Page 206 - Steam Turbines Design, Applications, and Rerating

Rotor Dynamics Technology 185

(a)

(b)

Figure 10.12 Subsynchronous frequencies of relatively high
amplitude on highly successful steam turbines: (a) 35,640 hp at
6112 r/min; (b) six-stage boiler feedwater pump drive turbines.
(General Electric Company, Fitchburg, Mass.)

been no direct correlation between the occurrence of subsynchronous
vibration in the turbines and such parameters as types of bearings,
operating speeds, horsepowers, steam conditions, or precision of rotor
balance. Frequency spectrum data thus indicate that the presence of
subsynchronous vibration components is not uncommon in turboma-
chines that have operated without distress for many years.

10.15 Labyrinth and Cover Seal Forces
The two elements that contribute directly to decreasing the lateral sta-
bility of a rotor are the labyrinth seals and the sealing strips on the