The Acoustic Detection of Generator Stator Winding Insulation Defects and Aging

Role, 1 Introduction The generator is subject to gradual aging due to the combined effect of electrical heating and mechanical stress during operation. Aging causes defects such as air gap delamination in epoxy mica insulation. The presence of defects not only reduces the service life of the insulation. Moreover, the operational reliability of the color ring system may even be of great significance in causing sudden stoppages.

The diagnostic technique of insulation has been vigorously developed. Common non-destructive testing techniques include traditional dielectric parameters such as dielectric loss, volume 8 and polarization index 0; partial discharge history 0 detection, such as electrical and acoustic measurements; and acoustic hammering Wait.

Although these detection methods can reflect the insulation status of the whole generator or the whole root bar, they can not reflect the degree of aging and damage to the location and insulation of the defects. .

The measuring device, which has undergone electro-thermal and mechanical stress acceleration, has undergone an old chemistry test, pass, domain frequency domain and wavelet transform analysis. The plant can more objectively reflect the acoustic spectrum of the aging state and defect information of the bar. A simple and accurate method for determining the type of epoxy mica insulation.

2 Measurement Principles Vibration and sound are closely linked. Mechanical vibrations often cause a wide variety of gifts to be reported and stimulate the vibrating particles of old media. Under the interaction of particles, vibrations propagate from point to point and form acoustic waves. In the air, it can also be disseminated in liquid medium such as flexible medium transfer funds project National Natural Science Fund project 59937260 Electrical insulation diagnosis and aging mechanism research; Xie Heng 194 males, Jiangxi nationality. Prof., Ph.D., chief of on-line monitoring and diagnostic technology for electrical insulation of electrical equipment, 15; Senior Member.

broadcast. The particle in the medium causes the displacement relative to the equilibrium position due to the passage of the sound wave. The change of the sound wave can be understood by measuring the vibration displacement of the particle. This is the basic principle of the detection of acoustic physics. When sound waves travel to two different media interfaces, they also have refraction and reflection like light waves, whether reflected on the media surface or not. Also pray for the body to pray. Both will change the form of the vibration of the sound wave and this change in sound will depend on the acoustic impedance of the media surface and the density of the media.

Generator stator winding adopts epoxy mica tape wrapped insulation, which belongs to fine layered medium and has longitudinal periodicity.

Since the fineness of the single-layer master tape thickness is small enough for the wavelength of the acoustic wave propagating in the medium, the composite media behavior can be considered as a uniform anisotropic medium. Under the long-term effect of electrothermal and mechanical stress, the insulating layer around the stator will cause defects such as air gap delamination or peeling due to aging. These defects cause changes in insulator density and acoustic impedance. Therefore, the propagation characteristics of sound in insulation will change accordingly.

For ease of calculation, we use a circular thin plate model with a fixed edge and no tension to describe the frequency of the vibration of the same thin plate in the internal defect of the insulation. The following formula can be used to calculate the coefficient of vibration in different vibration modes. , for the radius of the defect; for the insulation of the village material, Poisson's ratio; for the Young's model; 4 is the thickness of the insulation above the defect.

The following is the same as the basic frequency of the vibration of the team=3.20 substituting type, the other frequency of vibration mode is as follows: 3 Experiment 3.1 The sample test bar is the standard model bar provided by Harbin Daji Research Institute. The wrong conductor size is 1315!

In order to prevent the test line squeezed and under the long-term support is called production of the bar in the fixed + slot fastening state. During the test, the bar is fixed with a movable jig. 1. During the test, the gain of the vibrator is fixed, and the distance between the vibrating hammer and the sample surface is adjusted to ensure that the measurement conditions are basically the same.

3 Touching chuck 4 Digging rubber gasket 3.2 Acoustic detection system The device used for acoustic detection is self-developed 01-type insulation defect detection, measurement system 2.

During the measurement, the intense force signal generated by the vibrator is applied to the test bar under the action of the control loop of the device. The acoustic signal generated by the test bar is amplified and converted into magic, and then sent to the computer for data processing by the data acquisition card.

1 Acoustic signal detector 2 Sampling card 3 Laptop 4 Exciter 5 Acoustic sensor 6 Excite hammer 2 Acoustic detection system 4 Measurement results and discussion 4.1 Time domain and frequency domain analysis of acoustic detection results Typical model of aging bar Time domain and frequency domain waveforms. We can see that the amplitude of the time domain waveform decays rapidly after about one cycle of oscillation, forming a characteristic waveform consisting essentially of two peaks and one small peak. Correspondingly, in the frequency spectrum of 1 transform, the main frequency component is about 2%.

Results of acoustic testing after 2000 hours of electrothermal and mechanical stress aging.

We can observe that in the time domain waveform of the electric aging sample, we can see that there are more oscillations around the small peak in the time-domain waveform of the electric aging test. Frequency component.

However, no observable defects were found from the observation of the specimens and the observation of artificial tapping.

Epoxy mica insulated bar, under the action of high electric field, partial discharge occurs in the insulator. The high-energy particles generated by the partial discharge bombard the polymer surface, causing macromolecule chain breaking and insulation surface damage. Therefore, the density of the insulating body decreases, and the adhesion between epoxy and mica deteriorates and fine delamination occurs. In accordance with the aforementioned circular thin plate model and the fundamental frequency will drift in the high frequency direction. Therefore, the change of the time-frequency characteristics of the acoustic signal of the sample after the electrical aging is a high-frequency component formed due to the decrease in the density of the insulator.

Due to the accelerating effect of thermal stress, the sample has obvious air-opening and local delamination. From the time domain waveform, we can clearly see the overlap of the waveform at the initial rise and the broadening of the first peak. In the corresponding frequency spectrum, frequency components near Zhang appear, and the frequency band of the main frequency component narrows and drifts toward the low frequency direction.

Similarly, the basic frequency of the circular sheet model is 103. This is due to the measured results.

Learn test results. Similar to the detection result of the electric aging sample, there are also several oscillations near the small peak in the time domain waveform, and a large frequency component around 22 appears in the frequency spectrum.

The mechanical stress exerted on the test bar causes the polymer macromolecule to be broken by mechanical fatigue.

On the other hand, through fatigue bending, the effects of degumming between epoxy and mica will result in fine delamination within the insulator, which will cause the acoustic signal to drift toward high frequencies.

4.2 Acoustic detection results of wavelet analysis should be wavelet transform spectrum. The streamlet transform decomposes the acoustic signal into sets of multiple-track bands with the same size in logarithmic coordinates. When the resolution cell element changes with the change of the scale factor, the frequency domain resolution performance is poor, and the time domain resolution performance is better. When it increases, the frequency domain resolution increases and the time domain resolution decreases. Because of its good time-scale localization characteristics, wavelet transform can not reflect the frequency domain characteristics of signals well, and can give a better description of its feature in time domain. To satisfy the city 1 Ning, which is the basic wavelet, the continuous wavelet transform milk of 612, then the signal is defined as it corresponds to 612 feet on the function of the flat, on the decomposition of the function of the scale and time.

The scale is calculated as a result. In each of these, a wavelet transform describes the characteristics of the sub-dominant acoustic signal produced by the test bar under the action of an exciter. While 0 and 1 respectively represent the scale 2 transformations, they reflect that the exciter knocks the test bar insulated at the scale, = 1 wavelet transform, the most human amplitude can be observed to be called hair; 1x and 2x; only the amplitude of the mechanically stress-aged specimen has little change with respect to the amplitude of the unaged specimen.

In the scale, =2, the unaged sample has an oscillation attenuation peak at 81218 with an amplitude of approximately 1.

In the same scale analysis, the electric aging specimens had two peaks, and the amplitude was reduced to 0.040.03. The heat aging specimens were called 1 positive and 1 negative. The amplitudes were also changed to 0.250.4 and 0.4, respectively. The attenuation was very fast, and there was a small oscillating peak on the datum line. The mechanical stress-aged sample had only 0.04 oscillation attenuation peak at the amplitude. Therefore, the amplitude of the acoustic signal of the aging sample is significantly smaller than the amplitude of the unaged sample. The above two-scale analysis shows that after aging, the body density of the sub-dielectric insulation in the sample decreases, which leads to The change in the impedance of the insulation will also cause the number of reflections in the sound propagation process to increase.

Acoustic waves are attenuated to reduce the amplitude.

In the analysis of scale=3, the spectra of unaged specimens clearly have peaks at about 58 and 18, amplitudes of 2.1 and 5, respectively, while the oscillating attenuation peaks of the electro-aged specimens are at about 610 sen. 1020 served in two places with amplitudes of 1 and 0.5. Heat-aged samples also had two oscillating peaks. The amplitude similarity is about 3, and the amplitude of the unaged sample is similar. In the spectrum of the mechanically stress-aged sample, there are envelope peaks within the 5151 envelope that resemble a half sine wave. In the analysis with an amplitude of approximately 4 in the scale, the amplitude of the unaged bar was approximately 0.8. After a setting of approximately 671 was set. Stable at about 0.3. The amplitude of electrothermal aging specimens also tends to be similar. The mechanical attenuation should be slow, and the amplitude of the aging specimen should be maintained at about 0.8.5. The above two-scale analysis shows that the low-frequency characteristics of the heat-aged wire rod are basically the same as those of the unaged specimen. That is, thermal aging does not significantly affect the surface resistance of the test bar. The difference between the unaged and unaged specimens in the aged aging test specimens indicates that the partial discharges during the electrical aging and the low density regions formed only in the polymer body of the Ting engine, and the corona discharges along the surface also changed the ring. Trial clouds pay off, the state of the face.

In the mechanical stress aging test, it is mainly fixed fixtures to 5 conclusions acoustic detection method for the insulation of generator windings insulated with epoxy mica. Insulation defects can be quickly and easily detected and positioned accurately.

Acoustic method is used for the aging research of epoxy mica insulation. Through the change of the time-frequency characteristic spectrum of acoustic signals and wavelet analysis of different scales, the nature of the defects in the insulator can be judged. Therefore, it provides a powerful auxiliary analysis method for studying the aging mechanism of epoxy mica insulation.

By acoustic detection, we can think that the electrical aging and mechanical stress aging will mainly reduce the density of organic insulators. This small effect is an effect within the microscopic scale. The heat aging is to discuss the key role of epoxy cloud layering, that is, it is the main factor for macro defects.

3 Ding Qinghai, et al. The Application of Chaotic Fractal and Wavelet Theory in the Feature Extraction of Passive Acoustic Signals 1. Journal of Acoustics, 199 points 24. Continued from page 4. 43 Zhuo Fang, et al. Research on active power filter for phase-line system. Journal of Xi'an Jiaotong University, 200034 Zhuo Fangshen, Yang Jun, Hu Junfei, Wang Zhao'an. Structure and Control of Main Circuit of Active Power Filter with Phase Lines . Electrician of New Energy Technology, 2000, 19216.