Small wind / Buyer questions
Mechanical interfaces
Are bearing reference speed and limiting speed interchangeable?
The short answer
No. A thermal reference speed and a limiting speed describe different bases. The former uses defined reference heat-balance conditions; limiting values can reflect lubrication or mechanical restrictions. A wind-generator bearing must satisfy the applicable operating constraints, rather than select the largest rpm printed in a catalogue.
Read the label beside each speed
NSK separates grease/oil limiting speeds, thermal reference speed and mechanical limiting speed. The heat generated and removed under reference conditions does not represent every housing, lubricant quantity or external heat source. A mechanical limiting value also does not guarantee satisfactory temperature in a poorly cooled assembly. These definitions explain why several speeds can legitimately appear for one bearing without being contradictory.
Compare the actual operating environment
Identify speed range, load, lubricant method, seals, cage, temperature and heat paths through the shaft and housing. A changed seal or cage can alter restrictions even when envelope dimensions remain identical. A brief factory run below one listed limit is not a thermal equilibrium assessment. Conversely, a low reference value cannot be interpreted without the maker’s permitted adjustment method and the actual installation conditions.
Request the governing speed assessment
Ask the equipment supplier which speed quantity governs the selected bearing and how the real application satisfies it. Require the precise designation and any manufacturer-approved correction or thermal calculation. NSK’s labels do not establish MARSTON rotational speed or permission to exceed any stated rating. Do not treat a thermal reference speed as a protection setting or copy a mechanical limit into a controller. The immediate selection decision needs the catalogue meaning and actual operating assumptions together. Where seals or lubrication method change, ask whether the speed data sheet remains applicable to that exact variant. Reusing the basic bearing’s largest speed label can conceal the restriction introduced by the proposed construction.
Sources
Examples are illustrative. Confirm product-specific performance, compatibility and supply scope in the applicable documents.