Deterioration determination method for high-voltage cable and guidance device

Abstract

To provide a technique capable of identifying not only the type but also the location of deterioration in a high-voltage cable.SOLUTION: A deterioration determination method for a high-voltage cable disconnects both ends of a conductor of a high-voltage cable from a power system when determining deterioration of the aged high-voltage cable 1 in its installed state, connects and any one of a water tree deterioration diagnosis device 2, a dielectric loss tangent diagnosis device 3, and a partial discharge diagnosis device 4 to the high-voltage cable, performs water tree diagnosis to determine the degree of water tree deterioration on the basis of discharge characteristics after applying a DC voltage to the high-voltage cable, performs partial discharge diagnosis in a case where deterioration of the high-voltage cable is diagnosed in at least one of the water tree diagnosis and the dielectric loss tangent diagnosis when performing the dielectric loss tangent diagnosis to determine the degree of deterioration from a dielectric loss tangent of the high-voltage cable, determines deterioration in the entire cable when no partial discharge is detected in the partial discharge diagnosis, and determines deterioration at a partial discharge portion identified by the partial discharge diagnosis when partial discharge is detected in the partial discharge diagnosis.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a degradation determination method and guidance device for preventing electrical accidents caused by insulation degradation of high-voltage cables. [Background technology]

[0002] Steelworks have many high-voltage cables that were installed 30 to 40 years ago and are still in use. The degree and manner of deterioration of high-voltage cables varies greatly depending on their installation conditions, such as buried, culvert (underground conduit), or overhead. If the insulation of high-voltage cables deteriorates and a ground fault or short circuit occurs, it can not only affect production but also cause a fire, so it is important to understand the degree of deterioration and the location of the deterioration.

[0003] CV cables (cross-linked polyethylene insulated vinyl sheath cables), which are widely used as high-voltage cables, can sometimes suffer from water tree deterioration in the insulation layer, so there is a high need to properly diagnose the deterioration of high-voltage cables.

[0004] Patent Document 1 discloses a method for diagnosing water tree degradation in a power cable. This water tree diagnostic method measures the voltage V applied to the power cable and the ground current i flowing in a shield material provided around the insulation of the power cable. Then, a capacitive current ic and a resistive current ir are calculated from the voltage V applied to the power cable and the capacitance and resistance of the power cable. A current it resulting from water tree degradation is calculated using a predetermined formula from the measured ground current i and the calculated capacitive current ic and resistive current ir. Deterioration of the power cable is diagnosed based on the calculated current it and the voltage V applied to the power cable.

[0005] Patent Document 2 discloses a diagnostic device and method for determining the degree of deterioration of a power cable using the dielectric tangent (tanδ) method. The dielectric tangent (tanδ) is a value defined as tanδ = Ir / Ic = 1 / ωCRp, where Ic is the current flowing through an ideal capacitor C and Ir is the current (energy loss) flowing through a parasitic resistance Rp connected in parallel to the ideal capacitor. This diagnostic device electrically separates both ends of a power cable conductor from the power system using a separator, and measures the dielectric tangent between the separator connected to one end of the conductor and the sheath using a conventional measuring device. The measured value is then corrected to take into account the components of the other cables and the separator to determine the dielectric tangent of the power cable alone, and deterioration diagnosis is performed based on the dielectric tangent.

[0006] Furthermore, Patent Document 3 discloses a location system and method for measuring partial discharges in a power cable using a partial discharge diagnosis method and locating the location of the partial discharge. In this location system, a pair of electrode plates is wrapped around at least two locations spaced apart in the longitudinal direction of a CV cable whose conductor ends are connected to a power grid, and high-frequency partial discharge signals that are generated at specific locations in the CV cable by current flow from the power grid and propagate through the CV cable are detected by each pair of electrode plates. The location of the partial discharge is then located based on the detection time difference between these partial discharge signals and the propagation speed of the partial discharge signal, which has been calculated in advance.

[0007] Meanwhile, Patent Document 4 discloses a method for diagnosing and judging cable degradation by combining the dielectric loss tangent (tanδ) method and the partial discharge diagnostic method. This method measures tanδ from the relationship between the voltage applied to the cable and the current flowing in the cable's grounding wire, while attaching a current transformer to the grounding wire and measuring partial discharges occurring in the cable based on the output of this current transformer. In this case, the dielectric loss tangent (tanδ) method evaluates the overall insulation characteristics of the cable, while the partial discharge diagnostic method evaluates the local insulation characteristics of the cable, which is said to enable more appropriate judgment of cable degradation. Patent Document 4 also describes a degradation judgment method that can perform these diagnostic methods simultaneously without requiring reconnection of equipment.

[0008] Patent Document 5 also discloses a method for determining cable degradation by combining the dielectric loss tangent (tanδ) method and the partial discharge diagnosis method. In this degradation determination method, both ends of a high-voltage cable conductor are disconnected from the power grid, allowing the high-voltage cable to be connected to a dielectric loss tangent diagnostic device or a partial discharge diagnostic device by switching between them. The degree of degradation is determined based on the dielectric loss tangent determined by the dielectric loss tangent diagnostic device connected to the high-voltage cable. If the determined degree of degradation is above a predetermined level, partial discharge diagnosis is performed using the partial discharge diagnostic device connected to the high-voltage cable instead of the dielectric loss tangent diagnostic device. If partial discharge is not detected by the partial discharge diagnosis, the entire cable is determined to be degraded. If partial discharge is detected by the partial discharge diagnosis, the partial discharge location identified by the partial discharge diagnosis is determined to be degraded. This method is said to enable the identification of not only the degree of cable degradation but also the type and location of degradation, thereby enabling more appropriate determination of cable degradation. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-44177 [Patent Document 1] Japanese Patent Application Publication No. 2017-122738 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-035243 [Patent Document 4] Japanese Patent Application Publication No. 9-269352 [Patent Document 5] Japanese Patent Application Publication No. 2023-39678 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the above-mentioned conventional techniques have the following problems. The water tree diagnosis disclosed in Patent Document 1 is a method for diagnosing insulation deterioration in the insulating material provided around the conductive core wire of a high-voltage cable. However, water tree diagnosis alone cannot diagnose insulation deterioration at the joints and terminals where high-voltage cables are connected. Furthermore, water tree diagnosis cannot identify the location where deterioration of the high-voltage cable's insulating material has occurred, which makes it difficult to properly determine the state of deterioration of the high-voltage cable.

[0011] The measurement of dielectric loss tangent (tanδ) disclosed in Patent Document 2 can diagnose insulation deterioration including the joints and terminals where high-voltage cables are connected, and therefore can determine whether or not the high-voltage cable as a whole has deteriorated. However, even if it is possible to determine whether or not the high-voltage cable as a whole has deteriorated, it is not possible to identify the location where deterioration has occurred in the insulation material of the high-voltage cable, which poses a problem that it is difficult to appropriately determine the state of deterioration of the high-voltage cable.

[0012] The partial discharge diagnosis disclosed in Patent Document 3 can identify the location where deterioration of the insulation material of a high-voltage cable has occurred. However, partial discharge diagnosis applies a high voltage to the high-voltage cable, which places a large amount of stress on the high-voltage cable, and partial discharges occurring at locations where the insulation has deteriorated can cause insulation breakdown to progress, which can lead to the risk of the high-voltage cable being diagnosed becoming unusable.

[0013] The method disclosed in Patent Document 4 is a method for determining cable deterioration by combining the dielectric loss tangent method and the partial discharge diagnosis method. In this case, too, the partial discharge diagnosis increases stress on the high-voltage cable, which may lead to the progression of insulation breakdown in the high-voltage cable being diagnosed.

[0014] The assessment method disclosed in Patent Document 5 can reduce stress on high-voltage cables by determining whether partial discharge diagnosis is necessary depending on the degree of deterioration diagnosed by the dielectric loss tangent method. However, while dielectric loss tangent diagnosis can diagnose deterioration in so-called bridging water trees, it has the problem of difficulty in diagnosing deterioration in unbridging water trees. Therefore, there is room for improvement in the risk of overlooking deterioration in high-voltage cables depending on the timing of high-voltage cable diagnosis. Here, a bridging water tree refers to a water tree that has progressed from the conductor of a high-voltage cable to the outer layer of the insulator. An unbridging water tree refers to a water tree that has progressed partway through the insulator but has not yet penetrated the outer layer of the insulator.

[0015] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for determining the deterioration of a high-voltage cable that efficiently realizes the determination of the deterioration of the high-voltage cable and reduces the stress on the high-voltage cable being determined, and also to provide a guidance device that provides guidance for the efficient determination. [Means for solving the problem]

[0016] The present invention, which aims to advantageously solve the above-mentioned problems, provides a method for determining the deterioration of a high-voltage cable that has deteriorated over time while it is still in an installed state, comprising: a connection switching step of disconnecting both ends of the conductor of the high-voltage cable from the power system and connecting one of a water tree deterioration diagnosis device, a dielectric loss tangent diagnosis device, and a partial discharge diagnosis device to the high-voltage cable; a water tree diagnosis step of performing a water tree diagnosis to determine the degree of water tree deterioration from discharge characteristics after applying a DC voltage using the water tree deterioration diagnosis device connected to the high-voltage cable; and a deterioration determination step of determining the degree of water tree deterioration from the dielectric loss tangent determined by the dielectric loss tangent diagnosis device connected to the high-voltage cable. a partial discharge diagnosis step of performing a partial discharge diagnosis using the partial discharge diagnosis device connected to the high-voltage cable; and a determination step of determining a deterioration state of the high-voltage cable, wherein the partial discharge diagnosis step is performed when it is determined that the high-voltage cable has deteriorated by at least one of the water tree diagnosis and the dielectric tangent diagnosis, and in the determination step, if no partial discharge is detected in the partial discharge diagnosis, it is determined that the entire cable has deteriorated, and if a partial discharge is detected in the partial discharge diagnosis, it is determined that the deterioration has occurred at a partial discharge location identified in the partial discharge diagnosis.

[0017] The method for determining the deterioration of a high-voltage cable according to the present invention includes the steps of: a. Selecting at least one of the following: in the water tree diagnosis step, applying a DC voltage lower than the rated voltage of the high-voltage cable; in the dielectric loss tangent diagnosis step, supplying an AC current of a frequency lower than the commercial frequency to measure the dielectric loss tangent; and in the partial discharge diagnosis step, detecting partial discharges that occur by applying a damped oscillating voltage to the high-voltage cable; b. In the determination step, when it is determined that no deterioration of the high-voltage cable has occurred in either the water tree diagnosis or the dielectric loss tangent diagnosis, it is determined to continue using the high-voltage cable; would be the preferred solution.

[0018] The guidance device of the present invention is a guidance device that determines the deterioration of a high-voltage cable that has deteriorated over time and provides guidance while the cable is still in an installed state, and includes a deterioration diagnosis unit having a water tree deterioration diagnosis device that is connected to the high-voltage cable and determines the degree of water tree deterioration from discharge characteristics after applying a DC voltage, a dielectric loss tangent diagnosis device that is connected to the high-voltage cable and performs a dielectric loss tangent diagnosis that determines the degree of deterioration from a measured dielectric loss tangent, and a partial discharge diagnosis device that is connected to the high-voltage cable and performs a partial discharge diagnosis, a first diagnosis result acquisition unit that acquires the results of the water tree diagnosis by the water tree deterioration diagnosis device, or the results of the water tree diagnosis by the water tree deterioration diagnosis device and the results of the dielectric loss tangent diagnosis by the dielectric loss tangent diagnosis device, and a second diagnosis result acquisition unit that acquires at least the results of the water tree diagnosis and the dielectric loss tangent diagnosis. The degradation diagnosis system is characterized by comprising: a degradation diagnosis request unit that requests a partial discharge diagnosis by the partial discharge diagnosis device provided in the degradation diagnosis unit when any of the high-voltage cables indicates that the high-voltage cable is deteriorated; a second diagnosis result acquisition unit that acquires the diagnosis result of the partial discharge diagnosis of the high-voltage cable performed in response to the request from the degradation diagnosis request unit; a degradation status determination unit that determines that the entire cable is deteriorated when the diagnosis result of the partial discharge diagnosis does not detect partial discharge, and determines that the degradation is at a partial discharge location identified in the partial discharge diagnosis when the diagnosis result of the partial discharge diagnosis detects partial discharge; and a presentation unit that displays at least one piece of information selected from the diagnosis result of any of the water tree diagnosis, the dielectric loss tangent diagnosis, and the dielectric loss tangent diagnosis, the degradation status of the high-voltage cable, and instructions for a next process.

[0019] The guidance device according to the present invention is c. the presentation unit presents a determination result that the high-voltage cable is normal when both the diagnosis result of the water tree diagnosis by the water tree deterioration diagnosis device and the diagnosis result of the dielectric loss tangent diagnosis by the dielectric loss tangent diagnosis device indicate that no degradation has occurred in the high-voltage cable; d. Further, a connection switching means is provided for switching the connection between the high-voltage cable and the water tree degradation diagnostic device, the dielectric loss tangent diagnostic device, and the partial discharge diagnostic device, and the connection between the high-voltage cable and each diagnostic device is switched by the connection switching means based on an external input or an instruction from the degradation diagnostic unit, would be the preferred solution. [Effects of the Invention]

[0020] According to the present invention, it is possible to efficiently determine the deterioration of a high-voltage cable while reducing the stress on the high-voltage cable being determined. Furthermore, it is possible to automatically and objectively determine at least one of the degree of deterioration and the type of deterioration, thereby enabling rational maintenance and management of the high-voltage cable.

[0021] Furthermore, the guidance device of the present invention presents the results of the deterioration diagnosis of the high-voltage cable as guidance, so that the maintenance and management of the high-voltage cable can be carried out rationally. [Brief explanation of the drawings]

[0022] [Figure 1] 1(a) is a block diagram showing the configuration of a high-voltage cable deterioration determination device according to one embodiment of the present invention, which is used in a high-voltage cable deterioration determination method according to one embodiment of the present invention, and FIG. 1(b) is an enlarged cross-sectional view of the high-voltage cable taken along the line AA. [Figure 2] FIG. 2 is a block diagram showing an example of the configuration of a water tree diagnosis unit 2 using the reverse absorption current method according to the embodiment. [Figure 3] FIG. 2 is a block diagram showing an example of the configuration of a tan δ diagnosis unit 3 for performing the tan δ diagnosis according to the embodiment. [Figure 4] FIG. 2 is a block diagram showing an example of the configuration of a partial discharge diagnosis unit 4 for performing partial discharge diagnosis according to the embodiment. [Figure 5]FIG. 2 is a block diagram schematically showing an equivalent circuit 50 configured inside an insulator 12 including a deteriorated portion such as a void in partial discharge diagnosis according to the embodiment. [Figure 6] 4 is a graph showing an example of a damped oscillation waveform supplied to an electric circuit in partial discharge diagnosis according to the embodiment. [Figure 7] 4 is an example of a flowchart showing the procedure of a method for determining deterioration of a high-voltage cable performed using the deterioration determination device for a high-voltage cable according to the embodiment. [Figure 8] 10 is a flowchart illustrating another example of the procedure of the method for determining deterioration of a high-voltage cable, which is performed using the device for determining deterioration of a high-voltage cable according to the embodiment. [Figure 9] 10 is a graph showing the accuracy of each deterioration state obtained as a result of a water tree diagnosis using the water tree diagnosis unit 2 according to the embodiment. [Figure 10] 4 is a graph illustrating the results of a dielectric loss tangent (tan δ) diagnosis using the tan δ diagnosis unit 3 according to the embodiment. [Figure 11] 4 is a graph illustrating the time transition of a test voltage T and a partial discharge pulse signal P obtained as a result of partial discharge diagnosis using the partial discharge diagnosis unit 4 according to the embodiment. [Figure 12] 6 is a graph illustrating the results of partial discharge diagnosis using the partial discharge diagnosis unit 4 according to the embodiment. [Figure 13] FIG. 10 is a block diagram showing the configuration of a high-voltage cable deterioration determination device according to another embodiment of the present invention, which is used in a high-voltage cable deterioration determination method according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] <High voltage cable deterioration assessment> Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Here, Fig. 1 is a block diagram showing a schematic configuration of a high-voltage cable deterioration determination device according to an embodiment of the present invention, which can be used to execute a high-voltage cable deterioration determination method according to an embodiment of the present invention.

[0024] As shown in Fig. 1(a), the high-voltage cable deterioration determination device 10 of this embodiment is configured to determine deterioration of the high-voltage cable 1 in an installed state by disconnecting cable heads 1a, 1b provided at both ends of the conductor of the aged deteriorated high-voltage cable 1 to be diagnosed from a high-voltage distribution panel (not shown) of the power system. The installed state refers to the high-voltage cable 1 being buried, in a culvert (underground conduit), or overhead. The deterioration determination device 10 includes a water tree diagnosis unit 2 as a water tree diagnosis device, a tan δ diagnosis unit 3 as a dielectric loss tangent (tan δ) diagnosis device, and a partial discharge diagnosis unit 4 as a partial discharge diagnosis device.

[0025] The high-voltage cable 1 to be subjected to deterioration assessment is a cross-linked polyethylene-insulated vinyl sheath cable (CV cable) that uses cross-linked polyethylene as an insulating material. Figure 1(b) shows an enlarged cross-sectional view of the high-voltage cable 1 indicated by AA in Figure 1(a). A cross-linked polyethylene-insulated vinyl sheath cable is a cable in which a conductive conductor (core wire) 11 is covered with a cross-linked polyethylene insulator 12, and the outer periphery is covered with a shielding layer (copper tape) 13 and a vinyl sheath sheath layer 14. The conductor 11 and shielding layer 13 of the high-voltage cable 1 are made of conductive materials, while the insulator 12 and sheath layer 14 are made of insulating materials. In addition, semiconductive layers are formed between the conductor 11 and the insulator 12 and between the insulator 12 and the shielding layer 13.

[0026] The high-voltage cable 1 includes a cable head 1a at one end of the conductor 11 of the high-voltage cable 1, a cable head 1b at the other end of the conductor 11 of the high-voltage cable 1, and a sheath grounding wire 1c that grounds one end of the shielding layer 13 surrounding the conductor 11 of the high-voltage cable 1. The high-voltage cable 1 may also have a cable joint 1d midway.

[0027] The deterioration determination device 10 may include a probe 9 detachably attached to a cable head 1a at one end of the conductor of the high-voltage cable 1 and a sheath grounding wire 1c that grounds one end of the sheath surrounding the conductor. Alternatively, the deterioration determination device 10 may be configured so that each unit is detachably connectable to the conductor 11 and shielding layer 13 of the high-voltage cable 1 via the probe 9. In this case, as shown in Fig. 13, the deterioration determination device 10 may include a connection switching device 5 that electrically connects the conductor 11 and shielding layer 13 of the high-voltage cable 1 using the probe 9 and switches connections between the water tree diagnosis unit 2, tan δ diagnosis unit 3, and partial discharge diagnosis unit 4 by electrical circuits.

[0028] The high-voltage cable deterioration determination device 10 according to this embodiment includes a determination device 6 configured as a normal computer that operates based on a pre-set program. The high-voltage cable deterioration determination device 10 also has a display device 7 connected to the determination device 6, which is configured to display the determination results made by the determination device 6. The display device 7 is, for example, a CRT, and by displaying the determination results made by the determination device 6 on its screen, it functions as part of a guidance device that prompts the worker in charge of diagnosing the high-voltage cable to perform work in accordance with the determination results.

[0029] <Water tree diagnosis> The water tree diagnosis unit 2 performs water tree diagnosis, diagnosing deterioration of the high-voltage cable 1 based on the discharge characteristics after applying a DC voltage to the high-voltage cable 1. The CV cable's insulator 12 is made of cross-linked polyethylene, which has excellent insulating and heat-resistant properties. Deterioration can occur over time due to moisture and ultraviolet rays. Furthermore, moisture adhesion, combined with the influence of an electric field, makes the insulator 12 more susceptible to cracking. This type of deterioration is called water tree deterioration. Known water tree diagnosis methods include the DC leakage current method, the residual charge method, and the reverse absorption current method, and any of these methods can be used. In this embodiment, the reverse absorption current method (IRC method) is preferably used. The reverse absorption current method, also known as the isothermal relaxation current method, is a diagnostic method for detecting water trees based on the discharge characteristics after applying a DC voltage to the high-voltage cable. The reverse absorption current method does not apply high voltage like the DC leakage current method, so it can reduce stress on the high-voltage cable being diagnosed. Furthermore, unlike the residual charge method, it does not require large diagnostic equipment.

[0030] FIG. 2 shows an example of the configuration of a water tree diagnosis unit 2 using the reverse absorption current method. The water tree diagnosis unit 2 shown in FIG. 2 is connected to the conductor 11 of the high-voltage cable 1 via a probe 28a and to the shielding layer 13 via a probe 28b. The water tree diagnosis unit 2 includes a grounding wire 23, and the shielding layer 13 is grounded via the probe 28b. The water tree diagnosis unit 2 comprises an electric circuit using a DC power supply 21, a resistor 22, an ammeter 24, an amplifier 25, an AD converter 26, and a relay switch 27. The AD converter 26 is also connected to a water tree diagnosis section 20. The water tree diagnosis section 20 is connected to a determination device 6 via a communication cable 8a. In response to a request from the determination device 6, the water tree diagnosis section 20 may perform a water tree diagnosis and communicate the diagnosis results to the determination device 6.

[0031] In the water tree diagnosis, a DC voltage is applied between the conductor 11 and the shielding layer 13 by the DC power supply 21 for a predetermined time (step S21). The DC voltage is preferably 0.5 to 1.5 kV, and the predetermined time is preferably 30 to 50 minutes. For example, a DC voltage of 1.0 kV is applied between the conductor 11 and the shielding layer 13 for 30 minutes. After the application of the DC voltage in step S21 is completed, the relay switch 27 switches the connection of the electrical circuit to discharge the current through the resistor 22 for a predetermined time (step S22). The discharge time in step S22 is preferably 5 to 10 seconds, and is preferably 5 seconds. After the discharge for the predetermined time in step S22 is completed, the relay switch 27 switches the connection of the electrical circuit, and the further discharged current, i.e., the reverse absorption current, is measured by the ammeter 24 for a predetermined time (step S23). The measurement time for the reverse absorption current by the ammeter 24 is preferably 30 to 50 minutes, and is preferably 30 minutes. The current value of the reverse absorption current measured by the ammeter 24 is amplified by an amplifier 25 and sent to the water tree diagnosis unit 20 via an AD converter 26 .

[0032] The water tree diagnosis unit 20 diagnoses water tree degradation in the high-voltage cable 1 based on the change in the reverse absorption current over time. At this time, the reverse absorption current contains combined information on the insulator 12, the boundary between the insulator 12 and the conductor 11, and the relaxation time of the water tree. Since the relaxation time becomes longer when water tree degradation occurs, water tree degradation is determined based on the change in the reverse absorption current over time. Specifically, the water tree diagnosis unit 20 calculates the product of the measured reverse absorption current It and the measurement time t in step S23 to determine the change in the value It × t over time. Then, as the water tree degradation in the high-voltage cable 1 progresses, the peak position of the value It × t shifts toward the longer time side, and therefore the presence or absence of water tree degradation is diagnosed by referring to a database accumulated with previously detected water tree degradation.

[0033] The tanδ diagnostic unit 3 performs tanδ diagnosis, diagnosing the deterioration of the high-voltage cable 1 by applying an AC voltage to the high-voltage cable 1 and measuring its dielectric loss tangent. This tanδ diagnosis is a diagnostic method that evaluates the tanδ of the insulator by applying an AC voltage to the high-voltage cable and a lossless standard capacitor and using the current flowing through them. The tanδ diagnosis is a method for diagnosing the deterioration of the high-voltage cable 1 by regarding the insulator 12 of the high-voltage cable 1 as a capacitor and utilizing the characteristic that the current phase of losses occurring in the insulator 12 lags behind the lossless current flowing through an ideal insulator. In this case, the phase delay angle δ of the current flowing through the insulator 12 with respect to the lossless current flowing through an ideal insulator is called the dielectric loss angle, and its tangent is called the dielectric loss tangent (tanδ). The tanδ diagnostic unit 3 can be realized using a known configuration, such as that shown in Figure 2 of Patent Document 2.

[0034] FIG. 3 shows an example of the configuration of a tan δ diagnosis unit 3 for performing tan δ diagnosis. The tan δ diagnosis unit 3 shown in FIG. 3 includes an AC power supply 31, an RC parallel circuit 34 (capacitor 34a and resistor 34b) as a lossless standard capacitor, and a tan δ diagnosis unit 30. The tan δ diagnosis unit 30 is connected to the determination device 6 via a communication cable 8a. In response to a request from the determination device 6, the tan δ diagnosis unit 30 may perform tan δ diagnosis and communicate the diagnosis results to the determination device 6. The tan δ diagnosis unit 3 is connected to the conductor 11 of the high-voltage cable 1 via a probe 38a and to the shielding layer 13 via a probe 38b. The tan δ diagnosis unit 3 includes a grounding wire 33, and the shielding layer 13 is grounded via the probe 38b. As a result, an RC parallel circuit 35 (capacitor 35a and resistor 35b) is formed in the high-voltage cable 1 as an equivalent circuit, in parallel with the RC parallel circuit 34 of the tan δ diagnosis unit 3. In this case, if the insulator 12 of the high-voltage cable 1 is deteriorated due to voids or the like, the loss in the RC parallel circuit 35, which is the equivalent circuit, increases, causing a delay in the current phase.

[0035] When a preset voltage is applied by the AC power supply 31, the tan δ diagnostic unit 30 detects a phase shift between the current flowing through the RC parallel circuit 34 and the current flowing through the high-voltage cable 1, thereby calculating the dielectric loss tangent (tan δ). The tan δ diagnostic unit 30 may also calculate an increase in tan δ, Δtan δ, when the voltage applied by the AC power supply 31 is increased. The tan δ diagnostic unit 30 uses at least one of the calculated tan δ and Δtan δ to diagnose whether degradation has occurred in the high-voltage cable 1, based on a preset reference value. The diagnostic result of the tan δ diagnostic unit 30 is sent to the determination device 6 via the communication cable 8b.

[0036] The tan δ diagnosis performed by the tan δ diagnosis unit 3 preferably employs the VLF (Very Low Frequency) method, which measures the dielectric tangent by supplying an extremely low frequency current from the AC power supply 31. In this case, the frequency of the current supplied from the AC power supply 31 is, for example, 0.1 Hz. By using the VLF method, the charging current can be reduced compared to methods using commercial frequency (60 Hz), and the tan δ diagnosis unit 3 can be made more compact. Furthermore, the energy loaded on the high-voltage cable 1 is small, and the use of a low-frequency AC power supply reduces stress on the high-voltage cable.

[0037] In tan δ diagnosis using the VLF method (VLF-tan δ diagnosis), for example, the rated voltage of the high-voltage cable 1 is set to U0, and tan δ is measured at each applied voltage, for example, 0.5×U0, 1.0×U0, and 1.5×U0, for a total of 5 to 10 times. The average of these measurements may be calculated and used as the measured value of tan δ. The difference between the measured values ​​of tan δ at applied voltages of 1.5×U0 and 0.5×U0 may be used as the Δtan δ. The standard for diagnosing the degradation of the high-voltage cable 1 is defined in IEEE std 400.2TM-2013 IEEE Guide for Field Testing of Shielded Power Cable Systems Using Very Low Frequency. According to this standard, the tan δ diagnosis unit 30 determines the diagnostic result as "good," "needs attention," or "severe degradation" based on the measured value of tan δ. In this case, if the result is "good," the high-voltage cable 1 is diagnosed as not being degraded, whereas if the result is "needs attention" or "severe degradation," the high-voltage cable 1 is diagnosed as being degraded.

[0038] <Partial discharge diagnosis> The partial discharge diagnosis unit 4 performs partial discharge diagnosis to determine deterioration of the high-voltage cable 1 by detecting partial discharges occurring in the high-voltage cable 1. Partial discharge diagnosis is a method of diagnosing defects in the insulator 12 by detecting pulse signals associated with partial discharges, since when a small gap or the like occurs in the insulator 12 of the high-voltage cable 1, an electric field concentrates at that part, causing a weak discharge. Here, the partial discharge diagnosis method is a method that not only detects partial discharges occurring in the high-voltage cable 1 but also identifies the location of the partial discharge. One method of identifying the location of the partial discharge is to observe the direct arrival wave and reflected wave of a partial discharge pulse from the high-voltage cable 1 with a pulse detector and analyze the waveforms. In this case, the partial discharge diagnosis unit 4 can be realized using a known configuration such as that shown in Figure 4 of Japanese Patent Laid-Open No. 05-045405, which is described as prior art in Patent Document 3.

[0039] In this embodiment, it is preferable to use a damped oscillatory waveform method for the partial discharge diagnosis unit 4, which detects partial discharge by applying a damped oscillating voltage to the high-voltage cable 1. The damped oscillatory waveform method is also called a DAC (Dumped AC) method and is advantageous in that it can easily distinguish between partial discharge and noise. The damped oscillatory waveform method identifies the location of a partial discharge based on the difference in arrival time between a partial discharge signal generated in the high-voltage cable 1 and a partial discharge signal reflected at the end of the high-voltage cable 1.

[0040] Fig. 4 shows an example of the configuration of a partial discharge diagnosis unit 4 for performing partial discharge diagnosis. The partial discharge diagnosis unit 4 shown in Fig. 4 is connected to the cable head 1a at one end of the conductor 11 of the high-voltage cable 1 via a probe 48a, and is connected to the shielding layer 13 via a probe 48b. The partial discharge diagnosis unit 4 is provided with a grounding wire 43, and the shielding layer 13 is grounded via the probe 48b.

[0041] The partial discharge diagnosis unit 4 includes a power supply 41, a resistor 44, a coil 45, and a capacitor 46. The partial discharge diagnosis unit 4 also includes a first switch 47a and a second switch 47b for opening and closing an electric circuit formed by these components. The partial discharge diagnosis unit 4 further includes a partial discharge detector 49 for detecting pulse signals due to partial discharges occurring in the insulator 12, including pulse signals transmitted directly to the partial discharge diagnosis unit via the shielding layer 13 and pulse signals due to reflected waves from ends of the high-voltage cable 1 that are not connected to the probes 48a and 48b, and a partial discharge diagnosis unit 40 for analyzing the pulse signals detected by the partial discharge detector 49 and diagnosing the presence or absence of deterioration occurring in the high-voltage cable 1 and the location of the deterioration. The partial discharge diagnosis unit 40 is connected to the determination device 6 via a communication cable 8a. In response to a request from the determination device 6, the partial discharge diagnosis unit 40 may perform partial discharge diagnosis and communicate the diagnosis results to the determination device 6.

[0042] The partial discharge diagnosis unit 4 uses the electric circuit configured as described above to configure an electric circuit including a capacitor and a resistor inside the insulator 12 of the high-voltage cable 1. FIG. 5 schematically shows an equivalent circuit 50 as an equivalent electric circuit configured inside the insulator 12. The equivalent circuit 50 shown in FIG. 5 is configured with a resistor 53, a capacitor 51 with capacitance C1 of the cable, and a capacitor 52 with capacitance C2 of a void v formed in the insulator 12. In this case, if a deteriorated portion such as a void v exists in the insulator 12, a partial discharge occurs when a voltage is applied, and the capacitance C2 of the capacitor 52 changes. Therefore, the partial discharge diagnosis unit 4 diagnoses whether a partial discharge is occurring by measuring the impedance of the equivalent circuit shown in FIG. 5.

[0043] Specifically, in partial discharge diagnosis using the partial discharge diagnosis unit 4 shown in FIG. 4, first, the first switch 47a is closed and the second switch 47b is open, and the power supply 41 is charged so that the voltages become +U(V) and −U(V). Next, by opening the first switch 47a and closing the second switch 47b, resonance occurs in an LC circuit including the coil 45 and capacitor 46. As this resonance decays, a damped oscillating voltage is applied to the insulator 12. FIG. 6 shows an example of a damped oscillating waveform supplied to the electric circuit in this manner. The damped oscillating voltage has a frequency of, for example, 30 to 400 Hz, and is generated so that the voltage decays to 0 V 10 seconds after the first switch 47a is opened and the second switch 47b is closed. The damped oscillating waveform can be adjusted by selecting the resistor 44, coil 45, and capacitor 46. The partial discharge detector 49 then detects partial discharges occurring in the insulator 12 when the damped oscillating voltage is applied as a pulse signal. This makes it possible to detect the occurrence of partial discharge in the insulator 12. Furthermore, the partial discharge detector 49 detects a pulse signal that reaches the partial discharge detector 49 directly via the shielding layer 13 and a pulse signal due to a reflected wave from an end of the high-voltage cable 1 that is not connected to the probes 48a, 48b, and identifies the location where the discharge has occurred from the time difference when these pulse signals are detected.

[0044] The partial discharge diagnosis unit 40 acquires this information detected by the partial discharge detector 49 and sends the diagnosis result for the deterioration of the high-voltage cable 1 to the determination device 6 via the communication cable 8c. In this case, if the partial discharge detector 49 detects a partial discharge, the partial discharge diagnosis unit 40 sends information about the occurrence of a partial discharge in the high-voltage cable 1 and information about the position where the partial discharge occurred to the determination device 6 as the diagnosis result. On the other hand, if the partial discharge detector 49 does not detect a partial discharge, the partial discharge diagnosis unit 40 sends information to the determination device 6 that no partial discharge has occurred in the high-voltage cable 1 as a result of the partial discharge diagnosis as the diagnosis result.

[0045] <How to determine the deterioration of high-voltage cables> A method for determining the deterioration of a high-voltage cable using the above-mentioned water tree diagnosis method, tan δ diagnosis method, and partial discharge diagnosis method will be described with reference to Fig. 7. Fig. 7 is a flowchart showing an example of a method for determining the deterioration of a high-voltage cable performed using the above-mentioned device for determining the deterioration of a high-voltage cable.

[0046] Degradation assessment of a high-voltage cable can be performed periodically at preset intervals, or unexpectedly when some abnormality occurs. The method for assessing degradation of a high-voltage cable according to this embodiment starts at either timing (step S0). In this case, the assessment device 6 acquires information indicating that degradation diagnosis of the high-voltage cable 1 to be diagnosed will begin. Upon acquiring the information indicating that degradation diagnosis of the high-voltage cable 1 will begin, the assessment device 6 outputs information indicating that water tree diagnosis of the high-voltage cable 1 will begin to the display device 7. When the information indicating that water tree diagnosis of the high-voltage cable 1 will begin is displayed on the display device 7, the worker, upon seeing this, prepares to perform the water tree diagnosis. That is, the worker connects the probe 28a and the probe 28b of the water tree diagnosis unit 2 to the conductor 11 and the blocking layer 13 of the high-voltage cable 1 to be diagnosed, respectively. Then, the water tree diagnosis of the high-voltage cable 1 is performed by operating the water tree diagnosis unit 2.

[0047] The water tree diagnosis unit 2 performs a water tree diagnosis to diagnose degradation of the high-voltage cable 1 based on the discharge characteristics after applying a DC voltage from the DC power supply 21 to the high-voltage cable 1 (step S1). In step S1, for example, a DC voltage of 1000 V is applied between the conductor 11 and the shielding layer 13 for a predetermined time of 30 minutes. The discharge time after applying the DC voltage is, for example, 5 seconds. The subsequent reverse absorption current measurement time may be, for example, 30 minutes. The water tree diagnosis unit 20 then determines water tree degradation of the high-voltage cable 1 based on changes in the measured reverse absorption current over time. The water tree diagnosis unit 20 sends the determination result of water tree degradation of the high-voltage cable 1 to the determination device 6. The determination result of water tree degradation may be sent to the determination device 6 as, for example, "good" if water tree degradation has not occurred, or "bad" if water tree degradation has occurred.

[0048] In this case, the results of the water tree diagnosis may be displayed as "Activity" for each of the following items: "Perfect," "Mid Life," "Old," and "Critical," as shown in FIG. 9. "Perfect" indicates a healthy state with no degradation, while "Mid Life" indicates a state where degradation is slightly progressing, indicating that the high-voltage cable is still usable but that trend monitoring is required. "Old" indicates degradation and indicates a high probability of insulation breakdown in the near future. "Critical" indicates a severely deteriorated state, indicating a high probability of insulation breakdown. "Activity" indicates the accuracy of these degradation states. That is, the water tree diagnosis result shown in FIG. 9 is determined to be "Mid Life." In this case, the water tree diagnosis result may be determined as "Good" if it is "Perfect" or "Mid Life," and as "Bad" if it is "Old" or "Critical," and the result may be sent to the determination device 6.

[0049] When the determination device 6 receives the determination result of water tree deterioration of the high-voltage cable 1 from the water tree diagnosis unit 20, it then outputs information to the display device 7 indicating that a tan δ diagnosis of the high-voltage cable 1 will begin. When the information indicating that a tan δ diagnosis of the high-voltage cable 1 will begin is displayed on the display device 7, the worker, upon seeing this, prepares to perform the tan δ diagnosis. That is, the worker connects the probe 38a and the probe 38b of the tan δ diagnosis unit 3 to the conductor 11 and the blocking layer 13 of the high-voltage cable 1, respectively. Then, the tan δ diagnosis of the high-voltage cable 1 is performed by operating the tan δ diagnosis unit 3.

[0050] The tan δ diagnosis unit 3 applies an AC voltage from the AC power source 31 to the high-voltage cable 1 and measures the dielectric loss tangent to diagnose the degradation of the high-voltage cable (step S2). In step S2, for example, three levels of AC voltage—0.5U0, 1.0U0, and 1.5U0—are applied as test voltages, where U0 is the rated voltage of the high-voltage cable 1, to measure tan δ (dielectric loss tangent). Δtan δ may also be calculated based on the tan δ measurement results. For example, as shown in FIG. 10, the tan δ values ​​measured for each test voltage can be obtained. The tan δ diagnosis unit 30 then determines the degree of degradation of the high-voltage cable 1 from the measured tan δ values ​​using the tan δ diagnosis criteria defined by the IEEE and shown in Table 1. If the degradation level is "good" according to the tan δ diagnosis criteria, the tan δ diagnosis unit 30 determines that no degradation has occurred. If the degradation level is other than "good," the tan δ diagnosis unit 30 determines that degradation has occurred (failure) and sends the determination result to the determination device 6.

[0051] [Table 1]

[0052] The determination device 6 acquires the results of the water tree diagnosis from the water tree diagnosis unit 2 and the results of the tan δ diagnosis from the tan δ diagnosis unit 3. If the water tree diagnosis and / or tan δ diagnosis indicate that the high-voltage cable 1 is degraded, the determination device 6 decides to perform a partial discharge diagnosis on the high-voltage cable 1 (step S3: Yes). On the other hand, if the results of both the water tree diagnosis and the tan δ diagnosis indicate that the high-voltage cable 1 is not degraded, the determination device 6 decides not to perform a partial discharge diagnosis (step S3: No). If the water tree diagnosis and the tan δ diagnosis for the high-voltage cable 1 both result in a "good" result, no degradation is found in the diagnosed high-voltage cable 1, and the degradation diagnosis for the high-voltage cable 1 may be terminated without performing a partial discharge diagnosis. That is, the determination device 6 allows the high-voltage cable 1 that was the subject of the diagnosis to continue to be used as a normal high-voltage cable until the timing of the next degradation diagnosis (step S8). In this case, the timing of the next degradation diagnosis will be the next periodic diagnosis or unexpected diagnosis. The determination device 6 may store the diagnosis results of the high-voltage cable 1 that has been diagnosed in a storage unit of the determination device 6 so that the results can be used as a diagnosis history of the high-voltage cable 1.

[0053] On the other hand, when the determination device 6 decides to perform a partial discharge diagnosis on the high-voltage cable 1, it then outputs information to the display device 7 indicating that a partial discharge diagnosis of the high-voltage cable 1 will be started. When the information indicating that a partial discharge diagnosis will be started is displayed on the display device 7, the worker, seeing this, prepares to perform the partial discharge diagnosis. That is, the worker connects the probe 48a and the probe 48b of the partial discharge diagnosis unit 4 to the cable head 1a and the blocking layer 13 at one end of the conductor 11 of the high-voltage cable 1, respectively. Then, the partial discharge diagnosis of the high-voltage cable 1 is performed by operating the partial discharge diagnosis unit 4.

[0054] The partial discharge diagnosis unit 4 diagnoses the deterioration of the high-voltage cable 1 by detecting partial discharges occurring in the high-voltage cable 1 (step S4). For the partial discharge diagnosis, a damped oscillation waveform method is preferably used, in which a damped oscillating voltage is applied to the high-voltage cable 1 to detect partial discharges. The partial discharge diagnosis unit 4 applies a damped oscillating wave-shaped test voltage T between the cable head 1a of the high-voltage cable 1 and the grounded insulator 12, as shown in Fig. 11, and monitors whether or not a partial discharge pulse signal P due to the test voltage T is detected between the cable head 1a and the insulator 12. If a partial discharge pulse signal P is detected within a predetermined time after the application of the test voltage T, that is, after the test voltage T exceeds a predetermined level at the rising edge of each wave, as shown in the lower part of Fig. 11, the partial discharge diagnosis unit 4 performs a test The time difference between the arrival time of a pulse signal (direct wave) traveling directly from the partial discharge location to the cable head 1a and the arrival time of a pulse signal (reflected wave) traveling from the partial discharge location in the direction opposite to the cable head 1a toward the cable head 1b after application of the test voltage and reflected by the other end (cable head 1b) of the conductor of the high-voltage cable 1 and traveling back toward the cable head 1a is calculated for each wave, and the source location (the length of the conductor from the cable head 1a to the source location) is located from these time differences, and the diagnosis result is sent to the partial discharge diagnosis unit 40 via the communication cable 8. For example, in the diagnosis result shown in Figure 12, the source locations located by the pulse signal of the first wave (level P1), the pulse signal of the second wave (level P2), and the pulse signal of the third wave (level P3) among the multiple damped oscillating waves of the test voltage T are all approximately 500 m apart, and it is estimated that the diagnosis result is valid.

[0055] From the diagnosis result, the partial discharge diagnosis unit 40 determines whether or not a partial discharge pulse signal due to the test voltage has been detected between the cable head 1a and the shielding layer 13, and sends the determination result, including information on the location where the partial discharge has been detected, to the determination device 6. On the other hand, if no partial discharge pulse signal is detected, the determination result indicating that no partial discharge has been detected is sent to the determination device 6.

[0056] If the determination device 6 obtains a determination result in the next step S5 that partial discharge has not been detected based on the determination result from the partial discharge diagnosis unit 40, it proceeds to step S7 and outputs a diagnosis result that "the entire high-voltage cable 1 to be evaluated will be updated" because deterioration has been determined in the water tree deterioration or tan δ diagnosis and it is therefore assumed that water tree deterioration or insulation paper deterioration has spread throughout the cable.

[0057] On the other hand, if a pulse signal of partial discharge due to the above test voltage is detected in step S5, the determination device 6 proceeds to step S6 and outputs the diagnosis result that "the location where discharge was detected will be partially updated" together with the location of the partial discharge identified by the partial discharge diagnosis unit 4.

[0058] The display device 7 then displays the diagnosis results from the determination device 6, such as "renew the entire high-voltage cable 1 being evaluated" or "renew the portion where discharge was detected." The worker in charge of diagnosing the deterioration of the high-voltage cable 1 can perform work corresponding to the diagnosis results displayed on the display device 7. In other words, the display device 7 displays these diagnosis results from the determination device 6, thereby instructing the worker on the next step. In this case, if the diagnosis result is "renew the portion where discharge was detected," the display device 7 displays information on the location of the partial discharge identified by the partial discharge diagnosis unit 4, making it possible to easily identify the location where deterioration has occurred in the high-voltage cable 1, thereby enabling efficient partial renewal of the target high-voltage cable.

[0059] 8 is a flowchart showing another example of a method for determining deterioration of a high-voltage cable using the above-described deterioration determination device for a high-voltage cable. In this example, a deterioration determination of a high-voltage cable is started at the timing of a periodic diagnosis or a sudden diagnosis (step S10). First, a water tree diagnosis is performed in the same manner as described above (step S11). Then, the determination result of the water tree diagnosis is transmitted to the determination device 6. The determination device 6 acquires the determination result of the water tree diagnosis from the water tree diagnosis unit 2, and if the water tree diagnosis determines that the high-voltage cable 1 is deteriorated, decides to perform a partial discharge diagnosis on the high-voltage cable 1 (step S12: Yes). On the other hand, the determination device 6 acquires the determination result of the water tree diagnosis from the water tree diagnosis unit 2, and if the water tree diagnosis determines that the high-voltage cable 1 is not deteriorated, decides to perform a tan δ diagnosis on the high-voltage cable 1 (step S12: No). Then, a tan δ diagnosis is performed in the same manner as described above (step S13). Then, the determination result of the tan δ diagnosis is transmitted to the determination device 6. The determination device 6 acquires the determination result of the tan δ diagnosis from the tan δ diagnosis unit 3, and if the tan δ diagnosis determines that the high-voltage cable 1 has deteriorated, it decides to perform a partial discharge diagnosis on the high-voltage cable 1 (step S14: Yes). On the other hand, if the determination result of the tan δ diagnosis indicates that the high-voltage cable 1 has not deteriorated, it decides not to perform a partial discharge diagnosis (step S14: No). The deterioration diagnosis of the high-voltage cable 1 may be terminated without performing a partial discharge diagnosis. In other words, the determination device 6 allows the high-voltage cable 1 that has been diagnosed to continue to be used as a normal high-voltage cable until the timing of the next deterioration diagnosis (step S19).

[0060] Similarly to the above, a partial discharge diagnosis is performed (step S15) based on an instruction from the determining device 6. Depending on whether partial discharge is detected (step S16), the deterioration of the high voltage cable is determined (steps S17, S18).

[0061] In the above example, an operator switches the probes based on instructions from the determination device. Alternatively, a connection switching device 5 may be provided that switches between the high-voltage cable 1 and the water tree deterioration diagnosis unit 2, the dielectric loss tangent diagnosis unit 3, and the partial discharge diagnosis unit 4, and the connection switching device may switch between the high-voltage cable 1 and each unit based on instructions from the determination device 6.

[0062] As described above, the deterioration determination device 10 can function as a guidance device that provides guidance for diagnosing deterioration of a high-voltage cable that uses cross-linked polyethylene as an insulating material. Specifically, the determination device 6 can function as a first determination result acquisition unit that acquires the determination result of a water tree diagnosis that determines deterioration of a high-voltage cable based on discharge characteristics after applying a DC voltage to the high-voltage cable 1, and the determination result of a tan δ diagnosis that determines deterioration of a high-voltage cable by applying an AC voltage to the high-voltage cable and measuring its dielectric tangent. If at least one of the determination results of the water tree diagnosis and the tan δ diagnosis indicates that the high-voltage cable 1 is deteriorated, the determination device 6 can function as a partial discharge diagnosis request unit that requests a partial discharge diagnosis by displaying on the display device 7 a message indicating that a partial discharge diagnosis will be performed to diagnose deterioration of the high-voltage cable 1 by detecting partial discharges occurring in the high-voltage cable 1. Furthermore, the determination device 6 can function as a second determination result acquisition unit that acquires the determination result of the partial discharge diagnosis of the high-voltage cable 1 performed in response to a request from the partial discharge diagnosis request unit. If the determination result of the partial discharge diagnosis is that no partial discharge is detected, the determination device 6 diagnoses that the entire cable has deteriorated, and if the determination result is that a partial discharge is detected, the determination device 6 diagnoses that the deterioration is at the partial discharge location identified in the partial discharge diagnosis, and displays the diagnosis result on the display device 7. In this way, the diagnosis result of the high-voltage cable 1 by the deterioration determination device 10 is displayed on the display device 7, which functions as a presentation unit.

[0063] <effect> As described above, according to the method for determining degradation of a high-voltage cable of this embodiment, if the high-voltage cable to be diagnosed is diagnosed as not degraded by the water tree diagnosis and tan δ diagnosis, there is no need to perform a partial discharge diagnosis. A partial discharge diagnosis applies a high voltage to the high-voltage cable, which places a large stress on the high-voltage cable. Partial discharges occurring in areas where the insulation is degraded can further progress the insulation breakdown, potentially making it impossible to continue using the high-voltage cable to be diagnosed. However, according to this embodiment, if the high-voltage cable is diagnosed as not degraded by the water tree diagnosis and tan δ diagnosis, it is confirmed that the high-voltage cable is healthy, so unnecessary degradation diagnoses can be omitted, thereby improving the efficiency of degradation determination.

[0064] For example, in water tree diagnosis, the DC test voltage is about 1 kV. In addition, in tan δ diagnosis, the AC voltage is a maximum of about 1.5 times the rated voltage of the high-voltage cable (0.75 to 10.50 kV). In contrast, in partial discharge diagnosis, a voltage of 1.5 to 2.5 times the rated voltage is applied to detect partial discharge. Therefore, water tree diagnosis and tan δ diagnosis impose less stress on high-voltage cables than partial discharge diagnosis. In particular, when the DC leakage current method is applied to water tree diagnosis, the test voltage is about three times the rated voltage. For example, a test voltage of 30 kV is applied to an 11 kV cable. In contrast, the reverse absorption current method (IRC method) can limit the test voltage to about 1 kV, which is lower than the rated voltage. Therefore, in this embodiment, the reverse absorption current method is preferably used for water tree diagnosis.

[0065] Furthermore, when the VLF method is applied to tan δ diagnosis, it is preferable in that it applies an ultra-low frequency AC current, for example, 0.1 Hz, compared to methods that use commercial frequency (60 Hz) as the AC power source, so that the energy load on the high-voltage cable is small and stress on the high-voltage cable can be reduced.

[0066] Furthermore, the method for determining high-voltage cable deterioration according to this embodiment performs both water tree diagnosis and tan δ diagnosis on the high-voltage cable to be determined. Water tree diagnosis has high diagnostic accuracy for water tree deterioration. However, because water tree diagnosis is intended to diagnose deterioration of the high-voltage cable's insulator 12, it is difficult to diagnose insulation deterioration at the cable heads 1a and 1b or even at the joint 1d. On the other hand, tan δ diagnosis can diagnose insulation deterioration throughout the entire cable, including the cable heads 1a and 1b and the joint 1d. However, tan δ diagnosis can diagnose deterioration in bridging water trees, i.e., water trees that have progressed from the conductor of the high-voltage cable to the outer layer of the insulator. On the other hand, it is difficult to diagnose deterioration in unbridging water trees, i.e., water trees that have progressed halfway through the insulator but have not yet penetrated the outer layer of the insulator. For these reasons, the method for determining high-voltage cable deterioration according to this embodiment performs both water tree diagnosis and tan δ diagnosis. This improves the accuracy of diagnosing whether or not a high-voltage cable is deteriorated. It is preferable to perform the water tree diagnosis first and then perform the tan δ diagnosis only when water tree deterioration has not occurred, as this reduces the load on the high voltage cable.

[0067] In the method for determining degradation of a high-voltage cable according to this embodiment, a partial discharge diagnosis is performed on the high-voltage cable when the high-voltage cable is diagnosed as degraded in at least one of the water tree diagnosis and the tan δ diagnosis. When the high-voltage cable is diagnosed as degraded in at least one of the water tree diagnosis and the tan δ diagnosis, the high-voltage cable is determined to be defective. Therefore, the partial discharge diagnosis is performed not for the purpose of diagnosing the degradation of the high-voltage cable, but to identify the location of the degradation. As described above, the partial discharge diagnosis is a diagnostic method that places a great deal of stress on the high-voltage cable. However, since the water tree diagnosis and the tan δ diagnosis indicate that a defect has occurred in the high-voltage cable, some kind of action, such as repair or replacement of the high-voltage cable, is necessary. Therefore, even if the partial discharge diagnosis may cause significant damage to the high-voltage cable, if the location of the insulation degradation of the high-voltage cable can be identified, partial repair or replacement of the high-voltage cable can eliminate the need to discard the entire high-voltage cable. This reduces the cost of materials and construction required for replacing the entire high-voltage cable.

[0068] The guidance device according to this embodiment can guide an operator in an efficient and effective diagnostic method as a procedure for determining the deterioration of a high-voltage cable. By determining the deterioration of a high-voltage cable according to the guidance device according to this embodiment, guidance is provided from among multiple diagnostic methods so that the minimum necessary diagnostic work is required. Furthermore, since a degradation determination method that reduces stress on the high-voltage cable being determined is presented, the risk of damage to the high-voltage cable that may occur due to the deterioration diagnosis can be reduced. Furthermore, since the partial discharge diagnosis indicates locations where insulation deterioration has occurred in the high-voltage cable, the work of partially repairing or replacing the high-voltage cable can be made more efficient.

[0069] Although the above description has been based on the illustrated embodiment, the present invention is not limited to the above embodiment. As shown in Fig. 13 as another embodiment, a high-voltage cable 1 to be assessed and a high-voltage cable deterioration assessment device 10 may be connected in advance by probes 9, and a connection switching device 5 may be provided that can switch the connections of each probe with a water tree diagnosis unit 2, a tan δ diagnosis unit 3, and a partial discharge diagnosis unit 4, so that the electrical connections between the high-voltage cable 1 and each diagnosis unit can be automatically switched in accordance with a deterioration assessment command issued by a determination device 6. This allows the high-voltage cable deterioration assessment in this embodiment to be performed automatically, enabling efficient assessment.

[0070] 7 and 8, it is not necessary to perform the water tree diagnosis and tan δ diagnosis after the water tree diagnosis, with the water tree diagnosis being performed first. In other words, the order of the water tree diagnosis and tan δ diagnosis may be reversed from that of the above embodiment. In any case, it is sufficient that the water tree diagnosis and tan δ diagnosis are performed before determining whether or not to perform the partial discharge diagnosis. [Industrial Applicability]

[0071] Thus, the high-voltage cable deterioration determination method and guidance device of the present invention can diagnose deterioration of aged high-voltage cables while they are installed, and can identify not only the degree of deterioration of the high-voltage cable but also the type and location of the deterioration, which allows for a decision on whether the high-voltage cable needs to be replaced, thereby preventing electrical accidents caused by the deterioration of the high-voltage cable.Furthermore, because the location of the deterioration can be identified, the extent of replacement of the high-voltage cable can be limited, thereby reducing replacement costs. [Explanation of symbols]

[0072] 1 High voltage cable 1a, 1b cable head 1c Sheathed ground wire 1d Cable Joint 2 Water Tree Diagnostic Unit 3 Tanδ Diagnostic Unit 4 Partial discharge diagnostic unit 5. Connection switching device 6 Judgment device 7 Display device 8, 8a, 8b, 8c communication cables 9 Probe 10. (High voltage cable) deterioration detection device 11 Conductor (core wire) 12 Insulators 13 Shielding layer (copper tape) 14 Sheath layer 14 20 Water Tree Diagnostics Department 21 DC power supply 22 Resistance 23 Ground wire 24 Ammeter 25 amps 26 AD converter 27 Relay Switch 28a, 28b probes 30 Tanδ Diagnostic Department 31 AC power supply 33 Ground wire 34 RC parallel circuit (as lossless standard capacitor) 34a capacitor 34b resistance 35 RC parallel circuit (as equivalent circuit) 35a capacitor 35b resistance 38a, 38b probes 40 Partial discharge diagnostic unit 41 Power supply 42 Current 43 Ground wire 44 Resistance 45 coils 46 Capacitor 47a First Switch 47b Second Switch 48a, 48b probes 49 Partial Discharge Detector 50 Equivalent Circuit 51 Capacitor (of cable capacitance C1) 52 (Void v has capacitance C2) Capacitor 52 53 Resistance v Void (deteriorated area) P pulse signal P1, P2, P3 pulse signal level T test voltage

Claims

1. When assessing the deterioration of aged high voltage cables while they are still installed, a connection switching step of disconnecting both ends of the conductor of the high-voltage cable from the power grid and connecting any one of a water tree deterioration diagnostic device, a dielectric loss tangent diagnostic device, and a partial discharge diagnostic device to the high-voltage cable; a water tree diagnosis step of performing a water tree diagnosis to determine the degree of water tree deterioration from discharge characteristics after applying a DC voltage using the water tree deterioration diagnosis device connected to the high-voltage cable; a dielectric loss tangent diagnosis step of diagnosing a dielectric loss tangent to determine a degree of deterioration from the dielectric loss tangent determined by the dielectric loss tangent diagnosis device connected to the high-voltage cable; a partial discharge diagnosis step of performing a partial discharge diagnosis using the partial discharge diagnosis device connected to the high-voltage cable; a determination step of determining a deterioration state of the high-voltage cable; Including, When it is determined that the high-voltage cable has deteriorated based on at least one of the water tree diagnosis and the dielectric loss tangent diagnosis, the partial discharge diagnosis step is carried out; In the determination step, if a partial discharge is not detected in the partial discharge diagnosis, it is determined that the entire cable has deteriorated, and if a partial discharge is detected in the partial discharge diagnosis, it is determined that the deterioration has occurred at a partial discharge location identified in the partial discharge diagnosis. A method for determining the deterioration of high voltage cables.

2. the water tree diagnosis step includes applying a DC voltage lower than a rated voltage of the high-voltage cable; In the dielectric loss tangent diagnosis step, an AC current having a frequency lower than a commercial frequency is supplied to measure the dielectric loss tangent; the partial discharge diagnosis step detects partial discharges that occur when a damped oscillating voltage is applied to the high-voltage cable; Select at least one of The method for determining deterioration of a high-voltage cable according to claim 1.

3. In the determination step, when it is determined that no deterioration has occurred in the high-voltage cable in either the water tree diagnosis or the dielectric loss tangent diagnosis, it is determined to continue using the high-voltage cable.

3. The method for determining deterioration of a high-voltage cable according to claim 1 or 2.

4. A guidance device that determines the deterioration of a high-voltage cable that has deteriorated over time and provides guidance while the cable is still in its installed state, a degradation diagnosis unit including a water tree degradation diagnosis device that is connected to the high-voltage cable and determines the degree of water tree degradation from discharge characteristics after applying a DC voltage, a dielectric loss tangent diagnosis device that is connected to the high-voltage cable and performs a dielectric loss tangent diagnosis that determines the degree of degradation from a measured dielectric loss tangent, and a partial discharge diagnosis device that is connected to the high-voltage cable and performs a partial discharge diagnosis; a first diagnostic result acquisition unit that acquires a diagnostic result of the water tree diagnosis by the water tree degradation diagnosis device, or a diagnostic result of the water tree diagnosis by the water tree degradation diagnosis device and a diagnostic result of the dielectric loss tangent diagnosis by the dielectric loss tangent diagnosis device; a degradation diagnosis requesting unit that requests a partial discharge diagnosis by the partial discharge diagnosis device provided in the degradation diagnosis unit when at least one of the diagnostic results of the water tree diagnosis and the dielectric loss tangent diagnosis indicates that the high-voltage cable is deteriorated; a second diagnosis result acquisition unit that acquires a diagnosis result of a partial discharge diagnosis of the high-voltage cable performed in response to a request from the degradation diagnosis request unit; a deterioration status determination unit that determines that the entire cable has deteriorated if the diagnosis result of the partial discharge diagnosis indicates that no partial discharge has been detected, and that the deterioration has occurred at a partial discharge location identified by the partial discharge diagnosis if a partial discharge has been detected; a presentation unit that displays at least one piece of information selected from the results of the water tree diagnosis, the dielectric loss tangent diagnosis, and the dielectric loss tangent diagnosis, a deterioration state of the high-voltage cable, and an instruction for a next process. Guidance device.

5. 5. The guidance device according to claim 4, wherein the presentation unit presents a determination result that the high-voltage cable is normal when both the diagnosis result of the water tree diagnosis by the water tree degradation diagnosis device and the diagnosis result of the dielectric loss tangent diagnosis by the dielectric loss tangent diagnosis device determine that no degradation has occurred in the high-voltage cable.

6. further comprising a connection switching means for switching and connecting the high-voltage cable to the water tree deterioration diagnostic device, the dielectric loss tangent diagnostic device, and the partial discharge diagnostic device, 5. The guidance device according to claim 4, wherein a connection switching means switches between the high-voltage cable and each diagnostic device based on an external input or an instruction from a deterioration diagnostic unit.

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