Tips for Diagnosing Oil Filled Electrical Equipment

Responding to an emergency call regarding any type of oil filled equipment, can be a challenge. A major challenge to diagnosing an issue, is you can’t use your primary sense of vision, to see what happened. Electrical faults are typically contained within an oil filled transformer or breaker, provided the overcurrent protection was set up properly.

There may not be any visual signs of damage when looking at the outside of the equipment. You have to rely on your other senses to help diagnose the issue. But if you aren’t taught what to look for, you may be facing a different type of challenge. I am here to help give you tips on what you can look for.

My Transformer Faulted, What Now?!

When responding to a faulted oil filled transformer emergency call, the first thing you should do is follow your Lockout/Tagout procedures. The second would be to take oil samples; a general sample and a dissolved gas analysis sample.

The typical oil colors are as follows:

  • New Mineral Oil: almost clear, but a hint of yellow;
  • Old Mineral Oil: more distinguished yellow;
  • RTEMP: a darkish caramel color with the consistency of molasses;
  • Silicone: clear;
  • Biodegrade (Envirotemp, FR3, etc.): green or greenish hue.

They all have one thing in common! When an oil filled transformer fails/faults within the tank, the oil turns Black! They all have an aroma of burnt paper or a carbon smell. When these oils haven’t been subjected to a fault, they have unique aromas.

In the future, use your sense of smell to familiarize yourself with the scents. Side note, PCB’s have a unique scent as well!

FR3/Envirotemp – Greenish in color

FR3/Envirotemp Oil Sample


Silicone Oil – Clear

Silicone oil sample


Faulted Silicone Oil – Carbon is present

Faulted silicone oil example


Dissolved Gas Analysis Sample – Silicone Oil

Dissolved Gas Analysis Sample - Silicone Oil


Silicone Oil Dissolved Gas Analysis

Silicone Oil Dissolved Gas Analysis


RTEMP – Dark caramel color

RTEMP General oil sample


Dissolved Gas Analysis – RTEMP Oil

Dissolved Gas Analysis - RTEMP Oil


For more information about transformer oil samples, refer to this article.

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