A dynamic balancing method for eliminating unstable vibration of the shafting

Abstract

The present invention provides a dynamic balancing method for eliminating unstable vibration of the shafting, which can conveniently and effectively solve the abnormal vibration problems of high and intermediate pressure rotors commonly found in specific types of units. According to the shafting vibration characteristics of this type of unit, the method creatively adopts simultaneous counterweight addition on multiple balance planes inside and outside the high and intermediate pressure rotors, and uses a specific calculation method to eliminate the abnormal vibration of the high and intermediate pressure rotors caused by the decline of shafting stability through a single application of counterweight. This method minimizes the number of unit starts and stops during the vibration fault handling process, and is an effective dynamic balancing method for eliminating abnormal vibration of steam turbine generator units that has been proven through practice.

Description

Technical Field

[0001] The present invention relates to a dynamic balancing method for eliminating unstable vibration of the shafting, belonging to the technical field of steam turbine shafts. Background Art

[0002] The reasons for abnormal vibration of the shafting of large-capacity steam turbines are relatively complex. During long-term operation, reasons such as uneven settlement of the steam turbine foundation and dynamic changes in the elevation of the bearing pedestals during hot operation will reduce the load on the high and intermediate pressure rotor bearings, resulting in poor formation of the bearing oil film and a decrease in oil film stiffness, leading to an increase in vibration. Under the sequence valve operation mode, uneven gas flow forces may also cause gas flow excitation of the high and intermediate pressure rotors. The above reasons make it difficult to analyze and process the original vibration data during on-site high-speed dynamic balancing of the high and intermediate pressure rotors. Summary of the Invention

[0003] The object of the present invention is to provide a dynamic balancing method for eliminating unstable vibration of the shafting, which can maximize the elimination of power frequency vibration caused by rotor mass imbalance and enable the unit to operate safely and stably.

[0004] To achieve the above object, the present invention is realized through the following technical solutions:

[0005] Step 1: Overhaul and adjust the front and rear bearings of the high and intermediate pressure rotors of the large-capacity steam turbine, and take the lower limit of the installation standard value for the bearing top clearance.

[0006] Step 2: Test the journal elevation of the high and intermediate pressure rotors without removing the coupling, and compare and calculate it with the overhaul record during installation. During reinstallation, adjust the corresponding value of the journal elevation based on the change value of the journal elevation and according to the metal temperature difference between the front and rear bearings of the high and intermediate pressure rotors under operating conditions for compensation; since the foundation settlement and elevation change values of different units are different, this value is not unified and needs to be flexibly determined according to the actual situation of the unit and on-site treatment experience.

[0007] Step 3: Change the valve sequence of the sequence valve to the diagonal air intake mode to reduce the offset of the rotor in the horizontal direction; when the rotor rotates clockwise from the steam turbine to the generator direction, change the control valve that is opened in the third sequence under high load to a control valve that makes the force direction of the rotor be towards the lower right; to improve the force condition of the rotor, reduce the floating amount of the rotor towards the upper left under high load, and increase the oil film stiffness of the bearing in this direction.

[0008] Step 4: Conduct spectral analysis on the shaft vibrations at the measurement points of the front and rear bearings of the high and intermediate pressure rotors to find out the power frequency vibration components; decompose the vibration modes of the high and intermediate pressure rotors into co-directional vectors and reverse vectors.

[0009] If the first-order vibration mode is dominant, a set of weights with the same phase is applied to the balance holes at both ends inside the high-pressure and intermediate-pressure rotors. Since the radius of the added weights at this balance position is small and the balance holes are scattered, a set of weights with a phase opposite to that of the weights inside the rotor is also applied to the balance holes of the extension shaft coupling at the front end of the high-pressure and intermediate-pressure rotors.

[0010] If the second-order vibration mode is dominant, a set of weights with opposite phases is applied to the balance holes at both ends inside the high-pressure and intermediate-pressure rotors, and a set of weights with the same phase as the weights at the front end inside the high-pressure and intermediate-pressure rotors is applied to the balance holes of the extension shaft coupling at the front end of the high-pressure and intermediate-pressure rotors.

[0011] Preferably, in step 1, the contact area of the pillow block shims is controlled to be more than 75% and evenly distributed.

[0012] The advantages of the present invention are as follows:

[0013] (1) The main characteristics of the abnormal vibration of the high-pressure and intermediate-pressure rotors of large-capacity steam turbines are complex vibration spectra, which contain both power-frequency vibrations caused by rotor mass imbalance and low-frequency vibrations caused by gas flow excitation. Sometimes, there are also multiple-frequency vibrations caused by defects such as rotor micro-cracks. The purpose of this dynamic balancing method is to find the power-frequency components from the complex vibration spectra and, through the means of adding weights, eliminate the power-frequency vibrations caused by rotor mass imbalance to the greatest extent, so that the unit can operate safely and stably.

[0014] (2) The decrease in the stability of the shafting will cause the dynamic stiffness of the support system to decrease, thereby amplifying the vibration amplitude. Therefore, this dynamic balancing method first takes measures to enhance the stability of the shafting and improve the dynamic stiffness of the support system, so as to obtain a more accurate vibration component caused by rotor mass imbalance.

[0015] (3) In the on-site dynamic balancing work of the high-pressure and intermediate-pressure rotors of large-capacity units, the counterweight effect is often limited by the limitations of the dynamic balancing plane positions at both ends of the rotor. This dynamic balancing method selects appropriate off-rotor dynamic balancing planes for combination according to the shafting structure and rotor vibration mode characteristics, and uses a specific calculation method to obtain a better dynamic balancing effect by applying a combined counterweight at one time. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention.

[0017] Figure 1 It is a schematic diagram of the partial shafting structure of the steam turbine of the present invention.

[0018] Figure 2 It is a schematic diagram of the high-pressure control valve and the circumferential gas flow force direction of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] The present invention will be further described below by taking an on-site dynamic balancing test of a 660MW steam turbine generator set in a power plant as an example.

[0021] The turbine shafting structure of this unit is as follows Figure 1 As shown. When looking from the steam turbine to the generator, the rotor rotates clockwise.

[0022] Since the unit was put into operation after 168 hours of commissioning, the over-critical vibration and load vibration of the high- and medium-pressure rotors have continued to increase, and the power frequency and low-frequency vibrations have continued to grow. Finally, the No. 1 shaft vibration rose to 200µm, and the No. 1 shaft vibration exceeded the protection setting value of 254µm during high load, causing the unit to trip. During operation, the metal temperature of the No. 1 bearing was 10℃ lower than that of the No. 2 bearing, and the measurement found that the turbine foundation had uneven settlement, and the foundation settlement near the No. 1 bearing seat was 2mm more than the foundation of the No. 2 bearing seat.

[0023] (l) The bearing No. 1 of this unit is a four-piece tilting bearing. Inspection found that the alloy contact surface of the lower bearing No. 1 was partially worn, so it was scraped. The standard value of the bearing top clearance installation should be less than 0.7mm. The lower limit was taken during reinstallation. The actual top clearance was 0.61mm on the left and 0.62mm on the right. The contact area of ​​each pad of the bearing pillow was controlled to be more than 75% and evenly distributed.

[0024] (2) The high and medium pressure rotor shaft neck lift was re-measured without removing the coupling. The front lift of shaft neck No. 1 was 0.3mm / m, and the front lift of shaft neck No. 2 was 0.1mm / m. The data is shown in Table 1. It can be seen that the lift at shaft neck No. 1 has been significantly reduced. According to the foundation settlement and lift change data of the unit, appropriate space for uneven settlement was reserved during the maintenance before the dynamic balancing test, and the lift value of shaft neck No. 1 was increased by 0.30mm / m on the basis of the installation standard to compensate.

[0025] Table 1 High and medium pressure rotor lift values ​​(mm / m)

[0026]

[0027] (3) The unit has four high-adjustable valve nozzle groups. When looking from the turbine to the generator, the upper part is left 3 and right 4, and the lower part is left 1 and right 2. The direction of the circumferential airflow force is as follows: Figure 2As shown. The original valve sequence of the sequential valve operation is (3+4)→1→2. When the (3+4) valves are opened synchronously under low load, the resultant force after the vector superposition of the airflow force is horizontally to the right, causing the rotor center to shift to the right, which is easy to induce airflow excitation. When the third sequence No. 1 valve is fully opened under high load, the rotor is subjected to the airflow force to the upper left, causing the rotor to float in this direction to the maximum value. The increase in oil film thickness will reduce the dynamic stiffness of the support system and thus amplify the vibration value.

[0028] According to the analysis of the vibration characteristics of the unit, it is believed that by adopting the diagonal air intake method, the (2+3) valves are opened synchronously at low load, and the vector sum of the airflow force can theoretically offset each other, minimizing the horizontal offset of the rotor. Changing the third valve that opens in sequence at high load to the No. 4 valve that makes the rotor force direction to the lower right can improve the force condition of the rotor at high load. Therefore, before the dynamic balancing test, the valve sequence of the unit was changed to (2+3)→4→1.

[0029] (4) The unit has 24 screw holes drilled on both end faces of the high and medium pressure rotors, and balancing holes drilled on the plane of the coupling connected to the long shaft in the front box. Through spectrum analysis and vibration type iso- and anti-phase decomposition, the dynamic balancing scheme is determined as follows: apply a counterweight of 1300 grams ∠100° to the front end of the high and medium pressure rotors, apply a counterweight of 1300 grams ∠100° to the rear end, and apply a counterweight of 1100 grams ∠280° to the coupling between the high and medium pressure rotors and the long shaft. After the dynamic balancing test, the unit was restarted again. The vibration value of the high and medium pressure rotor No. 1 shaft increased from the original 200µm to 100µm. At a constant speed of 3000r / min and under high load, the maximum vibration value of the No. 1 shaft did not exceed 80µm. It meets the requirements for safe and stable operation of the unit.

[0030] The above example shows that by using this dynamic balancing method, by simultaneously applying counterweights to the balancing holes at both ends of the high and medium pressure rotors and the balancing holes of the long shaft coupling, the problem of excessive vibration of the high and medium pressure rotors of the 660MW steam turbine generator set was quickly and effectively solved.

[0031] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A dynamic balancing method for eliminating unstable vibration of the shafting, characterized in that, It includes the following steps: Step 1: Overhaul and adjust the front and rear bearings of the high and intermediate pressure rotor of the large-capacity steam turbine, and take the lower limit of the installation standard value for the top clearance of the bearings; Step 2: Test the journal elevation of the high and intermediate pressure rotor under the condition of not removing the coupling, and compare and calculate it with the overhaul record during installation. During reinstallation, adjust the corresponding value on the basis of the installation standard value according to the change value of the journal elevation and the metal temperature difference between the front and rear bearings of the high and intermediate pressure rotor in the operating state for compensation; Step 3: Change the valve sequence of the sequence valve to the diagonal intake mode to reduce the offset of the rotor in the horizontal direction; when the rotor rotates clockwise from the steam turbine to the generator direction, change the control valve that is opened in the third sequence at high load to the control valve that makes the force direction of the rotor be in the lower right direction; Step 4: Conduct spectrum analysis on the shaft vibration of the measuring points of the front and rear bearings of the high and intermediate pressure rotor to find out the power frequency vibration component among them; decompose the vibration mode of the high and intermediate pressure rotor into co-directional vectors and reverse vectors; If the first-order vibration mode is the main one, apply a set of weights with the same phase at the balance holes at both ends inside the span of the high and intermediate pressure rotor, and at the same time apply a set of weights with the opposite phase to the weights inside the span at the balance holes of the extension shaft coupling at the front end of the high and intermediate pressure rotor; If the second-order vibration mode is the main one, apply a set of weights with opposite phases at the balance holes at both ends inside the span of the high and intermediate pressure rotor, and at the same time apply a set of weights with the same phase as the weights at the front end inside the span of the high and intermediate pressure rotor at the balance holes of the extension shaft coupling at the front end of the high and intermediate pressure rotor.

2. The dynamic balancing method for eliminating the unstable vibration of the shafting according to claim 1, characterized in that, In the said Step 1, control the contact area of the pillow block pad iron to be more than 75% and evenly distributed.

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