All measures to improve the reliability of conventional DC transmission are still effective for improving the reliability of UHV DC transmission, and should be further strengthened. These mainly include: reducing the failure rate of components; adopting reasonable structural designs, such as modularization and open architecture; extensively applying redundancy concepts, such as parallel redundancy in control and protection systems and water cooling systems, and series redundancy in thyristors; strengthening equipment condition monitoring and self-diagnostic functions.
In response to problems existing in conventional DC projects, such as weaknesses that have caused pole or bipolar outages in DC systems, including station power supply systems, converter transformer protection relays, and single-component failures in DC protection systems, measures will be taken to improve these aspects in the design and construction of UHV DC transmission systems. In addition, training for operation and maintenance personnel will be strengthened, and the stock of spare parts for vulnerable components will be appropriately increased.
To improve the reliability of UHV DC transmission projects, the design principles can also ensure maximum independence between each pole and between each converter within a pole, avoiding fault propagation between them. This independence, in addition to the main circuit, also needs to consider: valve hall layout, power supply systems, water supply systems, cable trenches, control and protection systems, etc.
