The intent behind Dynamic Line Ratings (DLR) is to reduce power prices and emissions by increasing transmission capacity. Thanks to more transmission capacity, lowest marginal cost generators can access a larger market, which brings down power prices on average. But how many lines should be covered by DLR to increase capacity between regions?
Our CTO Dr. Henri Manninen supervised an interesting MSc thesis at Taltech that investigated the bottlenecks between Estonia and Latvia over the course of the year 2023 based on actual power flow data from the transmission system operator (link). The results showed that around a quarter of the 330 kV lines were significantly limiting capacity over the year.
Congestion on these lines limits cross-border transmission capacity and therefore causes price differences between the two countries. With additional capacity on these limiting lines the power prices between Estonia and Latvia would equalize more often.
Dynamic Line Ratings need to cover every span
Overhead lines are composed of spans, which are the roughly 400 meter sections of hanging conductors between towers. Each of these power lines may be around 100 km long, so each line is actually composed of around 250 sections. The entire line is limited by its weakest section.
How many spans of each line would need to be covered by DLR to increase the capacity of the line? We investigated this on the basis of a power line in Estonia with 61 spans (link). The results showed that almost all of the spans limited capacity over a year in case of a new power line in which there are no clearance problems (blue bars in the bottom graph). The weather conditions on all of the spans would need to be monitored to maximize its capacity.
In the above graph, the blue bars show the frequency of occurrence of critical spans under the assumption that the maximum operating temperature of each span is 75 degrees Celsius. Almost all of the spans limit capacity in this case. The red bars show the frequency of occurrence of critical spans when the maximum operating temperature was identified based on LiDAR data. In the line we studied there were in fact significant clearance limits on five spans, so the number of limiting spans was less when accounting for this, but still roughly a fifth. The spans with clearance issues would benefit from refurbishment.
This shows that roughly a quarter of the network would need to be covered by DLR to increase capacity between the two countries - a quarter of the lines limit capacity at some point over the year and almost all of the spans do, under varying weather conditions. Installing sensors on a quarter of all towers would be practically infeasible. This is the fundamental reason why DLR should be done without sensors, on the basis of weather modeling.
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