Consider Converting to HVDC, Part 3
Rachana Gururaj and M. Granger Morgan are with the Department of Engineering and Public Policy, Carnegie Mellon University. Liza Reed is with the Niskanen Center in Washington, D.C.
With a few exceptions, recent years have not seen much increase in the capacity of the U.S. transmission system. However, as more and more remotely located wind and solar is added to the power system, and as serious efforts to convert transportation and heavy industry from fossil fuels to zero-emission electricity increase, it is likely we'll need to find ways to move more power through the transmission system.
Historically, the response in such situations has been to build more transmission lines. But as many Commissioners and other readers of this journal have learned through painful experience, acquiring the right-of-way and obtaining all the other approvals needed to build new transmission lines can be very difficult — indeed, sometimes impossible.
In this article, we describe several ways the capacity of an existing high voltage AC (HVAC) transmission line can be increased and show that sometimes the most cost-effective strategy is to convert the line to high voltage DC (HVDC).
To efficiently move a given amount of power through a line, transmission engineers want to operate the line with as high a voltage, and as low a current, as possible. This is because the power that can be moved through a transmission line is proportional to the product of the voltage and current (P=VI), while the energy loss to resistance heating of the wires increases with the square of the current (I2R).