Ester-Transformer: High performance with increased sustainability

Successful short-circuit test of natural ester filled power transformer at the KEMA test facility in the Netherlands

A power plant in an environmentally critical area

A hydro power plant in an environmentally sensitive area always means a challenge for the power generating company. Eco-friendly natural ester as an insulation fluid in transformers offers clear benefits. When 50-year-old transformers in a hydropower plant in the U.S. needed to be replaced, Siemens was chosen as a supplier because of its expertise in the manufacturing of ester-insulated transformers.

Triple milestone transformer units

To meet the customer’s specific requirements for this project, the Siemens transformer plant in Linz (Austria) designed 14 natural ester-filled power transformers. They are rated at 125 megavolt-amperes (MVA) and have output voltages of either 345 or 230 kilovolts (kV). One of these transformer units has now been successfully tested at the KEMA test facility in the Netherlands and has passed type and routine tests, including a severe short-circuit test.


For Siemens, this single-phase generator-step-up transformer represents three milestones. It is the first 345 kV natural ester-filled generator step-up transformer worldwide, the first 345 kV natural ester-filled power transformer tested at the KEMA test facility and the first 345 kV natural ester-filled power transformer successfully tested for a project in the USA.

Impressive performance with higher eco-friendliness

The added benefit that Siemens Transmission Products can bring is industry leading expertise in designing and manufacturing transformers with alternative insulating fluids. In the case of these milestone transformers, the natural ester insulation fluid not only adds increased fire safety thanks to its higher fire and flash point but also doesn’t pose any environmental risk in the unlikely case of a leak because it is biodegradable.


‘‘Sustainability is important to Siemens and its customers, but foremost to the society in general. This triple milestone is yet another proof that Siemens Transmission Products is always striving to break new grounds together with our customers”, comments Dr. Beatrix Natter, CEO of Siemens Transmission Products.


By producing ester filled transformers, Siemens is contributing to the United Nations Sustainable Development Goals number 7 and number 9: “Ensure access to affordable, reliable, sustainable and modern energy for all” and “Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation”.

Siemens Transmission Products

Transmission products play a vital role in the energy value chain. Siemens Transmission Products offers all key elements including power transformers, gas-insulated and / or air-insulated switchgear and components, individually or bundled, with related engineering. With our global factory network and leading innovations we provide the highest level of quality and reliability to support our customers in achieving their objectives.