MEASUREMENT METHOD FOR DETERMINING IRON LOSSES

Abstract

A measurement method is for determining core losses, which serve to produce magnetic circuits for electrical machines. In order to allow an accurate measurement that is as quick as possible, it is proposed that a magnetic coupling is produced between a measuring coil connected in a capacitor and a core to be measured, and the measuring coil is then acted upon by an alternating frequency in order to measure the resonant frequency of the resulting resonant circuit and/or the quality of the resulting resonant circuit as a measure of the core loss.

Claims

1. Measurement method for determining laminated core losses, wherein a magnetic coupling is produced between a measuring coil connected to a capacitor to form a resonant circuit and a laminated core and the measuring coil is then acted upon by an alternating voltage, and wherein at least one of a resonant frequency of the resonant circuit or a quality of the resonant circuit is measured and loss of the laminated core is determined on the basis of the at least one of the measured resonant frequency or the measured quality.

2. Measurement method according to claim 1, wherein the resonant frequency of the resonant circuit is measured by changing the capacitance of the capacitor or by changing the frequency of the alternating voltage.

3. Measurement method according to claim 1, wherein the quality of the resonant circuit is measured through measurement of the bandwidth of a frequency transfer characteristic of the resonant circuit.

4. Measurement method according to claim 3, wherein the quality of the resonant circuit is determined by measurement of 3 dB bandwidth or 6 dB bandwidth.

5. Measurement method according to claim 1, wherein the magnetic coupling is produced by introducing the measuring coil into an internal space of the laminated core.

6. Measurement method according to claim 1, wherein at least one of the resonant frequency or the quality of the resonant circuit is measured at different angle positions of the measuring coil relative to the laminated core, or, during the measurement of the at least one of the resonant frequency or of the quality, a given angle position of the measuring coil relative to the laminated core is varied.

7. Measuring device formed to carry out a measurement method, wherein, in the measurement method, a magnetic coupling is produced between a measuring coil connected to a capacitor to form a resonant circuit and a laminated core and the measuring coil is then acted upon by an alternating voltage, and at least one of a resonant frequency of the resonant circuit or a quality of the resonant circuit is measured and a loss of the laminated core is determined on the basis of the at least one of the measured resonant frequency or the measured quality, and wherein the measuring device comprises at least one of a control or display device for displaying measurement results, as well as an alternating voltage generator and the measuring coil.

8. Measuring device according to claim 7, wherein the measuring coil is connected to a capacitor to form a parallel resonant circuit or a series resonant circuit.

9. Measuring device according to claim 7, wherein the capacitor is formed as an automatically adjustable capacitor.

10. Measuring device according to claim 7, wherein the measuring device comprises a network analyser which is connected to the resonant circuit in order to measure at least one of the resonant frequency or the quality of the resonant circuit.

11. Measuring device according to claim 10, wherein the resonant circuit is connected to an impedance matching unit via a circuit.

12. Measuring device according to claim 7, wherein the measuring device has a mounting fixture for holding at least one of the laminated core or the measuring coil.

13. Measuring device according to claim 12, wherein the mounting fixture has an actuator for rotating the laminated core, in order to allow a measurement at different angle positions between the measuring coil and the laminated core.

14. Measuring device according to claim 12, wherein the mounting fixture has an actuator for rotating the measuring coil, in order to allow a measurement at different angle positions between the measuring coil and the laminated core.

15. Measuring device according to claim 7, wherein the measuring coil is formed as an air coil.

16. Measuring device according to claims 7, wherein the mounting fixture has a shielding mechanism, in order to shield at least one of the laminated core or the measuring coil.

17. Measuring device according to claim 7, wherein the measuring device has a temperature sensor and is formed such that the measuring device automatically corrects measured value deviations caused by temperature fluctuations.

18. Production method for laminated cores, wherein individual magnetic steel sheet slats are provided with an insulation and stacked to form the laminated cores, and wherein losses of the laminated cores are then measured with a measuring device formed to carry out a measurement method, wherein, in the measurement method, a magnetic coupling is produced between a measuring coil connected to a capacitor to form a resonant circuit and a given laminated core and the measuring coil is then acted upon by an alternating voltage, and at least one of a resonant frequency of the resonant circuit or a quality of the resonant circuit is measured and loss of the given laminated core is determined on the basis of the at least one of the measured resonant frequency or the measured quality, wherein the measuring device comprises at least one of a control or display device for displaying measurement results, as well as an alternating voltage generator and the measuring coil.

19. Production method according to claim 18, wherein the losses of the laminated cores are measured before the laminated cores are provided with a winding.

20. Production method according to claim 18, wherein a limit value is set for losses of the given laminated core, and each of the given laminated core, the losses of which exceed the limit value, is at least one of identified as being defective or discarded.

21. Production method according to claim 18, wherein for quality assurance, for each given laminated core measured, a measured loss value is stored, and several measurement values are statistically evaluated.

22. Measurement method according to claim 3, wherein the quality of the resonant circuit is measured by determining a first frequency (f.sub.1) above and a second frequency (f.sub.2) below the resonant frequency of the resonant circuit at which an amplitude of the alternating voltage is the same size in each case.

23. Measuring device according to claim 9, wherein the capacitor is formed as a variable capacitor or as a capacitance diode.

24. Measuring device according to claim 10, wherein the network analyser is connected to at least one of the measuring coil or the capacitor in order to measure the at least one of the resonant frequency or the quality of the resonant circuit.

25. Measuring device according to claim 11, wherein the circuit is connected to the impedance matching unit between the resonant circuit and the network analyser.

26. Measuring device according to claim 15, wherein the measuring coil is formed as a shielded air coil.

Description

[0048] Further embodiments of the invention are shown in the figures and described below. There are shown in:

[0049] FIG. 1: a schematic block diagram of a measuring device according to the invention;

[0050] FIG. 2: a schematic structure of a measuring coil in the internal space of a laminated core;

[0051] FIG. 3: a frequency transfer characteristic with determination of the 3 dB point;

[0052] FIG. 4: deviations in the frequency response of a resonant circuit resulting from a change in impedance of the coil;

[0053] FIG. 5: influence of the quality of a resonant circuit on the transfer characteristic.

[0054] FIG. 1 shows a schematic block diagram of a measuring device 1. An alternating voltage generator 11, the alternating voltage of which can be set, supplies a measuring coil 21 via an amplifier 12. The measuring coil 21 is connected to an adjustable capacitor 22. The measuring coil 21 is magnetically coupled to a core 3. The measuring coil 21, the variable capacitor 22 and the core 3 together form a resonant circuit 2,

[0055] A network analyser 14 is connected to the resonant circuit 2 via a coupling circuit 13 which serves the impedance matching. The network analyser 14 has a control and display device 15, in order to present the measurement results.

[0056] In the control and display device, a temperature sensor 16 is arranged, in order to measure the ambient temperature. On the basis of the temperature measurement, temperature fluctuations can be recorded and computationally compensated for.

[0057] FIG. 2 schematically shows the positioning of the measuring coil 21 in a sheet iron core 3. In FIG. 2, the sheet iron core 3 is formed as a toroidal core. Alternatively, it is also possible to use and measure a conventional El core or other geometrical core shapes.

[0058] The measuring coil 21 is formed as an air coil and has a wire winding 211. This winding can, for example, consist of an insulated enameled copper wire. At the side of the measuring coil, a shielding 212 is arranged, which ensures that the magnetic flux of the coil is conducted into the core 3. The iron coil 21 is electrically connected to the measuring device 1 via an electrical connection not shown in FIG. 2.

[0059] FIG. 3 shows a frequency response of the resonant circuit 2 by way of example. The example shown is the frequency transfer characteristic of an LC circuit connected to a parallel resonant circuit. The frequency range is plotted on the x-axis. The y-axis shows the amplitude of the resulting alternating voltage on the resonant circuit itself. The range of the resonant frequency can be read off through the highest amplitude.

[0060] The frequencies f.sub.1 and f.sub.2 marked in FIG. 3 denote those frequencies at which the amplitude has dropped by 3 dB on both sides of the resonant frequency. This so-called 3 dB bandwidth can be simply measured via the network analyser. This bandwidth is a direct measure for the quality of the resonant circuit and thus for the losses of the respective core. The narrower this bandwidth compared to the resonant frequency, i.e. the closer the frequencies f.sub.1 and f.sub.2 are to each other, the higher the quality of the resonant circuit and the smaller the core losses. If the core losses increase, the bandwidth of the resonant circuit thus also increases. This can be simply determined through an increase in the difference between the frequencies f.sub.2-f.sub.1.

[0061] FIG. 4 is a graph showing, by way of example, the influence of a change in impedance on the resonant frequency of a resonant circuit. An increase in the impedance of the coil in a resonant circuit leads to a reduction in the resonant frequency.

[0062] FIG. 5 is a graph showing, by way of example, a frequency transfer characteristic of an attenuated resonant circuit in the case of different attenuations. The greater the attenuation of the resonant circuit, the smaller the resonance step-up in the range of the resonant frequency. This deviation in the resonance step-up can also be easily determined using measurement technology.

[0063] On the basis of the changed quality (Q) and the change in resonant frequency, with the measurement method according to the invention, there are two factors that can be simply accessed using measurement technology, in order to determine the losses in a core with high accuracy.

LIST OF REFERENCE NUMBERS

[0064] 1 measuring device

[0065] 11 alternating frequency generator I high frequency generator

[0066] 12 amplifier

[0067] 13 coupling circuit

[0068] 14 network analyser

[0069] 15 control and/or display device

[0070] 16 temperature sensor

[0071] 2 resonant circuit

[0072] 21 measuring coil

[0073] 211 winding

[0074] 212 shielding

[0075] 22 adjustable capacitor

[0076] 3 core/laminated core

[0077] f.sub.1, f.sub.2 frequency of the 3 dB point