JP2708988B2 - Current detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detecting device for a circuit breaker.

[0002]

2. Description of the Related Art Conventionally, when detecting a current value equal to or less than a rated current, a current transformer is provided outside a circuit breaker. However, there has been a problem that an installation space is required and construction is troublesome. For this reason, it has been required to incorporate a current transformer into a circuit breaker and process electric circuit information such as a current value, a power amount and a power factor in the circuit breaker.

In a circuit breaker, a current transformer and a trip device (release relay) are used as a means for detecting an overcurrent in a circuit without using a bimetal or an instantaneous electromagnet. In this example, the current transformer for each phase is built into the circuit breaker, the current in the circuit is converted to voltage, the signal is sent to the overcurrent detection circuit, and the trip device is driven when the output signal exceeds the set level. To cut off the electric circuit.

[0004]

However, a power supply circuit such as a trip circuit of a trip device inputs and rectifies an inter-phase voltage of an electric circuit, so that when a short-circuit current flows through the electric circuit,
There is a drawback that the inter-phase voltage is reduced, the voltage becomes unstable, and the trip device may not operate. In addition, the current transformer has a limit to the current value that can be detected because the current transformer saturates when a large current flows, and the output signal of the current transformer due to the residual magnetic flux density after the short-circuit current flows However, there is a disadvantage that the electric circuit information cannot be accurately detected.

[0005] In addition, there is a disadvantage that when the current transformer is built in the circuit breaker, the assemblability is poor. Therefore, an object of the present invention is to provide a current detection device capable of stabilizing a power supply at the time of short circuit, accurately detecting electric circuit information, and improving assemblability.

[0006]

According to a first aspect of the present invention, there is provided a current detecting apparatus comprising: a first current detecting circuit having a first current transformer for detecting a current up to a predetermined reference value including a rated current value; A second current detection circuit having a second current transformer with a gap for detecting a current equal to or greater than a predetermined reference value, and input signals from the first current detection circuit and the second current detection circuit.
And it outputs the electric path information Te control circuit and tripping circuit and said second current transformer is connected to the path which is operated by the output signal of the control circuit or <br/> the second current detection circuit And a power supply circuit having an input terminal connected to the output terminal of the switch and having an output terminal connected to the control circuit and the trip circuit.

[0007] 請 Motomeko second current sensing device, the current detection device according to claim 1, wherein the second current transformer has a core of a pair of L-shaped, respectively, one end of each piece of the cores And a pair of coil bobbins for inserting and fixing the bent portion of the core with a pin, and connecting each other piece of the core to the other end of the coil bobbin with a pin to form a gap between the pair of cores. It is characterized by the following.

[0008] Current detecting device according to claim 3 resides in that in Claim 1, together if provided with a leakage current detection circuit having a zero-phase current transformer, receives the output signal of the leakage current detection circuit to said control circuit, said A first current transformer and the second current transformer
The number is obtained by one less than the path number of poles, respectively. According to a fourth aspect of the present invention, there is provided a current detecting device according to the first aspect.
In the discharge device, a current transformer is housed inside with a wire groove on the front and rear surfaces, a lateral groove on the bottom surface, a screw hole on the bottom surface of the lateral groove, and a narrow groove on both side surfaces of the lateral groove. Case and
An electric wire penetrating the electric wire through hole and the current transformer, a movable contact connected to one end of the electric wire, and connected to the other end of the electric wire so that both sides are fitted in the narrow groove and aligned with the screw hole. Circuit breaker having a terminal plate having a through hole formed therein and a hole for accommodating the case and matching the screw hole
And Bo Di, in which a screw which is screwed into the threaded hole through the hole and the through hole.

[0009]

According to the present invention, when the current of the electric circuit is lower than the predetermined reference value, the output signal of the first current detecting circuit is processed by the control circuit and the electric current of the electric circuit such as the current value or the electric power is processed. Output information. When the current of the electric circuit is larger than a predetermined reference value, the output signal of the second current detection circuit is compared with the set level by the control circuit, and when the output signal exceeds the set level, an overcurrent detection signal is pulled. Input to the disconnection circuit to activate the tripping device. When a short circuit occurs, the output signal of the second current detection circuit is directly input to the trip circuit. At the time of this short circuit, the voltage between the phases decreases, but the output of the power supply circuit is stabilized because the output of the second current transformer is input to the power supply circuit.

[0010] In this way, by sharing the detection area by two current transformers, design is facilitated, given current transformer
Can also be diverted can electronic power electrocardiograph is to use a high-precision current transformer to detect the small current than the reference value, also predetermined
For currents greater than the reference value of
By using a current transformer, the saturation and residual
The output voltage error due to the influence of the magnetic flux density can be reduced,
To reduce saturation, increase the number of windings or increase the iron core cross-sectional area.
Since it is not large, it can be miniaturized and uses a Hall element.
Advantageously it in cost as compared to those who are, also because it connects the output terminal of the second current transformer to the input terminal of the power supply circuit, it is possible to stabilize the power supply circuit during a short circuit, The tripping device using the tripping circuit can be reliably operated.

[0011]

[0012] According to the current detecting device of the second aspect,
1 , the second current transformer includes a pair of L-shaped cores, and a pair of coil bobbins each of which inserts one of the cores from one end and fixes a bent portion of the core with a pin, Since each other piece of the core is connected to the other end of the coil bobbin by a pin to form a gap between the pair of cores, the pin position is set so as to have the function of claim 1 and obtain a gap dimension. By doing so, an accurate gap can be obtained, and the assemblability can be improved due to the connection by pins.

According to the current detecting device according to claim 3, in claim 1, comprising a leakage current detection circuit having a zero-phase current transformer, when receiving the output signal of the leakage current detection circuit in the control circuit together , since the number of the first current transformer and the second current transformer has one less than the respective number path of poles, in addition to having the effect of claim 1, ground and leakage by leakage current detection circuit , And the trip circuit can be operated. Although a zero-phase current transformer is added, the first current transformer and the second current transformer of each phase can be reduced, so that the size is not increased.

According to the current detecting device according to claim 4, claim
In addition to having the function of (1), the case in which the movable contact and the current transformer are accommodated and the terminal can be integrated into the circuit breaker body, so that the assemblability can be improved.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. That is, in FIG. 1, the current detection device of the circuit breaker includes a first current detection circuit 1, a second current detection circuit 2, a control circuit 3, a power supply circuit 4, and a trip circuit 5. . As shown in FIG. 5, the circuit breaker has a trip device 6 operated by the trip circuit 5 and a mechanism 50 operated by the trip device 6 to open the contact 7.

The first current detecting circuit 1 has a first current transformer 8 for detecting a current up to a predetermined reference value including a rated current value. The predetermined reference value in the embodiment is set to a quasi-overcurrent value slightly higher than the rated current, that is, a current value of 150% of the rated current, and a high-precision current transformer that can be detected with high accuracy is used. The second current detection circuit 2 has a second current transformer 9 for detecting a current equal to or higher than a predetermined reference value. The embodiment has a function of detecting an overcurrent and a short-circuit current. in this case,
When detecting the short-circuit current, the second current detection circuit 2 directly outputs a short-circuit detection signal by a known means.

The control circuit 3 receives the output signals of the first current detection circuit 1 and the second current detection circuit 2 and outputs electric circuit information such as electric current value of the electric circuit and overcurrent. In the embodiment, an A / D conversion circuit 10 for converting an analog signal into a digital signal
And a microcomputer (referred to as a microcomputer) 11 for inputting the A / D conversion circuit 10. That is, the output signal of the first current detection circuit 1 is sent to the microcomputer 11 through the A / D conversion circuit 10 to calculate and output electric circuit information such as current value and electric power by a known program or means. In addition, an output signal of the second current detection circuit 2 is input to determine whether or not an overcurrent occurs. When an overcurrent occurs, an overcurrent detection signal is output as electric circuit information.

The trip circuit 5 is operated by an output signal of the control circuit 3 or the second current detection circuit 2. That is,
The overcurrent detection signal of the control circuit 3 is input and input to the trip circuit 5, and the second current detection circuit 2 inputs the short-circuit current detection signal to the trip circuit 5 and directly drives the trip circuit 5.
The trip device 6 is activated by the output signal of the trip circuit 5,
The mechanism 50 of FIG. 5 operates to open the contact 7 connected to the electric circuit of FIG.

The power supply circuit 4 has an input terminal connected to the electric circuit (R phase, T phase) and connected to an output terminal of the second current transformer 9 and connected to the control circuit 3 and the trip circuit 5. Output end. In the embodiment, the inter-phase voltage and the like are rectified, and the first current detection circuit 1 and the A / D conversion circuit 1 of the control circuit 3 are rectified.
0, power is supplied to the microcomputer 11 and the trip circuit 5. In this case, the inter-phase voltage decreases at the time of short circuit, but since the output of the second current transformer 9 is input to the input terminal of the power supply circuit 4,
Output can be stabilized.

In FIG. 1, reference numeral 12 denotes a circuit case housing a first current detecting circuit 1, a second current detecting circuit 2, a control circuit 3, and a trip circuit 5. In FIG. 2, 13
Is a current transformer case having an opening 14 on one side surface, in which a wire through hole 15 is formed in a side plate 48 serving as a back wall facing the opening 14, and a recess 16 is formed on an outer surface of a bottom portion 47. A terminal guide groove 17 is formed on the inner surface of the substrate. The second current transformer 9 is connected to the electric wire through hole 15 inside the side plate 48.
, And the first current transformer 8 is arranged so as to be aligned with the front side thereof and is accommodated therein.

In FIG. 3, a first current transformer 8 and a second current transformer 9 are incorporated in a current transformer case 13, and a braided wire forming a part of an electric circuit through each of the current transformer cases 13 is shown in FIG. Through the through-hole 20 of the cover 18 that closes the opening 14 and welds the movable contact connecting portion at one end of the wire 19 to the movable contact 22 of the contact portion 7 and connects the terminal at the other end. The fixed terminal 21 (only a part is shown) is welded to the portion. Thus, the second current transformer 9 is arranged on the movable contact 22 side, and the first current transformer 8 is arranged on the load side terminal 21 side. Reference numerals 29 and 30 denote shafts, and reference numeral 46 denotes a movable contact.
The fixed terminal 21 is formed by bending a flat plate into a Z-shape.
A screw hole 23 is formed in one piece, a through-hole 24 is formed in the other piece, and both sides of one piece are guided into the terminal guide grooves 17 and inserted into the recesses 16, and the movable contact 22, the current transformer case 13 and the load side And the terminal 21 are integrated.

In FIG. 4, the current transformer case 13 is placed in the circuit breaker body 26, and a screw 25 (only a part is shown) is screwed into the screw hole 23 through a hole 27 formed at the bottom of the circuit breaker body 26. The current transformer case 13 and the terminal 21 on the load side can be fixed to the circuit breaker body 26 by tightening.
Therefore, the configuration is simple and the assembly is easy.

In FIG. 5, a current transformer case 13 having a load-side terminal 21, a first current transformer 8, and a second current transformer 9 built therein.
The movable contact 22 of the mechanism 50 is integrally inserted into the circuit breaker body 26, the mechanism 50 is fixed by fixing means (not shown), and the circuit breaker body 26 is fixed by the screw 25 as described above. Is done. Further, the circuit case 12 and the trip device 6 are incorporated, and the movable contact 2
A fixed contact (not shown) with a power supply side terminal having a fixed contact (not shown) facing the second movable contact 46 is incorporated in the breaker body 26 to assemble a circuit breaker.

According to this embodiment, when the current of the electric circuit is lower than the predetermined reference value, the output signal of the first current detecting circuit 1 is processed by the control circuit 3 and the electric circuit information such as the current value and the electric power is processed. Output. When the current of the electric circuit is larger than a predetermined reference value, the output signal of the second current detection circuit 2 is compared with a set level by the control circuit 3, and when the output signal exceeds the set level, an overcurrent detection signal is output. Is input to the tripping circuit 5 to activate the tripping device. When a short circuit occurs, the output signal of the second current detection circuit 2 is directly input to the trip circuit 5. During this short circuit, the inter-phase voltage decreases, but the output of the power supply circuit 4 is stabilized because the output of the second current transformer 9 is input to the power supply circuit 4.

By sharing the detection area with the two current transformers, the current transformer can be easily designed ,
Can also be diverted can electronic power electrocardiograph is to use a high-precision current transformer to detect the small current than the reference value, also predetermined
For currents greater than the reference value of
By using the current transformer 9, even if an overcurrent flows, saturation or
Output voltage error due to residual magnetic flux density can be reduced.
Increase the number of windings to reduce saturation
The size can be reduced because the product does not increase, and the Hall element
Compared to those using be advantageous in terms of cost, also because it connects the output terminal of the second current transformer 9 to the input terminal of the power supply circuit 4, it is possible to stabilize the power supply circuit during a short circuit Thus, the tripping device using the tripping circuit can be reliably operated.

In this way, the state of the electric circuit of the circuit breaker can be accurately known. Further, by using a high-precision current transformer, a current value up to a quasi-overcurrent value slightly exceeding the rated current can be detected with high accuracy. Further, in this embodiment, the terminal 21 on the load side is connected to the concave portion 1 of the current transformer case 13.
6 into the terminal guide groove 17 and the screw hole 23 of the terminal 21.
By tightening the screw 25 through the hole 27 of the circuit breaker body 26, the terminal 21 is integrally fixed to the circuit breaker body 26 via the current transformer case 13, so that the assembling property is further improved.

FIGS. 6 to 8 show a second embodiment of the present invention.
Shown in That is, this current detecting device is the first embodiment.
And the second current transformer 9 with a gap.
In the embodiment, a pair of L-shaped cores 33 and 35 and one piece of each of the cores 33 and 35 are inserted from one end side to form a core 3.
A pair of coil bobbins 32 and 38 for fixing the bent portions 37 of the cores 3 and 35 with pins 34, and the other pieces of the cores 33 and 35 are connected to the other end sides of the coil bibons 32 and 38 by pins 28, respectively. A gap G is formed between 33 and 35. 39, 40 are secondary side coils, 4
Reference numerals 1 and 42 denote coil terminals. In FIG. 8, reference numeral 43 denotes a pin hole for passing the pin 34 of the coil bobbins 32 and 35;
Reference numeral 4 denotes pin holes of the cores 33 and 35.

According to this embodiment, since the second current transformer 9 has the gap G in the cores 33 and 35, the error of the output voltage due to the influence of saturation and residual magnetic flux density can be reduced even if an overcurrent flows. In addition, it can contribute to stabilization of the power supply at the time of short circuit. Further, since the second current transformer 9 is configured as in the embodiment, an accurate gap can be obtained by setting the pin position so that the gap dimension can be obtained, and the assemblability is improved due to the connection by the pin 28. can do. In this regard, conventionally, the gap G is formed using a spacer or the like, but has a disadvantage that it is not easy to assemble.

Although a gap is provided in the core of the second current transformer 9 in the above-described embodiment, the first current transformer 8 or both may be used. A third embodiment of the present invention is shown in FIGS. That is, this current detection device is
In the embodiment, a leakage current detection circuit 45 having a zero-phase current transformer 51 is provided, an output signal of the leakage current detection circuit 45 is input to the control circuit 3, and a first current transformer 8 and a second The number of flowers 9 is one less than the number of poles of the electric circuit .

In the embodiment, the output signal of the leakage current detection device 45 is input to the A / D conversion circuit 10 of the control circuit 3.
Other configurations in FIG. 9 are the same as those in FIG. The first current transformer 8 detects up to 150% of the rated current with high accuracy, inputs the output signal to the first current detection circuit 1 , sends the signal to the microcomputer 11 through the A / D conversion circuit 10, And circuit information such as current value and electric power of the T phase. The circuit information such as the S-phase current value is obtained by inputting the output signal of the zero-phase current transformer 51 to the leakage current detection circuit 45 and sending the signal from the A / D conversion circuit 10 to the microcomputer 11. Together with the output signal of. When an overcurrent flows, the output signal of the second current transformer 9 is input to the second current detection circuit 2 in the R phase and the T phase, and sent to the microcomputer 11 through the A / D conversion circuit 10 to make a determination. And the S phase is a zero-phase current transformer 51.
Is input to the leakage current detection circuit 45 and sent from the A / D conversion circuit 10 to the microcomputer 11, and is calculated and determined together with the output signal of the second current transformer 9 to make a judgment.
To activate the tripping device 6 to cut off the electric circuit. When a short-circuit current further flows, the output signal of the second current transformer 9 is sent directly from the second current detection signal 2 to the trip circuit 5, and the trip device 6 is started. Also, if a leakage current flows,
The output signal of the zero-phase current transformer 51 is input to the leakage current detection circuit 45, sent to the microcomputer 11 through the A / D conversion circuit 10, determined, and the tripping device 6 is activated through the tripping circuit 5. Others are the same as the operation of FIG.

In FIG. 10, a first current transformer 8, a second current transformer 9 and a zero-phase current transformer 51 are housed in a current transformer case 13. In this case, the width of the current transformer case 13 at the center is about half the thickness, and the wire through hole 15 ′ at the center is formed large to pass three wires 19. A zero-phase current transformer 51 is built in the center of the current transformer case 13, and the two current transformers 9 and the first current transformer 8 are mounted on both sides thereof in the current transformer case 13 in this order. 52 is a groove for guiding the electric wire 19.

In FIGS. 11 to 13, the R-phase and T-phase electric wires 19 are passed through the first current transformer 8 and the second current transformer 9 and then turned back together with the S-phase electric wire 19 to produce a zero-phase current. The connecting part for the movable contact at one end of the electric wire 19 of each phase is welded to the movable contact 22 and the connecting part for the terminal at the other end is welded to the terminal 21 on the load side. That is, R, T
As for the phase electric wire 19, one end is welded to the end of the movable contact 22, the electric current is turned back through the first current transformer 8 and the second current transformer 9, and the other is passed through the zero-phase current transformer 51. Terminal 21 on the load side
To weld. For the S phase, the electric wire 1 is connected to the movable contact 22.
9 is welded through a zero-phase current transformer 51 and the other end is welded to the terminal 21 on the load side. The connection structure of the load-side terminal 21 connected to the electric wire 19 is the same as that of the first embodiment.

According to this embodiment, the zero-phase current detection circuit 4
5, the detection signal of the ground fault and the earth leakage can be obtained, whereby the tripping circuit 5 can be operated. That is, as in the first embodiment, the current value of the R and T-phase electric circuits, electric circuit information such as electric power can be accurately known by the first current transformer 8, and the state of the S-phase electric circuit can be reduced to zero. It can be accurately known by the signal of the phase current detection circuit 45 and the signal of the first current detection circuit 1, and is detected by the output signal of the second current transformer 9 having an overcurrent or short circuit, and the ground fault and the earth leakage are detected. It can be detected by the zero-phase current transformer 51. Although a zero-phase current transformer 51 is added, the first current transformer 8 and the second current transformer 9 of the S phase can be reduced, so that the size is not increased.

The R-phase and T-phase electric circuits 19 pass through the first current transformer 8 and the second current transformer 9 and the S-phase and the zero-phase current transformer 51, and one end of each phase electric circuit is connected. Since the connecting portion for the movable contact was used and the other end was used as the connecting portion for the terminal, the movable contact 2
2, the current transformer case 13 and the load-side terminal 21 can be integrated into a circuit breaker or the like, so that the assemblability can be improved.

Although the above embodiment has a three-pole structure,
The present invention can be applied to a multipolar structure having two or three or more poles. A first current detection circuit 1 and a second current detection circuit 2
May be shared by the first current transformer 8 and the second current transformer 9.

[0036]

According to the first aspect of the present invention, the design of the current transformer is facilitated by sharing the detection area with the two current transformers, and the detection of a current smaller than a predetermined reference value is achieved. to <br/> precision current transformer can also be diverted can electronic power electrocardiograph is used, also larger current than a predetermined reference value
Overcurrent by using a second current transformer with a gap.
Even if current flows, output voltage due to saturation and residual magnetic flux density
To reduce the voltage error and to prevent saturation.
Compact because it does not increase or increase the iron core cross-sectional area
In terms of cost compared to those using Hall elements.
Advantageously, and since the output terminal of the second current transformer is connected to the input terminal of the power supply circuit, the power supply circuit can be stabilized in the event of a short circuit, and the tripping device using the tripping circuit can be reliably used. There is an effect that it can be made to operate.

[0037]

According to the current detecting device of the second aspect ,
1 , the second current transformer includes a pair of L-shaped cores, and a pair of coil bobbins each of which inserts one of the cores from one end and fixes a bent portion of the core with a pin, Since each other piece of the core is connected to the other end of the coil bobbin by a pin to form a gap between the pair of cores, the pin position is set so as to have the function of claim 1 and obtain a gap dimension. By doing so, an accurate gap can be obtained, and the assemblability can be improved due to the connection by pins.

[0039] According to the current detecting device according to claim 3, in claim 1, comprising a leakage current detection circuit having a zero-phase current transformer, when receiving the output signal of the leakage current detection circuit in the control circuit together , since the number of the first current transformer and the second current transformer has one less than the respective number path of poles, in addition to having the effect of claim 1, ground and leakage by leakage current detection circuit , And the trip circuit can be operated. Although a zero-phase current transformer is added, the first current transformer and the second current transformer of each phase can be reduced, so that the size is not increased.

According to the current detecting device of the fourth aspect, the present invention provides
In addition to the effect of (1), the case in which the movable contact and the current transformer are accommodated and the terminal can be integrated into the circuit breaker body, so that the assemblability can be improved.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of a first embodiment of the present invention.

FIG. 2 is an exploded perspective view for explaining storage of a current transformer.

FIG. 3 is a perspective view showing connection of a current transformer.

FIG. 4 is a perspective view illustrating fixing of a current transformer case.

FIG. 5 is an exploded perspective view of the circuit breaker.

FIG. 6 is a perspective view of a current transformer according to a second embodiment.

FIG. 7 is a sectional view of the same.

FIG. 8 is a partially exploded perspective view thereof.

FIG. 9 is a block circuit diagram of a third embodiment.

FIG. 10 is an exploded perspective view for explaining storage of a current transformer.

FIG. 11 is a perspective view showing connection of a current transformer.

FIG. 12 is a sectional view of a current transformer.

FIG. 13 is a perspective view showing wiring of an electric circuit on the primary side of the current transformer.

FIG. 14 is an exploded perspective view of the circuit breaker.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first current detection circuit 2 second current detection circuit 3 control circuit 4 power supply circuit 5 trip circuit 8 first current transformer 9 second current transformer

Continuation of the front page (72) Inventor Takehiko Okada 1048 Odomo Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Works, Ltd. (56) References JP-A-60-13419 (JP, A) JP-A-60-98818 (JP, A) JP-A-57-95125 (JP, A) JP-A-55-77832 (JP, U) JP-A-55-38496 (JP, U)

Claims (4)

(57) [Claims] 1. A first current detection circuit having a first current transformer for detecting a current up to a predetermined reference value including a rated current value, and a first current detection circuit having a gap for detecting a current higher than the predetermined reference value. a second current detection circuit having a second current transformer, and a control circuit for outputting an input to electric path information output signal of the first current detection circuit and the second current detection circuit, the control circuit or the a tripping circuit operated by the output signal of the second current detection circuit, said control circuit and said having an input coupled to the output of the second current transformer is connected to said path And a power supply circuit having an output terminal connected to the trip circuit. 2. The current detection device according to claim 1, wherein
The second current transformer includes a pair of L-shaped cores,
Each of the cores includes a pair of coil bobbins each of which is inserted from one end side to fix a bent portion of the core with a pin, and the other end of the core is connected to the other end side of the coil bobbin by a pin. A current detection device, wherein a gap is formed between a pair of cores. 3. A comprising a leakage current detection circuit having a zero-phase current transformer, the leakage current when the output signal of the detection circuit is inputted to the control circuit both said first current transformer and the second
2. The current detection device according to claim 1, wherein the number of current transformers is one less than the number of poles of the electric circuit . 4. The current detecting device according to claim 1, wherein
A case in which a current transformer is housed inside having a through hole on the front and rear surfaces, a lateral groove on the bottom surface, a screw hole on the bottom surface of the lateral groove, and a narrow groove on both side surfaces of the lateral groove, An electric wire penetrating the through hole and the current transformer, a movable contact connected to one end of the electric wire, and connected to the other end of the electric wire so that both sides are fitted in the narrow groove and aligned with the screw hole. a terminal plate having a through hole is formed, comprising: a breaker board di having a hole aligned with the screw hole as well as accommodating the case, and a screw which is screwed into the threaded hole through the hole and the through hole current Detection device.