Determination of phenol, m-cresol and o-cresol in transformer oil by HPLC method

Paper and mineral transformer oil are the major insulating materials used in transformers. Besides them, various materials are used for insulation or construction purposes like hard paper, laminated wood, rubber, resins, coatings, adhesives and other. These materials are in contact with the oil, due to thermal and electrical stresses they degrade and finally breakdown, producing gaseous, liquid and solid degradation products. The degradation products are partly soluble in the oil and partly excreted in the form of sludge. Some degradation products are characteristic for specific materials, so-called markers, like furans for cellulose, phenol and cresols for phenolic resins. It was confirmed that phenol, m-cresol and o-cresol are not present in new oils and that their presence may indicate degradation of insulation material. Samples of laminated pressboard and laminated wood were exposed to accelerated ageing tests to confirm the origin of phenol, m-cresol and o-cresol in transformer oil.The paper describes the method for determination of phenol, m-cresol and o-cresol in transformer oil by a high performance liquid chromatography (HPLC). Sample preparation by liquid–liquid extraction, compound separation in a single run and detection with a photo diode array detector are also described.Detection of phenol, m-cresol and o-cresol in transformer oil from operating transformers by HPLC technique provides an additional diagnostic tool for assessing normal or abnormal condition of transformer insulation, and presents a complementary technique to dissolved gas analysis.

► Determination of phenol, m-cresol and o-cresol in transformer oil by HPLC.
► LLE–HPLC–DAD method validation.
► Application to real oil samples from operating transformers.
► An additional diagnostic tool for assessing the condition of transformer insulation.