Third Generation Manufacturing System Developed by Fujikura
As a pioneer in this field, Fujikura has been developing systems for the manufacture of extra high voltage XLPE cables since it first began supplying XLPE cables in 1960.
Developed by Fujikura as an improvement of its advanced second generation system, the computerized and automatically controlled third generation system is a ultra-clean system.
The First Generation
The first generation of XLPE cables, which have been used in commercial applications since the early 1960's, were manufactured using both the steam-curing-water-cooling system and the tandem extrusion system, in which the conductor shielding layer, insulation and insulation shielding layer are extruded from two cross-heads. Cables manufactured under these systems had many micro-voids in the insulation and irregularities between the insulation and the semi-conducting layer.
The Second Generation
The second generation system, commonly known as the "dry curing system," was developed during the 1970's specifically for the manufacturing of extra-high voltage cables, the electrical operating stress of which was much higher than 66 kV, as well as lower voltage cables. Fujikura's advanced second generation system offers the following features to assure highly reliable 275 kV XLPE cables.
A perfectly dry curing system utilizing silicone oil as its curing and cooling medium makeing possible the manufacture of void-free insulation.
A three-layer common extruding process by which the semi-conducting layer and insulation are extruded from one cross-head, makes possible the manufacture of boundaries free from irregularities.
A super-clean-material supply system that blocks contamination greater than 100 µm permits the manufacture of contamination-free insulation.
The Third Generation
The third generation system, which we feel is the ultimate stage of development, is specifically intended for the manufacture of large quantities of XLPE cables in the 230 kV to 500 kV class. These extra-high voltage XLPE cables require a stable and extra-high quality manufacturing process to prevent voids, irregularity and contamination. The latest technology has been incorporated into the system to meet those requirements, including:
Automatically controlled or computer-monitored systems guarantee high quality XLPE cables under stable manufacturing conditions.
Ultra-super-clean material supply system guarantees contamination free insulation including contaminations larger than 50 µm through the use of ultra-super-clean compounds and by converting the material supply room and the extruder room into 1,000 Class or 10,000 Class clean rooms. The quality of the contamination-free insulation can be perfectly checked by an automatic contamination detector in which a laser beam or a magnetic-type metal detector is used.
Manufactured cables are automatically and continuously monitored and their diameters, eccentricity and surface roughness are constantly checked by computer supported automatic measuring equipment.
Applied Automatic Measuring or Detecting Equipment
High quality XLPE cables are guaranteed by Fujikura's automatic measuring or detecting equipment shown below.
Automatic Contamination Detection by Laser Beam
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Crosslinked-polyethylene to be used as insulation is extruded in sheet form permitting automatic inspection for contamination by means of a laser beam. This mechanism is sensitive enough to detect contaminations more than 40 µm.
Metal Detector
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This detector makes use of magnetic field distortion to detect metal, assuring the absence of metal fragments larger than 70 µm in the material.
Automatic Diameter Measuring Equipment
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This device continuously measures the longitudinal outside diameter of the cable core with the aid of a laser beam that can oscillate 180¼.
The maximum, minimum and average outside diameter of the cores of the extruded cables can be measured up to a resolution of 0.01 mm.
Automatic Eccentricity Measuring Equipment
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Using magnetic field distortion, this equipment detects the centers of conductors and continuously measures the circumferential distance between the surface of the conductors and the detector section that rotates in contact with the cable core. This equipment thus makes it possible to automatically detect the rate of eccentricity of cable cores.
Automatic Detector of Surface Condition of Extruded Core
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This device uses a high-resolution-camera which photographs the illuminated cable surface and identifies surface irregularities and scratches by their differences in brightness, then processes the photographed image. This device automatically and continuously detects any scratches on the cable core surface.
Automatic Semi-conducting Tape Tear Detector
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This device continuously detects tears in semi-conducting tape by monitoring changes in a laser beam that is reflected from the semi-conducting tape wound around the conductors.
History of the High Voltage XLPE Cable
The XLPE cable has been expanding to the higher voltage and the higher electrical stress type for commercial use based on the manufacturing system developed from the first generation to the third generation.
[Note below graph]
High-voltage XLPE cables are designed based on the minimum breakdown value (the stress under which the statistical breakdown probability reaches zero) derived by statistically determining breakdown values over a large dispersion. The improvement of design stress directly translates into improvement of the statistical minimum breakdown stress of high voltage XLPE cables.
Outstanding Features of Fujikura XLPE Cables
Since first supplying XLPE-insulated cable in the 1950Õs, FUJIKURA has been supplying substantial quantities to satisfied customers.
The total length of 66kV and higher voltage XLPE cables supplied by FUJIKURA reached 4,000 km by the end of 1991. The first delivery of 110 kV XLPE cable was made in 1972; since then, substantial lengths of 110 kV and higher voltage XLPE cables supplied by FUJIKURA have demonstrated trouble-free operation.
In 1982, FUJIKURA supplied and installed 275 kV XLPE cables for the worldÕs longest cable route with this voltage.
Cable Construction
Copper-tape-shielded Cables
Copper-tape-shielded cables are applied only to small earth fault current capacity circuits, under soft conditions. These are the most economical and most easily handled cables.
Wire-shielded Cables
Wire-shielded cables are easy to handle and have a large earth fault current capacity. They may require a waterproof layer over the wire shield layer, depending on laying conditions.
Triplex-type Cables
Triplex-type cables, comprising three sheathed cores, can be supplied to meet your requirements.
Aluminum-sheathed Cables
Aluminum-sheathed cables, having a large earth fault current capacity in their sheaths, offer protection from water and mechanical damages. Corrugated aluminum-sheathed cables are conventionally used for direct burying of cables owing to their flexibility and weight as well as their resistance to damaging substances.
Stainless Steel-sheathed Cables
Stainless steel-sheathed cables offer protection from water and mechanical damages. Loss in metallic sheath is lower than that in aluminum-sheathed cables. To increase protection from an earth-fault current, copper wire shielding is applied under the sheath. Mechanical properties of this type of cable are the same as aluminum-sheathed cables.
Lead-sheathed Cables
Lead-sheathed cables are used in heavy-duty, anti-chemical cables. Lead, a metal possessing good anti-chemical characteristics, protects cable insulation completely from water and damaging substances. Care should be taken, however, because the lead sheath is not resistant to mechanical shocks.
Large Current Rating Cables
XLPE cables with huge conductor sizes have been developed for the large current rating cable. Since the huge conductor size imparts a large skin-effect factor to the conductor, actual AC conductor resistance is not decreased as much as by conventional huge conductors. The strand-insulated conductor with cupric oxide film, newly developed by FUJIKURA, has a very low skin-effect factor and a high current rating capacity, as shown in the diagrams below.
Cables with Water-proof Layer
These cables have a water-proof layer formed from laminated lead or aluminum tape under the PVC sheath to avoid water penetrating into the cable insulation through the PVC sheath. Such cables have a higher degree of water-proof properties and higher reliability. Cables with a water-proof layer are more easily handled compared with metallic sheathed cables.
Extruded Insulating Submarine Cables
To realize large capacity and long distance electric power transmission, FUJIKURA has continued enthusiastic development works since 1915 when our first submarine cable was installed. Especially, for DC submarine cables, FUJIKURA developed a special insulating material. This material allows us to manufacture very long cable in one process temperatures close to XLPE cables. Extruded insulated submarine cables enable the manufacture of very long transmission lines, with larger transmission capacities and higher reliability.
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