Model Test of Forced Vibration of Spring Isolation Foundation of 1000MW Half-Speed ​​Turbine Generator Set in Nuclear Power Plant

2, Yin Chunming 3, He Xiyang (1. Guangdong Electric Power Design and Research Institute, Guangzhou 510600, China 2. Separate and Solid (Qingdao) Vibration Control Co., Ltd., Qingdao, Shandong 266108, China 3. CGN Engineering Design Company, Shenzhen, Guangdong 518124) The most fundamental theory for model testing of spring isolation of wheel generator sets is similar theory. The most critical technology is modal analysis. In this paper, we use the similarity theory and the transfer function matrix equation of modal analysis to derive the similarity criterion equation of the forced vibration model test. The decisive similarity criterion of the r-order mode is determined as the r-order damping ratio D and the r-order tuning ratio r, which is inconclusive. The similarity criterion is the amount of vibration line displacement combination. When the forced vibration of the spring isolation base of the 1 000 MW half-speed nuclear power plant turbine generator set is tested, the damping ratio and tuning ratio of each mode must be equal, but whether the damping ratio of the model and the prototype can be equal , lack of verification. Moreover, the current damping ratio is not reasonable, and the model test does not give useful advice. The vibration system includes a steam turbine generator set, a foundation pedestal, a spring isolator and a damper. The model test is difficult to satisfy the similar theory in terms of the excitation frequency, excitation strength and distribution of the machine. Model tests are also difficult to meet the stiffness, compression, and system frequency requirements of spring isolators.

: Spring Vibration Isolation Fundamental Similarity Theory Model Test Forced Vibration Modal Analysis Transfer Function Matrix Literature Logo Code: Supplement Zhou Leijing, et al: Nuclear power plant 1000 MW half-speed steam turbine generator set spring vibration isolation foundation forced vibration model test 1 Introduction Lingao nuclear power plant conventional island The 1 000 MW steam turbine generator set decided to use a half-speed unit with a spring isolation base. Since the half-speed 1 000 M W-class unit and the spring isolation base are the first attempts in China, whether to carry out the basic model test requires us to analyze and study in theory.

The purpose of the model test is to predict the vibration of the prototype base pedestal by the vibration data of the model base pedestal test, and evaluate its dynamic characteristics, and on this basis determine the best design.

At present, the conventional method for the basic model test of steam turbine generator sets adopts a model with a geometrical ratio of 1 10, and applies a random excitation force to excite the model base vibration, and collects the response signal of the excitation force signal and the model base vibration displacement.

For the model test of the basic pedestal, the most fundamental theory is the similarity theory. The most critical technology is modal analysis. If the model test fully satisfies the similarity theory, the results of the model test can be applied to the prototype based on complete reliability. However, theoretical analysis proves that it is difficult for the model test to accurately satisfy the similarity theory, and it can only be geometrically similar and it is difficult to completely satisfy the similarity of physical properties.

2 The steam turbine generator set base pedestal forced vibration similarity criterion equation is derived. The vibration differential equation of the steam turbine generator foundation pedestal is subjected to the simple harmonic excitation force: [m], [c] and [k] are respectively systematic The nth order mass matrix, the nth order damping matrix and the nth order stiffness matrix, and F is the forced vibration exciting force magnitude vector.

The forced vibration response of the base pedestal of the steam turbine generator is: where X is the steady-state response complex amplitude vector of forced vibration. The Fourier transform is performed on the differential equation (1). In the formula: X ( ) is the Fourier transform of the system displacement response, F( ) is the Fourier transform of the forced vibration excitation force, and [ H ( )] is the system frequency response function. : The damping inside the reinforced concrete foundation is more complicated. For the convenience of calculation, the proportional damping assumption proposed by Rayleigh can be used. That is, the Fourier transform of the system displacement response is in the formula: r-order mode, M is r-order Modal mass, r-order modal damping and r-order modal stiffness.

The subscript 1 is used to represent the prototype, and the subscript 2 is the model. When the linear scale ratio of the model platen to the prototype platen is the same as the material properties, the elastic modulus is equal, and the r-order mode mass ratio is m r1, then the r-order mode The state stiffness ratio k is the r-order mode frequency r, and the r-order mode frequency ratio is obtained: Substituting these ratios into the equation (7), when the ratio of the r-order mode damping is obtained, the frequency response function matrix equation (7) is further The transformation can be used to derive the similarity criterion, the criterion equation and the similarity ratio of the physical quantities of the steady-state forced vibration of the base pedestal of the steam turbine generator set.

From the r-order mode frequency r, the r-order modal damping ratio D) and the r-order mode tuning ratio r are introduced, so that the frequency response function equation (7) and the response amplitude equation (6) are changed according to equation (13), The various modes, X can be expressed as the Wuhan University Journal (Engineering Edition) and this is the same equation as the single degree of freedom. For each modal component, there are generally three similarity criteria for the equation to be transformed into a vibration model test. In the equation and D are two dimensionless quantities, which are two similar criteria. The factor of the combination amount on the left side of the equation is analyzed. The dimension of the dimension of the factor of N is m, so the order of the left combination of the equation is m N = 1, that is, the dimensionless quantity. Therefore, the similarity criterion of the spring model of the turbo-generator spring isolation is the r-order mode tuning ratio modal damping ratio D and the combined quantity X). In these three similarity criteria, since the amplitude of the vibration of each point of the base pedestal is the required amount, the similarity criterion including it is the non-deterministic criterion X), and the tuning ratio of the r-order modal damping ratio to the r-order mode is Decisive criteria. The similarity criterion equation for the model test is equation (16).

Equation (16) shows that the sufficient and necessary condition that the model pedestal is similar to the r-order mode of the prototype pedestal is that the deterministic criterion is equal, that is, equal to r1. It is equal to the decisive similarity criterion, and the prototype is similar to the parameters of the model in the r-order mode. For example, Table 1 shows.

Structure L Linear scale E Elastic modulus Mass damping coefficient Stiffness frequency H ( ) Frequency response function Prototype structure (1) Model structure (2) Similarity ratio Note: The linear scale, elastic modulus, mass and stiffness of the prototype structure are assumed 1.

3 Several problems related to model test (1) When analyzing the vibration of the base block of the spring-isolated vibration of the steam turbine generator set, the mass, damping, stiffness and natural frequency refer to the parameters of the system. The system includes the steam turbine generator set and the foundation. The pedestal, the spring isolator and the damper, so the model test of the base pedestal cannot be limited to the simulation of the base pedestal itself. Avoiding the simulation of the machine, the simulation of the spring isolator and the damper, it does not become a system and cannot be called a real model test. Taking the disturbance as an example, the disturbance force is the exciting force transmitted by the residual unbalance of the rotors of each stage of the steam turbine generator to the base pedestal when the centrifugal force generated during the rotary motion is transmitted. From the centrifugal force to the transmission coefficient of the disturbance force, the domestic chaos is still unclear.

(2) Selection of damping ratio in model test. Damping has a significant effect on the magnitude of the forced vibration response. However, the current choice of damping ratio is still not reasonable enough.

The horizontal vibration measurement data of the flexible foundation column of Waigaoqiao Phase II steam turbine generator set is much larger than the vibration data calculated according to national regulations. One problem is the value of the damping ratio. The data of the damping ratio given by the national code is too large, greater than 0.06, and the calculated amplitude value is suppressed. It may be that the model test and the prototype test of the column vibration calculation data are smaller than the measured data, and the damping ratio is taken. There should be a statement of values, but the model test never gives the conclusion that the damping ratio must be reduced by the national specification. This means that the model test did not give the guidance it deserved. When designing a flexible fixed foundation for a 1 000 MW Siemens unit for a power plant, Sie Mens recommends that the damping ratio be 0.03. What is the value of Siemens? The technical parameter of the external damper is the damping coefficient. When performing the 1/10 model test, the damping coefficient should be reduced to 1/100 of the prototype, but when the geometry is similar, the volume is reduced to 1/1000, and the damping coefficient is proportionally reduced to 1/1000 of the prototype. It is also a contradiction that needs to be resolved.

(3) If the model test conforms to the similarity theory, the tuning ratio of one of the decisive similarity criteria must be equal. The natural frequency of the model base pedestal is 10 times the natural frequency of the prototype base pedestal, and the frequency of the model base pedestal excitation force must be 10 times the excitation frequency of the prototype base pedestal. For the half-speed nuclear power turbine generator set, the excitation frequency of the prototype base pedestal is 1 500 r/min (25 Hz), and the excitation frequency of the model base pedestal must be 15 000 r/min (250 Hz), which is difficult to achieve. of. Because the exciting force of the current model test is a finite frequency domain random force applied by the hammering method, the 250 Hz excitation force only accounts for a small, small part, and the rest become background noise.

The frequency of the excitation force is considered in conjunction with its intensity and response amplitude. If the response amplitude of the model base pedestal is equal to the response amplitude of the prototype base pedestal, the excitation force of the X model must be equal to 0.1 times the prototype excitation force, that is, the displacement of the response vibration of the model pedestal should be as Consistent with the prototype, because the vibration value of the spring vibration isolation base pedestal of the steam turbine generator set is small regardless of the control value or the measured value. When the background is supplemented by Zhou Leijing, et al.: The 1000 MW half-speed steam turbine generator set spring vibration isolation foundation forced vibration model test noise is greater than the vibration excited by the disturbance force, it will affect the measurement accuracy. The measuring instrument is no better, there are also errors.

The model test is difficult to satisfy the similarity in the frequency, intensity and distribution position of the exciting force (the excitation force is excited by the high-pressure rotor of the steam turbine, the medium-pressure rotor, the low-pressure 1 rotor, the low-pressure 2 rotor, the generator rotor and the exciter rotor). Theoretical requirements.

(4) The relationship between the natural frequency of the system, the spring stiffness of the spring isolator and the compression amount is difficult to satisfy the similar theory.

The compression of the prototype base pedestal spring isolator is about 28mm, so the system natural frequency f is the formula, k is the total stiffness of the spring isolator, m is the total mass of the system, and the spring compression is in cm. . According to the natural frequency similarity ratio of 10 1, the natural frequency of the model base system is about 30 Hz, so the compression of the model spring isolator is about such a small compression amount, because no matter how it is processed, between the springs. The height always has an error of 12 mm, that is, the machining error is much larger than the compression of the model base spring isolator. 0. 28 mm. If the compression of the model spring cannot be satisfied, the system frequency is difficult to satisfy the similar theory.

The rubber of a micro-compressive amount of elastic material can be selected. However, the horizontal stiffness of the rubber is extremely small, and its ratio to the vertical stiffness is extremely different from the performance of the coil spring. It is impossible to simulate a coil spring with a rubber material to satisfy the similar theory.

4 Conclusions From the similarity theory discussed above, the relationship between modal analysis and model tests, and several problems that are difficult to solve in model tests, the following conclusions can be drawn: (1) The vibration of the base pedestal is only part of the system vibration. The system includes a steam turbine generator set, a base pedestal, a spring isolator and a damper. The model test cannot simulate the vibration of the steam turbine generator set and has limitations.

(2) Damping has a significant effect on the magnitude of the forced vibration response, and the current selection of damping ratio is still not reasonable enough.

(3) The model test is difficult to satisfy the similar theory in terms of the frequency, intensity, and distribution position of the exciting force.

(4) The model test is difficult to satisfy the similar theory in the relationship between the natural frequency of the system, the spring stiffness of the spring isolator and the compression.

Thanks: Professor Zhou Xingeng from Tsinghua University, Dr. Gao Xingliang from Gustaving (Qingdao) Vibration Control Co., Ltd. and Sun Yigang from Hangzhou Steam Turbine Co., Ltd. have put forward many valuable suggestions for this article.

Cao Shuqian, Zhang Wende, Xiao Longxiang, Theory, Experiment and Application of Vibration Structure Modal Analysis [M]. Tianjin: Tianjin University Press, 2002.

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