I was innocently perusing the IEEE Power & Energy System “Transactions” contents and there it was, an article on 12-phase transmission lines. This caught my attention because I have never seen a 12-phase line. But, and I am bragging now, I have been involved in the early parts of some high-phase order (HPO) transmission line research and development in one of my past lives.

I used to work with some fellows who were so curious they made me look normal. Well, maybe that is a stretch. Let's go with practically normal. Back in the 1970s, Lionel Barthold (who was one of the founders and the first president of PTI, which is now a part of Siemens) collected a rather odd assortment of engineers at PTI to work on, among other things, a compact transmission line project. The crew included Ian Grant, a former GE engineer and New Zealander who is now in transmission planning at TVA; Jim Stewart, an academic and head of the Schenectady Chapter of the Society for the Preservation of Useless Information; and your humble correspondent, fresh from designing and building transmission lines for REA cooperatives in Louisiana. After completing the compact lines research for a New York funding agency and EPRI, our next target was HPO transmission.

To those of us on the inside, HPO transmission was an exceptionally keen idea. It embodied the ability to use lower voltages to transmit relatively large amounts of power over minimal rights-of-way. It was also a natural extension of the compact transmission work we had done. Using 3-ft (1-m) phase-to-phase spacing for a 115-kV class line, instead of the more usual 12-ft (~4-m) spacing, provided transmission with the physical profile of a distribution line. Unfortunately, we might have been too far ahead of the ultimate needs of our industry. Some have suggested that we were answering questions no one had asked. And that is a problem for a lot of research (it was a constant discussion topic when I was at EPRI), but what fun work!

The abstract to the IEEE paper that started me off here says, “Jointed 12-phase transmission lines are frequently used in power systems.” This makes me grin. I wonder if it could possibly be true. It certainly isn't true in this hemisphere. And I'm not sure if there are any HPO lines in Europe. If there are, please send me a note and straighten me out.

My involvement in the PTI work ceased when I left for PG&E in early 1980. But Jim and Ian continued to carry the torch. And the R&D line, which I had participated in designing, was built and energized at the Research Center in Malta, New York. That line actually showed up on the December 1980 cover of Transmission & Distribution World. That six-phase portal structure looks like a tennis racquet! The research project attracted a decent amount of industry interest with a lot of visitors from around North America and several from international utilities. And the project results further refined the design parameters for HPO lines and collected useful field operational data.

There was a subsequent demonstration project in the 1990s that I followed from my job at EPRI. New York State Electric and Gas (NYSEG) had a short 115-kV double-circuit line going from the Goudey to Oakdale substations near Binghamton that was modified and operated as a six-phase line. All of the NYSEG line operational experience was what the research had predicted. But one of the persistent questions by utility visitors to the research project concerned six-phase line protection: Would it be possible to program the relaying successfully to protect the increased complexity of the HPO line?

As luck would have it, one of the most significant outcomes of this demonstration line was what they learned from the two faults experienced during the three years of operation. The protection system functioned flawlessly. At least to the small cadre of researchers, a round of high-fives and fist-bumps were in order. The demonstration was successful and the potentially “deal killing” issue of relaying was laid to rest.

Stories about the research can be found in the October 1988 and May 1992 issues of T&D World. But, alas, the research project had run its course. And the equipment for six-phase energization of the demonstration line was retired, and the line returned to double-circuit 115-kV three-phase operation. As it turned out, since it was such a very short line, the transformer impedance (to provide the six-phase voltage) more than offset the reduced line impedance. Thus, the demonstration line's ability to carry load was diminished during six-phase operation. This peculiarity would certainly not be an issue with more conventional line lengths.

In fact, studies have shown that three six-phase 115-kV lines could have power-delivery characteristics that are equivalent to a 345-kV line and require a smaller right-of-way footprint. Yeah, we may have been answering questions that hadn't been asked way back then. But, it sure seems relevant today. And let's not let go of the opportunity to find applications for high-phase order transmission lines.