John Goss, Ceejay, Hong Kong
The greatest challenge facing today’s global power industry is to satisfy the ever growing demand for large quantities of electrical power efficiently, inexpensively and with minimal impact upon the environment.
It is sometimes the case that electricity is generated hundreds or even thousands of kilometres away from the urban populations or energy intensive industries that need it. However, when power is transmitted over extremely long distances using conventional transmission technology high energy losses can occur through for examples leakages from the windings, cores or surrounding structures such as insulators.
Ultra high voltage (UHV) power transmission in contrast is a highly efficient way of transmitting large quantities of electricity over long distances without experiencing high losses. UHV power transmission is defined as alternating current (AC) voltages of 1000 kV or higher, or direct current (DC) voltages of 800 kV or higher.
The performance gain of UHV transmission is due to the higher the voltage on the line, which means a lower the current, and therefore less energy is lost via the joule effect. At the same time, by transmitting more power over a single power line the number of power corridors required for the task can be reduced.
Potentially, UHV transmission offers an ideal solution to the pressing need for more electricity in our space restricted world. One country that is embracing this transmission technology is China, and it is pinning its hopes that UHV can help solve its massive energy dilemma.
UHV power transmission per se is not a new technology à‚— it was initially developed some 40 years ago à‚— but the technology has advanced to a point where it has become the technology of choice for bulk power transmission. The State Grid Corporation of China (SGCC), which is is the counties largest electric power supplier and employs a staggering1.5 million people, in particular has ambitious plans.
UHV power transmission
Currently, China has one operational UHV line, a 1000 kV AC demonstration power line, which entered commercial operation in January of this year. The UHVAC line connects the North China and Central China grids, beginning at the Jingdongnan substation in the coal-rich Shanxi Province, via the Nanyang switching station in Henan Province, and ending in the Jingmen substation in Hubei Province. The line, known as Jingdongnan- Nanyang-Jingmen covers a distance of 640 km and is the highest voltage system operating commercially anywhere in the world.
SCCG is also focusing on UHVDC transmission and is constructing two UHVDC lines, with a combined investment of 40 billion yuan ($5.9 billion). The two lines will transmit hydropower from the Sichuan Province to Shanghai and the southern regions of Jiangsu Province.
An SGCC spokesperson, Lu Jian commented “There is an urgent need for such UHV technologies to be able to deliver power because China’s massive energy resources and the centres of energy demand are so unevenly distributed.” Around 80 per cent of the country’s coal reserves are found in the northern and western regions and approximately 80 per cent of its hydroelectric power in western regions, while more than 75 per cent of China’s energy demand is concentrated in central and eastern regions.
According to SGGC, China’s electric power demand looks set to almost double to 7.4 trillion kWh by 2020, with the installed generating capacity increasing by a similar rate to 1.47 billion kW. SGCC expects UHV transmission capacity to reach 300 million kW by 2020, with 78 million kW dedicated to hydropower transmission.
China’s first UHVDC power link
As mentioned above, SGCC’s Sichuan to Shanghai 800 UHVDC pilot project is currently under construction. Once operational this will be the world’s longest power link, spanning 2000 km from western China to the highly industrialized coastal area in the east. It will have a capacity of 6400 MW. This is estimated to provide enough power to meet the needs of 31 million people, based on China’s average consumption per capita. The UHVDC link is scheduled for completion in 2011.
The main equipment contract was signed back in December 2007.With the exception of some of the DC equipments and some high-end converter transformers, all other main equipments of the pilot project are being supplied by Chinese manufacturers. They include China XD Group, XJ Group Corporation, TBEA Shenyang Transformer Group, Baoding Tianwei Baoding Electric, Beijing Power Equipment Group, Nanjing Nari-Relays Electric and Beijing Wanglin HVDC Engineering Technology. The international companies involved in this project are ABB and Siemens.
Another reason that marks this project as a world-first is that it will utilize 6 inch thyristor valves, an 800kV large capacity high voltage converter transformer and a 800 kV 4 kA smoothing reactor and bushing for the first time.
Why UHV makes sense
The Director General of the Chinese Society for Electrical Engineering (CSEE), Lu Yangchang observed “China’s great growth is expected to see it consume 7.4 trillion kWh of electric power in 2020, more than doubling the 3.43 trillion kWh consumed in 2008, and that under these circumstances, UHV power transmission lines will become essential.
When conveying same quantity of electric power, 1000 kV UHV power transmission lines can send the power three times the distance of traditional 500 kV power lines, while their electric losses account for only 25 per cent to 40 per cent of the traditional lines. UHV lines can also save 60 per cent of land used to construct the transmission lines.
Lu concluded “Delivering electric power with UHV lines also becomes more economical than transporting coal to generate electricity at the load centre.
Currently, China’s six power transmission grids charge local consumers diversified prices for electric power use. For example, in China’s coal resources rich regions in the north, such as Inner Mongolia and Xinjiang Province, electricity is charged at 0.30 yuan per kWh.
In direct contrast to this low rate in the eastern Zhejiang and Shanghai provinces electric power is charged at 0.46 yuan per kWh. So sending electric power with UHV transmission lines from the north to the east will lower charges by between 0.03à‚—0.08 yuan per kWh, compared with transporting power coal to generate power.
“It has become a natural choice for the country to distribute energy resources in greater areas to ensure national energy security. Developing UHV transmission lines may effectively solve the problem of sending large quantities of electric power over long distances,” Lu said.
As an example of the benefits if UHV power transmission, it is estimated that China’s first UHV power line will bring an additional 3 million kW of electricity generated by thermal coal power to Hubei Province and save the central China province the cost of purchasing and transporting an estimated seven million tons of thermal coal every year or 90 per cent of coal purchased from other provinces. This saved amount of energy is equivalent to building another Gezhouba hydropower plant which was the first hydro power plant constructed on the Yangtze River near Yichang City in Central China, consisting of 21 turbines.
In response, Shanxi Province has mapped out a strategy to give priority to directly transmitting electric power with UHV lines and other voltage lines to end users, while not neglecting coal transportation over the next two to three years.
In January 2009, the governor of Shanxi Province, Wang Jun said: “The coal rich province will invest 100 billion yuan in order to construct and run 25 thermal coal fired power plants with a total generating capacity of 20 million kW and 9000 km of UHV transmission lines of various voltages over the next two years.
“By 2011, this northern province will have a total of 70 thermal power plants with 55 million kW installed capacity. In this way the province will be able to deliver 120 billion kWh electric power to other provinces from the present 51 billion kWh.”
More UHV Lines Planned
In addition to the previously mentioned UHV transmission lines, China’s Central Government has approved another pilot 800 kV DC UHV transmission line linking Jinping in Sichuan Province with the southeastern Jingsu Province.
In November 2008, SGCC’s Sichuan Branch started to make early preparations to begin constructing converter stations from December 2009 onwards. The project is to be completed in 2012. The DC UHV line together with the other one under construction has a combined investment of 40 billion yuan.
Though the SGCC has not revealed the specific investment it is making into these three new AC lines, they have said that the SGCC would invest 83 billion yuan in UHV transmission lines in 2009 and 2010 in order to make long distance power transmission with UHV power lines more efficient. These significant investments can be divided into 57 billion yuan on UHV AC power transmission lines and 26 billion yuan for UHVDC power transmission lines.
Two other UHV lines with a combined investment of 40 billion yuan are already underway. The two DC lines would transmit electricity produced by hydropower in the Sichuan Province to Shanghai and the southern regions of Jiangsu Province. The SGCC has said that it plans to invest more than 100 billion yuan over the next three to four years on UHV power transmission lines to make long distance power transmission more feasible and efficient.
The general manager of SGCC, Shu Yinbiao said: “Although the current global economic slowdown has led to a smaller electric power demand for electric power in the country, China’s electric power sector remains less developed compared with per capita installed capacity in developed counties. SGCC will double installed capacities in 2020 over the existing volume.”
The President of the China Electric Power Research Institute, Zhang Wenling said “China needs to develop both AC UHV and DC UHV lines. The two have their own advantages in that AC UHV is suitable for backbone power grid construction and power grid connection whereas DC UHV is ideal to transmit electric power from China’s large scale hydropower and thermal coal fired power plants over very long distances.”
UHV Research Centre
The SGCC is currently conducting UHV DC tests in a complex, which covers an impressive 80 000 m2. This Chinese UHV DC research centre is the world’s largest laboratory of its kind.
The test centre is equipped with the longest transmission test line section in the world, with over 1100 metres strung over six towers that are 88 metres high. This represents the highest DC voltage grade of double circuit bi-pole testing line and the highest impulse voltage generator in China.
The facility also boasts the world’s largest test chambers for artificial climates and for ice coating tests and, with dimensions of 70 metres by 22 metres by 13 metres and a double frame it has the world’s largest corona cage.
The test centre’s DC voltage is sourced from a à‚±1200 kV/0.5 A generator. The testing complex, which is located in the Changping District of Beijing and both outdoor and indoor facilities, has commenced tests on atmospheric simulations and the potential effects of UHV transmission on the surrounding environment.