Vegetable oil transformer for ultra-high voltages

In the future, the device will link the 380-kV ultra-high voltage level with the 110-kV grid in the Bruchsal-Kändelweg substation plant near Karlsruhe, Germany. Transformers are usually cooled and insulated with mineral or silicone oil.

By comparison, vegetable oils are environmentally friendlier and less flammable. Until now, Siemens has used vegetable oil insulation in power transformers with voltages of up to 123 kilovolts (kV). The new transformer is designed for 420 kV.

A transformer increases or reduces the alternating current level for transporting electricity. Due to the high currents and voltages, it heats up and must be cooled with oil.

Until now, mineral or silicone oil has been used for this purpose. These oils dissipate the heat effectively and provide good insulation against electric sparkover. However, they are harmful to the environment and are highly flammable.

Rapeseed, soy or sunflower oils, on the other hand, are biodegradable and have a much higher flashpoint. A vegetable oil transformer can therefore be operated without additional protective equipment such as collecting tanks, even in zones with strict environmental requirements. With their comparatively better fire safety class, vegetable oil transformers can even be used in densely populated residential areas.

Siemens' new transformer weighs just under 340 tons and contains 100 tons of insulating oil. The oil comes exclusively from renewable vegetable resources. As a result, the device is the world's first power transformer on the 420-kV ultra-high-voltage level that does not require proof of its water hazard classification. TransnetBW, a grid operator in the German state of Baden-Württemberg, will place the environmentally friendly transformer into operation in late July.