This is a correct and very reasonable approach. In practice, the transformer manufacturer’s instructions and local national standards always have priority, because they reflect design limits, warranty conditions, and regulatory requirements. Any oil treatment or monitoring program should first comply with those documents. At the same time, GlobeCore’s recommendation to perform a test once per month is well aligned with common utility practice for critical units, because monthly trends allow early detection of moisture or gas growth without excessive sampling. The key is consistency: regular testing under the same conditions is often more valuable than the exact interval itself.

Beyond defining the testing frequency, it is important to focus on the value of tracking the breakdown voltage trend over time. A single BDV result provides information about the current condition of the insulating oil, but a series of measurements performed under comparable conditions can reveal gradual deterioration caused by moisture ingress, contamination, aging products, or improper storage and handling.
For reliable diagnostics, the sampling procedure, test cell preparation, electrode condition, and measurement parameters should be kept consistent, as these factors can significantly affect the obtained results. Modern portable breakdown voltage testers allow maintenance teams to perform regular field measurements and quickly evaluate whether oil quality remains within acceptable limits or if additional treatment is required.
The TOR-80 LSL Breakdown Voltage Tester is designed for this type of routine condition monitoring, providing a practical solution for checking transformer oil dielectric strength directly at the installation site and supporting data-based maintenance decisions.

You’re absolutely right — trend tracking is where BDV testing delivers real diagnostic value. For reliable trends, keep the sampling point and method consistent, avoid contamination or air entrainment during sampling, use the same test cell and electrode condition, and record test parameters (sample temperature, electrode gap and geometry, ramp rate, and whether the oil was prefiltered or degassed). Calibrate and clean electrodes regularly and log results in a local database so you can apply simple statistical control limits; a steady decline in dielectric strength often precedes other indications of moisture ingress, ageing or contamination and justifies follow‑up analyses such as water content, interfacial tension or dissolved gas testing.

Portable TOR-series testers are well suited to routine field monitoring because they support standardized procedures, on‑site measurements and data export for trend analysis, enabling maintenance teams to make data‑based decisions quickly. Tailor the sampling frequency to asset criticality — monthly for high‑risk or newly serviced units and quarterly or biannually for stable, noncritical equipment — and always interpret BDV trends together with complementary oil diagnostics before committing to oil treatment or outage planning.