A method for evaluating the thermal aging of an organosilicon insulation system for motor stator coils
By combining frequency domain dielectric spectroscopy and Havriliak-Negami model fitting with breakdown voltage testing, the problem of aging assessment of organosilicon insulation systems has been solved, enabling safe and reliable operation of motor stators. This method is suitable for aging assessment in high-temperature environments of nuclear power plants and aerospace motors.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DONGFANG ELECTRIC MACHINERY
- Filing Date
- 2026-02-28
- Publication Date
- 2026-06-02
AI Technical Summary
There is a lack of non-destructive testing methods for the silicone insulation systems of motor stators used in nuclear power plants and aerospace. Existing motor evaluation methods are not applicable to silicone insulation systems in high-temperature environments, which makes aging assessment difficult and affects the reliable operation and safety of motors.
Non-destructive testing was performed using frequency domain dielectric spectroscopy. The thermal aging state of the insulation system was evaluated by fitting the Cole-Cole diagram and the Havriliak-Negami model, and the Δε value was used as the criterion for judging the aging endpoint by combining the breakdown voltage test.
It enables convenient, reliable, and non-destructive thermal aging assessment of silicone insulation systems, ensuring the safe operation of motors in high-temperature environments and providing a guarantee for high-power and high-speed motors.
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Figure CN122131093A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of insulation materials technology, and more specifically to the field of a thermal aging assessment method for an organosilicon insulation system for motor stator coils. Background Technology
[0002] Motors used in nuclear power plants, aerospace, and other applications operate in high-temperature environments for extended periods, where conventional motor insulation systems are insufficient to meet safety requirements. The superior insulation properties of silicone insulation systems at high temperatures provide the foundation for the development of high-power and high-speed motors. They have decades of engineering application experience in traction motor insulation and can withstand long-term high-temperature operating environments. However, prolonged operation at high temperatures can still cause degradation of silicone insulation, leading to a series of physical and chemical reactions, resulting in insulation aging, inducing partial discharge, and even breakdown, affecting the reliable operation of the motor and, in severe cases, causing safety accidents.
[0003] Existing motor evaluation methods often target epoxy-mica composite insulation systems, which exhibit severe aging in high-temperature environments and are unsuitable for special-purpose motors. Currently, there is a lack of methods for aging assessment of silicone insulation systems. Exploring a convenient, reliable, and non-destructive insulation testing method is of profound significance for ensuring the safe operation of special-purpose motors. Summary of the Invention
[0004] The purpose of this invention is to address the lack of non-destructive testing methods for the silicone insulation system of special motor stators. This invention provides a method for evaluating the thermal aging of the silicone insulation system of motor stator coils.
[0005] To achieve the above objectives, the present invention specifically adopts the following technical solution: This invention provides a method for evaluating the thermal aging of an organosilicon insulation system for motor stator coils, comprising the following steps: S1. Non-destructive testing of the silicone insulation system of the motor is carried out using frequency domain dielectric spectroscopy to obtain the curves of the real part ε' and imaginary part ε'' of the complex dielectric constant as a function of frequency; S2. By using the Cole-Cole diagram and slope analysis, it was determined that the insulation system mainly exhibits a combination of single relaxation process and jump conductance process in the test frequency band. The FDS curve was fitted using the Havriliak-Negami model with the addition of the jump conductance term, and the relaxation intensity change Δε was extracted as the key parameter for thermal aging assessment. S3. By combining thermal aging experiments and breakdown voltage tests, a quantitative relationship between the relaxation strength change Δε and the breakdown voltage is established, and a threshold value for the relaxation strength change Δε is set as the criterion for judging the end point of insulation aging.
[0006] In one implementation, the following preprocessing is performed before step S1: A1. The stator coil is to be prepared using an organosilicon insulation system. The stator coil is to be prepared using a low-resin vacuum pressure impregnation process (low-resin means that the resin content in the insulation structure is relatively low and the fiber reinforcement content is relatively high; the vacuum is below 50Pa). The rated voltage of the stator coil is 6kV. A2. Wipe the insulation surface of the stator coil with anhydrous ethanol to remove impurities and ensure that the insulation surface is smooth; A3. After the insulation surface is fully dry, apply low-resistivity varnish to the straight end of the stator coil and high-resistivity varnish to the end of the stator coil, and let it stand for 24 hours. A4. The straight end of the stator coil is processed into a pseudo three-electrode structure. The middle of the straight end is wrapped with aluminum foil as a measuring electrode, and the two ends near the nose end are wrapped with narrow copper foil as shielding electrodes. The reserved wire part of the stator coil is short-circuited as the high voltage end. A5. Connect the measuring electrode and the high-voltage electrode to perform the initial FDS test.
[0007] In one implementation, after step A5, the following steps are performed: A6. After the initial FDS test, place the coil in a high-temperature oven and set a cycle. After each cycle, let the coil rest until it returns to room temperature. Then repeat steps A4 to A5 for multiple cycles. After each cycle, test the FDS curve.
[0008] In one embodiment, in step A5, the FDS test equipment used for FDS testing is IDAX-300, the peak voltage of the FDS test equipment is 200V, and the test frequency band of the FDS test equipment is set to 1mHz~1kHz.
[0009] In one implementation, in step A6, after the initial test, the coil is placed in a high-temperature oven and the temperature is set to 250°C. Each cycle lasts 10 days. After each cycle, the coil is left to stand until it returns to room temperature, about 20°C. Then, steps A4 to A5 are repeated for a total of 3 cycles. After each cycle, the FDS curve is tested.
[0010] In one embodiment, in step S1, the real part ε'(ω) and the imaginary part ε''(ω) of the complex permittivity increase, and this increase becomes more pronounced as the test frequency decreases.
[0011] In one implementation, step S2 is specifically performed as follows: S21. Derive the slopes of the relaxation polarization process and the conductance process in the linear portion, and obtain the slope ranges of different relaxation polarization models under the high and low frequency limits and the low frequency slope range of the conductance process. S22. The slope of the imaginary part of the FDS curve of the silicone-insulated coil under 250℃ thermal aging is between -1 and 0 at low frequencies, indicating that the conduction process is a jump conduction process. In addition, combined with the Cole-Cole diagram, it is determined that the silicone insulation of the coil mainly exhibits a single relaxation process within the test frequency range. Therefore, the HN model is selected to fit the FDS curve in combination with the form of jump conduction. S23. The least squares method is used for fitting, considering both the real and imaginary parts of the complex permittivity curves simultaneously, and converting them to logarithmic form. The objective function is set as follows: ; S23. Select parameter Δε as the fitting parameter for the change in the silicone insulation of the coil. The fitting result can be expressed as: .
[0012] In one implementation, step S21 involves dividing the conductance process into a jump conductance process and a direct current conductance process.
[0013] In one implementation, step S3 is as follows: The stator coils were continuously aged, and their passability was determined by a stator coil breakdown test. The voltage was increased uniformly at a rate of 1 kV / s until the stator coils broke down, and the breakdown voltage was recorded. A breakdown voltage exceeding 6 UN was considered acceptable. The breakdown voltage of each stator coil was recorded, and the breakdown voltage was correlated with the parameter Δε for each stator coil. Δε and breakdown voltage showed a negative correlation. A polynomial was used to fit Δε to the breakdown voltage V, and the results were as follows: ; According to the fitting results, when Δε is greater than 3.18, the stator coil breakdown voltage is unqualified, and the stator coil is considered to have reached the end of its life.
[0014] The beneficial effects of this invention are as follows: This invention innovatively proposes the application of frequency domain dielectric spectroscopy (FDS) technology to the testing of silicone insulation systems for motors. The research results indicate that thermal aging leads to an increase in polar groups within the silicone composite insulation, resulting in enhanced polarization and conductivity processes. This leads to an increase in both the real and imaginary parts of the complex dielectric constant, ε'(ω), which becomes increasingly pronounced with decreasing test frequency. The relaxation polarization slope at high and low frequency limits and the low-frequency conductivity slope were derived. Combined with the Cole-Cole plot, it was determined that within the measured frequency range (1 mHz to 1 kHz), the silicone insulation system exhibits a combination of single relaxation polarization and skipped conductivity processes. The FDS curve was fitted using a Havriliak-Negami (HN) model with added skipped conductivity. The thermal aging state was assessed using the parameter Δε. Combined with coil breakdown voltage tests, the relationship between Δε and breakdown voltage was obtained. It was determined that when Δε exceeds approximately 3.18, the coil no longer meets the requirements, indicating the aging endpoint has been reached. This method has significant engineering application potential. Attached Figure Description
[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.
[0016] Figure 1 This is a connection diagram for IDAX-300.
[0017] Figure 2 The FDS curve of the coil after thermal aging at 250℃.
[0018] Figure 3 This is a Cole-Cole diagram of an organosilicon coil.
[0019] Figure 4 This is a fitting diagram of the thermal aging of an organosilicon coil at 250℃.
[0020] Figure 5 The graph shows the fitting relationship between parameter Δε and thermal aging time.
[0021] Figure 6 The graph shows the relationship between the parameter Δε and the breakdown voltage. Detailed Implementation
[0022] To make the technical problems, technical solutions, and technical effects of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0023] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.
[0024] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.
[0025] In the description of the embodiments of the present invention, it should be noted that the terms "inner", "outer", "upper", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.
[0026] Example 1 like Figures 1 to 5 As shown in the figure, this embodiment provides a method for evaluating the thermal aging of an organosilicon insulation system for a motor stator coil, including the following steps: A1. Prepare to fabricate stator coils using an organosilicon insulation system. The stator coils are fabricated using a low-adhesion vacuum pressure impregnation process. The rated voltage of the stator coils is 6kV. A2. Wipe the insulation surface of the stator coil with anhydrous ethanol to remove impurities and ensure that the insulation surface is smooth; A3. After the insulation surface is fully dry, apply low-resistivity varnish to the straight end of the stator coil and high-resistivity varnish to the end of the stator coil, and let it stand for 24 hours. A4. The straight end of the stator coil is processed into a pseudo three-electrode structure. The middle of the straight end is wrapped with aluminum foil as a measuring electrode, and the two ends near the nose end are wrapped with narrow copper foil as shielding electrodes. The reserved wire part of the stator coil is short-circuited as the high voltage end. A5. Connect the measuring electrodes and high-voltage electrodes to perform the initial FDS test; the FDS test equipment used for the FDS test is the IDAX-300, the peak voltage of the FDS test equipment is 200V, and the test frequency band of the FDS test equipment is set to 1mHz~1kHz. The connection diagram is shown below. Figure 1 As shown; A6. After the initial FDS test, place the coil in a high-temperature oven at 250℃. Each cycle lasts 10 days. After each cycle, allow the coil to rest until it returns to room temperature (approximately 20℃). Then repeat steps A4-A5 for a total of 3 cycles. After each cycle, test the FDS curve. The results are as follows: Figure 2 As shown.
[0027] A7. Using frequency domain dielectric spectroscopy (FDS) technology, non-destructive testing was performed on the silicone insulation system of the motor to obtain the curves of the real part ε' and imaginary part ε'' of the complex dielectric constant as a function of frequency. The real part ε'(ω) and imaginary part ε''(ω) of the complex dielectric constant increased, and became more and more obvious as the test frequency decreased.
[0028] A8. Derive the slopes of the relaxation polarization process and the conductance process in the linear portion, and obtain the slope ranges of different relaxation polarization models in the high and low frequency limits, as well as the low-frequency slope range of the conductance process (jump conductance process and DC conductance process). The derivation process is attached below: The relaxation model can be expressed as: ; In the formula, Δε = εs - ε∞, τ is the relaxation time, α and β are related to the relaxation time distribution, and 0 < α ≤ 1, 0 < β ≤ 1. Under the high and low frequency limits, the real and imaginary parts of the spectrum can be written as follows: ; ; The slopes of the imaginary parts of different models are shown in Table 1: Table 1. Slope of the imaginary part ε"(ω) of the complex permittivity at high and low frequency limits.
[0029] Taking the skip conductance as an example, at low frequencies, the straight line can be represented as y = kf + b. Then, according to the expression for skip conductance, the straight line can be represented as: ; In the formula, f represents the test frequency, k represents the slope of the line, and b represents the intercept of the line. Further, we can obtain: ; Since 0≤γ≤1, the slope of the straight line of the jumping conductance at low frequencies is -1 to 0. Similarly, the slope of the DC conductance is -1. Combining the measured slope of the curve at low frequencies, it can be determined that the imaginary part of the FDS curve in the measured frequency range is a relaxation process. Combining the jumping conductance process, the HN model and the jumping conductance model are selected to fit the curve.
[0030] A9. Calculations show that the slope of the imaginary part of the FDS curve of the silicone-insulated coil under 250℃ thermal aging at low frequencies is between -1 and 0, indicating that the conduction process is a jump conduction process. Furthermore, combined with the Cole-Cole plot, it is determined that the silicone insulation of the coil mainly exhibits a single relaxation process within the test frequency range. Figure 3 As shown, the HN model combined with the form of jump conductance is therefore chosen to fit the FDS curve; A10. The least squares method is used for fitting, considering both the real and imaginary parts of the complex permittivity curves simultaneously, and converting them to logarithmic form. The objective function is set as follows: ; A11. The fitting results are as follows: Figure 4 As shown in Table 1, the relevant fitting parameters are used. The parameter Δε is selected as the fitting parameter for the change in the silicone insulation of the coil. The fitting results are as follows: Figure 5 As shown, it can be expressed as: .
[0031] A12. Continuously age the stator coils and determine their pass / fail status based on the stator coil breakdown test. Increase the voltage at a constant rate of 1kV / s until the stator coil breaks down, and record the breakdown voltage. A breakdown voltage exceeding 6UN is considered acceptable. Record the breakdown voltage of each stator coil and correlate it with the parameter Δε of each stator coil. Figure 6 As shown, Δε is negatively correlated with the breakdown voltage. A polynomial fitting was used to fit Δε to the breakdown voltage V, and the results are as follows: ; According to the fitting results, when Δε is greater than 3.18, the stator coil breakdown voltage is unqualified, and the stator coil is considered to have reached the end of its life.
Claims
1. A method for evaluating the thermal aging of an organosilicon insulation system for a motor stator coil, characterized in that, Includes the following steps: S1. Non-destructive testing of the silicone insulation system of the motor is carried out using frequency domain dielectric spectroscopy to obtain the curves of the real part ε' and imaginary part ε'' of the complex dielectric constant as a function of frequency; S2. By using the Cole-Cole diagram and slope analysis, it was determined that the insulation system mainly exhibits a combination of single relaxation process and jump conductance process in the test frequency band. The FDS curve was fitted using the Havriliak-Negami model with the addition of the jump conductance term, and the relaxation intensity change Δε was extracted as the key parameter for thermal aging assessment. S3. By combining thermal aging experiments and breakdown voltage tests, a quantitative relationship between the relaxation strength change Δε and the breakdown voltage is established, and a threshold value for the relaxation strength change Δε is set as the criterion for judging the end point of insulation aging.
2. The method for evaluating the thermal aging of an organosilicon insulation system for a motor stator coil according to claim 1, characterized in that, Before step S1, the following preprocessing is performed: A1. Prepare to fabricate stator coils using an organosilicon insulation system. The stator coils are fabricated using a vacuum pressure impregnation process, and the rated voltage of the stator coils is 6kV. A2. Wipe the insulation surface of the stator coil with anhydrous ethanol to remove impurities and ensure that the insulation surface is smooth; A3. After the insulation surface is fully dry, apply low-resistivity varnish to the straight end of the stator coil and high-resistivity varnish to the end of the stator coil, and let it stand for 24 hours. A4. The straight end of the stator coil is processed into a pseudo three-electrode structure. The middle of the straight end is wrapped with aluminum foil as a measuring electrode, and the two ends near the nose end are wrapped with copper foil as shielding electrodes. The reserved wire part of the stator coil is short-circuited as the high voltage end. A5. Connect the measuring electrode and the high-voltage electrode to perform the initial FDS test.
3. The method for evaluating the thermal aging of an organosilicon insulation system for a motor stator coil according to claim 2, characterized in that, After step A5, proceed with the following steps: S6. After the initial FDS test, place the coil in a high-temperature oven and set a cycle. After each cycle, let the coil rest until it returns to room temperature. Then repeat steps A4 to S5 for multiple cycles. After each cycle, test the FDS curve.
4. The method for evaluating the thermal aging of an organosilicon insulation system for a motor stator coil according to claim 2, characterized in that, In step A5, the FDS test equipment used for FDS testing is IDAX-300, the peak voltage of the FDS test equipment is 200V, and the test frequency band of the FDS test equipment is set to 1mHz~1kHz.
5. The method for evaluating the thermal aging of an organosilicon insulation system for a motor stator coil according to claim 3, characterized in that, In step A6, after the initial test, the coil is placed in a high-temperature oven and the temperature is set to 250°C. Each cycle lasts 10 days. After each cycle, the coil is left to stand until it returns to room temperature. Then, steps S4 to S6 are repeated for a total of 3 cycles. After each cycle, the FDS curve is tested.
6. The method for evaluating the thermal aging of an organosilicon insulation system for a motor stator coil according to claim 1, characterized in that, In step S1, the real part ε'(ω) and the imaginary part ε''(ω) of the complex permittivity increase, and this increase becomes more pronounced as the test frequency decreases.
7. The method for evaluating the thermal aging of an organosilicon insulation system for a motor stator coil according to claim 6, characterized in that, The specific process of step S2 is as follows: S21. Derive the slopes of the relaxation polarization process and the conductance process in the linear portion, and obtain the slope ranges of different relaxation polarization models under the high and low frequency limits and the low frequency slope range of the conductance process. S22. The slope of the imaginary part of the FDS curve of the silicone-insulated coil under 250℃ thermal aging at low frequency is between -1 and 0, indicating that the conduction process is a jump conduction process. In addition, combined with the Cole-Cole diagram, it is determined that the silicone insulation of the coil exhibits a single relaxation process within the test frequency range. Therefore, the HN model is selected to fit the FDS curve in combination with the form of jump conduction. S23. The least squares method is used for fitting, considering both the real and imaginary parts of the complex permittivity curves simultaneously, and converting them to logarithmic form. The objective function is set as follows: ； S24. Select parameter Δε as the fitting parameter for the change in the silicone insulation of the coil. The fitting result is expressed as: 。 8. The method for evaluating the thermal aging of an organosilicon insulation system for a motor stator coil according to claim 7, characterized in that, In step S21, the conductance process is divided into a jump conductance process and a DC conductance process.
9. The method for evaluating the thermal aging of an organosilicon insulation system for a motor stator coil according to claim 7, characterized in that, In S21, the slopes of the relaxation polarization process and the conductance process in the linear portion are derived, and the range of slope values for different relaxation polarization models under high and low frequency limits and the range of low-frequency slope values for the conductance process are obtained. The derivation process is as follows: The relaxation model can be expressed as: ； In the formula, Δε = εs - ε∞, τ is the relaxation time, α and β are related to the relaxation time distribution, and 0 < α ≤ 1, 0 < β ≤ 1. Under the high and low frequency limits, the real and imaginary parts of the spectrum can be written as follows: ； ； The slopes of the imaginary parts of different models are shown in Table 1: Table 1. Slope of the imaginary part ε"(ω) of the complex permittivity at high and low frequency limits. Taking the jumping conductance as an example, at low frequencies, the straight line can be represented as y = kf + b. Then, according to the expression for jumping conductance, the straight line can be represented as: ； In the formula, f represents the test frequency, k represents the slope of the line, and b represents the intercept of the line. Further, we can obtain: ； Since 0≤γ≤1, the slope of the straight line of the jumping conductance at low frequencies is -1 to 0. Similarly, the slope of the DC conductance is -1. Combining the measured slope of the curve at low frequencies, it can be determined that the imaginary part of the FDS curve in the measured frequency range is a relaxation process. Combining the jumping conductance process, the HN model and the jumping conductance model are selected to fit the curve.
10. The method for evaluating the thermal aging of an organosilicon insulation system for a motor stator coil according to claim 7, characterized in that, Step S3 is as follows: The stator coils were continuously aged, and their passability was determined by a stator coil breakdown test. The voltage was increased uniformly at a rate of 1 kV / s until the stator coils broke down, and the breakdown voltage was recorded. A breakdown voltage exceeding 6 UN was considered acceptable. The breakdown voltage of each stator coil was recorded, and the breakdown voltage was correlated with the parameter Δε for each stator coil. Δε and breakdown voltage showed a negative correlation. A polynomial was used to fit Δε to the breakdown voltage V, and the results were as follows: ； According to the fitting results, when Δε is greater than 3.18, the stator coil breakdown voltage is unqualified, and the stator coil is considered to have reached the end of its life.