Tag Archives: pantograph

Of ice and electricity

Photo of what winter weather may look like, westbound at Hawthorn Farm

Steven Vance recently forwarded me a question about why CTA‘s rails have been sparking. Unlike MAX trains which get power from an overhead wire system, their trains get power through a third rail system. However, arcing in both kinds of power systems during winter weather is typically caused by ice. Ice building up on the wire (or third rail as the case may be) acts as an electrical insulator, preventing the carbon shoe from making contact with the wire where the ice accumulates. This interruption in the flow of the current from the wire to the pantograph is visible as arcing.

Here’s a video of a MAX train pulling into & out of a platform where there was some ice on the catenary, and you can easily see the effect that it has:

To help clear ice from the overhead wire & prevent it from accumulating, a few of the Type 1s (107-112) are equipped with ice cutters which are put into use for major freezing rain/ice events. I don’t have a picture of any of them in use (though I’m willing to accept donations!), but they look like a second pantograph and function by heating/scraping ice from the overhead wire. Unlike the pantographs, ice cutters only draw current to heat the elements and not to provide power to the train, so they won’t arc the same way the pantographs do in ice. Their function is strictly to clear ice from the wire.

Pantograph (left) raised, ice cutter (right) lowered

If you’d ever seen one of these cars and wondered why it has two pantographs, wonder no more! It doesn’t – one pantograph, one ice cutter.

View from above; the ice cutter is the one closer to the coupled end, the pantograph is the one in contact with the wire closer to the vantage point. Bonus cameo appearance by car 235

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.

Washington Street

Washington Street in Hillsboro

Washington Street is the pre-empted area at the western end of the Blue Line. In this picture, you can see the pre-empts (all yellow horizontals since there are no trains moving through) on both sides of each intersection, though they’re a little easier to see on the left. Also in this picture, the way the overhead wire zigzags is clearly visible – remember this is done to evenly wear down the carbon shoe on the pantograph.

Another one for the electricity fans

I think I should just change the name of this blog to “Arcings of a TriMet Pantograph” since far and away that’s the sort of thing people are searching for when they end up here.

The other night I was on foot downtown; got this video.

And a still from the video:

pantograph arc at night

Which looks neat and all in a special-effects kind of way, but it’s not really a best practice..


Via Portland Afoot – TriMet’s proposed cuts to save money on the upcoming light rail line to Milwaukie.

Relevant to my interests –

  • Deleting ice caps on overhead caternary system: $1.1 million
  • Deleting track switch heaters: $1 million

I want to say that I can’t believe TriMet would seriously be so shortsighted to think that ice caps and switch heaters are a design feature that can be cut from the Orange Line Milwaukie light rail project to save money, but sadly of course I can. This isn’t the first time and it’s not going to be the last that there is a disconnect the size of Russia between the people who plan these things and the frontline workers (and riders!) that actually have to deal with the fallout of bad decision making.

Never mind the fact that TriMet spent $1,510,000 of stimulus money installing switch heaters and ice caps after the snow storm a few winters ago shut down sections of the alignment for days. Remember that?

Switches freezing at Gateway, ice building upon the overhead, trains not running on any kind of predictable schedule with bus bridge operators doing their best to get through it and haul around people who can’t opt to work from home in inclement weather?

Yet somehow that’s all in the distant past, so snow and ice measures are optional enough to float as proposed cuts to the Milwaukie rail project?

I also saw in the list of cuts that the art budget is going to be reduced by 10%, saving $320,000. Look, instead of needing to retrofit the alignment with critical features like switch heaters, how about we hold off on the art for now and retrofit that later instead? I’m not anti-art, I think in a lot of cases it can be pretty useful in that it can act as a graffiti deterrent on platforms. But does it add the same value to the line as things that will actually keep the trains running? Of course not.

On top of that there is also the planned reduction of bike parking from 460 spots to 413. No other details are given, so I don’t know if that means bike staples, lockers, or more bike and rides. If it’s the latter, can we please give up on that, after the not-really-a-smashing-success the one at Sunset has been? Two months after it opened and I’ve never seen more than 4 bikes in it at once.

But no, in their lack of concern for actual function, consideration is being given to removing aspects of the rail alignment that will keep it running during snowstorms.  Hey, maybe they should incorporate that into the Milwaukie Light Rail tag line!  How about

Milwaukie Light Rail

Enjoy it in the warmer months because when it snows you’ll be taking a bus anyway!