Verico regularly conducts turbine vibration checks before and after unit outages to ensure that the levels are within acceptable levels outlined by ISO 20816-2.
In order to operate effectively, the turbine is required to rotate within precise limits while under immense load from steam.
By monitoring the vibration levels and analysing the data, it can then be determined whether the turbine is able to continue operation, or whether work is required to ensure that it does not prematurely fail.
The turbines have proximity probes, accelerometers and tachometers installed at critical locations. Verico connects to all 20 proximity probes, 10 accelerometers and tachometer simultaneously to monitor all bearings during a turbine start up (run up), while it continuously runs (steady state), and when the turbine is stopped (run down).
There are certain parameters outlined in ISO 20816-2 that a turbine can operate within. The analysis process includes classifying the overall vibration during steady state as one of the following:
a: A newly commissioned machine
b: Acceptable for unrestricted long-term operation
c: Limited operation until next suitable remedial opportunity
d: Sufficient severity to cause damage
During a turbine run up to 3000 rpm, the turbine goes through different levels of vibration according to its speed. Part of the analysis includes ensuring that these levels are within certain limits depending on the speed. If the vibration levels are exceeded, the turbine must cease operation, and further investigation is required.
In addition to monitoring the actual vibration of the shafts with the proximity probes, the casing sensors (accelerometers) are also used to ensure that the bearings are operating within acceptable limits.
To analyse the data, various methods are used including:
• Vibration Trend
• Bode plots, Overall and 1x compensated including phase
• Polar plots 1x
• Shaft Centre line
By monitoring the turbine data, it is ensured that the turbine is operating within the very precise limits prescribed. This ultimately facilitates the safe operating and longevity of the machine.