What is the measurement and evaluation method of rotor natural frequency of large rotating unit?

When the natural frequency of the bearing is greater than the natural frequency of the rotor bearing system, the machine-support system is in a rigid support state; When the natural frequency of the bearing is less than that of the rotor bearing system, the machine-supporting system is in a flexible supporting state.

As for the evaluation standard of rotor vibration of large rotating units, almost all domestic and foreign vibration standards stipulate that the peak-to-peak value of journal vibration displacement near the bearing is used to measure it, but the specific values of the evaluation standard are not uniform enough. For centrifugal compressors and steam turbines used in petrochemical industry, API6 17 and API6 12 standards stipulate that the peak-to-peak value of rotor vibration displacement should not exceed a value or a smaller value of 25.4μm, a = 25.4 (12000/n)1/2, n for large oil. In the absence of manufacturer's regulations, it can also be considered that:

When it is less than a value, it is in an excellent state, and A is the smaller value of 25.4( 12000/n) 1/2 or 25.4μm;

When the value is greater than A and less than B, it is qualified, and B = (1.6 ~ 2.5) A. When the speed is low, take a large value, and when the speed is high, take a small value, and B can be set as a low alarm value.

When the value is greater than B and less than C, it is unqualified, and C = 1.5b, and C is high alarm value or interlock value; Values greater than c are not allowed.

In addition, when the increment of vibration value changes exceeds 25% of the alarm value (B value), it should be concerned.