The latest in high-speed train technology

High-speed trains crisscross Japan, much of Europe, and are starting to fan out across China. Here’s a look at some of the technological advances made in high-speed travel by two major train manufacturers, Bombardier in Canada, and Siemens, a German firm.

Train sets and locomotives
State-of-the-art high-speed (HS) trains don’t follow the traditional rules of the rails. Older trains still use one or two locomotives that contain all the traction motors and locomotives are positioned in the front as a pair, or the front and rear to better distribute the tractive forces.

Modern HS trains, however, put traction motors in almost every car for better force distribution and a more-comfortable ride. Distributing power over more axles also lets trains accelerate and decelerate faster. That’s because the powered wheels rely on friction between the wheels and rail to transmit power. Sending all the power to only two or three axles, especially when starting out from a dead stop, increases the likelihood that the power would overcome the friction and spin the wheels. There are also conditions, even with distributed power, when there’s not enough friction to get a large train rolling or up an incline. Ice or wet leaves, for example, can severely limit the frictional force and cause wheels to slip. To overcome this, HS trains carry dry sand, just like their slower-speed cousins. It gets dropped in front of powered wheels to increase frictional forces.

Spreading the tractive force between axles, mounting the traction motors below the floors, and eliminating the locomotive can give modern HS trains 20% more space for passengers in the same-length trains, according to Siemens.

The train set, which includes all the passenger cars, has a driving car. It is the lead car and features a sloped, aerodynamic nose and a relatively small compartment at the front of it to accommodate a windshield, the controls, and communication equipment, as well as the driver, the only person really needed to drive the train. The rest of the driving car is outfitted for passengers.

Most train sets are made up of eight to 10 cars hooked together with a driving car in the lead. But both Bombardier and Siemens make cars that can be part of 16-car train sets, which are about 1,400-ft long, or over a quarter-mile. The weight of such a train, including 1,200 passengers and their luggage, is around 1,000 tons.

On Bombardier’s Zefiro, configured as a 16-car train set, there are normally 32 traction motors, so half of the axles are powered. (Each car travels on a pair of two-axle bogies). And each motor contributes 600 kW, or 800 hp, giving the entire train set over 19 MW of installed power. Energy consumption, which varies with operating conditions, averages 0.08 kW-hr/mile/seat.

Siemens sums up energy efficiency another way, saying their Velaro train sets consume the equivalent of 0.33 liters of gasoline (about the amount of liquid in a can of soda) per seat per 100 km. And in terms of the environment, they emit about 14 gm of CO₂/passenger/mile.

To cut energy use, Bombardier’s HS trains rely on permanent-magnet motors, which need 4% less energy than asynchronous motors.

When HS trains are just getting rolling, they accelerate at about 1.6 fps2, which eventually increases to about 3 fps2, the upper limit in terms of passenger comfort. Braking deceleration is also about 3 fps2. This means a train traveling 200 mph takes about 2.4 miles to come to a stop, according to Siemens.

Power and braking
Most HS trains get electricity from overhead wires or catenaries using a pantograph. Today’s batteries could never be sized to supply the power needed and still fit on the train. Diesel engines turning generators is not considered environmentally friendly and the weight and storage of diesel fuel, along with fire safety, would pose other problems. Another option, using a shoe to take electricity from a third rail, much like light rail, creates too much friction between the shoe and rail at high speeds.

The biggest challenge with using pantographs to take power from the catenary is keeping the contact forces between the two within a given range — not too much friction but enough contact to make a solid electrical connection. And, according to Siemens, the technology for catenary/pantograph subsystems has been under development for decades and can be considered mature.