Evaluation of the Technical Condition of the Active Part of the High Power Transformer Based on Measurements and Analysis of Vibroacoustic Signals

Abstract

This article presents the results of research connected with the development and industrial use of vibroacoustic methods for the evaluation of the technical condition of the active part of transformers. The article presents the results of the analysis of vibrations generated by the high power transformer in which a defect was found on the basis of tests of oil carried out using the chromatography tests. In order to confirm the damage of the active part of this transformer, vibroacoustic measurements were performed in three states of its operation. The measurement using the classical vibroacoustic method included the registration of vibrations at the idle speed and during the load operation of the transformer. The original diagnostic method, so-called the modified vibroacoustic method, was also used during the measurement. The analysis of signals recorded using the classical vibroacoustic method was carried out in the frequency domain by indicating the amplitude of even harmonic vibrations. However, the analysis of signals measured during the commissioning of the transformer was conducted in the time-frequency domain using the short-time Fourier transform (STFT), continuous wavelet transform (CWT), and discrete wavelet transform (DWT). On the basis of the analysis of the results obtained it was stated that the increased level of vibrations of this transformer is a consequence of the loss of rigidity of the mechanical structure of its core.

Investigation of Distribution Transformers Vibrations in Terms of Core and Winding Condition Assessment

“…In the currently used approach to the analysis of vibroacoustic signals coming from the transformer [17][18][19][20], relatively high criteria values are adopted (the normal state is determined up to the value of 400 cm/s 2 of total RMS of vibration acceleration, while the emergency state is determined after exceeding 2500 cm/s 2 ). The values of vibration accelerations measured by the authors for the 12 non-repaired transformers in service range from about 10 to 395 cm/s 2 , so all these units are in a normal state, even transformers over 45 years in use.…”

“…In the works [17][18][19][20] we can find information about the transformer vibrations sources that has been assigned appropriate frequency ranges in the vibration spectrum:…”

“…In this part the total root mean square values of vibration acceleration obtained for transformers 16 and 25 MVA, which in accordance with Table 1 should not exceed the value of 400 cm/s 2 [17][18][19][20][21], were analyzed. Figure 8a,b show the total RMS values of vibration acceleration measured for ten transformers with a rated power of 16 MVA and seven transformers with a power of 25 MVA.…”

“…This article presents the results of vibration tests of power transformers with rated power of 16 and 25 MVA. These tests were carried out to check whether the criterion values presented in [17][18][19][20][21] (which refer to units with a rated power approximately ten times higher than the power of the transformers tested in this paper) would be useful in assessing the technical condition of the transformers we tested. The research began with the determination of the most favorable, in terms of the highest value of the recorded signals amplitude, places for the installation of vibroacoustic sensors.…”

Identification of electrical discharge forms, generated in insulating oil, using the optical spectrophotometry method

“…Dedicated methods were developed on the basis of phenomena accompanying ED and make it possible to detect and measure these phenomena, as well as locate the place of their occurrence. The following methods are currently used in the diagnostics of insulation systems in power devices: electrical method, acoustic emission method, ultra-high frequency method, gas chromatography method [1][2][3][4][5][6][7][8][9][10][11][12][13] and alternative methods, basis of the time difference on an energy accumulation curve of multiple signals [14].…”