Working on a not always reliable memory:
The BART third rail system was originally set up to only energize the third rail when needed, which suggests the substations are just feeding the adjacent third rail blocks with no ties between substations. The original third rails were steel I-beams with a reasonably thick layer of aluminum bonded to the steel to improve conductivity.
From what I gather from the article, the failure was on the Berkeley section, which was put underground to comply with a demand by the Berkeley city council after construction started for the overall system. My recollection was that Berkeley also required any new construction would entail undergrounding the utilities serving the site under construction - hear stories about where the resulting undergrounding would ony cover the distance between the two closest poles. There's a reason why the city got (and deserved) the nickname "Bezerkeley".
Having heard quite a few PG&E engineers tell about their work at the UCB EECS department Power Systems seminars - my semi-educated guess is that there was only one feeder from a BART traction power substation to the PG&E network. BART would have to pay extra if they wanted redundant feeds.
I would want to know how the power system for BART is configured before I would make any suggestions about what should be done. Do they take multiple feeds from PG&E and connect to their substation with the ability to network the rectifiers and transformers plus the DC feeders. Or is each rectifier node just one 34kv line to a transformer/rectifier unit feeding four DC breakers to the four rail blocks. [Track 1 E, Track 1 W, Track 2 E, Track 2 W] Or are there two transformer/rectifier units fed by one or two 34kv lines that have switching capability. Many possibilities. One 34kv line failure sould not cause a major outage with proper design.
I would think that the 34.5kV feeders only need to go to the nearest PG&E substation. IIRC, the maximum power draw for a BART train is on the order of 10MW, which translates to about 200A per phase on the 34.5kV feeders. I would hazard a guess that the feeders use aluminum conductors, with the larger diameter reducing voltage gradient on the insulation next to the conductor.
Wonder what the new power lines are going to be? Aluminum or copper? Maybe with Kapton insulation if it was me.
Have to wonder if BART would have used higher voltages than the 34,5 kV feeders now if was possible to have multi voltage transformers? That feeder voltage even lower than Amtrak's NEC voltages.
FWIW, the underground cables in my neighborhood were failing 11-13 years and had been installed in the late 1970's.
A bit frightening to think that my first time on BART was a bit over 49 years ago, January 29th, 1973 when the MacArthur - Richmond segment opened up.
1970 era 34.5 kV cable failed 4 days before start of scheduled replacements.
BART suspends Red Line service, Orange Line only between Richmond and MacArthur - Railway Track and Structures (rtands.com)
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