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What's Frying the Electrical Systems On BART Trains? (ieee.org)
Tekla Perry writes: Earlier this month, BART engineers shut down a substation in hopes that the closure would quiet the power surges that were frying the electrical propulsion equipment on BART cars -- a peak of 40 in just one day in February. The shutdown seemed to solve the problem, but BART officials weren't sure they'd really found the answer. Yesterday, the power surges popped up again, on an entirely different section of tracks, damaging 50 cars before BART closed off that section, rerouting passengers onto buses. Track inspections yesterday revealed nothing, and BART reports that it has reached out to experts around the country and asked them to fly in and help solve the mystery. Do you have a theory? Note: BART is the 5th-busiest heavy-rail rapid transit system in the U.S.
So the A & B cars having inductions motors seem to be fine, while the problem seems to be confined to the C cars having the DC motor. That's one difference.
Also, what else has changed? Take a look at wunderground to see that the Bay Area is having a wet season.
Why would the C cars have been mostly fine all along and having trouble now?
So there's charge building up in the DC motors that they can't handle and that makes them blow out. The charge has nowhere to go. What controls the flow of charge? Grounding. What can go wrong with grounding? Good grounds can go bad when a lot of discharge causes the sand in the soil to vitrify (melt into glass) after discharges and lightning strikes have been shooting through it for decades. Better grounds can unexpectedly form when more highly conductive paths form up. The AC induction motors will suffer a power loss but can handle the charge jumping back & forth in unexpected ways, while the DC motors can't.
Add it all up. This has to be a grounding problem aggravated by the wet season, and an underlying assumption that once you sink a ground it's good forever. It isn't.