JP2020034037A - Abnormality diagnosis method and abnormality diagnosis device of electric valve actuator - Google Patents

Abstract

To diagnose the abnormality of a rotary component of an electric valve actuator, by a motor current.SOLUTION: A valve 4 is driven by an electric valve actuator 1, a motor current in a middle opening area of the valve 4 is detected, and frequency components included in the motor current are analyzed, thereby diagnosing the abnormality of a rotary component. Further, a specific frequency due to the rotary component is extracted from the frequency component and is compared with a spectra at a normal time, thereby diagnosing the abnormality of the rotary component and solving a problem.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method and apparatus for diagnosing an abnormality of an electric valve actuator used in various plants such as a thermal power plant and a petrochemical plant.

  BACKGROUND ART In plants such as thermal power plants and petrochemical plants, a large number of electric valve actuators (hereinafter, also simply referred to as valve actuators) are used to control the flow of fluid such as water and steam flowing in piping. Once installed, such valve actuators are often used for decades. Although there are exceptions such as regulating valve applications, the opening and closing operation of many valves is infrequent, and the valve actuator is not updated even after several years of use.

  However, when the valve actuator is used for a long period of time, it is necessary to periodically check the degree of deterioration and the presence or absence of abnormality to ensure soundness. Under such circumstances, various proposals have been made for a method of diagnosing abnormality of the valve actuator.

  One of the most useful information in diagnosing abnormality of the valve actuator is load information of the valve actuator. Many of the abnormal events of the valve actuator appear as fluctuations in the load information, and therefore, torque information is often detected as one of the load information. For example, there is a method in which a torque sensor is permanently attached to a valve actuator, and the output of the torque sensor is periodically monitored and recorded to diagnose deterioration or abnormality of the valve actuator (see Patent Document 1).

  Further, an abnormality diagnosis method has been proposed in which load information is calculated from a voltage value and a current value of a motor without installing a torque sensor, and the load information is replaced with torque information (see Patent Document 2). Since the load information relates to the active power, it is a method of diagnosing based on the load information calculated from the voltage value and the current value of the motor.

  Further, there is an apparatus in which an acceleration sensor is attached to an appropriate position of a valve actuator, and a frequency analysis of a vibration waveform is performed based on an output of the acceleration sensor to detect an abnormality of the valve actuator or the valve body (see Patent Document 3).

JP-A-2002-130531 JP 2006-83928 A JP-A-2002-174549

  In the prior art, for example, in the abnormality diagnosis method of Patent Document 1, when performing abnormality diagnosis of a valve actuator, a permanent torque sensor must be attached to the valve actuator. However, in reality, few valve actuators have a permanent torque sensor. Therefore, when performing an abnormality diagnosis on an existing valve actuator to which a permanent torque sensor is not attached, it is necessary to temporarily attach a torque sensor. In that case, there is a problem that a modification for attaching the torque sensor to the valve actuator is required.

  Further, the abnormality diagnosis method of Patent Document 2 does not require a torque sensor, but needs to measure both the current value and the voltage value of the motor. The supply voltage to the motor is often 200 V or more, and there is a risk of electric shock or a short circuit accident when measuring a high voltage.

  Further, when a vibration sensor is temporarily attached to a valve actuator as in Patent Document 3, in order to measure mechanical vibration without attenuating it in a wide frequency band, the vibration sensor is mechanically firmly attached to a measurement target. Need to be installed. However, in the existing valve actuator, it is not easy to firmly attach the vibration sensor due to the presence of a coating film, rust, dust, and the like. In particular, in the case of a valve actuator installed at a high place or in a narrow space, workability is poor, and there is a problem that it is difficult to securely attach a vibration sensor to an appropriate position of the valve actuator.

  Among the above-described prior arts, in the abnormality diagnosis methods disclosed in Patent Literatures 1 and 2, the output information of the sensor is observed in a time domain. A valve actuator is a device for opening and closing a valve, and since torque information and the like associated with the opening and closing of a valve greatly changes along a time axis, it is useful to observe the torque information and the like in a time domain for abnormality diagnosis. It can be said that the method.

  However, merely observing torque information and the like in the time domain is not sufficient to diagnose deterioration or abnormality of rotating parts such as gears and bearings used in the valve actuator. Therefore, it is difficult to diagnose the deterioration or abnormality of the rotating component by the diagnostic methods disclosed in Patent Literature 1 and Patent Literature 2. Observation in the frequency domain is useful for diagnosing deterioration or abnormality of a rotating component.

  On the other hand, the invention disclosed in Patent Document 3 performs frequency analysis on a vibration waveform and observes the vibration waveform in a frequency domain, and is suitable for diagnosing deterioration or abnormality of a rotating component. However, as described above, it is difficult to securely attach the vibration sensor to a proper position of the valve actuator.

  The present invention has been made in view of the circumstances described above, and has as its object to diagnose and detect deterioration or abnormality of a rotating component of a valve actuator by using a motor current. Specifically, an object of the present invention is to diagnose a deterioration or abnormality of a bearing or the like which is a rotating part of a valve actuator by a motor current.

  According to a first aspect of the present invention, a valve is driven by an electric valve actuator, a motor current in an intermediate opening range of the valve is detected, a frequency component included in the motor current is analyzed, and a failure of a rotating component is diagnosed. This is a method for diagnosing abnormality of the electric valve actuator.

  According to a second aspect of the present invention, in the method for diagnosing abnormality of the electric valve actuator according to the first aspect, a specific frequency due to the rotating component is extracted from the frequency components and compared with a normal spectrum. Is what you do.

  According to a third aspect of the present invention, in the abnormality diagnosis method for an electric valve actuator according to the first or second aspect, an abnormality of the rotary component is diagnosed every time a predetermined period elapses.

  The invention according to claim 4 is a current sensor for detecting a motor current of the electric valve actuator, a filter for limiting a frequency band of an output of the current sensor, an A / D converter for converting an output of the filter, and the A / D converter. A frequency analysis unit for performing a Fourier transform on an output of the / D converter; and a storage unit for storing a result analyzed by the frequency analysis unit, and diagnosing an abnormality of a rotating component. An abnormality diagnosis device.

  According to the present invention, since it is possible to diagnose an abnormality of a rotating component only by detecting a motor current, there is no need to permanently or temporarily attach a torque sensor to a valve actuator. Therefore, abnormality diagnosis can be easily performed even for an existing valve actuator to which no torque sensor is attached. Also, there is no need to attach the vibration sensor to the valve actuator. Further, the motor current can be detected in a non-contact manner, and it is not necessary to measure the motor voltage at which an electric shock or a short circuit accident may occur. Therefore, high safety can be ensured in the abnormality diagnosis work. Further, the detection of the motor current can be completed in a short time because the power supply cable for supplying electric power to the motor need only be sandwiched between the clamps of the clamp meter. These advantageous effects of the present invention have a remarkable effect particularly in abnormality diagnosis of a valve actuator installed in a nuclear power plant. In other words, the detection of the motor current is possible even from a position distant from the installation location of the valve actuator, and the amount of exposure of the worker can be reduced.

FIG. 1 is a block diagram illustrating a schematic configuration of the present invention. FIG. 4 is a waveform diagram illustrating an example of a motor current of the electric valve actuator. FIG. 4 is a spectrum diagram obtained by Fourier-transforming a motor current in a normal state. It is the spectrum figure which performed the Fourier transform of the motor current in the state which advanced deterioration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. A valve actuator 1 shown in FIG. 1 has been widely used in the past, and its main part is composed of a motor 2 and a valve actuator main body 3 having a built-in reduction gear train for reducing the rotation of the motor 2. ing. Although not shown, the reduction gear train includes one composed of only a pair of worm gears, and one configured by adding a helical gear for reducing the rotation of the motor shaft at a stage preceding the worm gear.

  The motor 2 is mounted on a side surface of the valve actuator main body 3 with its axis orthogonal to the stem 5 of the valve 4. In many cases, a three-phase induction motor having excellent reliability such as durability is used as the motor 2.

  Power is supplied to the motor 2 from a commercial AC power supply 6 via a power cable 7. The motor current can be easily detected in a non-contact manner by clamping one of the power cables 7 with a clamp of a clamp meter as the current sensor 8. A commercially available general purpose clamp meter is sufficient, but a clamp meter with an output terminal is used.

  The filter 9 cuts unnecessary high-frequency components included in the current signal detected by the clamp meter, and also prevents an aliasing error that may occur at the time of sampling, and uses a low-pass filter. In the present embodiment, sampling is performed in 1 ms by connecting to an A / D converter through a low-pass filter having a cutoff frequency of about 390 Hz.

  The A / D converter 10 converts an analog signal into a digital signal, and belongs to a known technique. More specifically, what is provided as standard equipment in the analyzer as the frequency analysis means is sufficient.

  The frequency analysis unit 11 obtains data as a frequency spectrum by performing a fast Fourier transform (FFT) on the current signal as digital data.

  The storage unit 12 stores frequency spectrum data obtained by FFT with data acquisition date and time, and a non-volatile memory is used.

  The specific frequency extracting unit 13 focuses on the fact that a specific frequency spectrum increases with rotation when the rotating component is deteriorated or abnormal, and can be calculated based on the component specifications of the rotating component. For example, the specific frequency for a rolling bearing can be determined as follows.

  Table 1 shows a formula for calculating a specific frequency when spot flaws are present on each of the inner ring, the outer ring of the rolling bearing, and the rolling surface of the rolling element. Here, fi is a specific frequency (Hz) when the inner ring is damaged, fo is a specific frequency (Hz) when the outer ring is damaged, and fb is a specific frequency (Hz) when the rolling element is damaged. . Also, fr is the rotation frequency (Hz) of the inner ring (shaft), D is the pitch circle diameter of the bearing (mm), d is the diameter of the rolling element (mm), α is the contact angle (degree), and z is the number of rolling elements. Is shown.

  The determination of the presence or absence of an abnormality is evaluated based on the size of the spectrum at a specific frequency. If the spectrum of the specific frequency is not recognized, or even if it is recognized, it is determined to be normal if it is slightly larger than the size of the other frequency spectrum. On the other hand, if the spectrum of the specific frequency is recognized and is clearly larger than the other frequency spectrums, it is determined to be abnormal.

  In determining the magnitude of the spectrum of a specific frequency, it is effective to compare data over time. For example, abnormality diagnosis is performed every two years, and the time-series observation of the magnitude of the spectrum of a specific frequency is compared with the previous (two years ago) and two times before (four years ago) data stored in the storage unit. It is effective to do.

  Next, an abnormality diagnosis result according to the present invention will be described based on a specific example. FIG. 2 is an example of raw motor current data obtained when a ball valve as a test valve is closed. The vertical axis represents the current value, and the horizontal axis represents time. Since the valve actuator is provided with a hammer blow mechanism as a standard, the current value becomes almost no-load until a hammer blow occurs (t1).

  When a hammer blow occurs, the current value slightly increases, but remains at a very low current value. Next, when the operation by the hammer blow mechanism ends and the stem starts moving in the closing direction (t2), the motor current sharply increases. Although the motor current suddenly increases, it gradually settles to a stable state (t3).

  The current value in this stable state is not a large current value as compared with the current value when the valve element performs torque seating. Since the motor load is only a light load state, the motor rotation speed and the motor current value are stable. This region is called an intermediate opening region.

  Here, although the current value of the entire intermediate opening region is stable, when the time axis is divided into short time and observed, the current value fluctuates drastically. From the data in the time region shown in FIG. Significant information cannot be obtained regarding part abnormalities. This is the reason why it has been considered that current information alone is not useful for diagnosis in various diagnoses of valve actuators. However, the inventor of the present invention has found that even from a current signal which at first glance was considered to be incapable of obtaining significant information, by performing appropriate filtering, significant information on abnormality diagnosis of rotating parts is included. It came to the knowledge that it was.

  FIG. 3 shows an FFT analysis result of the current signal according to the present invention, which is data obtained in a new state where there is no abnormality in the rotating parts of the valve actuator. Peaks are observed at two points of a frequency of 50 Hz and 100 Hz. Since the power supply frequency is 50 Hz, these two peaks can be treated as a spectrum unrelated to the abnormality of the rotating component. Further, since no remarkable spectrum is recognized except for the two peaks, it can be determined that there is no abnormality in the rotating component.

  FIG. 4 is data showing FFT analysis results of a case in which a valve actuator installed in an actual plant and operated for 10 years or more was found to be damaged at one location of a bearing rolling element supporting a built-in worm shaft. . The fact that two peaks are observed at the frequency of 50 Hz and 100 HZ is the same as the data at the time of new product shown in FIG. 3, and these two peaks can be treated as spectra unrelated to abnormalities of the rotating parts.

  When FIG. 3 is compared with FIG. 4, a spectrum at 110 Hz, which was not noticeable in FIG. 3, is recognized in FIG. Therefore, the spectrum at 110 Hz will be considered. Regarding the bearing specifications in this case, the rotation frequency fr of the inner ring (shaft) is 0.97 Hz, the pitch diameter D of the bearing is 81 mm, the diameter d of the rolling element is 8.5 mm, the contact angle α is 17 degrees, and the The number z is 24. When the specific frequency fb when the rolling element is flawed is calculated from the formulas shown in Table 1 from the values of the bearing specifications, it is about 110 Hz. The peak of 110 Hz in the spectrum observed in FIG. 4 can be determined to be due to a flaw in the rolling element.

  As shown in this case, according to the present invention, it is possible to detect the motor current in the intermediate opening region of the valve, analyze the frequency components included in the motor current, and diagnose the abnormality of the rotating component.

  Note that the specific frequency when the inner ring or the outer ring has a flaw is almost one digit lower than the specific frequency when the rolling element has a flaw, so that the abnormality diagnosis method according to the present invention did not result in detection.

  As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and can be applied to various embodiments. For example, in the above-described embodiment, the embodiment in which the ball valve is used as the test valve and the closing operation is performed has been described. However, the embodiment is also applicable to the case where the opening operation is performed. Further, the test valve is not limited to a ball valve, but can be applied to other types of valves such as a gate valve.

  INDUSTRIAL APPLICABILITY The abnormality diagnosis method and abnormality diagnosis device according to the present invention can be used for deterioration and abnormality diagnosis of rotating parts of an electric valve actuator installed in piping of various plants and the like.

1 electric valve actuator (valve actuator)
2 Motor 4 Valve 8 Current sensor (clamp meter)
9 Filter
10 A / D converter
11 Frequency analysis unit (frequency analysis means, analyzer)
12 Memory

Claims (4)

  An electric valve actuator that drives a valve by an electric valve actuator, detects a motor current in an intermediate opening region of the valve, analyzes a frequency component included in the motor current, and diagnoses an abnormality of a rotating component. Abnormal diagnosis method.   The abnormality diagnosis method for an electric valve actuator according to claim 1, wherein a specific frequency due to the rotating component is extracted from the frequency components and compared with a normal spectrum.   3. The abnormality diagnosis method for an electric valve actuator according to claim 1, wherein the abnormality of the rotary component is diagnosed every time a predetermined period elapses. A current sensor for detecting a motor current of the electric valve actuator, a filter for limiting a frequency band of an output of the current sensor, an A / D converter for converting an output of the filter, and an output of the A / D converter. An abnormality diagnosis device for an electric valve actuator, comprising: a frequency analysis unit that performs a Fourier transform; and a storage unit that stores a result analyzed by the frequency analysis unit, and diagnoses an abnormality of a rotating component.

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