I first became aware of this technical issue when reading about the challenges facing the "longest train" record attempt.

https://www.theautopian.com/the-swiss-just-assembled-the-worlds-longest-passenger-train-and-the-challenges-they-faced-might-surprise-you/

"Additionally, the operators limited the trains to no more than 21 mph. The reason for this has to do with the train's regenerative braking. Kramer says that when going down a hill, the train's regenerative brakes feed energy back into the overhead grid, and there was a concern that with a train this big, the regen would blow fuses in the trains or literally melt the overhead catenary lines. To avoid overloading both the grid and the trains, the operators limited the train's speed and software to limit how much power gets fed back into the grid."