Simple introduction to Furan Testing

Furan testing shows the condition of the paper insulation with an oil sample. Over time, the cellulose insulating material will experience degradation. An aromatic compound is produced during this degradation called furan. Testing is performed for five furans:

• 5H2F (5-hydroxymethl – 2-furaldehyde) — oxidation;

• 2FOL (2-furfurol) — high moisture;

• 2FAL (2-furaldehyde) — overheating, old fault;

• 2ACF (2-acetylfuran) — rare, lightning;

• 5M2F (5-methyl – 2-furaldehyde) — local, severe overheat.

Furan results are used to determine an average expected degree of polymerization for the paper in the equipment. The calculated degree of polymerization is used to estimate percentage of solid insulation life remaining inside the transformer.

The amount of 2-furaldehyde in oil is usually the most prominent indicator of paper decomposition, which is figured in the following manner:

1. The solid insulation in a transformer is made up of kraft paper.

2. Kraft paper is made up of cellulose fibers.

3. Cellulose is a polymer formed from glucose molecules.

New kraft paper has an average cellulose polymer chain that is 1,000 glucose molecules to 1,200 glucose molecules long. The manufacturing and transformer drying process breaks down the cellulose. New paper in a new transformer, therefore, has shorter polymer chains—from 800 glucose molecules to 1,000 glucose molecules long.

Over time, there is a natural and steady breakdown of the polymer chains. As the polymer chains get shorter, the mechanical strength of the paper is reduced. The degree of paper polymerization has a direct correlation to the paper’s tensile strength. When the degree of polymerization has fallen to around 200, the paper is so weak that any stress will lead to failure. When the cellulose chain splits and two shorter chains are formed, the breakdown process forces out one or more of the glucose molecules. The breakdown also creates water, carbon monoxide and carbon dioxide. The glucose molecule chemically changes during this event and creates a compound containing a furan ring. Furans are measured in parts per billion. The life of the paper insulation is typically the life of the transformer.