مراقبة حالة عمود التوربين الغازي في محطة كهرباء الحلة / 2 باستخدام مقاييس الاهتزاز في بيئات مختلفة.

Condition Monitoring of Gas Turbine Shaft in AL- Hilla Power Station/2 Using Vibration Measurements in Different Environments.

The gas turbine rotors are subjected to different types and directions of loading like axial, bending, shear and thermal loading. This loading is changed periodically during the operation operation which can lead to crack initiation in the rotor shaft. When these cracks propagate to the extreme limit, it will lead to sudden failure of the shaft rotor.
Crack existence can be detected by observing the vibration parameters of the rotor, the vibration parameters is changed when the shaft is cracked. The most observable change in these parameters is the natural frequency and the response of vibration.
In this study, the vibration of Alhilla gas turbine rotor is studied with the existence of cracks and without them. The rotor was modelled analytically, numerically and experimentally. The numerical study was carried out using ANSYS software. For the experimental study, a test rig was built to model the real rotor. During the experiments, the rotor speed range was variated from zero to 10000 rpm. Experimentally two crack depths of 0.2 and 0.4 of the shaft radius was modeled in addition to the uncracked shaft.
The rotor was manufactured with high accuracy and was then balanced to rotate at a higher speed. The vibration of the rotor was measured using an accelerometer connected to a digital oscilloscope. The critical speed was detected when the accelerometer reading reaches to its highest value.
In the analytical study a single and a double crack was modelled having different depths and directions. While in the numerical analysis, the shaft was modeled to have a single crack at different depths.
The results that was obtained from this study show good agreement between analytical, numerical and the experimental modelling. In the case of the proper shaft, the critical velocity was found, and the error ratio between experimental analysis and numerical analysis is (3.07%), and between analytical analysis and experimental analysis is (2.78%). It was conducted from rotor modelling that when the depth of the crack was increased, the critical speed was decreased whereas the response and the orbit size of the shaft was increased.