The Weakest Link

Just like the proverbial chain an entire transmission line can be limited by its weakest link. But identifying the weakest link is not trivial, since it depends on the weather among other factors.

The span with the least wind

The weakest link of a high-voltage line is the section which reaches its maximum operating temperature first. It is determined by the wind in the specific location, since wind at a ninety degree angle cools the wires most effectively. In contrast, when wind blows along the wire then the cooling effect is significantly reduced.

The illustrations in this post show a case that we stumbled upon where the Dynamic Line Rating of an entire line is limited by a single span. In the shown hour wind happens to blow in parallel to a short section of the line. But the rest of the line experiences a significant wind cooling effect and could transport at least 50% more power.

Under Static Line Ratings when a single span limits an entire line it would make sense to refurbish this one span by for example lifting the towers and thus increasing its maximum operating temperature. But in this example the same span is not the weakest link when wind blows from different directions. The weakest link moves around depending on weather conditions, so refurbishing would not be a solution here, at least not most of the time.

Dynamic Line Ratings need accurate wind forecasts

This example shows the level of detail that Dynamic Line Rating solutions must contain. If the line were carelessly loaded by an additional 50% then there would be a risk of overheating that one span and causing structural damage, sparking a wildfire or worse. Dynamic Line Rating solutions must account with the wind in each span individually.