The move will increase the capacity of the Pacific Direct Current (DC) Intertie from 3.1GW to 3.22GW. The line carries both hydro and wind power to California.
The BPA said the upgrade, which is estimated to cost $428 million, would help avoid outages.
Equipment failures have at times caused BPA to reduce the capacity of the line, impacting customers who rely on it to move energy between the Northwest and California.
It said one of the issues with the line is that some of the parts are so old some they need to bought on eBay.
The project is subject to environmental review consistent with the National Environmental Policy Act. The upgrades are earmarked to takes place around 2015.