How to diagnose an electric motor

Abstract

An object of the present disclosure is to provide a new method capable of accurately diagnosing the deterioration state of an electric motor. A diagnostic method according to the present disclosure is a diagnostic method for an electric motor, which includes measuring molecular structure deterioration of an insulation coating of a coil of the electric motor and diagnosing the deterioration of the electric motor based on the degree of molecular structure deterioration. For example, the molecular structure deterioration of the electric motor coil can be measured using Fourier transform infrared spectroscopy.

Description

[Technical Field]

[0001] The present disclosure relates to a method for diagnosing an electric motor. [Background technology]

[0002] Generally, a large number of electric motors are in operation in large-scale factories such as chemical plants. Patent Document 1 shows that if there are approximately 12,000 electric motors in operation in one chemical plant, 40% of them are over 25 years old.

[0003] The Japan Electrical Manufacturers' Association recommends that electric motors be replaced every 15 years, but this is a guideline that assumes non-explosion-proof open types, and is not necessarily suitable for the main explosion-proof totally enclosed electric motors that operate in factory facilities. For this reason, in the case of explosion-proof totally enclosed electric motors, a rule of thumb based on past failure records has been adopted, with 40 years as a standard, and a policy of replacing equipment in order of importance.

[0004] Patent Document 1 also describes that conventional methods for diagnosing deterioration of the electric motors include daily five-sense diagnosis using current, sound, temperature, etc., online bearing vibration diagnosis, and periodic winding insulation resistance diagnosis to grasp the condition over time. Patent Document 1 also discloses a method for diagnosing deterioration of electric motors based on changes in the insulation state of the motor coils by conducting insulation breakdown tests on the coils of sample electric motors whose electrical characteristics are similar to those of the managed electric motors, thereby setting reference values ​​corresponding to the insulation characteristics of the managed electric motors.

[0005] Patent Document 2 discloses a technology that can detect changes in the insulation state of electric motor coils at an early stage and diagnose them quantitatively without adding dedicated equipment to an existing system. The inventions described in Patent Documents 1 and 2 are both characterized in that they evaluate the state of deterioration by focusing on changes in the insulation resistance of electric motor coils. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-162481 [Patent Document 2] Japanese Patent Publication No. 2020-20611 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present disclosure is to provide a new method capable of accurately diagnosing the deterioration state of an electric motor. [Means for solving the problem]

[0008] Examples of embodiments of the present disclosure are listed below. [1] A diagnostic method for an electric motor, comprising: measuring the molecular structure deterioration of the insulating coating of the coil of the electric motor; diagnosing deterioration of the electric motor based on the degree of molecular structure deterioration. [2] Item 1, the diagnostic method comprising measuring the molecular structure degradation using Fourier transform infrared spectroscopy. [3] 3. The diagnostic method according to item 1 or 2, comprising measuring the molecular structure degradation by non-destructive analysis. [4] 4. The diagnostic method according to any one of items 1 to 3, further comprising diagnosing the deterioration of the electric motor based on the degree of the molecular structure deterioration and an insulation resistance value of the electric motor. [5] 5. The diagnostic method according to claim 1, further comprising determining whether or not measurement of the molecular structure deterioration is necessary after measuring the insulation resistance value of the electric motor. [6] 6. The diagnostic method according to any one of items 1 to 5, comprising determining whether or not the electric motor needs to be renewed based on whether or not the degree of molecular structure deterioration of the electric motor is equal to or greater than a certain value. [7] If the insulation resistance value of the electric motor is less than a certain value, it is determined that the electric motor needs to be replaced, 7. The diagnostic method according to any one of items 1 to 6, further comprising determining whether or not the electric motor needs to be replaced depending on whether or not a degree of molecular structure deterioration of the electric motor is equal to or greater than a certain value when the insulation resistance value is equal to or greater than a certain value. [8] If the electric motor is less than a certain age, it is determined that the electric motor does not need to be replaced; If the electric motor is aged for a certain number of years or more and has an insulation resistance value less than a certain value, it is determined that the electric motor needs to be replaced; 8. The diagnostic method according to any one of items 1 to 7, further comprising determining whether or not the electric motor needs to be replaced based on whether or not a degree of molecular structure deterioration of the electric motor is equal to or greater than a certain value when the electric motor is equal to or greater than a certain age and the insulation resistance value is equal to or greater than a certain value. [9] 9. The diagnostic method according to any one of items 1 to 8, wherein the coating of the coil of the electric motor comprises at least one selected from the group consisting of formal, polyurethane, polyester, polyesterimide, polyamideimide, and polyimide.

[10] the coating of the coil of the electric motor comprises polyester; The Fourier transform infrared spectroscopy was used to measure the absorbance spectrum of the insulating coating surface of the coil of the electric motor, and the absorbance spectrum was measured in the range of 1600 to 1800 cm -1 , 1200~1400cm -1 , 1000~1200cm -1 , 600~800cm -1 and diagnosing deterioration of the electric motor by comparing the peak values ​​in each of the above with the absorbance spectrum of the insulating coating surface of a coil of a known electric motor before deterioration. [Effects of the Invention]

[0009] According to the present disclosure, a new method can be provided that can accurately diagnose the deterioration state of an electric motor. [Brief explanation of the drawings]

[0010] [Figure 1]Figure 1 shows a flow chart showing the conventional standards for updating electric motors. [Figure 2] Figure 2 is a graph showing the heat resistance life of enameled wire coating. [Figure 3] Figure 3 is a graph showing the lifespan of enameled wire coating at various temperatures and relative humidity levels. [Figure 4] Figure 4 shows the spectrum of the motor coil obtained by Fourier transform infrared spectroscopy. [Figure 5] Figure 5 shows the spectrum of the motor coil obtained by Fourier transform infrared spectroscopy. [Figure 6] FIG. 6 is a schematic diagram showing measurement points on a motor coil using Fourier transform infrared spectroscopy. [Figure 7] FIG. 7 is a schematic diagram showing measurement points on a motor coil using Fourier transform infrared spectroscopy and an insulation resistance meter. [Figure 8] Figure 8 is a flow chart showing the criteria for updating electric motors. [Figure 9] FIG. 9 is a correlation diagram of test values ​​performed on each motor. [Figure 10] FIG. 10 is a correlation diagram of test values ​​performed on each motor. [Figure 11] FIG. 11 is a correlation diagram of test values ​​performed on each motor. DETAILED DESCRIPTION OF THE INVENTION

[0011] A diagnosis method for an electric motor coil according to one aspect of the present disclosure will be described below with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to the embodiments, but extends to the inventions set forth in the claims and their equivalents.

[0012] <<Method for diagnosing electric motor coils>> The present disclosure provides a diagnostic method for an electric motor, which includes measuring the molecular structure degradation of an insulation coating of an electric motor coil and diagnosing the deterioration of the electric motor based on the degree of molecular structure degradation. Conventionally, it has been difficult to grasp the deterioration state of an electric motor from the viewpoints of the structure of the electric motor coil and diagnostic technology, making it extremely difficult to accurately diagnose the lifespan of an electric motor. For this reason, as shown in Figure 1, some have adopted a policy of gradually replacing equipment starting with the most important, with a 40-year service life as a standard based on past coil failure records. However, this policy lacks sufficient scientific and statistical support and lacks rationality, resulting in the need to replace electric motors that do not necessarily require replacement at great expense. Meanwhile, insulation resistance testing, which checks for the presence or absence of electrical leakage in an electric motor, has been considered as a conventional diagnostic method for an electric motor. While this method is effective in evaluating the electrical deterioration of an electric motor, the inventors have discovered that simply measuring the insulation resistance value of an electric motor is insufficient to predict physical damage due to a decrease in the mechanical strength (peel resistance) of the insulation coating inside the electric motor coil. Therefore, we focused on thermal degradation and degradation due to hydrolysis as causes of motor coil deterioration, and performed lifespan predictions for each factor. As a result, compared to the heat-resistance lifespan of enamelled wire coating shown in Figure 2, the lifespan reduction due to each temperature and relative humidity of enamelled wire coating shown in Figure 3 was significant, making it clear that the main cause of motor coil deterioration is molecular structure degradation caused by hydrolysis of the insulation coating. Based on this knowledge, we can measure the molecular structure degradation that occurs in the insulation coating and diagnose the state of deterioration of the motor based on the degree of degradation, making it possible to accurately diagnose the lifespan of the motor, which was previously difficult.

[0013] More specifically, Figure 2 shows that the heat-resistant lifespan of both polyamide-imide copper wire (AIW) and polyester copper wire (PEW) coatings exceeds approximately 10,000 years at an internal temperature of 96.1°C. Figure 3 also shows that at the same internal temperature of 96.1°C, the lifespan drops to less than 40 years when the relative humidity exceeds 9.5%. A relative humidity of 9.5% inside an electric motor corresponds to approximately 1.5 g of moisture, calculated from the air volume inside the motor. Since condensation has actually been observed inside electric motors, such a humid internal environment is quite possible. This suggests that the molecular structure degradation of electric motor coil insulation coatings is most likely due to hydrolysis rather than thermal stress. Therefore, it is possible to diagnose motor coil degradation by measuring the molecular structure degradation of the insulation coating due to hydrolysis. In other words, the present disclosure was discovered as a result of the above-mentioned trial and error, and is a method for measuring the molecular structure deterioration caused by hydrolysis of the insulating coating of an electric motor coil and diagnosing the deterioration of the electric motor based on the degree of molecular structure deterioration, thereby making it possible to provide a new diagnostic method for accurately diagnosing an electric motor.

[0014] The results in Figure 3 can be calculated from the following formula (1) and the life of the enameled wire due to hydrolysis in a forced degradation test of the coating.

[0015]

number

[0016] <Measurement of molecular structure degradation> Deterioration of the molecular structure of the insulating coating of an electric motor coil can be measured by, for example, nuclear magnetic resonance, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, etc. A further aspect of the present disclosure provides a diagnostic method that includes measuring the molecular structure deterioration using Fourier transform infrared spectroscopy (FTIR). This diagnostic method makes it possible to more quantitatively evaluate the deterioration information of the electric motor coil.

[0017] The inventors performed spectral analysis of new and deteriorated electric motor coils using Fourier transform infrared spectroscopy and confirmed spectral degradation in a specific wavenumber range. For example, Figure 4 shows a comparison of the spectra obtained by Fourier transform infrared spectroscopy for a new electric motor coil using polyester copper wire with three deteriorated coils with insulation resistance values ​​of 55,556 MΩ, 32,258 MΩ, and 19 MΩ. Figure 4 confirms that the spectral intensity gradually decreases in a specific wavenumber range as the insulation resistance decreases. This indicates that hydrolysis breaks the molecular bonds of the polyester-based insulating coating, causing a decrease in infrared absorption. In other words, spectral analysis of the insulating coating of an electric motor coil using Fourier transform infrared spectroscopy (FTIR) can measure molecular structure degradation, and the degree of molecular structure degradation can be used to diagnose the deterioration of the electric motor.

[0018] A specific example of FTIR testing of electric motors in this disclosure is described below in the section "Fourier Transform Infrared Spectroscopy (FTIR) Testing." However, this is not limited to this method as long as spectral analysis using Fourier Transform Infrared Spectroscopy is possible. Furthermore, molecular structure degradation can be measured using either destructive or nondestructive analysis. Destructive analysis may be used to measure molecular structure degradation on motors that have ceased operation, motors scheduled for disposal, or sample motors for obtaining reference data. This allows for analysis of the cause of degradation, reevaluation of insulation coating materials, and feedback for the introduction of new models. When diagnosing the lifespan of an electric motor during operation or maintenance, or from the perspective of speed and ease of measurement, molecular structure degradation is preferably measured using nondestructive analysis. For example, a handheld infrared spectrometer can be used, which can perform measurements simply by contacting and irradiating a probe or light onto the insulation coating surface. These methods allow for on-site evaluation of molecular structure degradation without scraping the coating of the electric motor coil or cutting out samples.

[0019] <Electric motor> An electric motor converts the current supplied from a power source into electromagnetic force to generate rotational motion, and is primarily composed of a stator, rotor, bearings, and housing. The stator is made up of an iron core and motor coils wound in its slots, and generates a rotating magnetic field when current is applied from the power source. Meanwhile, the rotor is located within the stator, and generates torque through electromagnetic interaction with the rotating magnetic field of the stator, transmitting rotational motion to the output shaft.

[0020] The motor coils are made of conductor wires inserted into stator slots. The conductor wires are usually made of copper or aluminum and are covered with an insulating coating. The coils are arranged for each phase, and when current is passed through each phase of the three-phase AC power supply, magnetic fields with different phases are generated.

[0021] The diagnostic method of the present disclosure can be applied to various types of electric motors, but is particularly useful for low-voltage motors, which are installed in large numbers in industrial facilities and for which coil replacement is difficult.Low-voltage motors are electric motors that operate at 750 V or less for direct current and 600 V or less for alternating current, and generally have a rated voltage of around 100 to 600 V, and are used in a wide range of applications such as fans, pumps, compressors, and conveying equipment.

[0022] Various organic polymer resins are used as insulating coating materials depending on the application and heat resistance requirements. Typical examples include formal (polyvinyl formal), polyurethane, polyester, polyesterimide, polyamideimide, and polyimide. In the electric motor coil diagnostic method of the present disclosure, the insulating coating of the electric motor coil preferably contains at least one selected from the group consisting of formal, polyurethane, polyester, polyesterimide, polyamideimide, and polyimide. Due to the susceptibility of molecular structure degradation due to hydrolysis, the insulating coating of the electric motor coil preferably contains polyester.

[0023] In a further aspect of the present disclosure, an insulating coating of a coil of an electric motor contains polyester, and an absorbance spectrum of the surface of the insulating coating of the coil of the electric motor is measured using Fourier transform infrared spectroscopy, and a wavelength of 1600 to 1800 cm is obtained. -1 , 1200~1400cm -1 , 1000~1200cm -1 , 600~800cm -1 and compare the peak values ​​in the absorbance spectrum of the insulation coating surface of a known electric motor coil before deterioration to diagnose the deterioration of the electric motor. For example, Fig. 5 shows the results of spectrum analysis using Fourier transform infrared spectroscopy on a new electric motor coil using polyester copper wire and a deteriorated coil. As shown in Fig. 5, -1 , 1200~1400cm -1 , 1000~1200cm -1 , 600~800cm -1 The peak values ​​of the spectra for each of the above are lower than those of a new coil, and by evaluating the degradation of the insulating coating due to hydrolysis using the spectral height obtained by FTIR, it is possible to more accurately diagnose the degradation of the motor.

[0024] A further aspect of the present disclosure provides a diagnostic method that includes diagnosing the deterioration of an electric motor based on the degree of molecular structure degradation and the insulation resistance value of the electric motor. Molecular structure degradation is an indicator of chemical degradation of the insulation coating itself, while insulation resistance is an indicator of the electrical integrity of the entire coil. These two indicators are complementary to each other, and using them together allows for more accurate diagnosis of the deterioration state of the electric motor. For example, the diagnostic method of the present disclosure may include separately diagnosing the insulation resistance value of the electric motor and the degree of molecular structure degradation of the coil, and diagnosing the electric motor by combining the respective diagnostic results. Alternatively, the diagnostic method may include calculating each diagnostic result as a score, and diagnosing the electric motor using an overall score calculated from the score based on the insulation resistance value and the score based on the degree of molecular structure degradation. In another aspect, the diagnostic method may include measuring the insulation resistance value of the electric motor and then determining whether or not to measure the molecular structure degradation based on the insulation resistance value of the electric motor. Alternatively, the diagnostic method may include measuring the molecular structure degradation and then determining whether or not to measure the insulation resistance value of the electric motor based on the degree of molecular structure degradation. For example, insulation resistance can be obtained by measuring the insulation resistance between each phase terminal wire (U, V, W) of the motor and the ground (earth) as shown in Figure 7. Alternatively, three to four locations can be randomly selected from the coil end of the motor coil, and the surface of the selected locations can be measured using a handheld FTIR to obtain a representative FTIR spectrum.

[0025] A further aspect of the present disclosure provides a diagnostic method that includes determining whether an electric motor needs to be replaced based on whether the degree of molecular structure deterioration of the electric motor is equal to or greater than a certain value. The degree of molecular structure deterioration can be determined by, for example, comparing the spectra obtained by Fourier transform infrared spectroscopy of a new electric motor coil using polyester copper wire with those of a deteriorated electric motor coil, as shown in Figure 5, and calculating the numerical ratio of the spectral heights of the new coil and the deteriorated coil at a specific frequency, thereby obtaining the numerical ratios shown in Table 1 below. If the molecular structure deterioration rate is less than 40%, it is possible to diagnose that the electric motor needs to be replaced.

[0026] [Table 1]

[0027] From the viewpoint of further improving diagnostic accuracy, it is more preferable to provide a diagnostic method that includes determining that the motor needs to be replaced if the insulation resistance value of the motor is below a certain value, and determining whether the motor needs to be replaced based on whether the degree of molecular structure deterioration of the motor is above a certain value if the insulation resistance value is above the certain value.As a result, even if the motor has an insulation resistance value of, for example, 100 MΩ or above and is evaluated as sound according to conventional diagnostic standards, by quantitatively evaluating the degree of molecular structure deterioration of the coil insulation coating, it is possible to predict deterioration in the strength of the insulation coating of the motor coil, which was difficult to detect using conventional diagnostic methods that use insulation resistance values, and it is possible to more accurately diagnose whether the motor needs to be replaced.

[0028] In another aspect of the present disclosure, a diagnostic method is provided that includes determining that an electric motor does not need to be replaced if the electric motor is less than a certain age, determining that the electric motor needs to be replaced if the electric motor is at least a certain age and its insulation resistance value is less than a certain value, and determining whether the electric motor needs to be replaced based on whether the degree of molecular structure deterioration of the electric motor is at least a certain value if the electric motor is at least a certain age and its insulation resistance value is at least a certain value. For example, FIG. 8 is a flowchart according to one aspect of the electric motor coil diagnostic method of the present disclosure. Each flow is as follows. (1) If the target electric motor is less than 40 years old, it will be determined that replacement is not necessary. (2) For motors that are 40 years or older and have undergone the judgment in (1), if the insulation resistance value is less than 100 MΩ, the motor is deemed to require replacement. If the insulation resistance value is 100 MΩ or more, the judgment in (3) is made. (3) Measure the molecular structural deterioration of the insulation coating of the motor coil, and if the degree of molecular deterioration is 40% or more, determine that renewal is not necessary. If it is less than 40%, proceed to the judgment in (4). (4) If the target motor is not a critical machine, it is determined that renewal is unnecessary; if it is a critical machine, it is determined that renewal is necessary. The above flow narrows the scope of diagnosis to voltage motors with an age of 40 years or more, thereby reducing unnecessary diagnostic procedures. Furthermore, by measuring insulation resistance before measuring molecular structure degradation, it is possible to avoid measuring molecular structure degradation for motors with insulation resistance values ​​of less than 100 MΩ that clearly require renewal, thereby improving the speed of the diagnostic process. Furthermore, the deterioration of the coating strength of the motor coil can be accurately evaluated by whether the degree of molecular structure degradation is less than 40%, making it possible to accurately determine whether the motor needs to be renewed. It is desirable to appropriately adjust the threshold values ​​for the age of the motor, insulation resistance, and degree of molecular structure degradation depending on the field environment in which the diagnostic method disclosed herein is applied, the type of motor used, etc. [Example]

[0029] Examples and comparative examples of embodiments of the present disclosure will be described below, but the present disclosure is not limited to the following examples and comparative examples.

[0030] 《Measurement method》 <Insulation Resistance Test> An insulation resistance test was conducted to evaluate the insulation performance of electric motor coils in a steady state. The test is performed by applying a DC voltage between the conductor and the insulation coating or iron core, and measuring the leakage current that flows at that time. The applied voltage was set in the range of 500V. The conductor part of the sample was connected to one electrode, and a metal foil or metal plate was attached to the coating surface as the other electrode. After applying the voltage, the current value was allowed to stabilize for one minute, and then the resistance value was calculated. The insulation resistance value was calculated using the following formula 2. R=V / I (formula 2) Here, V is the applied voltage (V) and I is the measured current (A). The test was carried out under normal temperature and humidity conditions (23±2°C, relative humidity 50±5%). The soundness of the insulation coating was confirmed by checking that the insulation resistance value obtained was not below 100 MΩ.

[0031] <Breakdown voltage test> A typical breakdown voltage test was conducted to evaluate the insulation performance of electric motor coils. The test is performed by applying a specified voltage between the conductor wire and its insulating layer, and measuring the voltage value when the insulating layer electrically breaks down. Specifically, a DC voltage is applied between 20 and 21 in Figure 7. The test voltage usually starts from 0 V and is gradually increased at a rate of 500 V / s. The voltage value at which a partial discharge or arc discharge occurs in the insulating layer and the current suddenly increases is taken as the breakdown voltage.

[0032] <Calculation of molecular structure degradation quantity using Fourier transform infrared spectroscopy (FTIR) testing> To evaluate the chemical degradation state and constituents of the insulating coating material of the electric motor coil, infrared absorption spectra were measured using a Fourier transform infrared spectrometer (FTIR). A portable (handheld) infrared spectrometer (Handheld FTIR) was used for the test, and the measurement wavenumber range was 4000 to 650 cm. -1 The measurement mode used was the total reflection method, and as shown in Figure 6, the probe was randomly selected at 3 to 4 points on the coil end of the motor coil and pressed directly against the sample surface to perform the measurement. The resolution was 4 cm -1 The number of accumulations was 32, and the resulting spectra were smoothed and baseline corrected before being compared with known polymer reference spectra.

[0033] <Determining coating strength through peel bending test> A peeling bending test was conducted to evaluate the adhesion and flexibility of the insulation coating of electric motor coils. The test involves winding a coated conductor wire a certain number of times around a mandrel of a specified diameter, or repeatedly bending it at a specified radius of curvature, and then observing the presence or absence of cracks, peeling, or discoloration in the coating. The sample length is approximately 200 mm, and the test temperature is 23±2°C, and the wire is bent 180° around a mandrel with a bending radius twice the conductor diameter, for example. After repeating this procedure multiple times, the coating surface is visually inspected, and if no obvious peeling of the coating is observed, the coating strength is deemed to be good.

[0034] Examples and Results The above tests were carried out on 20 low-voltage motors, including new and deteriorated ones. The values ​​obtained from each test are plotted in Figures 9 to 11.

[0035] [Implementation results] Figures 9 and 10 show that all motors deemed to require replacement due to reduced coating strength had a molecular structure degradation residual of 0.40 or less, demonstrating that it is possible to diagnose motors with reduced coating strength based solely on the molecular structure degradation residual value. Figure 10 also shows that motors with insulation resistance values ​​of 100 MΩ or greater and molecular structure degradation residuals greater than 0.40 can postpone replacement, enabling more accurate replacement decisions. Figure 11 also shows that motors with insulation resistance values ​​of 10,000 MΩ or greater, which would have been deemed healthy under conventional standards, have reduced coating strength. This demonstrates that conventional motor diagnosis based solely on insulation resistance values ​​is insufficient. [Industrial Applicability]

[0036] The present disclosure can be utilized, for example, in a method for diagnosing a group of electric motors in a chemical plant, and can also be utilized in diagnosing general electric motors. [Explanation of symbols]

[0037] 1 electric motor 2. Handheld FTIR 3. Insulation resistance tester 10. Motor coil 11 FTIR measurement points at the coil end 20 Insulation resistance tester measurement points for each phase (U, V, W) 21 Insulation resistance tester measurement points for earthing

Claims

1. A diagnostic method for an electric motor, comprising: measuring the molecular structure deterioration of the insulating coating of the coil of the electric motor; diagnosing deterioration of the electric motor based on the degree of molecular structure deterioration.

2. The diagnostic method of claim 1 , comprising measuring the molecular structural deterioration using Fourier transform infrared spectroscopy.

3. The diagnostic method according to claim 1 or 2, comprising measuring the molecular structure deterioration by non-destructive analysis.

4. 3. The diagnostic method according to claim 1, further comprising diagnosing deterioration of the electric motor based on the degree of molecular structure deterioration and an insulation resistance value of the electric motor.

5. 3. The diagnostic method according to claim 1, further comprising determining whether or not measurement of the molecular structure deterioration is necessary after measuring the insulation resistance value of the motor.

6. 3. The diagnostic method according to claim 1, further comprising determining whether or not the electric motor needs to be renewed based on whether or not the degree of the molecular structure deterioration is equal to or greater than a certain value.

7. If the insulation resistance value of the electric motor is less than a certain value, it is determined that the electric motor needs to be replaced, 3. The diagnostic method according to claim 1, further comprising: determining whether or not the electric motor needs to be replaced based on whether or not a degree of molecular structure deterioration of the electric motor is equal to or greater than a certain value when the insulation resistance value is equal to or greater than a certain value.

8. If the electric motor is less than a certain age, it is determined that the electric motor does not need to be replaced; If the electric motor is aged for a certain number of years or more and has an insulation resistance value less than a certain value, it is determined that the electric motor needs to be replaced; 3. The diagnostic method according to claim 1, further comprising: determining whether or not the electric motor needs to be replaced based on whether or not a degree of molecular structure deterioration of the electric motor is equal to or greater than a certain value when the electric motor is equal to or greater than a certain age and the insulation resistance value is equal to or greater than a certain value.

9. 3. The diagnostic method according to claim 1, wherein the insulating coating of the coil of the electric motor includes at least one selected from the group consisting of formal, polyurethane, polyester, polyesterimide, polyamideimide, and polyimide.

10. the insulation coating of the coil of the electric motor contains polyester; Using the Fourier transform infrared spectroscopy, the absorbance spectrum of the insulating coating surface of the coil of the electric motor is measured, and the absorbance spectrum is measured in the range of 1600 to 1800 cm －１ , 1200-1400cm －１ , 1000-1200cm －１ , 600-800cm －１ 3. The diagnostic method according to claim 1, further comprising: diagnosing deterioration of the electric motor by comparing the peak values ​​in each of the above with the absorbance spectrum of an insulation coating surface of a coil of a known electric motor before deterioration.

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