Enercon E-126 7.5MW still world's biggest

WORLDWIDE: Despite being launched five years ago, the second-generation Enercon EUR126 7.5MW wind turbine is still the largest in the world. The turbine's history dates back to August 2002 with the 4.5MW E-112 direct drive.

The E-112 was upgraded to 6MW in 2005 and 10 4.5/6MW turbines were installed in total. As of last month, 34 E-126 units are operational. The initial 6MW second-generation Enercon E-126 introduced in 2007 featured a concrete tower with a 135-metre hub height, and segmented steel-composite hybrid blades with a 127-metre rotor diameter.

Each E-126 tower consists of thirty-five tapering concrete rings and one steel yaw bearing connector. The tower foot diameter measures 14.5 metres and narrows to 4.1 metres on top. The bottom rings are manufactured in 120-degree sections for transport-logistical reasons. Smaller diameter rings comprise 180-degree halves, and the upper rings a full circle. All elements are post-tensioned with steel cables passing through holes in the concrete tower wall.

A box type structure inside the tower base contains four modular medium-voltage transformers and switchgear cabinets. The modular design enables continued operation at reduced output level after module failure.

Enercon turbines operate at 400V AC-voltage. This is converted to DC inside the nacelle and fed down the tower into several cabinets with in-house manufactured 300kW inverters at the tower base first floor. Here the DC-power is converted again into grid compliant AC-power to feed into the transformers.

Outside the carrier a platform provides access to twelve yaw motor drives and a 12-metre generator. The stator is electrically subdivided into four 90-degree generator sections and each section feeds power into a separate rectifier box, two on the left and two on the right.

Up until around 5MW output the generator relies on natural air-cooling. Air is pulled through the generator and leaves the nacelle again enabled by a circular gap between the rotating spinner and by the nacelle cover.

With increased output, but depending on ambient temperature and other variables, electric fans in the nacelle floor add to the cooling system's performance.

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