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The dawn of a new age of HVDC technology

Successful test of the world´s first 1100 kV UHVDC transformer

The most powerful HVDC transformer in the world has recently successfully passed its test phase in Nuremberg, Germany. The transformer will enable low-loss high-voltage direct-current (HVDC) power transmission over a record distance of 3,284 kilometers with a transmission capacity of twelve gigawatts. Siemens Transformers has thereby reached a completely new level of HVDC: thanks to the transformer, for the first time worldwide, direct-current electricity can be transmitted at a gigantic 1,100 kilovolts. The transformer not only enables transmission at a record voltage level, but is the most powerful tested transformer in the world, with a capacity of 587 megavolt-amperes. The HVDC line from Changji to Guquan will be operated by the transmission grid operator State Grid Corporation of China (SGCC).


AC can be transported at high voltages from the power plant to consumers with low losses, but this applies only to distances up to approx. 600 kilometers. Over longer distances, high AC voltages have increased transmission losses. Direct current transmission is used instead as a cost-effective way to provide low-loss power supply and to use the electrical energy more efficiently.


HVDC transformers are part of the converter station at the beginning of the transmission line which converts AC to direct current. This process is then reversed at the end of the line. Converting AC to DC helps to transfer the energy efficiently while cutting line losses by 30-50%. As a core component of the Changji-Guquan HVDC line, the tested transformer brings the voltage to 1100kV DC level.


Siemens completely designed all key components for its 1,100 kV converter transformers from scratch on the basis of many years of experience constructing HVDC transformers. The biggest challenge was the insulation system. For example, both valve bushings through which the current flows from the transformers into the valves are approximately 19 meters long. Overall, the transformers are 37.5 meters long, 14,4 meters high and 12 meters wide. In operation, the transformer weighs 909 metric tons. The efficiency of the converter transformer is well above 99% of the rated power.


“With the first successfully tested 1100 kV UHVDC transformer we have demonstrated our industry leading position. Our pioneering transformer technology supports a global power grid, called Global Energy Interconnection. In this way, we are making way for the interconnection of the global ultra high-voltage three-phase grids and ultra high-voltage DC grids on the 1,100 kV DC and 1,050 kV AC level. The innovations being implemented here will benefit our entire product range”, concludes Dr. Beatrix Natter, CEO of Siemens Transformers.