News from Japan

To address the swift expansion and critical demand for renewable energy, high voltage direct current (HVDC) electric power interconnections between power grids, nations, and even continents are set to assume a greater significance in ensuring a dependable and resilient power supply than they did in the previous decade. For instance, the inaugural 400-kV DC interconnection, linking Belgium and the UK using cables insulated with cross-linked polyethylene (XLPE), was established in 2019 [1] and has been operational to accommodate fluctuating power requirements, particularly in the UK. This HVDC link between Belgium and the UK, called the NEMO link, was constructed using innovative voltage source converters (VSC). On the other hand, numerous 350- to 450-kV HVDC systems employing conventional line-commutated converters (LCC) remain in the world, and some have been operated for over 25 years. In such LCC HVDC systems, cables insulated with oil-impregnated paper, such as self-contained fluid-filled (SCFF) or mass-impregnated (MI) cables, are used. However, some have deteriorated after a long service due to malfunctions such as oil migration and fatigue fracture of lead sheaths around insulation caused by heat cycles. In general, LCC, probably receiving lighter external stresses than undersea cables, seem to be more robust and require less maintenance than cable systems. Consequently, replacing outdated paper-insulated cables with XLPE cables is a beneficial upgrade, while keeping the same converter.