When Should Furanic Compound Testing Be Routine?

This is Part 4 of a seven-part series on furanic compounds in transformers. Part 3 covered when to run a furans test and how to act on the results. Here we will look at situations where it makes sense to run furans as a routine test. In Part 5, we will examine what furanic compound concentrations are considered significant and how to interpret those levels diagnostically.

Routine vs. Non-Routine Furans Testing

In Part 3, we covered three situations where furanic compound analysis is warranted on a non-routine basis: establishing a baseline, following up on abnormal DGA results, and monitoring at a shortened interval when active degradation is suspected. Each of those scenarios is triggered by a specific condition or diagnostic need.

There are also situations where waiting for an abnormal result before testing is not the right approach — where the value of the information, or the limitations of other diagnostic methods, justifies including furans analysis at every routine sampling and testing interval.

High-Value and Critical Transformers

For large, expensive, or operationally critical oil-filled transformers, the standard reactive testing sequence may introduce an unacceptable diagnostic gap. If dissolved gas analysis is performed routinely and furans are only added when DGA results turn abnormal, there is an inherent delay between the onset of solid insulation degradation and its detection.

The Cost of a Diagnostic Time Lag

For most transformers, that delay is a manageable trade-off. For critical assets — where the cost of unexpected failure, extended outage, or loss of insulation life significantly outweighs the cost of the test itself — it is not. In these cases, including furanic compound analysis as a routine test eliminates the lag and provides continuous visibility into solid insulation condition.

Silicone Fluid-Filled Equipment

The second scenario involves transformers insulated with silicone fluid rather than mineral oil. Silicone fluid undergoes limited thermal degradation under normal operating conditions, which does not materially affect its performance as an insulating medium. However, that degradation produces carbon monoxide and carbon dioxide as byproducts.

Why Carbon Oxide Interference Limits DGA

In mineral oil-filled equipment, elevated carbon monoxide is a recognized indicator of cellulose degradation and a standard trigger for furans follow-up. In silicone fluid-filled equipment, the fluid itself generates carbon oxides during normal operation. This background generation reduces the diagnostic value of CO as a marker for solid insulation breakdown — the signal is obscured by the noise.

Routine Furans Testing as a Workaround

Because DGA carbon oxide data is less reliable for monitoring solid insulation in silicone fluid-filled equipment, furanic compound analysis takes on a greater diagnostic role. With the exception of very small distribution-class silicone fluid-filled transformers, furans analysis is recommended at every routine sampling interval to maintain accurate visibility into the condition of the solid insulation.

Summary:

Two conditions support including furans analysis in every routine test interval rather than reserving it for triggered follow-up:

• Critical or high-value assets where the cost of a diagnostic time lag — in terms of potential insulation life loss or failure risk — exceeds the incremental cost of routine testing.
• Silicone fluid-filled equipment where carbon oxide generation by the fluid itself limits the reliability of DGA as a solid insulation monitor.

In This Series:

• Part 1: What Are Furanic Compounds and How Do They Form in Transformers?
• Part 2: How Do Furanic Compounds Indicate Active Paper Degradation in Transformers?
• Part 3: When Should You Test for Furanic Compounds in Transformer Oil?
• Part 4: When Should Furanic Compound Testing Be Routine?
• Part 5: What Furanic Compound Levels Are Diagnostically Significant?
• Part 6: How Are DP and Insulation Life Estimated from Furans Data?
• Part 7: How Does Oil Processing Affect Furanic Compound Results?