RU2138012C1 - Method for measuring running rates of turbine rotor blades - Google Patents

Abstract

FIELD: automatic contactless monitoring of turbine rotor blades in the course of tests and in service. SUBSTANCE: two eddy-current transducers are mounted on turbine stator. Transducers are spaced apart along turbine axis so that blade end does not jut beyond transducer sensitivity band. Transducers are relatively offset in rotor motion plane through certain angle. Transducers are excited by trains of pulse groups. Number of pulse groups equals that of blades. Time shift of trains exciting first and second transducers relative to each other corresponds to angular offset of transducers. Signals coming from transducers are used to determine radial clearances between blades and transducers. EFFECT: provision for determining axial displacement of turbine rotor. 5 dwg

Description

 The invention relates to measuring equipment and can be used for non-contact automatic control of the parameters of motion of the blades of the rotor of a turbomachine during testing and operation.

 A known method of measuring the gaps between the stator and the ends of the rotor blades, based on the excitation by an alternating magnetic field of an eddy current transducer in the gap measurement zone and fixing the maximum values of the measured signals of the transducers at the moment of passage of the blades of the center of the transducer [A. USSR N 1201672, IPC G 01 B 7/08, 1984].

 The disadvantage of this method is the low sensitivity and accuracy of the measurement, due to the limitation on the amount of electric power "applied" to the transducer due to the continuous excitation of the electromagnetic field in the measurement zone of the gap.

 Closest to the technical nature of the present invention is a method for measuring radial clearances in turbomachines, which consists in the interaction with the ends of the blades of a working turbomachine, an eddy current transducer synchronized with its rotation, excited by sequences from groups of pulses, and radial clearances between blades and the specified Converter [A. USSR N 1779908, IPC G 01 B 7/08, 1992].

 The disadvantage of this method is the low accuracy and information content of the measurement due to the impossibility of taking into account the influence of the axial displacement of the rotor blades of the turbomachine.

 The present invention solves the problem of improving the accuracy and information content of measuring the parameters of the motion of the blades of the rotor of a turbomachine, which will optimize the elements of its design and, therefore, create more economical samples of turbomachines.

 The problem is solved in such a way that in the known method, namely, with the ends of the blades of a working turbomachine, an eddy current transducer synchronized with its rotation is brought into interaction, excited by sequences of groups of pulses selected by the number of blades in the turbomachine wheel, and the number of pulses in each group choose from the condition of permissible unevenness of the envelope of the output signal of the eddy current transducer, and radial gaps between the blades and the indicated a browser, an additional transducer is introduced, the transducers are placed at such a distance along the axis of the turbomachine when, for all possible axial displacements, the controlled end of the blade does not leave the sensitivity zone of each transducer; taking into account the final dimensions of the converters, the second converter is displaced along the generatrix of the stator relative to the first; exciting the first and second converters with pulse trains, the pulse train for the second converter being shifted by the time determined by the rotor speed of the turbomachine and the angle of displacement between the converters; from the found values of the output signals of both transducers by solving a system of two equations obtained on the basis of the families of calibration characteristics of the transducers, determine the values of the radial clearance and axial displacement.

 In FIG. 1 is a diagram explaining the placement of the transducers on the stator of the turbomachine, where the blades 1 and 2 mounted on the rotor wheel 3 are shown, the transducers 4 and 5 placed on the stator 6, the synchronization sensor 7, the label 8 on the rotor shaft 9.

In FIG. 2-4 is a diagram explaining the essence of the method of measuring the motion parameters of the blades of a rotor of a turbomachine:
figure 2 - for the case when there is no displacement of the blades of the rotor of the turbomachine;
figure 3 - the blades of the rotor of the turbomachine are shifted to the right;
figure 4 - the blades of the rotor of the turbomachine are shifted to the left.

 Figure 2-4 shows the blade 1 and the transducers 2, 3. The interrogators are polled at a fixed angular position of the blade. In the absence of axial displacement (Fig. 2), the sensitivity of the transducers 2, 3 will be the same, with the axial displacement of the blade 1 to the right (Fig. 3), the sensitivity of the transducer 2 increases, and the sensitivity of the transducer 3 decreases. Similarly, with the axial displacement of the blade 1 to the left (Fig. 4), the sensitivity of the transducer 3 increases, and the sensitivity of the transducer 2 decreases.

 5 is a diagram illustrating an algorithm for determining radial clearance and axial displacement.

t_н2= t_н1+t_φ,
где t_н1, t_н2 - временной интервал от появления синхроимпульса до момента появления первой лопатки под первым и вторым преобразователем соответственно;
T_об - период вращения ротора турбомашины;
α_н - угол между первым преобразователем и серединой ближайшей лопатки в момент выдачи синхроимпульса;

время, затраченное на прохождение лопатки от первого преобразователя до второго (φ - угол смещения между преобразователями).The measurement of radial gaps between the stator and the ends of the blades of the rotor wheel and the axial displacements of the blades of the proposed method is as follows. The time interval between two adjacent clock pulses (pulses of the synchronization sensor) determines the value of the period T _{about the} rotation of the rotor of the turbomachine. The time intervals until the appearance of the first blade under both transducers are determined:

t _n2 = t _n1 + t _φ ,
where t _n1 , t _n2 is the time interval from the appearance of the clock to the appearance of the first blade under the first and second converter, respectively;
T _about - the period of rotation of the rotor of the turbomachine;
α _n is the angle between the first transducer and the middle of the nearest blade at the time of issuing the clock;

the time taken to pass the blade from the first transducer to the second (φ is the angle of displacement between the transducers).

 The obtained time intervals are counted from the moment the next sync pulse appears and the transducers are polled by groups of pulses, the number of which is selected from the condition of the permissible unevenness of the envelope of the output signal of the transducers.

Градуировочная характеристика каждого преобразователя представляет собой собранные в таблицы значения цифровых кодов, соответствующих максимумам огибающих выходных сигналов преобразователя, как функции радиального зазора при фиксированных значениях осевого смещения. Графически такая характеристика может быть интерпретирована в виде поверхности (фиг.5), координаты которой по вертикали характеризуют цифровой код, а в прямоугольных координатах - радиальный зазор и осевое смещение.Then the interval to the next scapula is counted.
t _l = T _r / N _l
where N _l - the number of blades on the rotor wheel,
and repeat the above steps until all of the shoulder blades are interviewed. Upon completion of the survey, for each blade, codes N _I and N _II are determined that correspond to the maxima of the envelopes of the output signals of the transducers, and their values determine the radial clearance δ and axial displacement S by solving a system of two equations derived from the calibration characteristics of the transducers:

The calibration characteristic of each converter is the values of digital codes collected in tables that correspond to the maximums of the envelopes of the converter output signals as a function of the radial clearance at fixed axial displacement values. Graphically, such a characteristic can be interpreted as a surface (Fig. 5), the vertical coordinates of which characterize the digital code, and in the rectangular coordinates - the radial clearance and axial displacement.

In Fig. 5, N _I ^* and N _II ^* are horizontal planes that differ in vertical coordinates, corresponding to the maxima of the envelopes of the output signal of the first and second converters. The intersection of the plane N _I ^* with the surface corresponding to the calibration characteristic for the first transducer occurs in space along a curve whose projection I onto the rectangular plane CLEAR-OFFSET corresponds to the set of values of radial clearances and axial displacements. Similarly, the intersection of the plane N _II ^* with the surface corresponding to the calibration characteristic for the second transducer is another curve in space whose projection II onto the CLEAR-OFFSET plane also corresponds to many values of radial clearances and axial displacements.

It is possible to determine the only pair of values of the radial clearance ((δ ^* ) ^* ) and axial displacement (S ^* ) for fixed codes N _I ^* and N _II ^* by searching for the intersection point of the projections of these curves. For this, you can use, for example, the Newton method [Bronstein I.N., Semendyaev K.A. Handbook of mathematics for engineers and students of technical schools, M.- "Science", 1986, p.497].

As an example of a specific implementation of the method, we consider measuring eddy current transducers with sensitive elements in the form of a section of a conductor [USSR Patent 1394912, MKI G 01 N 27/90. High temperature eddy current transducer / Skobelev O. P., Sekisov Yu.N., Khritin A.A.] gap δ between the ends of the blades 1, 2 of the wheel of the rotor 8 and the stator 6 of the turbomachine and the axial displacement of the blades S (figure 1). The converters 4, 5 are placed on the stator 6 along the axis of the turbomachine with an offset Δ S = 6 mm, while the second converter is shifted along the generatrix of the stator relative to the first by an angle φ = 0.5 ^o .

 After giving the command initiating the measurement process, at the first revolution the period of rotation of the top of the turbomachine is determined. Over the next two revolutions, the time interval from the appearance of the clock pulse to the moment the first blade appears under the first transducer and the time interval to the next blade is calculated.

 Next, the sequence of groups of power pulses of the first eddy current transducer is formed. In each group we form 3 pulses based on the condition of permissible unevenness of the envelope of the converter output signal. In response to each power pulse, the eddy current transducer excites an electromagnetic field that interacts with the blade in the sensitivity zone. As a result, the inductance of the converter varies depending on the axial displacement of the blades in the sensitivity zone and on the gap between the ends of the blades and the stator of the turbomachine. The output parameter of the eddy current transducer is converted into an electrical signal and a code proportional to the gap between the sensor and the blade.

 Similarly, the second transducer is polled.

After polling the transducers by approximating the samples in each group, codes corresponding to the maxima of the envelopes of the output signals of the transducers are determined. In the considered example for the first blade N _I ^* = 588 and N _II ^* = 467.

 The calibration characteristics for the converters obtained experimentally are presented in table 1 and table 2.

где α $\genfrac{}{}{0ex}{}{\text{I}}{\text{ij}}$ , α $\genfrac{}{}{0ex}{}{\text{II}}{\text{ij}}$ - коэффициенты аппроксимирующих полиномов (см. табл. 3, 4).As a result of approximating the calibration characteristics of the transducers by a polynomial of the third degree, the system of equations (1) takes the form

where α $\genfrac{}{}{0ex}{}{\text{I}}{\text{ij}}$ , α $\genfrac{}{}{0ex}{}{\text{II}}{\text{ij}}$ - coefficients of approximating polynomials (see tab. 3, 4).

As a result of solving the system of equations (2) by the Newton method, we obtain the desired radial clearance and axial displacement values equal to
δ = 1 mm, S = -1.5 mm.

 Thus, in comparison with the prototype, the proposed method provides more accurate information about the radial clearance between the stator and the ends of the rotor blades by taking into account the additional influence factor-axial displacement, and also allows you to determine the axial displacement of the rotor blades of the turbomachine itself, which increases the information content and accuracy of measurements of motion parameters rotor blades of a turbomachine.

Claims (1)

 A method of measuring the motion parameters of the rotor blades of a turbomachine, which consists in the interaction with the ends of the blades of a working turbomachine, an eddy current transducer synchronized with its rotation, which is excited by sequences from a group of pulses selected by the number of blades in the turbomachine wheel, and the number of pulses in each group is selected from conditions for permissible unevenness of the envelope of the output signal of the eddy current transducer and radial gaps between the blades are estimated from its signals and indicated transducers, characterized in that to solve the problem of increasing the accuracy and information content of the measurement, two transducers are used that are placed at such a distance along the axis of the turbomachine when, for all possible axial displacements, the controlled end of the blade does not leave the sensitivity zone of each transducer, the first and second transducers are excited pulse sequences, and the pulse sequence for the second Converter is shifted by the time determined by the speed of the turbomachine rotor values of the output signals of both transducers by solving a system of two equations obtained on the basis of the families of calibration characteristics of the transducers determine the values of the radial clearance and axial displacement.

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