by Hiroko Isaji
In 2011, Japan was hit by a large scaled earthquake off the coast of Tohoku region, which severely damaged its power facilities. In the case of oil-filled & insulated equipment such as transformers, there was a significant amount of oil spills and leakage due to the impact of earthquake and post effect. In Japan, areas affected by the earthquake took the lead in introducing natural ester dielectric equipment. However, in the 10 years of “post-earthquake in Tohoku and East Japan”, there has been little change. Reasons are that the history of ester-based dielectric fluid has been too short and less than that of Mineral Oil (MO), and there is little track record in field equipment, maintenance technology such as internal abnormality diagnosis of transformer equipment has not been established, and the price is higher than that of MO transformers. In addition, there has been a preconceived notion that natural esters are inferior to mineral oils in long-term stability due to their higher biodegradability.
Transformers installed in TSO and DSO substations in Japan are generally operated at a load factor of about 50%, so the internal temperature is relatively low. As a result, the progress of thermal deterioration of the transformer’s internal insulation is gradual, enabling operation beyond 30-year design life of the equipment by the transformer manufacturer. The Chubu Electric Power Research and Development Center I work for has been investigating the degree of Transformer deterioration to be removed for many years, and found that most of the transformers, even those that are 50 years old, can still be safely used if they have a sealed structure that does not allow outside air or moisture to enter in. That’s my impression. This is one of the reasons why MO transformers, which have supported a stable supply of electricity for many years, are highly trusted. We additionally, believe that one aspect of sustainability is the concept of long-term use with proper maintenance.
Transformers installed in TSO and DSO substations in Japan are generally operated at a load factor of about 50%, so the internal temperature is relatively low. As a result, the progress of thermal deterioration of the transformer’s internal insulation is gradual, enabling operation beyond 30-year design life of the equipment by the transformer manufacturer.
If you ask me if I’m a believer of mineral oil, that’s not the case. In recent years, with the standardization of ester-based dielectric fluids, the interest in ester-based fluids has been increasing. Japanese transformer manufactures are also accelerating the development of ester-based fluid-filled transformers, and are also supporting the carbon-neutral perspective, plus end user’s interest has increasing lately. We have currently been investigating domestic and foreign natural / synthetic ester-based dielectric fluid with long-term use in mind. There are various viewpoints such as the characteristics of each dielectric fluid, deterioration characteristics, compatibility with other materials, maintenance methods (abnormality diagnosis, etc.), economic efficiency, supply chain stability, precautions for use, etc., but what we’ve found most difficult is an evaluation of environmental load. LCA evaluation of transformers is desirable, but there has currently been no clarified standard for the calculation method globally (this is a global scope for the electric power industry, and it seems that a CIGRE WG will be set up though).
For example, there is a possibility that the optimal design of the transformer will differ depending on the type of fluids due to differences in its characteristics at the manufacturing stage of the transformer. Another point is whether the used ester fluids can be reused as dielectric fluids again, recycled as biofuel, or disposed of.
Since electric power companies are not manufacturers, they cannot directly design equipment, but I believe that the impact on society of how users choose equipment based on their opinions is by no means small. We are working hard every day so that our investigations and research can be useful in decision-making for a better future.
About Hiroko Isaji – Four years ago, I was assigned to the research institute in Chubu Electric Power Company, where conduct surveys and research on the themes of utilizing new technology for substation equipment and developing deterioration diagnostic technologies. Before that in my career, was in charge of maintenance, mainly for substation equipment. Although I had knowledge about appearance and functions of transformers, simply knew nothing about the internal structure and material properties of transformers, never thought about ester-based dielectric fluids in my career. In the new work environment, couldn’t keep up with internal discussions with less knowledge and experience, and felt discouraged. However, as I gradually acquire knowledge and come to think and form my own opinions, my interest deepens, and feel that this leads to my own growth as an engineer. Looking back, when I was a student in higher education, cemented the ambitious to work in Electric Power Industry because believed that “Role of energy industry can contribute to build a better global environment as a key factor.” And thought that “I’m working on that theme, which will lead to a reduction in the environmental load!” is a great motivation and engine for me to continue. Furthermore, since last year, have been blessed with opportunities to meet wonderful engineers from Japan and overseas, which has been a great stimulus. In particular, the dignified appearance of women who are active in the industry is, so powerful, supple and very dazzling. Like them, I want to become an engineer who can do my best without limiting myself because I am a woman or a mother.