Power cable has been used widely for power supply in the urban area. This article describes the importance, present status and future perspectives about the technology of power cable.

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The material recycling of the insulation of cross-linked polyethylene cable was studied. We successfully obtained thermoplastic recycled polyethylene from silane cross-linked polyethylene by using chemical reaction in supercritical alcohol.
Here, the continuous process for the recycling of silane cross-linked PE using supercritical alcohol was constructed. The mechanical and electrical properties of recycled polyethylene satisfied the requirement of the cable insulation. These results indicate that the cable to cable and wire to wire recycling of silane cross-linked polyethylene will possibly be accomplished by supercritical technology using extruder.
Moreover the environmental effect of this technology was evaluated by the amount of the carbon dioxide generated from the continuous process. These results indicate that recycling method using supercritical alcohol was useful for the reduction of the environmental pollution.

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A detection system for cables damaged by lightning stroke is developed using videos obtained from an aerial inspection of transmission lines. The system detects arc marks and cut wires. Arc marks are detected by statistical analysis of the brightness of a cable image. Cut wires are detected by comparing the contour of the cable, which was obtained with a video camera, with its ideal shape. The developed system was applied to videos of 20 cases, which included a damaged cable. The total number of images was 6000. The system could detect all types of cable damage. In 97.8% of images, the system worked well, making it suitable for aid in the inspection of transmission lines.

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Corona discharge may cause audible noise, and it is frequently generated from wet conductors of high-voltage AC overhead transmission lines. Audible noise arises more easily from new conductors that have lubricating oil on their surface than from aged conductors. In this paper, the corona characteristics, particularly audible noise, of conductors having various wetting properties is presented developing a corona-free conductor for AC overhead transmission lines. It was found that a conductor having a super-hydrophobic surface exhibited a minimized audible noise level, but it does not have sufficient durability for practical application. Furthermore, a conductor having a super-hydrophilic surface made by thermal spraying of TiO₂ showed good performance regarding the suppression of audible noise. The thermal spraying of TiO₂ seems to be an effective processing technique that has sufficient durability for practical application.

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Water tree is one of the degradation aspects of XLPE cables used for under-ground distribution or transmission lines. We have developed the loss current method using 3rd harmonic in AC loss current for cable diagnosis. Harmonic components in loss current arise as a result of the non-linear voltage-current characteristics of water trees. We confirmed that the 3rd harmonic in AC loss current had good correlation with water tree growth and break down strength. After that, we have applied this method to the actual 66kV XLPE cable lines. Up to now, the number of the application results is more than 130 lines.
In case of cable lines terminated at gas-insulated switchgear (GIS), we have to remove the lightning arrestor (LA) and the potential transformer (PT) out of the test circuit. The reason is that we are afraid that each of LA and PT disturbs the degradation signal from cable lines. It takes extra time (1 or 2 days) and costs more to remove LA and PT in GIS out of a circuit. In order to achieve easy and reasonable diagnosis, we have developed a new method for cable lines terminated at GIS, by utilizing a technique, which enables to reduce signal of LA and PT from disturbed signal of cable lines. We confirmed the effect of the new method by experiments with actual cables.

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Recently, composite insulators have been increasingly employed mainly from the economic viewpoint. We have been developed new type outdoor termination with composite insulator, which can be installed horizontally on the steel tower, in order to reduce the construction cost. In this outdoor termination, SF₆ gas is filled in the composite insulator and a cold shrinkable pre-molded rubber unit is applied instead of the combinational use of rubber-molded stress relief cone, epoxy resin insulator and spring unit. The application of composite insulator, SF₆ gas and cold shrinkable pre-molded rubber unit lights the total weight and makes it possible to install horizontally on the tower.
The composite insulator type outdoor termination for 77kV XLPE cable has already applied as commercial use and enabled to reduce the construction cost of power transmission lines. A 154kV new type outdoor termination has been developed and successfully completed the initial electrical test.
This paper describes the design and performance of both 77kV and 154kV new type outdoor termination, and the follow-up survey of 77kV outdoor termination in the commercial power transmission line.

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The joint of XLPE and Oil-filled cable is necessary and indispensable to meet the switch needs in replacing the oil-filled cable along with making of the underground power transmission system. However, because only connected space of the joint for the oil-filled cable is secured in narrow space of the existing manhole, the problem might be brought up to construction in the structure of the old model from the size and weight. Then, the compact joint that had reduced by about 80% of a structural size so far was developed by applying the high electric field technology according to making of EHV XLPE cable and the joint.

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A High Temperature Superconducting (HTS) cable has a bulk power transmission capacity as a candidate for the replacement of the aged cable and/or for the increase of the power transmission capacity, and its diameter is prefer to be smaller than inner diameter of the duct for the existing cables. To reduce the diameter of HTS cable, the cold dielectric (CD) type electrical insulation in which a cable core is immersed into liquid nitrogen (LN₂) should be adopted, and the thickness of its electrical insulation layer has to be optimized. Since a partial discharge (PD) in the electrical insulation layer of the CD type HTS cable is considered as a major causes for the aging of the insulation layer, PD-free design must be adopted for the CD type HTS cable.
This paper describes a design method for the electrical insulation layer of the CD type HTS cable adopting the PD-free design under ac stress, based on the experimental results such as a PD inception stress (PDIE), an impulse breakdown stress, and PD extinction characteristics under ac stress superimposed with an impulse stress. Moreover, the proposed design method was applied to a 500-m HTS cable and was verified by a field test.

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Water tree is one of the unique type of deterioration in XLPE cable, which is the primary cause of aging breakdown. Water tree, which bridges between conductor and shield, can be detected easily, such as DC leakage current method. However, 22kV class or above XLPE cable, most of breakdown occurs before water tree bridges, and there used to be no effective method for detecting non-bridged water tree.
In this paper, we've found residual charge in harmful water tree relaxes quickly with AC voltage application. To detect this type of residual charge, we've developed new diagnosis method with “direct-detect type residual charge method" and “short-term voltage up-down method". This new method found to be very effective for diagnosing over 22kV class XLPE cable lines.

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We have succeeded in development of two type nano-composite enameled wires in 2000. One is the inverter surge resistant enameled wire using polyester-imide/silica nano-composite material prepared by original sol solution mixture method, and the other is the super heat resistant enameled wire using polyimide/silica nano-composite material made by sol-gel method.
This report is mainly introduced in properties of the two type nano-composite products, and newly developed polyamide-imide/silica nano-composite inverter surge resistant enameled wire.

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When a new UHV substation is built in an urban region, generally, an existing underground transmission line shall be diverted and drawn into the new substation. Compared with above mentioned construction method, enormous cost reduction of switching facilities and cable construction is expected with applying a Y-Branch Joint (YJ) which is able to be a 3-way joint. The YJ has already been applied for 154kV class circuit, however, it has not been investigated for 275kV class circuit. Since both XLPE and Fluid-Filled cable are presently used in 275kV class underground cable line, an universal design YJ for both cables have been investigated. The YJ was applied a compact design which was based on our sophisticated electrical stress control technology for 500kV prefabricated type joint. Furthermore, the design was based on its prefabricated assembling technology. The YJ was verified its electrical and mechanical performance as 275kV cable joint by completion of its assembling test and a long term electrical test.

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As the deregulation in electric power industry has advanced in many countries, a spot market and a future market of the electric energy have already been formulated. In Japan, the foundation of a day-ahead spot market is scheduled for the 2005 fiscal year. This paper presents a method to evaluate the expected profit and risk of electric power supplier considering both of spot market and bilateral market. In this paper, Vasicek model is used as a fluctuation in spot price and demand of bilateral market, additionally Value at Risk (VaR) is used as a risk index.

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A fuzzy logic approach is proposed for identification and classification of faults based on records obtained during impulse tests on transformers. The outputs of three filters form the basis of identification. Experiments are performed on a physical lumped parameter model of a winding to identify breakdown, partial discharge and the presence of non-linear element within the winding. The location of breakdown can also be estimated.

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The aim of this letter is to show that the unstable equilibrium point of the Japanese standard one-machine infinite-bus system model is eliminated by adding a simple nonlinear complementary control input to the AVR, and then the critical clearing time of the system can be more enhanced in comparison with the PSS by introducing the proposed nonlinear generator control.

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Overvoltages as lightning surges and/or switching surges will affect power apparatuses and electric appliances, which make them of deterioration. However, recent AC testing apparatuses haven't been functions generating an impulse voltage. Moreover, the apparatuses with controlling an impulse voltage haven't been utilized except the low voltage function generator. Therefore, an AC phase controlled testing apparatus with an impulse voltage (0.8/6μs) has been developed in order to elucidate mechanism of the degradation in insulating materials with a AC power supply simulating the overvoltages.

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