Can Vegetable Oil Work in HV Transformers?

Application of Vegetable Oil in High-Voltage Power Transformers

Vegetable oil transformers are more environmentally friendly, safer, and longer-lasting compared to mineral oil transformers. As a result, their use is increasing both domestically and internationally. It is estimated that the number of vegetable oil transformers worldwide has already exceeded 2 million.

Among these 2 million units, the vast majority are low-voltage distribution transformers. In China, only one vegetable oil transformer rated at 66 kV or above has been put into grid operation, while the number overseas is relatively higher. Based on discussions with foreign transformer manufacturers, it is estimated that globally, the number of in-service vegetable oil transformers operating at 66 kV and above is likely fewer than 1,000. 

In terms of voltage class, the highest-rated vegetable oil transformer currently in service is a 420 kV unit manufactured by Siemens Germany, which has been operating safely since its commissioning in 2013. Since then, some manufacturers have developed and produced 500 kV vegetable oil transformers, but there are no records of grid connection to date. Additionally, the application of vegetable oil in DC systems is gradually attracting attention, with some research results beginning to be published, although no transformer manufacturers have yet announced related transformer production.

The limited application of vegetable oil in high-voltage transformers is mainly due to the fact that high-voltage transformers present higher technical barriers and greater challenges compared to distribution transformers. This poses challenges not only for transformer manufacturers but also for end-users.

• When applying vegetable oil in high-voltage transformers, its insulation performance under highly non-uniform electric fields must be fully considered, along with its dielectric constant. This requires transformer manufacturers to conduct completely new designs, accompanied by necessary research, development, and verification.

• Compatibility between large transformer components and vegetable oil must be considered—not only material compatibility but also adaptation to the unique insulation properties, oxidation characteristics, and viscosity characteristics of vegetable oil.

• Currently, operational and maintenance experience with vegetable oil power transformers is limited, and international and domestic standards are incomplete. End users also need to accumulate field application data. Close collaboration among transformer manufacturers, users, and vegetable oil producers is essential.

Of course, from an industry perspective, these technical bottlenecks are not insurmountable. The primary reason for the limited number of high-voltage vegetable oil transformers lies more in market dynamics. In many countries, high-voltage transformer replacement is infrequent, resulting in low demand. In contrast, China's vegetable oil and vegetable oil transformer industry is still in its early stages. The large-scale development of vegetable oil power transformers will take time. Zedian (a nickname for the author/editor) boldly predicts that, as time progresses and given China’s position as the world's transformer manufacturing base, China will inevitably become the leading force in the global vegetable oil power transformer market.