Unlocked by Ergon: Insulating liquids test – lesson #6: Breakdown voltage tests

The topic of the sixth lesson are:

• Breakdown voltage tests, history, methods, procedures, and clarifications

This lesson focuses on the breakdown voltage (BDV) test as one of the most fundamental and widely used diagnostics for insulating liquids in transformers. The instructor, Marius Grisaru, explains why BDV is the first test performed on transformer oil, how it links directly to dielectric strength and insulation reliability, and why it is extremely sensitive to moisture, particles, temperature, and oil flow.

The session provides a structured overview of the main international standards (ASTM D877, ASTM D1816, IEC 60156), clarifying their different test geometries, voltage rise rates, stirring practices, and typical application ranges. Participants learn how the choice of method affects sensitivity to contamination and how to select the most appropriate standard for new oils versus in-service diagnostics.

A significant part of the lesson is dedicated to practical execution: preparation and cleaning of electrodes, accurate gap setting, correct filling of the test cell, instrument setup, and common pitfalls that can produce misleadingly low or falsely reassuring results. The lesson then goes beyond basic test practice to explore the statistical nature of BDV, the influence of temperature and moisture, volume and electrode geometry effects, and the limitations of laboratory tests compared with real transformer operating conditions (flow, thermal gradients, static charge, and weakest-link behaviour).

Throughout, the emphasis is on using BDV as an early warning and trending tool, always interpreted together with other tests, rather than as a stand-alone pass/fail criterion.

Content of this lesson is fully vendor agnostic, but it is sponsored by Ergon!