Transformer oil provides insulation and cooling. Oil testing adds useful condition data, but no single gas or breakdown value is a complete fault diagnosis.
This guide is general information. HV/MV intervention and testing must be carried out by qualified personnel under the equipment manual and facility safety procedures.
Each test answers a different question
Breakdown voltage measures the stress a sample withstands. Moisture and acidity show other aspects of oil condition. Dissolved gas analysis (DGA) monitors gas levels and trends associated with thermal and electrical events.
- BDV: dielectric strength
- Moisture and acidity: contamination and ageing
- DGA: gas levels and rate of change
- Sampling conditions: context for interpretation
Sampling matters
Contamination, air exposure, incorrect containers and poor labeling can distort results. Record the transformer identity, sampling date and operating condition. The method and repeated test sequence belong in the report.
Translate data into action
Interpret gas patterns and rates alongside load history, previous oil results, electrical tests and inspection findings. A repeat sample, oil treatment or further investigation may be appropriate. Testing frequency follows risk and manufacturer guidance, not one fixed interval for all units.
BDV and DGA answer different questions
Breakdown-voltage testing describes the sample's dielectric strength, whereas dissolved-gas analysis follows trends associated with possible thermal or electrical events. Moisture and acidity add different information about oil condition. A single gas reading is not a complete diagnosis: gas ratios, rate of change, sample history and operating conditions must be considered together. Clean sampling containers and correct identification are essential to reliable results.
Decision checklist
- Transformer identity and sampling date
- Sampling method and clean container
- BDV, moisture and DGA where appropriate
- Trend against earlier samples
Related service
Request technical support →Frequently asked questions
Does low breakdown voltage always mean an internal fault?
No. Sampling quality, moisture and contamination can also affect the result.
Can DGA replace all other oil tests?
No. DGA, BDV, moisture and other measurements answer different questions.
Is the same annual interval right for every unit?
No. Manufacturer guidance, asset criticality and previous findings determine the test plan.
