By Ronald R. Hill and Zachary C. Patterson

Although traditional naphthenic oils have provided generally acceptable properties for transformer oils, tests have proven that an oil with a higher paraffinic carbon content can deliver improved performance and extended transformer life.

The composition of transformer oils, in particular the balance between naphthenic, paraffinic, and aromatic carbon contents, can play an important role in determining the performance and lifespan of transformers. Although traditional naphthenic oils have provided generally acceptable properties for transformer oils, tests have proven that an oil with a higher paraffinic carbon content can deliver improved performance and extended transformer life.

This article highlights the key properties of transformer oils with different chemical compositions and the tests that were undertaken in determining if oils with a higher paraffinic carbon content can deliver enhanced performance versus those with a higher naphthenic carbon content. These key properties include: 

• Oxidation stability which can affect transformer lifespan.
• Gassing tendency which can influence the ability of an oil to adsorb gas under partial discharge conditions.
• Aromatics content which can contribute to SHE benefits and negative gassing tendency.
• Low-temperature viscosities which can impact cold temperature operability.
• Heat transfer capabilities which can determine transformer loadings and size.
• Material compatibility which can affect leak prevention.

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