Protection against thrust-bearing damage

DEVELOPMENT of large modern turbogenerators has resulted in reduction of clearances between stationary and moving turbine parts to a bare minimum in order to achieve better turbine efficiency. Because the thrust bearing must be relied upon to maintain these clearances by absorbing any unbalance of thrust in a horizontal direction parallel to the turbine shaft, the importance of its performance has been enhanced greatly. With the older 50-mw class (and lower) units, thrust-bearing failure did not affect the turbine adversely, provided the steam valves were closed immediately after the bearing was wiped. However, with the large, modern, multistage 3,600-rpm units, failure of the thrust bearing usually results in damage to the turbine seals, even if catastrophic damage is prevented by an alert operator.