Trains

One other thing I wanted to mention is the complexity of supplying power to overhead lines. This is based off a thought experiment I had long ago, about whether a municipality could "grow into" an electric rail network, by initially underprovisioning the power system until more trains in service demanded that upgrade. My conclusion was that no, it doesn't quite work like that. These are my observations.

The primary issue is one of raw power. That is, delivering kilowatts over wires that could be very long. We can consider Denver's commute train operation, which specifies mainline speeds (>79 MPH), 25 kV AC power, and an output power of 620 HP (456 kW).

That 456 kW is the focus, since that's generally what's needed at either peak acceleration or at top speed. We should assume that overhead lines should not wreck themselves just because a train is running hard.

If there's only one train on an overhead line segment, then the power requires is the same as one train's draw, which is 456 kW here. The problem is that compared to what's typically provisioned for a home (200 Amp, 240v service; aka 48 kW) or a light commercial business (400 Amp, 120/208Y service, aka 144 kW), this is a massive amount of power.

And even when a power company does supply a neighborhood of homes or a commercial district, they use oil-filled transformers that can be intentionally overloaded by some 30-50% for hours, on the premise that peak electric loads would die down afterwards and the transformer can cool down. Also, not every home or business uses anywhere near full power, so transformers are also undersized accordingly.

But for a single train, the need for that 456 kW is very real, very present, and if the overhead line is even 10 miles, that's 8 minutes if the train passes through at 79 MPH. If only one train passes per hour, the average power is only 60 kW but I don't think any transformer rated for 60 kW could survive an overload of 456 kW for 8 minutes and cool down for the next 52 minutes. That oil will have boiled by then.

So in reality, to provision power for just one train per hour, the transformer has to be rated for something closer to 200 kW. An entire suburban subdivision might total up to 200 kW depending on the time of day, and somehow the power company would need to supply this to wherever the railroad's power conversion equipment is.

So in your story where different communities are working to rebuild tracks and electrify, the latter effort has some gargantuan hurdles. The nature of the electricity network precludes attaching a 200 kW transformer to any random point in the network. A residential neighborhood might be fed with a 7200v 600 Amp ring circuit, which also connects to adjacent neighborhoods. Attaching the transformer to this circuit would work, but it would singlehandedly be 5% of the ring capacity. And the ring has to be nearby the railroad's power equipment. So stringing new high-voltage power lines toward the railroad is highly likely.

And this plan isn't even great, because the train passing would cause a lot of issues for the neighborhoods' electricity voltage stability. There's also the problem of supplying 7200v (called "low voltage" in the industry) if the overhead lines are meant to be 25 kV. Converting voltage up at the consumer point is generally not a good idea for efficiency, so a realistic rail power system would need to attach to medium voltage (eg 36 kV) or high voltage wires. So now our transformer needs to be located somewhere near such wires, and also will cost more because of the high voltage rating. High voltage wires are only placed where they are by necessity, because they're awfully dangerous otherwise. Some communities may be miles away from the high voltage lines that eventually power their homes.

In terms of technical requirements, this is rapidly getting out of hand, and I cannot see how a community smaller than say 50k-100k people would have the electricity resources and knowledge to build out an electric rail supply. And it only goes up as this piece of track gets more trains per hour.

If your story does wish to hew towards the almost-insane engineering for electric rail systems, it might be worth examining how Caltrain in the California Bay Area electrified their 50 mile corridor, between Silicon Valley and San Francisco. IIRC, they needed 10 power transforming stations along the route, with special engineering for each one of them.

Overall, this is why rural areas (and even semi-urban) don't tend to have electrified rail, despite having electricity service for streetlights, homes, and retail. Because they really just can't do it.

That feels like an interesting political/economic angle-- a territory's power could be implied by how far its neighbours will extend wires towards it. Getting the train reliably to Boston might be worth wiring all the way and paying for the electricity, but we can roll the dice on batteries to Albany.