The data and findings discussed here come from the cited paper and do not represent test results from VISPEK equipment.
The color of insulating oil changes with changes in state, and continuous spectrum can convert this appearance difference into a calculable signal. This study, which pairs optical measurements with laboratory color indexes and retains another set of oil samples for validation, is suitable for understanding how a quick estimate of a color index can be established and what range it can represent.
Summary
The study measured the transmission absorption of insulating oil in a quartz cell, used the laboratory color index as a reference, compared the cut-off wavelength and visible area models, and verified it with another set of oil samples. The error of the cut-off wavelength route is small under the measured conditions; the color index is only a specific indicator and cannot replace all aging or electrical tests. Dark oils and different base oils require extended verification.
(AI-generated conceptual illustration for context; it is not data from the paper, a photograph of the research equipment, or a VISPEK product diagram.)
Why It Matters
Quantifying color changes with spectra can improve the consistency of inspection data and provide a basis for inspection priority.
Methods and Reference Measurements
Take the oil from the operating transformer, send one part to the laboratory to measure the color index according to ASTM D1500, and the other part to measure the transmission and absorption of 200–800 nm in a 10 mm quartz cell. Each sample is repeated three times. The wavelength corresponding to the absorbance cutoff point and the curve area of 360–600 nm are used to model respectively. The second set of 42 samples was used for verification to compare the absolute error and RMSE under different absorbance cut-off points.
Wavelengths and Acquisition Parameters
| Band/parameter | Original meaning and usage instructions |
|---|---|
| 200–800 nm | Original text collection range |
| About 300–700 nm | Color Index Dependent Absorption Changes |
| 360–600 nm | Independently verified curve area model; cutoff model with Abs=0.75 as the best verification point |
Key Findings
When the absorbance cutoff point is 0.75, the cutoff wavelength model has RMSE=0.1961, mean absolute difference 0.1632, and maximum absolute difference 0.4 on 42 verification samples; the area model RMSE=0.6274.
Limitations and Interpretation
Color index is a specific indicator and cannot replace all aging or electrical performance testing in oils; darker oils and different base oils require extended samples.
Band and model boundaries: Original scan 200–800 nm; this case uses color features and independent verification models located within the target range, especially the 360–600 nm area and visible cutoff wavelength.
Image copyright belongs to the paper’s original authors. License: CC BY 4.0.
Source Paper
Leong YS, Ker PJ, Jamaludin MZ, M Nomanbhay S, Ismail A, Abdullah F, Looe HM, Lo CK. (2018). UV-Vis Spectroscopy: A New Approach for Assessing the Color Index of Transformer Insulating Oil. Sensors (Basel, Switzerland) 18(7). https://doi.org/10.3390/s18072175
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VISPEK products shown for illustration; these were not the devices used in the cited study.