Typically, a qualified testing firm handles periodic testing of transformers. While this firm should lead in designing a good testing program, make sure you know enough about the tests to ensure they fit your actual situation.

A laboratory analysis of transformer oil tells you much about the condition of the transformer. The lab provides an analysis based on several characteristics, usually including:

  • Acidity (ASTM-D974)
  • Color (ASTM-D1500)
  • Dielectric strength (ASTM-D877)
  • Interfacial tension (ASTM-D971)
  • Water content (ASTM-D1533)

The person taking the sample should record the date, time, asset number, and oil temperature. To understand what the results mean, see ANSI/IEEE C57 .106, “IEEE Guide for Acceptance and Maintenance of Insulating Oil in Equipment.”

Improper collection can make the results misleading. ASTM-D923 describes the techniques for proper oil sample collection.