Welcome back to Volts, where every week is Transmission Week!
In my three transmission posts so far, I have focused mostly on the challenges of building new long-distance energy transmission lines in the US — the poor planning, the inefficient financing, the permitting and siting hassles.
Today I’m going to turn to a different subject: the various ways that the performance of the existing transmission system could be upgraded and improved through so-called “grid-enhancing technologies” (GETs).
To be honest, I probably should have tackled this subject first. Though new lines are going to be needed regardless, it is faster and cheaper to upgrade the existing system, with fewer regulatory barriers. GETs can achieve short-term relief from grid congestion while new lines are being developed.
There are three techs that are typically classified as grid-enhancing technologies, and I will focus on them in this post. In my next post, I’ll cover a couple of extra options that I haven’t found any other way to fit in.
Let’s jump in.
Closer monitoring to improve line performance
When electricity passes through transmission lines, they heat up. As they heat up, they sag. If too much electricity is run through a line, it can exceed its maximum operating temperature or sag to the point that it brushes up against trees or other structures, potentially sparking fires.
Grid operators want to avoid that, so they do not load lines to their full rated capacity. They set an operational limit well below theoretical capacity, to create a safety margin.
But how far below capacity should the limit be set? That is the question.
The heat and sag of a given line are changing in subtle ways all the time. They vary with the ambient temperature, humidity, barometric pressure, and wind speed. If it’s warmer, the line will heat up faster; if there’s a breeze, it will heat more slowly. Because the heat and sag are in constant flux, so too is the maximum safe capacity of the line.
“The number we love to quote is, an increase in wind blowing across a power line of three feet per second results in a 44 percent increase in the capacity of that power line,” says Jonathan Marmillo, co-founder of LineVision, a company that makes equipment for monitoring lines. “That’s the equivalent of a light breeze.”
(Note: this means that the capacity of transmission lines increases as the production of wind energy increases. Handy!)
But transmission system operators do not generally have that kind of real-time information about the heat and sag of their lines. They are forced to estimate, to use an average. In some cases, they assign a line a single “static rating,” well below full capacity. In some cases, they assign the lines seasonal ratings, adjusting for seasonal conditions. These estimates are, necessarily, conservative.
As a result, “most transmission lines are loaded at 40 or even 30 percent of their rated capacity,” says Marmillo. That’s an enormous amount of usable capacity going unused, to hedge against the lack of information.
That has changed with the development of “dynamic line ratings” (DLRs), whereby lines are continuously monitored and their capacity continuously updated.
DLRs have been around for a couple of decades, but the first generations of devices were cumbersome. They were installed directly on the power lines (which involved taking the lines out of commission) and proved unreliable in operation.
Technology marches on, though, and the latest generation of DLRs is vastly improved. LineVision’s DLR devices, for instance, have “no-contact” installation, which means no messing with the lines; they attach to the transmission tower. They are topped with LIDAR — the same technology used by autonomous vehicles — which gathers fine-grained data that is then crunched to determine the “net effective perpendicular windspeed,” the most important variable for determining line temperature. “We essentially use the conductor as a giant hot wire anemometer,” says Marmillo. Continued on link…