BART frying thyristors

[K6JEK]

We have a mini crisis out here on the left coast. Voltage spikes of unknown origin are frying the BART cars, taking them out of service forcing BART to bus their riders.

"It's a thyristor. You can't Google that. It costs a thousand dollars and takes twenty two weeks to make."

 That's a quote (more or less) from a BART engineer trying to explain what's going on. Well you can actually Google it, of course. I was surprised by 22 weeks to make. I don't know what to think about a semiconductor that costs a thousand bucks. 

Do any of you guys know anything about big stuff like the controls on trains? How did they used to do it? Big relays I bet. Is a 22 week lead time, thousand dollar thyristor par for the course?

Incidentally,  five minutes of Internet searching gave me a few tidbits. The infamous third rail is 1000 Vdc. Some cars have DC motors. Others have induction motors. That was a surprise.

[W1RKW]

Failure can be related mostly to mechanics.  Mounting of the replacement device is key.  Mounting surface of the heatsink needs to be clean as a whistle, smooth and flat.  Use manufacturer recommended heatsink compound. There are several types with different thermal transfer ratings. Also some can be conductive to some degree creating unwanted current paths. It's important to ensure the compound does not cause a conductive path between the electrical connections.  Observe manufacture torque or clamping specs when mounting the device.  On the electrical side of things, need to ensure voltage and current ratings are within spec.  Need to determine if turn-on or trigger pulse parameters are within the safe operating temperature ranges of the device. need to look at turn-on di/dt and if it's within acceptable levels. And if there are any spurious voltages on the gate.  

[KA0HCP]

One thousand dollars is peanuts in the spare parts business.

Sound like maybe they need to revert back to electron tube Thyratrons.  Readily available and can handle up to 2 kAmps.

http://www.excelitas.com/pages/product/Thyratrons.aspx

[K9PNP]

Don't know about the BART units,  but mining equipment using 275 VDC or thereabouts, used HEAVY duty manual switching and resistor banks to control motor speed.  Thought I had some pictures that my dad gave me on these, but can't find them.  According to him, they were pretty reliable.

[KL7OF]

seems like there should be a spare thyristor on the shelf somewhere.....Go Bart Go.......

[Tom WA3KLR]

About ten years ago I ran across a vendor of high voltage high power thyristors which were apparently used for utility company equipment inverters?  I wish I could remember the vendor.  As I recall they came in packages like hockey pucks.  I presume though that the BART engineers have beaten the bushes for sources by now.  Maybe the brand name will pop into my head soon.

The devices I'm trying to recall may well be vacuum tube technology - thyratrons.  I'm really stressing my gray cell here on this topic.

Here is  one source of the vacuum tube type of devices I was thinking of (hot and cold cathode/pseudospark) :

http://pulsepowersolutions.com/switches/

Looks like they are for higher voltage applications than rail cars.

[WD5JKO]

ABC News talks about Bart, and the issues. There is an expert using an oscilloscope. They show the hockey puck size thyristor:


http://abc7news.com/traffic/expert-runs-bart-test-car-as-officials-discuss-infrastructure-issues/1252774/

The system is 45 years old? Finding power semiconductors from that era will be challenging. Maybe Fair Radio has some. :-)

Jim
Wd5JKO

[KC4VWU]

Maybe we'll see some of their engineers at Dayton looking through the Mendelson's tents!

[RolandSWL]

A Russian guy at my job worked as a designer of railroad electronics before emigrating to the U.S.A.
He described these 'hockey-puck' thyristors as replacing the hollow state thyratrons. And yes, they take a long time to produce.
Maybe BART could source them from Russia. Svetlana brand?

RSWL.........

[W6TOM]

  Back 20 years ago I rode that miserable thing when I worked in San Francisco, the signs in the stations that told what the train was were Nixie Tube displays. One of my friends worked for Mike Quinn's Electronics at Oakland Airport, a grand emporium of wonderous electronic junk long gone. Those Nixie Tube signs used DTL logic, Quinn's kept BART's old Nixie Tube signs running for years, they were the only place BART could get the parts. I stopped working in SF in late 1996, those signs were still in use.

 BART has never been very good at updating their equipment, it would not surprise me at all if the thyristors are obsolete and unobtainium and that BART needs to have some special built.

[Opcom]

The time taken to manufacture a semiconductor product depends on the die dimensions, materials to be used, geometric complexity, etc.. There are a few basic tutorials about this but anything complete is usually in a thick expensive book.

Each process makes generally just one kind of change to the material, additively and subtractively forming it into the product over time and each individual process can take hours to days to complete.

Other operations that take time, besides just making the devices in raw form on the silicon wafer are passivation, back grinding, sawing, mounting to a leadframe or metal substrate/slug, lead wire bonding, encapsulation, marking, and various tests done at each step for quality purposes.

If a device is not being made, then its process has to be allocated in the throughput capacity of the plant, and the "22 weeks" starts at zero. If all of the devices being made are already allocated to existing sales orders to which a customer's end product production line is tied like clockwork, the same thing applies.

[Tom WA3KLR]

Jon,

Any updates on the experts and the source of the transients, replacement part and future solutions?

[flintstone mop]

Sounds like the BART "engineers' are really bad parts changers. And haven't a clue as to what is really going on with their system. They're just guessing the problem. There's probably a very loose connection or defective transformer somewhere in the system.

Fred

[W6TOM]

 No solution to the problem, glad I don't need to ride that miserable thing, BART management is certainly using it promote a 3 Billion Dollar Bond Issue they want to have on the ballot.

[KD6VXI]

There is the reason for the delay.   3 Billion Dollars.

Call me cynical,  but I've seen it more than once.   Delay a repair to get a bigger budget.

Bart was fun,  when I was a kid.   I can't imagine actually relying on it,  though.   Guess I'm too used to hopping in my car,  on my schedule.   New Yorkers,  Chicagoans,  Bay Areanites,  they all seem to do fine on public mass transit.

--Shane
KD6VXI

[W2PFY]

The first thing Bart need to do is change it's name to Fart since their service stinks so much! The second thing they need to do is get our class E guys out there to fix the problem once and fer all! I know that if they use class H modulators in there instead of those pesky thighatrons, things would run smoothly once again...Just saying....

[W6TOM]

 I worked in down town San Francisco from 1994 to1996 and two other one year periods in the late 80's and early 90's, my work was near the first station out of the transbay tube, Embarcadero Station. BART was the best alternative to get there from the Eastbay where I live, it was the best choice of a number of UNATTRACTIVE choices. If there was a problem it was never good and you were stuck.

 I recall going to the FCC office on Battery Street around 1985 to take the test for my FCC License, I took BART, walked down to Market Street to find the entrance to the Embarcadero Station LOCKED. A passer by told me the power had failed in the transbay tube and there were buses at the Eastbay bus terminal. Got the bus to the West Oakland Station, no one there to tell you WTF and waited in a line for 30 minutes, the wrong line!! Finally got the train to Bayfair Station, by then it was almost the end of the day, my plans were to take a half day off.

 As I said, I'm glad I don't need to ride that miserable thing. My only other experience is the MBTA in the Boston area. My sister's husband rides a diesel commuter train to Boston, that isn't to bad, I've taken it a few times. The Boston subway is bad or worse than BART.

[Tom WA3KLR]

A few excerpts from Wikipedia-BART:

BART revenue routes cover 104 miles (167 km) with 45 stations.[4] Trains run on exclusive right-of-way, in subways or elevated. The system uses a 5 ft 6 in (1,676 mm) Indian gauge[4] and mostly ballastless track instead of the 4 ft 8 1⁄2 in (1,435 mm) standard gauge and railroad ties used on United States railroads. As a result, all maintenance and support equipment must be custom built.

The maximum speed trains can travel is 80 miles per hour (130 km/h),[4] but BART does not typically operate trains at that speed except to help a train make up time.[6] The maximum speed BART uses during normal operations is 70 mph.[7]

Trains length ranges from four cars to a maximum of ten cars, which fills the 700 feet (213 m) length of a platform.[8] At its maximum length of 710 feet (216 m), BART has the longest trains of any metro system in the United States. The system also features car widths of 10.5 feet (3.2 m) (the same width as a Budd Metroliner), a maximum gradient of four percent, and a minimum curve radius of 394 feet (120 m) on the main lines .[9]
- - - - --
DC electric current at 1,000 volts is delivered to the trains over a third rail.[5] In stations the third rail is on the side away from the passenger platform, except the middle platform at the San Francisco International Airport station. This reduces the danger of a passenger falling on the third rail or stepping on it to climb back to the platform after falling off. On ground-level tracks, the third rail alternates from one side of the track to the other, providing breaks in the third rail to allow for emergency evacuations. Underground tunnels, aerial structures and the Transbay Tube have evacuation walkways and passageways to allow for train evacuation without exposing passengers to contact with the third rail, which is located as far away from these walkways as possible.[10]
- - - -
Traction motors

Prior to rebuilding,[102] the Direct Current (DC) traction motors used on the 439 Rohr BART cars were model 1463 with chopper controls from Westinghouse, who also built the automatic train control system for BART. The Rohr cars were rebuilt with ADtranz model 1507C 3-phase alternating current (AC) traction motors with insulated-gate bipolar transistor (IGBT) inverters. The Westinghouse motors are still in use on the Alstom C (C1) and Morrison-Knudsen C2 cars and the motors that were removed from the Rohr cars were retained as spare motors for use on them. Cars have a starting accelerating of 3.0 mph/s (4.8 km/(h·s)) and are capable of holding that acceleration up to 31 MPH. Residual acceleration at 80 MPH is 0.78 mph/s (1.26 km/(h·s)). Braking rates range from 0.45 mph/s (0.72 km/(h·s)) up to 3.0 mph/s (4.8 km/(h·s)) (full service rate).[103]
- - - -
Car types

BART operates four types of cars, built from three separate orders, totaling 662 cars.[2]

To run a typical peak morning commute, BART requires 579 cars. Of those, 535 are scheduled to be in active service; the others are used to build up four spare trains (essential for maintaining on-time service).[2][93] At any one time, the remaining 90 cars are in for repair, maintenance, or some type of planned modification work.[94]

[Opcom]

The first thing Bart need to do is change it's name to Fart since their service stinks so much! The second thing they need to do is get our class E guys out there to fix the problem once and fer all! I know that if they use class H modulators in there instead of those pesky thighatrons, things would run smoothly once again...Just saying....

already in use in Dallas for the DART. But we like to share!

[KD6VXI]

I thought that was the Fairfield terminal of Bart,  FART.....?

--Shane
KD6VXI

[KL7OF]

Did they get that train running yet??

[K6JEK]

Did they get that train running yet??

They have some trains running but haven't figured out the problem. Apparently only one section of track is affected.

BARTs moves about 400,000 passengers per day.

https://www.bart.gov/news/articles/2016/news20160316-0

[W6TOM]

  And if you thought that BART was a FUBAR, you ain't seen nothin'.... Stay tuned for California High Speed Rail!!!

[WD5JKO]

This issue sounds somewhat similar to the SCR based inverter systems used to generate 60HZ AC power from banks of storage batteries. This was back in the 1970's when power semiconductor choices were more limited. Those inverter systems had commutation circuits to turn off the SCR at the right instant. If that failed, then huge currents surged causing 1/0 cables to flinch until the fuse popped. Nuisance fuse  tripping was followed by larger fuse sizes. The inverters tested all did this, it was just a matter of time before you'd hear that familiar noise stop, the cables flinch, and then the fuse blow.

I would bet that the original design engineers who designed Bart back in the 1960's would better understand the issues plaguing Bart today, and would have already fixed the problem(s). I say this because the old school engineers in my opinion had a better grasp of the technologies involved, and were not too zeroed into a specific issue, i.e. they would see the forest before an individual tree.

Jim
Wd5JKO