Zhejiang Zhoushan: 500 kV Cross-Sea Transmission Lines Undergo First Dual-Line Maintenance

May 27, 2025 at 18:10 PM EDT

"Guojiao No.1" Team Pioneers Ultra-High Voltage Offshore Operation and Maintenance

On May 19, the Zhoushan 500 kV Interconnection Transmission and Transformation Project commenced its first dual-line maintenance since its commissioning. As the world’s highest-voltage cross-sea transmission line at present, this synchronized dual-line aerial maintenance at a height of 370 meters marks a new milestone in China’s ultra-high voltage offshore power line operation and maintenance technology.

Spanning Ningbo and Zhoushan, the Zhoushan 500 kV Interconnection Transmission and Transformation Project is China’s largest and most technically challenging cross-sea power grid project. Since its operation in 2019, it has transmitted over 33 billion kilowatt-hours of electricity, accounting for 47.52% of Zhoushan’s total electricity consumption during the same period, and serves as a core energy artery for the Zhoushan Archipelago New Area.

To ensure the smooth advancement of the Guotou Jineng (Zhoushan) Gas Power Generation Project and its supporting transmission infrastructure, and to facilitate Zhoushan’s transition from a power-receiving to a power-transmitting grid, State Grid Zhoushan Power Supply Company adjusted grid operation modes to create safe construction conditions. State Grid Zhejiang Electric Power Co,.LTD has coordinated the "Guojiao No.1" team and technical experts from Zhejiang Electric Transmission & Transformation Co,.LTD to conduct a centralized dual-line maintenance from May 19 to June 9, which is China’s first synchronized ultra-high voltage cross-sea line maintenance.

The maintained Luochun 5495 Line and Luoxiao 5496 Line span the Liangmaoshan in Ningbo and Dam aoshan in Zhoushan. The two 370-meter transmission towers span the 2,756-meter Luotou Waterway, an international shipping lane (Asia's largest cross-sea transmission span), with a net clearance height of over 84 meters. The importance of the lines and the difficulty of maintenance also pose a test to the entire Zhoushan power grid.

It is reported that the maintenance includes a number of refined maintenance tasks such as high-altitude line walking inspection of the long-span overhead lines, inspection of compression joint connections, and investigation of damper and spacer displacement. Maintenance personnel needed to climb the 370-meter cross-sea transmission towers on both sides of Ningbo and Zhoushan, carry out aerial operations on the wires with a height difference of 280 meters and more than 84 meters above the sea surface, and simultaneously carry out high-altitude line walking operations. At the same time as the high-altitude line walking operations, the maintenance of the 370-meter towers was also carried out, mainly including replacing the glass insulators and wind-induced vibration monitoring systems on the towers, and tightening the damper bolts of the long-span section of the conductors and ground wires.

It is worth noting that medium-sized cargo-carrying drones were applied to assist in the maintenance during this operation. During the line walking operation, the drones cooperated with the staff to transport accessories such as spacers that needed to be replaced, and assisted in carrying out operations such as inspection of tension clamp crimping quality and insulator replacement, effectively reducing the transportation burden and the work pressure of the staff.

During the maintenance, in order to ensure the safe and stable operation of the Zhoushan power grid, State Grid Zhejiang Electric Power Co,.LTD activated the Asian Games-level power protection standards, and coordinated the resources of the whole province for collaborative linkage. More than 1,000 emergency team members in the Ningbo and Zhoushan regions were on 24-hour standby, and 100 power generation vehicles responded in batches and degrees. "Air-sea-land" intelligent equipment was fully deployed. Drones patrolled the overhead lines and cables every day, and submarine cable patrol vessels and underwater robots inspected the channels twice a day. The early warning range of the submarine cables was expanded from 500 meters to 2 kilometers, building a power protection line with the joint effort of the whole province.

The collaborative implementation of this maintenance and the important energy access project not only lays a foundation for the scheduled commissioning of the power plant but also explores a new path for cross-sea line operation and maintenance through the centralized maintenance model. It is expected that after the official commissioning of the relevant projects, Zhoushan can increase the clean power supply by about 1 billion kilowatt-hours every year, which will further optimize Zhejiang's energy structure. As the first H-class gas gas-turbine project in Zhejiang Province, it realizes hydrogen-blending power generation and adjusts green hydrogen production capacity, providing support for Zhoushan to build a demonstration city for marine hydrogen energy applications.

It is expected that by the end of 2025, Zhoushan's clean energy power installed capacity will increase to more than 3.84 million kilowatts, and the natural gas consumption will reach about 230 million cubic meters, further consolidating its position as a clean energy base in the Yangtze River Delta.

Media Contact
Company Name: ZHEJIANG ELECTRIC POWER CORPORATION
Contact Person: Yuqing Fu
Email: Send Email
State: Zhou Shan
Country: China
Website: www.zj.sgcc.com.cn

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Zhejiang Zhoushan: 500 kV Cross-Sea Transmission Lines Undergo First Dual-Line Maintenance

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