What methods and sensors are used to measure the bearing seat and radial vibration respectively?

General vibration standard-evaluation standard according to bearing amplitude

According to the evaluation standard of bearing amplitude

1969 vibration standard of steam turbine generator set recommended by IEC is shown in table 1 (peak-peak, micron). The rating of steam turbine generator set specified by the former Ministry of Water and Electricity is basically consistent with IEC standard, as shown in Table 2 (peak-to-peak value).

Table 1 IEC vibration standard

Rotational speed (rpm)100015001800 3000 3600 600012000.

Measure 75 50 42 25 2 1 12 6 on the bearing.

Measure150100 84 50 42 2512 on the shaft.

Table 2 Vibration standard

Rotational speed (r/min) is excellent and qualified.

1500 30 50 70

3000 20 30 50

According to the evaluation standard of bearing vibration strength

ISO, the international organization for standardization, issued a series of vibration standards as the basis of machine quality evaluation. Relevant standards are introduced as follows:

⑴ ISO2372/ 1:

This standard was officially promulgated in 1974, and is applicable to the vibration intensity classification of machines with working speed of 600~ 12000r/min and bearing cover vibration frequency within the range of 10~ 1000Hz. It divides machines into four categories:

Class I is a fixed small machine or a small motor fixed on the whole machine, and its power is less than 15KW.

Class II is a medium-sized machine with no special foundation and power 15~75KW. Machines with power less than 300KW are rigidly installed on special foundations.

The third category is large rotating machinery on rigid or heavy foundation, such as steam turbine generator set.

Class Ⅳ is a large rotating machinery with light structure, such as steam turbine generator set.

Each machine has four quality grades: A, B, C and D, and the vibration intensity ranges corresponding to the same quality grade of various machines are somewhat different, as shown in Table 3. The meanings of the four quality segments are as follows:

Table 3 Various evaluation standards of machine vibration recommended by ISO 2372

Classification range of vibration intensity: grades of various machines.

Vibration intensity (mm/s) dB (dB) Level 1, Level 2, Level 3 and Level 4

0. 18-0.28

0.28-0.45

0.45-0.7 1.93-97

0.7 1- 1. 12 97- 10 1 B A A A

1. 12- 1.8 10 1- 105

1.8-2.8 105- 109

2.8-4.5 109- 1 13

4.5-7. 1 1 13- 1 17D C C B

7. 1- 1 1.2 17- 12 1D D C C

1 1.2- 18 12 1- 125

18-28 125- 129

28-45 129- 133 D D D D

45-7 1 133- 139

Grade A: excellent, the vibration is below the good limit, and the vibration state is considered to be good.

Grade b: qualified. Vibration is between good limit and alarm value. It is considered that the vibration state of the unit is acceptable (qualified) and can run for a long time.

Class C: It is still qualified, and the vibration is between the alarm limit and the shutdown limit. The unit can run for a short time, but monitoring must be strengthened and measures must be taken.

Grade d: unqualified. If the vibration exceeds the stop limit, stop the machine immediately.

The vibration intensity starts from the threshold value of 0.07 1mm/s that people can feel, and is divided into 15 orders of magnitude in the range of 7 1mm/s, and the ratio of two adjacent orders of magnitude is about 1.6, that is, the difference is 4 decibels.

⑵ ISO3945:

This standard is the measurement and evaluation of vibration intensity of mechanical vibration field of large rotating machinery. When formulating the evaluation standard, the performance of the machine, the stress caused by the vibration of the machine, the need for safe operation, the influence of the vibration of the machine on people and the surrounding environment and the characteristic factors of the measuring instrument are considered.

Obviously, the mechanical vibration measured on the surface of the machine can not represent the actual vibration stress, the motion state of key components or the vibration force transmitted by the machine to the surrounding structures in any case. Other parameters should be measured when there are special requirements. Table 4 gives the vibration intensity evaluation grade of large rotating machinery with power greater than 300KW and rotating speed of 600~ 12000 rpm.

Note: The reference value is 10-5 mm/s.

Table 4 ISO3945 Evaluation Grade

Support type of vibration intensity

Vibration intensity (mm/s) db (db) rigid support flexible support

0.46-0.7 1.93-97, okay, okay, okay.

0.71-1.1297-10/ok.

1.12-1.8101-105.

1.8-2.8105-109 satisfactory.

2.8-4.6109-113 satisfactory

4.6-7.1113-17 is not satisfied.

7.1-1.2117-121dissatisfied

11.2-18121-125 is not allowed to be dissatisfied.

18-28125-129 is not allowed.

28-45 129- 139 is not allowed.

The evaluation grade of vibration intensity specified in this standard depends on the supporting state of the machine system. It can be divided into two categories: rigid support and flexible support, which are equivalent to III and IV of ISO2372. For flexible support, the basic natural frequency of machine-support system is lower than its working frequency, while for rigid support, the basic natural frequency of machine-support system is higher than its working frequency.

Evaluation standard of axial amplitude

Ю 7919/1Measurement and Evaluation of Rotating Shaft Vibration-Part I General Provisions was formally promulgated in19860. ISO/DIS79 1 10-2 "measurement and evaluation of shaft vibration of rotating machinery-part ii: application guide for large turbo-generator sets" is formulated in 1987, which specifies the limit value of shaft vibration of turbo-generator sets above 50MW, as shown in tables 5 and 6, which are applicable to relative vibration and absolute vibration of shafts respectively.

Paragraphs a, b and c in the table have the same meanings as above. The shaft vibration is measured by eddy current sensor.

Table 5 Relative Vibration Limit of Turbine Generator Shaft (peak-to-peak displacement, micron)

Magnetic pole speed (rpm)

1500 1800 3000 3600

A 100 90 80 75

b 200 185 165 150

C 300 290 260 240

Table 6 Absolute Vibration Limit of Turbine Generator Shaft (peak-to-peak displacement, unit micron)

Magnetic pole speed (rpm)

1500 1800 3000 3600

a 120 10 100 900

B 240 220 200 180

C 385 350 300 290

Some explanations on vibration evaluation standard of bearing seat and shaft;

(1) According to ISO2372 and 79 19, we should pay attention to the following two standards.

Rule 1: When running at rated speed under stable working conditions in the whole load range, the vibration of each bearing seat and shaft should not exceed the specified limit.

Criterion 2: If the amplitude of bearing seat vibration or shaft vibration is qualified, but the change exceeds 25% of the alarm limit, the alarm should be given regardless of whether the vibration becomes larger or smaller. Because the vibration changes greatly, it indicates that the unit may have a fault, especially when the vibration changes greatly and quickly.

⑵ According to the situation in our country, the unit below 50MW generally only measures the vibration of the bearing seat, and does not require measuring the shaft vibration. Units with power above 200MW require simultaneous measurement of bearing seat vibration and shaft vibration. For units with a power of more than 50MW and less than 200MW, it is required to measure the vibration of the bearing seat, and the measurement of shaft vibration is carried out under working conditions or during the start-up of new units and fault analysis of units.

(3) Generally, there is no fixed proportional relationship between bearing seat vibration and shaft vibration. This is because the vibration of the two is related to many factors, such as oil film parameters, bearing seat stiffness, foundation stiffness and so on. Generally, a scale range can be given according to statistical data. According to ISO data, the ratio of shaft vibration to bearing seat vibration is generally 2~6.

The German Institution of Engineers issued the "Measurement and Evaluation of Turbine Shaft Vibration" in 198 1, which is referred to as VDI—2059. The vibration state of the unit is divided into three grades: good, alarm and shutdown, which are calculated by three formulas respectively. The relative vibration of the reconstructed shaft is shown in Table 7.

Table 7 VDI-2059 Relative Vibration Limit of Turbine Generator Shaft (peak-to-peak displacement, unit micron)

Rotation speed (rpm)

1500 1800 3000 3600

Ok124113 88 80

Call 232 212164150.

Stop 341311241220.

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