METHOD AND DEVICE FOR DETECTING ELECTRIC CURRENT IMPULSES OCCURRING AFTER STATIC CHARGING OF ROTATING MACHINE / PLANT PARTS IN A ROLLING BEARING

Description

[0001] The invention relates to a method and a device for detecting electrical current pulses occurring in a rolling bearing between the outer ring, rolling elements, and inner ring of rotating machine or plant components as a result of static charging. Furthermore, the invention also relates to a computer program product embodying this method and, as a specific application, to a wind turbine in which the solution according to the invention is implemented.

[0002] The application of the invention extends in principle to all rotating machine or plant components that are mounted on a stationary support structure by means of rolling bearings. However, wind turbine technology should be highlighted as a specific area of ​​application, where, in particular, damaging current passages through the rotor bearings, caused by static charging of the rotor blades, can lead to bearing damage. Investigations have shown that such current passages caused by static charging are a significant contributing factor to the formation of so-called WECs (white etching cracks). WECs are generally understood to be cracks in the microstructure of the bearing steel, which exhibits local white-etching areas consisting of very fine, nanocrystalline, carbide-free ferrite or ferrite with a very fine carbide distribution.The white, etched areas around the cracks are harder than the surrounding, unaffected microstructure of the bearing steel and lead to bearing damage over time. Therefore, reliable detection of electrical currents occurring in the bearing due to static charge is essential for monitoring the bearing condition and initiating timely maintenance measures if necessary.

[0003] EP 3 570 052 A1 describes a method for measuring a pulsed high-frequency event signal, in particular a partial discharge, in an electrical rotating machine, wherein the event signal is coupled out from a high-frequency electromagnetic field using a sensor during operation.

[0004] EP 1 835 598 A1 describes a method for indicating the occurrence of an electrical discharge in a lubricant between a rolling element and a raceway in a bearing of an electric drive system.

[0005] US 4 814 699 A describes a method for partial discharge detection and spark break measurement in high-voltage dynamo-electric machines for operational monitoring of the insulation condition of the stator winding and the connected electrical leads in turbogenerators.

[0006] EP 2 539 680 B1 discloses a technical solution for detecting damage to rolling bearings, albeit in the non-generic context of inverter-fed electric machines. For this purpose, an electric machine is connected to an inverter. To detect a discharge event passing through the rolling bearing, a measurement is taken in two different frequency bands. In one frequency band, the energy of the discharge event is determined in the single- to multi-digit megahertz range, while in another frequency band above one gigahertz, a coincident event is sought. Such a coincident event indicates that a damaging bearing current event must be assumed. This technical solution for detecting bearing currents is therefore quite application-specific and thus difficult to transfer to other fields of application.

[0007] The object of the present invention is to provide a method and a device for detecting current pulses flowing through a rolling or sliding bearing, especially as a result of static charging of rotating machine or plant parts, which can be reliably detected and evaluated using simple technical means.

[0008] The problem is solved process-related by claim 1. A corresponding apparatus is described in claim 4. Claim 7 specifies the particular application in the context of a wind turbine, and claim 8 relates to a computer program product embodying the method. Cross-referenced dependent claims describe advantageous embodiments of the invention.

[0009] The invention includes the process engineering teaching that the following steps are carried out to detect the characteristic electrical current pulses: Receiving electromagnetic radio waves emitted as a result of characteristic electrical current pulses in the frequency range above 50 MHz; processing the received signal by signal processing to extract the current pulse events contained therein, including filtering; analysis of the temporal course of the current pulse events for condition monitoring of the rolling bearing or sliding bearing.

[0010] The solution according to the invention is based on the finding that the characteristic electrical current pulses generated specifically as a result of static charging of rotating machine or plant components produce radio waves in a frequency range typical for this purpose, which become visible in the signal waveform as pulses with a relatively rapid decay phase. These current pulse events allow the identification of the current pulse events of interest in the frequency spectrum.

[0011] Preferably, an envelope generation process is used to extract the current pulse events, i.e., to process the received signal. According to a preferred embodiment, this process includes high-pass filtering of the received signal followed by rectification and subsequent low-pass filtering. This enables the processed signal to be analyzed by simple integration, using the area per second as a measured quantity, in order to quantify the occurring current pulse events and thus make them accessible for evaluation.

[0012] Alternatively, the analysis can also be performed by counting the number of current pulse events of the processed signal per unit of time in order to quantify the occurring current pulse events. In this case, the number per second is used as the metric for the subsequent evaluation.

[0013] The method according to the invention, which in particular comprises special signal processing, can be implemented in an electronic device, preferably consisting of a receiving unit, a signal conditioning unit, and an analysis unit. These components can, for example, be housed in a detection device that has an interface for connection to a plant condition monitoring system or a plant control system. The acquired measured values ​​can then be transmitted, for example, in the form of an analog signal to a condition monitoring system for further processing and evaluation. Alternatively or additionally, it is also conceivable to create a separate detection device as a standalone unit, preferably with an integrated alarm unit.The alarm unit could, for example, emit visual or audible signals to indicate that a critical storage condition has been reached. Naturally, the transmission of measured values ​​to a higher-level system can also be integrated into such a local device. The local device can, for example, be installed inside the bearing housing or in a gearbox, thus protecting it from external electromagnetic interference.

[0014] According to a preferred embodiment, the device according to the invention can be integrated into a wind turbine for detecting characteristic current flows occurring in a bearing due to static charging. This is because the rotor blades of a wind turbine are exposed to considerable static charging, particularly due to weather conditions, which is dissipated via the rotary bearing. The characteristic current flows that occur in this process can lead to electrical breakdowns and lightning discharges in the bearing area.

[0015] Furthermore, it should be noted that the solution according to the invention can also be implemented by a computer program product, the program code means for carrying out the method runs on a combined microprocessor-controlled signal processing unit with analysis unit or can be stored on a computer-readable data carrier.

[0016] Further measures improving the invention are described in more detail below, together with a description of a preferred embodiment of the invention, with reference to the figures. The figures show: Figure 1 shows a schematic block diagram of a device implemented in a wind turbine for detecting electrical current pulses flowing through a rolling bearing as a result of static charging of the rotor, and Figure 2 shows a schematic representation of an envelope generation for processing the received signal as a prerequisite for signal analysis.

[0017] According to Fig. 1 A wind turbine, shown here only schematically, has a rotor 1 which is rotatably mounted on a support structure 3 of a cabin (not shown in further detail) on a tower of the wind turbine via a rolling bearing 2 designed as a rotor shaft bearing.

[0018] During operation, the rotor blades of rotor 1 experience a static charge, which flows through the rolling bearing 2, specifically from the inner bearing ring 4, across the rolling elements 5, to the outer bearing ring 6 and into the grounded support structure 3. This process emits discharges in the rolling bearing 2 as electromagnetic radio waves, which are typically in a frequency range above 50 MHz.

[0019] A receiving unit 10, installed in the reception area, i.e., close to the rolling bearing 2, serves to receive 100 of the electromagnetic radio waves via an antenna 11 attached to it. A downstream signal processing unit 20 serves to process 200 the received signal by means of signal processing to extract the current pulse events contained therein, which in this embodiment particularly includes envelope generation. A subsequent analysis unit 30 serves to analyze 300 the temporal progression of the current pulse events for condition monitoring of the rolling bearing 2.

[0020] The receiving unit 10 is housed together with the signal processing unit 20 and the analysis unit 30 in a common detection unit 40, which is connected via a data transmission interface 50 to a plant condition monitoring system (not shown). Furthermore, an alarm unit 60 is also integrated into the detection unit 50, which serves as a local optical indicator of a critical condition.

[0021] The Fig. 2Figure 1 illustrates the envelope formation preferably carried out during the signal processing of the received electromagnetic radio waves. Accordingly, starting from the received signal, a high-pass filter 400 is first applied to eliminate irrelevant signal components. Subsequent rectification 500 removes the signal's subharmonics. Finally, a low-pass filter 600 shapes the area between the curve and the abscissa. This forms the basis for a preferably subsequent integration to use the area per unit time as a measurement for the current pulse events that occurred.

[0022] The invention is not limited to the preferred embodiment described above. Rather, variations thereof are also conceivable and are included within the scope of protection of the following claims. In particular, the solution according to the invention is not only applicable to wind turbines, but generally to non-conducted current discharge scenarios. Furthermore, it should be noted that the signal processing for acquiring the measured values ​​is not limited solely to generating an envelope of the received radio signal. Sampling methods or other suitable analyses can alternatively be used for this purpose. Reference symbol list

[0023] 1 Rotor 2 Rolling bearing 3 Support structure 4 Inner bearing ring 5 Rolling element 6 Outer bearing ring 10 Receiver unit 11 Antenna 20 Signal processing unit 30 Analysis unit 40 Detection device 50 Data transmission interface 60 Alarm unit 100 Receiving electromagnetic radio waves 200 Processing the received signal 300 Analysis for current pulse events 400 High-pass filtering 500 Rectification 600 Low-pass filtering Current flow Amplitude t Time

Claims

1. A method for detecting characteristic electrical current pulses flowing through a rolling bearing (2) or plain bearing as a result of static charging of rotating machine or system parts, comprising the following steps: - receiving (100) electromagnetic radio waves emitted as a result of the characteristic electrical current pulses in the frequency range above 50 MHz; characterised by: - processing (200) of the received signal by means of signal processing for extracting the current pulse events contained therein, comprising filtering, wherein the processing (200) of the received signal is carried out by envelope formation which comprises a high-pass filtering (400) of the received signal with subsequent rectification (500) and subsequent low-pass filtering (600); - analysis (300) of the temporal course of the current pulse events for monitoring the state of the rolling bearing (2) or plain bearing, wherein the analysis (300) determines a fading phase in a signal course of the radio waves.

2. The method according to claim 1, characterised in that the analysis (300) comprises an integration of the processed signal obtained by the low-pass filtering in order to quantify the current pulse events that have occurred.

3. The method according to claim 1, characterised in that the analysis (300) comprises counting the number of current pulse events of the processed signal per unit of time in order to quantify the current pulse events that have occurred.

4. A device for detecting characteristic electrical current pulses flowing through a rolling bearing (2) or plain bearing as a result of static charging of rotating machine or system parts, comprising: - a receiving unit (10) for receiving electromagnetic radio waves emitted as a result of the characteristic electrical current pulses in the frequency range above 50 MHz; characterised by: - a signal processing unit (20) for processing the received signal by means of signal processing for extracting the current pulse events contained therein, comprising filtering, wherein the processing (200) of the received signal is carried out by envelope formation which comprises a high-pass filtering (400) of the received signal with subsequent rectification (500) and subsequent low-pass filtering (600); - an analysis unit (30) for analysis of the temporal course of the current pulse events for monitoring the state of the rolling bearing (2) or plain bearing, wherein the analysis (300) determines a fading phase in a signal course of the radio waves.

5. The device according to claim 4, characterised in that the receiving unit (10), the signal processing unit (20) and the analysis unit (30) are accommodated in a detection device (40) which has a data transmission interface (50) for connection with a system state monitoring system or a system control system.

6. The device according to claim 5, characterised in that the detection device (50) is designed as a separate device with an integrated local alarm unit (60).

7. A wind energy system having a rotor (1) as a rotating machine or system part, which is rotatably mounted on a support structure (3) via at least one rolling bearing (2) or plain bearing designed as a rotor bearing, wherein a device according to one of claims 4 to 6 for detecting characteristic current flows occurring as a result of static charging of the rotor (1) in the at least one rolling bearing (2) or plain bearing between the bearing outer ring (6) and the bearing inner ring (4) is arranged close to the rolling bearing (2) or plain bearing.

8. A computer program product having program code means for carrying out the method according to one of claims 1 to 3, when the computer program product runs on a combined signal processing unit (200) with analysis unit (300) of a device according to one of claims 4 to 6.