I'm interested in the history of the 345 kV power level for high voltage transmission in the United States. I've got two (and a half) questions:

  1. According to this source 345 kV was first applied in 1953 by American Electric Power. Who has developed it and why have they chosen exactly this voltage? Because it is 3*115 kV and nearly 2*161 kV?

  2. When you look on this power network map you will notice, that 345 kV is still the most highest voltage for the transmission networks of the Midwest and Texas. Why does they still stick to 345 kV even for new-built power lines despite 500 kV would be much more economic (less losses at a similar right-of-way width)?

PS: I've thought that "Engineering" wouldn't be the right category for this question, but I was advised so at Meta.

  • $\begingroup$ Thanks for the great power network map. I fixed up your link for the AEP 345 kV line. The power network map is great, but we only need one copy. $\endgroup$ Oct 24, 2018 at 23:46

1 Answer 1


With the high voltage AC power lines, there are trade offs between losses due to resistance in the wires, where the higher voltages are better and losses due to capacitance to the air, etc. where lower voltages are better. That is why many big, high voltage power transmission is done with DC these days. For example, the 500 kVDC line from the Intermountain Power Plant (IPA) in Utah to Los Angeles.

Another factor is the higher AC voltages are considered by some to be bad for the environment. DC is ... better, not perfect but better. Something I did not see in the article, since the higher the voltage, the lower the current, the higher voltage AC produces less of a magnetic field, 345/500 less. In the case of IPA at full load, they are moving 1900 MW at 500 kV which works out to 3800 amps. That much will produce a good sized magnetic field, even from the height of the transmission towers.

(warstory) Years ago, I worked at power plant in a trailer under the startup lines that they said carried 10,000 amps. The magnetic fields made the text on the CRT computer monitors almost unreadable because it jiggled up and down by almost 1/8 inch. After a while, we got a patch from IBM that set the CRT refresh rate from 70 Hz to 60 Hz and everything was rock solid.(/warstory)


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