EN
Insulation Oil Test
Analysis of transformer insulating oil: moisture, acidity, dielectric strength and dissolved gas testing. Reported service from sampling to lab evaluation.
Insulation oil testing transfers the mineral or synthetic ester insulating liquid that serves both insulation and cooling in oil-filled transformers and switchgear — sampled under standardised discipline — to the laboratory for chemical and electrical parameter evaluation. Oil is the blood of the equipment: the moisture, acids and dissolved gases inside are early heralds of internal fault and ageing. The test is structured as a panel typically covering dielectric breakdown (basis strength), water content (Karl Fischer), acidity (neutralisation number), dissolved gas analysis (DGA), appearance and density.
Sampling Discipline
A wrongly taken sample yields a wrong result even on the right instrument; we therefore standardise sampling:
- Samples are drawn at low ambient humidity while the equipment is at rest or reference temperature; the draw valve is first cleaned and waste drained.
- Dark capped bottles or syringe-type vessels protecting from light and air are used; no open standing, labelling done at once.
- For moisture determinations, air contact is minimised and delivery within the analysis window (typically days) is ensured.
- Sampling point (lower valve, conservator line) and conditions (temperature, load) are recorded per equipment as a minute.
Parameters and Interpretation
Panel results are assessed against the equipment's age and history more than against single limits. Moisture is followed in mg/kg and vacuum dehydration comes to the agenda on units exceeding critical thresholds; a rising acidity flags oil oxidation and paper-varnish interaction; a low basis strength points to the particle-water-contamination trio to investigate; DGA (gas chromatography) classifies the internal fault type (discharge, overheating, arcing) through methods such as R-Rogers-Duval triangles. Detailed gas items are on our Dielectric Strength, Dissolved Gas and Acidity Test pages.
Legislation and Standards
The test is made within the operation-periodic maintenance duty of Law No. 6331 and the Regulation on High Current Electrical Installations. Technical references: IEC 60475 standardising sampling, TS EN 60422 / IEC 60422 for supervision of insulating liquids, IEC 60599 / IEC 60567 for DGA interpretation, IEC 60156 breakdown, IEC 60814 moisture, IEC 62021-1 acidity and TS EN ISO 3675 / ASTM D4052 density. Results are reported with laboratory accreditation and entered into the plant file as trends.
Outcome
The sample-reception-analysis-report chain is documented end-to-end; threshold exceedance and trend warnings become inputs to the facility's maintenance plan. Oil tests belong to our Transformer Tests and Analyses heading; to build your item plan and periods request a quotation via our contact page.
FAQ on Insulation Oil Test
The sample is taken representatively and air-free; then dielectric (breakdown) strength, dissolved water (moisture), acidity (TAN), density-viscosity, colour-gloss, particle count, interfacial tension and dissolved gas analysis (DGA) are examined. This item set jointly shows the electrical withstand, chemical degradation and fault gases inside the oil; it is read as a table rather than a single measurement.
Interpretation follows IEC 60599 and the relevant TS EN/IEC 60422 approach. In new-good oil the breakdown voltage is high (dry type typically above 60-70 kV), moisture low (ppm) and acidity low (mgKOH/g) within accepted limits; in operating oil these relax progressively by age-criticality, but a threshold crossing signals drying-change. DGA gas ratios (methane, ethylene, acetylene, hydrogen) mark the fault type.
For routine monitoring a representative sample is practically taken yearly (six months on critical-aged transformers). It is repeated immediately after a relay (Buchholz-differential) trip, abnormal heating, overload, lightning-arc event, oil leak-level drop or suspect odour-colour change. Keeping a series on the same oil volume is the pre-condition of trend reading; each sample is labelled with date-temperature-load data.
Rising moisture-acidity and falling breakdown strength indicate vacuum drying-filtration or oil change. In DGA, acetylene-ethylene dominance separates the arc-overheating fault type and sets urgency; high particle-contamination demands a clean-sealed system and filtration. The report gives the over-threshold items with a root cause and removal suggestion. Early intervention turns a planned oil treatment against the costly downtime-rewinding risk after a fault.