Anomaly detection system for differential transformer type displacement meter, differential transformer type displacement meter, and anomaly detection method.

Abstract

To provide an abnormality detection system for a differential transformer displacement meter that can detect abnormalities with higher accuracy, a differential transformer displacement meter, and an abnormality detection method.SOLUTION: An abnormality detection system for a differential transformer displacement meter 22 in which the output voltage output from a secondary winding 25 changes in accordance with the AC input voltage depending on the position of a movable iron core 26 includes an acquisition unit that acquires the voltage value of the output voltage at the timing of a predetermined phase of the input voltage, and a determination unit that performs an abnormality determination on the basis of a voltage difference between a voltage value obtained corresponding to a target period and a voltage value acquired corresponding to a period before the target period.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This disclosure relates to an anomaly detection system for differential transformer type displacement gauges, a differential transformer type displacement gauge, and an anomaly detection method. [Background technology]

[0002] In power plants, for example, a Linear Variable Differential Transformer (LVDT) is used to measure the opening degree of turbine steam control valves (stop valves, throttle valves, etc.). In a differential transformer, the piston shaft of the drive mechanism that opens and closes the turbine steam control valve via a linkage mechanism is connected to a movable iron core inside the differential transformer, and the voltage of two secondary coils, which are electromagnetically coupled to the primary coil via the movable iron core, is detected. By detecting the voltage of the secondary coils, it is possible to determine the displacement of the movable iron core, and thus the opening degree of the turbine steam control valve.

[0003] Patent Document 1 discloses a method for determining whether a wire break has occurred in a differential transformer type displacement meter by comparing the output voltage value of the secondary coil with a preset threshold. Patent Document 2 discloses a method for determining whether a wire break has occurred in a differential transformer type displacement meter by the rate of change of the output voltage value of the secondary coil per unit time. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 3786845 [Patent Document 2] Japanese Patent Publication No. 2019-145611 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, even if a break occurs on the common wire side of the secondary coil, for example, the output voltage of the secondary coil may not become 0V due to stray capacitance between the cables after the break, etc., causing the voltage to remain as a feedback voltage. In this case, it is not possible to detect an anomaly by comparing the output voltage value of the secondary coil with a threshold. For example, if the turbine steam control valve is controlled with an incorrect valve opening and power generation continues, it may disrupt the operation of the power plant.

[0006] Furthermore, if anomaly detection is performed based on the rate of change per unit time of the output voltage value of the secondary coil, there is a possibility of false detection of anomalies due to rapid voltage changes during emergency operations such as emergency shutdown of the turbine or shutdown of the generator system. In such cases, the workload of the responding operator may increase, and it may become difficult to enhance the functionality of the power plant, such as by enabling it to handle high load change rates.

[0007] This disclosure has been made in view of these circumstances and aims to provide a differential transformer type displacement sensor anomaly detection system, a differential transformer type displacement sensor, and an anomaly detection method that can detect anomalies with higher accuracy. [Means for solving the problem]

[0008] A first aspect of this disclosure is an abnormality detection system for a differential transformer type displacement meter in which the output voltage output from a winding changes in response to an AC input voltage depending on the position of a movable core, the abnormality detection system comprising: an acquisition unit that acquires the voltage value of the output voltage at a predetermined phase timing of the input voltage; and a determination unit that performs an abnormality determination based on the voltage difference between the voltage value acquired in response to a target period and the voltage value acquired in response to a period prior to the target period.

[0009] A second aspect of the present disclosure is an abnormality detection method for a differential transformer type displacement meter in which an output voltage output from a winding changes corresponding to an AC input voltage depending on the position of a movable iron core, the method including: a step of acquiring a voltage value of the output voltage at a timing of a predetermined phase of the input voltage; and a step of performing an abnormality determination based on a voltage difference between the voltage value acquired corresponding to a target period and the voltage value acquired corresponding to a period before the target period.

Advantages of the Invention

[0010] According to the present disclosure, there is an effect that an abnormality can be detected with higher accuracy.

Brief Description of the Drawings

[0011] [Figure 1] FIG. is a schematic configuration diagram of a power generation plant including an abnormality detection system for a differential transformer type displacement meter according to an embodiment of the present disclosure. [Figure 2] FIG. is a longitudinal sectional view showing a configuration example of a turbine steam control valve in a power generation plant according to an embodiment of the present disclosure. [Figure 3] FIG. is a longitudinal sectional view showing a connection example between a valve drive machine and a differential transformer type displacement meter in a power generation plant according to an embodiment of the present disclosure. [Figure 4] FIG. is a diagram showing an electrical equivalent circuit of a differential transformer type displacement meter in a power generation plant according to an embodiment of the present disclosure. [Figure 5] FIG. is a graph exemplifying the relationship between the position (stroke position) of a movable iron core and the output voltage of a secondary coil in a differential transformer type displacement meter according to an embodiment of the present disclosure. [Figure 6] FIG. is a diagram showing an example of a hardware configuration of a control device according to an embodiment of the present disclosure. [Figure 7] FIG. is a functional block diagram showing functions included in a control device according to an embodiment of the present disclosure. [Figure 8] FIG. is a diagram showing an example of an input voltage according to an embodiment of the present disclosure. [Figure 9]A diagram showing output voltages in each period and each phase according to an embodiment of the present disclosure. [Figure 10] A diagram explaining each element of Equation (1) according to an embodiment of the present disclosure. [Figure 11] A diagram showing changes in output voltage when a disconnection occurs according to an embodiment of the present disclosure. [Figure 12] An enlarged view around time T1 in FIG. 11 according to an embodiment of the present disclosure. [Figure 13] A diagram showing changes in evaluation values according to an embodiment of the present disclosure. [Figure 14] [[ID= fifteen ]]A flowchart of abnormality detection according to an embodiment of the present disclosure. [Figure 15] A diagram showing a schematic configuration of a six-wire circuit in a double-winding type according to an embodiment of the present disclosure. [Figure 16] A diagram showing a schematic configuration of a three-wire circuit in a single-winding type according to an embodiment of the present disclosure.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, an embodiment of a power generation plant 1 provided with an abnormality detection system for a differential transformer type displacement meter according to the present disclosure will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a power generation plant 1 provided with an abnormality detection system for a differential transformer type displacement meter according to an embodiment of the present disclosure. As shown in FIG. The power generation plant 1 according to the present embodiment mainly includes, as an example, a boiler 2, a steam turbine 3, a generator 4, a condenser 5, a feed water pump 6, a turbine steam control valve 7, displacement meters 20 and 21, and a control device 8.

[0013] In this embodiment, displacement gauges 20 and 21 are installed on the turbine steam control valves 7 (stop valve 11 and throttle valve 12) in the power plant 1 to measure the valve opening state. Differential transformer type displacement gauges 22 are used for the displacement gauges 20 and 21, and an abnormality detection system (abnormality detection unit 62, described later) is provided for the differential transformer type displacement gauges 22. The differential transformer type displacement gauge 22 is a device capable of measuring displacement, and can be applied to other devices besides the turbine steam control valves 7, as long as displacement measurement is required. In other words, the abnormality detection system according to this embodiment can be applied regardless of the application of the differential transformer type displacement gauge 22. As will be described later, in this embodiment, the case where the differential transformer type displacement gauge 22 is a 6-wire type (4-wire type if the secondary coil side is intentionally short-circuited) is described as an example, but other double-winding types may be adopted, or a single-winding type such as a 3-wire type may be adopted.

[0014] Boiler 2 converts the boiler feedwater sent from the feedwater pump 6 into superheated steam and supplies it to the steam turbine 3. Specifically, boiler 2 consists of an economizer, evaporator, superheater, etc. Boiler water is first heated in the economizer and then turned into steam in the evaporator. After that, it is further superheated in the superheater to become superheated steam. The superheated steam generated in boiler 2 is supplied to the steam turbine 3 via the turbine steam control valve 7. Note that the configuration of boiler 2 is not limited to the above and various configurations can be adopted, such as one that exchanges heat between the combustion gas produced by burning fuel in the furnace and the feedwater to boiler 2, or one that exchanges heat between the feedwater to boiler 2 and the high-temperature exhaust gas from a gas turbine, etc.

[0015] In the steam turbine 3 (hereinafter referred to as "turbine 3"), superheated steam generated in the boiler 2 is supplied, and the superheated steam expands to rotate the turbine blades. In other words, turbine 3 converts the energy of the superheated steam into rotational energy. Various configurations are applicable to turbine 3, such as a three-stage configuration of a high-pressure turbine, an intermediate-pressure turbine, and a low-pressure turbine, or a two-stage configuration of a high-pressure turbine and an intermediate-pressure turbine. The rotating shaft of turbine 3 is connected to the generator 4.

[0016] In the generator 4, the rotating shaft of the turbine 3 and the rotating shaft of the generator 4 are connected and rotated, converting the rotational energy generated by the turbine 3 into electrical energy. The electricity generated by the generator 4 is supplied to the power grid, for example, via a transformer.

[0017] The condenser 5 cools the steam that has finished working in the turbine 3 and returns it to the liquid phase as condensate. Specifically, the condenser 5 is equipped with heat transfer tubes to which cooling water such as seawater is supplied. Heat exchange occurs between the steam discharged from the turbine 3 and the cooling water, cooling the steam and returning it to water as condensate. The generated condensate is supplied to the feedwater pump 6 via a heater (not shown) and a deaerator (not shown).

[0018] The feedwater pump 6 supplies condensate, which has been supplied via a heater (not shown) and a deaerator (not shown), to the boiler 2 as boiler feedwater. By controlling the feedwater pump 6, it is possible to control the flow rate of boiler feedwater supplied to the boiler 2. Alternatively, the boiler feedwater supplied from the feedwater pump 6 may be further heated in a heater (not shown) before being supplied to the boiler 2.

[0019] The turbine steam control valve 7 controls the flow rate of steam supplied from the boiler 2 to the turbine 3. Specifically, the turbine steam control valve 7 consists of a stop valve 11 and a throttle valve 12. Figure 2 is an example of a diagram (vertical cross-sectional view) illustrating the configuration of the turbine steam control valve 7. As shown in Figure 1, the steam generated by the boiler 2 is supplied to the turbine 3 via the turbine steam control valve 7, which consists of a stop valve 11 and a throttle valve 12. Note that the stop valve 11 and the throttle valve 12 may be provided separately.

[0020] The turbine steam control valve 7 controls the large volume of steam flow required for power generation supplied from the boiler 2 to the turbine 3 by reliably stopping the steam supplied to the turbine 3 with the stop valve 11 and controlling the opening degree of the throttle valve 12. In some cases, the stop valve 11 also functions as a control valve that can control steam in the low flow rate range during acceleration.

[0021] As shown in Figure 2, the stop valve 11 is controlled by a stop valve driver 11a. Specifically, the piston shaft 11b is controlled by the stop valve driver 11a, and the opening degree of the stop valve 11 is adjusted via a link mechanism 11c connected to the piston shaft 11b. For example, when the piston shaft 11b is controlled by the stop valve driver 11a in the direction of arrow A, this drive is transmitted to the stop valve 11 via the link mechanism 11c, and the stop valve 11 moves in the direction of arrow A and opens (becomes fully open).

[0022] The throttle valve 12 also has a similar drive mechanism as the stop valve 11, and the opening degree of the throttle valve 12 is controlled by the throttle valve drive 12a. For example, when the amount of movement of the piston shaft 12b in the direction of arrow B is controlled by the throttle valve drive 12a, the throttle valve 12 moves in the direction of arrow B via the link mechanism 12c, and opens (opens) with its opening degree controlled. Figure 2 is an example of the drive mechanism for the stop valve 11 and the throttle valve 12, and it is also possible to control each valve by other methods. Furthermore, in the following description, unless otherwise specified, the stop valve drive 11a and the throttle valve drive 12a will be described as valve drivers.

[0023] The stop valve drive 11a and the throttle valve drive 12a are each equipped with displacement sensors 20 and 21, each consisting of two differential transformer type displacement sensors 22 (22a and 22b), to measure the fully open and fully closed state of the stop valve 11 and the opening degree of the throttle valve 12. Specifically, as shown in Figure 2, the displacement sensors 20 and 21 are provided so that the displacement of the piston shafts 11b and 12b in the stop valve drive 11a and the throttle valve drive 12a can be measured. Figure 3 is a diagram (vertical cross-sectional view) showing an example of the connection between the piston shaft 12b in the throttle valve drive 12a and the displacement sensor 21 (which has differential transformer type displacement sensors 22a and 22b). As indicated by the white arrows in Figure 3, the diagram on the left side of Figure 3 conceptually shows the internal structure of the differential transformer type displacement sensor 22 shown in the diagram on the right side of Figure 3. The configuration of the stop valve drive 11a is the same as that of the throttle valve drive 12a shown in Figure 3. As shown in Figures 2 and 3, the piston shaft 12b of the throttle valve drive 12a and the movable shaft 23 of the differential transformer type displacement sensor 22 are connected via a link mechanism 12d (or link mechanism 11d in the case of the stop valve drive 11a). In this embodiment, one throttle valve drive 12a is equipped with two differential transformer type displacement sensors 22 (22a and 22b). As will be described later, for example, if an abnormality occurs in one of the differential transformer type displacement sensors 22a (e.g., a broken wire), the control device 8 can switch to acquiring the measurement value from the other differential transformer type displacement sensor 22b, thereby enabling reliable measurement of the opening degree of the throttle valve 12 (or stop valve 11). It is also possible to equip the differential transformer type displacement sensor 22 as a single unit instead of two separate units. As shown in Figure 3, by connecting the piston shaft 12b of the throttle valve drive 12a to the differential transformer type displacement meter 22, for example, when the piston shaft 12b moves in the direction of arrow C, the movable shaft 23 of the differential transformer type displacement meter 22 moves (displaces) in the direction of arrow C, and this displacement is detected as an output voltage by the differential transformer type displacement meter 22. In the following description, when distinguishing between the two differential transformer type displacement meter 22 systems, they will be labeled as differential transformer type displacement meter 22a and 22b, and when not distinguishing between them, they will simply be labeled as differential transformer type displacement meter 22.Furthermore, since the internal configurations of the differential transformer type displacement gauges 22a and 22b are identical, they are given the same reference numerals, as shown in Figure 3.

[0024] The differential transformer type displacement meter 22 comprises a primary coil 24 (primary winding), a secondary coil 25 (secondary winding), a movable shaft 23, and a movable iron core 26. In the following description, when distinguishing between the two secondary coils 25, they will be labeled as secondary coil 25a and 25b; otherwise, they will simply be labeled as secondary coil 25. Figure 4 shows the electrical equivalent circuit of the differential transformer type displacement meter 22. Voltage is supplied to the primary coil 24 from the power supply 28. For example, the power supply 28 supplies an AC voltage of 6V to 10V (for example, with a frequency of 1kHz) to the primary coil 24. As shown in Figures 3 and 4, in order to accurately detect the long stroke of the piston shaft 12b, two secondary coils 25a and 25b are arranged side by side inside the differential transformer type displacement meter 22 in the direction of movement of the movable iron core 26. One side of each secondary coil 25a and 25b is connected as a common wire to standardize the reference value of the measured potential. Therefore, the secondary coils 25 are provided in two systems relative to the reciprocating direction of the movable core 26, and each secondary coil 25a and 25b is electromagnetically coupled to the primary coil 24 via the movable core 26. The voltage induced in each secondary coil 25a and 25b is measured by the measurement units (voltmeters) 27a and 27b and output to the control device 8.

[0025] The movable shaft 23 transmits the displacement of the piston shaft 11b of the stop valve drive unit 11a or the piston shaft 12b of the throttle valve drive unit 12a to the movable iron core 26, and is made of a material that does not affect the electromagnetic coupling of the primary coil 24 and the secondary coil 25.

[0026] The movable core 26 is connected to the piston shaft 11b of the stop valve drive 11a or the piston shaft 12b of the throttle valve drive 12a, and moves (displaces) in accordance with the reciprocating motion of the piston shaft. The movable core 26 is made of a magnetic material, and its displacement changes the degree of coupling (mutual inductance) between the primary coil 24 and the secondary coil 25. In other words, the position (displacement state) of the movable core 26 in the reciprocating direction changes with the opening degree of the stop valve 11 or the throttle valve 12, and the coupling state of the primary coil 24 and the secondary coil 25 is determined based on the position of the movable core 26 after displacement, and a voltage is induced in the secondary coils 25a and 25b based on this coupling state. In other words, since there is a correlation between the opening degree of the stop valve 11 or the control valve 12 and the voltage induced in the secondary coils 25a and 25b, it is possible to determine the opening degree of the stop valve 11 or the control valve 12 by measuring the output voltage induced in the secondary coils 25a and 25b.

[0027] As shown in Figure 4, a common wire (L1) is connected to one side of each of the secondary coils 25a and 25b, serving as the reference wire for output voltage measurement. This is to align the reference values ​​for voltage measurement by the respective measurement units 27a and 27b.

[0028] Figure 5 illustrates the relationship between the position (stroke position) of the movable core 26 and the output voltage of the secondary coil 25. The differential transformer type displacement meter 22 is installed so that the center position of the stroke of the piston shafts 11b and 12b coincides as closely as possible with the center position of the movable range of the movable core 26. The horizontal axis of Figure 5 shows the center position at the stroke position as 0%, and ±50% in the positive and negative directions. The vertical axis of Figure 5 shows the output voltage of the secondary coil 25a as VA and the output voltage of the secondary coil 25b as VB. Furthermore, in the differential transformer type displacement meter 22, the position of the movable core 26 is adjusted so that the voltages induced in each secondary coil 25 (VA and VB) are approximately equal at the center position relative to the upper and lower limits of the valve drive. Furthermore, the stroke position W1 on the horizontal axis of Figure 5 corresponds to the position of the movable core 26 corresponding to the upper limit of the movement of the piston shaft in the valve drive, and the stroke position W2 corresponds to the position of the movable core 26 corresponding to the lower limit of the movement of the piston shaft in the valve drive. In other words, the movable core 26 is displaced between positions W1 and W2, and consequently, the output voltage of the secondary coil 25 changes between VAmax and VAmin, and the output voltage of the secondary coil 25 changes between VBmax and VBmin.

[0029] When the movable core 26 is in the central position, the electromagnetic coupling state of the secondary coils 25a and 25b with respect to the primary coil 24 becomes approximately equal, and therefore the induced voltages (VA and VB) become approximately equal. As shown in Figure 5, when the movable core 26 moves in the positive direction (direction of arrow C in Figures 3 and 4), the coupling state between the primary coil 24 and the secondary coil 25a strengthens, and the coupling state between the primary coil 24 and the secondary coil 25b weakens. This is because more of the magnetic flux of the primary coil 24 passes through the secondary coil 25a via the movable core 26. On the other hand, the magnetic flux of the primary coil 24 passing through the secondary coil 25b decreases. Therefore, when the movable core 26 is displaced in the positive direction, the voltage induced in the secondary coil 25a increases, and the voltage induced in the secondary coil 25b decreases. Furthermore, when the movable core 26 is displaced in the negative direction (direction of arrow D in Figures 3 and 4), the voltage induced in the secondary coil 25b increases and the voltage induced in the secondary coil 25a decreases, due to a principle opposite to that when the movable core 26 is displaced in the positive direction.

[0030] For example, if output voltage VA1 is detected from secondary coil 25a and output voltage VB1 is detected from secondary coil 25b, it can be determined that the position of the movable core 26 is at +20%. From the position of the movable core 26 at +20%, the displacement of the piston shaft of the valve drive can be determined, and the opening degree of the stop valve 11 or the throttle valve 12 can be determined. The respective output voltages (VA and VB) measured in the secondary coil 25 are transmitted to the control device 8 and used for controlling the opening degree of the stop valve 11 and the throttle valve 12, and for detecting abnormalities (e.g., open circuit) in the differential transformer type displacement meter 22.

[0031] The control device 8 controls the opening degree of the turbine steam control valve 7 and controls the flow rate of steam supplied to the turbine 3. It also detects abnormalities in the differential transformer type displacement meter 22 provided for the turbine steam control valve 7. An abnormality is, for example, a break in the electrical circuit, one example being a break occurring at position O in Figure 4.

[0032] Figure 6 shows an example of the hardware configuration of the control device 8 according to this embodiment. As shown in Figure 6, the control device 8 is a computer system, and includes, for example, a CPU 110, a ROM (Read Only Memory) 120 for storing programs executed by the CPU 110, a RAM (Random Access Memory) 130 that functions as a work area when each program is executed, a hard disk drive (HDD) 140 as a mass storage device, and a communication unit 150 for connecting to a network, etc. A solid-state drive (SSD) may be used as the mass storage device. These components are connected via a bus 180.

[0033] Furthermore, the control device 8 may include an input unit consisting of a keyboard or mouse, and a display unit consisting of a liquid crystal display device or the like for displaying data.

[0034] The storage medium for storing programs executed by the CPU 110 is not limited to the ROM 120. For example, other auxiliary storage devices such as magnetic disks, magneto-optical disks, and semiconductor memory may also be used.

[0035] The series of processes required to implement the various functions described later are recorded in program form on the hard disk drive 140, etc. The CPU 110 reads this program into the RAM 130, etc., and performs information processing and calculations to realize the various functions described later. The program may be pre-installed on the ROM 120 or other storage media, provided in a state where it is stored on a computer-readable storage medium, or distributed via wired or wireless communication means. Computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, semiconductor memory, etc.

[0036] Figure 7 is a functional block diagram showing the functions of the control device 8. As shown in Figure 7, the control device 8 includes an opening degree control unit 61 and an abnormality detection unit 62 (abnormality detection system).

[0037] The opening degree control unit 61 controls the opening degree of the turbine steam control valves 7 (stop valve 11 and throttle valve 12). Specifically, the opening degree control unit 61 receives opening degree commands for the turbine steam control valves 7 (opening degree commands for the stop valve 11 and throttle valve 12, respectively) from a higher-level control unit that controls the entire turbine 3, and also obtains measured values ​​of the current opening degree of the turbine steam control valves 7 (opening degree of the stop valve 11 and throttle valve 12) from a differential transformer type displacement gauge 22. It then performs feedback control so that the opening degree command obtained from the higher-level control unit and the current opening degree of the turbine steam control valves 7 are approximately in agreement. In this embodiment, the turbine steam control valves 7 are controlled by feedback, but various methods can be applied to control the opening degree of the turbine steam control valves 7.

[0038] The abnormality detection unit (abnormality detection system) 62 detects abnormalities in the differential transformer type displacement meter 22. As described above, the differential transformer type displacement meter 22 is a displacement meter in which the output voltage output from the winding changes in response to the AC input voltage depending on the position of the movable core 26. In this embodiment, the abnormality detection unit 62 will be described in the case where it is applied to a double-wound type (6-wire type) differential transformer type displacement meter as shown in Figure 4. In this case, the winding is the secondary coil 25. It is also possible to apply the abnormality detection unit 62 to other double-wound or single-wound types.

[0039] As shown in Figure 7, the anomaly detection unit 62 includes an acquisition unit 71, a calculation unit 72, a determination unit 73, and a switching unit 74.

[0040] The acquisition unit 71 acquires the voltage value of the output voltage at a predetermined phase timing of the input voltage. The output voltage is the output voltage VA1 from the secondary coil 25a as a winding. Alternatively, the output voltage VB1 from the secondary coil 25b may be used as the output voltage.

[0041] Figure 8 illustrates the input voltage. As shown in Figure 8, the input voltage is a sine wave of a predetermined frequency. That is, the sine wave repeats with each period. Correspondingly, the output voltage is output from the secondary coil 25.

[0042] As shown in Figure 8, the input voltage has a predetermined number of two or more predetermined phases set within one cycle. Specifically, N predetermined phases are set within one cycle, and the unique number of each predetermined phase is j (from 0 to N-1). For example, as shown in Figure 8, predetermined phases are set at 45° intervals within one cycle (360°) of a sine wave. In the example shown in Figure 8, eight predetermined phases (a predetermined number N) are set, corresponding to 0° (j=0), 45° (j=1), 90° (j=2), 135° (j=3), 180° (j=4), 225° (j=5), 270° (j=6), and 315° (j=7). Each predetermined phase corresponds to one cycle, and similar settings are applied to other cycles. That is, N predetermined phases are set for each cycle.

[0043] The acquisition unit 71 then acquires the voltage value of the output voltage with respect to the input voltage. Specifically, it acquires the voltage value of the output voltage at the timing when the input voltage is in a predetermined phase. In the example in Figure 8, the output voltage value when the input voltage phase is 0° (j=0), the output voltage value when the input voltage phase is 45° (j=1), the output voltage value when the input voltage phase is 90° (j=2), the output voltage value when the input voltage phase is 135° (j=3), the output voltage value when the input voltage phase is 180° (j=4), the output voltage value when the input voltage phase is 225° (j=5), the output voltage value when the input voltage phase is 270° (j=6), and the output voltage value when the input voltage phase is 315° (j=7) are acquired. Then, the output voltage and the predetermined phase (specifically, the number j) are associated and stored in correspondence with the corresponding period.

[0044] In this way, the output voltage within one cycle is acquired. The acquisition unit 71 then maintains a dataset of output voltages corresponding to each cycle for a predetermined number of cycles. Specifically, the new cycle (i.e., the latest cycle) is set as the target cycle, and a predetermined number of past cycles are set as cycles prior to the target cycle. The target cycle is not limited to the new (latest) cycle, as long as it is a reference cycle. The predetermined number of cycles may be 1 (i.e., one past cycle), but it is preferable to set it to 2 or more. In this embodiment, the number of past cycles is set to 7. That is, the total number of cycles M, including the target cycle and past cycles, is 8. In this way, the output voltage values ​​for each predetermined phase in the target cycle (one) and the output voltage values ​​for each predetermined phase in each of the 7 past cycles are acquired. It is preferable that each past cycle is continuous with the target cycle and also continuous with each other.

[0045] Figure 9 shows the output voltages acquired for each period and phase. As shown in Figure 9, values ​​corresponding to each predetermined phase are acquired for each period (cycle). The total number of periods M is 8, with the target period set to i=0 and past periods shown as i=1 to 7(M-1). That is, the period immediately preceding the target period is the past period i=1, and the past periods are set up to i=7. In this way, the periods are set from i=0 to i=M-1.

[0046] Preferably, the acquired output voltage value is set as the value obtained by multiplying the output voltage value output from the secondary coil 25 by a predetermined constant. This allows for an appropriate value to be obtained according to the reading and number of digits that can be calculated by the acquisition unit 71 and the calculation unit 72, enabling highly accurate calculations. In this embodiment, as shown in Figure 9, the value obtained by multiplying the output voltage by a constant (voltage value) is denoted as S. Then, as an element corresponding to the period number i and the predetermined phase number j, S is set to S ij This is shown as follows. For example, the voltage value corresponding to period number i=0 (target period) and predetermined phase number j=2 (90°) is S 02 It is shown as follows. That is, when showing the voltage value of each element, S ijWhen the elements are not distinguished, they are indicated as S and explained accordingly.

[0047] The predetermined constant multiplied by the output voltage value is set to a number considerably larger than the voltage value, such as 5000 to 10000 (between 5000 and 10000). In other words, S is set as S = predetermined constant × output voltage value.

[0048] In this embodiment, a value obtained by multiplying the output voltage by a constant, as shown by S, is used. However, it is also acceptable to use the output voltage value directly as S without multiplying by a constant.

[0049] Thus, as shown in Figure 9, the acquisition unit 71 acquires output voltages corresponding to each period and each predetermined phase. Since the number of predetermined phases is N and the number of periods is M, N × M (8 × 8 = 64 in Figure 9) output voltages are acquired.

[0050] The calculation unit 72 calculates an evaluation value based on the value acquired by the acquisition unit 71. The evaluation value is a value that corresponds to the variation (variance) of the output voltage of the target period with respect to the output voltage of past periods. The larger the difference (larger the variation) between the output voltage of the target period and the output voltage of past periods, the larger the evaluation value will be. When the output voltage has a continuously stable waveform, the evaluation value will be small, and when the output voltage deviates from a stable waveform, the evaluation value will increase rapidly.

[0051] Specifically, the evaluation value is calculated using the following formula (1).

[0052]

number

[0053] Figure 10 is a diagram illustrating each element of equation (1). The element R1 is the voltage value (S) corresponding to the target period. 0j ) and the voltage value corresponding to the past cycle (S ij) shows the voltage difference from []. The voltage difference is the difference between voltage values corresponding to the same predetermined phase. Since the predetermined phases of the input voltages are equal, the voltage value corresponding to the target period and the voltage value corresponding to the period before it have a small voltage difference if there is no abnormality such as a disconnection, but if there is an abnormality, the voltage difference becomes large, enabling abnormality detection.

[0054] The element of R2 is the value obtained by squaring the voltage difference (squared value). By using the value obtained by squaring the voltage difference in this way, the positive and negative can be canceled. That is, regardless of the positive or negative of the voltage difference, it can be set as the square of the difference as a positive value.

[0055] The element of R3 is the value obtained by adding the squared values corresponding to each of the respective predetermined phases (added value). For example, the square of the voltage difference between the voltage value (S 00 ) of the target period and the voltage value (S 10 ) of the past period with i = 1, and the square of the voltage difference between the voltage value (S 01 ) of the target period and the voltage value (S 11 ) of the past period with i = 1, and the square of the voltage difference between the voltage value (S 02 ) of the target period and the voltage value (S 12 ) of the past period with i = 1, and the square of the voltage difference between the voltage value (S 03 ) of the target period and the voltage value (S 13 ) of the past period with i = 1, and the square of the voltage difference between the voltage value (S 04 ) of the target period and the voltage value (S 14 ) of the past period with i = 1, and the square of the voltage difference between the voltage value (S 05 ) of the target period and the voltage value (S 15 ) of the past period with i = 1, and the square of the voltage difference between the voltage value (S 06 ) of the target period and the voltage value (S 16 ) of the past period with i = 1, and the square of the voltage difference between the voltage value (S 07 ) of the target period and the voltage value (S 17 ) of the past period with i = 1, and the sum of these values. By calculating in this way, for a certain past period, the degree of difference between the target period and this past period is obtained.

[0056] R4 is the average value obtained by dividing the added value by a predetermined number N.

[0057] R5 is the sum of the average values ​​corresponding to each past cycle. This allows for anomaly detection by comparing the target cycle with multiple past cycles.

[0058] The evaluation value, as shown as R6, is the sum divided by the number of periods M (the target period divided by the number of past periods). Note that when i=0, the element of R1 becomes 0, so the i=0 pattern may be omitted. If the i=0 pattern is omitted, 1 / M in equation (1) becomes 1 / (M-1). Note that the reference voltage is set to i=0, and the voltage at i=0 may be the latest value, or the average value over the past few periods may be used.

[0059] In this way, an evaluation value is calculated based on the voltage difference between the target period and past periods. In particular, the positive and negative signs can be canceled out by taking the sum of the squares of the differences.

[0060] Although the evaluation value is constructed as shown in equation (1) (i.e., R6), R1, R2, R3, R4, or R5 may also be used as the evaluation value.

[0061] The determination unit 73 performs an abnormality determination based on the calculated evaluation value. In other words, the abnormality determination is performed based on the voltage difference (i.e., evaluation value) between the voltage value corresponding to the target period and the voltage value corresponding to the period prior to the target period.

[0062] Specifically, the determination unit 73 determines that an abnormality has occurred in the differential transformer type displacement gauge 22 if the evaluation value is equal to or greater than a preset threshold.

[0063] Figure 11 shows the change in output voltage when a wire break occurs. In Figure 11, the waveform of the output voltage when no wire break occurs is shown as P0 (dotted line), and the waveform of the output voltage when a wire break occurs is shown as P1 (solid line). In the example shown in Figure 11, a wire break occurs at time T1, causing the output voltage to deviate significantly from the waveform of P0, resulting in a waveform like P1. Figure 12 is a magnified view of the area around time T1 in Figure 11. Even when viewed in detail as in Figure 12, the output voltage deviates significantly from the waveform of P0, as shown in P1, due to the wire break.

[0064] Figure 13 shows the change in evaluation value corresponding to Figure 11, with the vertical axis being logarithmic. As shown in Figure 13, when no abnormalities such as wire breakage occur, the evaluation value is close to 0. However, when an abnormality such as wire breakage occurs and this effect appears in the output voltage as shown from T1 onwards in Figures 11 and 12, the evaluation value increases sharply. In the example shown in Figure 13, the evaluation value increases sharply from around 0 to an integer power of 10 around T1.

[0065] Therefore, the determination unit 73 uses a threshold value, for example, as shown in Figure 13, and determines that some kind of abnormality affecting the output voltage has occurred in the differential transformer type displacement gauge 22 when the evaluation value exceeds the threshold value. The threshold value is determined in advance through tests, simulations, etc.

[0066] The switching unit 74 switches the differential transformer type displacement gauges 22 based on the determination result obtained from the determination unit 73. If the determination unit 73 determines that an abnormality has occurred, the switching unit 74 switches the differential transformer type displacement gauge 22 that measures the opening degree of the turbine steam control valve 7 from the differential transformer type displacement gauge 22 that was determined to have an abnormality to the other differential transformer type displacement gauge 22.

[0067] For example, when the system is operating using the differential transformer type displacement meter 22a (for example, when the differential transformer type displacement meter 22b is in standby mode), the control device 8 obtains measurement results from the differential transformer type displacement meter 22a. If the control device 8 determines that there is an abnormality in the differential transformer type displacement meter 22a, it switches to the differential transformer type displacement meter 22b, which was in standby mode, and obtains measurement results from the differential transformer type displacement meter 22b.

[0068] Next, the flow of abnormality detection by the control device 8 described above will be explained with reference to Figure 14. The flow in Figure 14 is executed after the voltage values ​​of each predetermined phase in the target cycle have been acquired. For past cycles, the voltage values ​​have been acquired before the target cycle.

[0069] First, an evaluation value is calculated (S101). Then, it is determined whether the evaluation value is above a threshold (S102). If the evaluation value is not above a threshold (NO judgment in S102), the process is terminated. If the evaluation value is above a threshold (YES judgment in S102), the differential transformer type displacement meter 22 is switched (S103), and the process is terminated. Specifically, if the control device 8 is using the detection result of the differential transformer type displacement meter 22a and a YES judgment in S102 is made, it is presumed that an abnormality (disconnection) has occurred in the differential transformer type displacement meter 22a, and the differential transformer type displacement meter 22 is switched (switched to the differential transformer type displacement meter 22b in standby mode) so that the control device 8 uses the measurement result of the differential transformer type displacement meter 22b.

[0070] Figure 15 shows a schematic configuration of a 6-wire circuit in the double-wound type shown in Figure 4. As shown in Figure 15, when an input voltage is applied to the primary coil 24, the electromagnetic coupling state between the primary coil 24 and the secondary coil 25 changes depending on the position of the movable core 26. That is, the output voltage (voltage between C and D, voltage between E and F) output from each of the secondary coils 25 (i.e., windings) changes depending on the position of the movable core 26. Alternatively, instead of looking at the output voltage of each secondary coil 25, one side of each output terminal of the secondary coil 25 (for example, C and E) can be intentionally short-circuited (jumpered) and the output of the two secondary coils 25 can be viewed as a single output voltage (voltage between D and F) (4-wire type). Furthermore, a double-wound type other than 6-wire or 4-wire may be used.

[0071] Next, we will explain the case where the differential transformer type displacement gauge 22 is a single-winding type. Figure 16 shows a schematic configuration of a three-wire circuit in a single-winding type. As shown in Figure 16, an input voltage is applied between the ab and ab terminals of coil 29, and the output voltages output from the ab and b terminals of coil 29 (i.e., windings) change depending on the position of the movable core 26. Thus, a single-winding differential transformer type displacement meter 22 may be used. In particular, the voltage fluctuation during a break is smaller in the three-wire type compared to the six-wire type, but by using an evaluation value based on the concept of variation, it is possible to detect abnormalities with high accuracy.

[0072] As described above, the differential transformer type displacement sensor abnormality detection system, differential transformer type displacement sensor, and abnormality detection method according to this embodiment make it possible to improve the accuracy of abnormality detection by determining an abnormality based on the voltage difference between the voltage value of the output voltage at a predetermined phase timing in the target period of the input voltage and the voltage value of the output voltage at the same predetermined phase timing in a period earlier than the target period of the input voltage. Since the predetermined phases of the input voltages are the same, the voltage difference between the voltage value corresponding to the target period and the voltage value corresponding to an earlier period is small if there is no abnormality, but if there is an abnormality such as a broken wire, the voltage difference will be large, thereby enabling abnormality detection.

[0073] By using the squared value of the voltage difference, the positive and negative signs can be canceled out.

[0074] When multiple past cycles are set, anomaly detection can be performed based on the sum of the average values ​​corresponding to each past cycle. This allows for comparison between the target cycle and multiple past cycles, thereby improving the accuracy of anomaly detection.

[0075] For example, if a system has two secondary coils 25 and one side of each secondary winding is connected as a common wire to match the reference value of the measured potential, even if a break occurs in one of the secondary coils 25, voltage may leak back from the other normal (non-broken) secondary coil 25, resulting in residual voltage in the broken secondary coil 25. However, the above method can improve the accuracy of anomaly detection. Also, because the evaluation value changes significantly due to the anomaly, threshold setting becomes easier (high robustness).

[0076] This disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0077] In this embodiment, we have described a case where the anomaly detection system is applied to a differential transformer type displacement meter, but it can also be applied to various other types of sensors.

[0078] The abnormality detection system for the differential transformer type displacement meter, the differential transformer type displacement meter, and the abnormality detection method described in each embodiment above can be understood, for example, as follows. An anomaly detection system (62) relating to this disclosure is an anomaly detection system (62) for a differential transformer type displacement meter (22) in which the output voltage output from a winding (25) changes in response to an AC input voltage depending on the position of the movable core (26), and comprises an acquisition unit (71) that acquires the voltage value of the output voltage at a predetermined phase timing of the input voltage, and a determination unit (73) that performs an anomaly determination based on the voltage difference between the voltage value acquired in response to a target period and the voltage value acquired in response to a period prior to the target period.

[0079] According to the anomaly detection system (62) relating to this disclosure, the accuracy of anomaly detection can be improved by determining anomalies based on the voltage difference between the voltage value of the output voltage at a predetermined phase timing in the target period of the input voltage and the voltage value of the output voltage at the same predetermined phase timing in a period prior to the target period of the input voltage. Since the predetermined phases of the input voltages are the same, the voltage difference between the voltage value corresponding to the target period and the voltage value corresponding to the earlier period is small if there is no anomaly, but the voltage difference becomes large if there is an anomaly, thereby enabling anomaly detection.

[0080] The abnormality detection system (62) relating to this disclosure may also have the determination unit (73) perform the abnormality determination based on the squared value obtained by squaring the voltage difference.

[0081] According to the anomaly detection system (62) relating to this disclosure, the positive and negative signs can be canceled out by using the squared value obtained by squaring the voltage difference.

[0082] The anomaly detection system (62) according to this disclosure has two or more predetermined phases (N) set within one cycle, and the determination unit (73) may perform the anomaly determination based on an added value obtained by adding the squared values ​​corresponding to each of the predetermined phases.

[0083] According to the anomaly detection system (62) described herein, by setting multiple predetermined phases within one cycle and observing the sum of the voltage differences in each predetermined phase, it is possible to improve the accuracy of anomaly detection.

[0084] The anomaly detection system (62) relating to this disclosure may also have the determination unit (73) perform the anomaly determination based on the average value obtained by dividing the added value by a predetermined number (N).

[0085] According to the anomaly detection system (62) relating to this disclosure, anomaly detection can be performed by looking at the average value, which is obtained by dividing the added value by a predetermined number. For example, setting a threshold for anomaly detection becomes easier.

[0086] The anomaly detection system (62) relating to this disclosure may have two or more past cycles set as cycles prior to the target cycle, and the determination unit (73) may perform the anomaly determination based on a total value obtained by summing the average values ​​corresponding to each of the past cycles.

[0087] According to the anomaly detection system (62) relating to this disclosure, when multiple past cycles are set, an anomaly determination is made based on the sum of the average values ​​corresponding to each past cycle. This makes it possible to compare the target cycle with multiple past cycles to make an anomaly determination, thereby improving the accuracy of the anomaly determination.

[0088] The anomaly detection system (62) relating to this disclosure may also have the determination unit (73) perform the anomaly determination based on an evaluation value obtained by dividing the total value by the target period and the number of past periods (M).

[0089] According to the anomaly detection system (62) relating to this disclosure, anomaly detection can be performed by looking at the evaluation value as an average, based on an evaluation value obtained by dividing the total value by the number of cycles. For example, setting a threshold for anomaly detection becomes easier.

[0090] In the abnormality detection system (62) relating to this disclosure, the voltage value may be a value obtained by multiplying the output voltage value output from the winding (25) by a predetermined constant.

[0091] According to the anomaly detection system described herein, sensitivity can be improved by using a voltage value obtained by multiplying the output voltage value output from the winding (25) by a predetermined constant.

[0092] The abnormality detection system (62) according to this disclosure may also have the determination unit (73) determine that an abnormality has occurred in the differential transformer type displacement meter (22) when the evaluation value is equal to or greater than a preset threshold.

[0093] According to the anomaly detection system (62) relating to this disclosure, it is possible to perform highly accurate anomaly detection by comparing an evaluation value based on the voltage difference with a threshold value.

[0094] The abnormality detection method according to this disclosure is an abnormality detection method for a differential transformer type displacement meter (22) in which the output voltage output from a winding (25) changes in response to an AC input voltage depending on the position of the movable core (26), and the abnormality detection method comprises the steps of: acquiring the voltage value of the output voltage at a predetermined phase timing of the input voltage; and making an abnormality determination based on the voltage difference between the voltage value acquired in response to a target period and the voltage value acquired in response to a period prior to the target period. [Explanation of Symbols]

[0095] 1: Power plant 2: Boiler 3: Turbine (steam turbine) 4: Generator 5: Condenser 6: Water supply pump 7: Turbine steam control valve 8: Control device 11: Stop valve 11a: Stop valve driver 11b, 12b: Piston shaft 11c, 11d, 12c, 12d: Link mechanism 12: Adjustment valve 12a: Regulator valve drive 20, 21: Displacement gauge 22, 22a, 22b: Differential transformer type displacement meter 23: Movable axis 24: Primary coil (primary winding) 25, 25a, 25b: Secondary coil (secondary winding) 26: Movable Iron Core 27a, 27b: Measurement section 28: Power supply 29: Coil 61: Opening degree control unit 62: Anomaly detection unit (anomaly detection system) 71: Acquisition part 72: Arithmetic section 73: Judgment section 74: Switching section

Claims

1. An anomaly detection system for a differential transformer type displacement meter in which the output voltage output from the winding changes in response to the AC input voltage depending on the position of the movable core, An acquisition unit that acquires the voltage value of the output voltage at a predetermined phase timing of the input voltage, A determination unit that performs abnormality determination based on the voltage difference between the voltage value acquired corresponding to the target period and the voltage value acquired corresponding to a period prior to the target period, An anomaly detection system equipped with the following features.

2. The abnormality detection system according to claim 1, wherein the determination unit performs the abnormality determination based on the squared value obtained by squaring the voltage difference.

3. Two or more predetermined phases are set within one cycle. The abnormality detection system according to claim 2, wherein the determination unit performs the abnormality determination based on an added value obtained by adding the squared values ​​corresponding to each of the predetermined phases.

4. The abnormality detection system according to claim 3, wherein the determination unit performs the abnormality determination based on the average value obtained by dividing the added value by the predetermined number.

5. Two or more past periods are set as periods prior to the aforementioned target period. The abnormality detection system according to claim 4, wherein the determination unit performs the abnormality determination based on a total value obtained by summing the average values ​​corresponding to each of the past cycles.

6. The abnormality detection system according to claim 5, wherein the determination unit performs the abnormality determination based on an evaluation value obtained by dividing the total value by the target period and the number of past periods.

7. The abnormality detection system according to any one of claims 1 to 6, wherein the voltage value is the value obtained by multiplying the output voltage value output from the winding by a predetermined constant.

8. The abnormality detection system according to claim 6, wherein the determination unit determines that an abnormality has occurred in the differential transformer type displacement meter when the evaluation value is equal to or greater than a preset threshold.

9. A method for detecting abnormalities in a differential transformer type displacement meter, in which the output voltage output from the winding changes in response to the AC input voltage depending on the position of the movable core, A step of acquiring the voltage value of the output voltage at a predetermined phase timing of the input voltage, A step of determining an anomaly based on the voltage difference between the voltage value acquired corresponding to the target period and the voltage value acquired corresponding to a period prior to the target period, An anomaly detection method having the following characteristics.

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