SHANGHAI, Dec. 23 (Xinhua) -- When a line graph showing the amplifying superconducting electricity level jumped to its peak on the monitoring screen on an August day this year, the control hall in Shanghai burst into warm applause.

It marked the 35 kV kilometer-level superconducting power transmission demonstration project reaching its full-load operation.

The 1.2-kilometer cable laid in the city is the world's longest kilometer-level superconducting cable, and is the only cable of its kind globally to be put into operation in an urban core, while it is also the only cable of its type that has been installed entirely in ducts. In addition, it has the largest transmission capacity when it comes to 35 kV.

Superconducting power transmission exploits the phenomenon of superconductivity to transmit large amounts of electricity with close-to-zero losses, representing one of the most revolutionary cutting-edge technologies in today's power industry.

Its principle is to reduce the power transmission resistance of superconducting materials to close to zero in low-temperature liquid nitrogen. The transmission capacity of one superconducting cable is equivalent to four to six conventional cables at the same voltage level, thus saving about 70 percent of underground pipe space.

The demonstration project is located between two 220 kV substations in Xuhui District, downtown Shanghai. The total line length is 1.2 kilometers and the design current is 2,200 amperes.

It is the result of two decades of efforts by engineers at Shanghai Electric Cable Research Institute (SECRI) under Shenergy Group, an enterprise which has specialized in electric cable over the past 60 years and which spearheads the superconducting transmission industry.

"If superconducting cables are widely used, the problems of high electricity density and limited space in super-large cities like Shanghai can be solved," said Huang Chongqi, a member of the Chinese Academy of Engineering and an expert in superconducting cables.

The SECRI team regards the path of independent innovation as key to pioneering in this frontier industry.

"Our self-design helped reduce the cost of superconducting raw materials, once monopolized by foreign countries, by nearly two-thirds," said Huang, a senior SECRI engineer.

The detection and isolation of weak electric signals in the superconducting cable system was a world-class technical challenge. SECRI engineers worked independently to acquire key test data, which effectively enhanced their standard-setting capability at the world's first international standard conference for superconducting cables.

According to data released by the National Development and Reform Commission in September 2022, China had built the world's largest power system, with its length of transmission lines above 35 kV reaching 2.26 million kilometers, equivalent to circling Earth 56 times.

The 1.2 km version found in Shanghai is an exception when compared with average power lines, but a good starting point, said Huang. "Next, 5km-level and 10 km-level cables will be developed."

"We used to import all the high-voltage cables, but then the homegrown ones started catching up." said Zong Xihua, a deputy chief engineer of SECRI. "Now, we have made an early start in superconducting power transmission technology and taken a lead globally thanks to two decades of research and development efforts."