Western Interconnection

The other major wide area synchronous grid is the Eastern Interconnection.

The Western Interconnection stretches from Western Canada south to Baja California in Mexico, reaching eastward over the Rockies to the Great Plains.

Interconnections can be tied to each other via high-voltage direct current power transmission lines (DC ties) such as the north-south Pacific DC Intertie, or with variable-frequency transformers (VFTs), which permit a controlled flow of energy while also functionally isolating the independent AC frequencies of each side.

[4] Together, wind, solar, and hydro resources account for 47% of installed capacity.

While the resource mix is changing, with wind and solar eclipsing coal in installed capacity, in 2021 coal still generated slightly more power than wind and solar combined, down from twice as much in 2017.

The two major and three minor NERC Interconnections, and the nine NERC Regional Reliability Councils.
High voltage power grid in the United States in kilovolts (kV)
500+
400-500
300-400
200-300
100-200
<100