Method for non-destructive inspection of stator winding insulation

Abstract

The invention relates to a method for non-destructive examination of at least partial regions of the insulation (7) of a stator winding (1) of an electrical machine (2), in particular of a generator or a high-voltage motor, characterized in that the non-destructive examination is carried out in situ at the site of installation of the electrical machine (2) using terahertz measurement technology. Furthermore, the invention relates to an examination device (24) for carrying out the method.

Description

Technical Field

[0001] The present invention relates to a method for non-destructive inspection of at least a portion of the insulation of the stator winding of an electric motor, particularly a generator or a high-voltage motor. Background Technology

[0002] The stator windings of generators, such as turbines and hydroelectric generators, have an insulating portion. This insulating portion typically comprises multiple overlapping layers of insulating tape wound around the winding bar. The insulating tape layers are impregnated with resin, which is cured after winding. Regarding the shape, the winding bar includes: a straight section, the majority of which is inserted into a slot in the stator or stator core laminations; and two involute-bent sections connecting the two free ends of the straight section, extending outward from the stator slots. Because the stator plate is grounded, the insulating portion in the slot region includes a weakly conductive outer layer, known as coil-side corona protection (Auβenglimmschutz), to control the potential distribution within the insulating portion. In the edge region of the straight section, the coil-side corona protection extends outside the slots by a weakly conductive end-englimmschutz to gradually control the potential on the bar surface and increasingly reduce the electric field within the insulating portion.

[0003] During generator operation, structural changes occur in the stator winding insulation due to electrical, thermal, mechanical, and chemical loads. This results in accelerated, long-term aging of the insulation, causing damage such as microcracks or delamination. To prevent generator damage, it is necessary to identify this aging phenomenon and its extent early, and to eliminate it promptly if necessary. In this context, the stator winding insulation is inspected regularly and maintained as needed.

[0004] Currently, partial discharge measurement is used, for example, to detect aging phenomena in stator winding insulation. However, this proven method, which is generally considered a comprehensive measurement, can only cover the portion of the stator winding insulation where the electric field is sufficiently strong—namely, the area within the stator slots where the winding bars are located, and approximately 30% of the front insulation length under corresponding suspension corona protection. Aging phenomena also occur in the remaining areas of the winding bars, making it impossible to completely detect aging phenomena in the stator winding insulation using only partial discharge measurement. Furthermore, it is impossible to pinpoint the detected aging phenomena to the required extent during partial discharge measurement because the measurement accuracy during the partial discharge pulse is approximately 1.2 m.

[0005] Another known method for detecting aging in stator winding insulation is high-voltage testing. However, in cases of significant aging, high-voltage testing can cause irreparable breakdowns, and therefore it is rarely used.

[0006] Another feasible method is to use endoscopes or mirrors to detect surface defects or damage to the insulation. However, deeper defects cannot be detected by these methods and remain invisible accordingly. Summary of the Invention

[0007] Based on the prior art, the object of the present invention is to provide an alternative method for non-destructive inspection of at least a portion of the insulation of the stator winding of an electric motor.

[0008] To achieve the aforementioned objective, the present invention proposes a method of the type mentioned earlier, characterized in that non-destructive inspection is performed in situ at the motor mounting location using terahertz measurement technology.

[0009] Terahertz measurement technology is based on electromagnetic waves in the frequency range of 0.1 to 10 terahertz with wavelengths from 3 mm to 30 μm. Terahertz radiation can penetrate non-conductive materials due to its low photon energy, and its short wavelength provides spatial accuracy, enabling the decomposition of defects into terahertz images and thus precise defect location. Furthermore, terahertz technology enables depth-dependent analysis and can detect defects located deep within insulation. Because the radiation is non-ionizing and therefore harmless to biological materials, no special protective measures are required, making the technology well-suited for use in industrial environments. Due to the on-site inspection and diagnosis of the insulation according to the invention, repair measures can be taken immediately upon detection of defects. In this way, the risk of unwanted failures in the corresponding motor during operation can be significantly reduced, thereby avoiding the costs associated with such failures. Because terahertz technology allows for precise descriptions (reports) of the type, extent, and location of defects in the insulation, the progress of detected defects that are not immediately eliminated due to their small extent can be observed and recorded. Accordingly, it is feasible to make relatively reliable statements predicting the impact of different defects on the service life of insulation, which is becoming increasingly important in this context: due to the continuous increase in the share of renewable energy and the significant changes in generator operation, the experience gained to date can only be applied conditionally. Inspection data and insights obtained using terahertz technology can also be used for future insulation design.

[0010] According to one embodiment of the method according to the invention, non-destructive testing is performed on the externally accessible portions of the insulation, particularly only on these externally accessible portions. This particularly relates to those portions of the insulation that are involute bends surrounding the stator winding or winding bar and extend outward from the stator slots. For such portions, as detailed at the outset, inspection using partial discharge measurements is unsuitable because the electric field is not strong enough in these areas.

[0011] Advantageously, non-destructive testing is performed using a terahertz sensor that moves along the surface of the portion of the insulation to be inspected and performs measurements at different measurement locations.

[0012] The sensor signal emitted by the terahertz sensor is preferably introduced into the surface of the area to be inspected in the insulation at a predetermined angle, wherein the predetermined angle is preferably 90°. Due to the limited space available for positioning the terahertz sensor, it is entirely possible that at a specific measurement location, it is not easy to maintain the preferred angle of 90° and it must be changed accordingly.

[0013] According to one embodiment of the invention, the signal received by the terahertz sensor as a response to an emitted signal is stored together with the corresponding position and orientation of the terahertz sensor at the time the signal was emitted, relative to a predetermined coordinate system. In this way, defects in the detected insulation can be accurately located based on the coordinate system.

[0014] Preferably, a terahertz sensor is used to scan the surface of the area to be inspected in the insulation, generating two-dimensional profiles or cross-sectional images through the insulation. This is done by recording complete depth information of the insulation at each measurement point, a process known as depth scanning. In terahertz measurements, this depth information is obtained, in particular, via a frequency-modulated continuous wave (EMCW) method. Here, the frequency difference between the frequency ramp emitted in the receiving path of the measurement system and the frequency ramp reflected by the insulation is detected using frequency mixing. From this detected frequency data, operational or depth information of each reflecting layer of the insulation is generated.

[0015] Advantageously, based on the generated two-dimensional cross-section or cross-sectional image, a quasi-3D image of the portion of the insulation to be inspected is generated.

[0016] According to one embodiment of the invention, the movement of the terahertz sensor is automatically performed using an electromechanical displacement unit, particularly in the form of an articulated arm robot that holds the terahertz sensor, thereby enabling very precise, flexible and reproducible guidance during non-destructive testing.

[0017] An electromechanical displacement unit can be mounted on the rotor of a motor and can move on the rotor. To move the electromechanical displacement unit on the rotor, the displacement unit can have a driven unit, for example, equipped with wheels. The driven unit can have a magnet on its underside so that it can move above the rotor.

[0018] Alternatively, the electromechanical displacement unit can be fixed to the stator of the motor in a first position, released after multiple measurements, and then fixed to the stator in a second position, different from the first, to perform other measurements. This variation, unlike the first, has the disadvantage that the displacement unit must be manually repositioned multiple times. However, it has the advantage that the electromechanical displacement unit is less complex in structure and thus less expensive to manufacture due to the elimination of the need for a drive mechanism.

[0019] Furthermore, the present invention provides an inspection device designed for performing the method according to the present invention, the inspection device comprising an electromechanical displacement unit and a terahertz sensor disposed on the electromechanical displacement unit.

[0020] Electromechanical displacement units are advantageous for articulated arm robots.

[0021] According to the first variant, the electromechanical displacement unit is designed to be mounted on the rotor of an electric motor and to move on the rotor in a manner driven by the motor.

[0022] Alternatively, the electromechanical displacement unit is designed to be fixed on the stator of the motor in a first position, released after performing multiple measurements, and fixed on the stator of the motor in a second position, different from the first position, in order to perform other measurements.

[0023] Preferably, the terahertz sensor has at least one dielectric measuring tip, which is angled particularly in the region of its free end to account for the narrow space available for positioning the terahertz sensor during the execution of the method according to the invention. At least one measuring tip can be surrounded by a rigid sheath to prevent damage and / or bending of the measuring tip.

[0024] Alternatively, the terahertz sensor can have a quasi-optical free-beam system designed to direct terahertz radiation toward the measurement location. The quasi-optical free-beam system can, for example, be implemented in the form of miniaturized mirror optics. Attached Figure Description

[0025] Other features and advantages of the invention become clear from the following description with reference to the accompanying drawings.

[0026] Figure 1 A schematic three-dimensional partial view of the stator windings of an electric motor is shown, which is configured as a generator.

[0027] Figure 2 Shown in Figure 1 A schematic perspective view of a single stator bar of the stator winding shown in the figure;

[0028] Figure 3 Shown in Figure 2 A magnified view of section III in the image, showing the involute-bent section of the stator bar;

[0029] Figure 4 Shown in Figure 1 A schematic perspective view of the four winding bars of the stator winding shown in the figure;

[0030] Figure 5 A cross-sectional view is shown, illustrating an upper winding bar and a lower winding bar, which are arranged in a manner that... Figure 1 The stator windings shown are in the common slots of the stator;

[0031] Figure 6 A perspective view is shown, illustrating an inspection apparatus according to a first embodiment of the invention during the execution of an inspection method according to the invention;

[0032] Figure 7 A perspective view is shown, illustrating an inspection apparatus according to a second embodiment of the invention during the execution of the inspection method according to the invention; and

[0033] Figure 8 A schematic diagram is shown, illustrating a terahertz sensor 16 with its measuring tip inserted between two winding rods. Detailed Implementation

[0034] Figures 1 to 5 A portion of the stator winding 1 of an electric motor 2 is shown, wherein the motor is, in this context, a generator, such as a turbine generator or a hydroelectric generator. The stator winding 1 comprises a plurality of winding bars 3. (Reference) Figure 2 and Figure 3Each winding rod 3 is made of multiple fixed and compacted conductor strands 4, and has a central straight section and two involute curved sections 6, which are connected to the straight section 5 on both sides. Each winding rod 3 is covered with an insulation portion 7. The insulation portion 7 includes a base insulation portion 8 that completely covers the straight section 5 and the curved section 6. Here, the base insulation portion 8 is made of insulating tape, which is wound around the winding rod 3 in multiple overlapping layers. The insulating tape is impregnated with resin, which is cured after winding. In addition, the insulation portion 7 includes: coil edge corona protection 9, which covers the straight section 5 but not the curved section 6; and dangling corona protection 10 in the transition region between the straight section 5 and the curved section 6. The coil edge corona protection 9 and the dangling corona protection 10 are currently made of conductive tape.

[0035] As in Figure 1 As shown, the straight section 5 of the winding bar 3 is inserted into the slot 11, which is formed in the annular stator 12 of the motor 2. Currently, each pair of winding bars 3 is arranged radially stacked one above the other in a single slot 11, more specifically, first the lower winding bar 3a, then the upper winding bar 3b, which are fixed in the respective slots 11 by wedges 13. The curved section 6 of the lower winding bar 3a is oriented intersecting with the curved section 6 of the upper winding bar 3b, as shown in... Figure 1 As indicated by arrows 14 and 15, the bent segments 6 at the two free ends of each lower winding rod 3a are connected to the free ends of the bent segments 6 of the upper winding rod 3b, and vice versa. These connections are achieved via connecting elements not shown in detail.

[0036] During generator operation, the insulation 7 undergoes structural changes due to electrical, thermal, mechanical, and / or chemical loads. This results in accelerated aging of the insulation 7, leading to long-term damage, such as microcracks, delamination, and defects. To prevent generator damage, it is necessary to identify these aging phenomena and their extent early and eliminate them promptly when necessary.

[0037] According to the present invention, non-destructive testing of the insulation portion 7 is performed in situ at the installation location of the motor 2 using terahertz measurement technology in an externally accessible area of ​​the stator winding 1. This primarily involves the portion of the insulation portion 7 surrounding the bent section 6 of the rod 3, but may also involve other accessible portions of the insulation portion 3, such as those through cooling openings, if necessary.

[0038] Terahertz measurement technology is a technique that utilizes electromagnetic radiation within the terahertz range, specifically between 0.1 and 10 terahertz. This electromagnetic radiation can penetrate materials impermeable to visible and infrared light, especially non-metallic materials, enabling the detection of damage to the insulation component 7. The wavelength of the radiation is in the range of 30 μm to 3 mm, providing good spatial resolution. Correspondingly, the detected defects can be well located. The energy of the radiation is very low, therefore it poses no harm to human health.

[0039] In order to execute this method, as it is in Figures 6 to 8 As shown, an inspection device 24 with a terahertz sensor 16 is used here, wherein the terahertz sensor 16 moves along the surface of the portion of the insulation 7 to be inspected and performs measurements at different measurement positions. The sensor signal emitted by the terahertz sensor 16, in the form of electromagnetic radiation in the terahertz range, is introduced into the surface of the portion of the insulation 7 to be inspected at a predetermined angle, preferably 90°. To take into account the narrow installation space between adjacent bent sections 6 of the winding bar 3, combined with the preferred predetermined angle, the terahertz sensor 16, as it is in… Figure 8 As exemplarily shown, it advantageously has one or more dielectric measuring tips 25, which are angled in the region of their free ends. Correspondingly, the terahertz sensor 16 can be introduced between adjacent curved sections 6 of the winding rod 3, such that the free ends of the measuring tips 25 are oriented perpendicular to or at least approximately perpendicular to the surface 26 of the insulating portion 7, on which the measuring tips should be guided. The measuring tips 25 are currently surrounded by a rigid sheath 27, which protects the measuring tips 25 and prevents bending. Alternatively, instead of curved dielectric measuring tips, the terahertz sensor 16 can also have a miniaturized quasi-optical free-beam system designed to direct the emitted terahertz radiation to the corresponding measurement location within a preferred predetermined angular range.

[0040] The movement of the terahertz sensor 16 is currently performed automatically using an electromechanical displacement unit 17, which is configured as an articulated arm robot holding the terahertz sensor 16, with its arm segments 18 interconnected via multiple hinges 19. For example, in Figure 6 As shown, the electromechanical displacement unit 17 can be mounted on the rotor 20 of the motor 2 and can move on the rotor. For this purpose, a motor-driven drive unit 21 is provided, which includes wheels, etc. On its underside, the drive unit 21 is provided with a magnet (not shown in detail) so that the drive unit can also move above the rotor 20. Alternatively, it is also possible to, as in Figure 7As shown, the electromechanical displacement unit 17 is fixed to the stator 12 of the motor 2 at a first position, and released after performing multiple measurements. It is then fixed to the stator 12 at a second position, different from the first position, to perform additional measurements. For this purpose, the electromechanical displacement unit 17 has a base unit 22 with a suitably configured fixing mechanism 23 capable of releasably fixing the base unit 22 to the stator 12.

[0041] The signal received by the terahertz sensor 16 as a response to the emitted signal is then stored together with the corresponding position and orientation of the terahertz sensor 16 or its(multiple) measuring tips 25 at the time of signal emission with respect to a predetermined coordinate system. During each measurement, a depth scan of the insulation portion 7 is performed in the direction of the emitted signal, and a two-dimensional profile of the insulation portion 7 is generated accordingly. The depth information is preferably obtained via a frequency-modulated continuous wave method. From multiple such profiles along the direction of motion of the terahertz sensor 17, a quasi-3D image of a portion of the inspected insulation portion 7 can be constructed. The location of any defects contained therein can then be accurately located based on the coordinate system.

[0042] Although the details of the invention have been illustrated and described in detail with reference to preferred embodiments, the invention is not limited to the disclosed examples, and other variations can be derived by those skilled in the art without departing from the scope of protection of the invention.

Claims

1. A method for non-destructive examination of at least a partial region of an insulation (7) of a stator winding (1) of an electric machine (2), characterized in that the non-destructive examination is performed in situ at the installation site of the electric machine (2) using terahertz measurement technology, wherein the non-destructive examination is performed using a terahertz sensor (16) which is moved along a surface of the partial region of the insulation (7) to be examined and performs measurements at different measurement positions, wherein the movement of the terahertz sensor (16) is performed automatically using an electromechanical displacement unit (17), and wherein the electromechanical displacement unit (17) is arranged on a rotor (20) of the electric machine (2) and is moved thereon, or wherein the electromechanical displacement unit (17) is fixed at a first position on a stator (12) of the electric machine (2) and is released after performing a plurality of measurements, and, for performing further measurements, the electromechanical displacement unit is fixed at a second position on the stator (12) of the electric machine (2), the second position being different from the first position.

2. The method of claim 1, wherein, The non-destructive examination is performed on a partial region of the insulation (7) which is accessible from the outside.

3. The method of claim 1, wherein, Sensor signals emitted by the terahertz sensor (16) are introduced into the surface of the partial region of the insulation (7) to be examined at a predetermined angle.

4. The method of claim 3, wherein, Signals received by the terahertz sensor (16) as a response to the emitted signals are stored together with the respective position and orientation of the terahertz sensor (16) with respect to a predetermined coordinate system at the point in time when the signals were emitted.

5. The method according to any one of claims 2 to 4, characterized in that, The surface of the partial region of the insulation (7) to be examined is scanned using the terahertz sensor (16) and a quasi-3D image of the partial region of the insulation (7) to be examined is generated in such a way that the complete depth information of the insulation (7) is recorded at each measurement point, wherein the depth information is obtained in the terahertz measurement.

6. The method of claim 5, wherein, Based on the generated quasi-2D sections or section images, a quasi-3D image of the partial region of the insulation (7) to be examined is generated.

7. The method of claim 2 or 3, wherein, The electromechanical displacement unit (17) is an articulated-arm robot which holds the terahertz sensor (16).

8. The method of claim 1, wherein, The electric machine (2) is a generator or a high-voltage motor.

9. The method of claim 1, wherein, The non-destructive examination is performed on a partial region of the insulation (7) which surrounds a section (6) of the stator winding (1) which is curved in the form of an involute and which projects out of a slot (11) of the stator (12).

10. The method of claim 3, wherein, The predetermined angle is 90°.

11. The method of claim 5, wherein, The depth information is obtained in the terahertz measurement by means of a frequency-modulated continuous-wave method.

12. An examination device (24) which is designed to perform the method according to any one of claims 1 to 11, the examination device comprising an electromechanical displacement unit (17) and a terahertz sensor (16) arranged on the electromechanical displacement unit.

13. The inspection device (24) according to claim 12, characterized in that The electromechanical displacement unit (17) is an articulated-arm robot.

14. The inspection apparatus of claim 12 or 13, characterized in that The electromechanical displacement unit (17) is designed to be arranged on a stator (12) of the electric machine (2) and to be moved on the stator in a motor-driven manner.

15. The inspection device (24) according to claim 12 or 13, characterized in that The electromechanical displacement unit (17) is designed to be fixed at a first position on a stator (12) of the electric machine (2) and to be released after a plurality of measurements have been carried out and to be fixed at a second position on the stator (12) of the electric machine (2) for carrying out further measurements, the second position being different from the first position.

16. The inspection device (24) according to claim 12 or 13, characterized in that The terahertz sensor (16) has at least one dielectric measuring tip (25).

17. The inspection device (24) according to claim 12 or 13, characterized in that The terahertz sensor (16) has a quasi-optical free-beam system which is designed to direct the terahertz radiation to the measurement location.

18. The inspection device of claim 14, wherein, The electric machine (2) is a generator or a high-voltage motor.

19. The inspection device (24) according to claim 16, characterized in that The dielectric measuring tip (25) is angularly configured in the region of its free end.

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