The HVDC Volgograd–Donbass is a long bipolar ±400 kV high voltage direct current powerline used for transmitting electric power from Volga Hydroelectric Station at Volgograd in Russia to Donbas in eastern Ukraine and vice versa. The Volgograd–Donbass system was the second HVDC scheme built in the former Soviet Union, following the Moscow–Kashira HVDC scheme which had already been shut down. The Volgograd–Donbass system can transfer a maximum power of 750 MW. When completed in 1965, its operating voltage of ±400 kV was the highest in the world, and remained so until the completion of the ±450 kV Nelson River scheme in 1977. The scheme is today in a bad state and only operated with a voltage of 100 kV. Nevertheless, it is still being modernized, as a Google Map Picture of its crossing with M-4 motorway at shows, where one can see that new pylons for the crossing of the motorway are under construction. There are concerns over potential mercury contamination in the area near the Ukrainian terminal due to the risk of it being destroyed in the Ukrainian-Russian War. Some towers of the line north of Smile at were destroyed in the war. Volzhskaya converter station The terminal at Volga Hydroelectric Station, Volzhskaya converter station, is situated on the dam of the power plant at . Each of the poles consist of four series connected three-phase valve bridges, which form two series connected twelve pulse bridges. Originally all valves of the scheme were mercury arc valves designed for a voltage of 100 kV and a maximum current of 938 Amperes. Unusually for valves of such high current rating, each valve used only a single anode but because the peak reverse voltage rating was quite limited, two valves were connected in series in each converter arm. The valves used oil-cooled cathode tanks and natural air-cooled anode insulators, with internal grading electrodes inside the porcelain. Each valve stood 3.5 m tall and weighed about 2 tonnes. In 1977 one mercury arc valve group was replaced by a thyristor valve group. The converter transformers of Volzhskaya converter station are fed directly from the generators of the Volga Hydroelectric Station with 14 kV three-phase AC, whereby two parallel switched generators feed their power into one transformer. The transformers have beside the two secondary windings required for the realization of the 12 pulse valve bridges a third winding for feeding electric power in the