HVDC or high-voltage, direct current electric power transmission systems contrast with the more common alternating-current systems as a means for the bulk transmission of electrical power. The modern form of HVDC transmission uses technology developed extensively in the 1930s in Sweden at ASEA. Early commercial installations include one in the USSR in 1951 between Moscow and Kashira, and a 10-20 MW system in Gotland, Sweden in 1954[#endnote_ieee_spectrum].