Transmission Voltage Stagnation

EHV efficiency versus real-world constraints: the pros and cons of "right-sizing" the grid.

The Hidden Cost of "In-Kind" Replacement

In the world of transmission planning, the path of least resistance is often the one already traveled. When an aging 138 kV or 230 kV line reaches the end of its useful life, the default regulatory and operational impulse is often "in-kind" replacement—swapping old towers for new ones of the same voltage. The scope is a straightforward rebuild; regulators see a familiar voltage rating, and the project slides through as a reliability necessity. It is safe, predictable, and capital-efficient in the short term.

It can also be a trap.

For developers and transmission planners eyeing the competitive landscape shaped by FERC Order 1000 and the forward-looking mandates of FERC Order 1920, the real opportunity is taking a comprehensive look at "right-sizing." Specifically, it lies in understanding the leverage gained by upgrading to the heavyweights of the U.S. grid: the 345 kV, 500 kV, and 765 kV line.

The Numbers Game: Why 345, 500, and 765?

Before diving into the economics, it is worth addressing a common question from industry newcomers: Why these specific numbers in transmission and distribution?

Early electrical standards used multiples of 11 kV (11, 22, 33, 66, 132, and later ~230 and 345 kV derivatives)—a historical convention that accounted for roughly 10% voltage drop while delivering round numbers to loads. However, 500 and 765 EHV lines broke this pattern as they were engineered from first principles.

• 230 kV: The workhorse of regional sub-transmission.

• 345 kV: The standard "bulk" voltage for much of the Eastern Interconnect.

• 500 kV: The preferred backbone for the Western Interconnect and parts of the Southeast.

• 765 kV: The highest commercial voltage class in the U.S., pioneered by AEP in the late 1960s.

  
  

The "Power Density" Advantage: 765 kV vs. The Rest

The primary argument for building larger high-voltage lines is not just about moving more power; it is about moving it efficiently within a smaller footprint.

Voltage Class	Typical ROW Width	Typical Tower Height	Conductor Configuration	Typical Line Losses (per 100 miles)
230 kV	~100–150 ft	~90–120 ft	Single or twin bundle	~3–5%
345 kV	~150–200 ft	~120–150 ft	Twin bundle	~2–4%
500 kV	~200–250 ft	~130–160 ft	Triple bundle	~1–2%
765 kV	~200–250 ft	~150–180 ft	Quad or hex bundle	~0.5–1%

1. The Capacity Multiplier

The relationship between voltage and power capacity is not linear—it is roughly quadratic.

This means doubling your voltage doesn't just double your capacity; it quadruples it.

• One 765 kV line carries as much power as three 500 kV lines.

• One 765 kV line carries as much power as six 345 kV lines.

  
  

If you are a Transmission Planner looking at a congested corridor, you have a choice: build six separate 345 kV double-circuit towers, or build a single 765 kV backbone.

2. The Efficiency (Loss) Argument

In a FERC Order 1000 competitive bid, cost isn't just Capital Expenditure (CapEx); it's the Net Present Value (NPV) of the total system cost. This is where higher voltages can shine.

• Line Losses: A typical 345 kV line might experience losses of 2-4% over long distances. A 765 kV line cuts that to roughly 0.5% to 1%.

• The Impact: Over a 40-year asset life, the savings from reduced line losses can amount to hundreds of millions of dollars—often enough to offset the higher upfront cost of the towers and transformers.

3. Right-of-Way (ROW) Efficiency

Land is the most finite resource in infrastructure. A standard 765 kV line requires a right-of-way of about 200 feet. To move the same amount of power using 345 kV lines, you would need a combined ROW width of over 600–900 feet. By increasing voltage, we maximize the "power density" per acre of land disturbed—a critical metric for permitting and environmental scoring.

A single 765-kV transmission line can carry the same amount of electricity as six 345-kV lines, while requiring only a fraction of their combined right-of-way, maximizing land efficiency and reducing impacts on landowners.

The Cons: Why Isn't Everything EHV?

If EHV is so superior, why isn't it everywhere? There are real constraints.

• High Upfront Cost and Regulatory Risk: Building a 765 kV line is expensive upfront with a long payback period. The transformers are massive, that can cost $5-10 million each and weigh 400 tons. In 2025, this prompted complaints around MISO's LRTP Tranche 2.1, which is an example of regulatory risk where planning assumptions and cost allocations are being challenged. This can delay projects and makes the case for faster, modular solutions.

• Technological Substitutes: A combination of behind-the-meter generation, co-located power, energy storage, and demand response, among others, can relieve congestion and shave peaks without new EHV lines. Each MW met locally is a MW that doesn't need to travel over an EHV corridor.

• Operational Flexibility: A 765 kV line is substantial corridor. If it trips offline, it drops a massive amount of power (often 2,000+ MW) instantly. The grid around it must be robust enough to absorb that shock without collapsing. This often means you cannot build a 765 kV line into a weak tranmission area without massive substation reinforcements.

The FERC Order 1000 Connection: Winning the Future

This is where the technical details meet market strategy.

Under FERC Order 1000, the Federal Energy Regulatory Commission removed the federal Right of First Refusal (ROFR) for regional transmission facilities. This opened the door for non-incumbent developers to propose projects that are "more efficient or cost-effective" than what the local utility might plan.

More recently, FERC Order 1920 has doubled down on this by requiring transmission providers to evaluate "right-sizing" replacement transmission facilities.

This creates a specific wedge for expertise:

1. The "Right-Sizing" Play: Instead of letting an incumbent simply rebuild a 230 kV line in-kind (which they can often do without competition), a competitive planner can demonstrate that upgrading that corridor to 345 kV or 500 kV provides regional benefits (congestion relief, lower losses) that outweigh the incremental cost.

2. The Regional Backbone: Competitive processes favor projects that solve multiple problems at once. A 765 kV project doesn't just serve local load; it acts as an interstate superhighway, smoothing out Locational Marginal Prices (LMPs) across entire RTO zones.

Conclusion

Transmission planning is no longer just about connecting Point A to Point B; it is about optimizing across multiple variables. While 230 kV and 345 kV will remain tranmission workhorses, the future of regional reliability—the bold efficiency of 500 kV and 765 kV must be considered.