JP6803974B2 - Devices and methods for measuring the current strength of one individual conductor in a multi-conductor system - Google Patents

Description

The present invention relates to an apparatus and method for measuring the current intensity of one individual conductor of a multi-conductor system.

Multi-conductor cables containing at least two conductors are used for alternating current transmission and, rarely, for direct current transmission. In the case of a multi-conductor cable, each conductor is individually insulated according to the voltage. In that case, all conductors are typically twisted together and once again covered with a common insulating material.

The measurement of the current in one individual conductor of such a multi-conductor system can be performed by a diversion resistor, a ring core current transformer, a Rogowski coil, or by a sensor system based on a magnetic field probe. However, the disadvantage is that the conductors to be measured must be individually accessible, which often means that multi-conductor cables must be disassembled.

Patent Document 1 proposes a measurement system that enables measurement of a current in one individual conductor that cannot be directly accessed by a multi-conductor system without damaging the multi-conductor system. The measurement system includes at least two magnetic field sensors, which are located on a printed circuit board around a multi-conductor system. These magnetic field sensors are suitable for measuring a single magnetic field resulting from a linear combination of magnetic fields of multiple individual current conductors and converting that magnetic field into an electrical signal. The measurement system also has a signal evaluator, which allows the signals of at least two magnetic field sensors and at least one distance of the current conductor to one of those magnetic field sensors in the current conductor. The current strength is determined. Unfortunately, this measurement system is sensitive to external magnetic fields, which can distort the measurement of current in conductors.

German Patent Application No. 102016210970.7.

An object of the present invention is to provide an apparatus and a method capable of measuring an electric current in a multi-conductor system which is not directly accessible.

This problem is solved by the apparatus according to any one of claims 1 to 13 and the method according to claim 14 .

The device according to the invention for measuring the current intensity in one current conductor of the multi-conductor system having at least two current conductors has at least two magnetic field sensors. The magnetic field sensors is to measure one field the resulting linear combination of the magnetic field of a plurality of individual current conductors are formed so as to convert the magnetic field into an electric signal. The first magnetic field sensor is arranged in an arc on the first radius around the current conductor, and the second magnetic field sensor is arranged in an arc on the second radius around the current conductor. The first radius is larger than the second radius. Furthermore, the device according to the invention has a signal evaluation device, the signal evaluation device, a difference of at least two magnetic field sensors of the signal, by a first distance or second distance, the current strength of the current conductor Formed to determine. The first distance is at least one distance of the current conductor to the first magnetic field sensor, and the second distance is at least one distance of the current conductor to the second magnetic field sensor.

By assigning the sensor signals of the two magnetic field sensors to different distances with respect to the current conductor and forming the difference between these sensor signals, an external magnetic field, especially a uniform external magnetic field, with respect to the measurement result of the current intensity in the current conductor is not preferable. The impact is significantly reduced. Dismantling of multi-conductor systems to allow direct access to individual current conductors is advantageously avoided. Furthermore, the expansion of the measurement range can be advantageously achieved.

In an advantageous embodiment and development of the present invention, the first and second magnetic field sensors are arranged on one common printed circuit board. All magnetic field sensors, which mean both magnetic field sensors on the first radius and magnetic field sensors on the second radius, can be placed on their common printed circuit board and placed around and secured around a multi-conductor system. .. Therefore, the relative position and distance between the magnetic field sensors and the relative position and distance of the magnetic field sensor with respect to the current conductor to be measured are constant during the measurement. This advantageously allows for fixed measurements.

In an advantageous embodiment and development of the present invention, the first magnetic field sensor is arranged on the first printed circuit board and the second magnetic field sensor is arranged on the second printed circuit board. Therefore, it is advantageous to choose the first radius and the second radius independently of each other.

In an advantageous embodiment and development of the present invention, the printed circuit board is formed as a flexible printed circuit board. Therefore, advantageously, printed circuit boards with magnetic field sensors can be variously placed around the multi-conductor system. In doing so, the multi-conductor system can have a variety of shapes, especially circular or elliptical. Moreover, the perimeter of the multi-conductor system and the length of the first and / or second printed circuit boards need not be exactly matched to each other. Advantageously, it is sufficient if the printed circuit board can be partially placed around the multi-conductor system. By fixing the flexible printed circuit board around the multi-conductor system, it is guaranteed to keep the distance of the magnetic field sensor constant to each individual conductor to be measured. Advantageously, flexible printed circuit boards can be installed in new multi-conductor systems as well as in older equipment already in use. The fixing can be performed by, for example, a flexible fastening member, a bolt joint, or an adapter member formed in the fitting portion.

In other advantageous embodiments and developments of the invention, the number of magnetic field sensors on a printed circuit board is equal to or greater than the number of current conductors. Advantageously, the current intensity can then be determined for each individual conductor of the multi-conductor system. The magnetic field sensor has a different distance to the current conductor to be measured. Since the magnetic field of one just passing current conductor decreases in inverse proportion to its distance, the linear coupling of the magnetic fields of multiple individual current conductors infers the current intensity at one particular individual conductor. be able to.

In other advantageous embodiments and developments of the invention, the number of magnetic field sensors on the first and second printed circuit boards is equal. In doing so, it is advantageous that one first magnetic field sensor and one second magnetic field sensor are associated with each other in pairs. Both sensors can generate a signal used to determine the current in the current conductor to be measured. The difference between these two signals can advantageously minimize the effects of an external magnetic field, especially a uniform external magnetic field.

In other advantageous embodiments and developments of the invention, the ratio of the first radius to the second radius is in the range between 1.1 and 3. Within this range, the measurement signals of the first and second magnetic field sensors are different enough on the one hand to exclude the external magnetic field from the measurement and still the same magnitude on the other hand to be able to calculate the current intensity. It is in the range.

In other advantageous embodiments and developments of the present invention, the first magnetic field sensor and the second magnetic field sensor are arranged so as to be aligned with each other in the radial direction, that is, from the center point of the multi-conductor system. They are arranged in a straight line. At that time, the sensitive directions of both magnetic field sensors are oriented parallel to each other. Advantageously, this arrangement of both magnetic field sensors can minimize the effect of a uniform external magnetic field on the determination of the current in the current conductor.

In other advantageous embodiments and developments of the invention, at least one of the magnetic field sensors is a fluxgate sensor or hall sensor. A fluxgate sensor is a sensor that is a magnetometer for determining a magnetic field as a vector. Fluxgate sensors are also referred to as Felsta probes. A magnetic field of 0.1 nT to 5 mT can be measured by a fluxgate sensor. Hall sensors take advantage of the Hall effect for magnetic field measurements. Advantageously, the Hall sensor does not change the magnetic field under test. This is because magnetically active materials must not be used in Hall sensors.

In other advantageous embodiments and developments of the present invention, the first and second magnetic field sensors are arranged substantially planarly with each other. In this case, both printed circuit boards are also arranged substantially planarly with each other. The sensitive directions of each magnetic field sensor are oriented parallel to each other.

In other advantageous embodiments and developments of the invention, the printed circuit board is arranged around the multi-conductor system so that the surface normals of the printed circuit board are parallel to the axial direction of the multi-conductor cable. .. In this arrangement, the radial distances of the first and second magnetic sensors and the radial distances of the first and second magnetic sensors to the center point of the multi-conductor system are constant. Moreover, this distance is known because the distance of the magnetic field sensor to the center point of the system can be easily determined via the length of the perimeter. Therefore, this arrangement can advantageously ensure the flexibility required in the printed circuit board assembly stage, and is measured in the measurement stage with a spatially rigid radial arrangement between the magnetic field sensors. The spatially rigid radial arrangement of the magnetic field sensor with respect to the current conductor to be power can be advantageously ensured.

In other advantageous embodiments and developments of the invention, the printed circuit board as being disposed at least 180 ° arcuate around a multi-conductor system, the length of the printed circuit board is selected. Printed circuit boards can be placed around various multi-conductor systems with different perimeters and perimeter shapes.

In other advantageous embodiments and developments of the present invention, the signal evaluation device is arranged on the printed circuit board. In that case, it is advantageous that only the entire device needs to be mounted to measure the current intensity in one current conductor, and the additional mounting of a signal evaluation device is advantageously avoided. be able to.

In the method according to the invention, the current intensity of one current conductor in a multi-conductor system is determined by evaluating at least two electrical signals from at least two magnetic field sensors in a signal evaluator. This method uses the apparatus according to the present invention. The first magnetic field strength is determined from the first signal, and the second magnetic field strength is determined from the second signal. Further, the first distance between the first magnetic field sensor and the current conductor is known, or the second distance between the second magnetic field sensor and the current conductor is known. Using Biot-Savart's law, the current strength of a current conductor is determined from the difference between the first and second magnetic field strengths and the first or second distance.

Other embodiments and other features of the invention will be described in more detail with reference to the following figures.

FIG. 1 shows a cross-sectional view of a measuring device having a multi-conductor system. FIG. 2 shows a plan view of a measuring device having a multi-conductor system. FIG. 3 shows a multi-conductor system with a magnetic field sensor band having a surface normal extending parallel to the axis of the multi-conductor system.

FIG. 1 shows a measuring device 1 and a multi-conductor cable 14 in a cross-sectional view. Multi-conductor cable 14 includes three current conductors 7. These current conductors 7 are symmetrically arranged around the virtual center of the multi-conductor cable 14 in this embodiment. However, it is also possible that the current conductors 7 are not symmetrically arranged within the multi-conductor cable 14.

A measuring device 1 for measuring the current intensity in at least one current conductor 7 is arranged around the multi-conductor cable 14. Measuring device 1 includes a flexible printed circuit board 2. On the flexible printed circuit board 2, two bands are arranged on the first radius R1 and the second radius R2 , respectively, and these bands include a plurality of magnetic field sensors 3 and 4 . In this example, on the flexible printed substrate 2, the first magnetic field sensor 3 is on the first radius R1 around the center of the multiconductor system 14, and the first magnetic field sensor 3 is on the second radius R2 around the center of the multiconductor system 14. A second magnetic field sensor 4 is arranged in. In that case, the first radius R1 is larger than the second radius R2.

Above each of these two radii R1 and R2 around the center of the multi-conductor cable 14, there are at least as many magnetometers 3 and 4 as the current conductors 7 present in the multi-conductor system 14. The first and second magnetic field sensors 3 and 4 are arranged so as to be aligned on the straight line 10 when viewed from the center of the multi-conductor cable 14. This also means that the sensitive directions 11 of the two magnetic field sensors 3 and 4 are arranged parallel to each other. FIG. 1 shows a pair of sensors 16. The sensitive directions 11 of the first magnetic field sensor 3 and the second magnetic field sensor 4 are arranged parallel to the peripheral edge of the flexible printed circuit board 2. The surface normals 17 of the flexible printed circuit board 2 are arranged parallel to the axial direction of the multi-conductor system 2. The first radius R1 and the second radius R2 depend on the insulation, the geometry of the conductor arrangement, the current intensity and the type of magnetic field sensor used. In this example, the first radius R1 of the first magnetic field sensor 3 is R1 = 70 mm, and the second radius is R2 = 54 mm. Since the sensitive directions 11 of both magnetic field sensors are arranged in parallel, the magnetic sensitive directions of the magnetic field sensors 3 and 4 are arranged at the same angle α _S with respect to the current conductor 7 to be measured. One of the paired magnetic field sensors 3 and 4 related to each other is on the outer radius R1 having a first distance 5 with respect to the current conductor 7 of the multiconductor system 14 and the other of the magnetic field sensors 3 and 4. Is on an inner radius R2 having a second distance 6 with respect to the current conductor 7 of the multiconductor system 14. Based on the magnetic field difference between the magnetic field sensors inside and outside the sensor pair (ie, between the first magnetic field sensor 3 and the second magnetic field sensor 4) and the first distance 5 or the second distance 6. , The current in the current conductor 7 can be determined.

In this example, for the three current conductors 7 to be measured, six magnetic field sensors are arranged on the radius R1 and six magnetic field sensors are arranged on the radius R2. In this example, both magnetic field sensors 3 and 4 are fluxgate sensors. Alternatively, a Hall sensor can be used.

The signal evaluation device 8 is electrically connected to the flexible printed circuit board 2 in order to evaluate the signals of the magnetic field sensors 3 and 4. The signal evaluation device 8 obtains the current intensity in the individual conductor 7 of the multi-conductor system 14 from at least two signals of at least two magnetometers 3 and 4 having two different radii R1 and R2, particularly from the magnetometer pair 16. Formed to determine. By using two magnetic field sensors 3 and 4 arranged concentrically around the current conductor and parallel orientation with respect to the sensitive direction 11, the magnetic field difference is used to determine the disturbing effect of the external magnetic field on the result. It can be significantly reduced.

Since the flexible printed circuit board 2 is shorter than the peripheral length of the multi-conductor cable 14, a first opening 15 toward the multi-conductor cable 14 is left.

At least the first distance 5 or the second distance 6 must be known in order to determine the current intensity in the current conductor 7. In this example, since the geometry of the multi-conductor cable 14 is known, the distance between the current conductor and the two magnetic field sensors 3 and 4 is known. If the geometry of the multi-conductor cable 14 is unknown, the magnification can be determined. A defined current intensity is supplied through the current conductor 7 to determine the magnification, and then the magnetic fields are measured by the first and second magnetic field sensors 3 and 4. A magnification can then be calculated, which can also be used here as well when an unknown current intensity is passed through the current conductor 7.

FIG. 2 shows a plan view of the multi-conductor cable 14 and the measuring device 1. In this figure, the following can be well recognized. That is, the surface normal line 17 of the flexible printed circuit board 2 is arranged parallel to the current conductor 7 that conducts electricity in the multiconductor cable 14. Further, since the flexible printed circuit board 2 is shorter than the circumference of the multi-conductor cable 14, the opening 15 can be recognized. Further, the signal evaluation device 8 is arranged on the flexible printed circuit board 2.

The determination of current strength is based on Biot-Savart's law:

The Biot-Savart law shows that a current conductor of minute length dl at position r'through the current I has a magnetic field strength dH at position r.

According to Equations 2 to 7, M currents can be determined from N sensor signals by the method of least squares. In that case, H _μ1 is the magnetic field strength measured at the position (x _μ1 y _μ1 ) in the equation μ1 by the first magnetic field sensor 3. H _μ2 is the magnetic field strength measured at the position (x _μ2 y _μ2 ) in the equation represented by μ2 by the second magnetic field sensor 4. I _θ is the current at the position (x _θ y _θ ), and thus the current at the current conductor 7.

The angle α _Sμ1 is an angle between the magnetic field sensitive direction of the sensor μ1 and the x-axis of the coordinate system 9 in FIG. The angle α _Sμ2 is an angle between the magnetic field sensitive direction of the sensor μ2 and the x-axis of the coordinate system 9. The coordinate system 9 relates to equations 2-7.

FIG. 3 shows a multi-conductor system 14 having a measuring device 1, wherein the first magnetic field sensor 3 on the first band 12 and the magnetic field sensor 4 on the second band 13 are normals of those bands. The wires 17 are arranged so as to be parallel to the axial direction of the multi-conductor system 14. Since the first band 12 and the second band 13 are tightly coupled to each other, it is possible to ensure a spatially strong radial arrangement around the current conductor 7 during operation or measurement. Advantageously, the flexible band system including the first and second bands 12, 13 has at least one opening 15, thus ensuring mechanical flexibility during the installation of the measuring device 1. it can.

Not only the mounting of the flexible printed circuit board 2, but also the mounting of the first and second bands 12 and 13 makes it possible to easily add the measuring device 1 to the existing equipment without major changes, or to perform temporary measurement. Allows, especially during the initial turnover of equipment.

1 Measuring device 2 Flexible printed substrate 3 First magnetic field sensor 4 Second magnetic field sensor 5 First distance 6 Second distance 7 Current conductor 8 Signal evaluation device 9 Coordinate system 10 Straight line 11 Sensitive direction 12 First band 13 Second band 14 multi-conductor cable (multi-conductor system)
15 Aperture 16 Magnetic field sensor pair 17 Surface normal R1 First radius R2 Second radius

Claims (14)

A device (1) for measuring the current intensity in one current conductor (7) of a multi-conductor system (14) having at least three current conductors (7).
The device (1) has at least two magnetic field sensors (3, 4) and a signal evaluation device (8).
The magnetic field sensors (3, 4) are each formed to measure one magnetic field resulting from the linear combination of the magnetic fields of the current conductor (7) and convert the magnetic field into an electric signal.
The first magnetic field sensor (3) is arranged on the circumference of the first radius (R1) around the center of the multi-conductor system (14), and the second magnetic field sensor (4) is said. Arranged on the circumference of a second radius (R2) around the center of the multi-conductor system (14) , the first radius (R1) is larger than the second radius (R2).
The signal evaluation device (8) is a first distance (3) between the signals of the at least two magnetic field sensors (3, 4) and at least one of the first magnetic field sensors (3) with respect to the current conductor (7). 5) and by at least one of the current second distance to the conductor (7) and (6) relative to the second magnetic field sensor (4) is formed to determine the current intensity in the current conductor (7) The device (1). The apparatus (1) according to claim 1, wherein the first and second magnetic field sensors (3, 4) are arranged on one common printed circuit board (2) or a plurality of different printed circuit boards (2). The apparatus (1) according to claim 2, wherein the one or more printed circuit boards are flexible printed circuit boards. The number of the magnetic field sensors (3, 4) on the first radius (R1) and the second radius (R2) is equal to or equal to the number of the current conductors (7), respectively, or the current conductors ( The device (1) according to one of claims 1 to 3, which is larger than the number of 7). The apparatus according to one of claims 1 to 4, wherein the number of the magnetic field sensors (3, 4) on the first and second radii (R1, R2) is equal. The apparatus according to one of claims 1 to 5, wherein the sensitive directions (11) of the first and second magnetic field sensors (3, 4) are oriented in parallel with each other. The apparatus according to one of claims 1 to 6, wherein the ratio of the first radius (R1) to the second radius (R2) is in the range of 1.1 to 3. 10. One of claims 1 to 7, wherein the first magnetic field sensor (3) and the second magnetic field sensor (4) are arranged so as to be aligned with each other (10) in the radial direction. apparatus. The apparatus according to one of claims 1 to 8, wherein the first magnetic field sensor (3) and the second magnetic field sensor (4) are arranged in a plane with each other. The device according to one of claims 1 to 9, wherein at least one of the magnetic field sensors (3, 4) is a fluxgate sensor or a hall sensor. The printed circuit board (2) is arranged around the multi-conductor system (14) so that the surface normal (16) of the printed circuit board (2) is parallel to the axial direction of the multi-conductor system (2). The device according to claim 2 , or one of claims 3 to 10, which directly or indirectly cites claim 2 . Claim 2 , claim 2 , the length of the printed circuit board (2) is selected such that the printed circuit board (2) is arranged in an arc at least 180 ° around the multi-conductor system (14). The device according to claim 11 or one of claims 3 to 10 , which directly or indirectly cites 2 . 2. One of claims 3 to 10 , which directly or indirectly cites claim 2 , wherein the signal evaluation device (8) is arranged on the printed circuit board (2) , claim 11. Alternatively, the device according to 12 . A method of evaluating at least two electrical signals by the apparatus according to any one of claims 1 to 13.
The first magnetic field strength (H1) is determined from the first signal of the first magnetic field sensor, and the second magnetic field strength (H2) is determined from the second signal of the second magnetic field sensor.
Using Biot-Savart's law, the difference between the first and second magnetic field strengths (H1, H2) and the first between the first magnetic field sensor (3) and the current conductor (7). A method of determining the current intensity of the current conductor (7) from the distance (5) or the second distance (6) between the second magnetic field sensor and the current conductor (7).