JPH088053B2 - Circuit breaker - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a circuit breaker.

[Background technology]

An abnormal current, for example, when a short circuit occurs, a conventional example (Japanese Patent Laid-Open No. 57-196440) for extinguishing the arc by inserting a shield plate for extinguishing the arc between the movable contact and the fixed contact is disclosed.
As shown in the figure, there were the following drawbacks. That is, since the shield plate 101 moves between the fixed contact 102 and the movable contact 103 in conjunction with the opening / closing operation of the movable contact 100 by the operation of the link mechanism portion of the opening / closing / tripping means 104, it is possible to move from the occurrence of a short circuit. Open / close / trip means 1 until contact 103 begins to open 1
Since the delay time due to the operation of the link mechanism part of 04 is about 2 to 4 ms, and the moving contact 103 is about 3 to 6 ms from the start of the opening to the completion of the opening, the shield plate 101 from the occurrence of the short circuit.
Requires about 5-10ms to complete the operation. In Fig. 7, the spring force of the opening spring is set to a large value so that the shield plate 101 has about 5
The arc waveform when the operation is completed in ms is shown. Q ₁ is the contact arc voltage, Q ₂ is the breaking current, and Q ₃ is the estimated short-circuit current.

Thus, even if the spring force of the opening spring is set to a large value and the shield plate 101 is operated, the peak value of the short-circuit current is reached due to the delay of about 5 ms. The peripheral molded product and the shielding plate 101 are largely damaged. If the spring force of the opening spring is increased,
Since the load of operating the handle becomes large, it becomes an operation burden.

As a result, there is a drawback in that it is not possible to shorten the time until the operation of the shield plate 101 is completed and it is not possible to obtain a large blocking capacity.

In addition, the shield plate 1 is linked to the opening / closing operation of the movable contact 100.
Since 01 enters between the fixed contact 102 and the movable contact 103,
Since the shield 101 operates even during on / off operation,
There is a drawback that the shield plate 101 is greatly worn due to repeated on / off operations.

[Object of the Invention]

An object of the present invention is to shorten the time from the occurrence of a short circuit to the completion of the operation of the shield plate without increasing the operating load of the handle, thereby increasing the shielding capacity and reducing the abrasion of the shield plate. It is to provide a circuit breaker capable of doing so.

[Disclosure of Invention]

The circuit breaker of the present invention includes a fixed contact having a fixed contact, a movable contact having a movable contact that opens and closes with respect to the fixed contact, and an electromagnet that detects an abnormal current of a load.
In conjunction with the operation of the electromagnet, an arc-extinguishing shield plate that enters between the movable contact and the fixed contact in the closed state and the movable contactor are opened and closed by a handle, and an abnormal current of the load is detected. Opening and closing of the movable contactor, which is opened by the shield plate in conjunction with the detection unit, for trip opening
And means for tripping.

According to the configuration of the present invention, in the normal on / off operation, the shielding plate for extinguishing the arc does not work together, and when an abnormal current, for example, a short-circuit current flows, the operation of the opening / closing / trip means works in conjunction with the operation of the electromagnet. The shield plate can be inserted between the fixed contact and the movable contact without interruption to quickly disconnect the movable contact and the fixed contact. Therefore, it is possible to reduce the abrasion of the shield plate due to repeated on / off operations, and there is no influence of the delay time due to the operation of the opening / closing / tripping means, until the shield plate completes its operation after the abnormal current is generated. The time can be shortened, and therefore the arc interruption time can be shortened, so that a large interruption capacity can be realized. Moreover, it is not necessary to increase the spring force of the opening spring of the opening / closing / tripping means, and it is not necessary to increase the operating load of the handle.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 6. That is, this circuit breaker has a fixed contact 2 having a fixed contact 1, a movable contact 4 having a movable contact 3 that opens and closes with respect to the fixed contact 1, an electromagnet 5 that detects an abnormal current of a load, The shield plate 9 for extinguishing the arc, which enters between the movable contact 3 and the fixed contact 1 in the closed state in conjunction with the operation of the electromagnet 5, and the movable contactor 4 are opened / closed by the handle 6 and a load is applied. And an opening / closing means 8 for opening and closing the movable contactor 4 which is opened by the shield plate 9 in conjunction with the detection unit for detecting the abnormal current.

In FIG. 1, reference numeral 10 has an opening (not shown) for assembling parts on the side surface (direction perpendicular to the paper surface of FIG. 1) and 1
When the circuit breaker has a plurality of poles and constitutes a circuit breaker having a plurality of poles, the cases 10 are arranged in parallel and are connected by passing caulking pins (not shown) through the connection holes 13. 11 is a load side terminal provided at one end of the case 10,
Reference numeral 12 is a power supply side terminal provided at the other end of the case 10, and 14 is a case mounting groove.

The opening / closing / trip means 8 includes a handle 6, a frame 15, an operation link 19, an operating shaft 20, a movable frame 30, a latch link 23, a trip link 24, and an opening spring 42.
It is composed of the electromagnet 5 and the detection unit as an example. The frame 15 is held in the case 10. The handle 6 is rotatably provided on the upper end of the frame 15 in FIG.
A part thereof is exposed and a reset protrusion 68 is formed inside the case 10. A movable shaft 18 is provided at an inner end portion of the handle 6, one end of an operation link 19 is connected to the movable shaft 18, and an operation shaft 20 is connected to the other end. In addition, the movable shaft 18 and the frame 15
A handle return spring 22 having a pulling action is suspended between a spring receiver 21 provided at a lower position of the handle 6 and urges the handle 6 to the neutral position shown in FIG. The upper end of the latch link 23 is rotatably connected to the fixed shaft 16, and the operating shaft 20 slidably contacts one side surface of the lower end of the latch link 23. A trip link (24) is rotatably provided by a fixed shaft (25) on a frame (15) at a position opposite to the operating shaft (20) of the latch link (23).

The trip link 24 includes a latch portion 24a at the tip, a short-circuit response portion 27 at an intermediate portion, an overcurrent response portion 26 extending above the fixed shaft 25, and a return spring 28. The return spring 28 has a winding portion supported by the fixed shaft 25, one end of which is engaged with the overcurrent response portion 26, and the other end of which is engaged with the frame 15, so that the trip link 24
Is urged to rotate clockwise in FIG. 1, and is positioned by a stopper (not shown) provided on the frame 15 at the position shown in FIG. In this state, the latch portion 24a is in a latched state in which the lower end portion of the latch link 23 is abutted and locked, and the latch link 23 is regulated so as not to rotate counterclockwise around the fixed shaft 16.

A pair of guides 29 are provided on the side wall of the case 10 below the operation link 19, and a movable frame 30 is guided between the guides 29 so as to be slidable in the vertical direction in FIG. The movable frame 30 is formed with a bearing recess 31 (see FIG. 5) at the upper end thereof, and the bearing recess 31 can be engaged with the operating shaft 20 in a state of preventing the operating shaft 20 from moving downward.

The electromagnet 5 is of a plunger type, and has a movable part 7 as a plunger, a coil cylinder 33 having the movable part 7 therein, a yoke 40 extending over both ends of the coil cylinder 33, and a coil cylinder inside the yoke 40. A coil 32 wound around 33, a fixed iron core 41 facing the movable portion 7 in the coil cylinder 33, a return spring (not shown) interposed between the movable portion 7 and the fixed iron core 41, and an operating link 35. It is composed of. The yoke 40 is fixed to the frame 15 below the trip link 24. The movable part 7 is provided with a movable rod 7a which penetrates the fixed iron core 41 integrally or separately, and has a brim-shaped engaging part 34 at the upper end of the movable part 7, and the engaging part 34 operates the electromagnet 5. Are opposed to each other so as to engage with the short-circuit response portion 27 of the trip link 24. The operation link 35 is rotatably held on the case 10 by a fixed shaft 36 below the movable rod 7a. This operating link 35 has an L-shape and has a fixed shaft 36 at its bent portion, a winding portion of a return spring 37 is hooked on the fixed shaft 36, one end of the return spring 37 is locked to the bottom surface of the case 10, and the other end. Is locked to the actuation link 35 to urge the actuation link 35 clockwise, and the spring action presses the lower end of the movable rod 7a upward with one end 35a of the actuation link 35, and The coil tube 33 is positioned by being locked to the inner step of the upper end of the coil tube 33. A return spring (not shown) can be used as the return springs 28 and 37.

The electromagnet 5 detects a short-circuit current by setting the spring force of a return spring (not shown), but a bimetal 38 is provided in the case 10 to detect an overcurrent. bimetal
The base end of 38 is fixed to the load side terminal 11, a gap adjusting screw 39 is provided at the tip, and the tip of the gap adjusting screw 39 faces the overcurrent response portion 26.

The movable contactor 4 is supported in a state in which an intermediate portion thereof is biased upward by an opening spring 42, the movable contact 3 is fixed to a tip portion thereof, and a curved portion 43 of a rear end portion 43a is a lower end of the electromagnet 5. The lower end of the movable frame 30 is connected by a shaft 30a between the opening spring 42 and the movable contact 3 so that the movable contact 3 contacts the fixed contact 1 by the movable frame 30. The movable contactor 4 is pressed in the direction to move. The opening spring 42 has a larger spring force than the handle return spring 22.

The shield plate 9 is formed of an insulating member having a wedge-shaped tip portion 9a, and is slidably supported by a guide groove 46 formed in the case 10 as shown in FIG. It is located laterally between the fixed contact 1 and the movable contact 3, has an engaging hole 47 at the rear end, and the other end 35b of the operating link 35 is engaged with the engaging hole 47. A notch 65 is formed at the rear end of the shield plate 9 to pass the movable rod 7a. The shield plate 9 is pulled by the actuating link 35 by the return spring 37 and is positioned at the retracted position shown in FIG. The movable rod 7a is moved downward by the operation of the electromagnet 5 to return the operation link 35 to the spring.
When pressed against 37, the operating link 35 rotates counterclockwise to move the shielding plate 9 forward by the other end 35b.
As a result, the tip portion 9a of the shield plate 9 enters between the movable contact 3 and the fixed contact 1 in the closed state and shields both of them in the open state. At this time, the movable contactor 4 performs the opening operation against the spring action of the contact pressure given by the opening spring 42.

The fixed contactor 2 is arranged on the lower side of a partition plate 66 which partitions the lower side of the opening / closing / trip means 8 of the case 10, and the fixed contact 1 is opened / closed by being passed through a notch 67 formed in the partition plate 66. It faces the trip means 8 side. The base end portion of the fixed contactor 2 having the fixed contact point 1 at the tip end portion has an extending portion 49 extending partway toward the rear end portion of the movable contactor 4. As a result, when a current flows between the movable contact 4 and the fixed contact 2 while the movable contact 3 and the fixed contact 1 are in contact with each other, an electromagnetic repulsive force is generated, and in the case of an abnormal current, the electromagnetic repulsive force is large. Then, in order to push up the movable contact 3, the opening spring 42 is compressed to open the movable contact 3 to assist the opening operation by the shield plate 9. The base end portion of the fixed contactor 2 extends from the extending portion 49 thereof to the opposite side via the lateral U-shaped bending portion 50,
The opposite side extension portion 44 has a curved portion 45 in the middle portion, is engaged with a fixed shaft 48 provided in the case 10 and is rotatably supported,
Further, a spring 56 is provided closer to the base end 49 'than the fixed shaft 48 to urge the fixed contact 1 in a direction away from the movable contact 3, and the base end 49' is fixed by the plunger 51 of the polar electromagnet 50. Held in.

The polarized electromagnet 50 is provided to connect a remote control control and a timer circuit to have a timer function, and includes a plunger 51, a coil frame 55 around which a coil 52 is wound, yokes 53, 54, and yokes 53, 54. Permanent magnet 69 interposed between
(The magnetic poles are represented by N and S), and the first armature 51a of the plunger 51 contacts the yoke 53 and the second armature 51b.
The stable state is shown in FIG. The base end 49 ′ of the fixed contact 2 is engaged with the groove 57 of the protruding portion of the plunger 51, and the fixed contact 1 is held in the fixed state as the fixed contact 1 by the holding force of the permanent magnet 69 via the plunger 51. To be done. When the coil 52 of the polarized electromagnet 50 is energized, the plunger 51 moves to the opposite side due to excitation, and the fixed contact 2 rotates clockwise around the fixed shaft 48, so that the fixed contact 1 moves from the movable contact 2. Break apart.

In order to form an internal electric circuit of this circuit breaker, it is possible to connect between the bimetal 38 and the coil 32 of the electromagnet 5, between the coil 32 and the movable contact 4, and between the fixed contact 2 and the power supply side terminal 12, respectively. Tow wires 57-59 are connected. Therefore, the internal circuit is the load side terminal when viewed from the load side terminal 11 side.
11 → bimetal 38 → flexible electric wire 57 → coil 32 → flexible electric wire 58 → movable contact 4 → movable contact 3 → fixed contact 1 → fixed contact 2 → flexible electric wire 59 → power supply side terminal 12.

Incidentally, 60 is an energization indicator lamp whose example is a light emitting diode connected to the coil 52 of the polarized electromagnet 50 to display the energization state, and 61 is a window of the case 10 corresponding to the energization indicator lamp 60.
Translucent display board provided on 62, 63 is a gap adjusting screw
A cover plate provided in the window 64 of the case 10 corresponding to 39.

The operation of this circuit breaker will be described. That is, FIG. 1 shows the circuit breaker in the ON state, and FIG. 3 shows the OFF state. When the handle 6 is tilted counterclockwise from the OFF state to the state shown in FIG. 1, the handle 6 rotates about the fixed shaft 16 and the movable shaft 18 rotates counterclockwise. The operating link 19 moves downward while the operating shaft 20 slides on the latch link 23, so that the operating link 19 rotates in a vertical posture.
At this time, the handle return spring 22 is pulled. By the movement of the operating shaft 20, the movable frame 30 having the bearing recess 31 that engages with the operating shaft 20 is guided by the guide 29 and moves downward. The movable contact 4 is pressed by the lower end of the movable frame 30 and rotates counterclockwise from the state of FIG. 3, the movable contact 3 first contacts the fixed contact 1, and then the movable contact 3 contacts the fixed contact 1. In the contact state, the movable contact 3 rotates clockwise around the fixed contact 1 as a fulcrum, and the contact pressure is given by compressing the opening spring 42. At the same time, the movable contact 2 rolls on the surface of the fixed contact 1. By (rolling), the welding bridge is destroyed when contact welding occurs due to the arc at the time of turning on. Opening spring
Since 42 is compressed, its reaction force is applied to the operation link 19 via the movable frame 31, and when the movable shaft 18 crosses the reversing dead center intersecting the line connecting the fixed shaft 16 and the operating shaft 20, the opening The spring 42 pushes up the movable shaft 18 to urge the handle 6 in the tilted direction. The movable shaft 18 is locked by a stopper (not shown), and the handle 6 maintains the state shown in FIG. Therefore, the power supply side terminal
When 12 and the load side terminal 7 are connected to the load of the line, a current flows through the internal electric circuit.

When the handle 6 is tilted from the ON state of FIG. 1 to the state of FIG. 3, the movable shaft 18 rotates clockwise in the opposite direction to the above operation, and the actuating shaft 20 is latched by the biasing force of the opening spring 42.
It slides to 23 and moves upwards, the movable frame 30 moves upwards, and the movable contactor 4 performs a separating operation. When the curved portion 43 at the base end of the movable contactor 4 abuts on the lower end of the electromagnet 5, the movable contactor 4 rotates about the contact point as a fulcrum, and the movable contact 3 is largely separated from the fixed contact 1.

FIG. 4 shows a state immediately after the short circuit current of the abnormal current flows, and FIG. 5 shows a state in which the opening / closing / trip means 8 has completed its operation. When a short-circuit current flows in the internal electric circuit, the trip link 24 is rotated around the fixed shaft 25 by the operation of the electromagnet 5, and the latch link 23 is released. At the same time, the operation link 35 is rotated at the lower end of the movable rod 7a to advance the shield plate 9, and the shield plate 9 is slid on the surface of the movable contact 3 by its tip portion 9a to pry the movable contact 3 to move it. It enters between the contact 3 and the fixed contact 1. As a result, the shield plate 9 blocks the arc generated at the time of opening the electrode and also reliably destroys the contact welding.

Following this operation, the trip operation by the third opening / closing / trip means 8 to reach the state of FIG. 5 is such that the trip link 24 rotates counterclockwise and its latch portion 24a moves to the lower end portion of the latch link 23. When you release from the side,
The latching link 23 rotates counterclockwise around the fixed shaft 16 by the force of the actuating shaft 20 pressing the latching link 23 based on the opening spring 42, and the actuating shaft 20 separates from the bearing recess 31 of the movable frame 30. . At the same time, the movable frame 30 moves upward due to the biasing force of the opening spring 42, the movable contact 4 moves apart accordingly, and the curved portion 43 of the movable contact 4 comes into contact with the lower end of the electromagnet 5 to move the curved portion 43. The movable contactor 4 rotates around the center, and the movable contact 3 further separates from the separated position by the shield plate 9. The open position of the movable contactor 4 is regulated by a stopper (not shown). Further, when the operating shaft 20 is separated from the bearing recess 31, it is not affected by the opening spring 42, so that the handle return spring is
The action of 22 causes the movable shaft 18 to rotate clockwise, so that the handle 6 is in a neutral posture. The trip display is performed according to the neutral posture of the handle 6.

When the current in the internal electric circuit is cut off due to the trip opening, the attraction force of the electromagnet 5 disappears and the movable portion 7 is returned by a return spring (not shown), and at the same time the shield plate 9 is returned. However, the movable contactor 4 is maintained in the open state by the operation of the opening / closing / tripping means 8.

For resetting after the repair of the short-circuit accident, the handle 6 in the neutral posture is tilted from the state shown in FIG. 5 to the off state shown in FIG. Since the movable shaft 18 rotates clockwise by the rotation of the handle 6, the operation link 19 is pulled up, and the operating shaft 20 engages with the bearing recess 31 of the movable frame 30. Also, the reset protrusion 68 of the handle 6
Causes the latch link 23 to rotate clockwise around the fixed shaft 18, the return spring 28 causes the trip link 24 to return, and the latch portion 24a is locked to the side surface of the lower end portion of the latch link 23. As shown in FIG. 3, the latch link 23 is brought into the latched state. This turns off.

Next, when an overcurrent flows in the internal electric circuit in the ON state, the electromagnet 5 does not operate the movable portion 7 because the return spring 37 has a spring force larger than the attractive force, but the bimetal 38 bends due to self-heating. The tip of the gap adjusting screw 39 pushes the overcurrent response portion 26 of the trip link 24, which causes the trip link 24 to rotate and release the latch link 23. The subsequent trip operation of the opening / closing / tripping means 8 is the same as described above.

When a current is applied to the coil 52 of the polar electromagnet 50 in the ON state of FIG. 1, the plunger 51 moves upward in FIG. 1, and the rear end portion 49 of the fixed contactor 2 rotates clockwise. The fixed contact 1 is separated from the movable contact 3. Therefore, the internal current is cut off even when the handle 6 is in the ON position.
On the contrary, even if the fixed contact 1 is in the state shown in FIG.
Since it is turned off by tilting the switch to the off position, the off priority is given in any case.

With this configuration, according to this embodiment, the shielding plate 9 for extinguishing the arc does not interlock with a normal on / off operation, and when an abnormal current, for example, a short-circuit current flows, it interlocks with the operation of the electromagnet 5. The shield plate 9 can be inserted between the fixed contact 1 and the movable contact 3 to rapidly disconnect the movable contact 3 and the fixed contact 1 regardless of the operation of the opening / closing / tripping means 8. Therefore, it is possible to reduce the abrasion of the shield plate 9 due to the repeated on / off operation, and there is no influence of the delay time due to the operation of the opening / closing / tripping means 8, and the shield plate 9 operates after the abnormal current is generated. Since the time required for completion can be shortened and therefore the arc interruption time can be shortened, a large interruption capacity can be realized.

According to the experiment, the time until the operation of the shield plate 9 was completed was 2 ms. FIG. 6 shows an arc voltage waveform diagram at that time. Q ₅ is estimated short-circuit current, Q ₆ is cut-off current, although Q ₇ is contact arc voltage, since the cut-off current decreases as compared with FIG. 7, the fixed contact 1, the movable contact 3, the case 10, shielding plate It can be seen that the damage due to the arc such as 9 is small.

Further, unlike the conventional case, since it is not necessary to increase the operating speed of the shield plate 9 by increasing the spring force of the opening spring 42, the operating load of the handle 6 is not increased.

Further, in this embodiment, after the trip link 24 is operated by the movable portion 7 of the electromagnet 5 to pull out the latch link 23,
Since the shield plate 9 is actuated by the movable rod 7a, the load on the movable portion 7 when the movable contact 4 is forcibly opened is reduced and the movable contact 4
If the contact is welded, it can be destroyed. Further, the electromagnet 5 is provided with a detection unit for detecting an abnormal current.
Since it is also used for, the configuration becomes simple.

A second embodiment of the present invention is shown in FIGS. That is, in the above-described embodiment, the electromagnet 5 also serves as the detection unit, but in this embodiment, the bimetal 38 for detecting an overcurrent is used as an embodiment. In this case, when the short-circuit current flows, the bimetal 38 operates later than the operation of the electromagnet 5.
Therefore, at the time of short circuit, while the movable contact 3 is opened by the shield plate 9 as shown in FIG. 10, the shield plate 9 enters between the movable contact 3 and the fixed contact 1, and then the bimetal 38 is released as shown in FIG. The trip link 24 is operated to trip the latch link 23, and the opening / closing / trip means 8 is trip opened. Others are the same as those in the first embodiment.

Although the movable frame 30 and the movable contactor 4 are connected by the shaft 30a in the above embodiment, the movable frame 30 may be brought into contact with the movable contactor 4 only. Further, the tip portion 9a of the shield plate 9 is formed into a taper so that the shield plate 9 can be inserted between the contacts. However, a taper to insert the shield plate 9 into the side portions of the movable contact 3 and the fixed contact 1 is formed. It's okay.
Further, in the above embodiment, the shield plate 9 is driven by the electromagnet 5 via the actuation link 35, but it may be driven directly.

Further, in this invention, the opening / closing / tripping means is not limited to the above embodiment. For example, the present invention can be applied to a slow-entry fast-breaking type and a reversing spring-type fast-breaking fast-entering type that are configured by the same type of link mechanism as the embodiment. Further, regarding the abnormal current, the above-mentioned embodiment targets the short-circuit current, but it can be applied to the overload current generated by the arc.

〔The invention's effect〕

According to the circuit breaker of the present invention, in a normal on / off operation, the shielding plate for arc extinguishing does not work together, and when an abnormal current, for example, a short-circuit current flows, the opening / closing / tripping means of the opening / closing / tripping means interlock with the operation of the electromagnet. The shield plate can be inserted between the fixed contact and the movable contact to quickly disconnect the movable contact and the fixed contact without depending on the operation. Therefore, it is possible to reduce the abrasion of the shield plate due to repeated on / off operations, and there is no influence of the delay time due to the operation of the opening / closing / tripping means, until the shield plate completes its operation after the abnormal current is generated. The time can be shortened, and therefore the arc interruption time can be shortened, so that a large interruption capacity can be realized. Moreover, there is no need to increase the spring force of the opening spring of the opening / closing / tripping means, and the operating load of the handle need not be increased.

[Brief description of drawings]

FIG. 1 is a sectional view of an ON state of a first embodiment of the present invention,
2 is a partial perspective view showing the shield plate portion, FIG. 3 is a sectional view in an off state, FIG. 4 is a sectional view showing the operating state of the shield plate immediately after the trip, and FIG. 5 is a state in which the trip operation is completed. 6 is a sectional view showing the arc voltage waveform of this embodiment, FIG. 7 is a conventional arc voltage waveform diagram, and FIG.
FIG. 9 is a sectional view showing an off state, FIG. 10 is a sectional view showing an operating state of the shielding plate immediately after the trip, and FIG. 11 is a sectional view showing a state where the trip operation is completed. FIG. 12 and FIG. 12 are partial cross-sectional views of a conventional example. 1 ... Fixed contact, 2 ... Fixed contact, 3 ... Moving contact,
4 ... movable contact, 5 ... electromagnet, 6 ... handle, 7
...... Movable part, 8 ...... Open / close / trip means, 9 ...... Shield plate

Claims (3)

[Claims] 1. A fixed contact having a fixed contact, and a movable contact having a movable contact that opens and closes with respect to the fixed contact.
An electromagnet that detects an abnormal current in the load, an arc-extinguishing shield plate that enters between the movable contact and the fixed contact that are closed in conjunction with the operation of this electromagnet, and the movable contactor that is opened and closed by the handle. A circuit breaker comprising: an opening / closing means for tripping and opening the movable contact, which is opened by the shield plate, in conjunction with a detecting section for operating and detecting an abnormal current of a load. 2. The circuit breaker according to claim 1, wherein the detecting portion of the opening / closing / tripping means is the electromagnet. 3. The circuit breaker according to claim 1 or 2, wherein the shield plate has a wedge-shaped tip portion.