JP6524011B2 - Vibration diagnostic apparatus and vibration diagnostic method - Google Patents

Description

  The present invention relates to an excitation diagnostic apparatus and an excitation diagnostic method. More specifically, the present invention relates to a technique for measuring vibration characteristics of a rotating body of a rotary machine such as a horizontal axis multistage pump.

  Horizontal axis multistage pumps are arranged in oil fields, thermal power plants and the like. The horizontal axis multi-stage pump is a rotary machine that rotates a centrifugal impeller composed of a plurality of stages with a rotary shaft to generate a centrifugal force, and raises the pressure of fluid by the centrifugal force. In such a rotating machine, a rotating body is supported by a bearing and rotates. The rotating body has unique vibration characteristics. And with the aged deterioration of a rotary body or a bearing, the vibration characteristic changes. There are many techniques for grasping such vibration characteristics of a rotating body.

  The vibration diagnostic apparatus with a vibrating function disclosed in Patent Document 1 applies a vibrating force to a large rotating machine such as a turbine or a pump, and acquires a vibrational response from a sensor attached to the rotating machine. Then, the vibration characteristic of the rotary machine is acquired based on the excitation force and the vibration response. The operating rotational speed of large rotating machines is relatively low. However, the vibration diagnostic apparatus with the excitation function of Patent Document 1 can generate an excitation force having a frequency higher than the operation rotational speed. Therefore, regardless of the operating state (during stop, during operation), for example, even when the natural frequency is present in the region of the rotational speed higher than the operating rotational speed, the natural frequency can be specified.

  The vibration characteristic measuring device of Patent Document 2 applies an excitation force to a rotating body via a non-contact bearing, and acquires the amplitude of the rotating body from a sensor. Then, the vibration characteristic of the rotating body is acquired based on the excitation force and the amplitude. The excitation force that can be applied to the rotating body at this time includes vibration that cancels the unbalanced movement of the rotating body. Then, when detecting the response of the rotating body by the excitation force, the margin with respect to the allowable value of the amplitude becomes large. Therefore, for example, when the vibration characteristic is examined in the condition where the fluid flows around the rotating body, the seal for preventing the backflow of the fluid is not broken.

JP-A-8-15100 Patent No. 5827492

  For example, in the seal mechanism (details described later) included in the horizontal axis multistage pump described above, when the destabilizing force is generated due to leakage of high pressure water, abnormal flow, etc., this destabilizing force is Affects stability. Of course, the horizontal axis multistage pump is designed to generate a stabilizing force which exceeds this destabilizing force. However, when the destabilizing force exceeds the stabilizing force, self-oscillation called seal whirl occurs. The self-excited vibration occurs at the natural frequency of the “primary bending mode” (details described later) having the smallest natural frequency among a plurality of natural modes. Then, in order to predict the occurrence of self-excited vibration, it is necessary to grasp the vibration characteristic of the primary bending mode of the rotating body.

  By the way, in the vibration of the primary bending mode actually measured, two vibrations overlap and are included. One of them is the vibration of the pure bending mode (detailed later) and the other is the vibration of the rigid body mode (detailed later). That is, in order to predict the occurrence of self-excited vibration caused by the seal whirl, it is necessary to accurately grasp the vibration characteristics of the pure bending mode and the rigid body mode.

The vibration characteristics of the pure bending mode and the rigid body mode should be reflected in an overlapping manner in the vibration characteristics analyzed by the vibration diagnostic device with vibration function of Patent Document 1 and the vibration characteristic measuring device of Patent Document 2 . However, neither Patent Document 1 nor Patent Document 2 has a viewpoint of analytically grasping the pure bending mode and the rigid body mode, and a separate measure is necessary to accurately predict the self-excited vibration caused by the seal whirl. there were.
Then, an object of the present invention is to accurately predict the occurrence of self-oscillation of the rotating body due to the seal whirl.

The excitation diagnostic apparatus according to the present invention comprises a magnetic bearing for non-contacting supporting the shaft end of the rotating body of the rotary machine and applying an oscillating force to the rotating body according to a predetermined excitation control signal, and a coupling of the magnetic bearing or the rotary machine A vibration measurement unit for measuring the vibration of the rotating body at three positions in total of two positions supporting the rotating body other than the magnetic bearing and a current supply for supplying current to the magnetic bearing An excitation / response processing unit that outputs to the current supply unit an excitation control signal for controlling the magnetic bearing to excite the rotating body, and measures a vibration response to the excitation control signal of the rotating body; Bei example a vibration-response processor pressurized shall be performed from the vibration response at any position of the coupling of magnetic bearing or rotating machine, a signal is subtracted the vibration response at the position of the two bearings, the It features.
Other means will be described in the form for carrying out the invention.

  According to the present invention, it is possible to accurately predict the occurrence of self-excited vibration of the rotating body due to the seal whirl.

It is a figure explaining the structure of a horizontal axis multistage pump. It is a figure explaining the composition of an excitation diagnostic device. It is a figure explaining the centrifugal force by a mass concentration point. It is a waveform of the time series of vibration in case a rotating body carries out unbalanced rotation. It is a figure explaining natural frequency. It is a figure explaining fluid force of clearance. It is a figure which shows the amplitude of primary bending mode. It is a figure which shows the amplitude of pure bending mode. It is a figure which shows the amplitude of rigid body mode. It is a figure explaining the position and number of objects of the vibration measurement part of this embodiment. It is a figure which shows the relationship between rotational speed and excitation frequency.

  Hereinafter, a mode for carrying out the present invention (referred to as “this embodiment”) will be described with reference to the drawings and the like, with an example of attaching a vibration diagnosis device to a horizontal axis multistage pump. The vibration diagnosis apparatus is not limited to the horizontal axis multistage pump, and can be attached to a rotary machine (turbine, motor, compressor, etc.) having a rotary body such as a rotary shaft.

(Horizontal axis multistage pump)
The structure of the horizontal axis multi-stage pump 50 will be described with reference to FIG. The horizontal axis multi-stage pump 50 has a rotating shaft 51, a centrifugal impeller 53, bearings 52a, bearings 52b, bearings 52c, a housing 54, an inlet 54a, an outlet 54b, a sealing mechanism 55, and a coupling 56. The rotating shaft 51 is rotationally driven by a driving source (not shown) such as a turbine or an electric motor connected via the coupling 56.

  A multistage rotary impeller 53 is attached to the rotary shaft 51. When a fluid such as water is injected into the housing 54 from the inlet 54a, it contacts the root (portion close to the rotation shaft 51) of the first stage rotary impeller 53 (from the left in FIG. 1). Then, the fluid receives the centrifugal force generated by the first stage rotary impeller 53, and moves to the tip of the first stage rotary impeller 53 (a part far from the rotary shaft 51), and further, the second stage The base of the rotary impeller 53 is guided.

  Then, the fluid receives the centrifugal force generated by the second stage rotary impeller 53, moves to the tip of the second stage rotary impeller 53, and is guided to the root of the third stage rotary impeller 53. Be done. The fluid repeats such movement and is eventually discharged out of the housing 54 from the outlet 54 b. Naturally, the pressure at the discharge of the fluid is greater than the pressure at the time of injection.

  The bearing 52a and the bearing 52b support the rotating shaft 51 in the circumferential direction. The bearing 52c sandwiches the rotary plate projecting from the rotary shaft 51 in the circumferential direction from the left and right direction of the drawing, and supports the rotary shaft 51 in the axial direction. The bearing 52a, the bearing 52b, and the bearing 52c may or may not be in contact with the rotary shaft 51 or the rotary plate. A magnetic bearing exists as a type of bearing that supports the rotating shaft 51 without contacting the rotating shaft 51 or the like.

  When the bearing 52a and the bearing 52b are magnetic bearings, the bearing 52a and the bearing 52b float and support the rotating shaft 51 in the air by the magnetic force generated by the current flowing through its own coil. When the bearing 52c is a magnetic bearing, the bearing 52c suspends and supports the rotating plate at a certain position by the magnetic force generated by the current flowing through the coil.

  The direction of the rotation axis 51 is taken as the Z axis, the horizontal direction among the directions orthogonal to the Z axis is taken as the X axis, and the vertical direction is taken as the Y axis. The bearing 52c fixes the position of the rotating shaft 51 in the Z-axis direction, and the bearing 52a and the bearing 52b fix the positions of the rotating shaft 51 in the X-axis and Y-axis directions. Among the above-described configurations, a configuration that rotates integrally with the rotation shaft 51 is referred to as a “rotating body”. The rotating body includes a rotating shaft 51 and a centrifugal impeller 53. Among the above-described configurations, a configuration that is stationary with respect to the rotation shaft 51 is referred to as a "stationary body". The stationary body includes a housing 54 and a sealing mechanism 55.

  When the rotating body rotates while in contact with the stationary body, the constituent parts wear. Therefore, a clearance for preventing contact is provided between the rotating body and the stationary body. Of course, a space that is to be an original passage of fluid is provided between the rotating body and the stationary body. Such a space is not called a gap. High pressure fluid may leak from the original passage into the contact prevention gap. When such a leak occurs, the volumetric efficiency of the horizontal axis multistage pump 50 decreases. Therefore, the seal mechanism 55 is disposed at an appropriate position so as to seal the gap between the stationary body and the rotating body.

  For example, the seal mechanism 55 is attached to the housing 54 so as to seal the gap between the housing 54 and the centrifugal impeller 53 at positions of both ends of the centrifugal impeller 53 in the Z-axis direction. . Although these sealing mechanisms 55 appear as a total of 18 rectangles in FIG. 1, they are actually nine rings arranged along the inner circumference of the housing 54 and perpendicular to the Z axis.

  Further, on the outlet 54 b side of the housing 54, a sealing mechanism 55 is attached to the housing 54 so as to seal a gap between the housing 54 and the rotation shaft 51. Although this sealing mechanism 55 looks like an L-shape in total of two in the figure, it is actually a single collared men's hat-shaped ring disposed along the inner periphery of the housing 54 perpendicularly to the Z axis. Thus, the sealing mechanism 55 prevents the high pressure fluid from leaking.

(Excitation diagnostic device)
The configuration of the excitation diagnostic apparatus 1 will be described with reference to FIG. The excitation diagnostic apparatus 1 is an apparatus externally attached to the horizontal axis multi-stage pump 50 in a manner. The vibration diagnosis apparatus 1 includes a magnetic bearing 11, a vibration measurement unit 12, a current supply unit 13, a vibration / response processing unit 14, and a cable connecting these components. The dashed cable carries the signal and the solid cable carries the power.

  There are three vibration measurement units 12, and these are a vibration measurement unit 12a, a vibration measurement unit 12b, and a vibration measurement unit 12c. The vibration measuring unit 12a acquires, in time series, a locus drawn by the center of the rotation shaft 51 on the XY plane at the position of the bearing 52a on the Z axis. The data acquired in this way is a time-series waveform itself in which the center of the rotation axis 51 is drawn on the XY plane, and it is natural that the shape of this waveform is specified by the amplitude, period and phase.

  In principle, the vibration measurement unit 12a is mounted at the position of the bearing 52a on the Z-axis. However, if this is not possible due to the connection between facilities, it is sufficient that the vibration measurement unit 12a be mounted near the position of the bearing 52a on the Z axis. Even in that case, it is preferable that only the sensor part that acquires the locus in time series is attached to the position of the bearing 52a on the Z axis (the same applies to the vibration measuring unit 12b and the vibration measuring unit 12c described later).

  The vibration measuring unit 12b acquires, in time series, a locus drawn by the center of the rotation shaft 51 on the XY plane at the position of the bearing 52b on the Z axis. The vibration measurement unit 12c acquires, in time series, a locus drawn by the center of the rotation shaft 51 on the XY plane at the position of the magnetic bearing 11 on the Z axis. The vibration measuring unit 12a, the vibration measuring unit 12b, and the vibration measuring unit 12c send time-series trajectories of the rotation axis 51 drawn on the XY plane to the excitation and response processing unit 14 at the respective positions on the Z axis.

  The magnetic bearing 11 applies an excitation force to the rotating shaft 51. The magnetic bearing 11 has the structure of the magnetic bearing described above, generates a magnetic force by causing the current received from the current supply unit 13 to flow to its own coil, and the magnetic force generates an excitation force on the XY plane with respect to the rotating shaft 51. Contactlessly give. The excitation force may be any force, but typically it is a force that swings the rotation shaft 51 so that the center of the rotation shaft 51 draws a circle on the XY plane.

  The magnetic bearing 11 has, for example, two coils horizontally opposed in the X direction with the rotary shaft 51 interposed therebetween, and has two coils vertically opposed in the Y direction. The excitation / response processing unit 14 generates four cosine wave signals having phases shifted by 90 degrees each having an arbitrary period and amplitude. Then, the vibration / response processing unit 14 sends a cosine wave signal to the current supply device 13 as a vibration control signal. The frequency of the cosine wave indicated by the excitation control signal is called "excitation frequency". The excitation frequency is the number of oscillations per unit time when the rotary shaft 51 receives an excitation force.

  The current supply unit 13 generates a current having a waveform of the cosine wave signal sent from the vibration / response processing unit 14 and sends it to the magnetic bearing 11. The magnetic bearing 11 causes the sent current to flow through the four coils. Then, at the position of the magnetic bearing 11 on the Z axis, the magnetic bearing 11 applies a force to the rotating shaft 51 such that the center of the rotating shaft 51 draws a circle on the XY plane.

(Force on the rotating body)
As forces applied to the rotating body other than the excitation force, there exist centrifugal force at a mass concentration point (hereinafter, also simply referred to as “centrifugal force”) and fluid force of clearance (hereinafter, simply referred to as “fluid force”). The rotating body is, of course, designed such that the circumferential mass concentration point is located on the Z axis. However, in terms of construction, it is very difficult to create a rotating body in this manner, and in fact, the position of the mass concentration point may be slightly deviated from the Z axis. Furthermore, even if the position of the center of gravity is on the Z-axis at the start of operation, deviation may occur after a certain point due to deformation due to aging of the rotating body or partial loss.

(Centrifugal force by mass concentration point)
The centrifugal force according to the mass concentration point will be described along FIG. When the mass concentration point of the rotating body deviates from the Z axis (axial center) due to the above-mentioned deformation or the like, a centrifugal force in the circumferential direction is generated. Then, the rotating body vibrates minutely. Such vibrations are called "unbalanced vibrations". The unbalanced vibration can be modeled as a circular motion of the mass concentration point G in FIG.

  When the rotating body having the mass gravity point G rotates, centrifugal force acts on the mass concentration point G, and the rotating body is displaced in the direction of the mass concentration point G. Such displacement occurs continuously with the rotation of the rotating body, causing unbalance vibration. The number of revolutions of the mass concentration point G per unit time is the unbalanced rotational frequency. As the rotational speed of the rotating body is changed by the drive source, the unbalanced rotational frequency also changes, but the unbalanced rotational frequency is always equal to the rotational speed of the rotating body.

  FIG. 4 is a time-series waveform of vibration of a rotating body at a certain rotational speed (unbalanced rotational frequency). The magnitude of the unbalance vibration is the amplitude Am in FIG. As the rotational speed of the rotating body changes, the amplitude also changes. At this time, the amplitude significantly increases at a specific rotational speed as compared to the rotational speeds before and after that. Such rotational speed is called the natural frequency of the rotating body.

  The natural frequency will be described with reference to FIG. The horizontal axis in FIG. 5 is the rotational speed of the rotating body. The vertical axis is the amplitude. There are two peaks in FIG. 5 on the vertical axis. The value on the horizontal axis corresponding to each peak is the natural frequency.

  Although only two natural frequencies are displayed in FIG. 5, generally, two or more natural frequencies of any object, not limited to the rotating body, are present. Then, an object vibrating at each natural frequency exhibits a shape unique to that natural frequency. Usually, a plurality of natural frequencies are called a first order natural frequency, a second order natural frequency, a third order natural frequency,... In ascending order of frequency. In general, the shapes exhibited by vibrating objects are referred to as a first order mode, a second order mode, a third order mode,... In ascending order of frequency. As the order of first order, second order, third order, etc. increases, the number of so-called "nodes (fixed points)" increases.

  The rotating body of the present embodiment is supported at two places in the axial direction by bearings 52a and 52b. Depending on the rotating machine, the number of bearings supporting the rotating body may be three or more. In any case, the number of nodes in the primary mode is equal to the number on which the rotating body is supported.

  In that sense, the mode oscillating as shown in FIG. 7 (details described later) is the “primary mode” for the rotating body of the present embodiment. In the field other than the rotary machine, for example, the shape in the case where an object fixed at one place is bent with the one place as a fulcrum may be called “primary mode”. In order to clarify the distinction from this, in the present embodiment, the shape of FIG. 7 is also referred to as “primary bending mode”.

(Fluid force of clearance)
The fluid force of the clearance will be described along FIG. FIG. 6 is a view of the rotating body as viewed from the Z-axis direction. Due to the centrifugal force due to the mass concentration point, the center of the rotating body deviates from the position of the Z axis (is eccentric). Fluid flows in the gap (clearance, shaded portion in FIG. 6) between the stationary body and the rotating body. When the rotating body rotates inside the stationary body at the rotational speed N, the fluid in the gap rotates at the rotational speed λN.

  Furthermore, due to the force from the fluid rotating at the rotational speed λN, the rotating body also revolves at the rotational speed λN. At this time, force (fluid force) is applied to the rotating body by moving the fluid in a swirling manner. Such fluid movement is called seal whirl. Λ (0 <λ <1) of a fluid is a constant value determined by the density, temperature, viscosity, etc. of the fluid. Here, λN means λ × N.

  When the frequency λN of the vibration generated by rotation (rotation) of the fluid at the rotational speed λN becomes equal to the natural frequency of the rotating body, the amplitude of the rotating body becomes remarkably large. It is a feature of the present embodiment to predict the frequency N of the rotating body in such a state. The revolution of the rotating body of FIG. 6 is represented by the “rigid body mode” without deformation of the rotation axis. FIG. 9 is a diagram showing a rigid body mode. When the rigid body mode frequency λN becomes equal to the first-order natural frequency of the rotating body, the amplitude of the vibration of the rotating body increases. This is self-oscillation caused by the seal whirl.

  The fluid force of the clearance not only causes the self-excited vibration but also affects the vibration characteristics of the rotating body. Specifically, the fluid force changes the stiffness (spring) and damping of the sealing mechanism 55, the bearing 52a and the bearing 52b. Then, the natural frequency of the rotating body also changes. The rigidity (spring) and damping of the sealing mechanism 55, the bearing 52a and the bearing 52b change according to the rotational speed of the rotating body. After all, when the rotational speed changes, the natural frequency of the rotating body also changes.

  FIG. 7 shows the magnitude of the amplitude of the rotating body when self-excited vibration occurs at each position of the Z axis. In the primary bending mode of FIG. 7, the rotating body vibrates with deformation (U-shape) with two points shifted slightly outward from the position of the bearing on the Z-axis. If the amplitude of the rigid body mode (FIG. 9) resulting from the seal whirl is subtracted from the amplitude of the primary bending mode of FIG. 7, the amplitude as shown in FIG. 8 remains. The mode of FIG. 8 is called "pure bending mode". "Net" here means "net".

  In the rigid body mode of FIG. 9, the rotating body vibrates without deformation. And there is no point corresponding to the clause. That is, the rigid body mode is not influenced by the shape of the rotating body or the support point. That is, it can be said that the mode of vibration caused by the seal whirl is the rigid body mode of FIG. In the pure bending mode of FIG. 8, the rotating body is fixed at the position of the bearing 52a and the bearing 52b on the Z-axis, and vibrates with deformation (U-shape). A mode obtained by subtracting the amplitude of the rigid body mode caused by the seal whirl from the amplitude of the primary bending mode in FIG. 7 is a pure bending mode.

(Position and number of vibration measurement units)
The position and number of the vibration measurement units 12 according to the present embodiment will be described with reference to FIG. This is a premise of the processing procedure (details described later) performed by the vibrating vibration device 1. In the present embodiment, the vibration measurement unit 12 is disposed not only at the position of the magnetic bearing 11, but also at the positions of the bearing 52a and the bearing 52b of the Z axis. The reason is as follows.

Even if the vibration measurement unit 12 is disposed only at the position of the Z-axis magnetic bearing 11 (right end in FIG. 10), the vibration response to the excitation force can be measured. However, the value of the vibration response in the magnetic bearing 11 is originally small and it is difficult to measure a significant value. Even if it can be measured, this position is largely influenced by the rigid body mode, and it is difficult to extract the vibration response of the pure bending mode.
-At the position of the magnetic bearing 11, it is difficult to measure the vibration response of the rigid body mode only. Although details will be described later, the vibration response of only the rigid body mode can be clearly measured at the positions of the bearings 52a and 52b. Then, as a result of subtraction, it is possible to clearly measure the vibration response of the pure bending mode.

The processing procedure performed by the vibration / response processing unit 14 of the vibration / vibration device 1 of the present embodiment is as follows. In addition, it is a premise of the following processing procedure that the fluid force resulting from the seal whirl is given to the rotating shaft 51.
(Step 1)
The vibration / response processing unit 14 receives a measurement signal of the rotational speed N of the rotating body. In this state, the vibration / response processing unit 14 applies the vibration force of the vibration frequency に お い て in the magnetic bearing 11 to the rotating shaft 51 via the magnetic bearing 11. The excitation / response processing unit 14 gradually increases the value of ν. Then, the rotation shaft 51 vibrates at the same frequency as the vibration frequency ν. The excitation / response processing unit 14 fixes the excitation frequency 、 and proceeds to step 2.

(Step 2)
The vibration / response processing unit 14 receives vibration data (for example, the value of amplitude) from the vibration measurement unit 12 c, and based on the vibration control signal generated by itself and the received vibration data, the vibration response S ₁₁ (ν Calculate). Similarly, the excitation / response processing unit 14 calculates S _{52 a} (ν) and S _{52 b} (ν). S ₁₁ (ν) is a vibration response at the position of the magnetic bearing 11, S _52a (ν) is a vibration response at the position of the bearing 52a, and S _52b (ν) is a vibration response at the position of the bearing 52b is there.

(Step 3)
The excitation / response processing unit 14 obtains the vibration response Z (v) of the pure bending mode using Equation 1.

Z (v) = S ₁₁ (v)-(S _52a (v) + (S _52b (v) -S _52a (v)) d ₂ / d ₁ )
(Formula 1)

As shown in FIG. 10, _{d 1} is the distance between the bearing 52a and the bearing 52 b, _{d 2} is the distance between the bearing 52a and the magnetic bearings 11. In the first term S ₁₁ (ν) on the right side of Equation 1, the vibration response of the pure bending mode and the vibration response of the rigid body mode are reflected in an overlapping manner. On the other hand, the second term of the right side of the expression _{1 "S 52a (ν) +} (S 52b (ν) -S 52a (ν)) d 2 / d 1" can be said to be vibration response of the rigid body modes. Therefore, Z (v) on the left side, which is the result of subtracting the second term from the first term, is the vibrational response of the pure bending mode.

(Step 4)
The excitation / response processing unit 14 represents the vibration response Z (v) of the pure bending mode by the real part and the imaginary part of the complex number as shown in Equation 2. The equation 2 is a so-called coquad function, and the right side of the equation 2 is obtained by processing the right side of the equation 1 and expressing it as a complex number. j is an imaginary unit, Z _R (ν) is a real part, and Z _I (ν) is an imaginary part. Then, the vibration / response processing unit 14 fluctuates the vibration frequency 、 to obtain a vibration frequency よ う such that the real part Z _R (ν) = 0 as the natural frequency ω ₁ of the primary bending mode. Furthermore, the excitation / response processing unit 14 obtains an excitation frequency よ う that makes the imaginary part Z _I (ν) = 0 as the frequency λ N of the rigid body mode.

Z (ν) = Z _R (ν) + jZ _I (ν) (Expression 2)

“Z _R (ν) = 0” is a conditional expression in which the motion equation with respect to the rotation axis 51 has a solution. “Z _I (ν) = 0” is a conditional expression in which the fluid force of the clearance becomes an unstable force. When Z _R (ν) = 0, the excitation frequency は is equal to the natural frequency ω ₁ of the primary bending mode. Furthermore, Z _I (ν) can also be expressed as Equation 3. D on the right side of Equation 3 is a coefficient including damping of the seal mechanism 55, the bearing 52a, and the bearing 52b.

Z _I (ν) = D (ν−λN) (Equation 3)

When the left side of Equation 3 is 0, the right side of Equation 3 is also 0. Then, on the right side of Equation 3, either D = 0 or ν−λN = 0 should hold. Of these, D is usually D ≠ 0. Therefore, −−λN = 0 holds, and eventually, when Z _I (ν) = 0, ν = λN.

The excitation / response processing unit 14 increases the rotational speed N with an arbitrary step width, and repeats the processing of steps 1 to 4 by a predetermined number (for example, m times). Then, m combinations (first combination) of “rotational speed N” and “natural frequency ω ₁ of primary bending mode” are obtained. Then, m combinations of “rotational speed N” and “rigid body mode frequency λN” (second combination) are also obtained.

(Step 5)
The excitation / response processing unit 14 dots m points indicating the first combination on a coordinate plane (FIG. 11) having a rotational speed N on the horizontal axis and an excitation frequency ν on the vertical axis, Dot m points to indicate the second combination. Usually, the locus of the first combination (● in FIG. 11) is a straight line parallel to the horizontal axis, and the scale of the point of intersection with the vertical axis of the straight line is ω ₁ . The locus of the second combination (o in FIG. 11) is a straight line passing through the origin, and its inclination is λ.

(Step 6)
The excitation / response processing unit 14 obtains horizontal axis coordinates of an intersection point of the two straight lines. This value is a value of N such that ω ₁ = λ N (the natural frequency of the primary bending mode is equal to the frequency of the rigid body mode). At the value of N (▲ in FIG. 11), the rotating shaft 51 starts self-oscillation due to the seal whirl.

(principle)
The principle behind the above procedure is that when the rigid body mode frequency λ N becomes larger than the natural bending frequency ω ₁ of the primary bending mode, self-excited vibration caused by the seal whirl occurs.

The value of S _52a (ν) in Equation 1 and FIG. 10 is often equal to the value of S _52b (ν). Therefore, Equation 1 can be simplified as Equation 4 below.

_{Z (ν) = S 11 (} ν) -S 52a (ν)
Or Z (ν) = S ₁₁ (ν) −S _{52 b} (ν) (Equation 4)

(Reconfirmation of the position and number of vibration measurement units)
As described above, the reason for increasing the number of vibration measurement units 12 is to facilitate measurement of the vibration response of the pure bending mode. For that purpose, it is desirable to arrange the vibration measurement unit 12 at a plurality of (2, 3,...) Positions of the Z axis. Usually, it is easy to arrange the vibration measurement unit 12 at the position of the two bearings 52a and 52b of the horizontal axis multistage pump. The problem is where to place the third vibration measurement unit 12.

  In the above, the example which arrange | positions the 3rd vibration measurement part 12 in the position of the magnetic bearing 11 was demonstrated. However, the third position is not limited to this. Since it is not possible to place the vibration measurement unit 12 between two bearings of a horizontal axis multistage pump in general, a suitable position outside the two bearings 52a and 52b will be selected as the third position . For example, the position of the Z-axis coupling 56 is preferable as the third position.

  A rotary machine such as a horizontal axis multi-stage pump often has a vibration measurement unit at the position of the bearing originally. In this case, the vibration measurement unit 12 of the vibration diagnosis apparatus 1 may receive the data of the vibration measured by the vibration measurement unit of the rotary machine.

(Effect of the embodiment)
The excitation diagnostic apparatus of the present embodiment has the following effects.
(1) The vibration diagnosis apparatus can be easily externally attached to an existing horizontal axis multistage pump or the like.
(2) The excitation diagnostic apparatus can easily extract the portion corresponding to the pure bending mode in the vibration response of the rotating body.
(3) The vibration diagnostic apparatus can accurately predict the occurrence of self-oscillation of the rotating body due to the seal whirl by dividing the vibration response of the pure bending mode into the real part and the imaginary part.

DESCRIPTION OF SYMBOLS 1 Vibration diagnostic apparatus 11 Magnetic bearing 12a, 12b, 12c Vibration measurement part 13 Current supply part 14 Vibration / response processing part 51 Rotating shaft 52a, 52b, 52c Bearing 53 Centrifugal impeller 54 Housing 54a Inlet 54b Outlet 55 Sealing mechanism 56 Coupling

Claims (6)

A magnetic bearing that supports the shaft end of the rotating body of the rotating machine in a non-contact manner and applies an oscillating force to the rotating body by a predetermined excitation control signal;
Vibration to measure the vibration of the rotor at a total of three locations of the magnetic bearing or the coupling of the rotary machine and the position of two bearings supporting the rotor other than the magnetic bearing Measurement unit,
A current supply unit for supplying current to the magnetic bearing;
An excitation / response process that outputs the excitation control signal that controls the magnetic bearing to excite the rotating body to the current supply unit, and measures the vibration response of the rotating body to the excitation control signal. Department,
Bei to give a,
The excitation / response processing unit
Performing signal processing to subtract the vibration response at the positions of the two bearings from the vibration response at any position of the magnetic bearing or the coupling of the rotary machine;
An excitation diagnostic apparatus characterized by The current supply unit
The vibration control signal is received from the vibration / response processing unit, a current is generated based on the received vibration control signal, and the generated current is supplied to the magnetic bearing.
The magnetic bearing is
Receiving the current from the current supply unit, and applying an excitation force of a predetermined excitation frequency to the rotating body based on the excitation control signal by the received current;
The excitation diagnostic apparatus according to claim 1, characterized in that The excitation / response processing unit
Measuring a vibration response of the rotating body having a frequency equal to the vibration frequency;
The excitation diagnostic apparatus according to claim 2, characterized in that The excitation / response processing unit
Change the excitation frequency,
Dividing the vibration response subjected to the signal processing into a real part and an imaginary part;
The excitation frequency at which the real part becomes zero is determined as the natural frequency of the primary bending mode,
Determining the excitation frequency at which the imaginary part becomes zero as the frequency of the rigid body mode,
The excitation diagnostic apparatus according to claim 3 , characterized in that The excitation / response processing unit
Determining the rotation speed at which the natural frequency of the primary bending mode obtained is equal to the frequency of the rigid body mode obtained as the rotation speed at which the self-excited vibration of the rotating body is generated;
The excitation diagnostic apparatus according to claim 4 , characterized in that The excitation and response processing unit
Outputting a predetermined excitation control signal for controlling the magnetic bearing so as to excite the rotating body of the rotary machine to the current supply unit;
The current supply unit
Supplying an electric current to the magnetic bearing that supports the shaft end of the rotating body in a non-contact manner;
The magnetic bearing is
Applying an excitation force to the rotating body by the excitation control signal;
The vibration measurement unit
Measuring the vibration of the rotor at a total of three locations of the magnetic bearing or the coupling of the rotary machine and the position of two bearings supporting the rotor other than the magnetic bearing When,
The vibration / response processing unit
By subtracting the vibration response at the two bearing positions from the vibration response at any position of the magnetic bearing or the coupling of the rotary machine, the vibration response of the rotating body to the excitation control signal is obtained Measuring, and
A vibration diagnosis method of a vibration diagnosis apparatus comprising the vibration / response processing unit, the current supply unit, the magnetic bearing, and the vibration measurement unit.