Train troubles in S.F. Bay area (BART system)

Discussion in 'General Electronics Chat' started by jgessling, Mar 17, 2016.

  1. jgessling

    Thread Starter Active Member

    Jul 31, 2009
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    I'm curious if any of you with knowledge about high voltage trains can comment on this issue. Started a few weeks ago, train cars on our system have been knocked out of commission due to power spikes. That's a pretty vague description, but today's paper had a couple details. Please let me know what you think. Snippets from article at sfgate.com .

    BART mechanics said Thursday that they were closer to pinning down the problem. They said 50 train cars that failed Wednesday were hit with a power spike as they moved through a track crossover north of the North Concord station. On that stretch of track the power is reaching up to 2,000 volts — twice what BART expects for normal operations.


    On each of the broken-down cars, the surge caused a semiconductor device called a thyristor to fail. BART said the parts — which are critical to each car’s propulsion system — cost $1,000 to replace and must be specially manufactured. That will take months, and riders should expect delays and shorter, more crowded trains in the meantime.
     
  2. Glenn Holland

    Member

    Dec 26, 2014
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    I'm a retired electronic tech supervisor for the Muni Railway and very familiar with the propulsion system and high/intermediate voltage power supplies on rail transit vehicles -IE- the Breda LRVs.

    The "thyristor" is an silicon controlled rectifier or SCR (or possibly a similar device called a "GTO") that is used in the chopper control (or inverter) for the traction motors. Muni's trains run on 600 volts and BART runs on 1000 volts, however the topology of the traction motor/propulsion system is approximately the same for both systems.

    I took a tour of BART's traction power substation at Lake Merritt and it's essentially a step down transformer (a "Y" primary with a "Y"/Delta secondary) connected to a large bank of diode rectifiers which provide a "12 pulse" DC power supply.

    The output of the rectifier bank is 1000 VDC which is connected to the third rail using "pipe cables" which are sealed conduit pressurized with inert gas. These rectifiers are very simple and they should not produce such large power surges capable of damaging the propulsion system.

    If there's 2000 volts or more on the third rail, my initial thought is the step down transformer may have a short between the primary and secondary, but this would also knock out the diode rectifiers as well as the train propulsion.

    Are you a mechanic or vehicle technician and do you know who is in charge of vehicle maintenance & repair? I would like to visit BART and get a better idea of what's happening with these power surges.
     
    Last edited: Mar 17, 2016
  3. wayneh

    Expert

    Sep 9, 2010
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    Interesting. I've ridden BART many time from SFO to Palo Alto. I'll be watching to see how this turns out.
     
  4. jgessling

    Thread Starter Active Member

    Jul 31, 2009
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    14
    I'm only a longtime (and mostly disgruntled) BART rider. Some other tidbits that I've read. The substation near the end of the Concord line is now shutdown because it was suspected of generating these high voltage spikes. And a tech posted that he overheard a supervisor blaming a broken ground strap ( not sure where) for the problem and was going out to fix it. I'm doing my best to keep this a technical discussion, we can talk transit politics another place.
     
  5. Glenn Holland

    Member

    Dec 26, 2014
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    110
    There is an ongoing problem with copper thieves stealing cables from the BART and Muni tracks.

    However, I'm not sure how that would cause the voltage spike problem.
     
  6. jgessling

    Thread Starter Active Member

    Jul 31, 2009
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    BART has never gone to Palo Alto, maybe you mean somewhere else?
     
  7. wayneh

    Expert

    Sep 9, 2010
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    You have to make the connection from BART to Caltrain and on to PA at the Millbrae station.
     
  8. #12

    Expert

    Nov 30, 2010
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    I think something that worked for decades broke and (hopefully) competent people are fixing it.
    For $1000 a thyristor, you can afford to hire a competent person.;)
     
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