Method and equipment for detecting rotating stall and compressor

1. A method for detecting rotating stall in a compressor comprising a rotating rotor and a static stator, the rotor and the stator being subject to radial vibration and axial vibration, the method comprising:

measuring radial vibration of the rotor relative to the stator and correspondingly generating a vibration measurement signal;

calculating a frequency spectrum of the vibration measurement signal;

identifying a plurality of frequency bandwidths of the frequency spectrum;

neglecting one first frequency bandwidth of the plurality of frequency bandwidths if the rotation frequency of the rotor falls within the first frequency bandwidth;

neglecting at least one second frequency bandwidth of the plurality of frequency bandwidths if the rotation frequency of the rotor falls below the second frequency bandwidth;

determining the maximum magnitude of the spectrum in each of the non-neglected frequency bandwidths; and

carrying out a comparison between each of the determined maximum magnitudes and a predetermined value,

wherein rotating stall is considered occurring if at least one of the comparisons shows that the corresponding determined maximum magnitude is greater than the predetermined value.

2. The method of claim 1 , wherein the plurality of frequency bandwidths are fixed.

3. The method of claim 2 , wherein the plurality of frequency bandwidths are non-overlapping and adjacent.

4. The method of claim 2 , wherein the plurality of frequency bandwidths have different widths.

5. The method of claim 1 , further comprising:

identifying a further frequency bandwidth below all frequency bandwidths of the plurality of frequency bandwidths, wherein the further frequency bandwidth is used for detecting surge of the compressor.

6. The method of claim 1 , wherein the plurality of frequency bandwidths of comprises between about four and about ten frequency bandwidths.

7. The method of claim 1 , wherein measuring radial vibration of the rotor relative to the stator and correspondingly generating a vibration measurement signal comprises measuring components of the radial vibration according to two different directions.

8. The method of claim 7 , wherein the two different directions are perpendicular.

9. The method of claim 7 , wherein a single electronic processing unit is used for treating different or distinct measurements of radial vibration of the same compressor or of several compressors.

10. The method of claim 1 , wherein measuring radial vibration of the rotor relative to the stator and correspondingly generating a vibration measurement signal comprises measuring the radial vibration on both sides of the rotor.

11. The method of claim 1 , wherein neglecting one first frequency bandwidth of the plurality of frequency bandwidths, if the rotation frequency of the rotor falls within the first frequency bandwidth comprises measuring the rotation frequency of the rotor, or determining the rotation frequency of the rotor based on the maximum magnitude of the spectrum in each of the frequency bandwidths of the plurality of frequency bandwidths.

12. An apparatus for detecting rotating stall in a compressor comprising a rotating rotor and a static stator, the rotor and the stator being subject to radial vibration and axial vibration, the apparatus comprising:

at least one sensor configured to measure radial vibration of the rotor relative to the stator and correspondingly generate a vibration measurement signal, and

an electronic processing unit configured to:

calculate a frequency spectrum of the vibration measurement signal;

identify a plurality of frequency bandwidths of the frequency spectrum;

neglect one first frequency bandwidth of the plurality of frequency bandwidths if the rotation frequency of the rotor falls within the first frequency bandwidth;

neglect at least one second frequency bandwidth of the plurality of frequency bandwidths if the rotation frequency of the rotor falls below the second frequency bandwidth;

determine the maximum magnitude of the spectrum in each of the non-neglected frequency bandwidths;

carry out a comparison between each of the determined maximum magnitudes and a predetermined value, and

signal a rotating stall condition if at least one of the comparisons shows that the corresponding determined maximum magnitude is greater than the predetermined value.

13. A compressor comprising at least one rotating rotor and a static stator, and an apparatus for detecting rotating stall, wherein the apparatus comprises:

at least one sensor configured to measure radial vibration of the rotor relative to the stator and correspondingly generate a vibration measurement signal, and

an electronic processing unit configured to:

calculate a frequency spectrum of the vibration measurement signal,

identify a plurality of frequency bandwidths of the frequency spectrum,

neglect one first frequency bandwidth of the plurality of frequency bandwidths if the rotation frequency of the rotor falls within the first frequency bandwidth,

neglect at least one second frequency bandwidth of the plurality of frequency bandwidths if the rotation frequency of the rotor falls below the second frequency bandwidth,

determine the maximum magnitude of the spectrum in each of the non-neglected frequency bandwidths,

carry out a comparison between each of the determined maximum magnitudes and a predetermined value, and

signal a rotating stall condition if at least one of the comparisons shows that the corresponding determined maximum magnitude is greater than the predetermined value.