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

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

  1. jgessling

    Thread Starter Well-Known Member

    Jul 31, 2009
    76
    30
    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
    469
    162
    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
    13,436
    4,274
    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 Well-Known Member

    Jul 31, 2009
    76
    30
    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
    469
    162
    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 Well-Known Member

    Jul 31, 2009
    76
    30
    BART has never gone to Palo Alto, maybe you mean somewhere else?
     
  7. wayneh

    Expert

    Sep 9, 2010
    13,436
    4,274
    You have to make the connection from BART to Caltrain and on to PA at the Millbrae station.
     
  8. #12

    Expert

    Nov 30, 2010
    17,840
    9,178
    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.;)
     
  9. Glenn Holland

    Member

    Dec 26, 2014
    469
    162
    Here's the latest "No Brainer" explanation about what went wrong.

    In the area where the electrical/electronic failures were occurring, the rails had been "re-profiled" or shaved with a high speed grinder mounted on a special track maintenance vehicle. This process left billions of steel particles on the track way that were stirred up when the trains went over the area and they were eventually drawn into the traction motors and electrical/electronic cabinets.

    In accordance with Electricity 101-A, metal particles will conduct and cause catastrophic failures!!! There are also strong magnetic fields around the components with high current that will attract steel particles off the ground. However the 1970s vintage trains with DC traction motors (commutators) were especially vulnerable.

    Since the 1980s, high voltage electronics in transit vehicles are mounted within sealed enclosures with cooling air directed over external heat sinks so the components never come in contact with the outside air.
     
  10. MrChips

    Moderator

    Oct 2, 2009
    14,282
    4,195
    Geez.

    Even I would know that when I am drilling, grinding and filing holes on a metal chassis for an electronic project, it makes sense to vacuum out all the metal bits out of the chassis before assembling.
     
  11. Glenn Holland

    Member

    Dec 26, 2014
    469
    162
    Most railroads are not electric and metallic particles are not a problem.

    However with 600 to 1000 VDC powered trains, metal particles can create problems big time -especially in tunnels where dust accumulates and never gets washed away by rain. I used to work at a rail transit agency in the San Francisco Bay Area and the tunnels and underground control rooms were absolutely filthy with dust of all forms. Minute steel shavings from wheel wear could be found on anything with a magnetic field, such as motors, relays, and transformers.

    With all the contamination, it's a wonder there weren't even more failures. o_O
     
Loading...