Wear of Steam Turbine Journal Bearings at Low Operating Speeds

Worn steam turbine bearings were inspected and measured during overhaul periods to determine the extent and nature of the wear. Significant wear was found to exist on turbines using low turning gear speeds (10 rpm or less), and the wear occurred in spite of the presence of lift-pump systems. An analysis of the effect of geometric changes from wear on bearing lubrication at low speeds showed that a limited amount of wear may enhance lubrication. The analysis predicts that an optimum amount of wear exists beyond which the altered geometry would accelerate wear. Considerations were also made of the minimum speeds required to generate lubricant films sufficient to avoid bearing damage by the debris sizes typically found in turbine-generator lubricant systems.