Ph.D. M.A. Biyalt, head of the vibration diagnostics and adjustment department, QUARTZ Group LLC, Omsk;
Ph.D. A.V. Kistoichev, associate professor,
A.V. Baleevskikh, student,
E.F. Kovalchuk, student, Federal State Autonomous Educational Institution of Higher Professional Education "Ural Federal University named after the first President of Russia B.N. Yeltsin", Ekaterinburg

Flexible couplings are usually used to transmit small torques. Previously, they were installed in turbines with a unit capacity of up to 100 MW. In modern powerful turbo units, flexible couplings are no longer used due to the high resistance that arises when transmitting significant torques. However, in small drive units and various auxiliary mechanisms (pumps, blowers, compressors), they are widely used due to their properties:

1. The ability to soften shocks and impacts.

2. Elastic couplings can serve as a means of protection against resonant torsional vibrations that occur in the mechanism due to uneven rotation.

3. Elastic couplings allow relatively large displacements of the axes of the connected shafts. At the same time, due to the deformation of the elastic elements, the shafts and supports are loaded with relatively small forces and moments.

At the same time, flexible couplings have the following disadvantages: difficulty (impossibility) of precise adjustment of its working elements for uniform transmission of torque; resulting in increased wear of the coupling elements during operation. Malfunctions in the operation of a flexible coupling can cause the vibration of the unit to depend on the load (torque value), destruction of the coupling elements, or even jamming.

In the article, based on our own experience, as well as the experience of our colleagues, we examined another aspect of the vibration behavior of a unit that has a flexible coupling as part of the shafting - this is the tendency of such units to low-frequency vibration in the presence of defects in the flexible coupling. In this work, I would like to approach the identified problem from a slightly different angle and consider low-frequency vibration as a diagnostic sign of a developed defect in a flexible coupling. The need for this is most eloquently illustrated by the following example.

In the article, perhaps for the first time, it was noted that improper operation of a flexible coupling can lead to the occurrence of low-frequency vibrations. The author comes to this conclusion after lengthy comprehensive tests of the PT-50-90/16 unit, which came out of a major overhaul, which included studies of the vibration dependence:

1. on the amount of steam flow into the production outlet at a constant electrical load;

2. from electrical load in condensing mode;

3. from electrical load at constant steam flow into the extraction;

4. on fresh steam consumption;

5. on the temperature of the oil entering the bearings.

During the tests, the dependence of the magnitude of low-frequency vibration on the power generated by the HPC was revealed. After normalizing the operation of the coupling, the low-frequency vibration disappeared.

The considered case illustrates well that the absence of clear diagnostic signs of a particular defect leads to an increase in time and costs for vibration adjustment of the unit. For this reason, one of the directions scientific activity Ural Federal University specialists are developing and clarifying diagnostic signs of the most characteristic defects in shafting lines. Diagnostic signs of malfunction of flexible couplings, which appear in the vibration signal, are quite well known:

■ increase in reverse vibration;

■ the appearance of a “load vector” (table);

■ the appearance of a number of high-frequency harmonics in the vibration spectra of support bearings (Fig. 1 and 2).

As the experience of setting up the PT-60-130 t/a shows, these diagnostic signs can be quite clearly manifested in the vibration behavior of the unit, however, low-frequency vibration may be absent or its level may remain insignificant. The breakdown of the unit into low-frequency vibration occurs after some operating time, if measures have not been taken in a timely manner to normalize the operation of the flexible coupling. This rule is best illustrated by the example of our experience in diagnosing and setting up the K-1700 compressor unit with a capacity of 10 MW.

Table. Results of vibration measurements on the front bearings of the PT-60-130 turbine unit in the presence of a defect in the flexible coupling.

For a long time, the unit worked without any special comments, but later, during the operating mode, self-excited low-frequency oscillations of the electric motor rotor began to occur periodically, which clearly indicated a loss of stability.

When the unit was started up and loaded, the vibration levels increased abruptly (due to the amplitude of the low frequency vibration), but the overall vibration level did not exceed the level of protection activation. Typically, in such cases, the unit was stopped and started again until a low-voltage emergency occurred (sometimes this required several starts). At a certain stage of such operation, a technological need arose not to turn off the compressor even in the event of an emergency. In this mode (with vibration levels up to 10.0 mm/s), the unit worked for almost 10 days and after that was taken out for repairs. During an inspection of the electric motor bearings, destruction of the babbitt was discovered in the form of chips on the lower and upper halves of the liners of both bearings, and therefore the bearings were replaced.

Thus, the above cases, in our opinion, allow us to assert that the presence in the vibration spectrum of the supports of units that have a flexible coupling as part of the shafting, traces of low-frequency vibrations, and even more so their disruption in the low-frequency coupling, may indicate the appearance of significant deviations in the operation of the flexible coupling . These deviations can be not only the result of the development of defects in the coupling itself, but also a consequence of the influence of external factors (disturbances in thermal expansion, regime misalignments). This statement can be easily confirmed by the explanation given in the explanation of the role of the flexible coupling in the mechanism of occurrence of low-frequency shocks.

As is known, reliable operation flexible couplings, even in the absence of misalignment, largely depend on the uniformity of torque transmission around the circumference. Uneven tangential gaps between the transmission elements and the teeth of the coupling halves, wear and deformation of the transmission elements, different pitches of the teeth on the coupling halves or “crown”, burns, poor-quality lubrication and many other reasons lead to uneven transmission of torque around the circumference of the coupling, which was visually confirmed in the ones discussed above cases.

As a result of the uneven transmission of torque in the plane of the coupling, a transverse force arises equal to the resultant of the forces transmitted by the transmission elements, schematically shown in Fig. 3.

The force, which can be conventionally called “driving”, is similar to the force from imbalance and causes increased reverse vibration. Such a force, as it arises and increases, “unwinds” the rotor in the bearing bores and increases precession. A change in torque, and therefore in transmitted power, leads to a change in the indicated force, which is reflected by an increase in reverse vibration with increasing load, i.e. the appearance of a “load” vector. And most importantly, during sudden loading or unloading of the unit, this force is the same destabilizing force that, by displacing the rotor journals in the bores of the bearing liners, can lead to the occurrence of precessional motion with an angular velocity equal to half the angular velocity of the rotor, i.e. to a breakdown in the NChV. Moreover, the more developed the defect of the flexible coupling, the higher the value of the “driving” force, and therefore the higher the tendency of the unit to fail in the low-pressure component. This exactly corresponds to the classical mechanism of the appearance of a circulating force in a bearing bore, which is usually used to explain this process.

conclusions

An analysis of numerous cases of the occurrence of low-voltage accidents on turbine units that have a flexible coupling as part of the shaft line, as well as other rotary machines (compressors, superchargers, pumps, etc.), shows that the cause of failure, in most cases, lies in the unsatisfactory operation of the flexible coupling. That. with other aggravating factors, namely the proximity of the rotor’s natural frequency to half of the rotation frequency (25 Hz), increased clearances in bearings, etc., units with flexible couplings should be considered prone to failure in the low-frequency cycle (naturally, when the operating conditions of the flexible coupling deteriorate ) and give Special attention to inspect this unit during the repair process.

Based on a generalization of experience in diagnostics and vibration adjustment of rotary machines, the features of failure in the low-frequency vibration of units that have a flexible coupling in their design are considered, and a mechanism for loss of stability is proposed and the determining role in this mechanism for the appearance of deviations in the operation of the coupling is shown.

It is proposed to consider the appearance of low-frequency disturbances on the supports of rotary machines as a diagnostic sign of the appearance of significant deviations in the operation of a flexible coupling.

Literature

1. Biyalt M.A. The role of flexible couplings in the occurrence of low-frequency vibration / M.A. Biyalt, A.V. Kistoichev, E.A. Zonov, E.V. Urev // Heavy engineering. 2012. No. 2. P. 40-48.

2. Trunini E.S. Self-oscillations of a high-pressure rotor // Electric stations. 1964. No. 3. P. 80-81.

3. Kistoichev A.V. About diagnostic signs of the presence of liquid in the central bore of rotors // A.V. Kistoichev, E.V. Uryev, M.A. Biyalt/Electric stations. 2012. No. 6. P. 57-62.

4. Kistoychev A., Uriev E. Diagnostic of Transversal NonCircular Crack in Turbomachine Rotors // 12th International Scientific and Engineering Conference “HERVIC0N-2008”. Poland, Kielce-Przemysl, 2008. P. 56-62.

5. Biyalt M.A. The role of flexible couplings in the occurrence of low-frequency vibration / M.A. Biyalt, A.V. Kistoichev, E.A. Zonov, E.V. Urev // Heavy engineering. 2012. No. 2. P. 40-48.

Acceleration - all these concepts are probably familiar to you. In this article we will look in more detail at such an important topic as vibration. Each of us encounters this phenomenon in everyday life.

What is vibration? The definition can be given as follows: these are oscillatory mechanical movements that are transmitted directly to the human body. Its main physical characteristics are the frequency and amplitude of vibrations. Vibration is measured by amplitude in centimeters or meters, and by frequency - in hertz.

How should vibration be assessed based on acceleration and speed?

At any speed and acceleration continuously change. The acceleration is greatest on the centerline of the oscillation, and in the extreme positions it is smallest. With this in mind, vibration is measured using acceleration and speed. The decibels are reported from the reference vibration velocity (conditional), which is equal to 5∙10 8 m/s, as well as vibration acceleration - 3∙10 4 m/s 2 . Vibration acceleration and vibration velocity are expressed relative to zero thresholds in decibels. The perception threshold is approximately 70 dB. The low-frequency vibration frequency does not exceed 32 Hz, and the high-frequency vibration is more than 32 Hz.

Sources of vibration

These are electric and pneumatic mechanized hand tools, various equipment and machines, vehicles, and machine tools, widely used in construction, industry, everyday life, agriculture, and transport. Vibration is widely used not only in technology, but also in medicine for the treatment of muscle and nervous diseases (vibration massage, vibration therapy).

Impact of vibration

Vibration is a factor that has great biological activity. Direction, depth and nature of physiological changes different systems human body are determined by its spectral composition, levels and physical properties human body. An important role in the genesis of these reactions is played by analyzers - cutaneous, visual, motor, vestibular, etc.

It should be noted the large role that the biochemical properties of the human body play in the subjective perception of vibration. Its effect on the body is mediated by such phenomena as the physical impact of contact on the surface, the spread of vibrations through tissues, the direct reaction in tissues and organs to the impact, irritation of mechanoreceptors, which cause subjective and neuroreceptor reactions.

Today, significant clinical and experimental material on this problem has been accumulated. A study of vibration has shown that motor function disorders arising under its influence are caused by both direct muscle damage and disturbances in the regulatory effects of the central nervous system. The predominance of diffuse shifts in this case can be explained by changes in the functioning of superspinal structures, and the greater severity of local changes in the muscles can be explained by their direct traumatization. The most sensitive to the effects of local vibration are the sections of the sympathetic nervous system, which regulate the tone of peripheral vessels, and the sections of the peripheral nervous system, which are associated with tactile and vibration sensitivity.

The study of vibration gave the right to assert that the parameters of its impact primarily determine the direction of vascular disorders. With mechanical vibrations with a frequency of more than 35 Hz, spastic phenomena occur in the capillaries, and below that a picture of capillary atony is observed. The most dangerous region from the point of view of the possible development of vasospasm is the frequency range from 35 to 250 Hz.

Negative influence during work operations

Vibration can directly interfere with the performance of work operations, and also indirectly affect human performance, reducing it. Some authors conducting vibration research consider it as a strong stress factor that has a negative impact on psychomotor performance. In addition, mental activity and the emotional sphere suffer, and the likelihood of accidents increases.

Oscillatory speed

It has been established that noise and vibration have an energetic effect on the human body. Therefore, the latter began to be characterized by a spectrum of oscillatory speed expressed in centimeters per second, or measured in decibels, like noise. Conventionally, a speed of 5∙10 6 cm/sec was accepted as the threshold value of mechanical vibrations. Only in direct contact of the body with the shaking body or through others in contact with it solids mechanical vibrations are felt (perceived). Upon contact with their source, which emits (generates) a bass sound, vibration (of the lowest frequencies), a shock is also perceived along with the sound.

General and local

A distinction is made between general and local vibration depending on the distribution of mechanical vibrations throughout parts of the human body. With local shock, only the part of the body that is in direct contact with the surface that is shaking is subject to shock. Most often these are hands. This happens when working with some hand tools or when holding machine parts and other shaking objects.

Local vibration is sometimes transmitted to parts of the body that are connected by joints to the organs directly exposed to it. But the amplitude of vibrations of these parts of the body is usually lower, since as vibrations are transmitted through tissues (especially soft ones), they gradually attenuate. On the contrary, general vibration affects the entire body. This occurs mainly from mechanical vibrations of the surface where the worker is located.

Vibration disease

When the human body is exposed to vestibular stimuli, the assessment and perception of time is disrupted, and the speed of information processing is reduced. causes low frequency vibration. The most pronounced changes are observed at frequencies in the range from 4 to 11 Hz.

Long-term exposure to vibration leads to persistent pathological disorders in the human body. A comprehensive analysis of this pathological process led to its identification into a separate nosological form - vibration disease. It continues to hold one of the leading places among other occupational diseases. It is generated by the use of manual machines that do not meet regulatory requirements, as well as by the increasing specialization of labor, which leads to an increase in the total time of exposure to mechanical vibrations on the body. As the duration and intensity of exposure to vibration increases, the likelihood of developing this disease increases. Individual sensitivity is essential. Overwork, coldness, noise, alcohol intoxication, muscle tension etc. increase the harmful effects.

Stages of vibration disease

There are 4 stages of this disease according to severity:

Initial (I);

Moderately expressed (II);

Expressed (III);

Generalized (IV, extremely rare).

Negative effects of general vibration

General low-frequency vibration, especially in the resonant range, can cause long-term trauma to bone tissue and intervertebral discs, displacement of organs located in the abdominal cavity, as well as lower back pain, degenerative changes in the spine, chronic gastritis, etc.

In women exposed to such exposure for a long time, there is an increase in the frequency of gynecological diseases, premature births, and spontaneous abortions. Low-frequency vibration in women causes circulatory problems in the pelvic organs.

Mechanical vibrations in residential buildings

Vibration research is very important to carry out not only in industrial buildings, but also in residential buildings. The fact is that it poses a danger not only to the health of workers, but also to some other groups of the population. In residential buildings, vibration affects humans through the use of industrial installations, transport, and engineering and technological equipment. Urban rail transport has the greatest impact on the body in terms of vibration intensity: railways, open areas metro.

The vibration arising from the movement of trains in buildings has an intermittent regular nature. The amplitude of oscillations decreases with distance from its source. Speaking about the propagation of vibrations along the floors of a multi-storey building, it should be said that on the upper floors, depending on the resonance, both an increase and decrease in vibration can be observed. At the same time, the types of premises structures do not have a significant impact on its levels in residential premises under identical soil conditions. Sometimes high vibration levels are observed from engineering and technological equipment located in the buildings themselves (elevators), as well as built-in objects.

Protection methods

Vibration protection is very important in enterprises. Normalization of its levels, hygienically justified, is the basis for the prevention of vibration disease. The direction, nature, and duration of the action are taken into account. In the Russian Federation, sanitary legislation regulates the levels of mechanical vibrations that must be observed in the workplace.

General vibration protection

The effect of vibration on humans should be reduced as much as possible. Occupational safety is a system of quantitative and qualitative characteristics and indicators that form the specifics of elements that ensure the absence of harmful effects of mechanical vibrations on the human body. Vibration protection is provided by:

Using vibration-proof machines;

Vibration protection;

Design production premises and technological processes that ensure compliance with sanitary standards in the workplace;

Organizational and technical measures, the purpose of which is to improve the operation of used machines, organize their timely repairs, as well as control vibration parameters;

Creation optimal modes work and rest.

Personal protective equipment used when exposed to general vibration is vibration-proof shoes, soles, and insoles. The most effective among all means of protection can be considered the elimination of direct human contact with shaking equipment. This is done by using remote control, replacement and automation of technological operations.

Means of protection against local vibration

Reducing its negative impact is achieved by:

By reducing its intensity directly at the source (using handles with shock-absorbing or vibration-damping devices);

By using external protective equipment, that is, elastic damping devices and materials placed between the operator’s hands and the source of mechanical vibrations (vibration-isolating gloves, mittens, gaskets and liners).

An important role in the set of measures aimed at reducing the negative impact of vibration on the human body is given to work and rest regimes. The total time of contact with her, according to the work schedule, should be limited during the shift. It is recommended to take two breaks for physiotherapeutic procedures, active rest etc. The duration of the first should be 20 minutes (this break should be taken 2 hours after the start time of the shift). The duration of the second is 30 minutes, it should be 2 hours after the lunch break. it should last at least 40 minutes. The duration of continuous one-time exposure to mechanical vibrations on the body should be no more than 10-15 minutes.

General health and medical-biological measures used to prevent vibration disease include the following:

Hydrotherapy for hands (baths with warm water (+37-38 degrees) or the use of dry air heating;

Industrial gymnastics;

Self-massage and mutual massage of the shoulder girdle and arms;

Ultraviolet irradiation;

The use of vitamins, as well as other general strengthening measures (oxygen cocktail, psychological relaxation room, etc.).

The importance and relevance of this topic is confirmed by the fact that it is studied at school. Vibration is discussed, in particular, in the textbook "Physics" (grade 11). Of course, at school it is studied in more detail general view. In particular, vibrations of the Earth are considered. The frequency of our planet is 7.83 Hz. This quantity is called the Schumann wave, or the Schumann resonance frequency. Some, however, believe that in Lately The vibrations of the Earth change. For example, Ancu Dinca, a Romanian physicist, believes that by December 2012 they should have reached 12.6-12.8 Hz. The vibrations of a person must correspond to the vibrations of the planet. Those who can tune into the new frequencies will benefit spiritually, as Anku Dinke believes. Human vibrations are a topic for a separate article.

Reduced low frequency vibration

Low frequency vibration (LF) is vibration with a frequency equal to half the rotation speed, i.e. w Wb =w BP / 2. The main sources of low-frequency vibration are plain bearings when the hydrodynamic lubrication process in the oil wedge is disrupted due to a sharp change in loads in the machine or a change in oil temperature, or due to an increase in internal structural clearances in the bearings.

In this case, the rotor journal in the bearing is displaced from the center of rotation by the amount of eccentricity, around which the rotor receives additional rotation with a frequency equal to half the main rotation frequency of the rotor.
This additional rotation is called precession with rapid rotation W, which is the cause of low-frequency vibration:

those. w Wb = w BP / 2.

For example. If the rotation frequency w BP = 314 Hz, 3000 rpm, then the vibration frequency is

w Wb = 157 Hz, 1500 rpm.

To reduce low frequency vibration you should:

* optimize static and dynamic loads on all rotor plain bearings, avoiding sudden changes in loads in the machine;

* do not allow changes in oil temperatures in the machine’s lubrication system below standardized values;

* maintain the values ​​of internal clearances in plain bearings within the normative values;

* in the event of low-frequency vibration, even if points 1, 2, 3 are observed, use a “lemon” boring of the internal diameter on a specific bearing, at which the lateral clearances X B are made doubled from the size of the upper gap X B, i.e. X B = 2 X V. For example, if
X B = 0.002 d, That X B = 0.004 d (d– diameter of the bearing journal).

Reduction of high frequency vibration (HF)

High-frequency vibration HF is vibration with a frequency twice the rotational speed, i.e.

w Wb = 2w BP.

HF occurs due to a violation of the transverse stiffness in the rotor sections, which leads to inequality in the axial moments of inertia JX ¹ JY, causing double disturbance per rotor revolution.

For example. If the rotation frequency is w VR = 314 Hz (¦ = 50 Hz), then the vibration frequency will be w Vb = 628 Hz, (¦ = 100 Hz).

For example, in the electric power industry, the source of high-frequency vibration is often the rotors of electrical machines, manufactured with a violation of the concentricity of the outer diameter or when they are repaired by replacing sections of electrical windings. In this case, to equalize the transverse stiffness and reduce high-frequency vibration, false grooves are made on the rotor barrel in the corresponding sections.

5.4.2. Methods protected from vibration along the paths of its propagation

They are used both to reduce vibration of the equipment itself and to reduce hygienic vibration on supporting surface machines.
According to GOST 26568-85, methods of vibration protection along propagation paths are divided into:

* vibration damping;

* vibration damping;

* vibration isolation;

* organizational measures and personal protective equipment against vibration.

Vibration damping

The reduction in vibration occurs due to the conversion of vibrational energy into thermal energy by increasing the active resistance of the system m, mainly due to. increasing external and internal friction h (5.5).

At the design stage, the method is implemented when selecting the materials from which the rotor and stator parts are made. The coefficients of internal friction (internal losses) h of structural materials cast iron and steel have low values ​​and vary in the range: h = 0.001-0.01 for StZ...St40, Cr10...Cr45.

These materials are vibration-active and practically do not reduce vibration. The use of alloyed materials with a high coefficient h = 0.02 - 0.1 using manganese Mn, chromium Cr, nickel Ni, titanium Ti, cobalt Co, as well as polymer materials leads to the absorption of vibrational energy by these materials and a decrease in equipment vibration. At the operational stage, rubber-based sheet or mastic materials are used to cover the external surfaces of machines, such as Izol tape, anti-vibration, VD-17 mastic, batyl rubber.

The reliability of the coating and the operating efficiency of these materials depend on the quality of processing of the external surfaces of the equipment before coating. Electroplating has good vibration damping properties
(h = 0.01) and various lubricants (h = 0.02 – 0.04). The effectiveness of vibration damping is achieved in all operating modes, but especially in the resonant region when the reactance of the oscillatory system is equal to zero.

Vibration damping

Vibration is reduced by increasing the system reactance

In the pre-resonance region, the effect is achieved by increasing the rigidity of the oscillatory system TO, for example, a car body, by choosing the appropriate body configuration (the spherical shape has maximum rigidity) or by introducing additional stiffeners.

In the over-resonance region, vibration damping is realized by increasing the mass of the oscillatory system, usually by increasing the mass of the machine foundation M. The choice of foundation mass is made according to the formula:

Where M– mass of the machine foundation, kg; T– weight of the machine itself, kg; f f – natural frequency of the foundation, Hz; f p – operating (forced) frequency of the machine, Hz.

Analysis of formula (5.8.) shows:

if ¦ f / ¦ p = l – resonance on the foundation. Invalid operating mode M ³ ¥ ;

If f f/ fр = 1.41 – heavy duty operation of the foundation, M = 40m.

If f f/ fр = 3...4 – optimal area of ​​operation of the foundation, with f f/ f p = 3,
M³ 5 T, at f f/ f p = 4, M³ 2.7 m;

In thermal power engineering to reduce vibration steam turbines Dynamic vibration dampers can be used in the form of vertical elongated pins installed on opposite connectors of the machines. Some reduction in vibration is achieved due to the anti-phase oscillatory process of the studs during turbine operation. The effect depends on the right choice masses of vibration-damping studs with corresponding frequencies of natural vibrations.

Vibration isolation

Where k– rigidity of vibration isolator (rubber, spring), N/m; m– vehicle weight, kg.

If, for example, the machine is mounted on spring vibration isolators, then the rigidity of the oscillatory system is assumed to be equal to the stiffness of the springs.

Analysis of formula (5.9.) shows:

If f R / f o = 1 – resonance occurs. TO n = ¥ . The use of vibration isolation is pointless;

If f R / f o = 1.41, TO n = 1. There is no effect from the use of vibration isolation;

If f R / f o = 3..4, TO n = 1/8 .. 1/15, the optimal area of ​​application of vibration isolation. At the same time, if TO P< 1/15, наступит потеря устойчивости из-за того, что низкое значение TO n is achieved with low vibration isolator rigidity. If
TO n > 1/8, then the vibration isolators will have large dimensions and metal consumption. If the transmission coefficient is known, then the reduction in vibration at the machine foundation, in dB, can be determined.

Vibration

Vibration is a mechanical oscillatory movement directly transmitted to the human body. The main physical characteristics of vibration are the amplitude and frequency of vibrations. The amplitude of vibration displacement is measured in m or cm, and the vibration frequency is measured in hertz.

Considering that with any oscillatory motion the speed and acceleration continuously change (the vibrations are greatest on the center line and the smallest in the extreme positions), vibration is assessed by speed and acceleration.

For vibration, decibels are counted from a conventional reference vibration velocity equal to 5 10 8 m/s, vibration acceleration - 3 10 4 m/s 2.

Vibration velocity and vibration acceleration are expressed in dB relative to their zero thresholds. In this case, the vibration perception threshold is about 70 dB.

Vibration velocity and vibration acceleration are assessed within standard octaves with geometric mean frequencies - 1; 2; 4; 8; 16; 31.5; 63; 125; 250 Hz and above. Vibration with a frequency of up to 32 Hz is considered low-frequency, and more than 32 Hz is considered high-frequency.

The advantages of single-numeric integral indicators, such as dose or equivalent level, have determined the interest of researchers in dose assessment of vibration. If for noise this approach is sufficiently justified, which is reflected in the ISO R-1999 (1971) standard, then with regard to vibration there are only a few experimental works.

It should be noted that the current GOST 12.1.012-78 regulates the maximum vibration limit according to the kinematic parameter of vibration velocity, and the dose is an energy parameter that takes into account the level of vibration and the time of its action.

Sources of vibration are pneumatic and electric hand mechanized tools, various machines and equipment, machine tools, and vehicles widely used in industry, construction, transport, agriculture and everyday life. Vibration is widely used not only in technology, but also in medicine for the treatment of certain nervous and muscle diseases (vibration therapy, vibration massage).

Vibration is one of the factors with great biological activity. The nature, depth and direction of physiological changes in various body systems are determined by the levels, spectral composition of vibration, as well as physiological properties human body. In the genesis of these reactions, analyzers play an important role - vestibular, motor, visual, cutaneous, etc.

It should be noted the important role of the biochemical properties of the human body in the subjective perception of vibration. The effect of vibration on the body is mediated by the following phenomena: physical impact on the contact surface, propagation of vibrations through tissues, direct reaction to impacts in organs and tissues, as well as irritation of mechanoreceptors, causing neuroreceptor and subjective reactions.

Currently, experimental and clinical material has been accumulated emphasizing the role of reflex regulatory influences of the central nervous system in the occurrence of functional changes in the neuromuscular system in individuals exposed to vibration. These studies show that motor function disorders that occur under the influence of vibration are caused by both disturbances in the regulatory effects of the central nervous system and direct muscle damage. In this case, the predominance of diffuse shifts can be explained mainly by changes in the activity of superspinal structures, while the greater severity of local changes in the muscles can be associated with their direct trauma.

Particularly sensitive to the action of local vibration are the parts of the sympathetic nervous system that regulate the tone of peripheral vessels, as well as parts of the peripheral nervous system associated with vibration and tactile sensitivity.

It has been proven that the direction of vascular disorders is determined, first of all, by the parameters of the applied vibration. Spastic phenomena in the capillaries occur with vibration above 35 Hz, and below, a predominantly picture of atony of the capillaries or their spastic-atonic state is observed. The frequency range of 35-250 Hz is most dangerous with regard to the development of vasospasm.

Vibration can directly interfere with work operations or indirectly negatively affect human performance. A number of authors consider vibration as a strong stress factor that has a negative impact on psychomotor performance, the emotional sphere and mental activity of a person and increases the likelihood of accidents.

Behind last years It has been established that vibration, like noise, has an energetic effect on the human body, so it began to be characterized by a spectrum based on vibrational speed, measured in centimeters per second or, like noise, in decibels; The threshold vibration value is conventionally taken to be a speed of 5 10 6 cm/sec. Vibration is perceived (felt) only in direct contact with a vibrating body or through other solid bodies in contact with it. When in contact with a source of vibrations that generates (produces) sounds of the lowest frequencies (bass), along with the sound, shaking, that is, vibration, is also perceived.

Depending on which parts of the human body are affected by mechanical vibrations, local and general vibration are distinguished. With local vibration, only that part of the body that is in direct contact with the vibrating surface, most often the hands, is subject to shock (when working with hand-held vibrating tools or when holding a vibrating object, machine part, etc.). Sometimes local vibration is transmitted to parts of the body connected to the joints directly exposed to vibration. However, the amplitude of vibrations of these parts of the body is usually lower, since as vibrations are transmitted through tissues, especially soft ones, they gradually attenuate. General vibration spreads to the entire body and occurs, as a rule, from the vibration of the surface on which the worker is located (floor, seat, vibration platform, etc.).

When exposed to vestibular stimuli, which include vibration, the perception and assessment of time is disrupted, and the speed of information processing decreases. Low-frequency vibration causes impaired coordination of movement, with the most pronounced changes observed at frequencies of 4-11 Hz.

Long-term exposure to vibration leads to persistent pathological disorders in the body of workers. A comprehensive analysis of this pathological process served as the basis for identifying it as an independent nosological form of an occupational disease - vibration disease.

Vibration disease continues to occupy one of the leading places among all occupational diseases. The reason for this is both the use of manual machines that do not meet the requirements of sanitary standards, and the developing specialization of labor, leading to an increase in the time the body is exposed to vibration. The danger of developing vibration disease increases with increasing intensity and duration of vibration; In this case, individual sensitivity is essential. Harmful effect vibrations increase noise, cooling, overwork, significant muscle tension, alcohol intoxication, etc. Conventionally, a distinction is made between local vibration, which acts mainly on the hands of workers, and general vibration, when vibration occurs when the floor, seat (workplace) vibrates the entire body is exposed.

In contrast to local vibration, when exposed to general vibration, clinical symptoms associated with disorders of brain activity arise. In this case, the vestibular apparatus especially often suffers, headaches and dizziness appear. According to the severity of the pathological process, there are 4 stages of the disease:

I -- initial,

II - moderately expressed,

III - pronounced,

IV - generalized (extremely rare).

In addition to the stages, the most typical syndromes are noted: angiodystonic, angiospastic, vegetative polyneuritis, neurotic, vegetomyofasciitis, diencephalic and vestibular.

Low-frequency general vibration, especially the resonant range, causing long-term trauma to the intervertebral discs and bone tissue, displacement of the abdominal organs, changes in the motility of the smooth muscles of the stomach and intestines, can lead to pain in the lumbar region, the emergence and progression of degenerative changes in the spine, chronic lumbar diseases. sacral radiculitis, chronic gastritis.

Women exposed to prolonged exposure to general vibration have an increased incidence of gynecological diseases, spontaneous abortions, and premature births. Low-frequency vibration causes circulatory problems in the pelvic organs in women.

Human tissues have different abilities to transmit vibration. The best conductors of vibration are bones and soft tissues. Joints are effective vibration dampers. As the frequency of vibration increases, the amplitude of vibrations of body parts decreases as they move away from the point of application. For example, in the frequency range of 50-70 Hz, about 10% of the energy of the transmitted vibration reaches the head to a person located on the vibration platform. Vibration with a frequency of more than 100 Hz is practically not transmitted throughout the human body and is mostly local.

The organs that directly perceive vibrations are divided into two groups. The first includes the balance organs (vestibular apparatus), located in the inner ear. By interacting with the corresponding connections in the brain, they work as an integral meter of angular and linear accelerations. The information sent to the brain by the balance organs, which are influenced by vibrations, can be distorted, disorienting, and in some cases irritating and causing a state of illness in a person. The forces and movements caused by vibration are sensed by a large number of mechanoreceptors throughout the body. Some of them, located in muscles and tendons, signal the position of the body and the loads acting on it. They interact with the part of the central nervous system that regulates body position and movement. These receptors respond to any changes, including low-frequency ones.

The second group includes receptors located in the skin and connective tissues. They perform the functions of touch, responding to higher frequencies (about 30 Hz). Vibrations also have a certain effect on the body through the organs of vision and hearing.

The nature of the effects of vibration on a person depends on their duration. Disturbances in the physiological functions of the body that occur under the influence of vibrations tend to intensify with increasing duration of exposure.

Vibration and high vibration levels in the environment pose a health hazard not only to workers in production conditions, but also to other groups of the population. Sources of vibration in residential buildings are: transport, industrial installations, engineering and technological equipment of buildings. In terms of the intensity of vibrations, urban rail transport has the most impact on people: shallow and open radii of the metro, railway lines. The vibration that occurs in buildings from the movement of trains has a regular intermittent nature. As you move away from the source, the amplitude of the oscillations decreases.

When vibrations propagate along the height of a multi-story building, both weakening and strengthening of vibration are observed on the upper floors, depending on the resonance. The studied types of building structures under identical soil conditions do not have a significant effect on vibration levels in residential premises.

In some cases, high levels of vibration are recorded from engineering and technological equipment of the buildings themselves (elevators) and built-in objects.

Prevention of vibration disease is based on hygienically justified regulation of vibration levels. In this case, the direction, duration of action, and nature of vibration are taken into account. IN Russian Federation Vibration levels at workplaces in production premises, on mining, agricultural, land reclamation, road construction machines, railway and road transport, and on ships are regulated by sanitary legislation.

The main regulatory legal acts regulating the parameters of industrial vibrations are: " Sanitary standards and rules for working with machines and equipment that create local vibration transmitted to the hands of workers" No. 3041-84 and "Sanitary standards for vibration of workplaces" No. 3044-84.

Currently, about 40 state standards regulate technical requirements for vibration machines and equipment, vibration protection systems, methods for measuring and assessing vibration parameters and other conditions.

Bibliography

1) Arustamov E.A. Life safety. - M.: 2001.

2) Garin V.M. Ecology for technical universities. - Rostov-on-Don: 2001.

3) Kriksunov E.A., Pasechnik V.V., Sidorin A.P. Ecology. - M.: “Drofa”, 2004.

The reliability of turbine and generator operation is largely determined by their vibration state.

Increased vibration resulting from poor-quality manufacturing, installation, repair or poor-quality operation of the unit is a source of all
possible emergency situations and even major accidents. It should be noted “that the harmful effects of even moderate vibrations tend to accumulate and manifest themselves in a variety of forms. This can be expressed in the appearance of fatigue cracks in the turbine rotor, control valve rods, cast iron supports, gears, etc. Under the influence of vibration, the mutual fastening of parts is disrupted, the rigid connection of stators and bearings with the foundation plates is disrupted, and shaft misalignment increases.

With increased vibration, there is a risk of damage to the turbine labyrinth seals, hydrogen seals and the generator water cooling system. Significant vibrations of the shaft on the oil film can cause the occurrence of centers of semi-dry friction, which increases the risk of melting of the bearings.

Vibration also has an adverse effect on the operation of the turbine control system and control devices. It should also be noted the negative impact of vibration on operating personnel. This impact is determined both by the increased noise level and the direct, physiological effect of vibration on the human body.

All these circumstances impose very stringent requirements for the regulation of vibrations. According to the PTE, the vibration state of a turbine unit is assessed on the following scale:

On turbine generators of block installations with a capacity of 150 MW or more, vibration should not exceed 30 microns.

Vibration should be measured in three directions: vertical, horizontal-longitudinal and horizontal-transverse. If the vibration of at least one of the bearings in one of the three directions exceeds the “satisfactory” value for a given type of machine, then the vibration state of the entire unit is considered unsatisfactory, and the turbine must be repaired to eliminate vibration.

The vibration state of the unit must be determined when it is put into operation after installation, before the unit is taken out for major repairs, and after major repairs. If the vibration condition of the unit is excellent and good, the frequency of vibration measurements should be once every 3 months. If there is a noticeable increase in bearing vibration, measurements should be carried out according to a special schedule. Turbine units with a satisfactory vibration assessment can be put into operation only with the permission of the chief engineer of the district administration (power plant), and measures must be taken in the very near future to improve the vibration condition of the unit.

To assess the vibration state of a turbine unit, the vibration level must be determined not only at operating speeds, but also when the turbine passes a critical speed. Research has shown that the transition of the “rotor-support” system through critical speeds during the process of starting and stopping the unit can be accompanied by a very significant increase in the amplitude of oscillations. Although in this case the increased vibration acts for a relatively short time, several starts and stops of the machine with unacceptably large amplitudes of rotor vibrations at critical speeds may be sufficient to render steam and oil seals unusable. In the worst cases, interference occurs in the flow part of the turbine, a residual deflection of the rotor appears, the babbitt of the bearing liners is destroyed, cracks appear in the foundation, etc.

A significant increase in vibration at critical speeds is caused by a significant imbalance of the rotor due to its own forms of dynamic deflection of the shafts. As practice shows, this imbalance can also be eliminated using special balancing methods, bringing the level of vibration of bearings at critical speeds to a value of about 30-50 microns. Therefore, the vibration state of a turbine unit passing through critical speeds with increased vibration cannot be considered satisfactory if, even at the operating rotation speed, the vibration of the bearings exceeds the norm.

Existing tolerances normalize the amplitude of bearing vibrations only depending on the rotation speed of the rotors, without taking into account the frequency composition of these vibrations. However, numerous measurements show that vibration of bearings, shafts and other machine elements often causes problems. non-snusoidal character. Oscillations of the fundamental frequency, equal to the rotor speed, are superimposed by components of higher and sometimes lower frequencies. In some cases, oscillations close to sinusoidal are observed, with frequencies different from the fundamental one.

For units with a rotation speed of 3000 rpm with a main oscillation frequency of 50 Hz, a high-frequency component of 100 Hz is most often found, and low-frequency components with frequencies close to the lowest critical speed of the rotor-support system (usually 17-21 Hz) occur ) or to half the operating frequency (~25 Hz).

The presence of higher harmonics of significant amplitude indicates the action of significant loads on the oscillating system, which can be several times higher than the loads causing oscillations of the fundamental frequency. However, since the issue of the relationship between the spectral composition of vibration and its danger to the turbine has not been sufficiently studied, we can limit ourselves to only pointing out the need to adopt more stringent vibration tolerances in the case of significant high-frequency components. As for low-frequency vibrations, due to their instability and ability to suddenly and sharply increase, they pose an undoubted danger to the machine. Therefore, if noticeable low-frequency components are detected in the vibrations of bearings and rotors, the vibration state of the turbine unit cannot be considered satisfactory.

Some consideration of the frequency composition of vibration is provided for by VDI standards, which have become widespread in European practice. According to these standards, the equivalent vibration velocity amplitude measured at the operating speed of the rotors is taken as the main vibration characteristic

If the measured oscillations are decomposed into harmonic components with angular frequencies coi, (02, ..., (o„ and the corresponding amplitudes At, Ar,., ., An, then the equivalent amplitude of the extra-velocity can be calculated using the formula

Vskb = K"L^shg, + LChsoCh + . . . + AinP*„ = = VVh + V", + . . . + Wn, (3-14)

Where is Vi, . . ., Vn - amplitude values ​​of vibration velocity of each of the harmonic components.

For the case of measuring beats with maximum l/max and minimum Vrnui values ​​of vibration velocities

VSKB = K^max + VW (3-15)"

In table 3-7 shows the standards for permissible vibration of turbo-aggregate bearings.

Gats according to VDI data at a fundamental frequency of 50 Hz

The draft international standard for machine vibration proposes the use of effective vibration velocity amplitude as a criterion

Ueff = l-"eq (3-16>

As a quantity directly measured by electrical measuring instruments. Levels

■assessments of the vibration state of machines according to Ueff correspond to the same levels given for Ueq in VDI standards. These standards take into account the harmonic composition of the measured vibration due to components having a frequency higher than the rotation frequency.

An assessment of the vibration state of a turbine unit will not be complete if the level of vibration of its foundation is not taken into account. Typically, a properly designed and well-executed foundation has a double vibration amplitude with a well-balanced rotor that does not exceed 10-20 microns. A noticeable upward deviation from the given values ​​indicates foundation defects.

When considering the vibration issues of modern large turbine units, it is necessary to take into account the fact that the vibrations of bearings in modern units increasingly reflect the true vibrations of the turbine shaft. This is explained primarily by the increased mass and rigidity of the supports of large turbine units. An important role in this phenomenon is also played by the damping properties of the oil wedge existing between the shaft journal and the bearing.

According to experimental data on large units, the vibration amplitude of the shaft ends can be 10-15 times greater than the bearing vibration amplitude, and these vibrations can be out of phase with each other. There were also cases when the protrusion of one or more rotor blades did not lead to a noticeable increase in bearing vibration, while shaft vibrations increased significantly. This shows that for a number of turbine units, vibration of bearings is not a reliable safety criterion, and it is necessary for these units in each individual case to experimentally establish the relationship between vibrations of turbine shafts and bearings. The transition to large unit capacities of turbine units increases the requirements for their vibration reliability, as a result of which the elimination of significant vibrations and determining the cause of their occurrence are tasks of paramount importance.

The main reasons causing unit vibrations include the following:

A) dynamic imbalance of the rotors;

B) violation of the alignment of the rotors;

B) weakening the rigidity of the system;

D) work in the field of resonant speeds;

D) loss of shaft stability on an oil film;

E) the appearance of disturbing forces of electromagnetic origin.

The occurrence of dynamic imbalance of rotors can be caused by two reasons:

1) redistribution of masses around the circumference of the rotor or the application of new unbalanced masses to the rotor;

2) displacement of the main central axis of inertia of the rotor relative to the axis of its rotation.

In both cases, an unbalanced centrifugal force occurs, proportional to the square of the speed, causing vibration of the revving frequency unit.

The causes of imbalance in turbine and generator rotors can be the breakage of blades and tires, destruction of disks, poor-quality balancing when shoveling rotors, overwinding of generator rotors, uneven wear of blades, uneven salt contamination of the blade apparatus, etc.

A displacement of the axis of inertia of the rotor relative to the axis of rotation may occur due to a weakening of the fit of parts on the shaft or deflection of the shaft. Deflection of the rotor during assembly may occur as a result of misalignment of the keys relative to the KEYWAYS, poorly made disk attachments, etc. During operation, deflection of the rotor - can be caused by thermal imbalance, thermal instability of the metal, rotor, interference in the flow part, as well as incorrect start-up and shutdown modes of turbines, causing rotor deflection.

The phenomena discussed above lead to the appearance of a primary deflection, which is a consequence of the primary imbalance of the rotor. The appearance of primary deflection causes secondary imbalance, which occurs as a result of deviation of the axis of inertia from the axis of rotation during dynamic deflection of the rotor. This secondary imbalance is difficult to determine due to the difficulty of measuring the dynamic deflection along the length of the rotors under operating conditions, but approximate calculations show that it can be several times greater than the primary imbalance of the rotor.

Dynamic deflection at critical speeds usually reaches; maximum values, which leads to a significant increase in the total imbalance and, as a consequence, to increased vibration of the bearings. The predominant influence of dynamic deflection on vibration is observed mainly in the rotors of modern medium and high power generators operating near the second critical speed. As a result, the criterion for assessing the balance of generator rotors is the vibration amplitude of the bearings and shaft at operating and critical rotation speeds.

One of the reasons for the increase in vibration of the unit may be the misalignment of the rotors. The influence of misalignment on the vibration of turbines significantly depends on the degree of balance of the rotors and is different depending on the type of couplings. With rigid or semi-rigid couplings, bolting the coupling restores normal alignment rotors. In this case, there is a redistribution of the load on the bearings from the weight of the connected rotors. Without being a direct source of dynamic forces that excite vibrations, such a redistribution of the static load changes the parameters of the rotor-support system. For example, the complete unloading of one intermediate support increases the span of the shaft between them. supports and changes its critical speed, which in turn can lead to one of the critical speeds approaching the operating speed of the unit. If, as a result of redistribution of the static load, one of the supports is partially unloaded, this can contribute to the excitation of low-frequency oscillations caused by shaft instability. on an oil film at low radial loads on the bearing. Flexible couplings can accommodate significant shaft misalignment (up to 0.3 mm) without causing noticeable vibration. However, in the case of oil contamination, sludge deposits and the presence of work hardening on the working surfaces of the moving elements of the coupling, a sharp increase in the coefficient of friction between these elements occurs, which can lead to partial or complete jamming of the coupling. In this case, the connected rotors begin to work with a displacement of the center of gravity relative to the axis of rotation, which causes vibration.

During operation, misalignment of the rotors or redistribution of the load on the bearings is possible due to a violation of the correct thermal expansion of the turbine cylinders. This phenomenon is associated with jamming of bearing housings or cylinders on keys, emphasis on spacer bolts, one-sided heating or cooling of the cylinder, etc.

Along with uneven heating of the cylinders, vibration can also occur due to uneven heating of the machine foundation. Such phenomena were observed during the operation of 300 MW turbines, in which the difference in the vertical thermal expansion of the foundation columns reached 2 mm.

The reason that causes uneven heating of the foundation may be the close proximity of steam lines, valves, and heaters with insufficient or damaged insulation. A characteristic sign of misalignment of the unit for this reason is a gradual increase in vibrations over several days from the moment of startup, since, as observations have shown, heating of the foundation lasts several days (for K-300-240 turbines up to 7 days). To eliminate vibrations caused by this phenomenon, it is necessary to carefully isolate high-temperature components and parts located in the immediate vicinity of the foundation, installing water screens in the most heated places, and also check and, if necessary, carry out additional balancing of the rotors.

Another reason for the occurrence of vibration during the operation of large units is the subsidence of the exhaust pipes of the turbine with the bearings built into them when the vacuum is drawn and from the weight of the circulating water in the water chambers of the condenser. For turbines with a power of 100-300 MW, the subsidence of the supports under the influence of vacuum is estimated to be of the order of 0 ,1-0.15 mm. This reason can be detected by measuring the level of vibration when the vacuum on the turbine changes. biggest change vibrations are observed on CND bearings.

In Fig. Figure 3-17 shows the dependence of the transverse vibrations of the rear LPC bearing on vacuum for the VK-100-2 turbine. Although the vibrogram presented on the graph reflects a number of reasons causing vibration, including thermal misalignment due to deterioration of the vacuum, however, the influence

Changes in vacuum can be seen quite clearly. This effect of vacuum can be largely eliminated by installing a low-pressure rotor with some elevation relative to the other shafts when centering the unit.

With a constant value of unbalance or misalignment of the rotor, an increase in the amplitude of oscillations may result from a decrease in the static rigidity of the system.

During operation of a turbine unit, weakening of rigidity may be caused by the following reasons:

A) weakening of the mutual fastening of the components of the rotor support: liners, bearing housings, foundation frames, foundation crossbars;

B) separation of the bearing chair from the foundation slab (“overturning” of the bearing chair);

B) disruption of the connection between the bearing seat and the turbine cylinder resting on it;

D) disruption of the connection between the turbine cylinder and its supports on the foundation;

D) the appearance of cracks in the load-bearing elements of the foundation.

These phenomena can occur as a result of poor-quality installation or assembly after repair, as well as during operation due to disruption of the normal thermal expansion of the turbine. Separation of the bearing chair from the foundation slab is also caused by structural defects in its connection to the turbine cylinder. A decrease in the rigidity of the supports can cause, in addition, a change in the natural frequency of oscillations of the “rotor-support” system as it approaches resonance. Vibration resulting from weakening of the rigidity of the supports, as a rule, has a sinusoidal shape and a reverse frequency. Sometimes high-frequency overlaps are observed, distorting the sinusoidal nature of the oscillations. with the appearance of microshocks in cracks or joints of structural elements. Distinctive feature This vibration is dependent on the thermal state of the turbine.

The reliability of the turbine unit largely depends on the proximity of the critical rotation speeds of the rotor-support system to the nominal rotation speed. If the rotor operates in the critical frequency range, even a slight imbalance can lead to a significant increase in the vibration level. To prevent such phenomena, all manufacturing plants carefully calculate the rotors of turbines and generators using all their own modes of shaft vibration.

However, performing calculations is very difficult due to the lack of initial data on the influence of the elasticity of the oil film, the compliance of supports, etc. As a result, the actual critical rotation speed of the turbine unit, determined experimentally, sometimes turns out to be in significant discrepancy with the calculated one. This leads to the fact that on a number of turbine units the operating speed is in the region of the second critical frequency, which significantly increases the level of vibration at operating frequencies. First of all, this applies to generators that have very heavy weight rotor per unit shaft length. For these units, the calculated second critical frequency is already close to the operating frequency, and if we take into account that the inaccuracy of the initial data affects primarily the higher critical frequencies of the shaft, we can come to the conclusion that getting into resonance at the operating frequencies of these machines is very likely.

As the experiment shows, for a number of generators the detuning of the actual second critical frequency from the operating frequency does not exceed 4-8% (TV2-150-2, TVF-200-2, TGV-200), which cannot be considered satisfactory.

For some generators, as well as for most turbines, the second critical frequency lies above the operating speeds. In this case, there is a danger of a gradual decrease in the resonant frequency of the system due to a decrease in the rigidity of the supports during long-term operation of the turbine unit. This process is greatly facilitated by the increased vibration level of the turbine unit.

Considering the issue of the influence of critical frequencies on the operation of the unit, it should be noted that with the transition in large units to the use of rigid couplings and a limited number of supports, the influence of the rigid connection between the shafts on the critical speed of the entire shaft line increases. Although the critical frequencies of the shaft line in this case are determined mainly by the resonant vibrations of individual shafts, the rigid connection between the rotors and the absence of intermediate supports cause additional problems. In this case, there is a noticeable increase in the critical frequencies of the shafting relative to the resonances of uncoupled rotors. All these circumstances must be taken into account when detuning the shaft from the resonant rotation speed. According to a number of commissioning organizations, the minimum permissible detuning of the shaft from the resonant speed at the second resonant frequency should be at least 10%.

Of all the reasons that excite vibrations of a turbine unit, the least studied and most dangerous is considered to be low-frequency vibration caused by the loss of stability of the shaft on the oil film. These oscillations belong to the category of self-oscillations and are caused by hydrodynamic forces arising

In an oil wedge. bearings, as a result of which this type of vibration is called “oil” vibration.

This type of vibration has not yet been sufficiently studied, and there are no clear ideas about the cause of its occurrence. Experiments show that it is not associated with mechanical imbalance of the rotor, but depends mainly on the dynamic characteristics of the oil layer, which describe its elastic and damping properties, as well as on the location of the shaft axis relative to the liner bore. As is known, in a stationary rotor the center of the axle is located under the center of the liner bore O i with static eccentricity bo (Fig. 3-18a). When the shaft rotates between the journal and the liner, a oil layer, on which the shaft floats in the direction of rotation. With increasing rotation speed, the center of the axle moves along the O-Ob arc, which is the line of moving equilibrium of the axle, and the eccentricity b decreases. Theory and experiments show that in the case of significant floating of the shaft, when 6^0.7bo, the shaft loses stability and begins to move relative to its equilibrium position on the line of moving equilibrium O0-0\. This movement occurs along a closed path and is called shaft precession.

The angular velocity of this precession, i.e. the frequency of oscillation of the axle, is close to half the rotational speed or to the first critical speed of the shaft. Typically, this frequency lies between the critical speeds of the “rotor-support” system in the direction of its axes of maximum and minimum rigidity.

Precession can be of three types: decaying, steady and increasing (Fig. 3-18.6). The first type of precession (oscillations at point O") cannot be considered dangerous, since the damped process of oscillations brings the center of the axle, at any initial deviation, back to the stable equilibrium curve O-Oi. The second type of precession (oscillations at point O") corresponds to established small oscillations of the axle around the stable equilibrium position. The occurrence of such oscillations indicates that the stability limit has been reached, the transition through which leads to the initiation of increasing precession (oscillations at point O"). Increasing precession causes intense vibrations of the axle, the amplitude of which can reach destructive values. Shaft vibrations, transmitted through the oil layer, in turn excite significant low-frequency vibration of the bearing.

Long-term operating experience, as well as experimental results, show that the excitation of low-frequency vibrations depends mainly on the oil temperature, the peripheral speed of the shaft journal and the specific pressure on the bearing. A decrease in the specific pressure on the bearing, as well as an increase in oil viscosity and peripheral speed, have a beneficial effect on the occurrence and development of low-frequency vibration.

A decrease in the specific pressure on a bearing during operation may be caused by:

A) wear of the babbitt of the lower half of the liner and, as a result, an increase in the shaft support area;

B) a decrease in the load from the rotor on the bearing due to improper alignment of the rotors, defects in couplings or improper thermal expansion of the cylinders;

C) incorrect sequence1 of opening the control valves * as a result of which a steam force arises, pushing the rotor upward and thereby unloading the bearing from the weight of the rotor.

One of the common causes of “oil” vibration in large units is low oil temperature at the bearing inlet. Tests carried out on a number of machines revealed a very definite dependence of the low-frequency amplitude
component of bearing vibrations depending on oil temperature.

In Fig. Figure 3-19 shows a graph of the dependence of the oscillation amplitude of the bearings of the TGV-200 generator on the oil temperature. As can be seen from the graph, an increase in oil temperature from 43 d<э 53°С, что соответ­ствует изменению его вязкости при­мерно в 1,5 раза, снижает уровень низкочастотной вибрации в 5-6 раз. Проблема борьбы с низкочастот­ной вибрацией особенно остро воз­никла в связи с освоением турбо­агрегатов большой мощности, где высокая окружная скорость цапфы создает благоприятные условия для возникновения этого типа автоколе­баний. Для решения этой проблемы в последнее время в конструкцию опорных подшипников крупных ма­шин вносится ряд конструктивных изменений. Одним из мероприятий является уменьшение относительной длины подшипника для увеличения удельного давления на масляный клин. Вторым, весьма эффективным, мероприятием является замена ци­линдрической расточки вкладышей подшипника овальной («лимон­ной») расточкой (рис. 3-20). При та­кой расточке верхний зазор в под­шипнике делается примерно в 2 ра­за меньше бокового.

This causes another oil wedge to form on the top half of the liner. The upper oil wedge dampens the resulting vibrations well and, in addition, increases the pressure on the axle, eliminating the root cause of “oil” vibration. A further development of this should be the creation of bearings with a split upper liner, where it is possible to create not one, but several oil wedges.

A special group of reasons that cause vibration of a turbine unit are disturbing electromagnetic forces. These forces are a consequence of the violation of the electromagnetic symmetry of the generator and significantly depend on the electrical load. When the turbogenerator is idling and the excitation is removed, these forces are absent, which makes it easy to distinguish them from exciting forces caused by mechanical reasons.

Violation of the electromagnetic symmetry of the generator can be caused by:

A) turn short circuits in the rotor;

B) uneven air gap between the stator and the rotor barrel;

B) a periodic change in the force of magnetic attraction between the rotating rotor and the stator, due to a finite number of POLES."

Turning short circuits in the generator rotor are the most common source of oscillations.

Niya coming from the generator. Practice shows that many generators operate with turn short circuits in the rotor winding. The presence of short-circuited turns distorts the distribution of the total magnetic flux of the rotor, which leads to the appearance of asymmetric forces of attraction between the rotor and the stator. These forces are always directed along the axis of the poles and are identical in nature to the forces from the mechanical “imbalance of the rotor. The one-sided electromagnetic force of attraction causes sinusoidal oscillations of the rotor and bearings with a reverse frequency. The second consequence of turn short circuits in the rotor winding is asymmetrical heating of the rotor across the cross section, which can cause its thermal deflection and excite vibration of a purely mechanical nature.

The non-concentric location of the rotor barrel in the stator bore also leads to the appearance of a periodic force, causing vibrations of the rotor and stator. This force, unlike the previous one, has a double revolving frequency. The main reasons for the appearance of an uneven air gap are the natural deflection of the rotor under the influence of its own weight and its displacement during alignment with the turbine rotor. When the generator operates, the rotor floats on an oil film, and, in addition, the gap may change due to vibration of the rotor due to mechanical imbalance.

All these reasons cannot be eliminated, but practice shows that under normal conditions these vibrations have a small amplitude and do not pose a danger. If the active steel of the core is not pressed satisfactorily or the stator housing design is not sufficiently rigid, significant stator vibration may occur. According to testing data of the TV2-100-2 turbogenerator, in some cases sinusoidal oscillations with a frequency of 100 Hz and a double amplitude of 100-150 μm were observed on the stator housing and end shields.

The accelerations, and therefore the inertial forces acting on the stator elements in the presence of such high-frequency vibrations, are very large, and this can lead to fatigue failure of fastening parts, welds, gas cooler tubes, etc. Stator vibration is further enhanced if the winding The rotor has short-circuited turns.

Considering issues related to oscillations of generator stators, one cannot fail to note another source of excitation of oscillations - the unevenness of the forces of mutual attraction of the rotor and stator around the environment. ness.

For two-pole generators, the interaction force between the rotor and stator varies circumferentially by ±33%. average value, and the maximum interaction force exceeds the minimum by 2 times. As the number of poles increases, the uneven force of attraction between the rotor and stator decreases. So, for a four-pole machine this unevenness in relation to the average value is ±6.7%, and for an eight-pole machine it is less than ±2%.

For most modern turbogenerators with an operating speed of 3000 rpm, the exciting force in question has double the rotation frequency. Increased stator vibration (with a frequency of 100 Hz) is transmitted through the foundation to the generator bearings, superimposed on fluctuations in the main rotation frequency.

Determining the causes of vibration in a modern turbine unit is a very difficult task. This work is usually performed by research, commissioning and repair organizations that have qualified personnel and all the necessary equipment.

To analyze the sources of increased vibration, the following characteristics are taken: speed, mode, contour.

The speed characteristic (Fig. 3-21) is the dependence of the amplitude and phase of vibration or its individual components on the rotor speed. From polyharmonic oscillations, the fundamental harmonic of the reverse frequency and low-frequency components are necessarily distinguished. Based on the speed characteristic, the type of rotor imbalance and the shape of forced oscillations at different rotation frequencies are determined. Using speed characteristics, nonlinear sources of excitation of increased vibration are also identified.

The operating characteristics represent the dependence of vibration on the operating mode of the machine: thermal and electrical load, thermal state of the turbine, vacuum, oil temperature, etc. Some of these characteristics are shown in Fig. 3-ІІ7 and 3-19. Such characteristics make it possible to determine the separate influence of each of the operating factors and machine vibration.

Contour characteristics (Fig. 3-22) show the change in vibration along the contour of the element under study, which makes it possible to evaluate the weakening of the rigidity of the vibrating system. Using contour characteristics, loosening of the bearings to the foundation slab or the slab to the foundation is detected. Based on the type of characteristics, defects such as deep cracks in support and foundation elements can be identified. The research program also includes monitoring a number of machine components and elements that are a common source of vibration excitation. The alignment of the rotors, the condition of the couplings, rotor necks and bearings are checked. If the vibration characteristics indicate significant imbalance of the rotor, the shaft is checked with a deflection indicator, after which the rotors are balanced. In cases where research has revealed a noticeable dependence of vibration on the excitation current or temperature of the generator rotor, the rotor winding is monitored for the absence of turn short circuits.

120 80 40 O 40 VO 120 2D, µm 2A, µm

I I.1___ 1-1_______ 1111 I L-l I "

240 W0 80 О 80 /80 240 f, gravel<р, град

Rns. 3-22. Contour vibration characteristic (arrows indicate measurement locations).

2A - double amplitude of oscillations; f - phase shift angle.

Note that in order to determine the causes of vibration, constant operational monitoring of vibration of bearings and other components of the unit plays a paramount role. Constant monitoring makes it possible to take into account a number of operational factors that directly affect the magnitude of vibration, as well as to trace the dynamics of vibration growth during operation during the overhaul period.

In conclusion, it should be said that since the vibration level is the most important objective indicator of operational reliability, the permissible vibration standards are constantly revised towards reducing the vibration amplitude.