Yesterday I toured the light rail system currently under construction in Seattle, known as Link. The initial route is 15.4 miles long, and is scheduled to start service next year. Overall, construction is 80% complete at this time, with some segments 100% complete.

If you think our power systems are complex, here's how these trains are powered:

•   Seattle City Light provides 26,000 volts AC  to a number of substations along the route.

•   The substations reduce the AC voltage with transformers, and then rectify it to provide 1500 volts DC to the catenary. I was told that almost all other light rail systems operate at 750 volts, but using 1500 volts reduced the size and weight of the catenary wiring.

•   The traction motors in the trains are AC, which they stated provided better control than DC. Thus, within the trains DC power is inverted back to AC.

•   I asked why the two conversions (AC to DC, and then DC to AC) were needed. Apparently, use of AC on the track is not a good thing; the catenary is positive, and the track is negative (and of course ground). It seems that it's not good practice to ground one side of an AC line on these systems.

Another tidbit: the maximum grade is 6% which is reached at only one place in the route - about two miles east of the airport.