World's largest transformer with plant-oil-based insulating liquid commissioned

TransnetBW GmbH has recently commissioned the world's largest transformer using plant-oil-based insulating oil at its new substation in Bruchsal. In doing so, the company is relying on an innovative technology with considerable benefits for environmental and fire protection. The plant-oil-based insulating material is biodegradable, yet allows for very high operating temperatures.

The transformer, which was developed and manufactured by Siemens in Nuremberg, has an output of 300 MVA. A VACUTAP® VR® on-load tap-changer from Maschinenfabrik Reinhausen (MR) is being used for voltage regulation. The new transformer connects the 380 kV high voltage level to the 110 kV network in the lower-level distribution network operator.

Benefits of vacuum technology with alternative insulating liquids
The almost maintenance-free vacuum interrupter technology is particularly well suited for alternative insulating liquids because switching arcs are enclosed completely within the hermetically sealed vacuum interrupters. Plant-based oils and natural esters must be protected from permanent contact with atmospheric oxygen to prevent negative changes (oxidation & esterification). To avoid this kind of oil aging process, suitable measures were implemented so that both the transformer and the tap changer can be regarded as units hermetically sealed off from ambient air. The absence of oil aging and the use of vacuum switching technology result in considerably longer OLTC maintenance intervals of up to 600,000 switching operations as well as reduced operating costs and increased transformer availability. In most cases, the tap-changer oil no longer needs to be replaced during the entire lifespan of the transformer, meaning that waste oil is also no longer produced.

“At TransnetBW, we see plant-oil-based insulating oil as the technology of the future. It combines technical benefits with outstanding environmental sustainability and is based on renewable raw materials,” explains Michael Schäfer, manager of network projects at TransnetBW. “Furthermore, we are expecting raw material problems with mineral oils in the future that could have a negative impact on the quality of the oils. That is another reason why the importance of insulating liquids made of plant oils will increase.”

The transformer in the Bruchsal substation is a key component of the environmental strategy of the Baden-Wuerttemberg transmission grid operator. The machine weighs approximately 400 metric tons, consists of approx. 50,000 individual parts and holds 100,000 liters of plant-based insulating oil. Together with manufacturer Siemens, TransnetBW will regularly perform tests over several years to monitor the quality and material properties of the oil.

Configuring regulated power transformers for alternative insulating liquids
Due to the many diverse configuration options available, OLTC applications using alternative liquids require special attention. Therefore, the individual operating conditions of every application must be fully discussed between transformer manufacturer and tap-changer manufacturer. Through its globally unique expertise in regard to alternative insulating liquids, MR offers customers in-depth consulting services which ensure well-designed and safely operating OLTC applications. With over 200 OLTC installations using alternative liquids in operation worldwide, including special applications such as traction transformers, test-field transformers and transformers for off-shore wind parks or desert mining facilities, MR has a unique range of experience to draw from. For first-time applications, our service team will also supervise the commissioning of the tap changer and monitor initial operation, if requested.