Nakatani, Tokyo, d R b rt R, Priddy Japan; a part interest 22 Filed: June 2,1971 [57] ABSTRACT [21] APP] Nod 149,167 A permanent magnet and a conductor of magnetic material which is attracted by the magnet are arranged in biased relationship to each other so as to move [52] U.S. Cl ..335/16, 335/170 away f each other Current fl occurs through [51] lltl. Cl. ..H0lh 77/10 the conductor in substantial alignment i the [58] Fleld of Search ..335/16, 195, 170, 179, 204 direction of that portion of magnetic flux emanating from the magnet that passes through the conductor. [56] References C'ted When the current has a great magnitude such as short UNITED STATES PATENTS circuit current, the magnet and the conductor are pulled apart. The resulting movement of the conduc- 3453566 7/ 1.969 Kasahara tor is effective to interrupt the current path. At least 3,605,047 9/1971 Kasahara ..335/170 one pole of the magnet is attached with a magnetizable member for increasing the speed of interruption.

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m K015 y LY wmq CIRCUIT BREAKER BACKGROUND OF THE INVENTION The present invention relates to a circuit breaker which provides an electrical interruption of a circuit upon current flow in excess of a given magnitude therethrough.

The inventor has previously proposed in US. Pat. No. 3,453,566 issued July 1, 1969, and entitled Automatic Current Limiting Circuit Breaker the provision nitude to hold the conductor attracted thereto against the biasing force. The subject matter of the present invention distinguishes from that of my prior U. S. Pat. No. 3,453,566 and No. 3,605,047 in the orientation of magnetization of the permanent magnet relative to the direction of current flow through the conductor. More particularly, in the present invention the conductor is netic flux produced by the current flow through the conductor and the flux emanating from the permanent magnet. Accordingly, the disposition of the magnet and the direction of current flow through the conductor have been chosen such that both of the fluxes run substantially in parallel relationship. Whenan extremely high current passes through the conductor of such circuit breaker, it is likely that the permanent magnet undergoes magnetization by the flux of extreme magnitude that results from the current flow. The magnetization will vary the force of attraction that acts between the magnet and the conductor, with consequent change in the interruption characteristic of the device or even the loss of the proper function as a circuit breaker. Also, the interruption characteristic may be disadvantageously influenced by the direction in which the current passes through the conductor.

It is an object of the present invention to provide a circuit breaker in which an instantaneous flow of high current does not cause demagnetization of a permanent magnet used therein, thereby maintaining its characteristic unchanged.

It is another object of the invention to provide a circuit breaker having an interruption characteristic which is not influenced by the direction of current flow.

It is a further object of the invention to provide a circuit breaker which has an interruption characteristic not influenced by the current to be interrupted and the direction thereof and which provides a rapid interruption, thereby achieving a high current limiting capability.

It is still another object of the invention to provide a circuit breaker which performs an instantaneous interruption of short circuit current without causing any change in characteristic and which performs a delay interruption for a current relatively slightly in excess of the rated current.

SUMMARY OF THE INVENTION In accordance with the present invention, a permanent magnet and a conductor of magnetic material are arranged so as to be capable of relative movement, and a biasing force is applied thereto in a direction to urge them to move away from each other. The force of attraction exerted by the magnet is of sufficient magadapted to carry current in a direction which is sub stantially parallel to the direction in which the flux emanating from the magnet passes through the conductor. When the current exceeds a given magnitude, a relative movement occurs between the magnet and the conductor to provide a circuit interruption. In the device according to the invention, high current through the conductor instantaneously causes both the conductor and magnet to be magnetized to the identical polarities, the resulting force of repulsion serving the intended interruption. Hence, it is noted that the purpose of the magnet here is to hold the conductor in position. Because of the quadrature relationship between the magnet flux and the flux resulting from current flow, the possibility that the magnet may be demagnetized is eliminated. Upon reversal of the direction of current flow, there is a similar force of repulsion acting, so that since the attraction exerted by the magnet remains the same, the identical interruption characteristic is obtained for a reversed current flow.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the invention will become apparent from the following description thereof with reference to several embodiments shown in the drawings, in which:

FIG. 1 is a front elevation, with front plate removed and partly in section, of a circuit breaker according to one embodiment of the invention,

FIG. 2 is a section along the line A-A shown in FIG. 1,

FIG. 3 is a plan view of a conductor of magnetic material,

FIG. 4 is a similar view to FIG. 1 of another embodiment of the invention, with front plate removed,

FIG. 5 is a plan view of another example of the conductor of magnetic material,

FIG. 6 is a similar view to FIG. 1, but showing a further embodiment of the invention,

FIG. 7 graphically shows a example of the waveform of current interrupted,

FIG. 8 is a front elevation of a testing equipment in which the invention is applied and FIG. 9 graphically shows the test current and interruption waveform.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2 the circuit breaker includes a casing 1 which comprises, for example, a front plate 1a, rear plate 1b, top plate 10, bottom plate 1d, and a pair of left and right hand side plate 1e and 1f.

Terminal members

2 and 3 extend through the opposite ends of the bottom plate 1d so as to project outwardly of the casing 1. The terminal members have their inner ends bent toward each other, and hence are of an inverted L-shape. Across the inner ends of the

terminal members

2 and 3 extends a conductor of magnetic material 4, which has its one end securedto the terminal member 3 and its other end formed with a contact 6 which is positioned opposite a contact formed on the free end of the terminal member 2. A permanent magnet 7 is located adjacent the top plate and in opposing relationship with the conductor 4, the magnet 7 being carried at one end of a leaf spring 8 that extends parallel to the top plate 10 and has its other end secured to the right hand side plate 1f of the casing.

The conductor of magnetic material 4 comprises a lamination of a layer of magnetizable material 9, such as soft iron, soft ferrite or magnetic compensating steel, for example, and a conductive layer 10, formed of copper, for example. The magnetic layer 9 is located nearer the magnet 7. The magnet is oriented so that the flux emanating therefrom and passing through the conductor 4 runs substantially parallel to the current path through the conductor 4. Thus, in the example shown, the opposite poles S and N of the magnet 7 are positioned opposite to the both side plates 1e and If, and may be attached with pole pieces ll and l2, respectively, as required. The conductor 4 is urged away from the magnet. At this end, in the example shown, the terminal member 3 is formed of a conductive leaf spring, with its resilience tending to urge the conductor 4 toward the bottom plate 1d.

Above the permanent magnet 7 secured to the leaf spring 8 is formed an opening 13 in the top plate 10, and an operating member 14 is placed therein. The operating rod is adapted to be depressed downwardly against the resilience of the leaf spring 8 to move the magnet toward the bottom plate 1d.

In the arrangement shown, when the current applied across the

terminal members

2 and 3 is below a given magnitude, the magnet 7 and the conductor 14 are held attracted to each other with the

contacts

5 and 6 in electrical contact to permit electric conduction.

However, when a high current in excess of the given magnitude, such as short circuit current, passes through the

terminal members

2 and 3, such current instantaneously magnetizes both the magnetic layer 9 of the conductor 4 and the magnet 7 to identical polarities. Referring to FIG. 2, it will be seen that a current 16 that passes through the conductor 4 produces a flux 17, shown in dotted lines, which passes through the magnetic layer 9 as well as the magnet 7 or its pole pieces 10, l 1. As a result, both the layer 9 and the magnet 7 are magnetized to identical polarities, as indicated by letters ms and ms, with consequence that a force of repulsion acts therebetween. The sum of such a force of repulsion and the biasing force imparted by the conductive leaf spring 3 overcomes the force of attraction acted upon the layer 9 by the flux emanating from the magnet 7 itself, thereby causing the conductor 4 to move angularly toward the bottom plate 1d, as indicated by dotted line position. Thus the

contacts

5 and 6 are separated from each other to provide a circuit interruption.

To restore the engagement between the

contacts

5 and 6 again, the operating rod member is depressed inside the casing against the resilience of the leaf spring 8 to cause the magnet 7 to approach the magnetic layer 9 in dotted line position to hold it by attraction, whereupon the operating member 14 is released. Then the resilience of the leaf spring 8 serves to raise the magnet 7 together with the conductor 14 upwardly to bring the

contacts

5 and 6 into contact again. If the circuit in which the circuit breaker is connected still remains in the same condition as the initial occurrence of short circuit current, the current flow through the

terminal members

2 and 3 causes a rapid interruption again. Thus the device provides a trip-free operation.

While in the above description, the conductor 4 comprises a lamination of the magnetic layer 9 and the conductive layer 10, it may be formed of a single material. Such an example is shown in FIG. 4 wherein the conductor 4 consists of a monolithic plate of magnetic compensating steel, for example, which is both magnetizable and electrically conductive. In this example, the

terminal members

2 and 3 are mounted on the left and right hand side plate 1e and 1f, respectively, and the magnet 7 is secured to the inner side of the top plate 10 with its only one pole attached with a pole piece 11 that affords the sole contact with the conductor 4 directly.

In this instance, the flux emanating from the magnet 7 and passing through the conductor 4 is again made to have the same direction as the current flow in the latter, and at this end, the magnet 7 has N- and S-poles on the left and right hand sides thereof as viewed in FIG. 4. Consequently, it will be readily appreciated that when a high current in excess of a given magnitude passes through the

terminal members

2 and 3, such current instantaneously magnetizes both the conductor 4 and the contacting pole piece 1 l to the identical polarities to induce repulsion therebetween, thereby causing the conductor 4 to move angularly toward the bottom plate 1d and thus separating the

contacts

5 and 6. The operating member 14 is located in the bottom plate 1d and is surrounded by a coiled spring 19 which normally urges the operating member 14 to project externally of the casing. The operating member 14 of this example is adapted to be pushed inside the casing against the resilience of the spring 19 in order to abut against and push up the conductor 4, which has angularly moved toward the bottom plate 1d, into engagement with the pole piece 11. When the operating member 14 is pushed up, the conductor 4 is attracted to the magnet 7 after a projection 23 formed on the inner end of the operating member 14 has engaged and raised the terminal member 2 upwardly, and subsequently upon releasing the operating member 14, the terminal member 12 returns to its original position, thereby making an engagement between the

contacts

5 and 6 and allowing a trip-free operation.

With the device of the invention, a circuit interruption is not obtained as a result of above mentioned magnetization to the identical polarities and associated repulsion for a current level relatively slightly in excess of the rated current, that is, for a current which is from 300 to 1,000 percent of the rated current. However, when the conductor 4 is formed of a magnetic compensating steel, as illustrated in the embodiment of FIG. 4, a great variation in magnetic permeability that occurs in the magnetic compensating steel with temperature change enables a current flow of level in excess of the current rating to produce a circuit interruption as a result of reduced force of attraction exerted by the magnet 7 upon the conductor 4 which is overcome by the resilience or biasing force of the leaf spring, since the conductor 4 is sufficiently heated by Joule heat to exhibit a substantially reduced permeability. Such a delayed interruption can also be achieved in the embodiment shown in FIG. 1 by using, for example, a magnetic compensating steel, soft ferrite or the like for the magnetic layer9.

As illustrated in FIG. 5, the conductor of magnetic material 4 may be formed in its portion adjacent the magnet with

serrations

40, 41 which are close each other and extendin opposite directions from opposite sides of the conductor 4, thereby forming a current path 22 that extends perpendicularly to the flux emanating from the permanent magnet 7. The current flow through this path produces a flux which run parallel to the flux emanating from the magnet 7, and which therefore cancels or repels the latter flux. This results in a contribution to increasing the repulsion between the conductor and the magnet, thereby enabling even faster interruption.

In order to provide a faster interruption, the permanent magnet may be attached with a magnetic plate extending from at least one of its ends in opposing relationship with the conductor. As an example, FIG. 6 shows magnetic plates 20 and 21 arranged opposite the conductor of magnetic material and secured at one end to the exterior surface of the pole pieces 11 and 12, respectively. These magnetic plates 20, 21 have the same width as the conductor '4 and may be formed of the same material as the pole pieces 11 and 12. Preferably, these magnetic plates 20, 21 are adjustably mounted on the magnet 7 so as to make the distance (1 between the magnetic plate 20, 21 and the conductor 4 variable.

In this instance,- the magnetization, by the current flow through the conductor 4, of the magnet 7 as well as the conductor 4 to the identical polarities remains the same as before, and in addition, the magnetic plates 20, 21 are also magnetized to the same polarities as the conductor and the magnet are magnetized. As a consequence, repulsion acts also between the magnetic plates 20, 21 and the conductor 4, thus permitting separation between the conductor 4 and the magnet 7 at a correspondingly lower current level. Considering the condition inwhich the conductor 4 is held attracted to the magnet 7, the magnetic plate 20 and the opposing portion of the conductor 4 are magnetized to the same polarity N, while the magnetic plate 21 and the opposing portion of the conductor 4 are magnetized to the other same polarity S, so that repulsion is normally acting between these opposing parts and this permits an interruption to be achieved at a lower current level. Stated differently, for a given current level, the arrangement of FIG. 6 provides a more rapid interruption, and also the current limiting capability is improved.

It is seen that the greater the opposing area of the magnetic plates 20, 21 and the conductor 4 and the less the distance d therebetween, the lower is the current level required to provide a circuit interruption. Utilizing this fact, the distance a, may be made variable so that it is adjusted in accordance with the need of a particular application so as to vary the current level at which an interruption takes place. The magnetic plates 20, 21 may also be replaced by pole pieces 11, 12 having an increased thickness, the latter thus serving the combined functions of inherent pole pieces and magnetic plates. While the pole pieces ll, 12 originally have a given thickness determined by its inherent functioning, the device of the invention may utilize an increased thickness thereof in order to increase the opposing area with the conductor 4. If desired, the magnetic plates 20, 21 may be attached to the pole pieces 11, 12 with non-magnetic material interposed therebetween. In this instance, a varying degree of attraction may be available between the magnetic plates 20, 21 and the conductor 4.

Now experimental results will be described. A structure shown in FIG. 6 has been constructed using phosphor bronze as leaf spring material for the

terminal members

2 and 3. The terminal member 3 had such a resilience as to produce a biasing force of 20 grams acting on the conductor 4 toward the dotted line position. The conductor 4 was formed of a plate of magnetic compensating steel measuring 30 X 9 X 0.6 mm. The permanent magnet 7 had a longitudinal length of 4 mm along the conductor 4, a height of 8 mm and a width of 9 mm, with its force of attraction amounting to 30 grams. Pole pieces 11 and 12 each comprised a soft iron piece of 1.0 mm in thickness, Magnetic plates 20 and 21 of soft iron each measured 6 mm long, 9 mm wide and 0.6 mm thick, with the distance d, to the conductor 4 of 1.5 mm.

Contacts

5 and 6 were AgCu contacts of 3 mm indiameter and 1.5 mm in height. The circuit breaker of above construction had a rating of 3 amperes, at volts 60 Hz. When a positive half-wave having a peak current value of 66 amperes was supplied to the circuit breaker, the

contacts

5 and 6 opened in 3.6 milliseconds. The waveform of current observed is depicted in FIG. 7A, and the voltage across the

terminal members

2 and 3 is shown in FIG. 7B. It is noted that the current waveform is observable for a period of T during which time the voltage remains low, but increases subsequent to the interruption of the current. The period T required for the interruption is slightly less than a quarter of a cycle of the current applied.

When a negative half-wave having a peak current value of 44.7 amperes was supplied to this sample, the interruption occurred in 4 milliseconds.

To further demonstrate the effectiveness of the invention, another structure as shown in FIG. 8 was constructed. A base 30 of bakelite was formed with a pair of projections 31 and 32, on which were secured copper plates constituting the

terminal members

2 and 3, respectively, with a spacing of 30 mm therebetween. Across these copper plates was mounted the conductor 4 of non-annealed magnetic compensating steel, the conductor being 0.8 mm thick and 30 mm wide. The permanent magnet 7 was secured to one end of a pivotal arm 33 which was urged away from the conductor 4 by means of a coiled spring 34 with a biasing force of grams when the magnet is held attracted with the conductor as shown. The magnetic plate 20 of soft iron, 24 mm long, 30 mm wide and 0.8 mm thick, was mounted on the magnet 7 with d 2.7 mm spaced from the conductor 4. The force of attraction acting between the magnet 7 and the conductor 4 in their position shown measured 260 grams. Across the

terminal members

2 and 3 was applied at a voltage of 40 volts, 60I'Iz, stepped down from a 6000 volt supply, a current having an effective amplitude of 6650 amperes and an asymmetrical effective value of 8150 amperes (see FIG. 9A). In 7 milliseconds from the initiation of current supply, the magnet 7 moved apart from the conductor 4 and the arm 33 moved about the pivot 35. The angular movement of the arm was utilized to open a switch (not shown) of the present detection circuit, whereby the alternating voltage (FIG. 93) applied to this circuit terminated.

When a positive going current having an effective value of 3,770 amperes was applied during its rising period to this structure, the magnet 7 moved apart from the conductor 4 in 20 milliseconds. With a negative going current having an effective value of 3,810 amperes and applied during the negative rising period, it took 32 milliseconds until the magnet separated. With a current of I 10 amperes, the magnet 7 separated in 12 seconds. For a current of 444 amperes, the magnet 7 moved apart in 0.5 second. These two latter cases represent the so-called delayed operations in which the conductor 4 is heated by Joule heat owing to the current flow, to reduce its magnetic permeability.

-While the invention has been described with reference to particular embodiments thereof, it should be apparent that various modifications and changes will readily occur to those skilled in the art. Therefore, it is intended that the appended claims cover all such modifications and changes asfall within the scope of the invention.

What is claimed is:

1. A circuit breaker comprising a permanent magnet, conductor of magnetic material normally held attracted to the magnet and capable of relative movement with respect to the magnet, means for providing a biasing force to move the magnet and the conductor apart from each other, means for connectingthe conductor in circuit so as to cause a current flow through the conductor in a direction substantially parallel to the direction of that portion of magnetic flux emanating from the magnet which passes through the conductor, and means for interrupting a circuit in response to the relative movement between the magnet and the conductor, said movement occurring when said current flow exceeds a given magnitude.

2. A circuit breaker according to claim 1 in which said conductor of magnetic material comprises a magnetic layer positioned adjacent the magnet, and a conductive layer laminated therewith. I

3. A circuit breaker according to claim 1 in which the conductor comprises a magnetic material which undergoes a relatively large variation in magnetic permeability with a change in temperature.

4. A circuit breaker according to claim 1 in which the conductor comprises a magnetic material which undergoes little variation in magnetic permeability with a change in temperature.

5. A circuit breaker according to claim 1, including reset means to restore the conductor and the magnet into an attractively associated relationship after they have moved apart.

6. A circuit breaker according to claim 1 in which the conductor is held in place by a conductive leaf spring, the resilience of which affords said biasing force to move the conductor and the magnet apart from each other- 7. A circuit breaker according to claim 5 in which the magnet is mounted on a spring, and said reset means is eflective to cause the magnet to approach the conductor that has moved apart therefrom and to hold it attracted, against the resilience of said spring, the resilience of the spring being effective to return the magnet and the conductor that is held attracted thereto to their original position.

8. A circuit breaker according to claim 1, further including a magnetic member attached to at least one pole of the magnet and arranged adjacent the conductor in opposing relationship therewith.

9. A circuit breaker according to claim 1, further including a pair of magnetic members attached to opposite poles of the magnet and arranged adjacent the conductor in opposing relationship therewith.

10. A circuit breaker according to claim 1, in which the conductor is arranged stationarily and the magnet is mounted on an angularly movable arm, said arm providing a mechanical output to actuate a switch means in response to the angular movement of the arm occurring when the current through the conductor exceeds a given magnitude, said switch means interrupting a circuit other than the circuit in which said conductor is connected.

Claims

1. A circuit breaker comprising a permanent magnet, conductor of magnetic material normally held attracted to the magnet and capable of relative movement with respect to the magnet, means for providing a biasing force to move the magnet and the conductor apart from each other, means for connecting the conductor in circuit so as to cause a current flow through the conductor in a direction substantially parallel to the direction of that portion of magnetic flux emanating from the magnet which passes through the conductor, and means for interrupting a circuit in response to the relative movement between the magnet and the conductor, said movement occurring when said current flow exceeds a given magnitude.

2. A circuit breaker according to claim 1 in which said conductor of magnetic material comprises a magnetic layer positioned adjacent the magnet, and a conductive layer laminated therewith.

6. A circuit breaker according to claim 1 in which the conductor is held in place by a conductive leaf spring, the resilience of which affords said biasing force to move the conductor and the magnet apart from each other.

7. A circuit breaker according to claim 5 in which the magnet is mounted on a spring, and said reset means is effective to cause the magnet to approach the conductor that has moved apart therefrom and to hold it attracted, against the resilience of said spring, the resilience of the spring being effective to return the magnet and the conductor that is held attracted thereto to their original position.