How do they do that? is a series for The Source that explores the technology that helps keep Metro running and passengers and other commuters moving. Some of it applies directly to the trains, buses and freeways and some of it runs in the background — invisible to nearly everyone but essential to mobility in our region.
How do they do that? Power the trains
In politics the third rail is an issue so powerful, politicians do their best to avoid it. In the subway the third rail is a line of track so powerful, patrons make sure they avoid it.
And rightly so, since Metro’s trains run on 800 volts – enough to propel a packed rush-hour train at speeds of up to 70 mph through the Red Line tunnel between Hollywood/Highland and Universal City station.
On subway trains, the third rail is the source of the electrical delivery system. The same power is delivered to light-rail lines such as the Blue, Gold, Green and Expo lines via an overhead catenary system. No petroleum gas for the trains. No CNG (compressed natural gas). Just good old-fashioned electricity.
Where does the electricity come from? Like petroleum gasoline and compressed natural gas, Metro buys it. Electricity can be a product of nuclear, coal, gas, oil, water, wind or solar farm sources. In Metro’s case, the intermediary source is utility companies, including LADWP and Pasadena Water and Power — the same companies that supply power to many of our homes.
Although Metro buys many millions of dollars a year in electricity to power the rail lines, electricity is a whole lot less expensive than petroleum gasoline or even CNG. And CNG, as we’ve said in the past, is much less expensive than petroleum gas.
Like the CNG used to power its bus fleet, the electricity Metro buys is produced in North America, which means it escapes the pricing spikes of petroleum produced by unstable countries. And this, of course, is a good thing, especially right now, with gasoline prices rushing upward.
The other benefit to electricity is that Metro’s train lines will become greener as utilities develop more renewable power sources. Subways and light rail already produce fewer greenhouse gases per passenger mile than most cars — and should improve as more wind, solar and geothermal power plants come online.
Also, electricity as a power source is generally quite reliable, both in terms of supply and in terms of subway and light-rail performance. But it does have its weaknesses.
While the third rail on subway track is installed in a protected environment inside the subway tunnel, light rail can be subject to weather. Light-rail cars are linked to the power source via catenary wires installed overhead 12 to 16 feet above ground. (Catenary, for those of you who took and remember physics, is the curve assumed by a cord or chain – or even a spider web — that hangs freely between two fixed points.)
But back to the weather issue. Remember the massive storm of January, 2010 that tipped a tree onto the Gold Line catenary lines in South Pasadena? The line was closed for hours while a bus bridge ferried passengers around the spot where electricity was shut down. South Pasadena is a perfect example of what happens when the power is cut off … although in that case a tree was also blocking the tracks.
Despite occasional stoppages ordered by Mother Nature the catenary system seems to work pretty well. Maybe that’s in part because the system has had more than 100 years of refinement. The first tram with overhead lines was presented by Warner von Siemens (yes, the same company that constructed some Metro Rail cars) at the International Electric Exposition in Paris in 1881. The installation was removed after the event but the light-rail thought persisted. And we’re glad it has.
Categories: How do they do that?