JP2000147023A - Large-aperture current probe with sensitivity-adjusting function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily adjust the sensitivity of Rogowskii coil used for measuring surge currents of a current probe, which measures an electric current in a noncontacting state in accordance with the state of the measurement site, without being influenced by the size and shape of an object to be measured nor by the measurement conditions. SOLUTION: The sensitivity of a Rogowskii coil 1 of a current probe is adjusted, in such a way that the coil 1 is wound a plurality of times around an object 3 to be measured and the number of turns of the coil 1 is changed, a plurality of Rogowskii coils are installed to the object 3, and the number of the connected coils is changed in accordance with the measurement condition, a ferromagnetic material is inserted into the coil 1, or the coil 1 is covered with a metallic shield having slits, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-diameter current probe used for measuring a surge current in a non-contact current measurement.

[0002]

2. Description of the Related Art Conventionally, in a method of measuring a lightning surge current or the like using a Rogowski coil, it is not necessary to change the shape of an object to be measured, and current can be measured in a non-contact manner. Alternatively, it is most often used as a method for measuring a lightning surge current flowing through a structure such as a pillar or a beam of a building.

FIG. 10 is a diagram showing the principle configuration of a Rogowski coil. In the figure, the Rogowski coil has a coil 32 in which an insulated conductor is wound around an annular coil support 31 at a uniform pitch, and a return line 33 in which the terminal wire is folded back through the center of the coil 32. The structure is such that the first insulated wire and the folded insulated wire are pulled out from a close position. Therefore, the coil 32 corresponds to A in FIG.
As shown in the cross-sectional view taken along the line A, the return line 33 enters the inside of the coil 32 wound in an annular shape. The DUT 3 shown in the figure is an annular coil support 31 on which the coil 32 is wound.
Penetrates inside. When a current flows in the longitudinal direction of the DUT 3, that is, in a direction perpendicular to the plane of the drawing, the magnetic field penetrating the annular coil support 31 changes, and the coil 32
And a surge current is obtained by supplying the induced voltage to a subsequent circuit of the Rogowski coil.

FIG. 11 shows the source of the surge current and the DUT 3.
Are electromagnetically coupled to the coil 32, and the state in which the Rogowski coil composed of the annular support 31, the coil 32 and the return line 33 is connected to the integration circuit that is the subsequent circuit is an equivalent circuit. Show. In the figure, a current source 34 of a surge current flowing through the device under test is electromagnetically coupled to an inductance 35 of a Rogowski coil, and a resistor 36 formed by the coil 32 and the return line 33 and a current source 34 between the coil 32 and the return line 33. The Rogowski coil is equivalently represented by the combined stray capacitance 37. An integrating circuit as a subsequent circuit for compensating the frequency characteristic of the measurement system is represented by a resistor 38 and a capacitor 39. Here, in order to change the current detection sensitivity of the Rogowski coil, the time constant of the integrating circuit composed of the resistor 38 and the capacitor 39 is changed, or the diameter of the coil is changed in order to change the inductance 35 of the Rogowski coil. Need to be changed. In this case, in the method by changing the integration circuit constant, it is necessary to reduce the time constant as shown in FIG.
₁ → C ₅ ), so that the frequency band that can be used is narrowed by increasing the sensitivity. FIG. 12 shows a calculation example regarding a change in the sensitivity characteristic due to the change in the integration circuit time constant.
The horizontal axis represents the frequency, and the vertical axis represents the voltage-current conversion coefficient described later. In the method of changing the coil diameter, the sensitivity can be increased by increasing the diameter of the coil support. However, it is not easy to change the coil diameter at an actual measurement site, and coils having different diameters are not easily obtained. Had to be prepared more than once.

[0005]

As described above, when measuring the lightning surge current of pillars, beams, etc. of a building, the value of the lightning surge current varies greatly depending on the measurement location. It was necessary to replace with a different Rogowski coil, and the measurement was complicated. An object of the present invention is to provide a large-diameter current probe with a sensitivity adjustment function that can easily switch the sensitivity at the measurement site without impairing the frequency characteristics.

[0006]

A coil having an insulated conductor wound at a uniform pitch on an annular coil support, and a return line folded back from one end through the center of the coil,
It has a structure in which the lead wire at the beginning of winding and the folded lead wire are drawn out close to each other.When a current flows through the DUT and the magnetic field penetrating the coil changes, a voltage is induced in this coil, and a current is generated from this voltage. In a current probe used for surge current measurement using a Rogowski coil having a required mechanism, in claim 1, the current probe has a structure that changes the number of windings of the Rogowski coil around an object to be measured. I have.

According to a second aspect of the present invention, a plurality of the Rogowski coils for the current probe are attached to the object to be measured, and the combined output voltage is obtained by changing the number of the attached Rogowski coils.

According to a third aspect of the present invention, the magnetic permeability is changed by inserting and removing a ferromagnetic substance into and from the Rogowski coil for the current probe, thereby changing the inductance of the coil.

According to a fourth aspect of the present invention, a metal shield having a slit is provided in the Rogowski coil for the current probe, and the sensitivity can be adjusted without changing the physical shape of the coil by changing the gap between the slits. I have.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a current probe using a Rogowski coil, a sensitivity V corresponding to a voltage-to-current conversion coefficient given by a voltage induced by a current I flowing through an object 3 is approximately expressed by the following equation. Will be revealed.

[0011]

(Equation 1)

Here, n is the number of turns of the coil per unit length, a is the cross-sectional area of the coil, μ is the magnetic permeability, and H is the magnetic field. When measuring the current of a straight conductor, the magnetic field generated by the current I is

[0013]

(Equation 2)

## EQU1 ## When the coil makes one round of the conductor, Equation (1) is

[0015]

(Equation 3)

And therefore:

[0017]

(Equation 4)

## EQU1 ## As shown in FIG. 1, when the coil makes M turns (four turns in the figure) around the conductor, the expression (1) becomes

[0019]

(Equation 5)

Therefore,

[0021]

(Equation 6)

Thus, a voltage that is M times higher than that of the equation (4) in the case of one rotation appears. That is, the sensitivity V can be adjusted by changing the winding number M. On the other hand, assuming that the output voltage of one coil is V _i , as shown in the equivalent circuit of FIG.

[0023]

(Equation 7)

## EQU1 ## If the same coil as the N pieces used, since the output equals the coils, if the output of one coil and V _a, V = NV _a next, sensitivity becomes N times.
That is, the sensitivity V can be adjusted by changing the number of coils used for measurement. Also, (Equation 4)
As shown in the equation, the sensitivity V is proportional to the magnetic permeability μ. Therefore, as shown in FIG. 8, the sensitivity can be adjusted by inserting a flexible ferromagnetic material such as rubber ferrite inside the coil.

(1) FIG. 1 is a view showing an embodiment in which a Rogowski coil according to the present invention is installed on an object to be measured. In the figure, a Rogowski coil 1 is
Is wound spirally (four turns in the figure), so that it can be obtained from the output detection terminal 2 having a sensitivity four times that of the case of one turn. Therefore, winding 1
By tapping each time and switching the tap, it is possible to effectively adjust the current sensitivity.

(2) FIG. 2 is a view showing another embodiment of a Rogowski coil according to the present invention. In the figure, four unit parts 4 each composed of a Rogowski coil are arranged in the figure so as to surround the DUT 3, each unit part 4 has a voltage detection terminal 5, and each voltage detection terminal 5 is added. FIG. 3 shows an equivalent circuit of the present embodiment. As shown in the figure, the output of the voltage detection terminal 5 of each coil is separately connected to an integrating circuit. The outputs of the integrating circuits are sequentially connected in series by a connection line 6 and are drawn from these connection points. A wire is connected to each contact of the switch 7, and the output is taken out from the terminals 8 and 9 after the number of connected coils is changed by switching the switch 7.
In this case, since an integrating circuit is connected to each coil, even if the number of unit components 4 is switched, constants other than the coupling coefficient of the transformer in the equivalent circuit do not change. Therefore, there is an advantage that the sensitivity can be easily adjusted without affecting the frequency characteristics.

The circuit configuration shown in FIG. 4 is also possible with the coil configuration shown in FIG. As shown in the figure, the voltage detection terminal 5 of the unit component 4 is connected to each contact of the switch 7, and the variable resistor 11 and the variable capacitance capacitor 12 that constitute the integration circuit are common, and according to the number of unit components 4 to be connected. By adjusting the time constant in conjunction with the connected coil, the frequency characteristic is corrected, and the output voltage is obtained from the output terminals 13 and 14. FIG. 5 shows the result of the sensitivity measurement of the present embodiment. In the figure, the horizontal axis represents frequency, and the vertical axis represents voltage-current conversion coefficient. As shown in FIG. 5, the sensitivity, that is, the current-voltage conversion coefficient can be changed without changing the frequency characteristic by changing the number of coils installed on the device under test.

(3) FIG. 6 shows still another embodiment of the Rogowski coil connection method combining a plurality of unit components 4 according to the configuration of FIG. In the figure, the Rogowski coil unit has a structure including an integrating circuit and detecting a voltage obtained by adding voltage detecting terminals 16 and 17 which are output terminals of the integrating circuit by an adding circuit 18. Since such an addition circuit 18 also has a function as a buffer amplifier, the degree of freedom in designing the integration circuit can be increased.

(4) FIG. 7 shows another embodiment of Rogowski coil connection combining unit parts 4 according to the present invention. In the figure, the integration circuit is not included in the Rogowski coil unit.
The number of the adding circuits 21 is equal to the number of the coils connecting the outputs of 9 and 20.
Is a structure for detecting the added voltage. in this case,
Since the integration process can be performed after the addition by the addition circuit 21, FIG. 7A is included in the addition circuit or after the addition process by the addition circuit as shown in FIG. 7B. Can be loaded with an integrating circuit.

(5) FIG. 8 is a view showing another embodiment of a current probe having a sensitivity adjustment function using a Rogowski coil according to the present invention. FIG. 8A shows a Rogowski coil 2
2 shows a cross section of a structure in which a ferromagnetic substance 23 is inserted into the inside 2, in which a coil 22 having this cross section is arranged so as to wind around the DUT 3. here,
The ferromagnetic material is flexible like a fluororesin-based material, and if the space inside the coil 22 is filled with a self-lubricating material, the position of the ferromagnetic material in the coil 22 can be stabilized. In addition, the ferromagnetic material can be smoothly taken in and out. FIG. 8B shows a structure in which a plurality of Rogowski coil units 22 are arranged on the DUT 3, and a ferromagnetic substance 23 is inserted into each of the Rogowski coil units 22. As the ferromagnetic material, a flexible ferromagnetic material such as rubber ferrite is suitable. Here, when a magnetic material is inserted inside the coil, the time constant of the integration circuit needs to be changed. However, if the insertion amount of the ferromagnetic material is determined in advance and the time constant of the corresponding integration circuit is determined, the sensitivity can be easily adjusted by switching the switch. According to the method of inserting the ferromagnetic material into the coil, as described in the equations (1) to (6), the magnetic permeability can be effectively increased, so that the current probe is small and has high sensitivity. Becomes possible.

(6) FIG. 9 shows still another embodiment of the Rogowski coil according to the present invention, which has a structure in which the outside of the coil 26 is covered with a metal shield having a slit. In this structure, the current flowing in the DUT 3 is detected by the magnetic flux leaking from the slit 28, and the sensitivity can be adjusted by the width of the gap between the slits. FIG. 9A is a cross-sectional view showing the state of the metal shield coating in the present embodiment. That is, the structure is such that the Rogowski coil 26 is covered with the metal shield 27 having the slit 28 in the longitudinal direction of the Rogowski coil 26. In the case of FIG. 9B in which a plurality of coils are arranged on the DUT 3, the entire coil stack is formed by a metal shield 2 having a slit 30.
9 shows a structure covered by the cover 9. At this time, it is of course possible to separately shield each unit component. As described above, by covering the coil with a metal body having a slit in part, the influence of an external electric field can be eliminated, and stable measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a current probe according to an embodiment of the present invention.

FIG. 2 is a coil configuration diagram showing another embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram showing one method of coil connection according to the configuration of FIG. 2;

FIG. 4 is an equivalent circuit diagram showing one method of coil connection according to the configuration of FIG. 2;

FIG. 5 is a sensitivity frequency characteristic diagram by a coil configuration according to the configuration of FIG. 2;

FIG. 6 is an equivalent circuit diagram showing one method of coil connection according to the configuration of FIG. 2;

FIG. 7 is an equivalent circuit diagram showing one method of coil connection according to the configuration of FIG. 2;

FIG. 8 is a coil configuration diagram showing still another embodiment of the present invention.

FIG. 9 is a coil configuration diagram showing still another embodiment of the present invention.

FIG. 10 is a conceptual diagram showing a configuration of a conventional Rogowski coil.

FIG. 11 is an equivalent circuit diagram in a configuration of a conventional Rogowski coil.

FIG. 12 is a sensitivity frequency characteristic diagram showing an influence of an integration circuit in a conventional configuration.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 Rogowski coil 2 Detection output terminal 3 Device under test 4 Unit part 5 Voltage detection terminal 6 Connection line 7 Switch 8, 9 terminal 11 Variable resistor 12 Variable capacitor 13, 14 Output terminal 16, 17 Voltage detection terminal 18 Addition circuit 19 , 20 Voltage detection terminal 21 Addition circuit 22 Rogowski coil 23 Ferromagnetic material 26 Rogowski coil 27 Metal shield 28 Slit 29 Metal shield 30 Slit 31 Toroidal coil support 32 Coil 33 Return line 34 Current source 35 Inductance 36 Resistance 37 Composite stray capacitance 38 Resistance 39 Capacitor

Claims (4)

[Claims] 1. A coil having an insulated conductor wound at a uniform pitch on an annular coil support, and a return line folded back from one end of the coil through the center of the coil. The insulated conducting wire and the end of the folded return line are drawn out in close proximity to each other, and a magnetic field generated by a current flowing through an object to be measured passing through an annular portion of the annular coil support is generated by the magnetic field. The logo is arranged so as to penetrate through the annular portion formed by the coil, and the magnetic field changes due to the change of the current, whereby a voltage is induced in the coil and a current is obtained from the induced voltage. In a probe that performs a surge current measurement using a ski coil, the winding number of the coil wound around the object to be measured is wound a plurality of times, and the winding number is switched according to the measured current value. Sensitivity adjustment function large diameter current probe according to claim. 2. A coil having an insulated conductor wound on an annular coil support at a uniform pitch, and a return line folded back from one end of the coil through the center of the coil. The insulated conducting wire and the end of the folded return line are drawn out in close proximity to each other, and a magnetic field generated by a current flowing through an object to be measured passing through an annular portion of the annular coil support is generated by the magnetic field. The logo is arranged so as to penetrate through the annular portion formed by the coil, and the magnetic field changes due to the change of the current, whereby a voltage is induced in the coil and a current is obtained from the induced voltage. In a probe that performs surge current measurement using a ski coil, a plurality of coils are attached to the object to be measured, and during measurement, the number of connected coils is changed according to the measured current value. Sensitivity adjustment function large diameter current probe, characterized by switching the detection sensitivity. 3. A coil having an insulated conductor wound on an annular coil support at a uniform pitch, and a return line which is folded back from one end through the center of the coil. The insulated conducting wire and the end of the folded return line are drawn out in close proximity to each other, and a magnetic field generated by a current flowing through an object to be measured passing through an annular portion of the annular coil support is generated by the magnetic field. The logo is arranged so as to penetrate through the annular portion formed by the coil, and the magnetic field changes due to the change of the current, whereby a voltage is induced in the coil and a current is obtained from the induced voltage. In a probe that performs a surge current measurement using a ski coil, the magnetic permeability in the coil is changed by inserting and removing a ferromagnetic substance in and out of the coil according to the measured current value, thereby changing the current sensitivity. Sensitivity adjustment function large diameter current probe, wherein the switching. 4. A coil having an insulated conductor wound at a uniform pitch on an annular coil support, and a return line folded from one end of the coil through the center of the coil. The insulated conducting wire and the end of the folded return line are drawn out in close proximity to each other, and a magnetic field generated by a current flowing through an object to be measured passing through an annular portion of the annular coil support is generated by the magnetic field. The logo is arranged so as to penetrate through the annular portion formed by the coil, and the magnetic field changes due to the change of the current, whereby a voltage is induced in the coil and a current is obtained from the induced voltage. In a probe for measuring a surge current using a ski coil, the coil is covered with a metal shield member having a slit portion, and the current detection is performed by changing a slit gap of the metal shield. Sensitivity adjustment function large diameter current probe, characterized by switching the sensitivity.