Electromechanical system comprising at least one electric machine and method for detecting stator winding faults - Patents.com

Abstract

An electromechanical system (1) comprising at least one electric machine (3), the electric machine (3) comprising a stator (4) having at least one stator winding (5) and a rotor (7), the rotor (7) comprising at least one temperature sensor (8, 9) arranged at a distance from the axis of rotation (11) of the rotor (7), the electromechanical system (1) comprising a monitoring device (12) designed to monitor the operation of the electric machine (3), the monitoring device (12) being configured to monitor the temperature of at least one of the electric machine systems (1). In an operating mode, a fault condition (39) is evaluated, the fulfillment of which indicates a fault in the stator winding (5) or at least one of the stator windings (5), in particular a stator insulation fault, and the fulfillment of the fault condition (39) is determined by temperature values ​​(34) obtained during at least one rotation of the rotor (7) by temperature sensors (8, 9), the plurality of temperature values ​​(34) being obtained at different times during each individual rotation of the rotor (7) in at least one operating mode.

Description

[Technical Field]

[0001] The present invention relates to an electromechanical system comprising at least one electric machine, the electric machine comprising a stator having at least one stator winding, and a rotor. Furthermore, the present invention relates to a method for detecting stator winding faults in the windings of the stator of an electric machine.

[0002] During operation of an electric machine, the stator insulation of the stator windings can become damaged, for example, due to wear and tear. In powerful electric machines, such as wind turbine generators, the resulting short circuit can lead to intense local heating that can damage components, for example, demagnetize magnets, or even cause a fire. It is therefore very important to detect turn faults in the stator windings, especially turn-to-turn short circuit faults, as early as possible to avoid further damage to the electric machine.

[0003] EP 3879282 A1 discloses a technique for early detection of insulation faults in generators. The current flowing through an electric circuit is measured by a current sensor, and the measured current is used to calculate a parameter depending on the impedance of at least a part of the electric circuit to determine the state of the insulation. While this technique may allow early detection of faults, it may be desirable to use a more direct technique to detect serious errors that result in strong localized heating.

[0004] EP 3922843 A1 proposes using at least two temperature sensing elements at different locations on a wind turbine's power generating assembly to detect overheating of the generator. It proposes using temperature sensors at the phase connectors of the stator winding, the hottest point of the generator, and possibly additional locations. While this approach could in principle be used to detect stator winding faults in an electric machine, robust winding fault detection requires a fairly large number of temperature sensors to ensure that each relevant part of the winding has a temperature sensor located nearby.

[0005] It is therefore an object of the present invention to enable detection of winding faults in the windings of the stator of an electric machine that can be implemented with lower technical complexity.

[0006] This problem is solved by an electromechanical system comprising at least one electric machine, the electric machine comprising a stator having at least one stator winding and a rotor, the rotor comprising at least one temperature sensor arranged at a distance from the rotor's axis of rotation, the electromechanical system comprising a monitoring device designed to monitor the operation of the electric machine, the monitoring device evaluating, in at least one operating mode of the electromechanical system, a fault condition, the fulfillment of which indicates a fault in the stator winding or at least one of the stator windings, in particular a stator insulation fault, the fulfillment of the fault condition being determined by temperature values ​​obtained during at least one rotation of the rotor by the temperature sensor, the plurality of temperature values ​​being obtained at different times during each individual rotation of the rotor in the at least one operating mode.

[0007] Faulty stator windings, especially stator insulation faults, typically result in strong localized heating of the stator at radial locations close to the air gap between the stator and the rotor. Therefore, in principle, localized heating can be detected using temperature sensors mounted on the stator. However, this requires multiple temperature sensors positioned around the periphery of the stator.

[0008] The electromechanical system according to the present invention therefore employs at least one temperature sensor attached to the rotor and positioned at a distance from the rotor's axis of rotation, such that as the rotor rotates, the temperature sensor essentially scans along the rotor-facing surface of the stator, and thus the use of a single temperature sensor is sufficient to detect winding faults in a given axial section of the stator.

[0009] When a winding fault results in localized heating of a region of the stator, the distance between the rotor temperature sensor and the heated region changes over time during each rotor rotation due to the off-axis placement of the temperature sensor. Therefore, the measured temperature value oscillates synchronously with the rotor rotation. Such oscillations of the measured temperature value with rotation angle, and therefore with time, can be easily and robustly detected, thereby enabling stator winding fault detection with fewer components and less complex implementation.

[0010] In principle, it would be sufficient to determine a measure of the variation of the temperature values ​​during one or more revolutions, for example the difference between the maximum and minimum temperatures, and / or to determine a statistical property of the temperature values, such as the standard deviation or variance of the temperature values, and to determine whether a fault condition is met based on this difference or standard deviation or variance or a similar measure.

[0011] However, it has been found that an even more robust determination is possible if the temperature values ​​are determined over multiple revolutions, especially at an essentially constant rotation speed: if the rotation speed fluctuates by less than 5% or 10%, the speed can be considered essentially constant.

[0012] Fluctuations in temperature values ​​over time due to changes in the distance between the temperature sensor and the area heated by the fault result in a nearly periodic signal due to the fault. Therefore, the presence of a signal with a known, fixed frequency can be detected. This allows several techniques to improve the signal-to-noise ratio and therefore the robustness of the fault detection. For example, bandpass filtering, Fourier analysis, and / or lock-in techniques can be used.

[0013] When a fault condition is met, the monitoring device can change the control of the electromechanical system, for example, to brake the electric machine to a standstill, or send a signal to the control device to do so. Additionally or alternatively, when a fault condition is met, a signal can be sent to a further device, such as a central control unit at the wind park, a mobile communication device of a service representative, or a server at the service company.

[0014] The evaluation of the fault condition can be performed in near real time during operation of the electric machine, allowing countermeasures to be taken when a winding fault is detected to avoid further component damage. Additionally or alternatively, the evaluation of the fault condition and / or, in general, the analysis of the obtained temperature values ​​can also be performed offline at a later point in time, for example to analyze the progression of the fault and its effects over time.

[0015] The fulfillment of a fault condition can be determined by the amplitude of the frequency components of the sequence of acquired temperature values. In particular, the fault condition can be fulfilled if, or only if, the amplitude is greater than or equal to a given threshold. The amplitude can be determined directly, for example, using Fourier analysis or lock-in methods. However, it is also possible to use, for example, band-pass filtering, especially in the digital domain, as well as, for example, envelope tracking or rectification and low-pass filtering of the band-pass filtered signal to determine the amplitude.

[0016] Preferably, the temperature values ​​are determined periodically at a fixed frequency in at least one operating mode. At a fixed rotational speed, the sampling frequency corresponds to a fixed angular frequency, and relevant frequency components can be easily determined based on the rotational speed. If the rotational speed varies and / or the same frequency components need to be analyzed at different rotational speeds, adaptive bandpass filters or other signal processing techniques can be used.

[0017] Instead of using a fixed time frequency for temperature acquisition, it is also possible to acquire temperature values ​​at a fixed angle of rotation of the rotor. In this case, the frequency components are angular frequency components, and the frequency components analyzed may in particular be of angular frequency 1 / 360°, thus detecting events occurring once per rotation.

[0018] In at least one operating mode of the electromechanical system, the monitoring device can determine the rotor's rotational speed and / or control the electric machine and / or at least one further component of the electromechanical system to adjust the rotor's actual rotational speed to a given rotational speed. The frequency components are selected based on the determined rotational speed and / or the given rotational speed. Preferably, the frequency components are centered on the rotor's rotational frequency. Because temperature oscillations caused by localized heating are not, in principle, perfect sine waves, it is also possible to analyze the amplitudes of harmonics of the rotor's rotational frequency. However, centering the frequency components around the rotational speed is advantageous because the presence of a single winding fault, and therefore a single localized heating area, typically results in the strongest signal at this fundamental frequency.

[0019] In a preferred embodiment, exactly one temperature sensor located at a single axial end of the rotor or at a magnet of the rotor, or exactly two temperature sensors located at different axial ends of the rotor or magnet or at different magnets of the rotor, are used to determine the temperature values. The location at the axial ends of the rotor may in particular consist of the location of the respective temperature sensors in the last 10% or 5% of the rotor length and / or location in the region of the end windings of the stator may be selected.

[0020] The use of a single temperature sensor at a single end of the rotor and / or in the region of a single end winding, especially at the drive end facing the hub if the electric machine is part of a wind turbine, can be advantageous because such temperature sensors are often used anyway in generators to manage the temperature of the magnets in the rotor. Such a temperature sensor can be used, for example, to limit the current and / or rotational speed of the stator windings to avoid overheating and therefore demagnetization of the magnets. In such cases, the electric machine system according to the present invention and / or the method according to the present invention described below can be implemented with very little modification of such existing electric machine systems, for example, by adding additional monitoring devices or, in the simplest case, by modifying existing monitoring devices through a software update. Therefore, the electric machine system and method according to the present invention can be implemented with very low technical complexity and offer a straightforward upgrade path for many existing electric machine systems.

[0021] The use of exactly two temperature sensors, located at different axial ends of the rotor, to determine temperature values ​​can be advantageous because such an arrangement allows for very robust detection of winding faults in both end windings of the stator. It has been found that most winding faults that appear during normal operation of an electric machine are end winding faults. At the same time, the use of only two temperature sensors allows the implementation of the invention with minimal effort and complexity.

[0022] In an alternative embodiment, multiple temperature sensors distributed along the length of the rotor can be used to provide temperature values ​​for multiple axial sections of the electric machine. This allows for more robust detection of outer winding faults in the stator end windings and more precise location of winding faults. However, in most use cases, using exactly two temperature sensors provides the best compromise between robustness and accuracy of fault detection and location and the effort required to implement the present invention.

[0023] Preferably, the electromechanical system includes a position sensor for determining the angular position of the rotor and / or the time when the rotor reaches a given angle of rotation, and the monitoring device determines the angular position of the fault based on the sequence or sequences of acquired temperature values ​​and the time of acquisition of at least one of the temperature values ​​and / or the respective angular position acquired at at least one time in the sequence, when the given angle of rotation is reached. Using such a position sensor allows the angular position of the highest temperature value, or preferably the maximum of a temperature sequence determined from the temperature values, to be determined, thereby enabling the location of areas of localized heating and therefore winding faults around the stator. If a relatively low sampling rate is used to determine the temperature values, a more precise angular position can be determined, for example, by using interpolation or by determining the position of the temperature maximum between the sampled temperature values ​​taking into account the phase of the analyzed angular frequency components.

[0024] The monitoring device and / or control device of the electromechanical system may be designed to control the electric machine and / or at least one further component of the electromechanical system when a trigger condition is met to reduce the rotational speed from an initial value to a lower final value, the rotational speed being kept below the final value by the monitoring device and / or control device in the first operating mode.

[0025] In other words, the rotational speed can be reduced below an initial value that is specifically used during normal operation of the electromechanical system, for example to generate electricity in a wind turbine. By keeping the rotational speed below the final value during the first operating mode, a more detailed mapping of the temperature distribution along the circumference of the stator can be described by the temperature values, even when temperature sensors with relatively low bandwidths and / or relatively large sampling intervals between temperature values ​​are used.

[0026] In a direct-drive wind turbine, the initial value can be, for example, within the range of 2 to 16 revolutions per minute, or generally within the range of rotational speeds used to supply rated power to the power grid. Operation at the initial rotational speed can continue until thermal stability is reached, which can be a possible trigger condition or one of the possible trigger conditions. Rotation can then be slowed down, for example, to an idle stop where the generator rotates at a fraction of the rated speed, for example, less than 2 revolutions per minute.

[0027] At such low speeds, even thermal sensors with relatively low bandwidths can be used to robustly detect and preferably locate winding faults. Even if a relatively high sampling rate is used for the temperature values ​​and a high bandwidth is used for the temperature sensor, it may still be advantageous to use a slower final value for the rotational speed during the first operating mode, since this reduces the influence of the thermal inertia of the temperature sensor itself and surrounding components on the measurement, resulting in a better signal-to-noise ratio during fault detection. Generally, sufficiently robust fault detection can be achieved if the product of the rotational speed used and the number of stator winding slots is less than half the number of temperature samples taken per minute.

[0028] The trigger condition may be satisfied only after the electric machine has operated at or above a given speed for a given minimum time, and / or when additional temperature values ​​from at least one additional temperature sensor indicate a stable temperature distribution within the electric machine, and / or when a smoke detector in the electric machine system provides an alarm signal, and / or when the electrical signal, particularly the power output provided by the electric machine, is within a given range of values. During startup of the electric machine, the stator temperature along the air gap may vary significantly, which may result in false fault detection when temperature value oscillations due to rotor rotation are evaluated to detect stator winding faults. This problem can be avoided by using a minimum operating time before acquiring temperature values. However, because the time required to reach thermal equilibrium may depend on, for example, the ambient temperature and other operating parameters of the electric machine, it may be advantageous to evaluate additional temperature values ​​to more robustly detect the equilibrium state of the electric machine.

[0029] In the simplest case, the trigger condition can evaluate whether the additional temperature value reaches or exceeds a given threshold value, which indicates a sufficient warm-up time for the electric machine to reach thermal equilibrium. However, additionally or alternatively, it is also possible to compare the additional temperature values ​​provided by multiple additional temperature sensors. In this case, the trigger condition can be satisfied, for example, only if the difference between the additional temperature values ​​provided by the additional temperature sensors is below a given threshold value, which indicates thermal equilibrium. Alternatively or additionally, the trigger condition can also be evaluated by a separate monitoring system, for example, based on an electrical signal.

[0030] The satisfaction of the fault condition and / or the transmission of a fault signal to internal components and / or external devices of the electric machine system when the fault condition is satisfied, and / or the modification of the operation of the electric machine system when the fault condition is satisfied may be determined by at least one additional piece of information, each of which indicates whether power is supplied to the power grid by the electric machine, and / or the operating state of a cooling system of the electric machine, and / or the amount of power currently supplied to or by the electric machine.

[0031] Various cases have already been described above in which a fault signal can be sent to an internal component or an external device and / or the operation of the electric machine system can be changed when a fault condition is met. In the simplest case, one or more of these measures can be taken directly when a fault condition is met. In this case, the fault condition can optionally also be determined by at least one additional piece of information as described above. In that case, the additional information can be used, for example, to perform fault detection only when there is no power supplied to the power grid and / or when the cooling system of the electric machine is operating and / or when no or little power is supplied to and / or by the electric machine. This condition can, for example, be equivalent to the aforementioned idling stop while the generator of the wind turbine is operating at a relatively low speed without transferring power to the power grid and while the cooling system is operating to improve the thermal balance.

[0032] In some use cases, it may be advantageous to potentially trigger multiple actions when a fault condition is met, where the fault condition is independent of at least one of the aforementioned additional information, and where this additional information is only used to limit the sending of signals and / or changes to the system's behavior to when a fault is detected in a particular situation.

[0033] The electric machine system can include a cooling system or systems for actively cooling a stator and / or rotor of the electric machine, the cooling system being active during a first mode of operation. Use of the cooling system in the first mode of operation can enable a more stable temperature at a surface of the stator facing the air gap in the absence of a winding fault, and therefore can improve detection and location of winding faults.

[0034] The temperature sensor can be a thermistor, a platinum thin-film resistance temperature sensor, or an optical fiber temperature sensor. Additionally or alternatively, the temperature sensor can preferably have a bandwidth of at least 10 Hz or at least 20 Hz. The aforementioned sensor design is particularly useful for achieving a high bandwidth of the temperature sensor. The higher bandwidth of the temperature sensor allows for evaluation of fault conditions at higher rotor rotational speeds and / or allows for stronger fluctuations in temperature values, particularly frequency components, with larger amplitudes at a given rotational speed, thus improving the signal-to-noise ratio and more robust detection of stator winding faults. With a sufficiently high sample rate and sensor bandwidth, it may be possible, for example, to use normal power generation of the wind turbine's generator as at least one operating mode. Therefore, fault detection can optionally be used without limiting the rotational speed.

[0035] A heat conducting means, in particular a thermal paste, can be arranged radially between the stator and rotor, at least partially filling the air gap between the stator and rotor. Because the present invention uses a temperature sensor arranged on the rotor to detect local stator temperature changes, the amplitude of temperature value changes due to winding faults is limited by the low thermal conductivity of the air in the air gap. By using a smaller air gap or at least partially filling the air gap with a heat conducting means having good thermal conductivity, the amplitude of temperature value changes, and therefore of frequency components in particular, due to the presence of a stator winding fault can be increased, thus improving the signal-to-noise ratio for the measurement and the robustness of fault detection.

[0036] Known heat conduction properties of a medium, e.g., an air gap, can be used to determine the delay caused by heat conduction from an insulation fault, or generally from the stator to the rotor, and to compensate, for example, for errors in the determined location of a detected fault due to this delay.

[0037] For example, if sufficient sensitivity is achieved by using a high bandwidth sensor and the thermal conductivity across the air gap is reasonably high, even faults in the stator windings that result in a relatively small temperature rise can be detected. In this case, it may be possible to detect a weakening of the stator insulation before it completely fails, resulting in a short circuit.

[0038] The electromechanical system can be a wind turbine, with the electric machine forming the generator of the wind turbine. Alternatively, the electromechanical system can include multiple wind turbines, each of which uses at least one of the electric machines as a generator. As mentioned above, detecting stator winding faults is very important in the field of wind turbines. At the same time, wind turbine generators use relatively low rotational speeds, thus allowing for high robustness of fault detection using the described technique. If the electromechanical system includes multiple wind turbines, a common monitoring device can be used to evaluate the temperature values ​​provided by each of the wind turbines. The common monitoring device can be integrated into one of the wind turbines, for example, or can be located separately from all the wind turbines, for example, in a wind park management center.

[0039] In addition to the electric machine system, the present invention also relates to a method for detecting a stator winding fault in a stator winding of an electric machine, the electric machine comprising a stator having at least one stator winding and a rotor, wherein a fault condition is evaluated, the fulfillment of which indicates a fault in the stator winding or at least one of the stator windings, in particular a stator insulation fault, and the fulfillment of the fault condition is determined by temperature values ​​acquired during at least one rotation of the rotor by a temperature sensor, the temperature values ​​being acquired at different times during each individual rotation of the rotor. The method of the present invention can be implemented in particular using the electric machine system of the present invention. Regardless of the use of the electric machine system of the present invention, the features described with respect to the electric machine system of the present invention can be transferred to the method of the present invention, along with the advantages described above, and vice versa.

[0040] Other objects and features of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings, which are merely sketches of the principles designed for purposes of illustration only and are not intended to be limiting of the invention. [Brief explanation of the drawings]

[0041] [Figure 1] 1 is a diagram of an exemplary embodiment of an electromechanical system in accordance with the present invention; [Figure 2] 4 is a flowchart of an exemplary embodiment of a method for detecting stator winding faults according to the present invention. [Figure 3] 3A and 3B are diagrams of exemplary measurements used in the method according to FIG. 2 to detect and locate winding faults.

[0042] 1 shows an electromechanical system 1 comprising an electric machine 3. In this example, the electromechanical system 1 is a wind turbine 2 having a local monitoring device 12 that monitors the operation of the electric machine 3 and controls further components 18, such as the current supplied to the stator windings 5, and further components 18, in this example the blades of the wind turbine mounted on a hub 17. In particular, the monitoring device 12 is designed to detect the presence of a fault in the stator winding 5. Alternatively or additionally, an external monitoring device 15 can be used for this purpose, which can be arranged, for example, in a management center 16 of a wind park comprising several wind turbines 2 to manage the electric machines 3 of these wind turbines 2.

[0043] The exemplary wind turbine 2 includes a nacelle 13 mounted on top of a tower 14 and a stator 4 mounted on the nacelle 13. The wind turbine 2 is a direct drive wind turbine 2, and therefore the rotor 7 is mounted directly to the hub 17. The rotor 7 is rotatably mounted around the stator 4 by bearings 19.

[0044] The rotor 7 includes two temperature sensors 8, 9, each mounted at an axial end of a magnet 10 of the rotor 7. The temperature sensors 8, 9 are offset relative to the rotor's axis of rotation 11 and move along the circumference of the stator 4, and more specifically along the end turns 6 of the windings 5 ​​of the stator 4, as the rotor rotates. If the winding 5 contains a fault, particularly in one of the end turns 6, the temperature of each temperature sensor 8, 9 will temporarily increase as the respective temperature sensor 8, 9 passes through the area heated by the fault.

[0045] This feature is used to detect such winding faults by monitoring device 12. An exemplary method used for this purpose will now be described with further reference to FIG.

[0046] In general, the method, which will be described in more detail below, evaluates for a fault condition 39, the fulfillment of which indicates a fault in the stator winding 5 or at least one of the stator windings 5, in particular a stator insulation fault. The fulfillment of the fault condition 39 is determined by previously recorded temperature values ​​taken during multiple revolutions of the rotor 7, with multiple temperature values ​​34 taken at different times during each individual revolution of the rotor 7.

[0047] 2 assumes that the wind turbine 2 is at a standstill at the start of the method. In step S1, the normal start-up procedure of the wind turbine 2 is initiated by the monitoring device 12, for example by opening a brake (not shown), adjusting the angle of the wind turbine blades forming the further components 18, and, once a sufficient rotational speed has been reached, connecting the generator formed by the electric machine 3 to the power grid. A cooling system 23 for actively cooling the stator 4 can also be activated immediately upon start-up or after a certain operating time.

[0048] In step S2, various operating parameters of the electric machine 3 are recorded, namely the time 25 that the wind turbine 2 has been operating at or above a given rotor speed, and the current rotational speed 26. Optionally, a temperature value 27 may also be recorded by the temperature sensor 21. Additionally or alternatively, at least one electrical signal may also be obtained, in this example the power output 48 currently provided by the generator.

[0049] These values ​​are then used in step S3 to evaluate trigger condition 47. Trigger condition 47 may be satisfied when, among other things, predetermined operating conditions are reached, such as given values ​​or ranges of values ​​of rotational speed 26, temperature, power output 48, and / or operating time 25. Additionally, other inputs may be evaluated by trigger condition 47, such as signals from smoke detectors 49 and / or signals indicative of calibration requirements.

[0050] The trigger condition 47 may be satisfied, for example, when the time 25, speed 26, and temperature values ​​27 exceed their respective thresholds. Additionally or alternatively, the temperature difference between the temperature values ​​recorded via the temperature sensors 8, 9 and the temperature value recorded by the temperature sensor 21 may be compared to a further threshold as part of the trigger condition 47, as this temperature difference is a measure of the thermal balance within the electric machine 3.

[0051] While the trigger condition 47 is not satisfied, operation of the wind turbine 2 continues at its normal operating speed, in particular supplying current to the power grid.

[0052] Once the trigger condition 47 is satisfied in step S3, it can be assumed that a test for stator insulation faults can be initiated. To this end, the monitoring device 12 controls the electric machine 3 and other components 18, in particular the turbine blades, to reduce the rotational speed 26 of the rotor 7 from an initial value 28 to a lower final value 29, for example, one rotation every 2-4 minutes. As already explained in detail in the general description, a lower rotational speed can reduce the influence of the thermal inertia of the temperature sensors 8, 9 and attached components, such as magnets 10, on the measured temperature value 34, thus enabling a more robust measurement.

[0053] In step S5 it is checked whether the rotational speed 26 has reached a final value 29 and therefore an operating mode 33 for detecting faults in the stator winding 5 has been reached. If this is not the case, step S4 is repeated to continue reducing the rotational speed 26. Once the operating mode 33 has been reached in step S5, a respective temperature value 34 is acquired by each of the temperature sensors 8, 9, and simultaneously the angular position 35 of the rotor 7 is acquired using the position sensor 22, in step S6.

[0054] In the preceding description it has been assumed that it is necessary, or at least desirable, to slow down the rotation of the rotor 7 before fault detection. In these cases it may be advantageous to limit fault detection to certain circumstances, such as pre-alarm of the smoke detector 49 or start-up of the wind turbine 2, to limit the time for which the rotational speed is reduced. Alternatively, as already explained in the general description, if a sufficiently high sample rate and bandwidth of the temperature sensors 8, 9 is used, slowing down the rotor 7 can be avoided and steps S3 and S4 can therefore be skipped.

[0055] In step S7 it is checked whether acquisition of the temperature values ​​34 and angular positions 35 has already been performed for a given number of revolutions of the rotor 7. If this is not the case, step S6 is repeated. The acquisition of the temperature values ​​34 and angular positions 35 is preferably repeated at a fixed period and therefore at a fixed sample rate.

[0056] Once the measurements of step S6 have been made for a given number of rotations, the average rotation speed 36 is determined in step S8 and used to select a matching frequency component 37 from the sequence 45 of temperature values ​​34 shown in FIG.

[0057] To better understand this step and the previous preparatory steps, the following description further refers to the exemplary measurement data shown in FIG. 3. In the diagram shown in FIG. 3, the x-axis 41 indicates the progression of time, and the y-axis 42 indicates the different values ​​of the different curves shown in the diagram. The curves, which have an approximate sawtooth shape, show the change in angular position 35 over time. The angular position oscillates fairly rapidly, corresponding to a relatively large angular velocity of rotor 7, until time 43, when trigger condition 47 is met. Once trigger condition 47 is met, the rotation slows down as indicated by the reduction in the slope of angular position 35 between time 43 and time 44. At time 44, operating mode 33 is reached, and the rotational speed, and therefore the rate of change of angular position 35, remains approximately constant.

[0058] The sequence 45 of temperature values ​​34 shows that the temperature values ​​34 remain fairly constant while the rotor 7 is rotating relatively fast due to the limited bandwidth and thermal inertia of the temperature sensors 8, 9. When lower rotational speeds are reached, the sequence 45 of temperature values ​​34 from the temperature sensors 8, 9 exhibits a clear oscillation having a frequency that is the same as the frequency of rotation of the rotor 7 if a winding fault is present in the end winding 6 as shown in FIG.

[0059] Overall, the temperature values ​​34 in sequence 45 decrease over time as the rotational speed of the rotor 7 decreases because lower currents are induced in the stator windings 5 ​​at lower rotational speeds, and therefore less heat is generated by a winding fault. To further illustrate this effect, line 46 shows the temperature of the stator body 20 of the stator 4 at a location relatively close to the windings 5.

[0060] Note that line 46 and sequence 45 are scaled differently. Line 46 spans a temperature range of approximately 15°C, while the range of temperature values ​​34 is limited to a range of approximately 5°C.

[0061] Due to the relatively small temperature variations at the temperature sensors 8, 9, it is advantageous to apply further processing to the sequence 45, for example, instead of simply taking the difference value between the maximum and minimum values ​​during one revolution as a measure for the presence of a fault.

[0062] In the example of step S8, the frequency components 37 of the sequence 45 are extracted by applying a bandpass filter, the center frequency of the bandpass filter being coincident with the average rotation speed 36.

[0063] Alternatively, the frequency components 37 can be extracted, for example, using a Fourier transform of the sequence 45 or by a lock-in method. The extraction of the frequency components 37 eliminates or at least suppresses low-frequency components due to the temperature drift to lower temperatures caused by the reduced heating at lower rotor speeds mentioned above, and eliminates or at least suppresses high-frequency quantization noise introduced by the resolution limits of the temperature sensors 8, 9. The quasi-periodic nature of the sequence 45 is therefore used to improve the signal-to-noise ratio.

[0064] In step S9, the amplitudes 38 of the frequency components are determined. As mentioned above, if bandpass filtering is used, the amplitudes can be determined, for example, by rectifying the frequency components 37 and lowpass filtering or averaging the resulting signal. If Fourier transform or lock-in amplification is used, the amplitudes 38 are provided directly.

[0065] In step S10, a fault condition 39 is evaluated. In this example, the fault condition 39 simply compares the amplitude 38 with a given threshold. If the threshold is exceeded for the temperature value 34 provided by one of the temperature sensors 8, 9, it is assumed that a fault exists in or near the end winding 6 at the respective end of the stator 4.

[0066] If the fault condition 39 is not satisfied, normal operation of the electromechanical system 1 is resumed in step S16. In the case of the wind turbine 2, the rotational speed of the rotor 7 is returned to normal rotational speed and power is again fed into the grid.

[0067] On the other hand, if the fault condition 39 is met in step S10, the fault angular position 40 is determined in step S11. The fault angular position 40 is indicated by a vertical line placed at the local maximum of the oscillating sequence 45 in Figure 3. Since the angular position 35 for each temperature value 34 is explicitly recorded, the maximum angular position 40 can be read directly.

[0068] Then, in step S12, the angular position 40 and additional information about the detected fault can be communicated to an external device, for example the wind park control center 16, a mobile device of a service representative, or the like.

[0069] In many cases, it is also advantageous to take the wind turbine 2 out of operation after the fault condition 39 is fulfilled. However, depending on the sensitivity of the fault detection, it is possible that the fault condition 39 is already fulfilled when a short circuit has not yet occurred.

[0070] Thus, in step S13, the additional information 30, 31, 32 can be recorded, and in step S14 it can be determined whether the additional information 30, 31, 32 and the amplitude 38 indicate the need for shutdown, in which case the monitoring device 12 can control the electric machine 3 and further components 18 to shut down the wind turbine 2 in step S15. If not, operation can continue normally in step S16.

[0071] In this example, additional information 30 relates to whether electric machine 3 is connected to the grid, additional information 31 relates to the operating state of cooling system 23, and additional information 32 may relate to the amount of power supplied to or by electric machine 3. Using the above-mentioned additional information 30-32 may allow, for example, continuing to supply power to the grid at a lower value only if fault condition 39 indicates insulation degradation without the occurrence of a fault and / or if the generator is fault tolerant, e.g., designed to allow operation within safe operating limits in the presence of a turn-to-turn short circuit fault.

[0072] The use of temperature sensors 8, 9 mounted on the rotor 7 to detect winding faults in the stator windings 5 ​​has the advantage that only a single temperature sensor 8, 9 is required to sample the entire circumference of the stator 4. However, as already explained with reference to Figure 3, the presence of an air gap between the stator 4 and the temperature sensors 8, 9 will significantly reduce the amplitude of the measured temperature oscillations in the presence of a winding fault. Returning to Figure 1, it is therefore advantageous to use conductive means 24, in particular thermal paste, to partially fill the air gap and thus improve the thermal coupling of the temperature sensors 8, 9 to the windings 5.

[0073] Although the present invention has been described in detail with reference to preferred embodiments, the invention is not limited to the disclosed examples, and those skilled in the art can derive other variations from the disclosed examples without departing from the scope of the invention.

Claims

1. An electromechanical system comprising at least one electromechanism (3), wherein the electromechanism (3) comprises a stator (4) having at least one stator winding (5) and a rotor (7), wherein the rotor (7) comprises at least one temperature sensor (8, 9) positioned at a distance from the rotation axis (11) of the rotor (7), and the electromechanical system (1) comprises a monitoring device (12) designed to monitor the operation of the electromechanism (3), and the monitoring device (12) in at least one operating mode of the electromechanical system (1) An electromechanical system characterized in that, a failure condition (39) is evaluated, the satisfaction of the failure condition (39) indicates a failure of the stator winding (5) or at least one of the stator windings (5), particularly a stator insulation failure, the satisfaction of the failure condition (39) is determined by temperature values ​​(34) acquired by the temperature sensors (8, 9) during at least one rotation of the rotor (7), and a plurality of temperature values ​​(34) are acquired at different times during each individual rotation of the rotor (7) in at least one operating mode.

2. The electromechanical system according to claim 1, characterized in that the satisfaction of the failure condition (39) is determined by the amplitude (38) of the frequency component (37) of the sequence (45) of the acquired temperature value (34).

3. The electromechanical system according to claim 1 or 2, wherein the monitoring device (12) determines the rotational speed (36) of the rotor (7) in at least one operating mode of the electromechanical system (1) and / or controls the electromechanism (3) and / or at least one further component of the electromechanical system (1) to adjust the actual rotational speed (36) of the rotor (7) to a given rotational speed (36), and the frequency component (37) is selected based on the rotational speed (36) and / or the given rotational speed (36).

4. The electromechanical system according to claim 1 or 2, characterized in that exactly one temperature sensor (8, 9) located at a single axial end of the rotor (7) or on the magnet (10) of the rotor (7), or exactly two temperature sensors (8, 9) located at different axial ends of the rotor (7) or the magnet (10), or on different magnets (10) of the rotor (7), are used to determine the temperature value (34).

5. The electromechanical system according to claim 1 or 2, comprising a position sensor (22) for determining the angular position (35) of the rotor (7) and / or the time at which the rotor (7) reaches a given rotation angle, wherein the monitoring device (12, 15) determines the angular position (40) of the fault based on the sequence (45) or sequence (45) of the acquired temperature values ​​(34) and the respective angular position (35) acquired at the time of acquisition of at least one of the temperature values ​​(34) and / or at least one time in the sequence (45) that reaches the given rotation angle.

6. The electromechanical system according to claim 1 or 2, wherein the monitoring devices (12, 15) and / or control devices of the electromechanical system (1) are designed to control the electromechanism (3) and / or at least one further component (18) of the electromechanical system (1) when a trigger condition (47) is met to reduce the rotational speed (26) from an initial value (28) to a lower final value (29), and the rotational speed (26) is maintained at or below the final value (29) by the monitoring devices (12, 15) and / or the control device in a first operating mode (33).

7. The electromechanical system according to claim 6, characterized in that the trigger condition (47) can be satisfied only after the electromechanical machine (3) has been operating at or above a given speed (26) for a given minimum time (25), and / or an additional temperature value (27) from at least one additional temperature sensor (21) indicates a stable temperature distribution within the electromechanical machine (3), and / or an alarm signal is provided by the smoke detector (49) of the electromechanical system (1), and / or an electrical signal, in particular an output (48) supplied by the electromechanical machine (3), is within a given range of values.

8. The electromechanical system according to claim 1 or 2, wherein the satisfaction of the failure condition (39) and / or the transmission of a failure signal to the internal components and / or external devices of the electromechanical system (1) when the failure condition (39) is satisfied, and / or the change in the operation of the electromechanical system (1) when the failure condition (39) is satisfied, is determined by at least one additional piece of information (30-32), each of which additional piece of information (30-32) indicates whether the electromechanism (3) supplies power to the power grid, and / or the operating state of the cooling system (23) of the electromechanism (3), and / or the amount of power currently supplied to or by the electromechanism (3).

9. The electromechanical system according to claim 1 or 2, comprising a cooling system (23) or a cooling system (23) for actively cooling the stator (4) and / or rotor (7) of the electromechanical system (3), wherein the cooling system (23) is active during the first operating mode (33).

10. The electromechanical system according to claim 1 or 2, characterized in that the temperature sensors (8, 9) are thermistors, platinum thin-film resistance temperature sensors, or optical fiber temperature sensors, and / or the temperature sensors (8, 9) have a bandwidth of at least 10 Hz or at least 20 Hz.

11. The electromechanical system according to claim 1 or 2, characterized in that a heat conduction means (24), particularly a thermal paste, is radially arranged between the stator (4) and the rotor (7) and at least partially fills the air gap between the stator (4) and the rotor (7).

12. The electromechanical system according to claim 1 or 2, characterized in that the electrical system (1) is a wind turbine (2), and the electromechanical device (3) forms a generator for the wind turbine (2), or the electromechanical system (1) comprises a plurality of wind turbines (2), and each of the wind turbines (2) uses at least one of the electromechanical devices (3) as a generator.

13. A method for detecting a stator winding failure in the winding (5) of the stator (4) of an electrical machine (3), wherein the electrical machine (3) comprises a stator (4) and a rotor (7) having at least one stator winding (5), wherein the rotor (7) comprises at least one temperature sensor (8, 9) positioned at a distance from the rotation axis (11) of the rotor (7), a failure condition (39) is evaluated, the satisfaction of the failure condition (39) indicates at least one of the stator windings (5) or the stator winding (5), in particular a stator insulation failure, the satisfaction of the failure condition (39) is determined by temperature values ​​(34) obtained by the temperature sensor (8, 9) during at least one rotation of the rotor (7), wherein a plurality of temperature values ​​(34) are obtained at different times during each individual rotation of the rotor (7).

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