The Next Interstate System: 765-kV Transmission

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AEP advocates a 765-kV transmission overlay for the entire United States.

by Michael Heyeck, P.E.

The United States is the world’s greatest economy, yet we live today with regionalized electricity marketplaces fraught with billions of dollars of congestion, paid for by unsuspecting consumers who are victimized by the inertia that prevents electric grid improvement.

AEP advocates the development of a 765-kV transmission overlay for the entire United States. Regional boundaries should be shattered so states with resources can employ them for economic development and share with states lacking resources or the ability to site generating plants.

Merging Reliability and Market Efficiency for Security

Reliability is not a given. Planning processes yield just-in-time transmission plans that are inevitably delayed by siting issues. In addition, planners separate reliability from market efficiency, yielding a system that meets a definition of reliability without considering everyday market dynamics. The U.S. consumer deserves a vibrant wholesale electricity marketplace where access to low-cost and environmentally friendly generation is unimpeded, and where reliability and market efficiency merge for security of the nation’s electricity supply.

The answer to the country’s present-day need is as clear as President Eisenhower’s vision of an interstate highway network, which he signed into law in 1956. He knew a national overlay highway network would enable the economic well-being of Americans via robust interstate commerce, while promoting national security through better mobility for defense. Likewise, the nation needs an interstate electric transmission system to enable greater market efficiency and to ensure a higher degree of reliability for reasons of national security and economic vitality.

In 1966, AEP boldly announced an interstate network of high-capacity 765-kV transmission, enabling diverse siting of new 1,300 MW generating units to serve a growing economy. Today, AEP’s 2,100-mile 765-kV network surpasses any other in the United States. It has enabled the now-fragile interregional marketplace that the nation has now outgrown.

Why 765-kV? At this voltage, several times the power of lower voltage lines can be transmitted over long distances with only 200 feet of right of way. (See table.)

Transmission at 765-kV also offers greater reliability due to its line design. With only one line outage per 100-mile year, 765-kV reliability surpasses all other voltage classes.

In addition, 765-kV faults are usually momentary and involve only one of three phases, allowing application of single-phase switching.

Station equipment for 765-kV has matured and transformer bank sizes up to 3,000 MVA have been demonstrated throughout the world. The necessity of using banks of single-phase transformers allows sparing to be easily achieved with a fourth single-phase transformer connectable to any phase without physical moves, reducing outage duration.

Click here to enlarge image

AEP’s 765-kV system is alternating current (AC) transmission, which lends itself to ready integration with existing and future infrastructure. Direct current (DC) transmission is also useful over long distances, but cannot be integrated well without significant cost.

I-765, the Interstate System

On Jan. 31, 2006, AEP announced the first new leg of the 765-kV interstate system, appropriately named I-765, in aligning with President Eisenhower’s vision. The proposal included a 550-mile line from West Virginia to New Jersey.

The benefits of this I-765 project include a 5,000 MW transfer capability increase from the Midwest to the Mid-Atlantic states, a peak system loss reduction of 280 MW, and significant congestion reduction. Gross congestion paid by consumers in PJM alone topped $2 billion in 2005.

AEP's Wyoming-Jacksons Ferry 765-kV line with 6-bundle conductor. The line, which connects stations in Wyoming County, W.Va. and Jacksons Ferry, Va., was energized on June 20, 2006. (AEP Photo)
Click here to enlarge image

Beyond the incentives and better siting processes of the Energy Policy Act of 2005, the electric industry has a societal responsibility to improve use of rights of way and to employ new technologies when building transmission.

  • AEP will apply new technology to make the I-765 project the highest capacity, most reliable line in the country.
  • New circuit breaker technology and state-of-the-art flexible AC transmission systems will facilitate independent operation of the three phases and greater capacity levels for the line.
  • Six-bundle per phase conductor arrangement will reduce by half the noise of older four-bundle conductor arrangements. Six-bundle was first used commercially in the United States for AEP’s recently completed 90-mile Wyoming-Jacksons Ferry 765-kV line traversing West Virginia and Virginia.
  • Wyoming-Jacksons Ferry mitigated line visibility with tower and conductor designs that blend with surroundings. AEP civil engineers achieved longer mountain-to-mountain spans nearing 4,000 feet to eliminate tree cutting in valleys.

President Eisenhower overcame sub-stantial inertia to put his vision of a national interstate highway system into law. Now it’s time for all transmission developers in the United States to overcome inertia and consider 765-kV when building the next interstate system for our nation’s future.


Michael Heyeck, P.E., is senior vice president, transmission, at American Electric Power. AEP owns the nation’s largest electricity transmission system. The 39,000 mile network includes more 765-kV extra-high voltage transmission lines than all other U.S. transmission systems combined.

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