The TOR-80 breakdown voltage tester is used for this purpose. It provides fully automated and accurate measurement of dielectric strength up to 80 kV according to international standards.

That’s correct. Considering this, it’s important to understand that breakdown voltage testing is not just a one-time measurement, but a key diagnostic solution for assessing transformer reliability over time.
Devices such as the TOR-80 breakdown voltage tester apply a gradually increasing voltage to an oil sample until an electrical discharge occurs, which reflects the dielectric strength of oil — its ability to resist electrical stress without failure. This parameter is highly sensitive to contaminants, including moisture and particles, which significantly reduce insulating performance.
What’s often overlooked is that a single BDV value is less informative than a series of measurements. In practice, multiple breakdown tests are performed on the same sample, and the average result is used to evaluate oil condition. A downward trend over time can indicate progressive contamination or aging —even before the values fall below critical thresholds (typically around 30 kV for in-service oil).
Furthermore, BDV testing is crucial for maintenance decisions. It helps determine whether oil requires filtration, dehydration, or full regeneration, which makes it a practical solution not only for diagnostic evaluation, but also for planning corrective actions.
If you want to better understand the testing procedure, the key influencing factors, and how to interpret the results in real operating conditions, I recommend reviewing this article: https://globecore.com/oil-testing/transformer-oil-breakdown-voltage-measurements/.

You’re correct — breakdown voltage (BDV) is best used as a trend diagnostic rather than a single-pass pass/fail number. Standards such as IEC 60156 and ASTM D877/D1816 define the test geometry, temperature control and voltage ramping so results are comparable; in practice labs run multiple breakdown tests on the same sample (commonly 5–6 measurements) and use the averaged value to assess dielectric strength and track changes over time. Typical test parameters used in routine monitoring include a 2.5 mm electrode gap and a controlled voltage rise rate (many labs use ~2 kV/s), but follow the chosen standard or your company procedure for exact settings.

For reliable, actionable BDV data pay attention to sample handling and test conditions: keep oil temperature controlled, avoid entrained gas and particulate contamination, degas or filter samples if required for repeatability, clean electrodes between runs, and allow proper high‑voltage discharge recovery. Use a tester that logs and exports results so you can build trend charts; a sustained downward trend or values approaching service thresholds (roughly ~30 kV for many in‑service oils) indicates the need for corrective maintenance such as filtration, dehydration or full regeneration. Equipment like the TOR‑80 supports standard procedures, adjustable ramp rates and result reporting, which makes it straightforward to automate repeated measurements and base maintenance decisions on statistically meaningful BDV trends.