High-Capacity Grid ActThis bill requires public electric utilities to use the best-available transmission conductor for certain interstate transmission lines (i.e., power lines) in order to recover the costs of the conductor through consumers' electric bills.Specifically, in any filing seeking to recover the costs of a transmission conductor for the transmission line and in any proceeding to determine if the costs may be recovered through rates, the bill directs the Federal Energy Regulatory Commission to presume that (1) the use of a best-available transmission conductor is a prudent practice and that the associated costs are just and reasonable, and (2) the use of a transmission conductor that is not a best-available transmission conductor is not prudent and that the associated costs are not just and reasonable.A best-available transmission conductor is a conductor that (1) provides the greatest feasible and commercially available energy-carrying capacity at a given voltage level, (2) provides the highest feasible and commercially available electrical efficiency at that voltage level, and (3) mitigates thermal sag (drooping of power lines) at the maximum rated transmission-carrying capacity of the facility.The bill applies to projects to (1) construct new transmission facilities; or (2) modify, upgrade, or replace an existing transmission line.