Machine protection for Asian power plant

?Condition monitoring company Sensonics has reported growing demand for machine protection systems in Asia, including installations of its equipment at power plants in China and, most recently, for an interesting project at a facility in Vietnam.
The UK company supplied transducers and its Sentry G3 turbine protection system for the 110MW Russian built turbine operating at the PhaLai thermal power plant. These were for a range of applications including; shaft position, cylinder expansion, turbine block expansion, shaft vibration, eccentricity and speed.
The Vietnam site has two power plants: an older facility with eight boilers and four 110MW turbines, all Russian built; and a newer facility with two boilers and two Japanese manufactured 300MW turbines.
According to Sensonics, the ‘retrofit’ project was fairly complex and included a number of measurement modes that the Sentry G3 system was required to monitor. These included, for example, shaft position measurement and protection; where the relative position of the turbine shaft is monitored within the bearings.
The system automatically shuts down the turbine if the relative position moves outside a pre-set window. For the 110MW machine, this will occur if the shaft moves towards the generator side by more than 1.2mm or when the shaft moves towards the turbine side by more than 1.7mm.
The measurement was implemented on the turbine utilising proximity sensors mounted opposite a collar machined as part of the shaft. A similar technique was employed for both the HP (high pressure) and LP (low pressure) cylinder expansion channels.
The G3 module is capable of implementing a range of measurement algorithms. For the PhaLai project one module hardware type was used to cover all channels (24 channels in a 3U x 19” footprint), thereby simplifying the customer spares holding.
Another feature of the system is its HP eccentricity interlock: the algorithm was loaded into the module and configured to measure true peak-to-peak shaft eccentricity between speeds of 3rpm and 300rpm. The algorithm processes the signal with a 50-pole digital tracking filter within this speed window to eliminate the effects caused by shaft imperfections.
Above 300rpm, a standard RMS technique is utilised up to the running speed of 3,000rpm - similar to the standard shaft vibration measurement employed on the other rotor sections, where the radial movement is monitored within the bearings.
A speed algorithm was loaded into the last channel to cover the measurement range of 0-4000 rpm, providing two alarms for over-speed of 10% and 16%, in comparison with the rated speed. This channel also provides a phase marker output for harmonic analysis of the vibration signals.
Following the installation of the Sensonics system on the older Russian built turbine, engineers at the PhaLai plant are now planning to use the monitoring systems on other machines, the supplier said.