串列轉子軸承系統之對心懸垂線分析

Alignment and Sag Line Analyses for Rotor Trains

賴彥伯(Yen-Bo Lai)

指導教授 ： 楊大中 博士

元智大學/工程學院/機械工程學系/碩士(2004年)

摘要

大型串列轉子軸承系統如汽輪發電機組之軸系，其各軸段之間以聯軸器連結，而轉子重量由多個軸承支撐著。串列轉子受重力作用致使各軸段之軸心線在軸承支撐點間下垂，由此等懸垂線所串接構成的連續曲線，稱為懸垂線。一般情況下，軸承高程之對心調配未能達到最佳狀態，其聯軸器接合面會受到剪力與彎矩作用，造成各聯軸器鎖緊螺桿亦承受剪力與拉力負荷等不必要之疲勞負荷。
為增加串列轉子軸承系統之壽命與安全性，避免此等不必要之疲勞負荷，在機組安裝時(處於冷機狀態)通常應安排進行軸承高程之對心調配作業調整軸承座高度，以促使該軸系在實際運轉(熱機狀態)時，各個聯軸器之接合面處均呈現無剪力與彎曲負荷之狀態。在運轉狀態下(熱機狀態)，若能達到各聯軸器接合面均呈現無剪力與彎矩負荷之條件，則此時之軸系即可稱為處於理想對心條件。
本研究提出一套可應用於實際串列轉子系統之對心調配分析軟體。推導適用於轉子懸垂線分析之含自重效應形狀函數，建立轉子軸承系統分別分析出無油膜效應、含油膜效應與軸承基座效應時之軸承高程與軸承負荷，並由軸承負荷獲取各軸承振動參數，以利其後續之動態研究。且針對現場作業之需求，建立具有轉軸狀態分析之方法。
本文之對心調配分析軟體包含無油膜效應、含油膜效應與軸承基座效應，其能準確的符合在運轉狀態下，各聯軸器接合面之零剪力與彎矩值之汽輪發電機需求。其能以質量內外徑與勁度等效內外徑方式輸入轉子之幾何尺寸，所以在執行關於轉子軸承系統之分析上比現有之有限元素分析軟體更為精確且簡便。
本研究針對一簡易串列轉子模型，一550MW汽輪發電機組，與一500MW汽輪發電機組進行分析，並與廠家資料與ANSYS分析結果比較。分析結果(懸垂線形狀、軸承高程、軸承反作用力、剪力與彎矩)均相當精確，說明理想對心之軸承高程分析流程的可行性。由轉軸節點之位置旋轉座標驗證方法與軸承反作用力，可得知在相同要求之情況下，轉軸之理想對心懸垂線形狀在任何狀況下具有唯一性。若無法正確得到軸承參數時，可以利用無油膜效應之分析方法推算出軸承反作用力，進而作簡單之對心分析。由含軸承基座效應之結果得知增加軸承基座效應對轉軸懸垂線位置並無太大影響，但若在做動態分析時則需要考慮其對軸承勁度與阻尼矩陣之影響，其中軸承基座係數Kyy對理想對心之計算影響較大。

關鍵字

對心調配 ； 懸垂線 ； 串列轉子 ； 軸承基座 ； 軸承性能表

並列摘要

Large rotor trains such as steam turbine generator sets are assembled from shaft segments, connected by couplings and supported by bearings. The catenary shaft centerline of the rotor train is called sag line. If the elevations of the bearing pedestals are not properly adjusted, shear forces and bending moments exist in the interfaces of the couplings, which will result in the shear and tension fatique loading on the tight bolts of the couplings.
In order to enhance the life and safety of the rotor-bearing systems, shaft alignment has to be conducted by adjusting bearing elevations, to minimize the uncessary fatique loads of shear forces and bend moments in the coupling interfaces. The condition that the sag line with zero shear forces and bend moments in the coupling interfaces of the rotor train under operating conditions is called perfect alignment condition。
This research aims at sag line alignment analysis and provides software that can be applied to the practical large rotor trains. The shape functions that include the gravity effect were derived and used to establish the rotor-bearing-foundation models. These models were used for the calculations of bearing elevations and bearing loads under various conditions: (1) rigid supports, (2) with oil film bearing effects, (3) with oil film bearing and foundation effects. The dynamic coefficients of bearings can be obtained from the bearing loads for subsequent dynamic analyses.
The software for alignment and sag line analyses of rotor trains has been developed in this study, including the effects of rigid supports, oil film bearing, and foundations. The shearing forces and bending moments at the coupling interfaces are forced to minimum by adjusting the elevations of the bearings. Since the mass diameters and effective stiffness diameters can be input in modeling the geometry of the rotors, the flexibility and accuracy of this software is superior to the general-purpose finite element programs.
A simple rotor train model, a 550MW turbine generator and a 500MW turbine generator were analyzed. The results were compared with the data provided by the manufactures and the results by using ANSYS software. The results show that the calculated sagline positions, bearing elevations, bearing reaction forces, and the shear forces and beaing moments in the coupling interfaces are accurate. The shape uniqueness of the perfectly aligned sagline is verified by properly rotating the sag line. Since the vertical reaction forces of bearings do not change significantly, the bearing loads can be approaximated by using the rigid supports, if the accurate bearing operational models are not available. The foundation does not affect the position of the sag line significantly, but has to be considered in deriving the stiffness and damping coefficients of the bearings.

並列關鍵字

Alignment ； Sag Line ； Rotor train ； Foundation ； Someya Table

參考文獻

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