It may seem like that spending all evening watching TGV cab rides on YouTube would not yield any lessons1, and usually you would be correct. But after watching a cab-ride yesterday, I did learn a few things about overhead electrical systems that I found quite interesting.

Auto-generated description: An abstract black and white pixelated design resembles a simplistic face with a rectangular shape.
French railway sign indicating neutral zone. Credit: Peter Bereczki
For example, I learnt about [neutral sections](https://en.wikipedia.org/wiki/Overhead_line#Neutral_section_(phase_break)), which are areas of the track that are unpowered. When the overhead power is sourced from different grids with potentially different frequencies, any bridging between the two can cause significant problems. So these are zones where the train is required to coast through with the traction system disconnected from the power. I'm not aware of this being a thing on our suburban system — apparently it's more of an issue for AC systems — but Wikipedia does suggest that there are some rail lines in this country that have track-side magnets that automates this: passing by the magnets operate a circuit breaker providing power to the traction motors.

I also learnt about mid-point anchors. I’ve seen these around our system with relatively newer infrastructure, I was curious as to why they needed to exist, and why they aren’t present in the older sections. Turns out they’re required when both the catenary and overhead lines are attached with tensioning equipment. These are usually weights, and since neither wire are attached to anything fix, they can moving freely along the track. Hence the need for these anchors to prevent that from happening. I also realised that in the older infrastructure, the catenary are connected to the gantries, which remove the need for such things.

Example of mid-point anchors on the Melbourne suburban system. Credit: Driver667

Anyway, forgive the rambling and nerdy post. I’ve have a fascination in these electrical systems and I always find such factoids interesting. Probably helps that finding this out offsets the negative feelings I got from spending all evening watching YouTube.

  1. I’m still recovering from a cold, or at least thats the excuse I’m going with. ↩︎