One of the most important items of Turbine Supervisory Monitoring is the accurate and reliable monitoring of the Rotor Thrust Position.
It is one of the most critical measurements in rotating machinery, in that if the thrust bearing should fail for any reason, the rotating shaft would then be permitted to move, and the resulting rotor-to-stator contact will inevitably have serious consequences for the machine. Such incidents can become financially overwhelming – considering the cost of the turbine rebuild and the associated loss of production – and can also be a serious hazard to the Health and Safety of plant personnel.
Current best practice indicates that to adequately monitor thrust position, dual probes are recommended to achieve the level of reliability required for this important parameter. The main benefit of the dual probe arrangement is the redundancy provided in case of failure of one or other of the probes, but also in some cases, particularly if being used for tripping, voting may be used to prevent spurious trip events. Often, thrust probes are installed inside the machine bearing case and are inaccessible from the outside while the machine is running, therefore, it is vital that any installed probes will perform reliably up until the next scheduled outage.