Saturday, December 15, 2012

Keep Your Powder Dry

 It was raining off and on all day, so keeping anything dry required some effort.  We had visitors coming to ride the Happy Holidays train, which is good, but many of them were carrying umbrellas that seemed rather incongruous.  What can you do?

With painting out of the question, I spent most of the day stripping paint. All of the large areas of the old green paint on the 36 are now gone, which is very satisfying.  There are lots of little places that need to be processed, perhaps another day's work or so, but this tiresome job is nearly complete.  Whew!

I'm sure you're bored with this, however, so what were other people doing?

Recognize this man?  Probably not, because he's wearing all the proper protective gear: goggles, respirator, ear muffs, and gloves.  Our volunteers' safety is important!  Anyway, this is Ray Pollice using a wire wheel to clean up part of one of the woodworking machine.  This is hard, unglamorous work, but the results are worth it.

And this is a template Tim Peters was making for the end platform on the 1024.  It's marked with the locations of all the holes that will need to be drilled in the replacement wooden buffer.  I went through a similar process when replacing one end on the 308.  Because the car is slightly more than 8' wide, a piece has to be patched onto one end, as indicated by the Jorgenson clamp at the end nearest the camera.

 Finally, here's something that I found quite interesting.  Our electric cars use lots of these 30A or so cartridge fuses for 600V DC.  Recently, Joel noticed that one of the fuses for the heaters in the 749 was emitting steam!  When the fuse was taken apart, it looked like this:

DC cartridge fuses are filled with a flame-retardent powder so that if the fuse opens, a chemical reaction will extinguish the arc.  The powder burns up and you are left with a small amount of ash in the cartridge.  In this case, however, the seal was bad so the powder had absorbed moisture from the air.  And when the fuse melted, the wet powder continued to conduct electricity, although it heated up and started to produce steam.  The arrow points to part of the ribbon fuse itself.  Fuses designed for AC don't need this chemical, because the current passes through zero every half cycle, and arcs tend to extinguish themselves much faster.

As a practical matter, I don't think there's much that operating crews can do about this.  It seems like a very unusual situation -- I'd never encountered it, and I've blown out several fuses over the years.  Just don't store your spare fuses under water.  Anyway, there's your physics lesson for today.  And this will probably be on the next test, too!


Anonymous said...

Off topic, but since you mentioned it, AC arcs above a certain voltage will not self extinguish. Even at the common 480Y/277 V industrial voltage arcs will keep burning. For that reason, many AC fuses are filled with silica that will fuse into glass when the fuse element burns up. And we know glass is a good insulator since we see so many glass insulators on old telegraph poles.
Signed, DOUG (Dumb Old Utility Guy)

Joel Ahrendt said...

By the way, it was Joe and Greg, and not me that discovered the smoking fuse.

Anonymous said...

This brings up one of my questions. It's remarkable that the volunteers are able to restore much of these historic cars to a shape as good or better than when in service. And, it is more than great that some of them are in regular "service" and our kids and grandkids are able to experience the fun of transportation of the early 20th century.
However, it seems that diagnosing, repairing and restoring these vehicles requires a great deal of skill. Understanding the wiring layout of 100 year old rolling stock is not something that is taught in school these days. And, there is a skill to maintaining traction motors and compressors that is hard to come by. Maybe some of the current Rapid Transit systems have technicians that understand the concepts, since they maintain similar equipment, those that have actually worked on interurbans are very limited.
So, my question is one of passing on your expertise. This blog and the IRM blogs have laid out some tutorials on roofing, and recently on stringing overhead wire properly. Is there a repository of more detailed information on the operation and maintenance of these historical cars?
Sorry for the length of the question.\

Lee Wells

Randall Hicks said...

That's an excellent question. Most of the more hands-on type of skills are passed along in informal training, our very haphazard apprenticeship program. And there's a natural incentive to teaching other people how to do things. I would much rather show you how to inspect and lubricate armature bearings than be stuck doing myself every time. So then it becomes part of the institutional memory. For more technical items such as control systems, there's more documentation from the old days than you might think. A number of books of various sorts were printed to teach people how to maintain the equipment back when it was cutting-edge technology, and these books are prized parts of our technical libraries. And then, we are in touch with many other museums around the country, and can usually find the needed expertise for some new problem elsewhere. For instance, our friend Jeff Hakner stopped by recently to share his knowledge of GE PCC controls. And I would say that's basically the same way it works in other departments, such as steam. So that's how our repository of knowledge works. Hope that helps.