UHV – international standards to be set

Oct 24, 2006 - Engineer Live

Ultra high voltage (UHV) transmission is one of the most promising ways of helping electricity suppliers meet their ever-growing demand. A new set of international standards should help to speed this development

Studies by the US Department of Energy (DOE) indicate that the world's electrical consumption is set to rise dramatically. Its latest annual energy outlook report predicts that consumption will hit 30 116 billion kWh by 2030, up from 15 400 billion kWh in 2006.

The OECD countries will account for 13 208 billion kWh of this 2030 figure, with the USA itself expected to be the largest consumer at 6969 billion kWh. Growth in demand in the OECD countries is expected to average about 1.5 per cent every year for the next 23 years.

However, the figures are even more dramatic for the non-OECD countries. Sometime over the next ten years, their electricity consumption will surpass that of the OECD countries, rising to an estimated 16 908 billion kWh by 2030. That's an average annual increase of 3.9 per cent over the same period. The report also shows that China (4.8 per cent per year), India (4.6 per cent per year) and Brazil (3.2 per cent per year) will be the most rapidly growing countries in terms of demand.

Today, therefore governments and utilities need to plan to supply large amounts of electrical energy efficiently, inexpensively and with minimal impact on the environment.

In countries with growing populations and rising economies, such as Brazil, China and India, the challenge will be to deliver large quantities of electricity from power generating stations to urban centres that can be thousands of kilometres away. Ultra high voltage (UHV) offers the promise to meet this challenge.

UHV is needed to deliver electricity to cities without increasing the number of transmission lines. In growing cities where demand is on the rise but room for transmission lines is limited this is critical because it means only one power line corridor is needed, not several. No surprise, therefore, that the USA, Brazil, Canada, China, Russia and Japan are already active in developing UHV.

The main issues for this technology involve equipment reliability - protection for people - and stability, such as uninterrupted service when a line fails. New transformers, circuit-breakers and associated equipment and new transmission lines designed for UHV will need to be developed.

International standards for this do not exist yet so they, too, need to be developed to ensure the safe and efficient use of this technology. It is a technical challenge for manufacturers and utilities, and a regulatory issue for governments - one that is now being addressed by the International Electrotechnical Commission (IEC) and the International Council on Large Electric Systems (CIGRE). Founded in 1921, CIGRE is one of the leading worldwide organsiations on electric power systems.

Setting the standard

The world’s two leading organisations involved in this question have agreed to begin defining the technical and safety specifications for this promising new technology that is set to help deliver the world’s increased electrical energy demands.

The IEC and CIGRE are to join forces to develop international standards for UHV to ensure the safe and efficient use of this technology in areas likely to include reliability and maintenance. They will also define the tests for measuring electromagnetic radiation from power lines.

IEC and CIGRE agreed on the joint work at the recent international conference on UHV held in Beijing, China, which was attended by the world's leading experts on this technology.

One of today’s challenges is to supply growing demand for large amounts of electrical energy efficiently and with a minimal impact on the environment. Electricity can be generated thousands of kilometres away from the urban populations to whom it needs to be delivered and during transmission it loses energy.

UHV generally means ac voltages of 1000 kV or higher, or dc voltages of 800 kV or higher. It is a highly efficient means of transmitting large quantities of power over a transmission line. This is because higher voltage on the line means lower current and therefore less energy being lost from the Joule effect: lower voltage means higher current, which means greater heating of the transmission line, which means energy lost as heat.

China surges on

Because of huge energy requirements needed to keep its economy growing, China's efforts with UHV are already quite advanced. According to the Peoples Daily online, the cornerstone was recently laid for China's first UHV grid, a demonstration project starting in the southeastern part of Shanxi, running through Nanying and finishing at Jingmen. The project is the beginning of a new chapter in grid construction that focuses on the integration of UHV grids with grids of a different size at different levels around the country.

China has an unbalanced distribution of primary energy and electrical power. Abundant energy resources are available in western China. More than two thirds of exploitable water resources are centred in Sichuan, Tibet and Yunnan, while over two thirds of coal resources are around Shanxi, Shaanxi and the western part of Inner Mongolia. The economy is more developed in eastern China, with over two-thirds of electrical power directed to the east of the Beijing-Guangzhou railway. There is as much as 2000 km between the energy bases in the west and the power load centres in the east.

“As the ultra-high voltage transmission technology available at present cannot meet the needs of future power growth, the development of the power grid and technological innovation must be expedited. The power industry and scientific development can be optimised through the construction of an ultra-high voltage grid to satisfy sustainable and rapid development of the economy,” said Liu Zhenya, president of the State Grid Corporation of China (SGCC) to the Peoples Daily.

The UHV grid, a power transmission network with 1000 kV ac and 800 kV dc, expands across great distances, has a large capacity, occupies just a little land and uses only a small amount of power to transmit.

Lu Yanchang, chairman of the Chinese Society of Electrical Engineering (CSEE), used figures to extol the advantages of an UHVe grid: the transmission power of 1000 kV ac is 4-5 times that of 500 kV, and the transmission power of 800 kV dc is over twice that of 500 kV. Power can also be transmitted across an area three times the current range and land resources can be saved if the electric current is transmitted by an UHV ac line, with only 25-40 per cent consumption of 500 kV.

The Shanxi-Nanyang-Jingmen test demonstration project will be completed in 2008. According to a group of experts from the Chinese Academy of Engineering, it will become an important channel for energy transmission once its in operation, benefiting power distribution in the northern and middle parts of China.

According to SGCC, as part of the eleventh five-year plan, the UHV will be 4200 km in length, with a capacity to transform 39 million kVA. China is about to launch two projects that will carry 800 kV dc; from Xiangjiaba hydropower station to eastern China and from Xiluodu hydropower station to central China.

By 2020 or so, says the Peoples Daily, the UHV grid frame will be fully functional. It will have the capacity to transmit 200 million kW and will account for over 20 per cent of China's total power capacity. By then, it will be possible to transmit large quantities of electricity from neighbouring countries to China as well.