Turbines of the year 2019: Drivetrains

Focus shifts to medium-speed geared and direct-drive solutions.

Conical approach… RWTH Aachen’s alternative to double-row tapered roller bearings
Conical approach… RWTH Aachen’s alternative to double-row tapered roller bearings

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GOLD Conical FlexPad journal bearing

The development of a radical conical journal bearing design for large-scale turbines started around three years ago as a PhD project at Germany’s RWTH Aachen technical university.

This disruptive technology could become a viable alternative for double-row tapered roller bearings while offering the benefits of compactness, low weight, up-tower exchangeability and shorter nacelles.

The main challenge, according to the lead researcher and patent holder, proved to be coping with main-shaft deflections during rotation within the bearing housing.

These movements, resulting from rotor-induced bending moments, are passed on to the shaft, where the negative effects of the tilting would cause fast wear at the bearing edges.

The solution was a segmented bearing composed of multiple flexible pads, FlexPads, made from soft, adaptable surface material bolted to a flexible support structure to ensure uniform load-carrying distribution.

The alignment of parallel pads to the shaft without edge-wear was validated during comprehensive dynamic bench-testing and is now guaranteed under all operating conditions.

Even after 8,000 journal-bearing-critical start-up tests, equivalent to around two fifths of a turbine life, the design showing only minor wear.

The next envisaged step is fitting the bearing unit in a megawatt-class turbine with three-point gearbox suspension, to gain the necessary field experience.

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