Evaluating the Effectiveness of Refractometric Sensors for Transformer Oil Ageing Monitoring
Bibliographic record
Abstract
With the growing emphasis on online ageing detection methodologies for transformer oil—a critical component of high-voltage networks that provides insulation, cooling, and state-of-health information for transformers—there is increasing recognition of their advantages over traditional offline methods. Offline techniques are often limited by challenges such as sample contamination, misinterpretation of results, exposure of on-site personnel to hazards, loss of man-hours, high costs associated with all five stages of detection, and their restriction to scheduled maintenance practices. Consequently, online ageing sensors for transformer oil are gaining significant traction in the field of high-voltage instrumentation. This study evaluates the effectiveness of refractometric optical fibre sensors for ageing detection in transformer oil, leveraging the advantages of fibre optic sensors, including immunity to high-voltage interference, lightweight design, and high sensitivity compared to other sensor types, such as cross-capacitance sensors. The research utilised intensity-modulated fibre optic sensors with varying sensing lengths, as well as the FISO Quebec Fabry-Pérot phase-modulated optical fibre sensor and Universal Multichannel Instrument. Industrial transformer oil samples—including Miden eN 1204 natural ester oil, Polaris GX mineral oil, Nytro Bio 300X vegetable oil, and Midel eN 7131 synthetic ester oil—were degassed, dried, and subjected to accelerated thermal ageing at 115°C. These samples were then characterised for key ageing markers, including interfacial tension, total acidity number (TAN), dissolved decay products (via UV-Vis spectroscopy), particle count, turbidity, and moisture content. The sensitivity analysis revealed that intensity-modulated optical fibre sensors are influenced by the length of the sensing region and the wavelength of the optical source, and they exhibit lower repeatability compared to phase-modulated optical fibre sensors. The FISO Quebec Fabry-Pérot phase-modulated optical fibre sensor demonstrated superior performance, with outputs that are less affected by twists and a rapid settling time of under 0.5 minutes across all four transformer oil types. Thermal response analysis using the FISO Quebec Fabry-Pérot sensor, which has a thermal coefficient of 0.0004 RIU/°C, indicated that the natural ester oil (NE 1204) and Nytro Bio 300X vegetable oil exhibited better thermal stability compared to Polaris GX mineral oil and synthetic ester oil. The enhanced thermal response properties of Nytro Bio 300X were attributed to the presence of antioxidants. Furthermore, correlation analysis between ageing markers from the aged transformer oil samples and the refractive index outputs of the FISO Quebec Fabry-Pérot sensor confirmed its reliability for identifying ageing markers in NE 1204 natural ester oil and Nytro Bio 300X. This reliability is evidenced by a high linear coefficient of determination exceeding 90% and low prediction errors of about 10% for moisture, interfacial tension, and turbidity when validated with independent datasets.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".