Why Does FR3® Natural Ester Fluid Generate Ethane?

This article is Part 2 of a two-part series on FR3 natural ester dielectric fluid. Part 1 addressed what FR3 is, how it compares to mineral oil, and the key properties that make it advantageous for transformer applications. Here we will address the causes of ethane generation in FR3 fluid, how to distinguish stray gassing from fault indicators, and SDMyers’ diagnostic and monitoring protocols.

Natural ester-filled transformers — particularly those containing FR3 fluid — are known to generate ethane, and sometimes hydrogen, as stray gases under normal operating temperatures. While this behavior is not universal, it occurs frequently enough that it does not, on its own, constitute an abnormal DGA result. The challenge for asset managers and diagnostic engineers is determining whether detected ethane represents benign stray gassing or the early signature of an electrical fault.

Ethane Generation in FR3: Normal or Not?

FR3 fluid has a documented tendency to produce ethane and, in some cases, hydrogen under temperatures consistent with standard transformer operation. This distinguishes it from mineral oil, where ethane generation at low concentrations would more reliably indicate thermal activity.

Because this behavior is characteristic of the fluid — not necessarily the transformer — elevated ethane alone should not trigger an automatic fault determination. That said, the absence of a fault does not mean the result should go uninvestigated. SDMyers treats any ethane detection as a data point requiring context, not a conclusion in itself.

How SDMyers Evaluates Elevated Ethane

Initial Detection: Assumed Low-Level Overheating

When ethane is detected in a transformer with no prior history of significant ethane concentration — including new units — SDMyers classifies the result as evidence of low-level overheating and initiates a shortened retest interval. This conservative posture applies even when the transformer is listed as spare or de-energized; all units are treated as operationally significant assets.

Stabilized Ethane at or Below 400 ppm

If the transformer is FR3-filled and ethane has stabilized at 400 ppm or below, SDMyers typically recommends returning to a standard one-year retest interval. However, this recommendation is conditional: all other dissolved gases must also remain stable. A stable ethane reading alongside elevated or rising concentrations of other gases does not support a stray gassing conclusion.

When Other Gases Change the Diagnosis

The presence of methane, ethylene, or acetylene alongside ethane shifts the diagnostic picture significantly. These gases — particularly ethylene and acetylene — are associated with active thermal and electrical faults, respectively. Their presence indicates that the transformer is not simply generating stray gas; it is exhibiting signs of active overheating or arcing.

In these cases, stray gassing cannot be the working hypothesis, and a more aggressive investigation protocol is warranted. The full dissolved gas profile must be evaluated in combination, not gas by gas in isolation.

Further Testing and Diagnostic Protocol

When ethane is detected, SDMyers conducts additional testing to determine the root cause before issuing a final assessment. This approach reflects the dual priorities of asset protection and continuity of power — both of which depend on accurate, evidence-based diagnosis rather than reflexive alarm or dismissal.

The goal of further testing is to establish whether the ethane is being generated as a function of the fluid’s chemistry under normal conditions, or whether it is co-occurring with fault gases that indicate an actionable problem.

Summary:

• FR3 fluid characteristics: Natural ester fluids like FR3 can generate ethane and hydrogen at normal operating temperatures — a behavior that is fluid-specific and does not automatically indicate a fault.
• Context is required: Ethane detection triggers further investigation, not an immediate fault classification; the full DGA profile must be evaluated before drawing conclusions.
• New or historically clean units: First-time ethane detection is treated as evidence of low-level overheating and prompts a shortened retest interval, regardless of the unit’s operational status.
• Stabilized ethane ≤ 400 ppm: When ethane stabilizes at or below this threshold and all other gases remain stable, a standard one-year retest interval is appropriate.
• Co-occurring fault gases change the assessment: The presence of methane, ethylene, or acetylene alongside ethane indicates active overheating — not stray gassing — and requires a different diagnostic response.
• Reference resource: For detailed dissolved gas interpretation in FR3 fluid, consult the FR3 Dissolved Gas Guide published by Cooper, the original producers of Envirotemp FR3.

In This Series:

• Part 1: What Is FR3 Fluid and Why Is It Used in Transformers?
• Part 2: Why Does FR3 Natural Ester Fluid Generate Ethane?