Positive displacement pump utilized in lube oil system for turbomachinery

Abstract

Discloses a backup lube oil pump system for a steam turbine lube oil system. The primary and secondary pump system of the prior art lube oil system normally includes a primary centrifugal pump affixed to the turbine shaft and ac and dc motor-driven pumps to supply lubrication during start-up and shutdown when the primary pump cannot maintain flow due to low rotational speed. If the turbine is coasting down due to an ac power failure, the ac motor-driven backup pump is inoperative. The dc (battery) driven backup pump becomes the only backup left and the failure of batteries if not charged regularly can render it as a poor backup system. In the invention a backup lube oil system having high reliability utilizes a positive displacement lube oil pump driven by a rotor-driven permanent magnet generator. The pump is in parallel with a primary check valve in the lube oil feed line, so that the positive displacement backup lube oil pump is supplying oil at all times to the shaft bearing. Upon coast-down of the rotor, the PDP driven by the permanent magnet generator maintains a continuous flow of oil to the shaft bearings to a speed which is sufficiently low to prevent bearing damage in case the primary and other backup systems fail to do so.