Current-measuring device for an electric machine

Abstract

The invention relates to a current-measuring device (4) for an electric machine, comprising a sensor (6), a first flux-conducting element (9), and a first distancing element (11), wherein the first distancing element (11) distances end regions of the first flux-conducting element (9), or the first distancing element (11) distances the first flux-connecting element (9) from a second flux-conducting element (10). In a method for measuring a current of an electric machine (1), a current-measuring device (4) of the aforementioned type is used.

Description

[0001]202009557 1 Description Current measuring device of an electrical machine The invention relates to a current measuring device of an electrical machine and a method for measuring current for an electrical machine. In an electrical machine, the operating parameters and / or test parameters thereof can be measured. Examples of such parameters are a current or a voltage. Such measured values, i.e. an actual current or an actual voltage, can be used for the regulation, control and / or monitoring of the electrical machine. The monitoring of the electrical machine can also be referred to as condition monitoring. The electrical machine is, for example, a motor or a generator. The electrical machine can be a synchronous machine or an asynchronous machine.If such electrical machines have a high power in the megawatt (MW) range, this also results in correspondingly high electrical currents and voltages. For example, for the purposes of condition monitoring and test field purposes, the current on the rotor of synchronous machines is measured and transmitted using slip ring transformers or contactless telemetry systems. Since the excitation currents can reach magnitudes of > 1000 A, special measuring devices are required to measure them, and these should be as cost-effective as possible. In addition to the specific problem of measuring the current on the rotor, the problem also exists for stator currents, which must be made accessible to a monitoring system. Shunts can be used to measure the excitation currents in synchronous machines. For a current range of > 1000 A, these components are large and very expensive to manufacture individually.Current transformers can be used as an alternative to shunts, but these are also large and expensive. Furthermore, rotating applications, such as the rotor of an electrical machine, require a robust design suitable for centrifugal force. 202009557 2 Current transformers or Rogowski coils are not suitable for direct currents. Special LEM current transformers, which are suitable for direct currents, are difficult to obtain for the desired measuring range and are also very expensive. Measurement via shunts also has the disadvantage of not being potential-free. Current measurement for AC stator currents can be carried out using potential-free current transformers, since they operate with voltages of up to several kV. Current transformers require a certain amount of installation space and are also relatively expensive components. For example, it is generally not possible to additionally integrate a monitoring system into existing protection or measuring circuits.Additional converters then represent a cost factor that cannot be neglected. One object of the invention is to provide a simple current measuring device for an electrical machine. A further object of the invention is to provide a simple method for measuring current for an electrical machine. One solution to the problem is given by claim 1 or claim 9. Embodiments are given, for example, by at least one of claims 2 to 8 and 10. A current measuring device for an electrical machine has a sensor. The sensor is in particular a Hall sensor, also called a Hall effect sensor or Hall current sensor or Hall sensor. Hall sensors measure magnetic fields and thus indirectly the current via the magnetic field law. Nevertheless, Hall sensors are often also referred to as current sensors. Hall current sensors can be used to measure direct and alternating currents, whereby these are in particular in the range between 1000 A and 10,000 A.The current measuring device has a first flux-conducting element and a first spacing element. The current measuring device thus has at least one flux-conducting element and at least one spacing element. In the current measuring device, the first spacing element distances end regions of the first flux-conducting element, or the first spacing element distances the first flux-conducting element from a second flux-conducting element. In one embodiment of the current measuring device, the first spacing element distances end regions of the first flux-conducting element. In a further embodiment of the current measuring device, the first spacing element distances the first flux-conducting element from the second flux-conducting element. Using a Hall-effect sensor (Hall sensor) for measuring a magnetic field, which can be caused by a current-carrying conductor, a measurement of the current (the electric current) can be carried out.The sensor is, in particular, integrated into a chip. The sensor is therefore, in particular, an integrated component. The measurement takes place primarily at the chip level. For this purpose, there are various sensors that can measure magnetic fields in one or more spatial axes. The sensor must be arranged appropriately in the spacer element. The magnetic field penetrates the sensor, whereby materials can also be used specifically to conduct the magnetic field in the immediate vicinity of the chip. By using a flux-conducting element and a spacer element, it is practically possible to measure almost any current with a single chip. A chip with a limited magnetic field measuring range can therefore be used. In one embodiment of the current measuring device, the design is based on measuring the magnetic field surrounding the conductor through which the current flows.Since the Hall sensor has a specific field direction and maximum evaluable field strength, the structure can be designed so that the field strength can be easily adjusted and, secondly, a relatively homogeneous field profile is present in the area of ​​the sensor, in order to be particularly insensitive to tolerances. 202009557 4 In one embodiment of the current measuring device, its structure is potential-free and, in particular, includes digital signal processing, which enables the transmission of the sensor signal over longer distances with little or no interference. In one embodiment of the current measuring device, at least one flux-conducting element, together with at least one spacing element, surrounds a current conductor. This can also result in at least one air gap. This arrangement can guide the magnetic field of an electrical conductor through which current flows.In one embodiment of the current measuring device, at least one flux guiding element and / or at least one spacing element is replaceable. In one embodiment of the current measuring device, its adaptation to different currents or field strengths takes place through a variable use, i.e. an exchange, of one or more spacing elements and / or one or more flux guiding elements. Spacing elements can be regarded as variable spacers between flux guiding elements. The flux guiding elements can be realized, for example, by an electrical sheet or by several electrical sheets stacked on top of one another. This results in a guide sheet structure. In one embodiment of the current measuring device, flux guiding elements are made of a material with a particularly narrow hysteresis loop, such as mu-metal. This makes it possible to influence the achievable measuring accuracy (in particular, an advantageous improvement in measuring accuracy).In one embodiment of the current measuring device, the flux-conducting element or flux-conducting elements, particularly in an area surrounding an electrical conductor, are geometrically shaped such that their geometric shape follows the magnetic field lines around the electrical conductor. 202009557 5 In other words, the field ultimately follows the magnetic conductor. In one embodiment of the current measuring device, a sensor carrier with the sensor is used with geometrically different flux-conducting elements and / or with geometrically different spacing elements that are to be exchanged. The sensor carrier is, for example, an electronic circuit board or a carrier for an electronic circuit board on which the sensor is located.In one embodiment of the current measuring device, it has at least one connecting element which connects the spacing element to the flux-conducting element, wherein the connecting element in particular comprises a non-magnetic material. The connecting element is, for example, a bracing device, a cable tie, a screw, etc. Copper or plastic, for example, can be used as the material. In one embodiment of the current measuring device, the sensor is arranged in a spacing region. For example, the sensor and / or the sensor carrier can be held by a spacing element or positioned in it. In one embodiment of the current measuring device, the sensor is arranged in a region of homogeneous magnetic field lines. This enables improved measurement accuracy.In one embodiment of the current measuring device, the sensor is arranged at a minimum distance from a conductor (electrical conductor). This makes it easier to position the sensor in an area in which the magnetic field is homogeneous. 202009557 6 In one embodiment of the current measuring device, at least one flux guiding element is made of laminated material. This makes it possible to reduce eddy currents or eddy current losses. In one embodiment of the current measuring device, it has a radio device for the wireless transmission of the measurement signals detected by the sensor. In a method for measuring a current of an electrical machine, a current measuring device according to one of the described embodiments is used. In one embodiment of the method, a rotor current or a stator current of an electrical machine is measured.The variability of the current measuring device means that the same sensor can be used in different electrical machines with different power outputs. In one embodiment of the method, at least one spacing element is exchanged to measure different currents, in particular different maximum currents. This allows a current measuring device to be used flexibly. The variability of the current measuring device means that costs can be kept comparatively low compared to a shunt. Furthermore, a comparatively very compact design can result. A further advantage of the current measuring device can arise from a non-intrusive type of installation (the circuit does not have to be opened). A further advantage of the current measuring device can arise from its possible potential-free design. Potential-free operation can be important, especially with high currents or voltages.The possible use of an integrated Hall sensor in combination with a microcontroller (especially an inexpensive microcontroller) and / or simple components (e.g., metal sheets for flux-conducting elements, 3D-printed plastic structures for spacing elements 202009557 7 or brass screws) results in very low costs and a flexible and robust design. One embodiment of the current measuring device or method may offer opportunities for savings compared to the previously used shunt, and further savings potential may arise if the sensor is also used for current measurement in other areas (e.g., condition monitoring systems or similar). The features of the individual claimed or described embodiments can be readily combined with one another. The invention is illustrated and explained in more detail below using exemplary figures.The same reference numerals designate similar elements in the various figures. The features shown in the figures can be combined by a person skilled in the art to form new embodiments without departing from the invention. They show: FIG. 1 an electrical machine, FIG. 2 a current measuring device and FIGS. 3 to 8 further current measuring devices. The illustration according to Figure 1 shows an electrical machine 1 with a stator 2 and a rotor 3. The electrical machine 1 has an electrical connection with electrical current conductors (conductors) 5, 5', 5''. A current measuring device 4 is provided for measuring an electrical current (current) in the conductor 5. The illustration according to Figure 2 shows a current measuring device 4 for an electrical current conductor (electrical conductor) 5. The electrical conductor 5 in Figure 2 has a round cross-section. A current flow through the electrical conductor 5 is represented by a symbol 15.This symbol 15 has a circle and a cross located within this circle. The current measuring device 4 has a first flux-conducting element 9, which has end regions 19, 19' and a magnetic conducting region 21 located therebetween. The magnetic conducting region 21 of the flux-conducting element 9 guides the magnetic field around a conductor according to its course. The end regions 19, 19' serve to homogenize or parallelize the magnetic field in a defined region. This region is a spacing region 26, which is created by a first spacing element 11. In this region 26, parallel magnetic field lines 20 can form. In this region, where the parallel magnetic field lines 20 can form, a sensor 6 is positioned on a circuit board 7. The sensor 6 can, for example, be pushed together with the circuit board 7 into a recess of the spacing element 11 orbe positioned. The illustration in Figure 3 shows a current measuring device 4 for an electrical conductor 5. The electrical conductor 5 in Figure 3 also has a round cross-section. A current flow through the electrical conductor 5 is represented in Figure 3 by a symbol 15'. This symbol 15' has a circle and a point located in this circle. The point and the cross (see Figure 1) indicate different current directions in this context. According to Figure 3, the conductor 5 has an insulation 8 with a thickness 16. The electrical conductor 5 and the insulation 8 form a cable 27 whose cross-section is shown. The spacing element 11 is directly adjacent to the insulation 8 of the conductor 5. The sensor 6 is at a first distance 17 from the cable 27. The sensor 6 is at a second distance 18 from the electrical conductor 5.The distances 17, 18 are so large that the sensor 6 lies in a region with parallel magnetic field lines. This is to be ensured in particular for different current intensities. The illustration in Figure 4 shows a current measuring device 4 for an electrical current conductor (electrical conductor) 5. The electrical conductor 5 in Figure 4 has a rectangular cross-section. Also shown are a first flux guiding element 9 202009557 9 and a second flux guiding element 10. The first flux guiding element 9 has end regions 19 and 19''. The second flux guiding element 10 has end regions 19' and 19 '''. The first flux guiding element 9 is spaced from the second flux guiding element 10 in the end regions 19 and 19' by the first spacing element 11. Furthermore, the first flux guiding element 9 is spaced from the second flux guiding element 10 in the end regions 19'' and 19'''' by the second spacing element 12.The sensor 6 is located on the circuit board 7 in the first spacing element 11. The first spacing element 11 creates a first spacing region 26 with a distance 25 between the end regions 19 and 19'. The second spacing element 12 creates a second spacing region 26' with a distance 25' between the end regions 19' and 19''. A connecting element 24 connects the first spacing element 11 to the first flux-guiding element 9 and the second flux-guiding element 10 in the spacing region 26. A connecting element 24' connects the first spacing element 11 to the first flux-guiding element 9 and the second flux-guiding element 10 in the spacing region 26'. The flux-guiding elements 9, 10 have magnetic conducting regions 21, 21'. In the conducting area, the respective flux guide element has an arcuate or circular shape. Figure 5 shows a current measuring device 4 for an electrical conductor 5.The flux-guiding elements 9, 10 are made of laminated metal, with two laminates 22, 22', 23, 23' being shown for each flux-guiding element 9, 10 in Figure 5. This allows eddy current losses to be reduced. The illustration in Figure 6 shows a current measuring device 4 for an electrical current conductor 5. The electrical conductor 5 in Figure 6 has a rectangular cross-section with insulation 8. The illustration in Figure 7 shows a current measuring device 4 for an electrical current conductor 5. The electrical conductor 5 in Figure 7 is spaced from the spacing elements 11, 12 202009557 10 by spacer elements 13, 14. The current conductor 5 is positioned in the current measuring device 4 by a first spacer element 13 and a second spacer element 14, both of which are insulators. The illustration in Figure 8 shows a current measuring device 4 for an electrical current conductor 5.The spacing elements 12, 13 have notches 30, 31, 32 and 33 into which the flux-guiding elements 9, 10 protrude. The notches border the position of the sensor 6. The sensor 6 in Figure 8 has a different geometry than the sensors 6 in Figures 2 to 7. This shows that sensors with different geometries can be used. The position of the sensor must be selected or rotated such that a successful measurement can be carried out. Different sensors must therefore be rotated (e.g., by 90 degrees) to achieve a suitable measurement. The sensor must be oriented according to the magnetic field direction in the measuring environment and in the sensor.

Claims

202009557 11 Patent Claims 1. Current measuring device (4) for an electrical machine, with a sensor (6), with a first flux-conducting element (9), and with a first spacing element (11), wherein the first spacing element (11) distances end regions of the first flux-conducting element (9) or wherein the first spacing element (11) distances the first flux-conducting element (9) from a second flux-conducting element (10).

2. Current measuring device (4) according to claim 1, wherein at least one flux-conducting element (9, 10) together with at least one spacing element (11, 12) surrounds a current conductor (5, 5', 5").

3. Current measuring device (4) according to claim 1 or 2, wherein at least one flux-conducting element (9, 10) and / or at least one spacing element (11, 12) is replaceable. 4.Current measuring device (4) according to one of claims 1 to 3, wherein it has a connecting element (24, 24') which connects the spacing element (11, 12) to the flux-conducting element (9, 10), wherein the connecting element (24, 24') in particular has a non-magnetic material.

5. Current measuring device (4) according to one of claims 1 to 4, wherein the sensor (6) is arranged in a spacing region (26, 26').

6. Current measuring device (4) according to one of claims 1 to 5, wherein the sensor (6) is arranged in a region of homogeneous magnetic field lines (20).

7. Current measuring device (4) according to one of claims 1 to 6, wherein the sensor (6) is arranged at a minimum distance (18) from a current conductor (5, 5', 5''). 202009557 12 8. Current measuring device (4) according to one of claims 1 to 7, wherein at least one flux-conducting element (9, 10) is laminated.

9. Method for measuring a current of an electrical machine (1), wherein a current measuring device (4) according to one of claims 1 to 8 is used.

10. Method according to claim 9, wherein at least one spacing element (11, 12) is exchanged for measuring different currents.

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