Land cables reshape inter-island power transmissions

An inter-island power transmission network that uses a land cable running through the sea in China started operation very recently, marking another milestone in the country's development of marine power transmission technology.

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

The State Grid Zhoushan Power Supply Company, the project's developer, said that at present, the inter-island energy transmission in China mainly uses submarine cables. However, China's coastal waters have dense waterways and busy ships, which can easily damage submarine cables when anchoring.

Compared with submarine cables, land cables usually have pipelines that are buried deeper than the anchoring depth, leaving no risk of external damage such as anchoring damage, making them especially suitable for energy transmission between short-distance islands. They also have lower costs, lower requirements for the construction environment, less difficult to construct and have faster administrative approval, the company said.

In order to overcome problems during the project's construction, a number of tests were carried out in the early stages, the company said. It conducted a detailed geological survey of the project's cross-sea section and selected the most suitable crossing strata based on the geological conditions.

In addition, the company carried out calculation on the stress of the cables, and cooperated with the Zhoushan Institute of Oceanography to conduct simulation experiments, to optimize the design repeatedly. To reduce the tension and friction of the cable during traction — a process of the construction — the company adopted wire rope traction, installing an "exoskeleton" for the cable, and using pipeline lubrication materials to reduce friction, ensuring that the cable was intact during the dragging process.

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

With the continuous improvement of construction technology and experience, the prospect is to achieve medium and long distance inter-island grid connectivity, while forming a new energy transmission pattern, said the company.

Liuyukun@chinadaily.com.cn