Relationship bearing stability and support bearing

Shafting stability is often constrained to the stability of rotating machine, we need to continue to modify the design parameters of the shaft One of the major security operation designed to ensure that the unit has sufficient stability margin. Since the shaft for more modified parameters, if the blind modify many of the design parameters is usually difficult to achieve the purpose of improving stability. Theory and practice have shown that changes in the structure type or bearing design parameters can effectively improve the stability of shafting. However, as the complexity of such a large turbine generator shaft 10 a total of seven sliding bearings.
Some bearing a greater impact on the stability of the shaft, the impact of some of the bearing is small. Which have a greater impact on the stability of the structure type or design parameters bearing only change possible to achieve the purpose of improving stability.
Based on the work force each bearing made under the stability limit state defined contribution bearings for shaft stability coefficient and sensitive bearings, and the relations between stability and each support shaft bearing. Theoretical analysis and numerical calculation show that this is important for the stability and improve the fault diagnosis of large rotating machinery rotor-bearing system.
Under 2 free vibration equation film masterpiece stability limit state power shaft is (several hundreds of ZM + D + K) Z 20 (1) where: a few of eigenvalues, M, D K are the mass, damping. and stiffness matrix, Z is the displacement vector. When the bearing in the stability limit state equation (1) has a pair of zero real part of the eigenvalues ​​for a long time a scholar J. And a corresponding pair of conjugate eigenvectors towel and west. This article discusses the displacement response are real numbers, then with the pair of conjugate modes corresponding complex modal parameters is conjugate pairs. In the stability limit state shafting response to initial conditions. During the week of work not only for the intrinsic parameters of the system function, but also a function of the complex modal parameters. The complex modal parameters are determined by the initial condition of the system, it is the film coefficient _ cut, function or system function as initial conditions. For a practical unit for random interference is always present, it is difficult to determine the unit's initial condition .3 vehicle stability is defined by the Order of the shaft bearing sensitive contribution coefficient for the i-th bearing shaft stability contribution factor the B twenty-one W / G (1 3) where G is all less than zero and relatively successful, this treatment is greater than the sum of the contribution that all coefficients equal to zero l. Shaft Bearing assume only consume or provide energy to the system, then in the sum of all bearing stability limit state for power it is zero, that is the sum of the contribution coefficient of zero.
Typically, the energy consumption for the negative work of bearing system, prompting a negative power system stability for the greater contribution factor that is greater and so the first two 徐龙祥: Relationship shaft stability and support bearing 171 bearing it the greater contribution to the stability of the shaft; on the contrary, positive work bearing in whirl process continue to provide energy to the system, excitation system instability, as the positive power coefficient greater contribution that is more likely to stimulate the smaller bearings system instability. Based on this knowledge, the relationship between stability and each support shaft bearing can be expressed as: (1) The contribution factor is greater than zero bearing prompting system is stable, Contribution coefficient greater bearing on the stability is greater. (2) The contribution factor is less than zero bearing excitation system instability, the contribution factor smallest shaft bearing is the most dangerous bearing oil film instability or oil whip often the first excited by the bearings. (3) Shaft stability depends bearing dynamic coefficients of sensitive and appropriate changes in these parameters bearing structure type or design can effectively improve the stability of the shaft; and changes in non-sensitive bearing structure type or design parameters, the shaft Department of stability change is very small.
4 cases and discussion is considered a model of rotor-bearing system, a total of five plain bearings.
 Shaft section and the junction of the shaft section called natural nodes, in addition to the rotor of the left and right side, also known as natural nodes, so a total of 27 natural nodes rotor. When the rotor is discretized into 25 total sets quality in each lumped mass perception of specific slices. (L) 2, No. 5 bearing contribution coefficient greater than zero. They promote the stability of the system, while the other three bearing the excitation system instability. (2) the minimum contribution coefficient bearing 3 which is the most dangerous shaft bearings;. Contribution factor for the bearing shaft 5 maximum it is the safest bearings, the absolute value of the contribution factor is much larger than the other three bearings. two bearings. This shows that the king said bearings are bearings and bearing sensitive non-sensitive bearing 1.2.
Bearing stability depends primarily on dynamic coefficients of sensitivity of appropriate changes in the structure of the bearing type or bearing design parameters sensitive can effectively improve the stability of the shaft system; but to change the structure or type of non-sensitive bearing shaft stability parameters based sauce. changes little. 4 turbine and generator rotor with the coupling into one supported by the seven after three oil wedges bearings. Calculations show that instability speed of the unit is 3 2 30 (r / m in). The results contribution factor and the absolute value of each bearing are shown in Table 6. , 6, 7 which are sensitive to bearing two bearings, which shows the stability of the unit depends primarily on two bearings. Appropriate changes in both the structure type or design parameters of the bearing, the unit is expected to be greatly improved stability, and to change the structure type or design parameters other five bearing unit stability change little. Two S, T, respectively, gas oil and oval wedge bearings, calculated according to the turbulence due to the low margin domestic stability 20 0MW Turbine in recent years occurred in varying degrees of bearing film instability or oil whip, resulting in a huge economic losses River. To ensure that these units stable, safe operation, the need for active 2 0 M w Shafting transform design, known by the end of Table 6, the generator 6, 7 two elliptical bearing bearing change, not only can effectively improve the shafting stability and transformation costs to a minimum. Domestic units concerned Xuzhou Power Plant Unit 6 had been bearing the transformation of industrial test results show that the change is elliptical bearing parts of the bearing, the unit performed well Chuan. Speed ​​test to 334. Oil Whip did not occur (r / m in) when, and vibration is greatly reduced compared to the previous bearing modifications. This shows bearing modification, the rotor system stability margin has been greatly improved. You can also see from Table 6, contribution coefficient No. 6 bearing a minimum, it is the entire crew of the most dangerous bearing oil film instability or oil whip often the first excited by the bearings. This conclusion has several experimental results homemade 2 0 M w units confirmed. For example Xuzhou Power Plant Unit 6 overhaul after the accident due to start in 1986, found that on the 6th of bearing vibration greater speed test to 32 (). Oil whip occurs when (r / m in) or more, and each oscillation excited by the 6th bearings first.
5. Conclusion
(L) the stability of the shaft bearing depends on the dynamic performance of sensitive and appropriate changes in these parameters bearing structure type or design can effectively improve the stability margin of shafting.
(2) The contribution factor is minimal bearing shaft bearing the most dangerous, often the first film oscillation excited by the bearings. This conclusion has several homemade 20 oMW experimental results confirmed by Turbine.