Chapter 5 Reasons and Features of Rotor Vibration

Transcription

1 Chapter 5 Reasons and Features of Rotor Vibration By Dr. Danmei Xie

2 The main purposes of this course increase understanding of rotor vibration phenomena provide a means for controlling or eliminating these vibrations Basic theory of vibration Reasons and features of vibration Methods of rotor balancing 1 2 Vibration Signal Analysis Reasons and features of Rotor Vibration

3 Introduction and basic concepts Vibration theory Rigid rotor balance Flexible rotor balance Reasons and features of rotor vibration Fault diagnosis Case study Test//

4 5.1 Vibration Signal Analysis Time domain waveform plot bar plot orbit (Axle center locus) plot bode plot Nyquist plot spectrum domain (FFT) plot waterfall plot//

5 键相 B A 1 瓦 2 瓦 3 瓦 4 瓦 5 瓦 6 瓦 7 瓦 8 瓦 3300 型电涡流传感器 9200 型速度传感器 Bently P DAIU

6 Time domain waveform No 1 BRG No 2 BRG No 3 BRG No 4BRG X No 5 BRG No 6 BRG No 7 BRG No 8 BRG Y

7 Bar Bar Plot X Y Alarm

8 Orbit (Axle center locus) Plot No 1 BRG No 2 BRG No 3 BRG No 4BRG No 5 BRG unbalance misalignment Oil whip Orbit No 6 BRG No 7 BRG No 8 BRG

9 Bode plot speed Speed(n/10rpm) X Time (s) X Speed(n/10rpm) speed Y Time (s) Y No 1 BRG No 3 BRG No 5 BRG No 7 BRG No 2 BRG No 4BRG No 6 BRG No 8 BRG

10 Nyquist plot speed phase No 1 BRG No 3 BRG No 5 BRG No 7 BRG No 2 BRG No 4BRG No 6 BRG No 8 BRG

11 Component Frequencies Of A Square Wave Form. Rotor vibration and its balance- Dr. Danmei Xie

12 Spectrum domain (FFT) plot No 1 BRG No 2 BRG No 3 BRG No 4BRG X No 5 BRG No 6 BRG No 7 BRG No 8 BRG Y

13 Waterfall plot No 1 BRG No 2 BRG No 3 BRG No 4BRG X No 5 BRG No 6 BRG No 7 BRG No 8 BRG Rotor vibration and its balance- Dr. Danmei Y Xie

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15 Holographic Spectrum Traditional on-site balancing methods are usually based on information from a single sensor with vertical and horizontal vibrations being regarded as two separate components In fact, the motion of rotors is a kind of complicated spatial movement It is impossible for measurements made by using only unidirectional sensors to objectively and reliably reflect the movement status of the rotors The information from the sensors must be fused The authors have presented an on-site dynamic balance method based on a fusion of information from a variety of sensors.

16 The essence of the matter consists in fully integrating the information fusion technology with flexible rotor dynamic balance technology In the meantime, advanced computer simulation and a genetic algorithm-based optimization are employed to simplify balanced operations, thus enhancing the balance accuracy and efficiency The demerits of the balance method based on a single sensor were analyzed, and the working principle of a shafting holographic dynamic balance method was described In addition, the effectiveness of the method in question has been verified by the on-site dynamic balance of several 300 MW turbogenerator units

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19 Signature Analysis R BPF = RB * F shaft F Shaft = shaft frequency RB = # of Rotor Bars Which frequencies exist and what are the relationships to the fundamental exciting frequencies. What are the amplitudes of each peak How do the peaks relate to each other If there are significant peaks, what are their source//

20 Sequence of analysis 1) Assemble equipment 2) Record operational parameters of machine- lubricating oil temperature, load, history of mal operation, work done 3) Run machine until it reaches normal operating temperature 4) Take readings at designated points. Analyse frequency of any high readings //

21 5) If possible measure vibration at different speeds 6) Note changes in temperature, load etc. during measurement period 7) If possible double check readings 8) Determine source of vibration using identification table 9) Remedy fault//

22 5.2 Reasons and features of Rotor Vibration Forced vibration caused by mechanical exciting force Forced vibration caused by electro-magnetic exciting force Forced vibration caused by weakening of system stiffness Low frequency vibration (Oil whirl or Oil whip, Aerodynamic forces ) Axial oscillation of brgs Vibration caused by rotor cracks (esp. transverse)//

23 5.2.1 Forced vibration caused by mechanical exciting force 1) Rotor unbalance mass 2) Bent rotor (Hog And Sag) 3) Rotor misalignment 4) Rub between moving parts and static parts//

24 1) ROTOR UNBALANCE MASS Mass unbalance is the most common cause of vibration problems It occurs when the rotor mass centerline does not line up with the axis of rotation The term mass centerline refers to the line that joints the centers of mass of imaginary thin slices into which the rotor may be divided Figure 10.1 illustrates a simplified case of a rotor with mass unbalance In reality, the mass centerline looks like a snake wrapped closely around the axis of rotation//

25 Unbalance Rotating unbalanced centrifugal Shaft centre of gravity Axis of rotation Shaft mass center line Figure 10.1 Mass unbalance Couple Unbalance Overhung Rotor Unbalance

26 A.Causes of UNBALANCE MASS Operating conditions that can increase rotor unbalance Some of them change unbalance temporarily and others permanently (until maintenance is performed) Examples of permanent changes are: Loss of a rotor part in the most extreme cases, the resultant unbalance can be catastrophic, but sometimes the lost part is so small that only a small increase in vibration results Corrosion deposits or wear, e.g., due to erosion, abrasion, scoring, etc. In most cases, changes in mass unbalance are small and they develop slowly The most typical cause of a temporary change in mass unbalance is transient thermal bowing of the rotor. This happens when one side of the shaft is warmer than the opposite side//

27 Examples of operating conditions Fast load changes cooling or heating of the rotor can be so fast that slight differences in the deposits on the shaft surface can interfere with heat transfer and produce a slightly uneven temperature in the rotor Rubbing the frictional heat produced at the site of rubbing makes one side of the shaft hotter Hogging Partial plugging of some cooling passages (e.g., by oil) in generators Asymmetrical currents in individual rotor windings in electric motors and generators the windings carrying larger currents get hotter than their counterparts//

28 B. Features of unbalance I. Vibration frequency equals rotor speed II. III. Vibration predominantly RADIAL in direction Stable amp + phase at a certain speed IV. Amp increases as square of speed before ω cr V. Vibration phase shifts at ω cr VI. Time domain waveform is sine wave VII. VIII. while the axis curve is bent into a spacious curve under the dynamic condition and rotates around the static axis curve with the rotating speed of rotor, the orbit is elliptical/oval or circular Vibration does not change with the oil temperature, oil pressure and steam flow //

29 The spacious distribution of rotor centroid

30 A Spectrum domain plot Fir Tree shape 1x 2x 3x 4x μm Orbit Plot Waterfall plot

31 2) BENT ROTOR (Hog And Sag) Mass unbalance and coupling misalignment can be affected by shaft deformations referred to as hog and sag. They are most pronounced in long shafts like in steam turbine generators Hog is an upward bending of the rotor and happens when the top of the shaft is hotter then the bottom This temperature differential is produced by thermal stratification of the fluid around the rotor That is, the colder and therefore heavier fluid collects at the bottom, while the warmer and hence lighter fluid is pushed to the top This process takes place when the rotor is left stationary and the machine is cooling down or is being warmed up// 40

32 Hogging is a fast process It may take only several minutes to bow the shaft enough to close some radial clearances in the machine An attempt to turn the rotor in this condition could damage the machine s internals (e.g., turbine blades) and brgs through rubbing Incidentally, hogging also affects the machine s casing its bowing introduces a mass unbalance, which does not affect the casing rotor hogging is faster and larger than casing hogging The reason for this is that the rotor changes its temperature faster than the casing, which is heavier and therefore needs more heat transfer to change its temperature//

33 Sag is a downward bending of the rotor under its own weight Some, very small, sag is present during normal operation because the rotor is not infinitely rigid But when the rotor is stationary, sag increases because the same part of the rotor is subjected to a constant stress for an extended period; the top half is in compression, while the bottom half is in tension A similar process, which we all have seen, affects a loaded bookcase shelf Unlike hogging, sagging is a slow process and it takes days rather than minutes to develop to a troublesome level//

34 Eccentricity transducer Shaft position afer a180turn Eccentricity Shaft Bearing Bearing Figure 10.3 Hog and sag

35 图 8 N300 型汽轮机的组合中压转子

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37 B. Features of rotor bent I. Bent shaft problems cause high axial vibration II. 1X RPM dominant if bend is near shaft center III. 2X RPM dominant if bend is near shaft ends IV. Phase difference in the axial direction will tend towards difference V. Vibration related with load or temp VI. High reproducibility or repeatability //

38 Shaft eccentricity is another term that is closely associated with hogging and sagging Eccentricity is a measure of the rotor deflection from the perfectly straight line Figure 10.3 shows how rotor eccentricity is measured The measurement is unavailable when the rotor is stationary In plants, eccentricity is monitored only on HP turbine rotors This allows us to avoid turbine run up when the rotor is bowed. Eccentricity of these rotors can be caused by sagging or hogging However, rubbing or excessively fast heating or cooling of the rotor can also produce it// Eccentric Rotor 231

39 Regardless of its cause, shaft bowing has adverse consequences, and they depend on rotor speed At high speeds, shaft bowing will result in high vibration because the rotating unbalanced centrifugal force will be excessive At low speeds, however, that force will be too small to produce high vibration even when shaft bowing is sufficient to cause mild rubbing If we monitored bearing vibrations only, we may be unaware of rotor bowing, but it could wear/damage seals Monitoring rotor eccentricity, however, would warn us about the danger//

40 3) Rotor misalignment Coupling Parallel Angular Bearing Elevation Angular 瓢偏 不同心 The left shaft and its brgs are infinitely stiff In practice, both shafts and its brgs are somewhat flexible Hence, reaction forces exerted by the right shaft on the left shaft cause it to vibrate

41 Shafting of a turbo-generator unit with 1000MW By Dr. Danmei Xie ----Wuhan University

42 Aligning the supports of a rotor to account for static deformation. (a) Inflected shape of the two spans when the joint is disconnected; (b) inflection of the rotor after the supports of the second span have been raised. Note that all deformations are grossly exaggerated.

43 A. Causes of misalignment(coupling and bearing) Coupling(Shaft) misalignment can change during operation I. Machine casing with bearing pedestals can become deformed due to uneven thermal expansion or mechanical stresses II. Concrete machine foundation can thermally expand, or settle or crack due to aging III.A bearing can become loose in its housing, the housing can crack or its connection to the casing or foundation can become loose IV.brgs can suffer an excessive local wear called wiping The first condition is the most frequent and it usually occurs during operational transients such as equipment startups and shutdowns, or load changes//

44 Other reasons of misalignment Disagreement of the concentricity between the cylinder and the rotor of the turbine Deviation of bearing pedestal in each directions Coupling faults Non-satisfied ellipticity or run-out roundness//

45 Features of misalignment I. Characterized by high axial vibration II phase change across the coupling III. 2X RPM often larger than 1X RPM IV. Typically high 1 and 2 times axial vibration V. Not unusual for 1, 2 or 3X RPM to dominate VI. Severe conditions give higher harmonics VII. Sensitive to load change VIII.Orbit is of 8 shape IX. Different lub oil pressure //

46 B. Features of misalignment Angular misalignment & Parallel Misalignment 1x 2x 4x Radial

47 G(f) A 1 f 2 f 3 f 4 f 1x 2x 3x 4x f μm

48 Misaligned Bearing I. Vibration symptoms similar to angular misalignment II. Attempts to realign coupling or balance the rotor will not alleviate the problem. III. Will cause a twisting motion with approximately phase shift side to side or top to bottom//

49 4) RUB (between moving parts and static parts) Kinds of rub

50 Position Between gland sealing strips and rotor Between blade tip and casing Between sealing strip of diaphragm and rotor

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52 Between blade tip and casing Between diaphragm and rotor

53 gland sealing strips

54 A. Causes of rub I. Tight clearance II. III. Vibration Deformation//

55 A common problem in newly rebuilt or modified rotors is a slight rubbing condition as the rotor is initially operated Rotor rubs are not a phenomenon which continues over an extended period; they usually increase the clearances until the rub has been cleared or, if not corrected, they will wear away the internal clearances until the machine cannot be operated The shape of the orbit display will differ depending upon the relationship of the shaft speed to the first natural frequency and the severity of the rub//

56 B. Features of Rotor Rub I. Spectra displays of rub conditions are characterized by distinct frequencies that occur at multiples of a fundamental frequency II. Usually generates a series of frequencies which may excite natural frequencies III. Subharmonic( 亚谐波 ) frequencies may be present IV. Rub may be partial or through a complete revolution V. The severity of the rub will affect the shape of the orbit A light rub will produce a "tear drop" shaped orbit, with the point of the tear drop coinciding with the impact spot As the rub gets heavier the orbit will flattened and may appear as an excessive preload//

57 Truncated waveform 1x speed<2m 2x 3x light rub heavy rub 2 3 x 1x 4 x 3 5 x 3 2x 7 x 3 1/2x rub 1/3x rub Figure 10.5 Rub

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59 Orbit

60 5.2.2 Forced vibration caused by electro-magnetic exciting force A. Causes I. turn to turn short II. rotor coil foreshortening III. electrical grounds IV. mechanical imbalances V. Overheating VI. blocked ventilation passages VII. wedge stick slip, coil stick slip and bearing wipe//

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62 F L =Line frequency Amplitude 1X 2X 2XF L Frequency 12kcpm (a) stator eccentricity shorted laminations and loose iron Amplitude 1/3 F L sidebands around 2X F L 1X (b) power supply phase problems (loose connector) Frequency

63 rotor SYNCHRONOUS MOTOR (Loose Stator Coils) stator Features of Electrical Problems (1) I. Loose stator coils in synchronous motors generate high amplitude at coil pass frequency II. The coil pass frequency will be surrounded by 1X RPM sidebands//

64 Features of Electrical Problems (2) ROTOR PROBLEMS I. 1X, 2X, 3X, RPM with pole pass frequency sidebands ( 边带 ) indicates rotor bar problems. II. 2X line frequency sidebands on rotor bar pass frequency ( 通频 ) (RBPF) indicates loose rotor bars. III. Often high levels at 2X & 3X rotor bar pass frequency and only low level at 1X rotor bar pass frequency//

65 Features of Electrical Problems (3) ECCENTRIC ROTOR (Variable Air Gap) I. Eccentric rotors produce a rotating variable air gap, this induces pulsating vibration II. Often requires zoom spectrum to separate 2F L and running speed harmonic III. Common values of F P range from CPM//

66 5.2.3 Forced vibration caused by weakening of system stiffness A. Causes of stiffness weaken I. Weakening of the system stiffness in such places as bearing bush, bearing pedestal, and foundation frame etc II. III. Gaps developed between the bearing pedestal and the foundation bedplate Cracks developed in the loading foundation elements//

67 vertical horizontal axial bearing bush bearing pedestal

68 tilting pad 武汉大学动力与机械学院 谢诞梅 68

69 椭圆瓦 武汉大学动力与机械学院 谢诞梅 69

70 武汉大学动力与机械学院 谢诞梅 70

71 Combined Thrust and Journal Bearing 武汉大学动力与机械学院 谢诞梅 71

72 Opened shaft seal 武汉大学动力与机械学院 谢诞梅 72

73 Shafting of a turbo-generator unit with 1000MW By Dr. Danmei Xie ----Wuhan University

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75 上汽前轴承箱纵销 武汉大学动力与机械学院 谢诞梅 75

76 上汽 #1 低压缸横销 武汉大学动力与机械学院 谢诞梅 76

77 东汽前台板 武汉大学动力与机械学院 谢诞梅 77

78 武汉大学动力与机械学院 谢诞梅 东汽中台板 78

79 武汉大学动力与机械学院 谢诞梅 东汽发电机励磁端台板 79

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81 武汉大学动力与机械学院 谢诞梅 81

82 Stg 10T G-X 12CrMoNiWVNbN X 10CrMoWVNbN St10TS St 461 TS 20 Cr Mo Ni V 47 St 461 TS 20 Cr Mo Ni V 47 武汉大学动力与机械学院 谢诞梅 82

83 Features of Mechanical Looseness (1) Caused by structural looseness of machine feet Distortion of the base will cause soft foot problems I. Phase analysis will reveal aprox phase shift in the vertical direction between the baseplate components of the machine//

84 Features of Mechanical Looseness (2) Caused by loose pillow block ( 座架 轴台 ) bolts I. Can cause 0.5, 1, 2 and 3X RPM II. Sometimes caused by cracked frame structure or bearing block//

85 Features of Mechanical Looseness (3) I. Phase is often unstable II. Will have many harmonics III. Can be caused by a loose bearing liner, excessive bearing clearance or a loose impeller on a shaft//

86 5.2.4 Low frequency vibration Self-excitation vibration Caused by Oil film whirl/whip of bearings Working fluid (rotor clearance)

87 Oil whirl or /and oil whip Rotors running on journal bearings show particular dynamic problems linked intrinsically with the behavior of the fluid film within the bearings( oil whirl and oil whip) The oil whirl (sometimes referred to as half-frequency whirl) is a whirling of the rotor, which takes place at a frequency of about half the speed of rotation Oil whirl is superimposed on the other whirling motions, particularly the synchronous whirling caused by unbalance Its amplitude is usually not large and does not constitute an actual problem At a speed that is usually not far from twice the first critical speed, the motion becomes more severe and can rapidly degenerate in a very violent, often destructive-oil whip

88 The oil in a plain journal bearing moves around at a speed that is about half of the peripheral velocity of the journal, providing a sort of rotating damping whose speed of rotation is about half the spin speed In the region of the Campbell diagram, which lies below the straight line, note that the behavior of the system is unstable, and the threshold of instability can be found easily by intersecting the lowest branch of the Campbell diagram (Figure) If the lowest branch of the Campbell diagram is a horizontal straight line, as is the case of the Jeffcott rotor, the threshold of instability occurs at twice the critical speed of the rotor.

89 A Campbell diagram plot represents a system's response spectrum as a function of its oscillation regime-vibration sources with natural resonances The form of the diagram is like a spectral map, but the amplitude could be represented by a circular or rectangular plot, the larger the amplitude the larger the circle or rectangle.

90 f (Hz) k= f dmax 避开区 f dmin k= n(r/s) D f dmax f dmin C A 安全区 k=2 B n 2 =49 避开区 n 1 =50.5 汽轮机强度 10 级研究生用 Dr. 谢诞梅

91 Multi-phase marks 2 phase marks

92 This fault is caused by a condition which prevents the rotor from creating a stable oil wedge on which ride An improperly designed bearing is the usual source for oil whirl conditions, but a change in the fluid viscosity or machine alignment state are other possibilities Generally, an oil whirl condition precedes an oil whip condition Spectral and orbit analysis can be used to identify either condition This phenomenon creates an individual sub synchronous frequency which can occur within a frequency range from 35% to 48% of rotor speed, depending upon the machine/bearing design or construction As the machine accelerates the whirl frequency will increase as machine speed increases//

93 The orbit will be more or less round in shape with an amplitude that nearly approximates the bearing clearance, and when the phase angle is superimposed upon the display, the orbit will appear to have two phase marks on it This characteristic is due to filtering at shaft speed and the fault being generated at a subsynchronous frequency The two phase marks will not be displayed symmetrically on the orbit because the whirl frequency is not at exactly machine speed// 123

94 Mutiple phase marks Locked onto resonance/freq Entire clearance used

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98 名称特点问题 圆轴承 三油楔圆轴承 椭圆轴承 可倾瓦轴承 袋式轴承 不同轴承特点 进油口在下瓦中分面附近 只有 1 个油楔 进油口设在下瓦偏垂直位置两侧和上瓦, 有 3 个油楔 进油口在下瓦中分面附近, 只有 1 个油楔, 垂直方向直径略大于水平 由若干可绕其支点转动的轴瓦弧段组成, 可形成若干油楔 轴瓦中间段与两端面之间形成深度为 0.7mm 的小台阶, 形成油袋 ; 下瓦有顶轴油囊 可能失稳 可能失稳 无失稳现象 有可能失稳 600MW 超临界机组汽轮机设备 武汉大学谢诞梅

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101 Oil whip occurs during the later stages of an oil whirl condition and it has a distinctive orbital display The display, with the phase input superimposed on the display, appears to have several phase marks This display will be round in shape and the amplitude will greater that the amplitude noted during oil whirl The size of the orbit will be larger because the shaft uses up the entire bearing clearance as an oil wedge can no longer be established by the rotor and the shaft is in direct metal to metal contact with the bearing The orbit display will no longer rotate because the oil whirl frequency has coincided with the first natural resonance, or critical speed, and has "locked" onto this frequency Oil whip is a dangerous condition because the rotor uses up the entire bearing clearance and is in direct metal to metal contact that will wear away the bearing rapidly and destroy the rotor if not corrected//

102 An improperly designed bearing is the usual source for oil whirl conditions But a change in the fluid viscosity or machine alignment state are other possibilities Generally, an oil whirl condition precedes an oil whip condition. Spectral and orbit analysis can be used to identify either condition. This phenomenon creates an individual sub synchronous frequency (within a frequency range from 35% to 48% of rotor speed), depending upon the machine/bearing design or construction As the machine accelerates the whirl frequency will increase as machine speed increases//

103 Usually occurs at % of running speed Vibration amplitudes are sometimes severe Whirl is inherently unstable, since it increases centrifugal forces therefore increasing whirl forces Whirl speed will lock onto rotor critical. If the speed is increased the whip frequency will not increase. When oil whip occurs, the amplitude is usually not affected with rotor speed and load//

104 2) self-excitation vibration caused by rotor clearance When a fluid, either liquid or gas, occupies the space between two concentric cylinders, one rotating and one stationary, the fluid is set into motion in the gap This can happen in rotating machinery in fluid-lubricated brgs, seals, around pump impellers, or in any fluid filled gap between rotor and stator//

105 5.2.5 Cracked Shaft The presence of a crack causes an imbalance in the rotor stiffness, resulting in changes in the dynamics of the rotor The presence of a crack is detected by changes in the vibration characteristics as measured on the bearing housings. Transverse Longitudinal Symmetric Torsional Tensile

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107 A change in the vibration level A change in the operating phase angle And/or a change in the resonance frequency as the machine starts or stops Spectral analysis can be used to identify this fault, but observing filtered, synchronous orbits with the phase angle superimposed on the orbit allows rapid identification of this condition//

108 Changes in the filtered amplitude can be determined using orbits analysis By superimposing the phase angle input signal onto the orbit a shift in this parameter can be easily determined By noting the operating speed at which the resonance frequencies occur, a change in this frequency may indicate the "possibility" of a crack existing The "possibility" must be emphasized and carefully analyzed because many other causes can produce these changes, such as, a damaged or loose bearing support, foundation problems, loose rotating parts...basically anything that can influence the "system" mass, damping, and/or stiffness//

109 Amplitude Change Phase Change 2X

110 5.3 Torsional vibration Damage Caused By Excessive Torsional Vibrations Speedup rotor fatigue life loss Cause moving parts damage Cause LP blade fatigue damage

111 5.3.2 reasons of torsional vibration Caused by mechanical reasons Load rejection Quick Closing Valve(QCV) Others (fast action of ST DEH system, partial admission ) Caused by electrical reasons Caused by electrical reasons Short circuit of electric system High speed reclock(hsr) Subsynchronous resonance(ssr) Aperiodic ( 非周期 )synchronize Uneven load in three phases

112 5.2.6 Other Sources of High Axial Vibration A. Valve vibration B. Torsional vibration of rotor C. Axial vibration of brgs D. Sub- resonance( 亚谐 次同步 ) E. Worn thrust brgs F. Grid disturb //

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114 Brg Eccentricity of brg Insufficient of tightness Rub between sft and brg Insufficient of oil supply Oil whirl Oil whip Trbn rotor Unbalance Bent (thermal bending) Rip off Rub Steam whirl Transverse cracks Couplings Misalignment Bolt insufficient tightness Gen rotor Unbalance Bent (thermal bending) Asymmetric EM force Disturbance of EM Asymmetric stiffness Brg pedestal& bed plate insufficient stiffness Loosen of bed plate Deformation brg pedestal or casing Foundation Uneven settlement

115 Chapter 6 Fault Diagnostic Systems Condition Monitoring for Steam Turbines

116 Condition Monitoring for Steam Turbines What is today s definition? We want an early warning so that when the operating condition of the turbine is changing, action can be taken to identify the failure mode When the failure mode is properly identified, proper corrective action can be planned or taken to maintain or return the machine to reliable operation.

117 Part I Condition Monitoring for Steam Turbines To develop effective condition monitoring we need to understand a little about the machine. What does a turbine actually do? Steam comes in and goes out right? The steam comes in under a certain set of pressure, temperature, and flow conditions; and goes out under another set of pressure temperature and flow conditions. The change in steam conditions occurs because we are using some of the energy in the steam to rotate the turbine rotor.

118 Just for a quick view, here is a decent description of a steam flow path in a multi-stage turbine: Courtesy of Power Magazine

119 Part I Condition Monitoring for Steam Turbines Here is one small mechanical drive turbine. This one was actually used to drive a positive displacement oil pump.

120 Part I Condition Monitoring for Steam Turbines Here is a small industrial power generation turbine. Note the mechanical layout of this machine

121 Part I Condition Monitoring for Steam Turbines Here is a big multi-casing utility class machine Courtesy of Power Magazine Note that a lot of the mechanical details from the smallest to the largest machines are very similar

122 Part I Condition Monitoring for Steam Turbines What kind of monitoring can we do on a turbine? Steam conditions and flow rate. Vibration. Lubricant/bearing conditions. Rotor speed/load or power. Auxiliary system operation. Noise/Sound levels.

123 Part I Condition Monitoring for Steam Turbines What kind of failures typically occur to turbines? Bearing failures from: Loss of lubrication Lubrication contamination Excessive load Valve failures: Solid particle damage Erosion Fatigue Overspeed protection Governor/Regulation failure Blade failures: Foreign object damage Erosion Fatigue Steam seal failures: Wear Erosion Corrosion Insulation failure Coupling failures Hydraulic system failure Alignment Changes

124 Part I Condition Monitoring for Steam Turbines Lets look a little closer at some of the failure modes. Bearing failures can occur from: Loss of lubrication Lubrication contamination Excessive load Electrolysis Fatigue Faulty assembly Wear/wiping Corrosion Cavitation/erosion

125 Part I Condition Monitoring for Steam Turbines Lets look a little closer at some of the failure modes. Blade failures: Foreign object damage Can cause damage to leading edge, trailing edge, shroud, etc. Can damage the stationary and/or rotating blades. Erosion Can be caused by moisture in the steam or solid particulates in the steam. Can affect the stationary and rotating blades. Fatigue Will more typically affect the rotating components and typically be a catastrophic event if the condition is not identified during an inspection.

126 Part I Condition Monitoring for Steam Turbines Machine Condition Discussion: Called in to evaluate condition of machine. Site management knew that routine maintenance had been deferred for a significant amount of time. Could they defer further or were there indications of developing problems? What were the results of the condition assessment? Vibration levels were good (below 0.7 mils) using proximity probes. Power output was down. Steam discharge conditions were at saturated steam conditions. Steam leakage at shaft seals was excessive, causing constant moisture contamination in the lube oil system. My recommendation Rotor vibration was and not its to balance defer - Dr. the Danmei overhaul. Xie

127 Part I Condition Monitoring for Steam Turbines Blade failure/damage:

128 Part I Condition Monitoring for Steam Turbines Blade failure/damage:

129 Part I Condition Monitoring for Steam Turbines Blade failure/damage:

130 Part I Condition Monitoring for Steam Turbines Valve failures: What happens to valves? Erosion of the plug Erosion of the seat Corrosion of the spindle or stem Galling of the spindle or stem in the guide bushings or brgs. Wear of the guide bushings or brgs Wear of the linkage components The steam admission valve or stop valve or emergency stop valve is part of the equipment protection!

131 Part I Condition Monitoring for Steam Turbines Steam Seal failures: What happens to steam seals? Larger machines with actual seal strips (labyrinth seals) Wear of the seal tip height Corrosion of the mating surfaces Corrosion of the segments and housing. Corrosion and failure of segment springs Smaller machines with carbon seal rings Wear of the carbon rings Wear of the shaft surface Corrosion and wear of the housing faces.

132 Part I Condition Monitoring for Steam Turbines Steam Seal failures: What happens to steam seals?

133 Part I Condition Monitoring for Steam Turbines Steam Seal failures: What happens to steam seals?

134 Part I Condition Monitoring for Steam Turbines Alignment Definition What does alignment mean to coupled rotating machines? Misalignment at installation or refurbishment Thermal growth changes Piping strain Sleeve bearing damage In short we are looking for the two (or more) shaft centerlines to be concentric to each other. If the shaft centerlines are not concentric to each other, then the shafts through the coupling try to force themselves together. Depending on the coupling type, this aligning force may show Itself as various vibration signature changes or indications, or if severe enough bearing temperatures or conditions may be affected. What can cause misalignment?

135 Part I Condition Monitoring for Steam Turbines Alignment Definition What does alignment internal to a single machine mean? In short We want to have the shaft/rotor within a certain position relative to the casing. Some machines behave better with the rotor not centered in the casing. Some machines behave better with the rotor centered. A very typical indication is a rub condition in the vibration data. What can cause misalignment? Basically the same conditions apply to internal and external misalignment. Misalignment at installation or refurbishment Thermal growth changes Piping strain Sleeve bearing damage

136 Part I Condition Monitoring for Steam Turbines Remaining failure modes: Overspeed protection Sticking bolt Worn linkage Incorrect electronic settings Governor/Regulation failure Worn parts Contaminated system Hydraulic system failure Worn components Contaminated system Insulation failure Air gaps It has become wet Pieces are missing Incorrect installation Coupling failures Lubrication failure Wear Fatigue

137 Part I Condition Monitoring for Steam Turbines Failure modes and monitoring methods: We have to perform the following: Realistically determine the most appropriate uses of the available tools. Determine the realistic limits of the monitoring tools. Determine what we cannot measure or monitor. Determine what is appropriate per piece of equipment.

138 Part I Condition Monitoring for Steam Turbines What kind of monitoring can we do on a turbine? Steam conditions and flow rate. Vibration. Lubricant/lubrication conditions. Rotor speed/load or power. Auxiliary system operation. Noise/Sound levels.

139 Part I Condition Monitoring for Steam Turbines Steam Conditions What kind of readings do we want to take? Depends on the machine, what kind of readings do we have available or can we take? Is it a small machine with little instrumentation or is it a large machine with a considerable amount of instrumentation? Minimal measurements would be temperature and pressure upstream and downstream of the turbine. If you can include flow, power, inlet chamber pressure you will know a considerable amount about the power characteristics of the turbine. Look for: A change in downstream conditions from what is normal. It could be an increase in downstream pressure Also understand what the design conditions may mean (i.e. get a copy of some steam tables)

140 Part I Condition Monitoring for Steam Turbines Steam Tables Mechanical Engineering Reference Manual Michael R. Lindeburg

141 Part I Condition Monitoring for Steam Turbines Vibration What kind of readings do we want to take? Depends on the machine. If it is a small machine Is it a sleeve bearing, anti-friction bearing, or combination machine? Mag-based accelerometers are going to be severely limited with sleeve bearing machines. But smaller horsepower machines are not going to typically have proximity probes installed unless the machine is very critical to the process. What kind of data are we going to see on sleeve bearing machines using mag-based accelerometers?

142 Part I Condition Monitoring for Steam Turbines PdM Routes What data do I want? For vibration: Horizontal and vertical on each bearing. Locate the thrust bearing and take an axial reading. Also include a speed reading if at all possible. What are we looking for? Vibration Changes Running speed multiples Increase in 1X Increase in noise floor Has the speed changed?

143 Part I Condition Monitoring for Steam Turbines For larger machines with installed shaft vibration monitors: Compare the shaft data to casing data. How do those data sets compare? Are they at different amplitude levels, but similar characteristics? Are they different characteristics? Multiples on the casing, not on the shaft data? Different noise floor levels? Different phase indications? Does the orbit shape generally agree with where you see higher vibration levels on the casing? Remember, we are looking for changes. Having absolute limits for operation and equipment protection is one thing, but all the monitoring instruments calculate vibration levels slightly differently. In the field, it is hard to have an absolute anything.

144 Part I Condition Monitoring for Steam Turbines Lubrication /lubricant conditions Again, what kind of machine do we have? Large or small? If it is big enough to have a sump, then we can perform typical oil analysis testing. Viscosity, water, particulates, and spectrographic for routine Monitoring. If it is not big enough for sump but uses oilers to ensure an oil supply for the bearing housing there are still things that need to be correct for a machine to achieve a reasonable time between repairs. Oil level in the oiler. Oil level in the bearing housing. Oil color in the oiler. Inspect the housing cavity for typical indications of contamination or condition during routine overhauls.

145 Part I Condition Monitoring for Steam Turbines Lubrication /lubricant conditions What are we looking for in an oil analysis? There are three major condition groups that oil analysis can monitor: Oil Condition Viscosity Additive packages Oil Contamination Moisture Particulates Equipment Condition Wear particles Material or source Ferrography

146 Part I Condition Monitoring for Steam Turbines Rotor speed/load or power. Is there any permanent monitoring available? Load Speed If no permanent monitoring is available, is there anything else you can use to verify operating load? Is a place on the shaft available for an optical or laser tachometer? Is the process controlled by inlet or discharge valves? Are there any flow indications? These items become even more critical for a variable load process!

147 Part I Condition Monitoring for Steam Turbines Auxiliary System Operation. On larger machines, there are considerable auxiliary systems that may also indicate development of a significant issue. Gland steam or Seal steam systems Shaft leakage increased More use of steam Changing pressure conditions Hydrogen seal oil systems Higher flow rates from increased shaft leakage Hydrogen purity issues Changing pressure conditions Cooling water conditions Conductivity Flow or pressure changes

148 Part I Condition Monitoring for Steam Turbines Auxiliary System Operation. On larger machines, there are considerable auxiliary systems that may also indicate development of a significant issue. Condenser conditions Vacuum pressure changes Condensate temperature changes Air in-leakage changes Feedwater Heater conditions Steam inlet/outlet condition changes Condensate inlet/outlet condition changes

149 Part I Condition Monitoring for Steam Turbines Noise/Sound levels. With modern ultrasound technologies, it should be possible to monitor and trend changing conditions within these machines. We should be able to monitor the following: Valve conditions at known positions, especially when closed Turbine noise levels at known conditions Bearing noise levels at known conditions

150 Part I Condition Monitoring for Steam Turbines Summary There are considerable technologies that are available for use However, the tools we have discussed today are only several pieces of an overall reliability program. Preventive, Predictive, and Proactive or Reliability Centered components are all necessary to improve reliability and minimize overall operational cost. Basically, the more we know about the machine, the better we can diagnose a changing condition.

151 6.1 Background It s said that almost half of the efficient machine diagnostic methods were born in the laboratories of shipbuilding industry worked from the later sixties It is well known that practically all the diagnostics has appeared in the Navy of USA, Russia and Great Britain, that means where this problem was very actual and where there were no problem with financing the investigations and where the best scientists and engineers were working

152 Object Data Acquiring Data Analysis Fault Diagnosis Fault Recovery Processing Fig. 6.1 Process of Machine Fault Diagnosis

153 But the measuring means were not so common that time to make the vibrational diagnostics so popular as it is nowadays In practice these means became real in the beginning of nineties when the instruments became to be designed on the basis of microcomputers Only then the complicated methods of vibration analysis became accessible to a wide class of users Now each 2-3 years there appears a new generation of measuring and analyzing techniques One can say that modern instrument comprises of a transducer and microcomputer Nowadays the so called virtual instruments when the instrument is a combination of a transducer and a personal computer are wide spread.

154 But detailed machine diagnostics by vibration means not only the methods of diagnostics and measuring and process analyzing instruments There are two more mandatory ( 强迫 )components A data base of the results of measurements during long period of time of a large number of equipment with the possibility to receive any data and to make its analysis The methods of making the diagnostic decision

155 But there are two more methods to solve the problems of this second component - the development of artificial intellect. One method is to develop the learning artificial intellect system where on the first stage the teaching of the system is conducted by the software architect and then the user supplements the system by the rules that he needs. The second method is to design a self learning (adaptive) system with strict learning algorithms written by the designers

156 Nowadays in the world practice three main types of machine condition monitoring and diagnostic systems by vibration are used: Portable systems Stand systems On-line (stationary) systems

157 Machine condition monitoring system of any type must have four main subsystems: Measurement transducers and communication means; Means to analyze the signals(fft, wavelet) Means to save the data and to display them, usually a personal computer Machine condition monitoring application software (subsystems to work with the data bases, to display the results of analysis, comparison with the alarm levels, drawing the trends)

158 If machine condition monitoring system must fulfill also the diagnostic functions then it should include a subsystem that generates the diagnostic decisions. It can be: an expert an operator that uses the expert subsystem-based on fuzzy set theory (fuzzy math) a subsystem with artificial intellect that functions as an expert

159 The first fuzzy matrix No Sorts of fault ~ 0.51~ 3~5 ~ 0.5f 0.49f 1 1f 0.39f f 1 2f 1 1 f Unbalance Parts ripped off Thermal bend Gland impact and rubbing Rubbing of axis direction Bearing misalignment Eccentricity between bearing & steam turbine Odd Fre f 1 High Fre f Axis crack Insufficient of shrunk fit Loose of bearing.block Grid Fre f 1

160 No Sorts of fault ~ 0.51~ 3~5 ~ 0.5f 0.49f 1 1f 0.39f f 1 2f 1 1 f 1 1 Odd Fre f 1 High Fre f 1 Grid Fre f 1 11 Loose of b. pedestals Inaccurate coupling Self-excited of rotor clearance Sub- resonance Oil film whirl Oil film oscillation Steam turbulence Electromagnetic excitation Valve vibration Grid disturb 100

161 The Second fuzzy matrix N o Sorts of fault Amp *. * Saltation in oper. Amp vary with load Vib **. In axis direction Shaft track change Amp. Saltation at n cr Amp not vary with load Amp incr. with speed Amp. Saltation in run-up Shaft swing incr. Vib. Vary with. F em ** 1 Unbalance Parts ripped off Thermal bend Gland impact and rubbing Rubbing of axis direction Bearing misalignment Eccentricity between bearing & steam turbine Axis crack Insufficient of shrunk fit Loose of bearing.block

162 N o Sorts of fault Loose of b. pedestals Inaccurate coupling Self-excited of rotor clearance Amp *. * Saltation in oper. Amp vary with load 100 Vib **. In axis directi on Shaft track change Amp. Saltati on at n cr Amp not vary with load Amp incr. with speed Amp. Saltati on in run-up 14 Sub- resonance Oil film whirl Oil film oscillation Steam turbulence Electromagnetic excitation Shaft swing incr. Vib. Vary with. F em ** Valve vibration Grid disturb 100

163 频率 时变 负荷 转速 序号故障类型 1 初始不平衡 频率特征时变特征 负荷 转速 f 1 n cr 次谐波 2f 1 缓慢急剧启动停机 2 转子部件脱落 3 转子弹性热变形 4 汽封碰磨 5 轴向碰磨 6 轴线不对中 7 轴承对轴颈偏心 8 轴裂纹 9 联轴器齿轮磨损 10 转子间隙自激 11 轴承供油不足 12 油膜涡动 13 油膜振荡 14 基础松动

164 运行状态 序号 故障类型转速负荷 蒸汽压力 蒸汽温度 阀门开度 真空 排汽温度 轴承油压 轴承油温 轴瓦温度 膨胀胀差 励磁电流 发电机温度 电网扰动 稳定运行 变负荷运行 1 初始不平衡 2 转子部件脱落 3 转子弹性热变形 4 汽封碰磨 5 轴向碰磨 6 轴线不对中 7 轴承对轴颈偏心 8 裂纹 9 联轴器齿轮磨损 10 转子间隙自激 11 轴承供油不足 12 油膜涡动 13 油膜振荡 14 基础松动

165 6.3 Trends New methods of vibration analysis (wavelet, gray theory) New methods of faults diagnosis Condition monitoring and predictive maintenance Coupled vibration between lateral and torsional vibration of the rotor Coupled vibration between long moving blade and the rotor Modeling of the mechanical system has been recognized as very important in the prediction and analysis of vibration Stability of rotor-dynamic system Sensitivity analysis of rotor rigidity and damping etc.

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167 once-add method Holospectrum 全息 ( 谱 ) 国家自然科学基金项目 ( ) 节选 气动 / 结构耦合动力学系统目标敏感性分析的快速准确计算方法及优化设计研究 杨旭东 西北工业大学 多支承 弹性转子系统弯扭耦合振动及控制模拟研究 张俊红 天津大学 多自由度柔性转子 - 柔性静子系统的非线性全周碰摩研究 张 文 复旦大学 柔性转子模糊动平衡原理 屈梁生 西安交通大学 基于模型确认的复杂机械结构动态仿真精确建模方法 郭勤涛 南京航空航天 转子结构动力学行为与疲劳裂纹扩展耦合分析 荆建平 上海交通大学 微型超高速旋转机械转子系统动力学建模与分析 祝长生 浙江大学 柔性多体系统刚柔耦合动力学若干问题研究 洪嘉振 上海交通大学 非线性挠性转子系统不平衡量在线识别方法的研究 郑水英 浙江大学 基于时间序列图像的 MEMS 结构试验模态分析与动力学特征参数识别 何小元 东南大学 多重故障非线性转子系统关键理论及远程诊断的研究 闻邦椿 东北大学 大规模电力系统多运行方式下低频振荡的协调控制 杜正春 西安交通大学 高速水轮机转子系统与减振问题 徐 华 西安交通大学 大型水轮机组水力振动机理探讨 曹树良 清华大学

168 超高速主轴系统非平衡振动的主动抑制机理研究张东升西安交通大学 核电管线基于振动的损伤识别与监测方法研究周邵萍华东理工大学 复杂激励下飞机载流管道系统振动疲劳分析技术研究郑敏南京航空航天大学 高速列车高频激扰振动机理及传递规律研究任尊松北方交通大学 高速铁路高架桥引起的环境振动的预测方法研究曹艳梅北方交通大学 潜艇机械非线性混沌振动快速识别技术研究刘树勇海军工程大学 振动系统同步可靠性研究李鹤东北大学 旋转叶片 - 机匣碰磨的精细化建模与振动局部化研究李朝辉东北大学 非线性振动系统谐振同步机理及稳定性控制关键问题研究 透平机械复杂机电系统动力学行为与振动 噪声靶向抑制原理及方法研究 李小号 高金吉 东北大学 北京化工大学

169 Thanks Dr. Danmei Xie whu.edu.cn QQ: