Electricity highway powers through China
Siemens case study on a 1,500 km transmission line in China.
In China, Siemens has put an “electricity highway” into operation that works with a voltage of 800 kV. The transmission line stretches from remote, rainy Yunnan province to the industrial region in the Pearl River delta and its major cities of Guangzhou and Shenzhen. The high-voltage direct-current transmission (HVDC) system stretches over nearly 1,500 kilometers — that’s equivalent to the distance from the south of Germany to the southern tip of Italy.
The highway is now fully operational. The second pole was recently switched on, raising the transmission capacity to 5,000 megawatts or roughly the generating capacity of five large power plants. The voltage increase, from the previous 500 kV to 800 kV, reduces transmission losses, which are now only two percent per 1,000 kilometers. In addition, there is a loss of less than 1.5 percent for the converter stations at the transmitting and receiving terminals.
Another HVDC line with 800 kV has already gone into operation in China, for which Siemens supplied components including transformers. Siemens thus offers the transmission technology of the future, with which clean power from renewable sources can be transported over thousands of kilometers — practically a blueprint for the DII (Desertec Industrial Initiative) desert power project.
Because the electricity is generated using hydropower, there is no need for fossil-fired power plants, which translates into savings of 30 million tons of carbon dioxide per year. HVDC systems are a component of the Siemens portfolio of environmental products, with which the company generated sales of approximately €23 billion in fiscal 2009.
Another advantage of HVDC systems is that the flow of energy can be controlled as desired and used to stabilize the grid to which they are connected. Furthermore, HVDC acts like an automatic firewall in the event of cascading grid disturbances and thus can prevent blackouts.
Siemens developed a new transformer the size of a single-family home for the world-record voltage of 800 kV. Ten of the super transformers are required for the Yunnan-Guangdong system. One of several major challenges facing the experts in Nuremberg was the lack of any defined standards for this scale of system. The very high operating voltage meant that they had to design exceptionally effective insulation systems.
To achieve the requisite insulating clearances in air, the two valve bushings through which the current flows from inside the transformer to the converters are 14 meters in length. A new and specially air-conditioned production hall had to be built for the 800 kV transformers to prevent the insulation absorbing moisture from the air during final assembly.