Thanks for giving me the opportunity OZ.

Real Time Thermal Rating (RTTR) systems for transmission and distribution cables.

This is a long one but it describes one of the biggest unmet needs of the bulk electricity power industry.

There is a tremendous need for physical sensing in the power industry.  And one area where huge savings can be realized both in terms of dollars and carbon foot print is the accurate modeling of power conductor temperatures in real time. Not just underground or submarine cable systems but the vast network of overhead lines that make up continental bulk power grids.

The amount of power that a powerline can transfer is determined by its maximum operating temperature.  Typically that limit is a function of design sag. Those high voltage lines that you see hanging from those ugly towers get hot. Imagine 1000 amps of current being carried on a conductor that is 2 inches in diameter. There is a lot of radiant heat generated that is dissipated by natural convection when there is zero wind speed. Wind speed is a major factor in the cooling of these conductors. Other ambient conditions affecting the temperature of the conductor is the ambient temperature and solar radiation.

How hot do these conductors get? The maximum operating temperature for aluminum is 150’C that is when annealing begins to occur which over time will make the conductor brittle. That is typically not the most limiting parameter. It is the sag that occurs when lines get hot which causes the lines to droop into buildings, trees, earth... Of course contact with ground creates a fault where electricity travels through the ground back to the power sources until that line is automatically removed from service (typically .05 seconds).

The maximum operating temperature for lines can vary dramatically. Worst case the maximum operating temperature can be as low as 60’C right up to 150’C with the average around the 100’C range.

In hot summer weather the current carrying capacity of the grid is reduced significantly meaning that the transfer capability to move low cost energy to displace high cost resources becomes curtailed. System cost and carbon footprint rises. Consider that on a global scale.

How can we monitor the temperature of our high voltage lines that make up the bulk power grid? Today we use weather stations and make assumptions that the ambient conditions of our lines are represented by weather data from the closest weather stations to those lines. And then we apply a forecast up to 3 hours in advance of what the worst case ambient condition will be to allow flows to be managed on those lines in advance of those conditions. It is an extremely conservative process because it has to be. Overloading a line creates more than just an unsafe condition it causes damage and reduces the design sag limits…it permanently sags the line resulting in the need for very costly restring of the line (millions of dollars).

Today we have fiber optics for communications associated with the protection and control of lines that are actually strung on the skywires of those towers that carry the power conductor. Skywires are grounded and are designed to shield the lines from lightning strikes. So why not string fiber optics that will provide real time ambient conditions removing some of the guesswork and conservative application of thermal limit monitoring.

Better yet why not run the fiber optics in the line itself?

Or how about sampling the line with LIDAR so real time measurements of line condition are available. That would be a breakthrough for the power grid.

What we are doing today is really low tech and expensive to our economy and our ecology.