Development of Vibrations Indicators for Rotating Machines Monitoring: Case of Gas Turbines

The vibration monitoring of rotating machinery use indicators, their different values allow us to run or not the machines, If the limit value, defined by the norms of these indicators exceeded limits an analysis and fault investigations will be required. These limits are defined by norms, we cite norm ISO 10816.

By a new and particular calculations of machines vibrations responses we will try in this modest work to define, in a simple way, development of a new calculation method for the vibrations rotating machines response and vibration limites opttimization.

We have used numerical calculation by finished differences where it will be used the model spring–mass system, we calculated the response of the system according to operation parameters of the model elements used (rigidity, damping and frequency).

The maximal free response of spring-masse system is function of the damping and stiffness coefficients; it is represented by the efforts opposed to that of the excitation. It’s represented by the ratio of stiffness coefficient to that of damping and including expression of only natural frequency [1-3].

The ratio of maximal forced vibrations, at a constant frequency, and the free vibrations is equal to the ratio of damping and the stiffness coefficients.

In previous study we have optimized norms limits of machines vibration by using the constant ratio of still admissible values to admissible for all groups of machines according the norm ISO 10816-1. We supposed that the admissible absoluate vibrations values according norms corresponds to equilibrium. We have added the admissible limit vibrations to the still admissible values, and to other thresholds. An approximation calculation indicate that we can increase norms only once.

An algorithm for fault diagnosis in industrial rotating machines facing new operating conditions emergence is developed on the basis of input indicators, extracted from vibrations spectrums. Indicators selection is used to improve diagnosis performances by the help of a hybrid approach using several selection criteria and different classifiers [4-6].

In this study we also elaborated a new indicator definition of machines vibrations, we choses importants machines, gas turbines. The indicator is the ratio of absolute to relative vibration, it’s the absolute vibrations of bearing per unit of rotor vibrations displacement. It’s the ratio of the RMS absolute value of the bearing to the rotor vibrations velocity, which gives us information on the evolution of the defaults.

This concept of vibration indicators of rotating machines, allows to have more possibility to monitor them. Norms used are ISO 10816-4 and ISO 7919-4, which include absolute and relative value thresholds.

We hope that on machines exploitation, the practical application of these indicators will be useful, And also that this work will be developed in future and will contribute to scientific research in this area.