Power transmission line evaluation system and power transmission line evaluation method

Abstract

This power transmission line evaluation system comprises: a power supply that is connected to a power transmission line including a power cable having a conductor, an insulating layer, and a shielding layer in this order in the radial direction of the conductor, the power supply being capable of applying a voltage between the conductor and the shielding layer; and a charge quantity measurement unit that is connected in series between the power supply and the power transmission line, and that measures the quantity of charge, which is the integrated value of a current flowing between the conductor and the shielding layer of the power transmission line.

Description

Power transmission line evaluation system and power transmission line evaluation method

[0001] The present disclosure relates to a power transmission line evaluation system and a power transmission line evaluation method.

[0002] Various methods have been disclosed for evaluating the insulation layer of a power cable (for example, Patent Document 1).

[0003] JP 2013-29450 A

[0004] According to one aspect of the present disclosure, there is provided a power transmission line evaluation system including: a power source connected to a power transmission line including a power cable having a conductor, an insulating layer, and a shielding layer in that order in the radial direction of the conductor, and capable of applying a voltage between the conductor and the shielding layer; and a charge amount measuring unit connected in series between the power source and the power transmission line, and measuring a charge amount which is an integral value of a current flowing between the conductor and the shielding layer of the power transmission line.

[0005] FIG. 1 is a schematic diagram showing a power transmission line evaluation system according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram showing an enlarged view of the configuration near the power transmission line in FIG. 1. FIG. 3 is a schematic diagram showing an enlarged view of the configuration near the radio unit in FIG. 1. FIG. 4 is a block diagram showing a management center. FIG. 5 is a flowchart showing a power transmission line evaluation method according to an embodiment of the present disclosure. FIG. 6 is a diagram showing the sequences of a voltage application process and a charge amount measurement process. FIG. 7 is a schematic diagram showing a conventional insulating material evaluation system.

[0006] [Problem to be Solved by the Present Disclosure] An object of the present disclosure is to evaluate the condition of a power transmission line based on the charge amount characteristics of the power transmission line.

[0007] Effect of the Present Disclosure According to the present disclosure, the state of a power transmission line can be evaluated based on the charge amount characteristics of the power transmission line.

[0008] [Explanation of Embodiments of the Present Disclosure] <Insights Obtained by the Inventors> First, insights obtained by the inventors will be described.

[0009] The inventors have developed a method for evaluating the insulating material contained in the insulating layer of a power cable by using the so-called current-integrated charge method (also called the Q(t) method).

[0010] In previous studies by the inventors, for example, an insulating material evaluation system 90 as shown in Fig. 7 was used. Specifically, the insulating material evaluation system 90 included, for example, a power supply 920, a switch 922, a switch 924, and a charge amount measurement unit 930 including a capacitor 932 and a switch 934.

[0011] The evaluation target was a sheet 910 containing an insulating material. A first electrode 912 and a second electrode 914 were provided on the front and back surfaces of the sheet 910. Furthermore, a guard electrode 916 was provided on the back surface of the sheet 910 so as to surround the outer periphery of the second electrode 914, and the guard electrode 916 was grounded.

[0012] In a conventional insulating material evaluation method, for example, a power supply 920, a switch 922, a switch 924, and a switch 934 are used to apply a square wave voltage between a first electrode 912 and a second electrode 914, thereby causing charges flowing in the thickness direction of a sheet 910 containing an insulating material to be accumulated in a capacitor 932. In this way, the amount of charge accumulated in the capacitor 932 is measured. Note that the characteristic obtained by measuring the amount of charge, which is the integral value of the current flowing through the evaluation object, is also referred to as the "charge amount characteristic" below.

[0013] In conventional insulating material evaluation methods, the characteristics of an insulating material, including at least one of the dielectric constant, space charge characteristics, electrical conductivity, etc., have been evaluated based on the charge amount characteristics of the insulating material obtained by the above-mentioned measurements.

[0014] However, in the conventional insulating material evaluation system 90, the evaluation target was limited to a thin sheet 910, and the voltage that could be applied by the power supply 920 was low. For this reason, the insulating material evaluation system 90 was unable to evaluate the charge quantity characteristics of a power transmission line, including a power cable, that is actually laid in the field.

[0015] Therefore, after extensive research, the inventors developed a power transmission line evaluation system that can evaluate the charge quantity characteristics of a power transmission line by directly applying a voltage to the power transmission line that is actually laid on-site.

[0016] However, it has been found that the above-described power transmission line evaluation system has the following new problems due to the circuit configuration and the like.

[0017] (i) In the above-described conventional insulating material evaluation system 90, the charge amount measuring unit 930 was placed closer to the earth than the sheet 910 to be evaluated. As a result, the measurement computer was directly connected to the measurement system including the capacitor 932 as the charge amount measuring unit 930. The insulating material evaluation system 90 having such a configuration was installed in an environment such as a laboratory where the level of noise generated from the earth could be easily controlled. For this reason, there was no malfunction in the measurement computer.

[0018] However, power transmission line evaluation systems that apply ultra-high voltages to power transmission lines have been tested in various indoor and outdoor environments. This has resulted in a tendency for noise levels from the earth of factories and other locations outside the power transmission line evaluation system to be high. This noise level is particularly likely to be high when various power supplies (such as inverter control power supplies) in the factory are located near the power transmission line. In such cases, if the charge measurement unit is located closer to the earth than the transmission line being evaluated, noise is likely to be generated from the earth, and this noise may affect the measurement accuracy of the charge measurement unit.

[0019] Furthermore, in a power transmission line evaluation system in which the charge measurement unit is located closer to the earth than the power transmission line, the reference potential of the power transmission line is in a floating state via the charge measurement unit, which can cause the power transmission line to become unstable.

[0020] Furthermore, in a power transmission line evaluation system in which the charge measurement unit is located closer to the earth than the power transmission line, if an electrical malfunction occurs in the charge measurement unit, the grounding system for the power transmission line may change. As a result, there is a risk that an unexpected current may flow or an unexpected voltage may be applied to the power transmission line. As a result, there is a risk that the electrical malfunction may affect the entire power transmission line evaluation system, which is subject to high voltage.

[0021] (ii) To avoid the effect of (i) above, the inventors considered a configuration in which the charge measurement unit is located at a high potential near the positive electrode of the power supply. In this case, because the charge measurement unit is at a high potential, it was not possible to directly connect a measurement computer to a measurement system including a capacitor as the charge measurement unit. Therefore, a wireless unit that wirelessly transmits charge data measured by the charge measurement unit was provided in the power transmission line evaluation system.

[0022] However, when the voltage applied from the power source to the transmission line was gradually increased, for example, when the applied voltage exceeded 400 kV, communication from the wireless unit of the transmission line evaluation system was cut off.

[0023] When the inventors investigated the cause, they found that the housing containing the charge measurement unit and the radio unit had a high potential equal to the positive pole of the power supply as a reference potential. Meanwhile, for example, in the antenna of the radio unit, which has a coaxial structure, the electrically shielding second conductor is at the same potential as the housing, but the first conductor located at the center of the antenna is not directly electrically connected to the housing. As a result, an unintended excess charge accumulated in the first conductor of the antenna. This is believed to have resulted in a communication failure in the radio unit. Therefore, even with the arrangement described in (ii), it was difficult to stably acquire charge data.

[0024] As a result of further intensive research to solve the above-mentioned new problems (i) and (ii), the inventors discovered the configuration of a power transmission line evaluation system that can stably evaluate the state of a power transmission line.

[0025] The present disclosure is based on the above findings made by the inventors.

[0026] <Embodiments of the Present Disclosure> Next, embodiments of the present disclosure will be listed and described.

[0027] [1] A power transmission line evaluation system according to one aspect of the present disclosure includes: a power source connected to a power transmission line including a power cable having a conductor, an insulating layer, and a shielding layer in this order in a radial direction of the conductor, and capable of applying a voltage between the conductor and the shielding layer; and a charge measurement unit connected in series between the power source and the power transmission line, and configured to measure a charge, which is an integral value of a current flowing between the conductor and the shielding layer of the power transmission line. With this configuration, it is possible to evaluate the state of the power transmission line based on the charge characteristics of the power transmission line.

[0028] [2] In the power transmission line evaluation system described in [1] above, the power supply is configured to be able to apply a DC voltage or a square wave voltage of 10 kV or more between the conductor and the shielding layer of the power transmission line. With this configuration, the amount of charge on the power transmission line can be measured under conditions similar to those during actual operation of the power transmission line.

[0029] [3] In the power transmission line evaluation system described in [1] or [2] above, the power source has a positive electrode connected to the conductor of the power transmission line and a negative electrode grounded to earth together with the shielding layer of the power transmission line, and the charge measurement unit is connected in series between the positive electrode of the power source and the conductor of the power transmission line. This configuration enables stable evaluation of the state of the power transmission line.

[0030] [4] The power transmission line evaluation system according to [3] above, further comprising a wireless unit connected to the charge measurement unit and capable of wirelessly transmitting the charge amount data measured by the charge measurement unit to an external device. With this configuration, the charge amount data can be obtained wirelessly in a stable and safe manner.

[0031] [5] The power transmission line evaluation system according to [4] above, further comprising a housing that houses the charge measurement unit and part of the radio unit and is connected to the charge measurement unit and the radio unit as a common reference potential, the housing being connected between the positive electrode of the power supply and the charge measurement unit so as to be at an equipotential with the positive electrode of the power supply. With this configuration, the charge measurement unit can accurately measure the amount of charge between the conductor and the shielding layer of the power transmission line.

[0032] [6] In the power transmission line evaluation system described in [5] above, the radio unit includes: a signal processing unit connected to the charge measurement unit within the housing and configured to generate a data signal including the charge data and process external signals, an antenna connected to the signal processing unit and configured to transmit the data signal to the outside and receive the external signals, and a coil connected to the housing as the reference potential and connected in parallel to the signal processing unit and the antenna. This configuration enables stable evaluation of the state of the power transmission line.

[0033] [7] A power transmission line evaluation method according to another aspect of the present disclosure includes the steps of: preparing a power transmission line including a power cable having a conductor, an insulating layer, and a shielding layer in this order in a radial direction of the conductor; applying a voltage between the conductor and the shielding layer using a power source connected to the power transmission line; and measuring an amount of charge, which is an integral value of a current flowing between the conductor and the shielding layer of the power transmission line, using a charge measurement unit connected in series between the power source and the power transmission line. With this configuration, it is possible to evaluate the state of the power transmission line based on the charge characteristics of the power transmission line.

[0034] [Details of the embodiment of the present disclosure] Next, one embodiment of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. At least some of the embodiments described below may be combined in any manner.

[0035] <One embodiment of the present disclosure> (1) Transmission line evaluation system An outline of a transmission line evaluation system 20 according to one embodiment of the present disclosure will be described with reference to Figures 1 to 4. In Figure 1, the switching system of the power source 200 and the charge amount measurement unit 300, and the low-voltage shield ring 194 are omitted. In Figure 1, bent portions of the transmission line 10 are omitted, and the transmission line 10 is shown in a straight line. In Figure 2, a cross section of a portion constituting the transmission line 10 is shown.

[0036] As shown in Figures 1 to 4, the power transmission line evaluation system 20 of this embodiment is configured to evaluate the condition of the power transmission line 10 based on the amount of charge of the actually installed power transmission line 10, for example, by the current integral charge method.

[0037] Specifically, the power transmission line evaluation system 20 of this embodiment includes, for example, a power source 200, a charge amount measuring unit 300, a wireless unit 400, a housing 500, and a management center 60.

[0038] 1 and 2 , in this embodiment, a transmission line 10 to be evaluated includes, for example, at least a power cable 100. The power cable 100 has, for example, a conductor 101, an inner semiconductive layer (not shown), an insulating layer 103, an outer semiconductive layer (not shown), a shielding layer (metallic shielding layer) 105, and a sheath (reference numeral not shown), which are arranged in this order from the central axis of the conductor 101 toward the outside in the radial direction of the conductor 101.

[0039] The power cable 100 may be configured for DC or AC. Even if the power cable 100 is configured for AC, a DC voltage or a square wave voltage is applied to the power transmission line 10 including the power cable 100 from the power source 200 of the power transmission line evaluation system 20.

[0040] In this embodiment, the power transmission line 10 may further include, for example, at least one of a terminal connection portion 120 and an intermediate connection portion 140 .

[0041] The intermediate joint 140 constitutes, for example, a portion of the power transmission line 10 where a pair of power cables 100 are connected. Specific examples of the intermediate joint 140 include an intermediate joint including a cold-shrinkable rubber insulating unit and a factory joint (FJ) formed by wrapping insulating tape around the joint in a factory. The intermediate joint 140 includes, for example, a metal sleeve that connects the conductors 101 of the pair of power cables 100, an insulating unit that surrounds the outer periphery of the metal sleeve, and a shielding member that is connected to the shielding layer 105 of the power cable 100.

[0042] The termination connection part 120 constitutes, for example, a part of the power transmission line 10 where the power cable 100 is connected to an overhead transmission line or a predetermined device. A specific example of the termination connection part 120 is an outdoor termination connection part. The following describes, for example, a case where the termination connection part 120 is configured as an outdoor termination connection part.

[0043] At the termination connection part 120, the power cable 100 is stripped in stages from the axial tip of the conductor 101 toward the opposite side. That is, the conductor 101, insulating layer 103, outer semiconductive layer, shielding layer 105, and sheath of the power cable 100 are exposed in this order from the tip side of the conductor 110 toward the opposite side. An insulating rubber unit may be provided around the exposed outer semiconductive layer of the power cable 100.

[0044] The terminal connection portion 120 includes, for example, a porcelain bushing 122 and a lower fitting 124 .

[0045] The porcelain bushing 122 is configured as a tubular insulating member and is provided so as to surround the outer periphery of the power cable 100. The porcelain bushing 122 is configured to ensure insulation around the power cable 100 that has been stripped in stages.

[0046] The porcelain tube 122 is erected in the vertical direction. The power cable 100, which has been stripped in stages, is inserted into the porcelain tube 122. The conductor 101 of the power cable 100 is fixed to the upper part of the porcelain tube 122. The inside of the porcelain tube 122, excluding the power cable 100, is filled with an insulating medium (reference number not shown) such as insulating oil or insulating gas.

[0047] The porcelain tube 122 has a plurality of flanges (folds, not shown) on the outer periphery of the porcelain tube 122, the diameter of which increases toward the outside of the porcelain tube 122. This ensures an insulation distance between the conductor 101 and the earth.

[0048] The lower fitting 124 is provided at the axial lower part of the porcelain tube 122 and closes the opening at the axial lower part of the porcelain tube 122. The lower fitting 124 is connected to the shielding layer 105 of the power cable 100 and is grounded together with the shielding layer 105. In this way, the shielding layer 105 of the entire power transmission line 10 is grounded.

[0049] The transmission line 10 has a first end 10a in the axial direction of the conductor 101 (the direction in which the transmission line 10 is laid), and a second end 10b opposite the first end 10a. The above-mentioned termination connection parts 120 are provided near the first end 10a and the second end 10b of the transmission line 10, respectively.

[0050] A high-voltage shield ring 192 is provided at each of the first end 10a and the second end 10b of the transmission line 10 so as to surround the tip of the conductor 101. Two high-voltage shield rings 192 may be provided at each of the first end 10a and the second end 10b of the transmission line 10. This makes it possible to suppress electric field concentration near the tip of the conductor 101 during measurement.

[0051] Furthermore, a low-voltage shield ring 194 may be provided to each of the pair of termination connection parts 120 of the power transmission line 10 so as to surround the lower fitting 124. This makes it possible to suppress electric field concentration near the lower fitting 124 during measurement.

[0052] In the power transmission line evaluation system 20 of this embodiment, the first axial end 10a of the conductor 101 of the power transmission line 10 is connected to the positive electrode 202 of the power source 200 via the charge amount measuring unit 300, as described below. This causes a high voltage to be applied to the conductor 101 of the power transmission line 10 by the power source 200.

[0053] On the other hand, a second axial end 10b of the conductor 101 of the power transmission line 10 is open.

[0054] In the present disclosure, also in the above-mentioned terminal connection part 120 and intermediate connection part 140, the metal member connected to the conductor 101 of the power cable 100, the insulating member having insulating properties similar to the insulating layer 103 of the power cable 100, and the shielding member connected to the shielding layer 105 of the power cable 100 are described as the "conductor 101," the "insulating layer 103," and the "shielding layer 105," respectively, just as in the power cable 100.

[0055] (Power Supply) The power supply 200 is, for example, connected to the above-described power transmission line 10 and configured to be able to apply a voltage between the conductor 101 and the shielding layer 105 of the power transmission line 10 .

[0056] Specifically, the power supply 200 has, for example, a positive electrode (+ electrode, high-voltage electrode) 202 and a negative electrode (- electrode, ground electrode) 204. The positive electrode 202 of the power supply 200 is connected, for example, to the conductor 101 of the power transmission line 10 (via the charge measurement unit 300 described below). The positive electrode 202 is connected to the conductor 101, for example, at a position close to the first end 10a of the power transmission line 10. On the other hand, the negative electrode 204 of the power supply 200 is grounded, for example, together with the shielding layer 105 of the power transmission line 10. With this configuration, the power supply 200 is configured to be able to apply a voltage between the conductor 101 and the shielding layer 105 of the power transmission line 10.

[0057] The power supply 200 is configured to be able to apply, for example, a voltage equivalent to the voltage applied to the transmission line 10 during actual operation of the transmission line 10, between the conductor 101 and the shielding layer 105 of the transmission line 10 being evaluated. Specifically, the power supply 200 is configured to be able to apply, for example, a DC voltage or a square-wave voltage of 10 kV or more, 100 kV or more, or 400 kV or more, between the conductor 101 and the shielding layer 105 of the transmission line 10. The term "square-wave voltage" as used herein refers to, for example, a square-wave voltage having a first voltage equal to or greater than 0 V and a second voltage that is a positive voltage higher than the first voltage. Furthermore, the power supply 200 is configured to be able to gradually increase the voltage from 0 V to the above-mentioned upper limit voltage that can be applied.

[0058] (Charge Quantity Measuring Unit) The charge quantity measuring unit (Q(t) meter) 300 is connected in series, for example, between the power source 200 and the power transmission line 10. The charge quantity measuring unit 300 is configured to measure the charge quantity Q(t), which is the integral value of the current I(t) flowing between the conductor 101 and the shielding layer 105 of the power transmission line 10 (i.e., through the insulating layer 103 of the power transmission line 10 when the power transmission line 10 is normal).

[0059] Specifically, the charge measurement unit 300 includes, for example, a capacitor 320 and a voltmeter (not shown). The capacitor 320 is, for example, connected in series between the power source 200 and the transmission line 10 and configured to accumulate charge flowing between the conductor 101 and the shielding layer 105 of the transmission line 10. The voltmeter is, for example, configured to measure (continuously at predetermined time intervals) the voltage between the electrodes of the capacitor 320 transmitted from the buffer circuit. Note that an operational amplifier (not shown) that transmits the voltage between the electrodes of the capacitor 320 to the voltmeter may be provided between the capacitor 320 and the voltmeter. When the known capacitance of the capacitor 320 described above is C and the voltage between the electrodes of the capacitor 320 measured by the voltmeter is V, the capacitor 320 satisfies Q(t) = CV. This equation allows the amount of charge Q(t), which is the integral value of the current I(t) flowing between the conductor 101 and the shielding layer 105 of the transmission line 10, to be calculated.

[0060] Hereinafter, information relating to the charge amount Q(t) determined by the charge amount measurement unit 300 will also be referred to as "charge amount data."

[0061] In this embodiment, the electric charge measuring unit 300 is connected in series, for example, between the positive electrode 202 of the power source 200 and the conductor 101 of the power transmission line 10. That is, the electric charge measuring unit 300 is disposed in the power transmission line evaluation system 20 at a position closer to the positive electrode 202 of the power source 200 than the power transmission line 10, and at a position where the electric charge measuring unit 300 has a high potential.

[0062] (Radio Unit) The radio unit 400 is configured to be able to transmit and receive various signals wirelessly.

[0063] In this embodiment, the wireless unit 400 is configured to be connected to the charge amount measurement unit 300, for example, and to be able to wirelessly transmit to the outside the charge amount data measured by the charge amount measurement unit 300. As a result, even if the charge amount measurement unit 300 is placed at a position where it is at a high potential close to the positive electrode 202 of the power source 200, the charge amount data from the charge amount measurement unit 300 can be stably acquired by the management center 60, which will be described later, through wireless communication by the wireless unit 400.

[0064] There are no particular limitations on the specific wireless communication method used by the wireless unit 400. However, the wireless communication method used by the wireless unit 400 may be, for example, a short-range wireless method based on the ZigBee (registered trademark) standard. The wireless frequency band used by the wireless unit 400 may be, for example, the 2.4 GHz band.

[0065] The radio section 400 will be described in detail later.

[0066] (Other) A battery (not shown) for driving the charge amount measuring unit 300 and the wireless unit 400, and a recording unit (not shown) for storing charge amount data may also be provided near the charge amount measuring unit 300.

[0067] (Housing) The housing 500 is configured as, for example, a metal container, and houses the charge amount measuring unit 300 and part of the wireless unit 400. The housing 500 is connected to, for example, the charge amount measuring unit 300 and the wireless unit 400 as a common reference potential (frame ground).

[0068] The housing 500 is connected, for example, between the positive electrode 202 of the power source 200 and the charge amount measurement unit 300, and is at the same potential as the positive electrode 202 of the power source 200. On the other hand, the housing 500 is not connected between the charge amount measurement unit 300 and the conductor 101 of the power transmission line 10 to be evaluated. With this configuration, it is possible to prevent a charge amount component based on floating electrostatic capacitance generated between the housing 500 and the earth from being superimposed on the measurement result of the charge amount measured by the charge amount measurement unit 300.

[0069] 1 and 4 , the management center 60 is provided, for example, at a location away from the power transmission line 10, and is configured to manage each part of the power transmission line evaluation system 20 and the transmission line 10 to be evaluated. In this embodiment, the management center 60 may be provided, for example, near the power source 200.

[0070] The management center 60 is configured to control, for example, the power supply 200 and also to control the charge amount measuring unit 300 and the wireless unit 400 through wireless communication with the wireless unit 400 .

[0071] Furthermore, the management center 60 is configured to receive, for example, a data signal from the wireless unit 400 and evaluate the state of the power transmission line 10 based on the charge amount data obtained from the data signal.

[0072] Specifically, as shown in FIG. 4, the management center 60 includes, for example, a control unit 620 and a center radio unit 640 .

[0073] The control unit 620 is configured as a general-purpose computer and includes, for example, a CPU (Central Processing Unit) 622, a RAM (Random Access Memory) 624, a storage device 626, and an I / O port 628. The RAM 624, the storage device 626, and the I / O port 628 are configured to be able to exchange data with the CPU 622. The I / O port 628 is connected (by wiring) to, for example, the center radio unit 640 and the power supply 200.

[0074] The storage device 626 is configured to store, for example, a power transmission line evaluation program, charge amount data, etc. The storage device 626 is, for example, a hard disk drive (HDD) or a solid state drive (SSD).

[0075] The RAM 624 is configured to temporarily store programs, information, etc. that are read from the storage device 626 by the CPU 622 .

[0076] The CPU 622 is configured to execute, for example, each process in a power transmission line evaluation method described later by executing a predetermined program stored in the storage device 626. The power transmission line evaluation method will be described in detail later.

[0077] The predetermined programs for executing the above-described processes by control unit 620 are installed and used in, for example, a computer configured by control unit 620. The programs may be provided by being stored in a non-transitory computer-readable storage medium prior to installation. Alternatively, the programs may be provided to the computer via center radio unit 640, for example.

[0078] The center radio unit 640 is configured to transmit and receive predetermined information or signals between itself and the radio unit 400, for example, by wireless communication conforming to the wireless communication method of the radio unit 400. Specifically, the center radio unit 640 can control the charge amount measuring unit 300 and the radio unit 400 by wirelessly transmitting various signals from the control unit 620 to the radio unit 400. Furthermore, the center radio unit 640 can obtain the charge amount data by wirelessly receiving a data signal including the charge amount data from the radio unit 400.

[0079] (2) Configuration of Radio Unit The configuration of the radio unit 400 of this embodiment will be described with reference to Figures 1 and 3. Figure 3 shows a cross-sectional view of the antenna 440.

[0080] As shown in FIGS. 1 and 3, the wireless unit 400 of this embodiment includes, for example, a signal processing unit 420, an antenna 440, and a coil 460.

[0081] (Signal Processing Unit) The signal processing unit 420 is connected to the electric charge amount measuring unit 300, for example, inside the housing 500. The signal processing unit 420 is configured to generate a data signal including the electric charge amount data obtained by the electric charge amount measuring unit 300, and to supply the data signal to the antenna 440, which will be described later.

[0082] On the other hand, the signal processing unit 420 is configured to process, for example, an external signal. Specifically, when the signal processing unit 420 receives a signal from the management center 60 via an antenna 440 (described later), the signal processing unit 420 transmits the signal from the management center 60 to the charge amount measuring unit 300 and performs predetermined processing based on the signal from the management center 60.

[0083] (Antenna) The antenna 440 is connected to the signal processing unit 420, for example, and configured to transmit a data signal generated by the signal processing unit 420 to the outside and to receive a signal from the outside.

[0084] In this embodiment, the antenna 440 is configured as, for example, a so-called sleeve antenna, and specifically includes, for example, a first conductor (center conductor) 441, an antenna insulating layer 442, a second conductor (outer conductor) 443, and an antenna sheath (protective layer) 444.

[0085] The first conductor 441 is configured as, for example, a metal wire and is connected to the signal processing unit 420. The antenna insulating layer 442 includes, for example, an insulating material and is provided so as to surround the outer periphery of the first conductor 441. The second conductor 443 is configured as, for example, a metal layer such as a metal mesh and is provided so as to be spaced apart from the first conductor 441 via the antenna insulating layer 442 and surround the outer periphery of the antenna insulating layer 442. The second conductor 443 is connected, for example, to the housing 500 which serves as a reference potential. The antenna sheath 444 includes, for example, an insulating material and is provided so as to surround the outer periphery of a portion of the second conductor 443.

[0086] Here, a portion of the first conductor 441 is exposed to the outside, for example, from an end of the antenna sheath 444 in the axial direction of the first conductor 441. On the other hand, the second conductor 443 is folded back at the end of the antenna sheath 444 in the axial direction of the first conductor 441. As a result, a portion of the second conductor 443 is exposed outside the antenna sheath 444. The exposed length of the first conductor 441 from the antenna sheath 444 is, for example, λ / 4, where λ is the wavelength of the signal generated by the signal processing unit 420.

[0087] The first conductor 441 and second conductor 443 of the antenna 440 having the above configuration make it possible to transmit the data signal generated by the signal processing unit 420 to the outside.

[0088] (Coil) The radio unit 400 of this embodiment further includes, for example, a coil (inductor, reactor) 460 .

[0089] Here, in the power transmission line evaluation system 20 of this embodiment, as described above, the housing 500 that houses the charge amount measuring unit 300 and the wireless unit 400 has a reference potential that is equipotential with the positive electrode 202 of the power source 200.

[0090] Under these circumstances, charge amount measuring unit 300 measures the voltage (potential difference) between the two electrodes that is generated by the accumulation of charge in capacitor 320. Therefore, even if one electrode of capacitor 320 and housing 500 are at a high potential, the potential difference between the two electrodes of capacitor 320 is smaller than the applied voltage of power supply 200, and therefore there is no problem in measuring the amount of charge accumulated in capacitor 320.

[0091] On the other hand, as described above, antenna 440 of radio unit 400 operates like a capacitor by having first conductor 441 and second conductor 443. In antenna 440, second conductor 443 connected to housing 500 has a high potential as a reference potential, while first conductor 441 may be in a floating state where the potential is not fixed. As a result, there is a possibility that unintended excess charge may accumulate in first conductor 441 and second conductor 443 of antenna 440.

[0092] Therefore, in this embodiment, the coil 460 is connected to the housing 500 as a reference potential, and is connected in parallel to the signal processing unit 420 and the antenna 440. That is, the coil 460 is connected to the first conductor 441 of the antenna 440 connected to the signal processing unit 420 and the second conductor 443 of the antenna 440 connected to the housing 500.

[0093] When a DC voltage or a square wave voltage is applied from the power supply 200, the frequency is zero or low, and therefore the impedance of the coil 460 is low. As a result, no potential difference occurs between the first conductor 441 and the second conductor 443 of the antenna 440. As a result, unintended accumulation of excess charge in the first conductor 441 and the second conductor 443 of the antenna 440 can be suppressed.

[0094] On the other hand, when transmitting and receiving signals using the antenna 440, the frequency is high in accordance with the wireless communication standard, and therefore the impedance in the coil 460 is high. This allows the first conductor 441 and the second conductor 443 of the antenna 440 to be considered electrically insulated. As a result, the antenna 440 can stably transmit and receive signals.

[0095] (3) Power Transmission Line Evaluation Method Next, the power transmission line evaluation method of this embodiment will be described with reference to FIGS.

[0096] 5 , the power transmission line evaluation method of this embodiment includes, for example, a power transmission line preparation step S100, a system construction step S200, a voltage application step S300, a charge amount measurement step S400, a data communication step S500, and an evaluation step S600. The power transmission line evaluation method of this embodiment may be considered as a method of using a charge amount measurement device (Q(t) meter). Hereinafter, the operation of each part of the power transmission line evaluation system 20 is controlled by a control unit 620 of the management center 60.

[0097] (S100: Power Transmission Line Preparing Step) First, a power transmission line 10 including a power cable 100 is prepared. At this time, the power transmission line 10 may be prepared in, for example, a state in which it will actually be laid on site, or a state close to that.

[0098] (S200: System Construction Step) After the power transmission line 10 is prepared, the power transmission line evaluation system 20 including the power source 200, the charge amount measuring unit 300, the wireless unit 400, and the housing 500 is constructed.

[0099] In this embodiment, the charge amount measuring unit 300 is connected in series between the positive electrode 202 of the power source 200 and the conductor 101 of the power transmission line 10 .

[0100] In this embodiment, the charge amount measuring unit 300 and part of the wireless unit 400 are housed in a housing 500. The housing 500 is connected to the charge amount measuring unit 300 and the wireless unit 400 as a common reference potential. Furthermore, the housing 500 is connected between the positive electrode 202 of the power source 200 and the charge amount measuring unit 300, making the housing 500 and the positive electrode 202 of the power source 200 equipotential.

[0101] Furthermore, at this time, in this embodiment, the coil 460 of the radio unit 400 is connected to the housing 500 as a reference potential, and is also connected in parallel to the signal processing unit 420 and the antenna 440 .

[0102] (S300 and S400: Voltage Application Step and Charge Amount Measurement Step) After the system construction step S200 is completed, the voltage application step S300 and charge amount measurement step S400 are performed simultaneously or consecutively.

[0103] The power source 200 is controlled by the management center 60 to apply a voltage V(t) between the conductor 101 and the shielding layer 105 of the power transmission line 10 using the power source 200 connected to the power transmission line 10 .

[0104] At the same time as or immediately after the start of voltage application by the power supply 200, a control signal for controlling the charge measurement unit 300 is transmitted from the management center 60 to the wireless unit 400. As a result, the charge measurement unit 300 connected in series between the power supply 200 and the transmission line 10 measures the charge Q(t), which is the integral value of the current I(t) flowing between the conductor 101 and the shielding layer 105 of the transmission line 10.

[0105] Here, an example of measuring the charge quantity Q(t) will be described with reference to FIG.

[0106] As shown in FIG. 6 , for example, a square wave voltage V(t) is applied between the conductor 101 and the shielding layer 105 of the power transmission line 10 .

[0107] When a square-wave voltage V(t) is applied, a current I(t) calculated by the following equation (1) flows between the conductor 101 and the shielding layer 105 of the power transmission line 10: I(t) = Idisp(t) + Iabs(t) + Icond(t) (1) where, Idisp(t) is the instantaneous charging current immediately after the application of the square-wave voltage V(t). Iabs(t) is the absorption current associated with the accumulation and movement of space charge between the conductor 101 and the shielding layer 105 of the power transmission line 10. Icond(t) is the conduction current (leakage current) flowing between the conductor 101 and the shielding layer 105 of the power transmission line 10.

[0108] In the charge measurement unit 300, the capacitor 320 stores the charge flowing between the conductor 101 and the shielding layer 105 of the power transmission line 10. The voltmeter of the charge measurement unit 300 measures the voltage between the two electrodes of the capacitor 320 transmitted from the buffer circuit. As a result, the charge Q(t), which is the integral value of the current I(t) flowing between the conductor 101 and the shielding layer 105 of the power transmission line 10, can be calculated using the following equation (2):

[0109]

[0110] Here, Qdisp(t) is the charge amount (electrode charge amount) due to the instantaneous charging current, and Qabs(t) and Qcond(t), which are calculated as the charge amount Q(0) at t = 0, are the absorbed charge amount and the conducted charge amount, respectively.

[0111] In this way, the charge amount measuring unit 300 can determine the charge amount Q(t), which is the integral value obtained by integrating the current I(t) after the rise of the square wave voltage V(t). Furthermore, by continuously measuring the charge amount Q(t) at predetermined time intervals using the charge amount measuring unit 300, it is possible to obtain information on the change over time in the charge amount Q(t). The charge amount data, which is information on the charge amount Q(t), is used in the evaluation step S600, which will be described later.

[0112] Once the charge amount data has been obtained in this manner, the voltage application by the power supply 200 and the measurement of the charge amount by the charge amount measuring unit 300 are terminated.

[0113] (S500: Data Communication Step) The data communication step S500 is performed when the charge amount data becomes necessary at the management center 60. For example, the data communication step S500 may be performed after the voltage application step S300 and the charge amount measurement step S400 are completed. Alternatively, for example, the data communication step S500 may be performed in real time while the voltage application step S300 and the charge amount measurement step S400 are being performed.

[0114] The data communication step S500 of this embodiment includes, for example, a request signal transmission / reception step S520 and a data transmission / reception step S540.

[0115] (S520: Request signal transmitting / receiving step) When the management center 60 needs the charge amount data, it transmits a request signal to the wireless unit 400. The wireless unit 400 receives the request signal from the management center 60 via the antenna 440.

[0116] (S540: Data transmission / reception step) When the wireless unit 400 receives a request signal from the management center 60 via the antenna 440, the signal processing unit 420 of the wireless unit 400 generates a data signal including the charge amount data measured by the charge amount measuring unit 300. After the data signal is generated, the antenna 440 of the wireless unit 400 transmits the data signal to the management center 60.

[0117] The management center 60 receives the data signal from the wireless unit 400 via the center wireless unit 640. As a result, the management center 60 acquires a data signal including the charge amount data.

[0118] (S600: Evaluation Step) When the management center 60 receives the data signal from the wireless unit 400, the management center 60 evaluates the state of the power transmission line 10 based on the charge amount data obtained from the data signal.

[0119] 6, in this embodiment, the charge quantity Qdisp(t)=Q(0) at the start of application of the square wave voltage V(t) (t=0) is calculated. In this way, the current integral charge method can clearly calculate Q(0) as the initial value of the charge quantity Q(t).

[0120] In this embodiment, the charge amount Q(tm) is calculated after a time tm has elapsed since the start of application of the square wave voltage V(t) at t=0. Furthermore, the charge amount ratio Rc (=Q(tm) / Q(0)) of the charge amount Q(tm) after the time tm has elapsed relative to the initial charge amount Q(0) is calculated. The charge amount ratio Rc allows quantitative evaluation of the change in the charge amount Q(t) over time.

[0121] The management center 60 evaluates the state of the power transmission line 10 based on at least one of the initial value Q(0) of the charge amount, the charge amount Q(tm) after the time tm has elapsed, and the charge amount ratio Rc obtained as described above.

[0122] This completes the evaluation of the power transmission line 10 of this embodiment.

[0123] (4) Summary of the Present Embodiment According to the present embodiment, one or more of the following effects are achieved.

[0124] (a) In the power transmission line evaluation system 20 of this embodiment, a power source 200 connected to the power transmission line 10 is configured to be able to apply a voltage between the conductor 101 and the shielding layer 105 of the power transmission line 10. Furthermore, a charge measurement unit 300 is connected in series between the power source 200 and the power transmission line 10, and is configured to measure a charge Q(t), which is an integral value of a current I(t) flowing between the conductor 101 and the shielding layer 105 of the power transmission line 10. Such a power transmission line evaluation system 20 can evaluate the charge characteristics of a power transmission line 10 including a power cable 100 that is actually laid in the field. This makes it possible to evaluate the state of the power transmission line 10 based on the charge characteristics of the power transmission line 10.

[0125] (b) In this embodiment, the power supply is configured to be able to apply a DC voltage or a square-wave voltage of 10 kV or more between the conductor 101 and the shielding layer 105 of the transmission line 10. This makes it possible to measure the amount of charge Q(t) of the transmission line 10 under conditions similar to those during actual operation of the transmission line 10. As a result, it becomes possible to detect in advance any malfunction of the transmission line 10 that may occur during operation of the transmission line 10 based on the amount of charge Q(t) of the transmission line 10.

[0126] (c) In this embodiment, the charge measurement unit 300 is connected in series between the positive electrode 202 of the power source 200 and the conductor 101 of the power transmission line 10. In other words, the charge measurement unit 300 is not located closer to earth than the power transmission line 10 to be evaluated, but is located closer to the positive electrode 202 of the power source 200 than the power transmission line 10, at a position where the electric potential is high.

[0127] The above-described arrangement of the electric charge measuring unit 300 makes it possible to prevent noise from the earth from propagating to the electric charge measuring unit 300, even in a situation where the noise level from the earth is high, such as in a factory outside the power transmission line evaluation system 20. This makes it possible to prevent a decrease in the measurement accuracy of the electric charge measuring unit 300 due to noise from the earth.

[0128] The above-described arrangement of the charge measurement unit 300 allows the shielding layer 105 of the power transmission line 10 to be reliably grounded to earth. This prevents the reference potential of the power transmission line 10 from becoming floating. In other words, it is possible to stabilize the grounding of the power transmission line 10.

[0129] Furthermore, due to the above-described arrangement of the electric charge measurement unit 300, even if an electrical malfunction occurs in the electric charge measurement unit 300, it is possible to suppress changes in the grounding system for the power transmission line 10. This makes it possible to suppress unexpected currents from flowing or unexpected voltages from being applied to the power transmission line 10. As a result, it is possible to suppress the influence of an electrical malfunction from affecting the entire power transmission line evaluation system 20.

[0130] In this way, the power transmission line evaluation system 20 makes it possible to stably evaluate the condition of the power transmission line 10.

[0131] (d) In this embodiment, the power transmission line evaluation system 20 further includes a wireless unit 400 that can wirelessly transmit to the outside the charge amount data measured by the charge amount measurement unit 300. As a result, even if the charge amount measurement unit 300 is placed at a position close to the positive electrode 202 of the power source 200 and at a high potential, the charge amount data can be obtained wirelessly in a stable and safe manner.

[0132] (e) In this embodiment, the housing 500 that houses the charge amount measuring unit 300 and part of the wireless unit 400 is connected between the positive electrode 202 of the power source 200 and the charge amount measuring unit 300, and is at the same potential as the positive electrode 202 of the power source 200.

[0133] Here, when the metal housing 500 is not grounded, floating capacitance may occur between the housing 500 and the ground. For example, when the housing 500 is connected between the electric charge measurement unit 300 and the conductor 101 of the power transmission line 10, a capacitor formed by the conductor 101 and the shielding layer 105 of the power transmission line 10 to be evaluated and a floating capacitor formed by the housing 500 and the ground are arranged in parallel at a position closer to the ground than the electric charge measurement unit 300. Therefore, the measurement result by the electric charge measurement unit 300 includes not only a charge component based on the capacitance generated between the conductor 101 and the shielding layer 105 of the power transmission line 10 to be evaluated, but also a charge component based on the floating capacitance generated between the housing 500 and the ground. As a result, the accuracy of the electric charge measurement by the electric charge measurement unit 300 in measuring the electric charge of the power transmission line 10 may be reduced.

[0134] In contrast, in the present embodiment, the housing 500 is connected between the positive electrode 202 of the power source 200 and the charge amount measurement unit 300, so that only the capacitor formed by the conductor 101 and the shielding layer 105 of the transmission line 10 to be evaluated is disposed at a position closer to the earth than the charge amount measurement unit 300. This makes it possible to prevent a charge amount component based on stray capacitance occurring between the housing 500 and the earth from being superimposed on the measurement result of the charge amount measured by the charge amount measurement unit 300. As a result, it is possible to prevent a decrease in the measurement accuracy of the charge amount of the power transmission line 10 by the charge amount measurement unit 300.

[0135] (f) In this embodiment, the housing 500 that houses the charge amount measuring unit 300 and part of the radio unit 400 has a common reference potential that is equipotential with the positive electrode 202 of the power supply 200. Under these circumstances, the coil 460 of the radio unit 400 is connected to the housing 500 as the reference potential, and is also connected in parallel to the signal processing unit 420 and the antenna 440.

[0136] As described above, when a DC voltage or a square wave voltage is applied from power supply 200, the impedance of coil 460 is low. This makes it possible to prevent unintended accumulation of excess charge in antenna 440. As a result, it becomes possible to prevent wireless communication failures caused by charge accumulation in antenna 440 of radio unit 400.

[0137] On the other hand, as described above, when signals are transmitted and received by the antenna 440, the impedance of the coil 460 becomes high. This allows stable transmission and reception of signals between the antenna 440 of the wireless unit 400 and the management center 60.

[0138] In this way, by stably performing wireless communication using the wireless unit 400 having the coil 460, it becomes possible to stably evaluate the state of the power transmission line 10.

[0139] <Other Embodiments of the Present Disclosure> Although the embodiments of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the present disclosure.

[0140] In the above embodiment, the management center 60 is connected to the power source 200 by wiring from the I / O port 628 and is configured to control the power source 200, but the present disclosure is not limited to this. The management center 60 may also be configured to control the power source 200 by wireless communication using the center wireless unit 640.

[0141] In the above embodiment, the case has been described in which the management center 60 is configured to control the power source 200 and also to control the charge amount measuring unit 300 and the wireless unit 400 via wireless communication with the wireless unit 400, but the present disclosure is not limited to this case. The management center 60 may, for example, separately have a power supply control unit that controls the power source 200 and a measurement system control unit that controls the charge amount measuring unit 300 and the wireless unit 400 via wireless communication with the wireless unit 400.

[0142] In the above embodiment, the antenna 440 is configured as a sleeve antenna, but the present disclosure is not limited to this. The antenna 440 may be configured as, for example, a dipole antenna.

[0143] In the above embodiment, a case has been described in which a rectangular wave voltage is applied to the power transmission line 10 to measure the amount of charge in the voltage application step S300 and the charge amount measurement step S400, but the present disclosure is not limited to this case. In the voltage application step S300 and the charge amount measurement step S400, the amount of charge in the power transmission line 10 may be measured while increasing the DC voltage applied to the power transmission line 10 in a stepwise manner.

[0144] <Supplementary Notes> The following supplementary notes are provided regarding aspects of the present disclosure. The aspects referenced by the numbers in brackets [ ] to which the supplementary notes below depend correspond to the aspects described in <Embodiments of the present disclosure>.

[0145] [8] The power transmission line evaluation system according to [6], wherein the antenna has a first conductor connected to the signal processing unit and a second conductor connected to the housing, the second conductor being spaced apart from the first conductor and serving as the reference potential, and the coil is connected to the first conductor and the second conductor of the antenna.

[0146] [9] The power transmission line evaluation system according to any one of [4], [5], [6], and [8], further comprising a management center that receives the data signal from the wireless unit and evaluates a state of the power transmission line based on the charge amount data obtained from the data signal.

[0147]

[10] The power transmission line evaluation system according to [9], wherein the management center is configured to control the power source and to control the charge amount measuring device and the wireless unit by wireless communication with the wireless unit.

[0148]

[11] The power transmission line evaluation system according to [9] or

[10] , wherein the management center is configured to transmit a request signal to the radio unit, and the radio unit is configured to transmit the data signal including the charge amount data to the management center when the request signal is received from the management center via the antenna.

[0149] REFERENCE SIGNS LIST 10 power transmission line 10a first end 10b second end 20 power transmission line evaluation system 60 management center 90 insulating material evaluation system 100 power cable 101 conductor 103 insulating layer 105 shielding layer 120 terminal connection part 122 porcelain tube 124 lower metal fitting 140 intermediate connection part 192 high voltage part shield ring 194 low voltage part shield ring 200 power supply 202 positive electrode 204 negative electrode 300 charge amount measuring part 320 capacitor 400 radio part 420 signal processing part 440 antenna 441 first conductor 442 antenna insulating layer 443 second conductor 444 antenna sheath 460 coil 500 housing 620 control part 622 CPU 624 RAM 626 storage device 628 I / O port 640 Center radio unit 910 Sheet 912 First electrode 914 Second electrode 916 Guard electrode 920 Power supply 922 Switch 924 Switch 930 Charge amount measuring unit 932 Capacitor 934 Switch

Claims

1. A power transmission line evaluation system comprising: a power source connected to a power transmission line including a power cable having a conductor, an insulating layer, and a shielding layer in this order in the radial direction of the conductor, and capable of applying a voltage between the conductor and the shielding layer; and a charge amount measuring unit connected in series between the power source and the power transmission line, and measuring the amount of charge, which is the integral value of the current flowing between the conductor and the shielding layer of the power transmission line.

2. The power transmission line evaluation system according to claim 1, wherein the power source is configured to be able to apply a DC voltage or a square wave voltage of 10 kV or more between the conductor and the shielding layer of the power transmission line.

3. A power transmission line evaluation system according to claim 1 or claim 2, wherein the power source has a positive electrode connected to the conductor of the power transmission line and a negative electrode grounded to earth together with the shielding layer of the power transmission line, and the charge measurement unit is connected in series between the positive electrode of the power source and the conductor of the power transmission line.

4. The power transmission line evaluation system according to claim 3, further comprising a wireless unit connected to the charge amount measuring unit and capable of wirelessly transmitting the charge amount data measured by the charge amount measuring unit to an external device.

5. The power transmission line evaluation system according to claim 4, further comprising a housing that houses the charge measurement unit and part of the radio unit and is connected to the charge measurement unit and the radio unit as a common reference potential, the housing being connected between the positive electrode of the power supply and the charge measurement unit and configured to be at the same potential as the positive electrode of the power supply.

6. The power transmission line evaluation system according to claim 5, wherein the radio unit comprises: a signal processing unit connected to the charge amount measuring unit within the housing, generating a data signal including the charge amount data and processing signals from outside; an antenna connected to the signal processing unit, transmitting the data signal to the outside and receiving the signals from outside; and a coil connected to the housing as the reference potential and connected in parallel to the signal processing unit and the antenna.

7. A method for evaluating a power transmission line, comprising the steps of: preparing a power transmission line including a power cable having a conductor, an insulating layer, and a shielding layer in this order in the radial direction of the conductor; applying a voltage between the conductor and the shielding layer using a power source connected to the power transmission line; and measuring the amount of charge, which is the integral value of the current flowing between the conductor and the shielding layer of the power transmission line, using a charge measurement unit connected in series between the power source and the power transmission line.

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