EP1474610B1 - Warning before pump limit or in case of blade failure on a turbomachine - Google Patents

Description

The invention relates generally to the technical field of turbocompressors, as used for example in gas turbines (in particular as aircraft engines) or in power generation or in the chemical industry. In particular, the invention relates to the field, in time to detect a compressor pumps emerging during operation of the turbocompressor, so that appropriate countermeasures can be taken. The invention further relates to blade damage of a rotor of a turbomachine, such as a steam or gas turbine. The gas turbine may be an aircraft engine or a stationary gas turbine, each having rotors in the compressor and turbine.

Turbo compressors generally have a stability limit depending on their performance characteristics. If, during operation of the turbocompressor, this stability limit is inadvertently exceeded (for example due to an entry disturbance or due to changes in temperature or soiling), then strong unsteady currents (rotating tearing, pumping) occur, which can quickly lead to destruction of the machine. It is therefore customary to provide for the design of the turbocompressor a sufficient distance between the working line and the stability limit, as a safety margin, all disturbances are taken into account, which could reduce the surge margin. By such a fixed safety distance, however, a considerable working range of the compressor is lost with good efficiency.

In order to further increase the efficiency and / or the power density in modern constructions, considerations have been made as to how turbo compressors can be safely operated in the vicinity of the stability limit. It is known that when the pumping state approaches (falling short of a predetermined minimum distance from the pumping limit), the operating line of the compressor can be lowered rapidly or the pumping limit can be shifted. This can be done, for example, by opening a blow-off valve and / or by adjusting vanes and / or by reducing the fuel supply. In order to determine the approach of the surge line, different approaches have already been pursued.

From DE 693 25 375 T2 a method for monitoring and controlling a compressor is known in which pressure fluctuations within a compressor stage are measured and analyzed with regard to their frequency components. If at least one characteristic Peak occurs in a dependent of the speed and the number of blades frequency range, a warning signal is generated depending on the shape of the occurred at least one peak. The warning signal can be used for control purposes, for example, by lowering the load or reducing the fuel injection rate to avoid the emerging critical state.

US Pat. No. 6,231,306 B1 shows a control system for preventing a stall in a turbocompressor. A mean value of the squared amplitude of a relevant frequency range is calculated from a measurement signal determined by a pressure sensor. The mean is normalized and compared to a threshold. If the threshold is exceeded, either a drain valve is opened or the vane position is changed.

From DE 694 11 950 T2 a method for the detection of a pumping state is known in which the engine exhaust gas temperature and the engine compressor speed are evaluated.

There is a need to further improve the known methods in terms of their reliability and / or the required effort for the sensor and signal processing.

The invention accordingly has the task of proposing a calculation method in order to reliably detect an emerging pumping state in a turbocompressor in such a timely manner that suitable measures for pump avoidance can still be made. In addition, a blade damage of a rotor of a turbomachine should be detected as early as possible. An object of preferred embodiments of the invention is to achieve this goal with as few additional sensors as possible, that is to say with as few sensors as possible which are not already provided in the turbocompressor anyway. A further object of preferred embodiments of the inventions is to avoid complex arithmetic operations in order thereby to achieve a high reaction speed (data processing in real time) with relatively low computing power.

These objects are achieved by a method for determining a warning with the features of claim 1, a method for operating a gas turbine or a turbomachine according to claim 10 or 14, a turbocompressor according to claim 11 and a gas turbine according to claim 13. The dependent claims relate to preferred embodiments of the invention.

The invention is based on the basic idea of identifying circumferential disturbances which occur during the approach to the stability limit of the compressor. In experiments in which the compressor was slowly throttled to the surge limit, such circumferential faults could be observed in advance of the compressor instability. The circulation speed in the annulus of the compressor is dependent on the compressor and possibly also on the speed. The disturbances can be both long-wave (modal) and short-wave (in the form of so-called spikes ).

According to the invention, a combined criterion for the warning is provided. This criterion is composed, firstly, of the subcriterion that the characteristic, periodic interference patterns occur clearly in the measurement signal of a temperature, pressure or flow velocity sensor, and secondly, from the subcriterion that the measurement signal of the first sensor coincides with the measurement signal of a second sensor, which in Circumferential direction of the turbocompressor or turbomachine offset from the first sensor is correlated. Other temperature, pressure or flow velocity sensors may be provided. The warning is given depending on the extent to which these two subcriteria are met.

The invention provides reliable early or early detection of pump damage based on the identification of said characteristic signal structures that occur as the operating point approaches the surge line or blade damage. The instrumental effort is low because the required at least two sensors in conventional compressors either for other reasons already exist or they can be added at least without difficulty. Also, the calculation effort for determining the two sub-criteria mentioned above is not particularly high, because in particular no complex frequency analyzes are required. By virtue of the invention, a rapidly responding surge limit warning or a warning for a blade damage can be delivered with relatively low computing power.

In the wording used in this document, the term "pumps" is to be construed in the broadest sense and includes in addition to the actual pumping ( surging ) and the rotating stall in the compressor. Accordingly, the term "pumping limit" is understood to mean any warning signal that indicates an impending stall or pumping condition in the compressor.

The inventively provided at least two temperature, pressure or flow velocity sensors are arranged offset in the circumferential direction of the turbocompressor or the turbomachine against each other. They may have a circumferential distance of 180 ° or even less, for example 90 °, 60 °, 45 ° or 30 °. Although more than two temperature, pressure or flow rate sensors are provided, they may not necessarily be arranged at a uniform circumferential distance. The at least two sensors are preferably located in a common axial plane of the turbocompressor or turbomachine. This may be, for example, the plane in front of the first rotor; other levels are also possible.

The inventively determined at least two measurement signals correspond to the output signals of each one of the temperature, pressure or flow velocity sensors. The term "correspond" does not necessarily mean an identity; Rather, the output signal of a sensor can, for example, be scaled (multiplication by a constant or variable factor) or shifted (addition of a constant or variable value, for example for averaging) or inverted (multiplication by -1 or inverse) to obtain the corresponding measurement signal from it receive. Furthermore, the measurement signals are preferably digital value sequences which have been obtained by analog-to-digital conversion (and possibly further processing steps) from the analog sensor output signals.

When determining the periodicity value and the correlation value, a first or a second time offset is used according to the invention. In various embodiments of the invention, the first and / or the second time offset are constant (depending on the type of compressor, if applicable) or dependent on the respective rotational speed or other parameters (for example the compressor pressure). Also, the invention is not limited to calculating only one periodicity value and one correlation value each; Rather, embodiments are also provided in which a plurality of these values (typically with different time offset values or for different measurement signals) are always calculated and evaluated.

The steps of the method according to the invention are preferably carried out by a program-controlled device, for example a digital signal processor (DSP). However, implementations with hard-wired digital logic or analog implementations are also conceivable. The order of enumeration of the method steps in the claims should not be construed as limiting; rather, these process steps also be executed in a different order or in whole or in part in parallel or semi-parallel (interlocking).

In preferred embodiments, the warning is issued when the product of the periodicity value and the correlation value exceeds a predetermined threshold. In other embodiments, instead of product formation, another function is used that links the two mentioned values such that large periodic signal changes and / or high signal correlation lead to the issuing of the warning. In other embodiments, the threshold value calculation can be carried out independently for the two values, wherein the warning is preferably output only when both threshold values are exceeded.

To calculate the periodicity value and / or the correlation value, the required measurement signals are preferably evaluated in a sliding window of a predetermined window width (fixed or dependent on measured values). The window width significantly determines the required computational effort and can therefore also be changed depending on the available computing power. The sampling frequency of the sensors and the signal evaluation is in preferred embodiments in the order of 1 kHz to 2 kHz.

Preferably, it is provided to calculate the periodicity value as an average value (scaled or non-scaled) of the quadratic deviation of two measurement points each shifted by the first time offset from one another. The evaluated measurement signal is previously subjected to a mean value adjustment in some embodiments. In alternative embodiments, instead of the quadratic deviation, the amount difference or the cubic difference in amount is formed. Instead of the mean value calculation, a simple summation can also take place in execution alternatives (in particular if the window width and / or the first time offset is constant). Overall, the periodicity value should indicate the extent to which structures with strong periodic signal changes occur in the measurement signal.

In order to calculate the correlation value, in preferred embodiments the mean value of the product is calculated from two measurement points of two different measurement signals staggered by the second time offset. Again, in alternative embodiments, a summation instead of averaging done, and instead of the product calculation, another function can be used. Overall, the correlation value should be indicate how exactly the two measured signals considered coincide when shifted by the second time offset.

In some embodiments of the invention, the detected warning is displayed only to a pilot or other operator. Preferably, however, an operating parameter of the turbocompressor is changed in response to the surge limit warning in an automatically proceeding process step in order to avoid compressor pumping. For example, a blow-off valve can be opened or the stator vanes of the turbocompressor can be adjusted.

If the turbocompressor is part of a gas turbine, stabilization of the flow can also be achieved when the surge limit is approached by thrust nozzle adjustment, injection or blow-off, VGV adjustment or fuel modulation, before the compressor becomes aerodynamically unstable.

The said measures have the result that the gas turbine (for example, the aircraft engine) can be operated closer to the surge limit under many operating conditions than would be possible with a static surge margin. This leads to improved efficiency and improved fuel economy characteristics (lower thrust specific fuel consumption SFC). Even if this possibility is not exploited, the reliability of the gas turbine increases, because disturbances that would lead to instability without a control, are detected in advance and eliminated by a controlled increase in the surge margin.

If a gas turbine (in particular an aircraft engine) is newly developed using the invention, the improvements achievable by the invention can be taken into account in order to design the new development, where appropriate, to a higher turbine stage load or to optimize the required surge margin as needed.

In preferred embodiments, the turbomachine, the turbocompressor and the gas turbine are further developed with features that correspond to the features just described or the features mentioned in the dependent method claims.

• Fig. 1 eine schematische Schnittansicht durch eine als Flugzeugtriebwerk ausgestaltete Gasturbine mit einer daran angeschlossenen Steuereinheit,
• Fig. 2 ein Datenflussdiagramm eines Auswertungsverfahrens bei dem beschriebenen Ausführungsbeispiel, und
• Fig. 3 eine beispielhafte Darstellung des zeitlichen Verlaufs zweier mittelwertbereinigter Messsignale.

Other features, advantages and objects of the invention will be apparent from the following detailed description of an embodiment and several alternative embodiments. Reference is made to the schematic drawings in which:

• 1 is a schematic sectional view through a designed as an aircraft engine gas turbine with a control unit connected thereto,
• 2 is a data flow diagram of an evaluation method in the described embodiment, and
• 3 shows an exemplary representation of the time profile of two mean-value-adjusted measurement signals.

The twin-shaft gas turbine 10 shown in FIG. 1 is known per se. It has a multi-stage low-pressure compressor 12 and a multi-stage high-pressure compressor 14. The flow direction is followed by a combustion chamber 16, a high-pressure turbine 18 and a low-pressure turbine 20. The low-pressure compressor 12 and the low-pressure turbine 20 are connected by a common (inner) shaft, and likewise the high-pressure compressor 14 and the high-pressure turbine 18 are connected to a common (outer) shaft ,

The gas turbine 10 is configured in the present embodiment as an aircraft turbine. In alternative embodiments, the invention is also intended for single-shaft gas turbines, gas turbines with three or more shafts, stationary gas turbines (for example in power plant technology) and compressors for other applications (for example, process engineering, ventilation technology).

Two sensors 22, 24 are arranged in a common axial plane in the flow direction in front of the first rotor of the high-pressure compressor 14. The sensors 22, 24 are circumferentially offset from each other, in the present embodiment by 180 °. In the embodiment described herein, the sensors 22, 24 are piezoelectric pressure sensors known as such. In alternative embodiments, flow velocity sensors are provided instead.

Output signals s ₁ , s _{2 of} the sensors 22, 24 are supplied to a control unit 26, which is designed as a digital signal processor (DSP) with the required additional circuit. Two analog / digital converters 28, 30 convert the analogue sensor output signals s ₁ , s ₂ into digital measuring signals p ₁ , p ₂ at a sampling frequency of approximately 1 kHz to 2 kHz.

The measurement signals p ₁ , p ₂ are processed by a surge limit warning determination module 32 in a manner to be described below. When approaching a critical State, the surge limit warning determination module 32 outputs a surge limit warning W to an influencing module 34, which in turn alters the operating parameters of the gas turbine 10 by a plurality of control signals c ₁ , c ₂ , c _x to stabilize the operating state of the gas turbine 10 and thus avoid pumping , In the present exemplary embodiment, these are, in particular, a first control signal c ₁ which activates blow-off valves (not shown in FIG. 1), a second control signal c ₂ , which briefly reduces the fuel supply, and further control signals c _x , which effect, for example, a thrust nozzle adjustment or a vane adjustment , These measures are known per se.

In the present exemplary embodiment, the surge limit warning determination module 32 and the influencing module 34 are designed as program modules of the digital signal processor (DSP) forming the control unit 26. In alternative embodiments, these modules may also be implemented by analog or digital circuitry. Because the evaluation method according to the invention requires only relatively low computing power, the digital signal processor of the control unit 26 can take on further tasks, which may be associated in particular with the regulation of the gas turbine 10.

In the data flow diagram of Fig. 2, the function of the surge limit warning determination module 32 is shown in greater detail. First, in the processing steps 40 and 42, a corresponding averaged signal p ₁ or p _{2 is} respectively formed from the two measurement signals p ₁ and p ₂ . In the present exemplary embodiment, moving average values p ₁ and p _{2 of} the measuring signals p ₁ and p _{2 are} calculated during a time window which is considerably longer (for example ten or a hundred times) than a fluctuation of the measuring signals p ₁ and p ₂ to be determined. The mean value signals p ₁ and p ₂ are from the respective measurement signal p ₁ and p ₂ subtracted. Overall, the mean-value-corrected measurement signals p ₁ and p ₂ thus result according to the equations p ₁ = p ₁ -p ₁ or p ₂ = p ₂ -p ₂ .

An exemplary course of the two mean-value-adjusted measurement signals p ₁ and p ₂ is shown in FIG. 3. Obviously, these signals show significant periodic signal level changes (the maximum differences in the measurement signal p ₁ are observed for the time offset t ₁ of approximately 0.6 compressor revolutions indicated in FIG. 3). Furthermore, a clear correlation between the two measuring signals p ₁ and p ₂ can be identified if they are compared with a time offset t ₂ of approximately one compressor revolution. The three oblique, dotted lines in FIG. 3 show this correlation for three signal maxima.

Returning to FIG. 2, in calculation step 44, a periodicity value W _{1 is} determined, which indicates a measure of the occurrence of periodic signal level changes in the mean-value-adjusted measurement signal p ₁ . In alternative embodiments, the periodicity value W _{1 could} also be calculated from the non-average-adjusted measurement signal p ₁ or one of the measurement signals p ₂ or p ₂ , or two periodicity values could be calculated for the measurement signals p ₁ and p ₂ (or for the measurement values p ₁ and p ₂ ).

To calculate the periodicity value W ₁ , the mean value of the squared signal differences of every two measuring points of the measuring signal p _{1 is} calculated within a sliding time window of N measuring points, the respective measuring points p ₁ (i + t ₁ ) and p ₁ (i) being in each case distinguish a given time offset t ₁ . In formula notation, the calculation step 44 can be expressed as follows: $${\mathrm{<figure-callout\; id="1"\; label="W"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">W</figure-callout>}}_1=\frac{1}{\mathrm{N}-{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">t</figure-callout>}}_1},{\displaystyle {\Sigma }_{\mathrm{i}=1}^{\mathrm{N}-{\mathrm{t}}_1}{\left[{\tilde{\mathrm{p}}}_1\left(\mathrm{i}+{\mathrm{t}}_1\right)-{\tilde{\mathrm{p}}}_1\left(\mathrm{i}\right)\right]}^2}$$

For a given profile of the measurement signal p ₁ depends the amount of periodicity W _1, inter alia, on the choice of the time offset value from t _1. The periodicity value W ₁ is maximum when, as shown in FIG. 3, the time offset t _{1 is} approximately half the signal period. In different embodiments, the time offset t _{1 is} either fixed (for a specific compressor design) or dependent on operating parameters of the compressor (eg the instantaneous speed).

Calculation step 46 in FIG. 2 relates to the determination of the correlation value W ₂ from the measurement signals p ₁ and p ₂ . The correlation value W ₂ indicates how well the two measurement signals p ₁ and p ₂ on the basis of a second time offset t ₂ are correlated with each other. This calculation enables the targeted identification of circulating faults. Here, too, the original measurement signals p ₁ and p _{2 can be} used instead of the mean-value-adjusted measurement signals p ₁ and p ₂ in alternative embodiments.

In the calculation of the correlation value W ₂ , the mean value of products is calculated within the sliding time window with the window width N, which results from a respective measurement point of the first measurement signal p ₁ and a measurement point of the second measurement signal p ₂ . The two multiplied measuring points p ₁ (i + t ₂ ) and p ₂ (i) differ by the time offset t ₂ . In formula notation, this calculation step 46 can be expressed as follows: $${\mathrm{<figure-callout\; id="2"\; label="W"\; filenames="imgf0003.png"\; state="\{\{state\}\}">W</figure-callout>}}_2=\frac{1}{\mathrm{N}-{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="imgf0003.png"\; state="\{\{state\}\}">t</figure-callout>}}_2},{\displaystyle {\Sigma }_{\mathrm{i}=1}^{\mathrm{N}-{\mathrm{t}}_2}\left[{\tilde{\mathrm{p}}}_1\left(\mathrm{i}+{\mathrm{t}}_2\right)\cdot {\tilde{\mathrm{p}}}_2\left(\mathrm{i}\right)\right]}$$

Similar to the first time offset t ₁ , the second time offset t ₂ can also be fixed or variable. While in the embodiment described here the window width N is identical for both calculation steps 44, 46, different (fixed or variable) window widths are provided in execution alternatives.

In the next optional steps 48 and 50, the periodicity value W ₁ and the correlation value W ₂ are scaled by reference to the inlet and / or outlet pressure of the compressor. The pressure values used for this can either originate from further sensors or be derived from the abovementioned mean value signals p ₁ and p ₂ . The results of the scaling result in a scaled periodicity value W ₁ and a scaled correlation value W ₂ , which are multiplied together in the following step 52. The product W ₁ -W ₂ is subjected to a threshold value comparison in step 54. If the product W ₁ -W ₂ exceeds a predetermined threshold value, a surge limit warning W is triggered, which is supplied as an input signal to the influencing module 34 (FIG. 1).

The scaling steps 48, 50 are not necessarily required; Rather, in step 52, the values W ₁ and W _{2 can be} directly multiplied together. The threshold used in step 54 may be fixed or variable; In particular, it is also possible to obtain the same result as with a scaling of the values W ₁ and W ₂ by a corresponding change of the threshold value. In further alternative embodiments, in step 52, not the product but another function is calculated, for example the sum or the sum of the squares.

By the method described can be achieved overall safe compressor operation in an economically interesting operating range near the surge limit (higher efficiency) and increased disturbance tolerance of the compressor, especially with regard to entry problems.

Similarly, blade damage to a rotor in the compressor or turbine section 12, 14 or 18, 20 of a turbomachine, such as the gas turbine 10 of Fig. 1, may be indicated as warning (W) by the method described above and further ill effects avoided , z. B. by switching off this turbomachine, the z. B. an aircraft engine and subsequent repair or replacement of the damaged blade or blades.

Claims (15)

1. Method for determining a surge limit alarm (W) in a turbocompressor (12, 14) or an alarm (W) in the event of blade damage to a rotor (12, 14) of a turbomachine, comprising the steps:

   - determination of at least two measurement signals (p₁, p₂; p̃₁, p̃₂), which correspond each to the output signals (s₁, s₂) of one of at least two pressure, flow-rate or temperature sensors (22, 24) arranged offset relative to one another in the circumferential direction of the turbocompressor or rotor (12, 14),

   - calculation of a periodicity value (W₁; W̃₁) from at least one of the measurement signals (p₁, p₂; p̃₁, p̃₂), which indicates a measure for the occurrence of periodic signal level variations of the at least one measurement signal (p₁, p₂; p̃₁, p̃₂) at a predetermined first time interval (t₁),

   - calculation of a correlation value (W₂; W̃p₂) from the at least two measurement signals (p₁, p₂; p̃₁, p̃₂), which indicates a measure for the similarity of the at least two measurement signals (p₁, p₂; p̃₁, p̃₂) to one another at a predetermined second time interval (t₂), and

   - determination of the alarm (W) from the periodicity value (W₁; W̃₁) and the correlation value (W₂; W̃₂).
2. Method according to Claim 1, in which the alarm (W) is emitted when the product of the periodicity value (W₁; W̃₁) and the correlation value (W₂, W̃₂) exceeds a predetermined threshold value.
3. Method according to Claims 1 or 2, in which at least one of the measurement signals (p₁, p₂) is a mean-value-cleared measurement signal (p̃1, p̃₂).
4. Method according to any of Claims 1 to 3, in which the periodicity value (W₁, W̃₁) is calculated from at least one of the measurement signals (p₁, p₂; p̃₁, p̃₂) within a sliding time window of predetermined window width (N).
5. Method according to any of Claims 1 to 4, in which the periodicity value (W₁; W̃₁) is calculated as a mean value, if necessary scaled, of the squared deviation of in each case two measurement points of one of the measurement signals (p₁, p₂; p̃₁, p̃₂) offset with respect to one another by the first time interval (t₁).
6. Method according to Claims 4 and 5 in which, to calculate the periodicity value (W₁, W̃₁), an unscaled periodicity value (W₁) is determined in accordance with one of the following equations: $${\mathrm{W}}_1=\frac{1}{\mathrm{N}-{\mathrm{t}}_1}\cdot {\displaystyle {\sum }_{\mathrm{i}=1}^{\mathrm{N}-{\mathrm{t}}_1}{\left[{\mathrm{p}}_1\left(\mathrm{i}+{\mathrm{t}}_1\right)-{\mathrm{p}}_1\left(\mathrm{i}\right)\right]}^2}$$

   

   or $${\mathrm{W}}_1=\frac{1}{\mathrm{N}-{\mathrm{t}}_1}\cdot {\displaystyle {\sum }_{\mathrm{i}=1}^{\mathrm{N}-{\mathrm{t}}_1}{\left[{\tilde{\mathrm{p}}}_1\left(\mathrm{i}+{\mathrm{t}}_1\right)-{\tilde{\mathrm{p}}}_1\left(\mathrm{i}\right)\right]}^2}$$

   

   
   in which p₁ is the evaluated measurement signal without mean-value clearing and p̃₁ is the evaluated measurement signal with mean-value clearing, respectively, N is the window width of the sliding evaluation time window, and t₁ is the first time interval.
7. Method according to any of Claims 1 to 6, in which the correlation value (W₂; W̃₂) is calculated from the at least two measurement signals (p₁, p₂; p̃₁, p̃₂) within a sliding time window of predetermined window width (N).
8. Method according to any of Claims 1 to 7, in which the correlation value (W₂ W̃₂) is calculated as a mean value, if necessary scaled, of the product of in each case two measurement points of two different measurement signals (p₁, p₂; p̃₁, p̃₂) offset with respect to one another by the second time interval (t₂).
9. Method according to Claims 7 and 8 in which, to calculate the correlation value (W₂; W̃₂), an unscaled correlation value (W₂) is determined in accordance with one of the following equations: $${\mathrm{W}}_2=\frac{1}{\mathrm{N}-{\mathrm{t}}_2}\cdot {\displaystyle {\sum }_{\mathrm{i}=1}^{\mathrm{N}-{\mathrm{t}}_2}\left[{\mathrm{p}}_1\left(\mathrm{i}+{\mathrm{t}}_2\right)\cdot {\mathrm{p}}_2\left(\mathrm{i}\right)\right]}$$

   

   or $${\mathrm{W}}_2=\frac{1}{\mathrm{N}-{\mathrm{t}}_2}\cdot {\displaystyle {\sum }_{\mathrm{i}=1}^{\mathrm{N}-{\mathrm{t}}_2}\left[{\tilde{\mathrm{p}}}_1\left(\mathrm{i}+{\mathrm{t}}_2\right)\cdot {\tilde{\mathrm{p}}}_2\left(\mathrm{i}\right)\right]}$$

   

   
   in which p₁ is the first evaluated measurement signal without mean-value clearing and p̃₁ is the first evaluated measurement signal with mean-value clearing, respectively, p₂ is the second evaluated measurement signal without mean-value clearing and p̃₂ is the second evaluated measurement signal with mean-value clearing, respectively, N is the window width of the sliding evaluation time window, and t₂ is the second time interval.
10. Method for the operation of a gas turbine (10), comprising the steps:

    - determination of a surge limit alarm (W) by a method according to any of Claims 1 to 9, and

    - alteration of at least one operating parameter of the gas turbine (10) in reaction to the surge limit alarm (W), to avoid compressor surging.
11. Turbocompressor (12, 14) with a control unit (26) and at least two pressure, flow-rate or temperature sensors (22, 24) arranged offset relative to one another in the circumferential direction of the turbocompressor (12, 14), such that the control unit (26) is designed to implement the steps of a method according to any of Claims 1 to 9 in order to determine a surge limit alarm (W).
12. Turbocompressor (12, 14) according to Claim 11, in which the control unit (26) comprises a surge limit alarm determination module (32) and an influencing module (34), such that the surge limit alarm determination module (32) serves to determine the surge limit alarm (W) and the influencing module (34) is designed, by emitting at least one control signal (c₁, c₂, c_x), to influence at least one operating parameter of the gas turbine (10) in reaction to the surge limit alarm (W) in order to avoid compressor surging.
13. Gas turbine with a turbocompressor according to Claims 11 or 12.
14. Method for operating a turbomachine (10), comprising the steps:

    - determination of an alarm (W) in the event of blade damage to a rotor, by a method according to any of Claims 1 to 9, and

    - detection and storage of the alarm (W) with a view to repair or replacement.
15. Method according to Claim 14, in which conclusions about the extent of the damage are drawn from the type of the alarm (W).

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