The sustainable reduction of greenhouse gases and the phase-out of fossil fuels are among the most urgent tasks of our time. This applies in particular to the energy sector, where renewable energies and ecologically safe materials are being increasingly used. This applies not only to energy generation itself, but also to the systems and components used for energy transmission. More and more energy suppliers and transformer manufacturers are using alternative insulating liquids in place of mineral oils in transformers and tap-changers.
„Green oils“ – insulating liquids for a reduced carbon footprint
Mineral oils are still the standard in transformers and tap-changers. But there are more sustainable alternatives. Rainer Frotscher, an expert in insulating fluids, explains what is important.
„Green oils“ – insulating liquids for a reduced carbon footprint
Mineral oils are still the standard in transformers and tap-changers. But there are more sustainable alternatives. Rainer Frotscher, an expert in insulating fluids, explains what is important.
For decades, mineral oils have been the standard for insulating liquids in transformers, tap-changers, and other oil-filled energy technology equipment. Now, people in the industry are increasingly looking for alternatives. What are the actual reasons for opposing the use of mineral oils?
Technically speaking, mineral oils have favorable properties that are required for the safe operation of transformers, tap-changers, and other equipment, such as their electrical insulating ability, cooling ability, arc-extinguishing capacity, lubricity, viscosity, and material compatibility. They are also comparatively inexpensive. A major disadvantage, however, is their high flammability and risks to soil and water protection. Considering the scarcity of oil reserves, mineral oils are also at odds with today's efforts to design and operate energy systems sustainably. Fire safety, eco-friendliness and conservation of limited resources are criteria that are gaining more and more importance.
Can you explain this using specific examples?
Global decarbonization is urgently necessary to curb climate change. For energy supply systems, this means increased use of renewable energies and the decentralization of energy production. In other words, there will be more and more small, distributed power plants and transformers, often installed in ecologically sensitive areas, such as in watersheds or offshore. At the same time, the demand for electricity is growing globally and concentrating in urban areas. High-voltage lines are being routed into the cities, meaning that power transformers need to be installed directly in the urban environment. It is especially important here to fill the equipment with biodegradable and/or flame-retardant liquids.
Environmentally friendly often means higher costs. Are sustainable oils not significantly more expensive than mineral oil-based insulating liquids?
The acquisition costs for transformers and tap-changers filled with alternative liquids are moderately higher in comparison. These added costs are quickly compensated for, however, when you consider the mentioned advantages in lifecycle costs. Greater fire and explosion safety, for example, means fewer restrictions for operation, fewer protective measures, lower insurance costs. This is precisely how improved environmental sustainability can reduce costs, as cost-intensive measures, such as building oil catch basins, for example, are no longer necessary. Tap-changers with vacuum technology enable longer maintenance intervals, which also reduces the operating and maintenance costs.
What sustainable alternatives to mineral insulating oil are available today?
In past years, a whole range of different alternative insulating liquids has been developed. Biodegradable liquids are particularly relevant to transformers and tap-changers. These can be bio-based hydrocarbons or natural and synthetic ester fluids. There are also silicone oils, which, while flame-retardant and extremely stable, are difficult to dispose of.
Not all liquids are equally well-suited for use in tap-changers. The bio-based hydrocarbons currently available are highly fluid. This gives them improved cooling ability and excellent flow properties in the cold, but they are worse at lubricating the mechanical moving parts of a tap-changer than mineral oil. The more viscous ester fluids, on the other hand, are excellent at lubrication. However, they exhibit different dielectric breakdown behavior compared to mineral oil under certain conditions, which must be considered when designing insulating lines.
„Our tap-changers with alternative insulating liquids have been proven in hundreds of uses in the field.“
Which specific insulating liquids do you recommend?
That depends on the respective application. As I mentioned, tap-changers have complex requirements for insulating liquids due to their technical characteristics – and depending on the application, different insulating liquids will be differently suited. For example, it is important to clarify here which tap-changer technology is to be used: oil or vacuum technology? What are the exact conditions of use? What are the electrical, mechanical, and thermal requirements? As a rule, tap-changers with vacuum technology are better suited for use with alternative liquids than tap-changers with oil switching technology, primarily because arcs are extinguished within hermetically sealed vacuum interrupters. The surrounding insulating liquid therefore has no effect on the switching capacity, is not pyrolyzed and thus ages more slowly. This allows maintenance intervals to be extended to up to 600,000 tap-change operations.
Sounds like a complex task. How does MR support its customers in finding the right solution?
The operator of the regulating transformer generally specifies a certain insulating liquid. We then check whether it can be used with the desired tap-changer type, or we select an appropriate tap-changer and configure it accordingly. Every solution is tailored precisely to the respective requirement, making it almost unique. Our tap-changers with alternative insulating liquids have been proven in hundreds of uses in the field – including special applications, such as traction transformers, test field transformers, transformers for offshore wind parks or mobile emergency transformers. We not only support our customers in the system configuration, but also accompany them over the entire lifecycle, from the design phase, installation and commissioning, operation, and service to modernization.
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Detailed information on alternative insulating liquids can be found in our technical publication.
- Flame resistant insulating liquids
- Requirements for liquids and suitable tap changers
- Configuration of adjustable power transformers
