Recently, China's first 220-kilovolt hybrid insulation oil transformer was successfully put into operation at the 220-kilovolt Tianjia Substation of State Grid Chongqing Bishan Power Supply Company. The successful operation of this transformer marks a major breakthrough in the application of hybrid insulation oil technology at the 220-kilovolt voltage level, promoting the transformation and upgrading of China's power equipment towards a green and low-carbon direction. 

"Blended oil" enhances the reliability of power transformers 

For a long time, traditional power transformers have relied on pure mineral oil as the insulating medium, which has drawbacks such as insufficient heat resistance and rapid aging. Compared with traditional mineral oil, hybrid insulating oil combines the stability of mineral oil with the antioxidant properties of vegetable oil, and has superior performance in terms of breakdown voltage, flash point, acid value, and heat dissipation. The thermal aging rate of insulating paper in hybrid insulating oil is low, and its lifespan is 1.91 times that of insulating paper in mineral insulating oil, effectively enhancing equipment reliability and extending service life. 

The development of hybrid insulating oil is no easy task. The biggest challenge lies in how to ensure that vegetable oil and mineral oil can coexist stably for a long time while both electrical and physical properties meet the national standard GB 2536-2011. Professor Hao Jian, a doctoral supervisor at Chongqing University, introduced that in the past decade, the team has conducted hundreds of formula adjustments and accelerated aging tests. Eventually, the team successfully broke through key technical bottlenecks such as the modification of high-proportion vegetable insulating oil and the performance control of hybrid insulating oil products, and innovatively solved the compatibility problem at the molecular level of hybrid insulating oil. 

The team has developed a mixed insulating oil formula of "60% mineral oil + 40% vegetable oil", whose electrical, physical and chemical properties fully comply with the national standard GB 2536-2011, and its key indicators are significantly better than those of traditional mineral insulating oil. The life assessment based on laboratory methods such as IEC 60296 shows that this mixed insulating oil can significantly extend the life of oil-paper insulation systems. 

In addition, this hybrid insulating oil overcomes the drawback that pure vegetable oil filling often requires the modification of the transformer shell structure. It can be directly used for the replacement of existing mineral oil transformers without any alterations to the internal structure of the transformer, significantly lowering the application threshold and transformation costs. 

Technical support ensures the application of laboratory achievements. 

To ensure that research achievements smoothly transition from the laboratory to the complex and demanding power grid field, the technical team of State Grid Chongqing Electric Power Research Institute has played a crucial "bridge" and "escort" role. 

To transform the "bonsai" in the laboratory into the "forest" of the power grid and apply it to 220-kilovolt large transformers, we must solve a series of problems such as engineering-scale amplification, long-term reliability verification, and on-site construction techniques. Liu Xiong, deputy director of the Equipment Condition Evaluation Center of State Grid Chongqing Electric Power Research Institute, introduced that in the previous grid operation of 10-kilovolt to 110-kilovolt transformers, the team established a detailed online monitoring and regular assessment system, accumulating tens of thousands of hours of key operation data. These first-hand data have proved the excellent performance and stability of the hybrid insulating oil in actual operating environments, completely eliminating concerns about engineering applications and paving the way for its application in 220-kilovolt grades. 

The team from State Grid Chongqing Electric Power Research Institute was deeply involved in the engineering verification of the previous achievements and took the lead in formulating a complete set of core process specifications and technical standards for the production, replacement, and testing of hybrid insulating oil transformers. Chen Zhengyu, the on-site technical director of State Grid Chongqing Electric Power Research Institute, said, "The application of hybrid insulating oil in 220-kilovolt voltage levels allows no room for error. We relied on a strict on-site supervision system to strictly control key process nodes such as the selection of core materials, the purification treatment accuracy of hybrid insulating oil, the maintenance of ultimate vacuum degree during vacuum oil injection, and the temperature and time control of hot oil circulation. At the same time, we optimized the construction process, for instance, by adopting innovative methods such as staged vacuuming and stepwise temperature increase, ensuring that the construction quality was first-class in one go and enabling the successful one-time operation of this 220-kilovolt transformer, which was the first to apply hybrid insulating oil." 

A relevant official from State Grid Chongqing Electric Power Company stated that in the future, they will continue to deepen research on hybrid insulating oil technology, actively take the lead in formulating relevant industry technical standards, and continuously promote the application of the technology. They will focus on promoting the large-scale application and promotion of hybrid insulating oil technology in transformers of 220 kV and below voltage levels, contributing to the low-carbon transformation of China's power equipment and its leap to the high end of the industrial chain.