On December 20, 2017, the world’s first mechanical HVDC circuit breaker was successfully installed in the ±160 kV Nanao multi-terminal flexible DC transmission system by China Southern Power Grid. This marked a significant breakthrough as it was the first fully self-developed mechanical HVDC circuit breaker specifically designed for flexible DC systems. The successful deployment represents a major milestone in China's ongoing efforts to innovate and lead in high-voltage direct current (HVDC) technology. The project was part of the first batch of "Made in China 2025" landmark projects under the National Energy Administration. It utilized an integrated "production, learning, research, and application" model, enabling rapid fault clearance in complex environments. Developed jointly by China Southern Power Grid, Huazhong University of Science and Technology, and Siyuan Electric Co., Ltd., the 160 kV mechanical HVDC breaker employs coupled high-frequency artificial zero-crossing technology, allowing bidirectional current interruption. With a breaking capacity of 0–9 kA and a response time of about 3.5 milliseconds, it is highly reliable and efficient. Despite harsh conditions such as salt, humidity, and strong winds, the compact design—occupying only 34 square meters—reaches international advanced standards. This innovation marks the first real-world application of a mechanical HVDC circuit breaker globally. By developing its own advanced topology, the project eliminated intellectual property risks and overcame traditional challenges like high-voltage energy storage and rapid triggering. This achievement turned a long-standing dream into reality, offering a new path for high-voltage DC current interruption. In terms of technical and economic benefits, the 160 kV mechanical HVDC breaker uses mature, domestically produced components, ensuring high reliability, low loss, and cost-effectiveness. Its small footprint and direct outdoor installation significantly reduce construction and maintenance costs, making it ideal for flexible DC grid development. Through the Nanao multi-terminal flexible DC platform, the project team solved critical issues related to fast fault location and isolation. The system can now locate and isolate faults within 2 milliseconds, greatly improving the flexibility and reliability of the network. This advancement addressed previous limitations in on-line switching and fault removal, enhancing overall system performance. China Southern Power Grid has consistently prioritized science and technology innovation, achieving global leadership in UHV DC, flexible DC, and large AC/DC power grids. By implementing key projects, the company is driving the development of "Made in China" and advancing the new equipment industry. The success of the 160 kV mechanical HVDC breaker not only supports renewable energy integration but also sets a benchmark for future DC grid technologies.

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