Permissible unbalance (imbalance) Calculator - Main bearing Specification

This Calculator should be used as a fall back and worst case scenario.It will simply tell you what Unbalance Level your main bearing is meant to handle and should / will survive in the long term!
 

1. In advance to testing done by third parties, the reference value provided by the OEM, a particular division of the OEM, the OEM’s  successor or any entity in its place,  is obviously significantly higher than the value calculated with the help of ISO 1940-1. It should be concerning if the number exceeds more than twice the ISO 1940-1 number.
    

2. Mass turbine testing for unbalance was performed without provision of a predetermined unbalance Value by the OEM, a particular division of the OEM, the OEM’s successor or any entity in its place. In this case it might happen that the OEM seemingly adjusts the unbalance threshold to declare the vast majority of turbines below a “now” presented threshold which exceeds a ISO 1940-1 value by more than the factor 2.
    

   • In this case it is necessary to look for the technical data for the next turbine part or component which will be directly affected by rotor unbalance. This part is the main bearing. ISO 1940-1 provides a formula on how to calculate the maximal permissible unbalance based on the maximal permissible radial force the bearing is specified for.
      

   • This value is typically higher than permissible imbalance since it also needs to compensate for load scenarios not directly related to mass unbalance.  It typically is in the range of 2 to 3 times the G16 Value. If the value provided for permissible unbalance is near or even above the number resulting from a calculation based on the  maximal permissible radial force the bearing is specified for than bearing failure should be expected and the number should be adamantly questioned.