SUMMARY The long‐term dc properties of DC‐XLPE insulation materials, which have been developed for dc use, were investigated. It was found that the lifetime of DC‐XLPE under dc voltage application is extended by the addition of nano‐sized filler. The time dependence of the space charge distribution at 50 kV/mm was observed for 7 days. Almost no accumulation of space charge in DC‐XLPE was found. The 250‐kV DC‐XLPE cables and accessories were manufactured and subjected to a type test and PQ test for use in the Hokkaido–Honshu dc link facility owned by the Electric Power Development Co., Ltd. These tests were performed under conditions that included a polarity reversal test for line commutated converter (LCC) systems as recommended in CIGRE TB 219. The test temperature was 90 °C. The type test and PQ test were successfully completed. The DC‐XLPE cable and accessories were installed in summer 2012 for the Hokkaido–Honshu dc link. After the installation of the dc extruded cable system, a dc high‐voltage test at 362.5 kV (=1.45 PU) for 15 min was successfully completed in accordance with CIGRE TB 219. This dc extruded cable system was put into operation in December 2012 as the world's highest‐voltage extruded dc cable in service and the world's first dc extruded cable for a LCC system including polarity reversal operation.

No abstract

No abstract

formation of space charges. One is interfacial polarization due of a tree channel, and the other is carrier injection from the tree tip at ne (XLPE) cables are used in wet ades as a result of water-tree forwater trees have been proposed, nent is measured under ac voltage such as the one where t The authors have countries other than Japan Figure 1. A simple two-layered dielectric as model to consider the difference in the recorded space charge profiles induced by charges existing in different media.that the pulsed electrical perturbation exerts the same Lorentz forces on all the resident charges and that a well-defined acoustic pressure pulse is generated from each charge. As a simple example, let us assume that there exists a two-layered dielectric with its boundary parallel to the two electrodes. One can find easily that the Lorentz force is reciprocally proportional to the permittivity of the dielectric in which the charge exists, on the condition that the electric field is only dependent on the permittivity and not on the conductivity. For a PWP system, let us assume that a thin uniform charge layer of density X exists in parallel with the two electrodes as shown in Figure 1. One can find that the dielectric flux densities, D A entering the electrode A and DB entering the electrode I 1070-9878/98/ $3.00 0 1998 IEEE

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.