FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
& THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
CIRCUIT BREAKER;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANIZED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

DESCRIPTION
TECHNICAL FIELD
[0001] The present invention relates to a circuit breaker equipped with an electromagnetic trip device using an oil dashpot and, more particularly, relates to an improvement of suction force in the electromagnetic trip device. BACKGROUND ART
[0002] In an electromagnetic device that constitutes an electromagnetic trip device of a conventional circuit breaker, a fixed core of an oil dashpot system is firmly fixed to one leg portion in an L-shaped yoke made of a magnetic plate and a movable iron piece is pivotally supported on the other leg portion while facing the pole contact surface of the fixed core. Then, the movable iron piece is retained by inserting a brace member on the yoke side into a window hole or a cutout groove of the movable iron piece. Furthermore, a spring that biases the movable iron piece so as to enlarge a gap between the movable iron piece and the pole contact surface of the fixed core is provided. Further, one end of a core provided in an oil dashpot of the fixed core is coupled to one leg portion of the L-shaped yoke to constitute a magnetic circuit; and the movable iron piece that makes the magnetic circuit a closed circuit is made to pivot by utilizing suction force to open an opening and closing mechanism unit.

[0003] In this specification, when a configuration is tried to reduce the electromagnetic trip device in size while maintaining a tripping load of a trip mechanism unit, there is a case where sufficient suction force for tripping the trip mechanism unit cannot be obtained. Therefore, there is known an electromagnetic trip device which is provided with a bent portion and improves the suction force by increasing a pole contact area by the bent portion, with the aim of increasing the suction force without changing the number of turns of a coil constituting the electromagnetic device. The bent portion is made such that the end of the other leg portion of the yoke is perpendicularly bent on the fixed core side; and the number of turns of the coil influences on inverse time limit characteristics of the circuit breaker. (For example, refer to Patent Document 1.) RELATED ART DOCUMENT PATENT DOCUMENT
[0004] Patent Document 1: Japanese Unexamined Patent Publication No..2001-307614, FIG. 5 SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0005] In the electromagnetic trip device in the above-mentioned conventional circuit breaker, a magnetic gap between the movable iron piece and the fixed core is formed on the outer side than the inside of the coil where magnetic flux is concentrated; and accordingly, a leakage magnetic flux coefficient

increases, which is generally said. Thus, magnetic flux passing through the movable iron piece becomes small and the suction force is reduced. Furthermore, a magnetic gap between the fixed core and the bent portion of the yoke becomes smaller than the magnetic gap between the fixed core and the movable iron piece; and accordingly, although the pole contact area increases, the magnetic flux passing through the movable iron piece is reduced. As a result, this may become a factor that will obstruct an improvement of the suction force.
[0006] The present invention has been made to solve the foregoing problem and is to obtain a circuit breaker which can effectively improve the suction force of an electromagnetic trip device without changing the number of turns of a coil of an electromagnetic device constituting the electromagnetic trip device, the number of turns of the coil influencing on inverse time limit characteristics of the circuit breaker. MEANS FOR SOLVING THE PROBLEMS
[0007] According to the present invention, there is provided a circuit breaker including: a movable contact having a movable contact point at one end; a fixed contact having a fixed contact point connected to and separated from the movable contact point; a first external terminal connected to the fixed contact; an opening and closing mechanism unit which opens and closes the movable contact; an electromagnetic trip device which is connected to the movable contact and trips the opening and closing mechanism unit;

and a second external terminal connected to the electromagnetic trip device. The electromagnetic trip device includes: a yoke made of a magnetic plate; a fixed core firmly fixed to one leg portion of the yoke; a coil which is wound around the fixed core and is connected to the movable contact and the second external terminal; and a movable iron piece which is pivotally retained to the other leg portion of the yoke and has a first suction surface facing the pole contact surface of the fixed core. In the circuit breaker, the movable iron piece includes a leakage flux reduction portion which reduces leakage magnetic flux between the yoke and the movable iron piece.
ADVANTAGEOUS EFFECT OF THE INVENTION
[0008] According to the present invention, the suction force of the electromagnetic trip device can be increased without increasing the number of turns of the coil which influences on inverse time limit characteristics of the circuit breaker, whereby a reduction in size of the circuit breaker can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a longitudinal sectional view showing the whole configuration of a circuit breaker according to Embodiment 1 of the present invention;
FIG. 2 is an enlarged side view showing an electromagnetic trip device according to Embodiment 1 of the present invention; FIGS. 3(a), 3(b) are views each showing a movable iron piece of the electromagnetic trip device according to Embodiment 1 of the

present invention, FIG. 3(a) is a plan view, and FIG. 3(b) is a
side view;
FIGS. 4 (a) , 4 (b) are relevant part enlarged side views each showing
a magnetic path of the electromagnetic trip device according to
Embodiment 1 of the present invention;
FIG. 5 is an enlarged side view showing a state during the occurrence
of overcurrent of the electromagnetic trip device shown in FIG.
2;
FIG. 6 is an enlarged side view showing an electromagnetic trip
device according to Embodiment 2 of the present invention;
FIG. 7 is an enlarged longitudinal sectional view showing the
electromagnetic trip device according to Embodiment 2 of the present
invention;
FIGS. 8(a), 8(b) are views each showing a movable iron piece of
the electromagnetic trip device according to Embodiment 2 of the
present invention, FIG. 8(a) is a plan view, and FIG. 8(b) is a
side view;
FIG. 9 is an enlarged side view showing an electromagnetic trip
device according to Embodiment 3 of the present invention;
FIG. 10 is an enlarged longitudinal sectional view showing the
electromagnetic trip device according to Embodiment 3 of the present
invention; and
FIGS. 11(a), 11(b) are views each showing a movable iron piece of
the electromagnetic trip device according to Embodiment 3 of the
present invention, FIG. 11(a) is a plan view, and FIG. 11(b) is

a side view.
MODE FOR CARRYING OUT THE INVENTION [0010] Embodiment 1.
FIG. 1 is a longitudinal sectional view showing the whole configuration of a circuit breaker according to Embodiment 1 of the present invention; FIG. 2 is an enlarged side view showing an electromagnetic trip device; FIGS. 3(a), 3(b) are views each showing a movable iron piece of the electromagnetic trip device, FIG. 3(a) is a plan view, and FIG. 3(b) is a side view; FIGS. 4(a), 4(b) are relevant part enlarged side views each showing a magnetic path of the electromagnetic trip device, FIG. 4 (a) shows magnetic flux A, and FIG. 4(b) shows magnetic flux B; and FIG. 5 is an enlarged side view showing a state during the occurrence of overcurrent of the electromagnetic trip device shown in FIG. 2.
[0011] In FIG. 1, a circuit breaker 101 is configured using a housing 10 composed of a base 11 and a cover 12, both of which are made of insulation material. Circuit interrupting units (for example, three units in the case of three phase) connected to an electrical path are arranged on the base 11 in parallel to each other for each pole; and an opening and closing mechanism unit 30 having a well-known retardant mechanism is arranged on an upper portion of the central circuit interrupting unit. [0012] The cover 12 covers the circuit interrupting units of the respective phases on the base 11 and the opening and closing mechanism unit 30; and an operating handle 31 of the opening and

closing mechanism unit 30 protrudes from a window hole 12a of the cover 12.
Furthermore, the circuit interrupting units of the respective phases are configured to be the same as each other. A crossbar 13 is common to the circuit interrupting units of the respective phases and is arranged on the base 11 so as to be orthogonal to the circuit interrupting units of the respective phases.
[0013] Each circuit interrupting unit of each phase has: a power supply side terminal 20 serving as a first external terminal provided on the base 11; a fixed contact 21 which is extendedly provided from the power supply side terminal 20 and has a fixed contact point 22; a movable contact point 23 connected to and separated from the fixed contact point 22; a movable contact 24 which has the movable contact point 23 at one end and is retained by the crossbar 13 to be movable up and down; an electromagnetic trip device 40 which is connected to the movable contact 24 via a flexible copper stranded wire 25 and trips the opening and closing mechanism unit 30; and a load side terminal 26 serving as a second external terminal which is connected to the electromagnetic trip device 40 and is provided on the base 11. The fixed contact point 22 and the movable contact point 23 constitute opening and closing contact points, which open and close the electrical path. Furthermore, an arc extinguishing device 27 having an arc extinguishing plate 27a is provided near the fixed contact point 22 and the movable contact point 23. If the movable contact point

23 comes in contact with the fixed contact point 22, an electrical circuit between both terminals 20, 2 6 is ON; and if the movable contact point 23 is separated from the fixed contact point 22, the electrical circuit between both terminals 20, 26 is OFF. [0014] The crossbar 13 is moved up and down by the opening and closing mechanism unit 30; and when the crossbar 13 is moved up and down, each movable contact 24 of the circuit interrupting unit of each pole is moved up and down at the same time. The movable contact point 23 is connected to and separated from the fixed contact point 22 by the up and down movement of the movable contact 24. Furthermore, the opening and closing mechanism unit 30 includes a well-known trip bar 33 to be driven by the electromagnetic trip device 40 of each pole.
[0015] As shown in FIG. 2, the electromagnetic trip device 40 includes: a coil 41 which is connected to the movable contact 24 at one end and to the load side terminal 2 6 at the other end and is wound in order to convert an energization current into magnetic flux; an L-shaped yoke 42 which is made of a magnetic plate and through which the magnetic flux of the coil 41 passes; and an oil dashpot 43 which is firmly fixed to one leg portion of the yoke
42 and determines inverse time limit characteristics by controlling
the time at which a core is suctioned to a pipe cover by viscosity
of oil by utilizing the magnetic flux of the coil 41. The oil dashpot
43 is composed of a pipe 44 around which the coil 41 is wound; a
pipe cover 45 which functions as a cover of the pipe 44; a core

47 provided in the pipe 44 together with oil 46; and a core spring
48 which is provided between the core 47 and the pipe cover 45 and biases the core 47 in a direction away from the pipe cover 45. Incidentally, a wording "fixed core" described in CLAIMS is the above-described oil dashpot 43.
[0016] Furthermore, the electromagnetic trip device 40 is provided with: a movable iron piece 4 9 which faces the pipe cover 45 and is pivotally retained by a retaining portion 42a provided on the other leg portion of the yoke 42; an extension portion 42b in which the yoke 42 is extended from the retaining portion 42a that retains the movable iron piece 49; and a movable iron piece spring 50 which is laid across in a tensioned condition between the extension portion 42b and an end portion 49b of the movable iron piece 49 and biases the movable iron piece 49 in a direction to be separated from the pipe cover 45. Further, as shown in FIGS. 3(a), 3(b), the movable iron piece 49 is provided with: a first suction surface 49a to be suctioned to the pipe cover 45; a through hole 49c through which the extension portion 42b of the yoke 42 passes; a bent portion 4 9d which faces the through hole 4 9c and is for forming a magnetic circuit to the yoke 42; and a driving portion 49f which drives the trip bar 33. Then, when an overcurrent flows, the core 47 is suctioned in the direction of the pipe cover 45 and thereby increasing magnetic flux that passes through the movable iron piece 49. As a result, suction force that suctions the first suction surface 49a is also increased and the movable

iron piece 49 pivots by overcoming against the biasing force of the movable iron piece spring 50. A configuration is made such that the driving portion 49f drives the trip bar 33 of the opening and closing mechanism unit 30 by this turn of the movable iron piece 49.
[0017] Hitherto, in the electromagnetic trip device 40, it is difficult to sufficiently enhance the suction force of the movable iron piece 49 in order to maintain the inverse time limit characteristics of the circuit breaker 101. Consequently, in the case of only for alternating current, the opening and closing mechanism unit 30 is tripped by utilizing the inertia force of the movable iron piece 49 due to vibrations of the movable iron piece 49 at a commercial frequency. On the other hand, when the circuit breaker equipped with the electromagnetic trip device 40 is applied to a direct current electrical path, the movable iron piece 49 does not vibrate and thus the inertia force of the movable iron piece 49 cannot be utilized as in an alternating current electrical path. Consequently, in the case of the path for direct current, the number of turns of the coil, the viscosity of the oil, the core spring, and the like need to be changed.
[0018] In order to solve this, in this present embodiment, there is provided: the extension portion 42b in which the yoke 42 is extended from the retaining portion 42a that pivotally retains the movable iron piece 49 as described above; and a second suction surface 49e which faces the extension portion 42b and is formed

in an inverse U-shape.
This becomes a figure which is totaled by the magnetic flux A which directly passes through the yoke 42 from the bent portion 49d of the movable iron piece 49 as shown in FIG. 4 (a) and the magnetic flux B which passes through the yoke 42 via the extension portion 42b after passing through the second suction surface 49e of the movable iron piece 49 as shown in FIG. 4(b). More specifically, in a state where the movable iron piece 49 is suctioned to the pipe cover 45, a contact area between the movable iron piece 49 and the yoke 42 is increased to reduce leakage magnetic flux between the yoke 42 and the oil dashpot.
Incidentally, a wording "leakage flux reduction portion" described in CLAIMS is the above-described second suction surface 49e and then extension portion 42b.
[0019] Next, the interrupting operation of the circuit breaker 101 will be described.
When a current flows in the electrical path, an exciting current flows in the coil 41; and magnetic flux generated by the exciting current passes through the magnetic circuit including: the yoke 42 → the core 47 → a first magnetic gap Gl between the core 47 and the pipe cover 45 → the pipe cover 45 → a second magnetic gap G2 between the movable iron piece 4 9 and the pipe cover 45 → the movable iron piece 49. At this time, when an overcurrent of equal to or more than a predetermined value flows in the electrical path, magnetic flux made by the overcurrent generates

suction force that suctions the core 47 to the pipe cover 45 and this suction force exceeds the biasing force of the core spring 48. Then, the core 47 is suctioned to the pipe cover 45 side by viscous resistance of the oil 46 after a predetermined time as shown in FIG. 5; and the first magnetic gap Gl is reduced from LI during the normal time shown in FIG. 2 to L2 shown in FIG. 5. The core 47 is suctioned to the pipe cover 45 and the first magnetic gap Gl is reduced; and thus, the magnetic flux A of the second magnetic gap G2 between the movable iron piece 49 and the pipe cover 45 is gradually increased. Further, the magnetic flux B also passes through between the second suction surface 49e of the movable iron piece 49 and the extension portion 42b of the yoke 42; and therefore, it becomes a figure which is totaled by the flux A and the flux B to increase suction force to be exerted on the movable iron piece 49.
[0020] By this increased suction force, the movable iron piece 49 pivots and the driving portion 49f pushes the trip bar 33; and thus, the crossbar 13 of the opening and closing mechanism unit 30 is driven to separate the movable contact 24 from the fixed contact 21. The movable contact point 23 is separated from the fixed contact point 22 by the movement of the movable contact 24. When the movable contact point 23 is separated, an arc generated by the flowing current is extinguished by the arc extinguishing device 27 and interruption is completed.
ON/OFF operation is the same as that of a well-known circuit

breaker and therefore description thereof will be omitted. [0021] According to the present embodiment, the second suction surface 4 9e is provided on the movable iron piece 4 9 and the extension portion 42b facing the second suction surface 49e is provided on the yoke 42; and therefore, the leakage magnetic flux of the retaining portion 42a of the movable iron piece 49 by the yoke 42 is reduced, the number of turns of the coil 41 can be reduced while maintaining the suction force in which the oil dashpot 43 suctions the movable iron piece 49, and a reduction in size of the circuit breaker can be achieved.
[0022] Furthermore, the second suction surface 49e is provided on the movable iron piece 49 and the extension portion 42b facing the second suction surface 49e is provided on the yoke 42; and thus, the leakage magnetic flux of the retaining portion 42a of the movable iron piece 49 by the yoke 42 is reduced. Therefore, if the number of turns of the coil 41 is adjusted, it becomes possible that the suction force in which the oil dashpot 43 serving as the fixed core suctions the movable iron piece 49 is made to increase and commoditizing of the electromagnetic trip device 40 for alternating current and for direct current can be achieved. [0023] Embodiment 2.
FIG. 6 is an enlarged side view showing an electromagnetic trip device of a circuit breaker in Embodiment 2; FIG. 7 is a longitudinal sectional view of the electromagnetic trip device shown in FIG. 6; and FIGS. 8 (a) , 8 (b) are views each showing a movable

iron piece of the electromagnetic trip device shown in FIG. 6, FIG. 8(a) is a plan view, and FIG. 8(b) is a side view.
Generally, a leakage magnetic flux coefficient is largely different between a hinge type in which a magnetic gap is formed in the outside of a coil and a plunger type in which the magnetic gap is formed in the inside of the coil. When it is viewed on the same magnetic gap, there is known that a leakage flux coefficient y of the plunger type is about 0.75 times as great as that of the hinge type. If this is converted into suction force, it shows that the suction force of the plunger type is (1/0.75)2=1.77 times as great as that of the hinge type.
[0024] Therefore, in this present embodiment, as shown in FIG. 6 and FIG. 7, in an electromagnetic trip device 401, a plunger 51, that is, a protrusion portion is provided on a movable iron piece 49 so that a second magnetic gap G3 between the movable iron piece 49 and a pipe cover 451 is formed in the inside of a coil 41, and the pipe cover 451 of an oil dashpot 43 is arranged in the inside of the coil 41. As shown in FIGS. 8 (a) , 8 (b) , a torso portion 51a of the plunger 51 is movably retained by the movable iron piece 49 at a neck portion 51b of the plunger 51. The other configuration is the same as Embodiment 1 and therefore description thereof will be omitted.
Incidentally, a wording "leakage flux reduction portion" described in CLAIMS is the plunger 51 in addition to the above-described second suction surface 49e and the extension

portion 42b.
[0025] According to the present embodiment, the second suction surface 49e is provided on the movable iron piece 49 and the extension portion 42b facing the second suction surface 49e is provided on the yoke 42; and therefore, the leakage magnetic flux of the retaining portion 42a of the movable iron piece 49 by the yoke 42 is reduced, the number of turns of the coil 41 can be reduced while maintaining the suction force in which the oil dashpot 43 suctions the movable iron piece 49, and a reduction in size of the circuit breaker can be achieved.
[0026] Furthermore, in the electromagnetic trip device 401, the plunger 51 is provided on the movable iron piece 49 so that the second magnetic gap G3 is formed in the inside of the coil 41 and the pipe cover 451 of the oil dashpot 43 is arranged in the inside of the coil 41; and therefore, the leakage magnetic flux coefficient y pertaining to the second magnetic gap G3 between the movable iron piece 49 and the pipe cover 451 is further reduced, the number of turns of the coil 41 can be reduced while maintaining the suction force in which the oil dashpot 43 suctions the movable iron piece 49, and a further reduction in size of the circuit breaker can be achieved.
[0027] Furthermore, the plunger 51 is provided on the movable iron piece 49 so that the magnetic gap G3 is formed in the inside of the coil and the pipe cover 451 of the oil dashpot 43 is arranged in the inside of the coil 41; and therefore, the leakage magnetic

flux coefficient y pertaining to the second magnetic gap G3 between the movable iron piece 4 9 and the pipe cover 451 is further reduced. Thus, if the number of turns of the coil 41 is adjusted, the suction force in which the oil dashpot 43 serving as the fixed core suctions the movable iron piece 49 is made to increase, commoditizing of the electromagnetic trip device 401 for alternating current and for direct current can be achieved, and a reduction in size of the circuit breaker can also be achieved.
[0028] Furthermore, the leakage magnetic flux coefficient y pertaining to the second magnetic gap G3 between the movable iron piece 49 and the pipe cover 451 is further reduced; and therefore, a reduction in size of the pipe 44, the pipe cover 451, the core 47, and the core spring 48 can also be achieved. [002 9] Embodiment 3.
FIG. 9 is an enlarged side view showing an electromagnetic trip device of a circuit breaker according to Embodiment 3; FIG. 10 is a longitudinal sectional view of the electromagnetic trip device shown in FIG. 9; FIGS. 11(a), 11(b) are views each showing a movable iron piece of the electromagnetic trip device shown in FIG. 9, FIG. 11(a) is a plan view, and FIG. 11(b) is a side view.
In the present embodiment, as shown in FIG. 9, a convex shape 49g, that is, a protrusion portion is provided on a movable iron piece 4 9 in place of the plunger 51 provided on the movable iron piece 4 9 in Embodiment 2. [0030] Furthermore, as shown in FIG. 10, a pipe cover 452 has

a concave shape 452a; and a magnetic gap G4 is formed in the inside of a coil 41 by the combination of the concave shape 452a and the convex shape 49g of the movable iron piece 49. In the case where the plunger 51 described in Embodiment 2 is provided on the movable iron piece 49, the number of components is 2; however, if in the case of the convex shape 49g in this present embodiment, the configuration can be made by one component of the movable iron piece 49 as shown in FIG. 11. The other configuration is the same as Embodiment 2 and therefore description thereof will be omitted. Incidentally, a wording "leakage flux reduction portion" described in CLAIMS is the convex shape 4 9g in addition to the above-described second suction surface 49e and the extension portion 42b.
[0031] According to the present embodiment, the second suction surface 49e is provided on the movable iron piece 49 and the extension portion 42b facing the second suction surface 49e is provided on the yoke 42; and therefore, the leakage magnetic flux of the retaining portion 42a of the movable iron piece 49 by the yoke 42 is reduced, the number of turns of the coil 41 can be reduced while maintaining the suction force in which the oil dashpot 43 suctions the movable iron piece 49, and a reduction in size of the circuit breaker can be achieved.
[0032] Furthermore, in the electromagnetic trip device 402, the convex shape 49g is provided on the movable iron piece 49, the concave shape 452a is provided in the pipe cover 452 of the oil

dashpot 43, and the second magnetic gap G4 between the movable iron piece 49 and the pipe cover 452 is formed in the inside of the coil 41; and therefore, a leakage magnetic flux coefficient y is further reduced, the number of turns of the coil 41 can be reduced while maintaining the suction force in which the oil dashpot 43 suctions the movable iron piece 49, and a reduction in size of the circuit breaker can be further achieved.
[0033] In addition, the convex shape 49g is provided on the movable iron piece 49, the concave shape 452a is provided in the pipe cover 452 of the oil dashpot 43, and the second magnetic gap G4 between the movable iron piece 49 and the pipe cover 452 is formed in the inside of the coil 41; and therefore, the leakage magnetic flux coefficient y is reduced. Thus, if the number of turns of the coil 41 is adjusted, the suction force in which the oil dashpot 43 serving as the fixed core suctions the movable iron piece 49 is made to increase, commoditizing of the electromagnetic trip device 402 for alternating current and for direct current can be achieved, and a reduction in size of the circuit breaker can also be achieved.
[0034] Moreover, the leakage magnetic flux coefficient y pertaining to the second magnetic gap G4 between the movable iron piece 49 and the pipe cover 452 is further reduced; and therefore, a reduction in size of, the pipe 44, the pipe cover 452, the core 47, and the core spring 48 can also be achieved. DESCRIPTION OF REFERENCE NUMERALS

[0035] 10 Housing, 11 Base, 12 Cover, 20 Power supply side terminal, 21 Fixed contact, 22 Fixed contact point, 23 Movable contact point, 24 Movable contact, 26 Load side terminal, 30 opening and closing mechanism unit, 40 Electromagnetic trip device, 41 Coil, 42 Yoke, 42b Extension portion, 43 Oil dashpot, 49 Movable iron piece, 49a First suction surface, 49e Second suction surface, 101 Circuit breaker.

WE CLAIM :
1. A circuit breaker comprising:
a movable contact having a movable contact point at one end;
a fixed contact having a fixed contact point connected to and separated from said movable contact point;
a first external terminal connected to said fixed contact;
an opening and closing mechanism unit which opens and closes said movable contact;
an electromagnetic trip device which is connected to said movable contact and trips said opening and closing mechanism unit; and
a second external terminal connected to said electromagnetic trip device,
said electromagnetic trip device including:
a yoke made of a magnetic plate;
a fixed core firmly fixed to one leg portion of said yoke;
a coil which is wound around said fixed core and is connected to said movable contact and said second external terminal; and
a movable iron piece which is pivotally retained to the other leg portion of said yoke and has a first suction surface facing the pole contact surface of said fixed core,
wherein said movable iron piece includes a leakage flux reduction portion which reduces leakage magnetic flux between said yoke and said movable iron piece.

2. The circuit breaker according to claim 1,
wherein said leakage flux reduction portion includes: an extension portion in which said yoke is extended from a retaining portion that pivotally retains said movable iron piece;
and
a second suction surface which faces said extension portion and is provided on said movable iron piece.
3. The circuit breaker according to claim 1,
wherein said leakage flux reduction portion is a protrusion portion which is provided on the first suction surface and protrudes toward the pole contact surface of said fixed core.
4. The circuit breaker according to claim 3,
wherein the pole contact surface of said fixed core is provided in the inside of said coil.
5. The circuit breaker according to claim 1,
wherein said leakage flux reduction portion of said movable iron piece includes:
an extension portion in which said yoke is extended from a retaining portion that pivotally retains said movable iron piece;
a second suction surface which faces said extension portion and is provided on said movable iron piece; and
a protrusion portion which is provided on the first suction surface and protrudes toward the pole contact surface of said fixed core.
6. The circuit breaker according to claim 5,

wherein the pole contact surface of said fixed core is provided in the inside of said coil.