DISTRIBUTION LINE INTEGRITY EVALUATION DEVICE AND DISTRIBUTION LINE INTEGRITY EVALUATION METHOD

Abstract

To provide a distribution line soundness evaluation device and a distribution line soundness evaluation method which can evaluate soundness of a distribution line.SOLUTION: A soundness evaluation device 1 comprises: a power source unit 11 which outputs voltage whose frequency changes over time; a selection unit 12 which selects any two phases of a distribution line DL connected to a connection unit 10, makes the selected one phase an application phase and makes the other phase a ground phase; a detection unit 13 which detects voltage between the application phase and the ground phase and detects the current flowing in the application phase; a calculation unit 14 which obtains a first resonant frequency being a peak frequency appearing on the lowest frequency side and a current phase being a phase of the current to the voltage from the detection result of the detection unit 13; and an evaluation unit 15 which controls the selection unit 12 to obtain the first resonant frequency and current phase while changing the combination of the phase to be the application phase and the phase to be the ground phase, and evaluates soundness of the distribution line on the basis of the first resonant frequency and current phase obtained for each combination.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a power distribution line health evaluation device and a power distribution line health evaluation method. [Background technology]

[0002] In recent years, there has been a tendency for power outages to become prolonged due to natural disasters such as heavy rain, typhoons, and earthquakes. In order to prevent such prolonged power outages, efforts are being made to deploy power supply vehicles as temporary power sources and to build regional microgrids that utilize distributed power sources. In order to quickly restore power over a wide area using these power sources (temporary power sources, distributed power sources), it goes without saying that the distribution lines connecting the power sources to consumers must be sound.

[0003] However, for example, damage to utility poles can cause abnormalities in distribution lines. Abnormalities in distribution lines include breaks and ground faults that occur in a single phase, and short circuits that occur in two or more phases. If it is possible to evaluate the soundness of the affected distribution lines (presence or absence of breaks, ground faults, or short circuits) from the interconnection point of the temporary power source, this can be used to determine whether repair work is necessary or to determine the priority of power restoration, which can ultimately lead to a quicker restoration of power.

[0004] The following Patent Document 1 discloses a technique for locating a singular point where the impedance of a power transmission line changes. Specifically, the technique disclosed in the following Patent Document 1 applies a frequency continuously modulated wave (FMCW) to the power transmission line, and locates the distance from the application point to the singular point based on the time delay until the reflected wave generated at the singular point of the power transmission line returns to the application point of the frequency modulated continuous wave. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-49223 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, although the technology disclosed in the above-mentioned Patent Document 1 can locate singular points in a transmission line, it is considered difficult to evaluate the soundness of a distribution line because a distribution line is equipped with various pieces of equipment (for example, pole transformers required for supplying power to consumers) that are not installed on a transmission line.

[0007] The present invention has been made in view of the above circumstances, and has an object to provide a distribution line health evaluation device and a distribution line health evaluation method that can evaluate the health of a distribution line. [Means for solving the problem]

[0008] In order to solve the above problems, a distribution line health evaluation device (1) according to a first aspect of the present invention includes a connection unit (10) to which a three-phase distribution line (DL) to be evaluated is connected, a power supply unit (11) that outputs a voltage whose frequency changes over time, a selection unit (12) that selects any two phases of the distribution line connected to the connection unit, and sets one of the selected phases as an applied phase connected to the power supply unit and the other selected phase as a grounded phase that is grounded, a detection unit (13) that detects a voltage between the applied phase and the grounded phase and detects a current flowing through the applied phase, and The power distribution system includes a calculation unit (14) that performs frequency analysis of the current detected by the detection unit to determine a first resonance frequency, which is the frequency of a peak that appears on the lowest frequency side, and determines a current phase, which is the phase of the current relative to the voltage, based on the voltage and current detected by the detection unit; and an evaluation unit (15) that controls the selection unit to determine the first resonance frequency and the current phase while changing the combination of the phase to be the applied phase and the phase to be the grounded phase, and evaluates the soundness of the power distribution line based on the first resonance frequency and the current phase obtained for each combination.

[0009] Furthermore, a second aspect of the present invention provides a distribution line health assessment device in accordance with the first aspect of the present invention, wherein the distribution line has an R phase, an S phase, and a T phase, and the assessment unit controls the selection unit to change the combination as follows: A combination in which the R phase is the applied phase and the S phase is the ground phase A combination in which the S phase is the applied phase and the R phase is the ground phase A combination in which the S phase is the applied phase and the T phase is the ground phase A combination in which the T phase is the applied phase and the S phase is the ground phase A combination in which the T phase is the applied phase and the R phase is the ground phase A combination in which the R phase is the applied phase and the T phase is the ground phase

[0010] Furthermore, a distribution line health evaluation device according to a third aspect of the present invention is a distribution line health evaluation device according to the first or second aspect of the present invention, wherein the evaluation unit evaluates the distribution line to be healthy if the first resonant frequencies obtained for each combination are equal and the current phases obtained for each combination all indicate a lead.

[0011] Furthermore, a fourth aspect of the present invention is a distribution line health evaluation device according to the first or second aspect of the present invention, wherein the evaluation unit evaluates the distribution line to be a three-phase short circuit when the first resonant frequencies obtained for each combination are equal and the current phases obtained for each combination all indicate a delay.

[0012] Furthermore, a fifth aspect of the present invention provides a distribution line health evaluation device in accordance with the first or second aspect of the present invention, wherein, when the first resonant frequency obtained in any two of the combinations is higher than the first resonant frequency obtained in the other combinations, the evaluation unit evaluates that an open circuit has occurred in the applied phase in the combination in which the first resonant frequency is higher.

[0013] Furthermore, a sixth aspect of the present invention provides a distribution line health evaluation device according to the first or second aspect of the present invention, wherein the evaluation unit evaluates that a ground fault has occurred in the application phase when the current phase shows a lag, when the first resonant frequencies obtained in any two of the combinations are lower than the first resonant frequencies obtained in the other combinations and the application phase when the current phase shows a lag is the same.

[0014] Furthermore, a seventh aspect of the present invention is a distribution line health evaluation device according to the first or second aspect of the present invention, wherein the evaluation unit evaluates that a two-phase short circuit has occurred between the application phase when the current phase shows a lag and the ground phase when the first resonant frequency obtained in any two of the combinations is lower than the first resonant frequency obtained in the other combinations and the application phase when the current phase shows a lag is different.

[0015] A method for evaluating the health of a power distribution line according to one aspect of the present invention includes the steps of: selecting any two phases of a three-phase power distribution line (DL) to be evaluated that are connected to a connection section (10) to which the DL is connected; setting one of the selected phases as an applied phase that is connected to a power supply section (11) that outputs a voltage whose frequency varies over time; and setting the other selected phase as a ground phase that is grounded (S11); detecting a voltage between the applied phase and the ground phase; and detecting a current flowing through the applied phase (S12); performing a frequency analysis of the detected current to determine a first resonant frequency that is the frequency of a peak that appears on the lowest frequency side; and determining a current phase that is the phase of the current relative to the voltage based on the detected voltage and current (S13); and determining the first resonant frequency and the current phase while changing the combination of the phase that is the applied phase and the phase that is the ground phase; and evaluating the health of the power distribution line based on the first resonant frequency and the current phase obtained for each combination (S15). [Effects of the Invention]

[0016] According to the present invention, it is possible to evaluate the soundness of a power distribution line. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram for explaining the soundness of a power distribution line. [Figure 2] FIG. 10 is a diagram illustrating an example of a signal used to detect a change in impedance according to the state of a power distribution line. [Figure 3] FIG. 10 is a diagram showing how measurements are performed while changing the combination of applied phases and ground phases. [Figure 4] FIG. 10 is a diagram showing an example of frequency characteristics of a current obtained by a test. [Figure 5] FIG. 10 is a diagram showing an example of a current phase obtained by a test. [Figure 6] This is a diagram summarizing the test results of the power distribution line. [Figure 7] 1 is a block diagram showing a configuration of a main part of a power distribution line health evaluation device according to an embodiment of the present invention; [Figure 8] 1 is a flowchart illustrating an example of a method for evaluating the health of a power distribution line according to an embodiment of the present invention. [Figure 9] 9 is a flowchart showing details of the process performed in step S15 in FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a power distribution line health evaluation device and a power distribution line health evaluation method according to an embodiment of the present invention will be described in detail with reference to the drawings. The configurations of the following embodiments are merely examples, and the present invention is not limited to the configurations of the embodiments. First, the principle of evaluating the health of a power distribution line will be described below, and then the power distribution line health evaluation device and the power distribution line health evaluation method according to an embodiment of the present invention will be described.

[0019] <Principles of distribution line integrity evaluation> FIG. 1 is a diagram for explaining the soundness of a distribution line. Here, the soundness of a distribution line DL is an index showing whether or not an abnormality has occurred in the distribution line DL. Examples of the soundness of a distribution line DL include "sound" shown in FIG. 1(a), "disconnection" shown in FIG. 1(b), "ground fault" shown in FIG. 1(c), and "short circuit" shown in FIG. 1(d). The distribution line DL to be evaluated is, for example, a three-phase distribution line having R, S, and T phases as shown in FIG. 1.

[0020] "Healthy" in Figure 1(a) means that there are no abnormalities (disconnections, ground faults, or short circuits) in the distribution line DL, and power can be supplied to consumers through the distribution line DL. "Disconnection" in Figure 1(b) means that one of the phases of the distribution line DL is disconnected. The example shown in Figure 1(b) shows that the R phase of the distribution line DL is disconnected.

[0021] The "ground fault" shown in FIG. 1(c) refers to a state in which any phase of the distribution line DL comes into contact with the ground (g), causing a current to flow to the ground. The example shown in FIG. 1(c) shows a state in which the R phase of the distribution line DL has a ground fault. The "short circuit" shown in FIG. 1(d) refers to a state in which multiple phases of the distribution line DL are in electrical contact, causing a current to flow between the multiple phases of the distribution line DL. The example shown in FIG. 1(d) illustrates a state in which the R and S phases of the distribution line DL are short-circuited (a two-phase short circuit), and a state in which the R, S, and T phases of the distribution line DL are short-circuited (a three-phase short circuit).

[0022] The "break" shown in Figure 1(b), the "ground fault" shown in Figure 1(c), and the "short circuit" shown in Figure 1(d) are all conditions in which power cannot be supplied to consumers via the distribution line DL. Note that the "break" shown in Figure 1(b) and the "ground fault" shown in Figure 1(c) are abnormalities occurring in a single phase of the distribution line DL, while the "short circuit" shown in Figure 1(d) is an abnormality occurring in two or more phases of the distribution line DL.

[0023] The impedance between each phase (R phase, S phase, T phase) of the distribution line DL and the ground (g) changes depending on the state of the distribution line DL illustrated in Fig. 1. For example, in the case of a "break" illustrated in Fig. 1(b), such a change in impedance occurs because the impedance between the broken R phase and the unbroken S phase differs from the impedance between the unbroken S phase and the unbroken T phase.

[0024] In this embodiment, the soundness of the distribution line DL is evaluated by focusing on such changes in impedance. Specifically, to investigate the changes in impedance, a signal whose frequency changes over time is applied to the distribution line DL, and the frequency characteristics of the flowing current and the phase of the current relative to the voltage in the low-frequency band (hereinafter referred to as "current phase") are obtained. More specifically, the frequency characteristics and current phase of the current are obtained while changing the combination of the phase to which the signal is applied (applied phase) and the phase to which the signal is grounded (grounded phase) among the three phases (R phase, S phase, and T phase) of the distribution line DL. Then, the soundness of the distribution line DL is evaluated based on the frequency characteristics and current phase of the current obtained for each combination of the applied phase and the grounded phase.

[0025] Fig. 2 is a diagram showing an example of a signal used to detect changes in impedance according to the state of a power distribution line. The signal shown in Fig. 2 is a low-voltage FMCW (Frequency Modulated Continuous Wave) signal whose frequency is continuously modulated. This FMCW signal is a signal whose voltage changes in a sinusoidal manner, and whose frequency changes linearly from a start frequency fs to an end frequency fe during an application time Ts. In the example shown in Fig. 2, because the end frequency fe is higher than the start frequency fs, the frequency of the FMCW signal gradually increases over time (the length of one cycle becomes shorter), as shown in Fig. 2.

[0026] Here, the combinations of the applied phase and the ground phase in the distribution line DL are the following six patterns. R phase is the applied phase, S phase is the ground phase (R-Sg) · S phase is the applied phase, R phase is the ground phase (S-Rg) · S phase is the energized phase, T phase is the ground phase (S-Tg) T phase is the energized phase, S phase is the ground phase (T-Sg) T phase is the applied phase, R phase is the ground phase (T-Rg) R phase is the applied phase, T phase is the ground phase (R-Tg)

[0027] In this specification and drawings, a pattern in which the applied phase is the X phase and the ground phase is the Y phase may be expressed as "X-Yg." The X phase is any of the R phase, S phase, and T phase, and the Y phase is any of the R phase, S phase, and T phase other than the X phase. For example, the pattern "R-Sg" refers to a combination in which the R phase is the applied phase and the S phase is the ground phase.

[0028] Figure 3 shows how measurements are performed while changing the combination of applied phases and ground phases. Figure 3(a) shows how measurements are performed when the R phase is the applied phase and the S phase is the ground phase (pattern "R-Sg"), and Figure 3(b) shows how measurements are performed when the S phase is the applied phase and the T phase is the ground phase (pattern "S-Tg"). Note that Figure 3 illustrates an example in which a disconnection occurs in the R phase of the distribution line DL, as shown in Figure 1(b).

[0029] The voltage source VS shown in Figures 3(a) and 3(b) outputs the above-mentioned FMCW signal between output terminals T1 and T2. In the example shown in Figure 3(a), output terminal T1 of the voltage source VS is connected to the R phase of the distribution line DL, and output terminal T2 of the voltage source VS is connected to the S phase of the distribution line DL and is also connected to the earth (g) (grounded). In the example shown in Figure 3(b), output terminal T1 of the voltage source VS is connected to the S phase of the distribution line DL, and output terminal T2 of the voltage source VS is connected to the T phase of the distribution line DL and is also connected to the earth (g) (grounded).

[0030] FIG. 4 shows an example of the frequency characteristics of the current obtained by the test, and FIG. 5 shows an example of the current phase obtained by the test. The test was conducted on a distribution line DL with a length of approximately 2.8 km from the voltage application end (the end where the FMCW signal is applied) to the terminal, using the "R-Sg" pattern as shown in FIG. 3(a). The test on the distribution line DL was conducted both when the distribution line DL was in a healthy state and when an abnormality occurred in the distribution line DL. The abnormalities in the distribution line DL were assumed to be an R-phase break, an R-phase ground fault, or a short circuit between the R and S phases, located approximately 1.5 km from the voltage application end to the terminal of the distribution line DL.

[0031] For the test on the distribution line DL, an FMCW signal with an effective voltage of approximately 12 V, a start frequency fs of 0.1 kHz, and an end frequency fe of 400 kHz was used. The application time Ts of the FMCW signal to the distribution line DL was 40 ms.

[0032] The current frequency characteristics shown in Figure 4 were obtained by performing a fast Fourier transformation (FFT) on the current waveform obtained through testing. As shown in Figure 4, when the distribution line DL is healthy, current peaks appear when the modulation frequency of the FMCW signal is approximately 23 [kHz] and approximately 72 [kHz]. The current peaks shown in Figure 4 represent resonances occurring in the impedance of the distribution line DL as seen from the voltage application end. Here, the frequency of the peak that appears on the lowest frequency side is defined as the first resonance frequency f1. In the example shown in Figure 4, the first resonance frequency f1 is approximately 23 [kHz] when the distribution line DL is healthy.

[0033] When the distribution line DL is healthy, the frequency characteristics of the obtained current are substantially the same regardless of the six patterns (R-Sg, S-Rg, S-Tg, T-Sg, T-Rg, R-Tg) of the applied phase and the ground phase of the distribution line DL. Therefore, when the distribution line DL is healthy, the first resonant frequency f1 is approximately 23 kHz, regardless of the six patterns (R-Sg, S-Rg, S-Tg, T-Sg, T-Rg, R-Tg) of the applied phase and the ground phase of the distribution line DL.

[0034] 4, the frequency characteristics of the current obtained when an abnormality occurs in the distribution line DL are significantly different from the frequency characteristics of the current obtained when the distribution line DL is healthy. Furthermore, the frequency characteristics of the current vary depending on the type of abnormality occurring in the distribution line DL, and the first resonant frequency f1 also varies depending on the type of abnormality occurring in the distribution line DL. Specifically, the first resonant frequency f1 is approximately 23 kHz when the distribution line DL is healthy, but increases to approximately 46 kHz when an R-phase break occurs, and decreases to approximately 3 kHz when an R-phase ground fault occurs or when an R-phase and S-phase short circuit occurs.

[0035] The first resonant frequency f1 increases when there is an R-phase break in the distribution line DL because the inductance component, which is a series circuit element of the line, and the capacitance component, which is a parallel circuit element, are smaller than when the distribution line DL is sound. The first resonant frequency f1 decreases when there is a ground fault in the R-phase of the distribution line DL or when there is a short circuit between the R and S phases of the distribution line DL because a current path is formed via the conductor or the ground (g). Note that when there is a ground fault in the R-phase of the distribution line DL, the power spectrum decreases compared to when there is a short circuit between the R and S phases of the distribution line DL because ground resistance is also added.

[0036] The current phase shown in Figure 5(a) is when the distribution line DL is healthy, and the current phase shown in Figure 5(b) is when an R-phase ground fault occurs. Referring to Figure 5(a), the current waveform leads the voltage waveform, so the current phase φ0 is "leading." The "leading" of the current phase φ0 occurs because the impedance of a healthy distribution line DL is observed as capacitive reactance. Referring to Figure 5(b), the current waveform lags the voltage waveform, so the current phase φ0 is "lag." The "lag" of the current phase φ0 occurs due to the resistance and inductive reactance of the line.

[0037] FIG. 6 is a diagram summarizing the test results of the power distribution line. In FIG. 6, the first column CL1 shows the state of the power distribution line DL. The second column CL2 shows the classification of the first resonant frequency f1 and the current phase φ0 for each state of the power distribution line DL. The third column CL3 shows the first resonant frequency f1 and the current phase φ0 for each state of the power distribution line DL obtained by the test. The classification shown in the second column CL2 is derived from the test results shown in the third column CL3. Note that important first resonant frequencies f1 and current phases φ0 shown in the third column CL3 in FIG. 6 are hatched.

[0038] As shown in FIG. 6, when the distribution line DL is healthy, the first resonant frequency f1 is 23 [kHz] for three patterns (R-Sg, S-Rg, S-Tg) and 24 [kHz] for the remaining three patterns (T-Sg, T-Rg, R-Tg). Therefore, when the distribution line DL is healthy, the first resonant frequency f1 is the same for all patterns. Note that, when the variation in the first resonant frequency f1 among multiple patterns is within a few [kHz], it can be said that the first resonant frequency f1 among the multiple patterns is the same. Furthermore, when the distribution line DL is healthy, the current phase φ0 is "leading" in all patterns.

[0039] When an R-phase break occurs in the distribution line DL, the first resonant frequency f1 in two patterns (R-Sg, R-Tg) is higher than the first resonant frequency f1 in the other four patterns (S-Rg, S-Tg, T-Sg, T-Rg). Therefore, when an R-phase break occurs in the distribution line DL, the first resonant frequency f1 is higher only in the two patterns (R-Sg, R-Tg) in which the break phase (R-phase), in which the line is shortened, is used as the application phase. Furthermore, when an R-phase break occurs in the distribution line DL, the current phase φ0 is "leading" in all patterns.

[0040] When a ground fault or short circuit occurs in the R phase of the distribution line DL, the first resonant frequency f1 in two patterns is lower than the first resonant frequency f1 in the other four patterns, and the current phase φ0 in these two patterns is "lagging." Here, when a ground fault occurs in the R phase of the distribution line DL, the first resonant frequency f1 is lower and the current phase φ0 is "lagging" only in two patterns (R-Sg, R-Tg) in which the ground-fault phase (R phase) is the applied phase. In contrast, when a short circuit occurs in the R phase of the distribution line DL, the first resonant frequency f1 is lower and the current phase φ0 is "lagging" only in two patterns (R-Sg, S-Rg) in which the short-circuited phase (R phase) is the applied phase or ground phase.

[0041] When a three-phase short circuit occurs in the distribution line DL, the first resonant frequency f1 is the same in all patterns, just as when the distribution line DL is healthy. However, when a three-phase short circuit occurs in the distribution line DL, the current phase φ0 is "delayed" in all patterns.

[0042] When an S-phase or T-phase break occurs in the distribution line DL, the classification of the first resonant frequency f1 and the current phase φ0 is the same as when an R-phase break occurs. Specifically, when an S-phase break occurs in the distribution line DL, the first resonant frequency f1 increases and the current phase φ0 becomes "leading" in only two patterns (S-Rg, S-Tg) in which the broken phase (S-phase) that shortens the line is the applied phase, and the current phase φ0 becomes "leading" in both patterns. Also, when a T-phase break occurs in the distribution line DL, the first resonant frequency f1 increases and the current phase φ0 becomes "leading" in only two patterns (T-Sg, T-Rg) in which the broken phase (T-phase) that shortens the line is the applied phase, and the current phase φ0 becomes "leading" in both patterns.

[0043] When a ground fault occurs in the S-phase or T-phase of the distribution line DL, the classification of the first resonant frequency f1 and the current phase φ0 is the same as when a ground fault occurs in the R-phase. Specifically, when a ground fault occurs in the S-phase of the distribution line DL, the first resonant frequency f1 decreases and the current phase φ0 becomes "lagging" only in two patterns (S-Rg, S-Tg) in which the ground-fault phase (S-phase) is the applied phase. Also, when a ground fault occurs in the T-phase of the distribution line DL, the first resonant frequency f1 decreases and the current phase φ0 becomes "lagging" only in two patterns (T-Sg, T-Rg) in which the ground-fault phase (T-phase) is the applied phase.

[0044] When the S-phase and T-phase of the distribution line DL are short-circuited, the classification of the first resonant frequency f1 and the current phase φ0 is the same as when the R-phase is short-circuited. Specifically, when the S-phase of the distribution line DL is short-circuited, the first resonant frequency f1 is low and the current phase φ0 is "lagging" only in two patterns in which the short-circuited phase (S-phase) is the applied phase or the grounded phase. Also, when the T-phase of the distribution line DL is short-circuited, the first resonant frequency f1 is low and the current phase φ0 is "lagging" only in two patterns in which the short-circuited phase (T-phase) is the applied phase or the grounded phase.

[0045] In this way, the first resonant frequency f1 and the current phase φ0 can be classified according to the state of the distribution line DL from the test results of the distribution line DL. Therefore, the first resonant frequency f1 and the current phase φ0 are obtained by changing the combination (pattern) of the applied phase and the ground phase among the three phases (R phase, S phase, and T phase) of the distribution line DL to be evaluated. Then, the obtained first resonant frequency f1 and the current phase φ0 can be classified using FIG. 6 to evaluate the soundness of the distribution line DL.

[0046] <Power distribution line health evaluation device> Fig. 7 is a block diagram showing the configuration of the main parts of a power distribution line health evaluation device according to one embodiment of the present invention. As shown in Fig. 7, the health evaluation device 1 of this embodiment includes a connection unit 10, a power supply unit 11, a selection unit 12, a detection unit 13, a calculation unit 14, an evaluation unit 15, and an output unit 16. Such a health evaluation device 1 evaluates the health of the power distribution line DL (powered outage power distribution line DL) connected to the connection unit 10.

[0047] The connection part 10 is a part to which the three-phase distribution line DL to be evaluated is connected. The connection part 10 includes a first connection part 10a to which the R phase of the distribution line DL is connected, a second connection part 10b to which the S phase of the distribution line DL is connected, and a third connection part 10c to which the T phase of the distribution line DL is connected. Note that the distribution line DL to be connected to the connection part 10 is put into a power outage state (a state in which no power is being supplied) before being connected to the connection part 10.

[0048] The power supply unit 11 outputs a voltage to be applied to the power distribution line DL connected to the connection unit 10. Specifically, the power supply unit 11 outputs a voltage whose frequency changes over time. For example, the power supply unit 11 outputs a voltage whose frequency changes linearly over time, a voltage whose frequency changes stepwise over time, or a voltage whose frequency changes sinusoidally over time. Note that the voltage output by the power supply unit 11 is not limited to the voltages exemplified above, and may be any voltage whose frequency changes over time. For example, the power supply unit 11 outputs the FMCW signal described above.

[0049] The power supply unit 11 and the selection unit 12 are connected by a power supply line L1 and a ground line L2. The power supply line L1 is a line to which a voltage (such as the above-mentioned FMCW signal) output from the power supply unit 11 is applied, and the ground line L2 is a grounded line. In other words, the voltage (such as the above-mentioned FMCW signal) output from the power supply unit 11 is applied between the power supply line L1 and the ground line L2.

[0050] Under the control of the evaluation unit 15, the selection unit 12 selects any two phases of the distribution line DL connected to the connection unit 10, connects one selected phase to the power line L1 to set it as an applied phase, and connects the other selected phase to the ground line L2 to set it as a ground phase. Here, there are three combinations of two phases selected by the selection unit 12: a combination of R phase and S phase, a combination of S phase and T phase, and a combination of T phase and R phase. In addition, there are two combinations of which of the two phases selected by the selection unit 12 is to be used as an applied phase or a ground phase. Therefore, all combinations of phases that become applied phases and phases that become ground phases are the six patterns (R-Sg, S-Rg, S-Tg, T-Sg, T-Rg, R-Tg) mentioned above.

[0051] The detection unit 13 is provided on the power line L1 and ground line L2 that connect the power supply unit 11 and the selection unit 12, and detects the voltage between the power line L1 and the ground line L2 (the voltage between the applied phase and the ground phase) and the current flowing in the power line L1 (applied phase). The detection unit 13 detects the voltage between the power line L1 and the ground line L2 and the current flowing in the power line L1 when the voltage of the power supply unit 11 is applied for each of the above patterns. The detection unit 13 also includes a voltmeter (not shown) that detects the voltage between the power line L1 and the ground line L2 and an ammeter (not shown) that detects the current flowing in the power line L1.

[0052] The calculation unit 14 performs a frequency analysis of the current detected by the detection unit 13 to determine the frequency of the peak that appears on the lowest frequency side (the first resonant frequency f1 described above). Specifically, the calculation unit 14 performs a fast Fourier transform on the current waveform detected by the detection unit 13 to determine the frequency of the peak that appears on the lowest frequency side as the first resonant frequency f1. Furthermore, the calculation unit 14 determines the phase of the current relative to the voltage (the current phase φ0 described above) based on the voltage and current detected by the detection unit 13.

[0053] The evaluation unit 15 controls the selection unit 12 to cause the calculation unit 14 to obtain the first resonant frequency f1 and the current phase φ0 while changing the combination (pattern) of the phase to be used as the applied phase and the phase to be used as the ground phase. Then, the evaluation unit 15 evaluates the soundness of the distribution line DL based on the first resonant frequency f1 and the current phase φ0 obtained for each pattern. Here, the evaluation unit 15 evaluates the soundness of the distribution line DL by classifying the obtained first resonant frequency f1 and current phase φ0 using the classification method described with reference to FIG. 6.

[0054] Specifically, the evaluation unit 15 evaluates that the distribution line DL is healthy if the first resonant frequencies f1 obtained for each pattern are equal and the current phases φ0 obtained for each pattern all indicate a "leading" state. The evaluation unit 15 evaluates that the distribution line DL has a three-phase short circuit if the first resonant frequencies f1 obtained for each pattern are equal and the current phases φ0 obtained for each pattern all indicate a "lagging" state. If the first resonant frequencies f1 obtained for any two of the six patterns are higher than the first resonant frequencies f1 obtained for the other patterns, the evaluation unit 15 evaluates that an open circuit has occurred in the application phase of the pattern in which the first resonant frequency f1 is higher.

[0055] The evaluation unit 15 evaluates that a ground fault has occurred in the application phase when the current phase φ0 shows a lag if the first resonance frequency f1 obtained in any two of the six patterns is lower than the first resonance frequency f1 obtained in the other patterns and the application phase when the current phase φ0 shows a lag is the same.The evaluation unit evaluates that a two-phase short circuit has occurred between the application phase when the current phase φ0 shows a lag and the ground phase if the first resonance frequency f1 obtained in any two of the six patterns is lower than the first resonance frequency f1 obtained in the other patterns and the application phase when the current phase φ0 shows a lag is different.

[0056] The output unit 16 outputs the evaluation result of the evaluation unit 15 to the outside. The output unit 16 is provided with a display device such as a liquid crystal display device, and outputs the evaluation result of the evaluation unit 15 to the outside by displaying the evaluation result of the evaluation unit 15 as characters or the like. Alternatively, the output unit 16 is provided with, for example, a communication device that communicates with an external device, and outputs the evaluation result of the evaluation unit 15 to the outside by transmitting the evaluation result of the evaluation unit 15 to the external device.

[0057] The soundness evaluation device 1 may be configured such that the connection unit 10, power supply unit 11, selection unit 12, detection unit 13, calculation unit 14, evaluation unit 15, and output unit 16 are provided in one housing, or in different housings. For example, the housing in which the connection unit 10, power supply unit 11, selection unit 12, and detection unit 13 are provided may be different from the housing in which the calculation unit 14, evaluation unit 15, and output unit 16 are provided.

[0058] Furthermore, the calculation unit 14, the evaluation unit 15, and the output unit 16 may be realized by a computer such as a desktop computer or a notebook computer. In other words, the functions of the calculation unit 14, the evaluation unit 15, and the output unit 16 may be realized by software and hardware working together by causing a computer to execute a program that realizes the functions of the calculation unit 14, the evaluation unit 15, and the output unit 16.

[0059] <Distribution line integrity evaluation method> Fig. 8 is a flowchart showing an example of a method for evaluating the health of a power distribution line according to an embodiment of the present invention. The processing of the flowchart shown in Fig. 8 is started, for example, when a user of the health evaluation device 1 connects a power distribution line DL that is in a power outage state to the connection unit 10, and then operates an operation unit (not shown) of the health evaluation device 1 to issue an instruction to start the health evaluation processing.

[0060] When the processing of the flowchart shown in FIG. 8 starts, first, the evaluation unit 15 of the soundness evaluation device 1 controls the selection unit 12 to select a combination (pattern) of a phase to be used as an applied phase and a phase to be used as a grounded phase of the distribution line DL connected to the connection unit 10 (step S11). The selection unit 12, under the control of the evaluation unit 15, selects any two phases of the distribution line DL connected to the connection unit 10, sets one selected phase as an applied phase, and sets the other selected phase as a grounded phase. For example, the selection unit 12 selects the R phase and the S phase of the distribution line DL connected to the connection unit 10, sets the R phase as an applied phase, and sets the S phase as a grounded phase. The evaluation unit 15 is aware of the combination (pattern) of the phases used as applied phases and the phases used as grounded phases.

[0061] Next, the power supply unit 11 outputs an FMCW signal. The FMCW signal output from the power supply unit 11 is applied to the distribution line DL via the power line L1 and the selection unit 12 in this order. For example, when the R phase of the distribution line DL is selected as the application phase and the S phase is selected as the ground phase, the FMCW signal is applied to the R phase of the distribution line DL. The detection unit 13 detects the voltage between the R phase and the S phase when the FMCW signal is applied to the distribution line DL, and also detects the current flowing through the R phase (step S12).

[0062] Next, the calculation unit 14 performs a frequency analysis of the current detected by the detection unit 13 to determine a first resonant frequency f1, and calculates a current phase φ0 based on the detected voltage and current (step S13). Specifically, the calculation unit 14 performs a fast Fourier transform on the current waveform detected by the detection unit 13, and determines the frequency of the peak that appears on the lowest frequency side as the first resonant frequency f1. The first resonant frequency f1 and the current phase φ0 calculated by the calculation unit 14 are output to the evaluation unit 15 and stored in association with a pattern recognized by the evaluation unit 15 (a pattern of a phase set as an applied phase and a phase set as a ground phase).

[0063] Next, the evaluation unit 15 determines whether or not the selection of all patterns has been completed (step S14). If it is determined that the selection of all patterns has not been completed (if the determination result in step S14 is "NO"), the evaluation unit 15 controls the selection unit 12 to select a new pattern (step S11) and to perform the processes of steps S12 and S13 shown in FIG. 8.

[0064] On the other hand, if it is determined that the selection of all patterns has been completed (if the determination result in step S14 is "YES"), the evaluation unit 15 evaluates the soundness of the distribution line DL based on the first resonant frequency f1 and the current phase φ0 obtained for each pattern (step S15). Specifically, the evaluation unit 15 evaluates the soundness of the distribution line DL by classifying the first resonant frequency f1 and the current phase φ0 obtained for each pattern using the classification method described with reference to FIG.

[0065] Fig. 9 is a flowchart showing details of the processing performed in step S15 in Fig. 8. When the processing of the flowchart shown in Fig. 9 starts, first, the evaluation unit 15 determines whether or not the first resonant frequencies f1 of all patterns are equal (step S21). If it is determined that the first resonant frequencies f1 of all patterns are equal (if the determination result in step S21 is "YES"), the evaluation unit 15 determines whether or not the current phases φ0 of all patterns are "leading" (step S22).

[0066] If the evaluation unit 15 determines that the current phase φ0 of all patterns is "leading" (if the determination result in step S22 is "YES"), it evaluates that the distribution line DL is healthy (step S23). On the other hand, if the evaluation unit 15 determines that the current phase φ0 of all patterns is "lagging" (if the determination result in step S22 is "NO"), it evaluates that a three-phase short circuit has occurred in the distribution line DL (step S24).

[0067] On the other hand, if it is determined in step S21 that the first resonant frequencies f1 are not equal for all patterns (if the determination result in step S21 is "NO"), the evaluation unit 15 determines whether the first resonant frequencies f1 are high in only two of the six patterns (step S25). If it is determined that the first resonant frequencies f1 are high in only two patterns (if the determination result in step S25 is "YES"), the evaluation unit 15 evaluates that a break has occurred in the application phase in which the first resonant frequency f1 is high (step S26).

[0068] On the other hand, if it is determined that the first resonant frequency f1 is low in only two patterns (if the determination result in step S25 is "NO"), the evaluation unit 15 determines whether the application phases in the patterns in which the current phase φ0 is "lagging" are the same (step S27). If it is determined that the application phases in the patterns in which the current phase φ0 is "lagging" are the same (if the determination result in step S27 is "YES"), the evaluation unit 15 evaluates that a ground fault has occurred in the application phase in which the current phase φ0 is "lagging" (step S28).

[0069] On the other hand, if it is determined that the application phases in the pattern in which the current phase φ0 is "lagging" are different (if the determination result in step S27 is "NO"), the evaluation unit 15 evaluates that a two-phase short circuit has occurred between the application phase in which the current phase φ0 is "lagging" and the ground phase (step S29). With the above processing, the series of processing shown in FIG. 9 is completed. When the series of processing shown in FIG. 9 is completed, the series of processing shown in FIG. 8 is also completed, and the evaluation result of the evaluation unit 15 is output (for example, displayed) by the output unit 16.

[0070] As described above, the health evaluation device 1 according to this embodiment first selects any two phases of the distribution line DL connected to the connection 10, sets one of the selected phases as an applied phase, and sets the other selected phase as a ground phase, and applies an FMCW signal. Next, the device detects the voltage between the applied phase and the ground phase and the current flowing through the applied phase, and calculates a first resonant frequency f1 and a current phase φ0 based on the detected voltage and current. The device then calculates the first resonant frequency f1 and the current phase φ0 while changing the combination of the applied phase and the ground phase, and evaluates the health of the distribution line DL based on the first resonant frequency f1 and the current phase φ0 obtained for each combination. In this way, this embodiment can evaluate the health of the distribution line DL. This can be used, for example, to determine the need for repair work or the priority of power restoration, which ultimately contributes to early power restoration.

[0071] Although one embodiment of the present invention has been described in this specification, this embodiment is presented as an example and is not intended to limit the scope of the invention. These embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are intended to be included within the scope of the invention and its equivalents as defined in the claims, as well as within the scope and spirit of the invention.

[0072] The program for implementing the soundness assessment device 1 described above may be stored in a computer-readable storage medium and loaded into a computer system for execution. The term "computer system" as used herein includes hardware such as an OS and peripheral devices. The term "computer-readable storage medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into a computer system. The term "computer-readable storage medium" also includes storage devices that retain a program for a certain period of time, such as volatile memory (RAM) within a computer system that serves as a server or client when the program is transmitted via a network such as the Internet or a communication line such as a telephone line. The program may also be transmitted from a computer system storing the program in a storage device to another computer system via a transmission medium or by transmission waves within the transmission medium. The term "transmission medium" used to transmit the program refers to a medium capable of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may also be used to implement some of the functions described above. Furthermore, the above-mentioned functions may be realized in combination with a program already stored in the computer system, that is, a so-called differential file (differential program). [Explanation of symbols]

[0073] 1. Soundness evaluation device 10 Connection 11 Power supply section 12 Selection section 13 Detector 14 Arithmetic section 15 Evaluation Section DL distribution line

Claims

1. a connection portion to which a three-phase distribution line to be evaluated is connected; a power supply unit that outputs a voltage whose frequency changes over time; a selection unit that selects any two phases of the distribution line connected to the connection unit, and sets one of the selected phases as an applied phase connected to the power supply unit and the other selected phase as a grounded phase that is grounded; a detection unit that detects a voltage between the applied phase and the ground phase and detects a current flowing through the applied phase; a calculation unit that performs a frequency analysis of the current detected by the detection unit to determine a first resonance frequency, which is the frequency of a peak that appears on the lowest frequency side, and that determines a current phase, which is the phase of the current relative to the voltage, based on the voltage and current detected by the detection unit; an evaluation unit that controls the selection unit to obtain the first resonant frequency and the current phase while changing a combination of a phase to be the applied phase and a phase to be the ground phase, and evaluates the soundness of the power distribution line based on whether the first resonant frequency is the same or different and whether the current phase is advanced or delayed for each combination; A power distribution line health evaluation device comprising:

2. the distribution line has an R phase, an S phase, and a T phase, The soundness evaluation device according to claim 1 , wherein the evaluation unit controls the selection unit to change the combination as follows: A combination in which the R phase is the applied phase and the S phase is the ground phase A combination in which the S phase is the applied phase and the R phase is the ground phase A combination in which the S phase is the applied phase and the T phase is the ground phase A combination in which the T phase is the applied phase and the S phase is the ground phase A combination in which the T phase is the applied phase and the R phase is the ground phase A combination in which the R phase is the applied phase and the T phase is the ground phase

3. 3. The health assessment device according to claim 1, wherein the assessment unit assesses the power distribution line to be healthy if the first resonant frequencies obtained for each of the combinations are equal and the current phases obtained for each of the combinations all indicate a lead.

4. 3. The health assessment device according to claim 1, wherein the assessment unit assesses that the distribution line is three-phase short-circuited when the first resonant frequencies obtained for each of the combinations are equal and the current phases obtained for each of the combinations all indicate a delay.

5. 3. The health evaluation device according to claim 1, wherein, when the first resonant frequency obtained in any two of the combinations is higher than the first resonant frequency obtained in the other combinations, the evaluation unit evaluates that an open circuit has occurred in the application phase in the combination in which the first resonant frequency is higher.

6. 3. The health evaluation device according to claim 1, wherein, when the first resonant frequencies obtained in any two of the combinations are lower than the first resonant frequencies obtained in the other combinations and the application phases when the current phases show a lag are the same, the evaluation unit evaluates that a ground fault has occurred in the application phase when the current phase shows a lag.

7. 3. The health assessment device according to claim 1, wherein the assessment unit assesses that a two-phase short circuit has occurred between the application phase when the current phase shows a lag and the ground phase when the first resonant frequency obtained in any two of the combinations is lower than the first resonant frequency obtained in the other combinations and the application phase when the current phase shows a lag is different.

8. selecting any two phases of the distribution line connected to a connection part to which the three-phase distribution line to be evaluated is connected, and setting one of the selected phases as an applied phase connected to a power supply part that outputs a voltage whose frequency varies over time, and setting the other selected phase as a grounded phase that is grounded; detecting a voltage between the applied phase and the ground phase and detecting a current flowing through the applied phase; a step of performing a frequency analysis of the detected current to determine a first resonance frequency, which is the frequency of a peak that appears on the lowest frequency side, and determining a current phase, which is the phase of the current relative to the voltage, based on the detected voltage and current; determining the first resonant frequency and the current phase while changing a combination of the phase to be the applied phase and the phase to be the grounded phase, and evaluating the soundness of the power distribution line based on whether the first resonant frequency is the same or different and whether the current phase is advanced or delayed for each combination; A method for evaluating the integrity of a power distribution line.

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