JP2020024101A - Clamp sensor and clamp meter - Google Patents

Abstract

To provide a clamp meter that can measure a small current flowing through a large-area structure including a to-be-measured conductor with high accuracy while suppressing an influence of an external magnetic field without using a metallic shield or the like.SOLUTION: A clamp sensor 2 of a clamp meter 1, which has a structure in which a flexible joint core 4 is interpolated into a coil holding tube 5, surrounds a large-area structure including a to-be-measured conductor and closes itself. When an electric current flows through the to-be-measured conductor, measured currents are inputted into a measurement device 3 from an inner coil and an outer coil according to their number of turns, the coils being arranged in the coil holding tube 5. A computing equation "Ia=f(ΔI)" is stored in storage means 31, in which an inner correction current value Ia is computed based on a differential current value ΔI between an outer coil measurement current value IB and an inner coil measurement current value IA. Using this computing equation, the inner correction current value Ia is calculated by computation means 32; a true measured value I is calculated without an influence of an external magnetic field by subtracting the inner correction current value Ia from the inner coil measurement current value IA; and furthermore, a current value of the to-be-measured conductor is calculated.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a clamp sensor capable of handling a large area structure including a conductor to be measured, and a clamp meter capable of detecting a current using the clamp sensor.

  When measuring the current of the conductor to be measured (or measuring the leakage current in the circuit) without turning off the circuit power supply, clamp the conductor to be measured with a clamp sensor and set the current flowing through the conductor to be measured (or the leakage current in the circuit). 2. Description of the Related Art There is known a clamp meter which obtains a current value from a magnetic field generated by the above-mentioned method. If an AC circuit is to be detected, a CT (Current Transformer) type clamp meter that converts a measured current into a secondary current according to a turns ratio of a coil is widely used (for example, see Patent Document 1). ). In the CT-type clamp meter, in order to cut off the influence of an external magnetic field, a method is adopted in which a shield made of a ferromagnetic material having a high magnetic permeability covers the sensor section to forcibly cut off the external magnetic field (for example, And Patent Document 2).

  In addition, in a large structure (such as a pillar) including the conductor to be measured, the cross section of the clamp location has a large area. When measuring the current of such a large-area structure, a Rogowski coil-type clamp meter that can perform current detection by clamping the entire structure can be used (for example, see Patent Document 3).

JP 2018-031608 A JP-A-11-295346 JP 2011-174770 A

  However, although the CT clamp sensor described in Patent Document 1 described above can measure a small current of mA level, a standard commercial product has a clamp diameter of only about 70 mm, and has a large area including a conductor to be measured. Large structures cannot be clamped together with structures. On the other hand, the Rogowski coil (air-core coil) described in Patent Literature 2 can clamp a large-area structure including a conductor to be measured with a large diameter, but measures a low current of 10 A or less (a minute leakage current or the like). Can not. In addition, in the Rogowski coil type clamp meter, a shield structure cannot be adopted to cut off the influence of an external magnetic field.

  In the maintenance and inspection of electricity, it is necessary to measure a small leakage current (or ground current) to determine the quality of the insulation state. Even if the target is a large-area structure, a minute current is required to determine the insulation state. Measurement must be possible. In addition, in the measurement of a minute current by the clamp meter, the detection error due to the influence of the external magnetic field cannot be ignored, and the measurement accuracy is reduced.

  Therefore, the present invention can suppress the influence of an external magnetic field without using a metal shield or the like that hinders an increase in the clamp diameter and weight, and can detect a minute current flowing in a large-area structure including a conductor to be measured. An object is to provide a clamp sensor and a clamp meter.

  In order to solve the above-mentioned problem, the invention according to claim 1 can connect the both ends to form a connection core that forms an annular core that surrounds the conductor to be measured in a non-contact manner, and a coil can be arranged on the outer periphery of the connection core. A coil body having an inner space in which the connection core can be inserted, and a first attachment / detachment end of the connection core and a second attachment / detachment end from each end. A flexible inner tube having a length that allows each end to be exposed and that can be deformed without difficulty following the deformation of the connecting core; and an inner coil formed by winding a magnet wire around the outer surface of the inner tube. A middle tube arranged to cover the outside of the inner coil, and an outer coil formed by winding a magnet wire around the outer surface of the middle tube. Cover with Both interpolates couple core into the inner hollow portion of the coil body, characterized in that the current through the measured conductor in the inner coil and the outer coil was simultaneously detectable.

  According to a second aspect of the present invention, in the clamp sensor according to the first aspect, the connecting core is formed of a high-permeability soft magnetic material, and the first connecting portion is formed at a pair of ends that are most separated from each other. By using a plurality of connection element bodies forming the second connection part and connecting the first connection part and the second connection part to each other so as to form a rotatable uniaxial joint, a rosary-like joint having both ends opened. A first connecting portion of the connecting element at one end that is not connected is a first attaching / detaching end, and a second connecting section that is not connected at the other end of the connecting element is a second attaching / detaching end. By connecting the first detachable end portion and the second detachable end portion, all the connection element bodies constitute an annular core closed in an annular shape.

  According to a third aspect of the present invention, in the clamp sensor according to the second aspect, the connecting element of the connecting core is formed by laminating a plurality of base materials that are plates of a high magnetic permeability soft magnetic material. The base material has a convex edge protruding in an arc shape equidistant from an axial position connected so as to form a uniaxial joint on one end side, and the projecting edge is The other end side is provided with a concave edge portion which is depressed in an arc shape with the same degree of curvature as the portion, and the connection element body is formed by alternately stacking the convex edge portion and the concave edge portion of the base material. With the configuration, the first connecting portion and the second connecting portion have a fitting structure in which the convex edge portion and the concave edge portion mesh with each other, and each of the connection element bodies connected by the uniaxial joint. The base material should be able to rotate within the required range without interference between the convex and concave edges. The features.

  In order to solve the above-mentioned problem, a clamp meter according to claim 4 includes the clamp sensor according to any one of claims 1 to 3, and each of the clamp meter includes an inner coil and an outer coil of the clamp sensor. A measuring device is provided for acquiring the detected inner coil measurement current value and outer coil measurement current value, and calculating a current value flowing through the conductor to be measured based on the inner coil measurement current value and the outer coil measurement current value. And

  The invention according to claim 5 is the clamp meter according to claim 4, wherein the windings of the outer coil and the inner coil are the same, and when the clamp sensor is not affected by an external magnetic field, the inner coil measuring current is measured. The value and the measured value of the outer coil current are matched.

  According to a sixth aspect of the present invention, in the clamp meter according to the fifth aspect, the measuring device includes a difference current that is a difference between the outer coil measurement current value and the inner coil measurement current value acquired from the clamp sensor. Storage means for storing an arithmetic expression for obtaining an inner correction current value generated by the external magnetic field acting on the inner coil from the value, and calculating the inner correction current value by using the arithmetic expression of the storage means; Calculating means for obtaining a true measurement value by the clamp sensor by subtracting the inside correction current value from the value, and obtaining a current value flowing through the conductor to be measured from the true measurement value.

  According to a seventh aspect of the present invention, in the clamp meter according to the fifth aspect, the measuring device includes a difference current that is a difference between the outer coil measurement current value and the inner coil measurement current value acquired from the clamp sensor. Storage means for storing an arithmetic expression for obtaining an outer correction current value generated by the external magnetic field acting on the outer coil from the value, and calculating the outer correction current value using the arithmetic expression of the storage means to obtain an outer coil measurement current value. Calculating means for obtaining a true measurement value by the clamp sensor by subtracting the outside correction current value from the value, and calculating a current value flowing through the conductor to be measured from the true measurement value.

  ADVANTAGE OF THE INVENTION According to the clamp sensor which concerns on this invention, the annular core of a necessary and sufficient diameter can be comprised by the connection core which connected the connection element body by the appropriate number according to the large area structure containing the measured conductor to be measured. . The first core portion surrounds the large-area structure with the first core portion and the second core portion opened, and the first core portion is connected to the second core portion to form an annular core. The coil is placed by the body. Therefore, if the large-area structure is clamped by the clamp sensor, a secondary current corresponding to the turn ratio of the coil can be obtained from the inner coil and the outer coil from the change in the magnetic field caused by the AC current to be detected. The measuring device that obtains the inner coil measurement current value and the outer coil measurement current value from the clamp sensor calculates the true measurement value in which the influence of the outer coil and the inner coil on the external magnetic field is corrected, and calculates the true measurement value from the true measurement value. Calculate the value of the current flowing through the measuring conductor. Thus, the clamp meter can measure a small current without being affected by an external magnetic field.

It is a schematic structure figure of a clamp meter concerning an embodiment of the present invention. 3A and 3B show a clamp sensor used in a clamp meter, wherein FIG. 3A is a partially cutaway plan view, and FIG. It is a bird's-eye perspective view of a basic link which constitutes a connection core. It is a top view of the base material which comprises a basic link. It is assembly explanatory drawing of the basic link using a base material. (A) is a rear view of the basic link. FIG. 7B is an enlarged schematic end view taken along line VIb-VIb of FIG. (A) is a top view of the connected 1st basic link and 2nd basic link. FIG. 7B is an enlarged schematic end view taken along line VIIb-VIIb of FIG. 7A. It is a manufacturing process explanatory view of a coil body. It is an assembly process explanatory view of a clamp sensor. FIG. 5 is an explanatory diagram of a method of using the clamp meter according to the present embodiment when measuring a ground current (or a leakage current) of a utility pole. It is explanatory drawing of the measurement principle by an inner coil and an outer coil.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a schematic configuration of a clamp meter 1. The clamp meter 1 performs a predetermined calculation based on a clamp sensor 2 for clamping a line to be measured and a detection current of the clamp sensor 2, and converts a measurement result into a digital value. (Or an analog value).

  The clamp sensor 2 includes a connection core 4 serving as an annular core surrounding the conductor to be measured in a non-contact manner by connecting both ends thereof, and a coil holding tube 5 for holding a state in which a coil is arranged on the outer periphery of the connection core 4. . The connecting core 4 can be bent and stretched by removing the first detachable end 4a and the second detachable end 4b, as described later. Therefore, when a large-area structure (for example, a utility pole) including the conductor to be measured is surrounded by the clamp sensor 2 and the first detachable end 4a and the second detachable end 4b are connected, an annular core surrounding the peripheral surface of the utility pole is formed. can do. The connection core 4 serving as an annular core functions as a closed magnetic path for efficiently passing a magnetic flux generated by a current flowing through the conductor to be measured.

  Further, the coil holding tube 5 has flexibility and insulation that can be deformed without difficulty following the deformation of the connection core 4. Therefore, when the connecting core 4 is closed to form an annular core, the coils in the coil holding tube 5 are also arranged in an annular shape, and the magnetic flux generated by the alternating current flowing through the conductor to be measured concentrates on the annular core. A secondary current flows through the coil of the coil holding tube 5 so as to cancel this change in magnetic flux. Since the secondary current can be obtained as a magnitude corresponding to the turns ratio of the coil in the coil holding tube 5 with respect to the primary current flowing through the conductor to be measured, the detection sensitivity capable of detecting a small current of about several mA is detected. Is easy to set.

  Further, in order to prevent the operation of clamping a large-area structure by the clamp sensor 2 from becoming complicated, a first connection guide 6 is provided on the first detachable end 4a side of the connection core 4 in the clamp sensor 2 of the present embodiment, and a second connection guide is provided. A second connection guide 7 is provided on the detachable end 4b side. As the first and second connection guides 6 and 7, a known existing appropriate structure capable of easily attaching and detaching the first detachable end 4a and the second detachable end 4b can be applied. The connection cable 8 extends from the first connection guide 6 of the clamp sensor 2 and is connected to the measuring device 3.

  The measuring device 3 receives a detection signal from a coil (described later in detail) in the coil holding tube 5 via the connection cable 8 and converts the detection signal (voltage signal) into current information by a shunt resistor for current detection. Convert. The measuring device 3 includes at least a storage unit 31 that previously stores an arithmetic expression for calculating a current value flowing through the conductor to be measured from the current detected by the clamp sensor 2, and an arithmetic unit 32 that performs an arithmetic operation using the arithmetic expression And a function of a display unit 33 for visually displaying the calculation result. In addition, a function of storing a history of measured values, a function of outputting history information to the outside, a sound output function of notifying a measurement result, a warning, or the like by voice may be added to the measuring device 3.

  FIG. 2 shows a schematic structure of the clamp sensor 2 described above. The clamp sensor 2 can be used in any direction depending on the direction of the conductor to be measured. However, in the following description, for convenience, the cross-sectional direction that can be clamped by the clamp sensor 2 is defined as a horizontal direction (or a horizontal direction). The direction orthogonal to the vertical direction is described as a vertical direction (or a vertical direction). Therefore, FIG. 2A shows the inside of a part of the clamp sensor 2 cut out in a horizontal direction, and FIG. 2B shows the inside of a part of the clamp sensor 2 cut out in a vertical direction. It is a thing.

  The connection core 4 includes, for example, a first basic link 40-1, a second basic link 40-2,..., A twelfth basic link 40-12, a thirteenth basic link 40-13, 14 basic links 40-14. The first to fourteenth basic links 40-1 to 40-14 have the same shape, and are simply referred to as the basic link 40 unless it is necessary to distinguish them. These first to fourteenth basic links 40-1 to 40-14 are formed by laminating a base material 41, which will be described later, and fixing the base material 41 with a rivet 42. The second connecting portion 14b is formed.

  When connecting the first basic link 40-1 and the second basic link 40-2, the second connecting portion 40b of the first basic link 40-1 (this is called a first basic link second connecting portion 40-1b. And the same) and the second basic link first connecting portion 40-2a are connected by a uniaxial joint connecting portion 43 so as to form a rotatable uniaxial joint. When connecting the second basic link 40-2 and the third basic link 40-3, the second basic link second connecting portion 40-2b and the third basic link first connecting portion 40-3a are connected to the uniaxial joint connecting portion. 43. The same applies to the case where the third basic link 40-3 to the twelfth basic link 40-12 are connected, so that the description is omitted. When connecting the twelfth basic link 40-12 and the thirteenth basic link 40-13, the twelfth basic link second connection part 40-12b and the thirteenth basic link first connection part 40-13a are connected to a uniaxial joint connection part. 43. When the thirteenth basic link 40-13 and the fourteenth basic link 40-14 are connected, the thirteenth basic link second connection part 40-13b and the fourteenth basic link first connection part 40-14a are uniaxially connected. They are connected by a part 43. Thus, the connection core 4 has a rosary connection structure with both ends open. At this time, the first basic link 40-1a which is not connected to the first basic link 40-1 which is the connection element at one end remains, and the 14th basic link which is the connection element at the other end remains. The fourteenth basic link second connection part 40-14b which is not connected to 40-14 remains.

  Therefore, the first basic link first connecting portion 40-1a can be the first detachable end 4a, and the fourteenth basic link second connecting portion 40-14b can be the second detachable end 4b. By connecting the first detachable end 4a and the second detachable end 4b, an annular core in which the first to fourteenth basic links 40-1 to 40-14 are closed annularly can be configured. Note that the first basic link 40-1 to the fourteenth basic link 40-14 are all connected by unifying the direction of the uniaxial joint in the up-down direction, thereby forming the first basic link 40-1 to the fourteenth basic link. The rotation direction of 40-14 can be restricted to the horizontal direction. As described above, if the rotation direction of the first basic link 40-1 to the fourteenth basic link 40-14 is regulated in the horizontal direction, the connection between the first detachable end 4a and the second detachable end 4b is also reduced. It can be performed in a substantially horizontal plane.

  On the other hand, the coil holding tube 5 holds a coil by using a flexible tube as a coil bobbin. Specifically, a magnet wire 521 is wound around the outer peripheral surface of the inner tube 51 to form the inner coil 52, which is covered with the middle tube 53, and a magnet wire 541 is wound around the outer peripheral surface of the middle tube 53 to form the outer coil 54. The coil 55 is formed. Then, the outer surface of the coil body 55 (the surface on which the outer coil 54 is formed) is covered with an insulating outer layer tube 54 to form the coil holding tube 5.

  The inner tube 51, the middle tube 53, and the outer tube 56 have flexibility and insulation that can be easily deformed following the deformation of the connection core 4. The inner tube 51 has an inner space 51b into which the connection core 4 can be inserted, and a length capable of exposing the first detachable end 4a and the second detachable end 4b of the connection core 4 from each end. It is. The inner layer tube 53 and the outer layer tube 56 are also set to have approximately the same length, and each end is covered with an insulating cap 57. From one side of the coil holding tube 5, an inner first lead wire 521 a and an inner second lead wire 521 b which are a winding start portion or a winding end portion of the magnet wire 521 constituting the inner coil 51 are drawn out. Similarly, the outer first lead wire 541a and the outer second lead wire 541b which are the winding start portion or the winding end portion of the magnet wire 541 constituting the outer coil 54 are drawn out.

  Next, the detailed structure of the basic link 40 constituting the connecting core 4 will be described. FIG. 3 shows an appearance of a basic link 40 which is a connecting element body. The basic link 40 includes a first base material 41-1, a second base material 41-2,..., Which is a plate material (for example, a thickness of 1 mm) made of a high-permeability soft magnetic material (for example, Permalloy). This is a structure in which a sixth base material 41-6 and a seventh base material 41-7 are stacked. In a state where the first base member 41-1 to the seventh base member 41-7 are overlapped, they are integrally fixed by a rivet 42 of a caulking fixing system. The first to seventh base materials 41-1 to 41-7 have the same shape, and are simply referred to as the base material 41 when there is no particular need to distinguish them.

  FIG. 4 shows a plane of the base material 41 (for example, a surface facing the upper surface 41a). The base member 41 is a long plate member having a gentle arc shape, and generally includes an outer arc edge 411 and an inner arc edge 412 which are two sides in the longitudinal direction, and a convex edge 413 which is two sides in the short direction. And a concave edge 414. For example, assuming an arc of R160 [mm] from the virtual origin O (hereinafter, referred to as a virtual center arc), an arc approximately 3.5 [mm] away from the virtual center arc (for example, R163.5 from the origin O). The outer arc-shaped edge 411 is formed so as to overlap with the [mm] arc. The inner arc-shaped edge portion 412 is formed so as to overlap with an arc (for example, an arc of R156.5 [mm] from the origin O) which is about 3.5 [mm] away from the inside of the virtual center arc. The convex edge portion 413 is provided on one short side of the base member 41 (for example, on the left side when viewed from the upper surface 41a or on the right side when viewed from the lower surface 41b). The concave edge portion 414 is provided on the other short side of the base material (for example, on the right side when viewed from the upper surface 41a or on the left side when viewed from the lower surface 41b). The distance between the outer arc-shaped edge portion 411 and the inner arc-shaped edge portion 412 is about 7 [mm] (3.5 [mm] × 2), and the first to seventh base members 41-1 to 41-7 are used. Since the overlapped thickness is also about 7 [mm], the longitudinal cross section of the basic link 40 in the lateral direction is substantially square.

  A first fixing hole 415a, a second fixing hole 415b, and a third fixing hole 415c each having a diameter of 2 mm are provided on the virtual center arc of the base material 41. For example, for an imaginary line passing from the origin O to the center of the second fixing hole 415b, the angle from the origin O to the center of the first fixing hole 415a is the same as the angle from the origin O to the center of the third fixing hole 415c. The opening positions of the first to third fixing holes 415a to 415c are determined so that In this case, when the two base materials 41 are overlapped so that the upper surface 41a and the lower surface 41b face each other (when the convex edge 413 and the concave edge 414 are overlapped with each other, ), All three holes in the two base materials 41 overlapped can be matched. That is, when the two base members 41 are aligned so that the respective second fixing holes 415b communicate with each other, the first fixing holes 415a and the third fixing holes 415c in one base member 41 are connected to the other base member 41. Overlap the third fixing hole 415c and the first fixing hole 415a. At this time, the two base materials 41 overlapped with each other can keep the outer arc-shaped edge 411 and the inner arc-shaped edge 412 in alignment.

  Therefore, when the basic link 40 has a structure in which a plurality of (for example, seven) base materials 41 are stacked, as shown in FIG. 5, the directions of the base materials 41 can be alternately changed and stacked. First, a second base member 41-2 having a lower surface 41b facing upward is stacked under a first base member 41-1 having an upper surface 41a facing upward. The third base member 41-3 with the upper surface 41a facing upward is placed under the third base member 41-3. The fourth base member 41-4 with the lower surface 41b facing upward is placed under the lower surface. The fifth base member 41-5 with the upper surface 41a facing upward is stacked thereunder. A sixth base member 41-6 with the lower surface 41b facing upward is superimposed below it. A seventh base member 41-7 with the upper surface 41a facing upward is laid underneath. The rivet 42 is inserted into the first to third fixing holes 415c penetrating from the first base member 41-1 to the seventh base member 41-7 thus stacked, and is caulked and fixed. As shown in FIG. 6, the rivet 42 has the head 42a positioned on the upper surface 41a side of the first base member 41-1 and the shaft 42b is inserted through the first to third fixing holes 415a to 415c. The caulking portion 42c is formed on the lower surface 41b side of the seventh base member 41-7.

  The first and second connecting portions 40a and 40b of the basic link 40 formed by laminating the first to seventh base members 41-1 to 41-7 as described above have a convex edge 413 and a concave edge. The edge portions 414 are alternately overlapped. The first connecting portion 40a has a structure of “concavo-convex unevenness concave and convex concave” from the first base material 41-1 to the seventh base material 41-7, and the second connecting portion 40b is formed from the first base material 41-1. The structure of “convex unevenness unevenness” is formed toward the seventh base material 41-7. That is, the first connecting portion 40a and the second connecting portion 40b of the basic link 40 have a fitting structure that meshes with each other.

  In addition, the first connecting portion 40a and the second connecting portion 40b of the basic link 40 are connected by the uniaxial joint connecting portion 43, so that the first connecting portion 40a and the second connecting portion 40b become convex uniaxial joints which can be smoothly rotated. The protruding shape of the portion 413 and the concave shape of the concave edge portion 414 are set as follows.

  On the side of the convex edge portion 413 of the base member 41, a communication hole 416 for connection by the uniaxial joint connection portion 43 is provided. The position of the communication hole 416 is determined such that an arc having a radius r1 from the center of the communication hole 416 substantially overlaps with the bulging edge of the convex edge 413 (see each convex edge 413 in FIG. 5). Further, when the two basic links 40 are overlapped in the opposite direction, an arc having a radius r2 from the center of the communication hole 416 adjacent to the concave edge portion 414 overlaps with the concave edge of the concave edge portion 414 (for example, , Each concave edge 414 in FIG. 5). At this time, if “r1 ≦ r2” is set, all of the communication holes 416 of the pair of basic links 40 are meshed with one first connecting portion 40a and the other second connecting portion 40b. The opening position can be adjusted.

  In designing the base member 41 described above, if both the convex edge portion 413 and the concave edge portion 414 have an arc-shaped range close to 180 °, the first connection portion 40a and the second connection portion of the pair of basic links 40 are provided. Rotation becomes impossible with the portion 40b engaged. Therefore, it is desirable to appropriately set the arc-shaped range of the convex edge 413 and the concave edge 414 according to the allowable rotation range. In addition, it is preferable that the convex edge 413 and the concave edge 414 have an outer edge shape that is smoothly connected to the outer arc edge 411 and the inner arc edge 412, respectively. If there is a step or an acute angle at the connection between the convex edge 413 and the concave edge 414 and the outer arc-shaped edge 411 and the inner arc-shaped edge 412, the connecting core 4 is inserted into the coil holding tube 5. In such a case, there is a risk that the inner surface of the inner tube 51 may be damaged.

  However, in the base member 41 of the connecting core 4 used in the clamp sensor 2 of the present embodiment, the width in the short direction (the separation distance between the outer arc edge 411 and the inner arc edge 412) is approximately r1 [mm] × 2. Therefore, when the arc-shaped range of the convex edge 413 is set to approximately 180 °, a connection portion between one end of the convex edge 413 and the outer arc edge 411 and the other end of the convex edge 413 and an inner arc are formed. The connection portion with the edge portion 412 becomes smooth, and no step is formed. On the other hand, the connecting portion between one end of the concave edge portion 414 and the outer arc-shaped edge portion 411 and the connecting portion between the other end of the concave edge portion 414 and the inner arc-shaped edge portion 412 are chamfered (for example, R1). Therefore, the connection was made smooth so that no corners were formed.

  When the radius r1 for determining the convex edge portion 413 and the radius r2 for determining the concave edge portion 414 are equal, when the first connection portion 40a and the second connection portion 40b of the pair of basic links 40 are connected, Depending on the processing accuracy, there is a possibility that the opening position of the connection port 416 cannot be adjusted. Even if the processing accuracy is good and “r1 = r2” and the opening position of the connection port 416 is exactly matched, the convex edge 413 and the concave edge 414 are in surface contact in a long range. If the convex edge portion 413 and the concave edge portion 414 are in surface contact with each other, the sliding resistance is increased accordingly, and there is a possibility that the work of deforming the connecting core 4 becomes difficult. However, if the radius r1 of the convex edge portion 413 is extremely smaller than the radius r2 of the concave edge portion 414, when the first connection portion 40a and the second connection portion 40b are engaged with each other. The facing area is reduced. When the facing area between the first connecting portion 40a and the second connecting portion 40b decreases, the magnetic resistance at the connecting portion between the base materials 41 may be increased, and the strength at the connecting portion between the base materials 41 may decrease. Issues are also a concern. Therefore, when the first connecting portion 40a and the second connecting portion 40b of the pair of basic links 40 are engaged with each other, it is set so that the convex edge portion 413 and the concave edge portion 414 are in point contact with each other. It is desirable to keep. For example, as shown in FIG. 4, when the radius r1 for determining the convex edge 413 is set to 3.5 [mm] and the radius r2 for determining the concave edge 414 is set to 3.6 [mm], the connection is established. There is no hindrance to the work of deforming the core 4 and the magnetic resistance does not extremely increase at the connection portion.

  FIG. 7 shows a configuration example of the uniaxial joint connecting portion 43 that connects the pair of basic links 40 having the first detachable end portion 4a and the second detachable end portion 4b configured as described above. The first connection portion 40a and the second connection portion 40b are engaged with each other so that the opening positions of the communication holes 416 in all the convex edge portions 413 are matched, and the connection screw 431 is inserted in this state. When the head of the connecting screw 431 presses against the upper surface 41a of the first base member 41-1, the screw tip of 431 protrudes from the lower surface 41b of the seventh base member 41-7 as appropriate, so that the flat washer 432 and the spring washer are provided. 433 is inserted and fastened with a nut 434.

  At this time, if the nut 434 is excessively tightened, smooth rotation of the basic links 40 is hindered. Conversely, if the nut 434 is excessively weak, it becomes difficult to maintain the shape of the connecting core 4 itself. The operation when clamping the conductor to be measured becomes complicated. Therefore, it is also important for the function of the uniaxial joint connecting part 43 to maintain an appropriate fastening state. For example, after the nut 434 is tightened to the connection screw 431 with a predetermined tightening torque (for example, 1.8 [kgf · cm]), the nut 434 is returned by 90 ° to loosen the nut 434 by a predetermined amount. 435 is applied and fixed in this tightened state. By doing so, the smooth rotation between the basic links 40 is not hindered, and the shape of the connecting core 4 itself is not made difficult, so that the handling of the connecting core 4 in the measurement operation is improved, and the workability is improved. It can also contribute to improvement.

  An example of a manufacturing process of the coil body 55 in which the inner coil 52 can be arranged on the outer periphery of the connection core 4 described above will be described with reference to FIG. First, a flexible and insulating inner layer tube 51 having a cylindrical outer peripheral surface 51a is prepared. The inner tube 51 includes an inner space portion 51b having a diameter sufficient for inserting the connection core 4 and a degree that the first connection portion 40a and the second detachable end portion 4b of the connection core 4 protrude from the openings at both ends. Is the length of The inner tube 51 is fixed linearly by penetrating a linear metal rod 58 into the inner space 51b of the inner tube 51 (see FIG. 8A). With this configuration, the rigid metal rod 58 can be set as a rotation axis on a shaft-rotating winding machine, so that the magnet wire 521 is attached to the outer peripheral surface 51a of the inner tube 51 by a single-layer or multiple-layer by the winding machine. Thus, the inner coil 52 can be formed efficiently (see FIG. 8B).

  After the inner coil 52 is formed on the outer peripheral surface 51 a of the inner tube 51, the inner tube 53 is covered so as to cover the inner coil 52, and the magnet wire 541 is wound on the outer peripheral surface 53 a of the inner tube 53 in a single layer or multiple layers. Go to form the outer coil 54 (see FIG. 8 (c)). Thereafter, the inner tube 51 is detached from the winding machine, and the metal bar 58 is extracted (see FIG. 8D). Thus, a coil having a double structure of the inner coil 52 formed by winding the magnet wire 521 on the outer surface of the inner tube 51 and the outer coil 54 formed by winding the magnet wire 541 on the outer surface of the middle tube 53. The body 55 is formed (see FIG. 8E). The winding start portion and the winding end portion of the magnet wire 521 and the magnet wire 541 are used as an inner first lead line 521a, an inner second lead line 521b, an outer first lead line 541a, and an outer second lead line 541b, respectively. be able to.

  The coil body 55 formed as described above is inserted into the coil insertion portion 56a of the flexible and insulating outer layer tube 56 (see FIG. 9A), so that the outer coil 54 is removed. The surface can be covered with an outer tube 56. The outer tube 56 has substantially the same length as the coil body 55, and the coil insertion portion 56a has a diameter necessary and sufficient for inserting the coil body 55. After the coil body 55 is inserted into the outer layer tube 56, insulating caps 57 for securing a creepage distance are attached to both ends thereof to form the coil holding tube 5 (see FIG. 9B). Next, the connecting core 4 is inserted into the core insertion space 5a (the same as the inner space 51b of the inner tube 51) of the coil holding tube 5, and the first detachable end 4a and the second The detachable end portions 4b are respectively exposed. Thus, the clamp sensor 2 can be configured (see FIG. 9C).

  As shown in FIG. 9C, a first detachable end 4a and a second detachable end 4b are exposed at both ends of the clamp sensor 2 as appropriate. Therefore, the conductor to be measured is bent so as to be surrounded by the clamp sensor 2, and the first connecting portion 40a as the first attaching / detaching end 4a and the second connecting portion 40b as the second attaching / detaching end 4b are fitted and connected. The operation of turning the core 4 into an annular core may be performed by a user. However, it is not a very efficient operation for the user to visually perform accurate alignment between the first connecting portion 40a and the second connecting portion 40b. Therefore, in the clamp sensor 2, the first connection guide 6 is provided on the first detachable end 4a side so that the first detachable end 4a and the second detachable end 4b can be fitted and removed efficiently. The second connection guide 7 is provided on the side of the second detachable end 4b. In addition, the attachment / detachment structure by the first connection guide 6 and the second connection guide 7 is not particularly limited, and an appropriate existing attachment / detachment structure may be adopted.

  FIG. 10 shows a usage example of the clamp meter 1 including the clamp sensor 2 configured as described above. By simply removing the first connection guide 6 and the second connection guide 7 of the clamp sensor 2 and connecting the first connection guide 6 and the second connection guide 7 in a state surrounding the power pole 9, the power pole 9 can be entirely clamped. Thus, the measurement of the ground current Ie and the leakage current Ir of the telephone pole 9 can be easily performed. Moreover, unlike the Rogowski clamp sensor, it is possible to measure a small current of about 0.5 mA to 5 mA. Further, according to the clamp meter 1 according to the present embodiment, even when three electric wires are separated from each other in a switchboard in a three-phase three-wire circuit, the three separated electric wires are collectively used by the clamp sensor 2. Since it can be clamped, it is possible to measure a small leakage current in the circuit. Further, according to the clamp meter 1 according to the present embodiment, even with a thick three-phase three-wire lead-in line parallel to the telephone pole, these lead-in lines can be collectively clamped to measure a minute leakage current. .

  When the conductor to be measured is clamped by the clamp sensor 2, a measured value corresponding to the current flowing through the conductor to be measured can be obtained from both the inner coil 52 and the outer coil 54. Moreover, since the number of turns of the inner coil 52 and the number of turns of the outer coil 54 are matched, the current value detected by the inner coil 52 and the current value detected by the outer coil 54 are substantially the same. Therefore, the measuring device 3 should be able to calculate an appropriate current value using either the detected value of the inner coil 52 or the detected value of the outer coil 54.

  However, since the clamp sensor 2 does not have a function of shielding an external magnetic field, if an external magnetic field in the measurement environment acts on the clamp sensor 2, the detection values of the inner coil 52 and the outer coil 54 will be different. As a function for correcting a measurement error due to such an external magnetic field and performing high-accuracy current measurement, a storage unit 31 and a calculation unit 32 are provided in the measurement device 3. Hereinafter, the principle by which the influence of the external magnetic field can be corrected will be described with reference to FIG.

  FIG. 11 shows that, when the frequency and amplitude of the alternating current flowing through the conductor to be measured are fixed and the magnitude of the external magnetic field (alternating magnetic field) acting is changed, the inner coil 52 and the outer coil 54 of the clamp sensor 2 respectively FIG. 4 is a characteristic diagram illustrating a change in a detected current value. When no external magnetic field is applied, the value of the current measured by the inner coil 52 (hereinafter referred to as the inner coil measured current) and the value of the current measured by the outer coil 54 (hereinafter referred to as the outer coil measured current) are both I. [A]. However, when the external magnetic field acts on the clamp sensor 2, the inner coil measurement current value and the outer coil measurement current value increase accordingly.

  When the external magnetic field acting on the clamp sensor 2 increases, both the inner coil measurement current and the outer coil measurement current increase, but the outer coil 54 closer to the external magnetic field is more strongly affected. The increase in the coil measurement current becomes significant. Since only the middle tube 53 having the same thickness and the same material is interposed between the inner coil 52 and the outer coil 54, the sensitivity difference between the inner coil 52 and the outer coil 54 with respect to the external magnetic field is constant. That is, the value of the error generated in the inner coil 52 due to the influence of the external magnetic field (hereinafter referred to as the inner correction current value Ia) and the value of the error generated in the outer coil 54 due to the influence of the external magnetic field (hereinafter referred to as the outer correction current value Ib) ) Should have a predetermined relationship. Therefore, if an arithmetic expression indicating the relationship between the two is specified, the current flowing through the conductor to be measured can be obtained with high accuracy while eliminating the influence of the external magnetic field.

  For example, if the linearity is extremely strong as in the change characteristics of the inner coil measurement current and the change characteristics of the outer coil measurement current illustrated in FIG. The relationship can be represented by a simple arithmetic expression of the proportionality constant k. Even when the inner coil measurement current and the outer coil measurement current change non-linearly, since the sensitivity difference between the inner coil 52 and the outer coil 54 with respect to the external magnetic field is constant, a quadratic function, a cubic function, or the like is required. The relationship between the two can be expressed by the used arithmetic expression.

  Here, the case where the magnitude of the external magnetic field is H [A / m] is considered. The value of the inner coil measurement current is IA, which is higher than the true measurement value I [A] by the inner correction current value Ia. That is, “IA = I + Ia”. On the other hand, the value of the outer coil measurement current is IB, which is higher than the true measurement value I [A] by the outer correction current value Ib. That is, “IB = I + Ib”. However, since both the inner correction current value Ia and the outer correction current value Ib are unknown numbers, the measurement value I cannot be directly obtained from these relational expressions.

  Therefore, attention is paid to a difference current value ΔI, which is a difference (IB−IA = Ib−Ia) between the outer coil measurement current value IB and the inner coil measurement current value IA. Since the relationship between the inside correction current value Ia and the outside correction current value Ib can be expressed by an arithmetic expression, the relationship between the inside correction current value Ia and the difference current value ΔI (= Ib−Ia) can also be expressed by an arithmetic expression. That is, the inner correction current value Ia is uniquely determined from the difference current value ΔI, and this arithmetic expression is set to “Ia = f (ΔI)”. If an arithmetic expression of “Ia = f (ΔI)” determined according to the characteristics of the clamp sensor 2 is stored in the storage means 31 in advance, the arithmetic means 32 calculates the outer coil measurement current value IB and the inner coil measurement current IB. The inside correction current value Ia according to the current value IA can be obtained.

  The true measurement value I is obtained by subtracting the inner correction current value Ia from the inner coil measurement current value IA. Therefore, the calculation means 32 can obtain the true measurement value I by performing the calculation of “IA−f (ΔI)”, and the true measurement value can be obtained by a predetermined calculation formula taking into account the detection sensitivity based on the number of turns of the inner coil 52. By applying the value I, the value of the current flowing through the conductor to be measured can be obtained.

  Since the outer correction current value Ib is also uniquely determined from the difference current value ΔI, the arithmetic expression stored in the storage means 31 is “Ib = f (ΔI)”, and the arithmetic means 32 is “IB−f (ΔI)”. , The true measurement value I may be obtained. When the true measurement value I is obtained, the current value flowing through the conductor to be measured can be obtained by applying the true measurement value I to a predetermined arithmetic expression that takes into account the detection sensitivity based on the number of turns of the outer coil 54.

  As described above, according to the clamp meter 1 according to the present embodiment, by utilizing the characteristics of the clamp sensor 2 including the inner coil 52 and the outer coil 54, the error caused by the external magnetic field from the inner coil measured current value and the outer coil measured current value is utilized. Can be corrected. Therefore, it is possible to suppress the influence of the external magnetic field on the clamp sensor 2 and to obtain the current flowing through the conductor to be measured with high accuracy without using a metal shield or the like that hinders the increase in the clamp diameter and the weight reduction. A simple clamp meter 1 can be provided.

  In the clamp meter 1 of the present embodiment, the arithmetic expression for obtaining the inner correction current value or the outer correction current value is simplified by matching the number of turns of the inner coil 52 and the outer coil 54. However, when the clamp sensor 2 has to be created by changing the number of turns of the inner coil 52 and the outer coil 54, the detection sensitivity of the coupling core 4 to a magnetic field change and the detection sensitivity to an external magnetic field are different between the two coils. A relatively simple arithmetic expression cannot be used. Therefore, it is necessary to set a complicated arithmetic expression for obtaining the inner correction current value or the outer correction current value in consideration of a correction requirement for canceling the difference between the detection sensitivities of the two coils. Alternatively, if an arithmetic expression that converts the number of turns of one coil to the number of turns of the other coil is set, the converted measurement current value when the number of turns of the coil is the same can be obtained. The relatively simple arithmetic expression described above can be applied as it is.

  The embodiments of the clamp sensor and the clamp meter using the clamp sensor according to the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to this embodiment, and may be embodied by diverting known existing equivalent technical means as long as the configuration described in the claims is not changed.

DESCRIPTION OF SYMBOLS 1 Clamp meter 2 Clamp sensor 3 Measuring device 31 Storage means 32 Computing means 4 Connecting core 4a First detachable end 4b Second detachable end 40 Basic link 40a First connecting part 40b Second connecting part 43 Uniaxial joint connecting part 5 Coil holding tube 5a Core insertion space 51 Inner tube 52 Inner coil 521 Magnet wire 53 Middle tube 54 Outer coil 541 Magnet wire 55 Coil body 56 Outer tube

Claims (7)

A clamp sensor comprising: a connection core serving as an annular core surrounding the conductor to be measured in a non-contact manner by connecting both ends, and a coil body capable of disposing a coil on the outer periphery of the connection core,
The coil body has an inner space in which the connection core can be inserted, and the connection body has such a length that a first detachable end and a second detachable end of the connection core can be exposed from each end. A flexible inner layer tube that can be deformed without difficulty following the deformation of the core, an inner coil formed by winding a magnet wire around the outer surface of the inner layer tube, and a cover arranged to cover the outside of the inner coil. A middle tube, and an outer coil formed by winding a magnet wire around the outer surface of the middle tube,
While covering the outer surface side of the coil body with an insulating outer layer tube, a connecting core is inserted into the inner space of the coil body, and the current flowing through the conductor to be measured can be simultaneously detected by the inner coil and the outer coil. Characteristic clamp sensor.   The connection core is formed of a high-permeability soft magnetic material, and uses a plurality of connection bodies each having a first connection portion and a second connection portion formed at a pair of ends that are furthest apart from each other. By connecting the second connecting portion so as to form a rotatable uniaxial joint, a rosary-like connecting structure having both ends opened is formed, and the first connecting portion of the connecting element body at one end that is not connected is connected. As a first detachable end, a second unconnected portion of the other end of the connecting element body as a second detachable end, and connecting the first detachable end and the second detachable end, 2. The clamp sensor according to claim 1, wherein all of the connecting elements constitute an annular core closed in an annular shape. The connection body of the connection core is configured to have a required thickness by laminating a plurality of base materials which are plate materials of a high magnetic permeability soft magnetic material,
The base material has a convex edge protruding in an arc shape equidistant from an axial position connected so as to form a uniaxial joint on one end side, with a curvature approximately equal to the projecting edge. At the other end side, a concave edge portion depressed in an arc shape shall be provided,
The first connection part and the second connection part are mutually convex edge part and concave edge part by alternately laminating the convex edge part and the concave edge part of the base material to form a connection body. And the base material of each connecting element connected by a uniaxial joint rotates within a required range without interference between the convex edge and the concave edge of each other. The clamp sensor according to claim 2, wherein the clamp sensor can be used. The clamp sensor according to any one of claims 1 to 3,
Obtain the inner coil measurement current value and the outer coil measurement current value respectively detected from the inner coil and the outer coil of the clamp sensor, and calculate the current value flowing through the conductor to be measured based on the inner coil measurement current value and the outer coil measurement current value. A clamp meter provided with a measuring device for calculating the following.   The coil of the outer coil and the inner coil have the same winding, and the measured current value of the inner coil and the measured current value of the outer coil match when the clamp sensor is not affected by an external magnetic field. The clamp meter according to 1. The measuring device,
A storage for storing an arithmetic expression for obtaining an inner correction current value generated by an external magnetic field acting on the inner coil from a difference current value which is a difference between the outer coil measurement current value and the inner coil measurement current value obtained from the clamp sensor. Means,
The inside correction current value is calculated using the arithmetic expression of the storage means, and the true measurement value by the clamp sensor is obtained by subtracting the inside correction current value from the inside coil measurement current value, and the measured conductor is measured from the true measurement value. Calculating means for determining a current value flowing through
The clamp meter according to claim 5, comprising: The measuring device,
A storage for storing an arithmetic expression for obtaining an outer correction current value generated by an external magnetic field acting on the outer coil from a difference current value which is a difference between the outer coil measurement current value and the inner coil measurement current value obtained from the clamp sensor. Means,
The outer correction current value is calculated using the arithmetic expression of the storage means, and the outer correction current value is subtracted from the outer coil measurement current value to obtain a true measurement value by the clamp sensor, and the conductor to be measured is calculated from the true measurement value. Calculating means for determining a current value flowing through
The clamp meter according to claim 5, comprising:

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