IOTECH has written about potential problems with turbine rotors, and how its technology can help with troubleshooting these failures.
Turbines are usually drivers for large electric generators, pumps and compressors in utilities and other process industries. They range in size and generation capacity, and often run for a long time without repairs.
However, they must be monitored and maintained. A key part of turbines is their rotors, which must retain good alignment, balance, lubrication and other factors to avoid vibrations which can cause extensive damage.
Usually, turbines use built-in seismic or displacement vibration sensors to continuously monitor the bearings for adverse vibration.
Oil wedge, oil whirl and oil whip are three progressively serious problems which can cause rotor vibrations. They are caused by uneven oil distribution around the shaft in the journal bearing. This can be caused by misalignment, improper oil viscosity, or design failures in the bearing.
Another common problem is rub, where the turbine rotor contacts the stationary components such as seal rings, and the inside diameters of the bearings. This is usually resolved after running the machine for some time, but sometimes the wear can damage the machine.
To diagnose problems with the turbine, engineers and technicians use data acquisition systems and look at amplitude waveforms of the turbine-rotor shaft displacements. By looking at the shape of the plotted waves, they can determine the cause of the vibrations.
In some cases, the sensors embedded in the turbine could be damaged. IOtech’s ZonicBook is designed for such circumstances.
The unit records signals from radial multiple proximity sensors and tachometer signals mounted on the bearings of the turbine. Accompanying software can calculate and calibrate ratio functions from the signals connected to the governor speed sensor.
After vibration and speed data is recorded, the software creates a waterfall plot of vibration frequencies and amplitudes to characterise the turbine’s behaviour at various speeds.
Although the results are not as precise as they would be if the sensors are working, it is possible for a skilled operator to determine the most likely cause of the vibration.
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