3.2. Equipment defects at the “mechanism” level

Imbalance of the rotating masses of the rotor is one of the most common defects in rotating equipment, usually leading to a sharp increase in vibration of the units. For this reason, diagnostic issues and methods for eliminating imbalances should be given great attention.

Before considering this issue, it is necessary to make a small methodological digression. The fact of the presence of a rotor mass imbalance, when it tends to rotate not relative to its geometric axis, but relative to the axis of the center of mass, which in this case do not coincide, is defined in the literature by different terms. These are “imbalance”, and “imbalance”, and “imbalance”. If you carefully read the literature, you can find several more similar terms. In the text of our work we will use the Russian word “imbalance”, which is familiar to us, and if, for some reason, you do not like it, then we sincerely apologize to you.

The problem of correctly diagnosing the presence of unbalances in operating equipment is an important aspect in the work of every vibration diagnostic service. Vibration diagnostic tools are the most effective means for quickly eliminating imbalances in equipment. They form the basis of a whole section of vibration work called vibration adjustment of equipment.

Below we will consider the most general issues of diagnosing imbalances in the most common practical manifestations. A clear knowledge of these standard manifestations of imbalance will allow the attentive reader to develop more specific rules for recognizing imbalances. These adaptive rules, specified by you, will take into account the specific features of unbalances characteristic of “your” equipment.

3.2.1.1. General issues in diagnosing imbalances

The nature of the occurrence of unbalance in equipment can be different and result from many design and operation features of various units. In general, after some systematization and generalization, all this variety of reasons for the appearance of imbalances can, of course, conditionally be combined into groups. This:

• A defect in the manufacture of a rotating rotor or its elements that occurred at the factory, at repair company, missed as a result of insufficient quality final control at the equipment manufacturer, the result of shocks during transportation, poor storage conditions.
• Incorrect assembly of equipment during initial installation or after repairs, poor-quality fastening of elements.
• The result of processes of uneven wear and destruction of the rotating rotor structure, its aging, the appearance of various residual deformations after abnormal conditions, especially dynamic impacts.
• The result of periodic impacts of real technological processes and operating features of this equipment, leading to uneven heating and bending of the rotors.

Regardless of the reasons for their occurrence, according to their external signs, the specificity of their manifestation in the overall vibration picture, all imbalances can be divided into two types - static imbalance and dynamic imbalance. The features of the manifestation of these main types of imbalances in vibration signals and the spectra obtained on their basis, the features of their diagnostics, will be discussed in this chapter below, in separate subsections.

The main, most often encountered and familiar to everyone, signs of the presence of unbalances of rotating rotors in vibration signals can be considered the following:

• The timing vibration signal is quite simple, with a fairly small number of high-frequency harmonics. The vibration signal is dominated by vibration with a period corresponding to the rotational speed of the shaft - the rotational frequency of the rotor.
• The amplitude of all harmonics of a “mechanical nature” (usually the harmonics from the first to the tenth) in the spectrum is significantly less, no less than 3 to 5 times, the amplitude of the harmonic of the rotor’s reverse frequency. If we compare in terms of power, then at least 70% of the vibration signal power should be concentrated in the reverse harmonic.

These signs of unbalance occur in all vibration signals recorded at the support bearing. They are most pronounced in the vertical and transverse directions.

The simple and understandable diagnostic rule that “imbalance goes around in circles” is almost always completely true. The ratio of the amplitude of the first harmonic in the vertical direction to the similar harmonic in the vibration signal in the transverse direction is in the range of approximately 0.7 ¸ 1.2 and rarely goes beyond its boundaries.

Typically, the first harmonic in the vertical direction is equal to, or more often slightly less than, the first harmonic of vibration in the transverse direction. The exception is machines with structural specific features. An example is turbogenerators, in which the vertical component of vibration is always greater. The reason is the uneven radial rigidity of the rotor, in which the longitudinal slots of the winding are concentrated near the poles. It is necessary to understand that the uneven radial stiffness of the rotors is most pronounced in the second harmonic, which is not so important when diagnosing unbalances.

Deviations from this rule also occur with increased lateral clearances in the support bearings, which leads to increased rotor mobility in the transverse direction. This is also possible with very large differences in the compliance of the bearing struts in the vertical and transverse directions.

The level of vibration in the axial direction, when unbalanced, is most often less than the level of vibration in the radial direction. This rule is not observed if the supports are highly flexible in the axial direction and (or) if there is an imbalance that occurs when the shaft bends for any reason. With such an imbalance in the vibration of the axial direction, the first harmonic may not be predominant; significant harmonics of other frequencies, for example, the second and third, may be present in the signal.

Typically, the vibration pattern of unbalance appears simultaneously on two bearings of the controlled mechanism. Only on one of the bearings is unbalance diagnosed quite rarely, and only in cases where it is completely concentrated directly in the bearing area.

If, when measuring vibration, it is possible to change the operating speed of the rotor, then it is usually clearly visible that, most often, with increasing rotation speed, vibration from unbalance increases intensively. Despite the apparent simplicity of such a statement, we are forced to note with regret that carrying out vibration measurements at a variable rotation speed leads to a complication of the unbalance diagnostic procedure. The problem is aggravated by the appearance of peaks in the graph of the dependence of vibration on rotation speed, corresponding to the “critical rotor frequencies”. Few diagnosticians correctly understand the meaning of the terms “first critical frequency”, “second critical frequency”, etc. These questions relate to the field of modal analysis, are quite complex, and most importantly, are important only for very large rotors. We simply do not have enough space for a detailed consideration of this issue; all those interested in this issue need to turn to other sources.

In the absence of other condition defects, with a constant rotor speed, vibration from its imbalance quite often depends on the operating mode of the unit and is associated with its load. In other words, depending on the operating mode of various equipment, mass imbalance will manifest itself in vibration measurements to varying degrees.

In each type of equipment this effect will manifest itself for different reasons:

• In electrical machines (electric motors), an increase in load leads to an increase in the electromagnetic forces of mutual attraction between the rotor and stator, which leads to a decrease in vibration signs of unbalance.
• In centrifugal pumps and fans, an increase in productivity also leads to stabilization of the position of the pump rotor (fan impeller) relative to the stationary elements of the flow part. It should be noted that the opposite effect is also possible here - in the presence of geometric asymmetry or defects in the flow part, with an increase in the productivity of pumping equipment and fans, the signs of imbalance will increase.

Vibration from unbalance, in many cases, is dangerous not only because of its amplitude, it is an exciting factor that leads to the “manifestation” of signs of other defects in the condition of the equipment. The principle of “mutual multiplication” of the influence of several defects operates here. If there is no exciting force, which most often comes from the rotor mass imbalance, then other defects, mainly the support system of the unit, do not appear.

The features of the manifestation of imbalance in equipment and the degree of its influence on the condition of the units are at first glance very simple. However, practice repeatedly confirms the complexity and versatility of the manifestation of imbalances in equipment. It is somewhat reminiscent of the well-known saying of practical doctors - surgeons. “Which of all operations is the simplest - appendicitis. Which operation is the most difficult - also appendicitis.” All this is possible in equally say something about imbalance. It seems to us that anyone who has been seriously involved in diagnosing and eliminating imbalances will agree with this statement.

Let's explain this with a practical example.

Against the background of a well-functioning unit, vibration suddenly increases significantly. Operational services invite two vibration specialists (this is our theoretical option). The diagnostics of the condition carried out by both specialists using the spectra of vibration signals clearly indicates the presence of a whole “bouquet” of defects in the unit. Then there are two possible scenarios for the development of events.

One specialist makes a categorical conclusion about the poor condition of the bearings, unsatisfactory alignment, the presence of defects in the foundation, etc. In this formidable diagnosis, the rotor mass imbalance is mentioned in passing, as a defect that occurs, but is not the most dangerous. The main conclusion is very categorical - the unit has several serious and developed defects. The unit must be stopped and repair work carried out. You definitely need to forget about the possibility of “holding out” until scheduled repairs.

The second diagnostician makes a more in-depth, competent analysis of the condition of the unit. For example, he believes that the first rotation harmonic in the vibration signal spectrum is a consequence of the presence of unbalance, and the oil harmonic accompanying the increased clearance in the bearing arises only due to the exciting effect of the force from the unbalance. The final vibration of a sliding bearing support is determined by several parameters - increased clearance in the bearing, misalignment and slight imbalance that excites these vibrations. Problems of the state of alignment of mechanisms and the state of the foundation are analyzed in a similar way.

Consequently, these vibrations of the unit, both bearing and foundation, are caused by one reason - the imbalance of the rotor masses, although, at first glance, the imbalance is not the main defect. The diagnostician makes a decision to carry out balancing in their own bearings. As a result of eliminating the imbalance, the force that excites oscillations of the oil wedge disappears and the vibration, most often, sharply drops to a normal value. Defects in the bearings and foundation were and remain, but they no longer manifest themselves in vibration, there is no exciting force. The vibration of the unit is normal, complete success in vibration adjustment of the unit!

An experienced diagnostician’s in-depth knowledge of the physical processes in equipment, even if in some cases intuitive, brings positive results, of which the following can be highlighted:

• The operation has at its disposal an apparently safe unit operating within the permissible range of vibration levels. This unit, under certain conditions, can “calmly” be modified until scheduled repairs, when it is possible to eliminate any defects.
• A specialist who has a good understanding of the causes of vibration in specific equipment significantly increases his rating.
• A less experienced diagnostician, who apparently did everything correctly, loses his rating; the condition of the unit improved without eliminating the defects he identified, which means they never existed. In fact, most of the defects he identified did not disappear, they simply ceased to be diagnosed based on the spectra of vibration signals, but this no longer interests anyone.

This example, quite indicative and standard, is given to demonstrate a small part of the problems of various types that arise when diagnosing and eliminating imbalances in equipment various types.

You can also refer to a more profound statement by a well-known specialist in rotor balancing, author of the popular book A. S. Goldin - “if there is an unbalance - balance, if there is no imbalance - balance too.” He always brilliantly implemented this important postulate in practice.

If we summarize this information, we can come to a correct understanding of the work to “calm down equipment,” which in many cases is more effective than the work to “eliminate equipment defects.” This issue is not simple and unambiguous, so we will not delve into it, leaving the consideration of the subtleties to the reader.

3.2.1.2. Static imbalance

This is the simplest, but also the most common type of unbalance in rotating rotors. Diagnosing it does not cause big problems; it is quite easy to diagnose. If the static imbalance is significant, it can even be determined when the equipment is out of service, without the use of vibration monitoring devices. A stationary rotor with a strong static imbalance will always tend to establish itself in a position where the heaviest point is at the bottom. To reduce the influence of friction in the bearings, the rotor can be brought into slow rotation by hand, then it can be more accurately positioned with the heavy point down. Diagnosing unbalance in this way is possible until the static moment from unbalance is greater than the total moment from friction in the bearings and rotor seals.

Typically, such a simple procedure for finding the location of the unbalance is not enough to balance rotors that rotate at significant speeds. A standard practical situation is that the rotor, when turned off, can stop in any position, there is no external imbalance, but vibration is increased during operation. The procedure for more accurate and definitive diagnosis of the presence of unbalance, and subsequent balancing, must always be carried out at the operating speed of rotation of the rotor, using modern vibration measuring instruments - vibration spectrum analyzers - to diagnose unbalance.

To illustrate the features of the manifestation and diagnosis of imbalance using vibration signals, in Figure 3.2.1.1. The vibration signal recorded on the support bearing of the mechanism in the dimension of vibration velocity and its calculated spectrum are presented.

According to 3.2.1.1.a., the shape of the vibration signal is very close to the classical sinusoidal signal, the frequency of which is equal to the rotor rotation frequency, the first harmonic of the rotation frequency.

Shown in Fig. 3.2.1.1.b. The picture of the distribution (power) of vibration over the main harmonics, corresponding to static unbalance, is outwardly simple and understandable. The spectrum is clearly dominated by the harmonic peak of the rotor rotation frequency. The spectrum also contains (may be present) the second and third harmonics from the rotor rotation frequency. All these additional harmonics, in amplitude, are much smaller than the return harmonic, usually tens of times.

In the signal and in the spectrum shown in Figure 3.2.1.1., for generality and conditional complication of the diagnostic picture, several “minor” harmonics are also shown. They are shown in the low-frequency part of the spectrum, and a certain set of harmonics is also shown there, in the form of a “raise in the frequency band”, or a “hump” on the spectrum. The same “hump” can also exist in the high-frequency zone of the spectrum, at frequencies exceeding 1000 hertz. You should not pay special attention to them; these are harmonics of the second diagnostic level, indirectly caused by unbalance or friction in the seals.

We have already said above that such a pattern of distribution of harmonics in the vibration spectrum usually occurs in two directions (vibration measurements), vertical and transverse. Moreover, the amplitudes of the first harmonics in these two spectra, on each bearing, are usually approximately equal in magnitude. The difference in the amplitudes of rotational harmonics across bearings can be large, up to several times.

With static imbalance of the rotor masses, in the axial direction, a lower overall vibration level (RML) most often occurs. Let us explain the reasons for the occurrence of vibration itself in the axial direction, since in some methodological recommendations According to vibration diagnostics, there is information that when there is imbalance, there is no axial vibration. This of course happens, but quite rarely. In most practical cases, when there is unbalance, there is an axial vibration component, and often it is also increased.

Vibration, in its original interpretation, is a projection of the precession trajectory of the spatial vibration vector of the controlled point (bearing) onto the direction of the vibration sensor installation axis. The bearing precession curve (the trajectory of the end of the spatial vibration vector of the controlled point), due to the force from the imbalance, theoretically, should pass in a plane perpendicular to the rotor axis.

In practice, the picture of the precession of the controlled point is more complex. Movement in a plane perpendicular to the axis of rotation always leads to movement of the controlled point in the axial direction. This occurs due to the peculiarities of fastening the bearing inside the support, unequal rigidity of the supports along different axes, vibrations of the bearing around a horizontal axis perpendicular to the axis of rotation of the rotor, etc. All this adds up and leads to the emergence of a significant axial component in the movement of the bearing when unbalanced

When the mass of a rotating rotor is unbalanced, axial vibration is almost always present, but it has some peculiarities. In terms of level, it is always less than the radial components. In the spectrum of axial vibration, significant second and third harmonics can occur, along with the first harmonic of the reverse frequency. The greater the movement of the bearing support, the higher the relative amplitude of higher harmonics, especially the second, in the axial vibration spectrum.

Elimination of mass imbalance of a rotating rotor cannot be performed without recording the angular phase of the “position of the heavy point of the rotor” relative to the coordinates of the rotor - the zone of increased rotor mass. To control this parameter, vibration signals during registration are synchronized using a mark, usually glued to the shaft of the unit, and a specialized phase marker. For synchronous machines with a stable synchronous rotation speed, as a synchronizing mark, you can take any parameter of the sinusoid of the supply network, since this parameter differs from the phase position of the rotor only by the value of the load angle of the synchronous electric machine. When the unit is idling, this parameter is practically zero.

Each of the three main harmonics in the vibration signal, which are important in diagnosing unbalance, has its own angular (initial) phase. The actual position of the unbalance point is determined by the initial phase of the first harmonic of the vibration signal, while the phases of higher harmonics usually depend on the design features of the rotor of the equipment being diagnosed, and usually only complicate the search for the unbalance point.

For the value of the initial phase of the first harmonic of the vibration signal, when diagnosing static unbalance, the following diagnostic signs can be specified.

• The phase of the first harmonic must be sufficiently stable, stationary, i.e., not change over time.
• The phase of the first harmonic in the vertical direction should differ from the phase of the first harmonic in the transverse direction by approximately 90 degrees. This is all explained quite simply - the heavy point of the rotor, when rotating, will sequentially move from one measuring axis to another, from vertical to transverse, and again to the vertical axis.
• The phases of the first harmonics of identical vibration projections on two different bearings of the rotor being diagnosed should differ little from each other. With a purely static unbalance, there should be no phase shift at all. When a dynamic unbalance is superimposed on a static imbalance, the phase shift along the bearings begins to increase. With a phase shift of 90 degrees, the contribution of static and dynamic unbalances to the overall vibration is approximately the same. With a further increase in the dynamic component in the imbalance, the phase shift of the first harmonics on the two bearings increases, and at 180 degrees the total imbalance has a purely dynamic root cause.

Additionally, regarding the diagnosis of static unbalance, it can be noted that if during the research process it is possible to measure vibration at different rotor speeds, this will increase the accuracy of the diagnosis. The amplitude of the first harmonic in the vibration spectrum, caused by static unbalance, will change with speed, and will increase approximately in proportion to the square of the rotor speed.

The identified purely static imbalance of the rotor masses can be quite simply corrected by workers of vibration diagnostic services by installing one or more balancing weights in a zone diametrically opposite to the heavy point in one or more correction planes. A similar result is achieved by the “removal of excess metal” procedure, but only on the heavy side of the rotor.

3.2.1.3. Dynamic imbalance

The reason for the emergence of the term “dynamic imbalance” is quite simple. From the name itself it clearly follows that it appears only when the rotor rotates, i.e. only in dynamic modes. In static modes, with a stationary rotor, dynamic unbalance is not diagnosed in any way; this is its main difference from static unbalance.

The reason for the occurrence of dynamic imbalance can be explained using a fairly simple example. The rotor must be mentally “cut” like a log into several disks. The resulting disks will be located on a common shaft, but each of them may have different properties.

There are three practical options:

• The ideal case is when all the resulting disks do not have a static imbalance, then the rotor assembled from these disks will also not have an imbalance.
• Individual rotor disks had static unbalances. The rotor was assembled from disks so that it also has an unbalance in total. We are not yet considering the question of whether it is static or dynamic.
• The ideal case is when individual disks with static unbalance are combined into a single whole so that the assembled rotor has no unbalance. Static imbalances of individual disks were completely mutually compensated.

These three practical cases of manufacturing a composite rotor, for example, the impeller of a multistage pump, allow us to consider all the main types of unbalances encountered in practice. Considering these three cases, it can be argued that in the third, most complex case, the rotor has a dynamic unbalance, and in the second case - static and dynamic unbalance at the same time.

In Fig. 3.2.1.2. There are two schematic drawings showing composite rotors assembled from disks, each of which has a static unbalance, and of the same magnitude.

In diagram 3.2.1.2.a. shows a rotor assembled from discs with unbalances. The pump rotor assembly is designed in such a way that the total unbalance of the entire rotor is equal to the sum of the disc unbalances, i.e., all unbalances are located in the same angular zone of the rotor. This is a practical example of obtaining static unbalance.

In diagram 3.2.1.2.b. a rotor assembled from 4 discs with unbalances is also shown. But in this case, the pump rotor was assembled in such a way that the total unbalance of the entire rotor is zero, since two disks, on one side, are mounted with unbalances in one direction. For the other two disks, on the other side of the pump rotor, the imbalance is directed in the opposite direction, i.e., rotated 180 degrees.

In static mode, the unbalance of such a composite rotor will be equal to zero, since the existing unbalances of the pump impellers are mutually compensated. A completely different picture of centrifugal forces arising on the rotor and transmitted to the support bearings will occur when the rotor is rotated. The two forces shown in the bottom figure will create a dynamic moment, creating two forces acting on the two journal bearings in antiphase. The faster the rotor rotates, the stronger the dynamic torque acting on the bearings will be.

This is dynamic imbalance.

Although we did not give such a definition of static unbalance in the previous section, it may sound like this: “Static unbalance is concentrated in one corner zone of the rotor, and is localized along the longitudinal axis of the rotor at a point at some distance from the support bearings.”

In this case, the following definition can be used for dynamic unbalance: “The dynamic unbalance is distributed along the longitudinal axis of the rotor, and at different points along the rotor axis the angular localization of the unbalance is different.”

In practice, there is never only a purely static imbalance or a purely dynamic one - there is always their sum, in which there is a contribution from each type of imbalance. This even led to the appearance in the literature and in the practice of some diagnosticians of the term “oblique pair of forces”, which reflects the manifestation of the sum of imbalances of two types.

By the phase shift of the first harmonics of the rotation frequency on two support bearings of one rotor (in synchronized or synchronous spectra), it is possible to evaluate the contribution of each type of unbalance to the overall vibration picture.

When the phase shift of the first harmonics is approximately 0 degrees, we are dealing with a purely static unbalance; at 180 degrees, we are dealing with a purely dynamic unbalance. At 90 degrees of phase shift of the first harmonics, the contribution from both types of unbalance is approximately the same. At intermediate values ​​of the shear angle, it is necessary to interpolate to estimate the contribution of one or another imbalance. We have already mentioned this feature when describing static unbalance; here we present it in a slightly different form.

Concluding the conversation about dynamic imbalance, it should be said that the amplitude of the first harmonic in the vibration spectrum, when the rotation speed changes, changes proportionally more than a square of the degree of change in the rotor speed. This is explained by the fact that each force from a local imbalance is proportional to the square of the speed (rotation frequency). With dynamic imbalance, two factors are superimposed on this.

First, dynamic imbalance excites vibrations proportional to the difference in forces. But if you square the difference in forces as one single force, you get the same result. If you square each force separately and then subtract the squares, you will end up with a completely different figure than in the first case, much larger.

Secondly, forces from dynamic imbalance act on the rotor and begin to bend it. As it accelerates, the rotor changes its shape so that the center of mass of a given part of the rotor shifts towards the existing imbalance. As a result, the actual amount of unbalance begins to increase to an even greater extent, further increasing the bending of the rotor and the vibration of the support bearings.

Axial vibration with dynamic unbalance usually has a slightly larger amplitude than is the case with purely static unbalance. This mainly occurs due to a more complex deflection of the rotor, and greater mobility of the bearing supports in the axial direction.

3.2.1.4. Non-stationary imbalance

Many problems in vibration diagnostics of defects in rotating equipment are created by non-stationary unbalance, which can sometimes slowly increase, and sometimes appear unexpectedly, and also unexpectedly disappear. Moreover, at first glance, there are no patterns in this process. For this reason, this type of imbalance is sometimes called "stray".

Naturally, in this case, as usual, the classic remark is true that “there are no miracles in the world, there is a lack of information.” There is always a specific reason for the appearance of a non-stationary imbalance, and the diagnostician’s task is to correctly identify it.

It is quite difficult, and even impossible, to give any general recommendations for diagnosing such a cause of increased vibration in equipment. The causes of non-stationary imbalance are usually identified only as a result of fairly scrupulous, often lengthy, studies.

Below we will simply look at the features of diagnosing a non-stationary imbalance using the simplest practical examples, which relate to the most common causes leading to the occurrence of such a defect. In practice, more complex and confusing cases occur, but this happens much less frequently.

Thermal imbalance

This is the most common type of unbalance that changes during operation, to which the term “wandering unbalance” is well suited.

For example, in the rotor of a large electric machine, for some reason, one of the through channels through which cooling air or gas passes in the axial direction becomes clogged. Or, in an asynchronous electric motor, damage occurs to one or several rods of a short-circuited cage located nearby. Both of these reasons lead to the same defect. Let us describe the features of the manifestation of such a defect in more detail.

In our practical example The rotor of the electric machine, before assembly, was balanced on a balancing machine, and has the necessary balancing quality parameters. After turning on the pumping unit for the first approximately 15 ÷ 20 minutes, engine vibration is normal, but then it begins to increase, and after about two hours it reaches its maximum, after which it no longer increases. Diagnostics using the vibration signal spectrum gives a picture of a classic imbalance. The unit is stopped for vibration adjustment.

The next day, diagnostic service specialists begin balancing work on the pump unit, naturally in idle mode. After completing the balancing work, measuring vibrations in idle mode gives a favorable picture - everything is normal. When starting up in operating mode, the pattern of slow increase in vibrations is repeated without changes in the same sequence.

In this simple, almost textbook case, everything is explained very simply. Due to the violation of the uniform airflow of the rotor through the internal channels, it heats up unevenly and after some time, determined by the thermal heating time constant, it bends. Similarly, everything happens when there are defects in the short-circuited cage of an asynchronous electric motor - the rotor zone where the defective rods are located turns out to be less heated, the rotor also bends, and bearing vibrations begin to increase due to the appearance of thermal imbalance.

To diagnose this reason, you should monitor the change in vibrations during start-up and warm-up. Using remote pyrometers, the rotor temperature can be monitored. Based on the magnitude of the vibration phase, it is possible to clarify the area of ​​local thermal overheating of the rotor.

It is clear that it is impossible to balance such a rotor for normal operation in all equipment modes. It can be balanced for one process condition, but this must be done at a given load. However, in this case, the rotor will have increased vibrations in idle mode, or immediately after the unit is put into operation. This will happen for the reason that at start-up the temperature field of the rotor will be unsteady, and it will not have increased vibration due to the installed balancing weights.

Complete elimination of such an imbalance is only possible by eliminating the causes of uneven heating of the rotor during operation.

Aerodynamic and hydraulic imbalances

These two types of non-stationary imbalance, as well as thermal imbalance, are associated with the technological operating conditions of rotating equipment. It’s just that in the above example, the unbalance was caused by thermal bending of the rotor when operating under load, and in these examples it is caused by hydraulic or aerodynamic forces.

If we diagnose a fan or pump of a centrifugal operating principle, then we almost always have several active blades on the impeller (rotor), which eject the working fluid, liquid or gas, at a certain angle from the center to the periphery of the rotor. This leads to the fact that each blade will be affected by its own force.

These radial reaction forces acting on the rotor blades are always mutually compensated, since the blades are located around the circumference at equal angles. But this only happens when all the impellers and guide vanes of the pump or fan have no mechanical defects.

Otherwise, it will happen if there are defects on the working blades - chips, cracks, changes in the angle of inclination. In this case, complete compensation of radial forces around the circumference of the impeller will not occur; there will be a force in the area of ​​the defective blade. From the point of view of analyzing vibration processes, we will have a radial uncompensated force, an available frequency equal to the rotor rotation frequency, i.e. the first harmonic. In other words, we will have in the spectrum of the vibration signal all the signs of unbalance, hydraulic or aerodynamic.

The main difference from the usual unbalance in this case will be that the magnitude of the uncompensated radial force causing the first harmonic of vibration will depend on the load of the pump or fan, i.e. it depends on the technological parameters of the equipment, the unbalance itself will be non-stationary.

Let us show the effect of aerodynamic imbalance using the example of a boiler fan, the performance of which is regulated by opening special dampers - dampers. Such fans are widely used in practice.

The installation angle of one of the blades differed from the installation angles of all other blades - this was an operating defect. Due to this, the aerodynamic radial force of this blade acting on the rotor shaft was less than the force of the other blades. After installation, the fan wheel was balanced at the operating rotor speed, with the dampers fully open. Since the fan performance was zero, aerodynamic imbalance could not appear. The fan was put into operation.

During operation in operating mode, with the dampers open, an alarming level of vibration began to be registered on the fan bearings. A vibration diagnostic service representative diagnosed the unbalance under load, and balancing work began. The fan was taken out of service and access to the impeller was opened. The picture of imbalance has disappeared, which is quite understandable. In this mode, with zero productivity, the wheel was balanced before. In operating mode, the fan operated with a different performance, with different values ​​of the radial aerodynamic forces, which created a picture of imbalance.

After checking the installation angles of the working blades and identifying the cause of the defect, it was decided to balance the wheel in operating mode, with the side shields closed, at the load with which the fan worked most often. Subsequently, after scheduled repairs, there were no problems with this fan.

Unbalance with hysteresis

This is a very interesting practical case of diagnosing an imbalance that we encountered in our practice.

An unbalance was diagnosed at the turbogenerator exciter, and work began to eliminate it during a maintenance shutdown. An interesting feature was revealed. When starting up the turbine unit, there was no imbalance; it appeared abruptly a few minutes after the rotor began to rotate at operating speed. Since the launches were without an electrical load, driven by a turbine, the issue of thermal bending immediately disappeared.

During the test start-up, when an imbalance appeared, the turbine unit was slowly stopped, reducing the rotor speed. At a frequency of approximately 0.6 from the nominal, the unbalance disappeared. The rotor speed was increased again, and the unbalance again arose at a frequency of 0.97 nominal. Repeated accelerations and run-downs of the rotor showed approximately the same picture.

It was assumed that the hysteresis of unbalance on the rotor is due to the presence of an elastic element, which, under the influence of centrifugal forces at almost the nominal speed, shifts to a slightly larger radius and leads to unbalance. It returns to a smaller radius when the rotation speed decreases. Unbalance hysteresis is caused by increased friction when the element moves in the groove.

The diagnosis was completely confirmed. The rotor winding element was able to move in the groove with great force. When the centrifugal force exceeded the displacement force, the winding section bent and shifted. The hysteresis was caused by friction forces when the winding moved in the groove. The winding was secured in one position with an additional wedge, and the problem disappeared.

Let us repeat that this case of non-stationary unbalance is not a common one; it is presented here to illustrate the variety of forms of manifestation and the difficulties of diagnosing unbalances in practical work.

Electromagnetic imbalance

This is also very interesting example manifestations of non-stationary imbalance. It can manifest itself in synchronous electric motors and generators, as well as in asynchronous electric motors.

The paradox of the manifestation of such an electromagnetic imbalance lies in the fact that it has its maximum manifestation at idle speed of the electric machine. As the unit load increases, the first harmonic in the vibration signal spectrum may decrease or even disappear completely, i.e., according to formal criteria, the rotor mass imbalance corrects itself.

The explanation for this phenomenon is quite simple. As the load on the electric machine increases, the magnetic induction in the gap between the rotor and stator of the electric machine increases. Since the tangential component of the electromagnetic forces, which provides the torque of the electric machine, is evenly distributed in the gap, it begins to play a stabilizing role, centering the rotating rotor in the electromagnetic (!) gap of the stator.

If before this the rotor had an imbalance, due, for example, to mechanical deflection of the rotor, then with increasing load the rotor will stabilize in the gap, because the deflection will be eliminated by the tangential forces of electromagnetic attraction of the rotor to the stator. Formally, this will correspond to a decrease in the level of unbalance of the rotor of an electric machine.

3.2.1.5. Methods for eliminating rotor mass imbalance

Regarding the unbalance of rotating rotors, we can say that this defect “is the full property of the vibration diagnostic service.” If the vibration diagnostic service detects a defect in the electric motor, then the electrical service will fix it; if a bearing defect is detected, then it will be eliminated by a repair team of mechanics. If an imbalance is diagnosed in the equipment, then the vibration diagnostic service itself is responsible for eliminating it.

There are two most common ways to eliminate mass imbalance in rotating rotors:

• Elimination of imbalances using portable devices (or built-in functions of monitoring systems) - balancing the rotors in their own supports (bearings). In this case, disassembly of the equipment is carried out to a minimum extent, sufficient to access the balancing planes. As a rule, during such work, unbalance is eliminated by installing or removing balancing weights of appropriate mass and design.
• Balancing on acceleration and balancing stands (RBC). This balancing is performed after the rotors are manufactured, or after they are repaired. The rotor is installed on the stand supports, driven into rotation, and balanced. The possibilities for adjusting masses here are much greater; you can use corrective weights on the balancing planes, or you can mechanically remove excess mass at any point of the rotor.

Before we begin to briefly examine these two methods of eliminating imbalances, it is necessary to make some general methodological comments.

First, it is necessary to determine the size of the measured vibrations

In practice, the values ​​of vibration velocity and vibration displacement are most often used. Measurements in the dimension of vibration acceleration are not used due to the strong “noise” of the signals. A completely correct question arises: which units of measurement are preferable, in which case will our work be more effective?

There is no completely unambiguous answer to this question, due to the mathematical interconnection of vibration velocity and vibration displacement signals. From the vibration velocity signal, the vibration displacement signal can be unambiguously obtained. It should be noted that “in the opposite direction” there is no such completely unambiguous connection. Such signal conversion, as mathematicians say, can only be performed with an error equal to the “integration constant.” True, it can be noted that such accuracy, due to the symmetry of the power of our vibration signals relative to the time axis, is usually quite sufficient for practice.

In this regard, it seems that the issue of choosing the dimension of presentation of vibration signals during balancing work is, to a greater extent, determined by the personal preferences of each specialist. It is much more pleasant for him to say that the rotor is balanced “at zero” (the first harmonic of vibration displacement is zero) than to say that the residual vibration is of some, even small value. This reason, of course, is “ostentatious”, of secondary importance, but it is also significant.

A more interesting question is, what actually is the main sign of a successful completion of the balancing process? Is this the complete elimination of the first harmonic in the vibration signal, or something else? Perhaps more important is the “calming” of the unit; we completed the section on static unbalance with a description of an example of this approach. It is clear that this is a more complex and qualified approach to balancing critical and expensive units.

We understand that this is the subject of a separate and rather complex discussion, so we will conclude it by only identifying the problem. It should be solved by specialists, generally speaking methodologically, and each practical diagnostician individually, in relation to his applied activities.

Secondly, before describing the problems and features of practical balancing of rotors, it is necessary to determine the set of “significant harmonics”

It is enough to take into account the parameters of one first harmonic, or it is necessary to take into account, for example, the second and third harmonics in the vibration signal spectrum.

At first glance, it seems obvious that the entire process of rotor balancing, whether in its own supports or on a balancing stand, should be carried out according to the parameters of the first harmonic in the vibration signal spectrum. We can safely say that in 95% of practical cases, knowledge of the amplitude and phase of the first harmonic is sufficient for successful balancing.

The situation is more complicated with the remaining 5% of balancing cases. Most often, this is no longer the “craft” of balancing, but the “art” of analyzing and carrying out balancing work. This is no longer the elimination of imbalance, but a comprehensive vibration calming of the rotors of powerful and complex units.

It is not for nothing that specialists in balancing complex rotors (to which the author of this work does not consider himself) state that the rotor of a turbogenerator operating in normal vibration mode does not always have ideal parameters when taken out for repair. This statement is based on the fact that such a rotor installed on an RBC always has a residual unbalance.

So, it is proposed to carefully fix such an imbalance, and after the rotor is out of repair, this imbalance is just as carefully restored. Only in this case can we expect the turbogenerator to operate without increased first harmonics. We can only guess about all the complexities of oscillation processes in such rotors, but, as it seems to us, in this case it is desirable to take into account a larger number of harmonics, especially the second and third ones.

Let's return to the rotor balancing procedure itself, and naturally start with balancing in their own supports. This is the most common practical balancing procedure.

First of all, it is necessary to explain the process of balancing in its own supports. This procedure, although seemingly quite simple, can effectively reduce vibration of operating equipment without disassembly.

To do this, let's look at Figure 3.2.1.3.
This figure shows three stages of single-plane balancing of the rotor in its own supports.

a). Recorded on operating equipment increased vibration, which has an amplitude V 0 and a corresponding phase angle. To do this, a mark was glued to the unit shaft and a phase marker was used, and a vibration recording sensor was installed on the rotor support bearing in the vertical direction.

b). After a temporary stop of the unit, a test weight was mounted on the balancing plane of the rotor, usually in an arbitrary direction. According to the installation location of our load (in the figure), it should have created the vibration vector shown in the figure and equal to V Г1. The peculiarity of this balancing procedure is that the value of this load, for further calculations, can be specified by the user in any units - grams, pieces, washers, nuts, millimeters, etc. You just need to understand that in these same units you get the calculation results for installing the “correct” balancing weight.

Here we can define a very important parameter used in balancing – influence coefficients. In different literary sources, the concept of influence coefficients is given somewhat differently, so we will not strive for maximum accuracy of description, we will only describe the physical meaning. The influence coefficient is a vector quantity, a proportionality coefficient that shows how to determine the amount of the required correction weight for a given type of unit and for a given balancing plane.

Speaking in simple words, this is the conversion factor for residual vibration from imbalance into the value of the correction weight. Let the reader not be intimidated by obtaining values ​​of one dimension from parameters of a completely different dimension; the dimension of influence coefficients is quite complex, including vibration, mass, and linear dimensions.

Let's return to our balancing example. The unit is put back into operation, and the parameters of the first vibration harmonic are recorded again. We received the vibration vector in the “test” run V P, shown in the figure. It is clear that this vector is the sum of two vectors - the vector of the residual unbalance on the rotor V 0, and the vector of the unbalance introduced by the test weight V Г1. The main goal of further vector calculations is to determine the magnitude of the residual imbalance vector. This value can be determined through the parameters of the introduced imbalance vector. It is quite clear that this can only be done in the system of units of measurement accepted by the diagnostician (non-standard or any).

c). Knowing the magnitude of the residual imbalance vector (even in nuts or millimeters) makes it possible to determine the parameters of the “correct” correction weight in the same units. It must be located diametrically opposite to the vector of the residual rotor unbalance, have an equal value with it, and be located at the same radius as the test load. The test weight itself must either be removed from the rotor, or it must be a composite vector included in the correction weight.

The balancing process (in a favorable case) can be considered complete at this point, or, if necessary, another similar iteration will be needed.

Currently, almost all vibration measuring instruments and vibration signal analyzers are equipped with a built-in function for balancing rotors in their own supports, so this procedure in 90% of cases does not cause major problems for diagnosticians. In another 5 ÷ 7% of cases, the rotor can be balanced, but in this case the number of iterations (test runs) with the installation of weights can reach ten or more. In 2% of cases, it is not possible to balance the rotor on site, despite all the efforts of the diagnostician. This happens for one reason or another, which we touched upon very superficially above.

Balancing on balancing stands

There are several names in the literature for specialized devices designed to balance rotors. These include balancing stands, balancing machines, and accelerating balancing machines. We will use the term balancing stand in further discussion.

The name of the balancing device does not say anything about the balancing process. Changes arise when using stands of different operating principles. The following classification can be given for this parameter:

• Pre-resonance balancing stands. Pre-resonance is a stand in which the frequency of natural (resonant) oscillations of the bearing supports is significantly higher than the rotor rotation frequency in balancing mode.
• Resonance balancing stands. Such stands have maximum sensitivity in resonance mode.
• Over-resonance balancing stands. In such stands, the frequency of the natural resonant oscillations of the supports is significantly lower than the rotor rotation frequency in balancing mode.

The description of the design features and operation of balancing stands is so extensive that we will not even attempt to do so. We would rather suggest that you turn to the works of well-known specialists in this field, for example A.S. Goldin, E.V. Uryev, in which the curious reader may find answers to all his questions.

Let us complete our discussion of ways to manifest and eliminate imbalances of various types by clarifying some terms used in practice. Despite the presence of two types of unbalances, static and dynamic, the balancing procedure is always, or almost always, called dynamic balancing. This is an absolutely correct term, but it only reflects that unbalance diagnosis is carried out on a rotating rotor, when this can be done better and more accurately. In this case, the type of unbalance does not have any determining significance, especially when multi-plane balancing is carried out.

Our production devices for balancing

• SBU – a series of balancing machines of the resonant type with a horizontal axis of rotation
• ViAna-1 – vibration analyzer, “in-place” rotor balancing device
• Diana-2M – two-channel vibration signal analyzer with balancing
• ViAna-4 – universal 4-channel recorder and vibration signal analyzer, rotor balancing
• Atlant-8 – multi-channel synchronous recorder and vibration signal analyzer

Description:

Currently, much attention is paid to the introduction of energy-saving technologies and solving problems of imbalance and improving the system of measurement and accounting of natural gas at all levels of its technological process extraction, transportation and use.

Improving the gas measurement and metering system in order to reduce imbalances and introduce energy-saving technologies in the gas industry

V. A. Levandovsky, CEO,

O. G. Gushchin, Ph.D. tech. Sciences, Technical Manager, Elster Gaselectronics LLC,

A. V. Fedorov, Executive Director,

N. L. Egorov, leading researcher, CJSC "Metrological Center of Energy Resources"

In 1998, two Russian-German enterprises, Gazelektronika LLC and ElsterRusGazPribor LLC, were created to meet the needs of the domestic market for gas measuring equipment. In November 2004, as a result of the reorganization of Gazelektronika LLC in the form of a merger with it, ElsterRusGazPribor LLC was renamed into ELSTER Gazelektronika LLC, which is their successor not only in rights and obligations, but also in preserving production traditions regarding the production of modern high-precision and reliable gas measuring equipment, the development of advanced technologies in the field of energy saving and the implementation of work on the creation of new devices for the gas industry.

Currently, much attention is paid to the introduction of energy-saving technologies and solving problems of imbalance and improving the system of measurement and accounting of natural gas at all levels of its technological process of production, transportation and use. This is confirmed by the program to improve the gas measurement and accounting system, implemented by Mezhregiongaz LLC and Regiongasholding OJSC in the following areas:

Identification of the volume of gas consumed in the gas distribution network and its reflection in contractual relations with gas distribution companies;

Streamlining the rationing of gas consumed by the population;

Improving measurement and accounting tools at gas distribution systems of gas transportation organizations and gas consumers;

Creation of a full-fledged system for measuring the flow of gas transported through the gas distribution system.

The imperfection of the gas metering system and the low accuracy of commercial metering units are the main reasons for the inefficient use of natural gas, imbalances and financial losses in the supplier-consumer system. Therefore, measures related to the introduction of energy-saving technologies in the gas industry and the implementation of the above areas are of an organizational, legal and technical nature and should be aimed at identifying and eliminating the causes of inefficient use of natural gas, imbalances and financial losses.

This article discusses the problem of reducing the imbalance of natural gas in the supplier-consumer system and does not affect the accounting policies existing in the gas industry.

Balance of gas quantity in the supplier-consumer system

A schematic diagram of a gas measurement and metering system that allows minimizing imbalances at all levels of the technological process of production, transportation and use of natural gas is presented in the figure.

When using technically sound gas metering units (GMS), the above scheme will make it possible to implement the simplest and fairest way to eliminate the imbalance from the standpoint of a specific supplier and consumer by compensating for the share of losses (D V post, D V loss), due to the error of their GMS, from the total imbalance (D V e) .

where V consumption, V consumption, ∆ post, ∆ consumption – the accounting amount of gas and the limits of absolute errors of the gas supply system of the supplier and consumer, respectively;

∆V post, ∆V poti – imbalances of the supplier and consumer, respectively;

∆V e – general unbalance.

By the magnitude of the imbalance ∆V e it is possible to judge the correct functioning of the gas metering system during its transportation, distribution and use. The correct operation of the gas metering system is confirmed by the following inequality:

	(2)
		(3)
		(4)

where ∆V add – permissible unbalance value;

∆ consumption – total absolute error of UG consumers.

Failure to comply with (2) indicates a malfunction of the gas transmission or metering system. The situation is analyzed by the supplier's metrological services.

To do this, at the first stage, the consumed volumes of gas in the reporting period are compared with the periods that correspond to the fulfillment of (2).

If there is no comparison base, control measurements are carried out at consumer metering stations using measuring instruments with a higher accuracy class. For this purpose, areas for installing control measuring systems must be provided at consumer metering stations. The control results are considered positive if the following inequality is satisfied:

where V counter, ∆ counter – the amount of gas and the absolute error of the control measuring complex.

Fulfillment of (5) does not replace the function of verifying the consumer metering unit, but only indicates that the measurements are carried out with an error that does not exceed the error of the consumer metering unit by more than twice. That is, a controlled ultrasonic gas can be either metrologically suitable or unsuitable.

Failure to satisfy inequality (5) means that the controlled complex is metrologically unsuitable. If the consumer metering units have passed control and are found to be metrologically suitable, then the supplier’s UZG should be checked.

The question arises to what extent the indicated expansion of the error can distort the ∆V add criterion.

Let us consider a gas distribution system with N consumers, the consumption volumes and relative errors of which we will assume for simplicity to be approximately the same: V consumption ≈ idem, d V consumption ≈ idem. In this case, the absolute measurement errors at consumer metering stations will also be approximately the same: ∆V consumption ≈ idem. In the case of large differences in these quantities, it is necessary to form groups of consumers with approximately the same values ​​of these quantities and carry out all discussions within the framework of one group, and then combine them. Using formula (4) we get

If the control results are positive, you can write down

Dividing the numerator and denominator by V post and taking V post = NV loss, we get

(8)

Thus, monitoring consumer metering units using a working measuring instrument with a sufficiently large N makes it possible to identify a metrologically faulty unit if its error exceeds the permissible limits by the amount of error of the control measuring instrument. Moreover, if the control results are positive, then even with a metrologically faulty metering unit within the accepted limits, measurement errors have little effect on the unbalance value. This is due to the fact that the result of summing up gas volumes from consumers has a significantly smaller error compared to the error in measuring gas volumes from the supplier.

The described control method makes it possible to exclude metrological sources from the imbalance or, conversely, to indicate them if its value is approximately greater than |∆ post | +2∆ consumption (when calculating in specific conditions, this value is determined more accurately), or if the relative value of the imbalance is approximately greater than twice the relative error of the supplier’s metering unit. This conclusion is valid if we accept the assumption that the errors of all consumer metering units go beyond the permissible limits, but do not exceed the sum of the permissible limits of the monitored and control measuring instrument. If only part of the metering units is metrologically faulty, the described control method is effective with a lower unbalance value. If all consumer metering nodes have passed the control with positive results, you should check the supplier's metering node using a standard and, depending on the result, proceed to search for other sources of imbalance.

The following remark needs to be made regarding (8). This formula, like similar formulas for geometric summation of errors, is valid for N< 10. При N >10 formula may not be fair. This is due to the fact that not excluded correlated systematic errors, the sources of which are, for example, standards, can amount to 1/3 of the permissible error limit of the measuring instrument, and they do not decrease with increasing N. This means, in particular, that the value of ∆input obtained from formula (4) must be compared with the value, and if then you should accept

1. Balance of gas quantities must be carried out in order to assess the functioning of gas transportation, distribution, use and accounting systems. The criterion for the correct functioning of these systems is the permissible value of the unbalance.

2. In order to exclude the metrological characteristics of consumer metering units from the causes of imbalance, in most cases it is sufficient to monitor these units using working measuring instruments with fairly good (best-in-class) accuracy.

3. Important components of the balance are: an assessment of actual losses, as well as an assessment of the amount of gas in pipelines, especially at high pressure, obtained as a result of using a perfect gas metering system (see figure).

Literature

1. Zakgeim A.L., Fridman A.E. On the problem of imbalance of readings of commercial energy metering means // Vestn. gas. club "Gaz-Inform", 2004, No. 1.

2. Fedorov A.V., Egorov N.L. Expertise regulatory documents on metrological support for natural gas accounting in the Moscow region: Research report, 2004.

I don’t know how things are at the GDS of other legal entities - I can only talk about the GDS of my transgas.

Transgaz is a gas supplier to the IWG, which supplies gas to direct consumers and makes payments to them. Therefore, Transgaz, as a legal entity, has no financial interest in distorting flow readings, and representatives of the IWG cannot carry out any manipulations with gas flow measuring instruments at Transgas gas distribution stations (these are not their objects).

A situation where the IWG cannot collect payment from consumers for all gas released from gas distribution stations are found everywhere and, as practice shows, in 99% of cases this is not due to incorrect (in every sense) measurement of gas flow at gas distribution stations. Representatives of the IWG annually visit all our state registration stations with inspections. At the flow measurement units, they sealed everything that was possible (and even what we thought was impossible to seal). All parameter changes are recorded in electronic archives computers and are duplicated (via the telemechanics system) on the computers of the dispatch service.

“Zero loss” is more likely to be typical for pressure sensors (especially “absolute” sensors), but if the gas flow rate begins to differ from the average statistical values, then an investigation of the reasons immediately begins.

Therefore, I suggest "do not look for a black cat in a dark room, especially if it is not there."

Alexey Georgievich, I didn’t intend to “look for cats”, the question was just asked about theoretical the possibility of manipulating the balance at the gas distribution system - theoretically there are possibilities...

As for practically, I completely agree with you, the probability is quite low - as far as I know, everyone regional office There are intermediate suppliers of Transgas, with their own metering units... And it seems that the balances in the system are monitored quite strictly - how much came into the system through booster stations, the same amount should come out through the gas distribution system, so in order to cheat efficiently, you need to simultaneously tighten up the SI at all stages gas supplies, which is quite unlikely...

But when gas enters the MRG, much more black holes appear there, for example - not only does the MRG use a different gas density for calculations (relative, in air), but they also somehow average it according to some of their calculations (for season, six months, year - it’s hard to say) - it’s possible that everything is legal there, but from the outside it looks suspicious...

Again, temperature coefficients for SI without temperature correction, installed on the street - where is it taken into account that the SI is located on the street, how are they applied? And if the SI is installed indoors, but the flow rate is quite large (dispenser, boiler) and the gas does not have time to warm up and is quite cold, is this taken into account somewhere?!

FEDERAL STATE UNITARY ENTERPRISE

"ALL-RUSSIAN RESEARCH
INSTITUTE OF METROLOGICAL SERVICE"

(FSUE "VNIIMS")

STATE STANDARD OF RUSSIA

TYPICAL MEASUREMENT PROCEDURE
(DEFINITIONS) QUANTITY OF NATURAL GAS FOR
BY CONSUMERS IN THE TERRITORY OF THE RF

Registered in the Federal Register of Measurement Methods under No.
FR.1.29.2002.00690

MOSCOW
2002

DEVELOPED BY FSUE "VNIIMS"

PERFORMERS: B.M. Belyaev

A.I. Vereskov (topic leader)

APPROVED BY FSUE "VNIIMS" 09.12.2002

REGISTERED BY FSUE "VNIIMS" 09.12. 2002

INTRODUCED FOR THE FIRST TIME

TYPICAL MEASUREMENT PROCEDURE
(DEFINITIONS) QUANTITY OF NATURAL GAS FOR
DISTRIBUTION OF IMBALANCE BETWEEN SUPPLIERS AND
BY CONSUMERS IN THE TERRITORY OF THE RF

The methodology was developed taking into account the requirements of GOST R 8.563-96 GSI. Methods for performing measurements, MI 2525-99 “GSI. Recommendations on metrology approved by the State Scientific Metrological Centers of the State Standard of Russia”, “Rules for Gas Supply to the Russian Federation”, approved by the Government RF on February 5, 1998 under No. “Gas Accounting Rules”, registered with the Ministry of Justice of Russia on November 15, 1996 under No. 1198.

1 AREA OF USE

1.1. This methodology establishes the procedure for measuring (determining) the amount of natural gas to distribute the imbalance between suppliers and consumers in the Russian Federation using the “Natural Gas Balance” program.

2. METHOD OF MEASUREMENT

To measure (determine) the amount of natural gas during the imbalance distribution, statistical processing of the initial data is carried out:

2.1.1. Determine the structure of connections in the “supplier-consumer” system.

2.1.1.1. The total number n of suppliers and consumers (hereinafter referred to as participants in the accounting transaction or participants) is determined. Each participant is assigned one individual number, which can take a value from 1 to n.

2.1.1.2. The total number m of gas transfer points (hereinafter referred to as points) is determined and numbers from 1 to m are assigned to them.

2.2. The procedure for measuring (determining) gas quantity values ​​during accounting operations (hereinafter referred to as accounting values).

The determination of accounting values ​​is carried out in accordance with the method of statistical data analysis set out in the Appendix. The solution to the problem of determining accounting values ​​is algorithmic in nature and is implemented using the Natural Gas Balance program developed by the Federal State Unitary Enterprise VNIIMS. The algorithm for calculating accounting values ​​is given in the Appendix. All calculations according to the method are carried out using the program in automatic mode.

2.2.1. The data listed in clause . is processed using the “Natural Gas Balance” program according to one of the options in clause. As a result we get:

2.2.1.2. Corrective values ​​to the original measurement results, equal to the difference between the accounting and measured values.

2.2.1.3. The value of the imbalance of the initial measurement results at each point, equal to the difference between the sum of measurements of suppliers and the sum of measurements of consumers at this point (hereinafter referred to as the initial imbalance at the point).

2.4.1. The choice of one of the solution options for item (both options are implemented in the program) is left to the user of the technique. In doing so, we are guided by the following considerations.

Accounting values ​​uj determined according to clause . differ from the original measurement results vj by no more than the maximum permissible absolute error ∆j. This condition was introduced because its violation may cause disagreement among the participants in the accounting transaction. In this option, the imbalance distribution may be either complete or incomplete, depending on the specific numerical values ​​of the source data.

In this regard, a second option for solving the problem is provided - according to paragraph . The imbalance is distributed completely, and the condition of limited correction may be fulfilled or violated.

2.4.2. The best solution to the problem is to make the residual unbalance equal to zero with limited correction of the initial measurement results. To investigate this possibility, the program analyzes the source data. Receive

3.2. Mathematical software takes into account the special type and structure of data for specific tasks. The structure of connections in the “supplier-consumer” system must be specified by the customer software in the form of a diagram (drawing) and table and agreed with the developer. For an example of specifying the structure of connections, see appendices.

3.3. It is possible to select the value of the control parameter p (see appendix, p.), which affects the solution of the problem as follows: its value determines whether the imbalance will be distributed to a greater extent between the participants in the accounting transaction, who account for large quantities, or its distribution will be more even among all participants. Based on this, select the most appropriate parameter value in the range specified in paragraph. The following options are possible.

3.3.1. When developing a program, a specific parameter value is selected and recorded.

3.3.2. The results of data analysis and recommendations for choosing the p value obtained by the program are used. A statistical hypothesis is checked about the correspondence of the errors of the measurement results to the normal distribution (the check is performed by the program in automatic mode). If the hypothesis is accepted, the recommended value is p = 2.

3.3.4. The sequence of actions formulated in paragraph 1 is implemented by the program automatically.

3.4. It is possible to record the initial measured (or determined by consumption standards) values ​​of the amount of gas for some of the participants. These values ​​are included in the source data, but are not adjusted (this means that the accounting values ​​are equal to the values ​​in the source data, which are used to calculate the imbalance value and remain unchanged in the process of solving the problem). When making payments under the program, this possibility can be implemented in relation to any of the participants, in particular, when supplying gas to household consumers.

4.4. When making measurements with gas meters without temperature compensation in accordance with GOST R 50818-95 “Diaphragm volumetric gas meters,” correction factors are used to bring the measured volume of gas to standard conditions in accordance with MI 2721-2002 “Typical methodology for performing measurements with membrane gas meters without temperature compensation.”

4.5. Measurement conditions. When performing measurements, the following conditions are observed.

4.5.1. Working gas - natural gas - according to GOST 5542-87 “Natural flammable gases for industrial and municipal purposes.”

4.5.2. Operating conditions: the passport data of the measuring instrument corresponds to the actual operating conditions for the given region.

4.6. Processing of measurement results.

4.6.1. To obtain accounting values, correction values ​​(equal to the difference between the accounting and measured values), correction coefficients to measurement results (equal to the ratio of the accounting value to the measured value), the data listed in paragraph is processed according to the method described in section.

4.6.2. The calculation is carried out using the Natural Gas Balance program.

4.6.3. Accounting values ​​for the amount of gas and correction factors for measurement results are calculated and applied by the operating organizations of the gas distribution system.

4.6.4. An example of calculating accounting values, correction values, correction factors for measurement results is shown in the Appendix.

4.7. Registration of measurement results and calculation of accounting values.

4.7.2. The information listed in paragraph is stored in a computer database of operating organizations of the gas distribution system.

APPENDIX A

The calculation example is based on the Natural Gas Balance program developed by the Federal State Unitary Enterprise VNIIMS.

It is required to determine accounting values ​​and distribute the imbalance in the amount of gas based on the measurement results for the reporting period in the “supplier-consumer” system with the structure of connections shown in the figure in the appendix. The diagram shows 10 participants in the accounting operation and 3 gas transfer points. All participants are involved in the distribution of imbalance. In the example, the numbering of participants shown in the figure is adopted.

Raw numerical measurement data vj(m3) and error limits ∆ j the following:

In accordance with this scheme and rule, a table is formed. The first line corresponds to the first point. 1 is placed in the first and second positions of the first line, because These positions correspond to suppliers; -1 is placed in the third, fourth and fifth positions, because these positions correspond to consumers; 0 is placed in the remaining positions of the first line, since participants with numbers 6 - 10 are not related to the first point. The lines corresponding to the second and third paragraphs are filled in similarly. Get the table:

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