Three US Interconnections
Prerequisites
The United States does not have one electrical grid. It has three, barely connected to each other. The Eastern Interconnection, the Western Interconnection, and ERCOT (most of Texas) operate as separate synchronized systems linked by only 2.1 GW of DC ties. For context, US peak demand exceeds 700 GW.
Within each interconnection, all generators rotate in synchrony at 60 Hz. Power flows freely across state lines within the same interconnection. But between interconnections, power can only transfer through a handful of HVDC converter stations. The Eastern and Western interconnections share about 1.3 GW of transfer capability. ERCOT connects to the Eastern grid through about 0.8 GW. These are tiny straws between vast pools.
Understand why this matters. If wind is blowing hard in the Great Plains (Eastern Interconnection) while California (Western) faces a shortage, only 1.3 GW can flow between them. The isolation means surplus generation in one interconnection cannot help shortages in another.
Why did Texas create a separate grid in the first place?
Regulatory arbitrage. ERCOT was intentionally kept isolated from interstate commerce to avoid federal (FERC) regulation. By not crossing state lines, Texas utilities operated under state jurisdiction only. This regulatory independence came at the cost of isolation. During Winter Storm Uri (2021), ERCOT could not import significant power from neighboring systems because the DC ties were too small.
The three-interconnection structure is a legacy of history and regulation, not engineering optimization.
The three US grid interconnections are linked by approximately 2.1 GW of DC ties against peak demand exceeding 700 GW. This means:
The transfer capability between interconnections is less than 0.3% of peak demand. While isolation does contain failures, it also prevents resource sharing. The tradeoff became visible during Winter Storm Uri, when ERCOT could not import enough power to prevent blackouts.
The answer is BLesson complete
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