CN1748129A - Method for determination of the stress on blades of a turbine machine during operation and corresponding device for carrying out said method - Google Patents

Abstract

The method serves to determine the vibrational state of turbine blades (4), arranged on a rotor shaft, mounted such as to rotate in a housing and/or of guide vanes. At least one electromagnetic wave (31) is transmitted into a flow channel in the vicinity of the blades (4), using means (8) for the generation of at least one electromagnetic wave. The electromagnetic waves (31) are at least partly reflected from at least one blade (4). The reflected part (32) of the at least one electromagnetic wave is received by means for receiving (8) and the vibrational state of the corresponding blade (4) is determined from a signal corresponding to the at least one received electromagnetic wave (32).

Description

Method for in-service determination of stresses on turbine blades and corresponding equipment for carrying out the method

The invention relates to a method for determining the stresses in rotor blades mounted on a rotor shaft rotatably mounted in a casing in a turbomachine. Furthermore, the invention relates to a method for determining the stresses of guide vanes in a turbomachine which are mounted in a rotationally fixed manner on the casing, and to a device for carrying out the method.

Turbines, such as steam turbines or gas turbines, are used in industrial technology as thermodynamic machines in order to convert the energy stored in a gas flow into mechanical energy, in particular rotary motion.

In order to achieve the highest possible overall efficiency in terms of energy utilization in a gas turbine, the inlet temperature of the gas from the combustion chamber into the flow channel of the gas turbine is generally chosen to be as high as possible. Such an inlet gas temperature is, for example, about 1200°C in the prior art.

In order to enable the blades installed in the turbine flow channel to withstand physical loads, especially thermal stress, it is known in the prior art to coat the surface of the blades and a thermal insulation layer (Termal-Barrier-Coating, TBC for short). However, this coating of the blade is subject to aging, during which, depending on the duration of operation, the coating is eroded from the blade over time. A blade with a damaged surface coating will experience severe wear which leads to blade failure. The result is reduced turbine power or even turbine damage.

In the prior art, therefore, the service life of such blades is usually determined on the basis of test results and empirical values, wherein the turbine is always disassembled at the end of such an operating cycle in order to check the surface coating of the rotor blades. A disadvantage is that dismantling of the turbine is costly and time-consuming, and the maintenance intervals here are defined in such a way that the above-mentioned damage is to be substantially avoided. Furthermore, this leads to a maintenance service being carried out even if the actual wear limit has not been reached.

Furthermore, the blade loads during operation due to the rotational movement and due to the gas flow acting on the rotor blades are high. At the same time, the loads caused solely by the gas flow around the guide vanes cannot be ignored.

During operation, the working blades and guide blades are always in mechanical vibration. If these vibrations are too strong, cracks can form in the blade, which in extreme cases can cause the blade to break. In particular broken rotor blade parts can penetrate metal walls, for example the casing walls of a turbine, due to their high functionality. In addition to damaging the turbine, it also endangers persons in the vicinity.

By monitoring the vibrations of the blades during operation, it is possible to react quickly and eliminate the cause of the vibrations if necessary.

According to WO 95/35484, the vibration of the turbine blades can be monitored by means of microwaves. Therein, a microwave duct is positioned near the set of rotating blades of the turbine, precisely in such a way that when the rotor shaft rotates, the ends of the blades, ie blade tips, sweep over the openings of the microwave duct. A continuous wave of microwave energy is then emitted through the microwave conduit to the rotating set of blades. When the blade tip passes through the continuous wave trajectory, a reflected wave is generated, which together with the emitted wave forms a standing wave. The standing wave collapses as soon as the blade tip continues to move, and is re-established when the following blade tip comes before the opening. Each blade tip passes the trajectory of the continuous wave each time, emitting a signal in the rhythm of the blade tip sweeping across the opening. Deviations from the normal rhythm provide information about the state of blade vibration. According to another embodiment, the intensity of the reflected wave is measured, which likewise changes in rhythm to the swept blade tip. The evaluation of the signal here takes place analogously to the embodiments described above. With this known device, however, it is only possible to obtain information about the vibration state to a limited extent. Because the emitted waves are reflected at the tip of the blade, only those vibration modes that are particularly characteristic at the tip of the blade can be detected. In the region between the rotor shaft and the tip of the blades there are particularly distinctive patterns which cannot be detected with this device. Especially in the case of impellers of special design in which all blade ends of an impeller are connected to each other by a ring, it is not possible to use the known device for blade vibration monitoring. Because in this impeller only the mode of vibration occurs in the area between the rotor shaft and the tip of the blade, which itself is fixed by the ring and cannot vibrate. Furthermore, with this known device it is in principle not possible to measure the vibrations of the guide vanes.

It is therefore the object of the present invention to provide a method and a device for carrying out the method by means of which a more comprehensive monitoring of the stress situation of the rotor blade and/or the guide blade during operation can be achieved.

In order to achieve this object, the present invention proposes a method for determining the stresses in a rotor shaft mounted on a rotor shaft rotatably supported in a casing in a turbomachine, wherein the device for generating at least one electromagnetic wave is operated At least one electromagnetic wave is emitted in a flow channel in the blade area, the at least one electromagnetic wave is at least partially reflected by at least one working blade, the reflected part of the at least one electromagnetic wave is received by means for receiving, and according to the A signal corresponding to the received at least one electromagnetic wave determines the stress of the rotor blade.

The effect is used here that the reflected portion of the at least one electromagnetic wave contains information about the stress state of the blade or the degree or amount of damage to the blade relative to the nominal state, which can be determined by evaluating the received signals. For this purpose, in particular the amplitude and/or phase and/or spectral distribution of the signal can be taken into account as parameters.

Furthermore, the invention proposes a method for determining the stresses of guide vanes mounted in a turbomachine in a rotationally fixed manner on the casing, wherein at least one electromagnetic wave is emitted in a flow channel in the region of the guide vanes by means of generating at least one electromagnetic wave At least one electromagnetic wave, said at least one electromagnetic wave is at least partially reflected by at least one guide vane, the reflected part of said at least one electromagnetic wave is received by means for receiving, and according to the corresponding to the received at least one electromagnetic wave The signal determines the stress on the guide vane.

Furthermore, a combination of the two methods described above is proposed in order to determine the stresses on the rotor and guide vanes simultaneously or separately.

The invention also proposes a method according to which the surface quality of the blade is determined as a measure of stress. It is thus possible for the first time not only to determine the corresponding state of the blades without disassembling the turbine, but also to monitor this during turbine operation. For example, maintenance of the turbine can advantageously be carried out when it is determined by the stress that a wear limit concerning the surface quality has been reached. Therefore, the maintenance interval can be extended according to actual needs. The costs incurred by repairing the turbine are significantly reduced, and in particular the downtime is considerably shortened. To carry out the method, multiple beams of electromagnetic waves can also be emitted, which can, for example, also be emitted distributed along the circumference of the flow channel. Of course, reflected parts can likewise be picked up at different positions on the circumference of the flow channel in order thereby to obtain additional and/or more precise information about the surface quality condition. Of course, this method can also be used dually to determine the surface quality of guide vanes arranged in a turbomachine, but in this case the means for generating at least one electromagnetic wave and for receiving them are mounted on the rotatably mounted rotor shaft superior.

It is thus advantageously also possible to monitor the surface quality of non-rotating components of the turbomachine. For example, means for emitting at least one electromagnetic wave distributed along the circumference of the turbine can be used, a suitable arrangement being possible here. Correspondingly, means for receiving can be provided in order to receive reflected electromagnetic waves. In order to reduce the operating costs of such an arrangement, it can be provided, for example, that it is operated in a pulsed and/or multiplexed manner with time-differentiated circuits. Furthermore, it can be provided that a device is used for emitting at least one electromagnetic wave and simultaneously for receiving it, which is arranged on the housing in the region of the guide vanes to be monitored.

Furthermore, it is proposed that, depending on a surface structure to be determined, at least one electromagnetic wave with an adapted wavelength adapted to its surface shape is used. This can advantageously be achieved, particularly advantageously, in which the damage is reflected on the at least one electromagnetic wave in order to provide, for example, a high signal level to the evaluation unit, from which the surface quality is determined.

According to a further refinement, the device for generating at least one electromagnetic wave is used to receive at least one electromagnetic wave. As a result, the components on the turbine as well as the assembly and construction costs can be reduced. For example, one antenna can be used for both transmission and reception.

Furthermore, it is proposed to determine the surface quality as a function of the intensity of the at least one received electromagnetic wave. The evaluation of the signal can thus advantageously be carried out with simple and inexpensive means. In addition, other applicable wavelengths, such as millimeter waves, etc. may also be used.

Furthermore, the invention proposes to determine the vibration state of the blade as a measure of the stress. This makes it possible to determine, in addition to the vibration states of the blade tips, also vibration states whose vibration modes are particularly pronounced in the mid-blade region, ie between the blade tip and the rotor shaft. The advantage of this method is that the information about the vibration state of the blade is more extensive and more accurate than the prior art. Damage caused by vibration modes which are particularly pronounced in the central region of the blade can be avoided by taking timely measures.

To carry out the method, multiple beams of electromagnetic waves can also be emitted, which can, for example, also be emitted distributed along the periphery of the flow channel. Of course, the reflected portion can likewise be picked up at different positions on the periphery of the flow channel in order thereby to obtain additional and more precise information about the state of vibration of the rotor blade. Of course, this method can also be used dually for determining the vibration state of the guide vanes arranged in the turbine, in which case the means for generating at least one electromagnetic wave and for receiving them can also be mounted on the rotatably mounted rotor shaft superior.

Furthermore, the invention proposes a method for determining the state of vibration of a guide vane mounted in a turbomachine in a rotationally fixed manner on the housing, in which a flow channel in the region of the guide vane is generated by means of at least one electromagnetic wave transmitting at least one electromagnetic wave, said at least one electromagnetic wave being at least partially reflected by at least one guide vane, the reflected portion of said at least one electromagnetic wave being received by means for receiving, and corresponding to at least one received electromagnetic wave The signal determines the vibration state of the guide vane.

Furthermore, a combination of the above two methods for determining the vibration state is proposed in order to determine the vibration state of the rotor blade and the guide blade simultaneously or separately.

Advantageously, therefore, vibration states of non-rotating components of the turbomachine can also be monitored. For example, means for emitting at least one electromagnetic wave distributed along the circumference of the turbine can be used, a suitable arrangement being possible here. Correspondingly, means for receiving can be provided in order to receive reflected electromagnetic waves. In order to reduce the operating costs of such an arrangement, it can be provided, for example, that it is operated in a pulsed and/or multiplexed manner with time-differentiated circuits. Furthermore, it can be provided that a device is used for emitting at least one electromagnetic wave and simultaneously for receiving it, which is arranged on the housing in the region of the guide vanes to be monitored.

Furthermore, it is proposed to use at least one electromagnetic wave having a wavelength adapted to the respective surface shape. It can thus be advantageously achieved, particularly advantageously, that vibrations are reflected on the at least one electromagnetic wave in order, for example, to provide the evaluation unit with a high signal level, from which the vibration state is determined.

Furthermore, it is proposed to use at least one radar wave as at least one electromagnetic wave. As a result, known devices for generating and transmitting radar waves can advantageously be used. Outlays and costs can thereby be further reduced. In addition, by using radar waves an adaptation can be achieved with respect to the vibration frequency and/or damage of the blade, so that an advantageous signal level can be obtained for monitoring the vibration state and/or the surface quality.

According to a further configuration proposal, the device for generating at least one electromagnetic wave is also intended to receive at least one electromagnetic wave. As a result, the components on the turbine as well as the assembly and construction costs can be reduced. For example, a radar antenna can be used both for transmitting and for receiving.

Furthermore, it is proposed to determine the vibration state of the blade on the basis of a frequency comparison between the at least one emitted electromagnetic wave and the at least one received electromagnetic wave. An evaluation of the signal can thus advantageously be carried out with simple and inexpensive means. In addition, other applicable wavelengths, such as millimeter waves, etc. may also be used.

It is also proposed to simultaneously determine the surface quality and the vibration state of the blade as a measure of the stress. In addition to saving time and money, simultaneous measurements provide more comprehensive information on blade stresses, allowing more rapid action when damage is indicated.

Furthermore, the invention proposes a device for carrying out the method according to the invention, which has means for generating an electrical oscillation, means for generating at least one electromagnetic wave from said oscillation, means for receiving at least one electromagnetic wave, and an evaluation A unit for analyzing signals corresponding to at least one receivable electromagnetic wave. Advantageously, the means for generating at least one electromagnetic wave and for receiving it are accommodated in the flow channel of the turbine. These devices can each be formed by antennas, which are suitable for generating and emitting or receiving electromagnetic waves and for generating a corresponding signal. The means for generating electrical oscillations may for example consist of an electronic oscillator operatively connected to an antenna for generating at least one electromagnetic wave. The means for receiving at least one electromagnetic wave is preferably operatively connected to an evaluation unit capable of determining information about the state of vibration and/or the surface quality of the blade from the signals provided by the receiving means.

Furthermore, it is proposed that the device for generating at least one electromagnetic wave is suitable both for emitting and for receiving at least one electromagnetic wave. In this way the number of components is further reduced. For example, the means for generating at least one electromagnetic wave is operatively connected to the means for generating oscillations via a coupling means. A signal corresponding to the at least one received electromagnetic wave is fed into the evaluation unit via the coupling device. It is also possible to provide a plurality of coupling devices and antennas, which are connected, for example, in parallel to a plurality of associated evaluation units or in a time-divided multiplexed manner, for example, to one evaluation unit.

According to an advantageous further development of the invention, the device for generating at least one electromagnetic wave is at least one radar antenna. The radar antenna can have a compact design and small dimensions. The radar antenna is suitable not only for emitting at least one radar wave, but also for receiving at least one radar wave. For this purpose, it can be connected, for example, to a circulator, by means of which the oscillations can be fed to the antenna, and at the same time the reception signal provided by the radar antenna can be transmitted to the evaluation unit. Particularly advantageously, methods according to the Doppler principle can be used, in which the received wavelength differs from the transmitted wavelength. By means of suitable, especially electronic, simultaneous operation of the emission and reception of electromagnetic waves. Furthermore, it is also possible to emit a radio-frequency pulse, in which case the device for generating at least one electromagnetic wave is switched to reception during the pulse intervals. Energy and costs for generating the at least one electromagnetic wave can thus be saved.

According to a further design proposal, the device for generating at least one electromagnetic wave is installed in a turbine, in particular a gas turbine. Precisely in the area of large machines, the device according to the invention enables economical monitoring of the blades, whereby particularly expensive downtimes for maintenance and repair measures can be further shortened. For example, an increase in the availability of power plants equipped with gas turbines can be achieved. Furthermore, the device according to the invention can be designed in such a way that the influence on the gas flow in the flow channel of the turbine is kept to a low degree.

Further advantages and features of the invention are explained in detail below with reference to the drawings. The same structural parts are provided with the same reference symbols in the different figures. For the functions of the same structural parts, refer to the description of the first embodiment. In the attached picture:

Figure 1 shows a prior art gas turbine in a partially cutaway perspective view;

Figure 2 represents a partial enlarged view of the gas turbine shown in Figure 1 and the device according to the invention;

Fig. 3 represents and implements the principle circuit diagram by the method of the present invention;

Fig. 4 shows the working blade of the gas turbine in Fig. 1;

Fig. 5 shows the guide vane of the gas turbine in Fig. 1;

Figure 6 represents a schematic circuit diagram of another design for monitoring the guide vanes; and

Figure 7 shows an antenna arrangement for monitoring a working blade.

Figure 1 shows a prior art gas turbine 1 designed for high gas inlet temperatures of about 1200°C. The gas turbine 1 has rotor blades 4 mounted on a rotor shaft 3 rotatably mounted in a casing 2 . In addition, guide vanes 11 are connected to the housing 2 in a rotationally fixed manner ( FIGS. 4 , 5 ). In particular, the rotor blades 4 and the guide blades 11 are each provided with a surface coating 12 , 13 in order to withstand the physical loads in the flow channel 6 of the gas turbine 1 .

As shown in FIG. 2 , the turbine 1 is equipped with the device according to the invention, which has an antenna 8 , in particular a radar antenna, which protrudes into the flow channel 6 of the gas turbine 1 . The radar antenna 8 is arranged in the region of the rotor blades 4 to be monitored, in particular between two rotor blade groups. The radar antenna 8 serves as means for emitting at least one electromagnetic wave and also as means for receiving at least one electromagnetic wave. The radar antenna 8 is communicatively connected to a circulator 16 . Furthermore, the device according to the invention has a radio-frequency generator 14 which is operatively connected via an amplifier 15 to a circulator 16 . The circulator 16 is simultaneously connected to a receive amplifier 17 and to a mixer 18 , which is itself simultaneously connected to the radio-frequency generator 14 . The outlet of the mixer 18 is connected to an evaluation unit 19 (FIG. 2).

In the embodiment shown in Figures 2 and 3, the principle of Doppler radar is used. Here, at least one electromagnetic (radar) wave 31 with a fixed wavelength is emitted, which is reflected by a monitored object (=rotor blade 4 ) that is moving relative to the antenna 8 . Through this relative movement, the receiving wavelength in at least one electromagnetic wave reflecting portion 32 is shifted relative to the transmitting wavelength according to known physical effects, and the antenna 8 generates a corresponding signal.

FIG. 3 shows in detail the execution of the method of the exemplary embodiment referred to here and is explained below.

An electronic radio frequency generator 14 generates a radio frequency with a fixed and predeterminable wavelength, which is preferably equal to one of the frequencies f ₀ listed in Table 1. f ₀ /GHz 2.4 5.8 twenty four 61 122 245 f _D /KHz 6.032 14.577 60.32 153.3 306.6 459.9

Table 1

This high frequency is supplied to an amplifier 15 which feeds the amplified high frequency via a circulator 16 to the antenna 8 . Antenna 8 generates at least one corresponding radar wave 31 based on the incoming high-frequency energy and emits it according to its radiation characteristics. A working blade 4 passing by the radar antenna 8 reflects a portion 32 of the radar wave back to the antenna 8 where the blade causes a wavelength change due to relative motion of the blade relative to the antenna 8, including rotational motion and vibration. According to the design shown here, that is, the rotation frequency is 60 Hz and the effective distance between the rotation axis and the blade 4 position detected by the at least one radar wave 31 is about 1 m, according to the formula

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}$

The frequency f _D corresponding to the wavelength change is found. In the formula, f ₀ is the frequency of the at least one transmitted wave 31, v(t) is the relative velocity of the surface of the working blade 4 and the guide vane 11 reflecting the at least one electromagnetic wave 31 with respect to the antenna 8, and C _is The propagation speed of the at least one electromagnetic wave 31 , 32 .

The at least one reflected electromagnetic wave 32 is re-converted into an electrical signal via the antenna 8 , and the signal is supplied to the circulator 16 . The circulator 16 now separates the received signal from the transmitted signal and supplies it to a receive amplifier 17 . From the receive amplifier 17 this signal reaches the mixer 18 where it is mixed with a signal corresponding to the high frequency of the high frequency generator 14 . In this process, the phases of the radio frequency of the radio frequency generator 14 and the signal of the reception amplifier 17 are taken into account accordingly. The output signal of mixer 18 provides a signal having a frequency difference between the receive frequency and the transmit frequency. This signal with the frequency _f listed in Table 1 is supplied to the analysis unit 19, which analyzes the corresponding rotor blades according to the characteristics (=amplitude and/or phase and/or its spectral distribution) of this signal 4 Vibration state and/or surface quality condition. The determined analysis results are sent to the monitoring point for alarm or further transmitted to the central monitoring station through a display device or an alarm device not shown further. The evaluation unit can also be equipped with a comparison function, by means of which it can be determined whether a predeterminable threshold value has been reached. For example, when a threshold value is reached, a warning signal can be issued automatically that the turbine 1 should be maintained. Preferably, the strength of such a signal can be used as a threshold parameter for this purpose.

The antenna 8 is designed and arranged such that the at least one reflected electromagnetic wave 32 is at least partially Doppler shifted (=frequency shifted) relative to the at least one emitted electromagnetic wave 31 . FIG. 7 shows various antennas 81 , 82 and 83 with associated radiation characteristics 810 , 820 or 830 as exemplary embodiments and configurations. The antennas 81 , 82 and 83 are installed in the flow channel 6 in the region of the rotor blades 4 and/or guide blades 11 to be monitored between the blade groups. A design as a whip antenna or a coaxial antenna, in particular as a coaxial dipole antenna, is expedient. However, other antenna forms are also conceivable. The radiation characteristics can be designed to be symmetrical, such as antennas 81 and 83 , but can also be designed to be asymmetrical, such as antenna 82 . In order to generate a Doppler shift as large as possible, it is advantageous to pass the moving part, here the rotor blade 4 , through the spatial range covered by the radiation characteristic 810 , 820 or 830 . Thus the rotor blade 4, either in its entirety or only in a defined area of its surface (see the contour curved in multiple directions shown in FIG. This movement process is particularly advantageous. With this configuration, however, it is also possible to determine the Doppler shift caused by vibrations of only the stationary part, in this case the guide vane 11 , relative to the antenna 81 , 82 or 83 . In this case, the Doppler shift is due only to the vibratory motion and not to the relative motion caused by the rotational motion.

In principle, the antennas 81 , 82 and 83 can also be operated passively in addition to the active operation described here, ie the purposeful emission of at least one electromagnetic wave 31 for detecting the rotor blade 4 and/or the guide blade 11 . In passive operation, the antennas 81 , 82 and 83 do not emit any radiation, but only receive electromagnetic radiation which is present in the flow channel 6 , in particular due to damage to the rotor blade 4 and/or guide blade 11 . These antennas 81, 82 and 83 are therefore only intended to "listen".

According to a further embodiment of the invention, the rotor blades 11 and/or the guide blades 11 of the gas turbine 1 are monitored by means of a pulse radar. FIG. 6 shows a schematic circuit diagram of such a design for testing guide vanes. In the region of the guide vanes 11 , which are connected in a rotationally fixed manner between the gas turbine 1 and the casing 2 , transmitting antennas 5 are arranged distributed along the circumference of the flow channel 6 of the gas turbine 1 for transmitting at least one electromagnetic wave 31 . The antennas 5 are connected to a radio-frequency generator 9, which supplies each antenna with a radio frequency. The radio-frequency generator 9 is a pulse generator which generates short radio-frequency pulses with a predeterminable pulse-to-pulse ratio and distributes them to the antenna 5 connected thereto by multiplexing them in a time-differentiated circuit. Furthermore, receiving antennas 7 for receiving reflected electromagnetic waves 32 are installed distributed along the circumference of the flow channel 6 . The receiving antenna 7 is connected to a multiplexer 20, which also functions as a receiving amplifier. According to this configuration, each antenna 7 is connected to the evaluation unit 19 discontinuously in time by means of the multiplexer 20 . At the same time, the evaluation unit 19 receives the radio frequency from the radio frequency generator 9 . Furthermore, evaluation unit 19 receives a channel selection signal via line 21 , which transmits information about the selected antenna 7 to evaluation unit 19 . The guide vane monitoring shown here operates in pulses, so that the overall energy consumption can be kept low. Furthermore, it can be achieved that the component for generating at least one electromagnetic wave can be designed overall for a low thermal load.

The present invention should not be considered limited to the examples. It is also within the scope of protection that a plurality of radar antennas for transmitting and/or for receiving can also be provided, for example in order to have measurement redundancy or also to achieve a higher accuracy.

Furthermore, according to the invention, the vibration state and the surface quality of the blade can be measured simultaneously.

The invention is not limited to using only one beam or one type of electromagnetic wave 31 , 32 . The invention of course also includes transmitting and receiving multiple or multiple electromagnetic waves or wave spectra.

Claims (17)

1. A method for determining the stresses of rotor blades (4) mounted on a rotor shaft (3) rotatably supported in a housing (2) in a turbomachine (1), wherein, by generating at least The device (5, 8) of a beam of electromagnetic waves emits at least one beam of electromagnetic waves (31) in a flow channel (6) in the region of the working blades (4), said at least one beam of electromagnetic waves (31) being transmitted by at least one working blade ( 4) at least partially reflected, the reflected portion (32) of said at least one electromagnetic wave is received by means (7, 8) for receiving, and the working blade (4) is determined from a signal corresponding to the received at least one electromagnetic wave ) stress. 2. A method for determining the stress of a guide vane (11) mounted torsionally fixed on a casing (2) in a turbomachine (1), wherein the device (5 for generating at least one electromagnetic wave (31) , 8) emitting at least one electromagnetic wave (31) in a flow channel (6) in the region of the guide vanes (11), said at least one electromagnetic wave (31) being at least partially reflected by at least one guide vane (11), said at least one The reflected portion (32) of the beam of electromagnetic waves is received by means (7, 8) for receiving, and the stress of the guide vane (11) is determined from a signal corresponding to the received at least one beam of electromagnetic waves. 3. according to the described method of claim 1 and 2, it is characterized in that: on the rotor shaft (3) that is provided with working blade (4) and guide vane (11) of described turbine (1), not only the working blade is determined (4) and determine the stress of the guide vane (11). 4. The method as claimed in one of claims 1 to 3, characterized in that the surface quality of the blade is determined as a measure of the stress. 5. The method according to claim 4, characterized in that, depending on a surface structure to be determined, at least one electromagnetic wave (31) with a wavelength adapted to the respective surface shape is used. 6. The method as claimed in one of claims 1 to 5, characterized in that the device (8) for generating at least one electromagnetic wave is also used for receiving at least one electromagnetic wave (32). 7. The method as claimed in one of claims 4 to 6, characterized in that the surface quality of the blade is determined as a function of the intensity of the at least one received electromagnetic wave (32). 8. The method as claimed in one of claims 1 to 3, characterized in that the vibration state of the blade is determined as a measure of the stress. 9. The method as claimed in claim 8, characterized in that at least one electromagnetic wave (31) with an adapted wavelength adapted to the respective surface shape is used. 10. The method as claimed in claims 1 to 9, characterized in that at least one radar wave (31) is used as at least one electromagnetic wave. 11. The method as claimed in one of claims 8 to 10, characterized in that the device (8) for generating at least one electromagnetic wave is used to receive at least one electromagnetic wave (32). 12. The method according to any one of claims 8 to 11, characterized in that: by comparing the frequency of the at least one emitted electromagnetic wave (31) with the frequency of the at least one received electromagnetic wave (32) In contrast, to determine the vibration state of the blade. 13. The method as claimed in claim 1, characterized in that the surface quality and the state of vibration of the blade are simultaneously determined as a measure of the stress. 14. An apparatus for implementing the method according to any one of the preceding claims, comprising means (9) for generating an electrical oscillation, means (5, 5, 8) A device (7, 8) for receiving at least one electromagnetic wave (32) and comprising an analysis unit (10) for analyzing and evaluating said at least one receivable electromagnetic wave (32). 15. The device according to claim 14, characterized in that the means (8) for generating at least one electromagnetic wave are suitable both for emitting and for receiving at least one electromagnetic wave (31, 32). 16. Device according to claim 14 or 15, characterized in that said means (5, 8) for generating at least one electromagnetic wave (31) is a radar antenna. 17. The device according to one of claims 14 to 16, characterized in that the device (5, 8) for generating at least one electromagnetic wave (31) is installed in the flow of the turbine (1), especially a gas turbine Inside the channel (6).

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