Axial Compressor Blade Tip Timing

1.0 BLADE TIP TIMING OVERVIEW                                                                  
Blade Tip Timing (BTT) provide diagnostic and protection tools to monitor rotating components. Non-contacting sensors are installed through the Turbine’s Axial Compressor casing looking at the tip of the airfoils to monitor the Time of Arrival (ToA) of each blade while in operation. During normal operation, ToA should be consistent within a given window of time defined by the features of the Blade (geometry, material, rotor speed and operating stresses on the blade). Any fault or anomaly in the blade or in the rotor can affect ToA of the tip and therefore can be detected. Four (4) Frame 7 rotors were saved from catastrophic failure because of early detection of R1 blade cracks using BTT.
                                                                                                                                                                                                                                                                                          Protection - Some Defects affecting the blades (cracks) can affect ToA as long as they change deflection of the blades. Change in ToA can be linked to the presence of a crack of a given dimension in a given location.
Monitoring - Some rotor dynamics anomalies such as unbalances and rubbing can also affect ToA and therefore they can be detected by the system that can help diagnosis integrating vibration data coming from traditional sensors.  

High-efficiency filter houses would guard against pits forming from salt ingress; however, there are other causes (see page # 15) of blade liberation such as:

• Domestic Object Damage (DOD)
• Misaligned IGV’s (Inlet Guide Vanes)

To develop and deploy non-contact, blade tip timing based, health monitoring systems that proactively detect cracks in compressor blades, with the following attributes:
• Rugged...