To protect the environment, our oil-bearing plants are equipped with oil-impermeable catchment and protection systems and are regularly inspected. Soil and water pollution is thus effectively prevented in the event of an incident at the plant. In environmentally sensitive areas, we have been using Ester-filled transformers during transformer replacements for years. In contrast to mineral oils, Ester is only generally hazardous to water.
Conventional transformers in which mineral oil is used as an insulating and cooling agent are not permitted, for example, in water protection areas or in areas with increased fire protection requirements. EnBW has been investigating the use of transformers in which vegetable oil was used as an insulating agent since 2010. In June 2016, the EnBW subsidiary Netze BW started a major field test in which 102 of its stations in Baden-Württemberg were equipped with "eco-transformers" containing vegetable oil instead of mineral oil. In total, our subsidiary Netze BW operates around 26,500 local network transformers, which convert electricity from medium voltage to the low voltage commonly used in households and businesses.
The major advantages of plant oils are that they are biodegradable and only classified as being “generally hazardous to water.” There are thus ecological advantages to operating a transformer in drinking water protection zones that uses plant oil. In addition, natural esters have a significantly higher flash point than mineral oils. This means that bio-oil transformers can also be installed in difficult conditions with respect to fire protection standards, such as urban areas with high population densities. Plant oils can be produced from renewable raw materials grown in Germany such as rapeseed or sunflowers and could become a cost-efficient alternative to standard insulating materials based on crude oil in the foreseeable future.