Method for measuring rotational speed of electric machine

Abstract

Method for measuring the rotational speed of an electric machine comprising a rotor (3), a stator (4), at least one radar system (1) and a data processing device (2), and wherein the at least one radar system (1) is arranged such that it can detect a part of the rotor (3) and a part of the stator (4), and wherein the at least one radar system (1) is arranged such that it can detect a part of the rotor (3) and a part of the stator (4). The rotational speed of the rotor (3), the width of the air gap and a vibration characteristic indicator for the stator (4) are ascertained on the basis of the measured values detected by the radar system.

Description

Technical Field

[0001] The present invention relates to a method for measuring the rotational speed of an electric motor. The electric motor is preferably, but not limited to, a large electric motor, such as a motor used in a hydroelectric power generation facility. Background Art

[0002] Methods for measuring the rotational speed of electric motors are known from the prior art. In many cases, a sensor is used to scan a toothed disc (see, for example, US Pat. No. 11,486,251 B2). Inductive sensors and Hall sensors are known as sensors (see, for example, DE 10 2004 046 824 A1). Furthermore, the use of optical sensors is also known.

[0003] DE 10 2010 009 663 A1 discloses a method for measuring the rotational speed of an electric motor using a radar system. Furthermore, the disclosed method can also detect the air gap width and the vibration of the working spindle. US 5 760 731 A discloses another method for measuring the rotational speed of an electric motor using a radar system, wherein rotor vibrations can also be detected. US 2019 / 0 020244 A1 discloses a method for monitoring the air gap using a radar system. DE 10 2018 123 845 A1 discloses a method for monitoring the winding heads of a rotor of an electric motor using a radar system, wherein the radar system can detect deformations of the winding heads. DE 102014 215 008 A1 discloses a method for determining the angle of attack of a rotor blade of a turbine using a radar system. Summary of the Invention

[0004] The object of the present invention is to specify an alternative method which, as an additional advantage, allows the detection of another characteristic variable of the electric machine in addition to the detection of the rotational speed and the air gap width.

[0005] According to the invention, this object is achieved by the embodiments corresponding to the independent claims. Further advantageous embodiments of the invention can be found in the dependent claims.

[0006] According to the invention, this object is achieved by using a specially designed radar system. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present invention will be described below with reference to the accompanying drawings. The accompanying drawings show in detail:

[0008] Figure 1 shows the radar system;

[0009] Figure 2 An electric machine in a non-claimed embodiment is shown;

[0010] Figure 3shows a motor in another non-claimed embodiment;

[0011] Figure 4 shows a motor in another non-claimed embodiment;

[0012] Figure 5 shows a motor in another non-claimed embodiment;

[0013] Figure 6 Showing a motor according to the present invention;

[0014] Figure 7 shows a motor in another non-claimed embodiment;

[0015] Figure 8 An electric machine is shown in another non-claimed embodiment. DETAILED DESCRIPTION

[0016] Figure 1 A radar system used in the method according to the present invention is shown in a highly schematic diagram. The radar system is designated 1. A radar system typically comprises a transceiver having a transmitting antenna and a receiving antenna, and a control unit. The transmitting antenna and the receiving antenna can be implemented independently as two separate antennas, or as a single antenna that can perform both transmitting and receiving functions. The control unit typically includes a microprocessor that controls the transceiver and processes the received signals. Radar system 1 can be designed, for example, as a CW (continuous wave) or FMCW (frequency modulated continuous wave) radar system. In any case, radar system 1 is designed to provide a measured value representing a distance over time. This can be the distance between radar system 1 and an object detected by radar system 1, or the distance between two objects detected by radar system 1 (i.e., the distance difference). Figure 1 The dashed line in FIG represents the cone beam of radar system 1, that is, the radiation characteristic of the transmitting antenna. Radar system 1 is connected to a data processing device, which is indicated by 2. This connection can be implemented by wire or wirelessly. The data processing device 2 will be omitted in the following figures.

[0017] Figure 2An electric motor suitable for carrying out a non-claimed method is shown. The electric motor comprises a stator, which is designated by 4, and a rotor, which is designated by 3. The dashed line here indicates the axis of rotation of the rotor 3. Within the scope of the present application, the term "rotor" is used very broadly. In addition to the "actual rotor" which is common in common language usage, all objects connected to the "actual rotor" belong to the rotor according to the understanding of the present application, i.e. all objects that rotate with the "actual rotor". This can also include objects that do not belong to the electric motor according to common language usage. Accordingly, according to the understanding of the present application, for example, in the case of an electrically operated model aircraft, the propeller belongs to the rotor of the electric motor, or in a hydroelectric power plant, the impeller of the hydraulic machine belongs to the rotor of the electric motor (see Figure 8 The connection between the relevant objects and the "actual rotor" can be direct, so that they rotate at the same speed as the "actual rotor," or indirect via a transmission, so that the speeds are different. In the second case, there is a known relationship between the different speeds, so that the multiplication of one speed by a known constant yields the other speed.

[0018] exist Figure 2 In the motor, the rotor 3 comprises a shaft and a toothed disc connected to the shaft and denoted by 5. The motor also comprises a radar system denoted by 1. In principle, the radar system 1 is arranged so that it can detect a portion of the rotor 3. Figure 2 In the example, the portion of rotor 3 detected by radar system 1 is toothed disc 5. Here, toothed disc 5 includes protrusions that enable radar system 1 to transmit periodic, time-varying pitch values ​​to data processing device 2 as rotor 3 rotates. When one tooth of toothed disc 5 is directly in front of the radar system, the radar system detects a smaller pitch than when no tooth is directly in front of it. The number of teeth on the toothed disc and the rotor's rotational speed determine the frequency of alternating long and short pitches. Since the number of teeth on the toothed disc is known, the rotor's rotational speed can be calculated from the detected pitch values.

[0019] The method comprises the following steps:

[0020] - S1: During the rotation of the rotor 3, the radar system 1 detects periodic pitch values ​​that vary over time and transmits them to the data processing device 2;

[0021] - S2: The data processing device 2 calculates the rotational speed of the rotor 3 based on the transmitted spacing value.

[0022] The inventors have realized that the rotors of many electric machines are constructed so that a toothed disc for speed measurement can be omitted. This is exemplified by Figure 3Many rotors consist of a lamination stack that is held together by tension bolts. The ends of the tension bolts protrude beyond the lamination stack. They are usually arranged evenly around the axis of rotation. Figure 3 The arrangement shown can detect the ends of the tension bolts, which periodically appear and disappear in front of the radar system as the rotor rotates. This produces a sequence of spacing values ​​similar to that detected using a toothed disc. Depending on the design of the respective motor, other rotor regions can be used for speed measurement. Further examples of this are described in conjunction with the other figures of this application.

[0023] However, another aspect of the present invention should first be discussed. The inventors have realized that, with the aid of the arrangement according to the present invention, other important characteristic variables of the electric motor can be determined and monitored without the need for additional devices. One possible additional characteristic variable is vibration. Vibration monitoring allows for the timely identification of faults and the avoidance of associated damage to the electric motor. The inventors have realized that, with the aid of a radar system, it is possible not only to detect the distances required for speed measurement, but also to simultaneously detect changes in the distances that provide information about the vibrations of the electric motor. For this purpose, it may only be necessary to increase the sampling rate accordingly for vibration measurement. The vibration characteristic indicators thus determined primarily relate to the part of the rotor detected by the radar system. Since the vibrations propagate throughout the entire rotor independently of the cause of the vibrations, the vibration characteristic indicators thus determined are always a measure of the running smoothness of the electric motor. In other words, according to the present invention, vibration measurement can always be combined with speed measurement (i.e., in any conceivable arrangement of the radar system).

[0024] Thus, the method according to the present invention optionally additionally comprises the following steps:

[0025] - S3: Calculation of at least one further characteristic indicator of the rotor 3 by the data processing device 2 based on the transmitted spacing value;

[0026] Therein, the at least one further characteristic indicator is a vibration characteristic indicator.

[0027] The inventors have recognized that, in addition to vibration characteristics, there are other characteristics that can be determined simultaneously with the speed determination. The determination of which additional characteristics are determined depends on the design of the motor and the arrangement of the radar system. The following figures illustrate some conceivable arrangements and the associated characteristics to be determined.

[0028] Figure 4An unclaimed electric motor is shown, which includes numerous ventilation slots arranged in the stator. Only one of these slots is shown and is designated by 6. A radar system 1 is positioned within the illustrated ventilation slot 6 so that it can detect the outer contour of the portion of the rotor located within the stator. The beam emitted by the radar system 1 penetrates the air gap of the electric motor, which is located between the stator and the portion of the rotor located within the stator, in the radial direction. This arrangement allows the air gap width to be determined from the spacing value detected by the radar system 1, thereby enabling monitoring of the air gap. In other words, the characteristic indicator of the additional calculation of the method according to the present invention is the air gap width.

[0029] Figure 5 Shown in a cross-section perpendicular to the axis of rotation of the motor Figure 4 Layout plan. Combined with Figure 5 It can be explained how the speed of an electric motor can be determined using the arrangement shown. This is achieved by the fact that in most electric motors, the outer contour of the rotor part arranged inside the stator is not a perfect cylindrical surface. In the electric motor shown, the rotor winding consists of conductor bars arranged in slots in the rotor body. The conductor bars are held in the slots by slot wedges. The so-called teeth are located between the slots. The slot wedges are slightly set back inwards relative to the teeth. This results in an outer contour similar to that of a toothed disk, which makes it possible to measure the speed using the arrangement shown. Many other motors have similar outer contours, such as those with rotors in the form of salient-pole rotors. If the outer contour deviates from the cylindrical shape, the method according to the invention can always be used in the manner described. If this is not the case (although this is the case in most electric motors), then this can of course be achieved by installing small protrusions or creating small slots.

[0030] Figure 6 The arrangement according to the invention shows that, in addition to monitoring the vibrations of the air gap and the rotor, the arrangement also enables vibration monitoring of the stator. Figure 4 and Figure 5 As shown, the beam of the radar system 1 penetrates the air gap in the radial direction. Figure 4 and Figure 5 The difference is that the radar system 1 is arranged outside the stator 4. Here, the beam of the radar system 1 penetrates the stator 4 through a suitable opening in the stator 4 and detects a portion of the rotor. At the same time, the radar system 1 detects a portion of the stator 4, which allows it to be monitored for vibration. The advantage here is that the radar system 1 is decoupled from the stator 4 with respect to vibration. The stator 4 and the radar system are connected to a base, designated by 7. A vibration decoupling device, designated by 8, is arranged between the base 7 and the radar system 1. The method according to the present invention comprises the following steps:

[0031] - S4: The time-varying distance value to the detected part of the stator is detected by the radar system 1 and transmitted to the data processing device 2;

[0032] - S5: The data processing device 2 calculates the vibration characteristic index of the stator 4 according to the spacing value transmitted in S4.

[0033] Figure 7 An unclaimed arrangement is shown that allows for the determination of another characteristic variable of the relevant electric machine. The electric machine includes a winding head, which is formed by winding ends that protrude axially beyond the rotor body and is designated by 9. The radar system 1 is arranged so that it can detect the rotor in the area of ​​the winding head 9. The arrangement shown allows for the determination and monitoring of the deformation of the winding head 9 caused by the action of centrifugal forces. It has been shown that the design of the winding head 9 allows for simultaneous measurement of the rotational speed without any problems.

[0034] As already mentioned above, according to the present application, the rotor includes all objects connected to it and rotating with it. In a hydroelectric power plant, this is, for example, the impeller of a hydraulic machine connected to a motor. Figure 8 An unclaimed arrangement is shown, comprising such an impeller, designated 10. Impeller 10 rotates in a so-called impeller ring, designated 12. Impeller 10 is of Kaplan type and includes a plurality of pivotable blades, of which only one is shown and designated 11. Radar system 1 is arranged so that it can detect the radial ends of blades 11 through windows in impeller ring 12, which move past the windows as impeller 10 rotates. The radar beam penetrates the gap between the windows and the impeller ends in the radial direction. As can be seen from the description, the illustrated arrangement enables monitoring of the gap width and the vibrations of impeller 10. Measuring the impeller speed, and therefore the motor speed, is also straightforward, as the radar system periodically detects small and large gaps as impeller 10 rotates. Small gaps are detected when a blade end is in front of the window. Large gaps are detected when the gap between two adjacent blades is in front of the window. Furthermore, the illustrated arrangement enables the measurement of the Kaplan impeller's opening as an additional characteristic variable, since the opening is clearly correlated to the duty cycle of the periodic pitch signal. The duty cycle is the ratio of the duration of a small pitch value to the duration of a large pitch value. When blades 11 are pivoted, i.e., when the impeller's opening is at its minimum, the gap between the blades is at its minimum, and thus the duty cycle is at its maximum. At maximum opening, the gap is at its maximum, and thus the duty cycle is at its minimum. The duty cycle and the opening calculated from it can be used as feedback for the turbine regulator.

[0035] The method for measuring motor speed according to the present invention can be easily modified to enable absolute determination of the rotor's azimuthal position. To do this, it is sufficient to ensure that the spacing signal detected by the radar system provides a specific spacing once per complete rotor revolution. This defined, unique event can then be used for position calibration. This unique event can be generated, for example, by installing additional protrusions or grooves at appropriate locations within the rotor area detected by the radar system. If the direction of rotation is also to be determined, a second radar system can be used for this purpose, arranged similarly to the first radar system, only offset in the azimuthal direction.

[0036] Based on the examples described, a person skilled in the art can easily deduce other application cases of the method according to the invention for specific electric machines without requiring any inventive step.

[0037] Reference Signs List

[0038] 1 Radar system

[0039] 2 Data processing device

[0040] 3 rotors

[0041] 4 stator

[0042] 5 chainrings

[0043] 6 ventilation gaps

[0044] 7 Base

[0045] 8 Vibration decoupling device

[0046] 9 Winding head

[0047] 10 Impeller of hydraulic machinery

[0048] 11 blades

[0049] 12 Impeller ring

Claims

1. A method for measuring the rotational speed of an electric machine, the electric machine comprising a rotor (3), a stator (4), at least one radar system (1) and a data processing device (2), and wherein: The at least one radar system (1) is arranged such that it can detect a portion of the rotor (3), and wherein the electric machine comprises an air gap arranged between the rotor (3) and the stator (4), and wherein the portion of the rotor (3) detected by the at least one radar system (1) is arranged in the interior of the stator (4), and wherein the at least one radar system (1) is arranged such that it can detect at least a portion of the stator (4), and wherein the method comprises the following steps: - S1: During the rotation of the rotor (3), the at least one radar system (1) detects periodic pitch values ​​that vary over time and transmits them to the data processing device (2); - S2: calculating the rotational speed of the rotor (3) based on the transmitted pitch value by the data processing device (2); - S3: calculating at least one further characteristic indicator of the rotor (3) by the data processing device (2) based on the transmitted spacing value, wherein the at least one further characteristic indicator includes the width of the air gap; - S4: detecting a time-varying distance value from the detected part of the stator (4) by means of the at least one radar system (1) and transmitting the value to the data processing device (2); - S5: Calculating a vibration characteristic index for the stator (4) based on the spacing value transmitted in S4 by the data processing device (2).

2. The method for measuring the rotational speed of a motor according to claim 1, wherein: The at least one further characteristic of the rotor comprises a vibration characteristic.

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