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.
Why don’t pantographs wear out or break?
Oh they do.
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.
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?
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.