China's first domestically developed ±800 kV flexible DC wall bushing has been successfully commissioned.

On June 11, at the Liuzhou Converter Station of the Wudongde Power Transmission to Guangdong and Guangxi UHV Multi-Terminal Flexible DC Demonstration Project (shortened as the “Kun-Liu-Long DC Project”), the first ±800 kV flexible DC wall bushing independently developed by China Flexible DC Wall Bushing Manufacturer was successfully energized and has been operating stably. The commissioning of this project has drawn significant attention from major mainstream media outlets.

The successful operation of the ±800 kV flexible DC wall bushing signifies that China has broken through foreign technological blockades in the field of UHV flexible DC wall bushings and filled the domestic gap in the localization of ±800 kV flexible DC transmission wall bushings. This achievement follows a series of prior successes by China Flexible DC Wall Bushing Manufacturer: in 2012, it successfully developed ±125 kV and ±800 kV converter transformer bushings, ±50 kV and ±600 kV wall bushings, and 550 kV and 1100 kV oil-SF6 impregnated paper bushings; in 2018, it developed China’s first ±1100 kV valve-side impregnated paper bushing for converter transformers; in 2019, it created the world’s first ±1100 kV DC epoxy-core SF6 gas composite-insulated wall bushing; and in 2020, it independently developed China’s first ±800 kV impregnated paper valve-side bushing and ±800 kV impregnated paper wall bushing.

 This latest milestone marks the full localization of China’s UHV AC/DC bushing product portfolio by China Flexible DC Wall Bushing Manufacturer. It holds profound significance for resolving core technology bottlenecks (“chokepoint” issues), strengthening China’s power transmission and transformation industrial chain, driving domestic industrial and technological upgrades, and accelerating the localization of critical components for UHV power systems.

Staying True to Its Central SOE Mission and Shouldering the Responsibility of Localization

For a long time, UHV DC bushings have constrained the localization of China’s UHV projects and hindered the rapid development of the nation’s power industry. As a leader in the power equipment manufacturing sector, China Flexible DC Wall Bushing Manufacturer has consistently committed itself to advancing China’s UHV equipment capabilities. In the field of UHV DC bushings, the company delivered the world’s first ±1100 kV DC epoxy-core SF6 composite-insulated wall bushing for the Changji–Guquan project in 2018—a product that was installed flawlessly on the first attempt and successfully passed the high-end pole II energization test, and has operated reliably on the grid for nearly two years. 

In 2019, China’s first ±1100 kV impregnated paper valve-side bushing for converter transformers passed all tests on its first try, with overall technical performance reaching international leading standards, laying the foundation for batch localization of DC bushings. In November 2020, the company independently developed China’s first ±800 kV impregnated paper valve-side bushing and first ±800 kV impregnated paper wall bushing, which were deployed in the Qinghai–Henan ±800 kV UHV DC transmission project, providing a full series of mass-produced bushings that have performed well to date. On June 10, 2021, China’s first ±800 kV flexible DC wall bushing was officially energized and put into operation at the ±800 kV Liuzhou Converter Station.

China Flexible DC Wall Bushing Manufacturer has continuously excelled in the UHV field, delivering one outstanding achievement after another. Behind this glory lies the responsibility and commitment of a central state-owned enterprise (SOE) to build national heavy equipment, as well as the unwavering mission and belief of its employees to stay true to their original aspirations and strive for excellence.

Overcoming “Chokepoint” Challenges and Achieving Technological Leapfrogging

The Kun-Liu-Long DC Project is China’s first UHV multi-terminal DC demonstration project and the world’s first UHV flexible DC project. It holds world records for the highest voltage level, largest transmission capacity, and longest transmission distance among flexible DC projects, representing the pinnacle of technical difficulty and engineering complexity in today’s power transmission and transformation field. The ±800 kV flexible DC wall bushing developed by China Flexible DC Wall Bushing Manufacturer for this project is highly sophisticated, technically demanding, and was delivered under tight deadlines.

Flexible DC wall bushings serve as the sole passage between the valve hall and DC yard in a UHV converter station. They carry ultra-high voltage and high current, fulfilling critical functions of current conduction, insulation, and mechanical support—essentially acting as the “throat” of the DC transmission system and the only channel for DC current to enter and exit the valve hall. Without this passage, external power cannot enter, and internal power cannot be transmitted, rendering the converter station inoperable.

However, key core technologies for bushing equipment have long been monopolized by a handful of foreign manufacturers. China has heavily relied on imports, lacking pricing power and facing exorbitant maintenance costs. Only through persistent innovation and achieving technological self-reliance can China avoid being constrained by others. After years of R&D and testing, China Flexible DC Wall Bushing Manufacturer has realized domestic production of bushings, resolved the “chokepoint” issue in domestic DC transmission technology, broken foreign monopolies, and transformed China from a “follower” to a “leader” in critical DC equipment.

To ensure timely project delivery, China Flexible DC Wall Bushing Manufacturer established a Leading Group for the Major ±800 kV Flexible DC Wall Bushing Project and a Lean Improvement Working Group, focusing on special inspections and lean rectification efforts in areas such as process control and quality enhancement, and carefully formulated implementation plans and safeguard measures.

Guided by a strong sense of political responsibility and historical mission, the company reinforced accountability, implemented rigorous process controls, and overcame multiple core technological challenges—including core casting and curing control and highly reliable current-carrying sealing structures—to ensure smooth progress of the R&D mission. To develop the optimal design for the ±80 V flexible DC wall bushing, the group integrated internal and external resources, coordinated cross-functional elements, and organized more than ten design and manufacturing seminars with numerous research institutes and industry experts. These efforts enabled thorough understanding of operational issues and merits of foreign counterparts, ensuring optimized design of insulation, current-carrying capacity, and mechanical performance from the outset.

Upholding the Craftsmanship Spirit to Build National Heavy Equipment

China Flexible DC Wall Bushing Manufacturer has always placed great emphasis on supplier quality management. It conducted extended audits of raw materials from suppliers to ensure compliance with national standards and technical specifications, guaranteeing that component quality meets required technical criteria. Technical briefings were provided to prevent substandard materials from entering the production process and compromising DC product quality.

During manufacturing and testing, the company further refined its existing DC bushing manufacturing system by incorporating expert recommendations. It added or improved four specialized process documents—including assembly work instructions for DC wall bushings—and four specialized quality control documents, such as the ±800 kV Wall Bushing Quality Control Measures Table. Prior to each production step for the ±800 kV bushing, specialized training, technical briefings, and assessments were conducted; during production, technical guidance and monitoring were provided; and after each phase, “look-back” reviews were carried out to enable timely summarization and continuous improvement.

Production strictly followed standardized management practices. An hour-by-hour inspection plan was implemented, and pre-production capability assessments were conducted across six dimensions: personnel, equipment, materials, methods, environment, and measurement. Technical staff provided detailed briefings to operators to ensure all preparations met startup requirements. Throughout production, operations strictly adhered to process flows and the “Three Adherences” principle (adherence to drawings, processes, and standards), with meticulous attention to detail, rigorous process control, and a relentless pursuit of perfection to keep every minor quality factor under control.

Hardship Forges Excellence

“As the final checkpoint before product delivery, we must ensure every unit shipped gives customers peace of mind and satisfaction,” said the Deputy Director of the Bushing Production Center and Head of the Test Station. Due to tight delivery schedules, the company’s test team adopted a 24/7 three-shift system to ensure on-time delivery. To minimize test preparation time, a cross-departmental emergency response team was formed. Upon call—whether on weekdays, weekends, midnight, or dawn—team members immediately mobilized to the high-voltage test hall to assist with on-site preparations. The high-voltage test hall was often brightly lit, with voices echoing: “Ready, start!” and “Slow down, hold steady”—as staff prepared for the next day’s tests.

After 14 months of arduous effort, the R&D team overcame numerous key technical hurdles, including structural design of large-scale flexible DC bushings, casting of massive cores, and assembly of oversized cores. The team mastered critical technologies and key processes, successfully developing the world’s highest-voltage ±800 kV flexible DC wall bushing. Compared with existing imported counterparts, this bushing offers 10% higher current-carrying capacity, 9% greater insulation margin, and 50% higher mechanical strength, with key performance indicators surpassing those of imported equipment. The project generated substantial technical and intellectual property outcomes, including 24 core patents. At the national-level product appraisal meeting, industry experts concluded that the main performance indicators of the ±800 kV flexible DC wall bushing reached international leading levels, and the product successfully passed the national technical certification.