article · Processes
Assessing the condition of insulating oil is vital to maintain reliable performance in electrical power transformers. Thermal ageing causes degradation of physical, chemical, and dielectric oil properties through the build-up of ageing by-products. While ultraviolet-visible absorption spectroscopy has been used previously, it produces broad spectra and cannot be deployed as an online sensor. Photoluminescence spectroscopy offers an alternative approach based on emission processes between a narrow band of electronic states, generating significantly narrower spectral bands. In laboratory tests on mineral oil aged under accelerated thermal conditions, measurements spanning wavelengths from 150 to 1500 nanometres revealed distinct patterns. Key parameters, specifically the full width at half-maximum and the enclosed spectral area, correlated directly with the extent of oil ageing and the dielectric dissipation factor. These findings demonstrate that photoluminescence spectroscopy provides an effective diagnostic tool for transformer oil monitoring.
Power transformers are critical components of electrical grids, and oil degradation can lead to catastrophic equipment failure. Existing optical assessment methods often lack precision and cannot easily monitor oil in real time. Demonstrating photoluminescence spectroscopy as an accurate diagnostic technique helps improve the detection of internal deterioration, supporting safer and more dependable grid operations.
This optical diagnostic technique could enable improved condition assessment tools for electrical utilities, power transformer manufacturers, and maintenance service providers. It offers potential advantages over ultraviolet-visible spectroscopy, including prospects for online sensing of oil degradation. However, because the evaluation remains at the laboratory stage using accelerated thermal ageing tests, further engineering and field validation are necessary before deployment as commercial monitoring hardware.
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Condition assessment of insulating oil is crucial for the reliable long-term operation of power equipment, especially power transformers. Under thermal aging, critical degradation in oil properties, including chemical, physical, and dielectric properties, occurs due to the generation of aging byproducts. Ultraviolet-visible (UV-Vis) spectroscopy was recently proposed for the condition assessment of mineral oil. However, this absorption technique may involve all electronic states of the investigated material which typically yield a broad spectrum, and thus cannot precisely reflect the electronic structure of aged oil samples. It also cannot be implemented as an online sensor of oil degradation. In this paper, photoluminescence (PL) spectroscopy is introduced, for the first time, for effective condition assessment of insulating oil. The PL technique involves emission processes that only occur between a narrow band of electronic states that are occupied by thermalized electrons and consequently yields a spectrum that is much narrower than that of the absorption spectrum. Aged oil samples with different aging extents were prepared in the laboratory using accelerated aging tests at 120 °C, under which 1 day of laboratory aging is equivalent to approximately 1 year of aging in the field. These aged samples were then tested using PL spectroscopy with a wavelength ranging from 150 nm to 1500 nm. Two main parameters were evaluated for quantitative analysis of PL spectra: The full width at half-maximum and the enclosed area under the PL spectra. These parameters were correlated to the aging extent. In conjunction with PL spectroscopy, the aged oil samples were tested for the dielectric dissipation factor as an indication of the number of aging byproducts. Interestingly, we find a correlation between the PL spectra and the dielectric dissipation factor. The results of PL spectroscopy were compared to those of UV-Vis spectroscopy for the same samples and the parameters extracted from PL spectra were compared to the aging b-products extracted from UV-Vis spectra. Finally, the corresponding physical mechanisms were discussed considering the obtained results and the spectral shift for each spectrum. It was proved that PL spectroscopy is a promising technique for the condition assessment of insulating oil when compared to conventional transformer oil assessment measuring techniques and even to other optical absorption techniques.
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DOI: 10.3390/pr9050732
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