Wind Turbine Main Bearing Life Calculator

L10 is the life that 90% of identical bearings reach under the same load and speed before the first sign of fatigue — equivalently, a 10% failure probability. Median life is roughly 5× L10. It is a statistical fatigue life, not a guarantee for any single bearing.

Because the failure mode often isn't classical rolling-contact fatigue. Low speed means a thin lubricant film; load zones shift with every gust and yaw event; idling periods let rollers skid (smearing). These produce micropitting and wear that ISO 281 doesn't model. Grease sampling for wear metals and regular borescope checks of the load zone catch what the life equation cannot.

C (basic dynamic load rating) is printed in every bearing datasheet — for example a large spherical/taper main bearing (C in the MN range) on a multi-MW main shaft at ~14 rpm. P is the equivalent dynamic load: for pure radial load it is simply the radial force; with combined radial + axial load use P = X·Fr + Y·Fa with X and Y from the datasheet.

Because L10 assumes clean lubricant, correct fit and alignment. In practice most bearings die of lubrication failure, contamination, misalignment or fitting damage rather than fatigue. If yours fail early, check the actual load path and the grease before blaming the bearing.

Use p = 3 for ball bearings and p = 10/3 for roller bearings (cylindrical, spherical, taper). Rollers carry load on a line contact rather than a point, so their life is less sensitive to load — that is what the higher exponent encodes.