Methods for improving the workability of natural ester insulating oils in power transformer applications: A review

• Published in: Electric power systems research 2018-10, Vol.163, p.655-667
• Main Authors: Ab Ghani, Sharin, Muhamad, Nor Asiah, Noorden, Zulkarnain Ahmad, Zainuddin, Hidayat, Abu Bakar, Norazhar, Talib, Mohd Aizam
• Format: Article
• Language: English
• Subjects: Additives; Antioxidants; Construction design; Design modifications; High voltages; Improvement; Insulating oil; Lightning; Low resistance; Lubricants & lubrication; Nanoparticles; Natural ester insulating oil; Organic chemistry; Oxidation; Oxidation resistance; Properties; Transformer; Transformers; Vegetable oils; Vegetable-based oil; Workability
• ISSN: 0378-7796; 1873-2046
• DOI: 10.1016/j.epsr.2017.10.008

[Display omitted] •Problems with NEI oils include low pour points and low oxidation stabilities.•Methods to improve the workability of NEI oils in power transformers are reviewed.•The benefits and challenges of each method are discussed.•The pour points of NEI oils can be depressed using PMMA additives.•The oxidation stabilities of NEI oils can be enhanced by adding antioxidants. Even though natural insulating oils (NEI) oils are environmentally friendly, these oils have not gained widespread use in high-voltage oil-immersed power transformers because of their unfavorable properties such as low pour point, low oxidation stability, low resistance to lightning impulse, and high kinematic viscosity. Hence, much effort has been made to overcome the disadvantages of NEI oils, including the addition of additives, modification of the chemical structure of oils and altering the transformer design to ensure compatibility with the oils. This review article is focused on the methods used to improve the workability of NEI oils in power transformers, namely, (1) depression of the pour point, (2) chemical modifications, (3) changes in the transformer design, (4) addition of nanoparticles, (5) addition of lightning resistance additives, and (6) addition of antioxidants. The benefits and challenges of each method are also discussed. It is believed that this review article offers new insight to scientists and researchers in this field.