JP6974111B2 - Power cable insulation deterioration detection device and insulation deterioration detection method - Google Patents

Description

The present invention relates to an insulation deterioration detection device for a power cable and an insulation deterioration detection method.

Conventionally, devices and methods for detecting insulation deterioration of power cables have been proposed. For example, in Patent Document 1, an AC voltage having a frequency of ± aHz, which is an integral multiple of the commercial frequency, is applied to the shielding layer of the power cable to be measured under a live line by an AC power supply, and the power cable is grounded via the AC power supply. A technique for diagnosing insulation deterioration of a live power cable by measuring the current flowing through the current with a current measuring means and diagnosing the degree of insulation deterioration of the power cable in a live state by a diagnostic means based on the current measured by the current measuring means. Is disclosed.

According to the technique of Patent Document 1, the superimposed voltage is an AC voltage, and unlike the DC voltage, the stray current generated through the sheath insulating resistor does not increase, and only the deterioration signal is amplified. ..

Japanese Patent No. 3317391

Here, depending on the current measurement line, noise other than the DC component current may be scattered. The presence of such noise can make it difficult to detect degraded signals due to the effects of the noise. It is desired that the influence of noise can be reduced and the detection accuracy of insulation deterioration can be improved.

An object of the present invention is to provide an insulation deterioration detecting device for a power cable and an insulation deterioration detecting method capable of detecting the insulation deterioration of the power cable with high accuracy.

The power cable insulation deterioration detection device of the present invention is electrically connected to and grounded to the shielding layer of the power cable, and is connected to an AC power source that applies an AC voltage to the shielding layer under a live line. A control unit that changes the output frequency applied by the AC power supply in a frequency region deviated from an integral multiple of the commercial frequency supplied to the power cable, and a current flowing from the power cable to the ground via the AC power supply. It is characterized by including a current measuring unit for measuring and a signal analysis unit for frequency analysis of the current measured by the current measuring unit.

In the method for detecting insulation deterioration of a power cable of the present invention, an AC voltage is applied from an AC power supply to the shielding layer of the power cable under a live line, and the output frequency of the AC power supply deviates from an integral multiple of a commercial frequency. The current flowing from the power cable to the ground via the AC power supply is measured by the current measuring unit while changing in the region, and the insulation of the power cable is based on the frequency analysis result of the current value measured by the current measuring unit. It is characterized by detecting deterioration.

The power cable insulation deterioration detection device according to the present invention is an AC power supply that is electrically connected to and grounded to the shielding layer of the power cable and applies an AC voltage to the shielding layer under a live line. , A control unit that changes the output frequency applied by the AC power supply in a frequency range deviating from an integral multiple of the commercial frequency supplied to the power cable, and a current measurement unit that measures the current flowing from the power cable to the ground via the AC power supply. And a signal analysis unit that analyzes the frequency of the current measured by the current measurement unit. According to the power cable insulation deterioration detecting device according to the present invention, there is an effect that the detection accuracy of the insulation deterioration can be improved by changing the frequency at which the signal indicating the insulation deterioration appears.

FIG. 1 is a schematic configuration diagram of an insulation deterioration detection device for a power cable according to the first embodiment. FIG. 2 is a diagram showing a display example of the frequency analysis result of the first embodiment. FIG. 3 is another diagram showing a display example of the frequency analysis result of the first embodiment. FIG. 4 is still another diagram showing a display example of the frequency analysis result of the first embodiment. FIG. 5 is a diagram showing a list display of frequency analysis results of the first embodiment. FIG. 6 is a schematic configuration diagram of the insulation deterioration detection device for the power cable according to the second embodiment. FIG. 7 is a flowchart relating to the insulation deterioration detection method of the power cable of the second embodiment. FIG. 8 is another flowchart relating to the method for detecting insulation deterioration of the power cable according to the second embodiment. FIG. 9 is a diagram illustrating an example of a band shift. FIG. 10 is a diagram illustrating another example of band shift.

Hereinafter, the insulation deterioration detection device and the insulation deterioration detection method for the power cable according to the embodiment of the present invention will be described in detail with reference to the drawings. The present invention is not limited to this embodiment. In addition, the components in the following embodiments include those easily conceivable by those skilled in the art or substantially the same.

[First Embodiment]
The first embodiment will be described with reference to FIGS. 1 to 5. The present embodiment relates to an insulation deterioration detection device for a power cable and an insulation deterioration detection method. FIG. 1 is a schematic configuration diagram of an insulation deterioration detection device for a power cable according to the first embodiment.

As shown in FIG. 1, the power cable insulation deterioration detecting device 1 (hereinafter, simply referred to as “cable deterioration detecting device 1”) according to the present embodiment includes an AC power supply 2, a diagnostic device 3, and a current measuring unit 4. And has a security circuit 5. The power cable 10 to be measured for deterioration detection is connected to the high voltage bus 12 via the cable terminal 11. The power cable 10 is, for example, a cross-linked polyethylene insulated vinyl sheath cable (CV cable). The power cable 10 has a core wire 10a and a shielding layer 10b. An insulating layer (not shown) is provided between the core wire 10a and the shielding layer 10b. The shielding layer 10b is a layer that covers the insulating layer from the outside, and is made of a conductive metal such as copper.

The AC power supply 2 applies an AC voltage to the shielding layer 10b under the live line. The AC power supply 2 includes an AC voltage generation circuit 21, a transformer 22, and a control unit 25. The AC voltage generation circuit 21 is a circuit that generates an AC voltage. The AC voltage generation circuit 21 outputs the AC voltage having the commanded output frequency f0. The transformer 22 boosts the AC voltage generated by the AC voltage generation circuit 21. The transformer 22 has a primary winding 23 and a secondary winding 24. The primary winding 23 is connected to the output side of the AC voltage generation circuit 21. One end side of the secondary winding 24 is electrically connected to the shielding layer 10b via the connecting wire 26. The other end side of the secondary winding 24 is grounded via the connecting wire 27. That is, the secondary winding 24 is interposed between the shielding layer 10b and the grounding portion 28. The connecting lines 26, 27, and the secondary winding 24 function as a grounding wire for grounding the shielding layer 10b. The connection line 27 may be grounded to a capacitor.

The control unit 25 controls the AC voltage generation circuit 21 based on an operation input to the operation unit 34, which will be described later. More specifically, the control unit 25 commands the AC voltage generation circuit 21 to output the output frequency f0 of the AC voltage to be generated, based on the command signal sent from the operation unit 34.

The current measuring unit 4 is provided on the connecting line 27. The current measuring unit 4 measures the current flowing through the connecting line 27, in other words, the current flowing between the secondary winding 24 and the grounding unit 28. That is, the current measuring unit 4 measures the current flowing from the power cable 10 to the ground via the AC power supply 2. The safety circuit 5 is connected in parallel to the secondary winding 24 and the current measuring unit 4, respectively. The safety circuit 5 protects the secondary winding 24 and the current measuring unit 4 from overcurrent and overvoltage.

The diagnostic device 3 includes a signal analysis unit 31, a synchronization circuit 32, a display 33, an operation unit 34, a data recording medium 35, and a determination unit 36. The signal analysis unit 31 performs frequency analysis of the current measured by the current measurement unit 4. The signal analysis unit 31 is communicably connected to the current measurement unit 4 and acquires the measurement result by the current measurement unit 4. The signal analysis unit 31 performs signal analysis on the acquired measurement result signal. The signal analysis unit 31 of the present embodiment executes signal analysis by fast Fourier transform (hereinafter, also referred to as “FFT”) on the acquired signal. The FFT calculates the current component for each frequency. The synchronization circuit 32 is a circuit that synchronizes the output frequency f0 of the AC voltage generation circuit 21 with the detection signal acquired by the signal analysis unit 31.

The display 33 is a display device that displays an image of the measurement result by the current measuring unit 4. The display 33 displays an image related to the measurement result by the current measuring unit 4 on the screen based on the information acquired from the signal analysis unit 31. The operation unit 34 is an operation input unit operated by the user, and is, for example, a switch, a dial, a button, a touch panel, or the like. The operation unit 34 is communicably connected to the control unit 25. A signal indicating an operation input to the operation unit 34 is transmitted to the control unit 25.

The data recording medium 35 is a recording medium that can be read and written by a computer. The data recording medium 35 records data related to the measurement result by the current measuring unit 4, for example, recording the data of the analysis result by the signal analysis unit 31 and the like. The data recording medium 35 may record a program executed by the signal analysis unit 31. The data recording medium 35 may be detachable from the diagnostic device 3.

The determination unit 36 determines the insulation deterioration of the power cable 10 based on the result of the signal analysis by the signal analysis unit 31. The determination method by the determination unit 36 will be described later.

The operation of the cable deterioration detection device 1 of the present embodiment and the cable deterioration detection method will be described in detail. The deterioration detection operation by the cable deterioration detection device 1 is started, for example, by a user command. The user inputs an operation instructing the operation unit 34 to start the deterioration detection operation. Further, the user inputs to the operation unit 34 an operation input for designating a width, a resolution, a speed, and the like as sweep conditions for changing the output frequency f0 of the AC power supply 2. The width of the sweep condition is the width of the frequency domain in which the output frequency f0 is changed. The resolution is the change width when the output frequency f0 is changed. The speed is the time from when the output frequency f0 is set to one value to when it changes to the next value.

When the user is instructed to start the deterioration detection operation, the control unit 25 generates an AC voltage by the AC voltage generation circuit 21. The output frequency f0, which is the frequency of the AC voltage applied to the shielding layer 10b by the AC voltage generation circuit 21, is instructed by the control unit 25. The control unit 25 sets the output frequency f0 to a frequency deviating from an integral multiple of the commercial frequency f1 supplied to the power cable 10, in other words, a frequency in the vicinity of an integral multiple of the commercial frequency f1. In the present specification, a frequency that is an integral multiple of the commercial frequency f1 is referred to as "N-fold frequency fn" (N = 0, ± 1, ± 2, ...).

When an AC voltage having a frequency deviating from the N-fold frequency fn is applied, the voltage V applied to the insulating layer of the power cable 10 is approximated by the following equation (1). However, ω1 = 2πf1, ω2 = 2πΔa, f1 is a commercial frequency, Δa is the frequency of the difference between the output frequency f0 and the N times frequency fn (hereinafter, simply referred to as “difference frequency”), and V1 is the voltage of the commercial power supply. V2 is the output voltage of the AC voltage generation circuit 21. That is, in addition to the voltage V1 of the commercial power supply, the AC voltage V2 having a frequency of the difference frequency Δa is applied to the power cable 10. In other words, the same state as when the voltage V2 having the difference frequency Δa is superimposed on the power cable 10 is realized. Therefore, deterioration diagnosis of the power cable 10 is possible based on the current component of the difference frequency Δa.
V = V1sinω1t-V2sinω2t ... (1)

The signal analysis unit 31 starts analysis of the signal acquired from the current measurement unit 4 in synchronization with the start of generation of the AC voltage by the AC voltage generation circuit 21. This synchronization is performed by the synchronization circuit 32. The synchronization circuit 32 acquires, for example, information regarding the operating state of the AC voltage generation circuit 21 from the control unit 25. When the operating state of the AC voltage generation circuit 21 is the state in which the AC voltage is generated, the synchronization circuit 32 issues a command to the signal analysis unit 31 to execute analysis of the signal acquired from the current measurement unit 4. conduct. The signal analysis unit 31 that has received the command to execute the analysis performs signal analysis on the signal acquired from the current measurement unit 4 while a predetermined predetermined period has elapsed. In the present embodiment, the predetermined period is, for example, 20 [seconds]. Therefore, the signal analysis unit 31 executes the FFT analysis on the signal acquired from the current measurement unit 4 within, for example, 20 seconds after receiving the command to execute the analysis.

Further, the signal analysis unit 31 frequency-analyzes the AC voltage applied to the power cable 10 by the AC power supply 2. The AC power supply 2 has a voltage measuring unit (not shown) that measures the AC voltage generated by the AC voltage generation circuit 21. The signal analysis unit 31 calculates the frequency characteristic of the voltage from the measured voltage acquired from the voltage measurement unit by FFT analysis. The current frequency characteristic data and the voltage frequency characteristic data calculated by the signal analysis unit 31 are recorded on the data recording medium 35 together with the AC voltage frequency data.

The display 33 displays a graph of the result of signal analysis by the signal analysis unit 31 on the screen. FIG. 2 is a diagram showing an example of a graph displayed on the display 33. In the upper and lower stages of FIG. 2, the horizontal axis indicates the frequency [Hz]. The upper vertical axis shows the voltage [V], and the lower vertical axis shows the current [A]. The upper part of FIG. 2 shows the frequency characteristics of the voltage applied (superimposed) to the power cable 10 by the AC voltage generation circuit 21. The lower part of FIG. 2 shows the frequency characteristics (FFT graph) of the current measured by the current measuring unit 4. FIG. 2 shows the frequency characteristics of the current measured when the value of the difference frequency Δa is Δ1.

The user can determine the deterioration of the power cable 10 based on the frequency characteristic in the lower part of FIG. This frequency characteristic indicates the current component of each frequency when the AC voltage is superimposed on the power cable 10 by the AC voltage generation circuit 21. It is considered that the magnitude of the current component at the difference frequency Δa (= Δ1) reflects the presence or absence of insulation deterioration of the water tree or the like in the power cable 10 and the degree of insulation deterioration. That is, when the value of the current component at the difference frequency Δa is large, there is a high possibility that the power cable 10 has deteriorated. Further, it is considered that the larger the value of the current component at the difference frequency Δa, the greater the degree of insulation deterioration of the power cable 10. The user can determine, for example, the presence or absence of insulation deterioration of the power cable 10 based on the comparison between the value of the current component at the difference frequency Δa and the determination value.

The difference between the value of the current component at the peripheral frequency and the value of the current component at the difference frequency Δa is likely to indicate the presence or absence of deterioration and the degree of deterioration of the power cable 10. Therefore, the user may determine the deterioration of the power cable 10 by comparing the value of the current component at the peripheral frequency with the value of the current component at the difference frequency Δa.

In the cable deterioration detection device 1 of the present embodiment, the control unit 25 switches the output frequency f0 of the AC voltage generation circuit 21 to a plurality of values. More specifically, the control unit 25 changes the output frequency f0 in the frequency domain deviated from the N times frequency fn. This frequency domain is a region near the N-fold frequency fn and does not include the N-fold frequency fn, that is, a frequency region adjacent to the N-fold frequency fn. Here, the neighborhood is, for example, a region defined within a predetermined frequency b [Hz] from the N times frequency fn. The predetermined frequency b may be, for example, 10 [Hz], 5 [Hz], 2 [Hz], or the like. Further, the size of the predetermined width c [Hz], which is the width of the frequency region in the vicinity, is appropriately determined within 1 [Hz] or 2 [Hz], for example. The frequency domain for changing the output frequency f0 may be a region including a frequency deviated by 1 [Hz] from the N times frequency fn. Further, this frequency domain may be a region centered on a frequency deviated by 1 [Hz] from the N times frequency fn.

The cable deterioration detection device 1 of the present embodiment sequentially changes the output frequency f0 to a plurality of values, and measures the current under the AC voltage of each output frequency f0. The cable deterioration detection device 1 measures the current flowing to the ground via the AC power supply 2 by the current measuring unit 4 at each output frequency f0. The cable deterioration detection device 1 provides the user with frequency characteristics obtained from the measurement results of the current measuring unit 4 for each value of the output frequency f0. The user determines the deterioration of the power cable 10 based on the frequency characteristic of the current value for each value of the output frequency f0. FIG. 3 shows the frequency characteristics of the measured current when the value of the difference frequency Δa is Δ2. The frequency Δ2 is higher than the frequency Δ1 in FIG. FIG. 4 shows the frequency characteristics of the measured current when the value of the difference frequency Δa is Δ3. The frequency Δ3 is a higher frequency than the frequency Δ2 in FIG. That is, each frequency Δ1, Δ2, Δ3 has the relationship of the following equation (2).
Δ1 <Δ2 <Δ3 ... (2)

As can be seen from FIGS. 2 to 4, the peak in the frequency characteristic of the current changes according to the change in the output frequency f0 of the AC voltage generation circuit 21. More specifically, as shown in FIGS. 2 to 4, the values Δ1, Δ2, and Δ3 of the difference frequency Δa have peaks PK1, PK2, and PK3 having maximum frequency characteristics, respectively. When the positions of the peaks PK1, PK2, and PK3 of the frequency characteristics change in accordance with the change in the value of the difference frequency Δa in this way, it can be determined with high reliability that the insulation of the power cable 10 has deteriorated. Further, the mountain PK1 existing when the difference frequency Δa is set to Δ1 (FIG. 2) does not appear when the difference frequencies Δa are set to Δ2 (FIG. 3) and Δ3 (FIG. 4). In this case, the degree of correlation between the difference frequency Δa of the applied AC voltage being the frequency Δ1 and the appearance of the mountain PK1 is high, and it is highly possible that the mountain PK1 indicates deterioration of the power cable 10. Therefore, the cable deterioration detection device 1 of the present embodiment can provide a determination material that enables the insulation deterioration determination of the power cable 10 to be performed with high accuracy.

An example of detecting cable deterioration by the cable deterioration detection device 1 of the present embodiment will be described in more detail. The control unit 25 of the present embodiment sets the difference frequency Δa to, for example, ± 1.2 [Hz], ± 1.1 [Hz], ± 1.0 [Hz], ± 0.9 [Hz], ± 0. Change to 8 [Hz]. That is, the control unit 25 changes the output frequency f0 to five different frequencies, for example, in increments of 0.1 [Hz]. FIG. 5 shows a graph of frequency characteristics acquired under the following conditions. The FFT analysis time below is the measurement period of the current to be analyzed by FFT. That is, in the present embodiment, the current is measured for T1 second by the current measuring unit 4 for one value of the difference frequency Δa, and FFT analysis is performed on the measured data for this T1 second. The FFT analysis time T1 is, for example, several tens of seconds.
Commercial frequency f1: 60 [Hz]
Integer N: 2 (N times frequency fn = 120 [Hz])
FFT analysis time: T1 [seconds]

The cable deterioration detection device 1 changes the difference frequency Δa from ± 1.2 [Hz] to ± 0.8 [Hz] in increments of 0.1 [Hz] every T1 second. The cable deterioration detection device 1 measures the current at each difference frequency Δa by the current measuring unit 4, and calculates the frequency characteristics from each measurement result by FFT analysis. The cable deterioration detection device 1 sequentially displays the FFT graph on the display 33 each time the current measurement and the FFT analysis are completed. As a result, the FFT graphs are sequentially and additionally displayed on the display 33 from FIGS. 5A to 5E. In the present embodiment, since the FFT analysis time is T1 [seconds], an FFT graph is added on the display 33 every T1 seconds.

In FIGS. 5A to 5E, the horizontal axis represents the frequency [Hz] and the vertical axis represents the current [A]. A broken line is shown as a mark at the position of the difference frequency Δa on the horizontal axis. As shown in FIG. 5A, in the frequency characteristics when the difference frequency Δa is ± 1.2 [Hz], a peak PKa is recognized in the difference frequency Δa. Based on this frequency characteristic, it is possible to determine that the power cable 10 has insulation deterioration. However, this mountain PKa may be generated by other causes such as noise. As shown in FIG. 5B, when the difference frequency Δa is switched to ± 1.1 [Hz], a mountain PKb is recognized at the position of 1.1 [Hz]. Therefore, it can be said that the frequency characteristic of FIG. 5B also suggests that the power cable 10 has insulation deterioration. As shown in FIG. 5 (c), the frequency characteristic when the difference frequency Δa is ± 1.0 [Hz] has a peak PKc at the position of 1.0 [Hz]. This mountain PKc has a larger degree of protrusion than the mountains PKa and PKb. Therefore, it is considered that the mountain PKc clearly indicates the existence of insulation deterioration in the power cable 10.

Further, as shown in FIGS. 5 (d) and 5 (e), even when the difference frequency Δa is set to ± 0.9 [Hz] and ± 0.8 [Hz], the peak PKd, which has clear frequency characteristics, respectively. PKe exists. Based on these data, the user can determine that the power cable 10 to be detected has insulation deterioration such as a water tree.

The cable deterioration detection device 1 of the present embodiment can determine the insulation deterioration of the power cable 10 by the determination unit 36 in addition to providing the frequency analysis result of the measured current. The determination unit 36 detects the insulation deterioration of the power cable 10 based on the frequency analysis result of the current value measured by the current measurement unit 4. For example, the determination unit 36 reads out the value of the difference frequency Δa and the data of the frequency characteristic corresponding to the difference frequency Δa from the data recording medium 35. The determination unit 36 acquires the magnitude of the current component at the difference frequency Δa from the read frequency characteristic data. The cable deterioration detection device 1 of the present embodiment calculates and records the frequency characteristics of the current at a plurality of difference frequencies Δa. Therefore, for the power cable 10 to be detected, there are a plurality of combinations of the value of the difference frequency Δa and the magnitude of the current component at the difference frequency Δa.

The basic method for determining whether or not the power cable 10 has deteriorated insulation is based on the comparison result between the magnitude of the current component and the determination value. For example, the determination unit 36 may determine that the power cable 10 has deteriorated insulation when the magnitude of the current component is equal to or greater than the determination value for at least one value of the difference frequency Δa. By doing so, it is possible to prevent erroneous determination in which insulation deterioration is overlooked. Further, the determination unit 36 may determine that the power cable 10 has deteriorated insulation when the magnitude of the current component is equal to or greater than the determination value at the value of the difference frequency Δa of a predetermined number or more. This predetermined number may be a number that is a majority of the total number in which the difference frequency Δa is changed. The determination unit 36 may determine that the power cable 10 has deteriorated in insulation when the magnitude of the current component is equal to or greater than the determination value in all the values of the changed difference frequencies Δa.

The determination unit 36 may determine the presence or absence of insulation deterioration based on the amount of protrusion of the peak PKx (x = 1,2,3, a, b, c, d, e) at the difference frequency Δa. The protrusion amount may be the difference between the average value of the magnitudes of the current components at frequencies near the difference frequency Δa and the peak value of the peak PKx. When this protrusion amount is equal to or greater than the determination value regarding the protrusion amount, it is determined that the power cable 10 has deteriorated insulation. Also in this determination, if the protrusion amount is equal to or greater than the determination value at at least one difference frequency Δa, it may be determined that the insulation has deteriorated. Alternatively, it may be determined that the power cable 10 has deteriorated in insulation when the protrusion amount is equal to or greater than the determination value at the value of the difference frequency Δa of a predetermined number or more.

Further, the determination unit 36 may determine the insulation deterioration based on the frequency region where the noise level is low. For example, in the frequency characteristics shown in FIG. 5, in the frequency range of 0.8 [Hz] to 1.2 [Hz] in which the difference frequency Δa is changed, the magnitude of the current component on the low frequency side is the current component on the high frequency side. Is smaller than the size of. That is, in this frequency domain, the low frequency noise level is smaller than the high frequency noise level. In the case of such a frequency characteristic, the determination unit 36 may determine the insulation deterioration based on the frequency characteristic obtained when the difference frequency Δa is a value on the low frequency side. As an example, for the power cable 10 showing the frequency characteristics as shown in FIG. 5, it is based on the frequency characteristics when the difference frequency Δa is set to a value on the lower frequency side than the center frequency of 1.0 [Hz]. The insulation deterioration may be determined.

Further, the determination unit 36 may perform weighting according to the noise level regarding the determination of insulation deterioration. For example, when the magnitude of the current component is equal to or larger than the determination value in a plurality of difference frequencies Δa, the weighting for the difference frequency Δa in the region where the noise level is low is increased, and the weighting for the difference frequency Δa in the region where the noise level is high is decreased. It may be possible to determine the insulation deterioration. As an example, when the current component is equal to or higher than the judgment value in the difference frequency Δa in the region where the noise level is low, 1 point is given to each of the relevant points, and the current component is the judgment value in the difference frequency Δa in the region where the noise level is high. In the above cases, 0.5 points will be added to each of the relevant points. If the current component is less than the determination value, 0 points are given to each of the relevant points. The presence or absence of insulation deterioration of the power cable 10 and the degree of insulation deterioration are determined based on the total points and the average points.

The determination unit 36 determines the insulation deterioration based on the comparison between the frequency characteristics when the AC power supply 2 applies the AC voltage and the frequency characteristics when the AC power supply 2 does not apply the AC voltage. May be good. By doing so, it is possible to reduce the influence of steady noise and improve the determination accuracy of insulation deterioration.

As described above, the cable deterioration detection device 1 of the present embodiment is electrically connected to and grounded to the shielding layer 10b of the power cable 10, and is alternating current to the shielding layer 10b under a live line. The AC power supply 2 to which a voltage is applied, the control unit 25 that changes the output frequency f0 applied by the AC power supply 2 in a frequency region deviated from an integral multiple of the commercial frequency f1 supplied to the power cable 10, and the AC from the power cable 10. It has a current measuring unit 4 that measures the current flowing to the ground via the power supply 2, and a signal analysis unit 31 that performs frequency analysis of the current measured by the current measuring unit 4. The cable deterioration detection device 1 of the present embodiment changes the difference frequency Δa, which is the difference between the N times frequency fn, which is an integral multiple of the commercial frequency f1, and the output frequency f0. In the frequency characteristic of the measured current, the frequency at which the signal indicating the insulation deterioration of the power cable 10 appears also changes according to the change in the difference frequency Δa. Therefore, the cable deterioration detection device 1 can reduce the influence of noise and improve the detection accuracy of the insulation deterioration of the power cable 10.

Further, an integral multiple of the commercial frequency f1 is an even multiple. As a result, the same state as when the voltage V2 having the difference frequency Δa is superimposed is realized. As a result, in the frequency characteristic of the measured current, the signal of insulation deterioration can appear at the difference frequency Δa.

In the cable deterioration detection method of the present embodiment, an AC voltage is applied from the AC power supply 2 to the shielding layer 10b of the power cable 10 under a live line, and the output frequency f0 of the AC power supply 2 is set to an integral multiple of the commercial frequency f1. The current flowing from the power cable 10 to the ground via the AC power supply 2 is measured by the current measuring unit 4 while changing in the shifted frequency region, and the power is based on the frequency analysis result of the current value measured by the current measuring unit 4. Detects insulation deterioration of the cable 10.

In the cable deterioration detection method of the present embodiment, the AC power supply 2 discretely changes the output frequency f0. At each of the discretely changing output frequencies f0, the current value is measured and the frequency analysis is performed. Based on the plurality of frequency analysis results obtained in this way, the insulation deterioration of the power cable 10 is detected. By variously changing the output frequency f0 of the AC power supply 2, the influence of noise included in the frequency analysis result of the measured current can be reduced. Therefore, the cable deterioration detection method of the present embodiment can improve the detection accuracy of the insulation deterioration of the power cable 10.

In the present embodiment, the integer N = 2 of the N times frequency fn is not limited to this, and the integer N may be another even number.

[Modified example of the first embodiment]
A modified example of the first embodiment will be described. The integer N may be an odd number. When the integer N is an odd number, the voltage V applied to the insulating layer of the power cable 10 is approximated by the following equation (3). In addition, α is a coefficient, ω1 = 2πf1, ω2 = 2πΔa.
V = (V1 + α ・ ω2) sinω1t ... (3)

That is, when the integer N is an odd number, the amplitude of the voltage applied to the power cable 10 changes according to the difference frequency Δa. Therefore, it is possible to detect the insulation deterioration of the power cable 10 based on the measurement result of the current before and after applying the AC voltage by the AC power supply 2. For example, the current is measured by the current measuring unit 4 before and during the application of the AC voltage by the AC power supply 2. The measurement results before and after the application are signal-analyzed by the signal analysis unit 31, respectively, and the frequency characteristics are calculated. Insulation deterioration of the power cable 10 is detected based on the comparison result between the frequency characteristics before application and the frequency characteristics at the time of application. In the comparison of the two frequency characteristics, for example, the magnitudes of the current components at the commercial frequency f1 and the N times frequency fn are compared.

The output frequency f0 of the AC power supply 2 may change in a frequency region deviated from one integral fraction of the commercial frequency f1. The output frequency f0 is represented by, for example, the following equation (4). In equation (4), M is an integer of 2 or more.
f0 = (f1 / M) ± Δa ... (4)

The frequency f2 of the deterioration signal obtained when such an AC voltage having an output frequency f0 is applied to the power cable 10 is as shown in the following equation (5). That is, it is possible to detect the insulation deterioration of the power cable 10 based on the current component of the frequency f2 from the frequency characteristics obtained by frequency analysis of the measured current.
f2 = | M · f0-f1 | ... (5)

In the AC power supply 2, the configuration for boosting the AC voltage generated by the AC voltage generation circuit 21 is not limited to the transformer 22. The AC power supply 2 may boost the AC voltage by, for example, a differential amplifier instead of the transformer 22. The sweep conditions (width, resolution, speed) for changing the output frequency f0 of the AC power supply 2 may be specified by the cable deterioration detection device 1 instead of being input by the user.

[Second Embodiment]
A second embodiment will be described with reference to FIGS. 6 to 10. Regarding the second embodiment, the same reference numerals are given to the components having the same functions as those described in the first embodiment, and duplicate description will be omitted. FIG. 6 is a schematic configuration diagram of the power cable insulation deterioration detection device according to the second embodiment, FIG. 7 is a flowchart relating to the power cable insulation deterioration detection method according to the second embodiment, and FIG. 8 is a second embodiment. Another flowchart relating to the insulation deterioration detection method of the power cable, FIG. 9 is a diagram illustrating an example of band shift, and FIG. 10 is a diagram illustrating another example of band shift.

The second embodiment differs from the first embodiment in that, for example, the cable deterioration detection device 1 has a function of estimating the cause of the inability to determine and a function of giving advice on how to deal with the problem. Further, the cable deterioration detection device 1 of the second embodiment has a function of improving the determination accuracy by shifting the frequency band of the AC voltage applied to the shielding layer 10b.

As shown in FIG. 6, the cable deterioration detection device 1 according to the second embodiment includes an AC power supply 2, a diagnostic device 3, a current measuring unit 4, a safety circuit 5, a switching circuit 6, and a DC power supply 7. The AC power supply 2, the current measuring unit 4, and the security circuit 5 are the same as the AC power supply 2, the current measuring unit 4, and the security circuit 5 of the first embodiment.

The switching circuit 6 is a circuit that switches the voltage applied to the shielding layer 10b to an AC voltage or a DC voltage. More specifically, the switching circuit 6 can electrically connect the shielding layer 10b to either the AC power supply 2 or the DC power supply 7. Further, the switching circuit 6 can cut off the shielding layer 10b from either the AC power supply 2 or the DC power supply 7. The switching circuit 6 has a first relay 61 and a second relay 62. The first relay 61 is interposed between one end side of the secondary winding 24 of the AC power supply 2 and the connecting wire 26. The first relay 61 connects or disconnects the secondary winding 24 and the connecting wire 26.

The DC power source 7 is a power source that outputs a DC voltage, and is, for example, a battery. The negative electrode of the DC power supply 7 is grounded via the connection line 27. The second relay 62 is interposed between the positive electrode of the DC power supply 7 and the connecting line 26. The second relay 62 connects or disconnects the DC power supply 7 and the connection line 26. The first relay 61 and the second relay 62 are opened and closed by, for example, the control unit 25.

The diagnostic device 3 of the second embodiment includes a signal analysis unit 31, a display 33, an operation unit 34, a determination unit 36, and a digital filter 37. The signal analysis unit 31, the display 33, and the operation unit 34 according to the second embodiment are the same as the signal analysis unit 31, the display 33, and the operation unit 34 of the first embodiment. The diagnostic device 3 may include a synchronization circuit 32 and a data recording medium 35, as in the diagnostic device 3 of the first embodiment.

As described below, the determination unit 36 of the present embodiment executes each step of estimating the cause of the inability to determine, giving advice on how to deal with the user, and improving the determination accuracy by band shifting. The determination unit 36 executes the above steps based on the program stored in advance. The determination unit 36 is connected to the control unit 25 of the AC power supply 2, and can control the operation of the control unit 25.

Further, the determination unit 36 is connected to the display 33 and causes the display 33 to display various information. For example, the display 33 displays a question to the user and advice to the user. The display 33 of the second embodiment has a touch panel. The user inputs an answer to the question displayed on the display 33 to the touch panel. The determination unit 36 makes various determinations and advices based on the answers input to the touch panel.

The digital filter 37 performs a filter process on the signal measured by the current measuring unit 4. The digital filter 37 detects a deterioration signal buried in noise by, for example, digital filter processing such as phase detection and a lock-in amplifier. The information after being processed by the digital filter 37 is displayed on the display 33, for example. The information after being processed by the digital filter 37 may be further analyzed by the signal analysis unit 31, and the analysis result may be displayed on the display 33. The determination unit 36 is connected to the digital filter 37. The determination unit 36 switches whether or not the digital filter 37 processes the signal detected by the current measurement unit 4.

The insulation deterioration detection method according to the second embodiment will be described with reference to FIGS. 7 to 10. The flowchart shown in FIG. 7 is executed in a state where the cable deterioration detection device 1 has been attached to the power cable 10 to be determined. The flowchart of FIG. 7 is started, for example, in response to a user's command to start measurement.

In step S1, the determination unit 36 measures the sheath insulation resistance Rs of the shielding layer 10b. The sheath insulation resistance Rs is measured in a state where the first relay 61 is open and the second relay 62 is closed. In the following description, a state in which the first relay 61 is open and the second relay 62 is closed, that is, a state in which the DC power supply 7 applies a DC voltage to the shielding layer 10b is referred to as a “first state”. .. Further, a state in which the first relay 61 is closed and the second relay 62 is open, that is, a state in which the AC power supply 2 applies an AC voltage to the shielding layer 10b is referred to as a "second state".

The determination unit 36 puts the first relay 61 and the second relay 62 in the first state by the control unit 25. The determination unit 36 calculates the sheath insulation resistance Rs based on the current value detected by the current measurement unit 4 in the first state. When the measurement of the sheath insulation resistance Rs is completed, the process proceeds to step S2.

In step S2, the determination unit 36 determines whether or not the sheath insulation resistance Rs is less than 250 [kΩ]. In step S2, the value of the sheath insulation resistance Rs measured in step S1 is compared with the determination value of 250 [kΩ]. As a result of the determination in step S2, if the sheath insulation resistance Rs is affirmatively determined to be less than 250 [kΩ] (step S2-Y), the process proceeds to step S3, and if a negative determination is made, the process proceeds to step S11.

In step S3, the determination unit 36 determines that the deterioration determination is impossible, and proceeds to step S4.

In step S4, the determination unit 36 asks the user whether the terminal has been cleaned. When the sheath insulation resistance Rs is lowered, one of the causes is considered to be contamination of the terminal of the shielding layer 10b. The determination unit 36 displays a question "Is the terminal cleaned?" On the display 33. When the user inputs the answer that "the terminal has been cleaned", the determination unit 36 proceeds to step S5. On the other hand, when the user inputs the answer that "the terminal has not been cleaned", the determination unit 36 advises that it is better to proceed to step S6, clean the terminal, and then start the remeasurement. Is displayed on the display 33. When step S6 is executed, this flow ends.

In step S5, the determination unit 36 asks the user whether the metal contact of the ground wire has been released. When the sheath insulation resistance Rs is lowered, one of the causes is considered to be metal contact of the connecting wire 26. The determination unit 36 displays a question on the display 33, "Have you taken measures to separate the connection line 26 from the metal?" When the user inputs the answer that "the connection line 26 is separated from the metal", the determination unit 36 proceeds to step S7. On the other hand, when the user inputs the answer that "the connection line 26 has not been separated from the metal", the determination unit 36 proceeds to step S8 and separates the connection line 26 from the metal before the start of remeasurement. The advice is displayed on the display 33. When step S8 is executed, this flow ends.

In step S7, the determination unit 36 asks the user whether the weather is rainy. If the sheath insulation resistance Rs is low, rainfall is considered to be one of the causes. The determination unit 36 displays a question "Is the weather rainy?" On the display 33. When the user inputs the answer "it is raining", the determination unit 36 proceeds to step S10 and displays an advice on the display 33 to measure by changing the day. When the terminal is cleaned (step S4-Y) and the ground wire is separated from the metal (step S5-Y), it is highly possible that the cause of the decrease in the sheath insulation resistance Rs is rainfall. The determination unit 36 displays on the display 33 the advice to perform the remeasurement when the weather is other than rainfall. When step S10 is executed, this flow ends.

When the user inputs the answer "it is not rain", the determination unit 36 proceeds to step S9. In step S9, the determination unit 36 determines that the determination is impossible. The determination unit 36 displays on the display 33 that it is difficult to determine the insulation deterioration of the power cable 10 in the current state. When step S9 is executed, this flow ends.

In step S11, the determination unit 36 determines whether or not the AC superimposed current Isa is less than 10 [nA]. The determination unit 36 measures the AC superimposed current Isa [A] with the first relay 61 and the second relay 62 as the second state. The determination unit 36 applies the AC voltage of the AC power supply 2 to the shielding layer 10b in the second state. The AC superimposed current Isa is a frequency analysis result of the current value measured by the current measuring unit 4, and is a value of the current component corresponding to the difference frequency Δa. The determination unit 36 determines in step S11 based on the value of the AC superimposed current Isa when the difference frequency Δa is set to 1.0 [Hz], for example.

As shown in FIG. 5, the determination unit 36 changes the value of the difference frequency Δa in a predetermined frequency region (for example, 0.8 [Hz] −1.2 [Hz]), and the difference frequency Δa. The AC superimposed current Isa may be calculated from the values PKa, PKb, PKc, PKd, and Pke of the current component at each value of. In this case, the AC superimposed current Isa may be, for example, the average value or the maximum value of each value PKa, PKb, PKc, PKd, Pke of the current component.

The determination unit 36 compares the value of the AC superimposed current Isa with the determination value of 10 [nA]. As a result of the determination in step S11, if it is affirmed that the AC superimposed current Isa is less than 10 [nA] (step S11-Y), the process proceeds to step S12, and if it is negative, the process proceeds to step S13.

In step S12, the determination unit 36 makes a good determination. The determination unit 36 displays the determination result that the insulation state of the power cable 10 is good on the display 33. When step S12 is executed, this flow ends.

In step S13, the determination unit 36 makes a temporary deterioration determination and proceeds to step S14.

In step S14, the determination unit 36 determines whether or not the sheath insulation resistance Rs is less than 1 [MΩ]. The determination value of the sheath insulation resistance Rs in step S14 is a value larger than the determination value of the sheath insulation resistance Rs in step S2. As a result of the determination in step S14, if the sheath insulation resistance Rs is affirmatively determined to be less than 1 [MΩ] (step S14-Y), the process proceeds to step S4, and if a negative determination is made, the process proceeds to step S15.

In step S15, the determination unit 36 determines whether or not the unbalanced charging current Iac is, for example, 100 [mA] or more. The unbalanced charging current Iac is a current value due to the three-phase unbalanced in the power cable 10. The determination unit 36 acquires the unbalanced charging current Iac. If the value of the unbalanced charging current Iac is large, the AC superimposed current Isa will be affected, making it difficult to determine deterioration. If it is determined affirmatively that the unbalanced charging current Iac is 100 [mA] or more in step S15 (step S15-Y), the process proceeds to step S16, and if a negative determination is made, the process proceeds to step S19.

In step S16, the determination unit 36 asks the user whether or not the cable length is, for example, 1 [km] or more. The determination unit 36 displays a question on the display 33, "Is the length of the power cable 10 1 [km] or more?". When the user inputs the answer that "the length is 1 [km] or more", the determination unit 36 proceeds to step S17 and inputs the answer that "the length is not 1 [km] or more". If so, the process proceeds to step S18.

In step S17, the determination unit 36 displays on the display 33 that the cause of the unbalanced charging current Iac may be an imbalance in capacitance due to a difference in the length of each phase. The determination unit 36 advises the user to investigate the imbalance of the capacitance in the power cable 10 by the display of the display 33 or the like in the power failure diagnosis or the like. When step S17 is executed, this flow ends.

In step S18, the determination unit 36 displays on the display 33 that the cause of the unbalanced charging current Iac may be an imbalance in capacitance due to a factor such as breakage of the shielding copper tape. The determination unit 36 advises the user to investigate the cause of the capacitance imbalance in the power cable 10 by displaying the display 33, such as by diagnosing a power failure. When step S18 is executed, this flow ends.

In step S19, the determination unit 36 shifts the band. The cable deterioration detection device 1 of the present embodiment executes a band shift when the unbalanced charging current Iac is less than the determination value (step S15-N). The determination unit 36 shifts the frequency band of the AC voltage applied to the shielding layer 10b by band shifting. By band shifting, the influence of noise can be reduced and the accuracy of determining insulation deterioration can be improved. The band shift will be described with reference to FIG.

In step S21, the determination unit 36 compares the magnitudes of the spectral values for each band. The spectral values compared in step S21 are the intermediate band spectral value TSP1 shown in [Equation 1] and the low frequency band spectral value TSP0 shown in [Equation 2].

FIG. 9 shows an example of the intermediate band B1 and the low frequency band B0. The intermediate band B1 is a band currently set as a frequency domain for changing the difference frequency Δa. The intermediate band B1 is, for example, a band of 0.8 [Hz] −1.2 [Hz]. The low frequency band B0 is a band on the lower frequency side than the intermediate band B1. The low frequency band B0 of the present embodiment is a band continuous with the intermediate band B1. The low frequency band B0 of the present embodiment is, for example, a band of 0.4 [Hz] −0.8 [Hz].

The spectral value TSP1 in the intermediate band is the sum of the spectral values of the intermediate band B1. In other words, the spectral value TSP1 in the intermediate band is the area of the region C1 in FIG. The spectral value TSP0 in the low frequency band is the sum of the spectral values of the low frequency band B0. In other words, the spectral value TSP0 in the low frequency band is the area of the region C0 in FIG.

In step S21, it is determined whether or not the spectral value TSP0 in the low frequency band is less than half the spectral value TSP1 in the intermediate band. As a result of the determination in step S21, if it is affirmed that the spectrum value TSP0 in the low frequency band is less than half of the spectrum value TSP1 in the intermediate band (step S21-Y), the process proceeds to step S22 and a negative determination is made. If so, the process proceeds to step S23.

In step S22, the determination unit 36 executes a band shift to the low frequency band B0. The determination unit 36 changes the difference frequency Δa of the AC voltage applied to the shielding layer 10b to the frequency value of the low frequency band B0. When the band shift is performed, the AC superimposed current Isa at the changed difference frequency Δa is measured. The newly measured AC superimposed current Isa may be, for example, the value of the current component when the center value of the low frequency band B0 is set as the difference frequency Δa. Alternatively, the difference frequency Δa may be changed to a plurality of values in the low frequency band B0, and the AC superimposed current Isa may be calculated from the values of the respective current components.

Since the spectral value TSP0 in the low frequency band is less than half the spectral value TSP1 in the intermediate band, it is considered that the noise level in the low frequency band B0 is lower than the noise level in the intermediate band B1. Therefore, by shifting the band to the low frequency band B0, it is possible to improve the determination accuracy of insulation deterioration. When step S22 is executed, the process proceeds to step S26.

In step S23, the determination unit 36 compares the magnitudes of the spectral values for each band. The spectral values compared in step S23 are the spectral value TSP1 in the intermediate band and the spectral value TSP2 in the high frequency band shown in [Equation 3].

FIG. 10 shows an example of the intermediate band B1 and the high frequency band B2. The high frequency band B2 is a band on the high frequency side of the intermediate band B1. The high frequency band B2 of the present embodiment is a band continuous with the intermediate band B1. The high frequency band B2 of the present embodiment is, for example, a band of 1.2 [Hz] -1.6 [Hz].

The spectral value TSP2 in the high frequency band is the sum of the spectral values of the high frequency band B2. In other words, the spectral value TSP2 in the high frequency band is the area of the region C2 in FIG.

In step S23, it is determined whether or not the spectral value TSP2 in the high frequency band is less than half the spectral value TSP1 in the intermediate band. As a result of the determination in step S23, if it is affirmatively determined that the spectral value TSP2 in the high frequency band is less than half of the spectral value TSP1 in the intermediate band (step S23-Y), the process proceeds to step S24 and a negative determination is made. If so, the process proceeds to step S25.

In step S24, the determination unit 36 executes a band shift to the high frequency band B2. The determination unit 36 changes the difference frequency Δa of the AC voltage applied to the shielding layer 10b to the frequency value of the high frequency band B2. When the band shift is made, the AC superimposed current Isa at the new difference frequency Δa is measured. The newly measured AC superimposed current Isa may be, for example, the value of the current component when the center value of the high frequency band B2 is set as the difference frequency Δa. Alternatively, the difference frequency Δa may be changed to a plurality of values in the high frequency band B2, and the AC superimposed current Isa may be calculated from the values of the respective current components.

Since the spectral value TSP2 in the high frequency band is less than half the spectral value TSP1 in the intermediate band, it is considered that the noise level in the high frequency band B2 is lower than the noise level in the intermediate band B1. Therefore, by shifting the band to the high frequency band B2, it is possible to improve the determination accuracy of insulation deterioration. When step S24 is executed, the process proceeds to step S26.

In step S25, the determination unit 36 executes the digital filter treatment. The determination unit 36 causes the digital filter 37 to process the signal detected by the current measurement unit 4, and causes the signal analysis unit 31 to analyze the processed signal. The determination unit 36 acquires the AC superimposed current Isa from the analysis result of the signal analysis unit 31. When step S25 is executed, the process proceeds to step S26.

In step S26, the determination unit 36 determines whether or not the AC superimposed current Isa is less than 10 [nA]. As a result of the determination in step S26, if it is affirmed that the AC superimposed current Isa is less than 10 [nA] (step S26-Y), the process proceeds to step S27, and if it is negative, the process proceeds to step S28.

In step S27, the determination unit 36 makes a good determination. The determination unit 36 displays the determination result that the insulation state of the power cable 10 is good on the display 33. When step S27 is executed, this flow ends.

In step S28, the determination unit 36 makes a deterioration determination. The determination unit 36 determines that insulation deterioration has occurred in the power cable 10. The determination unit 36 displays on the display 33 the determination result that the insulation deterioration has occurred in the power cable 10. When step S28 is executed, this flow ends.

As described above, the cable deterioration detecting device 1 of the present embodiment has a supporting means for giving advice to the user a means for reducing the noise of the current measured by the current measuring unit 4. In the present embodiment, the determination unit 36 and the display 33 correspond to the support means. When the sheath insulation resistance Rs is smaller than the reference value for determination (step S2-Y, step S14-Y), the determination unit 36 advises the user on noise reduction means. The means for reducing noise include cleaning the terminal (step S6), eliminating metal contact (step S8), changing the measurement date and time (step S10), and the like.

Further, when the unbalanced charging current Iac is equal to or higher than the determination reference value (step S15-Y), the determination unit 36 advises the user of noise reduction means. The means for reducing noise is an investigation of an imbalance in the capacitance of the power cable 10 (steps S17, S18) and the like.

The cable deterioration detection device 1 of the present embodiment can detect the insulation deterioration of the power cable 10 with high accuracy by reducing the noise of the current.

Further, the cable deterioration detection device 1 of the present embodiment has a determination unit 36 that changes the frequency region of the AC voltage applied to the shielding layer 10b by the AC power supply 2 based on the spectral distribution obtained by the frequency analysis. By changing the frequency domain of the AC voltage based on the spectral distribution, it becomes possible to detect the insulation deterioration of the power cable 10 with high accuracy. In the present embodiment, the determination unit 36 includes the sum of the spectra of the frequency domain before the change (for example, the intermediate band B1) and the sum of the spectra of the nearby frequency domain (for example, the low frequency band B0 and the high frequency band B2). To compare. When the determination unit 36 has a frequency region having a small total spectrum, the determination unit 36 shifts the frequency region of the AC voltage to the frequency region having a small total spectrum.

The cable deterioration detection device 1 of the present embodiment can detect the insulation deterioration of the power cable 10 with high accuracy by changing the frequency region of the AC voltage.

The method for detecting insulation deterioration of a power cable according to the present embodiment includes an advice step for advising the user to implement a means for reducing the noise of the current measured by the current measuring unit 4. The advice steps are, for example, steps S6, S8, S10, S17, S18. The power cable insulation deterioration detection method according to the present embodiment can detect the insulation deterioration of the power cable 10 with high accuracy by reducing the noise of the current.

The method for detecting insulation deterioration of the power cable of the present embodiment advises the user in the advice step to eliminate the decrease in the sheath insulation resistance Rs generated in the power cable 10. For example, in the advice step, advice is given such as cleaning the terminal (step S6), eliminating metal contact (step S8), and changing the measurement date and time (step S10). By reducing the noise of the current by such advice, the insulation deterioration of the power cable 10 can be detected with high accuracy.

Further, the method for detecting insulation deterioration of the power cable of the present embodiment includes a band change step. The band change step is a step (steps S22, S24) of changing the frequency region of the AC voltage applied to the shielding layer 10b by the AC power supply 2 based on the spectral distribution of the frequency analysis result. According to the power cable insulation deterioration detection method of the present embodiment, the insulation deterioration of the power cable 10 can be detected with high accuracy by changing the frequency range of the AC voltage.

As described above, the cable deterioration detection device 1 according to the present embodiment provides diagnostic support logic (FIGS. 7 and 8) for determining and selecting means for reducing the influence of noise from measurement conditions, measurement results, and FFT analysis results. Have. The display 33 displays measurement results, advice on eliminating noise factors, FFT analysis results, digital filter processing results, and the like.

Therefore, the cable deterioration detection device 1 of the present embodiment can advise the means for eliminating the noise factor caused by the measurement environment from the measurement conditions and the measurement results. Further, the cable deterioration detection device 1 of the present embodiment shifts the deterioration signal to a frequency band to which the influence of noise is less, based on the FFT analysis result (FIG. 8). Therefore, the cable deterioration detection device 1 of the present embodiment can reduce the influence of the measurement environment and noise regardless of the skill level of the user, and can determine the insulation deterioration of the power cable 10 with high accuracy.

The numerical value of the determination value in the above flowchart is an example, and may be different values. The cable deterioration detection device 1 may determine the presence or absence of insulation deterioration without performing band shift. For example, when the spectral value TSP1 in the intermediate band is smaller than a predetermined value, it is not necessary to compare the spectral value TSP1 in the intermediate band with the other spectral values TSP0 and TSP2. In this case, the presence or absence of insulation deterioration is determined based on the value of the AC superimposed current Isa in the intermediate band B1.

The criteria for determining the band shift are not limited to the illustrated criteria. In the above example, the band shift is performed when the other spectral values TSP0 and TSP2 are less than half of the spectral value TSP1 in the intermediate band. However, the coefficient multiplied by the spectral value TSP1 in the intermediate band is not limited to 1/2.

The contents disclosed in each of the above embodiments and modifications can be combined and executed as appropriate.

1 Cable deterioration detector (power cable insulation deterioration detector)
2 AC power supply 3 Diagnostic device 4 Current measuring unit 5 Safety circuit 6 Switching circuit 7 DC power supply 10 Power cable 10a Core wire 10b Shielding layer 11 Cable terminal 12 High voltage bus 21 AC voltage generation circuit 22 Transformer 23 Primary winding 24 Secondary winding Wire 25 Control unit 26, 27 Connection line 28 Grounding unit 31 Signal analysis unit 32 Synchronous circuit 33 Display (support means)
34 Operation unit 35 Data recording medium 36 Judgment unit (support means)
37 Digital filter 61 1st relay 62 2nd relay Δa Difference frequency B0 Low frequency band B1 Intermediate band B2 High frequency band f0 Output frequency f1 Commercial frequency fn N times frequency Iac Unbalanced charging current Isa AC superimposed current PK1, PK2, PK3 mountain PKa, PKb, PKc, PKd, PKe mountain Rs sheath insulation resistance TSP0 low frequency band spectral value TSP1 intermediate band spectral value TSP2 high frequency band spectral value V1 commercial power supply voltage V2 output voltage

Claims (12)

An AC power supply that is electrically connected to and grounded to the shielding layer of the power cable and applies an AC voltage to the shielding layer under the live wire.
A control unit that changes the output frequency applied by the AC power supply in a frequency range deviated from an integral multiple of the commercial frequency supplied to the power cable.
A current measuring unit that measures the current flowing from the power cable to the ground via the AC power supply, and
A signal analysis unit that analyzes the frequency of the current measured by the current measurement unit, and
Equipped with
An insulation deterioration detecting device for a power cable , wherein the integer multiple is an even multiple. An AC power supply that is electrically connected to and grounded to the shielding layer of the power cable and applies an AC voltage to the shielding layer under the live wire.
A control unit that changes the output frequency applied by the AC power supply in a frequency range deviated from an integral multiple of the commercial frequency supplied to the power cable.
A current measuring unit that measures the current flowing from the power cable to the ground via the AC power supply, and
A signal analysis unit that analyzes the frequency of the current measured by the current measurement unit, and
Supporting means for advising the user on means for reducing noise of the current measured by the current measuring unit, and
A power cable insulation deterioration detector characterized by being equipped with. The power cable insulation deterioration detecting device according to claim 1, further comprising a support means for advising the user on means for reducing noise of the current measured by the current measuring unit. The power cable insulation deterioration detecting device according to claim 2 or 3, wherein the support means advises the user of means for eliminating the decrease in the sheath insulation resistance generated in the power cable. Further, according to any one of claims 1 to 4, the present invention has a determination unit for changing the frequency domain of the AC voltage applied to the shielding layer by the AC power supply based on the spectral distribution obtained by the frequency analysis. Power cable insulation deterioration detector. An AC power supply that is electrically connected to and grounded to the shielding layer of the power cable and applies an AC voltage to the shielding layer under the live wire.
A control unit that changes the output frequency applied by the AC power supply in a frequency range deviated from an integral multiple of the commercial frequency supplied to the power cable.
A current measuring unit that measures the current flowing from the power cable to the ground via the AC power supply, and
A signal analysis unit that analyzes the frequency of the current measured by the current measurement unit, and
Based on the spectral distribution obtained by the frequency analysis, a determination unit that changes the frequency region of the AC voltage applied to the shielding layer by the AC power supply, and a determination unit.
A power cable insulation deterioration detector characterized by being equipped with. Apply AC voltage from the AC power supply under the live line to the shielding layer of the power cable.
While changing the output frequency of the AC power supply in a frequency region deviating from an integral multiple of the commercial frequency, the current flowing from the power cable to the ground via the AC power supply is measured by the current measuring unit.
Based on the frequency analysis result of the current value measured by the current measuring unit, the insulation deterioration of the power cable is detected .
A method for detecting insulation deterioration of a power cable , wherein the integral multiple is an even multiple. Apply AC voltage from the AC power supply under the live line to the shielding layer of the power cable.
While changing the output frequency of the AC power supply in a frequency region deviating from an integral multiple of the commercial frequency, the current flowing from the power cable to the ground via the AC power supply is measured by the current measuring unit.
Based on the frequency analysis result of the current value measured by the current measuring unit, the insulation deterioration of the power cable is detected.
Includes an advice step that advises the user to implement measures to reduce noise in the current measured by the current measuring unit.
A method for detecting insulation deterioration of a power cable. The method for detecting insulation deterioration of a power cable according to claim 7 , further comprising an advice step for advising the user to implement a means for reducing noise of the current measured by the current measuring unit. The method for detecting insulation deterioration of a power cable according to claim 8 or 9 , wherein in the advice step, the user is advised to eliminate the decrease in the sheath insulation resistance generated in the power cable. The power according to any one of claims 7 to 10 , further comprising a band changing step of changing the frequency domain of the AC voltage applied by the AC power supply to the shielding layer based on the spectral distribution of the frequency analysis result. Cable insulation deterioration detection method. Apply AC voltage from the AC power supply under the live line to the shielding layer of the power cable.
While changing the output frequency of the AC power supply in a frequency region deviating from an integral multiple of the commercial frequency, the current flowing from the power cable to the ground via the AC power supply is measured by the current measuring unit.
Based on the frequency analysis result of the current value measured by the current measuring unit, the insulation deterioration of the power cable is detected.
Includes a band change step that changes the frequency domain of the AC voltage applied by the AC power supply to the shielding layer based on the spectral distribution of the frequency analysis result.
A method for detecting insulation deterioration of a power cable.

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