Ground fault detection device, ground fault monitoring device, and ground fault monitoring system

Abstract

To provide a ground fault detection device, a ground fault monitoring device, and a ground fault monitoring system capable of stably detecting both ground faults caused by lightning strikes and ground faults caused by contact with flying objects such as birds and animals.SOLUTION: A ground fault detection device installed on a tower leg of a power transmission tower 2 and for detecting ground faults includes: a ground-fault current detection unit 12, 14 that outputs an activation signal triggered by current flowing through the tower leg; magnetic sensors 16 and 17 that measure magnetic flux density due to ground fault current; and a control unit 15 that causes the magnetic sensors 16 and 17 to measure the magnetic flux density due to the ground fault current when the activation signal is received from the ground-fault current detection unit 12, 14.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ground fault detection device, a ground fault monitoring device, and a ground fault monitoring system for detecting ground faults caused by lightning strikes, birds, or animals in power transmission towers. [Background technology]

[0002] Conventionally, techniques for detecting the occurrence of ground faults are known by detecting the ground fault current flowing through power transmission towers, as well as the electric and magnetic fields generated by said ground fault current (for example, Patent Documents 1-3). Here, a ground fault current is a phenomenon in which the insulation of the insulators on a transmission tower is destroyed, causing current to flow from the transmission line through the tower legs and overhead ground wires to the ground. Factors that cause the insulation of the insulators to be destroyed include lightning strikes on transmission towers and collisions with insulators by flying objects such as birds and animals. Lightning strike currents on transmission towers are large, ranging from several thousand to tens of thousands of amperes, so detection devices using simple search coils have already been commercialized. However, in the case of minor ground faults caused by contact with insulators by flying objects such as birds and animals, the current flowing through the tower legs is small, only a few tens of amperes, and the duration is short, less than a few cycles, so no effective detection and measurement means have been put into practical use. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-136605 [Patent Document 2] Japanese Patent Publication No. 2013-19753 [Patent Document 3] Japanese Patent Publication No. 2007-163381 [Overview of the project] [Problems that the invention aims to solve]

[0004] In recent years, there has been a demand for ground fault detection devices that can appropriately detect both ground faults caused by lightning strikes and ground faults caused by contact with flying objects such as birds and animals. However, measuring the minute ground fault currents generated by contact with flying objects such as birds and animals requires the use of highly sensitive current transformers (CTs). However, when highly sensitive current transformers are installed on the legs of transmission towers to detect ground fault currents generated by contact with flying objects such as birds and animals, a huge di / dt (rate of change of current) during a lightning strike can induce a huge impulse voltage in the coil of the current transformer, potentially destroying the measurement circuit. This makes it difficult to detect both ground faults caused by lightning strikes and ground faults caused by contact with flying objects such as birds and animals. Furthermore, when a ground fault current occurs following a lightning strike current, the core of the current transformer can become saturated due to the magnetic field generated by the lightning strike current, causing the current transformer to temporarily malfunction and making it impossible to measure the ground fault current.

[0005] Furthermore, while conventional systems can detect the presence or absence of ground fault current, simply detecting its presence is insufficient for estimating the cause of minor ground faults and the degree of damage to insulators, etc. It is desirable to be able to output ground fault monitoring data that shows the magnitude of the ground fault current and the waveform of the ground fault current (the change in the magnitude of the ground fault current over time). In addition, from a maintenance standpoint, it is preferable that this ground fault monitoring data can be transmitted to remote locations.

[0006] The present invention aims to provide a ground fault detection device, a ground fault monitoring device, and a ground fault monitoring system that can reliably detect both ground faults caused by lightning strikes and ground faults caused by contact with flying objects such as birds and animals, and can remotely transmit ground fault monitoring data that takes into account the magnitude of the detected ground fault current. [Means for solving the problem]

[0007] This invention The first perspectiveThe ground fault detection device is installed on the base of a transmission tower and is a ground fault detection device that detects ground faults, comprising: a ground fault current detection unit that outputs an activation signal triggered by the current flowing through the tower base; a magnetic sensor that measures the magnetic flux density due to the ground fault current; and a control unit that, when it receives the activation signal from the ground fault current detection unit, causes the magnetic sensor to measure the magnetic flux density due to the ground fault current. The ground fault current detection unit comprises a current transformer having a core and a coil, and a ground fault current detection circuit in which a varistor and / or resistor are arranged on the circuit. In the current transformer, when the ground fault current flowing through the tower leg passes through the core, an induced voltage is induced by the coil, and a secondary current generated in accordance with the induced voltage is output. The ground fault current detection circuit is capable of attenuating the secondary current flowing on the circuit by the varistor and / or the resistor. . The above-described ground fault detection device may further include a communication unit capable of transmitting data to a remote location, and the control unit may be configured to transmit ground fault monitoring data, which takes into account the magnitude of the ground fault current based on the measured magnetic flux density, to the communication unit. In the above-described ground fault detection device, the magnetic sensor has multiple measurement axes, and the control unit can be configured to generate ground fault monitoring data by synthesizing the measurement data of magnetic flux density at the multiple measurement axes acquired from the magnetic sensor. The above-described ground fault detection device can be configured to generate ground fault monitoring data that takes into account the waveform of the ground fault current, based on time-series data derived from the measurement data of the magnetic sensor. A ground fault detection device according to a second aspect of the present invention is a ground fault detection device installed on the base of a transmission tower and used to detect ground faults, comprising: a ground fault current detection unit that outputs an activation signal triggered by a current flowing through the tower base; a magnetic sensor that measures the magnetic flux density due to the ground fault current; and a control unit that, upon receiving the activation signal from the ground fault current detection unit, causes the magnetic sensor to measure the magnetic flux density due to the ground fault current. The control unit has a standby mode for suppressing power consumption and a measurement mode for activating upon the activation signal output from the ground fault current detection unit and measuring the ground fault current. The control unit generates ground fault monitoring data based on the measurement data of the magnetic sensor, and the ground fault monitoring data consists of first ground fault monitoring data obtained by integrating data based on magnetic flux density measurement data at first time intervals and second ground fault monitoring data obtained by integrating data at second time intervals that are closer together than the first time interval. ru. In the above-described ground fault detection device, the first ground fault monitoring data is time-series data obtained from the time of activation by the activation signal until a first hour has elapsed, and the second ground fault monitoring data is time-series data obtained from the time of activation by the activation signal until a second hour has elapsed, which is shorter than the first hour. The ground fault monitoring device according to the present invention is a ground fault monitoring device configured to communicate with the above-mentioned plurality of ground fault detection devices, which identifies a power transmission tower where a ground fault current has occurred based on ground fault monitoring data received from the plurality of ground fault detection devices, and outputs information regarding the generated ground fault current. This invention The third perspective The ground fault monitoring system related to this is A ground fault detection device installed on the base of a transmission tower to detect ground faults, comprising: a ground fault current detection unit that outputs an activation signal triggered by a current flowing through the tower base; a magnetic sensor that measures the magnetic flux density due to the ground fault current; and a control unit that, upon receiving the activation signal from the ground fault current detection unit, causes the magnetic sensor to measure the magnetic flux density due to the ground fault current; and a ground fault monitoring device configured to communicate with the plurality of ground fault detection devices, wherein the ground fault monitoring device identifies the transmission tower where the ground fault current occurred based on the ground fault monitoring data received from the plurality of ground fault detection devices and outputs information regarding the generated ground fault current. The aforementioned multiple ground fault detection devices are mounted above the insulators of the transmission towers, and the ground fault monitoring device detects the transmission tower on which the ground fault detection device that detected an upward ground fault current is mounted as the site of the ground fault. In the above-described ground fault monitoring system, the plurality of ground fault detection devices can be configured to store information about the transmission delay time when transmitting the ground fault monitoring data in advance, and to transmit the ground fault monitoring data after the transmission delay time has elapsed. [Effects of the Invention]

[0008] According to the present invention, the magnetic flux density of the ground fault current can be measured by a magnetic sensor triggered by the ground fault current detected by the current transformer. Therefore, even when using a low-sensitivity current transformer, minute ground fault currents caused by collisions with flying objects can be detected, and both ground faults caused by lightning strikes and ground faults caused by contact with flying objects can be reliably detected. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram illustrating the configuration of the ground fault monitoring system according to this embodiment. [Figure 2] This diagram illustrates the installation state of the ground fault detection device according to this embodiment. [Figure 3] This diagram illustrates the installation method of the ground fault detection device according to this embodiment. [Figure 4] This is a diagram showing the configuration of the ground fault detection device according to this embodiment. [Figure 5] This figure shows the electrical circuit of the ground fault current detection circuit according to this embodiment. [Figure 6]It is a graph for explaining the time from the occurrence of a ground fault current to the activation of the control circuit in the ground fault detection device according to this embodiment. [Figure 7] It is a graph for explaining a method of creating ground fault monitoring data. [Figure 8] It is a flowchart showing the ground fault monitoring process according to this embodiment. [Figure 9] It is a graph showing an example of the measurement results of the magnetic flux density measured in the embodiment. [Figure 10] It is a graph showing the relationship between the measurement time of the magnetic flux density measured in the embodiment and the ground fault observation data. [Figure 11] It is a diagram showing the test results of the lightning strike resistance test. [Figure 12] It is a diagram for explaining a method of detecting the occurrence point of a ground fault. [Figure 13] It is a diagram for explaining the transmission delay time of ground fault monitoring data.

Embodiment for Carrying Out the Invention

[0010] Hereinafter, based on the drawings, the ground fault monitoring system 1 according to this embodiment will be described. FIG. 1 is a configuration diagram of the ground fault monitoring system 1 according to this embodiment. As shown in FIG. 1, the ground fault monitoring system 1 according to this embodiment includes ground fault detection devices 10, 10a, a wide area communication network relay device 20, and a ground fault monitoring device 30. Note that the ground fault detection devices 10, 10a shown in FIG. 1 are denoted by reference numeral 10 for those without a wireless relay function and by reference numeral 10a for those with a wireless relay function. The wide area communication network relay device 20 is a communication device capable of communication such as 4G, 5G, and optical fiber.

[0011] In this embodiment, as shown in Figure 1, the ground fault detection devices 10, 10a and the wide-area communication network relay device 20 are attached to the transmission tower 2 and are able to exchange information with each other via wireless communication. The wide-area communication network relay device 20 is also able to exchange information with a ground fault monitoring device 30 installed in a remote location via wireless communication such as 4G or 5G, or via wired communication such as optical fiber. In this embodiment, one ground fault detection device 10a with wireless relay function is installed for several to several dozen ground fault detection devices 10. Preferably, the ground fault detection devices 10 and the ground fault detection device 10a with wireless relay function are installed within 5 km of each other, and the ground fault detection devices 10a with wireless relay function are installed within 50 km of each other. Furthermore, one of the ground fault detection devices 10a with wireless relay function that are connected via wireless communication is connected to the wide-area communication network relay device 20 wirelessly or via wired connection. In the example shown in Figure 1, the wide-area communication network relay device 20 is shown as being attached to the power transmission tower 2, but it can also be installed at a location away from the power transmission tower 2. Below, we will first describe the ground fault detection devices 10 and 10a according to this embodiment.

[0012] Figure 2 shows the mounting state of the ground fault detection devices 10 and 10a according to this embodiment to the transmission tower 2. As shown in Figure 2, the ground fault detection devices 10 and 10a according to this embodiment are fixed to the transmission tower 2 by the attached mounting arms 21 and 22. Also, as shown in Figure 2, the ground fault detection devices 10 and 10a mainly consist of a device body 11 and a current transformer 12, with a wiring cable 13 interposed between the device body 11 and the current transformer 12.

[0013] Figure 3 illustrates the method of mounting the ground fault detection devices 10 and 10a according to this embodiment. Figure 3(A) is a top view of the ground fault detection devices 10 and 10a according to this embodiment mounted on the transmission tower 2, and Figure 3(B) is a side view of the ground fault detection devices 10 and 10a according to this embodiment mounted on the transmission tower 2. As shown in Figures 3(A) and (B), the mounting arms 21 and 22 have longitudinal sections 211 and 221 and mounting sections 212 and 222 whose ends are branched into two at approximately right angles. As shown in Figure 3(B), the mounting sections 212 and 222 have a width H2 that is wider than the width H1 of the longitudinal sections 211 and 221, and the mounting arms 21 and 22 can be easily attached to the transmission tower 2 by wrapping the stainless steel belt 23 around the mounting sections 212 and 222 while pressing them against the transmission tower 2. The mounting arms 21 and 22 are not particularly limited as long as they are made of a non-magnetic material, and can be formed from metal fittings such as aluminum or aluminum alloy.

[0014] The current transformer 12 is attached to the base of the transmission tower 2, and is installed so that the base of the transmission tower 2 passes through the inside of the core of the current transformer 12. When a ground fault current flows through the base of the transmission tower 2, the di / dt (rate of change of current) at the moment the ground fault current occurs induces a voltage in the coil of the current transformer 12, and a secondary current is output to the main unit 11 via the wiring cable 13. Note that the ground fault current is generated by the dielectric breakdown of an insulator, and even in the case of a minor ground fault caused by contact with flying objects such as birds and animals, the di / dt (rate of change of current) at the time the ground fault current occurs is large. Therefore, even when a ground fault current is generated by contact with flying objects such as birds and animals, a secondary current can be output to the main unit 11.

[0015] The current transformer 12 in this embodiment only needs to be capable of detecting the presence or absence of ground fault current, and for example, a low-sensitivity current transformer with an electrical steel sheet as its core is used. When attempting to measure the ground fault current itself with a current transformer, it is necessary to increase the cross-sectional area of ​​the core in proportion to the magnitude of the current to be measured so that the core does not become saturated by the magnetic field generated from the current flowing through the wires passing through the core. Therefore, when detecting lightning strike currents, which generate large magnetic fields, it was necessary to use a very heavy and expensive current transformer. However, in this embodiment, the current transformer 12 is configured to detect the rising edge of lightning strike current and ground fault current (or the presence or absence of lightning strike current and ground fault current), so the cross-sectional area of ​​the core can be reduced compared to conventional current transformers, and the core material can be inexpensive electrical steel sheet instead of expensive materials such as ferrite. Furthermore, although electromagnetic steel sheets have very high non-permeability, they have the property that their non-permeability becomes 1 the moment magnetic saturation occurs. Therefore, when detecting the rise of a ground fault current (when exposed to a relatively low magnetic field), the ground fault current can be detected with high permeability. Also, when exposed to a strong magnetic field such as a lightning strike current, the non-permeability becomes 1, preventing excess energy from being transmitted to the coil. Moreover, since the voltage induced in the coil of the current transformer is generated in proportion to the rate of change of the current passing through the core (di / dt), even when a low-sensitivity current transformer 12 is used in this embodiment, a large di / dt at the start of the ground fault current or lightning strike current can provide a voltage sufficient to start the device body 11. In addition, in the current transformer 12 according to this embodiment, because the cross-sectional area of ​​the core is small, when a current above a certain level flows, the core saturates in that magnetic field, and at that moment the relative permeability of the core becomes 1. Therefore, it is possible to prevent an unnecessarily large amount of energy from being transmitted to the coil and to suppress the induced voltage to the coil.

[0016] Figure 4 is a diagram showing the configuration of the ground fault detection devices 10 and 10a according to this embodiment. As shown in Figure 4, the main body 11 of the ground fault detection devices 10 and 10a incorporates a ground fault current detection circuit 14, a control circuit 15, magnetic sensors 16 and 17, a communication unit 18, a storage unit 19, and a dry cell battery 110. In this embodiment, the current transformer 12 and the ground fault current detection circuit 14 are collectively referred to as the ground fault current detection unit.

[0017] Figure 5 is a circuit diagram of the ground fault current detection circuit 14. The ground fault current detection circuit 14 is a circuit that detects the induced voltage in the current transformer 12 caused by the ground fault current, and also functions as an overvoltage protection circuit. As shown in Figure 5, the ground fault current detection circuit 14 has a voltage suppression varistor 141, a voltage suppression Zener diode 142, and an optical isolation 143. The voltage suppression varistor 141 and the voltage suppression Zener diode 142 have the function of suppressing the induced voltage generated in the current transformer 12 due to the ground fault current and obtaining a voltage to output the start signal necessary for starting the control circuit 15. In addition, the optical isolation 143 can be configured using, for example, a photocoupler or a digital isolator, and physically isolates the circuit, and based on the induced voltage in the current transformer 12 due to the ground fault current, it outputs an electrical signal with the voltage of the dry cell battery 144 as a start signal to the control circuit 15. Thus, in this embodiment, the ground fault current detection circuit 14 can be composed of a varistor, diode, resistor, transistor, photocoupler, etc., making it possible to protect the device from impulse voltages caused by lightning strikes.

[0018] The control circuit 15 has the function of acquiring magnetic flux density measurement data from magnetic sensors 16 and 17 when a ground fault current occurs, and transmitting ground fault monitoring data based on this measurement data to the wide-area communication network relay device 20 via the communication unit 18. In this embodiment, the control circuit 15 is connected to a dry cell battery 110 and is in a standby state with minimal power consumption under normal circumstances (when no ground fault current occurs). When an activation signal is transmitted from the ground fault current detection circuit 14, the control circuit 15 switches to an operating state, activates the magnetic sensors 16 and 17, and starts measuring magnetic flux density. When the control circuit 15 receives the magnetic flux density measurement data from the magnetic sensors 16 and 17, it stores the measurement data in the storage unit 19 (for example, an external storage device such as a microSD®) and generates ground fault monitoring data based on the measurement data. Details of the method for generating ground fault monitoring data will be described later. Furthermore, once a certain period has elapsed since the magnetic sensors 16 and 17 began measuring magnetic flux density, the control circuit 15 terminates the operation of the magnetic sensors 16 and 17 and returns to standby mode. Under normal circumstances, the control circuit 15 can operate in standby mode with extremely low power consumption of approximately 20 μA. In this case, it can operate for more than 10 years on four AA lithium batteries.

[0019] Here, the magnetic sensors 16 and 17 according to this embodiment will be described. The magnetic sensors 16 and 17 are sensors that measure the magnetic flux density at the base of the transmission tower 2. In this embodiment, the magnetic sensors 16 and 17 are sensors capable of measuring magnetic flux density in three axial directions (in this embodiment, the X-axis direction (direction of extension of the transmission line), the Y-axis direction (direction of extension of the tower base), and the Z-axis direction (direction intersecting the extension direction of the transmission line on a substantially horizontal plane)). In this case, the magnetic flux density generated by the transmission line current can be measured in the X-axis and Y-axis directions, and the magnetic flux density due to a ground fault can be measured in the Z-axis direction. Therefore, the magnetic sensors 16 and 17 or the control circuit 15 can measure the magnetic flux density in the Z-axis direction as the magnetic flux density due to a ground fault, separately from the magnetic flux density due to the transmission line current. However, in this embodiment, the magnetic flux density in three axes is measured taking into account the tilt error of the ground fault detection devices 10, 10a (more precisely, the magnetic sensors 16, 17). However, the magnetic sensors 16, 17 are not limited to magnetic sensors that measure magnetic flux density in three axes, but can also be magnetic sensors that measure magnetic flux in one axis direction, such as measuring only in the Z axis direction (details will be described later).

[0020] The magnetic sensors 16 and 17 can measure magnetic flux density at regular time intervals (for example, every 2 milliseconds) and sequentially output the measured magnetic flux density to the control circuit 15. The type of magnetic sensors 16 and 17 is not particularly limited; for example, AMR magnetic sensors, GMR magnetic sensors, TMR magnetic sensors, etc., can be used, but in this embodiment, a highly sensitive TMR magnetic sensor is used. In this embodiment, a configuration with two magnetic sensors 16 and 17 is illustrated, but the system is not limited to this configuration, and a configuration with one or three or more magnetic sensors can be used.

[0021] Furthermore, the distance from the tower base to the magnetic sensors 16 and 17 is not particularly limited, but is preferably 50 to 150 mm. In this embodiment, the magnetic sensors 16 and 17 are arranged so that they are at different distances from the tower base. By arranging multiple magnetic sensors 16 and 17 at different distances from the tower base, the measurement range of magnetic flux density by the magnetic sensors 16 and 17 can be arbitrarily expanded. That is, the greater the distance from the tower base to the magnetic sensors 16 and 17, the more the magnetic flux density due to the ground fault current is attenuated. For example, the greater the distance from the tower base to the magnetic sensors 16 and 17, the more ground fault currents with higher current values ​​can be measured. By utilizing these properties, multiple magnetic sensors 16 and 17 can be placed at different distances from the tower base to measure ground fault currents with different current values ​​(for example, ground fault currents of 0.2 to 300A can be measured by placing them at a distance of 50mm from the tower base, and ground fault currents of 0.5 to 600A can be measured by placing them at a distance of 100mm).

[0022] Here, Figure 6 is a graph illustrating the time taken from the occurrence of ground fault current to the activation of the control circuit 15 in the ground fault detection devices 10 and 10a according to this embodiment. Figure 6(A) shows an example of the output of the ground fault current, the induced voltage of the current transformer 12, and the activation signal when dielectric breakdown occurs away from the AC zero-crossing point, and Figure 6(B) shows an example of the output of the ground fault current, the induced voltage (CT voltage) of the current transformer 12, and the activation signal (activation trigger) when dielectric breakdown occurs at the AC zero-crossing point.

[0023] As shown in Figure 6(A), if dielectric breakdown occurs away from the AC zero-crossing point, the ground fault current rises in a step-like manner. Therefore, before the ground fault current reaches its maximum, a spike-like induced voltage is generated in the current transformer 12, and an activation signal is output from the ground fault current detection circuit 14. In this case, as shown in Figure 6(A), the magnetic sensors 16 and 17 begin measuring the magnetic flux density approximately 10 microseconds after the occurrence of the ground fault current. Generally, the magnetic flux density due to the ground fault current can be observed for approximately 1 second after the occurrence of the ground fault current. Therefore, in the configuration according to this embodiment, it can be seen that the magnetic flux density due to the ground fault current can be sufficiently detected. Furthermore, although rare, as shown in Figure 6(B), even if dielectric breakdown occurs at the AC zero-crossing point, an activation signal is output from the ground fault current detection circuit 14 to the control circuit 15 when the ground fault current exceeds a certain level, and measurement by the magnetic sensors 16 and 17 begins. In this case, although it also depends on the magnitude of the ground fault current, for example, if the setting is configured to output an activation signal when the ground fault current reaches 10A, as shown in Figure 6(B), the magnetic flux density measurement by magnetic sensors 16 and 17 can begin approximately 5 milliseconds after the ground fault current occurs. Also, if the setting is configured to output an activation signal when the ground fault current reaches 20A, the magnetic flux density measurement by magnetic sensors 16 and 17 can begin approximately 3 milliseconds after the ground fault current occurs.

[0024] Next, the method for creating ground fault monitoring data by the control circuit 15 will be explained. Here, Figure 7 is a graph illustrating the method for creating ground fault monitoring data. Figure 7(A) shows the magnetic flux density measurement data (magnetic flux density on one axis) output from the magnetic sensors 16 and 17. Figure 7(B) shows the ground fault monitoring data based on the magnetic flux density measurement data acquired at 0.1-second intervals from the start of measurement by the magnetic sensors 16 and 17 until 2 seconds have elapsed. Figure 7(C) shows the ground fault monitoring data based on the magnetic flux density measurement data acquired at 0.01-second intervals from the start of measurement by the magnetic sensors 16 and 17 until 0.2 seconds have elapsed.

[0025] In this embodiment, the control circuit 15 first acquires the measurement results of the magnetic flux density in the three axes output from the magnetic sensors 16 and 17, as shown in Figure 7(A), and stores the measurement results of the magnetic flux density in the three axes in the storage unit 19 provided in the control circuit 15, with the recording start date and time as the file name. The amount of magnetic flux density measurement data stored by the control circuit 15 can be, for example, 2 bytes × 3 axes × 500 Hz × 2 seconds = 6000 bytes. Furthermore, since the zero point of the magnetic flux density measurement data fluctuates due to the effects of the ambient magnetic field and sensor drift, the control circuit 15 can set the average value of all data over 2 seconds for each measurement axis (X axis, Y axis, Z axis) as the zero point.

[0026] Furthermore, the control circuit 15 generates ground fault monitoring data by synthesizing the measured magnetic flux density data from the three axes. Specifically, the control circuit 15 acquires instantaneous magnetic flux density values ​​from the three axes at predetermined intervals and sums the vector lengths of the acquired instantaneous magnetic flux density values ​​from the three axes (Σ√(X 2 +Y 2 + Z 2 The sum of the vector lengths of the instantaneous magnetic flux density values ​​of the three axes is calculated as ground fault monitoring data. In this way, the influence of the mounting angle of the magnetic sensors 16 and 17 with respect to the current centroid axis can be reduced.

[0027] Furthermore, as shown in Figure 7(B), the control circuit 15, until 2 seconds have elapsed since the start of magnetic flux density measurement by the magnetic sensors 16 and 17, accumulates a composite value obtained by combining the instantaneous values ​​of the magnetic flux density of the three axes at 0.1-second intervals, and outputs the time-series data of the accumulated value as ground fault monitoring data (first ground fault monitoring data). Specifically, until 2 seconds have elapsed since the start of magnetic flux density measurement by the magnetic sensors 16 and 17, the control circuit 15 obtains a composite value by combining the instantaneous values ​​of the magnetic flux density of the three axes obtained at 0.002-second intervals (500Hz), and accumulates the composite value obtained at 0.002-second intervals at 0.1-second intervals. Then, the control circuit 15 outputs the time-series data of the calculated accumulated value as first ground fault monitoring data. Furthermore, in parallel with this, as shown in Figure 7(C), the control circuit 15, for the first 0.2 seconds after the start of magnetic flux density measurement by the magnetic sensors 16 and 17, integrates the instantaneous values ​​(measurement data) of the magnetic flux density of the three axes into a composite value, and outputs the time-series data of the integrated value as ground fault monitoring data (second ground fault monitoring data). Specifically, until 0.2 seconds after the start of magnetic flux density measurement by the magnetic sensors 16 and 17, the control circuit 15 synthesizes the instantaneous values ​​of the magnetic flux density of the three axes obtained at 0.002-second (500Hz) intervals to obtain a composite value, and integrates the composite value obtained at 0.002-second intervals into 0.01-second intervals. The control circuit 15 then outputs the time-series data of the calculated integrated value as second ground fault monitoring data. The control circuit 15 then transmits ground fault monitoring data (first ground fault monitoring data and second ground fault monitoring data) to the ground fault monitoring device 30 via the wide-area communication network relay device 20 through the communication unit 18.

[0028] In this embodiment, the control circuit 15 acquires instantaneous magnetic flux density values ​​(measurement data) for all three axes at 0.1-second intervals from the start of measurement until 2 seconds after the start, and generates ground fault monitoring data, resulting in 20 ground fault monitoring data entries. In parallel, the control circuit 15 also acquires instantaneous magnetic flux density values ​​(measurement data) for all three axes at 0.01-second intervals for the first 0.2 seconds from the start of measurement, and generates ground fault monitoring data, resulting in 20 ground fault monitoring data entries. In other words, in this embodiment, the control circuit 15 generates 40 ground fault monitoring data entries from the start of magnetic flux density measurement by the magnetic sensors 16 and 17 until 2 seconds have elapsed. Furthermore, in this embodiment, one ground fault monitoring data entry is represented by 2 bytes, so the amount of ground fault monitoring data from the start of magnetic flux density measurement by the magnetic sensors 16 and 17 until 2 seconds have elapsed is 2 × 40 = 80 bytes. As described above, in this embodiment, the magnetic flux density measurement data from the start of measurement by magnetic sensors 16 and 17 up to 2 seconds later is 6000 bytes. Therefore, by generating ground fault monitoring data based on the magnetic flux density measurement data, the amount of data can be significantly reduced.

[0029] The communication unit 18 transmits the ground fault monitoring data output from the control circuit 15 to the ground fault monitoring device 30 via other ground fault detection devices 10, 10a or the wide-area communication network relay device 20. In this embodiment, the communication unit 18 is also capable of performing LPWA wireless communication such as the LoRa communication standard, and can transmit the ground fault monitoring data in, for example, two packets. In this embodiment, since the measurement data of magnetic flux density in three axes (for example, 6000 bytes of data) is combined to generate ground fault monitoring data (for example, 80 bytes of data), it is possible to reduce the amount of data of the ground fault monitoring data transmitted by the communication unit 18, and as a result, relatively low-speed LPWA wireless communication can be used. The communication distance of wireless communication by the communication unit 18 varies depending on the model, but a model capable of wireless communication up to 5 km, preferably 50 km, is preferred. For example, in the example shown in Figure 1, a ground fault detection device equipped with a relatively inexpensive communication unit 18, which is preferable for communication of 5 km or less, is shown as ground fault detection device 10, and a ground fault detection device with a wireless relay function and a relatively expensive communication unit 18, which is preferable for communication of 50 km or less, is shown as ground fault detection device 10a. In this case, the communication unit 18 of the ground fault detection device 10, which is preferable for communication of 5 km or less, can have a radio wave output of, for example, 20 mW, and the communication unit 18 of the ground fault detection device 10a with a wireless relay function, which is preferable for communication of 50 km or less, can have a radio wave output of, for example, 250 mW. Furthermore, the communication unit 18 of the ground fault detection device 10, which is preferable for communication of 5 km or less, consumes little power and can be operated by dry cell batteries 110, but it can be configured to change the radio wave output from 20 mW to 250 mW as needed to transmit ground fault monitoring data, and in this case as well, it can be operated by dry cell batteries 110. On the other hand, the ground fault detection device 10a with wireless relay function requires the communication device 18 to be constantly in operation in order to relay wireless communication from the ground fault detection device 10, which results in high power consumption. Therefore, it is desirable to replace the dry cell battery 110 with a power supply consisting of, for example, a combination of a solar cell and a storage battery.

[0030] The wide-area communication network relay device 20 transmits ground fault monitoring data received from the ground fault detection devices 10 and 10a to a ground fault monitoring device 30 located at a remote location via wired or wireless communication. The wide-area communication network relay device 20 has, for example, an LTE / WiFi router and is capable of transmitting ground fault monitoring data to the ground fault monitoring device 30 over a distance of more than 50 km.

[0031] The ground fault monitoring device 30 is an information terminal such as a personal computer installed in a remote location, and receives ground fault monitoring data generated by each fault detection device 10, 10a from the wide-area communication network relay device 20. The ground fault monitoring device 30 comprises a processing unit and a storage device that stores transmission tower map data with location information of transmission towers 2 and location information of each fault detection device 10, 10a. The ground fault monitoring device 30 displays monitoring information based on the received ground fault monitoring data, along with transmission tower map data as shown in Figure 1, on a display device such as a display, thereby allowing the monitor of the ground fault monitoring system 1 to understand the occurrence and location of ground faults. In addition, the ground fault monitoring device 30 has a ground fault current display function that displays information showing details of the ground fault current (for example, the instantaneous value of the ground fault current, the duration, or the waveform information of the ground fault current) on the display when the user specifies the transmission tower 2 where the ground fault occurred. Furthermore, the ground fault monitoring device 30 can also be a smartphone or tablet carried by the monitor, and it can be configured to receive alert data based on ground fault monitoring data via email.

[0032] Next, the ground fault current monitoring process of the ground fault monitoring system 1 according to this embodiment will be described. Figure 8 is a flowchart of the ground fault monitoring process according to this embodiment. The flowchart shown below is initiated when a ground fault current is generated on the transmission tower 2 due to a lightning strike or collision with a bird or animal. In this embodiment, steps S101 to S107 are performed by the ground fault detection devices 10 and 10a, and steps S108 and S109 are performed by the ground fault monitoring device 30.

[0033] In step S101, the occurrence of a ground fault current induces an induced voltage in the coil of the current transformer 12 of the ground fault detection device 10,10a, and a secondary current corresponding to the induced voltage is output to the ground fault current detection circuit 14 of the device body 11 via the wiring cable 13. In step S102, the ground fault current detection circuit 14 outputs a start signal to the control circuit 15 based on the secondary current. Then, in step S103, the control circuit 15 receives the start signal and changes from the standby state to the operating state.

[0034] In step S104, the control circuit 15 starts the operation of the magnetic sensors 16 and 17, and begins measuring the magnetic flux density according to the ground fault current. The magnetic sensors 16 and 17 repeatedly measure the magnetic flux density and output the measured magnetic flux density data to the control circuit 15 as needed. In this embodiment, the magnetic sensors 16 and 17 measure the magnetic flux density in three axes and output the measured magnetic flux density data for all three axes to the control circuit 15.

[0035] In step S105, the control circuit 15 generates ground fault monitoring data based on the three-axis magnetic density measurement data acquired in step S104. Specifically, in this embodiment, the magnetic sensors 16 and 17 measure the three-axis magnetic flux density at 0.002-second intervals, and the control circuit 15 integrates the combined value obtained by combining the three-axis magnetic flux densities at 0.1-second intervals, generating the time-series data of the calculated integrated value as the first ground fault monitoring data. The control circuit 15 also generates the time-series data of the integrated value obtained by integrating the combined value obtained by combining the three-axis magnetic flux densities at 0.01-second intervals as the second ground fault monitoring data. The control circuit 15 then transmits the generated ground fault monitoring data (first ground fault monitoring data and second ground fault monitoring data) to the ground fault monitoring device 30 via the communication device 18 and the wide-area communication network relay device 20. In this embodiment, the control circuit 15 generates first ground fault monitoring data every 0.1 seconds until 2 seconds have elapsed since activation by the activation signal, and generates second ground fault monitoring data every 0.01 seconds until 0.1 seconds have elapsed since activation by the activation signal.

[0036] In step S106, the control circuit 15 determines whether 2 seconds have elapsed since the activation signal. If 2 seconds have not elapsed, the process returns to step S105 to generate the first ground fault monitoring data and / or the second ground fault monitoring data. If 2 seconds have elapsed since the activation signal, the process proceeds to step S107, where the control circuit 15 changes from the operating state to the standby state.

[0037] In step S108, the ground fault monitoring device 30 acquires ground fault monitoring data received from each fault detection device 10, 10a. Note that, for the sake of explanation, the flowchart in Figure 8 illustrates the process of receiving ground fault monitoring data in step S108. In reality, the ground fault monitoring device 30 receives the data as soon as it is transmitted in step S105. Then, in step S109, the received ground fault monitoring data is displayed on a monitor or similar device of the ground fault monitoring device 30, allowing the observer to understand the ground fault monitoring information based on the data. [Examples]

[0038] Next, an embodiment of the ground fault detection device 10,10a according to this embodiment will be described. In this embodiment, a prototype of the ground fault detection device 10,10a was manufactured, a current transformer 12 was attached to a test material for the tower leg, and a simulated ground fault current was applied to the test material for the tower leg. Figure 9 is a graph showing the instantaneous magnetic flux density values ​​of the three axes (X axis, Y axis, Z axis) measured in this embodiment when a simulated ground fault current was generated. As shown in Figure 9, in this embodiment, similar to the ground fault detection device 10,10a according to this embodiment, the magnetic flux density was measured until 2 seconds had elapsed after the magnetic sensors 16,17 were activated. In this embodiment as well, the Z-axis direction was set to intersect the extension direction of the power transmission line in a substantially horizontal plane, and the ground fault detection device 10,10a was positioned so that the magnetic flux density of the ground fault current could be measured in the Z-axis direction, resulting in a large measurement of the magnetic flux density in the Z-axis direction.

[0039] Furthermore, Figure 10 is a graph showing the relationship between the measurement time of magnetic flux density measured in this embodiment when a simulated ground fault current is generated and the measured magnetic flux density data. Specifically, Figure 10(A) shows ground fault monitoring data based on measured magnetic flux density data (instantaneous values ​​of magnetic flux density in three axes) accumulated at 0.1-second intervals from the start of measurement to 2 seconds later, and Figure 10(B) shows ground fault monitoring data based on instantaneous values ​​of magnetic flux density in three axes accumulated at 0.01-second intervals from the start of measurement to 0.2 seconds later. As shown in Figures 9 and 10, it was found that in the ground fault detection devices 10 and 10a according to this embodiment, when a ground fault current occurs, the control circuit 15 is activated, the magnetic flux density corresponding to the ground fault current is measured by the magnetic sensors 16 and 17, and ground fault monitoring data corresponding to the ground fault current is generated.

[0040] Furthermore, using the above prototype, a lightning strike resistance test was also conducted on the ground fault detection device 10,10a according to this embodiment. Specifically, first, the prototype was attached to a test material of a transmission tower leg, a simulated ground fault current of 200V / 10A was passed through it, and the magnetic flux density was measured at a position 200mm from the surface of the test material. The measurement results are shown in Figure 11(A). As shown in Figure 11(A), it was possible to measure the magnetic flux density in response to the simulated ground fault current. Next, a simulated lightning strike current of 3.873kA was passed through this prototype. The measurement results are shown in Figure 11(B). The simulated lightning strike current was set to become 0 within 100 microseconds, similar to a normal lightning strike current, and Figure 11(B) shows that the magnetic flux density due to the simulated lightning strike current was measured. From this, it was found that the ground fault detection device 10,10a according to this embodiment can start measuring the magnetic flux density within 100 microseconds of a lightning strike and can detect the presence or absence of a lightning strike. Furthermore, the ground fault detection devices 10, 10a and the prototype magnetic sensors 16, 17 according to this embodiment measure magnetic flux density at 2-millisecond intervals. However, as shown in Figure 11(B), in the second measurement of magnetic flux density (measurement of magnetic flux density 2 milliseconds after the start of measurement by magnetic sensors 16, 17), the measured value of magnetic flux density was almost 0. From this, it can be considered that the effect of the strong magnetic field caused by the lightning strike current on the magnetic sensors 16, 17 does not continue for more than 2 milliseconds, and that the ground fault current following the lightning strike current can be measured appropriately. Note that in Figure 11(B), the measured value is very low compared to the magnetic flux density shown in Figure 11(A). This is thought to be because, in Figure 11(B), the change in magnetic flux density lasts for only 100 microseconds, and the response of the magnetic sensor does not keep up.

[0041] Figure 11(C) is a graph showing the results of measuring magnetic flux density after applying a simulated lightning strike current of approximately 10kA multiple times, followed by a simulated ground fault current. As shown in Figure 11(C), even after applying a simulated lightning strike current of approximately 10kA multiple times, the detected magnetic flux density did not differ significantly from the measured value shown in Figure 11(A) before the simulated lightning strike current was applied. No damage was observed to the core characteristics of the current transformer 12, the coils of the current transformer 12, the ground fault current detection circuit 14, or the magnetic sensors 16 and 17 due to the simulated lightning strike current. This indicates that the system is practical even for ground fault currents that occur following lightning strike currents.

[0042] Next, with reference to Figure 12, the method for detecting the location of a ground fault in the ground fault monitoring system 1 of this embodiment will be described. When a ground fault occurs, the ground fault current is transmitted from the transmission tower 2 where the ground fault occurred to the transmission tower adjacent to that transmission tower 2 via the overhead ground wire, and the ground fault current flows sequentially to the adjacent transmission towers 2. For example, in the example shown in Figure 12, if a ground fault occurs in the central transmission tower 2, the ground fault current will also be transmitted to the transmission towers 2 adjacent to the left and right via the overhead ground wire. In this case, as shown in Figure 12, the current value of the ground fault current is divided vertically from the insulator where the ground fault occurred, so it is divided vertically from the insulator where the ground fault occurred, and further divided to the left and right from the transmission tower 2 where the ground fault occurred to the adjacent transmission towers 2. Thus, since the ground fault current attenuates the further away a transmission tower 2 is from the transmission tower 2 where the ground fault occurred, the ground fault monitoring device 30 can be configured to identify the transmission tower 2 where the ground fault occurred by comparing the current values ​​of the ground fault currents of each transmission tower 2.

[0043] Furthermore, as shown in Figure 12, in a transmission tower 2 where a ground fault occurs, a ground fault current flows upward at a position above the insulator where the ground fault occurred, and the magnetic flux density with a phase corresponding to the upward ground fault current is measured (see bottom of Figure 12). In contrast, in a transmission tower 2 where no ground fault occurs, even if ground fault detection devices 10, 10a are installed above the insulator, a ground fault current flows downward, and the magnetic flux density with a phase corresponding to the downward ground fault current is measured (see bottom of Figure 12). Therefore, in this embodiment, each ground fault detection device 10, 10a can be placed above the insulator, and the ground fault monitoring device 30 can be configured to identify the ground fault detection device 10, 10a attached to the transmission tower 2 where the ground fault occurred by detecting the ground fault detection device 10, 10a for which a magnetic flux density corresponding to the upward ground fault current has been measured. Furthermore, the ground fault monitoring device 30 can be configured to identify the transmission tower 2 where a ground fault has occurred with greater accuracy by combining the current values ​​of the ground fault currents detected by the ground fault detection devices 10 and 10a of each transmission tower 2 with the detection of the ground fault detection devices 10 and 10a that have measured the magnetic flux density corresponding to the upward ground fault current.

[0044] Furthermore, as mentioned above, when a ground fault current occurs, it flows sequentially to adjacent transmission towers 2 via the overhead ground wire, causing each transmission tower 2 to simultaneously transmit ground fault monitoring data, which could lead to a collision of ground fault monitoring data. Therefore, in this embodiment, control is performed to change the transmission timing of ground fault monitoring data for each ground fault detection device 10, 10a. Specifically, each ground fault detection device 10, 10a stores different information on the transmission delay time of ground fault monitoring data in advance, and is configured to transmit ground fault monitoring data after a predetermined transmission delay time has elapsed.

[0045] For example, as shown in Figure 13, each fault detection device 10,10a attached to each transmission tower 2 stores a specific delay number in advance as information about the transmission delay time of ground fault monitoring data. Then, when a ground fault current is detected, each fault detection device 10,10a can be configured to transmit ground fault monitoring data after the pre-stored delay number × 20 seconds. For example, in the example shown in Figure 13, a ground fault detection device 10,10a assigned the delay number "3" (a ground fault detection device 10,10a attached to a transmission tower 2 where a ground fault has occurred) can be configured to transmit ground fault monitoring data after 3 × 20 = 60 seconds have elapsed, and a ground fault detection device 10,10a assigned the delay number "4" can be configured to transmit ground fault monitoring data after 4 × 20 = 80 seconds have elapsed, thus avoiding collisions of transmitted ground fault monitoring data. The delay number can be set to a number from 0 to 6, for example, up to the ground fault detection device 10, 10a, which is seven towers away, as shown in Figure 13. In this case, it will take 140 seconds for transmission to be completed up to each ground fault detection device 10, 10a attached to the transmission tower 2 that is seven towers away. However, if we assume that the current division ratio of the ground fault current at each tower is 1 / 2, the value of the ground fault current at the transmission tower 2 where the ground fault occurred will be 1 / 256 of the value at the transmission tower 2 where the ground fault occurred, so it is assumed that the ground fault will hardly be detected. Therefore, it is considered that there is little need to use a delay number of 8 or higher for transmission towers that are eight or more towers away.

[0046] As described above, the ground fault detection devices 10 and 10a according to this embodiment include a current transformer 12 for detecting ground fault current, a ground fault current detection circuit 14 electrically connected to the current transformer 12 and outputting a start signal triggered by the ground fault current, magnetic sensors 16 and 17 for measuring the magnetic flux density due to the ground fault current, and a control circuit 15 that causes the magnetic sensors 16 and 17 to measure the magnetic flux density due to the ground fault current when a start signal is received. As a result, in the ground fault detection devices 10 and 10a according to this embodiment, the current transformer 12 does not need to measure the current value of the ground fault current, and only needs to be able to detect the presence or absence of a ground fault current. Therefore, a large, expensive, highly sensitive current transformer is unnecessary, and ground fault currents caused by lightning strikes as well as ground faults caused by collisions with flying objects such as birds and animals can be detected. Furthermore, in this embodiment, the current transformer 12 only needs to detect the presence or absence of ground fault current, so there is no need to consider the magnetic saturation of the core or the characteristics of the rectifier circuit, allowing for a simple configuration. In the event of a lightning strike, the core of the current transformer 12 saturates, suppressing the induced voltage of the coil and enabling protection of the device from overvoltage. Moreover, in this embodiment, the current transformer 12 does not need to measure current changes at 50 / 60Hz, so the cross-sectional area of ​​the core of the current transformer 12 can be reduced, and the number of coil turns can also be reduced, making it possible to manufacture the ground fault detection devices 10 and 10a at low cost. Thus, the ground fault detection devices 10 and 10a according to this embodiment can achieve stable detection of ground faults caused by lightning strikes and ground faults caused by contact with flying objects such as birds and animals, even with a relatively simple device configuration.

[0047] Furthermore, in order to estimate the cause of a minor ground fault and the degree of damage to insulators, it is not sufficient to simply detect the occurrence of a ground fault current; it is also necessary to measure the magnitude and waveform (time-series data of the magnitude of the ground fault current). In this embodiment, the magnetic flux density of the ground fault current is measured by magnetic sensors 16 and 17, and monitoring data based on the magnitude and waveform of the ground fault current can be generated, allowing the monitor to understand not only the presence or absence of a ground fault current but also its characteristics. In addition, normally, in order to detect the waveform of a ground fault current, the sensor system needs to be operated at all times, and if such a configuration is adopted, power consumption increases, so a power supply unit that combines, for example, solar cells and storage batteries is essential. However, a configuration using such a power supply unit presents the problem of difficulty in installation and maintenance on transmission towers. In contrast, in the ground fault detection devices 10 and 10a according to this embodiment, the control circuit 15 is activated when it receives an activation signal output from the ground fault current detection circuit 14, triggered by the ground fault current, and causes the magnetic sensors 16 and 17 to start measuring the magnetic flux density of the ground fault current. As a result, the power consumption in this embodiment is relatively low, and even with a configuration that incorporates a dry cell battery 110, it is possible to detect the ground fault current for a long period of time (for example, more than 10 years) without replacing the dry cell battery 110. Consequently, a power supply device combining a solar cell and a storage battery is not required, and the device can be made smaller, thereby improving the ease of installation and maintainability of the ground fault detection devices 10 and 10a.

[0048] Furthermore, in the ground fault detection devices 10 and 10a according to this embodiment, measurement of the magnetic flux density of the ground fault current can be started in a short time of about 5 milliseconds after the ground fault current occurs, making it possible to measure the ground fault current following the lightning strike current. In addition, the ground fault detection devices 10 and 10a according to this embodiment cannot measure waveforms corresponding to lightning strike currents with a duration of 0.1 milliseconds or less, but as shown in Figure 11(B), it is possible to detect and record the lightning strike itself, so for example, by using a lightning current sensor that combines a search coil and a capacitor separately, it is possible to measure the approximate magnitude of the lightning current. Also, in recent years, in order to protect power systems from ground faults caused by lightning strikes and flying objects, arc horns with lightning protection horns are sometimes installed on insulators, and in transmission towers equipped with such lightning protection horns, even if a ground fault occurs due to a lightning strike or flying object, there is almost no drop in the transmission line voltage (the arc is extinguished within half a cycle), and it has been impossible to detect the occurrence of a ground fault. However, the ground fault detection devices 10 and 10a according to this embodiment can detect a ground fault approximately 10 microseconds after a ground fault current occurs. Therefore, ground faults can be properly detected even on power transmission towers equipped with such arc horns that protect against lightning.

[0049] In addition, in the ground fault detection devices 10 and 10a according to this embodiment, the sum of the vector lengths of the instantaneous magnetic flux density values ​​in the three axes (X axis, Y axis, Z axis) of the magnetic sensors 16 and 17 (Σ√(X 2 +Y 2 + Z 2 By doing so, the influence of the tilt of the magnetic sensors 16 and 17 and the shape of the tower legs can be eliminated, and the magnetic flux density due to the ground fault current can be evaluated. Furthermore, in this embodiment, by arranging the magnetic sensors 16 and 17 so that their measurement axes are perpendicular to the vector of the magnetic field due to the transmission line current, it is possible to measure the ground fault current separately from the transmission line current even when the influence of the magnetic field due to the transmission line current is large.

[0050] In addition, in the ground fault detection devices 10 and 10a according to the present embodiment, since the measurement results of the three-axis magnetic flux density are synthesized to create ground fault monitoring data with a small data volume, it can be transmitted by LPWA communication with low power consumption, and the number of maintenance operations by battery replacement can be reduced. Further, since the ground fault monitoring data is transmitted to the ground fault monitoring device 30 at a remote location by wireless communication, information regarding ground faults can be monitored at a remote location without an operator going to the power transmission tower 2, and the workability of maintenance and the like can be improved.

[0051] As described above, the preferred embodiments of the present invention have been described. However, the technical scope of the present invention is not limited to the description of the above embodiments. Various changes and improvements can be made to the above embodiments, and forms with such changes or improvements are also included in the technical scope of the present invention.

[0052] For example, in the above-described embodiment, the configuration in which the total value (Σ√(X 2 +Y 2 +Z 2 )) of the vector lengths of the three-axis magnetic flux density instantaneous values is calculated as the ground fault monitoring data is illustrated. However, the present invention is not limited to this configuration. For example, when the inclination of the ground fault detection devices 10 and 10a is fixed by the mounting arms 21 and 22, and the magnetic flux density due to the ground fault current is separated from the magnetic flux density due to the transmission line current so that it can be detected by only one axis (for example, the Z-axis direction), the absolute value of the magnetic flux density due to the ground fault current (for example, Σ|Z|) may be calculated as the ground fault monitoring data.

[0053] In addition, in the above-described embodiment, the configuration in which the magnetic flux density is measured by the magnetic sensors 16 and 17 for 2 seconds after the magnetic sensors 16 and 17 are activated is illustrated. However, when the influence of the alternating magnetic field from the transmission line is large, for about 1 second after the ground fault current ends (for example, for about 3 seconds after the magnetic sensors 16 and 17 are activated), the measurement of the magnetic flux density by the magnetic sensors 16 and 17 is continued, and the measured value measured in the 1 second after the ground fault current ends is used as the background (noise component) to remove the noise due to the transmission line current from 0 to 2 seconds after the magnetic sensors 16 and 17 are activated.

[0054] Furthermore, in the above-described embodiment, the control circuit 15 is shown as being activated by receiving an activation signal from the ground fault current detection circuit 14. However, in addition to this configuration, the control circuit 15 may also be configured to be automatically activated at predetermined time intervals for calibration and diagnosis. For example, the control circuit 15 may be configured to be activated periodically at a predetermined frequency, such as once a day, to perform processes such as synchronizing the internal clock with the master station, detecting the attitude of the magnetic sensors 16 and 17 from an acceleration sensor (not shown), and performing hardware self-diagnosis. The control circuit 15 may also be configured to transmit the attitude of the magnetic sensors 16 and 17 and the results of the hardware self-diagnosis to the ground fault monitoring device 30 via the communication unit 18. The process when the control circuit is activated periodically can be completed in a few seconds, and the control circuit can return to the standby state after the periodic activation. Furthermore, since there is a possibility of ground faults occurring during periodic startup, the control circuit 15 can be configured to immediately start measuring ground fault current at 500kHz using magnetic sensors 16 and 17, regardless of whether or not there is ground fault current, after periodic startup. If a ground fault occurs, it can generate ground fault monitoring data and transmit it to the ground fault monitoring device 30. In this case, if no ground fault occurs, the measurement results from magnetic sensors 16 and 17 can be discarded. Note that the periodic startup process and the measurement process of the magnetic flux density of the ground fault current can be processed in parallel, so there will be no period of time when ground fault current cannot be measured.

[0055] In addition, while the above-described embodiment illustrates a configuration using a low-sensitivity current transformer as part of the ground fault current detection unit, the system is not limited to this configuration. For example, a search coil or Rogowski coil can be used instead of a current transformer. However, compared to a current transformer, search coils and Rogowski coils are too insensitive to detect minute ground fault currents caused by flying objects, and may require a separate, high-power, expensive, and fragile amplification amplifier. Therefore, a configuration using a current transformer is preferable. [Explanation of symbols]

[0056] 1…Ground fault monitoring system 10,10a...Ground fault detection device 12... Current transformer 13…Wiring cables 14...Ground fault current detection circuit 141...Voltage suppression varistor 142... Voltage suppression Zener diode 143…Optical insulation 144... Dry cell battery 15…Control circuits 16, 17… Magnetic sensors 18… Communications Department 19...Storage section 110... Dry cell battery 21, 22… Mounting arms 211,221…Longitudinal part 212,222… Mounting part 23…Stainless steel belt 20…Wide-area communication network relay equipment 30... Ground fault monitoring device 2... Power transmission towers

Claims

1. A ground fault detection device installed on the tower legs of a power transmission tower to detect ground faults, A ground fault current detection unit that outputs a starting signal triggered by the current flowing through the aforementioned tower legs, A magnetic sensor that measures magnetic flux density due to ground fault current, The system includes a control unit that, upon receiving the activation signal from the ground fault current detection unit, causes the magnetic sensor to measure the magnetic flux density due to the ground fault current, The ground fault current detection unit comprises a current transformer having a core and a coil, and a ground fault current detection circuit in which a varistor and / or resistor are arranged on the circuit. In the current transformer, a ground fault current flowing through the tower leg passes through the core, inducing an induced voltage in the coil, and a secondary current corresponding to this induced voltage is output to the ground fault current detection circuit. The ground fault current detection circuit is a ground fault detection device in which the varistor and / or resistor can attenuate the secondary current flowing through the circuit.

2. It further has a communication unit capable of transmitting data to remote locations, The ground fault detection device according to claim 1, wherein the control unit causes the communication unit to transmit ground fault monitoring data that takes into account the magnitude of the ground fault current based on the measured magnetic flux density data.

3. The aforementioned magnetic sensor has multiple measurement axes, The ground fault detection device according to claim 1 or 2, wherein the control unit generates ground fault monitoring data by synthesizing measurement data of magnetic flux density in the plurality of measurement axes obtained from the magnetic sensor.

4. The ground fault detection device according to any one of claims 1 to 3, wherein the control unit generates ground fault monitoring data that takes into account the waveform of the ground fault current based on time-series data based on measurement data from the magnetic sensor.

5. A ground fault detection device installed on the base of a transmission tower for detecting ground faults, A ground fault current detection unit that outputs a starting signal triggered by the current flowing through the aforementioned tower legs, A magnetic sensor that measures magnetic flux density due to ground fault current, The system includes a control unit that, upon receiving the activation signal from the ground fault current detection unit, causes the magnetic sensor to measure the magnetic flux density due to the ground fault current, The control unit has a standby mode for suppressing power consumption and a measurement mode for activating upon the activation signal output from the ground fault current detection unit and measuring the ground fault current. The control unit generates ground fault monitoring data based on the measurement data from the magnetic sensor. The ground fault detection device comprises a first ground fault monitoring data obtained by integrating data based on magnetic flux density measurement data at first time intervals, and a second ground fault monitoring data obtained by integrating data at second time intervals that are closer together than the first time interval.

6. The first ground fault monitoring data is time-series data obtained from the time of activation by the activation signal until the first hour has elapsed. The ground fault detection device according to claim 5, wherein the second ground fault monitoring data is time-series data obtained from the time of activation by the activation signal until a second time shorter than the first time has elapsed.

7. A ground fault monitoring device configured to communicate with a plurality of ground fault detection devices according to any one of claims 1 to 6, A ground fault monitoring device that identifies a transmission tower where a ground fault current has occurred, based on ground fault monitoring data received from the aforementioned multiple ground fault detection devices, and outputs information regarding the generated ground fault current.

8. A ground fault detection device installed on the base of a transmission tower to detect ground faults, comprising: a ground fault current detection unit that outputs an activation signal triggered by a current flowing through the base of the tower; a magnetic sensor that measures the magnetic flux density due to the ground fault current; and a control unit that, when it receives the activation signal from the ground fault current detection unit, causes the magnetic sensor to measure the magnetic flux density due to the ground fault current; and a plurality of ground fault detection devices, The system comprises a ground fault monitoring device configured to communicate with the aforementioned plurality of ground fault detection devices, The ground fault monitoring device identifies the transmission tower where the ground fault current occurred based on the ground fault monitoring data received from the plurality of ground fault detection devices, and outputs information regarding the generated ground fault current. The aforementioned multiple ground fault detection devices are mounted above the insulators of the transmission towers. The ground fault monitoring device is a ground fault monitoring system that detects a power transmission tower to which an upward ground fault current has been detected, among the plurality of ground fault detection devices, is attached, as the site of the ground fault.

9. The ground fault monitoring system according to claim 8, wherein the plurality of ground fault detection devices store information on the transmission delay time when transmitting the ground fault monitoring data in advance, and transmit the ground fault monitoring data after the transmission delay time has elapsed.

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