JP2017173224A - Excitation diagnosis device and excitation diagnosis method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately predict the occurrence of self-excited vibration of a rotor due to seal whirl.SOLUTION: An excitation diagnosis device of the present invention comprises: a magnetic bearing for contactlessly supporting a shaft end of a rotor of a rotary machine and applying an excitation force to the rotor by a prescribed excitation control signal; a vibration measurement unit for measuring the vibration of the rotor at one of coupling positions of the magnetic bearing or the rotary machine and a total of three locations of two bearings other than the magnetic bearing that support the rotor; a current supply unit for supplying a current to the magnetic bearing; and an excitation-response processing unit for outputting to the current supply unit an excitation control signal for controlling the magnetic bearing so as to excite the rotor, and measuring a vibration response of the rotor to the excitation control signal.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a vibration diagnosis apparatus and a vibration diagnosis 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 multistage pump.

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

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

  The vibration characteristic measuring apparatus 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. And the vibration characteristic of a rotary body is acquired based on an excitation force and an amplitude. The excitation force that can be applied to the rotating body at this time includes vibrations that cancel out the unbalanced motion of the rotating body. Then, when detecting the response of the rotating body due to the excitation force, the margin for the allowable value of the amplitude increases. Therefore, for example, when the vibration characteristics are examined under the condition where the fluid flows around the rotating body, the seal for preventing the backflow of the fluid is not damaged.

JP-A-8-15100 Japanese Patent No. 5827492

  For example, in the sealing mechanism (described later in detail) provided in the above-described horizontal shaft multistage pump, when an unstable force is generated due to leakage of high-pressure water, abnormal flow, etc., this unstable force causes the rotation of the rotating shaft and centrifugal impeller. Affects stability. Of course, the horizontal multistage pump is designed to generate a stabilizing force that exceeds this destabilizing force. However, when the destabilizing force exceeds the stabilizing force, self-excited vibration called seal whirl occurs. The self-excited vibration is generated at a natural frequency of a “primary bending mode” (detailed 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 characteristics of the primary bending mode of the rotating body.

  By the way, the vibration of the primary bending mode actually measured includes two vibrations overlapping each other. One of them is vibration in a pure bending mode (detailed later), and the other is vibration in a rigid body mode (detailed later). That is, in order to predict the occurrence of self-excited vibration due to 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 analyzed by the vibration diagnostic apparatus with the vibration function of Patent Document 1 and the vibration characteristic measuring apparatus of Patent Document 2 may reflect the vibration characteristics of the pure bending mode and the rigid body mode in an overlapping manner. . However, neither Patent Document 1 nor Patent Document 2 has an aspect of analytically grasping the pure bending mode and the rigid body mode, and a separate measure is required to accurately predict the self-excited vibration caused by the seal whirl. there were.
Therefore, an object of the present invention is to accurately predict the occurrence of self-excited vibration of a rotating body caused by a seal whirl.

The vibration diagnosis apparatus of the present invention includes a magnetic bearing that supports a shaft end of a rotating body of a rotating machine in a non-contact manner and applies a vibrating force to the rotating body by a predetermined vibration control signal, and a coupling of the magnetic bearing or the rotating machine A vibration measuring unit that measures vibrations of the rotating body at a total of three positions, that is, the position of any one of the two bearings other than the magnetic bearing and the position of the two bearings that support the rotating body, and a current supply that supplies current to the magnetic bearing A vibration control signal for controlling the magnetic bearing so as to vibrate the rotating body, and a vibration / response processing section for measuring a vibration response to the vibration control signal of the rotating body, It is characterized by providing.
Other means will be described in the embodiment 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 | shaft multistage pump. It is a figure explaining the structure of a vibration diagnosing device. It is a figure explaining the centrifugal force by a mass concentration point. It is a time-sequential waveform of the vibration when the rotating body rotates unbalanced. It is a figure explaining a natural frequency. It is a figure explaining the fluid force of clearance. It is a figure which shows the amplitude of a primary bending mode. It is a figure which shows the amplitude of a pure bending mode. It is a figure which shows the amplitude of a rigid body mode. It is a figure explaining the position and number of a vibration measurement part of this embodiment. It is a figure which shows the relationship between a rotational speed and an excitation frequency.

  Hereinafter, a mode for carrying out the present invention (referred to as “the present embodiment”) will be described with a focus on an example in which a vibration diagnosis device is attached to a horizontal multistage pump with reference to the drawings. The vibration diagnosis device is not limited to a horizontal multistage pump, and can be attached to a rotating machine (a turbine, an electric motor, a compressor, or the like) having a rotating body such as a rotating shaft.

(Horizontal multistage pump)
The structure of the horizontal axis multistage pump 50 will be described with reference to FIG. The horizontal shaft multi-stage pump 50 includes a rotary shaft 51, a centrifugal impeller 53, a bearing 52a, a bearing 52b, a bearing 52c, a housing 54, an inlet 54a, an outlet 54b, a seal 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 a coupling 56.

  A multistage rotary impeller 53 is attached to the rotary shaft 51. When fluid such as water is injected into the housing 54 from the inlet 54a (from the left in FIG. 1), it comes into contact with the root of the first stage impeller 53 (portion close to the rotation shaft 51). 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 (the part far from the rotation shaft 51). It is guided to the root of the rotary impeller 53.

  Next, 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 further guides to the root of the third stage rotary impeller 53. Is done. The fluid repeats such movement, and is finally discharged out of the housing 54 through the outlet 54b. Of course, the pressure at the time of discharging the fluid is larger 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 rotating plate protruding in the circumferential direction from the rotating shaft 51 from the left and right directions in the figure, and supports the rotating shaft 51 in the axial direction. The bearing 52a, the bearing 52b, and the bearing 52c may be in contact with the rotating shaft 51 or the rotating plate, or may not be in contact with each other. There is a magnetic bearing 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 support the rotating shaft 51 suspended in the air by a magnetic force generated by a current flowing through its own coil. When the bearing 52c is a magnetic bearing, the bearing 52c floats 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 rotating shaft 51 is the Z axis, the horizontal direction among the directions orthogonal to the Z axis is the X axis, and the vertical direction is 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 position of the rotating shaft 51 in the X-axis and Y-axis directions. Among the configurations described above, a configuration that rotates integrally with the rotating shaft 51 is referred to as a “rotating body”. The rotating body includes a rotating shaft 51 and a centrifugal impeller 53. Among the configurations described above, a configuration that is stationary with respect to the rotating shaft 51 is referred to as a “stationary body”. The stationary body includes a housing 54 and a seal mechanism 55.

  When the rotating body rotates while in contact with the stationary body, the constituent parts are worn. Therefore, a clearance (clearance) for preventing contact is provided between the rotating body and the stationary body. Of course, a space 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-preventing gap. When such leakage occurs, the volumetric efficiency of the horizontal axis multistage pump 50 decreases. Therefore, a seal mechanism 55 is disposed at an appropriate position so as to seal a gap between the stationary body and the rotating body.

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

  Further, a seal mechanism 55 is attached to the housing 54 on the outlet 54 b side of the housing 54 so as to seal a gap between the housing 54 and the rotary shaft 51. Although the seal mechanism 55 looks like two L-shapes in the figure in the figure, it is actually a single men's hat-shaped ring with a collar arranged perpendicularly to the Z-axis along the inner periphery of the housing 54. Thus, the seal mechanism 55 prevents high pressure fluid from leaking out.

(Excitation diagnosis device)
The configuration of the vibration diagnosis device 1 will be described with reference to FIG. The vibration diagnosis device 1 is a device externally attached to the horizontal axis multistage pump 50. The vibration diagnosis device 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 them. Signals pass through the dashed cable, and power passes through the solid cable.

  There are three vibration measuring units 12, which are a vibration measuring unit 12a, a vibration measuring unit 12b, and a vibration measuring unit 12c. The vibration measurement 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 drawn on the XY plane by the center of the rotation axis 51, and naturally, the shape of this waveform is specified by the amplitude, period, and phase.

  In principle, the vibration measuring unit 12a is attached to 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 is attached in the vicinity of 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 trajectory in time series is attached to the position of the bearing 52a on the Z-axis (the same applies to the vibration measurement unit 12b and the vibration measurement unit 12c described later).

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

  The magnetic bearing 11 gives an excitation force to the rotating shaft 51. The magnetic bearing 11 has the structure of the magnetic bearing described above, and generates a magnetic force by causing the current received from the current supply unit 13 to flow through its own coil. Give without contact. The exciting force may be any force, but is typically a force that swings the rotating shaft 51 so that the center of the rotating shaft 51 draws a circle on the XY plane.

  The magnetic bearing 11 has, for example, two coils that are horizontally opposed in the X direction across the rotating shaft 51 and has two coils that are vertically opposed in the Y direction. The excitation / response processing unit 14 generates four cosine wave signals whose phases having an arbitrary period and amplitude are shifted by 90 degrees. In addition, the vibration / response processing unit 14 sends the 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 times that the rotating shaft 51 is shaken per unit time when receiving the excitation force.

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

(Force on rotating body)
There are a centrifugal force (hereinafter simply referred to as “centrifugal force”) due to a mass concentration point and a fluid force of clearance (hereinafter also simply referred to as “fluid force”) as forces applied to the rotating body other than the excitation force. The rotating body is naturally designed so that the mass concentration point in the circumferential direction is located on the Z axis. However, in construction, it is very difficult to create a rotating body in this way. In practice, the position of the mass concentration point may be slightly shifted from the Z axis. Furthermore, even when the position of the center of gravity is on the Z-axis at the start of operation, there may be a shift after a certain point due to deformation of the rotating body over time or partial loss.

(Centrifugal force due to mass concentration point)
The centrifugal force due to the mass concentration point will be described with reference to FIG. When the mass concentration point of the rotating body is deviated from the Z-axis (axial center) due to the deformation or the like, a circumferential centrifugal force is generated. Then, the rotating body vibrates minutely. Such vibration is called “unbalanced vibration”. 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 center point G rotates, a 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 continuously occurs as the rotating body rotates, and unbalanced vibration occurs. The number of times the mass concentration point G circulates per unit time is an unbalanced rotational frequency. When 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 the vibration of the rotating body at a certain rotational speed (unbalanced rotational frequency). The magnitude of the unbalanced vibration is the amplitude Am in FIG. As the rotational speed of the rotating body is changed, the amplitude also changes. At this time, the amplitude is significantly larger at a specific rotational speed than the rotational speeds before and after the specific rotational speed. Such a rotation speed is called a natural frequency of the rotating body.

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

  Although only two natural frequencies are displayed in FIG. 5, there are generally two or more natural frequencies of an arbitrary object, not limited to a rotating body. An object that vibrates at each natural frequency exhibits a shape unique to the natural frequency. Usually, a plurality of natural frequencies are called a primary natural frequency, a secondary natural frequency, a tertiary natural frequency,... In order of increasing frequency. In general, shapes exhibited by a vibrating object are called a primary mode, a secondary mode, a tertiary mode,. The greater the order, such as primary, secondary, tertiary,..., The greater the number of so-called “nodes (fixed points)”.

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

  In that sense, a mode that vibrates as shown in FIG. 7 (detailed later) is the “primary mode” for the rotating body of the present embodiment. In fields other than rotating machinery, for example, the shape in the case where an object fixed at one place bends around the one place as a fulcrum may be referred to as a “primary mode”. In order to make this distinction clear, in the present embodiment, the shape of FIG. 7 is also referred to as “primary bending mode”.

(Clearance fluid force)
The fluid force of clearance will be described with reference to FIG. FIG. 6 is a view of the rotator viewed from the Z-axis direction. Due to the centrifugal force due to the mass concentration point, the center of the rotating body is deviated (eccentric) from the Z-axis position. A fluid flows in a 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 rotation speed N, the fluid in the gap rotates at the rotation speed λN.

  Further, upon receiving a force from the fluid rotating at the rotational speed λN, the rotating body also revolves at the rotational speed λN. At this time, a force (fluid force) is exerted on the rotating body by moving the fluid in a vortex. Such fluid movement is called a seal whirl. Λ (0 <λ <1) of a fluid is a constant value determined by the density, temperature, viscosity, and the like of the fluid. Note that λN means λ × N.

  When the vibration frequency λN generated when the fluid rotates (spins) at the rotation speed λN becomes equal to the natural frequency of the rotation body, the amplitude of the rotation body becomes remarkably large. It is a feature of this embodiment that the vibration frequency N of the rotating body in such a state is predicted. The revolution of the rotating body in FIG. 6 is represented by a “rigid body mode” that does not involve deformation of the rotating shaft. FIG. 9 is a diagram illustrating the rigid body mode. When the rigid body mode frequency λN becomes equal to the primary natural frequency of the rotating body, the amplitude of vibration of the rotating body increases. This is self-excited vibration caused by the seal whirl.

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

  FIG. 7 shows the magnitude of the amplitude of the rotator when the rotator causes self-excited vibration for each Z-axis position. In the primary bending mode of FIG. 7, the rotating body vibrates with deformation (U-shaped) with two points shifted slightly outward from the position of the bearing on the Z axis. When the amplitude of the rigid body mode (FIG. 9) caused by 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 a “pure bending mode”. “Pure” here means “net”.

  In the rigid body mode of FIG. 9, the rotating body vibrates without being deformed. And there is no point corresponding to the node. That is, the rigid body mode is not affected by the shape of the rotating body and the support location. That is, it can be said that the vibration mode 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 positions of the bearings 52a and 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 the pure bending mode.

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

Even if the vibration measuring unit 12 is disposed only at the position of the Z-axis magnetic bearing 11 (the right end in FIG. 10), the vibration response to the excitation force can be measured. However, the vibration response value 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 greatly 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 only in the rigid body mode. 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, the vibration response of the pure bending mode can be clearly measured as a subtraction result.

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)
A measurement signal of the rotational speed N of the rotating body is input to the vibration / response processing unit 14. In this state, the vibration / response processing unit 14 applies a vibration force having a vibration frequency ν in the magnetic bearing 11 to the rotating shaft 51 via the magnetic bearing 11. The vibration / response processing unit 14 gradually increases the value of ν. Then, the rotating shaft 51 vibrates at the same frequency as the excitation frequency ν. The excitation / response processing unit 14 fixes the excitation frequency ν and proceeds to Step 2.

(Step 2)
The vibration / response processing unit 14 receives vibration data (for example, amplitude value) from the vibration measurement unit 12c, and based on the vibration control signal generated by itself and the received vibration data, the vibration response S ₁₁ (ν ) Is calculated. Similarly, the vibration / response processor 14 calculates S _52a (ν) and S _52b (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 vibration / response processing unit 14 obtains the vibration response Z (ν) in the pure bending mode using Equation 1.

Z (ν) = S ₁₁ (ν) − (S _52a (ν) + (S _52b (ν) −S _52a (ν)) d ₂ / d ₁ )
(Formula 1)

As shown in FIG. 10, d ₁ is a distance between the bearing 52 a and the bearing 52 b, and d ₂ is a distance between the bearing 52 a and the magnetic bearing 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 “S _52a (ν) + (S _52b (ν) −S _52a (ν)) d ₂ / d ₁ ” on the right side of Equation 1 can be said to be a vibration response in the rigid body mode. Therefore, Z (ν) on the left side, which is the result of subtracting the second term from the first term, is the vibration response in the pure bending mode.

(Step 4)
The vibration / response processing unit 14 expresses the vibration response Z (ν) in the pure bending mode by a complex real part and an imaginary part as shown in Equation 2. Equation 2 is a so-called quadrature function, and the right side of Equation 2 is a complex number expressed by signal processing of the right side of Equation 1. 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 varies the vibration frequency ν, and obtains the vibration frequency ν such that the real part Z _R (ν) = 0 as the natural frequency ω ₁ of the primary bending mode. Further, the excitation / response processing unit 14 obtains an excitation frequency ν such that the imaginary part Z _I (ν) = 0 as the frequency λN of the rigid body mode.

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

“Z _R (ν) = 0” is a conditional expression in which the equation of motion 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 ν is equal to the natural frequency ω ₁ of the primary bending mode. Furthermore, Z _I (ν) can also be expressed as in Equation 3. D on the right side of Equation 3 is a coefficient including attenuation of the seal mechanism 55, the bearing 52a, and the bearing 52b.

Z _I (ν) = D (ν−λN) (Formula 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, ν−λN = 0 holds, and when Z _I (ν) = 0, ν = λN.

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

(Step 5)
The excitation / response processing unit 14 dots m points indicating the first combination on a coordinate plane (FIG. 11) having the rotational speed N on the horizontal axis and the excitation frequency ν on the vertical axis. Dot m points indicating the second combination. Normally, the trajectory of the first combination (● in Fig. 11) becomes a straight line parallel to the horizontal axis, the scale of the intersection of the longitudinal axis of the straight line is omega _1. The trajectory of the second combination (◯ in FIG. 11) is a straight line passing through the origin, and its inclination is λ.

(Step 6)
The vibration / response processor 14 obtains the horizontal coordinate of the intersection of two straight lines. This value is a value of N such that ω ₁ = λN (the natural frequency of the primary bending mode is equal to the frequency of the rigid body mode). At the value N (▲ in FIG. 11), the rotating shaft 51 starts self-excited vibration caused by the seal whirl.

(principle)
The principle behind the described process steps, the frequency of λN of rigid body modes is greater than the natural frequency omega ₁ of the primary bending mode, self-excited vibration generated due to Shiruhowaru is that.

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 _52b (ν) (Formula 4)

(Recheck the position and number of vibration measurement units)
As described above, the number of vibration measurement units 12 is increased in order to facilitate measurement of vibration response in the pure bending mode. For that purpose, it is desirable to arrange the vibration measuring units 12 at any plural (2, 3,...) Positions on the Z axis. Usually, it is easy to arrange the vibration measuring unit 12 at the positions of the two bearings 52a and 52b of the horizontal multistage pump. The problem is where to place the third vibration measuring unit 12.

  In the above description, the example in which the third vibration measurement unit 12 is disposed at the position of the magnetic bearing 11 has been described. However, the third position is not limited to this. Usually, since the vibration measuring unit 12 cannot be disposed between the two bearings of the horizontal shaft multistage pump, an appropriate position outside the two bearings 52a and 52b is selected as the third position. . For example, the position of the Z-axis coupling 56 is preferable as the third position.

  In many cases, a rotary machine such as a horizontal shaft multistage pump originally has a vibration measuring unit at the bearing position. In this case, the vibration measurement unit 12 of the vibration diagnostic apparatus 1 may receive vibration data measured by the vibration measurement unit of the rotating machine.

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

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

Claims (7)

A magnetic bearing that supports the shaft end of the rotating body of the rotating machine in a non-contact manner and applies an excitation force to the rotating body by a predetermined excitation control signal;
Vibration that measures vibrations of the rotating body at a total of three positions: the position of either the magnetic bearing or the coupling of the rotating machine, and the position of two bearings that support the rotating body in addition to the magnetic bearing. A measuring section;
A current supply unit for supplying current to the magnetic bearing;
Excitation / response processing for outputting the excitation control signal for controlling the magnetic bearing to vibrate the rotating body to the current supply unit and measuring the vibration response of the rotating body to the excitation control signal And
An excitation diagnostic apparatus comprising: The current supply unit is
Receiving the excitation control signal from the excitation / response processing unit, generating a current based on the received excitation control signal, and supplying the generated current to the magnetic bearing;
The magnetic bearing is
Receiving the current from the current supply unit, and applying the excitation force of a predetermined excitation frequency based on the excitation control signal to the rotating body by the received current;
The vibration diagnosis apparatus according to claim 1. The vibration / response processor is
Measuring a vibration response of the rotating body having a frequency equal to the excitation frequency;
The excitation diagnostic apparatus according to claim 2, wherein: The vibration / response processor is
Performing signal processing to subtract the vibration response at the position of the two bearings from the vibration response at any position of the magnetic bearing or the coupling of the rotating machine;
The vibration diagnosis apparatus according to claim 3. The vibration / response processor is
Changing the excitation frequency,
The vibration response subjected to the signal processing is divided into a real part and an imaginary part,
Find the excitation frequency at which the real part becomes zero as the natural frequency of the primary bending mode,
Obtaining the excitation frequency at which the imaginary part becomes zero as the frequency of the rigid body mode,
The vibration diagnostic apparatus according to claim 4, wherein: The vibration / response processor is
Determining a rotational speed at which the natural frequency of the determined primary bending mode is equal to the frequency of the determined rigid body mode as a rotational speed at which self-excited vibration of the rotating body is generated;
The vibration diagnostic apparatus according to claim 5, wherein: The vibration / response processor
Outputting a predetermined vibration control signal for controlling the magnetic bearing to vibrate the rotating body of the rotating machine to the current supply unit;
The current supply unit is
Supplying a current to the magnetic bearing supporting 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;
Vibration measurement unit
A step of measuring vibrations of the rotating body at a total of three positions: one of the position of the magnetic bearing or the coupling of the rotating machine and the position of two bearings supporting the rotating body in addition to the magnetic bearing; When,
The vibration / response processor is
Measuring a vibration response of the rotating body to the excitation control signal;
An excitation diagnosis method for an excitation diagnosis apparatus comprising the excitation / response processing unit, the current supply unit, the magnetic bearing, and the vibration measurement unit.