The article covers a choice of main vibration parameter at an assessment of a vibration state of vertical Francis hydroturbines. At present time vibration velocity and vibration displacement are adopted as main parameters of non-rotating parts vibration in the international standard ISO 10816-5:2000 «Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts — Part 5: Machine sets in hydraulic power generating and pumping plants» (further ISO 10816-5:2000).
The hydraulic turbines refer to the slow-speed machines with rotation speed from 60 to 600 rpm (∼ 1 - 10 Hz).
So maximum vibration displacements and dynamic stresses in hydraulic turbines supporting parts are in low-frequency region of vibration spectrum.
In this report comparative data of hydro units supporting parts vibration velocity and vibration displacement measurements are presented. Using these data assessment of hydro units vibration state has been done.
It is shown that the assessment of a hydro unit vibration state using parameter "vibration displacement" corresponds to the fundamental principles of operational reliability and fatigue strength of hydro units supporting parts.
It is noted that when hydro units operate at small and partial loads with high low-frequency unsteady flow (f < frot) we have the smallest vibration velocity and the greatest vibration displacement of hydro units supporting parts.
Specialists of LMZ (Saint-Petersburg) have developed Russian standard RD 24.023.117-88 «Vibration measurement and evaluation vibration state of vertical hydraulic turbines» which was published in 1989. In this document vibration displacement was considered as a main parameter. Evaluation of turbine vibration was performed according to the effecrive value of turbine supporting parts vibration displacement.