How is high voltage and high current DC usually distributed around an interurban third-rail train or subway system? My assumption has been that the running rails are at earth ground as they’re not standing up on ceramic insulators like the third rail. My other assumption is that there are multiple power stations powered by AC to counteract transmission losses as steel rails are not exactly the best conductors known to man. (the train system in question has 104 route miles)
That system has been having some problems of trains getting hit with double the normal voltage as they pass through an interlock. Instead of causing a brief blip of extra-fast, the high voltage (2,000 volts DC) is frying thyristors in the motor controllers.
Would it be possible for one of the power stations to lose its earth ground reference and have its ground float on up to the 1,000 volts of the next power station down the line when a train passes through the interlock? I’m just trying to visualize what could happen to hit the trains with double the normal voltage.
Special bonus: Figure this all out and identify a fix, and BART will probably hire you on the spot. Nearly sixty cars were disabled by this problem on Wednesday, and rather than risk losing more, they’ve shut down that section of the system, which is making a mess of traffic and people’s commute times. Alternately, do you have a source for apparently obsolete or otherwise insanely scarce thyristors? All I know is they’re big things that go for about $1,000 each, and the techs were saying it might be as long as 22 weeks for Powerex to make several dozen so they can start repairing the zapped ones.