This part of ISO 7919 gives guidelines for applying evaluation criteria for shaft Vibration under normal operating conditions, measured at or close to the bearings of gas turbine sets. These guidelines are presented in terms of both steady running Vibration and any magnitude changes which may occur in these steady values. The numerical values specified are not intended to serve as the only basis for Vibration evaluation since, in general, the vibratory condition of a machine is assessed by consideration of both the shaft vibration and the associated structural vibration (see the introduction to ISO 7919-1).

This part of ISO 7919 applies to all gas turbine sets (including those with gears) with fluid-film bearings, outputs greater than 3 MW and shaft rotational frequencies from 3000 r/min to 30000 r/min. Aircraft derivative engines are excluded, since they differ fundamentally from industrial gas turbine Sets, both in the type of bearings (rolling element bearings) and in the stiffness and mass ratios of the rotor and support structure. Depending on the construction and mode of operation, there are three principle groupings of gas turbine sets:

• single-shaft constant-speed gas turbine sets;
• single-shaft variable-speed gas turbine sets;
• gas turbine sets with separate shafts for hot gas generation and power delivery.