CN111006756A - Method for diagnosing periodic fluctuation vibration of shafting of steam turbine generator unit - Google Patents
Method for diagnosing periodic fluctuation vibration of shafting of steam turbine generator unit Download PDFInfo
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Abstract
The invention belongs to the technical field of equipment detection, and particularly relates to a method for diagnosing periodic fluctuation vibration of a shafting of a steam turbine generator unit, which comprises four steps, namely step 1, performing vibration preliminary analysis according to operation and vibration measurement data; step 2, carrying out stress analysis on a shaft system of the steam turbine generator unit; step 3, drawing a schematic diagram of bending strain of a shafting; step 4, introducing Hooke's law to carry out vibration analysis; for the vibration problem of periodic fluctuation of vibration amplitude, the actual conditions encountered by engineering are relatively few, and the periodic fluctuation vibration of the steam turbine generator unit recorded by the existing data includes beat vibration and friction vibration. However, if the periodic vibration rule and characteristics of the steam turbine generator unit are not completely matched with the friction vibration or the beat vibration, the Hooke's law is applied to vibration analysis by using the diagnosis method, so that the defect cause can be accurately positioned, and the actual engineering problem is solved.
Description
Technical Field
The invention belongs to the technical field of equipment detection, and particularly relates to a method for diagnosing periodic fluctuation vibration of a shafting of a steam turbine generator unit.
Background
Millions of kilowatt-level nuclear power turbine generator units designed and manufactured by eastern steam turbine limited companies often have periodic fluctuation vibration faults, and at present, some nuclear power generator units in the operation of medium-nuclear, wide-nuclear and national-nuclear have periodic fluctuation vibration faults.
The nuclear turbine generator unit has the following main characteristics of fluctuation vibration:
A. the amplitude of the fluctuation of 6 watts was the largest, the order of 5 watts and 8 watts, and the fluctuation of 1-4 watts and 7 watts was insignificant.
B. The wave vibration is automatically generated, and the wave vibration can automatically disappear after running for a period of time.
C. The 5, 6, 8 watt wave oscillations appeared simultaneously and disappeared simultaneously.
D. The 6 watt wave amplitude is always in anti-phase with 5, 8 watts.
E. The probability of the occurrence of periodic fluctuation vibration is high when the load is increased or decreased.
F. The vibration amplitude of 8 watts is high and exceeds the alarm value.
National vibration research center, the vibration research institute of the western-style safety and thermal engineering institute, the western-style safety transportation university, the Zhongyuan and other domestic vibration famous experts have been consulted for many times, but the fluctuating vibration still cannot be solved well.
Disclosure of Invention
The invention aims to provide a method for diagnosing the periodic fluctuation vibration of a shafting of a steam turbine generator unit, aiming at the defects in the prior art.
The technical scheme of the invention is as follows:
a method for diagnosing the periodic fluctuation vibration of a shafting of a steam turbine generator unit comprises the four steps of 1, performing vibration preliminary analysis according to operation and vibration measurement data; step 2, carrying out stress analysis on a shaft system of the steam turbine generator unit; step 3, drawing a schematic diagram of bending strain of a shafting; step 4, introducing Hooke's law to carry out vibration analysis;
the step 1 comprises the steps of analyzing vibration reasons on the aspects of oil inlet and return temperature, analyzing vibration reasons on the aspect of critical rotating speed, analyzing vibration reasons on the aspect of vibration change after no-load constant speed, and analyzing vibration reasons on the aspect of shaft vibration and bearing vibration change.
A turbo generator set shafting periodic fluctuation vibration diagnostic method, said step 1, carry on the vibration preliminary analysis according to operation and vibration measured data, enter the oil return temperature aspect and analyze the vibration reason;
the temperature difference between the oil inlet temperature and the oil return temperature of each tile during operation is analyzed, the temperature difference between the oil inlet temperature and the oil return temperature of each tile during operation is only 2.5 ℃, the temperature difference between the oil inlet temperature and the oil return temperature of each tile is between 6 and 8 ℃, and the temperature difference between the oil inlet temperature and the oil return temperature of each tile is obviously low, so that the load of each tile is inferred to be low; in comparison with the aspect of the watt temperature, although the 8 watt temperature is 91.4 ℃ which is the highest among the unit watts, the 8 watt temperature of the unit No. 4 is lower than that of the unit No. 1-3 of the nuclear power plant 8 watt at 98-100 ℃, so that the load of the unit No. 4 steam turbine generator unit 8 watt is lower than the design load by performing transverse analysis on the operation parameters of the watt temperature.
A turbo generator set shafting periodic fluctuation vibration diagnostic method, said step 1, carry on vibration preliminary analysis according to operation and vibration measured data, analyze the vibration reason in the aspect of critical rotational speed;
when the machine is stopped and the speed is reduced to be over critical, the shaft vibration at the position of 8 watts does not generate resonance, the phenomenon that the shaft vibration at the position of critical rotating speed does not generate a resonance peak is abnormal, and the vibration is analyzed by using the accessed special vibration monitoring software, and the vibration phase angle at the position of 8 watts does not generate mutation when the machine is stopped and the speed is reduced to be over critical, so that the shaft vibration at the position of 8 watts does not generate resonance when the machine is stopped and the speed is reduced to be over critical;
deducing the drift of the critical rotating speed of the unit at 8W, wherein the critical rotating speed, namely the natural frequency, of the shafting of the steam turbine generator unit is related to the material, the mass and the length of the rotor and is also influenced by the rigidity of the supporting system, the natural frequency of the shafting is changed when the supporting condition is changed, the supporting rigidity is reduced, and the natural frequency of the shafting is reduced;
a resonance peak appears when the speed is reduced to 744RPM, so that the fact that the supporting rigidity at the position of 8 watts is reduced is inferred, the material of a supporting system of the steam turbine generator unit in operation is not changed, the only possibility that the supporting rigidity is reduced is that the equivalent rigidity of an oil film is changed, the equivalent rigidity of the oil film is reduced to lead the critical rotating speed of a shaft system at the position of 8 watts to drift, and therefore resonance does not appear when the speed of the steam turbine generator unit is reduced to the designed critical rotating speed 985 RPM.
A turbo generator set shafting periodic fluctuation vibration diagnostic method, said step 1, carry on vibration preliminary analysis according to operation and vibration measured data, vibration change aspect analysis vibration reason after no-load constant speed;
the shaft vibration at 8W in the idling process of the turbo generator set reaching the rated rotating speed stably rises from 29um to 70um finally, the change of the shaft vibration after no-load and constant speed is analyzed in detail, and the oil film rigidity of 8W is reduced after the constant speed is achieved;
the analytical procedure was as follows:
according to the theory of forced vibration, the exciting force and the dynamic stiffness of the supporting system are two major factors influencing the forced vibration of the rotating machine, and the amplitude A of the forced vibration can be represented by the formula (5):
A＝α×F/Kd(5)
(5) where α is the coefficient, F is the excitation force, Kd is the dynamic stiffness, and from this analysis, the amplitude of the vibration is directly proportional to the excitation force and inversely proportional to the dynamic stiffness of the equipment support system, so decreasing the excitation force or increasing the dynamic stiffness can decrease the vibration amplitude, if the 8W vibration increases after a constant speed, it is likely that F is becoming larger or that the dynamic stiffness Kd is decreasing.
If the excitation force is unbalanced, there is a difference according to Newton's second law
If the excitation force generated by unbalance is generated, the excitation force can not be increased after the rated rotating speed is reached, so that the amplitude can not be increased after the rated rotating speed is reached;
the vibration amplitude at the position of 8 watts is only 29um at constant speed, which shows that the dynamic balance of a shafting is very good;
the excitation current of the generator is zero when the generator is in no load, and the possibility of additional excitation force formed by a thermal vector is eliminated, so that the shaft vibration at the position of 8 watts can be increased only, namely the dynamic stiffness Kd is reduced, the oil film stiffness is reduced under the condition that a steam turbine supporting system is not changed, and the oil film stiffness of 8 watts after the unit is in constant speed can be determined to be reduced by combining the condition that the turbine supporting system is stopped and the critical resonance peak does not appear.
A turbo generator set shafting periodic fluctuation vibration diagnostic method, said step 1, carry on the vibration preliminary analysis according to operation and vibration measured data, the vibration reason is analyzed in the aspect of shaft vibration and tile vibration change;
the shaft vibration at the position of 8 watts steadily rises in the idling process, but the tile vibration at the position of 8 watts keeps unchanged in the 8-watt shaft vibration rising process, so that the fact that the eccentricity of 8 watts is reduced when the unit idles is inferred, and the load of 8 watts after the constant speed of the steam turbine is gradually reduced and the shaft neck moves towards the center of a bearing bush and the temperature difference between oil inlet and return of 8 watts is abnormal can be judged by combining the reduction of the equivalent rigidity of an oil film of 8 watts and the abnormality of the temperature difference between oil inlet and return of 8 watts, so that the shaft vibration rises and the tile vibration keeps unchanged;
according to the relation between the vibration amplitude of the steam turbine unit and the load of the bearing and the rigidity of the oil film, the vibration amplitude of the steam turbine unit is related to the load borne by the bearing and the equivalent rigidity of the oil film, and the change of the equivalent rigidity of the oil film can cause the friction between the journal and the bearing bush. According to the rotor dynamics and the lubrication theory, the relation between the amplitude and the bearing load and the equivalent rigidity of the oil film is analyzed, and the following conclusion is drawn that the bearing load is increased, the thickness of the oil film is thinned, the equivalent rigidity of the oil film is increased, the friction degree between a journal and a bearing bush is increased, and the vibration amplitude is reduced; on the contrary, the bearing load is small, the oil film thickness is thickened, the oil film equivalent stiffness is reduced, and the vibration amplitude is increased;
finally, the 8W load of the steam turbine generator unit of the steam turbine is smaller than the design load.
A diagnostic method of the periodic fluctuation vibration of a turbo generator set shafting, step 2, carry on the force analysis to the turbo generator set shafting;
f7 is a load of 7 watts, F8 is a load of 8 watts, G4 is the weight of the generator rotor, and if the distance between 7 watts and 8 watts is L and the distance between the generator back wheel and 7 watts is L1, then in a static state, the following formulas (1) and (2) are necessarily established;
F7+F8＝G4 (1)
F7＝F8＝1/2·G4 (2)
as can be seen from the above analysis, after the turbo generator set is set at a constant speed, the load of 8 watts is gradually reduced, that is, F8 is reduced, at this time, an internal stress is formed between the LP2 rotor and the generator rotor, when the generator rotor is taken as a research object, the LP2 rotor applies a downward F1 stress to the generator rotor through the coupling, when the LP2 rotor is taken as a research object, the generator rotor applies an upward stress F2 to the LP2 rotor, F1 and F2 are a pair of an acting force and a reaction force, that is, F1 is F2, when the generator is taken as a research object, the following formulas (3) and (4) are established;
F7+F8＝G4+f1 (3)
when the 8-watt operation load is reduced, internal stress is generated between the generator rotor and the LP2 rotor, the main reason that the 8-watt load is reduced is that the 8-watt journal lift is too small, and the 8-watt lift is determined by the 6-watt journal lift of the standard lift of the shafting, so that the standard lift deviation of the steam turbine generator unit can cause the internal stress generated between the shafting after the unit operates.
A turbo generator set shafting periodic fluctuation vibration diagnostic method, said step 3, draw the shafting bending strain schematic diagram;
because of the deviation of the 6-watt reference raise, under the action of the internal stress f2, the LP2 rotor after the unit operates can upwards generate bending strain by taking 7 watts as a fulcrum, a shaft system generates upwards tiny bending deformation, the atoms of the material at the outer bending side of the shaft system bear tensile and compressive stress, and the atoms of the material at the inner bending side bear compressive stress, so that the deviation of the reference raise curve from a designed value is more, and the shaft system is not a continuous and smooth curve any more.
A turbo generator set shafting periodic fluctuation vibration diagnostic method, said step 4, introduce Hooke's law to carry on the vibration analysis;
when the strain amount is ∈, the elastic modulus of the axis system is E, and the bending stress is σ, equation (5) holds according to hooke's law.
σ＝Eε(5)
Within the elastic limit, the shafting can be regarded as an elastic vibrator, when f2 is kept unchanged, the strain epsilon of the LP2 rotor is always kept stable, the bending stress sigma is also kept stable, and the whole shafting can not generate fluctuation vibration. When the external condition changes, the 8 watt load F8 is easily changed, and as can be seen from the formula (4), when F8 is increased, the internal stress F1 is reduced, the balance state of the elastic vibrator is broken, and the shaft system rebounds in the direction opposite to the strain amount, so that the vertical fluctuation vibration around the new balance position is generated. The fluctuation vibration phenomenon of the No. 4 steam turbine generator unit of the factory can be easily explained according to the relation of stress and strain of the elastic vibrator in the formula (5), and the specific analysis is as follows according to a shafting bending strain diagram:
A. since 6 watts is close to the maximum strain position of the LP2 rotor, the 6 watt ripple amplitude is greater than 5 watts and 8 watts.
B. The fulcrum of the bending deformation of the LP2 rotor is 7 watts, so 7 watts will not fluctuate, but the phase angle will be reversed.
C. When the external conditions are changed and the elastic vibrator balance is broken, the fluctuation vibration can be automatically generated, and the problem of automatic fluctuation generation can be explained.
D. Since the vibration is always damped, the fluctuating vibration can be damped by itself until it disappears and balances itself in a new equilibrium position.
E. Under the action of internal stress, the LP2 rotor and the generator rotor generate bending strain, namely the LP2 rotor and the generator rotor form an elastic vibrator, so that 5-watt, 6-watt and 8-watt fluctuation vibration always occurs at the same time and disappears at the same time.
F. Because the bending deformation of the shafting takes the approximate middle point of the 7 watt and LP2 rotors as the starting point, the fluctuation amplitude of 6 watts is always in opposite phase with 5 and 8 watts after the balance of the elastic vibrator is broken.
G. When the load changes, the probability of balance being broken is high, and therefore, the probability of occurrence of periodic fluctuation vibration when the load is increased or decreased is high.
The invention has the beneficial effects that:
for the vibration problem of periodic fluctuation of vibration amplitude, the actual conditions encountered by engineering are relatively few, and the periodic fluctuation vibration of the steam turbine generator unit recorded by the existing data includes beat vibration and friction vibration. However, if the periodic vibration rule and characteristics of the steam turbine generator unit are not completely matched with the friction vibration or the beat vibration, the Hooke's law is applied to vibration analysis by using the diagnosis method, so that the defect cause can be accurately positioned, and the actual engineering problem is solved.
Drawings
FIG. 1 shows the force applied to the shafting according to the present invention.
FIG. 2 is a schematic diagram of the bending strain of the shafting according to the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the embodiments. The method for diagnosing the periodic fluctuation vibration of the shafting of the steam turbine generator unit shown in the figures 1-2 comprises the following steps:
step 1, carrying out vibration preliminary analysis according to operation and vibration measurement data
(1) And (3) analyzing the vibration reason in the oil inlet and return temperature aspect:
the temperature difference between the oil inlet temperature and the oil return temperature of each tile during operation is analyzed, the temperature difference between the oil inlet temperature and the oil return temperature of each tile during operation is only 2.5 ℃, the temperature difference between the oil inlet temperature and the oil return temperature of each tile is between 6 and 8 ℃, and the temperature difference between the oil inlet temperature and the oil return temperature of each tile is obviously low, so that the load of each tile is inferred to be low; in comparison with the aspect of the watt temperature, although the 8 watt temperature is 91.4 ℃ which is the highest among the unit watts, the 8 watt temperature of the unit No. 4 is lower than that of the unit No. 1-3 of the nuclear power plant 8 watt at 98-100 ℃, so that the load of the unit No. 4 steam turbine generator unit 8 watt is lower than the design load by performing transverse analysis on the operation parameters of the watt temperature.
(2) Analyzing the vibration reason in the aspect of critical rotating speed:
when the machine is stopped and the speed is reduced to be over critical, the shaft vibration at the position of 8 watts does not have resonance, the phenomenon that the shaft vibration at the position of critical rotating speed does not have a resonance peak is abnormal, and the vibration is analyzed by using the accessed special vibration monitoring software, and the vibration phase angle at the position of 8 watts does not have sudden change when the machine is stopped and the speed is reduced to be over critical, so that the phenomenon that the shaft vibration at the position of 8 watts does not have resonance can be determined.
Therefore, the drift of the critical rotating speed of the unit at the position of 8 watts is deduced, the critical rotating speed, namely the natural frequency, of the steam turbine generator set shaft system is related to the material and the mass of the rotor and the length of the rotor, and is simultaneously influenced by the rigidity of the supporting system, the natural frequency of the shaft system is changed when the supporting condition is changed, the supporting rigidity is reduced, and the natural frequency of the shaft system is reduced.
A resonance peak appears when the speed is reduced to 744RPM, so that the fact that the supporting rigidity at the position of 8 watts is reduced is inferred, the material of a supporting system of the steam turbine generator unit in operation is not changed, the only possibility that the supporting rigidity is reduced is that the equivalent rigidity of an oil film is changed, the equivalent rigidity of the oil film is reduced to lead the critical rotating speed of a shaft system at the position of 8 watts to drift, and therefore resonance does not appear when the speed of the steam turbine generator unit is reduced to the designed critical rotating speed 985 RPM.
(3) Analyzing the vibration reason in the aspect of vibration change after no-load constant speed:
the shaft vibration at 8W in the idling process of the turbo generator unit reaching the rated rotating speed stably rises from 29um to 70um finally, the change of the shaft vibration after no-load and constant speed is analyzed in detail, and the oil film rigidity of 8W is reduced after the constant speed is achieved.
The analytical procedure was as follows:
according to the theory of forced vibration, the exciting force and the dynamic stiffness of the supporting system are two major factors influencing the forced vibration of the rotating machine, and the amplitude A of the forced vibration can be represented by the formula (5):
A＝α×F/Kd (5)
(5) where α is the coefficient, F is the excitation force, Kd is the dynamic stiffness, and from this analysis, the amplitude of the vibration is directly proportional to the excitation force and inversely proportional to the dynamic stiffness of the equipment support system, so decreasing the excitation force or increasing the dynamic stiffness can decrease the vibration amplitude, if the 8W vibration increases after a constant speed, it is likely that F is becoming larger or that the dynamic stiffness Kd is decreasing.
If the excitation force is unbalanced, there is a difference according to Newton's second law
If the excitation force generated by unbalance is generated, the excitation force can not be increased after the rated rotating speed is reached, so that the amplitude can not be increased after the rated rotating speed is reached.
The vibration amplitude at the position of 8 watts is only 29um at constant speed, which shows that the dynamic balance of a shafting is very good.
The excitation current of the generator is zero when the generator is in no load, and the possibility of additional excitation force formed by a thermal vector is eliminated. Therefore, the shaft vibration at 8 watts can be increased only by reducing the dynamic stiffness Kd, and only reducing the oil film stiffness under the condition that the turbine support system is unchanged. And in combination with the absence of formants after the machine is stopped, the oil film rigidity of 8 watts after the set is fixed can be determined to be reduced.
(4) Analyzing vibration reason in the aspect of shaft vibration and bearing vibration change
The shaft vibration at 8 watts steadily increased during idle, but the tile vibration at 8 watts remained unchanged during the 8 watt shaft vibration increase. Therefore, the eccentricity of 8 watts is reduced when the unit idles, and the load of 8 watts is gradually reduced after the constant speed of the steam turbine and the journal moves to the center of the bearing bush by combining the reduction of the equivalent rigidity of the oil film of 8 watts and the abnormity of the temperature difference between the oil inlet and the oil return of 8 watts, so that the shaft vibration is increased and the bearing bush vibration is kept unchanged.
According to the relation between the vibration amplitude of the steam turbine unit and the load of the bearing and the rigidity of the oil film, the vibration amplitude of the steam turbine unit is related to the load borne by the bearing and the equivalent rigidity of the oil film, and the change of the equivalent rigidity of the oil film can cause the friction between the journal and the bearing bush. According to the rotor dynamics and the lubrication theory, the relationship between the amplitude and the bearing load and the equivalent stiffness of the oil film is analyzed, and the following conclusion is drawn that the bearing load is increased, the thickness of the oil film is thinned, the equivalent stiffness of the oil film is increased, the friction degree between a journal and a bearing bush is increased, and the vibration amplitude is reduced; and conversely, the bearing load is small, the oil film thickness is thickened, the oil film equivalent stiffness is reduced, and the vibration amplitude is increased.
In summary, it can be determined that the 8 w load of the steam turbine generator unit is smaller than the design load.
Step 2, carrying out stress analysis on a shaft system of the steam turbine generator unit
The stress diagram of the shafting is shown, F7 is a load of 7 watts, F8 is a load of 8 watts, G4 is the weight of the generator rotor, the distance between 7 watts and 8 watts is set to be L, and the distance between the generator back wheel and 7 watts is set to be L1, so that the following formulas (1) and (2) are necessarily established in the static state.
F7+F8＝G4 (1)
F7＝F8＝1/2·G4 (2)
From the above analysis, the load of 8 watts after the turbo generator set is fixed in speed is gradually reduced, that is, F8 is reduced, at this time, an internal stress is formed between the LP2 rotor and the generator rotor, the LP2 rotor applies a downward F1 stress to the generator rotor through the coupling with the generator rotor as a research object, and the generator rotor applies an upward F2 stress to the LP2 rotor with the LP2 rotor as a research object. f1 and f2 are a pair of an acting force and a reaction force (f1 ═ f2), and the following expressions (3) and (4) hold for the generator as a study object.
F7+F8＝G4+f1 (3)
When the 8-watt operation load is reduced, internal stress is generated between the generator rotor and the LP2 rotor, the main reason that the 8-watt load is reduced is that the 8-watt journal lift is too small, and the 8-watt lift is determined by the 6-watt journal lift of the standard lift of the shafting, so that the standard lift deviation of the steam turbine generator unit can cause the internal stress generated between the shafting after the unit operates.
Step 3, drawing a schematic diagram of bending strain of a shafting
Because of the 6-watt standard deflection, the LP2 rotor will generate bending strain upwards with 7 watts as a fulcrum under the action of the internal stress f2 after the unit is operated, the shaft system generates upward micro bending deformation, the atoms of the material at the outer bending side of the shaft system bear tensile and compressive stress, and the atoms of the material at the inner bending side bear compressive stress. The deviation of the reference raise degree curve from the design value is more, and the shafting is no longer a continuous smooth curve.
Step 4, introducing Hooke's law to carry out vibration analysis
When the strain amount is ∈, the elastic modulus of the axis system is E, and the bending stress is σ, equation (5) holds according to hooke's law.
σ＝Eε(5)
Within the elastic limit, the shafting can be regarded as an elastic vibrator, when f2 is kept unchanged, the strain epsilon of the LP2 rotor is always kept stable, the bending stress sigma is also kept stable, and the whole shafting can not generate fluctuation vibration. When the external condition changes, the 8 watt load F8 is easily changed, and as can be seen from the formula (4), when F8 is increased, the internal stress F1 is reduced, the balance state of the elastic vibrator is broken, and the shaft system rebounds in the direction opposite to the strain amount, so that the vertical fluctuation vibration around the new balance position is generated. The fluctuation vibration phenomenon of the No. 4 steam turbine generator unit of the factory can be easily explained according to the relation of stress and strain of the elastic vibrator in the formula (5), and the specific analysis is as follows:
A. since 6 watts is close to the maximum strain position of the LP2 rotor, the 6 watt ripple amplitude is greater than 5 watts and 8 watts.
B. The fulcrum of the bending deformation of the LP2 rotor is 7 watts, so 7 watts will not fluctuate, but the phase angle will be reversed.
C. When the external conditions are changed and the elastic vibrator balance is broken, the fluctuation vibration can be automatically generated, and the problem of automatic fluctuation generation can be explained.
D. Since the vibration is always damped, the fluctuating vibration can be damped by itself until it disappears and balances itself in a new equilibrium position.
E. Under the action of internal stress, the LP2 rotor and the generator rotor generate bending strain, namely the LP2 rotor and the generator rotor form an elastic vibrator, so that 5-watt, 6-watt and 8-watt fluctuation vibration always occurs at the same time and disappears at the same time.
F. Because the bending deformation of the shafting takes the approximate middle point of the 7 watt and LP2 rotors as the starting point, the fluctuation amplitude of 6 watts is always in opposite phase with 5 and 8 watts after the balance of the elastic vibrator is broken.
G. When the load changes, the probability of balance being broken is high, and therefore, the probability of occurrence of periodic fluctuation vibration when the load is increased or decreased is high.
For the vibration problem of periodic fluctuation of vibration amplitude, the actual conditions encountered by engineering are relatively few, and the periodic fluctuation vibration of the steam turbine generator unit recorded by the existing data includes beat vibration and friction vibration. However, the 5, 6 and 8 watt periodic vibration rules and characteristics of the steam turbine generator unit No. 4 in Fuqing nuclear power station are not completely matched with friction vibration or beat vibration, the characteristics and the rules of the periodic vibration generated by the steam turbine generator unit in the nuclear power station are analyzed, Hooke's law is applied to vibration analysis, and finally the obtained internal stress caused by shafting reference raise deviation is the root cause of the periodic fluctuation vibration generated by the unit, so that the defect cause is accurately positioned, and the unit fluctuation vibration problem is solved.
Claims (8)
1. A method for diagnosing the periodical vibration of the shafting of a steam turbine generator unit comprises the following four steps of 1, performing vibration preliminary analysis according to operation and vibration measurement data; step 2, carrying out stress analysis on a shaft system of the steam turbine generator unit; step 3, drawing a schematic diagram of bending strain of a shafting; step 4, introducing Hooke's law to carry out vibration analysis;
the method is characterized in that: the step 1 comprises the steps of analyzing vibration reasons on the aspects of oil inlet and return temperature, analyzing vibration reasons on the aspect of critical rotating speed, analyzing vibration reasons on the aspect of vibration change after no-load constant speed, and analyzing vibration reasons on the aspect of shaft vibration and bearing vibration change.
2. The method for diagnosing the periodic fluctuation vibration of the shafting of the steam turbine generator unit as claimed in claim 1, wherein: step 1, carrying out vibration preliminary analysis according to operation and vibration measurement data, and analyzing vibration reasons in the aspects of oil inlet and return temperatures;
the temperature difference between the oil inlet temperature and the oil return temperature of each tile during operation is analyzed, the temperature difference between the oil inlet temperature and the oil return temperature of each tile during operation is only 2.5 ℃, the temperature difference between the oil inlet temperature and the oil return temperature of each tile is between 6 and 8 ℃, and the temperature difference between the oil inlet temperature and the oil return temperature of each tile is obviously low, so that the load of each tile is inferred to be low; in comparison with the aspect of the watt temperature, although the 8 watt temperature is 91.4 ℃ which is the highest among the unit watts, the 8 watt temperature of the unit No. 4 is lower than that of the unit No. 1-3 of the nuclear power plant 8 watt at 98-100 ℃, so that the load of the unit No. 4 steam turbine generator unit 8 watt is lower than the design load by performing transverse analysis on the operation parameters of the watt temperature.
3. The method for diagnosing the periodic fluctuation vibration of the shafting of the steam turbine generator unit as claimed in claim 1, wherein: step 1, performing vibration preliminary analysis according to operation and vibration measurement data, and analyzing vibration reasons in the aspect of critical rotating speed;
when the machine is stopped and the speed is reduced to be over critical, the shaft vibration at the position of 8 watts does not generate resonance, the phenomenon that the shaft vibration at the position of critical rotating speed does not generate a resonance peak is abnormal, and the vibration is analyzed by using the accessed special vibration monitoring software, and the vibration phase angle at the position of 8 watts does not generate mutation when the machine is stopped and the speed is reduced to be over critical, so that the shaft vibration at the position of 8 watts does not generate resonance when the machine is stopped and the speed is reduced to be over critical;
deducing the drift of the critical rotating speed of the unit at 8W, wherein the critical rotating speed, namely the natural frequency, of the shafting of the steam turbine generator unit is related to the material, the mass and the length of the rotor and is also influenced by the rigidity of the supporting system, the natural frequency of the shafting is changed when the supporting condition is changed, the supporting rigidity is reduced, and the natural frequency of the shafting is reduced;
a resonance peak appears when the speed is reduced to 744RPM, so that the fact that the supporting rigidity at the position of 8 watts is reduced is inferred, the material of a supporting system of the steam turbine generator unit in operation is not changed, the only possibility that the supporting rigidity is reduced is that the equivalent rigidity of an oil film is changed, the equivalent rigidity of the oil film is reduced to lead the critical rotating speed of a shaft system at the position of 8 watts to drift, and therefore resonance does not appear when the speed of the steam turbine generator unit is reduced to the designed critical rotating speed 985 RPM.
4. The method for diagnosing the periodic fluctuation vibration of the shafting of the steam turbine generator unit as claimed in claim 1, wherein: step 1, carrying out vibration preliminary analysis according to operation and vibration measurement data, and analyzing vibration reasons in the aspect of vibration change after no-load and constant speed;
the shaft vibration at 8W in the idling process of the turbo generator set reaching the rated rotating speed stably rises from 29um to 70um finally, the change of the shaft vibration after no-load and constant speed is analyzed in detail, and the oil film rigidity of 8W is reduced after the constant speed is achieved;
the analytical procedure was as follows:
according to the theory of forced vibration, the exciting force and the dynamic stiffness of the supporting system are two major factors influencing the forced vibration of the rotating machine, and the amplitude A of the forced vibration can be represented by the formula (5):
A＝α×F/Kd (5)
(5) where α is the coefficient, F is the excitation force, Kd is the dynamic stiffness, and from this analysis, the amplitude of the vibration is directly proportional to the excitation force and inversely proportional to the dynamic stiffness of the equipment support system, so decreasing the excitation force or increasing the dynamic stiffness can decrease the vibration amplitude, if the 8W vibration increases after a constant speed, it is likely that F is becoming larger or that the dynamic stiffness Kd is decreasing.
If the excitation force is unbalanced, according to Newton's second law, F is M ω2r, if the excitation force generated by unbalance is generated, the excitation force can not be increased after the rated rotating speed is reached, so that the amplitude can not be increased after the rated rotating speed is reached;
the vibration amplitude at the position of 8 watts is only 29um at constant speed, which shows that the dynamic balance of a shafting is very good;
the excitation current of the generator is zero when the generator is in no load, and the possibility of additional excitation force formed by a thermal vector is eliminated, so that the shaft vibration at the position of 8 watts can be increased only, namely the dynamic stiffness Kd is reduced, the oil film stiffness is reduced under the condition that a steam turbine supporting system is not changed, and the oil film stiffness of 8 watts after the unit is in constant speed can be determined to be reduced by combining the condition that the turbine supporting system is stopped and the critical resonance peak does not appear.
5. The method for diagnosing the periodic fluctuation vibration of the shafting of the steam turbine generator unit as claimed in claim 1, wherein: step 1, performing vibration preliminary analysis according to operation and vibration measurement data, and analyzing vibration reasons in the aspect of shaft vibration and tile vibration changes;
the shaft vibration at the position of 8 watts steadily rises in the idling process, but the tile vibration at the position of 8 watts keeps unchanged in the 8-watt shaft vibration rising process, so that the fact that the eccentricity of 8 watts is reduced when the unit idles is inferred, and the load of 8 watts after the constant speed of the steam turbine is gradually reduced and the shaft neck moves towards the center of a bearing bush and the temperature difference between oil inlet and return of 8 watts is abnormal can be judged by combining the reduction of the equivalent rigidity of an oil film of 8 watts and the abnormality of the temperature difference between oil inlet and return of 8 watts, so that the shaft vibration rises and the tile vibration keeps unchanged;
according to the relation between the vibration amplitude of the steam turbine unit and the load of the bearing and the rigidity of the oil film, the vibration amplitude of the steam turbine unit is related to the load borne by the bearing and the equivalent rigidity of the oil film, and the change of the equivalent rigidity of the oil film can cause the friction between the journal and the bearing bush. According to the rotor dynamics and the lubrication theory, the relation between the amplitude and the bearing load and the equivalent rigidity of the oil film is analyzed, and the following conclusion is drawn that the bearing load is increased, the thickness of the oil film is thinned, the equivalent rigidity of the oil film is increased, the friction degree between a journal and a bearing bush is increased, and the vibration amplitude is reduced; on the contrary, the bearing load is small, the oil film thickness is thickened, the oil film equivalent stiffness is reduced, and the vibration amplitude is increased;
finally, the 8W load of the steam turbine generator unit of the steam turbine is smaller than the design load.
6. The method for diagnosing the periodic fluctuation vibration of the shafting of the steam turbine generator unit as claimed in claim 1, wherein: step 2, carrying out stress analysis on a shaft system of the steam turbine generator unit;
f7 is a load of 7 watts, F8 is a load of 8 watts, G4 is the weight of the generator rotor, and if the distance between 7 watts and 8 watts is L and the distance between the generator back wheel and 7 watts is L1, then in a static state, the following formulas (1) and (2) are necessarily established;
F7+F8＝G4 (1)
F7＝F8＝1/2·G4 (2)
as can be seen from the above analysis, after the turbo generator set is set at a constant speed, the load of 8 watts is gradually reduced, that is, F8 is reduced, at this time, an internal stress is formed between the LP2 rotor and the generator rotor, when the generator rotor is taken as a research object, the LP2 rotor applies a downward F1 stress to the generator rotor through the coupling, when the LP2 rotor is taken as a research object, the generator rotor applies an upward stress F2 to the LP2 rotor, F1 and F2 are a pair of an acting force and a reaction force, that is, F1 is F2, when the generator is taken as a research object, the following formulas (3) and (4) are established;
F7+F8＝G4+f1(3)
when the 8-watt operation load is reduced, internal stress is generated between the generator rotor and the LP2 rotor, the main reason that the 8-watt load is reduced is that the 8-watt journal lift is too small, and the 8-watt lift is determined by the 6-watt journal lift of the standard lift of the shafting, so that the standard lift deviation of the steam turbine generator unit can cause the internal stress generated between the shafting after the unit operates.
7. The method for diagnosing the periodic fluctuation vibration of the shafting of the steam turbine generator unit as claimed in claim 1, wherein: step 3, drawing a schematic diagram of bending strain of a shafting;
because of the deviation of the 6-watt reference raise, under the action of the internal stress f2, the LP2 rotor after the unit operates can upwards generate bending strain by taking 7 watts as a fulcrum, a shaft system generates upwards tiny bending deformation, the atoms of the material at the outer bending side of the shaft system bear tensile and compressive stress, and the atoms of the material at the inner bending side bear compressive stress, so that the deviation of the reference raise curve from a designed value is more, and the shaft system is not a continuous and smooth curve any more.
8. The method for diagnosing the periodic fluctuation vibration of the shafting of the steam turbine generator unit as claimed in claim 1, wherein: step 4, introducing Hooke's law to carry out vibration analysis;
when the strain amount is ∈, the elastic modulus of the axis system is E, and the bending stress is σ, equation (5) holds according to hooke's law.
σ＝Eε(5)
Within the elastic limit, the shafting can be regarded as an elastic vibrator, when f2 is kept unchanged, the strain epsilon of the LP2 rotor is always kept stable, the bending stress sigma is also kept stable, and the whole shafting can not generate fluctuation vibration. When the external condition changes, the 8 watt load F8 is easily changed, and as can be seen from the formula (4), when F8 is increased, the internal stress F1 is reduced, the balance state of the elastic vibrator is broken, and the shaft system rebounds in the direction opposite to the strain amount, so that the vertical fluctuation vibration around the new balance position is generated. The fluctuation vibration phenomenon of the No. 4 steam turbine generator unit of the factory can be easily explained according to the relation of stress and strain of the elastic vibrator in the formula (5), and the specific analysis is as follows according to a shafting bending strain diagram:
A. since 6 watts is close to the maximum strain position of the LP2 rotor, the 6 watt ripple amplitude is greater than 5 watts and 8 watts.
B. The fulcrum of the bending deformation of the LP2 rotor is 7 watts, so 7 watts will not fluctuate, but the phase angle will be reversed.
C. When the external conditions are changed and the elastic vibrator balance is broken, the fluctuation vibration can be automatically generated, and the problem of automatic fluctuation generation can be explained.
D. Since the vibration is always damped, the fluctuating vibration can be damped by itself until it disappears and balances itself in a new equilibrium position.
E. Under the action of internal stress, the LP2 rotor and the generator rotor generate bending strain, namely the LP2 rotor and the generator rotor form an elastic vibrator, so that 5-watt, 6-watt and 8-watt fluctuation vibration always occurs at the same time and disappears at the same time.
F. Because the bending deformation of the shafting takes the approximate middle point of the 7 watt and LP2 rotors as the starting point, the fluctuation amplitude of 6 watts is always in opposite phase with 5 and 8 watts after the balance of the elastic vibrator is broken.
G. When the load changes, the probability of balance being broken is high, and therefore, the probability of occurrence of periodic fluctuation vibration when the load is increased or decreased is high.
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