Mamoru Kanaoka

Development of 500-kV XLPE cables and accessories for long distance underground transmission line-Part I: insulation design of cables

This paper discusses the results of a basic study for the development of 500 kV XLPE power cables. The authors have established that the factors that decide the performance of todays XLPE cables are impurities in the insulator and protrusions on the semiconductive layer, and that the insulation performance of XLPE power cables is determined by the size of these defects. In model tests of XLPE power cables, the minimum insulation breakdown stress of cables was determined, to set the design values for 500 kV XLPE cable. As a result, it was found that it is possible to design cables having an insulation thickness of 25 mm. >

Development of 500-kV XLPE cables and accessories for long distance underground transmission line. III. Electrical properties of 500-kV cables

500-kV XLPE-insulated cable with an insulation thickness of 27 mm has been developed for long-distance transmission lines. Basic studies on 500-kV XLPE cable have shown that contaminants in the insulation may be the factor determining electrical performance. This hypothesis is justified by the good correlation obtained between statistical estimations of the size of the largest contaminant in the insulation and the electrical characteristics of full-sized cables. Voltage-withstand and long-term tests have confirmed the design values for minimum breakdown stress, for AC and impulse voltage, and for the degradation coefficients.

Development History of HVDC Extruded Cable with Nanocomposite Material

In this paper, the outline of the development history of HVDC cable with nanocomposite material is introduced. Nano-sized MgO-filler added into XLPE, which had been developed for HVDC cable insulation, was not investigated from the view point of nanocomposite material until 2001. Since then, nano-scale observation of the dispersion state of nano-sized MgO-filler in HVDC cable insulation has been carried out. It has been found that the dc material, which had been developed for 500 kV dc cable, is XLPE/MgO nanocomposite material in which nano-sized MgO homogeneously dispersed in nano-scale

Impulse breakdown superposed on ac voltage in XLPE cable insulation

This paper discusses tree inception and breakdown voltage characteristics of XLPE cable insulation subjected to impulse voltages superimposed on ac voltage. The tree initiation tests were performed on laboratory-molded specimens equipped with needle electrodes, whereas the breakdown tests were conducted on a full-sized cable. The impulse tree initiation stress was found to be dependent on the magnitude of the pre-applied ac stress and the relative polarities of the impulse and the ac peak at the instant of their superposition. Although the impulse polarity has an effect on the tree inception, the general behavior is that the tree inception stress always decreases with an increase of the pre-applied ac stress. This phenomenon is discussed in terms of the space charge effect and the influence of the impulse voltage application itself. The impulse strength of a full-sized cable insulation was found to be independent of the pre-applied ac stress as long as that stress did not exceed the operating stress of a 500 kV cable insulation. However, subjecting cable insulation to higher ac stresses before impulse application caused a reduction of its breakdown strength as compared with the insulation without ac prestressing.

Influence of defects on insulating properties of XLPE cable

The influence of defects on the insulating properties of XLPE (cross-linked polyethylene) cables was studied using XLPE cables containing artificial defects. It was confirmed that the AC breakdown strength of the cables decreases with the increase of void size, while the existence of voids does not have any effect on impulse breakdown strength. The contaminants and the protrusions decrease both AC and impulse breakdown strengths. The value of the life exponent, n, of the V-t characteristics of the XLPE cable containing voids was estimated to be smaller than that of the cables containing contaminants or protrusions. In addition to to the influence of those defects on initial and long-term performance of the cables, the influence of impulse voltage on the long-term performance of the cable, together with the behavior of the space charge accumulated around the defects, was investigated. It was found that impulse voltage greatly affects the long-term performance of cables containing voids.<<ETX>>

Development of 500 KV Cross-Linked Polyethylene Insulated Power Cable

A 500kV cross-linked polyethylene (XL PE) insulated power cable with conductor size of 2000 mm2 and insulation thickness of 35 mm has been designed and developed for the first time in the world.

Measurements on the frozen strain in XLPE insulated cables using thermo mechanical analysis

This study is presented on the frozen strain in XLPE measured by means of a thermomechanical analysis (TMA). The magnitude of the strain in XLPE insu lated cables ranges from 2 to 8 % and the cable insulation is stressed in tension for the axial and azimuthal directions and compression for the radial direction. Thermomechanical properties of XLPE are also measured, which are indispensable to evaluate strain distribution.

DC characteristics of cable insulating materials (part 1)

DC characteristics of cross-linked polyethylene (XLPE) are influenced by peroxide decomposition products and antioxidants. The former increases space charge accumulation and decreases volume resistivity, while the latter increases space charge accumulation. DC breakdown strength of a lowdensity polyethylene (LDPE) cable without additives is higher than that of a XLPE cable.

Development of 500-kV XLPE cables

A 500-kV XLPE insulated cable with an insulation thickness of 27 mm has been developed for long-distance transmission lines. Basic studies on the 500-kV XLPE cable have shown that contaminants in the insulation may determine electrical performance. This hypothesis is justified by the good correlation obtained between statistical estimations of the size of the largest contaminant in the insulation and electrical characteristics of full-size cables. Voltage-withstand and long-term tests have confirmed design values for minimum breakdown stress, ac and impulse voltage, and degradation coefficients.