 The concept's advocates describe it as being in a "visionary" stage, for which no new scientific breakthrough is required but which requires major technological innovations before it could progress to a practical system.A system for the United States is projected to require "several decades" before it could be fully implemented.One proposed design for a superconducting cable includes a superconducting bipolar DC line operating at ±50 kV, and 50 kA, transmitting about 2.5 GW for several hundred kilometers at zero resistance and nearly no line loss.