Shell MIDEL 7131 plays an important part in onshore wind applications because it offers advantages over other liquid-filled and dry type options.

A major benefit of using Shell MIDEL 7131 is increased fire safety. The fire point of mineral oil in conventional transformers is approximately 170°C; whereas with Shell MIDEL 7131 it is in excess of 300°C. Shell MIDEL’s fire safety may lead to a reduction in the requirements for additional fire protection.

Shell MIDEL-filled systems are not as susceptible to damage from vibrations and harmonic frequencies as dry-type solutions. Dry-type transformers can also suffer from sensitivity to water, micro-cracks, temperature variations, load fluctuations and pollution. Furthermore, a dry-type transformer cannot be made as compact as a Shell MIDEL 7131 filled system – a challenge where space is limited.

Substations provide the vital link between wind turbines and the electrical grid. As wind farms move further offshore, substations are positioned on purpose-built platforms – offering challenges including transformer fire safety and maintenance costs.

Offshore transformer fires are difficult to combat and could result in the wind farm being shut down. Filling a system with Shell MIDEL 7131 instead of mineral oil increases fire safety because Shell MIDEL 7131 has a much higher fire point (>300°C) and a 100% fire safety record. Furthermore, by specifying Shell MIDEL 7131 has proven possible to design significantly smaller offshore substations, without complicated transformer fire suppression.

In offshore substations a transformer’s performance is just as important as its fire safety. If the transformer fails to withstand the corrosive atmosphere it will need to undergo expensive unplanned maintenance – specifying a fluid such as Shell MIDEL that is extremely robust, oxygen stable and proven to work means greater assurance for operators.

Case Study: Siemens offshore transformer