METHOD AND SYSTEM FOR MONITORING SUB-SYNCHRONOUS TORSIONAL OSCILLATIONS OF A SHAFT LINE OF A STEAM TURBINE

• US 20160033321A1
• Filed: 07/23/2015
• Published: 02/04/2016
• Est. Priority Date: 07/31/2014
• Status: Active Grant

• Current Assignee: General Electric Technology GmbH (GE Vernova, Inc.)
• Original Assignee: Alstom Technology Ltd. (Alstom SA)
• Inventors: TOULEMONDE, Martin, PICAND, Sbastien, HUART, Boris
• Granted Patent: US 10,001,404 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: F01D 21/003 Arrangements for testing or measuring for measuring vibrations G01H
• CPC Class Codes: F01D 21/14 responsive to other specific conditions
• CPC Class Codes: F01D 5/10 Anti- vibration means specially adapted for radial flow machines or engines F01D5/04
• CPC Class Codes: F05D 2220/31 in steam turbines
• CPC Class Codes: F05D 2270/334 Vibration measurements
• CPC Class Codes: G01H 1/006 of the rotor of turbo machines
• CPC Class Codes: G01H 1/10 of torsional vibrations

Abstract

A method for monitoring sub-synchronous torsional oscillations of a shaft line of a steam turbine includes measuring a rotational speed of said shaft line over a period of time and generating, from the measured rotational speed, a signal representative of said rotational speed over said period of time. The method further includes performing a spectrum analysis on said signal to determine, for at least one given frequency, an amplitude of variation of said rotational speed at said given frequency, comparing said amplitude with at least one predetermined amplitude threshold for said frequency, and generating an alert signal if said amplitude exceeds at least one predetermined amplitude threshold.

Claims

1. A method for monitoring sub-synchronous torsional oscillations of a shaft line of a steam turbine, said method comprising:

measuring a rotational speed of said shaft line over a period of time (T₀) and generating, from the measured rotational speed, a signal representative of said rotational speed over said period of time (T₀),

performing a spectrum analysis on said signal to determine, for at least one given frequency (fr_i), an amplitude (A_i) of variation of said rotational speed at said given frequency (fr_i),

comparing said amplitude (A_i) with at least one predetermined amplitude threshold (A_i1, A_i2) for said frequency (fr_i), and

generating an alert signal if said amplitude (A_i) exceeds at least one predetermined amplitude threshold (A_i1, A_i2).

2. The method according to claim 1, wherein:

the performing a spectrum analysis comprises determining, for each of a plurality of frequencies (fr_i), an amplitude (A_i) of variation of said rotational speed at said frequency (fr_i),

the comparing comprises a comparison of the amplitude (A_i) determined for each frequency (fr_i) with at least one predetermined amplitude threshold (A_i1, A_i2) for said frequency (fr_i), and

the generating comprises generating an alert signal if at least one amplitude (A_i) determined for a frequency (fr_i) exceeds at least one of said predetermined amplitude thresholds (A_i1, A_i2) for said frequency (fr_i)).

3. The method according to claim 2, wherein said or each given frequency (fr_i) is a sub-synchronous oscillation resonance frequency of the shaft line.

4. The method according to claim 3, wherein the comparing comprises comparing, for said or each frequency (fr_i), said amplitude (A_i) with a lower (A_i1) and a higher (A_i2) predetermined amplitude thresholds for said frequency (fr_i).

5. The method according to claim 4, wherein the generating comprises generating an alert signal of a first type if said amplitude (A_i) is higher than the lower amplitude threshold (A_i1) and lower than the higher amplitude threshold (A_i2).

6. The method according to claim 5, wherein said steam turbine rotates a generator, and wherein the method further comprises reducing a power generated by the generator after an alert signal of the first type is generated.

7. The method according to claim 4, wherein the generating comprises generating an alert signal of a second type, different from said first type, if said amplitude (A_i) is higher than the higher (A_i2) amplitude threshold.

8. The method according to claim 7, further comprising a tripping of said steam turbine after an alert signal of the second type is generated.

9. The method according to claim 1, wherein the measuring comprises measuring a rotational speed of said shaft line at a plurality of measurement times (t_m) over said period of time (T₀).

10. The method according to claim 9, wherein the measuring comprises, at each measurement time (t_m), a measure, by a sensor, of a mean rotational speed of said shaft line on a given measurement period (T_m) preceding said measurement time (t_m).

11. The method according to claim 10, wherein the measure by the sensor comprises a detection of a movement of a toothed wheel mounted on said shaft line during said given measurement period (T_m).

12. The method according to claim 11, wherein said sensor is a non-contact sensor.

13. The method according to claim 1, wherein the spectrum analysis performing comprises applying a Fast Fourier Transform (FFT) to said signal.

14. A system for monitoring sub-synchronous torsional oscillations of a shaft line of a steam turbine, said system comprising:

a speed measurement device configured to measure a rotational speed of said shaft line over a period of time (T₀), and to generate, from the measured rotational speed, speed values forming a signal representative of said rotational speed over said period of time (T₀), and

an analysis unit configured to perform a spectrum analysis on said signal and to determine, for at least one given frequency (fr_i), an amplitude (A_i) of variation of said rotational speed at said given frequency (fr_i), said analysis unit being further configured to compare said amplitude (A_i) with at least one predetermined amplitude threshold (A_i1, A_i2) for said frequency (fr_i), and to generate an alert signal if said amplitude (A_i) exceeds at least one predetermined amplitude threshold (A_i1, A_i2).

15. The system according to claim 14, wherein said speed measurement device comprises at least one speed sensor.