The TAGG HVDC transmission system will consist of eight bi-pole converter stations; one AC/DC converter at each of six power insertion points and two terminal point DC/AC converters. These 500kV systems will be operated at currents up to 3,000 amps facilitating transmission of 3,000 MW per bipole.

The central electronic component in an HVDC converter station is the thyristor valve. These valves will be air insulated, water cooled, light-triggered thyristors capable of efficiencies and reliabilities approaching 99 percent.

The selected converter and transmission technology is well established and has demonstrated excellent performance in various installations throughout the world. The five major HVDC systems in operation in North America are as follows:

• Quebec New England of Hydro Quebec, 2,000 MW, 900 miles.
• Nelson River Bi-pole 1 of Manitoba Hydro, 2 x 2,000 MW, 600 miles.
• Nelson River Bi-pole 2 of Manitoba Hydro, 2 x 2,000 MW, 600 miles.
• Pacific Intertie of BPA and LADWAP/SCE, 3,150 MW, 850 miles.
• Intermountain Intertie of Intermountain Power Agency, 1,600 MW, 450 miles.

HVDC systems enjoy the equivalent reliability and availability as AC transmission systems.