Can a bearing be unsuitable because its operating load is too low?

The short answer

Yes. Some bearings require a defined minimum operating load to maintain satisfactory rolling conditions. An oversized or lightly loaded bearing can therefore need review rather than automatically offer better performance. The requirement depends on the bearing, speed, lubricant and actual wind-generator duty.

Consider traction as well as contact pressure

Rolling elements and the cage must accelerate and move through the bearing while lubricant and inertia oppose that motion. With insufficient contact loading, damaging sliding can become a concern under some operating conditions. SKF identifies this mechanism for cylindrical roller bearings. The issue differs from exceeding a maximum rating: reducing force can reduce one demand while making rolling-element motion less satisfactory.

Review the low-load operating states

A generator support may have different loads during startup, light generation, unloaded operation or a factory test. Rotor weight may already provide adequate minimum load in an actual arrangement, but that must be checked from the support reactions rather than assumed. A test without the normal attached rotor can represent a different low-load condition. Neither the turbine kW rating nor the bearing’s large dynamic capacity settles this question.

Request the manufacturer’s minimum-load assessment

Ask the bearing or equipment supplier which minimum-load criterion applies over the intended speed and temperature range, and how the actual assembly meets it. Do not borrow SKF’s numerical factors from a different bearing family or add preload to solve the issue without design approval. No MARSTON bearing selection is inferred here. The useful decision is whether the submitted selection covers both high-load capacity and credible low-load operation of the exact support arrangement. The bearing maker may need the unloaded test duty as well as normal generation duty. A factory assessment with external rotor weight absent can create a low-load state that the installed machine does not encounter.