Magnetic saturation detection device, protection system, magnetic saturation detection method, and protection method

Abstract

A magnetic saturation detection device (560) derives the strain of an iron core (522) of a current transformer on the basis of a change in the resistance value of a resistor of a strain gauge (540). The magnetic saturation detection device (560) determines, on the basis of the strain of the iron core (522) of the current transformer, whether the iron core (522) of the current transformer is magnetically saturated.

Description

Magnetic saturation detection device, protection system, magnetic saturation detection method, and protection method

[0001] This application claims priority to Japanese Patent Application No. 2023-092323, filed on June 5, 2023, the contents of which are incorporated herein by reference in their entirety.

[0002] In current transformers, the iron core may become magnetically saturated during use. As a technology to deal with such magnetic saturation of the iron core, there is a current transformer (current transformer with transient characteristics) in which a gap is provided in part of the magnetic path (iron core), as described in Patent Document 1. The technology described in Patent Document 1 discloses using a non-oriented electromagnetic steel strip as the iron core material and reducing the gap in the magnetic path.

[0003] Japanese Patent Application Laid-Open No. 2001-230137

[0004] However, the technology described in Patent Document 1 is a technology for suppressing magnetic saturation of the iron core of a current transformer. Therefore, the technology described in Patent Document 1 cannot determine whether the iron core of a current transformer is magnetically saturated. Therefore, for example, it cannot accurately determine whether the value of the secondary current (output current) of the current transformer is affected by the magnetic saturation of the iron core. Therefore, a technology that can accurately determine whether the iron core of a current transformer is magnetically saturated is desired. The present disclosure has been made in consideration of the above problems, and aims to accurately determine whether the iron core of a current transformer is magnetically saturated.

[0005] The magnetic saturation detection device disclosed herein is a magnetic saturation detection device that detects magnetic saturation in the iron core of a current transformer, and has a first determination means that determines whether the iron core is magnetically saturated based on the measurement results of the strain in the iron core of the current transformer.

[0006] The protection system of the present disclosure is a protection system having a magnetic saturation detection device, and has a second determination means for determining whether or not there is a possibility of an abnormality in the object based on at least the secondary current of the current transformer, and a protection means for cutting off the primary current of the current transformer, wherein the primary current of the current transformer flows through the object, and the protection means performs the cutting off when the first determination means determines that the iron core is not magnetically saturated and the second determination means determines that there is a possibility of an abnormality in the object, and does not perform the cutting off in at least one of the cases where the first determination means determines that the iron core is magnetically saturated and the second determination means determines that there is no possibility of an abnormality in the object.

[0007] The magnetic saturation detection method disclosed herein is a magnetic saturation detection method for detecting magnetic saturation in an iron core of a current transformer, and includes a measurement step for measuring strain in the iron core of the current transformer, and a first determination step for determining whether the iron core is magnetically saturated based on the strain.

[0008] The protection method disclosed herein is a protection method that uses the magnetic saturation detection method, and includes a second determination step of determining whether or not there is a possibility of an abnormality in the object based on at least the secondary current of the current transformer, and a protection step of interrupting the primary current of the current transformer, wherein the primary current of the current transformer flows through the object, and the protection step performs the interruption when the first determination step determines that the iron core is not magnetically saturated and the second determination step determines that there is a possibility of an abnormality in the object, and does not perform the interruption in at least one of the cases where the first determination step determines that the iron core is magnetically saturated and the second determination step determines that there is no possibility of an abnormality in the object.

[0009] FIG. 1A is a diagram showing an example of the time waveform of a secondary current in a steady state. FIG. 1B is a diagram showing an example of a time change in a transient current and an example of a time change in a maximum magnetic flux density. FIG. 1C is a diagram showing an example of the time waveform of a secondary current in magnetic saturation. FIG. 2 is a diagram showing an example of an equivalent circuit of a current transformer. FIG. 3 is a diagram showing an example of the time waveforms of the magnetic flux density and magnetostriction of an iron core material. FIG. 4 is a diagram showing an example of the time waveforms of a transient current superimposed on the primary current of a current transformer and strain (iron core strain) occurring in the iron core. FIG. 5 is a diagram showing an example (part) of a power system. FIG. 6A is a diagram showing a first example of installation of strain gauges. FIG. 6B is a diagram showing a second example of installation of strain gauges. FIG. 7 is a diagram showing an example of the configuration of a magnetic saturation detection device.

[0010] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Note that the term "comparison objects" as being the same in terms of length, position, size, spacing, etc. includes not only cases where they are exactly the same, but also cases where they differ within the scope of the present disclosure (for example, differences within the tolerance range determined at the time of design).

[0011] (Background and Overview) First, the background to the development of this embodiment and an overview of this embodiment will be described. A current transformer is used, for example, to measure a current flowing through an object. The object includes, for example, at least one of a power line and a device. The power line and the device may be installed in a power system or may be installed outside the power system. The device may also be an electrical device such as a power control device. The object is not limited to a power line and a device, as long as the object passes through a current measured by the current transformer.

[0012] A current transformer has a secondary winding and an iron core. In the following description, the iron core refers to the iron core of the current transformer unless otherwise specified. The primary winding of a current transformer is an electric circuit (electric wire, etc.) through which the current to be measured flows. In a current transformer, the number of turns of the secondary winding is greater than the number of turns of the primary winding. The turns ratio of the secondary winding to the primary winding (number of turns of the primary winding N １ : Number of turns of secondary winding N ２ ) is 1:6, the secondary current I ２ is the primary current I １ 1 / 6 times (I ２=I １ / 6) (where loss in the current transformer is ignored). The primary current and secondary current are the currents flowing through the primary winding and secondary winding of the current transformer, respectively.

[0013] Since current transformers are measuring instruments, a decrease in measurement accuracy is a problem. One of the factors that decreases the measurement accuracy of a current transformer is magnetic saturation of the iron core. Here, magnetic saturation in this disclosure includes a state in which the magnetization does not change even if the absolute value of the magnetic field is increased (i.e., the relative permeability is approximately 1). However, magnetic saturation in this disclosure is not limited to this state. For example, when the iron core is magnetically saturated, the current transformation ratio (= I ２ / I １ This includes a state in which the relative permeability of the core is so small (approaching 1) that the relative permeability (R) of the core falls outside the allowable range for practical use. The allowable range for practical use may be determined, for example, based on the specifications of a device (e.g., a relay) that operates based on the secondary current of the current transformer, based on the specifications of the current transformer, based on the specifications of an object through which the primary current of the current transformer flows, or based on at least two of these specifications. A specific example of a state in which the core is magnetically saturated includes a state in which measurements cannot be made within the range of the class index of the current transformer. The range of the class index is the allowable range of error relative to the full scale.

[0014] In this embodiment, the object through which the primary current of the current transformer flows is a transformer, which is an example of equipment. This embodiment also illustrates a case where the allowable range for actual use is determined based on the specifications of the equipment that operates based on the secondary current of the current transformer. More specifically, this embodiment illustrates a case where the allowable range for actual use is determined based on the operating range of a bias differential relay 550, which will be described later.

[0015] For example, when a transformer connected to a power system is protected by a bias differential relay, the inflow and outflow currents of the transformer may be measured by a current transformer. The inflow current is the current flowing into the transformer (i.e., the primary current of the transformer). The outflow current is the current flowing out of the transformer (i.e., the secondary current of the transformer). In this embodiment, unless otherwise specified, the primary current and secondary current refer to the current transformer. Furthermore, in this embodiment, the primary current and secondary current of the transformer are referred to as the inflow current and outflow current, respectively, as necessary. In the following description, an object through which the primary current of the current transformer flows is referred to as the object to be interrupted as necessary.

[0016] The bias differential relay operates when the inflow and outflow currents are within a preset operating range. Specifically, the bias differential relay outputs a trip command to disconnect the transformer from the power grid. Note that disconnection refers to preventing power (current) from being supplied to the object to be disconnected (the transformer in this embodiment). Preferably, no power (current) is supplied to the object to be disconnected, meaning that no power (current) is supplied to the object to be disconnected. In this case, the power (current) supplied to the object to be disconnected is zero. However, no power (current) is not limited to no power (current) being supplied to the object to be disconnected. For example, no power (current) is supplied to the object to be disconnected, and may include a power (current) of a magnitude that cannot protect the object from the current flowing in the electrical circuit (the primary current of the current transformer). In this case, the power (current) supplied to the object to be disconnected may be greater than zero.

[0017] If the object to be interrupted is a device, the device is disconnected from the circuit through which the primary current of the current transformer flows (the primary current to the device is interrupted). If the object to be interrupted is a power line, a section of the circuit through which the primary current of the current transformer flows is disconnected from the power system (the primary current to that section is interrupted). The operating range of a ratioed differential relay (the range of inflow and outflow currents that activates the ratioed differential relay) is determined, for example, based on a ratio characteristic curve. A ratio characteristic curve is a curve that determines the conditions under which a ratioed differential relay operates (the relationship between inflow and outflow currents). The ratio characteristic curve is determined in the specifications of the ratioed differential relay. For example, a ratio characteristic curve can be represented on a coordinate system graph with the inflow current on the horizontal axis and the outflow current on the vertical axis. A ratio characteristic curve can also be represented on a coordinate system graph with the outflow current on the horizontal axis and the difference current (inflow current - outflow current) on the vertical axis. The ratio characteristic curve may also be represented by a coordinate graph with the scalar sum of the inflow and outflow currents on the horizontal axis and the vector sum of the inflow and outflow currents on the vertical axis. The inflow and outflow currents that define the ratio characteristic curve are converted to the primary or secondary side. For example, the inflow current that defines the ratio characteristic curve is expressed as a value converted to the secondary side.

[0018] In this embodiment, the case where the inflow and outflow currents are measured by a current transformer is exemplified. Furthermore, suppose that an error in the secondary current of the current transformer due to magnetic saturation of the iron core causes the inflow and outflow currents to fall within the operating range of the bias differential relay. In this case, the bias differential relay outputs a trip command even though it is not necessary to disconnect the transformer from the power grid. In other words, the bias differential relay performs unnecessary protective operation. Note that disconnecting the transformer from the power grid is performed, for example, by a switchgear.

[0019] Here, with reference to Figures 1A to 1C, we will explain how the secondary current of a current transformer changes when the iron core is magnetically saturated. As shown in Figure 1A, assume that a sinusoidal secondary current 111 flows outside the operating range of the ratio differential relay during steady state (when magnetic saturation is not occurring). In this state, as shown in Figure 1B, a transient current 121 that decays with a fixed time constant flows into the primary current I １When the magnetic flux density 122 of the iron core is superimposed on the magnetic flux density 122 of the iron core, the maximum magnetic flux density 122 of the iron core increases. When the iron core becomes magnetically saturated due to the increase in the maximum magnetic flux density 122 of the iron core, the time waveform of the secondary current 131 becomes a distorted wave, which is a time waveform that is significantly distorted compared to a sine wave, as shown in Figure 1C. As shown in Figure 1C, magnetic saturation of the iron core causes a negative error in the secondary current 131 of the current transformer. Furthermore, secondary current 132 is the secondary current when the iron core is not magnetically saturated. The negative error of the secondary current described above is an error with respect to secondary current 132.

[0020] Next, the mechanism by which a negative error occurs in the secondary current of a current transformer when the iron core is magnetically saturated will be described with reference to Fig. 2. Fig. 2 is a diagram showing an example of an equivalent circuit of a current transformer. In Fig. 2, I ０ indicates the excitation current. ０ denotes the magnetizing inductance. ２ indicates the DC resistance of the secondary winding. ２ indicates the leakage inductance of the secondary side. ｂ indicates the internal resistance (DC resistance) of the load 210. ｂ denotes the inductance of the burden 210. The burden 210 is a load of a current transformer. The burden 210 is, for example, the ratio differential relay described above.

[0021] In FIG. 2, the excitation inductance L ０ is large enough. Therefore, the secondary current I ２ is the excitation current I ０ The excitation inductance L ０ is proportional to the relative magnetic permeability of the iron core material. Therefore, as shown in Figure 1B, when the magnetic flux density of the iron core increases and magnetic saturation occurs, the relative magnetic permeability of the iron core material drops significantly, and the exciting inductance L ０ Therefore, the excitation current I ０ is the secondary current I ２ 1C is a time waveform in which the time waveform of secondary current 132 when magnetic saturation is not present is partially missing. This partially missing portion becomes the negative error described above.

[0022] As described above, when the iron core becomes magnetically saturated, a negative error occurs in the secondary current. Therefore, in order to deal with the magnetic saturation of the iron core, it is conceivable to provide a gap in the magnetic path (iron core) to use a current transformer with transient characteristics, as described in Patent Document 1, or to use a non-oriented electromagnetic steel sheet as the iron core material. However, this would result in a decrease in the steady-state excitation inductance L ０ becomes smaller, so the excitation current I ０ Therefore, in FIG. ２ Ga I １ ・N １ / N ２ Therefore, there is a risk that the measurement accuracy of the current transformer in steady state may decrease. Also, there is a limit to how much the negative error mentioned above can be reduced by improving the current transformer alone. １ ・N １ / N ２ is the primary current converted to the secondary side.

[0023] On the other hand, if it is possible to determine whether the iron core is magnetically saturated, it is possible to determine whether the negative error described above is occurring. Therefore, for example, if a negative error is occurring due to the magnetic saturation of the iron core, unnecessary protective operation of the biased differential relay can be suppressed by not performing a protective operation of the biased differential relay. Therefore, in this embodiment, as an application example of determining whether the iron core is magnetically saturated, a case where unnecessary protective operation of the biased differential relay is suppressed is illustrated. However, the application example of determining whether the iron core is magnetically saturated is not limited to suppressing unnecessary protective operation of the biased differential relay. For example, the relay for disconnecting the object to be disconnected (in this embodiment, a transformer) from the power system may be a relay other than a biased differential relay (e.g., an overcurrent relay).

[0024] The primary current of the current transformer may be the input current of the power line and the equipment, the output current of the power line and the equipment, or a current inside the equipment. The power line and the equipment may be any type that receives power and performs its function. The power line and the equipment may be distributed as products, or may not be distributed as products. The determination result of whether the iron core is magnetically saturated may be reflected in the display of the secondary current of the current transformer. For example, a display device that displays the value of the secondary current of the current transformer may display information indicating that the iron core is magnetically saturated along with the value of the secondary current of the current transformer. A display device that displays the value of the secondary current of the current transformer may display information indicating that the iron core is not magnetically saturated along with the value of the secondary current of the current transformer. A display device that displays the value of the secondary current of the current transformer may display information indicating whether the iron core is magnetically saturated along with the value of the secondary current of the current transformer. If the iron core is magnetically saturated, a display device that displays the value of the secondary current of the current transformer does not need to display the value of the secondary current of the current transformer. In this case, the display device that displays the value of the secondary current of the current transformer may also display information indicating that the iron core is magnetically saturated. Furthermore, at least one of the information indicating that the iron core is magnetically saturated and the information indicating that the iron core is not magnetically saturated may be displayed by a display device separate from the display device that displays the value of the secondary current of the current transformer. Furthermore, when the display device displays information indicating whether the iron core is magnetically saturated as described above, it is not necessary to reflect the determination result of whether the iron core is magnetically saturated in the operation of the device (the switchgear in this embodiment).

[0025] Furthermore, the application example of determining whether the iron core is magnetically saturated is not limited to suppressing unnecessary protective operation of a relay. For example, a current transformer may be connected to an ammeter. By applying the determination of whether the iron core is magnetically saturated to this example, it is possible to detect, for example, that the current value measured by the ammeter is incorrect due to magnetic saturation of the iron core of the current transformer. In this case, a relay and a switchgear may not be required.

[0026] Based on the above, the present inventor came up with the idea of ​​determining whether the iron core is magnetically saturated. It is conceivable to detect the magnetic saturation of the iron core based on the voltage or current of the windings. However, these do not directly represent the state of magnetization of the iron core. Therefore, the present inventor thought that by using the strain of the iron core, which changes in response to the state of magnetization of the iron core and changes rapidly as the state of magnetization of the iron core approaches a state of magnetic saturation, it would be possible to accurately determine whether the iron core is magnetically saturated. Here, strain refers to the change in the dimensions (length, width, etc.) of the iron core over time.

[0027] However, the strain of the iron core is expressed as the sum of the strain caused by changes in the magnetization of the iron core (magnetostriction) and strain caused by factors other than changes in the magnetization of the iron core. Factors other than changes in the magnetization of the iron core include temperature changes of the iron core. Therefore, the present inventors considered that, among the multiple types of strain included in the strain of the iron core, magnetostriction, which directly represents the state of magnetization of the iron core, could be used to more accurately determine whether the iron core is magnetically saturated. In the following description, the strain of the iron core (expressed as the sum of the aforementioned magnetostriction and strain other than magnetostriction) will be referred to as iron core strain as necessary. Furthermore, the strain generated in the iron core due to temperature changes of the iron core will be referred to as temperature strain as necessary.

[0028] An example of magnetostriction that occurs in an iron core when the iron core is magnetically saturated will be described below. FIG. 3 is a diagram showing an example of the time waveforms of the magnetic flux density and magnetostriction (material magnetostriction) of an iron core material. The iron core material is a soft magnetic material that constitutes the iron core. FIG. 3 illustrates a case where the iron core material is a grain-oriented electromagnetic steel sheet. FIG. 3 also shows an example of measurement of magnetostriction that expands and contracts in the rolling direction when a sample of grain-oriented electromagnetic steel sheet is excited with an AC current. The excitation direction in this AC excitation is the rolling direction. The time waveform of the excitation current used in this AC excitation is a sine wave.

[0029] In Figure 3, magnetostriction 321 of the core material is the magnetostriction that occurs when the core material is AC excited so that the magnetic flux density within the core material is high (when the core material is magnetically saturated). Furthermore, magnetostriction 322 of the core material is the magnetostriction that occurs when the core material is AC excited so that the magnetic flux density within the core material is low (when the core material is not magnetically saturated). When the core material is AC excited so that the magnetic flux density within the core material is high, and the core material becomes magnetically saturated, the amplitude of magnetostriction increases significantly in the elongation direction near the maximum magnetic flux density. That is, as shown in Figure 3, magnetostriction 321 shows a positive peak near the peak of magnetic flux density 311.

[0030] FIG. 4 shows the primary current I of the current transformer. １1B shows an example of the time waveforms of the transient current superimposed on the primary current of the current transformer and the strain (iron core strain) generated in the iron core. During steady-state operation, the transient current 411 superimposed on the primary current of the current transformer is zero. In contrast, during magnetic saturation, as described above with reference to FIG. 1B, the transient current 411, which decays with a constant time constant, is superimposed on the primary current of the current transformer. During the time when the magnetic field generated in the iron core by this transient current 411 and the magnetic field generated in the iron core by the AC current flowing as the primary current of the current transformer during steady-state operation are in the same direction, the magnetic field generated in the iron core becomes extremely large, resulting in magnetic saturation. As with iron core materials, when magnetic saturation occurs in the iron core, the amplitude of magnetostriction increases significantly in the elongation direction near the maximum magnetic flux density (see FIG. 3). As described above, iron core strain is expressed as the sum of magnetostriction and strain other than magnetostriction. Therefore, there is a positive correlation between iron core strain and magnetostriction. Therefore, as shown in Figure 4, the amplitude of the iron core strain 412 is small during steady state operation, but increases in the expansion direction (positive direction) during magnetic saturation. Thus, when the iron core is magnetically saturated, the amplitude of the iron core strain 412 changes significantly compared to when it is not magnetically saturated. Thus, the iron core strain varies significantly depending on whether the iron core is magnetically saturated. Therefore, using the iron core strain makes it possible to reliably determine whether the iron core is magnetically saturated. Furthermore, the time change in temperature strain is slower than the time change in magnetostriction when magnetic saturation occurs. Furthermore, during typical current transformer usage, the stress generated in the iron core due to external forces applied to the iron core by objects in contact with the iron core is small. Therefore, among the strains generated when the iron core of a current transformer is magnetically saturated, strains other than magnetostriction can be considered to be primarily temperature strain. Therefore, if the iron core strain increases suddenly, it can be assumed that the cause is magnetostriction. In other words, if the iron core strain increases suddenly, it can be considered that the iron core of the current transformer is magnetically saturated. Based on this, the present inventors have considered that by using the magnetostriction of the iron core, it is possible to more reliably determine whether the iron core is magnetically saturated.

[0031] As mentioned above, the iron core strain varies greatly depending on whether the iron core is magnetically saturated. Therefore, whether the iron core is magnetically saturated may be determined based on the result of comparing the instantaneous value of the iron core strain at a given time (i.e., one instantaneous value of the iron core strain) with a predetermined value.

[0032] Alternatively, a representative value (e.g., average value) of the core strain may be used to determine whether the core is magnetically saturated. This prevents a decrease in the accuracy of determining whether the core is magnetically saturated, even if the core strain is an outlier. For example, as shown in FIG. 4 , when the core is magnetically saturated, the average value (arithmetic mean value) of the core strain 412 changes. Therefore, for example, whether the core is magnetically saturated may be determined based on the results of comparing the change over time of the average value of the core strain 412 with a predetermined value. The change over time of the average value of the core strain 412 may be expressed, for example, as the difference between the arithmetic mean value of the instantaneous values ​​of the core strain 412 in a first period and the arithmetic mean value of the instantaneous values ​​of the core strain 412 in a second period.

[0033] However, as mentioned above, the iron core also expands and contracts due to temperature changes. That is, as mentioned above, iron core strain 412 includes temperature strain in addition to magnetostriction. Therefore, the average value of iron core strain 412 may also change due to temperature changes in the iron core. Therefore, if determining whether the iron core is magnetically saturated based on changes in the average value of iron core strain over time, there is a risk that the accuracy of determining whether the iron core is magnetically saturated may decrease if the temperature changes in the iron core are large.

[0034] Therefore, the present inventors have investigated a method for calculating magnetostriction based on the measurement results of iron core strain. Magnetostriction may be calculated, for example, by using a machine learning model such as a neural network. In this case, for example, instantaneous values ​​of iron core strain at multiple times may be included in the explanatory variables of the machine learning model. However, when magnetostriction is calculated using a machine learning model, there is a risk that the calculation time and calculation load will be large. In addition, a large amount of learning data must be collected.

[0035] As mentioned above, core strain varies greatly depending on whether the core is magnetically saturated or not. Furthermore, magnetostriction can be considered the factor that causes significant differences in core strain when the core is magnetically saturated. Furthermore, in current transformers, of the strains that occur when the core is magnetically saturated, strains other than magnetostriction can be considered to be primarily temperature strain. Furthermore, while magnetic saturation of the core occurs instantaneously due to an accident such as a transient current, temperature strain occurs due to changes in temperature, and therefore changes over time are small.

[0036] Based on the above, the present inventors considered that temperature strain can be expressed by using a representative value of multiple instantaneous values ​​of iron core strain at multiple times prior to the time at which it is determined whether the iron core is magnetically saturated. The present inventors then considered that it is possible to subtract temperature strain from iron core strain (i.e., to calculate magnetostriction) by calculating the difference between one instantaneous value of iron core strain (first instantaneous value) at the time at which it is determined whether the iron core is magnetically saturated and a representative value of multiple instantaneous values ​​of iron core strain (second instantaneous value) at multiple times prior to that time. The present inventors considered that it is possible to determine with high accuracy whether the iron core is magnetically saturated by determining whether the iron core is magnetically saturated based on the magnetostriction of the iron core calculated in this way.

[0037] In the following description, the representative value of multiple instantaneous values ​​(second instantaneous values) of the iron core strain at multiple times prior to the time at which it is determined whether the iron core is magnetically saturated will be referred to as the representative value of the iron core strain, as necessary.

[0038] Calculating the magnetostriction as the difference between one instantaneous value of the iron core strain at the time when it is determined whether the iron core is magnetically saturated and the representative value of the iron core strain corresponds to performing a calculation to subtract some or all of the strain other than magnetostriction from the iron core strain. In the following description, unless it is explicitly stated that the instantaneous value refers to values ​​at multiple times, it is assumed that the instantaneous value refers to a value at one time (i.e., one value).

[0039] In this embodiment, a case is illustrated in which the representative value of iron core strain compared with the instantaneous value of iron core strain is an average value (arithmetic mean value). However, the representative value is not limited to an average value. The representative value may be, for example, a median. In the following description, when the representative value of iron core strain is an average value, the representative value of iron core strain will be referred to as the average value of iron core strain as necessary. The value obtained by subtracting the average value of iron core strain from the instantaneous value of iron core strain represents the difference between the instantaneous value and the average value of iron core strain in the positive direction (elongation direction). In this embodiment, a case is illustrated in which whether the iron core is magnetically saturated is determined based on the value obtained by subtracting the average value of iron core strain from the instantaneous value of iron core strain. However, this is not necessarily required. For example, whether the iron core is magnetically saturated may be determined based on the value obtained by subtracting the instantaneous value of iron core strain from the average value of iron core strain. In this case, for example, the positive / negative relationship and the magnitude relationship can be changed in comparison with the case where the value obtained by subtracting the average value of iron core strain from the instantaneous value of iron core strain is used. For example, the value obtained by subtracting the instantaneous value of iron core strain from the average value of iron core strain exceeding a predetermined value can be replaced with the value obtained by subtracting the average value of iron core strain from the instantaneous value of iron core strain being lower than the predetermined value multiplied by −1.

[0040] The longer the period for calculating the average value of iron core strain, the more reliable the average value becomes, but the less frequently the average value needs to be updated. Therefore, the period for calculating the average value of iron core strain can be determined in advance from this perspective. For example, the average value of iron core strain may be calculated over a predetermined period corresponding to multiple periods of the time waveform of iron core strain. The average value of iron core strain may also be calculated each time an instantaneous value of iron core strain is obtained. For example, the iron core may be determined to be magnetically saturated if the value obtained by subtracting the latest average value of iron core strain from the latest instantaneous value of iron core strain exceeds a predetermined value (>0). Alternatively, the iron core may be determined not to be magnetically saturated if the value obtained by subtracting the latest average value of iron core strain from the latest instantaneous value of iron core strain does not exceed a predetermined value (>0). At least one of the instantaneous value of iron core strain and the average value of iron core strain does not need to be the latest value.

[0041] In the above case, whether the value obtained by subtracting the average value of the iron core strain from the instantaneous value of the iron core strain exceeds a predetermined value (>0) is an example of a judgment criterion for determining whether the iron core is magnetically saturated. Whether the judgment criterion is satisfied may be determined each time an instantaneous value of the iron core strain is obtained. Furthermore, whether the judgment criterion is satisfied does not necessarily have to be determined each time an instantaneous value of the iron core strain is obtained. In other words, the judgment criterion may be a condition that makes it possible to determine whether the iron core is magnetically saturated each time an instantaneous value of the iron core strain is obtained. In this way, even if an instantaneous value of the iron core strain is obtained, there may be cases where a judgment of whether the judgment criterion is satisfied is not performed. For example, the judgment criterion may be the first judgment criterion. In this case, a second judgment criterion for determining whether the first judgment criterion is satisfied may be further defined. The second judgment criterion may be defined based on at least one of the primary current (e.g., amplitude) of the current transformer, the measurement environment of the current transformer, and the state of the equipment connected to the current transformer. Furthermore, the second judgment condition may be, for example, a condition in which a judgment is made as to whether or not the first judgment condition is satisfied when an instantaneous value of the iron core strain is obtained after a predetermined period has elapsed since the previous judgment as to whether or not the first judgment condition is satisfied.

[0042] It is sufficient that the difference between the time when an instantaneous value of the iron core strain (one first instantaneous value) is obtained and the latest of the times (previous times) when multiple instantaneous values ​​(multiple second instantaneous values) for calculating the average value of the iron core strain are obtained is not excessively large. The time when the instantaneous value of the iron core strain is obtained and the latest of the times when multiple instantaneous values ​​for calculating the average value of the iron core strain are obtained may be the same or different.

[0043] Furthermore, the period for calculating the average value of the iron core strain may be, for example, one period instead of multiple periods. Furthermore, the period for calculating the average value of the iron core strain may be adjusted (updated) during actual use.

[0044] Furthermore, if the predetermined value compared with the value obtained by subtracting the average core strain from the instantaneous value of iron core strain is too large, it will be more likely that the iron core is not magnetically saturated when it is actually magnetically saturated. Conversely, if the predetermined value is too small, it will be more likely that the iron core is magnetically saturated when it is not actually magnetically saturated. The predetermined value compared with the value obtained by subtracting the average core strain from the instantaneous value of iron core strain may be determined in advance from this perspective. Furthermore, the predetermined value compared with the value obtained by subtracting the average core strain from the instantaneous value of iron core strain may be adjusted (updated) during actual use. In the following description, the predetermined value compared with the value obtained by subtracting the average core strain from the instantaneous value of iron core strain will be referred to as the saturation determination reference value as necessary.

[0045] When determining the saturation determination reference value, for example, the iron core strain may be derived at multiple timings when the magnetic field strength of the iron core is gradually increased from 0 (zero) to magnetically saturate the iron core. The iron core strain at the multiple timings may be derived, for example, by conducting at least one of experiments and numerical simulations. A time waveform of the iron core strain may be derived based on the iron core strain at the multiple timings derived in this manner. In this case, a value may be derived by subtracting the average value of the iron core strain from the instantaneous value of the iron core strain based on the time waveform at at least one of timings when the iron core is considered to be magnetically saturated and timings when the iron core is considered not to be magnetically saturated. The saturation determination reference value may be determined based on the value obtained by subtracting the average value of the iron core strain from the instantaneous value of the iron core strain derived in this manner.

[0046] The saturation judgment reference value preferably differs depending on the material of the iron core of the current transformer, the operating conditions of the current transformer, etc. For example, if the ratio of the secondary current to the primary current of the current transformer is 4 / 6 and the iron core material is a high magnetic flux density material described in "JIS C2553:2019 "Grain-oriented electromagnetic steel strips," the absolute value of the saturation judgment reference value is, for example, 0.8 × 10 －６In addition, when the ratio of the secondary current to the primary current of the current transformer is 4 / 6 and the iron core material is a normal material described in "JIS C2553:2019 "Grain-oriented electromagnetic steel strips"," the absolute value of the saturation judgment reference value is, for example, 1.1 × 10 －６ Or 0.8 x 10 －６ , 1.1 × 10 －６ , respectively, and 0.79 × 10 －６ , 1.09 × 10 －６ etc. may also be used.

[0047] When comparing the value obtained by subtracting the average value of the iron core strain from the instantaneous value of the iron core strain with the saturation judgment reference value, the saturation judgment reference value is a positive value (0.8 × 10 －６ and 1.1 × 10 －６ On the other hand, the value obtained by subtracting the sequential value of the iron core strain from the average value of the iron core strain is the saturation judgment reference value, and the saturation judgment reference value is a negative value (-0.8 × 10 －６ and −1.1 × 10 －６ etc.).

[0048] As described above, by using the instantaneous value of the core strain to determine whether the core is magnetically saturated, it is possible to detect whether the core is magnetically saturated within one cycle from the time when the magnetic saturation occurs. Therefore, the time lag between when the core actually becomes magnetically saturated and when it is determined that the core is magnetically saturated can be shortened (i.e., a highly responsive determination can be made). Furthermore, for example, when the temperature of the core changes significantly, it is preferable to calculate the magnetostriction based on the core strain. In this case, it is more preferable to calculate the magnetostriction so as to shorten the time lag between when the core actually becomes magnetically saturated and when it is determined that the core is magnetically saturated, and to increase the accuracy of determining whether the core is magnetically saturated. Based on the above, this embodiment illustrates a case in which whether the core is magnetically saturated is determined based on the difference between the instantaneous value and the average value of the core strain. However, the determination condition for determining whether the core is magnetically saturated is not limited to the condition using the difference between the instantaneous value and the average value of the core strain.

[0049] As shown in Figure 4, when the iron core becomes magnetically saturated, the instantaneous value of magnetostriction increases rapidly in the positive direction (elongation direction), and the iron core strain also shows a change similar to the change in the instantaneous value of magnetostriction. Therefore, for example, whether the iron core is magnetically saturated may be determined based on the difference between two instantaneous values ​​of iron core strain obtained at a fixed time interval. The fixed time may be determined based on, for example, the time from when the iron core begins to become magnetically saturated to when the iron core strain first reaches a peak in the time waveform of the iron core strain.

[0050] As described above, whether the iron core is magnetically saturated may be determined based on the results of comparing the instantaneous value of the iron core strain at a single time with a predetermined value. Alternatively, whether the iron core is magnetically saturated may be determined based on the results of comparing the time change of a representative value (e.g., average or median) of the instantaneous values ​​of the iron core strain at multiple times with a predetermined value. Also, whether the iron core is magnetically saturated may be determined based on the results of comparing the instantaneous value of the magnetostriction at a single time with a predetermined value. Alternatively, whether the iron core is magnetically saturated may be determined by using a representative value (e.g., average) of the instantaneous values ​​of the magnetostriction at multiple times.

[0051] (Magnetic saturation detection device, protection system, magnetic saturation detection method, protection method) A specific example of this embodiment will be described in detail below. Fig. 5 is a diagram showing an example of a power system to which the magnetic saturation detection device and protection system of this embodiment are applied. Note that Fig. 5 shows only a part of the power system. As mentioned above, Fig. 5 also shows equipment (transformer) as an example of the object to be protected.

[0052] In Fig. 5, a device 510 is installed in the power system. As described above, in this embodiment, the device 510 is a transformer. The transformer may be a single-phase transformer or a three-phase transformer. In the following description, the device 510 will be referred to as a transformer 510 as necessary.

[0053] Current transformer 520a is installed on the primary side (input side) of transformer 510. Current transformer 520a measures the inflow current (primary current) of transformer 510. Current transformer 520b is installed on the secondary side (output side) of transformer 510. Current transformer 520b measures the outflow current (secondary current) of transformer 510. Current transformers 520a and 520b have secondary windings 521a and 521b and iron cores 522a and 522b. Current transformers 520a and 520b may have the same configuration. Current transformers 520a and 520b may have different configurations. The configuration of current transformers 520a and 520b is determined based on, for example, the inflow current and outflow current of transformer 510. Current transformers 520a and 520b themselves are realized using known technology. Therefore, detailed description of the current transformers 520a and 520b will be omitted. Furthermore, in this embodiment, the iron cores 522a and 522b are configured using grain-oriented electromagnetic steel sheets. However, the iron cores 522a and 522b may be configured using iron core materials other than grain-oriented electromagnetic steel sheets (e.g., non-oriented electromagnetic steel sheets). Furthermore, an air gap may or may not be provided in the magnetic path of the iron cores 522a and 522b. The primary winding of the current transformer 520a is the electric wire 530a that constitutes the electrical path through which the inflow current of the transformer 510 flows. The primary winding of the current transformer 520b is the electric wire 530b that constitutes the electrical path through which the outflow current of the transformer 510 flows.

[0054] In this embodiment, the case where strain gauges 540a and 540b are attached to the iron cores 522a and 522b is illustrated. The strain gauges 540a and 540b may have the same configuration. The strain gauges 540a and 540b may have different configurations. The configuration of the strain gauges 540a and 540b is determined based on, for example, the material, size, shape, etc. of the iron cores 522a and 522b of the current transformers 520a and 520b.

[0055] In this embodiment, for simplicity of explanation, the current transformers 520a and 520b are illustrated as having the same configuration. Similarly, in this embodiment, the strain gauges 540a and 540b are illustrated as having the same configuration. In the following description, when there is no need to distinguish between the iron cores 522a and 522b, they will be referred to as the iron core 522 as needed. Similarly, in the following description, when there is no need to distinguish between the strain gauges 540a and 540b, they will be referred to as the strain gauge 540 as needed.

[0056] In addition, when protection is performed using a bias differential relay, one current transformer is generally installed on both the input side and the output side of the object to be protected (transformer 510 in this embodiment). As illustrated in Fig. 5, strain gauges 540a, 540b may be attached to both iron cores 522a, 522b of these two current transformers 520a, 520b. The strain gauge may be attached to the iron core of one of these two current transformers 520a, 520b, depending on the object to be protected, the configuration of the power system, etc., and may not be attached to the iron core of the other current transformer.

[0057] 6A and 6B are diagrams showing examples of installation of strain gauges 540. In Fig. 6A and Fig. 6B, the double-headed arrow shown on iron core 522 indicates the rolling direction of the grain-oriented electromagnetic steel sheets that make up iron core 522. Fig. 6A illustrates an example where iron core 522 is a wound core. Fig. 6B illustrates an example where iron core 522 is a stacked core. Note that, for convenience of illustration, lines representing the thickness of the grain-oriented electromagnetic steel sheets that make up iron core 522 are omitted in Fig. 6A and Fig. 6B.

[0058] 6A and 6B, the strain gauge 540 is preferably attached to the iron core 522 so that the strain detection direction (expansion / contraction direction) is approximately (preferably) the same as the rolling direction. The resistance value of the resistor in the strain gauge 540 changes as the iron core 522 expands or contracts in the rolling direction. The strain gauge 540 outputs this change in resistance value. The strain gauge 540 itself and the measurement of strain (iron core strain) using the strain gauge 540 can be realized using known technology. Therefore, detailed description of these is omitted.

[0059] As described above, in this embodiment, a case where the sensor for measuring the strain (iron core strain) of the iron core 522 of the current transformer is a strain gauge is exemplified. However, the sensor for measuring the iron core strain is not limited to a strain gauge. For example, the sensor for measuring the iron core strain may be a sensor (e.g., a laser displacement meter) for measuring the strain of the iron core 522 of the current transformer in a non-contact manner.

[0060] Furthermore, the sensor for measuring the iron core strain may be, for example, an accelerometer. However, in this case, an integration calculation is required to derive the iron core strain. Therefore, an integration constant must be determined. When the iron core is magnetically saturated, the iron core strain changes transiently. Therefore, it is not easy to accurately estimate the behavior of the integration constant. Therefore, it is preferable that the sensor for measuring the iron core strain is a sensor that measures a physical quantity (specifically, a physical quantity other than acceleration and speed) from which the iron core strain can be derived without an integration calculation.

[0061] Furthermore, this embodiment illustrates the case where iron core strain is measured in the rolling direction. However, iron core strain may also be measured in directions other than the rolling direction. In this case, the direction in which strain is likely to occur in the iron core material may be investigated. For example, the magnitude of strain in the magnetized iron core material may be derived in multiple directions. The magnitude of strain in the multiple directions may be derived, for example, by performing at least one of experiments and numerical simulations. The direction in which strain is likely to occur in the iron core material may be derived based on the magnitude of strain in the multiple directions derived in this manner. Iron core strain may be measured in the direction derived in this manner.

[0062] In this embodiment, the bias differential relay 550 determines whether the inflow and outflow currents of the transformer 510 are within their operating ranges based on the inflow current of the transformer 510 measured by the current transformer 520a and the outflow current of the transformer 510 measured by the current transformer 520b. This embodiment also illustrates a case in which the bias differential relay 550 outputs a trip command when the inflow and outflow currents of the transformer 510 are within their operating ranges. This embodiment also illustrates a case in which the bias differential relay 550 does not output a trip command when the inflow and outflow currents of the transformer 510 are not within their operating ranges. The bias differential relay 550 itself can be realized using known technology. Therefore, a detailed description of the bias differential relay 550 will be omitted. However, in general, the trip command output from the bias differential relay 550 is output to the switching device 570. Switching device 570 is a device, such as a circuit breaker, for disconnecting transformer 510 from the power grid. In contrast, this embodiment illustrates a case in which bias differential relay 550 outputs a trip command to magnetic saturation detection device 560 without outputting it to switching device 570. In the following description, the trip command output from bias differential relay 550 will be referred to as a provisional trip command as necessary to distinguish it from a trip command output from magnetic saturation detection device 560, which will be described later. Note that when transformer 510 is a three-phase transformer, it is preferable that a current transformer be provided for each phase and that a bias differential relay 550 be provided for each phase.

[0063] In this embodiment, the magnetic saturation detection device 560 determines whether the iron core 522 is magnetically saturated based on the measurement results of the strain (iron core strain) of the iron core 522. This embodiment also illustrates a case in which the magnetic saturation detection device 560 is electrically connected to the strain gauge 540 via a wire. This embodiment also illustrates a case in which the magnetic saturation detection device 560 derives the strain (iron core strain) of the iron core 522 based on changes in the resistance value of the resistor in the strain gauge 540. However, this is not necessarily the case. For example, the strain (iron core strain) of the iron core 522 may be derived externally from the magnetic saturation detection device 560. This embodiment also illustrates a case in which the instantaneous value of the iron core strain is handled. Therefore, it is preferable that the measurement system for the iron core strain (the coupling between the strain gauge 540 and the magnetic saturation detection device 560 and the coupling between each circuit in the magnetic saturation detection device 560) be DC coupled. The change in the resistance value of the resistor and the strain of the iron core 522 (iron core strain) may be input to the magnetic saturation detector 560 via wireless communication.

[0064] In this embodiment, a case is illustrated in which, when a temporary trip command is output from the biased differential relay 550 and the magnetic saturation detection device 560 determines that the iron core 522 is not magnetically saturated, the magnetic saturation detection device 560 outputs a trip command to the switching device 570. In addition, in this embodiment, a case is illustrated in which the magnetic saturation detection device 560 does not output a trip command to the switching device 570 in at least one of the cases in which the temporary trip command is not output from the biased differential relay 550 and the magnetic saturation detection device 560 determines that the iron core 522 is magnetically saturated. In this embodiment, a case is illustrated in which the switching device 570 disconnects the transformer 510 from the power grid when the switching device 570 receives a trip command output from the magnetic saturation detection device 560 (not from the biased differential relay 550). As described above, in this embodiment, even if the biased differential relay 550 has output a provisional trip command (i.e., the biased differential relay 550 has determined that the transformer 510 needs to be disconnected from the power grid), if the magnetic saturation detection device 560 determines that the iron core 522 is magnetically saturated, the trip command is not output to the switching device 570. Therefore, it is possible to suppress unnecessary protective operations as described in the section (Background and Overview).

[0065] Fig. 7 is a diagram showing an example of the configuration of a magnetic saturation detection device 560. In this embodiment, Fig. 7 illustrates a case in which the magnetic saturation detection device 560 includes a bridge circuit 561, a dynamic distortion amplifier 562, a smoothing circuit 563, a differential amplifier 564, a comparison circuit 565, a voltage generation circuit 566, and a switch circuit 567.

[0066] The bridge circuit 561 and the dynamic strain amplifier 562 are an example of a means for deriving the instantaneous value of the iron core strain, as described in the section (Background and Overview). The bridge circuit 561 converts the change in resistance value output from the strain gauge 540 into a voltage corresponding to the amount of strain. The dynamic strain amplifier 562 amplifies and outputs the output voltage of the bridge circuit 561. This embodiment illustrates a case where the signal output from the dynamic strain amplifier 562 is a signal indicating the instantaneous value of the iron core strain, and the signal output from the dynamic strain amplifier 562 is a signal indicating a voltage value. The bridge circuit 561 and the dynamic strain amplifier 562 may be known devices used in strain measurement.

[0067] The smoothing circuit 563 is an example of the means for deriving the average value of core strain described in the section (Background and Overview). In this embodiment, an example is shown in which the smoothing circuit 563 smooths and outputs a signal for a predetermined period corresponding to multiple cycles, out of the signals indicating the instantaneous values ​​of core strain output from the dynamic strain amplifier 562. In this embodiment, an example is shown in which the signal output from the smoothing circuit 563 is a signal indicating the average value of core strain, and the signal output from the smoothing circuit 563 is a signal indicating a voltage value.

[0068] The differential amplifier 564 is an example of a means for subtracting the latest average value of core strain from the latest instantaneous value of core strain, as described in the "Background and Overview" section. Subtracting the average value of core strain from the instantaneous value of core strain is an example of calculating magnetostriction. In this embodiment, the differential amplifier 564 amplifies and outputs the difference between the signal indicating the instantaneous value of core strain output from the dynamic strain amplifier 562 and the signal indicating the average value of core strain output from the smoothing circuit 563. In this way, this embodiment illustrates a case in which the signal output from the differential amplifier 564 is a signal indicating a value obtained by subtracting the latest average value of core strain from the latest instantaneous value of core strain, and the signal output from the differential amplifier 564 is a signal indicating a voltage value. In the following description, the signal output from the differential amplifier 564 will be referred to as a magnetostriction differential signal as necessary.

[0069] The comparison circuit 565 and the voltage generation circuit 566 are an example of means for determining whether the value obtained by subtracting the latest average value of the core strain from the latest instantaneous value of the core strain exceeds the saturation determination reference value, as described in the (Background and Overview) section. The voltage generation circuit 566 is an example of means for generating a reference voltage corresponding to the saturation determination reference value, as described in the (Background and Overview) section. The comparison circuit 565 compares the voltage value indicated by the magnetostriction difference signal output from the differential amplifier 564 with the reference voltage output from the voltage generation circuit 566. The comparison circuit 565 does not output a trip command if the former exceeds the latter. The comparison circuit 565 also outputs a trip command if the former does not exceed the latter. In this embodiment, the trip command indicates the value of the output voltage of the comparison circuit 565. In this embodiment, the output voltage of the comparison circuit 565 exceeding 0 (zero) corresponds to the output of the trip command. In this embodiment, the case where the output voltage of the comparison circuit 565 being 0 (zero) corresponds to not outputting a trip command is exemplified. In this case, the trip command is a command indicating that the output voltage of the comparison circuit 565 is a value greater than 0 (zero).

[0070] The switch circuit 567 is a circuit connected between the output terminal of the comparison circuit 565 and the input terminal of the switching device 570. In this embodiment, a case is illustrated in which the switch circuit 567 electrically connects the output terminal of the comparison circuit 565 to the input terminal of the switching device 570 when a temporary trip command is output from the biased differential relay 550 and the magnetic saturation detection device 560 determines that the iron core 522 is not magnetically saturated. In addition, this embodiment illustrates a case in which the switch circuit 567 does not electrically connect the output terminal of the comparison circuit 565 to the input terminal of the switching device 570 when a temporary trip command is not output from the biased differential relay 550. In this embodiment, a case is illustrated in which the switch circuit 567 is used to prevent the output of a trip command to the switching device 570 when a temporary trip command is output from the biased differential relay 550 and the magnetic saturation detection device 560 determines that the iron core 522 is magnetically saturated. In addition, in this embodiment, an example is given of a case where a temporary trip command is output from the proportional differential relay 550 and the magnetic saturation detection device 560 has not determined that the iron core 522 is magnetically saturated, in which case a trip command is output to the switching device 570 by using the switch circuit 567.

[0071] As described above, this embodiment illustrates a case in which the measurement step is realized by the operation of the strain gauge 540, the bridge circuit 561, and the dynamic strain amplifier 562. This embodiment also illustrates a case in which the first determination step and the first determination means are realized by the operation of the smoothing circuit 563, the differential amplifier 564, the comparison circuit 565, and the voltage generation circuit 566. This embodiment also illustrates a case in which the fact that the inflow and outflow currents are within the operating range of the biased differential relay 550 indicates a possibility of an abnormality in the object (in this embodiment, the transformer 510). This embodiment also illustrates a case in which the second determination step and the second determination means are realized by the operation of the biased differential relay 550 (determining whether the inflow and outflow currents are within the operating range of the biased differential relay 550). This embodiment also illustrates a case in which the protection step and the protection means are realized by the operation of the switch circuit 567 and the switching device 570. Furthermore, in this embodiment, a case where a protection system is realized by using strain gauges 540, bias differential relays 550, magnetic saturation detection devices 560, and switching devices 570 is exemplified. Note that a magnetic saturation detection system may also be realized by using strain gauges 540 and magnetic saturation detection devices 560. The magnetic saturation detection system may include bias differential relays 550 in addition to strain gauges 540 and magnetic saturation detection devices 560.

[0072] As described in the "Background and Overview" section, the application of determining whether the iron core is magnetically saturated is not limited to suppressing unnecessary protective operation of a bias differential relay. For example, determining whether the iron core is magnetically saturated may be applied to suppressing unnecessary protective operation of an overcurrent relay. Furthermore, information indicating that the iron core is magnetically saturated may be displayed on a display device that displays the value of the secondary current of a current transformer. In these cases, for example, the magnetic saturation detection device 560 may have a means (function) for determining that there is a possibility of an abnormality in the object to be interrupted (the transformer 510 in this embodiment) when the secondary current of the current transformer exceeds a predetermined value. In this case, the magnetic saturation detection device 560 preferably determines that there is a possibility of an abnormality in the object to be interrupted when the magnetic saturation detection device 560 determines that the iron core is not magnetically saturated and when the secondary current of the current transformer exceeds a predetermined value. In addition, the magnetic saturation detection device 560 may determine that there is no possibility of an abnormality in the object to be cut off when the magnetic saturation detection device 560 determines that the iron core is magnetically saturated or when the secondary current of the current transformer does not exceed a predetermined value.

[0073] Note that being within the operating range of the biased differential relay 550 is an example of a pre-set condition that requires interruption of the primary current of the object to be interrupted (the transformer 510 in this embodiment). The pre-set condition that requires interruption of the primary current of the object to be interrupted (the transformer 510 in this embodiment) is, for example, a condition that is defined as an interruption condition for the electric circuit in the specifications of the relay (the biased differential relay 550 in this embodiment). Generally, the electric circuit is interrupted immediately when such an interruption condition is met. In contrast, this embodiment illustrates a case in which the electric circuit is not interrupted if the iron core 522 is magnetically saturated, even if such an interruption condition is met.

[0074] In addition, this embodiment illustrates a case where the magnetic saturation detector 560 is realized by a hardware circuit. However, at least a portion of the magnetic saturation detector 560 may be realized by software. In this case, the magnetic saturation detector 560 may have, for example, one or more hardware processors such as a central processing unit (CPU) and one or more memories such as a random access memory (RAM) and a read-only memory (ROM). In this case, the magnetic saturation detector 560 may perform various calculations by, for example, executing one or more programs stored in the memory using one or more hardware processors. The various calculations include, for example, calculations for implementing the functions of the smoothing circuit 563, differential amplifier 564, comparison circuit 565, and voltage generation circuit 566 shown in FIG. 7 .

[0075] For example, the magnetic saturation detector 560 may convert the signal indicating the instantaneous value of magnetostriction output from the dynamic strain amplifier 562 into digital data. In this case, the magnetic saturation detector 560 may execute the functions of the smoothing circuit 563, the differential amplifier 564, the comparison circuit 565, the voltage generation circuit 566, and the switch circuit 567 according to software (computer program). The smoothing circuit 563 may perform the function of calculating the average value of the core strain using the instantaneous value of the core strain each time the instantaneous value of the core strain is obtained. The differential amplifier 564 may perform the function of calculating the value obtained by subtracting the average value of the core strain from the instantaneous value of the core strain each time the instantaneous value of the core strain is obtained. The comparison circuit 565 and the voltage generation circuit 566 may perform the function of determining whether the value obtained by subtracting the average value of the core strain from the instantaneous value of the core strain exceeds a saturation determination reference value. The function of the switch circuit 567 is, for example, to output a trip command to the switching device 570 only when a provisional trip command is output from the proportional differential relay 550 and the value obtained by subtracting the average value of the core strain from the instantaneous value of the core strain does not exceed the saturation judgment reference value.

[0076] Regarding the functions of the switch circuit 567, for example, the magnetic saturation detection device 560 may determine whether a temporary trip command has been received from the bias differential relay 550 before determining whether the value obtained by subtracting the average core strain value from the instantaneous value of the core strain exceeds the saturation judgment reference value. In this case, if a temporary trip command has been received, the magnetic saturation detection device 560 may determine whether the value obtained by subtracting the average core strain value from the instantaneous value of the core strain exceeds the saturation judgment reference value. Furthermore, if a temporary trip command has not been received, the magnetic saturation detection device 560 does not need to determine whether the value obtained by subtracting the average core strain value from the instantaneous value of the core strain exceeds the saturation judgment reference value. In this case, the magnetic saturation detection device 560 can omit the process of determining whether the value obtained by subtracting the average magnetostriction value from the instantaneous value of the magnetostriction exceeds the saturation judgment reference value if a temporary trip command has not been received.

[0077] In addition, in the present embodiment, the bias differential relay 550 and the magnetic saturation detection device 560 are separate devices. However, for example, the magnetic saturation detection device 560 may have the same functions as the bias differential relay 550.

[0078] The magnetic saturation detection device 560 may also be realized using dedicated hardware (for example, a field programmable gate array (FPGA) and an application specific integrated circuit (ASIC)).

[0079] The magnetic saturation detection device 560 shown in FIG. 7 may be a device for each of the strain gauges 540a and 540b. In this case, the magnetic saturation detection system may have two magnetic saturation detection devices 560, one for the strain gauge 540a and the other for the strain gauge 540b. In this case, temporary trip commands may be output in parallel from the bias differential relay 550 to the switch circuits 567 of the two magnetic saturation detection devices 560. The reference voltage value generated by the voltage generation circuit 566 may be different for each of the strain gauges 540a and 540b, or may be the same for both the strain gauges 540a and 540b. In addition, for example, all or part of the configuration of the magnetic saturation detection device 560 shown in FIG. 7 may be common to both the strain gauges 540a and 540b. In this case, the magnetic saturation detection system may have a single magnetic saturation detection device 560. For example, the switch circuit 567 may be common to both strain gauges 540a and 540b. In this case, the bridge circuit 561, dynamic strain amplifier 562, smoothing circuit 563, differential amplifier 564, comparison circuit 565, and voltage generation circuit 566 may be provided for each of the strain gauges 540a and 540b. In this case, the magnetic saturation detection device 560 may have two sets of the bridge circuit 561, dynamic strain amplifier 562, smoothing circuit 563, differential amplifier 564, comparison circuit 565, and voltage generation circuit 566. In this case, the switch circuit 567 may individually turn on and off the connection between the output terminal of the comparison circuit 565 for strain gauge 540a and the input terminal of the switching device 570, and turn on and off the connection between the output terminal of the comparison circuit 565 for strain gauge 540b and the input terminal of the switching device 570. The above may be realized by software (computer program) or dedicated hardware. Alternatively, the resistance value output from only one of the strain gauges 540 a and 540 b may be input to the magnetic saturation detector 560 shown in FIG.

[0080] (Summary) As described above, in this embodiment, the magnetic saturation detection device 560 derives the strain (iron core strain) of the iron core 522 of the current transformer based on changes in the resistance value of the resistor in the strain gauge 540. The magnetic saturation detection device 560 determines whether the iron core 522 is magnetically saturated based on the strain of the iron core 522 of the current transformer. Therefore, by determining whether the iron core 522 is magnetically saturated using the iron core strain, which changes suddenly as the iron core approaches magnetic saturation, it is possible to determine with high accuracy whether the iron core 522 is magnetically saturated. Furthermore, it is possible to determine whether the iron core 522 is magnetically saturated without making any major modifications to the current transformer 520, such as winding a coil around the iron core 522.

[0081] In this embodiment, the magnetic saturation detector 560 determines whether the iron core 522 is magnetically saturated based on one or more instantaneous values ​​of the iron core strain. Using the iron core strain makes it possible to obtain highly reliable instantaneous values. Therefore, it is possible to more accurately determine whether the iron core 522 is magnetically saturated.

[0082] Furthermore, in this embodiment, magnetic saturation detection device 560 determines whether iron core 522 is magnetically saturated using, as a determination condition, a condition that enables determination whether iron core 522 is magnetically saturated each time an instantaneous value of iron core strain is obtained. Therefore, it is possible to reduce the time lag from when the iron core actually becomes magnetically saturated to when it is determined that the iron core is magnetically saturated.

[0083] Furthermore, in this embodiment, the magnetic saturation detection device 560 calculates magnetostriction based on the iron core strain. The magnetic saturation detection device 560 determines whether the iron core is magnetically saturated based on the magnetostriction. Therefore, even if the iron core strain includes temperature strain that is too large to be ignored as strain other than magnetostriction, it is possible to further reduce erroneous determinations due to temperature changes in the iron core 522. This makes it possible to more accurately determine whether the iron core 522 is magnetically saturated.

[0084] In this embodiment, the magnetic saturation detector 560 calculates at least a portion of the iron core strain other than magnetostriction based on the measurement results of the iron core strain, and calculates magnetostriction based on the measurement results of the iron core strain and the strain other than magnetostriction. Therefore, magnetostriction can be calculated without calculating the magnetostriction itself.

[0085] In this embodiment, the magnetic saturation detector 560 determines whether the iron core 522 is magnetically saturated based on a first instantaneous value of the iron core strain and a representative value of multiple second instantaneous values ​​of the iron core strain. The multiple timings at which the multiple second instantaneous values ​​are obtained are timings prior to the timing at which the single first instantaneous value is obtained. Therefore, strains other than magnetostriction can be expressed by using the representative value of the multiple second instantaneous values ​​of the iron core strain. Therefore, strains other than magnetostriction can be easily calculated.

[0086] In this embodiment, the magnetic saturation detector 560 determines whether the iron core 522 is magnetically saturated based on the difference between one first instantaneous value of the iron core strain and a representative value of multiple second instantaneous values ​​of the iron core strain. Therefore, magnetostriction can be expressed by using this difference, and magnetostriction can be easily calculated.

[0087] Furthermore, in this embodiment, the magnetic saturation detection device 560 determines whether the iron core 522 is magnetically saturated based on the result of comparing the difference between one first instantaneous value of the iron core strain and a representative value of multiple second instantaneous values ​​of the iron core strain with the saturation determination reference value. Therefore, it is possible to easily and accurately determine whether the iron core 522 is magnetically saturated.

[0088] Furthermore, in this embodiment, bias differential relay 550 determines whether or not there is a possibility of an abnormality in transformer 510 based on at least the secondary current of current transformer 520. Magnetic saturation detection device 560 operates switching device 570 when there is a possibility of an abnormality in transformer 510 and iron core 522 is not magnetically saturated. Furthermore, magnetic saturation detection device 560 does not operate switching device 570 when there is at least one of the cases where there is no possibility of an abnormality in transformer 510 and where iron core 522 is magnetically saturated.

[0089] Therefore, when biased differential relay 550 determines that transformer 510 may have an abnormality and the secondary current (output current) of specific current transformer 520a or 520b is an abnormal value, it is possible to accurately determine whether the cause of the abnormality is due to magnetic saturation of iron core 522 of that specific current transformer, or due to a factor other than magnetic saturation of iron core 522 of that specific current transformer. Furthermore, magnetic saturation detection device 560 does not operate switching device 570 if iron core 522 is magnetically saturated, even if biased differential relay 550 determines that transformer 510 may have an abnormality. Therefore, unnecessary protective operation of switching device 570 can be suppressed.

[0090] (Other Embodiments) The above-described embodiments of the present disclosure can be realized by a computer executing a program. Furthermore, a computer-readable recording medium on which the program is recorded and a computer program product such as the program can also be applied as embodiments of the present disclosure. Examples of recording media that can be used include flexible disks, hard disks, optical disks, magneto-optical disks, CD-ROMs, magnetic tapes, non-volatile memory cards, and ROMs. Furthermore, the embodiments of the present disclosure can be realized by a programmable logic controller (PLC) or dedicated hardware such as an application-specific integrated circuit (ASIC). The above-described embodiments of the present disclosure merely illustrate specific examples of how the present disclosure can be implemented, and the technical scope of the present disclosure should not be interpreted as being limited by these examples. In other words, the present disclosure can be implemented in various forms without departing from its technical concept or main features.

[0091] The present disclosure can be used, for example, to measure current using a current transformer.

Claims

1. A magnetic saturation detection device for detecting magnetic saturation of an iron core of a current transformer, a first determining means for determining whether the iron core of the current transformer is magnetically saturated based on the measurement result of the strain of the iron core;

2. 2. The magnetic saturation detection device according to claim 1, wherein said first determination means determines whether said iron core is magnetically saturated based on one or more instantaneous values ​​of said strain.

3. 3. The magnetic saturation detection device according to claim 2, wherein the determination conditions for determining whether the iron core is magnetically saturated include a condition that makes it possible to determine whether the iron core is magnetically saturated each time one instantaneous value of the strain is obtained.

4. The magnetic saturation detection device according to any one of claims 1 to 3, wherein the first determination means calculates magnetostriction of the iron core based on the strain measurement results, and determines whether or not the iron core is magnetically saturated based on the magnetostriction.

5. 5. The magnetic saturation detection device according to claim 4, wherein the first determination means calculates at least a portion of the strain of the iron core other than magnetostriction based on the strain measurement results, and calculates the magnetostriction based on the strain measurement results and at least a portion of the strain other than magnetostriction.

6. the first determination means determines whether the iron core is magnetically saturated based on one first instantaneous value of the strain and a representative value of the plurality of second instantaneous values ​​of the strain; The magnetic saturation detection device according to any one of claims 1 to 3, wherein the timings at which the second instantaneous values ​​are obtained are timings prior to the timing at which the first instantaneous value is obtained.

7. 7. The magnetic saturation detection device according to claim 6, wherein the representative value is an average value.

8. 7. The magnetic saturation detecting device according to claim 6, wherein the first determining means determines whether the iron core is magnetically saturated based on the difference between the first instantaneous value and the representative value.

9. 9. The magnetic saturation detection device according to claim 8, wherein the first determination means determines whether the iron core is magnetically saturated based on a result of comparing a difference between the first instantaneous value and the representative value with a predetermined value.

10. The iron core is made of grain-oriented electromagnetic steel sheets, 4. The magnetic saturation detector according to claim 1, wherein the strain is a strain in the rolling direction of the grain-oriented electrical steel sheet.

11. 4. The magnetic saturation detection device according to claim 1, wherein the first determination means determines whether the iron core is magnetically saturated based on strain measured using a strain gauge.

12. A protection system having the magnetic saturation detection device according to any one of claims 1 to 3, a second determination means for determining whether or not there is a possibility of an abnormality in the object based on at least the secondary current of the current transformer; and a protection means for interrupting the primary current of the current transformer, The object is subjected to a primary current of the current transformer, The protection means performs the shutdown when the first determination means determines that the iron core is not magnetically saturated and the second determination means determines that there is a possibility of an abnormality in the object, and does not perform the shutdown when at least one of the following cases is determined: when the first determination means determines that the iron core is magnetically saturated, and when the second determination means determines that there is no possibility of an abnormality in the object.

13. The protection system of claim 12 , wherein the object is equipment or a power line.

14. A magnetic saturation detection method for detecting magnetic saturation in an iron core of a current transformer, comprising: a measuring step of measuring a strain of the iron core of the current transformer; a first determination step of determining whether or not the iron core is magnetically saturated based on the strain; A magnetic saturation detection method comprising:

15. A protection method using the magnetic saturation detection method according to claim 14, comprising: a second determination step of determining whether or not there is a possibility of an abnormality in the object based on at least the secondary current of the current transformer; a protection step of interrupting a primary current of the current transformer, The object is subjected to a primary current of the current transformer, The protection process performs the shutoff when the first determination process determines that the iron core is not magnetically saturated and the second determination process determines that there is a possibility of an abnormality in the object, and does not perform the shutoff when the first determination process determines that the iron core is magnetically saturated or the second determination process determines that there is no possibility of an abnormality in the object.