Transformer Oil Furan Testing

What Is Furan Testing?

Furan testing is an oil analysis used to evaluate the condition of the paper insulation inside an oil-filled transformer. While oil can be replaced or processed, the paper wrapped around the transformer windings cannot be easily inspected or replaced. Its condition is therefore an important factor in determining the transformer’s overall health and remaining service life.

What Are Furans?

Furans are chemical compounds produced when cellulose-based materials, including transformer paper and pressboard insulation, begin to deteriorate. This deterioration can be accelerated by heat, moisture, oxygen, acids, normal aging, and electrical or thermal faults.

As the paper insulation breaks down, furanic compounds migrate into the transformer oil. Measuring these compounds provides a practical, non-invasive way to assess the condition of the internal paper insulation without opening or de-energizing the transformer to obtain a physical paper sample.

Why Is Furan Testing Important?

Paper insulation provides both electrical insulation and mechanical strength within a transformer. As it deteriorates, it becomes weaker and more brittle, increasing the risk that the transformer may not withstand electrical, thermal, or mechanical stress.

Furan testing can help asset owners:

• Identify deterioration of cellulose insulation
• Evaluate aging trends over time
• Detect unusual or accelerated paper degradation
• Estimate the condition and remaining life of the insulation
• Make more informed maintenance and replacement decisions

Results are most valuable when compared with previous samples. A rising furan concentration may be more significant than a single isolated result, which is why routine transformer oil testing and trending are important. Furan analysis also complements dissolved gas analysis (DGA), fluid quality testing, loading history, and other transformer condition data.

How Is Furan Testing Performed?

A transformer oil sample is collected and sent to the laboratory for analysis. MVA tests the sample for specific furanic compounds using high-performance liquid chromatography, commonly called HPLC. This process separates, identifies, and measures the compounds present in the insulating oil.

The most commonly monitored compound is 2-furaldehyde, also known as 2FAL, because it is closely associated with the degradation of cellulose insulation. The concentration of 2FAL can be used with other transformer information to help estimate the paper’s degree of polymerization, or DP, a measure of its remaining mechanical strength.

Furan testing is performed in accordance with ASTM D5837, which covers the measurement of furanic compounds produced by the degradation of cellulose-based electrical insulation.

Understanding Cellulose Insulation Degradation

The main component of transformer insulation paper is cellulose, a natural polymer made from glucose. Over time, heat, moisture, oxygen, and acids can break apart its molecular chains through a process called depolymerization. This process reduces the paper’s mechanical strength and produces degradation compounds that can be detected in the transformer oil.