Nation uses sub-seabed cables to transmit power

An inter-island power transmission network in Zhoushan, Zhejiang province, which is the first case in China to use land cables running beneath the ocean floor instead of traditional submarine cables to transmit electricity between islands, recently began operations.

Experts said the project marks another milestone in the country's advancement of marine power transmission technology and further contributes to China's offshore energy development.

The project uses a 10-kilovolt cable running from a preset channel that is 6 meters below the seabed in the northern waters of Zhoushan, Zhejiang province, and is 1 kilometer long. The cable runs from Zhoushan Island to Shangyuanshan Island.

State Grid Zhoushan Power Supply Co, the project's developer, said that using cables buried beneath the seabed, instead of simply being placed underwater, can help solve problems like potential cable damage from ships' anchoring and longer project approval time.

According to the company, at present, inter-island energy transmission in China mainly uses submarine cables. However, China's coastal waters have dense waterways and busy shipping lines, which may damage submarine cables when ships anchor.

Compared with submarine cables, land cables — which are buried deeper than anchoring depths — pose no risk of external damage, and are thus suitable for short-distance energy transmission between nearby islands. They also enjoy lower costs and less difficulty in construction, less stringent requirements and shorter administrative approval time, the company said.

It carried out a number of tests during the project's early stage, such as a detailed geological survey of the project's cross-sea section, and selected the most suitable crossing strata based on geological conditions. To reduce tension and friction of the cable during traction — a process of line laying — the company used wire rope traction as if installing an "exoskeleton" for the cable, and used pipeline lubrication materials to reduce friction, ensuring that the cable remained intact during the dragging process.

The company said this new form of energy transmission — land cables running beneath the seabed — will be widely used in power transmission between islands with a distance of less than 2 kilometers.

Lin Boqiang, head of the China Institute for Studies in Energy Policy at Xiamen University, said the vast potential of offshore energy development underscores the growing importance of offshore energy transmission systems.

A recent report by CNOOC Energy Economics Institute showed that last year, China's offshore oil and gas production volume is estimated to have reached new highs, and the integrated development of marine oil and gas with new energy will become a focal point. Offshore wind power is emerging as a key pillar in the development of offshore renewable energy.

"Going forward, inter-island and island-mainland power transmission will have greater room for development, spurring massive investment and business opportunities, amid growing demand for electricity used in the exploration and development of offshore energy sources. Technological advances will further reduce transmission costs," said Lin.

liuyukun@chinadaily.com.cn