In 1951 world’s first HVDC was installed between Moscow and Kashira, which was obviously installed as submarine cable. The line is no longer in use, it is unknown, when it was shut-down. Further information on: http://en.wikipedia.org/wiki/Elbe_Project ( English), http://ru.wikipedia.org/wiki/%D0%9F%D1%80%D0%BE%D0%B5%D0%BA%D1%82_%C2%AB%D0%AD%D0%BB%D1%8C%D0%B1%D0%B0%C2%BB ( Russian)
I do not believe, that all parts of this power transmission facility are gone, the halls in which the inverters stood may surely still exist, however used for other purposes today.
It would be great, if mappers in Moscow and Kashira region would be able to find out where the terminals of the line were and the course of the cable, from which it is unknown, if it is still in place.