A turbine generator is a converter-fed machine, so its bearings see the same shaft voltage as an industrial VFD motor — at 500 mm bore. Wind Turbines duty is very long life, oscillating pitch and yaw motion, moisture ingress; the material is what decides whether the bearing survives it.
| Industry duty | combined radial, axial and tilting-moment load over a 20-year life target |
|---|---|
| Typical media | moisture, salt air offshore, old grease |
| Housing temperature | −30 to +60 °C |
| Material and grade | silicon nitride ceramic (hybrid) — Si3N4 |
| Hardness | 1500 HV |
| Temperature ceiling | 800 °C for the balls, rings limit the bearing |
| Corrosion / chemical | none — inert to water, acids and coolant |
| Relative cost | ≈8–15× of a standard 52100 bearing |
The converter on a full-power turbine puts a common-mode voltage on the rotor, and the generator bearing is the path to earth. At the same time, a 500 mm bore running at 1,800 rpm is limited by ball mass. Silicon nitride answers both: it insulates the rotor and it is 60% lighter, so the same bearing runs cooler and faster.
| Position | Bearing type | Material / finish | Why it works there |
|---|---|---|---|
| Generator, non-drive end | Deep groove ball | Si3N4 hybrid, 52100 rings, C3, insulated | Breaks the circulating current path; large bore at speed. |
| High-speed gearbox stage | Angular contact ball | Si3N4, 70xx, paired | Lower ball mass reduces heat at the high-speed pinion. |
| Pitch drive | Deep groove ball | Si3N4 hybrid, sealed | Oscillating motion starves the film; ceramic balls need less lubricant. |
| Material | Fit here | Choose it when |
|---|---|---|
| Si3N4 | Best fit | Converter-fed generators and high-speed stages, with a grounding path at the other end. |
| 100Cr6 / 52100 | Workable alternative | With a grounding ring and a proven grease, steel remains the volume choice. |
| M50 | Workable alternative | Where gearbox oil temperature, not speed, is the limit. |
It stops the current crossing that bearing. The voltage still exists and must have a path — a grounding ring at the other end is the usual solution.
Cost and interference fits. A ceramic ring cannot take the same press fit as steel, and the housing design would have to change.
The grease or oil life usually ends them, not the ceramic. In an oil-lubricated generator they are expected to reach the first major service interval.
Hardness, temperature, corrosion and equivalents for silicon nitride.
Read →Typical duty, recommended types and suffixes for wind energy.
Read →Gearbox & main shaft — gearbox planet and helical stages, main shaft and generator positions.
Read →Yaw & pitch sliding — yaw drive bushes, pitch bearing spacers and blade root sliding surfaces.
Read →Send the position, bore size, quantity and the medium it sees. We reply with the material certificate, clearance class, lubricant and price within 30 minutes on working days.