............DC transmission has a number of advantages and is being more widely used. For example, a DC line, requiring only 2 conductors instead of the 3 needed for an AC line, costs about two-thirds as much. Further, in DC transmission the effective voltage is equal to the peak voltage, while in AC transmission the peak voltage is 40% higher. Since radio interference increases with the peak voltage and decreases as the conductor size is increased, the DC system can carry a higher effective voltage than an AC line of equivalent size and still maintain an acceptable radio interference level. Thus, in some long lines carrying bulk power from remote generating sites, power is generated as AC, boosted to a high voltage, converted to DC for transmission, then reconverted to AC and transformed to a lower voltage for use. The cost of the converter stations at either end is offset by the lower cost of the line. An example of DC transmission is Manitoba's Nelson River line, which carries power from generating plants on the Nelson River to Winnipeg, almost 1000 km south. DC transmission is also advantageous for transmitting power through submarine cables, such as the line from the British Columbia mainland to Vancouver Island. ........
.............As of 1982, Manitoba Hydro's Nelson River system, which began service in 1972, was the largest high-voltage DC transmission system in the world. In 1965 Hydro-Québec inaugurated its 735 kV Manicouagan line, thus becoming the first utility to go above 500 kV AC for transmission. Since even higher voltages will probably be needed in the future, the utilities are supporting research into transmission at voltages in excess of 1000 kV.