Field-balancing of a 140 mW gas turbine
Increased vibrations after overhaul
At one of the power plants of the world wide operating energy giant Power International high vibration occurred after a minor overhaul on a GE frame 9 gas turbine. During this overhaul different repairs on the bearings and the hot section turbine blades were performed. Due to the large number of activities performed and the many involved contractors it was unclear what was causing the high vibrations in the 140 mW turbine generator set-up.
Independent analysis
In order to determine the cause of the vibration and to find a lasting solution Van Geffen VMS was asked to conduct a full independent vibration investigation. It concerned however a turbine installation that was only equipped with a minimum number or acceleration sensors which also couldn't be measured with an external analysis system. Therefore were the turbine, the coupling and the generator retrofitted with a large number of proximity probes and additional accelerometers. After carrying trough an extensive test and measurement program it was possible to distinctly conclude that an imbalance in the hot section of the gas turbine was causing the high vibrations. Problems with the mounting of the turbine blades later on turned out to be the cause of this imbalance.
The mounting of new turbine blades would mean a new, time consuming and very costly overhaul. However, using the already installed vibration sensors and the gathered measurement data it was possible to perform a field balancing of the turbine rotor, directly after the measurement program. With the field balancing the vibrations were brought down to a level that the machine was able to run problem free till the next mayor overhaul in which the rotor would be removed anyway. The whole project, from first contact till the last balance run and the re-acceptance of the machine, took less than two week time. Besides that were a large part of the activities planned in such a way that the availability in the peak hours was maintained. A service and accomplishment that is unique within this sector.