Unexpected Vibrations in Gearbox Caused by System Integration Issues

Abstract

This case study deals with a 24MW turbo-compressor unit composed of a gas turbine, a speed reduction gearbox with a lube oil pump mounted on its low speed shaft and two compressors in series. The unit was subject to high radial vibrations at the gearbox low speed shaft during initial running phase. Technical investigation identified the root cause as lube oil pump working in aeration condition owing to a wrong pressure set point. Aeration, in turns, excited a torsional natural mode of the train. This case study highlights some of the implications of mechanical integration of machines and auxiliary systems, where the modification of operating parameters may lead to unwanted outcomes which may affect availability and integrity of the unit.