US3721786A

US3721786A - Circuit breaker

Info

Publication number: US3721786A
Application number: US00203234A
Authority: US
Inventors: Y Yoshioka
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1970-12-11
Filing date: 1971-11-30
Publication date: 1973-03-20
Anticipated expiration: 1990-03-20
Also published as: DE2161507A1; DE2161507B2; JPS5019330B1; FR2117646A5; IT943214B

Abstract

A puffer type circuit breaker is provided in which an arc extinguishing gas is compressed and released into an arc between contacts upon the initiation of an interrupting operation. The means for compressing the arc extinguishing gas is actuated by an electromagnetic driving means comprising at least two electromagnetic driving units provided by a primary coil and a short ring electromagnetically coupled to said primary coil, and the electromagnetic driving means exhibits a stepped electromagnetic driving force characteristic in response to the displacement in the driving direction when a predetermined current flows in the primary coil. Thus, current arcs for a range of small and medium currents may be extinguished by means of gases compressed by the driving forces generated in the neighborhood of the upper step portion of the stepped electromagnetic driving force characteristic and directed to the current arcs, while current arcs for a range of large currents may be extinguished by means of gases compressed by the driving forces generated in the neighborhood of the lower step portion of the stepped electromagnetic driving force characteristic and directed to the current arcs.

Description

United States Patent 1191 Yoshioka MSJMarch 20, 11973 Primary Examiner-Robert S. Macon AttorneyCraig, Antonelli & Hill [57] ABSTRACT A puffer type circuit breaker is provided in which an arc extinguishing gas is compressed and released into an arc between contacts upon the initiation of an interrupting operation. The means for compressing the arc extinguishing gas is actuated by an electromagnetic driving means comprising at least two electromagnetic driving units provided by a primary coil and a short ring electromagnetically coupled to said primary coil, and the electromagnetic driving means exhibits a stepped electromagnetic driving force characteristic in response to the displacement'in the driving direction when a predetermined current flows 'in the primary coil. Thus, current arcs for a range of small and medium currents may be extinguished by means of gases compressed by the driving-forces generated in the neighborhood of the upper step portion of the stepped electromagnetic driving force characteristic and directed to the current arcs, while current arcs for a range of large currents may be extinguished by means of gases compressed by the driving forces generated in the neighborhood of the lower step portion of the stepped electromagnetic driving force characteristic and directed to the current arcs.

7 Claims, 12 Drawing Figures PATENTEnmzolsu SHEET 10F 6 INVENTOR YOSHI 0 YOSHIOKA ATTORNEYS PATENTEUmzoms 3.7211786 OVERALL ELECTROMAGNETIC DRIVING FORCE u COMMUTATIONP W -T|ME (ms) IEERUPTQ PE SECOND 2 ARC E SEPARATION P'\ INTERRUPTING a; PERIOD ATTORNEYS PATENTEBHAmms 3,721,786

SHEET l 0F 6 FHG. 5o

INVENTOR Y HI Y0smo| A ATTO R N EYE PATENTEUIIAII20 I975 OVERALL INTERRUPTING CURRENT ELECTROMAG DRIVING FORCE SHEET 8 OF 6 COMMUTATION TIME (ms) PERIOD F IRs \SECOND INTERRUPT'NG INTERRUPTING ARC PERIOD PERIOD SEPARATION INVENTOR Y05HIO Y0 H|0KA ATTORNEY5 large CIRCUIT BREAKER BACKGROUND OF THE INVENTION produced upon the opening of contacts in the presence of an arc extinguishing gas atmosphere is extinguished by means of said gas compressed and directed to the are upon the initiation of an interrupting operation.

2. Description of the Prior Art Electromagnetic driving mechanism of the type designed to convert the electromagnetic energy of an interrupting current into a force for compressing an arc extinguishing gas are disclosed in US. Pat. application Ser. No. 582,925 (Japanese Patent Publication No. 8052/1968) in which the electromagnetic attractive and repulsive forces produced among three coils are utilized; and in the applicants copending U.S. Pat. application Ser. No. 821,319 filed May 2, 1969, now U.S. Pat. No. 3,621,171 issued Nov. 16, 1971 in which the electromagnetic driving mechanism comprises a primary coil having a large axial length and a short ring or coil also having a large axial length and disposed in the associated relation with the primary coil, thereby taking advantage of the electromagnetic repulsion force which is produced by a current flowing into the primary coil and an induced current produced in the short ring to cancel the magnetic flux due to the current flowing through the primary coil. These prior art devices have an advantage of the electromagnetic force increasing in proportion to the square of an interrupting current and thus ensuring positive supply of a high pressure gas and in these prior art devices it appears that an extremely large electromagnetic force or the driving force can be provided for interrupting a large current thus ensuring efficient interruption. In fact, however, there have been various problems with the prior art devices in that if the compression of a gas is optimalized to suit large interrupting currents (such as short circuit currents), the electromagnetic force available at the intermediate or small current values is reduced and thus efficient interruption cannot be ensured, while on the other hand if such an optimalization is effected to suit the intermediate or small currents, for the large interrupting currents a quite strong electromagnetic force is generated thus giving rise to such difficulties as damage to the primary coil, hard excitation in the primary coil, reaction force to the contacts operating mechanism, impact loads on the various mechanism of the device and so on.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a circuit breaker equipped with an improved electromagnetic driving means and thus capable of performing efficient interruption over a range of small and large interrupting currents.

It is another object of the present invention to provide a circuit breaker in which the electromagnetic driving means is designed to exhibit a stepped electromagnetic driving force characteristic, in response to the displacement in the driving direction when a predetermined current flows therein, thereby suppressing the inductance of the primary coil at the time the current to be interrupted is diverted into the primary coil to ensure an effective divertion.

A further object of the present invention is to provide a circuit breaker equipped with an electromagnetic driving means designed to exhibit a stepped electromagnetic driving force characteristic in response to the displacement in the driving direction when a predetermined current flows therein, whereby even if the discharge occurring before the closing of the contacts causes a current flow in the primary circuit, the resulting electromagnetic driving force is kept sufficiently small thereby ensuring a smooth closing operation.

The above and other objects and advantages of the present invention will be readily apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.

The circuit breaker according to the present invention comprises at least a pair of contacts adapted to part to induce an are, an electromagnetic driving means comprising at least two electromagnetic driving units provided by a primary coil and a short ring or coil electromagnetically coupled to said primary coil, the overall electromagnetic driving force characteristic of said electromagnetic driving means representing the electromagnetic force generated in accordance with the movement of the said means taking the form of a stepped curve in response to the displacement in the driving direction when a predetermined current flows into said primary coil, current diverting means for diverting the current to be interrupted into said primary coil, means adapted to be actuated by said electromagnetic driving means to compress an arc extinguishing gas, and a nozzle for directing a high pressure gas produced by said compressing means into said are, whereby the gas compressed by the driving force generated in the neighborhood of the upper step portion of said electromagnetic driving force characteristic is directed into arcs for a range of small and intermediate currents and the gas compressed by the electromagnetic force generated mainly in the neighborhood of the lower step portion of said characteristic is directed into arcs for the large currents.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of an embodiment of the circuit breaker of the present invention showing part thereof in longitudinal section.

FIG. 2 is a longitudinal sectional view showing the interrupting section of the circuit breaker shown in FIG. 1.

FIGS. 3a and 3b are diagrams useful for explaining the generation of driving force by the electromagnetic driving means in the breaker of FIG. 2.

FIG. 4 is a diagram useful for explaining the relationship between the overall electromagnetic driving force characteristics and the interruption of current.

FIGS. 5a and 5d are schematic diagrams showing in longitudinal section various modifications of the electromagnetic driving means used in the circuit breaker of FIG. ll.

FIG. 6 is a longitudinal sectional view of another embodiment of the circuit breaker of the present invention showing the interrupting section thereof.

FIG. 7 is a perspective view showing a component part of the circuit breaker of the invention illustrated in FIG. 6 with a portion broken away.

FIG. 8 is a diagram useful for explaining the relationship between the overall electromagnetic driving force and the interruption of current in a further embodiment of the circuit breaker according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, a grounded tank 1 contains sulfur hexafluoride (SF sealed thereinto under the pressure of 3.5 kg/cm for example, and in this atmosphere an interrupting section 2 which is not shown in detail is insulated and supported by an insulating support 3. Current is fed to the interrupting section 2 by way of a pair of bushings 4 and 5.

The bushing are similar in construction and as will be seen from the figure showing the bushing 5 in section the bushing 5 comprises a terminal strip 6, a sleeve 7, a metal tube 8, a conductor 9 and an insulating spacer l0, and the conductor 9 is insulated from the metal tube 8 and the grounded tank 1 by the sleeve 7 and the insulating spacer 10.

The bushings 4 and 5 are filled with the same SF gas as sealed into the grounded tank 1.

A current transformer 11 is also mounted on the outer periphery of the metal tube 8 to detect the passage of an excessive current through the conductor 9. The movable parts of the interrupting section 2 are actuated in either of the closing direction or the interrupting direction by an operating linkage provided on the outside of the grounded tank 1 and comprising an operating lever 13 extending through an air tight chamber 12 disposed at one end of the grounded tank 1 and an insulating rod 14 connected to the operating lever 13.

Next, the construction of the interrupting section 2 will be explained in detail with reference to FIG. 2.

In the figure, a movable main contact 22 and a movable arcing contact 23 are arranged opposite to and coaxially with a hollow fixed contact 21 which is electrically connected to the conductor in the bushing 4, with the

contacts

22 and 23 being secured to an electrically conducting operating rod 24. The operating rod 24 itself is connected to the insulating rod 14 by a suitable securing means 25. The operating rod 24 carries a puffer cylinder 26 and a puffer piston 28 constituting compressing means 27 with the puffer cylinder 26 is secured to the grounded tank 1 by means ofa short ring 29 and the insulating support 3. The puffer piston 28 and the short ring 29 are integrally formed with an electrically conducting metal and a current collector 30 is disposed between the puffer piston 28 and the operating rod 24.

Thus, with the circuit breaker in the closed position, current flows in a path through the fixed contact 21, movable main contact 22, operating rod 24, current collector 30, puffer piston 28 and short ring 29.

The operating rod 24 is provided through the intermediary of a stay 31 with a primary coil 32 which constitutes an electromagnetic driving means with the short ring 29 and thus a current path is provided through the operating rod 24, stay 31, primary coil 32,

current collector 34 and short ring 29 by means of a sliding plate 33 mounted on the outside of the primary coil 32 and the current collector 34 disposed on the lower end of the short ring 29. However, with the circuit breaker in the closed position, most of the current flows through the first-mentioned current path owing to the inductance of the primary coil 32. The divertion of a current into the latter current path takes place when an insulating layer 35 disposed on a portion of the outer periphery of the operating rod 24 interrupts the path between the operating rod 24 and the current collector 30 upon the interrupting operation.

As an interruption instruction is given so that the movable main and arcing

contacts

22 and 23 are separated from the fixed contact 21 by means of the insulating rod 14 and the operating rod 24, an arc is produced between the fixed contact 21 and the movable arcing contact 23. On the other hand, the movement of the operating rod 24 causes, as previously mentioned, current flow through the primary coil 32 and an electromagnetic repulsion force produced between the primary coil 32 and the short ring 29 is transmitted to the operating rod 24 by way of the stay 31, so that the puffer cylinder 26 is heavily moved and thus SF gas in the compressing means 27 is compressed producing a high pressure gas which is in turn directed through an insulating nozzle 36 into the arc between the contacts extinguishing the arc and thus completing the interruption.

The electromagnetic repulsion produced between the short ring 29 and the primary coil 32 will be explained hereunder with reference to FIGS. 3a and 3b.

As shown in FIG. 3a, the primary coil 32 comprises the coil wire wound at equal distance and then finished, as a whole, into a coil by means of molding, for example. On the other hand, the short ring 29 comprises two

short ring units

29a and 29b spaced away from the primary coil 32 at different distances. In the figure, the current collector 34 disposed on the short ring 29 and the sliding plate 33 mounted on the primary coil 32 are omitted.

When a predetermined current flows through the primary coil 32, an electromagnetic force of repulsion is produced between the primary coil 32 and the short ring 29, but the values of the induced currents in the

short ring elements

29a and 29b differ from each other owing to the different distances between these elements and the primary coil 32. For simplicity of discussion, let it be here assumed that the short ring elements 290 and 29b are provided separately. Then, if the center of the primary coil 32 moves to the right of the central axis a of the short ring element 29a, the electromagnetic force of repulsion generated between the primary coil 32 and the short ring element 29a results in a force tending to drive the primary coil 32 to the right, whereas when the center of the primary coil 32 comes to the left of the central axis of the short ring element 29a, generated therebetween tends to drive the primary coil 32 to the left. Thus, letting in FIG. 3 b the rightward drive of the primary coil 32 be represented in the upper portion above the one-dot chain line and the leftward drive of the coil in the lower portion blow the one-dot chain line, if then the primary coil 32 is moved in the axial direction of the operating rod 24 and the values of the electromagnetic repulsion force the electromagnetic force of repulsion at the various points are obtained and represented by a curve, the electromagnetic repulsion force characteristic is given as shown by a dotted line A in FIG. 3 b. In the similar manner, the electromagnetic repulsion force characteristic between the primary coil 32 and the short ring element 29b can be represented by a curve designated as a curve B.

Comparison between the two characteristics indicates that the maximum value, of the curve A is lower than that of the curve B, since the distance between the short ring element 29a and the primary coil 32 differs from that between the short ring element 29b and the primary coil 32.

Since it is in fact the primary coil 32 that actuates the operating rod 24, the driving force can be represented by combining the curves A and B together and the overall characteristics is thus as shown in FIG. 3 b by a solid line C.

Assuming that the extent of movement of the primary coil 32 is between a position X and a right position Y on the one-dot chain line in FIG. 3b, it will be readily apparent that the overall electromagnetic repulsion force characteristic obtained between the short ring 29 and the primary coil 32 is represented by a stepped curve.

According to the present invention, the driving forces corresponding to the stepped portions of the overall electromagnetic repulsion force characteristic are employed for the purpose of compressing an arc extinguishing gas.

For this purpose, the parting distance between the fixed contact 211 and the movable arcing contact 23 can be practically expressed in terms of the distance between the positions X and Y plus the distance traveled by the primary coil 23 before the time that an interrupted current is diverted into the primary circuit 32.

Next, the relationship between the stepped electromagnetic driving force (repulsion force) and the interruption of current will be explained with reference to FIG. 4.

In FIG. 4, curves D and B shows stepped electromagnetic driving forces obtainable for different values of current flowing through the primary coil 32 and, as previously mentioned, the driving forces are proportional to the square of the currents. Thus, it will be readily understood that the curve D shows the electromagnetic driving force characteristic for the small currents and the curve E shows the characteristic for the large currents and that the characteristic curve changes from the curve D to the curve E and vice versa with the variation of current values.

In this connection, the graph of FIG. 3b shows the relationship between the displacement in the driving direction and the electromagnetic driving force. In other words, it can be considered that FIG. 3b shows the curves obtainable when the primary coil 32 is moved at a constant speed relative to the short ring 29.

However, in the event that an electromagnetic driving force is produced between the primary coil 32 and the short ring 29 so that the primary coil 32 is accelerated by the driving force thus produced, the electromagnetic driving force increases as the current flowing through the primary coil 32 increases and thus the velocity of movement of the primary coil 32 increases. The characteristic curve therefore takes a compressed form with respect to the time. In FIG. 4, the characteristic curves D and E show the electromagnetic driving force characteristics taking into account the aforesaid changes with respect to the time due to the variation of current values.

Returning to FIG. 4, since the current that flows into the circuit breaker is an AC current, the value of the current successively varies with the lapse of time as shown by a curve F and thus the actual electromagnetic driving force varies with the lapse of time as shown by curvesG and H.

When an arc is formed, the arc is cooled and extinguished by means of a blast of an arc extinguishing gas directed thereinto for a certain period of time. Then, assuming that a straight line I represents the driving force (electromagnetic repulsion force) for providing a gas pressure required to ensure positive interruption, at a point in the vicinity of the first current zero point 2 following the initiation of interruption operation the current is diverted into the primary coil 32 thus producing an electromagnetic force of repulsion. In this case, however, no large electromagnetic driving force is obtained owing to the position at this time of the moving primary coil 32 and thus even at the second current zero point I, for the contacts 211 and 23 the extinction of the arc is not effected maintaining the arc in existence. As the primary coil 32 is moved still further so that the electromagnetic driving force gradually grows and eventually exceeds the straight line I, a strong blast of gas is directed into the are thereby extinguishing it at a point near the third current zero point The current waveform at this time is designated at F IN THE FIGURE) When a large current is to be interrupted, the electromagnetic driving force generated as shown by a curve H readily exceeds the straight line I and thus the extinction of the arc is easily effected at a point near the first current zero point t subsequent to the divertion of the current.

From the foregoing description it is evident that according to the present invention the extinction of the arc and interruption of current can be readily accomplished over a wide range of currents of small as well as large current values.

On the other hand, the electromagnetic driving force characteristic curves D and E take substantially the stepped forms and thus there will be no great variation of the maximum electromagnetic forces during the first and second interrupting periods even in the presence of a considerable variation in the contact parting phase.

For this reason, the circuit breaker according to the present invention is capable of taking advantage of stable electromagnetic forces which are not dependent on the contacting parting phase.

Next, consider the divertion of a current into the primary coil 32. In the cases of the electromagnetic driving force characteristic curves l) and E shown in FIG. 4, the electromagnetic driving forces during the initial period of the interrupting operation are considerably smaller than those during the later period of the interrupting operation. This is due to a large overlapping between the primary coil 32 and the short ring 29 indicating the fact that the essential inductance of the primary coil 32 is small during the initial period. This in turn means that the divertion of an interrupting current, that is, excitation of the primary coil 32 following the initiation of interrupting operation can be readily accomplished. This has an effect of making the current divertion position, i.e., the construction of the interrupting mechanism at the current collector 30 and the insulating layer 35 simpler.

Next, let us consider the electromagnetic forces acting on the primary coil 32. One of the electromagnetic forces is the driving force in the axial direction which acts between the short ring 29 and the primary coil 32 on the whole and in addition another electromagnetic force due to the current flowing through the primary coil 32 causing the coil itself to expand and still another electromagnetic force tending to press the primary coil 32 owing to the currents in the outer short ring 29 and in the inner primary coil 32 flowing in the opposite directions. The latter two electromagnetic forces act in radial directions and thus they are not employed for actuating the compressing means, rather they are harmful electromagnetic forces tending to cause damage to the primary coil 32.

According to the present invention, particularly when a large current is to be interrupted, a position in a relatively earlier stage is employed and thus the primary coil 32 and the short ring 29 overlap each other considerably. This causes a cancellation effect between the electromagnetic force causing the primary coil 32 to expand and the electromagnetic force caused by the current in the short ring 29 and tending to crush the primary coil 32, thereby substantially decreasing the radial electromagnetic forces tending to damage the primary coil 32.

Therefore, there is no need to construct the primary coil 32 rigidly as compared with those of the conventional devices and thus the weight of the movable parts can be reduced thereby makingit possible to effectively utilize the available electromagnetic driving force for gas compression.

The closing operation is completed when the operating rod 24 is returned to the illustrated position and the movable main contact 22 engages with the fixed contact 21. In this case, as the

contacts

21 and 22 approach each other, a discharge is caused prior to the closing since the circuit voltage has previously been developed between the

contacts

21 and 22. This preceeding discharge excites the primary coil 32 again so that an electromagnetic force of repulsion is produced between the primary coil 32 and the short ring 29 and thus owing to the fact that the primary coil 32 is directly connected to the operating rod 24 there is the danger of the produced electromagnetic repulsion force tending to oppose the operating force, thus making it impossible to accomplish the closing. According to the present invention, however, the electromagnetic repulsion force produced at the position of occurrence preceeding discharge, i.e., at the position corresponding to the early stage of interrupting operation, is relatively small and thus it does not cause a failure in the closing operation. This considerably reduces the un desirable effect on the interrupting operation subsequent to the closing operation.

FIGS. a through 5d illustrate various combinations of electromagnetic driving units for different stepped electromagnetic driving force characteristic requirements.

In FIG. 5a, a primary coil 51 having an increased number of turns at the left end thereof is mounted on the operating rod 24 by means of the stay 31 to cooperate with a cylindrical short ring 50.

In FIG. 5b, a stepped primary coil 61 is mounted similarly on the operating rod 24 by means of the stay 31 for cooperation with a cylindrical short ring 60.

In FIG. 50, an L-shaped short ring is associated with a similarly L-shaped primary coil 71 and there is a feature in that the distance between the short ring 70 and the primary coil 71 is increased at the flanged portions thereof.

In FIG. 5d, an inclined primary coil 81 is arranged for a cylindrical short ring 80. In this combination, the distance between the short ring and the primary coil 81 changes linearly. However, if one takes coil elements 81a, 81b and 810 constituting the left half and coil elements 81d, 81c and 81f constituting the right half of the primary coil 81 as a group, respectively, and consider the average driving forces produced by these groups, it will be readily understood that this combination is equivalent with that shown in FIG. 5b.

While the arrangement and construction of the short ring and primary coil are not the same in these combinations, if the respective combinations are analized into groups and the electromagnetic driving forces produced by these groups are considered as a whole, these combinations produce substantially stepped overall electromagnetic driving forces.

In addition, various other forms of the electromagnetic driving means which are capable of producing stepped electromagnetic driving forces may be conceived.

Referring now to FIG. 6, there is shown the interrupting section of a circuit breaker according to another embodiment of the present invention in which the electromagnetic driving means is provided with the required stepped electromagnetic driving force characteristic by using metals of different properties for its electromagnetic driving units, i.e., the short ring. In this interrupting section, the puffer puffer piston comprises a so-called floating puffer-type piston which is free to move relative to the puffer cylinder.

In the figure, in opposition to a fixed contact 101, a movable main contact 102 and a movable arcing contact I03 adapted to perform wiping operation are secured to an electrically conducting operating rod 104 which is connected to an insulating rod 105 by securing means 106 such as a bolt.

Disposed on the contact side of the operating rod 104 is an electrically conducting puffer cylinder 107 and an insulating layer 108 is formed on the outer periphery of the puffer cylinder 107 excepting a portion thereof.

On the remaining part of the operating rod 104 there is provided a current diverting means 109. As shown in FIG. 7, the current diverting means 109 comprises current collectors 110 and supporting guide plates for the puffer cylinder 107 which are alternately arranged circumferentially and both the collectors 110 and the guide plates 111 are also secured separately to an insulating support 1 l2.

The forward ends of the supporting guide plates 111 are secured to a ring member 113 having an L-shape in section by securing means 114 such as bolts and thus the plates 111 cooperate with the ring member 113 to positively secure the puffer cylinder 107.

Springs 115 are disposed in the radial direction between the ring member 113 and the current collectors 110 to ensure positive electrical connection between the puffer cylinder 107 and the current collectors 110.

While this current diverting means 109 performs slit arc extinction in the manner that will be explained later when the interruption of current is to be effected, in the event that damage is feared or has been done to the current collectors 110 due to the slit arc extinction, the current collectors 110 may be easily checked and replaced by simply removing the ring member 113.

As shown in FIG. 6, the current collectors 110 are provided with an insulating layer 116 on the inner side thereof. Thus, while the puffer cylinder 107 and the current collectors 110 remain connected with each other during the illustrated closing operation, during the interrupting operation both the insulating

layers

108 and 116 effect the slit arc extinction thus interrupting the path of current between the puffer cylinder 107 and the current collectors 110.

The operating rod 105 is provided with a primary coil 110 mounted at the other end thereof by means of an electrically conducting stay 117 and the other end of the primary coil 110 is connected through a current collector 119 to a sliding contact plate 120 which is electrically connected to the current collectors 110.

An insulating support 112 is provided at its end with a buffer member 121 and a short ring 122 is disposed to abut against the buffer member 121 and. in opposition to the primary coil 110.

The short ring 122 is integrally formed with a puffer piston 123 which is disposed floatingly relative to the operating rod 1041 by means of a spring 124 provided between the puffer piston 123 and the puffer cylinder 107.

The short ring 122 differs from the short ring 29 shown in FIG. 2 and it is perfectly cylindrical having no stepped portion. Instead, the short ring 122 comprises a portion 122a and a portion 122b which are for example made of copper and aluminum alloy, respectively.

The conductivity of copper differs from that of the aluminum alloy and thus when a current flows into the primary coil 110 the values of the induced currents in the two portions 122a and 12212 are not identical due to a difference in resistance values between them. For this reason, the short ring 122 has the same effect with the stepped short ring 29 shown in FIG. 2, that is, the overall electromagnetic driving force characteristic of this embodiment has a stepped form as shown in FIG. 3.

When an interruption is called for so that the operating

rods

105 and 104 cause the movable main contact 102 to separate from the fixed contact 101 and then the movable contact 103 parts from the fixed contact 101 after having performed its wiping operation, an arc is formed and drawn between the fixed contact 101 and the arcing contact 103. Simultaneously, as previously mentioned, the path of current through the puffer cylinder 107 and the current collectors 110 is interrupted causing a flow of current through the primary coil 118, current collector 119 and sliding contact plate 120. This current flow through the primary coil 118 produces an electromagnetic force of repulsion between the primary coil 118 and the short ring 122 moving the puffer piston 123 to the left against the spring 124 thus reducing the space defined by the puffer piston 1223 together with the puffer cylinder 107 in the manner as shown in the lower part of FIG. 6. When this occurs, a mass of SR, gas is compressed and directed into the are through an insulating nozzle 125 thereby cooling and extinguishing the arc and thus completing the interruption.

While the relationship between the stepped electromagnetic driving force and the interruption of current has been shown in FIG. 4, depending on the value of the fault current, it is possible that an excessively large electromagnetic driving force is produced so that the compressing means is actuated at a point premature with respect to the current change, that is, the compression operation ends at a point a long time before the current zero point.

Referring to FIG. 8, there is shown the relationship between the electromagnetic driving force and the interruption of current where the generation of an excessively large electromagnetic driving force is prevented and thus the compressing means is actuated at a suitable velocity with respect to the current change by employing a suitable combination of the short ring and primary coil, such as a combination of two short rings and two primary coils.

In the figure, as shown by curves 1D and E the electromagnetic driving force characteristics obtainable for a range of small currents and for a range of excessive currents when there is a predetermined current flow into the primary coil take forms which may well be considered as comprising two peaks having different crest values rather than considered to be stepped forms. Then, since an AC current flows into the primary coil, a curve G, represents the electromagnetic driving force characteristic for the small currents, whereas a curve 11 represents the electromagnetic driving force characteristic for the excessive currents.

In FIG. 8, the curves are drawn with the same thinking as in the case of FIG. 41 and the identical refei'ence characters as used in FIG. 4 designate the identical things or the equivalents thereof.

In the figure, while the relationship between the electromagnetic driving force and the current waveform is substantially the same as in FIG. 4, as will be seen from the curve 11,, particularly with the electromagnetic driving force produced for the excessive current there is a bottom in the current half wave at near its center and this considerably limits the driving force applied to the compressing means. Thus, the compressing means is actuated by a driving force which corresponds to the current waveform thereby ensuring an efficient blasting of compressed gas to complete the interruption.

It should be apparent from the foregoing description that according to the present invention the occurrence of an excessive electromagnetic driving force can be avoided even when the value of a current to be interrupted is large. Thus, over a range of both small and large currents, an efficient blasting of compressed gas into an arc is ensured so as to cool and extinguish the arc.

Furthermore, suppression of the initial inductance of the primary coil ensures an efficient divertion of a current to be interrupted into the primary coil.

Still furthermore, since there is a small electromagnetic driving force during the initial stage of driving, the occurrence of discharge prior to the closing operation will not result in a force which would prevent the closing operation, thereby ensuring a smooth accomplishment of the closing operation.

I claim:

1. A circuit breaker comprising at least a pair of contacts adapted for parting to induce an arc, electromagnetic driving means exhibiting a stepped electromagnetic driving force characteristic when a predetermined current flows thereinto, means for diverting a current to be interrupted into said electromagnetic driving means in response to an interruption instruction, means adapted to be actuated by said electromagnetic driving means to compress an arc extinguishing gas, and an insulating nozzle for directing a high pressure gas produced by said compressing means into said arc.

2. A circuit breaker according to claim 1, wherein said electromagnetic driving means comprises a combination of at least two electromagnetic driving units provided by a primary coil into which the interrupting current is caused to flow and a short ring or short coil electromagnetically coupled to said primary coil, whereby when there is a predetermined current flow in said primary coil, the characteristic of the summation of electromagnetic driving forces produced between said primary coil and said short ring or short coil has a stepped form.

3. A circuit breaker according to claim 1, wherein said electromagnetic driving means comprises a cylindrical primary coil into which the interrupting current is caused to flow, and a stepped cylindrical short ring or stepped cylindrical short coil electromagnetically coupled to said primary coil, whereby the electromagnetic driving force characteristic of said electromagnetic driving means has a stepped form when there is a predetermined current flow in said primary coil.

4. A circuit breaker according to claim 1, wherein said electromagnetic driving means comprises a cylindrical primary coil into the interrupting current is caused to flow, and a short ring electromagnetically coupled to said primary coil and comprising two metallic cylindrical portions of different materials mechanically connected with each other in the axial direction, whereby the electromagnetic driving force characteristic of said electromagnetic driving means has a stepped form when there is a predetermined current flow in said primary coil.

5. A circuit breaker comprising at least a pair of contacts adapted for parting to induce an arc, electromagnetic driving means exhibiting a stepped electromagnetic driving force characteristic when there is a predetermined current flow therein, means for diverting a current to be interrupted into said electromagnetic driving means in response to an interruption instruction, compressing means adapted to be actuated by said electromagnetic driving means to compress an arc extinguishing gas, and a nozzle for directing a high pressure gas produced by said compressing means into said arc, whereby the electromagnetic driving force according to said electromagnetic driving force characteristic increases in a rising step manner with the lapse of time.

6. A circuit breaker comprising at least a pair of contacts adapted for parting to induce an arc, electromagnetic driving means exhibiting an electromagnetic driving force characteristic with two peaks of different crest values when there is a predetermined current flow therein, means for diverting a current to be interrupted into said electromagnetic driving means in response to an interruption instruction, means adapted to be actuated by said electromagnetic driving means to compress an arc extinguishing gas, and a nozzle for directing a high pressure gas produced by said compressing means into said are, whereby the lower peak of said crest values of said electromagnetic driving force characteristic appears during the initial period with the lapse of time.

7. A circuit breaker according to claim 6, wherein said electromagnetic driving means comprises a combination of at least two electromagnetic driving units provided by a primary coil into which the interrupting current is caused to flow, and a short ring or short coil electromagnetically coupled to said primary coil, whereby the characteristic of the summation of electromagnetic driving forces produced between said primary coil and said short ring or short coil takes a form with two peaks of different crest values when a predetermined current flows in said primary coil.

t il l i

Claims

6. A circuit breaker comprising at least a pair of contacts adapted for parting to induce an arc, electromagnetic driving means exhibiting an electromagnetic driving force characteristic with two peaks of different crest values when there is a predetermined current flow therein, means for diverting a current to be interrupted into said electromagnetic driving means in response to an interruption instruction, means adapted to be actuated by said electromagnetic driving means to compress an arc extinguishing gas, and a nozzle for directing a high pressure gas produced by said compressing means into said arc, whereby the lower peak of said crest values of said electromagnetic driving force characteristic appears during the initial period with the lapse of time.