Don't blink! Secret of China's power transmission over 2,000 km in 7 msec
Starting the work from scratch, China has become a top runner in ultra-high voltage technology.
It takes only 7 milliseconds to transmit electricity from Baihetan, the world's second-largest hydropower station, in southwest China's Sichuan to east China's Jiangsu, making the 2,080-km-distance almost nothing.
The lightning-like speed of power transmission deeply roots in China's world-leading ultra-high voltage (UHV) technology. Trillions of kilowatt-hours (KWh) of electricity is transmitted across the country each year through UHV lines stretching a total length of more than 48,000 km.
Starting the work from scratch, China has become a top runner in this sphere. At present, it masters the whole range of UHV transmission technology and is capable of producing relative equipment. It is also the only country that realized large-scale commercial UHV transmission, and has taken the lead in formulating international standards for public UHV transmission grids.
WHAT IS UHV?
UHV power systems include 800 kilovolt (KV) direct current (DC) grids and alternating current (AC) grids above 1,000 KV, which excel in terms of capacity, efficiency and loss reduction of power transmission.
For example, 1,000 KV DC grids are capable of transmitting power to places 6 to 7 times as far as those for 500 KV ones, with the capacity up 4 to 5 times and power losses down to less than 25 percent.
WHY UHV IN CHINA?
Energy supply is crucial and challenging in China as the manufacturing powerhouse boasts a vast territory and has to deal with an unbalanced spatial distribution of energy.
For instance, there is a long distance between its main energy sources and major consumption centers. Two thirds of its coal reserves are in north China's Shanxi, Inner Mongolia and northwest China's Shaanxi, 80 percent of its hydropower is based in the southwest, while most of the wind and photovoltaic power resources are concentrated in the northwest and Inner Mongolia. At the same time, 70 percent of energy is consumed in east and central China.
With a long reach of power transmission of 2,000 km or even over 3,000 km, UHV grids can cover all major energy bases and power consumption centers in China, well bridging the gap between energy production and consumption.
RAGS TO RICHES THROUGH INNOVATION
Throughout the world, countries like the United States, Japan and Italy researched and developed UHV transmission technology, but due to various reasons have postponed relative projects, or lowered the transmission voltage level.
Without mature methods to learn from, ready-made tools to use, nor industry standards and specifications for field operation, China made its way to a master of a complete set of UHV transmission technology and equipment manufacturing through innovations.
It started preliminary study on UHV AC transmission in 1986, and completed the construction of its first megavolt UHV research line in 1994. In 2005, the State Council included UHV in China's national program for mid- and long-term scientific and technological development (2006-2020). A year later, the country included the complete set of UHV equipment into the guideline on advancing equipment manufacturing and approved a 1,000 KV UHV AC test demonstration project.
More than 1,000 experts spent over a decade in developing core UHV equipment -- the transformer and the converter valve, solving the most difficult problems of UHV technology.
Considered as the "heart" of UHV, the transformer is crucial to control voltage level and power losses. The biggest challenge for transformer design is to find a suitable material with sound insulating function and acceptable weight at the same time.
Among all materials, ceramics had the best insulation performance, but the weight of a single 1,000 KV UHV transformer made of ceramics could be as heavy as 400 tonnes, imposing a huge burden on the grids. To tackle this problem, Chinese scientists created a special kind of insulating paper, which can be cut into any shape and weighs much less.
In 2010, China successfully developed the world's first 800 KV/4,750 amp UHV DC converter valve, which has the highest current flow capacity and voltage level globally.
With world-leading electrical performance, structural design and key components, the valve can increase the transmission capacity of 800 KV UHV DC project by 5.6 percent and reduce costs by about 25 percent.
China has also realized rapid technological upgrading of converter valves by overcoming difficulties, such as heat dissipation, voltage peak suppression and electromagnetic compatibility through continuous innovations.
RECORD-BREAKING INFRASTRUCTURE
In January 2009, the 1,000 KV Southeast Shanxi - Nanyang - Jingmen UHV AC demonstration project was completed and put into operation, which boasted world-leading voltage level and technology.
As China's first UHV AC project with independent intellectual property rights, and the world's first UHV AC power transmission project put into commercial operation, it set a milestone for China's progress in UHV power transmission.
By completing this project, China acquired core UHV technology and the capability to produce the full set of relative equipment. It also broke the world record of developing major power transmission equipment and formed a series of national and international standards.
The Xiangjiaba-Shanghai 800 KV UHV DC power transmission project started operation in 2010, taking the lead in terms of voltage level, capacity and transmission distance among DC projects in the world.
With power transmission capacity up to 7 million KW, it can send 35 billion KWh of hydropower each year from southwest China's Sichuan to east China's Shanghai, contributing to 30 percent of the latter's power supply.
Since UHV technology was included in China's 12th Five-Year Plan (2011-2015) in 2011, UHV infrastructure construction has entered the fast lane. In the past decade, multiple policies were introduced to support UHV projects.
By the end of 2020, China had 30 UHV power transmission projects, boasting around 48,000 km of UHV lines. In the 2021-2025 period, China's State Grid Corporation plans to add 38 more such projects, with a total investment of 380 billion yuan (about 56.13 billion U.S. dollars).
GREEN ENERGY TRANSMISSION
Facilitating effective consumption of renewable energy, UHV technology has ramped up China's efforts of reducing carbon emissions and promoting green development.
In 2020, an UHV line that only transmits clean power, including wind, solar and hydro energy, from northwest China's Qinghai to central China's Henan went into service. Since then, many households in central China have used green power sent from a thousand km away.
As the world's first UHV line to transmit only carbon-free electricity, it could offer 40 billion KWh of power annually to central China, reducing 29.6 million tonnes of carbon dioxide emissions.
The amount of power transmitted through the project per second can satisfy the need of a family for two years, according to Li Binshan, head of a converter station of the project.
China has planned to build new energy supply and consumption systems that are based on large wind and photovoltaic farms, supported by clean and efficient coal power nearby as well as stable and reliable UHV transmission grids.
This is expected to further enhance the country's capability to fight climate change and enhance its competitiveness in the production and utilization of renewable energy.
Great coverage! Thanks.