Customer: Siemens Windpower/ABB
Location: UK

Application: Offshore Wind Turbine Transformers
Highest Voltage: 33kV
Rating: Up to 4MVA

Date: 2010


The Greater Gabbard offshore wind farm is located in the outer Thames estuary in the UK, approximately 14 miles from the coast. It boasts 140 wind turbines in two arrays making it the world’s largest offshore wind farm at the time of commissioning. The installation of the turbines commenced in 2010 and the whole windfarm was operational by September 2012.

Greater Gabbard wind farm

The wind turbine chosen for the project was the Siemens SWT3.6-107, a 3.6MW turbine that incorporated a Midel filled transformer in a transition piece in the tower. This particular design had some specific challenges that lead the designers to choose Midel filled units.

Firstly, cast resin was not suitable because the running temperature was too high and cooling would have been difficult to manage within the designed enclosure. Likewise, a compact high temperature fluid filled design was not appropriate for similar reasons. Finally a standard temperature rise transformer with fluid pumped to a remote cooler in the HV duct was chosen.

The transformers were located in the tower which meant that they could not be filled with mineral oil because it is too flammable for this type of installation. Therefore, Midel was the obvious choice because it is fire safe and environmentally friendly.

The transformers were manufactured by ABB Waterford, who had extensive experience of building Midel distribution transformers, but had not taken on a project such as this before. During the design and installation phase the Midel technical team provided support to ABB, advising on the handling of the fluid and correct impregnation of the solid insulation. Now the transformers are in operation the Midel technical team continue to provide support with DGA interpretation.

As a note of interest Midel transformers were also used for the auxiliary units on the two offshore substations for Greater Gabbard to increase fire safety.

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