The shrouded or bandaged blades are more and more often used in turbomachines of large capacity, mainly in steam turbines. To avoid accidents with extensive economic losses, there appears an urgent need to equip at least every stage of low pressure turbine (with respect to the dimensions of the installed blades) with modern measuring system that would provide information of blades loading in turbine operation, their damage and residual lifetime.

In cooperation with Doosan Škoda Power company and with the Institute of Thermomechanics of the Czech Academy of Science a system for contactless monitoring of turbine blades was developed. This system is based on the combined principle of scanning blades using optical probes with lense and magneto-resistive sensors.

The system allows adequate sampling of the measured signals (100 MHz) and implements the complete shrouded blade behavior analysis from sensing displacements of each blade through evaluation of Campbell and safe diagram (ie eigen forms of the bladed disc and its frequencies) to monitoring of the residual life of the blades. The system was tested in operation for monitoring of the last stage blades in LP part of 270MW steam turbine. Test operation at TG 270MW also allows the development and validation of a new method for blade condition monitoring using the rotor vibration sensors. This method is especially capable the identify the natural frequency of the blades and the development of frequency and amplitude over time. Thus monitoring procedure with relatively small costs (rotor vibration sensors is standard turbine instrumentation) can be obtained.