When good trains go bad: Pantograph edition

Working my way through a backlog of drafts as well as emailed and commented questions.. (and thanks to those who have pointed it out, I’m aware that some links in older posts are no longer working. At some point I’ll go through and see what I can do to fix them, but I think some of those news articles & blogs aren’t around anymore)

Today’s question is about pantographs.

токоприемник, a search which has brought a lot of people here,
presumably from Russia.

Why don’t pantographs wear out or break?

Oh they do.

Not my picture – this is the broken pantograph outside the tunnel by Goose Hollow that tied up the alignment for about 7 hours, January 31, 2009 

Pretty much everything on the train is breakable (this is not an invitation), though instances of something serious like a pantograph breaking are rare. Mechanics, operators, supervisors, and even the public tend to notice excessive arcing that often indicates something is wrong before a pantograph reaches a breaking point. Arcing when the lines are icy or where wires cross – such as around Pioneer Courthouse – is not unusual, but repeated arcing when it looks like the overhead is perfectly clear is not normal and could be indicative of something wrong with the pantograph.

As mentioned in the earlier pantograph post, the part of the pantograph that makes contact with the overhead wire is called the carbon shoe. The carbon on this is a lot like pencil lead – if you ran your finger over a carbon shoe, it’d leave a dusty black streak on your hand. This is the source of the gritty black dust on the trains which is most noticeable around the coupled cabs.

Carbon shoe dust

Also previously mentioned, the overhead wires are staggered so that they make a zigzag motion over the pantograph. This ensures that the carbon shoe wears down evenly across the length of its surface. Under normal wear and tear, a carbon shoe can last from 9 months to a year before it needs to be replaced.

It can happen sometimes that rather than sweeping back and forth over the carbon shoe, the catenary will instead wear a narrow groove into the carbon, causing the wire to become stuck in the groove and wear just that part of the carbon shoe down. Potentially the wire can saw down into the pantograph if the groove is not noticed and fixed – remember that the spring-loaded pantograph puts a considerable amount of upward pressure on the overhead wire. A groove in the carbon shoe will require the train be pulled out of service so that the carbon shoe can be replaced before the pantograph breaks. This is one potential cause of a pantograph breaking.

Another cause can be extreme heat, and we’re getting near that time again.. well, maybe, if we get any proper heat waves now that it’s summer. As I posted last year, hot weather causes the overhead wire to sag when the weights on the catenary poles hit bottom and can’t provide enough tension in the overhead wire.  When this happens, train speed is reduced to prevent the pantograph from getting caught in or pulling down the overhead wire, which would do significant damage to both.

It’s also possible that damage to the overhead wire can break a pan, such as intentional vandalism. This is part of the reason for sweep trains every morning as well as regular walking inspections of the overhead wires to check for any damage or anything else that looks questionable.

How can you tell something broke?

Aux Fail (the red light on the console), trailing Type 1 cab WB at Jeld Wen Field

In Type 1-3 cars, often the first visible indication that an operator sees that something went wrong with one of the pantographs is the “AUX FAIL” annunciator in the console lighting up (the reason why it’s lit in the above picture was actually for an HVAC fault in the Type 1, not anything with the pantographs, but I don’t personally have any pantograph problem photos. There are several different kinds of mechanical problems with the trains that will cause an aux fail). Type 4 consoles are different; the AUX FAIL annunciator reads AUX FAULT instead, there is also a MAJOR FAULT annunciator (though you can’t really see the annunciators in that linked picture), and there is also the TOD, or Train Operator Display screen next to the speedometer which displays mechanical problems with the train. And it goes without saying, but the train will also not operate properly if the pantograph is breaking or broken (moving sluggishly or not at all, lights going out, etc). Operators notify Control if there is any indication of a mechanical problem – an aux fail could be something benign like the HVAC blowers not working, but it could also be the first clue you have that your pantograph is currently being shredded.

So yes, pantographs can break, but it’s rare to have your trip disrupted because of a broken pantograph. The parts of them that are designed to wear out (such as the carbon shoe) are monitored and replaced when needed.

Of course, no post about broken pantographs would be complete without this (non-TriMet) video. Not really sure what the backstory of it is – some of the comments say it was done as a test but I don’t know if that’s true.

5 responses to “When good trains go bad: Pantograph edition

  1. I highly doubt it, but just to entertain the thought, do our trains have batteries? If they do, how do they work?

    I would assume that since the power in the train goes out when the pantograph breaks or goes down, any battery the trains may have don’t work in the same way, as say, a car battery works.


    • Actually they do – there is a low voltage power supply of 25 rechargeable nickel-cadmium batteries, which theoretically can power low-voltage systems in the train for about an hour (emergency lighting, pantograph raising/lowering, power for the brakes and doors, the coupler motors, etc) though in practice it’s probably closer to 20 minutes.

  2. I would place a bet that this was NOT done as a destructive test, but rather a test for the alignment of the catenary. TriMet does this when they open a new line, generally with a type 1 and 2 car towed by the BIG Unimog. The camera caught the disastrous result of a misaligned lower support arm for the overhead that was in the way of the pantograph. The panto struck it, leading to the destruction of the panto and subsequent supports and catenary. Also, having the 25,000V overhead finally coming down onto the roof of the loco/carriage, shorting and tripping the circuit breaker, I doubt they would want to go through the expense for a ‘test’ with all the mayhem caused. This European video shows what the railways there normally do with a special locomotive with cameras and other sensors to survey the line. The TGV has a special car, the Mélusine which can sandwich between the locomotive and the rest of the TGV trainset to watch the panto under normal operating conditions. They also have the Iris 320, a whole train devoted to test and measurement.

    • a test for the alignment of the catenary.

      Oh of course, that makes a lot of sense.

      TriMet does this when they open a new line, generally with a type 1 and 2 car towed by the BIG Unimog

      Right, I remember that for the Mall & 205 (if memory serves, also known as “how we found out that that cat pole by Union Station will need to be moved because it’ll take the mirror off of a trailing Type 1”)

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